' ' f NOAA Professional Paper 11 C K°'J\. ^f-ATES 0« ^ \ / Oxygen Depletion and Associated Benthic IVIortalities in New Yorl( Bight, 1976 Rockville, Md. December 1 979 \ V \ : \ U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration W H I DOCUMENT COLLECTION m _D ^=^ LT) eO r^ I CO « O a m 1-^ □ m == □ □ VVooc- grapi'.ic institution Foreword In July 1976, fishermen reported large numbers of dead surf clams and other bottom-dwelling organisms in an 8,600-square-kilometer area of the New Jersey continental shelf. The phenomenon continued through October of that year. Dur- ing this period scientists from the National Oceanic and Atmospheric Administra- tion (NOAA) expanded their routine surveys and monitoring in the region to determine the extent of the problem and assess the damage to the fisheries. Other researchers — from nearby States, universities, and private groups — joined in the study. They determined that the mortalities were caused by extremely low con- centrations of dissolved oxygen and by hydrogen sulfide poisoning in some bottom waters. At the height of the event, dissolved oxygen values in the water were measured at 2 milliliters per liter and sometimes at zero, in an area lying 10 to 100 kilometers off the 150 kilometers of coast between Sandy Hook and Cape May. Mortalities were greatest among surf clams, ocean quahogs, and other benthic animals. Scientists estimated that by October 1976 more than half of the surf clam population off the central New Jersey coast had died, and that a significant but smaller number of ocean quahogs and sea scallops also died. Lobster catches declined almost 50 percent during the period. As a result, in November the Federal Government declared the New Jersey coast a resource disaster area. Estimates of losses to commercial and recreational fishing industries, and related processing and service businesses, were as high as $550 million. Local fishermen were also concerned about the long-term impact of this event on their fisheries. This Professional Paper documents what we learned about resource and eco- nomic losses caused by the decline in oxygen in these waters during the summer of 1976. It also analyzes coastal oceanographic processes and conditions that af- fected water quality during this period, especially departures from those conditions that normally occur. Furthermore, this paper considers the possible role that human activities near the affected region may have had in triggering the event. The effects of adverse environmental factors on marine organisms are described as observed in the field and studied in the laboratory. The volume brings together our knowl- edge of the physicochemical makeup and ecology of these coastal waters. Finally, the likelihood of future oxygen depletion events is discussed. The research during that summer improved our knowledge of environmental changes in the region. The study indicates the importance of understanding and continuing research into coastal oceanographic processes if we are to manage our marine resources wisely in the future. /^UJJ^ James P. Walsh Deputy Administrator National Oceanic and Atmospheric Administration 111 Acknowledgments Wilmot N. Hess, Director of NOAA's Environmental Research Laboratories, who in- stigated and supported the scientific assessment of the 1976 event and conditions contributing to oxygen deficiency and benthic mortalities in waters of the New York Bight. Cynthia Williams, tc.i nical editor, Asheville, N.C. Stanley Chanesman and Ncal G. Millett, graphics editors, and Carol Cassidy. Marie Eisel, Karen Hennckson, Maxine Pinto, and Joan Rapaport, illustrators, NOAA Marine Ecosystems Analysis Program, New York Bight Project, Stony Brook, N.Y. Editorial Reviewers M. Grant Gross Christopher N. K. Mooers Chesapeake Bay Institute College of Marine Studies The Johns Hopkins University University of Delaware Baltimore, Md. Lewes, Del. Merton C. Ingham Chades A. Parker Atlantic Environmental Group Marine Ecosystems Analysis Program National Oceanic and Atmospheric National Oceanic and Atmospheric Administration Administration Narragansett, R.I. Stony Brook, N.Y. Bostwick Ketchum Woods Hole Oceanographic Institution Woods Hole, Mass. IV Contents Page FOREWORD iii ACKNOWLEDGMENTS iv CHAPTERS: 1. Historical and Regional Perspective 1 2. Temporal Development of Physical Characteristics 17 3. Atmospheric Conditions and Comparison With Past Records ... 51 4. Chemical Factors 79 5. Physical Conditions Compared With Previous Years 125 6. Bottom Oxygen and Stratification in 1976 and Previous Years . . 137 7. Water Movement on the New Jersey Shelf, 1975 and 1976 149 8. Diagnostic Model of Water and Oxygen Transport 165 9. Plankton Dynamics and Nutrient Cycling: Part 1. Water Column Processes 193 Part 2. Bloom Decomposition 219 10. Biological Processes: Productivity and Respiration 231 11. Impact on Clams and Scallops: Part 1. Field Survey Assessments 263 Part 2. Low Dissolved Oxygen Concentrations and Surf Clams — A Laboratory Study 277 12. Effects on the Benthic Invertebrate Community 281 13. Effects on Finfish and Lobster 295 14. Socioeconomic Impacts 315 15. A Perspective on Natural and Human Factors 323 16. Oxygen Depletion and the Future: An Evaluation 335 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 1. Historical and Regional Perspective Carl J. Sindermann' ami R. Lawrence Swanson~ CONTENTS Page I 3 4 9 9 12 14 14 The 1976 Oxygen Depletion Event Physical Description of the Bight Fish and Shellfish Stocks Organic and Nltrient Loadings Previous Mortalities and Oxygen Depletion Events in New York Bight Oxygen Depletion in Other Coastal Areas of the World Scope of Report References ' Sandy Hook Laboratory, Northeast Fisheries Cen- ter, National Marine Fisheries Service, NOAA, High- lands, NJ 07732 ' Office of Marine Pollution Assessment, NOAA, Rockville, MD 20852 THE 1976 OXYGEN DEPLETION EVENT In the summer and autumn of 1976. mass mortalities of shellfish and other marine species occurred in the New York Bight, apparently because of extreme oxygen de- pletion and hydrogen sulfide formation in bottom waters. First reports of a developing problem reached the scientific community during the July 4th weekend. Sport divers, lobstermen, and trawler fishermen observed and reported dead and dying animals of all kinds on fishing reefs and wrecks and on fishing grounds off the northern New Jersey coast. Within a few weeks, mortalities were reported southward some 90 km and seaward some 60 km. Planned surveys and monitoring in the Bight by the National Oceanic and Atmospheric Administration (NOAA) were increased in areal coverage and intensity to determine the extent of the problem and to assess the damage. At its maximum extent, oxygen-deficient bottom water — < 2.0 ml/I and sometimes with zero values of dissolved oxygen (D.O.) — was found from Sandy Hook to Cape May. a distance of 150 km along the New Jersey coast in a zone or corridor 10 to 100 km off the coast (fig. 1-1). This environmental event of major proportions involved an 8,600-km- area of the continental shelf off the coast of New Jersey. A mass mortality can be described as an unusual and rapid increase in mortality rate, of sufficient proportions to affect significantly the size of a population and to dis- turb, at least temporarily, the ecosystem of which the population is a part. Mass mortalities may be local, con- fined to a particular cove or estuary, or they may be wide- spread, sometimes affecting hundreds of kilometers of coastline. Causes of mass mortalities may be physical, chemical, or biological — or combinations that produce stress beyond the tolerance limit of individuals in the pop- ulation. Physical causes can include storms, seaquakes, temperature changes and extremes, upwelling. vulcanism, and people-induced changes such as dredging; chemical causes include contaminant chemicals, hydrogen sulfide generation, oxygen depletion, and salinity changes and NO A A PROFESSIONAL PAPER 11 40° 39° 10 20 30 40 50 90 100 STATUTE MILES 30 40 SO 60 100 NAUTICAL MILES FIGURE 1-1. — Oxygen-depleted bottom water in New York Bight and off New Jersey coast, August-September 1976. Dissolved oxygen content in ml/1. Water-column sampling: Atlantic Oceanographic and Meteorological Laboratories stations, solid circles; National Marine Fisheries Service stations, open squares. CHAPTER I extremes; and biological causes include algal blooms, dis- ease, predation, and toxins. Scientific literature has reported mass mortalities due to many of the above causes. Probably the most complete report is by Brongersma-Sanders ( 1957), who exhaustively reviewed all known mass mortalities in the sea. Other reviews include those of Sindermann (1970. 1976). In the 1976 New York Bight event, bottom water oxygen values were zero and hydrogen sulfide was formed in the central New Jersey coastal area off Atlantic City. Divers consistently reported a brownish flocculent layer beneath the thermocline in much of the affected area. Oxygen depletion persisted until October when lower surface tem- peratures and mixing broke down the pycnocline and grad- ually reoxygenated the bottom water. Fish, lobsters, and mollusks were found dead. Seden- tary forms — surf clams, ocean quahogs, and other benthic animals — had the greatest mortalities. From almost con- tinuous surveys, scientists estimated that more than half the surf clam population off the central New Jersey coast — over 100,000 metric tons (t) — had been destroyed by Oc- tober, with significant but smaller mortalities of ocean quahogs and sea scallops. Lobster catches declined by almost 50 percent during the period. Consequently, the Federal Government declared the New Jersey coast a re- source disaster area in November. The occurrence of mass mortalities in New York Bight is particularly significant considering the heavy stress that humans have placed on these coastal waters and the pend- ing efforts to manage this marine resource more effec- tively. It is known that people and their activities con- tribute to the Bight, mostly through the Hudson-Raritan estuarine system, large quantities of carbon and nutrients that would not otherwise get there. Some people consid- ered ocean dumping, particularly sewage sludge dumping within 22 km of the coast, to have been the cause of the oxygen depletion and resultant mass mortalities. If efficient and effective resource management is to be adopted, then it is essential to understand the complex responses of the marine ecosystem to natural and man- induced stimuli. Given this understanding, prediction of such events can be improved. If the contaminants from human activities are found to play a significant role, man- agement strategies can be adopted to lessen the likelihood of such catastrophic events in the future. This professional paper examines the extensive data base available in the context of the above issues. The scope of the problem proved so broad and the sources of data so dispersed that many scientists and organizations contributed to the analysis of the causes, extent, duration, and effects of the anoxic condition. A number of research groups — Federal, State, univer- sity, and industry — participated actively in data acquisi- tion and analysis. The National Science Foundation con- vened a workshop on the problem in October 1976. and the participating research groups organized their own workshops in November 1976. Proceedings of these work- shops have been published (Sharp 1976; National Marine Fisheries Service 1977). Initial indications from these efforts were that severe oxygen depletion developed in the bottom waters in re- sponse to a combination of anomalous environmental events superimposed on a coastal area characterized by reduced dissolved oxygen in an average summer. Atmospheric events included high February-March air temperatures with abnormally high river runoff in Feb- ruary and March, which was before the usual annual spring peak in April; reduction of storm activity during spring and summer to less than half the 25-year average; and a period of 4 to 6 weeks in June-July with unusually per- sistent south to southwest winds. Oceanic events included early (February-March) warm- ing of surface waters; early development of the halocline; and a massive bloom of the dinoflagellate Ceniliiim tripos over much of the Middle Atlantic Bight (continental shelf from Montauk Point, N.Y., to Cape Hatteras, N.C.). but concentrated in New York Bight. The bloom began in February, persisted at least until July, and was concen- trated at and just below the pycnocline. Oxygenation in the ocean occurs in the surface layers (photic zone) through air-sea interaction and photosyn- thesis and through advective processes. Thus, oxygen re- plenishment of deep waters often comes only from water that has been in contact with the surface layers. With this in mind, a hypothesis was developed that included the following components: 1) superimposition of high oxygen demand from a declining phytoplankton (Ceratiiim tripos) bloom on an area (New York Bight) already characterized by reduced dissolved oxygen in an average summer; 2) sealing off of this organically rich oxygen-demanding water mass early in spring by the early onset of a pyc- nocline; and 3) disruption of the usual spatial pattern of currents such that the bulk of the oxygen-demanding ma- terial is concentrated off the New Jersey coast. These elements supply the ingredients of disaster to marine an- imals. PHYSICAL DESCRIPTION OF THE BIGHT New York Bight is a 39,000-km- sector of the Middle Atlantic continental shelf between Montauk Point, N.Y., and Cape May, N.J., approximately 180 km wide from the Hudson-Raritan estuary to the shelf edge. Depths range between 30 and 60 m over much of the Bight, with the inner shelf off New Jersey being somewhat shoaler than that off Long Island. The shelf break generally occurs at a depth of 140 m. The most prominent topographic NOAA PROFESSIONAL PAPER 11 feature of the shelf is the Hudson Shelf Valley, a broad, shallow channel extending from the Bight Apex seaward to the outer shelf and Hudson Canyon (fig. 1-1). The surface of the shelf is a gently rolling plain that gradually increases in depth from the Apex at the mouth of the Hudson River to the edge of the shelf, a gradient of about 60 m in 100 km. North of the Hudson Shelf Valley the surface is veneered with sand. To the south, the surficial sediments are sand and gravel. Within the valley, nutrient- rich muds have accumulated since the postglacial sea be- gan to rise. Barrier beaches, bluffs, and estuaries are prominent coastal features of the Bight. Water movements in the Bight are highly variable in space and time. Over the middle and outer portions of the shelf, waters generally move to the southwest, parallel to the bathymetric contours. In the inner (nearshore) portion of the Bight, water movement and structure of the water column vary greatly with dominant seasonal influences. Boundaries between the regimes of the inner and outer Bight are poorly defined and constantly changing. Never- theless, the inner Bight has two major features: 1. A two-layer flow near the Hudson-Raritan estuary is dominated by the outflow of these rivers. In the surface layer, less dense water flows seaward, gen- erally parallel to the New Jersey coast. In the lower part of the water column, the denser water of the Bight flows into the estuary. Evidence for this two- layer flow is found in current meter measurements, which show a slight imbalance between the much stronger ebb and flood tidal components of cur- rents in the respective layers. 2. A clockwise circulation gyre (at least in the sta- tistical sense) persists outside the region of strong river influence. Its western edge tends to be aligned with the Hudson Shelf Valley. The importance of the Hudson Shelf Valley to oceanic processes on the shelf is just beginning to be realized. The flow of water can be either up or down valley. Over ex- tended periods of time, the flow has been measured up valley (Beardsley et al. 1976). However, in the inner Bight particulate material tends to be transported seaward and concentrated on the valley floor. Oceanic conditions in the Bight are largely controlled by the temperate, middle-latitude climate, which is dom- inated by maritime air from the tropics or subtropics for 9 or 10 months and by arctic air for 2 or 3 months (Lettau et al. 1976). Waters of the Bight undergo pronounced seasonal changes in temperature, salinity, and density. In winter, they are characterized by considerable horizontal and vertical homogeneity. In spring, freshwater outflow begins to establish a pycnocline, particularly over the inner shelf. In summer, heating of the surface layer produces thermal stratification and intensifies the pycnocline. Sea- sonal variations are great and changes are most rapid in the inner Bight. They decrease seaward over the midshelf region. A summer feature of deeper midshelf waters is the "cold pool," thought to be relict winter surface water (Bowman and Wunderlich 1977) of local or distant origin. However, the low dissolved oxygen content of this water suggests considerable modification at depth on the shelf (Gordon et al. 1976); and its southwest flow at speeds equal to or exceeding those of adjacent waters (Beardsley et al. 1976) indicate the pool is not stagnant. Atmospheric and oceanic processes and their variations play an important role in the chemical and biological proc- esses in the Bight. Also, human activities are known to have altered some chemical and biological phenomena. Knowledge about the extent and magnitude of these in- teractions is important in understanding oxygen depletion in the Bight. FISH AND SHELLFISH STOCKS The abundant fish and shellfish populations of the Mid- dle Atlantic Bight are important to the Nation's economy. Oceanic species of bivalve mollusks — surf clams, ocean quahogs, and scallops — are more numerous here than in any comparable coastal area in the United States. Surf clams harvested from the Middle Atlantic Bight constitute over 50 percent of the total landed weight of molluscan shellfish in the United States; the fishery for ocean qua- hogs is expanding rapidly, and populations of sea scallops are fished regularly in deep waters of the Bight. The National Marine Fisheries Service (NMFS) has con- ducted surveys of surf clam, ocean quahog, and scallop distribution and abundance in the Middle Atlantic Bight for a number of years. Results of April 6 to May 13, 1976, surveys by the RV Delaware 11 are given in figures 1-2, 1-3, and 1-4. Total estimated biomass of offshore surf clams in the Bight was 875,000 t of meats, with the New Jersey sector containing 207,000 t. Coastal stocks of surf clams in New Jersey (within 5 km of shore) were estimated at 34,000 t. Total estimated biomass of ocean quahogs in the Bight was 2.450,000 t of meats, with the New Jersey sector containing 818,000 1. Biomass estimates for sea scal- lops in the Bight are not available, but much of the stocks are composed at present of a single strong year class (1972). Scallops occupy about 11,500 km- of the shelf off New Jersey. Significant finfish species in the Middle Atlantic Bight include cod, summer flounder, bluefish, striped bass, mackerel, sea bass, and weakfish. A number of these spe- cies are taken by recreational as well as commercial fish- ermen; often the recreational catch predominates. Some species (such as striped bass) are estuarine-dependent; others, such as summer flounder and bluefish, migrate across bathymetric contours to and from the coast, or CHAPTER I - 40 - 39 Percentage of Sa Tiples w Ih [^Jumber Surf CI ams by Depth (m ol Area <184 184- 36 7- 550- >73 2 Samples 20 36 6 80 549 00 732 00 00 1 Long Island 10 2 New Jersey 16 7 76 7 66 00 00 30 3 Delmarva Peninsula 11 1 58 3 25 56 00 36 4 Virginia-North Carolina 7 7 84 6 7 7 00 00 13 Percentage of Samples with Surf Clams by Bushels Cape Hat teras 1 Long Island 2 New Jersey 3 Delmarva Peninsula 4 Virgmia-North Carolina 1,0 bu <1,0 to IM bu None Number ol or more >1/4 bu or less 88.4 Samples 1 2 46 58 87 00 11,0 256 63,4 82 45 134 35 8 46,3 67 00 4 4 52 2 43 4 23 Symbols 38 37 36 35 76- 75" 74" 73" 7 7' 71- FIGURE 1-2. — Distrihullon and abundance of surf clams in Middle Atlantic Bight, DcUiwarc II shellfish assessment cruise April d-May 13, 1476, NOAA PROFESSIONAL PAPER 11 FIGURE 1-3. — Distribution and abundance of ocean quahogs in Middle Atlantic Bight. Delaware II shellfish assessment cruise April 6-May 1.^. 1^76. CHAPTER I 76 75 74 73 72 4 1 - 40 N I '9 ■ 3 ■) 40 I lO ■ : • • • ' © Percentage Number Caught 71 Depth (m) - 4 1 40 39 -38 3 Delmarva Peninsula 4 Virginia-North Carolina Samples Mean Range Mean Range 540 81 1-43 474 305-75.3 378 18.6 1-103 51 4 32,0-84,1 23.9 4.6 1-11 558 36.0-79.9 0.0 0.0 - - Number of individuals in grab samples 37 36 35 72 71- FIGURE 1-4. — Distribution and abundance of sea scallops in Middle Atlantic Bight, Delaware II shellfish assessment cruise April f)-May 13. 1476. NOAA PROFESSIONAL PAPER 11 r Metric Tons 5,000 10,000 15,000 20,000 25,000 ^•(218.301) M enhaden Bluefish J Catfish Yellowtail Flounder I Shad Silver Hake Wahoo H Croaker Butterfish | Tuna I Yellow Perch Sport Fisheries Commercial Fisheries Kingfish Eel Tautog Black Drum Shark Spanish Mackerel Red Hake ] Bill Fishes I Cod ] Dolphin FIGURE 1-5. — Landings of recreational and commercial fish species in Middle Atlantic Bighl in 1470. (National Marine Fisheries Service 1973). CHAPTER 1 along bathymetric contours north and south through the Bight. Until 1977 a tew Middle Atlantic Bight species (e.g., mackerel and silver hake) were exploited heavily by foreign distant-water fleets and stocks were reduced. Most of the Middle Atlantic finfish stocks (other than mackerel) of interest to U.S. fishermen have not declined drastically in recent decades. Since 1970 increased land- ings have been reported for bluefish, and weakfish. The relative contributions of important Middle Atlantic Bight fish species to recreational and commercial landings are summarized in figure 1-5. ORGANIC AND NUTRIENT LOADINGS Potential eutrophication of Bight Apex waters was iden- tified by Segar and Berberian (1976). Had the 1976 anoxic event been confined to the Apex, an assessment of the cause might have been much simpler. However, the af- fected region extended nearly to Cape May, which added to the complexity of understanding the situation. Wastes from land (fig. 1-6) contributed to the general degradation of Apex waters and sediments (Swanson 1977). Of these, inputs of organic carbon and nutrients are of primary con- cern with respect to the oxygen-depletion event. Mueller and others (1976) summarized average anthro- pogenic loading of the Bight from various sources. Geo- graphically the sources are direct inputs to the Bight from ocean dumping and atmospheric fallout, flow from the Hudson-Raritan estuary through the Sandy Hook, N.J. — Rockaway, N.Y., transect, and contributions from the Long Island and New Jersey coastal zones. Types of inputs include sewage sludge, dredge spoil, and acid wastes from ocean dumping, atmospheric fallout, municipal and in- dustrial wastewaters, and runoff (gauged and urban). Daily mass loads of carbon, nitrogen, and phosphorus and the percentage contributed by geographic area are given in table 1-1. Figure 1-7 shows the percentage contribution by various sources. The values are estimates of total an- thropogenic loading and indicate relative significance of Table 1-1. — Daily mass loads of carbon, nitrogen, and phosphorus entering New York Bighl from human activities' Directly Sandy Hook New Long Mass into Rockaway Jersey Island load Bight- transect' coast coast lO^kg/d Percent Total organic carbon 2.60 37 Total nitrogen 0.52 29 Total phosphorus 0.14 51 ' Source: Mueller et al. 1976. ^ Ocean dumping and atmospheric fallout. ' Hudson-Raritan estuary. Percent Percent Percent 58 4 0.6 65 4 2.0 45 -) 2.0 each disposal activity. However, certain limitations must be considered when using the data. The values represent average maximum loads available to the Bight. They do not reflect the amount of any constituent lost by sedi- mentation, decay, leaching, and biological uptake (Muel- ler et al. 1976). This analysis of mass loading is important in developing carbon, nutrient, and oxygen budgets. If human activity is considered a significant driving force in causing oxygen depletion, we can more specifically iden- tify priority areas for better management. There are of course natural oceanic processes that sup- ply nutrients to the New York Bight. Their relative con- tributions have been estimated, but are incompletely understood. Any evaluation of relative impacts of an- thropogenic loading must include careful consideration of natural processes as well. PREVIOUS MORTALITIES AND OXYGEN DEPLETION EVENTS IN NEW YORK BIGHT Localized mortalities of fish and shellfish have been observed and reported previously from the New York Bight area. Causes of such mortalities usually have not been determined, but several of the mortalities had char- acteristics similar to the extensive 1976 inortalities. A fishkill was reported along the ocean side of Jones Beach in Hempstead Bay, N.Y., from September 17 to 22, 1951. Both surface and bottom waters were affected. Observation of large fluke (22-23 kg) among the dead fish suggested that the condition occurred well offshore. The cause of the problem was not positively identified (Perl- mutter 1952). Fishkills were reported off New Jersey in 1968, 1971, and 1974 (Ogren and Chess 1969; Young 1973; Young 1974). There might have been earlier similar events that were not observed or reported. Those documented resem- ble the event of 1976 in that: 1) sedentary organisms found around reefs and wrecks were killed; 2) reports originated from the same general area; 3) depressed oxygen levels were considered a contributing factor; and 4) suspended flocculent material was present in the water column. The 1976 episode differed from those of previous years in that; 1) it began before the end of June, compared with the August-October period of earlier occurrences, and 2) hy- drogen sulfide, not previously reported, was detected in lethal concentrations in 1976. It may have been present but not observed in earlier episodes. Previous reports of mortalities covered much smaller areas. The 1968 event, which appears to have been the most extensive of the earlier kills, included a zone from Sea Bright to Surf City, N.J., a distance of 7U km, and extended from 1 to about 10 km offshore. The total area NO A A PROFESSIONAL PAPER 11 FIGURE 1-6— Disposal sites in New York Bight Apex, 1976. 10 CHAPTER 1 munic i pal 29 7o \. indust r ia ^ 1% gauged 18 % dredge urban ORGANIC CARBON municipal 40% industrial 13 7. dredge chemical gauged 25 % dredge 12% NITROGEN muni ci pal 35 % urban 4% PHOSPHORUS FIGURE 1-7 -Average daily percentage contributions of organic carbon, nitrogen, ind phosphorus entering New York Bight from various sources. (Mueller et al. 1976) 11 NOAA PROFESSIONAL PAPER 11 was approximately 600 to 800 km- (Ogren and Chess 1969). Mortalities were reported on and near wrecks and reefs from early September until late October 1968. Spe- cies affected were ocean pout, cunner, lobsters, rock crabs, mussels, surf clams, and starfish. More active spe- cies such as tautog. black seabass, squirrel hake, conger eels, and round scad apparently were able to escape and were rarely reported among the mortalities. Fauna on wrecks offshore of Barnegat and Atlantic City was normal. Relevant observations made in the mortality area in 1968 were: 1) mortalities were restricted to waters less than 30 m deep; 2) bottom water temperatures, principally at wreck sites, were 14° to 16° C; 3) bottom-water dis- solved oxygen values were less than I.U ml/1; 4) a pro- nounced thermocline existed; and 5) a series of phyto- plankton blooms, beginning in July and extending to September, occurred along the New Jersey coast. Reex- amination of the same area in May and July 1969 disclosed that oxygen values near the bottom were more than 7.0 ml/1 and that wrecks had been repopulated by fish and crustaceans. No reports are available for 1970, but in early October 1971 lobsters and rock crabs were reported dead on several wrecks 12 km east of Point Pleasant, N.J., at depths of about 30 m, and also at Shark River Inlet (Young 1973). Bottom water temperatures at the wreck sites were high (18° C) and suspended flocculent material was noted low in the water column. Again, no reports are available for 1972 and 1973, but in August 1974 mortalities of ocean pout were observed on several wrecks off Point Pleasant (J. S. Young, per- sonal communication). Bottom-water dissolved oxygen values were 1.0 ml/1, with heavy suspended floccuJent material and bottom water temperatures of 14° to 15° C. In early September 1974 the Subsea Journal of the Manta Ray Diving Club of New Jersey reported dead lobsters and rock crabs on a wreck off Long Beach Island. N.J. Thomas et al. (1976) reported that significant summer depletion of bottom dissolved oxygen in the restricted area of the sludge and dredge material disposal sites, and also in an area close to the New Jersey shore off Asbury Park, occurred during summer 1974. Low dissolved oxygen con- centrations have been reported previously in New York Bight dumpsites (Pearce 1972). Dissolved oxygen concen- trations in dumpsites were higher in summer 1975 than in 1974 and above the level considered harmful to most ma- rine life. OXYGEN DEPLETION IN OTHER COASTAL AREAS OF THE WORLD There are other coastal areas in the world where ex- treme oxygen depletion in bottom waters is a frequent. sometimes annual, event (fig. 1-8). Deuser (1975) sum- marizes the general problem. To our knowledge, however, the New York Bight incident is the first of such magnitude that has occurred along an open coastal area where clas- sical upwelling is not a major factor. Marine fishkills related to oxygen depletion and hydro- gen sulfide buildup have been reported in warm shallow estuaries (May 1973) and in areas of upwelling and mass production of plankton, for example, off South America and Africa (Brongersma-Sanders 1957; Theede et al. 1969). A coastal upwelling region famous for its low oxygen, hydrogen sulfide production, and periodic mortalities is off the southwest coast of Africa in and near Walvis Bay. Scientific records of mortalities, summarized by Bron- gersma-Sanders (1947, 1957), extend back to 1837. Dead and dying fish, cephalopods, and bivalves have been ob- served with great frequency in December and January in the sea and on the beaches between 21° and 25° south latitude. The sea bottom of the region is highly organic, with high hydrogen sulfide content and anoxic bottom waters. Mass mortalities of fish are more severe in some years than in others and are often preceded by red to brown discoloration of the sea from algal blooms. The anoxic area involved is approximately 17,200 km", but interestingly there is a narrow coastal strip about 6 km wide, extending to a depth of 37 m, where sea life is normal and hydrogen sulfide does not occur. Similar mass mortalities of marine animals in a zone of upwelling have been reported by Falke ( 1950) from Con- cepcion Bay, Chile. Mass mortalities, particularly of benthic fauna, have occurred in the deeper basins of the Baltic, where anaer- obic conditions may persist for as long as four years (Se- gerstrale 1969). Total absence of oxygen beginning in 1957 caused the deeper parts of the Gotland, Gdansk, and Bornholm basins to become lifeless deserts in 1958-59. The total area affected was estimated at 41,200 km-. The stagnation was broken in 1962 by a strong inflow of saline water from the Kattegat. Significantly, great amounts of nutrients accumulated during the stagnation period. These were brought to the surface in 1962, resulting in an enor- mous increase in plankton populations. A similar event occurred in the early 1930s (Kalle 1943; Meyer and Kalle 1950). This periodic stagnation, broken by saline inflows and followed by uplift of nutrients, favors periodic in- crease in biological production — unlike other areas of con- tinuous anaerobiasis such as the deep (below 100 m) zones of the Black Sea, which constitute a nutrient sink and are unproductive of sea life. Oxygen depletion of bottom waters, with accompanying formation of hydrogen sulfide, occurred in Tokyo Bay in 1972 (Tsuji et al. 1973; Seki et al. 1974), presumably re- lated to an extensive red tide. Since red tides are becoming 12 CHAPTER I LU a: 13 NOAA PROFESSIONAL PAPER 11 increasingly frequent in eutrophic bays in Japan as well as elsewhere in the world, anoxic conditions in bottom waters can be expected to increase in severity concomi- tantly. Mortalities of benthic organisms, associated with bot- tom water of low oxygen content, occurred in the Gulf of Trieste in the North Adriatic in 1974 (Fedra et al. 1976). The authors reported scattered areas of decaying orga- nisms in a region formerly characterized by stable benthic populations. Oxygen depletion has occurred sporadically in Mobile Bay, Ala., one of the largest estuaries of the Gulf of Mexico. Stratification of the water column over a highly organic bottom results in summer oxygen depletion, and occasionally, because of winds, the water mass impinges on beaches. Fish and invertebrates may be trapped in the anoxic water near beaches — often in a disoriented or mor- ibund condition — where they are taken in great numbers by residents. This shoreline phenomenon is called a "ju- bilee." Loesch (1960) reported 35 such occurrences be- tween 1946 and 1956. but newspaper accounts go back to the 19th century (the earliest is 1867). Oxygen depletion in the bay could have occurred well before colonization of the area in the 160Us, but human activities (particularly dredging operations) have certainly intensified the situa- tion. May (1973) reviewed the history of such events and found no consistent increase in their frequency since 1946. He carried out detailed oxygen determinations during a jubilee in 1971 and found large areas of the bay with less than 0.7 ml/1 dissolved oxygen in bottom water. Mortal- ities of fish, crabs, and oysters were observed. SCOPE OF REPORT The investigations of the 1976 environmental event in the Middle Atlantic Bight make this event one of the best- documented examples of mass mortality in the sea. and of the impacts of such events on resource and food-chain species. It is a textbook-type study that focuses on solving many interrelated problems. Scientific studies on oxygen depletion in the Bight and adjacent coastal waters are continuing, especially since the possibility of repetition of the event at some level of intensity exists for future years. This report brings together the results of many studies on the 1976 oxygen-depletion event. It examines the geo- graphical extent of oxygen depletion and the environ- mental conditions preceding and during the event, and compares the 1976 conditions with historical information. Particularly useful in this regard were NMFS resource assessment data and the 1974-76 MESA current meter and water column chemistry data. The latter data sets for 1976 were used in the form of a model to diagnose the fluxes of dissolved oxygen into the affected region. An assessment is made of the causes, including the effects human activities might have had. Impacts on fishery re- sources and associated socioeconomic aspects are exam- ined. Finally, monitoring and prediction of future events are discussed. The terms "anoxia" and "anoxic" have been used to describe the 1976 summer oxygen depletion in New York Bight. Anoxic or anoxia refer to a condition where dis- solved oxygen values are zero. Zero values did not occur at all times everywhere in the Bight. The terms "anoxia" and "anoxic" were conveniently used during the investi- gations, and sometimes in this volume, in a less-precise sense to indicate a deficiency of oxygen. To adequately consider the causes and the major geo- graphic areas of impact, to more appropriately utilize the existing data bases, and to provide continuity of analysis, the Bight was subdivided into areal segments (fig 1-9). These segments were selected to approximate distinctive bathymetric features, such as the Hudson Shelf Valley (H), major regions of oxygen depeltion (Jl), and the re- gions most affected by human activities (A). For the most part, analyses conform to these arbitrarily generated seg- ments throughout the report — except where the idiosyn- crasies of individual data sets require some other scheme. REFERENCES Beardsley. R. C Boicourt. W. C and Hansen, D. V., 1976, Physical oceanography of the Middle Atlantic Bight, in M. G. Gross (ed.). Middle Atlantic Continental Shelf and New York Bight. Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:20-34. Bowman. M. J., and Wunderlich, L. D.. 1977. Hydrographic Properties. MESA New York Bighl Alias Monogr. 1, New York Sea Grant Institute. Albany. NY., 7S pp. Brongersma-Sanders. M.. 1947. On the desirability of a research into certain phenomena in the region of upwelling water along the coast of South West Africa. Proc. Kon Ned. Akad. Welensch. 50(6);659-665. Brongersma-Sanders, M.. 1957. Mass mortalities in the sea. in J. W. Hedgepeth (ed.). Treatise on Marine Ecology and Paleoecology. vol. 1, Geoi Soc. Amer. Mem. 67:941-1010, Deuser, W, G., 1975. Reducing environments, in J P Riley and G Skirrow (eds.). Chemical Oceanography, vol, .'1, 2d ed,. Academic Press, N.Y., 1-37. Faike, H., 1950. Das Fischsterben in der Bucht von Concepcion - Mit- tlechile (Fish Mortality in the Bay of Concepcion - Middle Chile). Senckenbergiana. (Frankfurt am Main, Germany), 31(1.2):57-77. Fedra, K. E., Olscher, M , Scherubel. C. Stachowitsch. M . and Wur- zian. R. S,. 1976, On the ecology of a North Adriatic benthic com- munity: distribution, standing crop, and composition of the macro- benthos. Mar Biol. 38:129-145, Gordon, A, L,, Amos. A. F.. and Gerard, R, D,, 1976, New York Bight water stratification, in M. G. Gross (ed). Middle Atlantic Conti- nental Shelf and New York Bight, Amer. Soc Limnol. Oceanogr. Spec. Symp., 2:45-57. Kalle, K., 1943. Die grosse Wasserumschichtung im Gotlandtief vom Jahre 1933/34. Ann. Hydrogr. 71:142-146, Lettau. B.. Brower. W, A., Jr., and Ouayle, R. G.. 1976 Marme Cli- matology. MESA New York Bighl Alias Monogr. 7, New York Sea Grant Institute, Albany, NY. 239 pp. 14 CHAPTER 1 Kl 10 2 30 4 J M f ^ 70 SO 90 100 STATUTE MILES 10 10 20 30 4C 50 60 70 80 90 100 110 20 ,30 140 150 KILOMETEHS t-l www HI 10 20 30 40 50 60 7Q 80 90 100 r 00 NAUTICAL MILES FIGURE 1-9. — Geographic subdivisions of New York Bight for an;ilvsis purposes. 15 NO A A PROFESSIONAL PAPER 11 Loesch, H., 1960. Sporadic mass shoreward migrations of demersal fish and crustaceans in Mobile Bay, Ala. Ecology 41:292-24^ May, E. B., 1973. Extensive oxygen depletion m Mobile Bay. Ala. Limnol. Oceanogr. lX(3):35.V3f>6. Meyer, P. F., and Kalle, K., 1950. Die biologische Umstimmung der Ostsee in den lelzten Jahnzehnten, eine Folge hydrographischer Wasserumschichtungen? Archiv fiir Fischereiwissenschafi 2:1-9. Mueller, J. A.. Jeris, J. S., Anderson, A. R., and Hughes, C. F.. 1976 Contaminant Imputs to the New York Bight. NOAA Tech. Mem ERL MESA-6. Environmental Research Laboratories, National Oceanic and Atmospheric Administration, Boulder, Colo., 347 pp. National Marine Fisheries Service. 1973. Sportfish emphasis document. Middle Atlantic Coastal Fisheries Center Informal Rep. No. 15, 79 pp. National Marine Fisheries Service, 1977. Oxygen depletion and associ- ated environmental disturbances in the Middle Atlantic Bight in 1976. Northeast Fisheries Center, Tech. Ser. Rep. No. 3, Sandy Hook Laboratory, Highlands, N. J., 483 pp. Ogren, L., and Chess, J., 1969. A marine kill on New Jersey wrecks. Underwater Naturalist 6(2):4-12. Pearce, J. B., 1972. The effects of solid waste disposal on benthic com- munities in the New York Bight, in Mario Ruivo (ed.). Marine Pollution and Sea Life. Fishing News (Books) Ltd.. London. 404-411. Perlmuttcr, Alfred. 1952. Mystery on Long Island. The Nen y'ork Stale Conservationist 6{A)-\\. The New York Conservation Department, Albany. NY. Segar, D. A., and Berberian, G. A., 1976; Oxygen depletion in the New York Bight Apex: causes and consequences, Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:220-239. Segerstrale. S. G.. 1969. Biological fluctuations in the Baltic Sea Progr. Oceanogr. 5:169-184. Seki. H.. Tsuji, T., and Hattori. A , 1974. Effect of zooplankton grazing on the formation of the anoxic layer of Tokyo Bay. Esiuar. Coastal Mar. 5c(. 2:145-151. Sharp, J. K. (ed.), 1976. Anoxia on the Middle Atlantic Shelf during the summer of 1976. Report of workshop held in Washington. DC. October 15 and 16. 1976. Contract No. OCE77(X)465. Office for the International Decade of Ocean Exploration, National Science Foun- dation. University of Delaware. Lewes. Del . 122 pp Sindermann, C. J., 1970. Principal Diseases of Marine Fish and Shellfish. Academic Press, New York, N.Y.. 369 pp. Sindermann, C. J., 1976. Oyster mortalities and their control. FAO Technical Conference on Aquaculiure. Tokyo. Japan. DOC FIR: Aq. 76/R34, FAO, Rome, 25 pp. Swanson, R. L., 1977. Status of ocean dumping research in New York Bight. J. Waterway. Port, Coaslal. and Ocean Division ASCE. vol. 103. no. WWl. Proc. paper 12722. pp. 9-24. Theede. H., Ponat. A.. Hiroki. K.. and Schlieper, C, 1969. Studies on the resistance of marine bottom invertebrates to oxvgen-deficiency and hydrogen sulfide. Mar. Biol. 2:325-337. Thomas, J. P., Phoel, W C, Steimle. F W. O'Reilly. J E . and Evans, C. A., 1976. Seabed oxygen consumption — New York Bight Apex.. in M. G. Gross (ed ), Middle Atlantic Continental Shelf and New York Bight, Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:354-369. Tsuji. J P , Seki, H.,and Hattori, A.. 1973. Resultsof red tide formation in Tokyo Bay. J. Water Pollution Control Fed. 46:165-172. Young, J. S., 1973. A marine kill in New Jersey coastal waters. Mar. Polluiwn Bull 4(5):70. Young, J S., 1974. Unpublished data on observations of fish mortalities related to wrecks. Sandy Hook Laboratory. National Marine Fish- eries Service. National Oceanic and Atmospheric Administration. Highlands. N.J. 16 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 2. Temporal Development of Physical Characteristics Robert B. Starr' and Frank W. Steimic- CONTENTS Page 17 Observations OF Water Coll'mn 19 Seasonal Progression in 1976 20 Oxygen Distribl'tion 46 Hurricane Belle 46 Bottom Environment in September 50 Summary 50 Acknowledgments 50 References ' Atlantic Oceanographic and Meteorological Labo- ratories, Environmental Research Laboratories, NOAA, Miami, FL 33149 ' Northeast Fisheries Center, National Marine Fish- eries Service, NOAA, Highlands, NJ 07732 OBSERVATIONS OF WATER COLUMN Environmental conditions in New York Bight waters were observed in 1976 by personnel of the Atlantic Ocean- ographic and Meteorological Laboratories (AOML) on four expanded water-column characterization (XWCC) cruises on NOAA ships George B. Kelez and Researcher (Hazelworth et al. 1977a, 1977b, 1978; Starr at al. 1977) and by personnel of the Sandy Hook Laboratory of the National Marine Fisheries Service (NMFS) on numerous vessels. Locations of XWCC station sites, and the vertical sections described here, are shown in figure 2-1. As many of these sites as possible were occupied on a repeat basis in April, May, June, and September 1976. This sequence of observations defines the physical conditions of the water column and the associated distribution of dissolved oxy- gen. Bight waters consist basically of relatively fresh shelf water with warmer, saltier continental slope water sea- ward and quite fresh Hudson-Raritan estuarine water at the Apex. Expanded water-column characterization cruise observations indicate that the spring/summer distribution of dissolved oxygen in bottom waters of the Bight is closely related to the strength and depth of the pycnocline. The pycnocline — that part of the water column where density increases rapidly with depth — is an inverse function of temperature and a direct function of salinity. In the Bight in spring and summer, temperature de- creases with depth and salinity increases with depth at a greater rate than during other seasons, causing density to increase rapidly with depth, and the depth of the pycno- cline to increase as spring advances into summer. When the pycnocline is well developed, it becomes a surface of density discontinuity and inhibits vertical mixing. Upper and lower limits of the pycnocline were determined from analyses of vertical density gradients based on density (sigma-r, (j,y values observed at 1-meter intervals of 3 Sigma-f((T,) is defined as [p(5,0-ljl000, where p(5,/) is the value of seawater density in COS units at standard atmospheric pressure. 17 NO A A PROFESSIONAL PAPER II . STATIONS i STATIONS '0 10 20 30 40 50 60 70 90 100 STATUTE MIL ES TJ IQ ?0 30 4C 50 60 70 80 90 100 nO ^20 130 MO 150 KILOMETERS 10 10 20 30 40 50 60 70 90 100 NAUTICAL MILES FIGURE 2-1. — Location of water-column sampling stations and sections along which observed values are plotted. 18 CHAPTER! depth. The pycnocline is poorly developed in spring, at which time it is characterized by a weak gradient (more than 0.05 or 0. 10 ct, units/m). As the season progresses the pycnocline becomes better developed and is characterized by stronger gradients (as much as 0.10 a, units/m), and there is greater variability of physicochemical conditions above and below the pycnocline. SEASONAL PROGRESSION IN 1976 The 1976 seasonal development of the pycnocline in New York Bight was controlled by two weather/climate- related events. Winter was severe enough to destroy the previous seasonal pycnocline in the shelf water through free and forced convection. The early onset of spring run- off from the Hudson-Raritan estuary established a hal- ocline in the Bight Ape.x. The dominant flow from the estuary in April was around Sandy Hook and south along the New Jersey coast (fig. 2-2). This dominant flow and the strongly developed halocline disappeared to the east. Virtually no temperature structure is apparent in the April cruise data (fig. 2-3), but a prominent salinity gradient is evident (figs. 2-4 and 2-5). By May. significant stratifi- cation is indicated in both temperature and salinity sec- tions (figs. 2-3. 