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- 



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