SECT. ] 



THE INFLUENCE OF ORGANISMS ON THE COMPOSITION OF SEA-WATER 



47 



an intermediate product and the possibility that preformed nitrate undergoes 

 denitrification are also neglected. 



In Table VIII, the concentrations of various products of decomposition 

 observed in the deep water of the Black Sea and of the Cariaco Trench are 

 compared with the concentrations calculated in this way. The agreement is 

 sufficiently good to indicate that the conditions observed in anoxic basins have 

 resulted in the main from the processes defined by the equations and that the 

 quantitative relations depend on the elementary composition of the plankton. 



Table VIII 



Comparison of Observed and Calculated Values for Concentration of Products 

 of Decomposition in Anoxic Basins, mg atoms/m 3 



Depth 



Oxygen at surface 



Concentrations at depth 



Black Sea 

 750 m 

 615 



Observed 



Calcd. 



Cariaco Trench 

 915 m 

 471 



Observed 



Calcd. 



P0 4 -P 

 CO3-C 

 NO3-N 



N 2 -N 

 NH 3 -N 



S 2 "-S 



7.08 

 696 « 



44 

 52.8 

 235 



750 

 

 43.8 

 69.4 



230 



2.42 



18.6° 



10.6 



20.4 



257 

 

 33.6 

 5.1 

 17.0 



a Corrected for preformed carbonate and nitrogen of surface water. 



Data from Danil'chenco and Chigirin (1929, 1929a), Skopintsev et al. (1958), Richards 

 and Vaccaro (1956) and Richards and Benson (1961). 



Sulfate is one of the major constituents of sea-water and is present in quanti- 

 ties sufficient to oxidize more than one hundred times the amount of organic 

 matter than can be formed from the phosphorus and nitrogen available. The 

 sulfate reduced under anoxic conditions in the Black Sea is less than 5% of 

 the content of the surface water (see Fig. 6). Under natural conditions in marine 

 waters, sulfate reduction is probably limited only by the amount of organic 

 matter which accumulates. This need not be true of fresh waters in which the 

 available sulfate is more readily exhausted. 



The oxygen content of the atmosphere is thought to have been produced in 

 large part by the photosynthetic reduction of carbon dioxide. It has recently 

 been suggested that the reduction of sulfates in anoxic basins or in marine 

 sediments may have contributed substantially in making oxygen available to 

 the atmosphere (Redfield, 1958). The supposition is that sulfides produced in 

 the process of sulfate reduction have been entrapped in the sediments and that 

 the carbon dioxide released at the same time remained in solution and, on 

 ultimate reduction by photosynthesis, supplied oxygen to the atmosphere. 