2-4, 2-6. and 2-7). The effect of the seasonal thermocline is evident in figure 2-2. The density structure, which was localized by the outflow of relatively freshwater from the Hudson-Raritan estuary in April, was under the influence of the thermal structure in May throughout the Bight, as indicated by depth of the ther- mocline. The strengthening of the halocline-controlled pycnoc- line by the rapidly developing thermocline waS a regional phenomenon. Locally a tongue of warm, low-salinitv water extended east and south from the mouth of the Hudson-Raritan estuary at the bottom of the pycnocline in May (figs. 2-6 and 2-7). Bowman and Wunderlich (1977) examined historical temperature, salinity, and density data for New York Bight. Their findings are presented as monthly mean tem- peratures, seasonal salinity cycles, and seasonal mean den- sity distributions. Relative to these climatological condi- tions, the April 1976 surface waters were about 1° to 2° C warmer than normal and bottom waters temperatures were up to 2.5° C warmer than usual. In May, the surface temperature remained slightly above normal, while the bottom temperature (7.5-9.0° C) was normal to slightly (1° C) below normal. Consequently, the Bight water col- umn was as thermally stratified as usual in May, a con- dition that might have existed earlier. Turbulent mixing processes are inhibited by stratifica- tion. Resistance to overturning (i.e., vertical exchange) in the water column was estimated by computing the change of a, within the pycnocline. This stability indicator is shown for April in figure 2-8 and for May in figure 2-9. The weak pycnocline offshore and the stronger pycnocline associated with the outflow from the Hudson-Raritan es- tuary along the northern New Jersey coast is evident in the April cruise observations. One month later, stratifi- cation resulting from thermal enhancement of the pyc- nocline is apparent throughout the region, both inshore and offshore. By late June, the horizontal temperature gradient at the bottom of the pycnocline increased inshore but did not change significantly offshore (fig. 2-10). However, the surface warmed approximately 7° C (fig. 2-11), and con- sequently a very strong thermocline developed. The sal- inity of the Hudson-Raritan outflow increased from 27'^c to 29%f, whereas no significant change occurred in the salinity distribution at the bottom of the pycnocline (fig. 2-12) relative to May (figs. 2-4 and 2-7). The effect of the strong thermocline on the density structure in June (fig. 2-13) is evident when compared to May (fig. 2-2). Consequently, the stability of the Bight-area water column increased significantly in June (fig. 2-14) compared to May (fig. 2-9), except for weakening of the halocline along the northern New Jersey coast associated with the declin- ing Hudson-Raritan outflow (fig. 2-12). Between the hal- ocline-supported, strong stability band along the northern New Jersey coast and the warmer offshore surface water is a relatively less stable zone of water extending south- ward from Long Island over the inner shelf floor (fig. 2-14). The June 1976 surface and bottom temperatures of 20° C and 7.5° C, respectively, were about normal as com- pared to Bowman and Wunderlich (1977). Salinities ranged about 1 .GF/cc above average; densities, while slightly higher than normal, had a typical gradient (Bowman and Wunderlich 1977). By June, the thermocline became the dominant factor in the stratification and, because of its strength (~ 12.0° C change within a layer 20-m thick), isolated the bottom waters from the surface. The June conditions were the most stable observed in 1976. The September data probably closely approximate the maximum seasonal development of water column strati- fication before its destruction by autumnal cooling and wind mixing. Water temperatures at the bottom of the pycnocline (fig. 2-15) were at their maximum and more variable than previously observed. The tongue of warm water was still present south of Long Island; and another tongue was present off central New Jersey. Differences in September and June water temperatures can be seen in figure 2-11, particularly for the Long Island section. Bottom waters, which were consistently colder than 8° C in June and earlier, warmed to about 10° C. A strong thermocline was still evident but was deeper in September. However, when the September data are compared with expendable bathythermograph (XBT) data obtained on 19 NO A A PROFESSIONAL PAPER 11 a NMFS cruise of August 6-17 (fig. 2-27). surface cooling is suggested. This effect could have resulted from passage of hurricane Belle (discussed later). By September, the salinity below the pycnocline had changed relative to June (fig. 2-12). It is difficult to com- pare the September and June salinity distribution at the bottom of the pycnocline because of the few observations in June. However, the salinity sections show a better de- veloped halocline in inshore waters in June, at which time bottom water was more saline off New Jersey and in the shelf valley than in September. Surface water off Long Island (section E-F) was fresher in September than in June. The source of this relatively fresh water appears to be the Hudson-Raritan estuary (fig. 2-12). The densitv difference, Aa,, was slightly less in Septem- ber than in June (figs. 2-13, 2-14, and 2-16). By Septem- ber the signature of the Hudson-Raritan outflow had dis- appeared, and, except for a relatively weak pycnocline associated with the fresher surface water off southwestern Long Island, there was no significant density difference in the pvcnocline off New Jersey and Long Island. How- ever, the pycnocline was weaker in these nearshore lo- calities than offshore. September presented a different picture than earlier months relative to the norm. Although surface tempera- tures were tvpical of the average, bottom waters, which had temperatures of 8° to 9° C (figs. 2-11 and 2-15), were considerably colder than the 12° C described by Bowman and Wunderlich ( 1977). Because salinity values continued to be somewhat high, densities were still above normal. Seasonal development of the pycnocline was not re- flected by significant changes in the depth or configuration of the pycnocline bottom or the salinity at the bottom of the pycnocline. With the exception of the Hudson-Raritan outflow, the bottom of the pycnocline seemed to be more closely related to the presence of offshore water. Because of the depletion of oxygen in the subpycnocline bottom layer (ch. 6), the depth of the pycnocline bottom was used to determine the thickness of the bottom layer for the four XWCC cruises (figs. 2-17 to 2-20). The pat- terns of bottom layer thickness reflect isobathic control. In June, the pycnocline bottom generally was 3 m higher in the water column off New Jersey than off Long Island (fig. 2-19). However, the depth of the ocean floor is con- siderably less off New Jersey so that the thickness of the subpycnocline layer was about 3 to 3 m less than off Long Island. By September the bottom of the pycnocline was observed at greater depths off Long Island, which tended to equalize the thickness of the subpycnocline layer off the two coasts. OXYGEN DISTRIBUTION Dissolved oxygen (D.O.) was determined by Winkler titration on all water samples collected at discrete depths with a Rosette multisampler attached to the conductivity- salinity-temperature-depth (CSTD) sensor. On the May and June cruises D.O. also was monitored with an oxygen probe on the CSTD, which functioned on a majority of the stations of these two cruises. Although slow in re- sponse time, this electrode allows a more accurate deter- mination of the depths of oxygen maxima and mmima than the discrete Winkler analyses. The distribution of average D.O. concentration in the subpycnocline layer for May and June is shown in figures 2-23 and 2-24. These distributions were derived by av- eraging all the Winkler-determined oxygen values below the pycnocline at each station for each of these months. The decrease in available oxygen and increase in patchi- ness of its distribution between May and June are evident. The vertical sections of D.O. for April, May, June, and September were determined from the water samples (figs. 2-21 and 2-22). The April oxygen range of 6.0 to 7.5 ml/ I was what would be expected for weakly stratified waters at that time of year. In May oxygen levels began to reflect the onset of stratification, with some depletion to under 5 ml/I in the bottom water and some increase to as much as 9 ml/I near the top of the pycnocline. In June, a very strong gradient in oxygen values developed through the pycnocline (figs. 2-13 and 2-22). High values (over 9 ml/ I) near the top of the pycnocline occurred offshore and low values (as little as 0.5 ml/i) were present below the pycnocline, particularly near the head of the Hudson Shelf Valley. Over the shelf valley, the minimum oxygen values were not observed at the bottom but in the 30- to 40-m depth range. By September, the high oxygen values in the top of the pycnocline disappeared so that the DO. in the mixed surface layer had average values of about 5.25 ml/I. Below this, seaward over the shelf, the oxygen gradient was very strong, from 5 ml/1 to 2 ml/i between 20 and 30 m depth. On the inner shelf floor (fig. 2-22). D.O. values were well below 2 ml/I, and off New Jersey below I ml/1. Close to shore, the oxygen content was below the detection limit of the Winkler titration. Offshore, in continental slope water, oxygen values ranged between 4 and 5 mI/1. As observed earlier in the Hudson Shelf Valley, the minimum generally was not at the bottom except near the head of the valley in Christiaensen Basin. The D.O. probe values were used to determine the depth of the main oxygen minimum above the bottom (figs. 2-25 and 2-26). In both cases, the minimum "grounded" in the vicinity of northern New Jersey and was terminated by the relatively highly oxygenated dis- charge from the Hudson-Raritan estuary, which in this location averaged about 5 ml/I, and showed no significant gradient across the pycnocline (figs. 2-21 and 2-22). The oxygen minimum was always below the base of the pyc- nocline but its distance from the bottom generally de- creased from May to June except in the Hudson Shelf 20 CHAPTER 2 Density (C~f) Kilom«t*rt I 20 40 60 80 100 86 87 88 APRIL 81 37 50 B A 32 ':^y__ 25 5 ■ ^"^^^ 26.0 NEW JERSEY ^^^ 20 40 60 80 100 — I 100 86 87 88 MAY 81 37 B 32 ^^^-= J4 5 24 5 "250^^^ NEW JERSEY ___^26 0- \ ^fi-i — " ^ FIGURE 2-2.— April and May 1976 dcnsitydr,) sections. 21 NO A A PROFESSIONAL PAPER 11 Temperature ( C ) APRIL Kilometers — I — 50 100 MAY 86 87 88 81 37 3; ._ji75k ■ ; ' ' \, /''''~7\._^ 20 40 — -^ v^ ^7 5 60 \ 80 r\r. ^ NEW JERSEY ^"^-\ 70 28 79 36 81 9C V\ ■ / ^8- 20 N. 65 7 75 40 \ ^ ^ r~- J 60 on LONG ISLAND ^ / \ 70 28 79 36 81 20 40 60 F 90 ^ - — -"lo- LONG ISLAND \ ^ ^ FIGURE 2-3.— April and May 1476 temperature {" C) sections. 22 chapter: Salinity (%o) Kilometers FIGURE 2-4.— April and May 1976 salinity (%o) sections. 23 NO A A PROFESSIONAL PAPER U SALINITY (%.) AT BOTTOM OF PYCNOCLINE - APRIL 1976 in to 20 30 40 so 90 100 STATUTE MILES 90 100 NAUTICAL MILES FIGURE 2-5.— April 1^76 distribution of salinity C^rf) at bottom of pycnocline. 24 CHAPTER 2 75° -40° 39° EMPERATURE ( C) AT BOTTOM OF PYCNOCLINE - MAY 1976 10 ID 20 30 40 50 60 70 80 90 100 STATUTE MILES IQ '0 go 30 40 50 60 70 80 90 IQQ HO 1^0 130 HO 150 KILOMETERS 20 30 40 50 60 '0_ 90 100 NAUTICAL MILES FIGURE 2-6. — Mav 1^76 distribution of temperature (' C) at bottom of pyenochne 25 NO A A PROFESSIONAL PAPER II SALINITY (%.) AT BOTTOM OF PYCNOCLINB - MAY 1976 73° 72° 10 20 30 40 50 60 70 90 100 STATUTE MILES 70 80 90 100 110 120 130 MO ISO KILOMETERS 10 20 30 40 50 60 90 100 NAUTICAL MILES FIGURE 2-7. — May 1976 distribution of salinity (^n) at bottom of pycnocline. 26 CHAPTER! 41V 7 (XWCC 8) -40° -39" 10 10 20 30 40 50 60 70 90 100 STATUTE MILES 1 10 20 30 40 50 60 70 80 90 100 MQ 120 130 ijQ 15 KILOMETERS 90 100 NAUTICAL MILES 10 20 30 40 50 60 70 FIGURE 2-8. — April 1976 distribution of pycnocltne density-difference (Act,) values. Expanded water-column characterization cruise 8. 27 NO A A PROFESSIONAL PAPER II 10 '0 20 30 40 50 60 70 SO 90 100 STATUTE MIL 10 10 20 30 4C 50 60 70 80 90 100 110 130 130 -T- 150 KILOMETERS 10 30 30 40 4 I 50 60 70 80 90 UH FIGURE 2-9. — May 1976 distribution of pycnoclinc density-difference (Air,) values. Expanded waler-column eharaeterization cruise 9. 28 CHAPTER 2 75° iMPERATURE (°C) AT BOTTOM PYCNOCLINE- JUNE 1976 -41° 71" 10 10 20 30 40 50 90 100 STATUTE MILES FIGURE 2-10, — June 1476 dislribution of temperature (' C) at bottom of pvcnoclinc. 29 NOAA PROFESSIONAL PAPER II Temperature ( C ) 20 40 60 80 70 28 79 36 SI F 90 __;^___ LONG r— 235-^^^^^ ISLAND Kilometers -i — 50 100 A SEPTEMBER B 86 87 88 81 37 3; V^jo ^_y '^"^^ — — 20 — 20 ■^^ ^^^^^^==-__ IR "-^--^"^^ t:,^^ 10 4U ~^°^~~~^ \ — ®~ ~ ' 60 \ 80 NEW JERSEY 10 ^~~^^2 FIGURE 2-11. — June ;ind September I47(i temperature (° C) sections. 30 CHAPTER! Salinity (%o) Kilometers 17 17 23 33 34 35 36 D C 37 38 3 9 _ I 7 17 23 33 34 35 36 37 20 40 60 80 100 20 40 60 - 80 D 38 39 ^" \ ■ /' ■ ' / ' ' ^ 31 5 ^ ■^ 32 ^^ 3" 5 / ^^^ \ V ^ -^33^ // HUDSON SHELF VALLEY ^ 70 28 79 36 81 90 .___-^'° 1^ y ■ V ^1 "i ~--32 5 "^^-^= LONG ISLAND \y \ FIGURE 2-12. — June and September 1976 salinity C^tr) sections. 31 NO A A PROFESSIONAL PAPER 11 Density (O^) Kilometers FIGURE 2-13. — June and September 1976 density ( to 20 30 iO ^r, ?0 60 90 100 STATUTE MIL ! h 20 30 4C bU 60 ^0 m yij lUO iiu 20 130 140 ISO KILOMETERS 10 20 30 10 5U 60 70 80 90 m FIGURE 2-28. — August-September 1976 distnbutiiin ol bottom temperature (° C). 47 NOAA PROFESSIONAL PAPER 11 BOTTOM SALINITY -40° 139° 10 10 20 30 *0 50 60 ?0 80 90 100 STATUTE Ml 10 10 30 30 4C. 50 60 70 80 90 100 110 120 130 140 150 KILOMETERS M M M W Wfc — 10 =^ — 20 30 _ 40 50 60 70 1 80 90 1 00 NAUTICAL MILES FIGURE 2-29— August-September 1976 distribution of bottom-salinity (%c). 48 CHAPTER 2 — 40° 10 10 20 30 40 50 60 ;o 90 90 100 STATUTE MIL 10 20 30 AC 50 60 70 80 90 100 no 1 20 r 30 140 150 KILOMETERS M l-l MM H^= 10 20 30 40 SO 60 70 80 90 101 00 NAUTICAL MILES FIGURE 2-30. — August-September 1976 distribution ot bottom dissolved oxygen (ml/1). 49 NOAA PROFESSIONAL PAPER 11 1 ml/I — a large area off the central New Jersey coast and a smaller area off northern New Jersey where the oxygen deficiency was first reported. These were separated by an area of relatively high but variable oxygen content. Hansen and H. B. Stewart, Jr., for suggestions and review; and to the officers and crew of the NOAA ships Albatross IV, George B. Kelez, and Researcher for their long and diligent hours. SUMMARY Study of the oceanic conditions and events, and their progression in the New York Bight during m76. indicates the presence of warmer-than-normal bottom waters early in the year. This is in accord with the findings of Hazel- worth and Cummings (ch. 3). and suggests a larger amount of offshore water in the Bight than usual. There may be a connection between this presence of offshore water and the large concentration of Ceratium tripos in the Middle Atlantic Bight in 1976. (See chapter 9, part 1.) By June, however, surface and bottom waters were nearly normal. The distribution of properties in the Hudson Shelf Val- ley and off New Jersey in May, June, and September, and at the hurricane Belle XBT and bottom-oxygen stations, suggests an onshore movement of water beneath the pyc- nocline. This agrees with the sluggish onshore set found in the current meter records by Mayer and others (ch. 7). The thickness of the subpycnocline layer is about 4 m less in May and June off New Jersey than off Long Island, though the bottom of the pycnocline is at a shallower depth off New Jersey. This difference in thickness was less in September. In both localities bottom water was effec- tively isolated from the surface by a relatively strong pyc- nocline. This pycnocline did not appear to be significantly stronger than normal, particularly early in the year. The occurrence of bottom water that was 2.5° C warmer than normal in April and 3° to 4° C colder than normal in the latter half of the season indicates advection of bot- tom water into the region. If the continental shelf were the source of this water, then it must have been subjected to anomalous conditions upstream when it was at the sur- face. Hurricane Belle had some effect on the water column down to at least 25 m. ACKNOWLEDGMENTS The authors are grateful to Thomas Azarovitz for the hurricane Belle XBT and bottom oxygen data; to D. V. REFERENCES Beardsley. R C, Boicourt, W. C. and Hansen. D V.. 1976. Physical oceanography of the Middle Atlantic Bight. Am. Soc. Limnol. Oceanogr. Spec. Symp. 2:20-34. Bigelow, H. B.. 1933. Studies of the waters on the continental shelf. Cape Cod to Chesapeake Bay. 1. The cycle of temperatures. Papers in Physical Oceanography and Meteorology 2(4). Massachusetts In- stitute of Technology and Woods Hole Oceanographic Institution. 135 pp. Bowman. M. J., and Wunderlich, L. D.. 1977 Hydrographic Properties. MESA New York Bight Atlas Monogr. 1. New York Sea Grant Institute, Albany. N.Y.. 78 pp. Hazelworth. J. B., Cummings. S. R.. Starr. R B . and Berberian. G. A.. 1977a. MESA New York Bight Project expanded water column characterization cruise (XWCC 8) NOAA ship George B. Kelez. April 1976, NOAA Data Rep ERL MESA-27. Marme Ecosystems Analysis Program Office. Environmental Research Laboratories. Boulder. Colo., 108 pp. Hazelworth. J. B.. Cummings. S. R,. Minton, S M.. and Berberian. G.A.. 1977b. MESA New York Bight Project expanded water col- umn characterization cruise (XWCC 11) NOAA ship Researcher. September 1976. NOAA Data Rep. ERL MESA-29. Marine Eco- systems Analysis Program Office. Environmental Research Labo- ratories, Boulder. Colo., 189 pp Hazelworth. J. B.. Starr. R B . Cummmgs. S R . and Berberian. G. A., 1978. MESA New York Bight Project expanded water column characterization cruise (XWCC 9) NOAA ship George B. Kelez. May 1976. NOAA Data Rep. ERL MESA-31. Marine Ecosystems Analysis Program. Environmental Research Laboratories. Boulder. Colo.. 184 pp National Oceanic and Atmosphcnc Administration, 1977. Marine Weather Review. Smooth Log. North Atlantic Weather. July and August 1976, Manners Weather Log. 21(1 ):2.S-31. Environmental Data and Information Service. Washington. DC Starr. R. B.. Hazelworth. J. B . Cummings. S R.. and Berberian. G. A.. 1977. MESA New York Bight Project expanded water column characterization cruise (XWCC 10) NOAA ship George B. Kelez. 28 June-1 July 1976, NOAA Data Rep. ERL MESA-28. Marine Ecosystems Analysis Program. Environmental Research Labora- tories. Boulder, Colo , 91 pp. Steimle. F. W.. 1977. Appendix III under Physical/Chemical Oceanog- raphy, in Oxygen depletion and associated environmental disturb- ances in the Middle Atlantic Bight in 1976. Northeast Fisheries Center Tech. Ser Rep. No. 3. National Marine Fisheries Service. Sandy Hook Laboratory. Highlands. N.J . pp. 41-64. 50 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 3. Atmospheric Conditions and Comparison With Past Records Henrv F. Dia:' CONTENTS Page 51 Introduction 52 Sea-Surface Temperature 55 Surface Wind Field 70 Wind Stress and Vertical Motion 77 Conclusions 77 Acknowledgments 77 References ' National Climatic Center, Environmental Data and Information Service, NOAA, Federal Building, Ashe- ville, NC 28801 INTRODUCTION During the first half of 1976, atmospheric conditions along the Middle Atlantic coast departed substantially from the climatological norm. Following a cold January associated with a moderately amplified trough pattern in the westerlies over eastern North America (Wagner 1976a), the mean circulation at 700 millibars (mb) over the eastern United States reverted to a generally fast zonal flow in February (Dickson 1976a). This pattern prevailed through March (Taubensee 1976a). The pattern of 700- mb heights provides a measure of the air circulation at low levels. Negative height anomalies indicate relatively cold conditions prevailing whereas positive departures from the mean height indicate relatively warm conditions. At 40° N latitude the height anomaly of the mean 700-mb surface along the U.S. east coast changed from about -20 m in January to around -1-45 m in February and + 50 m in March. These departures in February and March were reflected in anomalous pressure and circulation patterns (more typ- ical of spring conditions) that limited the transport of cold air from Canada to the United States. As a result, warm maritime air masses predominated over most of the coun- try, causing extreme warm conditions over the eastern two-thirds of the United States during these months. The April circulation pattern was close to normal, al- though mean temperatures in the eastern United States remained 1° to 2° C above the climatological mean (Wag- ner 1976b). The monthly mean pattern, however, masks the very large change that occurred between the first and second halves of the month. In the New England area mean 700-mb heights increased by more than 100 m and record cold weather during the first half of April was replaced by record warm weather in the second half. 51 NOAA PROFESSIONAL PAPER 11 During May and June strong sea-level pressure rises were observed over the Atlantic Ocean (Dickson 1976b; Taubensee 1976b), which resulted in an increase in the speed and persistence of southerly winds over the Bight. Atmospheric forcing is one of the dominant influences driving the New York Bight circulation and exchange processes (Mooers et al. 1976) and thus affects the marine ecosystem. Long-term changes in atmospheric circulation patterns can have a pronounced effect on the strength and persistence of this forcing. Dickson and Namias (1976) demonstrated how different circulation regimes affect the baroclinicity or cyclogenetic potential along the U.S. east coast, reducing or increasing the number and vigor of disturbances. To provide some measure of the relative strength of this forcing during the few months preceding the onset of the 1976 anoxia, the number of storm centers entering the Bight area bounded by 38°- 42° N and 70°-75° W was tabulated for February through June, 1950-76 (fig. 3-1), based on extratropical cyclone track charts (NOAA 1950-76). Minimum storm activity oc- curred in 1976. Although the average number of storms crossing this area during the 5 months is about 15. only 6 storms were recorded in 1976, and only a single storm was recorded in each of the months of February and March. The magnitude and persistence of these anomalous weather patterns during the few months preceding the period of bottom-water anoxia suggested a possible con- nection to the observed disruption of the marine environ- ment in the Bight. Sea-surface temperature is considered a relatively good indicator of the degree of stratification, however, with regard to its early onset, other factors may 1950 51 52 53 54 55 56 57 58 59 60 61 62 63 FIGURE 3-1. — Number of extratropical cyclones entering New York Bight area (38°-42° N, TC-TS" W). Februarv-June 1950-76. (NOAA 1950-76 data.) be important in determining the vertical density profile. For example, the temperature of the bottom layers, which are influenced by antecedent winter conditions, affects the surface of bottom temperature contrast. Another impor- tant element is the salinity of the surface waters. During the spring of 1976, low surface salinity contributed to early stratification. The surface wind field provides a measure of the large- scale circulation in the Bight. Anomalous winds, by mod- ifying the normal circulation and exchange (vertical mix- ing) processes of Bight waters, could have aided in the development and maintenance of oxygen depletion. Be- cause surface wind stress represents a primary driving force for oceanic motions, intensified or persistent up- welling/onwelling in the Bight could have been an impor- tant factor in the development of a phytoplankton bloom along the New Jersey coast. SEA-SURFACE TEMPERATURE Sea-surface temperature data were extracted from three principal digital files at the National Climatic Center (NCC): the New York Bight Atlas file (1949-73); the Tape Data Family-11 (TDF-11) file, 1870-1973; and the Global Weather Central Telecommunications file (1973-76). In addition, the National Weather Service's monthly publi- cation, Gulfstream, which contains monthly means of sea- surface temperature by 1° squares, was used for the period 1971-76 whenever the number of sea-surface temperature observations exceeded those in NCC files. Sea-surface temperatures were analyzed for a 2°-square area (39°-4r N, 72°-74° W) comprising most of the New York Bight region (fig. 3-2). This is the area used by Lettau et al. (1976) for the MESA New York Bight Atlas Monograph 7 on "Marine Climatology," and for which the tape data file covering the years 1949 to 1973 was created. To determine whether surface waters throughout the Bight were unusually warm during the 1976 months preceding the oxygen-depletion event, sea-surface tem- perature means for the months of February, March, and April — for the long-term records of 1876-1976 in the northwest marine area and 1896-1976 in the southwest marine area — were plotted as departures from the 1949-73 reference period mean (fig. 3-3). The northwest and southwest T-square marine areas of figure 3-2 include the greater portion of the zone of oxygen deficiency identified in chapter 1. A value was plotted only when four or more observa- tions were available for a given year/month. Values de- rived from fewer than 20 observations, which also fell beyond ± 3 standard deviations from the reference mean, were rejected. These limits were arbitrarily chosen to pre- vent undue biases either from too little data or from the 52 CHAPTER 3 NW MARINE AREA • BARNEGAT SW MARINE AREA NE MARINE AREA SE MARINE AREA FIGURE 3-2. — New York Bight 2''-square area for which sea-surface temperature data were analyzed. 53 NO A A PROFESSIONAL PAPER 11 NW Marine Area IB an BH SB 92 36 B H 8 12 IB 20 2H 2B 32 3B HB HH HB J2 SB 6B B4 BB 72 IB — I — I — ( — I — i — ( — I — \ — I — ( — I — ( — I — ) — I — ( — ) — I — ( — I — I — I — ( — t — ( — I — I — I — I — I — I — t — t — I — I — ( — \ — ( — I — I — t — I — I — ( — t — ( — ( — I — t — I — I — I — I — t — * — \ j :j j ^.■■■^:^H,.,.44^r^ r-^ Av.:/v^ I N = 25 -- -3 R = 84 -- -H -t — I — ( — I — ( — ( — 1 — \ — I — \ — I — I — ( — ( — ► — t — t — t — t — f— t — I — I — I — I — ( — ( — ( — I — \ — y — \ — \ — t — ( — \ — I — t — t — ( — ( — ( — I — I — J — t — t — I — ( — I — I — I — \ — I — t— H 3 2 — I — I — I — I — I — I — I — 1 — I — I — I — I — I — I — • — • — • — ' — I — I — I — >— ' — ' — I — I I I — I — I — >— t — ' — ' — ' — ' H -r T '^ 3 2 -- O -I -2 -3 -- -H -L -_ , ......J,., '-T^ r :.„; ^--H m >A^ . ^a^^ _j/ I N = 25 :; T, = 5.6°c OR = 1.1° -- -3 R = 64 -L -H I — I I I — I I I I i I I I I — I— I — I I I I I I — I — I — I I I — I — I — I I I I — I I I I I ' I — I > I — 'II I ' < -I + • -■■°° -2 -- -3 -- -H -L •» = ^..l7.3i^"»«*\°° A. . -r'■"^°°^"^'^-'7i^, -^Yfv: +2 T„ = 7.7°C I N = 25 1.0° -- -3 R = 63 -- -M I — I — I — 1 — I — I — 1 — ( — I — I — I — I — I — I — I — I — I — 1 — I — 1 — I — I — I — 1 — I — t — I — I — I — I — I — I — • — • — • — ' — t — ' — > — •— ' — ' — ' — I — ' — ' — ' 5B B 4 a 12 IB 2B 2H 2a 32 36 HB HH HB S2 S6 BB BH BB 72 76 1800 si 1900 s FIGURE 3-3.— Departure of February, March, and April New York Bight mean sea-surface temperatures from 1949-73 reference-period mean and long-term trend. The squares of the long-term trend Ime represent smooth (fifth-order polynomial least-squares fit) values. Numbers on right are mean and standard deviation for reference period (Tn and u^) and long-term record (T„ and I ' I I I ' I ' I ' I ' h i I ' I ' I ' I ' I ' I ' I , ' I ' I 7E flB an ea 92 BG B 12 IE ZB 2H 2S 32 36 HB MH 46 S2 SB BE 64 bB 17 75 1800 s 1900 s FIGURE 3-4. — Departure of February and March Central Park Observatory (New York City) mean air temperatures from the long-term mean and long-term trend. 56 CHAPTERS 75° 74° o EB41 OSV"H"« - X _L o CO (O o 75° 74° 73° 72° 71' 70° FIGURE 3-5. — Surface wind field observation stations (circles) and six grid points for which mean surface wind stress was computed. 57 NO A A PROFESSIONAL PAPER II \ •"CNJ A 7 J ml 7 '/ m V 7 V -/ .f „/ 7 V •V \ \ uA c\j/ m\ oij CO \ V, T ^ "/ -1 / , -/ I CM O o => ^ < o ^ en oj o _i 1 3 ^ -D o ■" o n CSJ S Z ^ 3 •- — D o ^ rj o > ^7 < ^ 5 o ^ o CO c u >^ U o u cL o 0) M E z 22 20 18 16 14 12 10 8 6 4 2 Constancy 1949 1955 1960 1965 Years 1970 1975 100 90 -\ 80 n 70 O 3 60 J 50 *:! 40 -9 30 20 10 FIGURE 3-9. — Average wind constancy and number of extratropical cyclone centers crossing New York Bight, February-June 1949-76. sultant winds from 24r-270° occurred about three times or slightly over 10 percent in the northern marine areas, one time from 2ir-240° (less than 5% of the time) in the southwest area, and three times (a little over 10%) in the southeast area. These figures indicate that the surface wind flow during February-March was somewhat more anomalous over the Southern Bight. April had a more even distribution from all sectors, consistent with the low wind constancies in figure 3-7. Wind patterns during May and June were close to the climatological norm. The most unusual character of the wind field during these months is its above-normal persistence. The relative absence of cyclonic activity between Feb- ruary and June 1976 should be retlectd in low wind var- iability as expressed by a higher constancy ratio. The high- est average constancy over this period coincided with the two minima in cyclonic activity over the Bight (in 1969 and 1976) during the 27-year period of record (fig. 3-9). Although constancy is a measure of the vector variance of wind and hence of its directional persistence, scalar variance gives a better measure of turbulence associated with wind. The choice of the 27-year (1949-75) record at John F. Kennedy International Airport (fig. 3-10) as an indicator of the larger scale behavior of the wind field offshore is a reasonable one, since, as may be seen in figure 3-7, changes in wind constancy during 1976 were mirrored by similar changes over the Bight. The wind variance in February and March 1976 was considerably below the long-term mean, as expected. During May, however, the variance was the highest since 1955. showing a substantial increase over 1975. April and June did not have marked differences from their respective means. Regardless of the particular response time of a water body to changes in atmospheric forcing, it might be ex- pected that in the New York Bight area major features in the wind field, such as its constancy, averaged over a month's time would in turn be reflected in the mean Bight circulation features. The wind data in figure 3-10 correlate well with current meter measurements (see chapter 7), which show a higher total current variance in the Bight during May 1976 than during 1975. The currents also have periods of northeastward flow in accordance with the higher wind constancies (sustained southwesterly winds) in May (fig. 3-7). 68 CHAPTER 3 1949 1955 1960 1965 1970 1975 ■a 0) 0) a V) •a c u c 10 9 8 7 6 5 4 3 2 1 / ^ \ o 12 11 10 9 Q < O 0) 4 3 1949 1955 1960 1965 1970 1975 10 9 8 7 6 5 4 3 2 April 1949 1955 1960 1965 Years 1970 1975 12 11 10 9 8 7 6 5 4 - 3 FIGURE 3-10. — Time profile of monthly average wind speed in m/s (solid line) and scalar wind variance in (m/s)- (dashed line) at John F. Kennedy International Airport, computed from 3-hourly obser- vations, 1949-76. Solid and open circles indicate means values for solid and dashed lines, respec- tively. 69 NO A A PROFESSIONAL PAPER 11 ■a (1) o a. (/> ■a c iS TO u W c (0 0) S 10 9 8 7 6 5 4 3 2 May 1949 1955 1960 1965 1970 1975 10 June 1949 1955 1960 1965 1970 1975 Years 12 11 10 9 8 7 6 5 4 3 12 11 10 9 8 7 6 5 4 3 2 < Si' 3 O (D ST FIGURE 3-10 — Time profile of monthly average wind speed in m/s (solid line) and scalar wind variance in (m/s)- (dashed line) at John F. Kennedy International Airport, computed from 3-hourly obser- vations, 1949-76 — continued. WIND STRESS AND VERTICAL MOTION Using the method described earher, the average monthly wind stress over the Bight for February-June is presented in figure 3-11. The average monthly surface wind stress vector had a component towards the north for all months February through June, consistent with the resultant wind flow analyses of figure 3-7. Whether a mean northward component of flow at the surface and offshore surface Ekman transport were set up in the Bight 2 to 3 months earlier than usual is not known. However, the results sug- gest the possibility of some anomalous circulation features during these months. There are two mechanisms for wind-driven upwelling. One operates in the open ocean, independent of coastal boundaries. It involves the open ocean divergence of the surface Ekman transport, which depends upon the curl of the wind stress and the change in the Coriolis parameter with latitude, and it applies to mid-shelf and outer-shelf regions. The other operates in coastal regions, and de- pends upon the existence of coastal boundaries. It involves the coastal divergence of the surface Ekman transport, which depends upon the orientation of coastal boundaries relative to the wind stress vector, and it applies to inner- shelf regions. The effects of both mechanisms have been evaluated for the bight and are discussed below. 70 CHAPTER 3 Feb ru o r y Mof c h "T" Sc ole: i =2x10'' I d yne 5 / c m ^ Moy 1 June 1 Resultant surface wind stress vectors; values centered at 40''N, 73°W. Februo ry March April May June ~r "T" "T" 1 Mean vertical motion into surface Ekman layer; values centered at 40''N, 73''W, positive upward. FIGURE 3-11. — Variation of monthly (a) mean surface wind stress over New York Bight (computed by using 10-day wmd vector averages) and (b) mean vertical motion at bottom of surface Ekman layer. February-June 1976. An estimate of the mean vertical motion through the bottom of the surface Ekman layer was calculated from the linearized steady state vorticity equation (see Mc- Lellan 1965) and is given by <^T, p.f\d / (2) where t, and Xy are, respectively, the zonal and meridional components of the stress vector, p„ is the water density, /is the Coriolis parameter, and p is the change in /with latitude. Except for March, the vertical motion induced by the curl of the wind stress is positive. This suggests that ("open-ocean") upwelling may have been prevalent in the Bight throughout the analysis period. A more appropriate indicator of the vertical motion field for the inner shelf is the upwelling index of Ekman mass transport given by: M ts>e % 00 e? genap G G S QGG 6O0 c® O0O©^„ O „ 0§0 Oe G aft G eesSBi^^So aSS^GOOG o g^ cb go o Q ^ o^y 00 0_ eO0 ° 0^"R^'^°^''^^^^^*^^^ o e 00 9*5 aiss Sffleg) so^ eg B e off® a Q 50tJ(C^J Q G Q Q£» 00 oe * e €B G 00 ° °0r%"le»_ 00 '-Hl ll li l l i n ff" ^S^I^^jpO EB en X o CD 00 o i: o cr -—, a LU t_i cj cr z 3 — 00 £ I. ^ 4 UJ O 86 CHAPTER 4 SB Q T5 '^ t "J C 5-. ri >-. TJ s '^ i: o -3 .0 -2 r3 a. c ^ 7. JZ 1 iJ St, X D -0 m >. '•J f- -0 JZ -:^ r. ->- ■— in (\j M d -CO -CE 1 — z 3 c >-, > c 1 3 > c ■0 c c 2 tx -~t d a C -a c c >c ^ S _J ( — F -n c .1/) -J — ) -— ) '-» c ^ LL l_ -3 r ] r ^ ■^ T^ -3 ■J c ,2 c X = c .0 > >-. c -lL - =11 r > QQ-9 OO'i 00'9 00-S QQ-tl 00'£ QO'e 00 ' I n/im N30XX0 QBAnossm "T i; i: — S ;/! T-3 ::Jj V -J C r^i 1^ a. 1 C g ^ z — ^ ^ y: ri ~ 0^ .J s c C -:: -0 *_t '-) u -1 J> ■-» y. c — :? y. I— oj s r- :t^ c y c X 3 -T 5-. >. '- C C = 5 /: o o t: o x ^ - c - c^-£ 3 c - en H3 c -0 3" % in Oj -0 E > -0 •J-. c > -C X 5E -a C 0. c c E F •0 > c 3 E --."-, 1/5 j: T3 1- I E ° o -^0 = oo'i ao'9 GO'S QO'll 00-e n/iw) N30JIX0 a3Aios9ia 00 -cP 87 NOAA PROFESSIONAL PAPER 11 ■^ v"^ « e ■ K. \ . { « « \ S \ , i 4 / / ■ e ■ ? ■ > Q e O o a oo / 1— — ) '^ D LU " O, SI B LJ Z EJ >; UJ B X '" LJ 01 CJ i. 1 1 1 1 — — 1 1 1- -J —1 1 h OS ffi E OQ-a QQ-i. OQ-9 OQ-S OO'li OO^e QO'2 00 -cP tS -l. ^ o o a: z f— UJ X (X o E o U5 ij-i LU en 1 1 1 1 1 1 1 — OQ-i OQ-9 OQ-S QO-h OO'E OO'a OO'l n/lWI N30iXO Q3A10SSia -— 1 a ao-(P o -3 E =;-. I- T • =, ir I. i § CHAPTER 4 f i e ee CO r- ai C\J i~ "~) UJ Q LiJ l_) Z >c LiJ X tiJ LiJ o LJ in m Q 00-6 OO'S OO'i QQ-9 OQ-S QQ'ti OO'S 00'2 00 ' 1 n/IWJ N30XX0 QSATOSSia 00 -(f / o s© UJ D O X o CQ en QQ-i OQ-9 OO'S QO'h Ofl-e QO'2 n/iwi N30ixo oiAiossia ^0^(f 89 NO A A PROFESSIONAL PAPER II t5 -u- Q t— o E Jfe ° O) Q EP Q X •" CD S 00 -6 OQ-9 QQ'S QQ-tl QO'e Q0"2 oo-cP OQ-i_ 00-9 GQ-s oo'h oo'c oca 00 " t 11/lWI N30JIXO Q3A10SSia oo-cP o < 4 4 < o UJ a: z t— UJ X E o r- m cn LgS" 1/1 4 UJ O 90 CHAPTER 4 '^ ■ \ y f « . f f f i . i □ BOX Ml DHTfi EXCEPT 1976 SCREENED 1 1 1 1 1 1 1 _J —I a: 1 1 i tS -^ a. 00-9 OQ-S QQ'tl OO'S n/iw) N30AX0 a3A30ssia 00 -cP CQ O >- Z Is f li B □ El X o CQ ^- O oi o OO'Q OO'L QQ-9 OO'S OQ'tl 00'£ OO'J (l/TWI N30AXO a3AT0SSia 00 (P 91 NO A A PROFESSIONAL I' A PER II f f CO ; OJ o CD sg" O (\J z a: CL- --> □ ^-J h- •=! u-l 00-9 OQ-S OO-fl oo'e n/iw) N30AX0 QBAiossia "^cP o o TS -Li- / 4»*>i- OJ ^ O (X X Q o CD en ^ 4 UJ D O QQ-g Qo-g ao'ii oo^e oo-a n/iwi N30JIX0 aaATossia 00 -cP 92 CHAPTER 4 < 1 < < < / en ^ CD S (I ..?. '--) OQ-8 QO^i QQ'g OQ-S QO'tl 00-£ QO'Z 00 • I n/HW) N30AX0 QBATOSSia 00 -cP t • \ \ \, / e ./ e «£* / ■ ?■ i e ^/© 8 ■ f /-^ / /< >- •f . ,/»a) _J —I z o cr Q UJ \ 1— UJ X cr Q UJ 1 o ■ s Z E / E 1^ a- -I a 1— "^ / CvJ 4 CSC o X D CD 00 -g 00 n/iwi s OQ-ti oo'e N30AX0 aaAHOSSIQ 00 -(P 94 CHAPTER 4 ^ e < / « / " ° ^sJn^' B Q CO X o CD oca OO'i 00-9 OQ'9 OO'tl OQ-e QO'2 n/IW) N39J.X0 QiAIOSSIQ o 01 o -tj H ^ in 1— z ro -(D z o ' — gg o r. z CE E tr -— ) a 00-cP / / CI E>o«l& it o I CO ^ X Q 0= o tii OJ cn QQ'i Qa"9 OQ-S OO'Ii OO'C QO-2 n/iwi N30AX0 a3Aiossia 00 -cP 4 D O iZ 95 NO A A I'ROfliSSIONAI. PAI'l.H II / / on ,_ 2: LU Q UJ LJ Z >c LU X LlJ LJ CC rr 01 LU Q 00 "9 OQ n/iwi ■s QQ•^ oQ-e N3CIJIX0 QiAlQSSIQ oq-lP CQ o >- u Z 'o -o o T ■ ,1 / e « «i& / • e © / . « « ««<»«» «« • f ■ - ^1 .. : 1 ■ ^ ^ >- ^ CO ^ Q LU (X ^ i 1— bj X CE UJ f m 1 1 1 — t \ 1 — — 1 1 1 -(/I z (X --) a UJ Oi D O 00-s oo-ii oo'e n/im N3GXX0 a3Aiossia 00 -(P 96 CHAPTER 4 in segment A is the data distribution good enough for the non-1976 years to fulfill conditions for drawing a regres- sion line. Depletion rates listed for 1976 all appear statis- tically significant (P<0.05) and are up to 10 times more rapid than non-1976 mean values; however, except for segment A, none of the non-1976 rates have correlation coefficients high enough to be considered significant at the P<0.05 level. The 1976 depletion rates shown in table 4-6 for 1976 compare very well with those determined by Han et al. (ch. 8). Note that the actual oxygen utilization rates, which consider advection, are about double the depletion rates (chapter 8, table 8-2). Recovery rates (J.D. 250 to 365) also are more rapid in 1976, but we consider this a natural result of the 1976 oxygen deficiency; that is, once stratification was broken up, equilibrium with the atmosphere was rapid, and re- covery rates in the depleted system were high. NUTRIENT DISTRIBUTION Nutrient distributions control productivity and its sub- sequent input of oxidizable carbon, thus reducing oxygen concentrations in bottom waters. The distribution of nu- trients in time and space in New York Bight has been examined in some detail during the last 3 or 4 years by several agencies and institutions. However, only late in 1976 did specific studies focus on the low oxygen condition which existed during that summer. The MESA New York Bight Project sponsored a series of extended water-col- umn characterization (XWCC) cruises throughout 1975 and during 1976. The following is a comparison of data from the early XWCC cruise with data collected by MESA and Brookhaven National Laboratory (BNL) during the severe oxygen-depletion event. All nutrient data reported here resulted from analysis of frozen or fresh samples, using Technicon AutoAnalyzer systems. Atlantic Oceanographic and Meteorological Lab- oratories (AOML) analyzed samples using standard Technicon techniques described in their manuals. These methods were checked against accepted methods of analy- sis (Strickland and Parsons 1968; Fanning and Pilson 1973). The results of this comparison are available in an AOML data report (Berberian and Barcelona 1978). Methods used by BNL are given in Walsh et al. (1977). Nutrient samples collected in most of the studies were frozen for later analysis in the laboratory because labo- ratory space aboard research vessels and analytical equip- ment availability were limited. Exceptions were the AOML cruise in September 1976 and BNLs Atlantic Coastal Ecosystem (ACE) cruises where nutrients were run aboard ship. Some changes can be expected from fro- zen samples, but previous studies have shown that the mean change between fresh and frozen samples is only about 10 percent (Thayer 1970) for orthophosphate, dis- solved silicon, nitrate, and nitrite. Changes in ammonium concentrations between fresh and frozen samples are sometimes very large and contamination is a problem, so ammonium was determined only in samples analyzed at sea. On the September 1976 cruise, samples were drawn in triplicate. One aliquot was analyzed aboard ship for nitrate plus nitrite. The other two aliquots were frozen and later analyzed at BNL and AOML to check whether or not differences occurred as a result of such storage. Those run fresh had a mean difference of -0.05 [xg-at/I for BNL frozen samples (table 4-7). AOML frozen samples were generally lower than the BNL frozen samples, with a mean difference of about 1.0 ^J.g-at/l. Since bottom sam- ples analyzed by the two laboratories showed essentially the same differences, it was concluded that differences are not related to the concentration of nitrogen but resulted from a systematic difference in handling and analysis. As a result, the values shown in the figure of this paper may have a <1 (xg-at/1 difference between data sets and this should be considered when making comparisons. AOML's nitrate samples with concentrations of 0.5 p.g- at/1 or less were recorded as zero on the figures herein, since AOML considers that the detection limit for the Tabi 1 4-7 — Comparison of concenlralions of nitrate plus nitrite measured in fresh or frozen samples on XWCC cruise 11. September 1976 Sample Concentration Number of Mean of Standard Range of description' differences hetween- samples differences deviation differences (jLg-at/l jig-at N/1 All samples A-B 162 -0.05 0.64 -5.83 to 1.61 All samples A-C 177 1.08 1.71 -2.30 to 9.82 All samples B-C 83 0.96 1.16 -2.16 to 4.83 Bottom sam pies A-B 27 -0.15 0.61 -1.76 to 0.95 Bottom sam pies A-C 22 1.09 1.34 -1.11 to 5.00 Bottom sam pies B-C 23 1.05 -1.35 -2.16 to 4.83 ' Compared samples are from same water sampling bottles and were either run fresh or were frozen m polyethylene bottles. - A = fresh samples run by BNL B = frozen samples run by BNL C = frozen samples run by AOML, 97 NO A A PROFESSIONAL PAPER II FIGURE 4-4. — NOAA AOML extended water-column characterization (XWCC) cruise transects I-V of 1975 and 1976 and Brookhaven National Laboratory (BNL) transect during oxygen-depletion event of 1976. analyses performed. This is not considered in table 4-7 or in the above discussion. The nutrient samples collected during the XWCC cruises over 1975 and 1976 (at nearly monthly intervals) and during several ACE cruises established a large data base for the area impacted by low oxygen concentrations in summer 1976. Nitrogen is emphasized in the results and discussion because (1) nitrogen compounds are closely coupled with oxygen during periods of denitrification (the biological reduction of nitrate, NO, , and nitrite, NO2", to nitrogen or nitrous oxide, NjO), which occur to some degree in areas where hydrogen sulfide is gen- erated (Redfield et al. 1963), and (2) nitrogen has been shown to be the nutrient that limits phytoplankton pro- duction in the Bight (Ryther and Dunstan 1971). This latter observation has been confirmed by samples col- lected in recent "'N uptake studies (Conway and Whi- tledge, personal communication), where orthophosphate concentrations greater than 0.5 p.g-at/1 were still available even when nitrogen was depleted. Two-thirds of this ni- trogen uptake by phytoplankton was ammonium and the remaining one-third was nitrate. Nitrate Possible correlations between low oxygen and nitrate distribution were examined over two similar offshore tran- sects (I and II in fig. 4-4) off the New Jersey coast where the oxygen deficiency was most pronounced. It was as- sumed that 1975 was a nearly normal year; at least no critical oxygen deficiencies were observed, although "nor- mal" depletion did occur in the bottom waters during the stratified season. Late winter and early spring conditions of February/March 1975 (fig. 4-5) indicate that nitrate concentrations of 1 to 2 |xg-at/l were present in the near- 98 CHAPTER 4 STATIONS 40 41 42 43 44 45 46 75 • • 40 50 80 100 120 HO DISTANCE OFFSHORE (km) 60 ISO 1 I I r L__J I \ \ L FIGURE 4-5A.— Nitrate concentrations for late winter 1975. XWCC cruise 2 transect I (A) and bottom (B) nitrate in p-g-at/l (Feb. 22— Mar. 5, 1975). 99 NO A A PROFESSIONAL PAPER II A 87 STATIONS 88 89 90 91 20 - X Q. HI Q 40 - 60 - 20 40 60 80 100 120 DISTANCE OFFSHORE (km) B "1 \ r 39°l I I'/ I J I \ I L 75 74° 73° 72° FIGURE +-5B— Nitrate concentrations for spring 1976 XWCC cruise 8 transect 11 (A) and bottom (B) nitrate in ng-at/1 (Apr. 12-16, 1976). 100 CHAPTER 4 shore region, with no values lower than 0.5 ji.g-at/1. At mid-shelf, values up to 8 |xg-at/l at 65 m depth were meas- ured. The bottom nitrate concentrations were above 4 \i.g- at/l on the outer shelf region, and some nitrate was prob- ably introduced to the Bight Apex by Hudson-Raritan river runoff. In spring 1976 off New Jersey (fig. 4-5), bottom nitrate concentrations were slightly lower than in early spring 1975. Concentrations at the inshore stations dropped to less than 0.5 (xg-at/l, probably as a result of the spring phytoplankton bloom. Concentrations at the deeper off- shore stations also declined. April 1976 bottom nitrate concentrations were high at the shelf edge off Long Island and corresponded closely to deep values observed in March 1975 off New Jersey (fig. 4-5). The BNL transects taken in April 1975 (fig. 4-4) and April-May 1976 show interesting differences between the 2 years (fig. 4—6). Inshore concentrations were markedly lower in 1976; nitrate values integrated over the euphotic zone were as low as 2.2 ixg-at/m- (Conway and Whitledge, personal communication). The nitrate gradient at the shelf break was smaller in 1976 than in 1975 and deeper source waters off the shelf contained 3 (xg-at/l less nitrate. This lower concentration in the deep water persisted over 2 weeks and could represent a deficiency in the 1976 source water. If so, any cross-shelf movement of this water would have brought less nitrate to the midsheif and inshore re- gions in 1976. A late spring sampling off New Jersey in May 1975 showed little or no nitrate inshore of the 60-m isobath (fig. 4-7). However, the deep water, which probably acted as a nitrate source, had concentrations similar to those observed in February-March 1975, indicating a general nitrate depletion on the shelf — most pronounced off New Jersey and less apparent off Long Island (area of transect V on fig. 4-4). A similar sampling in May 1976 found slightly higher nitrate near the bottom of the euphotic zone off New Jersey, but no value was greater than 1 p.g- at/l (fig. 4-7). The May 1976 bottom nitrate concentrations were negligible over the entire shelf. Note that the shelf break nitrate concentrations shown for May 1975 and May 1976 are similar; this weakens the evidence for depletion of nitrate in the 1976 "source" water. A 1975 summer section off New Jersey (fig. 4-8) showed nitrate values similar to those seen in May of that year. Data for about the same place and time in 1976 are limited, even though they were taken about the same time that the initial anoxic conditions arose; however, data collected at that time for that section are all below the detection limit of 0.5 |xg-at/l and are not shown in the figure. For the 1976 cruise also, all bottom nitrate values except those off the shelf were less than the detection limit. Apparently, bottom nitrate concentrations inside the shelf break were an order of magnitude less in 1976 than in 1975 — possibly 26 MAR -9 APR 1975 STATIONS 43 21 23 46 48 18120 I 22 I 45 I 24 I 25 26 27 28 29 .1.1 I I I L_j I I . .1 . 1 . . .1 I ..I . I 180 - B DISTANCE OFFSHORE (km) 20 APR -4 MAY 1976 STATIONS 6 8 10 12 20 40 60 80 100 120 140 DISTANCE OFFSHORE (km) FIGURE 4-6. — Nitrate concentratieins for spring 1^75 (A) and spring 1976 (B) BNL cross-shelf transect values in jjig-at 1 a result of reduced transport of nitrate across the shelf break or a result of denitrification. Late summer sections off New Jersey for 1975 and 1976 (fig. 4—9) both show the effects of bottom shoreward trans- port of nitrate-rich water. At this time in 1976, oxygen- deficient water was still located off some areas of the New Jersey coast. The bottom nitrate concentration increased 8 or 9 |xg-at/l off Long Island during both years, but some 101 NO A A PROFESSIONAL PAPER II 40 60 80 100 120 140 160 180 DISTANCE OFFSHORE (km) B 41' 40' 39' "1 r J__l \ \ I L 75 74" 73° 72" FIGURE 4-7A. — Nitrate concentrations during May 1975. XWCC cruise 4 transect I (A) and bottom (B) nitrate in p.g-at/1 (May 3-lU, 1975). 102 20 40 60 80 100 DISTANCE OFFSHORE (km) 39°l I i' I J L L J I L 75° 74° 73° 72° FIGURE 4-7B. — Nitrate concentrations during May 1976. XWCC cruise 9 transect II (A) and bottom (B) nitrate in [xg-at/l (May 17-24. 1976). 103 NO A A PROFESSIONAL PAPER II STATIONS 40 41 42 43 44 45 46 7J i i i i ^:j i i i' • • • • • 20 % • • • • • :'>, K • • • -- 40 - / / ^ \ y^ 2 X »- a. UJ ° 60 - / /. — 3 80 - V / 1. 100 - 1 1 1 1 1 1 il 1 20 40 60 80 100 120 140 DISTANCE OFFSHORE (km) 160 180 B 41' 40' n [ "1 — r 39°LJ h^!—\ \ \ L J I \ L I I L I \ \ \ L 75 74° 73 72° FIGURE 4-8A. — Nitrate concentrations during June 1975, XWCC cruise 5 transect I (A) and bottom (B) nitrate in M.g-at/1 (June 8-15. 