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 



