NO A A PROFESSIONAL PAPER 11 



the addition of sulfide to the system, affects solubility 

 behavior. For example, in a normal ocean system, the 

 oxidation state of iron is three, so iron would exist as 

 ferric, FE*' (Fe/III/). However, at the pH of seawater, 

 ferric hydroxide, Fe(OH),, is so insoluble that iron is im- 

 mediately removed from the dissolved phase and either 

 precipitates or exists as a colloidal suspension. The for- 

 mation of ferric hydroxide may also scavenge manganese 

 from seawater (manganese in normal seawater has an ox- 

 idation state of four). In anoxic systems, however, iron 

 is reduced to ferrous, Fe*- (Fe/II) and manganese to man- 

 ganous, Mn*- (Mn/II/). Since chemical species formed by 

 the +2 oxidation states of these metals are more soluble 

 (e.g., rhodochrosite) than those of higher states, the 

 amounts of these metals in the dissolved phase are mark- 

 edly increased in anoxic waters. 



5. Once chemical species that can provide energy for 

 oxidation of organic matter are depleted, the amount of 

 dissolved and particulate organic material should increase 

 as long as sources for the material are present (such as 

 surface productivity). There is evidence that this does oc- 

 cur, but it has not been demonstrated in all situations. 



Most of the above effects were noted during 1976 in 

 New York Bight. In fact, it is interesting that the system 

 responded so rapidly to the changing chemical environ- 

 ment at that time. 



1976 DISTRIBUTION OF OXYGEN 

 COMPARED TO OTHER YEARS 



During winter months. New York Bight waters are well 

 mixed and ventilated, with adequate D.O. throughout. As 

 density stratification develops in spring (ch. 2 and 5), oxy- 

 gen levels below the pycnocline begin to decrease. Smith 

 et al. (1974) described this process for the New York 

 Bight, which they term an outwelling area, and attributed 

 the depletion to three factors: 



1. Vertical density isolation restricting ventilation of 

 deep waters; 



2. Increased carbon inputs in the warm season caused 

 by increased productivity in surface waters; and 



3. Increased D.O. utilization caused by increased 

 temperature. 



Segar and Berberian (1976) reported that oxygen de- 

 pletion occurs every summer in the bottom water of the 

 Bight Apex. They attributed this depletion to plankton 

 productivity stimulated by nitrogen nutrients in the Hud- 

 son River discharge. This conclusion was based on oxygen 

 data collected between April 1974 and March 1975. To 

 what extent was 1976 different? 



Available 1976 data on bottom oxygen in New York 

 Bight were compared with the historical data base for 



other years to determine the extent to which oxygen de- 

 pletion occurred, and whether this depletion was more 

 severe than previously observed. The data base was com- 

 piled from National Oceanographic Data Center (NODC) 

 and NODC/MESA data files, and from cooperating in- 

 vestigators (table 4-1). 



Data coverage in space and time was less than ideal. 

 Data were heavily concentrated in the Bight Apex, and 

 an order of magnitude more data were available for the 

 years since 1973 than in all other years combined (fig. 

 4-1). The earliest year for which data are available is 1932. 

 Figure 1-9 in chapter 1 shows the area for which the data 

 base was set up as well as areal segments (boxes) chosen 

 for individual data display. 



Available data were first visually inspected for obvious 

 errors and to ensure uniformity of units; they were then 

 placed in a uniform format on a master computer tape. 

 Data on the tape were screened to make sure they were 

 below 10 m, below any existing thermocline, and within 

 10 m of the bottom (table 4-2). This ensured that only 

 bottom layer samples that were minimally affected by sur- 

 face mixing would be considered. A sample was tested for 

 a sample depth equal to or greater than 10 m. If temper- 

 ature was available, samples which did not have a tem- 

 perature equal to or less than that chosen to represent the 

 bottom of the thermocline were discarded. If no temper- 

 ature was available but a sample depth was. a test was 

 applied for the depth of bottom of the thermocline. If no 

 temperature or sample depth was available the point was 

 also discarded. Samples with depths not within 10 m of 

 the recorded bathymetric depth were discarded. Samples 

 with no bathymetric or sample depth were discarded un- 

 less the sample had been taken with a bottom-tripping 

 bottle. 



The results of this screening process are demonstrated 

 in figure 4-2 and summarized in table 4-3. Rougly 50 

 percent of the overall data did not survive our screening 

 tests. Coverage is particularly poor for years other than 

 1976 in segments Ml. M2, and M3, that is, off the southern 

 New Jersey coast. 



In figure 4-3 each area segment has two data plots. One 

 shows the screened bottom oxgyen points for all years 

 except 1976 plotted at ml 0,/l versus Julian day (J.D.), 

 and the other shows only 1976 screened data. 



We consider oxygen-depleted bottom water to be 2.0 

 ml/1 or less. All species of finfish tested by Azarovitz et 

 al. (ch. 13) avoid waters of 2.1 ml/1. Thurbergand Goodlet 

 (ch. 11, pt. 2) show extensive surf clam mortalities at 

 oxygen levels slightly below 2.0 ml/1. In all segments, ex- 

 cept Ml, M2, and M3 (where there are essentially no non- 

 1976 data to compare) and L3 (which is well offshore), 

 1976 was an anomalous year with regard to the extent of 

 oxygen depletion during the stratified season. Low bottom 

 oxygen values either occurred earlier and lasted longer in 



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