1975). 104 CHAPTER 4 STATIONS 86 87 88 89 90 91 I 1 \ * 1 • 1 • 1 1 1 Ao.25 • • • • • • 20 - / V • \ • • • • • • J ' / / • • • • • X LU Q 40 60 1 1 1 1 / 1 • A • 1 / / / • • • B 20 40 60 80 DISTANCE OFFSHORE (km) 100 I I I I L \ \ L__J I \ I L FIGURE 4-8B— Nitrate concentrations during June 1476. XWCC cruise 10 transect II (A) and bottom (B) nitrate in tJ.g-at/1 (June 28— July 1. 1976). 105 NO A A PROFESSIONAL PAPER 11 STATIONS 20 40 60 80 )00 DISTANCE OFFSHORE (km) B 41' 40' 39' L 72° FIGURE 4-9A.— Nitrate concentrations during autumn 1975 XWCC cruise 6 transect 1 (A) and bottom (B) nitrate in jig-at/1 (Sept. 29— Oct. 4, 1975). 106 CHAPTER 4 STATIONS X O. 86 87 88 89 90 91 \ 1 • I • i 1 k i \ • • • • m • 20 1 ^ • • • " • ^ — 5 • • - ^^ \\' — ^^^^ 0**'*^*^ __^^ ''X- V E 6h 5 4 3 2 1 - ■' I 1 1 1 1 1 1 1 1 1 1 1 • • 1 V / J - 0---0 1976 A \ ' - X / m^ \ ^^ \ \ ^ \ "^ ^-— — — ^ ^— — ^^^^^^ - - - - - - - - 1 1 1 1 1 1 1 1 1 1 1 1 M M J J MONTHS N FIGURE 4-17. — Total organic carbon (dissolved and particulate) m waters of a salt marsh on lower Delaware Bay in 1975 and 1976. (NOAA Salt Marsh data). 118 CHAPTER 4 be seen, the organic carbon in marsh water in 1976 gen- erally was equal to or lower than 1975, so there is no evidence of exceptional marsh output for 1976 unless flow rates out of the marshes were exceptional in 1976 as com- pared to 1975. The impact of this organic carbon on oxygen distribution in the Bight should be considered. A somewhat simplified stoichiometric relationship for primary productivity and organic breakdown has been established (Redfield et al. 1963), and can be written: [(CH^O.oft (NH,),6 H^POJ + 138 O^ ?± 106 CO, + 16 HNO3 + H3PO4 + 122 H2O. where the term in brackets represents an average chemical composition for marine phytoplankton. It is the product of analysis of elements in plankton and of nutrients in seawater and was intended as an average picture for the oceanic environment. If a semienclosed coastal system can be considered in equilibrium, these same ratios can hold. Analysis of TransX data (Sharp et al. 1979) indicates that sometimes Middle Atlantic coastal bottom waters do show the predicted molar ratios of fluxes of phosphate, D.O., and organic carbon. Therefore, it is possible to evaluate the impact of the measured organic carbon on bottom water D.O., using the idealized ratio of 138 moles of oxy- gen to 106 moles of carbon. We can postulate the D.O. for a starting point by using the concentration that would be in equilibrium with the atmosphere if there were no biological oxygen utilization. Bottom water salinity in the New York shelf region is about 32.75"/fH^„ and the tem- perature is about 9.6° C. The salinity is the average from chapters 2 and 5; temperature is an average of June through September for all segments from table 4-5. Using oxygen saturation tables (e.g., Riley and Skirrow 1975), this would give an oxygen content of 6.57 ml/1. With stoi- chiometric equivalence, this amount of oxygen would be used by respirational consumption of 0.225 millimoles C/ 1 or 2.70 mg C/1. Of course, all organic matter in the water will not be easily broken down by rapid heterotrophic activity. How- ever, organic content greatly in excess of 2.70 mg C/1 may suggest sufficient labile (oxidizable) material to pose a serious oxygen demand that, without oxygen replenish- ment, could hypothetically lead to oxygen depletion. For this consideration, total organic carbon (TOC) should be treated as the cause of the potential oxygen demand, and particulate matter may be less important than dissolved material; Duedall et al. (1977) showed that bacterial ox- idation of dissolved organic matter in sewage sludge occurs before oxidation of particulate matter. This opinion is also based upon the observation that particulates usually make up only 10 to 15 percent of the total organic matter (table 4-8) and upon the suspicion that the particulates are not a long-term (months) feature of the water column. The water column, not the benthic interface, has been shown to be responsible for the majority of the oxygen demand on an areal basis (Thomas et al. 1976). If an average oceanic DOC value is taken as 0.80 mg C/1 (Sharp 1975) and is viewed as the upper limit of refractory carbon in an oceanic environment, then anything greater than 0.8 can be considered labile. By adding 0.80 and 2.70, we get 3.50 mg C/1 as an amount sufficient to provide a 100- percent oxygen demand and leave the residual refractory oceanic value. From table 4-8, we can see that many of the samples in the Bight Apex have potential oxygen de- mands sufficient to cause anoxia if the organic degradation were rapid in comparison to oxygen replenishment. More startling is that all the averaged bottom water values (fig. 4-15) for the Apex have sufficient DOC to deplete the oxygen present if no oxygen renewal occurs. The bottom waters of the Bight are not physically stagnant and the general circulation is southwestward (Bumpus 1973; ch. 7). However, this circulation also develops gyres and areas of very sluggish circulation (ch. 8). Thus, unless a source of oxygen-rich, organic-poor water is postulated, we would expect the water in this region to continue to pose a large oxygen demand until the autumnal breakdown of the thermocline. Therefore, from examination of the data acquired dur- ing August-September 1976, it is concluded that DOC (1) was not exceptional in the Hudson-Raritan estuary; (2) was possibly higher than normal (compared to other coastal areas) in the lower portion of New York Bight; and (3) was extraordinarily high in the Apex. There is no way of knowing whether the high Apex values are unusual as compared to other years. If they are, they could have resulted from the combined effects of the large Ceratium bloom in summer 1976 and the estuarine circulation of the Apex. POC did not show exceptional values in these areas. In the Apex, the organic carbon values are more than sufficient to give a potential oxygen demand that could totally deplete the D.O. in the bottom waters. CHEMICAL RESPONSES In 1976 oxygen demand loading in the bottom waters of the Bight depleted D.O. levels to near anoxic or anoxic conditions over an area roughly equal to segments A, Jl, J2, Ml, and part of M2. We will now examine how the Bight chemistry changed as a resuU of this depletion by briefly discussing it in the light of other chemical events associated with anoxic development. Evidence for nitrate reduction is presented above in the discussion of nutrients where plots of NH^*, NO,", and NO3" versus D.O. are shown for cruise XWCC-11 (fig. 4-14). Although there is no clear evidence that NOr was removed from the system as oxygen declined, the peak 119 NOAA PROFESSIONAL PAPER 11 80 Q. 70 - LU (/) LU Z < 60 - ^ -J 40 h O CO Q 30 L O O 20 OQ O I- 10 - 1 1 ' 1 o ' 1 1 1 ■ 1 1 XWCC-11 - o o APEX A HUDSON □ REST OF BIGHT — — - A - — O O O — - D D ■ O D ^ o - A D O o - — D — - A - — A D D o — ■ (III .^1 1 lA 1 hi 1.0 2.0 3.0 4.0 5.0 6.0 DISSOLVED OXYGEN (ml/ 1) FIGURE 4-18. — Dissolved manganese and dissolved oxygen concentrations in bottom samples September 1976. XWCC cruise 11. 120 CHAPTER 4 in NOj" concentration at about 1.6 ml/1 oxygen, and an exponential increase in NHj* concentrations below 2.0 ml/1, are evidence that reduction of NO,~ to NO. and then to NHj* occurred. Whether or not reduction to el- emental nitrogen or N.O took place cannot be determined from the data available. There is ample evidence that SOj ' reduction occurred throughout the oxygen-depleted area (Steimle 1976). Hy- drogen sulfide was detected up to 15 m from the bottom in the oxygen-depleted area but not above the thermo- chne. Sulfide levels were high and reached 1.76 mg/1 (Draxler and Byrne, personal communication). The H^S was also evident in apparent upwelling of anoxic bottom water along portions of the central New Jersey coast and was probably partially responsible for the high mortalities of benthic organisms. Segar and Cantillo (1976) have shown that in the Apex, bottom dissolved manganese concentrations ranged from 1.0 ppb to as high as 40 ppb; the highest values were associated with bottom water near the Hudson-Raritan discharge. Dissolved iron concentrations ranged from 2.0 ppb to 40 ppb, with one sample of 92 ppb in June 1974, near the acid waste dumpsite. If the oxygen depletion was sufficient to reduce Mn(lV) to Mn(II), and Fe(III) to Fe(II), in areas where sulfide was present, we should have seen an increase in dissolved manganese and iron concentrations. Where oxygen was depleted the manganese concentration increased almost exponentially to very high values (fig. 4-18). We assume this must be due to reduction of manganese to Mn*- and the higher solubility of species formed by this oxidation state. An attempt to show the same effect for iron is given in figure 4-19; however, here the picture is not so clear. Even in low oxygen areas, values for dissolved iron were about the same as those in earlier years (Segar and Cantrllo 1976). Any increase in dissolved manganese and iron over the short time scale represented by the 1976 anoxic event probably results from dissolution of these metals from suspended particulate matter. A 2-month period probably is not long enough for appreciable amounts of these metals to diffuse out of the bottom sediments. Betzer (personal communication) pointed out that if this is so, manganese should appear in the dissolved phase before iron since it is more concentrated in the weak acid soluble phase of the particulate matter whereas iron is more concentrated in the refractory phase. This, then, may explain why XWCC-11 data showed no increase in dissolved iron in low oxygen areas. If the deficiency in oxygen had contin- ued for some time, the iron concentration would have increased as did manganese. Thus, the chemical responses in New York Bight in summer 1976 were very similar to those noted in other anoxic areas of the ocean. SUMMARY Dissolved oxygen in bottom waters of the New York Bight shelf (especially in the Apex and off the New Jersey coast) was severely depleted in 1976 compared to other years for which there are data. Although D.O. depletion is an annual occurrence during the warm season (that is, when the density stratification is strong), it occurred ear- lier in 1976 and was more severe. In certain areas, D.O. values were zero or near zero. Other than this severe oxygen depletion, no clear chem- ical differences were detected in the water column be- tween 1976 and other years represented by the data base. Apparently, there was no exceptional nutrient input to stimulate productivity. In fact, there is some evidence that fewer nutrients may have been available at the shelf break in 1976. If this is true, it might have affected the types of organisms found in shelf waters; that is, it could have favored production of organisms such as Ceratium tripos. Also, there is no chemical evidence of exceptional inputs of organic carbon either as POC or DOC although there is strong biological evidence for a very dense plankton bloom (Ceratium tripos), which certainly contributed to the organic loading. The high DOC levels present in the Bight had the capacity to cause the depletion observed. Clearly something was different in 1976, and perhaps this "something" was a natural occurrence. Since an ad- equate existing data base covers only a short time span (post-1970) and lacks many essential variables, we cannot ascertain what this was. It is significant that extraordinary DOC values exist in the Bight, especially in the Apex. Our limited data do not allow a comparison of 1976 DOC levels with those of previous years nor do they allow much insight into the chemical or physical nature or variations in space and time of the organic matter that is lumped into the category of DOC. More information on organic matter perhaps could provide insights into future events of a similar nature. The observed chemical responses of Bight seawater to the oxygen depletion were as expected, based on our knowledge of other low oxygen or anoxic areas in the ocean. When oxygen was depleted, nitrate was reduced to nitrite and then ammonium, sulfate was reduced to sulfide, and the solubility of certain metals changed as the reducing environment developed and caused changes in their oxidation states. ACKNOWLEDGMENTS Data from NOAA Salt Marsh samples for organic mat- ter were provided by Franklin R. Daiber of the University of Delaware. Data from TransX cruises are from a study by J. H. Sharp, University of Delaware, supported in part by NSF Grant OCE 76-82571. 121 NOAA PROFESSIONAL PAPER 11 60 Si Q. Q. 50 O Q LU O CO CO 40 30 I- O m 20 < I- O 10 o o D D o A T XWCC-11 o APEX A HUDSON D REST OF BIGHT o o J \ \ ^ \ ^ L o 8 1.0 2.0 3.0 4.0 5.0 6.0 DISSOLVED OXYGEN (ml/I) FIGURE 4-19. — Dissolved iron and dissolved oxygen concentrations in bottom samples September 1976, XWCC cruise 11. 122 CHAPTER 4 REFERENCES Berberian, G A., and Barcelona, M J., 1979 Comparison of manual and automated methods of inorganic micronutrient analyses, NOAA Tech. Mem. ERL AOML-40. Bumpus, D. F., 1973. A description of the circulation on the continental shelf of the east coast of the United States, Progress in Oceanography 6:111-157, Pergamon Press. Deuser, W. B., 1975 Reducing environments, in J. P. Riley and G Skirrow (eds.). Chemical Oceanography, 2d ed., vol. 3, Academic Press, New York, pp 1-37. Duedall, I. W., Bowman, M J ,and O'Connors, H B., 1975. Sewage sludge and ammonium concentrations in the New York Bight Apex, Esluar Coastal Mar. Set. 3:457-^63. Duedall, I. W., O'Connors, H. B , Oakley, S A , and Stanford, H. M., 1977. Short-term water column perturbations due to sewage sludge dumping in the New York Bight Apex, y Water Potlui Control Fed. Dugdale, R. C, Goenng, J J , Barber, R T, Smith, R L , and Packard, T. T., 1977. Denitrification and hydrogen sulfide in the Peru up- welling region during 1976, Deep-Sea Res 24:601-608 Fanning, K A., and Pilson, M. E. Q., 1973. On the spectrophotomatic determination of dissolved silica in natural waters. Anal. Chem. 45, 136 pp. IDOE Workshop on Anoxia on the Middle Atlantic Shelf During the Summer of 1976. October 15 and 16, 1976, in Washington, DC, J. H. Sharp (ed.). Menzel, D. W., and Vaccaro, R. F., 1964. The measurement of dissolved organic and particulate carbon in seawater, Limnol. Oceanogr. 9:138-142. National Marine Fisheries Service, 1977. Oxygen depletion and associ- ated environmental disturbances in the Middle Atlantic Bight in 1976, Northeast Fisheries Center Tech. Ser. Rep. No. 3, Sandy Hook Laboratory. Highlands, N.J., 471 pp Redfield, A. C, Ketchum, B H , and Richards, F. A , 1963. The in- fluence of organisms on the composition of seawater, in M. N. Hill (ed.). The Sea. vol. 2, Interscience (New York), pp. 2-77. Richards, F. A., 1965. Anoxic basins and fjords, in J. P. Riley and G. Skirrow, (eds.). Chemical Oceanography, vol. 1, Academic Press, New York, pp. 611-645. Richards, F. A., Cline. J. D . Breonokow, W. W., and Atkinson. L. P., 1965. Some consequence of the decomposition of organic matter in Lake Nitinat. an anoxic fjord. Limnol. Oceanogr. 10 (suppl): R185-R201. Riley, G. A., 1967. Mathematical model of nutrient conditions in coastal waters. Bull. Bingham Oceanogr. Coll. 19:72-80. Riley, J. P., and Skirrow, G. (eds), 1975. Chemical Oceanography, 2d, ed., Academic Press, New York, Appendix. Table 6. Ryther, J. H., and Dunstan. W. M . 1971 Nitrogen, phosphorus, and eutrophication in the coastal environment. Science 171: 1(K)8-1013. Segar, DA., and Berberian, G. A., 1976. Oxygen depletion in the New York Bight Apex: Causes and consequences, in M. G. Gross (ed). Middle Atlantic Continental Shelf and the New York Bight, Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:220-239. Segar, D. A., and Cantillo, A. Y., 1976 Trace metals in the New York Bight, in M. G. Gross (ed). Middle Atlantic Continental Shelf and the New York Bight, Amer. Soc. Limnol. Oceanogr. Spec, Symp. 2:171-198. Sharp, J. H., 1973. Total organic carbon in seawater, comparisons of measurements using persulfate oxidation and high temperature com- bustion. Mar. Chem. 1:211-229. Sharp, J. H., 1974. Improved analysis for "particulate" organic carbon and nitrogen from seawater, Limnol. Oceanogr. 19:984-989. Sharp, J. H., 1975. Gross analyses of organic matter in seawater: Why, how, and from where, in T. M. Church (ed). Marine Chemistry in the Coastal Environment, ACS Symposium Series 18, Amer. Chem. Soc, pp. 682-696. Sharp, J. H., 1976. A general box model approach, in J. H. Sharp (ed). Anoxia on the Middle Atlantic Shelf During the Summer of 1976, National Science Foundation Workshop Report, pp 63-70. Sharp, J. H., Church, T. M., and Culberson, C. H., 1979 Biochemical dynamics in Middle Atlantic coastal waters (in preparation) Smith, K. L., Jr., Rowe, G. T., and Clifford, C. H , 1974. Sediment oxygen demand in an outwelling and upwelling area, Tethvs 6:223-230. Steimie, F., 1976 A summary of the fish kill — anoxia phenomenon off New Jersey and its impact on resource species, in J. H. Sharp (ed), IDOE Workshop on Anoxia on the Middle Atlantic Shelf During the Summer of 1976. Strickland, J. D. H., and Parsons, T. R., 1968. A practical handbook of seawater analysis. Bull. Fish. Res. Board Can. 167, 311 pp. Thayer, G. W., 1970. Comparison of two storage methods for analysis of nitrogen and phosphorous fractions in estuarine water, Chesa- peake Sa. 11:155-158. Thomas, J. P., Phoel, W. C, Steimie, F W, O'Reilly, J E, and Evans, C. A., 1976. Seabed oxygen consumption in the New York Bight Apex, in M. G. Gross (ed. ), Middle Atlantic Continental Shelf and New York Bight, Amer. Soc. Limnol. Oceanogr. Spec. Svmp. 2:354-269. Walsh, J. J., Whitledge, T. E., Kelley, J. C, Hurtsman, S. A , and Pillsbury, R D.. 1977. Further transition states of the Baja Cali- fornia upwelling ecosystem, Limnol. Oceanogr. 22:264-280. 123 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 5. Physical Conditions Compared With Previous Years John B. Hazelworth and Shailer R. Cumniings' CONTENTS Page 125 Introduction 126 Density (sigma-t) 129 Temperature 129 Salinity 135 Dissolved Oxygen 135 Summary 135 Acknowledgments ' Atlantic Oceanographic and Meteorological Labo- ratories, Environmental Research Laboratories, NOAA, Miami, FL 33149 INTRODUCTION Dissolved oxygen content of water in New York Bight has an annual cycle. In general, it reaches its well-mixed maximum during the winter, then gradually decreases dur- ing spring, dropping to its minimum during summer. The minimum is considerably lower at the bottom than at the surface. In the autumn, cold air and storms cool surface water, break down the thermocline, introduce oxygen into the water, and cause mixing to greater depths. The oxygen content in the water increases until it again reaches its maximum during winter. The causes of the autumnal oxy- gen increases are physical and fairly well understood. The processes causing the spring and summer oxygen decline, however, are not as well understood. Apparently, atmos- pheric, biological, and chemical processes combine with physical processes to bring about the oxygen decrease. To compare 1976 physical conditions with those of pre- vious years, physical data were obtained from several sources: 1. Seven MESA expanded water-column character- ization (XWCC) cruises in 1975, four XWCC cruises in 1976, and nine water-column character- izion (WCC) cruises in 1974, all by NOAA's At- lantic Oceanographic and Meteorological Labo- ratories (AOML); 2. Monthly mean sea-surface temperatures, com- piled by NOAA National Marine Fisheries Serv- ice's (NMFS) Atlantic Environmental Group (AEG) from ship reports, and from data provided by NOAA Environmental Data and Information Service's National Climatic Center (NCC); 3. Oceanographic data from Lamont-Doherty Geo- logical Observatory of Columbia University; 4. Oceanographic data from NMFS laboratories at Sandy Hook, N.J., and Woods Hole, Mass.; 5. Oceanographic data from Virginia Institute of Marine Science (VIMS); and 125 NO A A PROFESSIONAL PAPER 11 6. Monthly mean sea-surface temperature at tide sta- tions at Atlantic City, N.J., from NOAA's Na- tional Ocean Survey. Since environmental conditions in New York Bight were extensively documented by XWCC cruises in 1975 and 1976, the primary comparisons were between these 2 years — 1976, a year of anoxic conditions, and 1975, a year without anoxic conditions. Four XWCC stations — 23, 38, 69, and 88 (station locations shown in fig. 2-1 of chapter 2) — were chosen for comparison, because they were con- sidered representative of the Bight Apex, Hudson Shelf Valley, Long Island shelf, and New Jersey shelf regions, respectively. DENSITY (Sigma-/) Physical properties in all four areas could be compared in 1975 and 1976, the only 2 years during which all XWCC stations were occupied. Station 23 was occupied several times during 1974, providing a long record. Depth vs. time plots of temperature, salinity, and density or sigma-/ (ct,) were drawn for 1975 and 1976 for each station. Similar plots were drawn for 1974 for station 23. Figure 5-1 shows the CT, plots for station 88. From the plots, a gross indication of the strength of the density gradient was computed, using surface-to-bottom differences of interpolated (midpoint of month) cr, divided by depth. Ratios of these monthly values were obtained for comparisons between years. Averages within years and stations were then computed from the monthly a, gradients (table 5-1). Monthly ct, gradients less than 0.01 were ex- cluded to eliminate the influence of nonstratified condi- tions on the mean. The mean of the 1976/1975 ratios was about the same for all stations, varying between 1.3 and 1.6, indicating that the a, gradient was uniformly stronger during 1976. In contrast, at station 23 the mean ratio between 1976 and 1974 was 1 .0, indicating the strength of the pycnocline was comparable in those years. A month-by-month compari- son of 1976/1975 ratios indicates ct, gradients were similar at all stations during July, August, and September, but were significantly greater in 1976 during April, May, and June, with the exception of June at station 88. During April 1975, isopycnic or nearly isopycnic conditions were observed. In April 1976, stratification was apparent at all stations and was most intense at station 23. Stratification was developed by May 1975, apparently about 2 to 4 weeks later than during 1976. Maximum stratification was reached sometime during the summer, varying in time from area to area. Maximum occurred during June or July in 1976, but not until July or August in 1975. After reaching a maximum, the gradient gradually decreased through Sep- tember. Table 5-1.- —Sigma-t gradients (^(JJm) Station Year Mar. Apr. May June July Aug. Sept Mean Station 38 1975 0.005 0.010 0.030 0.035 0.037 0.037 0.026 1976 0.007 0.029 0.040 0.053 0.040 0.039 0.035 Ratio 75/76 1.4* 2.9 1.3 1.5 1.1 1.1 1.6 Station 23 1974 0.059 0.075 0.072 0.132 0.092 0.074 0.084 1975 0.003 0.020 0.078 0.110 0.112 0.076 0.067 1976 0.046 0.059 0.092 0.100 0.088 0.069 0.076 Ratios 75/76 15.3* 3.0 1.2 0.9 0.8 0.9 1.4 76/74 0.8* 0.8 1.3 0.8 1.0 0.9 1.0 74/75 19.7* 3.8 0.9 1.2 0.8 1.0 1.5 Station 69 1975 0.011 0.020 0.070 0.101 0.100 0.068 0.062 1976 0,027 0.040 0.104 0.098 0.089 0.079 0.073 Ratio 76/75 2.4* 2.0 1.5 1.0 0.9 1.2 1.3 Station 88 1975 0.005 0.000 0.017 0.077 0.101 0.101 0.068 0.062 1976 0.026 0.015 0.050 0.071 0.107 0.119 0.066 0.071 Ratio 76/75 5.2* — • 2.9 0.9 1.1 1.2 1.0 1.4 •Value not used in the computation of the mean of the monthly ratios. 126 CHAPTER 5 SIGMA-t, STATION 88, 1975 u m ■* u u u u s 5 X X Jan Feb fAar Apr May ' Jun ' Jul ' Aug Sep Oct Nov Dec FIGURE 5-lA — Sigma-J vs. time at station 88 in 1975 SIGMA-t, STATION 88, 1976 H- + Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec FIGURE 5-lB.— Sigma-f vs. time at station 88 in 1976. 127 NO A A PROFESSIONAL PAPER 11 6.0 5.6 5.2 4.8 4.4 4.0 3.6 i- o l/> 28 < 2.4 2.0 1.6 1.2 0.8 0.4 0.0 OBSERVED VALUES A 1975 • 1976 STATION 69 "T ; 1 1 STATION 23 Mar Apr May Jun Jul Aug Sep Od Nov Dec MONTH STATION 88 OBSERVED VALUES ▲ 1975 • 1976 o 2.4 2.0 1.2 0.8 Jan Feb Mar Apr Mar Jun Jul Aug Sep Ocl Nov OBSERVED VALUES ■ 1974 ▲ 1975 • 1976 Jan Feb Mar Apr May Jun Jul Aug Sep Ocl Nov Dec MONTH FIGURE 5-2. — Sigma-/ differences between surface and 30 m vs. time for stations 69, 88, and 23. MONTH 128 CHAPTERS Density differences at station 88 (fig. 5-2) were signif- icantly greater during 1976 for March, April, and May, but were slightly less during the summer months. At sta- tion 23 the differences between April and May were sim- ilar in 1974 and 1976, but were considerably greater than for the corresponding time in 1975. At station 69 the strat- ification was more strongly developed in 1976 than 1975 until the autumnal breakdown. TEMPERATURE During the first half of 1976, the monthly mean air temperature had a number of anomalous features. Ac- cording to Diaz (ch. 3), January was somewhat colder than normal, whereas extreme warm air temperatures prevailed during February and March. During April the mean air temperature remained about 1° to 2° C above normal, but the monthly mean temperature masked a large change in April. Record cold weather prevailed dur- ing the first half of April, followed by record warmth in the second half. We can conclude that average air tem- peratures over New York Bight during the first 4 months of 1976 were only slightly above normal — record cold pe- riods partially offset record warm periods. Monthly mean sea-surface temperatures for the Bight Apex and Long Island area for 1975 and 1976 were com- pared with historical mean temperatures (fig. 5-3). The monthly mean sea-surface temperatures for February, March, and April 1976 exceeded the long-term mean and, qualitatively at least, correlate with the corresponding mean monthly air temperatures. Monthly sea-surface tem- perature anomalies (departure from 1949-76 mean) for 1974, 1975, and 1976 are compared in figure 5-4. They indicate that the mean monthly sea-surface temperatures for the January-April period were 1° to 2° C above normal for all 3 years. During the winters, temperatures decreased until February (fig. 5-3), when the mean monthly tem- perature was minimum. A spring warming trend was re- corded for March. An above-normal sea-surface temper- ature continued through spring and summer during all 3 years. In May and June 1975 temperature increases ex- ceeded the more normal conditions as reflected in May and June in 1976. Temperature variations with depth were plotted as a time series for station 88 (fig. 5-5). Temperature data from moored current meters (stations LT2 and LT4) sup- plemented the temporal data from cruises. (See chapter 7, fig. 7-7.) During March 1975 and 1976 the water was nearly isothermal, varying between 5° and 6° C. The March warming trend did not result in significant thermal structure until mid-April in 1976 and in late April 1975. By mid-April 1976, the mean surface temperature was 1.7° C warmer and the mean bottom temperature 1.2° C warmer than during the corresponding period in 1975. During May and June this differential continued. The ther- mocline during the summer months remained strong and at a near-constant depth. Surface and bottom tempera- tures in July and August were about the same for the 2 years. By September of both years (fig. 5-5) the temper- ature had begun to decrease, with a corresponding gradual deepening of the thermocline. By the first of October 1976, the surface temperature was about 3° C higher and the bottom temperature was about 1° C higher than at the corresponding time in 1975. From the moored-meter temperature data (fig. 5-5), the bottom temperature minimum for the 1975-76 winter varied between 4° and 5° C and was maintained from Jan- uary 23 to February 21, 1976, at which time the temper- ature began to increase. From about February 26, bottom temperature data were recorded for both 1975 and 1976. From that date until April 10, the bottom temperature was about the same for both years. After April 10, 1976, warming increased at a much greater rate than during the corresponding period of 1975. The moored-meter tem- perature data indicated the record warmth lasted until April 26. The temperature difference curves in figure 5-6 were constructed using interpolated values from figure 5-5 and a similar figure for station 69 (not shown). April and May had a slightly greater surface-to-bottom temperature dif- ferential in 1976 than in 1975. In summer 1975 and 1976 the temperature differential between surface and bottom waters was greater at station 69 than at station 88. SALINITY Salinity stratification was very prominent at all stations during April 1976, in contrast to the same period in 1975 when stratification was slight. During March, stratification was considerably greater in 1976 than in 1975 at station 88 (fig. 5-7). At station 23, however (fig. 5-7), stratifi- cation was quite low during March 1974 and 1976. The greatest contrast between years was in April in the Bight Apex (station 23). There, salinity stratification was sig- nificantly greater during April-May 1974 and 1976 than during the same period in 1975. At station 88 stratification was considerably greater in 1976 during March, April, and May than in 1975. At station 69 during April 1976 strat- ification was greater than April 1975 (fig. 5-7). During March and May, stratification was about the same for the 2 years. During the summer, stratification appeared to be greater during 1975 at stations 23 and 88 than in 1976. Armstrong (ch. 6) compared monthly discharge rates for the Delaware and Hudson rivers for 1976 with long- term means and extremes. The discharge rate usually reached a maximum in April when it was significantly 129 40 35 30 25 NOAA PROFESSIONAL PAPER 11 u o < 20 LU Q- 15 LU »- 10 I I I I I r Data From 40°-41 "N, 73°-7A''VJ, Bight Apex • ■• Range of Extremes o o Mean Temperature 1949-1976 D D Mean Temperature 1975 X X Mean Temperature 1976 Jan Feb Mar Apr Mar Jun Jul Aug Set Oct Nov Dec FIGURE 5-3. — Comparison of monthly mean sea-surface temperature for 1975 and 1976 witti range of historical values. +4 I 1 1 1 1 1 1 1 r U o >- -J < O < HI Q. FIGURE 5-4. — Comparison of monthly sea-surface temperature anomalies for 1974. 1975. and 1976. 130 CHAPTERS TEMPERATURE (°C), STATION 88, 1975 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec FIGURE 5-5A. — Temperature vs. time, station 88 in 1975. TEMPERATURE (°C), STATION 88, 1976 + Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec FIGURE 5-5B.— Temperature vs. time, station 88 in 1976. 131 NO A A PROFESSIONAL PAPER 11 1 1 1 1 < 1 1 1 1 1 1 1 1 1 1 1 a> - r > o - ^_-*— -^ Z 6 ^ a. t/) ^ o> ^ 3 < "-'' 4 ~- — --~__V^ 3 ♦==^5^^ "• ^^""^"*^^--— --_ C 3 '^'^•^r--^ D ^^^^^^~^~~^::;"^~-^ s - ^^^^^^^ Q. < CO Z3 ^^\\ 00 < 1\ , n 1 ION Q UJ > o - Z 6 — ""^ a. ^ *~ Ul N < - \ \ D - o Q \ > m ^ 1- < BSER 197 197 \ \ V I— o -4 • \ CO 1 , > 1 1 4 1 1 1 1 1 1 1 1 o. E H I U ID a (Oo)3aniva3di/\i3iv 132 CHAPTERS 2.5 ' 1 OBSERVED VALUES " A 1975 ' ' 1 STATION 88 _ o • 1976 fe^ 2.0 - - >- z _l < to 1.5 1.0 - V / / -\\ - < 0.5 0.0 ^ — ^M^^ y V Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 3.0 1 OBSERVED VALUES I 1 1 STATION 69 r 2.5 " A 1975 • 1976 fe5 2.0 - — >- 1.5 - ^ - ►— ' • z i ^'^ ^^s.^^^ — 1 < to 1.0 •r^ / ^v < 0.5 0.0 ^ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec FIGURE 5-7. — Salinity difference between surface and bottom vs. time, stations 2.'?, 88, and 69. 133 NO A A PROFESSIONAL PAPER 11 80 -"^ 7.0 \ E 6.0 Z LU .so o >- X o 4.0 30 00 8.0 "1 r 1 1 1 1 1 STATION 69 SURFACE o 2.0 — t/> u^ ▲ 1975 o 1.0 • 1976 BOTTOM Jan Feb Ma r Apr May Jun Jul Aug Sep Oct Nos Dec c: 7.0 - J 6.0 O 5° >- X O 4.0 3.0 to 2.0 Q 1.0 0.0 1 1 STATION 88 URFACE SURFACE A 1975 • 1976 BOTTOM Jon Feb Mc Max Jun Jul Aug Sep Oct Nov Dec FIGURE 5-8. — Surface and bottom dissolved oxygen vs. time, stations 69 and 88. 134 CHAPTER 5 greater than any other month. However, in 1976, an ab- normally high discharge rate was recorded during Feb- ruary, and was largely sustained into May. Thus, near- surface waters, especially at station 23, should show un- usually low salinity with correspondingly greater stratifi- cation. This is in part corroborated by the April high- density ratio (1976/1975) value of 15 at station 23 (table 1). The April and May 1976 salinity differences (fig. 5-7) are relatively higher than in 1975, implying that the dis- charge of the Hudson River was either greater or more confined to the Bight Apex during 1976. DISSOLVED OXYGEN In April 1976 surface oxygen values were higher and bottom oxygen values lower than in April 1975 (fig. 5-8). Consequently, oxygen stratification was pronounced by April 1976, but a well-mixed condition existed in April 1975. Stratification development was not apparent until June or July 1975. As summer progressed, surface oxygen decreased in both years, but generally continued over 100 percent sat- uration. The only exception was at station 88, where sur- face oxygen values fell slightly below lOU percent satu- ration during July, August, and September 1975. As summer advanced in both years, bottom oxygen val- ues decreased at rapid rates, but the 1976 rate was con- siderably greater. (See chapter 4.) SUMMARY Seasonal density stratification began about 1 month ear- lier in 1976 than in 1975 (April vs. May), because of early seasonal heating (thermal stratification) and, more im- portantly, strong and sustained river discharge (salinity stratification). Subsequently, the rate of bottom replen- ishment of dissolved oxygen from the sea surface was less than that of 1975. ACKNOWLEDGMENTS Adriana Cantillo and Dennis Mayer of ERL/AOML and Steacy Hicks of NOS provided necessary data. The following individuals contributed data sets used in the analysis: Tom Azarovitz of NMFS, Woods Hole; Art Ken- dall, Frank Steimle, and W. G. Smith of NMFS, Sandy Hook; Frank Aikman of Lamont-Doherty Geological Observatory; and E. P. Ruzecki of Virginia Institute of Marine Science. D. V. Hansen made helpful suggestions. The officers and crew of NOAA ships George B. Kelez and Researcher devoted long and diligent hours in ac- quiring data. 135 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 6. Bottom Oxygen and Stratification in 1976 and Previous Years Reed S. Armstrong' CONTENTS Page 137 Introduction 137 Climatological Conditions 139 Oxygen Cycle and Stratification 142 Stratircation and Dissolved Oxygen in 1976 143 Regional Aspects 147 Previous Benthic Mortalities 147 Summary 148 Acknowledgments 148 References ' Atlantic Environmental Group, National Marine Fisheries Service, NOAA, Narragansett, Rl 02882 INTRODUCTION The areal extent of the 1976 anoxic condition implies that broad-scale, climatic events may have contributed to the depletion of dissolved oxygen (D.O.). Although the area of depleted oxygen extended widely over the conti- nental shelf off New Jersey, it apparently did not develop to the north, off Long Island, nor to the south, off the Delmarva Peninsula. Therefore, if unusual climatic con- ditions did contribute to the anoxia and resulting benthic mortalities, then other distinct differences among these three regions of the Middle Atlantic Bight should be ap- parent. To examine the impact that climatic events in the marine environment may have had on the generation of anoxic conditions, historical and climatological data were com- piled for comparison with conditions observed in 1976. Included were monthly mean air and sea-surface temper- ature records and oceanographic data from the National Climatic Center (NCC), National Oceanographic Data Center (NODC), National Ocean Survey (NOS), and National Weather Service (NWS) of the National Oceanic and Atmospheric Administration (NOAA), and river dis- charge records from the U.S. Geological Survey. Data from oceanographic stations occupied in the area in 1976 were provided by NOAA National Marine Fisheries Serv- ice's (NMFS) Sandy Hook Laboratory, and NOAA En- vironmental Research Laboratories' Atlantic Oceano- graphic and Meteorological Laboratories (AOML). CLIMATOLOGICAL CONDITIONS Springtime conditions in 1976 began developing 1 to 2 months earlier than normal (ch. 3). Monthly mean air 137 NO A A PROFESSIONAL PAPER 11 30 ^ 20 u o O 3 a E 10 \ 1 1 \ 1 r 1 1 1 1 ■ Air Temperature at Atlantic City . - - _ Range of Exiremes ^^>^- ^ 1975-1976^ ' /^'/'' % ^29-Year Mean Souices NCC/EDS NWSandSlat Rep Serv US DepI flqri 1 1 1 1 1 1 1 1 1 1 1 -10 Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 30 [ 1 '• 1 1 1 1 1 1 ^ f 20 3 O Q) a E 0) 1 1 1 1 r~ Sea-Surface Temperature at Sandy Hook Range of Extremes (1945-1975) *"///_ 1975- 1976 -10 30 31-Year Mean Sou'ce N05 Tide Station Data _1 1 I I \ I I I Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct 1 1 1 1 i I I I I r Sea-Surface Temperature Over New Jersey Sfieif Source NCC/EDS J I FIGURE 6-1— Monthly mean air and sea-surface temperatures for New Jersey shelf. 1975-76 and historical record. 138 CHAPTER 6 temperature records at Atlantic City showed that in 1976 one of the coldest Januarys was followed by one of the warmest Februarys of the 30-year record. Sea-surface tem- peratures also followed this general trend (fig. 6-1). Al- though air and sea-surface temperatures in the spring were unusually warm, they were not unique. Perhaps more significant for hydrographic conditions than early warming was that the normal spring increase in river discharge in 1976 began about 2 months early. Monthly mean discharge for February 1976 in the Hudson River was greater than for any February of the preceding 29 years (fig. 6-2). The discharge rate in February was comparable to the normal peak discharge that typically occurs in April. A comparison of historical data and monthly mean dis- charge rates in 1976 indicated a record high discharge in February into Long Island Sound (48 years of record: 1929-76) and the second highest of record for the Dela- ware River (36 years of record: 1941-76). On the Dela- ware River, the monthly mean discharge in February 1976 (760 mVs) was greater than the long-term monthly mean for the peak discharge month (616 mVs in April). The February 1976 discharge rate into Long Island Sound (1,651 mVs) was almost as large as the average value for peak-month discharge (1,866 mVs in April). In their de- scription of the seasonal cycle of hydrographic conditions in the New York Bight Apex, Bowman and Wunderlich (1976) noted the close connection between the time of decrease in surface salinities and the usual March-April increase in discharge from the Hudson River. Therefore, an early river discharge of magnitude comparable to the normal spring peak value would have led to a 2-month earlier than normal freshening of surface waters over at least the Bight Apex. The results of these unusual climatic events during" the Dec Jan Feb c o E 1500 1000 500 Ap r Ma y Jun Jul 1 1 1 Record For Month 19 1947- 1975 Source: Data Irom USGS provisional record I I I 1 FIGURE 6-2— Monthly mean discharge of Hudson River at Green Island, N.Y., in 1976 and long-term means and extremes. first months of 1976 would probably have caused 1) de- struction of any remaining stratification in the shelf waters during the strong cooling in January, and 2) a 1- to 2- month earlier than normal reestablishment of stratifica- tion, resulting from the early decrease of surface salinities due to the early occurrence of spring discharge. Chapters 2 and 5 indicate that early warming had minimal effect on density structure. In principal, early warming should have worked in unison with river discharge and minimal storm activity to promote early stratification, since the salinity layering would not have been destroyed by overturning from the continued decline in surface water temperatures that is typical for that time of year. Indications of the early onset of thermal stratification in 1976 are described and compared with historical data in chapter 5. OXYGEN CYCLE AND STRATIFICATION The annual cycle of D.O. in bottom waters over the continental shelf off New Jersey is shown in figure 6-3. For this analysis the D.O. measurement at the greatest sampling depth in excess of 20 m for each station with bottom depths greater than 20 m and less than 60 m was used; values were compiled by cruises. These depth cri- teria were used to limit the analysis to shelf waters below the pycnocline during spring and summer, or comparable depths in months when the waters are unstratified. For each cruise, the bottom-water oxygen observations were averaged and plotted in figure 6-3, along with the range of values on the average date of station occupation, re- gardless of year. Data were used from 28 cruises (82 sta- tions) between 1932 and 1973. Observations were avail- able in all months. Hand-smoothed curves were drawn through the values to derive a mean annual trend. Rep- resentative maximum and minimum curves were drawn to depict the normal range of conditions. Stratification data were developed from temperature and salinity observations for the same stations used in the analysis of D.O. For each station, surface ct, values were subtracted from s X O _> O «/> (/> 8 ■? 6 2 - T 1 1 1 1 r "I 1 1 r •Hf P \ u Observations in 1976 ^ •• \ Annual Trend Smoothed Range of Values New Jersey Shelf •Ix X /tt -*-\ J L J L J L Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct • / c o ^^ 4 (A c 0) o ■ ft"- t Observations in 1976 New Jersey Shelf Smoothed Range of Values _ . . „„ T 1 Range of Valu Cruise Average *-{ \ . ^i ^ . 2 J for the Cruise _L J_ FIGURE 6-3. — Dissolved oxygen levels in bottom waters (>20 m) and vertical density stratification (surface-subpycnocline a, difference) of New Jersey-Cape May shelf waters. 1976 and historical record. Historical data from EDIS/NODC and WHOI (1961 publ.); 1975-76 cruise data from NMFS/SHL and ERL/AOML. 140 CHAPTER 6 Belle were excluded because of uncertainties about the storm's effects on the normal cycle of D.O. Parallel patterns in the normal annual cycles of strati- fication and D.O. in the bottom waters off New Jersey (fig. 6-3) imply a direct relation between the two. During autumn, surface cooling in shelf waters causes overturning and vertical mixing. This diminishes the stratification and replenishes oxygen in the bottom waters. By December and continuing through March, shelf waters are essentially unstratified and bottom waters are saturated with D.O. Further increases in bottom D.O. during winter result from increased oxygen solubility of the water brought about by decreasing water temperature. Bottom D.O. in- creases to the annual average maximum of about 7.0 ml/ 1 in March. Initiation of stratification normally begins during April when surface water density declines, because of warming (fig. 6-1), and river discharge increases (fig. 6-2). With the onset of stratification, vertical replenishment of oxy- gen into the bottom water becomes limited. Within the normal ranges and cycles of water circulation and biolog- ical activity, utilization exceeds replenishment, resulting in a decrease in oxygen concentration. Based on the his- torical data of figure 6-3, the annual minimum D.O. value occurs in August, averaging about 2.9 ml/1. In September, when surface cooling begins to destroy stratification, re- plenishment exceeds utilization and oxygen concentra- tions increase. To depict the correspondence between increase in strength of stratification and D.O. decline, monthly values of both were derived from the annual trend curves of historical data in figure 6-3. For each 1-month period from mid-March through mid-August (spanning the interval of developing stratification and of declining D.O.), monthly means of the strength of stratification were computed. Against these were plotted the amount that D.O. declined during the corresponding 1-month periods; the data points were connected by a hand-smoothed curve to give monthly rates of oxygen decline as a function of stratification (fig. 6-4). To provide some estimate of the range of conditions around the average trend curves, similar monthly com- putations were made from the smoothed ranges of values in figure 6-3, assuming that the high D.O. values corre- spond to weakest stratification and low oxygen to strongest stratification in a given month. Again, smooth curves were drawn through the data points. As stratification increases the rate of oxygen decline increases (fig. 6-4) as would be expected, since enhanced stratification acts to further isolate bottom waters from replenishment. Basically, the relationships in figure 6-4 represent the imbalance in replenishment and use of D.O. which, on the replenishment side, is strongly affected by stratification. The reason for the change in slope of these curves at greater stratification values (at about 3.5 u, units for the average curve) is unclear, but probably is associ- ated with seasonal changes in the structure of the pyc- Stratification ((^ Units) 12 3 4 0}=^ c~^ ^E 1 0)^^ Q ^ c ^ ^ -^o) -C >^ "t X 2 feo Max. Stratification, Mi n . Oxygen Min. Stratification Max. Oxygen Average New Jersey Shelf FIGURE &A -Relation between strength of stratification and decline in dissolved oxygen ,n bottom waters (>20 m) of New Jersey-Cape May shelf. 141 NO A A PROFESSIONAL PAPER 11 nocline, in circulation that could affect horizontal advec- tion of oxygen, or in the use of oxygen brought about by variations in biological oxygen demand. (See chapter 9, part 1.) STRATIFICATION AND DISSOLVED OXYGEN IN 1976 A comparison of D.O. observations made off New Jer- sey during cruises in December 1975 through September 1976 and historical data (fig. 6-3) shows that bottom oxy- gen concentrations were typical in December. However, D.O. concentrations in near-bottom waters were below normal by April, and progressively declined until late in the summer. The sharp drop in air and surface water tem- peratures in December-January probably destroyed the slight stratification that was present in December 1975 (fig. 6-3). In March, April, and May, the early increase in river discharge, and reduced storm activity, probably led to greater than normal stratification. Stratification was typical in June and into August, before the passage of hurricane Belle. Stations occupied by the NMFS Sandy Hook Laboratory immediately after the hurricane indi- cated a distinct decrease in stratification, particularly at shallower stations, but with less impact in deeper water. as discussed in chapter 2. In September 1976, stratification had weakened and values were typical for that time of year, except at one station with particularly weak strati- fication. Using the values of stratification observed in 1976 (fig. 6-3), the curves of figure 6-A can be used to model the cycle of bottom D.O. decline that could have been ex- pected from the strength of stratification alone during that year. For the modeling, the intense cooling of surface waters in January 1976 was assumed to have destroyed the stratification remaining from December, leaving the waters unstratified by mid-January. Beginning with no stratification in mid-January, the cruise-averaged values of stratification strength observed in 1976 were connected to define the average cycle during the season of stratifi- cation. Similar cycles were drawn connecting each of the minimum and maximum points, all beginning with the value of zero in mid-January. From these three cycles, monthly mean values were derived for each monthly in- terval from mid-January to mid-August. Monthly rates of decrease in D.O. were determined from the appropriate curves of figure 6-4. D.O. concentrations in the bottom waters off New Jer- sey were assumed to increase from December 1975 con- ditions (ranging from 5.4 to 6.6 ml/1, 6.0 average) at the normal rate for that time of year until mid-January. As- Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep FIGURE 6-5. — Dissolved oxygen content of bottom waters (>20 m) of New Jersey-Cape May shelf as predicted from stratification model and as observed in 1976. 