390 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



Black Sea is the result of this process, which was first discovered for the open 

 seas by Murray. 



The hydrogen sulphide formation proceeds in two phases : the sulphate is 

 first reduced to sulphide with the evolution of carbon dioxide, according to 

 the equation : 



CaS0 4 +2C->CaS+C0 2 



During the second phase the sulphide is decomposed by carbon dioxide, 

 hydrogen sulphide is evolved and a carbonate is formed 



CaS+2C0 2 +2H 2 O^Ca(HC0 3 ) 2 +H 2 S 

 Ca(HC0 3 ) 2 ->CaC0 3 +C0 2 +H 2 



Moreover, some intermediate products are also formed 



R2-S 2 3 and R2-S0 3 



In other words, the whole process can be expressed as 



so 4 2 --^so 3 2 -^s 2 o 3 2 -^s 2 - 



As has been shown by P. Danilchenko and N. Chigirin (1929), in the Black 

 Sea the carbonate content increases while there is a certain decrease of sul- 

 phates with depth {Table 153). 



Table 153 



The intermediate products of the reduction of sulphates, the amounts of 

 which increase with depth, were also found. 



Anaerobic bacteria, which take part in the putrefaction of albuminous 

 substances in the absence of oxygen, are the second source of the hydrogen 

 sulphide formed. Anaerobic sulphide is oxidized by oxygen penetrating from 

 above : these two gases are as it were antagonists, however, since both may 

 occur simultaneously (in small amounts) on the boundary of the oxidation- 

 reduction zones. Hydrogen sulphide can be oxidized by ozygen in the absence 

 of bacteria, but in the Black Sea hydrogen sulphide oxidizing bacteria were 

 recorded everywhere. 



The upper limit of hydrogen sulphide gives a very clear picture of the hori- 

 zontal course of the iso-surfaces (G. Neumann, 1953). In the centres of anti- 

 cyclonic rotation the iso-surfaces are raised while in centres of cyclonic ones 

 they are lowered (Fig. 188). As we have seen before, the contamination of the 



