44 



REDFIELD, KETCHUM AND RICHARDS 



[CHAP. 2 



approximately with the amounts estimated to be produced by the decomposi- 

 tion of organic matter as indicated by changes in the oxygen, sulfide and 

 phosphorus content of the water. They found that nitrate and nitrite were 

 present in mere traces in, or were absent from, these anoxic waters. Ammonia, on 

 the other hand, was present and varied in concentration in proportion to the 

 accumulation of sulfides. This observation indicates that sulfate does not act 

 as a hydrogen acceptor in oxidizing the ammonia liberated from organic matter 

 during sulfate reduction. 



The most conspicuous change in the composition of sea- water produced 

 under anoxic conditions is the appearance of hydrogen sulfide. The principal 

 source of sulfide sulfur in marine waters is the reduction of sulfates rather than 

 the sulfur of decomposing organic matter. In the Cariaco Trench, the presence 

 of 24 mg atoms/m 3 of sulfide sulfur is accompanied by an accumulation of only 

 one-tenth this amount of phosphate phosphorus. If both elements had been 

 derived from the decomposition of plankton, its organic matter must have 

 contained ten times as much sulfur as phosphorus. Data on the sulfur content 

 of plankton are lacking, but in the flesh of fish the sulfur present is somewhat 

 less than the phosphorus (Vinogradov, 1953). Consequently, it is unlikely that 

 much of the sulfide has been derived from the sulfur content of de- 

 composing organisms. 



Data from the Black Sea demonstrate in a more positive way that sulfate is 

 the source of the sulfide present in this anoxic basin. Skopintsev (1957) and 

 Skopintsev et'al. (1958) have found that as the sulfide concentration increases 

 with depth, the ratio of sulfate to chlorinity decreases, indicating that sulfate 



0.141 



_j 0.140 



a 



,\ 



o 0.139 



CO 



0.138 

 0.137 



0.2 



0.4 0.6 0.8 

 S 2 7CL 



Fig. 6. Relation of sulfide/chloride and sulfate/chloride ratios in waters of the Black Sea. 

 Numbers indicate depths of samples. Slope of line corresponds to AS 2 ~/ASO^ = 

 — 1.0. (From data of Skopintsev et al., 1958.) 



has disappeared from the water. Fig. 6 shows that these changes occur in 

 approximately the ratio required if one sulfide ion is formed from each sulfate 

 ion which disappears. By taking the accumulation of phosphorus as an index 

 of the quantity of organic matter which has been oxidized in the water of the 