142 CHAPTER 6 suming that stratification began 2 months earher than nor- mal in 1976 (February rather than April), the annual max- imum oxygen concentrations would have occurred in mid- January (ranging from 5.9 to 7.1 ml/1 and averaging 6.5 ml/1). If these January values of oxygen were then allowed to decrease at rates obtained from the relationship estab- lished in figure 6-4 (average curve), then the cycle of D.O. for 1976 can be estimated from stratification, along with the range of predicted conditions (fig. 6-5). Based on this model, minimum average concentrations in August would have been 1.75 ml/1, ranging from 0.15 to 3.30 ml/1, which is well below the normal annual minimum (2.9 ml/1). For comparison with the 1976 D.O. cycle as predicted from stratification, the cruise averages and ranges of D.O. concentrations are also shown in figure 6-5. It can be seen that stratification may account for the April and May D.O. concentrations, but, by the end of June and continuing through summer, actual conditions were much more se- vere than could have been anticipated from strength of stratification alone. Particularly during June, other factors must have affected the utilization-replenishment bal- ance — for example, the flow reversals in the bottom waters (ch. 7) and the increase in biological oxygen demand that resulted from the congregation, respiration, and decom- position of Ceratium in the subpycnocline waters. (See chapter 9, part 2.) REGIONAL ASPECTS Anoxic conditions and the resulting mortalities in 1976 were apparently limited to the shelf waters off the New Jersey — Cape May area and did not develop in waters of adjacent shelf regions to the northeast or south. To con- struct hypotheses for the cause of the geographic extent of anoxic conditions, data archived at NODC and obser- vations by the Woods Hole Oceanographic Institution (1961) were examined for annual cycles of water-column stratification and bottom-water D.O. concentrations in adjacent shelf areas. Using the methods employed in de- veloping figure 6-3 for the New Jersey — Cape May shelf waters, historical values were compiled into cruise aver- ages and ranges for the Long Island shelf region (areas LI and L2 in fig. 1-9 of chapter 1 ) . The values were plotted on the average date of station occupations, regardless of year, and annual trend curves and smoothed ranges of values were drawn (fig. 6-6). The compilation involved 40 cruises (123 stations) made in 1932-75, with observa- tions available in all months. Off Long Island, bottom D.O. concentrations normally are maximum in March (averaging about 7.0 ml/1), de- crease in spring and summer to the annual average min- imum in August of about 3.9 ml/1, and begin to increase in September. The annual cycle of D.O. parallels the cycle of density stratification. Although the annual cycles of bottom D.O. concentrations in the two areas were quite similar, oxygen decline off Long Island proceeded slightly more rapidly in April and May than off New Jersey, but less rapidly during summer, resulting in an average annual minimum about 1.0 ml/1 greater than off New Jersey. AOML cruises in December 1975 and in April, May, June, and September 1976 surveyed the waters off Long Island. A NMFS Sandy Hook Laboratory cruise in March 1976 provided data for computing stratification, but D.O. measurements were not made. AOML data, processed with the same depth limitations as used with the historical data, are shown for comparison as cruise averages and ranges (fig. 6-6). As off New Jersey, oxygen values were near normal in December, somewhat below normal in April, and distinctly below historical conditions in May, June, and September. Values in May through September were not as low as off New Jersey, but were almost as anomalous. Averages for the stations occupied in each area indicated that, at the end of June 1976, bottom D.O. concentrations were 2.6 ml/1 below the normal annual trend curve off Long Island and 3.8 ml/1 below normal off New Jersey for that time of year. Comparison of historical data and stratification values from the cruise data of 1975-76 shows the same general pattern off Long Island (fig. 6-6) as off New Jersey. In- dications of early stratification are apparent, with a return to normal for May through September. From the historical annual trend and range curves of figure 6-6, monthly rates of decrease in bottom D.O. concentration and monthly mean stratification values were determined. Following the same methods used for figure 6-4 for the New Jersey waters, figure 6-7 was developed to show the correspondence between stratification and rate of oxygen decline for bottom waters on the conti- nental shelf off Long Island. Figures 6-4 and 6-7 show the same tendencies. For stratification values greater than about one a, unit, however, the rates of oxygen decline per month (for comparable strength of stratification) are about one-third greater for New Jersey waters than for Long Island waters. Using the stratification data from observations made in the cruises of December 1975 through September 1976, monthly mean averages and ranges were computed, as- suming that 1 ) all stratification was destroyed by the strong cooling of January, and 2) stratification became estab- lished over most of the area in February 1976. From these monthly means of stratification, rates of decrease in bot- tom D.O. were determined from the appropriate curves in figure 6-7. In developing an estimate of the oxygen cycle as a function of stratification for 1976, it was assumed that the observed values in December 1975 increased at the normal (historical) rate until mid-January, yielding at that time an average concentration of 6.4 ml/1 (range 5.9 to 6.8 ml/I). To develop the curves in figure 6-8, a coun- terpart to figure 6-5, these values were then allowed to 143 NO A A PROFESSIONAL PAPER 11 C o O) >. X O ■o o o 6 1 — 1 1 1 1 1 1 1 1 1 1 ^ ^I""!,...!/!/ ~~ ■'^ - ^ / Annual Trend ^ "T* • • "^T / J' ^ / -L^. T^. Smoothed / Range of — • \ » X • • Values -L \ •, . 4 - \ • .•' / \ / ' \ / Observafions in 1976 ►! ~. y i- ; 2 — - n J. Long Island Shelf 1 1 1 1 1 1 I 1 1 1 1 c o x^ 4 M c a Nov Dec Jan Feb Mar Apr MayJun Jul Aug Sep Oct Observaf ions in 1976 ^^i-.n^ Smoothed Range of Values Annual Trend Cruise Average '11 Range of Values for the Cruise J I I Long Island Shelf J 1 I L. FIGURE 6-6. — Dissolved oxygen levels in bottom waters (>20 m) and vertical density stratification surface-subpycnocline a, difference) of Long Island shelf waters, 1976 and historical record. Historical data from EDIS/NODC and WHOI (1961 publ.); 1975-76 cruise data from NMFS/SHL and ERL/AOML. l^ 0)" 15 2 CHAPTER 6 Stratification (C^ Units) 12 3 4 ^*^«««,,,,^ 1 1 1 1 Max. Stratif i cation, ^^~*^?-^«..^_— ^ — -_ .^- Min. Oxygen Min. Stratification,/ ^^ N. Max. Oxygen / ' . >• / '. \ Average • • • • • • FIGURE 6-7. — Relation between strength of stratification and decline in dissolved oxygen in bottom waters (>20 m) of Long Island shelf. 8 Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep E 6 C O O) O ^ _> o From Maximum Stratification Average -1 [ Range of Observed , In 1976 Values J I I L Long Island Shelf J I 1 L. FIGURE 6-8. Dissolved oxygen content of bottom waters (>20 m) of Long Island shelf as predicted from stratification model and as observed in 1976. 145 NO A A PROFESSIONAL PAPER 11 decrease until mid-August at the rates defined by the ob- served strength of stratification. Also shown in figure 6-8 are the cruise averages and ranges of values observed during 1976. The estimated average minimum, in August, was 2.30 ml/1 (range 1.40 to 3.95 ml/1). The comparison in figure 6-8 of predicted bottom D.O. concentrations for the waters off Long Island with con- ditions observed in 1976 indicates that the stratification- dependent oxygen model accounts fairly well for the ob- served conditions in April and May. By the end of June, bottom D.O. concentrations were below the model values, but not as much as in the waters of the New Jersey — Cape May area (fig. 6-5). As with the waters off New Jersey, one or more additional circumstances must have devel- oped in the Long Island waters, particularly in June, to affect the replenishment-utilization ratio in such a way that the oxygen decline was more rapid. But the impact on the D.O. concentrations was not as intense for waters off Long Island as off New Jersey. South of New Jersey, over the continental shelf of the Delmarva Peninsula, no anoxia was reported in 1976. Pre- sumably the early warming and early occurrence of spring river discharge would also have influenced these waters. Historical observations in the NODC archives for that area were too sparse to demonstrate an annual cycle of bottom oxygen, and data were not available for describing developing conditions during 1976. Presumably, bottom D.O. concentrations off the Delmarva Peninsula normally follow an annual cycle similar to those off New Jersey and Long Island, but do not normally decrease to concentra- tions as low as off New Jersey. Possibly the differences in the annual cycle of bottom D.O. concentration between the New Jersey — Cape May areas and Long Island, and presumably the Delmarva Peninsula, are the result of bathymetric differences. Stearns (1969) noted that on the New Jersey side of the Hudson Shelf Valley, gravel deposits have caused the con- tinental shelf waters off northern New Jersey to be about 5 fm (9 m) shoaler than on the Long Island side of the valley. He pointed out that the effect of the gravel deposits is apparent in bathymetric charts: the 20- to 30-fm (37 to 55 m) isobaths are farther off New Jersey than off Long Island. To depict bathymetric differences of the continental shelf off Long Island, New Jersey, and the Delmarva Peninsula, average depth profiles were made for the three regions (fig. 6-9). The profiles were constructed from the bottom topography maps of Uchupi (1968) by computing the average distance offshore to selected isobaths con- toured on the maps (20, 40, 60, 80, 100, 140, and 200 m). In general, the continental shelf off New Jersey is shoaler than the shelf off Long Island and wider than the shelf off the Delmarva Peninsula. Figure 6-9 shows that the depth of the shelf is about 20 m less off New Jersey than off Long Island. Distance Offshore (km) 50 100 150 New Jersey. Cape May 200 FIGURE 6-9. — Average bottom depth profiles across selected areas of continental shelf in Middle Atlantic Bight. To explore how the difference in water depth in the Long Island and New Jersey areas might affect seasonal oxygen declines, the data displayed in figure 2-18 of chap- ter 2 were examined for differences in thickness of bottom water (pycnocline bottom to ocean bottom) for the two areas. The May cruise was chosen because it was made during stratified conditions and provided more extensive coverage than either the April or June surveys. Area av- erages of the thickness of subpycnocline or bottom waters from the coasts to the 60-m isobath were calculated for each of the two shelf regions. Average thicknesses were 13 m for the Long Island shelf and 9 m for the New Jersey shelf, reflecting the greater depth to the bottom off Long Island. With the greater volume of water that would tend to be isolated in the subpycnocline layer during the months of stratification off Long Island, and realizing that maximum oxygen concentrations are typically about the same in both regions, then there would be a volume of about 44 percent more oxygen available in the bottom waters off Long Is- land than off New Jersey. In the most simplistic case (where there is no advection and presuming that the bi- ological oxygen demand per unit area is the same in both shelf regions) the lesser volume of oxygen available in the thin layer of bottom water off New Jersey would be di- minished to lower concentrations. From the historical, annual trends of figures 6-3 and 6-6, D.O. values in the bottom waters off Long Island normally decrease a total of 3. 1 ml/1 (from the annual maximum in March of 7.0 ml/ 1 to the August minimum of 3.9 ml/1), and in bottom waters off New Jersey decrease about 4.1 ml/1 (from a maximum in March of 7.0 ml/1 to a minimum in August of 2.9 ml/1). That is, bottom D.O. concentrations normally decrease about one-third more off New Jersey than off Long Island. In a comparison of the averaged bathymetric profiles of the Delmarva Peninsula and the continental shelf off 146 CHAPTER 6 New Jersey (fig. 6-9), the most striking feature is that the New Jersey shelf is about 40 km, or 44 percent, wider than the Delmarva shelf, as measured from the coast to the 100-m isobath. Although no comparative evidence ap- parently exists, it would seem as though the narrower shelf off the Delmarva Peninsula would promote greater across- shelf exchange, which may tend to diminish any isolating effect of stratification development. The results from re- covered seabed drifters (Bumpus 1973) indicate slightly higher drift speeds and distinctly lower recovery rates for the bottom waters off Delmarva as compared to the New Jersey shelf. One interpretation of these results would be that the flushing rate of the bottom waters off the Del- marva Peninsula is greater, which might tend to maintain a higher rate of oxygen replenishment. PREVIOUS BENTHIC MORTALITIES Three previous episodes of benthic mortalities have been reported in the same area as the 1976 anoxia: Sep- tember through early October 1968, October 1971, and August 1974 (ch. 1). None of these earlier mortalities was as extensive or enduring as in 1976. Low D.O. concen- trations in bottom waters off New Jersey were reported with each occurrence. In comparing conditions during earlier mortalities and what occurred in 1976, indexes associated with unusual stratification were the only factors for which sufficient historical records exist. To determine whether conditions similar to 1976 occurred in the earlier cases of anoxia, and at other times, climatological records of sea-surface tem- perature from shore stations and discharge rates for the Hudson River at Green Island were examined for the 30- year period 1947-76. During this period, high discharge (arbitrarily defined as greater than 150 percent of the monthly mean) occurred five times in January (1949, 1950, 1952, 1973, and 1974) and four times in February (1949, 1951, 1954, and 1976). Shore station temperature records for Sandy Hook and Atlantic City, N.J., indicated early warming of the water (monthly mean for February warmer than for January) 12 times at Sandy Hook and 9 times at Atlantic City. Early warming was reported at Sandy Hook in 1970 and 1971, but at Atlantic City observations were not made those years. Early warming and high discharge coincided in 1949, 1952, 1954, 1974, and 1976. Therefore, these 5 years are considered potential times when anoxic conditions might have developed during summer in the shelf waters off New Jersey as the result of early onset of stratification. For the 30-year record, the greatest warming and discharge recorded in February were in 1976. Included in the list of potential years of early onset of stratification is 1974, one of the times of reported mortahties. The 1968 and 1971 instances are not included. The 1974 and 1976 mortalities were during summer, but the 1968 and 1971 mortalities were during autumn. The implication is that very low D.O. can result from an early spring or a late autumn; either would tend to lengthen the stratification period. The effect of a prolonged summer (late onset of cooling) can be derived from the relation between strength of strat- ification and monthly rate of D.O. decline as shown by the annual cycles of bottom D.O. and stratification (fig. 6-3). During summer, stratification usually is about 4.0 CT, units, which corresponds to an average, monthly rate of oxygen decline of about 2.0 ml/1. Typically, the average annual minimum oxygen is about 2.9 ml/1 in August. If the usual breakdown of stratification by surface cooling is delayed a month (October rather than September) then minimum bottom D.O. concentrations off New Jersey would be expected in September at an average concen- tration of about 0.9 ml/1. In examining conditions that might indicate the late arrival of autumn, surface temperatures were considered the only significant factor, because river discharge in sum- mer and autumn is typically small. In the 30-year record for the Hudson River (1947-76) the discharge for August is less than the monthly means for December, January, and February, and the September discharge was as great or greater than the monthly means for December through February only once — 1975. Sea-surface temperature rec- ords for Atlantic City (1947-76) show that August was typically the warmest month and September was warmer than August only seven times — in 1948, 1957, 1959, 1965, 1966, 1968, and 1971. Of these years the highest rate of September warming was in 1968 and the second highest in 1971. These are the years of autumn mortalities. There were no instances of early-spring and late-autumn con- ditions occurring in the same year. Included in the NODC historical data for bottom D.O. concentration (fig. 6-3) were some values in February and June 1968 and March 1971. At these times, bottom D.O. values were above or equal to the average trend values, implying that the low D.O. reported with the mortalities did not result from early onset of stratification. SUMMARY Based on historical oceanographic data, the DO. con- tent of bottom waters over the New Jersey-Cape May and Long Island continental shelves typically declines during spring and summer, reaching minimum values in August. The seasonal decline in D.O. closely parallels the devel- opment of density stratification, and the rate at which D.O. declines seems to correspond with the strength of stratification. Stratification tends to isolate bottom waters from vertical replenishment until September, at which time cooling of the surface and mixing begins to destroy the vertical structure. This results in increased replenish- 147 NO A A PROFESSIONAL PAPER 11 ment of bottom DO. Continued cooling and overturning through autumn and winter typically cause a steady in- crease in oxygen values to the annual maximum in March. The influence of stratification on rates of oxygen decline may be greater off New Jersey than in adjacent regions because of bathymetric differences. However, this assess- ment does not take into account any effects on D.O. con- centrations that might result from unusual advective and biologic processes. Comparison with the normal cycle of bottom D.O. indicates that concentrations were already below normal by April in 1976 throughout the New York Bight. In 1976, the early occurrence of increased river dis- charge accompanied by early warming led to the early development of stratification; above-normal stratification persisted through May. The early onset of stratification in 1976 would have contributed to the occurrence of ab- normally low bottom D.O. in the New York Bight in three different ways: 1. If D.O. concentrations increased as per the normal trend into January 1976 (as indicated from observations made in December 1975), then with a 2-month earlier than normal onset of stratification, maximum concentra- tions for the year, would have been in January at about 6.5 ml/1, which is 0.5 ml/1 less than the usual March max- imum of 7.0 ml/1. Given normal conditions through the rest of the year, the D.O. values in 1976 could have been somewhat below normal each month until autumn. 2. Normally, the season of strengthening stratification and declining D.O. lasts about 5 months (April-August). In 1976, this season was apparently lengthened as much as 2 months, because of the early onset of stratification. This means that 1976 had 7 months in which utilization of oxygen would have exceeded replenishment. 3. From March through May 1976, and probably be- ginning as early as February, stratification was stronger than normal and about typical for June through August. As a result, the decline in D.O. would have been greater than normal during as many as 4 months in 1976 and at typical rates during summer. Thus the cycle of bottom D.O. concentration would have proceeded at values below normal for as long as February through August. Historical observations, stratification values, and bot- tom D.O. decline rates were used to develop a graphic model. The model was then used to estimate the cycle of bottom D.O. concentration for 1976. These estimates were compared with 1976 observations and indicated that stratification, with the early arrival of spring conditions, accounted for the below-normal D.O. values in April and May. The model-derived estimate further implied that D.O. would have become almost totally depleted over the New Jersey shelf in August. But DO. measurements in the area during June indicate that concentrations fell much more rapidly than estimated, because of stratification alone. Similarly, model-derived estimates for Long Island shelf waters indicated that below-normal concentrations should have developed there in 1976, but not at such low values as off New Jersey. Also, in June, Long Island D.O. concentrations fell more rapidly than predicted from the model. Because stratification alone failed to explain the full magnitude of the oxygen depletion, there must be other contributory factors. Possibly the dramatic decline in bot- tom D.O. during June resulted from excessive demand from the presence of the large mass of Ceratium and, perhaps, from factors associated with the circulation. Since instances of anoxia-related mortalities have been reported during previous years in the New Jersey shelf waters, historical records of sea-surface temperature and of river discharge were examined for indications that the season of stratified conditions may have been longer than normal in these years. For the 30 years of records ex- amined conditions that could have caused a lengthening of the time the waters were stratified occurred 12 times, or 40 percent of the time. Of these potential cases, five resulted from the early arrival of spring and seven from the late arrival of autumn. Anoxic conditions and mor- talities were reported for the four most recent occurrences. This history of fairly frequent instances when stratifica- tion-related, depressed D.O. conditions may have devel- oped implies that future recurrences of anoxia should be expected. ACKNOWLEDGMENTS Steven K. Cook helped compile data, and J. Lockwood Chamberlin and Merton C. Ingham gave advice. The fol- lowing individuals provided data: E. L. Burke, William Embree, and Sheila Perry of the U.S. Geological Survey; Ellsworth C. Smith of NOAA NODC; Henry Diaz of NOAA NCC; James Hubbard and Charles Muirhead of NOAA National Ocean Survey; Thomas Azarovitz of NOAA NMFS, Sandy Hook; and George Berberian, Ad- riana Cantillo, and John Hazelworth of NOAA AOML. REFERENCES Bowman, M. J., and Wunderlich. L.D., 1976. Distribution of hydro- graphic properties in the New York Bight Apex, Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:58-68. Bumpus, D. F., 1973. A description of the circulation on the Bcontinental shelf of the east coast of the United States, Progress in Oceanog- raphy 6:111-157, Pergamon Press. Stearns, Franklin, 1969. Bathymetric maps and geomorphology of the Middle Atlantic Continental Shelf, Fish. Bull. 68:37-66. Uchupi, Elazar, 1968. Atlantic continental shelf and slope of the United States: Physiography, U.S. Geol. Survey Professional Paper 529-C, 30 pp. Woods Hole Oceanographic Institution, 1961. Biological, chemical, and radiochemical studies of marine plankton, reduced data report. Appendix C to WHOI Ref. No. 61-6, (unpublished manuscript). 148 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 7. Water Movement on the New Jersey Shelf, 1975 and 1976 D. A. Mover, D. V. Hansen, and S. M. Minton^ CONTENTS Page 149 Introduction 149 Data Processing 151 Time Scales 152 Temporal Variation of Currents 157 Regional Variation of Currents 157 Upwelling 157 Local Meteorological Effects 162 Summary 162 Acknowledgments 162 References ' Atlantic Oceanographic and Meteorological Labo- ratories, Environmental Research Laboratories, NOAA, Miami, FL 33149 INTRODUCTION Current meter moorings were maintained at several sites in the New York Bight during the late winter and spring of 1975 and from autumn 1975 throughout 1976. The strength and variation on various time scales of cur- rents observed on the continental shelf off New Jersey and Long Island, N.Y., were investigated to determine the differences between the 2 years. These differences may help explain why anoxic conditions developed in New Jer- sey near-bottom waters during summer 1976, but did not develop in summer 1975. Seven taut-wire moorings (with Aanderaa current me- ters and tethered surface spar buoys) were selected for analysis from those deployed during the 1975 and 1976 MESA current surveys (fig. 7-1, table 7-1). On the New Jersey shelf, three stations (Pll, 49, and LT2) were es- tablished in shallow water (about 30 m), and two (P12 and LT3) were in deeper water (60-70 m) near the shelf break. Off Long Island, two stations (P31 and LT4) were established near shore in 49 m of water. Because low dissolved oxygen (D.O.) concentrations were observed near the bottom, this analysis focuses on near-bottom motions. Weather data also were obtained from John F. Kennedy International Airport (JFK) and from two me- teorological data buoys, EB34 and EB41 (fig. 7-1). DATA PROCESSING Only the highest quality data were retained for analysis. Raw current-meter data (sampling intervals were mostly 30 minutes, some were 20-minute intervals) were scru- pulously edited. These were then 3-hour low-pass filtered and resampled hourly, resulting in a more manageable 149 NOAA PROFESSIONAL PAPER 11 to 20 30 <10 W 60 10 90 too STATure miles UIHHUUI 1= 10 10 20 30 ■IC 50 60 70 — 1 80 90 100 110 120 130 140 150 KILOMETERS pn=rwM M 1 - 10 — 1 20 30 40 50 60 70 80 90 10( 00 NAUTICAL MILES FIGURE 7-1. — Location of environmental buoys and current meter stations in New York Bight. 1975 and 1976. 150 CHAPTER 7 Table 7-1. — New York Bight 1975-76 current-meter and wind-obsenation stations and characteristics Station Water depth Distance from bottom Distance from surface Location' Latitude Longitude Years New Jersey shelf Pll 49S 49B LT2S LT2B New Jersey shelf break PI2 LT3D Long Island shelf P3I LT4S LT4B LT4C Meteorological stations JFK EB34 EB4I 33 5 28 39 16.6 73 55.3 1975 35 32 8 3 27 39 37.9 73 34.2 1975 32 29 9 3 23 39 23.8 73 42.9 1975-76 62 5 57 39 08.9 73 13.4 1975 70 11 59 39 15.7 73 01.6 1976 47 5 42 49 39.3 73 14.6 1975 49 46 8 1 3 41 48 40 33.6 72 18.6 1975-76 6 40 39 73 47 1975-76 5 40 05 72 58 1976 5 38 42 73 36 1975 Station locations are shown on figure 7-1. number of data points. Ortman ( 1978) described the meth- ods and editing criteria used. Raw weather data were used with sampling intervals of 1 hour for the EB stations and 3 hours for JFK. Water motion statistics were computed for appropriate time scales, and progressive vector dia- grams (PVDs) were plotted for these same time scales. For the statistics and the plots of velocity components, the coordinate system was rotated 48° clockwise so that the north component transformed into the upshelf (toward Cape Cod) component and the east component trans- formed into the offshelf (toward Bermuda) component. This rotation provides an approximation to the orientation of the bathymetry off both Long Island and New Jersey. Small-scale topographic variability prohibits conclusive statements about cross-shelf flow where the crossing angle is small. Because the PVD presentation is extensively used in the arguments that follow, it is useful to review what a PVD portrays. For a series of velocity measurements, a PVD is a virtual displacement diagram derived by inte- grating the velocity in time to yield a representation of water movement past the current meter. It is virtual dis- placement in the sense that a drogue at that depth would move along this displacement diagram (PVD) only if all water adjacent to the point of measurement (the current meter mooring) were moving in exactly the same way. The flow field would then be spatially homogeneous. This is not the case, because water particles distant from the current meter may have moved into a different flow field, which, if current meter measurements were available, would produce a different displacement diagram. The PVD does, however, yield valuable information about the cumulative displacement of water particles past the point of measurement. A PVD is a useful tool for visualization of the average and slowly varying components of flow. TIME SCALES The basic question addressed here is whether weakened or otherwise altered circulation during 1976 may have con- tributed to development of anoxic conditions by reducing advection of D.O. into the region or by concentrating oxygen-demanding material. This question does not have a simple answer within the confines of the data. As will be shown, the net movement over several weeks was in- deed less during spring and summer 1976 than during spring 1975. Over shorter periods, however, the measured currents usually were more energetic. This is revealed in the larger variance statistics in 1976 for corresponding months in the 2 years. Spectrum analyses show the in- creased variance to be distributed over a broad band of time scales, covering periods from at least 0.5 to 6 days. The measured tidal currents were greater in 1976 than in 1975, which is more likely to be due to uncertainty of measurement than true secular variation. Although there are undoubtedly measurement uncertainties in both years, the general trends are believed to be real. Increased var- iance at all frequencies, including tidal, can result from high-frequency mooring motion, usually induced by sur- face waves. The moorings (49 and LT2) used off New Jersey during 1975 and 1976 were almost identical, and 151 NO A A PROFESSIONAL PAPER 11 the weather differences seem insufficient to account for the differences in variance across all frequencies. The mooring sites were about 27 km apart; the LT2 mooring site (1976) is about 4 m shoaler than station 49. Some amplification of tidal currents is expected in shoaler water. In addition, the slightly stronger stratification occurring in 1976 (ch. 5) may have enabled internal gravity waves to be excited over a wider band of frequencies and more vigorous internal tides to have been generated. Perhaps more important, the LT2 bottom meter, being somewhat nearer to the surface (23 compared to 27 m), may have introduced more error into measurements in 1976. Intefpreting these data to address the cause of devel- opment of anoxic conditions implies selection of a time scale pertinent to the problem. For small (1-10 km) pol- lution problems, the relatively rapidly varying currents would be most important, and 1976 would likely be shown by our data to be a relatively favorable year for pollutant dispersal. Considerations of the oxygen demand on a static environment (Segar and Berberian 1976) or of the ob- served time and space scales of the D.O. distribution in the New York Bight (ch. 2 and 5) suggest that 30 days, or even a sequence of 30-day intervals, is appropriate for this problem. Hence, the data are presented in 30-day blocks. The vector mean flow over these intervals is prob- ably the property of greatest significance here, but we also discuss the total current variance or horizontal kinetic en- ergy to demonstrate the point about variability made above. TEMPORAL VARIATION OF CURRENTS Extremely low D.O. concentrations were not observed in 1975. Data from stations PI 1 and 49 in the region where very low D.O. concentrations were observed in summer 1976 are available for periods up to 90 days, starting from Julian day (J.D.) 65 in 1975. This spans the period of development of the pycnocline during spring (ch. 5). Re- sults from meters located below or in the bottom of the pycnocline during this time are summarized in PVD for- mat (fig. 7-2). These PVDs reveal irregular intervals of weaker or stronger flow, but they also show net monthly displacements of 100 to 120 km to the southwest and south at both stations (Pll and 49B). These data are part of the same data set used by Beardsley et al. (1976) and Hansen (1977) and are consistent in speed and direction with other data acquired at that time from other parts of the shelf. They also generally agree with drift bottle results acquired over several years (Bumpus 1973). Bumpus also sum- marized results from deployment of seabed drifters over several years. Results from drifter studies necessarily are biased toward shoreward movement, and Bumpus" (1973) summary typically indicates a region of diffluence in the most critical area off New Jersey during the summer. Re- gional patterns of confluence or diffluence are not well determined from such data, however. In addition, the near-bottom direct current meter meas- urements treated are 8 to 9 m above the bottom, and only up to 90 -days of record are available for analysis. How- ever, a considerable amount (nearly 12,000 hours) of data are available from the LTM site (Mayer et al. 1979) 4 to 8 m above the bottom, although in water about 15 m deeper and upshelf from the Hudson Shelf Valley. From almost 18 months of these data, it has been estimated that the average or normal flow at this level above the bottom is 1 to 1.5 cm/s toward 220° T. Well within the bottom boundary layer (1 m above the bottom), the picture is not as clear, because current velocities are less than 1 cm/s (with only about 6 months of data available) making it | difficult to reasonably estimate either speed or direction. With this limited data set, addition or deletion of several weeks of data can reverse the direction of the mean, so it is not meaningful to compare in detail our current meter data (up to 90 days in 1975) with Bumpus" seabed drifter results. The simple mean circulation described above is greatly complicated by events (mostly of meteorologic origin), some of which persist for as long as 3 months (Mayer et al. 1979). Most events, however, lie within the 3- to 10- day frequency band associated with energetic weather sys- tems. These events are manifest in the many observed upshelf velocities generated by an upshelf component of wind stress. A conceptual model follows; "Upshelf winds , cause offshore flow in the upper part of the water column, | which presumably causes a drop of coastal sea level, pro- viding a pressure gradient that drives a quasi-geostrophic upshelf flow of deeper water"" (Mayer et al. 1979). By now it should be clear how variable the circulation is on the Middle Atlantic shelf and how difficult it is to make definitive statements about the mean or normal cir- I culation. With regard to the background material con- sisting of a limited (90 days or less) current meter data set from 1975. we can say that it is consistent with what is believed known about "normal"" circulation in the Middle Atlantic Bight. A longer series of current meter observations in the New York Bight, including station LT2 off New Jersey, was obtained from October 1975 through summer 1976. Ten months of continuous record from a current meter located below the pycnocline during the stratified season | was available for the analysis of anoxic conditions off New Jersey. Figure 7-3 shows results from essentially the same level as the 1975 data in figure 7-2 for corresponding time periods. In October 1975 the displacement was about twice , that observed during the preceding spring, but slowed ' dramatically and reversed direction for about a month in November. During the subsequent several months the 152 CHAPTER 7 P-ll 1975 Feb 75; Mar '75; 125 50 KM N A 48= V / ^ / UP ^- E \ \ OFF 49- B 1975 Feb 75; 65 Mar 75; 95 Apr 75; 125 / 9biy 125* 1> i 155 FIGURE 7-2— Progressive vector diagrams of currents lor stations Pll and 49, February-March and February-April 1975, showing computed displacement (in km) of water by 3-day intervals (dots) within period of observation designated in Julian days. 153 NO A A PROFESSIONAL PAPER II Oct 280 FIGURE 7-3 — Progressive vector diagrams of currents for station LT2B. October 1975-July 1976. showing computed displacement (in km) of water by 3-day intervals (dots) within period of obser- vation designated m Julian days. Dec 75; 340 Jan 76; Feb 76; 065 035 Apr 76; May 76; 155 Jun 76; Jul 76; 185 50 KM 185 48' UP / / / ^- E \ 125 \ \ \ OFF 154 Table 7- -2.— New York CHAPTER 7 Bighl 1975-76 currenl data time-series subsets' Meter no. and location Start time (J.D.)- for subset no. 280 1 310 2 34C 3 5 4 35 5 65 6 95 7 125 8 155 9 185 10 Full series Nearshore stations New Jersey 1975 49S 49B -6.1 13 342 -3.4 1.8 224 -3.3 0.7 388 -2.7 2.1 128 -4.3 1.5 308 1975-76 LT2S LT2B P3! LT4S LT4B Shelf-break stations 1975 P12 Long Island 1975 1975-76 1976 LT3D -1.2 -8.1 -2.2 -5.1 -0.5 -4.4 3.(1 3.1 1.4 3.2 4.1 3.9 424 426 436 413 407 383 -6.6 1.8 -5.1 -1.9 -2.6 -1.6 -2.6 0.5 1.9 -0.8 -1.6 1.8 -0.6 -2.3 -0.0 0.3 0.8 -0.2 -1.7 -1.2 -1.4 -0.4 377 305 383 434 368 301 0.1 -2.0 436 -0.0 -1.8 303 221 234 346 141 90 -6.0 -0.1 3.9 1.8 4.9 5.6 2.3 4.9 381 329 344 314 -5.3 -0.3 -1.6 3.0 -2.4 -2.1 -2.5 -2.5 -2.7 -3.9 -2.1 -1.4 0.2 -3.2 -2.7 -0.9 -1.3 -0.9 -0.3 -0.2 -0.9 -1.1 301 307 344 405 393 216 257 198 J D 115 -6.3 32. 183 125 278 112 -1.1 -0.3 211 ' Numbers for each subset are: top. upshelf component in cm/s; middle, offshelf component in cm/s; bottom, total variance (dj-). ' Julian day calendar: 1975, days 1-365; 1976. days 1-166 (one added to each day beginning March 1 to account for leap year). currents were generally similar to those observed in spring 1975, but at somewhat lower net speeds, except for De- cember, typically 50 to 70 km per month. During May and June the flow maintained, or slightly increased, speed, but became more variable in direction, reversing the "normal" southwestward pattern. In July the flow contin- ued to be variable in direction and also diminished in speed. The net displacement during July was less than 40 km to the west northwest. During the first 2 weeks of August (not shown) net water movement virtually ceased. The net displacement observed during the 3 months be- tween May 4 and August 2, 1976, was about 120 km to- wards 340° T. Statistics of each 30-day segment are arranged for easy comparison in figure 7-4 and table 7-2. These consist of the vector mean (represented in table 7-2 as upshelf and offshelf components) and the total variance (u,'). The uncertainty in determination of the monthly mean values due to the relatively large variance is less than 1 cm/s. The substantial difference between the average flows of cor- responding months during spring 1975 and 1976, followed by a prolonged period (90 days) of onshore flow below the thermocline off New Jersey, is especially evident in figure 7-4. Flushing of the New Jersey coastal region is undoubt- edly important for the ecological health of the marine environment. The principal difference that might have affectea the flushing of the area and the development of anoxic conditions in 1976 was the reduction of speed and reversal (alongshore component directed upshelf) of di- rection of the water movement in the bottom layer off New Jersey, compared to spring 1975. 155 NO A A PROFESSIONAL PAPER 11 CM 00 U1 IT) o - O O O O 00 CM \ \ \ I \ to CM CO On - 1^ u1 in CM o lO m Q c ra X CO o CO CO ^o ^o O) c a. 3 c v i c o Q x> o « c 0) u c 3 O 0) O J ^ o c o c E u. Q 4) ^ •^ 01 r c . m — o 0) l/J c o o Cl 3 156 CHAPTER 7 REGIONAL VARIATION OF CURRENTS Another question associated with the development of anoxia is its apparent confinement to approximately the inner half of the continental shelf off New Jersey. Current meter observations made off Long Island (stations P31 and LT4) during the same times as those off New Jersey, and some shorter records from observations near the shelf- break off New Jersey (stations P12 and LT3), were studied to determine whether the interannual current variation observed in the region of anoxia was experienced through- out the entire New York Bight. Anoxic conditions were not observed at either site during 1976. Data from LT3 and P12 were available for only 1 month (J.D. 115-145 in April and May) common to both 1975 and 1976 (table 7-2). In 1975, the flow at station P12 was toward the southwest as elsewhere on the shelf, and at substantial speed. The 30-day displacement was over 200 km. In 1976, at station LT3D, the flow was to the south- west, as normally expected over the shelf, at a time when the flow closer inshore was reversed. The speeds at LT3D were about one sixth those of the previous year, even at a level farther (11 vs. 5 m) from the influence of bottom friction. The total variance at P12 is only about half that at LT3D, but this may be due to closer proximity of the current meter to the bottom on station P12 and to the fact that the subsurface float on this mooring was much farther below the surface. The best data for comparing conditions off Long Island with those in the anoxic area off New Jersey during 1975 are data from the bottom station. P31 (fig. 7-4). These data are inconsistent with most other data acquired at this time (Beardsley et al. 1976; Hansen 1977) in that the observed flow was weakly to the northwest, generally up- slope across the continental shelf. This measurement also was relatively close to the bottom (5 m) and consequently may have been perturbed by local bathymetry, although no likely cause appears on the best available bathymetric charts. When observations in this area were resumed in October 1975, a relatively strong southwestward flow was observed off both Long Island and New Jersey. In No- vember, off New Jersey a northeastward flow (LT2) was observed while off Long Island (LT4) there was a period of essentially no net flow; which was followed in Decem- ber and January by northwest and northward flows that were not observed off New Jersey. This 3-month midwin- ter perturbation of the normal southwestward flow over the shelf is of the same time and amplitude scales as that observed coincident with the development of anoxia off New Jersey, but anoxic conditions are not expected during the unstratified conditions of winter. From February through July the flow off Long Island was steadily to the southwest at speeds of 55 km/mo (2 cm/s) or more. The monthly means off Long Island do not indicate the slowing and reversal of flow that occurred off New Jersey during the summer. The July 1976 flow off Long Island is in fact slightly stronger than in the months immediately preced- ing. UPWELLING A possible aspect of the circulation that can contribute to development of anoxic conditions is upwelling, or shoreward and upward flow of water from below the pyc- nocline offshore. This water may tend to be somewhat higher in nutrients than typically found in coastal bottom waters. It is frequently not possible to discern in local current measurements the occurrence of upwelling, because the alongshore component of flow is much larger than the cross-shelf flow and the local orientation of the shelf bathymetry is insufficiently defined. It is apparent in figure 7-2 that the flow is generally parallel to the bathymetry (48°-228° T) much of the time. When the flow crosses the nominal isobath by more than 15° (ratio of components 1:4) for significant periods we believe meaningful state- ments can be made about local onshelf flow or upwelling. This crossing angle is about three times greater than our uncertainty in determining the shelf direction. Such situ- ations are identified in figure 7-4. Indication of net up- welling is seen off both Long Island and New Jersey. Off New Jersey it is associated primarily with the flow per- turbation of summer 1976. In the 13 months of observa- tions available (stations 49B and LT2B), upwelling and downwelling occurred five times each in the monthly means; shelf-parallel flow occurred in three monthly means. Off Long Island, upwelling occurred in 8 of the 12 monthly means available (stations P31 and LT4B). but occurred most strongly in connection with the midwinter current perturbation. The information on the monthly mean near-surface currents included in table 7-2 and fig- ure 7^, considered jointly with either the currents below the pycnocline or the winds observed at JFK, demonstrate only that the surface currents off Long Island were strongly influenced by local winds. LOCAL METEOROLOGICAL EFFECTS Recent studies (e.g., Beardsley et al. 1976) show that a large fraction of the kinetic energy in water movements in nearshore coastal waters is correlated with local winds. Because there are indications of anomalous atmospheric conditions during winter and spring 1976 (ch. 3), it is appropriate to review here the winds that influenced cir- culation in the New York Bight during these seasons of 1975 and 1976. For this purpose we obtained wind obser- 157 NO A A PROFESSIONAL PAPER 11 JFK 1975 10* dv"es sec OFF DOTS= lO-OAr INTERVALS TIME : JUIIAN DAY JFK 1975 STRESS JFK 1976 JFK 1976 STRESS "^ EB 34 EB 34 STRESS EB 4 EB 41 STRESS FIGURE 7-5— Progressive vector diagrams of wind and stress at JFK Airport from March through July, 1975 and 1976. and at environmental buoys EB34 and EB41 in 1976. 158 CHAPTER 7 vations at JFK and the two environmental buoys (EB34 and EB41). These are shown in PVD format for both velocity components and stress (figure 7-5). Time series of stress were computed according to Wu (1969). The stress data for both 1975 and 1976 clearly show the tran- sition in early May (J.D. 120-125) from the generally northwesterly winds characteristic of winter to the more southwesterly winds of summer (southerly at JFK in 1975). In late winter and early spring 1976, the winds at JFK were slightly weaker and more westerly than during the previous year. Data obtained from EB34 and EB41 show that the winds were more westerly in the southern reaches of the Bight. A relatively normal transition to summer conditions occurred about the first of May 1976 at JFK and EB34, but about 2 weeks earlier at EB41. A period of slightly greater than normal wind speed of unusual persistence from the south and southwest occurred during much of June. This period of persistent winds evidently caused a large amount of floatable material to wash ashore on Long Island (Swanson et al. 1977). Although these winds were clearly much stronger and steadier than those of June 1975, they were not dramatically different from those of July 1975. In July 1976 the winds again weakened and were more southwesterly. The major difference in low- frequency wind behavior between 1975 and 1976 seems to be that in 1976 there was a greater tendency for winds to have a westerly component in late winter and early spring and a long period during June 1976 when the winds were persistently from the southwest, in opposition to the normal flow of water. Early in the morning of August 10, 1976, hurricane Belle passed through the New York Bight (figure 7-6). Though unrelated to the genesis of anoxia in the Bight, this event is of interest in connection with possible ad- vective renewal of oxygen-depleted waters or increased vertical mixing (ch. 2), either of which may be expected to alleviate low D.O. conditions. Figure 7-6 shows the currents observed over the few days spanning the passage of the hurricane at stations LT2 and LT4. Prior to the hurricane, the normal semidaily tidal currents are most noticeable, especially at station LT2. These rotary tidal currents have speeds of 15 to 20 cm/s and produce no net displacement over a complete tidal cycle. The hurricane's time of arrival and speed of passage were such that its effects appear to be almost in phase with the tidal currents, approximately doubling their speed for about one cycle (one-half day). The sequence of enhanced flows is offshelf (SE), downshelf (SW), onshelf (NW), and upshelf (NE). Unlike the tidal currents, which are almost in phase at these two stations, the storm-induced disturbance at sta- tion LT2 occurred before that at LT4 by about 4 hours, about equal to the time it took for the hurricane to pass through the Bight. Following this is a period of weaker. but significant, residual flow upshelf at both stations, per- haps caused by the southerly winds following the hurri- cane. This upshelf flow is a continuation of the anomalous trend observed earlier at LT2 and may therefore have contributed to continuation rather than alleviation of an- oxic conditions. The current meters also sample and record temperature. Long temperature series from stations 49 and LT2 are used in chapter 5 so are not discussed extensively here. Some data, however, are of interest in connection with vertical mixing of D.O. and other constituents in the water column. At the time of the hurricane, because tempera- tures and dissolved oxygen are correlated (ch. 2), tem- perature can serve as an indicator for vertical transfer of D.O. Figure 7-7 shows temperature observations made concurrently with the current observations in figure 7-6. Before the passage of the hurricane, the temperatures at station LT2A, 13 m below the surface but above the thermocline, were above the maximum range of the sensor and therefore were not plotted in figure 7-7. During the storm the temperature dropped abruptly into the working temperature range of the thermistor or sensor. The tem- perature continued to drop more slowly during the sub- sequent 2 days. At meter LT2B, the temperature in- creased about 8° C, fluctuated over several degrees in about 4 hours, then after about half a day fell to less than 2° C above its initial value. Our interpretation is that the large transient temperature increase primarily reflects downwelling and offshelf flow followed by upwelling and onshelf flow of water described earlier at this level. The relatively small residual temperature change (2° C) is probably indicative of vertical mixing that can be expected to provide only a modest resupply of oxygen to the region below the pycnocline. More complete information about the vertical structure of temperature changes is available from station LT4. Four hours after the temperature increase at LT2B, a temper- ature rise of about 4° C occurred at 21 m depth at LT4A and persisted for several days. Near-surface temperatures (LT4S) rapidly decreased more than 8° C at about the same time as the final rapid temperature drop at LT2B. Subsequently, the temperatures at the 3- and 21-m depths were only slightly different and increased at about the same rate during the following days. This combination of responses suggests vertical mixing to a depth of more than 20 m and possibly upwelling and offshore flow of surface water. It is not clear why the changes observed at the 13- m depth at station LT2 were so much less than those observed in the upper 20 m at LT4. These differences probably cannot be explained by local mixing processes alone. More to the point regarding mixing across the pyc- nocline, aside from a transient 3° C increase for only about 4 hours at 8 m above the bottom and a 1° C increase spanning about 1'/: days at both 8 m and 1 m above the 159 NO A A PROFESSIONAL PAPER 11 (a) . . i/ // . vl l r— IOOt (n ■o c o «« -lOOi o E c •— -100-' ^ CO m LT2'B LT4.B o (A a. 3 0) o 10 13 FIGURE 7-6— Stick plots and rotated (48°) components of winds and currents during passage of hurricane Belle, August 9-13, 1976. 