CHAPTER 10 



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 



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