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



Table 156. The mean content of phosphate phosphorus and of nitrates in Black Sea 



Phosphate and nitrate contents were much lower in Datzko's data, mainly 

 in the to 100 m layer, where their amount is about half, and in deeper layers 

 it is only one-quarter to one-fifth. The nitrogen content is correspondingly 

 eight times lower, but at a depth of 300 m the data for both periods correspond. 

 The phosphate-nitrate cycle of the Black Sea is characterized by a frequent 

 shortage of nitrates in the summer, when the phosphates may remain unused. 

 The higher phosphate indices found by Danilchenko and Chigirin, as com- 

 pared with those of Datzko, can probably be explained by differences in the 

 methods used ; the first investigators included organic phosphorus, which is 

 scarcer in the deep-water layers than at the surface. Generally speaking the 

 amount of biogenic matter (phosphates and nitrates) in the inhabited deep 

 regions of the Black Sea ' is approximately of the same order as its content in 

 the waters of Central and Southern Caspian' (V. Datzko, 1954) and somewhat 

 lower than in the Sea of Azov. 



Datzko has also determined the carbon content of the Black Sea water, both 

 in solution and in precipitate {Table 157) ; it was found to be of the same order 

 at various depths of the Sea and similar to that of other seas. 



Thus the data given are lower than those for the Sea of Azov where the 

 average carbon content of dissolved substances was, according to the same 

 author in 1949-50, 5-44 mg/1; in suspension 0-82 mg/1; the total being 

 6-26 mg/1. 



A. Kriss (1958), examining the data on the sulphate and hydrogen sulphide 

 contents of the depths of the Black Sea, does not see any inverse correlation 

 between them, and therefore throws some doubt on the ideas of previous 

 investigators as to the formation of hydrogen sulphide from decomposed sul- 

 phates ; he gives as an example one of the stations {Table 158) from the paper 

 of B. Skopintsev and F. Gubin (1955). 