160 CHAPTER 7 STATION LT2 Water Depth = 32 m A = 13m Below Surface B = 23 m Below Surface STATION LT4 Water Depth = 49 m S = 3 m Below Surface A - 2 I m Below Surface B= 41 m Below Surface C = 48 m Below Surfoce 24 20 u o 16 < LU Q. 12 1 1 1 1 r ,/.____ LT2 ~A LT4 \ / '■■■■■'"■ A (^ : .■:''■■ .:. : '■■ .•••.•• B aJ A B - / ^-^O-CZ ■^^■- '■ -^ V 1 1 \ """ 1 I 1 10 II 12 DAYS (AUGUST 1976) FIGURE 7-7. — Seawater temperature data from stations LT2 and LT4 during passage of hurricane Belle. August 9-13. 1976. 161 NOAA PROFESSIONAL PAPER 11 bottom at station LT4, there was little temperature re- sponse below the thermocline to suggest mixing of D.O. across the pycnocline. We conclude that despite strong winds and surface waves hurricane Belle was too small and passed too rapidly to have had a lasting effect on either the advection or vertical mixing processes in the Bight. SUMMARY Our principal objective was to explore the differences between currents observed in 1975 and in 1976 as a pos- sible cause of, or contribution to, the important differ- ences in D.O. concentrations observed during these 2 years. Insufficient flushing of the coastal waters could be an important factor in the depletion of the D.O. reservoir. A distinct difference was observed in the flow beneath the pycnocline in the area of anoxia off New Jersey. The weak- ened flow and reversal of direction in 1976 altered the usual pattern of material transports in the Bight. Much is still unknown about mechanisms of shelf circulation and its variability, but one major influence certainly was the period of southerly and southwesterly winds from about J.D. 125-215 (early May through early August). Although these winds were not particularly unusual on any given day, their direction was persistently opposite the normal southwestward flow of shelf waters, and their cumulative effect over more than 2 months must have been consid- erable . Similar reversals of surface currents off New Jersey in summer were reported during the 1960s (Bumpus 1969). Bumpus primarily attributed these reversals to the low river discharge at the time. Anoxia or mass mortalities were not associated with these events. A likely reason that the southwesterly winds evoked so little response in water below the pycnocline off Long Island is that the water is about half again as deep off Long Island as off New Jersey. The pressure gradient response to wind stress in shallow water is expected to be nearly inversely proportional to depth, hence the shoaler waters off New Jersey are expected to be more responsive to local winds. Another possible cause of the weaker per- turbation of the current off Long Island is the spatial pat- tern observed in the wind stress (ch. 3). Wind stress was generally parallel to the shelf contours off New Jersey, but crossed the coast at a considerable angle off Long Island. Csanady (1976) explained that the alongshore com- ponent of wind stress is more important than the cross- shelf component in its influence on currents. During the period of observations, upwelling occurred primarily in association with the current perturbation off New Jersey, but not off Long Island. Before this time, however, upwelling occurred consistently off Long Island and may have contributed indirectly to the low D.O.'s observed by advection of nutrients into the region. Not- able here (clearer in ch. 8) is that during late spring and early summer 1976, circulation below the thermocline was favorable off New Jersey but not off Long Island for con- centration of Ceratium tripos by the mechanism described in chapter 9, part 1. The average onshelf flow (nearly 1.5 cm/s) observed off New Jersey during the 2 months before initial discovery of the benthic mortalities corresponds to a virtual displacement of about one-third the total shelf width per month. This is enough to have swept a large amount of these organisms from the outer shelf onto the inner shelf off New Jersey. We infer from the relatively minor response of water below the pycnocline, first, that even though hurricane Belle's winds were intense, its rapid rate of passage was such that its impact on vertical mixing below the ther- mocline in the Bight was not especially significant. To the extent that wind-induced mixing may result in asymmetric, upward, turbulent entrainment of water across the ther- mocline, rather than symmetrical vertical mixing, then very little downward flux of oxygen into the bottom water would occur under even more extreme conditions than those of hurricane Belle. Second, we infer that reduced vertical mixing as a result of anomalously low summer wind speeds is not a likely cause of the low D.O. concen- tration observed during some years. In the New York Bight every summer the density stratification is sufficiently strong that normal or even greater than normal wind-in- duced mixing cannot effectively transfer D.O. across the pycnocline. This implies that, once the summer stratifi- cation has become established, the only physical mecha- nism for oxygen renewal is by advection or by mixing along isopycnal surfaces that typically slope upward in the offshelf direction, but at very small angles. There is, of course, a period of time in spring and again in autumn when establishment or destruction of the pycnocline is critically dependent upon the occurrence and timing of atmospheric events. ACKNOWLEDGMENTS The officers and crew of the NOAA ships Researcher and George B. Kelez, are largely responsible for the cur- rent meter data used herein. D. Ortman, N. Larsen, and K. Gallery also assisted in this work. REFERENCES Beardsley, R L., Boicourt, W. C and Hansen. D. V.. 1976. Physical oceanography of the Middle Atlantic Bight, Amer. Soc. Limnot. Oceanogr. Spec. Symp. 2:2()-34. Bumpus, D. F. , 1969. Reversals in the surface drift in the Middle Atlantic Bight area, Deep-Sea Res. 16 (suppl): 17-23. 162 CHAPTER 7 Bumpus, D. F., 1973. A description of the circulation on the continental shelf of the east coast of the United States, Progress in Oceanographv 6:111-157, Pergamon Press. Csanady, G. T.. 1976. Mean circulation in shallow seas, J. Geophvs. Res. 81(30):5389-5399. Hansen, D. V., 1977. Circulation, MESA New York Bight Alias Monogr. 3, New York Sea Grant Institute. Albany, N.Y., 23 pp. Mayer, D. A., Hansen, D. V., and Ortman, D. A., 1979. Long-term current and temperature observations on the Middle Atlantic shelf, J. Geophys. Res. 84, No. C4: 1776-1792. Ortman, D., 1978. Current meter data processing and quality control methods, MESA Tech. Rep. ERL, NOAA Environmental Research Laboratories, Boulder, Colo. Segar, D. A., and Berberian, G. A., 1976. Oxygen depletion in the New York Bight Apex: Causes and consequences, Amer. Sac. Limnol. Oceanogr. Spec. Symp. 2:220-239. Swanson, R. L., Hansler, G. M., and Morotta, J., 1977. Long Island Beach pollution: June 1976, MESA Spec. Rep., NOAA Environ- mental Research Laboratories, Boulder, Colo. Wu, J., 1969. Wind stress and surface roughness at air-sea interface, /. Geophys. Res. 74(2): 444-445. 163 I I p Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 8. Diagnostic Model of Water and Oxygen Transport G. Han, D. V. Hansen, and A. Cantillo^ CONTENTS Page 165 Introduction 167 Model Description 167 TTieory and Averaging Schemes 168 Diagnostic Model 169 Model Application and Results 169 Water Fluxes 172 Oxygen Transport 179 Discussion 191 Conclusion 192 Acknowledgments 192 References ' Physical Oceanography Laboratory, Atlantic Oceanographic and Meteorological Laboratories, En- vironmental Research Laboratories, NOAA, Miami, FL 33149 INTRODUCTION To thoroughly analyze the 1976 oxygen depletion in New York Bight, the transport of oxygen through the area by currents must be carefully considered. Here the time- averaged water and oxygen fluxes through certain seg- ments of the Bight during the period of anoxia develop- ment in May and June 1976 are calculated. Segment boundaries and station locations are shown in figure 8-1. A simple mass transport model is employed to analyze the oxygen balance, using observations of density, oxygen, and current velocity fields to estimate the various terms. Our major contribution here is an estimate of the water fluxes, utilizing a vorticity balance diagnostic model of the steady-state circulation field from May 18 to June 29, 1976. This time interval was selected because suitable data were available and because the dissolved oxygen (D.O.) con- centration was decreasing rapidly, but anoxia had not yet developed. Thus, the role of oxygen and water fluxes in the development of the anoxic condition can be compared to the observed changes of D.O. with time. This will result in the estimate of the net oxygen utilization rates in each segment and the evaluation of the role of water transports on the net utilization rates. Segar and Berberian (1976) calculated oxygen utiliza- tion rates in the Bight Apex. Studies have also been done on the utilization of other dissolved constituents, such as nutrients (Garside et al. 1976). Previous studies have been hampered by poor knowl- edge ot water transports. Investigators have been forced to resort to arbitrarily chosen and vaguely defined volumes and flushing times to complete their analyses. Because chemical reactions frequently depend on concentrations, and most problems involve finding concentrations that 165 NO A A PROFESSIONAL PAPER 11 39' 1 TO 20 30 «C 50 eP 70 ao 90 100 110 130 130 140 15 KU.OweTERS 10 20 30 40 X 60 70 80 90 100 NAUTICAL MILES FIGURE 8-1. — New York Bight station locations, segment numbers, and boundary designations for diagnostic model of water and oxygen transport. 166 CHAPTER 8 result from the loading of an area, the determination of mixing volumes and transport rates is critical. Cases of point loadings are difficult to approach because we must know the details of advection and diffusion processes on smaller time and space scales than is usually possible. In addition, large concentration gradients complicate com- putation procedures and introduce errors in the results. When a substance is well distributed over a region, dif- fusion processes can be neglected by averaging over a large volume. Then simpler models of mass flow rates can be assumed and longer time and space scales can be used, which are usually a better match to the scales of obser- vations. Previous studies of transport in the Bight followed salt balance methods initiated by Ketchum et al. (1951). Their studies of the distribution of physical properties produced estimates of flushing (residence) times based upon dilution of seawater by the Hudson River outflow. Estimates of this sort may be valid for the Apex, where salinities are often low enough to make an accurate calculation. When considering the larger area of the continental shelf, how- ever, the alongshore component of circulation, which usually parallels the contours of the salinity distributions, produces far greater flushing in a small area of the shelf than a dilution ratio calculation would indicate. MODEL DESCRIPTION Theory and Averaging Schemes The basis for transport modeling is the conservation of material equation dp/dl + V-(uc) = 0. (3) Dc/Dt = Is (i; where c is the concentration of the material, S.? is the sum of sources and sinks, and D/Dt is the total or material derivative. Molecular diffusion effects are ignored here. When working in a Lagrangian coordinate system (fol- lowing a parcel of water), eq. (1) describes the balance between the time rate of change and the net production (l5>0) or net utilization (Ss<0) of the constituent. This strategy is used in laboratory experiments and sometimes attempted in field studies. In most field studies, however, , measurements are made in an Eulerian coordinate system I at fixed points in space so that material is advected past the points of observation. In this system the material de- rivative must be expanded and eq. (1) is written as dc/dt + V-(uc) = Is (2) where dc/dt is the locally observed rate of change of con- centration, u = (m, V, w) is the velocity vector, and V = d/dx,d/dy,d/dz) is the divergence operator. The equiv- alent relationship for conservation of water mass is Equation (2) shows that the material derivative is com- posed of the local time rate of change of c and the diver- gence of the flux of c; it is the sum of these which balances the sum of production and utilization. All these quantities are evaluated at a fixed position. Since we cannot accurately estimate these gradients on infinitesimal time and space scales, we must approximate the derivatives so that the observed time and space gra- dients are consistently treated. When observations in time are made at a spacing of T days, the resolution in space must be of the order of L = UT, where L, T, U are the characteristic length, time, and velocity. Thus, if T is of the order of 10 days and U is 5 cm/s or 5 km/d then L must be of the order of 50 km. If the temporal rates of certain processes are inferred from observations at time interval 7, then L is the smallest length scale that can be resolved. One way to approximate spatial gradients is to smooth the data over a selected volume segment. Transports be- tween segments are then treated as advective fluxes. Dif- fusion effects are introduced by assuming that each volume is well mixed. Any material entering the volume is "in- stantaneously" mixed over time 7" throughout the volume. The effective diffusion thus introduced contributes to the transport on scales smaller than those resolved. Because New York Bight waters were strongly stratified during the period of this study, we will average over an upper layer and over a lower layer, separated at the pyc- nochne. Vertical diffusion between layers is neglected because the strong stratification implies inhibited vertical mixing; vertical advective fluxes are included. If observations are available at two discrete times, / = /, and / = ?,, we must decide how to approximate the time derivative. We know the concentrations at /, and /,, but there is no way of knowing dc/dt |, , „. If we approx- imate 5c/ar by Ac/Ar where Ac = (cj-c,) and Ar = (^-fl), then we should use concentration and velocity data inter- polated to f = (/, -h r,)/2. After performing appropriate volume and time aver- ages, the discrete version of eq. (2) becomes AVC ^t + I.QC + QX = Is, and assuming constant density eq. (3) becomes ^V A/ + IQ + g, = 0, (4) (5) where the capitalized letters are now volume averaged quantities and Q is the outward horizontal volume flux, Q, the vertical flux, IQC the sum of divergence of con- centration flux around the boundaries of each segment. 167 NO A A PROFESSIONAL PAPER 11 and V the segment volume. Assuming incompressibility, water density has been taken equal to a constant density, Po, in eq. (5). To estimate these fluxes, we will use a diagnostic model of shelf circulation. Once the advective terms of eq. (4) are known, the time rate of change of concentration term can be related to the source and sink term. Diagnostic Model Computing water transport on the shelf requires spatial resolution of a velocity field greater than is normally avail- able from current meter observations alone. Calculation of the velocity field requires understanding the dynamics of shelf circulation; that is, understanding how water moves in response to the imposed forces, as well as having adequate measurements of all the various forcing and in- dicator fields. One major forcing field is wind stress. Only a portion of water transport on the shelf, however, is in the frictional layer driven directly by wind. Simple Ekman theory ex- plains how a wind stress along a coastline will transport surface water perpendicular to the coast, resulting in a cross-shelf gradient in surface elevation. The response to this force is a geostrophic velocity along the shelf. Hori- zontal density gradients and bottom friction will modify the vertical profile of horizontal velocity, but it is mainly the forcing by seasurface elevation gradients (set up by the wind stress) that determines the gross characteristics of the flow. At present we cannot calculate the barotropic compo- nent of flow from wind data alone. Winds acting on dif- ferent sections of the Middle Atlantic Bight produce var- ied responses, particularly at a bend in the coastline, such as in the New Yoric Bight. A "prognostic" dynamic model should be able to calculate flow directions, given wind stress, river discharge, bottom topography, and other boundary conditions. Such a model would probably have to include the entire Middle Atlantic Bight and be able to approximate many processes we now understand only poorly. A more limited approach, but one that can yield the required flow field, is to construct a "diagnostic" model as is done here. The model is a steady-state representation of the flow for which it is assumed that the structure of the density field is known and is not being changed by the velocity field. The general tlow condition must be known from current measurements at appropriate points to cal- culate boundary conditions which strongly influence the flow. This type of modeling might alternatively be con- sidered a formalism for interpolating or synthesizing over the field of available data. The result is tightly bound to the observed data. Wind stress does not enter the for- mulation explicitly but is reflected in the boundary con- ditions, calculated from current velocity data for the open boundaries and from a no-flux condition for the solid boundaries. Only the curl of the wind stress enters the model, and this is much less important than the other terms for the cases considered. The model addresses a condition which is not truly steady state but is actually a time average over a certain period. The period should be long enough to span any storm events but short enough to allow the approximation of an unchanging density field. The diagnostic model con- cept is supported by recent work of Csanady (1976), who hypothesized that short-term storms generate flows which tend to organize the density field into patterns such that the time-average flows can be analyzed from the density patterns with a simple linearized equation of motion. Thus, a reasonable averaging period is of the order of 5 to 30 days. The fundamental physical problem reduces to solving a differential equation for the shape of the sea surface. The model equation is; p„gJ{lH) + gJiaM) + k-(VxTj + -^^Poj— + V-^q = 0, (6) where C, is the elevation of the sea surface, H bottom depth, T„ surface wind stress, y linear bottom friction pa- rameter taken as 1600 cm following Csanady (1976), p„ reference density, k unit vector in the vertical direction, r" g gravitational acceleration, a = p dz. where z is the vertical coordinate, zero at the surface and positive up- ward, and m-n) = dx dy dy dx A complete description of this equation is not possible m here. Alternative forms of the model have been devel- ^ oped and described by Hsueh et al. (1976) and by Gait (1975). Gait's vorticity equation, used here, results from the linearized equations of motion on a rotating Earth and is derived by summing the transports in the surface Ekman layer, the geostrophic interior, and the bottom Ekman layer, and then imposing the continuity condition that the divergence of the transport must be zero. This is an ex- tension of the classical geostrophic current calculation to include frictional layers at the sea surface and over a slop- ing bottom. The diagnostic variable, ^, is used as the sur- face boundary condition for a calculation of the geos- trophic velocity profile. The equivalent condition in the deep ocean is the assumption of a depth of no motion. The terms in eq. (6) are interpreted consecutively as: bar- 168 CHAPTER 8 otropic-geostrophic, baroclinic-geostrophic, wind stress curl, and bottom friction components. To aid in visualizing the equations, consider a simplified system with constant density, no wind stress curl, and no bottom friction. Then only the barotropic term remains and eq. (6) becomes J(i. H) = 0. (7) A property of the operator, J, or the Jacobian, is that it is zero whenever one variable in the argument list is a function of the other variable. Equation (7) is satisfied if the surface elevation contours parallel the depth contours. Thus, in this simplified case, the geostrophic velocity field at all depths is described by the C, contours as streamlines. This flow is, of course, everywhere parallel to the bottom contours as well. Once eq. (6) is solved for the ^ field, the geostrophic velocity profile can be calculated at any depth z= o to z = -//by kx^i^i (8) where / is the Coriolis parameter. The current profiles derived from eq. (8) are somewhat simplified in that the vertical shear associated with the density gradients is as- sumed uniform. The complete velocity profile can be formed by superimposing the proper profiles for a surface and bottom Ekman layer. MODEL APPLICATION AND RESULTS Water Fluxes Results from the diagnostic model are used to calculate the water flux in the layer below the pycnocline. To apply the diagnostic model, the data required are depth {//), vertically integrated density (a), wind stress field (t„), and appropriate boundary conditions. To calculate the bound- ary conditions on t,, current meter data are needed on the two cross-shelf boundaries. Model equation (6) is solved for the surface elevation field using a finite element technique, developed by Gait (1975), on a grid shown in figure 8-2, where each triangle vertex is an STD station location. Values of //, a, and T^ are specified at these vertices. The station grid and density data were used from MESA cruise XWCC-9 (May 17-24, 1976). Several stations were added near the Hud- son Shelf Valley to better approximate the sharp depth gradients. Values of a were smoothly interpolated to these new stations. Figures 8-3 and 8-4 show the depth and a fields used in the calculations. Wind stress was calculated from EB34 wind velocity data; EB34 is located at midshelf just northeast of Hudson Shelf Valley (ch. 7, fig. 7-1). Wind stress was taken as constant over the domain (grid). Current meter records from the MESA 1976 survey were averaged over four separate time periods spanning May 18 to June 29, 1976. The four periods were selected so that wind and current conditions were relatively uri- form over each interval. The averaged currents and wind stresses are shown in figure 8-5. To solve the model equation, the surface elevation fidd must be specified around the entire boundary because (♦) is an elliptic equation. By calculating V^ between ea LU _J UJ LU o < z> 40° 39° 75° 74° 73° 72° FIGURE 8-7.— Solution of model for i. surface elevation (cm). May 18-23, 1976. 71" were available to find values of D.O. for regions outside the boundaries, these were approximated by vertically averaging D.O. at stations on the outside boundaries. Oxygen concentration data were not available for XWCC-10 at the northeastern and southern boundaries of the region. To compute the volume-averaged concen- trations for XWCC-10, all data available in each segment were utilized. The boundary concentrations for XWCC-10 were calculated by using the same ratio between the boundary and adjacent segment concentrations as was observed on XWCC-9. Oxygen fluxes were found for each segment boundary during the four separate intervals. The oxygen fluxes were calculated by multiplying the water flux through each seg- ment boundary (fig. 8-11) by the oxygen being trans- ported. The oxygen concentrations were different for each interval because they were linearly interpolated in time between the values for XWCC-9 and XWCC-10 (table 8-1) fluxes. The oxygen fluxes at each boundary were then averaged, in a manner similar to the water fluxes, to pro- duce an average over the entire 42-day interval (fig. 8-12). The first two terms in eq. (4) were calculated for each segment from the volume of the segment and the time rate of change on D.O. between XWCC-9 and XWCC-10 (table 8-1) and the divergence of the oxygen fluxes from the values in figure 8-12. The net utilization rate was calculated using eq. (4). Values of all terms in eq. (4) are listed in table 8-2. The residual term, 5, is a net utilization rate incorporating all sources of oxygen other than ad- vective fluxes, such as phytoplankton production and ver- tical diffusion, minus any utilization of oxygen, such as respiration of any ogranism and bacterial decay. DISCUSSION Use of the diagnostic model is limited both in concept and input data to representation of circulation patterns 179 NOAA PROFESSIONAL PAPER 11 70 80 90 '00 STATUTE MILES ' '0 20 30 aC 50 60 70 80 90 IQO liO ^X 130 140 15 KILOMETERS ■0 90 100 NAUTICAL MILES 20 30 40 SO 60 70 FIGURE 8-8. — Average velocity, 8 m above bottom, May 18-May 23, 1976, modeled and observed. ISO CHAPTERS -39° 10 10 20 30 40 W 70 80 ^90 100 STATUTE hilLES ' : 10 X 30 «C 50 63 70 60 90 iQO 'JO 120 130 140 IS O KiLOhtETERS 1 10 20 30 40 » 60 70 80 90 lOG NAUTICAL WILES HMM.iL Hb = 1 t— i i I i I .. i 1 1 FIGURE H-M. — Transport m bottom layer below pyenoeline for May 18-23, 1976. 181 NOAA PROFESSIONAL PAPER 11 10 10 20 30 40 SO 90 100 STATUTE MILES 1 10 20 30 40 y 60 70 80 90 100 '10 120 130 140 IS O KILOMETERS 10 20 30 40 W 60 70 60 W 100 NAUTICAL MILES FIGURE 8-l()A. — Schematic of water transport below pycnocline for May 18-23, 1976. 182 CHAPTER 8 10 10 20 30 40 50 90 100 STATUTE MILES 1 10 20 30 JC M 60 70 80 90 100 110 1 2 01 30 MO 15 KILOMETERS 10 20 30 40 50 60 70 BO 90 100 NAUTICAL MILES FIGURE 8-l(»B. — Schematic of water transport below pycnocline tor May 23-June 3. 1^76, 183 NO A A PROFESSIONAL PAPER 11 10 20 30 40 SO 60 70 90 100 STATUTE MILES 10 10 20 30 40 — 1 1 1 50 60 70 80 90 100 110 i?0 130 140 1S0 KILOMETERS 10 20 30 40 SO 60 F= 70 — 1 80 90 10( 00 NAUTICAL MILES FIGURE 8-lOC. — Schematic of water transport below pycnoclinc lor June 3-0. 1976. 184 CHAPTER 8 10 10 20 30 40 50 60 70 80 90 100 STATUTE MIL 10 10 20 30 4C 50 60 70 80 90 100 110 2C 130 _M0_ 150 KILOMETERS u u u w wi 10 — 1 20 30 40 =d fc= 50 60 70 80 90 10( 00 NAUTICAL MILES FIGURE S-U)D.— Schematic of water transport below pycnocline for June 13-29, 1976. 185 NO A A PROFESSIONAL PAPER II 41°K — ^40° 10 20 30 40 5C 6C HUUUTTV 90 100 STATUTE MILES 1 10 20 30 40 50 60 70 60 90 100 nQ 120 130 140 15 KILOMETERS 50 60 70 80 90 >00 NAUTICAL MILES 30 40 FIGURE 8-11. — Average water transport below pycnocline in New York Bight, May 18-June 29, 1976. 186 CHAPTER 8 Table 8-1. — Surface area, volume, and average dissolved oxygen concenlralions in New York Bight, 1976 Segment' of Bight LI L2 L3 A H Jl J2 Surface area (km-) 3905 4320 6490 1780 1440 3510 2760 Volume (km'): Upper layer 67.9 93.3 191 28.1 33.7 69.8 75.6 Lower layer 6.V3 119 347 31.3 56.2 34.7 47.7 Averaged dissolved oxygen (ml/I): XWCC-9 (May 17-24): Upper layer 6.85 6.94 7.16 6.38 7.37 6.63 6.80 Lower layer 5.41 5.23 5.74 5.52 6.02 5.17 5.41 XWCC-10 (June 28 to July Upper layer Lower layer 5.75 4.56 6.01 3.73 6.90 5.35 5.34 1.95 5.47 3.23 4.65 1.33 5.59 2.60 Boundary dissolved oxygen (ml/I): Boundary designators' _8 _9 iO U i2 13 U XWCC-9: Lower layer 5.11 5.58 5.34 5.67 fi 14 5.81 5.83 XWCC-10: Lower layer 1.31 2.68 4.99 5.00 5.72 4.14 4.91 Segment numbers and boundary designators refer to figure 8-1. averaged over selected time intervals such as shown in figure 8-8 . These patterns are consistent with the current velocities shown in figure 8-5 and are based upon both these current data and the density data described more extensively in chapters 2 and 7. The diagnosed currents are evaluated at much greater spatial resolution than can be obtained from current meters only. However, it is dif- ficult to demonstrate the veracity of the model in as much detail as it portrays. Because of the nature of the available oxygen data, as discussed previously, transports are in fact more useful than detailed velocity structure in application to the anoxia problem. Thus, the major results from the circulation model are presented instead as transports in the lower layer through the various boundaries of the several segments of New York Bight. These are shown in figure 8-10. Transport below the thermocline during the interval diagnosed is consistently to the southwest, into the Bight, all across the shelf off eastern Long Island. Off southern New Jersey, transport is predominantly southward, out of the Bight, over the outer shelf, and is directed weakly southward over the inner shelf on the average, but the transport undergoes large reversals over the interval. The lower layer flow in the Hudson Shelf Valley is predominantly shoreward into the Apex. In the Apex seg- ment, the diagnosed horizontal transport from all adjacent segments is into the Apex, causing the mass balance to be maintained by an estuarine-like upward flow through the pycnocline. Exchange with the estuary has been ig- nored because the required upwelling flux is more than 30 times the Hudson River discharge. A small but perhaps significant fraction of this upwelling probably occurs by horizontal transport into, and upwelling within, the es- tuary. Neglect of this detail does not invalidate the model for the present analysis. The implied vertical flow rate across the thermocline in the Apex segment is about 1.3 m/d, and the outer shelf segment has upwelling across the pycnocline of the order of 0.1 m/d. Diaz (chap. 3) used monthly mean wind values to compute the mean vertical motion in New York Bight during May and June as upward at about 0.04 and 0.02 m/d. respectively. The upwelling velocity, as determined with the diagnostic model but av- eraged over all the Bight as defined for the model, is upward at about 0.06 m/d. The discrepancy between these results can probably be attributed to the limit of accuracy in the diagnositc model and to the fact that Diaz's com- 187 NO A A PROFESSIONAL PAPER 11 40° ■39° 90 100 STATUTE MILES 10 1Q 20 30 40 SO 6Q 70 80 90 lOO I'D 120 '30 140 TS O KILOMETERS uuuuui 1 ■ ■ ' ' ■ 2Q 30 40 50 60 70 80 90 100 NAUTICAL MILES FIGURE 8-12— Average oxygen transport below pycnoclino in New York Bight. May 18-June 29. 1976. 188 CHAPTER 8 Table 8-2. — Water and oxygen transport characteristics in New York Bight. May IS to June 29. 1976 Segment of Bight' LI L2 L3 H Jl J2 Net advective input of water, (2,„ (lO'mVs) Water flushing time, V/&„ (d) Change in oxygen concentration with time. AC/A/ (10' ml/l/d) Divergence of oxygen flux, (IQC + Q.C)/V{\0 ' ml/l/d) Net oxygen utilization rate. S5/V(10-' ml/l/d) Oxygen ventilation time. CWrS.{QC),„d-' 24 26 63 26 29 7 33 31 53 64 14 23 58 17 20 -36 - 9 -85 -66 -91 -67 33 -21 - 7 -62 2 -80 -67 53 -57 -16 -148 -64 -172 -134 25 43 6(1 12 TT 24 13 ' Segment numbers refer to figure 8-1. putations are based on simple Ekman divergency ("Ek- man suction") upwelling appropriate to the open ocean rather than on coastal Ekman divergency appropriate to the coastal ocean. An objective estimate of the advective flushing time of the several segments of the Bight emerges from these calculations; that is, the ratio of the volume of each seg- ment to the flux into or out of the segment as determined by the diagnostic model for the conditions observed below the thermocline during spring and early summer 1976, V/ Q,„. As seen in table 8-2, these flushing times within the bottom layer varied from about 2 weeks to 2 months. The most rapid flushing occurred in the Apex; the slowest occurred off the New Jersey coast and in the outer seg- ments off Long Island. A comparison with table 8-1 shows a general correlation between flushing time and individual segment size; this is to be expected because current speeds are generally similar throughout the Bight. Also, the ratio of an appropriate dimension of a segment to the speed of the mean flow provides a first-order estimate of the ad- vective flushing time. The corresponding flushing time for the entire Bight was of the order of 75 days. Such calcu- lations are limited in that there is no assurance that water "flushed" from the Bight, or any part of it, does not return later. On the other hand, it also does not take into account the flushing effect of motions that occur on time scales much shorter than 10 days. Even in this year of extreme oxygen depletion, there were flows between the various segments in the Bight, and between the Bight and sur- rounding waters, which exchange these waters on time scales that are short compared to the seasonal cycle of thermal stratification. The oxygen flux calculations indicate a net advection of oxygen into the Bight as a whole, and into each segment defined for this analysis, except for the Hudson Shelf Val- ley. All segments characterized by upwelling had a net input of oxygen by horizontal advection. Those charac- terized by downwelling had a net loss of D.O. by hori- zontal advection, which was more than compensated by the downwelling of water with high D.O. The results of the primary objectives of these calcula- tions are summarized in table 8-2. Interpretation of these results requires an appreciation of how the values were obtained. We began with observations of the rate of de- crease in time of oxygen in the various segments. If there was no net transport of oxygen into or out of the segment, then the net utilization of oxygen would be the observed time rate of change of concentration. However, if there was some net advective flux of oxygen, say into a segment, then the net utilization rate, SS, in the segment is equal to the sum of the change of oxygen content in the segment, VAC/Ar, and that advected into the segment, IQC + QvC. To put the utilization rates into perspective, we calculated the utilization rate per unit volume, SS/V, for easy comparison with the observed time rate of change of concentration, AC/ A/, and for comparison of effective ratios between sections. It is readily seen in table 8-2 that in the inner and mid- shelf segments the actual utilization rate is approximately twice as large as would be inferred from the observed change of concentration alone. Furthermore, the utiliza- tion rate found for the seriously impacted areas in the Apex and the inner shelf off New Jersey is about 3 times greater than for other regions of the inner and middle shelf and more than 10 times higher than that found over the outer shelf. Segar and Berberian (1976) estimated the oxygen consumption rate during summer 1974 as 10' kg OJd for water below 10 m depth in the Bight Apex. By dividing the appropriate volume (26 km'), this is equal to a utilization rate of 0.27 x 10"' ml/l/d. Their estimate is some 55 percent greater than our values for the Apex, and 2 to 17 times greater than the other values from over the shelf. Although Segar and Berberian's rate is not greatly more than our maximum value, the unusual cir- 189 NO A A PROFESSIONAL PAPER 11 cumstances surrounding our 1976 data suggest that the rate calculated by Segar and Berberian is an overestimate, probably because much of the primary productivity con- tributing dominantly to their calculation is in fact advected out of the area rather than simply sinking through the thermocline. Another time scale of interest is an analog for oxygen of the advective flushing time for water. That is the ratio of the oxygen storage in a segment to the advective input of oxygen, CV/1,(CQ),„, which we will call the ventilation time. This ratio is a measure of the flow-thru rate of oxy- gen. Short ventilation times indicate that the availability of oxygen by advective flow-thru is large relative to am- bient oxygen storage. Ventilation times defined in this way exhibit the same general features as the water flushing time, but typically are 15 to 60 percent shorter, except in the outer shelf segment and the shelf valley where they are nearly equal. The implication of these results is that advection is more effective in supplying oxygen to the Bight than it is for simple renewal of water. These results are due, in part, to the reduced oxygen concentration values that occur regularly in the inner Bight during sum- mer relative to higher oxygen concentrations existing else- where available for transport to that region. An analysis of the errors in the calculation must be made to determine the significance of the results. Standard error of the means can be calculated for the D.O. con- centrations, but the errors in volume, V, and transport, Q, cannot be calculated from the available results. If the error in volume and transport is assumed to be 10 percent, it is the dominant error in calculation. The values of the net utilization rates are greater than one standard error of the rates for all the segments except L.3. The values of IS for segments A and Jl are 4.0 and 4.8 times the standard errors in S5, respectively. If the assumed errors in Q are increased to 20 percent of their magnitude, then the standard errors in I.S are still less than SS for the segments of critical interest — A, Jl, J2, and L2. It would be necessary to assume errors of 50 percent in Q to make the errors in 25 greater than the magnitude of 25 in seg- ment Jl. Thus, the important results of the calculations can be taken as meaningful even if the errors in approx- imating the transports are large. A drawback of diagnostic modeling is that it cannot forecast how details of the circulation would change under different wind or other forcing conditions. The model can be used to describe and analyze only conditions for which at least some current velocity data are available. The density field is held stationary over the entire 42- day interval because only one complete set of density ob- servations was available. This introduces errors in the transport calculation in equations (8) and (9), but the near- bottom velocity field is unchanged. Comparisons of ob- served and modeled velocities and the effect of the density field on model accuracy will be the subject of a further study. The results of our model are probably more ac- curate than a prognostic model, since the calculation is based upon a large amount of observed data. Another shortcoming of the method as presently used is that it is applicable to only the steady or most slowly changing components of the flow. Therefore, diffusion of oxygen by higher-frequency movements such as tidal cur- rents and storm-driven transient flows is not included in the diagnosis. This effect arises from simultaneous vari- ation of flow speed and oxygen concentration, the basic mechanism of turbulent transport, within the four time periods that were diagnosed and averaged. In defense of the present application, incorporation of a gradient dif- fusion mechanism of any sort into the model would in- dicate additional oxygen flux into the oxygen-deficient regions, thus strengthening the major conclusion of the investigation. In fact, the respiration rate calculated by Malone et al., using an independent approach (ch. 9, pt. 1), indicates that the sum of observed D.O. change and advective import are of approximately the correct mag- nitude to supply the oxygen utilization; hence, diffusive flux of oxygen seems to be relatively unimportant. The circulation pattern, both in the Bight Apex over 31 days of the study and all along the inner New Jersey shelf over 21 days of the study, shows convergent flow in the lower layer and upwelling through the pycnocline. Though the upper layer model results are not shown, the upper layer flow was offshore as is seen in the current meter data (fig. 8-5a, b, and d). The cause of the convergence in the Apex is the unusual flow pattern shown in figures 8-5a and d, where the nearshore flows in the lower layer off New Jersey and Long Island are both directed toward the Apex. Away from the Apex, the bottom Ekman layer transport, which is directed to the left of the alongshore flow, creates a strong convergence off New Jersey. This pattern of shoreward flow and convergence in the bottom waters, compensated by divergent seaward flow in the upper waters is kinematically similar to the circulation commonly observed in coastal plain estuaries. Festa and Hansen (1978) showed that particulate materials charac- terized by a suitable particle sinking velocity will tend to be concentrated by a flow field of this type, irrespective of whether they are introduced from the river or from the ocean. It is one of the causative mechanisms for the tur- bidity maximum that has long been known to occur in coastal plain estuaries. We expect that under the influence of the circulation observed in the New York Bight in the late spring of 1976, oxidizable particulate materials orig- inating in the Hudson Estuary, or elsewhere throughout the Bight, will have been concentrated in the Apex and along the inner shelf off New Jersey. Ceratium tripos are ideally suited to couple to this con- vergent pattern, as suggested in chapter 9, part 1, since 190 CHAPTER 8 they are capable of vertical motility and choose to remain below the pycnocline. Organisms which are transported into the convergent areas do not move through the pyc- nocline into the divergent area above. This leads to a concentration of organisms in the lower layer of the con- vergent areas off New Jersey and in the Apex. CONCLUSION The first conclusion to be drawn from the use of the diagnostic model is that even during May and June 1976, the replacement time of water in New York Bight was relatively short compared to the general seasonal cycle of property changes for the Bight as a whole and for the inshore segments of principal interest. A second conclu- sion is that oxygen depletion in the critical region during the May-June period was due to oxygen utilization about 3 times greater than in other regions of the inner shelf and nearly 10 times greater than that occurring over the outer shelf, rather than simply being due to the length of strat- ified season, stagnation, or advection of low-oxygen water. The most critically affected regions, in fact, had a relative advective oxygen input substantially greater than other areas. The key problem in examining the anoxia episode is explaining the high consumption rates that occurred off New Jersey during spring and summer 1976. Numerous causes have been suggested, including ocean dumping, estuarine discharge, primary production (Segar and Ber- berian 1976; ch. 10), and an anomalous bloom of dinofla- gellate organisms (ch. 9, pt. 2). All these suggestions do not adequately address the questions of why 1976 and why the inner shelf off New Jersey. Although observations obtained and techniques used are deficient for explicit quantitative modeling of carbon/oxygen relationships, or even the distribution of particulate material or Ceratium tripos in the Bight, a strong qualitative case can be made from results of the diagnostic circulation model of the Bight, and the model study of particulate material trans- port by Festa and Hansen (1976), that the 1976 anoxia episode off New Jersey came about in the following way. For reasons not well understood but probably related to the pattern of surface wind, and quite possibly to the heavy discharge from the Hudson River during early 1976, the circulation in and near the Apex was kinematically equivalent to that commonly occurring in coastal plain estuaries for the entire period from May 18 to June 29. A similar situation existed in the average along the entire inner New Jersey shelf over the last 26 days of the period. Such circulations tend to trap and concentrate suspended particulate matter having a small sinking velocity. This concentration process functions irrespective of where such particulate materials are introduced into the circulation pattern. Hence, particulates from the Hudson River, the dumping activities, and plankton productivity would have concentrated in the Apex and over the inner shelf off New Jersey. This concentration of oxidizable material had an exorbitant biochemical oxygen demand that depleted the oxygen supply in spite of reasonably active ventilation of waters below the thermocline. If Ceratium tripos, which are capable of relatively rapid movement (see chapter 9, part 2), seek a position below the thermocline, this behavior will couple to the circula- tion just as do inanimate particle distributions. In the case of Ceratium tripos the concentration mechanism can be expected to function with particular efficiency because the organism can optimize its vertical movement relative to that of the water. A principal outstanding question is whether Ceratium tripos did in fact contribute in a dom- inant way to the oxygen demand off New Jersey, or whether the concentration of other oxidizable particulates would have led to anoxia even in the absence of Ceratium tripos. Conditions in May and June 1975 have not been diag- nosed. But the comparison of current meter data between 1975 and 1976 made in chapter 7 shows that the convergent circulation pattern which fostered inshore concentration of particulates did not exist during spring 1975. Though we can calculate what occurred in 1976, the comparison of oxygen utilization rates to average rates suffers because we have a poor idea of what the average really is. Changes in both terms of the oxygen mass bal- ance, CLQC + QyC) and SS, contributed to the large de- crease in concentrations with time preceding the anoxic episode. A really illuminating result is that an order of magnitude change in these terms is not necessary to pro- duce the observed conditions. Relatively small changes, smaller than a factor of two, can considerably influence the mass balance. The simplicity of the oxygen mass bal- ance equation conceals many feedback loops between the water transport and oxygen production. Decreased trans- port will, for example, prevent nutrients from reaching an area, thus decreasing plankton growth rates. In the so- lution to these problems and others, such as nutrient sup- ply, organic loadings, and planktonic growth rates, and the oxygen consumption rates of all these constituents, lie the answers to why the anoxia developed off New Jersey in summer 1976. The oxygen transport is only a piece of the puzzle. 