550 



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



part of the Sea has been frozen, causing some clearings and the formation of 

 drifting ice fields. The fields drift at varying speeds and constantly collide 

 with each other : some get broken up, and at times one field is forced on top 



Temperature 

 IO /5 



Central Caspian 

 Southern Caspian 



Fig. 262. Diagram of vertical distribution of tem- 

 perature in winter and summer from the three parts 

 of the Caspian Sea (Knipovitch, 1923). 



of another. Thus there are formed embacles and lump ice, that is, big floes 

 which go aground and grow bigger on account of more drifting floes sliding 

 on top of them. The limit of solid ice is more or less permanent. It runs along 

 the 12 m isobath from the northern end of Kulaly Island to Tyuleni Island. 



Salinity 



The salinity of the Caspian Sea differs greatly from that of the ocean both in 

 the ratio of its components and in their sum. According to S. P. Brujevitch 

 (1937) the average composition of the waters of the Caspian Sea, the river 

 Volga and the ocean are determined by the data expressed in percentages 

 appearing in Table 226. 



The chlorine coefficient of the Caspian Sea may be taken as 2-396 (by Lebe- 

 dintzev, 2-386) and its average salinity as 12-80 to 12-85% . Alternatively the 

 salinity may be represented as in Table 227 (according to Knipovitch, 1923). 



As shown by the tables, Caspian waters are poor in sodium and chlorine 

 and rich in calcium and sulphates by comparison with the ocean ; this differ- 

 ence in the salt ratio makes its water approximate more to river water. 



The surface salinity of the Central and Southern Caspian is fairly uniform ; 

 it is contained between the isohalines of 12 and 13% . Only in the far south- 

 eastern corner of the Sea (Krasnovodsk Bay) is the surface salinity above 



