THE CASPIAN SEA 553 



relation to chlorine, magnesium and the sulphates. He considers the 'lake age' 

 of the Caspian to be about 1 5,000 years. 



In the salt balance of the Caspian Sea the carrying away of the salts beyond 

 the limits of the Sea by the wind plays a definite role. L. Blinov (1950) deter- 

 mines by means of complex computations the amount of salts carried away 

 from the surface of the Caspian Sea beyond its limits as 62,400 tons per day 

 (at an average wind speed of 6 m/sec), which is about 30 per cent of the total 

 accession of salts from the river inflow (according to S. P. Brujevitch it is 

 195,000 tons per day). 



Oxygen 



The oxygen conditions of the Caspian Sea are the result of the following fac- 

 tors. In summer the oxygen content at the surface of the Sea is near saturation : 

 98 per cent in the Central Caspian and 94 per cent in the Southern. In the 

 Northern Caspian the picture is rather more varied, but on the average the 

 oxygen content is more than 90 per cent. There is a slight supersaturation in 

 the winter throughout the whole surface of the Sea (103 to 105 per cent). 

 Changes in oxygen content with depth are shown in Table 229 and in Fig. 264. 



Table 229 



Average amounts and seasonal differences in the content of 



oxygen dissolved in water for various parts of the Caspian Sea 



as percentage of saturation 



The decrease of oxygen content with depth in the Caspian Sea is not nearly 

 so pronounced as that of the Black Sea. As we have seen, the much weaker 

 saline stratification does not hinder the penetration of the vertical displace- 

 ment of water into the depths. It is evident from the comparison given that in 

 the Central Caspian the oxygen content is higher than in the Southern. 



Substantial changes have taken place in oxygen distribution in the column 

 of Caspian waters in the 40 years since the last works of N. M. Knipovitch 

 (1914-15). Oxygen was then entirely absent near the bottom of the Central 