191 NO A A PROFESSIONAL PAPER 11 List of Symbols c = concentration of material S5 = sum of sources and sinks DIDt = total of material derivative dcldt = rate of change of concentration p = density of water Po = reference (constant) density T = time interval (days) T = transport in bottom layer Tb = transport in bottom friction layer L = length (km) t = discrete time (/,, /,, etc.) Q = horizontal volume flux Qv = vertical volume flux V = segment volume C = volume-averaged concentration quantities I.QC = divergence of concentration flux around boundaries of each segment H 8 y z f a V J i J k u U bottom depth acceleration of gravity elevation of sea surface surface wind stress linear bottom friction parameter vertical coordinate Coriolis parameter vertically integrated density divergence operator (d/dx, d/dy. d/dz) Jacobian operator unit vector unit vector unit vector in vertical direction velocity vector (u, v, w) velocity (cm/s or km/d) ACKNOWLEDGMENTS REFERENCES We thank the officers and crew of the NOAA ship George B. Kelez. and the MESA New York Bight Project Office and Operations Base, for setting and maintaining the current meter moorings; Oceanographic Division per- sonnel of the National Ocean Survey for initial processing of current meter data; the staffs of the Ocean Chemistry Laboratory and Physical Oceanography Laboratory of the Atlantic Oceanographic and Meteorological Laboratories, Miami, Fla., especially Robert Starr, John Hazelworth, and Shailer Cummings, for processing the density data, Dennis Mayer, Michael Minton, and Donald Ortman for processing current meter data, and Kathy Philips for typ- ing many drafts of the manuscript. We especially thank Jerry Gait who developed the diagnostic model and made the model coding available, and Glen Watabayashi, Ste- ven Smyth, and Carol Pease of the Pacific Marine Envi- ronmental Laboratories, Seattle, Wash., who aided in the model development. Csanady, G. T., 1976. Mean circulation in shallow seas, J. Geophys. Res. 81 (30):5389-5399. Festa, J. F., and Hansen, D. V., 1976. Turbidity maxima in partially mixed estuaries. A two-dimensional model. Estuar Coastal Mar. Sci. 4:309-323. Gait, J. A., 197.'i. Development of a simplified diagnostic model for interpretation of oceanographic data NOAA Tech. Rep. ERL-339-PMEL-25, NOAA Environmental Research Laborato- ries, Boulder, Colo., 46 pp. Garside, C, Malone, T. C, Roels, O. A., and Sharfstein, B. A., 1976. An evaluation of sewage-derived nutrients and their influence on the Hudson Estuary and New York Bight. Esluar. Coastal Mar. Sci. 4:2X1-289. Hsueh, Y., Peng, G., and Blumsack. S. L.. 1976. A geostrophic cal- culation of currents over a continental shelf. Mem. Sac. Royal Sci. L/f^f 6(10):31.'i-330. Ketchum, B. H.. Redfield, A. C, and Ayers. J. C, 1951. The ocean- ography of the New York Bight, Pap. Phys. Oceanogr. Meleorol. 12, 46 pp. Segar, D A., and Berberian. G A., 1976. Oxygen depletion in the New York Bight Apex: causes and consequences, Amer. Soc. Limnot. Oceanogr. Spec. Symp. 2:220-239. Smith, J. D., and Long. C. E.. 1976. The effect of turning in the bottom boundary layer on continental shelf sediment transport, Mem. Soc. Royal Sci. Liege 6(10): 369-396. 192 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 9. Plankton Dynamics and Nutrient Cycling Part 1. Water Column Processes Thomas C. Malone,^ Wayne Esaiasr and Paul Falkowski^ CONTENTS Page 193 Introduction 195 Ph-ttoplankton Ecology 195 Productivity 196 Distribution 196 Biology of Ceratium tripos 197 Plankton and Biological Oxygen Demand — January-September 1976 197 Water Column-Stratification and Dissolved Oxygen 197 Time-Course of the Ceralium Bloom 197 Vertical Distribution 198 Horizontal Distribution in Maximum Chlorophyll Layer 199 Growth and Respiration of Ceratium tripos 204 Suspended Particulate Organic Matter and Phytoplankton 204 Accumulation of Ceratium tripos off the New Jersey Coast 212 Conclusions 216 Acknowledgments 216 References ' Lamont-Doherty Geological Observatory, Palisades. NY 10964 ^ Marine Sciences Research Center, State University of New York, Stony Brook, NY 11794 ^ Oceanographic Sciences, Brookhaven National Lab- oratory, Upton, NY 11973 INTRODUCTION An extensive bloom of the dinoflagellate Ceratium tri- pos (O. F. MiJller) Nitzsch developed throughout the Middle Atlantic Bight (between 36° N, 41° N. and the continental shelf break) from January through July 1976. By late June-early July an oxygen minimum layer (<2.0 ppm) had developed below the thermocline between the 20- and 40-m isobaths off the New Jersey coast from At- lantic City to Sandy Hook. (See chapter 2.) Local anoxic conditions were most widespread east of Barnegat Inlet (39° 45'N) in early July and east of Great Bay (39° 30'N) by late July. Presence of this subthermocline oxygen min- mum layer and associated sulfide production apparently resulted in mass mortalities of demersal fishes and benthic invertebrates. (See chapter 12.) The occurrence of the C. tripos bloom and the subse- quent development of the oxygen minimum layer led to the hypothesis that C. tripos was involved in generating the biological oxygen demand (BOD) required to produce the oxygen minimum. In an effort to clarify the role of C. tripos, this paper addresses these questions: 1. What was the areal extent of the bloom and the time course of its development? 2. What were the most likely causes of the bloom and its collapse? 3. What were the effects of the bloom on the distri- bution of organic matter and dissolved oxygen? For this discussion, the New York Bight was divided into five regions (fig. 9.1-1); 1) Long Island coastal area, 2) New Jersey coastal area (<20 m deep within 5 km of the coastline), 3) lower Hudson estuary (including Upper and Lower Bays of New York Harbor), 4) the Apex (bounded by 40° lO'N and 73° 30'W), and 5) the outer Bight (south and east of the Apex to the shelf break be- tween Montauk Point and Cape May). 193 NOAA PROFESSIONAL PAPER 11 Sewage Sludge Dumpsitd 40» 39« 10 10 ?0 30 40 50 60 70 80 90 100 STATUTE MIL 10 10 20 30 40 50 60 70 80 90 100 110 120 130 140 1 50 KILOMETERS 10 20 30 40 SO 60 70 80 90 ia ] 1 1 FIGURE 9.1-1. — New York Bight regions, transects, and stations. 194 CHAPTER 9, PART 1 PHYTOPLANKTON ECOLOGY Productivity Major studies of phytoplankton productivity include: Ryther and Yentsch (1958), the outer Bigiit; Mandelli et ai. (1970), the Long Island coast; and Malone (1976a, 1976b, 1977a, 1977b), the lower Hudson-Raritan estuary and Bight Apex. The following synthesis is based on these studies and on reviews by Smayda (1976) and Yentsch (1977). Annual phytoplankton productivity generally decreases with depth and distance from the mouth of the Hudson- Raritan estuarine complex. Phytoplankton productivity in the Apex is about 430 g C/m-/yr. or 70 to 80 percent of the annual input of particulate organic carbon (POC) to the Apex. The remaining inputs are derived primarily from sewage wastes generated by the New York-New Jer- sey metropolitan population. (See chapter 15.) Phyto- plankton productivity in the outer Bight decreases from 160 to 100 g C/m-/yr as water column depth increases from less than 50 m over the continental shelf to 1,000 m over the slope. An important exception to this general trend is the high phytoplankton biomass and productivity often observed in the region of the shelf break (Fournier et al. 1977). The development of phytoplankton blooms along the shelf break appear to be a consequence of nutrient enrichment and vertical stability provided by a frontal system sepa- rating nutrient-poor shelf water from nutrient-rich slope water. Phytoplankton productivity in the Apex fluctuates be- tween 0.1 and 6.6 g C/m-/d (mean = 1.2 g C/m=/d com- pared to 0.1 to 1.1 gC/m-/d (mean = 0.4 g C/m-/d) in the outer Bight. Seasonal variations in the outer Bight appear to be characterized by winter-spring blooms. Over the midshelf area (<50 m) of the outer Bight, productivity is 0.5 to 1.0 g C/m-/d from November through April, but is less than 0.5 g C/m-/d the remainder of the year. Offshore (50-150 m), productivity exceeds 0.5 g C/m=/d during March-May. In contrast, seasonal variations in the Apex are char- acterized by two bloom periods coinciding with minimum time-dependent changes in surface temperature during February-March (2°-8° C) and June-July (19°-23° C). Chain- forming diatoms (netplankton retained on a 20-|a.m mesh screen) with mean euphotic zone generation times of 1 to 3 days usually dominate phytoplankton blooms in Feb- ruary-March. During these months the water column (20-30 m deep) is well mixed, the euphotic zone extends to the bottom, and phytoplankton populations are abun- dant throughout the water column. Maximum biomass occurs during this period. Phytoplankton productivity is generally higher during the June-July bloom period when small green algae (nannoplankton with mean spherical diameters less than 10 (jim) growing at mean euphotic zone generation times of 0.5 to 1.5 days dominate phytoplank- ton blooms. At this time, the water column is well strat- ified, with the thermocline between 5 and 15 m (5-20 m off the bottom); the euphotic zone is 5 to 15 m deep; and phytoplankton populations are concentrated near the sur- face, with maximum densities along the New Jersey coast within 20 km of the Hudson-Raritan estuary mouth. Major inputs of inorganic nutrients (in contrast to re- generated nutrients within the Bight) include estuarine runoff (mainly from the Hudson River) and fluxes onto the shelf in the region of the shelf break. Although ob- servations in the Bight as a whole are lacking in spatial and temporal resolution, they do indicate that phytoplank- ton biomass tends to be high and decreases slowly away from sites of nutrient input before thermal stratification. As the water column stratifies, the centers of maximum biomass move closer to the nutrient reservoirs that supply the euphotic zone. This leads to narrow zones of high production along the coastline and the shelf break, and to the development of a chlorophyll maximum in the ther- mocline over the midshelf. High productivity and the occurrence of two major bloom periods in the Apex reflect the 1) continuous input of nutrient-rich estuarine water (table 9.1-1), 2) effects of thermal stratification and coastal circulation on the dis- tribution of estuarine water, 3) rapid regeneration of nu- trients during summer (table 9.1-1), and 4) seasonal var- iations in grazing pressure, which peaks during late spring and summer. Winter diatom blooms develop, because of low grazing pressure. Apparently, very little diatom pro- duction is grazed, and most of the biomass produced sinks to the bottom over an unknown but larger area than the Apex. Thus, winter-spring diatom blooms in the Apex may be a factor in the development of oxygen minima below the pycnocline during summer. Summer nannoplankton blooms in the Apex are con- centrated in the surface layer where they are rapidly Table 9.1-1. —Seasonal comparison of dissolved nitrogen input by es- tuarine runoff and uptake by phytoplankton. proportion of phytoplank- ton demand supplied by runoff, and area required to assimilate the nitrogen input Dissolved nitrogen Proportion Area Months Input Uptake' by runoff required 10^ kg N/d Percent km- JFM 1.6 2.2 72 900 AMJ 1.6 2.7 59 700 JAS 1.2 2.1 57 670 OND 1.6 1.-5 107 1.150 ' Calculated from primary productivity (Malone 1976a. 1977b) and assuming a C:N assimilation ratio of 7.0 by weight. 195 NOAA PROFESSIONAL PAPER 11 grazed and dispersed before significant quantities sinic into the bottom layer. Sinking fecal material produced by graz- ing zooplankton may be a major mechanism by which organic matter of phytoplankton origin reaches the bottom layer during summer. Rough calculations indicate that the ammonia input to the Apex via regeneration provides 40 to 50 percent of the nitrogen required to support observed levels of phy- toplankton productivity in the Apex during spring and summer (table 9.1-1). The importance of ammonia re- generation is especially apparent during summer when phytoplankton productivity is high and dissolved inorganic nitrogen (DIN) concentration is low. Based on observed concentrations of DIN (typically less than 2.0 jjig-at/l) and primary productivity (usually greater than 1 g C/m"/d) in the Apex, DIN turnover times in the surface layer ranged from 12 hours to 2 days. Thus, zooplankton grazing, am- monia regeneration, and phytoplankton productivity ap- pear to be closely coupled during the warm summer months when the water column is well stratified. Vertical mixing and nutrient regeneration are the major mechanisms of euphotic zone enrichment over most of the Bight outside the plume of the Hudson River. Nutrient supplies are more discontinuous than in the plume, and thermal stratification limits rather than enhances the flux of nutrients into the euphotic zone. Consequently, phy- toplankton productivity is low throughout the summer and blooms are greatest in magnitude and most frequent dur- ing late winter and spring. Distribution The abundance and distribution of phytoplankton was reviewed by Malone (1977c). Phytoplankton cell densities usually range from W to 10'^ cells/1 in estuarine and coastal waters compared to 10^ to 10^ cells/1 in the Apex and 10^ to IC^ cells/1 in the outer Bight. Phytoplankton populations are typically dominated by diatoms (cold months) and chlorophytes (warm months) in estuarine and Apex water and by diatoms in the outer Bight. The diatoms Skeletonema costatum, Asterionella japon- ica, Leptocylindriis danicus, Thalassionema nitzschioides, and Chaeloceros debilis are abundant in both estuarine and Bight waters. Rhizosolenia alata, R. faeroense. Chae- loceros socialis. and Nitzschici closterium usually make up a larger proportion of the diatoms present in the outer Bight than in the Apex. The chlorophyte Nannochloris atonuis frequently dominates estuarine and Apex phyto- plankton during summer. The dinoflagellates Prorocen- trum micans, Peridiniiim spp. , and Ceratium spp. are often abundant during spring, summer, and autumn. Mandelli et al. ( 1970) described the species composition of the netplankton along the southern coast of Long Is- land. Phytoplankton biomass peaked during autumn and late winter. Blooms of S. costatum produced both peaks. Diatoms dominated the September-March 1966 period, whereas dinoflagellates were most abundant during the April-August 1966 period. Among the diatoms, S. cos- tatum, Thalassiosira sp., Chaetoceros sp., and R. alata were successively abundant from September through De- cember, and apparently again during February and March. Peridiniutn depressum and Ceratium massUence bloomed in April and May, respectively. Ceratium tripos was the dominant netplankton from June to August. During March 1967 a succession of species was observed: S. cos- tatum dominated during the first week; Thalassionema nitzschioides, Rhizosolenia sp., v4. japonica, and Nitzschia seriata, the second week; and Ceratium tripos, C. macro- ceros, C. furca. and Peridinium depressum. the last 2 weeks. This alternating pattern of diatom and dinoflagel- late abundance appears characteristic of shallow coastal waters off western Long Island. Recent observations along the New Jersey coast indicate that C. tripos was abundant during the summers of 1974 and 1975 (Myra Cohn, personal communication). Cell densities ranged from 40/ml to 740/ml (geometric mean = 133/ml in June 1975 and 222/ml in July 1975). Increases in C. tripos cell densities are also typical of Fire Island Inlet on the Long Island coast (Sylvia Weaver, New York University, personal communication). From 1973 to 1975, peaks in cell density (as high as 5/ml) occurred in May and June following slow increases beginning as early as Jan- uary 1974. Biology of Ceratium tripos Ceratium tripos (O. F. Mueller) Nitzsch, a large (cell volume 1-10 x 10*^ M-m') armored dinoflagellate (fig. 9.1-2), is a holoplanktonic, cosmopolitan species com- monly found along the east coast of North America from Cape Hatteras to the Gulf of Maine. Based on its distri- bution and on experimental growth studies (Cleve 1900; Bigelow 1926; Graham 1941; Nordli 1957), C. tripos is euryhaline and eurythermal, with a preference for the cooler waters (10°-20° C) and lower salinities (<33%p) of the continental shelf. The organism seldom occurs in large numbers (greater than 500 cells/1) and may often be overlooked. Maximum concentrations typically range from 1 to 5 x 10' cells/I; peaks reportedly occur during spring and summer. Two varieties of the species have been described. The larger, Atlantica Ostenfeld, is 100 to 170 p,m long and has equally well-developed anapical horns. Baltica Schutt is smaller (90 to 120 ixm long) with unequal anapical horns. C tripos var. Atlantica dominated the Ceratium popula- tion in New York Bight during the 1976 bloom. C. tripos var. Baltica was more abundant during 1977. C. tripos is photosynthetic, with maximum light-de- pendent division rates of about 0.3/d (Nordli 1957). As with most other species of Ceratium, cell division usually 196 CHAPTER 9, PART 1 occurs between midnight and sunrise, according to El- brachter ( 1973) who reported that C. tripos divides at rates of 0.03 to 0.3/d in coastal waters. He also reported dark survival times of 41 days in filtered seawater. Most species of Ceratium are phototactic and probably tend to aggregate at depths where light is optimal. C. tripos is usually most abundant near the bottom of the euphotic zone. Hasle (1950) reported light-dependent ver- tical migrations, but Nordli (1957) did not observe pho- totaxis in the laboratory. Large populations of C. tripos have been observed be- low the euphotic zone, but the extent to which this reflects photosynthetic growth at subeuphotic zone light intensi- ties, long dark survival times, or heterotrophic metabolism is unknown. Circumstantial evidence suggests that some ceratia may have the ability to metabolize organic particles (Hofender 1930; Von Stosch 1964; Norris 1969). Fal- kowski observed inclusions of exogenous origin in ceratia from the Long Island shelf, which suggest phagotrophic assimilation (Plate I). The extent to which C. tripos is subject to grazing mor- tality is not well documented. Elbrachter ( 1973) reported that recently divided ceratia were vulnerable to grazing by isopods and ciliates. However, grazing by copepods (the dominant grazers in New York Bight) appears to be minimal (Chervin, in press; Dagg, Brookhaven National Laboratory, personal communication). Finally, endoparasites, which inhibit cell division, have been observed in C. tripos (Von Arndt 1967; Elbrachter 1973). Consequently, parasitism may be one means by which population size is limited naturally. PLANKTON AND BIOLOGICAL OXYGEN DEMAND: JANUARY-SEPTEMBER 1976 Water-Column Stratification and Dissolved Oxygen Seasonal variations in water column stratification and dissolved oxygen (D.O.) in bottom water parallel each other off the New Jersey coast. (See chapter 2.) During winter, the water column is well mixed and D.O. concen- trations are near saturation (6-8 ml/I). As the water col- umn begins to stratify in April, D.O. concentration in the subpycnocline layer begins to decline so that concentra- tions are usually 10 to 40 percent of saturation (2^ ml/I) by July-August. Local anoxic conditions occasionally de- velop below the thermocline in the Christiaensen Basin (head of Hudson Shelf Valley) adjacent to the sewage sludge dumpsite (fig. 9.1-1) in the Bight Apex (National Marine Fisheries Service 1972). During summer 1976, the oxygen minimum layer was more widespread, existed over a longer period of time, and was characterized by lower oxygen concentrations than generally occur that time of year. Time-Course of the Ceratium Bloom C. tripos was abundant in the Apex at least as early as February 7, 1976, but did not increase substantially during February (fig. 9.1-3). Cell densities increased steadily from a geometric mean of 5.8 cells/ml to 29 cells/ml by the end of March. The growth rate of 0.06 doublings/d calculated from these changes yields a mean water column cell density of 240/ml by late May, which is within the range of densities reported from the layer of maximum cell density in the Apex at this time (fig. 9.1-3). A similar pattern was observed at Fire Island Inlet (fig. 9.1-3) where cell density increased from less than 0.1/ml in January to 22/ml by the end of March, a rate of 0.05 doublings/d. The population remained relatively stable through April and May and declined from a maximum of 50/ml in May to less than 0.1/ml by the end of July. This pattern roughly paralleled variations at a station 8 km south of Fire Island Inlet where cell density peaked in May and June and declined rapidly thereafter to near zero in August (fig. 9.1-4). Mean cell densities along the New Jersey shore peaked near mid-June (fig. 9.1-3). In the New York Harbor re- gion, cell densities were highest in March (29-75/ml), de- clined to 10/ml by the end of May, and remained constant at 10/ml through mid-July. Cell densities in the outer Bight increased from 1 to 60/ ml (mean = 10/ml) near the end of March to 10 to 400/ ml by mid-June (mean = 240/ml). Based on qualitative net phytoplankton samples collected from 10 m with a Hardy continuous plankton recorder (225 by 234 |xm mesh), C. tripos was present throughout the Bight in Jan- uary and increased to a maximum in May (fig. 9. 1-5). The decrease from May to June was probably a consequence of an aggregation of cells below the thermocline, as dis- cussed later. Vertical Distribution Vertical profiles of temperature, chlorophyll a, and C. tripos cell density showed little stratification from January through March when netplankton (phytoplankton re- tained on a 20-fjLm mesh screen) accounted for more than 80 percent of chlorophyll a in the water column. As the water column began to stratify in April, vertical distri- butions of chlorophyll (figs. 9. 1-6 and 9. 1-7) and C. tripos (fig. 9.1-8) began to show patterns of stratification, which varied systematically across the shelf. Based on continuous vertical profiles between April 30 and May 5, seaward of the shelf break (stations 93, 94) maximum chlorophyll-w concentrations occurred in the upper 25 m and diatoms dominated the phytoplankton (fig. 9.1-6). Across the shelf break (stations 95, 96, 97) a broad maximum between 10 and 35 m was observed, which was dominated by diatoms near the surface and by C. tripos at depth. Farther inshore (stations 98, 99, 101, 197 NO A A PROFESSIONAL PAPER 11 A B FIGURE 9. 1-2.— Scanning electron micrographs of C iripos showing sulcal opening (A) and three dimensional structure (B). Sulcal opening IS 33 M-m wide and does not appear to be covered by cell wall plates. Original magnification of B is 490 x . (Courtesy of M. Ledbetter, Brookhaven National Laboratory.) 66, 72), a strong narrow band maximum developed as diatom populations disappeared. The layer consisted al- most entirely of C. tripos (>90% of total cells) and was between 0.3 and 3 percent light depths in association with the 10° to 13° C isotherms. The depth of the layer, which was 1 to 3 m thick, decreased gradually from 35 m at station 98 (75 km offshore) to 20 m at station 72 (10 km offshore. ) This trend apparently persisted as thermal strat- ification continued to develop so that by May and June (fig. 9.1-7) most of the C. tripos population was concen- trated in a thin layer immediately below the thermocline, in association with the 10° C isotherm and between the 0. 1 and 10 percent light depths. Because of nannoplankton blooms in the upper 10 m and high concentrations of det- ritus, the C. tripos maximum was below the 1 percent light depth in the Apex and south along the New Jersey coast within 20 km of the shoreline to about Barnegat Inlet (39° 45'N). Horizontal Distribution in Maximum Chlorophyll Layer Areal distributions of C. tripos cell density in terms of population size must be interpreted in the context of tem- poral variations in the vertical distribution of cells. The population was distributed over the upper 30 to 40 m during January-March when the water column was well mixed and was aggregated near the base of the thermoc- line during April-June when the water column was ther- mally stratified. Within the Apex in February and March, population size increased with distance from the mouth of the estuary, especially along the New Jersey coast (fig. 9.1-8). This pattern was closely related to the flow of estuarine water (fig. 9.1-9) so that cell densities were lowest when the proportion of estuarine water was greatest. Conversely, maximum chlorophyll-a concentrations (fig. 9.1-10) par- alleled the distribution of low-salinity estuarine water, re- flecting the rapid response of diatom populations (domi- nated by Nitzschia seriata, with 5. costatum and Rhizosolenia sp. abundant) to nutrient enrichment. This pattern continued across the shelf along a southeast transect originating in the Apex and extending to the shelf break in late March (fig. 9.1-11). C. tripos reached max- imum cell density (60/ml) near the shelf break; Nitzschia seriata was most abundant in the Apex. Based on these observations and the degree to which C. tripos clogged zooplankton nets during March (fig. 9.1-12), high dens- ities of C. tripos had developed throughout New York Bight by the end of March; maximum densities occurred in offshore reaches of the outer Bight (midshelf to the shelf break). This inshore-offshore increase in cell density apparently persisted into April (fig. 9.1-5). As the water column stratified, distribution shifted so that by mid-May an inshore-offshore decrease in abun- dance was observed; maximum cell densities were located in the Apex near the head of the Hudson Shelf Valley (fig. 9.1-13). Nannoplankton accounted for most of the chlorophyll a in the surface layer throughout the Bight except for the center of high chlorophyll a (6 jig/l) off Long Island and a very patchy region off New Jersey where a maximum of 10 \i.gl\ was reported. C. tripos accounted for more than 85 percent of the chlorophyll a at all depths at these two locations. As thermal stratification continued to develop, C tripos distribution shifted to the southeast (fig. 9.1-14) so that by mid-June the center of maximum abundance was in about 60 m of water 80 km east of Seaside Park, N.J. (39°55'N, 73°15'W). Surface chloro- phyll-a concentrations were low throughout the outer 198 CHAPTER 9. PART I FIGURE 9.1-3. — Temporal variations in C. tripos cell density. January to August 1976. (Fire Island data by Sylvia Weaver; New Jersey coast data by Myra Cohn. Paul Hamer, Paul Olsen, and Frank Takacs.) Bight, but remained high within the Apex owing to the growth of nannoplanicton populations (fig. 9.1-14). Dur- ing May the isopleths of cell density roughly paralleled isobaths off the Long Island and New Jersey coasts. In June this pattern persisted only off the Long Island coast. Off New Jersey, isopleths of cell density were roughly normal to isobaths, and high cell densities intruded closer to the coastline. Consequently, high cell densities were distributed over a larger area of the New Jersey shelf in relatively shallow water (2C)-40 m). Comparable cell dens- ities over the Long Island shelf were in waters 40 to 60 m deep. Growth and Respiration of Ceratium tripos Measurements of photosynthesis in the Apex during February and March and off Long Island in late April- early May 1976 indicate that C. tripos was growing at a mean euphotic zone growth rate of 0.04 doublings/d (car- bon specific growth; C:Chl = 275), which is in the range of rates reported by Elbriichter (1973). Light-saturated rates were 0.3 to 0.4 doublings/d, in agreement with the cell division rates reported by Nordli (1957). Photosyn- thetic growth could account for the increase in population size observed before thermal stratification in 1976 (Jan- uary-March). 199 NOAA PROFESSIONAL PAPER 11 2n 1 - Om May 1976 y\ 2- 1- Om June 1976 10 20 30 I ITT 50 100 150 10 20 30 1 r 50 -f- 1 f 1 ■ 100 150 n O 100 150 2 -| 1 - OmJuly 1976 2 1 H Om August 1976 2-1 1 - 20m July 1976 10 20 30 1 — I — I — I ^1 "I 50 100 150 2n 1 20 m August 1976 1 — I — I — r-n ~i 50 100 150 MEAN SPHERICAL DIAMETER {\im) FIGURE 9.1-4 — Particle size frequency distributions from a station 8 km south of Fire Island Inlet, May to August 1976. (Data by Michael Dagg.) Once the water column stratified, the problem became more complex as euphotic zone nutrients were depleted and the C. tripos population aggregated near the base of the thermociine. Although maximum cell densities were observed in June, it is possible that population size did not increase. The population was large enough by the end of March to account for observed cell densities in the maximum layer during June, Changes in cell density could have resulted from concentration of the existing popula- tion as well as from the balance between growth and mor- tality, C. tripos photosynthesizes in the presence of sufficient light. In late April, C. tripos growth rates were 0,06 dou- blings/d averaged over the euphotic zone and 0,02 dou- blings/d at the 1 percent light depth. Local turbulence disrupted the C. tripos layer off Long Island in May (fig. 200 CHAPTER 9, PART 1 1976 ' I ' I ' I ' I ' I ' 1 ' I ' I I I ' I M I I I 2 4 6 8 10 12 14 2 4 6 8 10 12 H DISTANCE ALONG TRANSECT (MILES xlO) FIGURE 9.1-5 — Relative abundance of C inpos along Apex — continental slope transect. January to June 1976. (Data by Daniel Smith and Robert Marrero.) 201 NOAA PROFESSIONAL PAPER 11 CHLOROPHYLL a (mQ/I) 01 23450 1 2 3 4 50 FIGURE 9.1-6. — Vertical profiles of chlorophyll-a concentrations from 10 stations shown in figure 9-1, April-June 1976. 202 CHAPTER 9, PART I STATION A2 B3 C4 D5 E6 F7 a O FIGURE 9. -Distribution of chlorophyll a along the Apex and New Jersey transects, May-June 1976. 203 NO A A PROFESSIONAL PAPER 11 9.1-13), resulting in a uniform distribution of cells across the euphotic zone. Productivity at this station was 3.5 g C/m-/d, giving a mean euphotic zone growth rate of 0.2 doublings/d. A sample from 30 m (1% light depth) in the maximum layer in May had a productivity of 8 mg C/mV d and a growth rate of 0.04 doubhngs/d. Thus, cells in the maximum layer in the lower reaches of the euphotic zone were probably growing photosynthetically at very slow rates (20- to 30-day generation times). Within about 20 km of the New Jersey coast and 80 km of Sandy Hook, the bulk of the C. tripos population was below the compensation light depth (compensation inten- sity = 100-150 (xE/m^/d) between the thermocline and the bottom. Two independent estimates of respiration rates (from measured photosynthesis-light curves and from the carbon content of the cells) indicate that C. tripos respires about 3 percent of its cell carbon/d at 10° C. Con- sequently, some form of heterotrophic metabolism or con- tinuous recruitment from offshore photosynthetic popu- lations must have occurred to account for the observed increase in population density after the water column strat- ified. Suspended Particulate Organic Matter and Phytoplankton Levels of particulate organic carbon (POC) in the Apex water column from September 1973 through November 1975 fluctuated about a mean of 9.8 g C/m- (1 standard deviation = 2.9). The maximum turnover time of this organic matter is 2 to 15 days (annual mean = 8 days) and reflects the fact that particulate organic matter (POM) does not tend to accumulate in the water column under most circumstances. This rapid turnover of POM was not observed in Feb- ruary and March 1976 (fig. 9.1-15). During this period. POC accumulated in the water column to levels two to three times higher than previously observed. This incfease coincided with the initial phases of the C. tripos bloom (fig. 9.1-3). C. tripos accounted for 25 to 45 percent of suspended POC until the end of March when it accounted for 64 percent. Elimination of the carbon accounted for by C. tripos from the suspended POC pool gives water column POC concentrations that reflect the diatom bloom in early March and are in the range of values previously reported (fig. 9.1-15). The influence of C. tripos on the pool of phytoplankton- C in the Apex was significant (fig. 9.1-16). Before 1976, phytoplankton-C accounted for 15 to 45 percent of sus- pended POC, with proportions of 35 to 45 percent typical of phytoplankton blooms regardless of time of year and dominant species. During February and March 1976. how- ever, phytoplankton-C increased from 56 to 84 percent of the suspended POC pool. Removal of C. tripos brings the proportion of phytoplankton-C back into the range usually observed in the Apex and shows the diatom bloom peaking in early March (fig. 9.1-16). The gradual increase in the biomass of C. tripos and the subsequent accumulation of POC in in the water column did not appear to influence the typical development of the winter-spring diatom bloom. Temporal variations in copepod abundance and grazing rates indicate that very little of the diatom bloom is grazed at temperatures below 10° C (Chervin 1978). Above 10° C selective grazing could become important, because es- tuarine copepods (the major particle grazers in the Apex) do not eat C. tripos (Chervin 1978), and increased co- pepod grazing pressure during spring is probably a factor in transition from netplankton to nannoplankton-domi- inated phytoplankton blooms. C. tripos appears to be a slow-growing species subject to low predation pressure. Accumulation of Ceratium tripos off the New Jersey Coast The temporal and spatial distributions of C. tripos in the New York Bight show an increase and a shift in max- imum abundance from offshore before stratification to inshore as the water column stratified. The increase in cell density was most pronounced off the New Jersey coast. Two hypotheses, not mutually exclusive, have been sug- gested to account for these distributions. The first hypothesis is similar to the accumulation mech- anism demonstrated for Prorocentrum micans and other dinoflagellates in Chesapeake Bay (Tyler and Seliger 1978). It requires a two-layered circulation pattern with an onshore flow of bottom water and an offshore flow of surface water, organisms that aggregate in the bottom layer, and an ability to survive for extended periods of time at low light levels. A two-layered, thermohaline cir- culation has been described for New York Bight (Ketchum and Keen 1955; Bumpus 1964), and it has been well-doc- umented in this report that the C. tripos population ag- gregated near the upper boundary of the bottom layer. Possibly, most of the increase in population size occurred before stratification when the population was distributed throughout the euphotic zone and nutrients were plentiful. Once the water column stratified, C. tripos aggregated near the base of the thermocline throughout the Bight and the onshore movement of bottom water resulted in a shift in the location of maximum abundance from offshore to inshore. This process took place over 3 months (April- June), and, though we cannot determine whether the ob- served increase in cell density was a consequence of growth or an aggregation of cells, some form of anabolic metabolism was required to satisfy cellular respiratory demands during this period. Because the C. tripos layer was between the 1 and 3 percent light depths over most of the outer Bight more than 20 km from the New Jersey coast, it is likely that the population in this region was 204 CHAPTER 9, PART 1 21 February 76 C. tripos FIGURE 9.1-8. — Distribution of maximum C. inpos cell density m the Apex, February-March 1976. 205 NOAA PROFESSIONAL PAPER 11 21 February 76 Surface Salinity 1 March 76 Surface Salinity FIGURE 9.1-9 — Distribution of surface salinity in the Apex, February-March 1976. 206 CHAPTER 9, PART 1 1 March 76 Chlorophyll-a Maximum FIGURE 9.1-10. — Distribution of maximum cholorophyll-a concentration in the Apex. February-March 1976. 207 NO A A PROFESSIONAL PAPER 11 140 120 too 80 E i/i 60 40 20 - Li ■ Nitzschia seriata Ceratium tripos MARCH 1976 J. 20 m m STATION 3 at 30m depth 24m Om STATION 2 at 50m depth STATION 1 at 100m depth FIGURE 9.1-11 . — Histogram of C. tripos and Nitzschia seriata cell den- sity off Long Island and extending south across the shelf to the shelf break (stations 3, 2, and 1), March 1976. growing photosynthetically. Within 20 km of the coast, and especially in the region of the Hudson River plume, the C. tripos layer was usually below the 1 percent light depth. These observations suggest the hypothesis that coastal populations in the subeuphotic zone were main- tained and possibly increased by recruitment of actively growing, photosynthetic populations from farther off- shore. Though some form of shoreward entrainment must have taken place, several objections exist that question the im- portance of this mechanism. 1. A shoreward flow of bottom water would transport not only C. tripos into the region where the oxygen min- imum layer was pronounced but also oxygenated water. (See chapter 8, table 8-2.) 2. Estimates of photosynthetic growth rates at the 1 percent light depth were 0.02 to 0.04 doublings/d in both late April and in May. However, the rate of increase of population density from May to June off the New Jersey coast was 0.04 doublings/d. If the coastal population was being maintained by recruitment from offshore popula- tions, the increase in cell density probably reflected an increase in concentration rather than an increase in pop- ulation size. 3. Nitrate + nitrite concentrations were low throughout the water column across the shelf except in the Apex (fig. 9.1-17). The nitrogen budget for the Apex during May- July 1975 (table 9.1-1) indicates that the nitrogen supply to the euphotic zone and phytoplankton uptake rates are high and closely coupled, and that regenerated ammonia is a major source of nitrogen. Phytoplankton blooms dur- ing May and June are usually dominated by small-celled phytoplankters growing at mean euphotic zone rates of 0.5 to 2.0 doublings/d. These blooms are localized in the surface mixed layer (upper 10 m of the water column) and are most pronounced off the New Jersey coast in the plume of the Hudson River. There is no evidence that C. tripos influenced the development of these blooms during June 1976, and nannoplankton chlorophyll concentrations in the surface layer were similar to previous years. The nu- trients required for nannoplankton growth are derived from estuarine runoff and regeneration above the ther- mocline (Malone 1976b). Considering the distribution of C. tripos and its photosynthetic growth rate, it is unlikely that it was competing (or could compete) with nanno- plankton populations for these nutrients. If photoautotro- phy was involved in the maintenance or growth of the subthermocline population, nutrient inputs must have been greater than in previous years and must have in- volved onshore transport of bottom water across the shelf. However, if C tripos is capable of "luxury" nutrient up- take and can store nutrients for weeks or months, the nutrient distributions of May and June might not be a factor. (Luxury consumption of this magnitude has never been reported). The second hypothesis involves heterotrophic growth (or maintenance) by the C tripos population below the Hudson River plume off the New Jersey coast. This hy- pothesis is based on circumstantial evidence. 1. Growth of C. tripos had no obvious effect on growth of diatom populations during May and June in the Apex. Yet, growth of C tripos during February and March in- creased the POC content of the water column by a factor of 2 or 3 over previous years. 2. C. tripos did not respond (as reflected in distribution of biomass) to estuarine runoff as other photoautotrophic populations did. The observed downstream increase in biomass (in contrast with the distribution of diatoms in February and March and nannoplankton in May and June) would develop if C tripos were feeding phagotrophically on POM of estuarine origin or on phytodetritus. 3. C. tripos is euryhaline, with a salinity optimum of 20%c to 25%c. This suggests that the decline in abundance with decreasing salinity in the Apex was not related to salinity per se. Since C. tripos may have the ability to ingest POM, the observed accumulation of C. tripos in the water column may have been a consequence of phagotrophic uptake of 208 CHAPTER 9, PART 1 HEAVY Note: Based on degree to which 0.333^m mesh nets were clogged. SLIGHT FIGURE 9.1-12— Distribution of C. tripos during March 1''76 (Data from NMFS, Sandy Hook Laboratory.) 209 NOAA PROFESSIONAL PAPER 11 a. o o .a o 3 On (01 k _ 0) to > t) ^ o So 2 tu o 210 CHAPTER 9, PART 1 ^ i I UJ nSE^fe^-. 211 o O) 24 - 22 - 20 18 16 14 12 10 8 6 4 NO A A PROFESSIONAL PAPER 11 1 1 1 1 1 Vertical Bars = 1 s.d. } i A^ O Sept 73 -Dec 75 • Feb -March 76 A Feb -March 76 w/o C. tripos A A 6 9 Q ■^ A -L M ^0 _L M M J J MONTH N FIGURE 9.1-15. — Temporal- variations in mean water column particulate organic carbon content of the Apex, September 1973 to March 1976. POM that settled to the bottom or washed out of the system in previous years. Aggregation near the bottom of the thermociine would be advantageous in that the pop- ulation is in a region where POM tends to accumulate as it settles through the water column. By metabolizing POM in the water column, which was previously lost from the system, a substantial increase in water column BOD would be generated without necessarily increasing the input of inorganic nutrients or POM. Presumably, the bloom's collapse in June and July was a consequence of the exhaustion of nutrient supplies (in- ternal or external) or parasitism. Based on the proportion of C. tripos-C in the POC pool of the water column at the end of March (64%), it is possible that as the discharge of the Hudson River began to decline in May and June (fig. 9.1-18) the population off the New Jersey coast suf- fered mass mortalities due to limited food supplies. Graz- ing is unlikely, since copepods have been shown not to eat C tripos. CONCLUSIONS Although data were not collected synopticaily in time or space, coastal observations correlated well with those in the Apex and outer Bight (figs. 9.1-3, 9.1-5, 9.1-13, and 9.1-14). Temporal variations in C. tripos cell density at Fire Island Inlet reflect the early stages of the bloom before stratification, and mean cell densities along the New Jersey shore appeared to reflect at least the latter stages of the bloom during the period of thermal strati- fication. The C. tripos bloom apparently began throughout the New York Bight in January; maximum cell densities de- veloped in the midshelf to shelf break region in late March before the onset of thermal stratification. The temporal and spatial distributions of cells indicate that the popu- lation was increasing most rapidly in the outer Bight dur- ing March or that the outer Bight received a larger initial inoculum of cells than the inner Bight. The large area over 212 CHAPTER 9, PART 1 1 1 BLOOM II II 1 PERIODS I / \ 100 NETPLANKTON NANNOPLANKTON I— 1 u 90 - - 1 80 - • • • •• • - O O Sepf 73 -Dec 75 ^ • Feb-March 76 z 70 — A Feb-March 76 w/o C. trip9$ - ^ • a. 60 — - t— >■ X 50 Q. 40 ^ O ^ _ 30 — o A A ^ ^ AA O ^ ° ° °o - o o O 20 ' — A O o o — 10 n ^ 1 1 1 1 1 1 1 1 M M J J MONTH SON FIGURE 9.1-16. — Temporal variations in the proportion of water column POC accounted for by phytoplanklon in the Apex, September 1973 to March 1976. which the bloom occurred indicates that it did not develop in response to local nutrient enrichment of the coastal zone during the actual period of the bloom. This is sup- ported by the observation that C tripos cell densities were lowest in the Apex where local nutrient enrichment is greatest. The causes of the bloom, whether related to increased growth or decreased mortality rates, must have involved processes operative on spatial scales on the order of the continental shelf and time scales on the order of months to years. The temporal and spatial development of the bloom during April and May suggest an onshore transport of cells once the population began to aggregate below the ther- mocline. By mid-June a large population of cells was pre- sent below the thermocline in a relatively flat region of the New Jersey shelf between the 20- and 40-m isobaths. Much of this population was below the euphotic zone in a subthermocline layer about 10 m thick. This is in marked contrast to the population off the Long Island coast where the layer of maximum concentration was well off the bot- tom in a subthermocline layer about 30 m thick. (See chapters 2 and 8.) Maximum population size was probably achieved after March and before July; and population size declined rapidly during July. There is no evidence that the C. tripos bloom influenced the growth of netplankton diatoms or nannopiankton pop- ulations. The distribution and abundance of these groups were similar to previous years" observations. The role of C. tripos in the development of the oxygen minimum layer off New Jersey is difficult to evaluate in the absence of data on the time and space distribution of D.O. in the bottom layer and more complete information of the time and space distributions of POC, chlorophyll a. and C. tripos. The Bight Apex has been subjected to 213 NOAA PROFESSIONAL PAPER 11 STATION A2 B3 C4 D5 E6 F7 • • • ^-^0.5- • • • • • ■ • • ^^ 20 r • • • v. < 0.5 • • ^^:^^ ^x y • • • • 0. ^ ^^^^*^^^ 40 \J ^« ^ ^5 - 60 X^^ jT ^-^ ^ - 80 - V m • 100 - \ • ^10^ . 120 NITRATE + NITRITE \^ "^15 ^ ^^^^^^ 140 MAY 1976 j/g-at N / 1 \ — 20_ \ -^ 160 1 on - - 20 40 60 80 100 120 140 160 180 NITRATE + NITRITE JUNE 1976 i/g-at N / 1 FIGURE 9.1-17. — Distribution of dissolved nitrate + nitrite along the Apex transect, May-June 1976. 214 CHAPTER 9, PART 1 considerable organic loading over the past two decades, and the development of oxygen minimum layers and local anoxia have occurred previously during summer (ch. 1). Based on the effect of C. tripos on the content of POC in the water column and on the development of large, subthermocline populations, it is likely that C. tripos made a very significant contribution to the oxygen demand re- quired to account for the oxygen minimum layer. In the latter context, a flocculent suspension of organic matter at least 1 cm thick coated the bottom during July between Sandy Hook and Atlantic City from 5 to 50 km offshore. The floe consisted primarily of phytoplankton cells dom- inated by C. tripos. Microscopic examination indicated a steady increase in the decomposition of C. tripos cells during July. (See chapter 9, part 2.) A computer simulation model was used to explore the combined effects of benthic respiration and C. tripos res- piration on the rate of oxygen depletion below the ther- mocline. C. tripos respiration rates were calculated from the expression R = aW^ (Banse 1976) where a and h are temperature dependent constants and W and R are the weight of the cell in picograms (pg) of carbon and the respiration rate in picograms of carbon/cell/hour, respec- tively. The carbon content of C. tripos was calculated from both CHN analysis and regression of netplankton chlo- rophyll a on netplankton carbon. Values ranged from 1 20,000 to 30,000 pg/cell; a mean value of 25,000 was cho- I sen for calculating respiration rates. Using Q,,, = 2.3, the i carbon specific respiration rate of a single cell was cal- • culated to be 0.003/h at 10° C ( = 1.4 x 10 V' O./cell/ h). In 1977, C. tripos respiration was measured in the field using an oxygen polarographic electrode and an electron transport system assay. The resuhs of these direct meas- urements suggested a respiration rate of 1.39 ± 0.17 x 10 -^ |xl O./cell/h at 10° C, agreeing well with the rate calculated according to the expression given by Banse (1976). ij The following information was input: 1 . A mean benthic respiration rate of 11 ml 0_,/nr7h( 1 .0 mg-at 0,/m-/h) was calculated from Thomas et al. ( 1976) I for an "average" community in the Bight. 