824 



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



even at the 25 m horizon (Fig. 415) and even more so in the temperature near 

 the bottom (Fig. 416). The salinity of the western and eastern parts of the Sea 

 is practically the same — about 32 or 33% ; it remains practically unchanged 

 from surface to bottom. 



The phosphorus content of the Bering Sea waters is sufficient for the luxu- 

 riant development of phytoplankton (Fig. 417). 



The changes of temperature of water layers from the surface to the 200 to 



/60' 



68T 



no 



60°- 



50' 



160- 



. ъ*а 



*4j: 



50' 



170< 



180° 



/70 е 



160 е 



Fig. 415. Isotherms of the Bering Sea in 1932 at a depth of 25 m (Ratmanov). 



300 m level are clearly shown on the cross section from Cape Africa eastward. 

 Cold Kamchatka waters are pushed to the western side. At a depth of 300 to 

 400 m these differences are already indistinct (Fig. 418). 



The water masses of the Bering Sea may be divided into four layers accord- 

 ing to their chemical properties (V. Mokievskaya, 1956): (7) the surface 

 layer, most exposed to seasonal fluctuations of temperature, salinity and 

 chemical properties ; (2) the transition zone, which becomes thicker in spring 

 and summer (50 to 200 m) while its boundaries become less pronounced; 

 (3) a third layer, characterized by a lower oxygen content, down to 10 to 15 

 per cent of saturation, and the highest phosphorus content (over 100 mg/m 3 ) 



