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. 



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