2. Eddy diffusion coefficients of 1.0 cm-7s across the thermocline and 10 cm7s below the thermocline were used. 3. The thermocline was placed 25 m above the bottom. This situation existed off the coast of Long Island, but the thermocline was much closer to the bottom off the coast of New Jersey. 4. The overlying water was nearly saturated with oxy- gen, starting with 6.72 ml/l(= 0.6 mg-at 0;/l). 5. Using data collected on six cruises in New York Bight (Brookhaven National Laboratory data base), the follow- ing numbers of cells were placed in the bottom 20 m: (a) 0-5 m (above the bottom) 2 x 10^ cells/m' (consuming 2.8 X 10-^ ml Oj/l/h); (b) 5-10 m, 4 x 10^ cells/m' (con- suming 5.6 X 10' ml Ojyh); (c) 10-15 m, 6 x 10' cells/ m' (consuming 8.4 x lo" ' ml 0,/I/h; (d) 15-20 m, 2 x 10'*cells/mMconsuming2.8 x 10"- ml O./l/h). (Cells from the upper 5 m were excluded because they may be at or above the compensation depth and do not contribute sub- stantially to oxygen depletion.) The model output indicated that within two months the oxygen concentration in the bottom 5-m layer reaches a steady state concentration that is 45 percent of the initial oxygen concentration. The simulated rate of oxygen de- pletion below the thermocline is extremely sensitive to changes in eddy diffusivity, and small changes in diffusivity are sufficient to cause simulated anoxia. These calculations show the potential metabolic influ- ence of C. tripos. The water column integrated C. tripos respiration rate exceeds the benthic oxygen consumption rate by a factor of 20. Therefore, C. tripos biomass is a large potential source of BOD. Oxidation of the C. tripos biomass (3,255 mg-at C/m-) within 20 m of the bottom would require 8,463 mg-at OJm- or 71 percent of the initial oxygen content. Thus, the combined effects of res- piration and subsequent death and decay of the biomass were more than sufficient to produce anoxia. The occurrence of an oxygen minimum layer and local anoxic waters off the New Jersey coast in contrast to the Long Island coast may reflect differences in bottom to- pography, residence time of water in the bottom layer, and turbulent mixing. The shelf within 50 km of the coast is much flatter and shallower off New Jersey than off Long Island. Consequently, the C. tripos layer between the 20- and 40-m isobaths off New Jersey was distributed over the bottom surface in a subthermocline water column 5 to 15 m thick, whereas the C. tripos maximum off Long Island intersected the bottom along an isobath and was well off the bottom (>30 m) over most of its extent. In addition, high cell densities occurred over larger areas off New Jer- sey. These observations and the possibility that the resi- dence time of bottom water is longer off New Jersey than off Long Island could explain the development of a more intense and widespread oxygen minimum layer off New Jersey. Nannoplankton productivity per se was probably not a major factor in the 1976 oxygen depletion even though it normally accounts for most of the input of POM to the region. With the exception of winter-spring diatom blooms, which apparently go ungrazed, there is no evidence that a significant portion of phytoplankton production nor- mally accumulates below the thermocline during summer. The dominance of small-celled phytoplankton (usually less than 10 M-m in diameter), vertical chlorophyll-a distribu- tions, the importance of ammonia as a nitrogen source for phytoplankton, and the rapid increase in zooplankton grazing pressure during May and June are consistent with 215 NOAA PROFESSIONAL PAPER 11 MEAN MAY DISCHARGE 1946- 1976 MEAN JUNE DISCHARGE 1946-1976 3 5 7 9 13 15 17 19 21 23 25 27 29 31 I MAY »H- 3 5 7 9 II 13 15 17 19 21 23 26 27 29 JUNE *\ FIGURE 9.1-18— Freshwater flow of the Hudson River at Green Island during May and June 1476. (C. A. Parker— from U.S.G.S. data.) the rapid turnover of POC calculated for the Apex in the absence of C. tripos. In effect, the C. tripos bloom pro- vided a mechanism by which large quantities of POC were accumulated over several months. The change in the rel- ative abundance of phytoplankton species and the effects of this change on the distribution and quantity of POC in the subthermocline water column resulted in exceptionally high BOD in 1976. Unfortunately, we do not understand this type of species succession very well, and the basic question of why the C. tripos bloom occurred in the first place remains unanswered. ACKNOWLEDGMENTS The following individuals contributed data on Ceratium tripos abundance: Mark Brown (Louis Calder Conserva- tion and Ecology Studies Center), Myra Cohn (NMFS, Sandy Hook Laboratory), Michael Dagg (Brookhaven National Laboratory), John Mahoney (NMFS, Sandy Hook Laboratory), Paul Olsen (New Jersey Department of Environmental Protection), Sylvia Weaver (New York University), and Joseph Vaughan (New Jersey Depart- ment of Environmental Protection). The following also gave assistance and advice: Mira Chervin (Lamont-Doherty Geological Observatory), Chris Garside (Bigelow Laboratory for Ocean Sciences), Steven Howe (Brookhaven National Laboratory), Joel O'Connor (NOAA/MESA New York Bight Project), Jay O'Reilly (NMFS, Sandy Hook Laboratory), and James Thomas (NMFS, Sandy Hook Laboratory). REFERENCES Banse, K., 1976. Rates of growth, respiration and photosynthesis of unicellular algae as related to cell size — a review, J. Pliycol. 12:135-140. Bigelow. H. B., 1926. Plankton of the offshore waters of the Gulf of Maine, Bull. U.S. Bur Fish. 4(1:1-509. Bumpus, D. F,.1964. Residual drift along the bottom on the continental shelf in the Middle Atlantic Bight area, Limnol. Oceanogr. 10 (suppl.);R50-R53. Chervin, M. B., 1978. Assimilation of particulate organic carbon by estuarine and coastal copepods. Mar. Biol. 49:265-275. Cleve, P. T., 1900. The seasonal distribution of Atlantic plankton or- ganisms, Goteborgs Kundl. Vel-och Villerhels Sarnhalles Haiull.. 17, 36 pp. Elbrachter. M , 1973. Population dynamics oi Cerauuin in coastal waters of the Kiel Bay, Oiko.s (suppl.) 15:43-48. Fournier, R. O, Marra, J, Bohrer, R. and Van Det. M., 1977, Plankton dynamics and nutrient enrichment of the Scotian Shelf, J. Fish. Res. Board Can. 34:1004-1018. Garside, C, and Malone, T. C, 1978. Monthly oxygen and carbon budgets of the New York Bight Apex, Estuar. Coastal Mar. Sci. 6:93-104. Graham, H. W., 1941. An oceanographic study of the dinoOagellate genus Cera(/«m, Ecol. Monogr. 11:99-116. Hasle, G. R., 1950. Phototactic vertical migration in marine dinollagel- lates, Oikos 2:162-175. Hofneder, H., 1930. Uber die animalische Ernahurung von Ceratium hirundinella O. F. Miiller and uber die Rolle des Kernes bei dieser Zellfunktion, Arch. Protistenkunde l\:l-32. 216 CHAPTER 9, PARTI Ketchum. G. H.and Keen. D. J.. 1955 The accumulation of river water over the continental shelf between Cape Cod and Chesapeake Bay, Deep-Sea Res. 3, (suppl ):346-357. Malone, T. C. 1976a. Phytoplankton productivity in the Apex of the New York Bight: September 1973-August 1974. NOAA Tech. Memo. ERL MESA-5. NOAA Environmental Research Labora- tories, Boulder. Colo., UK) pp Malone. T. C, 1976b Phytoplankton productivity in the Apex of the New York Bight: Environmental regulation of productivity/chlo- rophyll a, Amer. Soc. Limnot. Oceanogr. Spec. Symp. 2:26l»-272. Malone, T. C, 1977a. Environmental regulation of phytoplankton pro- ductivity in the lower Hudson Estuary. Esluar. Coastal Mar. Set. 5:157-171. Malone. T. C, 1977b. Light-saturated photosynthesis by phytoplankton size fractions in the New York Bight. Mar. Biol. 42:281-292. Malone. T. C, 1977c Plankton Systematics and Distribution. MESA New York Bight Alias Monogr. 13. New York Sea Grant Institute. Albany. N.Y.. 45 pp. Mandelli, E. F., Burkholder. P. R.. Doheny, T. E.. Brody, R., 1970. Studies of primary productivity in coastal waters of southern Long Island. New York. Mar. Biol. 7:153-160. Nordli. E.. 1957. Experimental studies on the ecology of Ceratia. Oikos 8:200-252. Norris. D. R., 1969. Possible phagtrophic feeding in Cerattum lunula Schimper, Limnol. Oceanogr. 14:448-449. Ryther. J. H., and Yentsch. C. S., 1958. Primary production of conti- nental shelf waters off New York, Limnol. Oceanogr. 3:327-335. Smayda. T. J.. 1976. Plankton processes in Mid-Atlantic near-shore and shelf waters and energy-related activities, in B Manowitz (ed.). Effects of Energy-Related Activities on the Atlantic Continental Shelf. BNL Publ. 50484, pp. 70-94. Thomas, J. P., Phoel. W. C, Steimle, F. W. O'Reilly, J. E, and Evans. C. A., 1976. Seabed oxygen consumption in the New York Bight Apex, Amer. Soc. Limnol. Oceanogr. Spec. Symp. 2:354-369. Tyler, M. A., and Seliger. H. H., 1978. Annual subsurface transport of red tide dinoflagellate to its bloom area: Water circulation patterns and organism distributions in the Chesapeake Bay. Limnol. Ocean- ogr. 23:227-246. Von Arndt, E. A.. 1967. Untersuchungen an Populationen von Cerattum tripos f subsalsum Ostf. im Gegeiet der Sudkuste der Mechlenbur- ger Bucht, Wiss. z. Univ. Rostock 9( 10): 1 199-1206. Von Stosch. H. A., 1964. Zum Problem der sexuellen Fortflanzung in der Peridiniengattung Ceratium, Helgolander wiss Mieresunters 10:140-152. Yentsch, C. S.. 1977. Plankton Production. MESA New York Bight Atlas Monogr. 12. New York Sea Grant Institute. Albany. NY.. 25 pp. 217 NO A A PROFESSIONAL PAPER II B CHAPTER 9, PART 1, PLATE I. — Nomarski differential interference photomicrographs (A, B) of Ceralium stained with acetocarmine. N is cell nucleus; C, chloroplast; and E, nuclear inclusions of extracellular origin. Original magnification of A and B is 250 x . (Courtesy of W. Mann and P Falkowski, Brookhaven National Laboratory.) 218 Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 9. Plankton Dynamics and Nutrient Cycling Part 2. Bloom Decomposition John B. Mahoney^ CONTENTS Page 219 Introduction 219 Methods 220 Observations 221 Sandy Hook-Asbury Park 221 Manasquan 222 Barnegat-Atlantic City 222 Ceralium Inpos Decomposition Sequence and the Floe 224 Conclusions 229 Acknowledgments 229 References ' Sandy Hook Laboratory, Northeast Fisheries Cen- ter, National Marine Fisheries Service, NOAA, High- lands, NJ 07732 INTRODUCTION As discussed in part 1 of this chapter the combined BOD of the respiration of the Ceralium tripos population and the cell decomposition during the bloom decline and ultimate collapse would have been sufficient to produce the 1976 oxygen depletion in the New York Bight. This section is concerned with C. tripos decomposition. In early July, when the magnitude of the problem first became evident, divers observed a layer of flocculent material several meters thick at the thermocline and a denser accumulation at least 1 cm thick on the bottom. The floe was present throughout the oxygen-depleted area and persisted during the summer. Examination of initial samples of this material established that it was an aggre- gate of phytoplankton dominated by C. tripos. Signs of decay in this aggregate were obvious. The phytoplankton in the affected area was surveyed during the summer to obtain information on the time sequence and geographical pattern of the decomposition of the C. tripos population. METHODS Samples, mostly 1 liter in polyethylene bottles, were collected by divers or taken by water sampler casts. Since viability of the C tripos cells and the activity of other microorganisms and meiofauna were considered impor- tant assessments, use of a preservative was avoided when- ever possible. Live samples were kept cool until they reached the laboratory where they were refrigerated at 2° C. They were examined within 24 hours. Samples that could not be returned to the laboratory within a day were preserved with Lugol's iodine or buffered Formalin. Since the phytoplankton in most of the samples was clumped, only qualitative estimates of the relative abun- 219 NOAA PROFESSIONAL PAPER 11 Table 9.2-1. — Ceratium tripos presence in July-August 1976 in areas off New Jersey (See explanation of symbols at end of table.] A. Sandy Hook-Asbury Park area Date July 22 30 August 4 Distance from shore (km) 3.7 13 20 16 20 Depth (m); S +F(P) ♦ * + +A(P) 4-6 * +F +F * * + + +F 1++F 11-12 * +F +A +A ++A ++A ++A + + +A 17-18 * • * +F + +F 27 * * 30 * 34 41^4 B. Manasquan area Date July 4 9 15 17 20 24.... Distance from shore (km) 11 3 15 6.5 5.5 1 14 Depth (m); c ***** ** 8 * . . » * irj ***** ** IT *** * ■* ** JJ ***** * ^p + +F 18 * +A * +A(P) +A(P) + +F ++A(P) ++A(P) 20 * * 22 +A * + +A + + +F 24 +A + +F August 2 3.7 20 + F + A + +F + +A * + A + +A + +F * * + +F * + +A + + +A + +A + + +A + +F dance of the component species were made. Counts from four continuous, long-axis transects across a Sedgewict;- Rafter ceil under low power sufficed for this purpose. The terms "abundant" and "sparse" are used to express the count results. For example, a count of just a few C. tripos cells was classed sparse; counts in the neighborhood of 10 cells were classed moderately abundant; and higher counts were classed abundant. A phytoplankter designated dom- inant was the most numerous species in the sample. Ad- ditional examinations, such as for bacterial presence, were made on plain slides under high power. Photomicrographs were made with timed or flash exposure on Panatomic-X film. OBSERVATIONS Because decomposition of the C. tripos population seemed to progress from north to south, observations were grouped by general locale. The portion of the affected 220 CHAPTER 9, PART 2 Table 9.2-1 — Ceratium tripos presence in July-August 1976 in areas off New Jersey — continued C. Barnegat-Atlantic Cily area Date July 15 21 30 August 16 .... Distance from shore (km) 18 28 37 9 13 20 22 37 Depth (m): S • ♦ • * +A + +A 10_12 * ♦ * +F(P) +A ++A * + + ++F ++A 13 +A + +F 15-17 +A +A * +F * * * * ++F ++F ++A 19-20 +A +F , . . * ++F ++A + + +F 22 +F + + F + A ++A ++F + + +F * * Symbols: *, depth not sampled; 0. not observed; +. C. (npoi fragments; ++, mtact but nonmotile cells; + + + , motile cells; A, abundant; F, few; (P). preserved samples; **, deepest samples were 6 m above bottom. Unless otherwise noted the deepest samples were at the bottom. area between Sandy Hook and Asbury Park, N.J.. is the northern sector (ch. 9, pt. 1. fig. 9.1-1). The next sector south lies primarily oft Manasquan. N. J. The southern- most sector sampled is that off Barnegat to Atlantic City. N.J. Observations were organized chronologically. Be- cause the laboratory first encountered the oxygen deple- tion off Manasquan, the earliest sampling was in this area. Later, sampling was expanded both north and south as the extent of the problem became evident. Table 9.2-1 provides a synopsis of the C. tripos observations in these notes. Sandy Hook — Asbury Park C. tripos and, especially, Prorocentrum redfieldi were abundant at the surface, 3.7 km off Monmouth Beach on July 22. The rest of the water column was not sampled. C. tripos was sparsely present, surface to bottom, at a location 13 km east of Sandy Hook on July 30. The phy- toflagellate, Olisthodiscus lutens. was dominant at the sur- face. Floe was abundant only at the bottom. Much of the bottom floe appeared unstructured, but diatoms, including Skeletonema costatum. Leptocylindnis danicus and Cos- cinodiscus spp., were a major component. Visually, bac- teria were relatively minimal in numbers. Farther offshore, about 20 km off Sandy Hook on July 30, C. tripos was sparse at the surface, abundant at mid- depth (11 m), and not present at the bottom. The largest amount of floe was present at the bottom; it was predom- inantly dark brown to black. Again, diatoms were a major recognizable floe component and bacteria appeared sparse. At two locations on August 4, 16 km off Monmouth Beach and 20 km off Asbury Park, C. tripos was absent at the surface, but abundant at 11 to 12 m along with other flagellates, especially Dinophysis spp. and various diatoms and small nonmotile chlorophytes. Except for C. tripos, the same phytoplankton, although in lesser abundance, was present at 17 to 18 m; C tripos was present at this depth only at the location farthest offshore. Near and at the bottom (30-44m), C. tripos was absent but O. Inteus. many of the cells live, was numerous along with small nonmotile chlorophytes. Several species of diatoms, chiefly S. costatum, were present. Just a few bacteria were seen. Mansaquan The initial phytoplankton samples collected off New Jersey during the anoxia event were obtained on July 4 by a diver, at the bottom, 11 km off Manasquan. These contained a yellowish floe that, microscopically, appeared to be a phytoplankton aggregate. The dominant species, by biomass at least, was C tripos. C. fusus was also present as well as the diatoms, S. costatum, Coscinodiscus spp., Nitzschia seriata. Thalassiosira nordenskioldii, L. danicus, and others. Most of the Ceratium spp. cells were disrupted to various degrees and empty of cytoplasm, although a few live individuals were observed. Numerous bacteria, some motile, were seen in the mass. 221 NO A A PROFESSIONAL PAPER 11 On July 9, bottom samples from the same area, about 3 and 15 km, off Manasquan, also contained abundant floe. The general phytoplankton composition of the ma- terial was similar to that of the first samples, but further decomposition of the C tripos cells and a change from yellow to predominantly brown was evident. Live C. tripos were not seen. Bacteria appeared more abundant; ciliate protozoans were also abundant. On July 15, C. tripos still dominated the phytoplankton on the bottom in locations 6 to 7 km off Manasquan. About twice as many fragmented as intact C. tripos cells were seen; C. tripos appeared to make up 25 to 50 percent of the floe volume. Coscinodiscus excentricus was second in importance. The floe retained the brownish color. Be- cause these samples were treated with preservative, bac- terial presence was not estimated. C. tripos was absent in the bottom floe 3.7 km off Man- asquan by August 2; however, a few C. tripos cells and broken tests were present in the water column. The phy- toplankton, from the surface to the bottom, was domi- nated by S. costatum and L. danicus, followed by Ceratium minutum, Peridinium trochoideum, Dinophysis spp., and Prorocentrum micans. These were all numerous at the surface, but most were in decreased abundance at the other depths. P. trochoideum and small nonmotile chlo- rophytes, however, were also abundant at the bottom. The amount of floe in the water column and on the bottom appeared greatly reduced compared to the amount seen previously. The color of the floe was changed; under the microscope, white and black portions were about equal. Only a few bacteria were seen. Farther offshore (20 km) on August 2, in definite con- trast to the inshore location, all depths except the bottom had abundant intact or fragmented C. tripos. At 20 m, there was an increased amount of intact, and for about half the cells, motile C tripos. At 22 m, there were nu- merous, nearly all vigorously motile, C. tripos ceils. Ap- parent bacterial digestion of some of the fragmented C. tripos cells was observed. S. costatum and small non- motile chlorophytes were numerically dominant through the water column. O. luteus and P. trochoideum were abundant at the surface; O. luteus was also very abundant at the bottom. Barnegat — Atlantic City Three locations, about 18, 28, and 37 km off Barnegat. N.J., were sampled on July 15. Because divers found the floe to be primarily in the bottom waters, sampling was at 6 and 9 m off the bottom. At the 18- and 28-km stations, samples from both depths contained floe that was yellow or yellow-green with some blackish spots. Many of the C. tripos cells were disrupted. Bacteria in chains or as motile individuals were most evident in the samples collected 6 m off the bottom. At the farthest offshore station, decom- position did not appear as advanced. The floe was pre- dominantly yellow. Most C. tripos cells were intact; dis- rupted cells were in large fragments. Some motile C. tripos were observed. Again, bacteria were more evident in the lower depth sample. At 10 m, 5 km off Barnegat on July 21, only a small amount of fine floe particles and a sparse phytoplankton, including just a few C. tripos, were present. At 15 m, however, a fairly abundant, by comparison, floe was com- posed almost entirely of C. tripos. On July 30, 13 km off Barnegat, the surface had a mod- erate abundance of free, intact C tripos cells. At mid- depth, around 11 m, C tripos cells, most without cyto- plasm, were numerous; broken tests were more numerous than intact ones. The bottom had fewer and more decayed C. tripos. The floe was abundant only at the bottom. The floe ranged from yellow to dark brown or black. Much of the material was unstructured; diatoms, especially S. cos- tatum and L. danicus, composed most of the identifiable phytoplankton; bacteria were moderately abundant. At 20 km off Barnegat on July 30, C. tripos was absent at the surface. At middepth, numerous free, intact C. tripos cells dominated the phytoplankton (a mixed group of diatoms and dinoflagellates). At the bottom, a smaller abundance of intact and disrupted C. tripos was evident. The floe was most abundant, although moderately so, at the bottom. Various diatoms, especially S. costatum. were abundant in the floe. Apparent vigorous swarming of bac- teria around partially digested C. tripos and fungus dis- persed throughout the floe were observed. C. tripos was absent at two locations, about 22 and 37 km, off Barnegat on August 16. 5. costatum dominated the generally sparse phytoplankton, which also included a mixture of other diatoms, dinoflagellates, and smaller nannoplankton. On the bottom, the diatoms appeared to be in a state of advanced decomposition, judging from the appearance of the cells. Only a small amount of blackish floe was present. At the same time, however, farther to the south, 11 km off Atlantic City, C. tripos was moder- ately abundant at middepth although it was not seen in the rest of the water column. S. costatum was numerically dominant at all depths. Floe, yellow to greenish-brown, was abundant at the bottom. Bacteria appeared abundant in the floe. At locations 18.5 and 93 km off Atlantic City on Sep- tember 2, the bottom and middepth samples contained only a sparse amount of flne floe, at least 50 percent of which was black. A few diatoms were present, but no C. tripos. The phytoplankton was even less abundant in the surface samples; again no Ceratium spp. were seen. C. tripos Decomposition Sequence and the Floe With the decline of the bloom, the C. tripos cells, in senescence or death (flgs. 9.2-1, 9.2-2), formed into a 222 CHAPTER 9, PARTI m* 1 4 ^25iLH FIGURE 9.2-1. — An intact Ceratntin inpos cell; a fragment of another individual is adjacent. ^^5_u_, FIGURE 9.2-2. — A newly disrupted C tripos cell 223 NO A A PROFESSIONAL PAPER 11 flocculent aggregate. This floe was seen at various times and places during July and August, but, by far, most was at the thermocline (where the C. tripos bloom population had previously concentrated) and on the bottom. In the Manasquan area, less than 20 km from shore on July 4, nearly all of the C. tripos seen at the bottom were dead and these, broken or fragmented, composed most of the floe biomass (fig. 9.2-3). In the same area, less than a week later, the C. tripos dominance had become less clear; increased disruption of the cells was evident and the floe had darkened (fig. 9.2-4). With further decomposition (fig. 9.2-5), the material became even darker and far fewer C. tripos fragments were identifiable. By August 2, no C tripos were seen in the inshore bottom floe off Man- asquan (fig. 9.2-6). Therefore, in this area, except for refractory constituents, decomposition at the bottom of massive numbers of C. tripos, which presumably had be- gun in June, was complete by late July or early August. Temporal and geographical differences in the C. tripos decomposition are discussed in the next section. Figures 9.2-7 and 9.2-8 show microbial decomposition of the C. tripos. Figures 9.2-9 and 9.2-10 show one effect of the bloom decomposition: the gill of the mud shrimp, Axiiis serratus, is partially occluded with floe material. A con- centration of these animals, dead or dying, was found out of the substrate around 18 km off Barnegat on July 15. CONCLUSIONS C. tripos remained a significant portion of the bottom floe in the oxygen-deficient area between Manasquan and Barnegat at least until mid-July. Around the end of July, no C tripos were seen in bottom samples from off Sandy Hook and it had almost disappeared from the bottom floe off Manasquan, but it was still evident in the Barnegat area. The floe from the Manasquan area at this time was about equally black and white under the microscope, but the Barnegat floe retained much of the earlier yellow- brown appearance. By mid-August, the bottom samples from off Barnegat had no C. tripos and little floe; what was present appeared generally decayed. Bottom samples from off Atlantic City still contained abundant yellow- brown floe. Vaughan (1977) surveyed the C. tripos pop- ulation in southern New Jersey coastal waters between Great Bay and Cape May from July 21 to its complete disappearance around August 20. The decline of C. tripos abundance he observed had a pattern similar to that seen in the more northerly regions, but occurred later. In ad- dition, during late July and the first half of August, Vaughan (personal communication) found C. tripos pre- sent nearly always, even inshore, as individual, intact cells retaining cytoplasmic contents. Because a preservative was used, he was not able to determine whether the cells were alive when collected. However, the cells were at least not disrupted or aggregated in a detrital mass as they were to the north when the first samples were examined on July 4. The combined observations indicate that the decomposition proceeded earlier or at a more rapid rate in the Sandy Hook — Manasquan area and progressed southward. Some C. tripos concentrations, alive and apparently vigorous, were found around middepth between the mid- dle of July and early August off Sandy Hook, Manasquan, and Barnegat. They were all at stations 20 km or greater from the shore. During the same period, intact but non- motile cells and fragments of cells, but no live cells, were found at various depths less than 20 km from shore (table 9.2-1). This suggests that C. tripos survived better in off- shore waters. If so, a possible explanation (ch. 9, pt. 1) is that by May and June, the C. tripos population within 20 km of the shoreline between the Bight Apex and Bar- negat Inlet was light limited. Based on microscopic observations, some bacterial presence was associated with aggregates of phytoplankton material in the water column, but it was greatest at or near the bottom where most of the floe was also found. Also, general bacterial presence seemed to be associated with the presence of C. tripos (the notable exception was in the August 16 Atlantic City bottom sample in which abundant bacteria but no C. tripos were seen). Unmis- takable bacterial decomposition of C. tripos cells (fig. 9.2-7) was observed several times; fungus attack on C. tripos was also seen (fig. 9.2-8). Protozoans and small nematodes were fairly numerous in some samples and may have been feeding on the floe material, although this was not determined. Vigorous activity and clustering around the floe by ciliate protozoans seen in a number of samples did suggest feeding behavior. All these forms probably contributed to the decomposition process. The cell wall of C. tripos is cellulosic. In the Gulf of Maine and Georges Bank, Waksman et al. (1933) found extensive populations of bacteria able to use cellulose and hemicelluloses, al- though cellulose-decomposing marine bacteria were less abundant than species not having this capability. Bar- ghoorn and Linder (cited in Zobell 1945) found several species of marine fungi able to use cellulose. Marine cil- iates have been known to feed on bacteria, diatoms, or other protozoa (Lackey 1936). The presence of numerous O. luteiis (many individuals apparently in a senescent state) as a floe constituent in locations from Sandy Hook to Sea Girt, N.J., between July 22 and August 4 is interesting. This species bloomed intensely throughout the southern half of Lower New York Bay between June 6 and 13, 1976. Tidal action grad- ually washed the bloom water to the ocean. If we assume that the Olisthodiscus concentrations in the bottom floe originated in the bay, then inshore along the New Jersey 224 CHAPTER 9. PART 2 FIGURE 9.2-3. — C. iripos is the obvious major component of the aggregate; most of the material is relatively light in color. FIGURE 9.2-4. — C. iripos is still a ni.ijor component o( this floe, hut increased disruption of cell fragments is evident. The floe has darkened in spots. 225 NO A A PROFESSIONAL PAPER 11 FIGURE 9.2-5. — A few C. tripos fragments are identifiable but most of the material appears structureless. Most of the floe is dark. FIGURE 9.2-6.— C. inpos is not identifiable in the floe; diatoms are the only evident phytoplankton. 226 CHAPTER 9, PARTI t 5 a , FIGURE 9.2-7. — C. tripos horn bristling with motile rod bacteria; area being digested is largely eaten away. FIGURE 9.2-8.— Fungus dispersion in Hoc; C. tnpos cell in decomposition. 227 NO A A PROFESSIONAL PAPER U FIGURE 9.2-9 — Floe fragment lodged between gill filamenls of mud shrimp, Axius serralus. FIGURE 9.2-10.— Mud shrimp gill choked with floe material 228 CHAPTER 9. PART 2 coast the bottom received large quantities of phytopiank- ton from the bloom in Lower New York Bay. The Olis- thodisciis bloom may not have added measurably to the 1976 oxygen depletion, because it was small compared to the C. tripos bloom. Perhaps a more important implication is that material from chronic seasonal blooms of phyto- flagellates would contribute to annual bottom water oxy- gen sag in at least the coastal area near the bay. Segar and Berberian (1976) determined that oxidation of phyto- plankton material below the thermocline was a major cause of the low oxygen values they observed in the bot- tom waters of the Bight Apex. ACKNOWLEDGMENTS Frank Steimle coordinated the surveys that provided most of the water samples which were examined. The samples were collected primarily by Robert Reid, David Radosh, John Ziskowski, and Charles Byrne. REFERENCES Lackey, J, B., 1936. Occurrence and distribution of the marine protozoan species in the Woods Hole area, Biol. Bull. 7l)(2);264-278. Segar, D. A., and Berberian. G. A., 1976. Oxygen depletion in the New York Bight Apex: causes and consequences. Amer. Soc. Limnot. Oceanogr. Spec. Symp. 2:221)-239. Vaughan, J., 1977. Abundance determinations of the marine dinofla- gellate Ceralium tripos off the New Jersey coast during the summer and fall, 1976, Tech. Rep. No. 22, New Jersey Department of En- vironmental Protection, Nacote Creek Research Station. Absecon. N.J., 15 pp. Waksman, S. A., Carey, C. L., and Reuszer, H. W., 1933 Marine bacteria and their role in the cycle of life in the sea. I. Decomposition of marine plant and animal residues by bacteria, Btoi Bull. 65(l):57-79. Zobell, C. E., 1946. Marine microbiology. Chronica Botanica Co., Wal- tham, Mass., 240 pp. 229 I I Oxygen Depletion and Associated Benthic Mortalities in New York Bight, 1976 Chapter 10. Biological Processes: Productivity and Respiration James P. Thomas, Jay E. O'Reilly, Andrew F.J. Dra.xler. John A. Babinchak, Craig N. Robertson, William C. Phoel, Ruth 1. Waldhauer, Christine A. Evans, Albert Matte, Myra S. Cohn, Maureen F. Nitkowski, and Shearon Dudley^ CONTENTS Page 231 Introduction 231 Methods 233 Hydrographic and Nlitrient Conditions 239 Organic Carbon and Ph-itoplankton 244 Phytoplankton Productivity 247 Contributions to the DOC Pool 247 Oxygen Consumption 247 In the Water Column 249 By the Seabed 252 Net Oxygen Depletion and Utilization Rates 252 Anaerobic Metabolism 255 Probable Organic Carbon Sources 257 Expanded Apex Hypothesis 258 Summary 260 Acknowledgments 260 References ' Sandy Hook Laboratory, Northeast Fisheries Cen- ter, National Marine Fisheries Service, NOAA, High- lands, NJ 07732 INTRODUCTION This chapter describes the distribution and magnitude of biological processes in the water column and on the seabed in the New York Bight in August-September 1976. Whereas most previous chapters dealt with the establish- ment of oxygen depletion, this chapter discusses processes occurring about 2 months after the onset of the peak an- oxic condition. Major emphasis is placed on primary pro- ductivity and dissolved oxygen (D.O.) utilization in the water column and on the seabed. METHODS From August 24 to September 9, 1976, measurements were made of primary production, rates of oxygen con- sumption in the water-column and on the seabed, and of concentrations of nutrients, organic carbon, phytoplank- ton, chlorophyll a, and bacteria (fig. 10-1). Most of the data are presented in Thomas et al. (in press). Large-volume (20-30 1) Niskin bottles were used to collect all water samples. Five to nine depths in the water column were sampled, based on profiles of temperature, chlorophyll-fl fluorescence, and photosynthetically active radiation (PAR; 400-700 nm). A bottom-tripping Niskin bottle collected water 20 to 50 cm above the bottom. Ex- pendable bathythermographs (XBTs) and reversing ther- mometers were used simultaneously to measure temper- ature at all stations. A submersible pump was used to obtain vertical profiles of in vivo chlorophyll-a fluores- cence. A Lambda submersible quantum photometer was used to determine extinction of PAR. Salinity was measured with a Beckman RS 7-C induction salinometer. Alkalinity, sulfide, pH, ammonium, and par- ticulate organic carbon were determined using methods described by Strickland and Parsons (1972). Seawater 231 NO A A PROFESSIONAL PAPER 11 KILOMETERS 20 40 60 10 20 30 NAUTICAL MILES "S- p— j^ NEW nJ^'^^')^^ ,^i^^' JERSEY •■■^-^101>^02 5?^ N '4'' 205 .220 >NJ I •223 NJ 2 225 75^ _j 74° _j 73" •224 J 72° 4f 40- 39° FIGURE 10-1.— Stations sampled during NOAA ship Albatross IV cruise (AL-76-10), August 24-September 9. 1976. Transect 102-227 indicated bv solid line. 232 CHAPTER 10 samples filtered with Whatman GF/F filters were analyzed for nitrate, nitrite, phosphate, and silicate by NOAA Atlantic Oceanographic and Meteorological Laboratories (AOML), Ocean Chemistry Laboratory, on a four-chan- nel Technicon Auto Analyzer using procedures outlined in Hazelworth et al. (1974). Samples for dissolved organic carbon (DOC) were filtered using precombusted, rinsed glass fiber filters (Whatman GF/F) and analyzed by the University of Delaware Marine Chemistry Laboratory using the method of Menzel and Vacarro (1964) as adapted by Sharp (1973). Chlorophyll a was determined spectrophotometrically and corrected for phaeopigments (Strickland and Parsons 1972). Chlorophyll-^ netplankton (>20(xm) and nanno- plankton (<20|xm) size fractions were determined by se- rial filtration of seawater samples through 20 |xm Nitex and 0.45 ixm Millipore filters and reading acetone extracts on a fluorometer (Strickland and Parsons 1972). Phyto- plankton in whole water samples, preserved with KI-L, were speciated and enumerated using an inverted micro- scope . Phytoplankton primary productivity was measured us- ing the '■'C method as described by O'Reilly et al. (1976) and O'Reilly and Thomas (in press). Zooplankton larger than 300 \xm were removed with a Nitex screen before incubation, during subsampling of Niskin bottles. Dupli- cate light and dark bottles were incubated under sunlight (simulated in situ 100%, 68%, 47%, 30%, 11%, 4%, and 1%) and artificial light (photosynthetic capacity at satu- rating — 0.089 ly/min — light intensities). Following incu- bation, the organic '^C activity in netplankton (>20 |xm), nannoplankton (<20 ixm but >0.45 |xm), and dissolved organic matter (<0.45 jim) size fractions was determined by serial filtration through 20-fjLm and 0.45-fjLm filters and subsequent acidification and counting in a liquid scintil- lation counter. The rate of oxygen consumption (total plankton respi- ration) for each depth in the water column was estimated from changes in D.O. occurring between five initial and five final whole water samples incubated in acid-cleaned, baked (232° C for Ih) 300-ml BOD bottles. Of these 10 samples, 5 initial samples from each depth were fixed immediately according to the azide modification of the Winkler method (American Public Health Association 1975) and 5 final samples were incubated in the dark at ±r C of in-situ temperature for 12 to 24 hours, fixed as before, and fitrated using phenylarsine oxide in place of sodium thiosulphate and thyodene in place of starch (Kroner et al. 1964; U.S. EPA 1974). The average coef- ficient of variability for the five initial determinations was 2.20 percent (N = 134). Seabed (sediment plus bottom 12 cm of water) oxygen consumption rates were measured as described by Thomas et al. (1976b) after Pamatmat 1971. Rates of oxygen con- sumption by the seabed and water column are expressed both as oxygen consumed and as equivalent carbon oxi- dized, assuming a respiratory quotient (RQ) of 1 so that comparisons between production and decomposition of organic matter can be made. Total direct bacterial counts were made on surface and bottom water samples using a fluorescence technique (Hobbie et al. 1977). Bacterial biomass was calculated from cell measurements obtained from photographs and transparencies made of the bacteria during the counting procedure. HYDROGRAPHIC AND NUTRIENT CONDITIONS Figures 10-2 and 10-3A and 3B show the location, size, and shape of the low D.O. area and hydrographic con- ditions at the time of the cruise (about 2 months after the onset of severe oxygen depletion). Bottom water tem- perature was highest and salinity lowest along the New Jersey coast and toward the Hudson-Raritan estuary (fig. 10-2). The exception was station 41 (off Monmouth Beach, N.J.), which appeared affected by cooler and more saline water from the Hudson Shelf Valley. A strong ther- mocline and halocline combined to produce a sharp pyc- nocline (fig. 10-3A). At station 217 in the middle of the low D.O. area (fig. 10-33), the water was saturated with oxygen immediately above the pycnocline, while imme- diately below it was anoxic. Below the pycnocline in the anoxic area sulfide concentrations were especially high (fig. 10-3B)— 18.0 |jlM/1 at stations 213 (fig. 10-5) and pH was particularly low (7.3 to 7.4) compared to sur- rounding areas (7.5 to 7.9). The highest concentrations of nitrate and nitrite (fig. 10-4A) were found in the estuarine surface outflow, in the near-bottom water of the Hudson Shelf Valley (station 76) and in the colder, more saline bottom water away from the anoxic area (station 227). Beyond the Apex both nitrate and nitrite were depleted or nearly depleted in the waters above the pycnocline. In bottom water on the pe- rimeter of the anoxic area, small quantities of nitrite were present, whereas nitrate was absent. In the anoxic area concentrations of both nitrate and nitrite were highest just below the pycnocline where D.O. concentrations were zero. Otherwise, their concentrations were zero except for a trace of nitrite at the bottom depth at station 217. Ammonium concentration decreased from the estuary seaward, approaching zero to 0.5 fiM/l in surface water at the outer Apex (station 76) and beyond (fig. 10-4A). The highest concentrations of ammonium (30 |jlM/1) were found in the estuary. Away from the estuary, ammonium concentrations were highest in the bottom water of the oxygen-depleted area (station 213, 19 fjLM/1. fig. 10-5). 233 NO A A PROFESSIONAL PAPER 11 -" T A/EIV d^'v^S$>^ JERSEY jgii'&iv^?^'-^ /3 \ 4 0- ■ 136 \ -2' 40- 39° 75 74 73 DISSOLVED OXYGEN ml Oj/L 72° t' (^ NEW (JW^'VO^^^^^ JERSEY -"X.-. .- .:;i.>-«^ #^- "^^ -208 8 3- 8 5 TEMPERATURE °C 75 74 73° 72 41 40 39- !1 V^fe>ci-' iij^ JERSEY Mi\r,^,.j:^i^---^ ^32 2 ^\ .32 .1 \PV ",&"V^'A \ -32' -si I X .32 7 .' 32.0 N ,2^ -32 9 \ -32 7 32, \ y' \ ^33 3. "aTV"^:^ -32 .'V- •32: •32 3 32, / / 329 / 33.0 / 75° 32-8 • ^34 8 32 9 ' 33.0 ' 34',6 74 73 SALINITY %o 72° 41- 40 39 FIGURE 10-2. — Dissolved oxygen, temperature, and salinity in bottom water, August 24-September 9, 1976. All samples were collected by bottom-tripping Niskm bottle. 234 CHAPTER 10 STATION NUMBERS 227 24 32 40 48 56 64 88 96 104 112 DISTANCE (km) 28 136 144 152 160 168 176 184 FIGURE 1I>-3A. — Temperature, salinity, and sigma-/ along transect 1(12-227 of figure KH. August 24-September 9. 1976. Values offset to right of station sample depths 235 NO A A PROFESSIONAL PAPER U STATION NUMBERS ?2/ 227 96 104 112 120 128 136 144 152 160 168 176 184 DISTANCE (km) FIGURE 10-3B. — Dissolved oxygen, percent oxygen saturation, and sulfide along transect 102-227 of figure IIH. August 24-September 9, 1976. Values offset to right of station sample depths. 236 CHAPTER 10 102 109 201 STATION NUMBERS X7 FIGURE 10-4A. 96 104 112 120 128 136 144 152 160 168 176 184 DISTANCE (km) -Nitrate, nitrite, and ammonium along transect 102-227 of figure 10-1, August 24-September 9, 1976. Values offset to right of station sample depths 237 NO A A PROFESSIONAL PAPER 11 STATION NUMBERS 207 227 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184 DISTANCE (km) FIGURE 10-4B. — Phosphate, silicate, and rate of oxygen consumption along transect 1(12-227 of figure 1(1-1, August 24-September 9, 1976. Values offset to right of station sample depths 238 CHAPTER 10 Above the pycnocline, inorganic phosphorus concen- trations (fig. 1()-4B) were less than 0.4 p,M/l, except near the estuary where they reached 1.1 |xM/l. Away from the estuary, phosphate concentrations generally were higher below the pycnocline than above. The highest concentra- tion (3.6 p.M/1) was observed just below the pycnocline at station 213 in the anoxic area (fig. 10-5). Silicate concentrations were generally highest (5-20 |xM/l) in the subpycnocline waters throughout the area sampled, particularly where oxygen was low (fig. 10-4B). No silicate was detected in surface waters except at es- tuarine stations and at stations 200, 201, and 207 just north of the anoxic area. The highest concentrations of silicate (up to 20 \iMI\ ) were found in or just below the pycnocline at stations 226, 213, and 217 in and adjacent to the low D.O. area (fig. 10-5 and Thomas et al., in press). According to Richards (1965), during anaerobic decom- position sulfide should accumulate over phosphorus in an atomic ratio of 53:1. Our observed ratios of S:P (1.8:1 to 12.2:1) were considerably less. However, the anoxic sys- tems examined by Richards et al. (1965). such as Lake Nitinat, have a deep subpycnocline layer (100-200 m) where anoxia occurs at some distance below the oxygen interface. The thickness of the subpycnocline layer in the anoxic area for this study was 6 to 15 m. There was a direct relationship between S:P ratios and distance below the pycnocline (r = +0.82, n = 5). Oxygen appears to have diffused downward through the pycnocline to oxidize the sulfide, and thereby decreased (oxidized) the sulfide concentrations to the levels observed (A. Draxler and C. Byrne, NMFS, in press). ORGANIC CARBON AND PHYTOPLANKTON The DOC concentrations ranged from 1 to 13 mg C/1 (figs. 10-6 and 10-7A) and are considered unusually high compared to other areas (ch. 4). Concentrations generally decreased from the estuary to the shelf (fig. 10-6). How- ever, the highest concentrations of DOC were found in the middle and outer portions of the Apex (stations 41, 109, 34, 86, 76, 51; figs. 10-6 and 10-7A). Particulate organic carbon (POC) concentrations de- creased seaward from the estuary (fig. 10-6). At station 102 near the estuary, POC was generally distributed uni- formly with depth. Farther south along transect 102-227, progressively larger concentrations of POC were meas- ured in and below the pycnocline (fig. 10-7A). The ratio of integral DOC to integral POC. integrated from surface to bottom, ranged from 3:1 to 25:1 and was generally highest in the outer portion of the APEX where standing stocks of DOC were highest. Thus, most of the organic carbon in the New York Bight is in dissolved forms, which is generally true of most marine environ- ments (Riley 1973). Chlorophyll-a (Chla) concentrations generally de- creased from 3 to 6 mg/m^ near the estuary to 0.4 to 0.8 mg/m' offshore (fig. 10-6). Especially high concentrations of phytoplankton (16 mg Chla/m') occurred at station 34 near the sewage sludge disposal site (fig. 10-6). At stations outside the Apex, adjacent to the New Jersey coast, and in the oxygen-depleted area, large increases in chloro- phyll-a concentrations were observed in the pycnocline and directly above the seabed (fig. 10-7B). Most of the chlorophyll a was attributable to nannoplankton (<20 ixm) (fig. 10-7B). Proceeding away from the estuary, netplank- ton (>20 |xm) increased in relative abundance over nan- noplankton. However, the maximum netplankton contri- bution to the phytoplankton community biomass was only 66 percent at station 227. (See chapter 9, part 1.) Identification and enumeration of phytoplankton in whole water samples collected from the surface, pycnoc- line, and bottom water at stations 102, 109, 76, 201 . 217, and 227 further confirmed that nannophytoplankton pre- dominated over netphytoplankton. A spherical phyto- plankton species 1.5 to 3 |xm in diameter and fitting the description of Nannochloris alomus given by Ryther (1954) and Patten (1959) was numerically dominant in the 21 samples examined. Its cell densities in surface water generally decreased from 270.000 cells/ml near Sandy Hook (station 102) to 90.000 cells/ml offshore at stations 217 and 227. Cell densities for the remainder of the phy- toplankton community were 100 to 900 cells/ml. Other than the small chlorophyte (probably Nannochloris ato- mus), chain-forming diatom species such as Skeletonema costatum, Nitzchia seriata, Melosira sp.. Rhizosolenia de- licatula, and Chaetoceros curvisetum dominated in samples collected near bottom and in the pycnocline, whereas flag- ellated species such as Heterocapsa triquetra. Massartia rotundata. ( = Katodinium rotunatum), Peridinium tro- choideum. and Olisthodiscus liiteus dominated counts in surface samples. Ceratium tripos was not seen in any of the 21 samples examined. Mahoney (ch. 9, pt. 2) also noted the absence of C. tripos in his samples from late August. These findings verify that the C. tripos bloom, which occurred earlier in the year (Malone 1978), had dissipated by the end of August. Mandelli et al. (1970) observed that C. tripos was the dominant species in their sampling area during June-Au- gust 1966. They also noted a decline in diatom (netplank- ton) abundance during the summer. This finding has been confirmed by Malone ( 1976) and O'Reilly et al. ( 1976) for the Bight Apex and the Hudson-Raritan estuary. The general depletion of silicate in surface waters throughout the offshore and oxygen-depleted areas may have contributed to the relative abundance of nannophy- toplankton (phytoplankton requiring little or no silicate) 239 NO A A PROFESSIONAL PAPER 11 ^W'a;-. i. ' Ka < 1* am-g-J^U-^-'- ''^■"" (y^ftl.**(M) CO C\J CD (iu)Hid3a 240 O C\J IS •a ". E c '-J S S" o g O bu CHAPTER 10 JERSEY J^'i/^ji / r J 40 39 DISSOLVED ORGANIC CARBON CONCENTRATION mgC I weighted average (or entire water column 75- 74 73 72" X35^ 40- 39 PARTICULATE ORGANIC CARBON CONCENTRATION weigtited average for entire water column U^-^ NEW ■^m' 'long JERSEY /^^t^^'-- CHLOROPHYLL a_ CONCENTRATION mg/m^ weighted average tor the euphotic layer 39- 75 73 7? .-'5^5P^' 100 40- 39 AVERAGE PHOTOSYNTHETIC CAPACITY o( SURFACE WATER mgC/m3'h Illuminated at 09 ly/min 73 72° FIGURE U)-6. — Dissolved organic carbon, particulate organic carbon, chlorophyll a. and average photosynthetic capacity of surface water, August 24-September 9. 1976. 241 NO A A PROFESSIONAL PAPER 11 STATION NUMBERS 201 207 72 80 88 96 104 DISTANCE (km) FIGURE 10-7A. — Dissolved organic carbon, particulate organic carbon, and simulated in situ (SIS) primary productivity along transect 102-227 of figure 1()-1, August 24-Scptemhcr Q. \'-)7b. Values offset to right of station sample depths. 