THE CASPIAN SEA 



549 



rise of temperature of a few hundredths of a degree in the bottom layer of the 

 two Caspian Sea depressions. 



N. Gorsky (1936) explains this by two causes: the heat radiated from the 

 earth's crust, and the rise of temperature obtained as a result of the com- 

 pression of water at great depths (adiabatic process). 



The temperature conditions of the Northern Caspian differ considerably 



1000 SOUTHERN CASPIAN 



Fig. 261c. Isohalines (by chlorine) of the cross sections of the Caspian Sea 



(Brujevitch). 



from those of the Central and Southern. In consequence of its shallowness and 

 of the ease with which its water is displaced by wind and of the vigorous pheno- 

 mena of the on- and off-shore winds, stratification is hardly maintained at all 

 in the Northern Caspian. The isolines usually run vertically not horizontally, 

 i.e. changes of temperature, salinity, etc. run not from the surface of the Sea 

 to its bottom, but from the centre to the shores. Hence each of the three large 

 parts of the Caspian Sea has its own definite temperature characteristics (Fig. 

 262). 



Ice conditions 



Only the Northern Caspian has an ice-cover every winter. First of all, with 

 the onset of the frosts, huge 'young shore ice' is formed in the shallows where 

 the water is of low salinity. After two weeks the deeper part of the sea is 

 covered with ice. This delay is due to the higher salinity of the central part 

 of the Northern Caspian and to its greater swell which breaks the crust of the 

 congealing ice. Strong variable winds destroy the ice, even when the central 



