698 



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



Sea of Okhotsk and only 7 per cent in the Bering Sea at depths of between 

 1,000 and 1,500 m. Farther down the amount of oxygen rises again to 20 to 

 25 per cent of saturation. 



The satisfactory oxygen supply in the deeper waters of the Sea of Japan, in 

 spite of the isolation of its deep trench, is of special interest. The oxygen con- 

 tent of the deep waters of the Sea of Japan does not fall below 67 to 70 per 

 cent of saturation (P. Ushakov, 1953). This is due to strong processes of verti- 

 cal circulation in autumn and winter, caused by the cooling of the surface 

 waters. 



Three main masses of water (Fig. 336) may be distinguished in vertical dis- 



STATIONS 



322S 3223 322S 3230 323f 12J2 3233 



-b- 



H 1000 



Fig. 336. Boundaries of water masses and distribution of two species 

 of boreal Copepoda on the cross section southeast of Sangar Strait 

 (Beklemishev and Burkov). A — Boundary of water masses; В — 

 Front of Kuroshio current ; С — Upper boundary of the distribution 

 of Calanus cristatus (boreal cold-water species); D — Places of 

 occurrence of Calanus pacificus (south boreal thermophylic species). 

 la — Modified subtropical water mass in the zone of mixing ; lb 

 Subtropical water mass (proper); 2 — Cold intermediate layer; 3 

 — Zone of interaction of subtropical and sub-Arctic waters ; 4 — ■ 

 Intermediate layer of lowered salinity ; 5 — -Warm intermediate layer ; 

 6 — Deep oceanic waters. 



tribution over the Kuril-Kamchatka trench and in the Bering Sea (K. Morosh- 

 kin, 1955 ; A. Bogoyavlensky, 1955 and D. Smetanin, 1958 and 1959). These are: 



(7) Upper sub-Arctic water masses (0 to 200 m), wherein all indices are 

 subject to most pronounced seasonal alterations. These are the waters modi- 

 fied by local conditions (in the Bering Sea and over the Kuril-Kamchatka 

 trench). In their turn they may be divided into the surface layer subject to 

 summer heating (0 to 50 m), and a deeper (down to 200 m), cold intermediate 

 layer. The salinity of these waters is slightly higher than 32% . 



During the period of spring bloom the amount of oxygen reaches 1 30 to 

 175 per cent of saturation ; the amount of phosphates in terms of phosphorus 

 decreases from 60 or 70 to between 20 and 10 mg/m 3 or less ; that of nitrates 