242 CHAPTER 10 STATION NUMBERS 207 80 88 96 104 112 DISTANCE (km) FIGURE 10-7B. — Chlorophyll a. nannoplanklon/netplankton chlorophyll-K ratio, and assimilation number along transect 102-227 of figure K)-l, August 24-September 4, 1476. Values otiset to right of station sample depths. 243 NO A A PROFESSIONAL PAPER 11 over netphytoplankton above the pycnocline. The rapid growth of these small, nonsiliceous nannoplankton (e.g., Nannochioris atomus) was primarily responsible for the high productivity and low nutrient concentrations ob- served above the pycnocline during August-September 1976. PHYTOPLANKTON PRODUCTIVITY Integral daily rates of phytoplankton productivity were generally high throughout the Bight, ranging from 0.1 g C/m-/d at station 76 in the upper Hudson Shelf Valley to 12.7 g C/m-/d at station 34 in the central Christiaensen Basin (figs. 10-8 and 10-9A). Of the 21 stations, daily productivity exceeded 1 g C/m-/d at 11 stations and 3 g C/m-/d at 5 stations. Photosynthetic efficiencies per unit light energy and estimated growth rates (based on pro- ductivity to chlorophyll-fl ratios) were very high (table 10-1). At many stations, growth rates of phytoplankton exceeded two divisions per day. At highly productive sta- tions (i.e., station 34) adjacent to the estuary the euphotic layer was less than 10 m. whereas the euphotic layer at offshore stations was 20 to 40 m deep (figs. R)-8 and 10-9A). Outside the Apex, adjacent to the New Jersey coast (i.e., stations 200 and 213). the euphotic layer oc- cupied the entire water column (figs. 10-8 and 10-9). At these stations the typical vertical profile (i.e., station 34, fig. 10-9) with the highest productivity at or near the surface is not seen. Instead, the simulated in situ (SIS) and photosynthetic capacity (PC) primary productivity of these stations (i.e., station 200) is maximal below the pyc- nocline (thermocline, fig. 10-9A and B) and near the bot- tom (table 10-2 and fig. 10-9A). In the oxygen-depleted area (i.e., stations 213, fig. 10-9A) phytoplankton biomass was high below the pycnocline as evidenced by PC meas- urements. Vertical profiles of SIS and PC data for all stations can be found in Thomas et al. (in preparation). The levels of primary productivity observed in the Apex and the estuary are comparable to summer values reported by Malone (1976) and O'Reilly et al. (1976). The value of 12.7 g C/m-/d observed at station 34 near the sewage sludge disposal site seems anomalously high (fig. 10-8). However, the average concentrations of euphotic chlo- rophyll a were high (16 mg/m', fig. 10-6) and the ratio of integral daily productivity to integral chlorophyll a (79.8 g C/m^/d:g Chla/m") was within the range observed for the estuary and Apex (table 10-1). The productivity ob- served outside the Apex and in and around the low D.O. area seems high when compared with the values (0.2-0.3 g C/m^/d) estimated from chlorophyll and light data by Ryther and Yentsch (1958) for stations off Barnegat Inlet in late summer. However, comparison of our August-Sep- tember 1976 and June 1977 data for the same area shows that total primary productivity was about the same in both years for the entire area studied, but was slightly higher in June 1977 than in August-September 1976 for the low D.O. area. The euphotic layer did not occupy the entire water column in June 1977 in contrast to August-Septem- ber 1976. Photosynthetic capacity (at saturating artificial light in- tensities) in surface waters ranged from 50 to 100 mg C/ mVh in the Apex and near Sandy Hook to between 1 and 5 mg C/mVh along the 50-m isobath at the eastern edge of the sampling area off Delaware Bay (fig. 10-6). The largest change in this estuarine-offshore gradient was near stations 86, 76, and 51 at the outer perimeter of the Apex. Photosynthetic capacity and simulated in-situ produc- tivity of nannoplankton was much greater than that ob- served for netplankton (figs. 10-8 and 10-9A). Note that at station 200 (fig. 10-9A) netplankton productivity is greater than nannoplankton productivity below the pyc- nocHne. The predominance of netphytoplankton in bot- tom water was previously noted in the discussion on the distribution of phytoplankton species. The lowest nan- noplankton/netplankton productivity ratios observed, 1.0 to 1.5, were found at stations 41. 34. and 200 (fig. 10-8). During the June 1977 survey, nannophytoplankton also dominated primary productivity. Throughout our study area, phytoplankton above the pycnocline were metabolically active and community growth rates were high (table 10-1 ). Assimilation numbers of 10 and above (fig. 10-7) indicated that phytoplankton were not nutrient limited (Curl and Small 1965) even though low and near zero concentrations of nutrients (am- monium, nitrate, nitrite, and silicate) were observed in surface water. The high values for community primary productivity and high photosynthetic efficiencies above the pycnocline were due in part to the small size of the nannoplankters. high surface area to cell volume ratios, and high nutrient uptake rates, which are often (but not necessarily always) associated with smallness (Taguchi 1976). These actively growing populations may have con- tributed to maintenance of the depressed D.O. episode by continually loading bottom water with a portion of the surface layer production or organic matter derived from phytoplankton (i.e., fecal pellets. Malone 1978). Phytoplankton below the pycnocline, where light inten- sity was low (\'7c to 3% of surface intensity), had low assimilation numbers (fig. 10-7) and low photosynthetic efficiencies. High rates of photosynthetic capacity under optimal light conditions (fig. 10-9A), low assimilation numbers, and low chlorophyll/phaeopigment ratios where chlorophyll a was elevated indicate that the subpycnocline phytoplankton, though very abundant, were probably physiologically debilitated. They were not nutrient lim- ited, because nitrogen, phosphorus, and silica were abun- dant. 244 CHAPTER 10 NEW JERSEY / S 0- 5 - 10 \ TTTT": \ "r"^ '"---_. - — ^ . 20 \ , '•• "^ 70 SIS (200) PC LEGEND DI<5SOL\/ED ORGANIC MATTER RELEASE • ••••••• NANNOPLANKTON PRODUCTIVITY • -• NETPLANKTON PRODUCTIVITY • • TOTAL PRODUCTIVITY ® STATION NUMBER mgC/m^/h 10 f 7 SIS \ 2 B 5 I 20. pc FIGURE 1()-9A. — Vertical profiles of simulated in situ (SIS) and photosynthctic capacity (PC) total productivity, netplanklon productivity, nanno- plankton productivity, and dissolved organic matter release at stations 34, 200, and 213. Septemher 1, 3, and 4, iy7fi. 246 CHAPTER 10 B J I I I i_ 1 8- I i~ M 12- Q 16 20- ■ 9 UNITS 10 16 20 It _i — I — J I I l_X —I I I ' ■ UNITS 10 15 LEGEND •— •— • TEMPERATURE 'C o -o DISSOLVED OXYGEN, ml 0^/1 ■ ■ RATE OF OXYGEN CONSUMPTION, ml O /m3/h FIGURE 10-9B. — Vertical profiles of temperatures, dissolved oxygen, and rate of oxygen consumption in the water column at stations 34, 200, and 213, September 1, 3, and 4, l')7(i CONTRIBUTIONS TO THE DOC POOL The percentage of photoassimilated carbon released as dissolved organic matter (percentage of extracellular re- lease. PER) ranged from 7 to 34 (fig. 10-8). The highest PER values were in the middle and outer Apex where total primary productivity (fig. 10-8) and DOC concen- trations (fig. 10-6) were also highest. We suggest that phytoplankton production of dissolved extracellular car- bon may be contributing significantly to the DOC pool and thereby counteracting seaward dilution of DOC con- centrations. Considering the euphotic zone extracellular organic releases (fig. 10-8) and the euphotic standing stocks of DOC (fig. 10-6), the estimated turnover times for the DOC pool were 16 to 1.755 days. In general, it would take the phytoplankton community 120 to 200 days (most commonly observed frequencies) to release enough DOC to equal the euphotic stocks of DOC in the portion of New York Bight examined. These numbers take on added significance when one considers that the DOC pool is the largest (3 to 25 times POC) in the New York Bight. Some recent measurements demonstrate that hetero- trophic bacteria assimilate between and 30 percent of the DOC released by phytoplankton communities during relatively short-term (6-h) incubations (Derenbach and Williams 1974; Williams and Yentsch 1976; Iturriaga and Hoppe 1977). Consequently, the measurements under- estimate the rate of release of DOC from phytoplankton and overestimate turnover time. Because DOC may be partly related to PER, a portion of DOC may be very active biologically, making DOC important not only for its abundance, but also for its potential for decomposition and relevance to oxygen problems. OXYGEN CONSUMPTION In the Water Column Total plankton respiration rates in the New York Bight during the August-September 1976 cruise were moder- ately high, ranging from zero to about 25 ml 0,/mVh. Integral rates of carbon mineralization ranged from 0.0 to 5.9 g C/m-/d, assuming a respiratory quotient of 1 (figs. 10-4 and 10-10). In the low D.O. area, surface water rates were 2 to 5 ml O^/mVh, consequently integral rates of aerobic carbon mineralization were low (0.2-0.3 g C/mV d). Proceeding from the low D.O. area, higher integral mineralization rates occurred (up to 6 g C/m-/d) toward the deeper water to the southeast and in the shallower water of the estuary and Apex. For comparison, in the New York Bight during July 1977 the highest rate measured was 82 ml 0,/mVh. Pom- eroy and Johannes (1966) measured a rate of 0.17 ml Oy m^/h for the surface layer of the Sargasso Sea in July; 247 NO A A PROFESSIONAL PAPER 11 Table 10-1. — Synopsis of primary produclnily and related measurements in New York Bight, August-September 1976 Euphotic integral hourly production Percentage of total production Nanno- to net- plankton produc- Incu- Dura- 1976 Sta- Net- Nanno- Net- Nanno- tivity bation tion of Daily date tion plankton plankton DOM' Total plankton plankton POM- DOM ratio period exp. PAR' C/m^ 10.3 % % % % EST h Ei/m-/d Aug. 27 51 1.3 mg 28.0 39.6 3.3 70.8 74.1 25.9 21.6 1010-1847 8.62 12.0 28 109 26.3 180.5 42.8 249.6 10.5 72.3 82.8 17.2 6.9 14(X)-1716 3.27 24.9 30 45 1.2 63.8 5.1 70.1 1.7 91.0 92.7 7,.^ 53.5 07(K)-1415 7.25 29.5 30 69 15.3 120.9 21.6 157.8 9.7 76.6 86.3 13.7 7.9 1245-1845 6.00 29.5 31 101 9.9 90.3 12.2 112.4 8.8 80.3 89.1 10,9 9.1 0700-1300 6.00 34.9 Aug. 31 102 28.2 140.2 33,1 201.5 14.0 69.6 83.6 16.4 5.0 1300-1830 5.50 34.9 Sept. 1 41 165.2 170.3 137.8 473.3 34.9 36.0 70,9 29.1 1.0 0725-1345 6.33 33.2 1 34 167.8 245.4 149.9 563.1 29.8 43.6 73.4 26.6 1.5 1345-1830 4.75 33.2 2 76 .07 11.5 3.2 14.8 0.5 77.9 78.4 21.6 164.3 0810-1530 7.33 6.7 2 86 1.8 12.9 7.7 22.4 8.0 57.6 65.6 34.4 7,4 1330-1815 4.75 6.7 3 200 60.3 91.7 21.1 173.1 34.8 53.0 87.8 12.2 1.5 0733-1420 6.78 31.9 3 201 1.8 61.0 17.7 80.5 2.2 75.8 78.0 22.0 34.1 1420-1830 4.17 31.9 4 207 10.0 72.3 11.0 93.3 10.7 77.5 88,2 11.8 7.3 0740-1330 5.83 33.8 4 213 2.3 47.8 3.7 53.8 4.3 88.8 93.1 6.9 21.1 1330-1830 5.00 33.8 5 217 7.9 69.2 5.6 82.7 9.6 83.7 93,3 6.7 8.8 0815-1410 5.92 25.9 6 215 24.6 94.8 13.5 132.9 18.5 71.3 89.8 10.2 3.9 0730-1330 6.00 31.0 6 228 25.0 54.3 12.9 92.2 27.1 58.9 86.0 14.0 2.2 1330-1830 5.00 31.0 7 226 19.0 126.7 14.8 160.5 11.8 78.9 90.7 9.3 6.7 0740-1345 6.08 28.9 7 227 2.7 13.3 5.4 21.4 12.6 62.1 74.7 25.3 4.9 1345-1830 4.75 28.9 8 219 3.7 53.2 8.7 65.6 5.6 81.1 86.7 13.3 14.3 0755-1258 5.05 23.8 Sept. 8 205 1.2 22.8 3.1 27.1 4.4 84.1 88.5 11.5 19.1 1430-1830 4.00 23.8 ' DOM, photoassimilated carbon released as dissolved organic matter by phytoplankton - POM, particulate organic matter (netplankton -i- nannoplankton) produced during photosynthesis. ' PAR. pholosynthetically active radiation (400-700 nm). ■• Daily integral productivity = total euphotic integral hourly production x duration of experiment x (100/% daily PAR) ' Efficiency = f(g C/m-Zd '"'''^ '^ l"'"^ "' ) / (Einstein/m-/d— ^^^ —)]■ 100, After PlatI 1971. ■' ' ^ g C Einstein * MPZ, mean photic zone. ' Doublings per day = daily productivity: euphotic chlorophyll-a ratio / 30, Assuming 30:1 carbon/Chla (Eppley 1968). " After Bannister 1974. Barlow et al. (1963) measured an average rate of 272 ml 0,/mVh during the summer in the heavily fertilized eu- trophic Forge River estuary. Sirois (1974) measured 72 and 53 ml/O^/mVh in July and September, respectively, in the surface water of the lower Hudson River above the major influence of New York metropolitan area, about 15 km north of station 69. Farther north in the Hudson River, Sirois reported lower rates (44 and 24 ml O./mVh in July and September, respectively). During June 1977, a "normal" summer, total plankton respiration rates measured in the previously affected low D.O. area were about 2 g C/m'/d oxidized and were several times higher than the rates of integral aerobic respiration measured there during August-September 1976. Above the pycnocline, during August-September 1976, oxygen consumption rates were generally highest and de- creased with depth from the surface (figs. 10-4 and 10-9, station 34). Aerobic respiration in the water column above the pycnocline in the low D.O. area was much less, relative to adjacent stations, even though oxygen was near satu- ration and therefore not limiting (figs. 10-4 and 10-10; fig. 10-9B, station 213). Below the pycnocline, total plankton aerobic respiration rates were frequently near zero except at stations adjacent to the oxygen-depleted area (figs. 10-4 and 10-9B, station 200) and in the estuary (Thomas et al., in press). Below the pycnocline in the anoxic area no measurable aerobic respiration occurred (figs. 10-4 and 10-9B, station 213). However, the highest concentrations of phosphate and silicate were measured in the anoxic area just below the pycnocline, suggesting that anaerobic metabolism may have played a major role in the regeneration of nutrients from particulate and dissolved organic matter or that a residual buildup from previous aerobic metabolism was solubilized under low D.O. conditions or that water of higher nutrient concentration was advected into that area. 248 CHAPTER 10 Percent of Percentage Daily total PAR of daily Est. daily Photo- produc- Growth extinction par" integral synthctic Euphotic tivity to rate PAR due to Sta- during produc- effi- Euphotic Chlu MPZ'' euphotic doublings extinction phyto- tion incubation tivity' ciency^ depth integral Chia Chia ratio per day^ coefficient plankton" % mg C/m-/d % m mg Chla/m- mg/m' g C/m-/d g Chla/m' m '(base e) % 51 82 416 0.95 14n 22.7 1.62 18.3 0.6 -0.23 11.3 109 29 2,814 3.11 14n 41.7 2.98 67.5 2.3 -0.36 13.2 45 76 669 0.62 4,3 18.6 3.10 36.0 1.2 -1.06 4.7 69 28 3.381 3.16 5.4 31.1 5.76 108.7 3.6 -0.82 11.2 101 63 1.070 0.84 5n 18.3 3.66 58.5 1.9 -0.85 6.9 102 36 3,078 2.43 7.2 25.4 3.53 121.2 4.0 -0.66 8.6 41 75 3,995 3.31 9n 44.1 4.90 90.6 3.0 -0.42 18.7 34 21 12,737 10.56 lOn 159.6 15.96 79.8 2.7 -0.47 54.3 76 91 119 0.49 23n 17.9 0.78 6.6 0.2 -0.20 6.2 86 25 426 1.75 18n 28.9 1.61 14.7 0.5 -0.30 8.6 200 85 1,381 1.19 17n 50.5 2,97 27.3 0.9 -0.31 15.3 201 11 3,052 2.63 28n 47.6 1.7(1 64.1 2.1 -0.17 16.0 207 65 837 0.68 25n 15.6 0,62 53.7 1.8 -0.16 6.2 213 30 897 0.73 18n 19.8 1,10 45.3 1.5 -0.32 5.5 217 70 699 0.74 27 34.2 1,27 20.4 0.7 -0.16 12.7 215 64 1,246 Ml 17 38.3 2,25 32.5 1.1 -0.23 15.7 228 30 1,537 1.36 22n 30.0 1,36 51.2 1.7 -0.13 16.7 226 70 1,394 1.33 40n 32.7 0,82 42.6 1.4 -0.13 10.1 227 25 407 0.39 36n 13.0 0,36 31.3 1.0 -0.13 4.4 219 60 552 0.64 29n 21.8 0,75 25.3 0.8 -0.16 7.5 205 21 516 0,60 30n 20.6 0,69 25.0 0.8 -0.16 6.9 However, water of similar density (fig. 1(^3) on either side of the anoxic region had lower nutrient concentrations (fig. 10-4), suggesting that advection was not a factor. The highest concentrations of nutrients were often observed immediately below the pycnocline, suggesting that the seabed played a subordinate role in regeneration or dis- solution of nutrients. By the Seabed In the present study, rates of oxygen consumption by the seabed ranged between 0.7 and 38 ml 07m-/h (average 16.9 ml Oj/m-Zh, N = 31 stations). In a previous study over an annual cycle in the Bight Apex we measured a range between 1 and 68 ml OJm-lh (Thomas et al. 1976b). The average rates of seabed oxygen consumption in the Apex for summer 1974 and 1975 were similar (18.2 and 16.6 ml 0,/m"/h, N = 58 and 60 respectively). Smith and Teal (1973) measured low rates of seabed oxygen con- sumption (0.5 ml OJm'/h) on the continental slope south of New England. Pamatmat (1973) measured the metab- olism of the benthic community on the relatively pristine continental shelf off the Washington-Oregon coasts during summer. For depths 100 m or less he found rates of 2 to 12 ml Oj/m'/h (average 6.4 ml O^/m^/h, N = 8), which are generally lower than those in the New York Bight. Aerobic measurements of seabed oxygen consumption could not be made under in-situ oxygen conditions in the anoxic area because of the technique used. However, within and immediately surrounding the anoxic area, high rates of oxygen uptake (up to 37 ml OJm-Zh) were meas- ured when the cores were aerated above seabed in-situ levels (fig. 10-10). These high rates may have been caused in part by the rapid consumption of oxygen by sulfide as well as by microorganisms capable of surviving low D.O. and responding to input of oxygen. They also suggest that large inputs of oxidizable organic carbon to the seabed stimulated seabed oxygen consumption rates to levels higher than might be expected for that area. At the seabed in July, Mahoney (ch. 9, pt. 2) found decaying floe of C. tripos that may have been responsible for the elevated rates of seabed oxygen consumption measured in August- September. Rates of seabed oxygen uptake measured between the Apex and the northern perimeter of the low D.O. area during August-September 1976 do not appear different from those during August 1975. (See Thomas et al. 1976a, 1976b.) Measurements of seabed oxygen consumption were also taken in the area during June 1977 (Thomas, unpublished data). Comparing June 1977 with August- September 1976 is difficult, because of the temporal and 249 NO A A PROFESSIONAL PAPER 11 NEW m^ uong IS' ^ JERSEY £<^j^&^- j^^vW--- !|L>^ 40- 39 CARBON MINERALIZED n the WATER COLUMN by AEROBIC OXIDATION mgC m^ day 75 74 |ml02'm^' 5.4 1070 .58 < .01 102 13 8.5 1126 55.9 10.5 33.6 3078 4.89 < .01 109 21 13 1630 88.9 2.5 8.6 2814 1.94 < .01 41 20 12.5 1508 73.7 2.9 23.4 3995 3.59 < .01 34 36 17.5 4097 79.5 8.6 11.9 12737 3.91 < .01 86 18 11 1615 66.8 17.5 15.7 426 .32 0.15 76 50 17.5 1058 75.7 5.8 18.5 119 .14 .03 51 23 7.5 1131 31.5 28.8 39.7 416 .96 .10 200 21 13 1092 50.8 37.7 ILS"- 1381 1.64 .87 201 33 21 2508 87.6 8.9 3.5 3052 1.35 .25 207 31 19.5 1849 52.9 23.1 23.9" 837 72 .14 205 80 23 2917 43.1 48.1 8.8 516 .36 .04 219 41 23.5 1687 76.3 18.7 5.0 552 .36 .23 213 21 15.5 340 100.0 0' 0.0' 897 2.35 .41" 217 35 22 165 90.0 10.0 0.0 699 4.16 .43" 215 20 15 983 91.3 3.0 5.7 1246 1.05 3.59 228 22 12.5 1920 63.5 27.5 9.0 1537 .73 .92 227 40 29 2400 81.3 14.9 3.8 407 .19 .07 226 54 26.5 6455 87.5 5.1 7.4" 1394 .22 .18 ' P is the daily production using '"C method; R is the daily respiration using oxygen method (assumed R0= 1) ", No pycnocline present. ", May reflect an elevated rate caused by aeration of sediment core prior to rate measurements. ', Dissolved oxygen concentration was 0. Anaerobic rate could not be measured at ambient DO. concentration. ", Anaerobic metabolism estimated from phosphate accumulated below pycnocline. (See text.) 251 NO A A PROFESSIONAL PAPER 11 seabed on the periphery of the low D.O. area in 1976 was due to the combination of higher rates of seabed oxygen consumption and lower rates of total plankton respiration, presumably due to oxygen limitation and other unknown factors. It seems certain that the seabed received larger fluxes of oxidizable carbon in 1976 than in 1977. NET OXYGEN DEPLETION AND UTILIZATION RATES Atwood et al. (ch. 4) calculated oxygen depletion rates for subpycnocline waters. Depletion rates are regressions of observed oxygen concentrations versus time. From the slope of these regressions these authors estimated an av- erage oxygen depletion rate of 2.2 ml O./mVh for sub- pycnocline water (segments A, Jl, J2, Ml. and H in ch. 1, fig. 1-9) comparable to our study area. Han et al. (ch. 8) calculated an average net oxygen utilization rate of 4.0 ml Oj/mVh for May-June 1976 and included advective in- puts and outputs of oxygen and water for the various boxes in their model. In this study (August-September 1976), the measured rates of total plankton respiration in sub- pycnocline waters (average thickness 9.4 m) were 0.1 to 5.0 ml Oj/mVh and averaged 1.8 ml O./mVh. Our meas- ured rates of seabed oxygen consumption averaged 16.9 ml OJm-lh. Adding the oxygen consumed by the overlying subpycnocline waters results in an average of 3.7 ml O,/ mVh consumed below the pycnocline. This compares fa- vorably with the net utilization rates derived from the model of Han et al. (ch. 8). Despite this agreement it must be stated that our measurements of oxygen consumption in the water column were taken several months after the time frame used in the model. In June 1977 we again measured oxygen uptake both in the water column and on the seabed. From these we calculated that an average of 4.2 ml 0,/mVh was used below the pycnocline (27 m). For comparison, Tsuji et al. (1974), also dealing with a shallow (20 m) two-layered aerobic/anaerobic system, es- timated an oxygen utilization rate of 6.8 ml OJmVh, based on measured decreases in organic carbon over a 2-month period in conjunction with a red tide in the highly eu- trophic waters of Tokyo Bay. ANAEROBIC METABOLISM Our method for measuring aerobic respiration rates via oxygen changes could not be used in the anoxic subpyc- nocline water. However, we did observe high concentra- tions of sulfide in the subpycnocline waters of the anoxic area, indicating that anaerobic metabolism must have oc- curred. Estimates of anaerobic metabolism may be made using ^ Richards' model (1965) relating organic carbon, anaero- bically decomposed, to the phosphate liberated. In figure ^ 10-1 1, soluble reactive phosphate concentrations are plot- ted against oxygen concentrations for all samples collected during our cruise except those samples near the estuary (stations 45, 69, 101, 102, 109) and above the pycnocline at stations 41 and 34. The high concentrations of phos- phate plotted along the ordinate (1.35-3.6 |jlM-P/1) were measured in near-bottom anoxic water having high sulfide concentrations (figs. 10-3B and 10-5; stations 213, 217). Excluding points representing less than 0.1 ml OJl, the correlation coefficient between oxygen and phosphate is -0.85 (n = 83). The functional regression line (Ricker 1973), drawn in figure 10-11, intercepts the y-axis at a phosphate concentration of 1.03 |jlM/1. This value pro- vides an estimate of the phosphate concentration imme- diately before anoxia. Examining stations 213 and 217 (the low D.O. area), we estimate that 9,175 and 7,785 p.M-P/m', respectively, were more than the expected concentration of phosphate (1 p.M/1) in the 6-m and 15-m subpycnocline water, re- spectively, at the start of oxygen depletion. Multiplying the phosphate values by an atomic ratio of 106C:1P yields an estimated 12 and 10 g of organic carbon needed to account for the excess phosphate mineralized. The elapsed time between our visit to station 213 and the first reports of oxygen depletion in the vicinity of 213 was about 45 days. The estimated hourly rates of anaerobic metabolism of carbon for station 213 and 217 are 1.8 mg C/mVh and 0.6 mg C/mVh. These estimates are slightly lower than the measured aerobic rates of water column carbon miner- alization for subpycnocline water at stations adjacent to the low D.O. area (2-4 mg C/m'h) and are conservative, because some proportion of the inorganic phosphate formed diffused upward through the pycnocline. Bacterial densities and biomass were greater in oxygen- depleted areas than in adjacent regions (fig. 10-10, table 10-3). Different cell morphology and larger bacteria be- low the pycnocline in the anoxic area (fig. 10-12) suggest that different bacterial species or populations with differ- ent functional capabilities and responses developed there. The greater density of bacteria below the pycnocline in and surrounding the anoxic area (fig. 10-10) suggests an additional nutritive source, oxidizable organic carbon, present as DOC and FOC. Bacterial biomass in the bot- tom water of the low D.O. area in 1976 (table 10-3) was about twice the value reported by Barvenik et al. (1976) for spring 1974 and 1975 (48 mg C/m'). FOC and DOC substrates were comparable in both areas. We might ex- pect aerobic-anaerobic mineralization rates also to be comparable. 252 CHAPTER 10 3.8- 3.5- FIGURE 10-1 1 . — Regression of soluble reactive phosphate on dissolved oxygen for all samples collected August 24-September 9, 1976, ex- cept those near the estuary. High concentrations along ordinate (open circles) were measured in near-bottom water having high sulfide concentrations. 3.0- () 2.5- ■ 3. () 2.0- r = -0.85(n = 83) mM-P = 1.03 -0.180 ml02 1.5- o DISSOLVED OXYGEN ml O2/I 253 NO A A PROFESSIONAL PAPER 11 FIGURE 10-12. — Photograph of surface water bacteria (top) and bottom water bacteria (bottom) at station 213. September 4. \91b. Magnification and volume considered for each photograph are identical. 254 Station 213 213 219 219 CHAPTER 10 Table 10-3. — Bacterial carbon measurements at station 213 (anoxic area) and station 21^ (control area) Depth Bacteria measured Mean cell volume Bacterial cell density Bacterial carbon' Number surface 196 bottom 307 bottom 80 surface a \).m- X \Wm\ mg ( 0.1183 1.68 17.3 0.1755 5.93 90.6 0.1221 1.60 17.0 a 1.68 a ' Bacterial carbon was estimated by multiplymg mean cell volume by the number of bacterial cells per sample, and assuming a density of 1.1 g C/ m', a dry to wet weight ratio of 0.23 and a carbon to dry weight ratio of 0.344 (Ferguson and Rublee 1976). a. Not done. PROBABLE ORGANIC CARBON SOURCES Let us consider that the organic carbon contained in Ceratium tripos has already undergone aerobic decay at the time of anoxia (0 ml OJl). If the assumptions in the model by Malone et al. (ch 9, pt. 1) are correct, the C. tripos biomass consumed 71 percent of the oxygen lost below the pycnocline. In the temporally and spatially av- eraged scenario presented here, C. tripos carbon does not account for the excesses of phosphate that we believe originate anaerobically. The logical sources of organic carbon that could provide the organic material necessary to generate observed phos- phate concentrations are primary production, the DOC pool, and decaying benthic macrofauna. Decaying benthic macrofaunal biomass could have provided a significant proportion of the organic carbon anaerobically decom- posed. An estimated benthic macrofaunal biomass off Atlantic City near our stations 213 and 217 ranges from 25 to 100 g wet weight/m- (Wigley and Theroux 1976). A second estimate for this area is 67 g wet weight/m- of mollusca, annelida, echinodermata, and Crustacea (Boesch et al. 1977). A third estimate, based on the major mol- luscan biomass components (surf clam and ocean quahog), censused between 18.6 and 36.6 m off the New Jersey coast (April 1976) was 75 g shellfish meat/m- (Chang et al. 1976; Chang, personal communication). Most of the demersal finfish apparently avoided the low D.O. area (ch. 13) and consequently did not materially add to the carbon pool, which decomposed anaerobically. For discussion, we will use the upper value of 100 g wet weight/m- to represent the potential contribution by the benthos. This does not include the benthic meiofaunal biomass. However, using the upper value of 100 g wet weight/m- may amend this oversimplification. An estimate of total macrofaunal biomass of 5.5 g C/m- results from a conversion factor of 500 cal/g wet weight (F. W. Steimle, NMFS Sandy Hook Laboratory, personal communica- tion), which applies to the surf clam and other affected dominant benthic species and an oxi-caloric equivalent of 4.9 cal/ml O, (Odum 1971) and an RQ of 1. If all this biomass were actually killed and anaerobically decom- posed, it would represent 47 and 56 percent of the organic carbon anaerobically mineralized at stations 213 and 217, respectively. Atwood et al. (ch. 4) suggest that concentrations of DOC in excess of expected "normal" oceanic values (0.8 mg. C/1) may represent biologically labile carbon and a potential BOD load. If DOC in subpycnocline-low D.O. water was the sole resource of carbon mineralized ana- erobically to account for the observed phosphate concen- trations, then DOC at the beginning of our 45-day interval might have been double the concentrations observed be- low the pycnocline during our cruise (1.6 mg C/1). Sub- pycnocline DOC concentrations at station 213 are about half those above the pycnocline . This hypothesis is difficult to evaluate in the absence of DOC data before our cruise and poor quantitative understanding of the dynamic in- teractions between phytoplankton and bacteria and the DOC and POC pools in the New York Bight. In situ primary production can potentially supply to sub- pycnocline waters the quantity of organic carbon needed over the 45-day period. The photosynthesized carbon ac- tually available is the portion remaining after water col- umn aerobic carbon mineralization is subtracted from the rates of carbon photosynthesis. Total primary productivity and total water column respiration appear to be related, but offset in time. A large portion of the daily nutrient requirement of phytoplankton can be satisfied directly through upper water column respiration and mineraliza- tion of organic matter. Measured rates of daily integral total primary productivity in the oxygen-depleted area and vicinity were about 1 g C/m-/d (fig. 10-8). About 0.22 g C/m-/d would have to be supplied to the subpycnocline waters, which is about 22 percent of the daily photoassi- milated carbon. A production/respiration (P/R) ratio over the water column of 1.28 (assuming primary productivity = 1 g C/m-/d) would be required over the 45-day period to account for the observed phosphate concentrations. We observed P/R ratios between 0.5 and 2.0 (including esti- 255 NOAA PROFESSIONAL PAPER 11 NEW JERSEY 0.2 0.2 40^ 0.9 including anaerobic metabolism estimate J y 75" 74° 73" 72" FIGURE 10-13. — Production/respiration ratio for water column exclusive of seabed, August 24-September 9. 1976 Production is the daily total (SIS) using '■'C method. Respiration is the daily total plankton respiration usmg oxygen method (assumed RQ = 1). 256 CHAPTER 10 mate of anaerobic metabolism) in the vicinity of the oxy- gen-depleted area (fig. K>-13). On the average, the seabed consumed an amount of carbon equivalent to about 20 percent of the carbon photoassimilated throughout the water column per day. The seabed and water below the pycnocline together consumed a quantity of carbon equiv- alent to 57 percent of the carbon photosynthesized each day. This suggests that large fluxes of oxidizable organic carbon must have been supplied to subpycnocline waters daily. In fact, at stations in and adjacent to the oxygen- depleted area (photosynthetic capacity profile fig. 10-9A. stations 200 and 213) large increases in both netplankton and nannoplankton and in POC were observed in the pyc- nocline and below where PAR intensity was low. The assimilation numbers (productivity per unit biomass-chlo- rophyll a) for the pycnocline and subpycnocline phyto- plankton were low (fig. 10-7), and, in general, respiration greatly exceeded photosynthesis (table 10-2). EXPANDED APEX HYPOTHESIS Production (P) and respiration (R) ultimately balance one another since stoichiometrically the oxygen produced during photosynthesis should balance the oxygen con- sumed during respiration and mineralization of the newly photosynthesized carbon. However, very often production and respiration are uncoupled over time and space (both vertically and horizontally). For instance we know that P/ R ratios are much greater than 1 during the spring bloom, while following the bloom they are much less than 1. Our data (table 10-2) demonstrate the vertical uncoupling of photosynthesis and mineralization where P/R ratios above the pycnocline are considerably greater than 1 while those below are considerably less than 1. The large quantities of decaying organic carbon in Ceratium tripos transported to the subpycnocline waters of the New York Bight during 1976 further exacerbated the uncoupling of production and consumption activities above and below the pycnoc- line, respectively. Horizontally, additional organic carbon as sewage discharged to the Apex represents a BOD load, (i.e., not a source of photosynthetic oxygen) and will sup- port more respiration. Because of temporal and spatial partitioning of organic carbon and oxygen sources as de- scribed above, we believe that the eutrophic effects of riverborne, sewage-derived nutrients (including organic components) may actually occur over a larger area than the estimated affected area, based on the stimulatory ef- fects of inorganic nutrients alone (sans nutrient regener- ation) on primary production (Garside et al. 1976). Water column mineralization probably supplies the major portion of nitrogen-nutrients required by assimi- lating phytoplankton in the New York Bight. Garside et al. (1976) indicated that during the summer 120 t of dis- solved inorganic nitrogen (ammonium, nitrate, nitrite) are discharged into the Bight Apex. These authors estimated that the sewage-derived nitrogen (inorganic) would be assimilated by phytoplankton in a 257 km- area of the Apex during summer. If we consider the large quantities of daily and annual primary productivity measured in the lower Hudson-Raritan estuary — 6 to 8 g C/m-/d at summer maximum, 750 to 1053 g C/m-/yr (O'Reilly et al. 1976)— and the high concentration of phytoplankton biomass transported out of the estuary into the Apex (Duedall et al. 1976; Parker et al. 1976) then much more nitrogen as organic N will be transported from the estuary into the Bight during summer. Furthermore, the dissolved organic nitrogen (DON) contributed by sewage effluent could double the estimate of nitrogen loading based solely on ammonium, nitrate, and nitrite. Mueller et al. (1976) estimated that (average) 209 t of inorganic nitrogen (ammonium -i- nitrate -i- nitrite) and 130 t of organic nitrogen are transported into the Apex each day. Subtracting the Mueller et al. (1976) estimates of barged nitrogen via dredge materials (because the barged material might be expected to be derived from wastewater and gauged and nongauged runoff already counted in riverborne output) results in 172 t N/d of dis- solved inorganic nitrogen (DIN) and 104 t N/d of DON transported to the Apex. Ultimately, barged nitrogen is also added to the Apex but not as part of the river flow. This estimate of DIN is slightly greater than the Garside et al. (1976) estimate of total DIN (160 t N/d before es- tuarine phytoplankton uptake is subtracted). Few measurements of the relative proportions of DIN to DON are available for marine waters receiving sewage effluent. The data presented by Epply et al. (1972), col- lected near coastal sewage outfalls off California indicate that the average water column concentrations of nitrate plus ammonium are 1.2 times (by atomic weight) the con- centration of DON. Using the Mueller et al. data above. the ratio of DIN to DON in estuarine effluent is 1.7:1. At the time of our cruise, we measured an average of 33.2 \iMl\ of DIN for the entire water column under the Ver- razano Bridge at station 69. The average water column concentration of DOC was 4 mg C/1. If we assume an atomic composition ratio of 106C:16N, then this repre- sents 50.3 |xM/l of DON, or a DIN/DON ratio of 0.7; 1. The area actually stimulated by human nitrogen loading could be double the previous estimates (Garside et al. 1976) if the DON pool is biologically labile and not re- fractory to heterotrophic bacteria in the water column. Litchfield et al. (in press) show that substantial hetero- trophic activity and mineralization of organic nitrogen compounds do occur with the sediment bacteria in New York Bight. This activity also extends upward into the water column as well (C. D. Litchfield, personal com- munication). Both Ryther and Dunstan (1971) and Garside et al. 257 NOAA PROFESSIONAL PAPER 11 (1976) reported that inorganic nitrogen drops to very low levels between 20 and 50 km from New York Harbor. However, Garside et al. (1976) indicated that inorganic nitrogen probably does not limit chlorophyll-specific growth rates of phytoplankton within the Bight Apex. Therefore, the effect of additional large inputs of DON would be to enlarge the area of high phytoplankton pro- ductivity and biomass. During our survey, eutrophic concentrations of DIN decreased from 33 jjlM/1 in Lower Bay to just above de- tection at the outer perimeter of the Apex (50 km from station 69). This means that by the Apex and beyond most of the nitrogen in the water column is bound organically, as autotrophic and heterotrophic biomass and as DON. Despite the low euphotic DIN concentrations between 50 and 200 km from Lower Bay, we observed high rates of organic carbon production. Although average chlorophyll- a and POC concentrations decreased considerably (15:1, 8:1) from the estuary to the 50-m isobath, integral eu- photic zone concentrations (per square meter) of chlo- rophyll a and DOC decreased only slightly (table 10-1). The total water column P/R ratios (fig. 10-13) decreased from 3.5 in the Apex to 1.3 off Barnegat Inlet to 0.2 to 0.9 east of there and south offshore to Cape May. Thus active regeneration of nutrients and recycling of carbon had to occur to sustain the system as described above. Organic loading from the New York metropolitan area during 1976 was superimposed on and may have aggra- vated natural conditions leading to oxygen depletion (Se- gar and Berberian 1976). Future research should evaluate the stimulation of both production and decomposition processes in the water column and on the seabed by DIN and DON compounds in sewage wastes. One hypothesis to evaluate is that the initial effects of sewage-derived inorganic nitrogen is the stimulation of autotrophy in the Bight Apex. The "unused" Apex DON compounds plus the organic compounds photosynthesized in the Apex stimulate heterotrophy. However, the full effect of this heterotrophic stimulation (P/R<<1, and reduced oxygen concentrations) is delayed in time and occurs down the plume of the estuary, seaward of the Apex along the New Jersey coast. SUMMARY Between August 24 and September 9, 1976, about 2 months after the onset of oxygen depletion, data con- cerning primary production, water-column and seabed oxygen consumption, nutrients, organic carbon, phyto- plankton identification and abundance, chlorophyll ci, and bacteria were collected to document conditions. Our find- ings follow. 1. A strong, deep (12-20 m) pycnocline was present. 2. A subpycnocline low D.O. area with sulfide existed. 3. Nutrients generally were low above the pycnocline and were plentiful below except for nitrate and nitrite. 4. Nutrient regeneration supplied most of the nutrients required by phytoplankton, but the estuary appeared to be the major nutrient source for the Apex while in-situ nutrient regeneration appeared to be the major source for primary production offshore. 5. In the oxygen-depleted area the subpycnocline water had high concentrations of sulfide, ammonium, silicate, and phosphate. The highest concentrations were associ- ated with the pycnocline and not with the seabed. 6. Based on sulfide to phosphorus ratios measured in other anoxic systems, apparently more sulfide was pro- duced than was measured. The presence of sulfide suggests very active anaerobic metabolism during the oxygen de- pletion episode. 7. DOC concentrations were unusually high throughout the region, relative to other coastal/shelf areas. 8. Highest DOC concentrations were in the middle and outer Apex. 9. DOC was the largest organic carbon pool in New York Bight — 3 to 25 times more abundant than the POC present. 10. DOC concentrations appeared to counteract sea- ward dilution when compared to other forms of organic carbon. This suggested that significant additions to the DOC pool took place. 1 1 . Beyond the Apex, adjacent to the New Jersey coast, and in the oxygen-depleted area, large increases in chlo- rophyll-a and POC concentrations were observed in the pycnocline and directly above the seabed, suggesting or- ganic loading to the subpycnocline layer. 12. Most chlorophyll a was attributable to nannoplank- ton (<20 |xm). 13. The most abundant phytoplankton species present was a small (1.5-3m), spherical, unicellular green form, probably Nannochloris atonms. 14. Chain-forming diatom species dominated pycnocline and near-bottom waters; flagellated (motile) species dom- inated surface waters. 15. No Ceratium tripos, a large dinoflagellate, were ob- served in samples during the August-September 1976 cruise. 16. Integral daily rates of total phytoplankton primary productivity were high. Daily productivity exceeded 1 g C/m=/d at 11 of 21 stations surveyed and exceeded 3 g C/ m=/d at 5 of the stations. At many stations phytoplankton growth rates exceeded two divisions per day. 17. Comparison of our August-September 1976 and June 1977 data for the same area shows that total primary productivity was about the same both years for the entire area studied, but was slightly higher in June 1977 than in August-September 1976 for the oxygen-depleted area. 258 CHAPTER 10 18. At stations outside the Apex, adjacent to the New Jersey coast and in the oxygen-depleted area, the euphotic layer occupied the entire water column. At these stations the typical vertical profile, with the highest productivity at or near the surface, was not seen. Instead, the simulated in-situ and photosynthetic capacity primary productivity of these stations was maximal below the pycnocline. 19. Phytoplankton above the pycnocline appeared healthy, based on high productivity, high assimilation numbers, and high photosynthetic efficiencies. 20. Phytoplankton below the pycnocline appeared less healthy, based on low chlorophyll/phaeopigment ratios, low assimilation numbers, and low photosynthetic effi- ciencies. 21. The percent of photoassimilated carbon released as dissolved organic matter from phytoplankton was 7 to 34 percent and was highest where total primary productivity and DOC were highest, suggesting that phytoplankton release of dissolved extracellular products may be con- tributing significantly to the total DOC pool. 22. Total plankton respiration rates generally were high, up to 25 ml 0;/mVh or on an integral basis 5.9 g C/m-/d assuming an RQ of 1. 23. Total plankton respiration rates generally were high- est at or near the surface and decreased with depth except on the periphery of the oxygen-depleted area where rates were highest at or below the pycnocline. 24. In the oxygen-depleted area, total plankton respi- ration rates above the pycnocline were low, 2 to 5 ml O,/ mVh, or on an integral basis 0.2-0.3 g C/m-/d, assuming an RQ of 1. No measureable aerobic metabolism occurred below the pycnocline. 25. During June 1977, a "normal" summer, total plank- ton respiration rates measured were equivalent to about 2 g C/m-/d oxidized and were several times higher than the rates measured in the oxygen-depleted area during August-September 1976. I 26. Aerobic measurements of seabed oxygen consump- tion could not be made under in situ oxygen conditions in the oxygen-depleted area. However, within and im- mediately surrounding the oxygen-depleted area, high rates of oxygen uptake (up to 37 ml OJm-lh) were meas- ured, suggesting that additional organic loading of the seabed occurred in the vicinity of the oxygen-depleted area during 1976. 27. Rates of seabed oxygen consumption appeared to be higher around the periphery of the oxygen-depleted area during August-September 1976 than during June 1977. Rates of seabed oxygen consumption during June 1977 in the area of former oxygen depletion were com- parable to rates measured in surrounding areas. Away from the oxygen-depleted area no differences among the summers of 1975, 1976, and 1977 were readily apparent. 28. The contribution of the seabed to total oxygen con- sumption rates (water column plus seabed) was unusually high (>10%) around the periphery of the oxygen-deleted area, further supporting the idea that additional organic loading to the seabed took place during 1976. 29. The relatively greater contribution of the seabed to total (water plus seabed) oxygen uptake on the periphery of the oxygen-depleted area in 1976 was due to the com- bination of higher rates of seabed oxygen consumption and relatively lower rates of total plankton respiration compared with June 1977. 30. Our measurements of an average oxygen consump- tion rate below the pycnocline (includes bottom 9.4 m of water plus seabed) was 3.7 ml 0,/mVh. This measurement appears to support the net oxygen utilization rate estimate of 4.0 ml 0,/mVh derived by Han et al. (ch. 8) for May- June 1976. 31. Estimated rates of anaerobic metabolism for the subpycnocline waters of the oxygen-depleted area were based on observed phosphate concentrations and found to be slightly lower than aerobic rates of water column carbon mineralization for the subpycnocline water at sta- tions adjacent to the oxygen-depleted area. 32. The large increase in bacterial numbers and biomass and different morphology of bacteria in the subpycnocline waters of the oxygen-depleted area suggest the presence of additional labile organic material and its probable an- aerobic decomposition. 33. The logical sources of organic carbon, which could provide the organic material necessary to account for the estimated anaerobic metabolism and for the maintenance of low D.O., include decaying benthic macrofaunal bio- mass, DOC, and primary productivity. Decaying benthic macrofauna can account for only about 50 percent of the estimated anaerobic metabolism. The DOC pool is diffi- cult to evaluate because of scarcity of information and lack of understanding of the dynamic interactions among bacteria, DOC and POC pools, and phytoplankton. Pri- mary production appears to be the most likely major sup- ply of labile organic carbon, based on observed produc- tivity to respiration ratios. 34. Primary productivity and respiration were uncou- pled both vertically and horizontally as evidenced by P/R ratios above and below the pycnocline and over the New Jersey shelf. 35. Based on measurements of DIN and DOC for the entire water column in the Verrazano Narrows a DIN/ DON ratio of 0.7:1 was estimated (assumed atomic com- position ratio of 106C:16N). Thus the area actually stim- ulated by human nitrogen loading could be double pre- vious estimates which considered only DIN. 36. Wastes (including inorganic and organic nitrogen) from the New York metropolitan area are normally super- imposed upon the natural organic loading of the New York Bight. These compounds may affect the system well be- 259 NO A A PROFESSIONAL PAPER 11 yond the Apex by aggravating imbalances both in time and space between organic production and decomposition. 37. One hypothesis to evaluate is that the initial effects of sewage-derived inorganic nitrogen is the stimulation of autotrophy in the Bight Apex. The "unused" Apex DON compounds plus the organic compounds photosynthesized in the Apex stimulate heterotrophy. However, the full effect of this heterotrophic stimulation (P/R <<1, low D.O.) is delayed in time and occurs down the plume of the estuary, seaward of the Apex along the New Jersey coast. ACKNOWLEDGMENTS C. Garside, G. Han, M. Ingham, C. D. Litchfield, T. Malone, J. O'Connor, M. Pamatmat, J. Pearce, L. Pom- eroy, J. Sharp, and T. Whitledge read the manuscript and offered constructive criticism. G. Berberian (Atlantic Oceanographic and Meteorological Laboratories) pro- vided nutrient analyses; James O'Reilly and Terrance Smith (University of Rhode Island) gave field assistance with seabed rate measurements; K. Gashlin and A. Fischer gave field assistance with seabed and particulate carbon measurements; and C. D. Litchfield (Rutgers University) provided corollary information. 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