THE BERING SEA 



825 



lying beneath the transition zone: this third layer extends down to 1,500 m; 

 (4) the fourth layer stretches from 1,500 m down to the sea-bed: its oxygen 

 content rises to 20 per cent of saturation and its phosphorus content decreases 

 to 90 mg/m 3 . The upper two layers, formed in the Bering Sea itself, are the 

 most characteristic. The lower two layers are similar to the Pacific waters, to 

 which they owe their origin, since they penetrate freely into the Bering Sea 

 through the straits. 



Fig. 416. Isotherms near bottom of Bering Sea in 1932 (Ratmanov). 



A comparison of the structures of the column of water of the Bering Sea 

 and of the adjacent Pacific Ocean is most significant (Table 324). 



The amount of phosphorus in the Bering Sea is higher than that in the 

 Pacific Ocean, while its oxygen content is lower at depths of 1,000 to 2,000 m. 



The Bay of Anadyr and the adjacent shallows have, as a result of the vigor- 

 ous autumn and winter vertical circulation, a uniform distribution of oxygen 

 and other elements. During the period of intense development of phyto- 

 plankton (June) the amount of oxygen increases, that of phosphorus de- 

 creases to 20 mg/m 3 , and that of silica may amount to 100 mg/m 3 . 



A high concentration of plant food in the upper layer of the Sea is 



