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



short period of diatom plankton vegetation, to a considerable loss of terri- 

 genous substances and to a dispersion of diatoms in its mass. 



The 7 m long section of the core is characterized by the predominance in the 

 lower horizon of warm-water forms which, however, are not found at the 

 lower end of the core, and by the absence of Arctic species ; it resembles in its 

 composition the first and third horizons. 



According to the data given there were two periods of glaciation (Ice Ages) 

 and two inter-glacial periods when the temperature was higher. 



The 17 m long core may possibly have penetrated into the Quaternary 

 deposits ; during that period the Sea of Japan retained its marine nature. If 

 the Sea of Japan was ever isolated from the Ocean, this isolation cannot have 

 taken place in the second half of the Quaternary Period. 



A. Zhuze (1954) examined in a similar way the remains of the diatoms in 

 the soils of the Okhotsk and Bering Sea beds, taking 27 m long cores from a 

 depth of 3,355 m in the Sea of Okhotsk and a 16-5 m core from 3,638 m in 

 the eastern trench of the Bering Sea. He distinguishes five main horizons and 

 establishes the synchronism of the alterations of the two Seas, which have the 

 same characteristics as the soils of the Sea of Japan. Zhuze has also estab- 

 lished the local sequence: in the upper 150 to 185 cm the composition of the 

 diatoms tallies with that of the present period. The second 3-5 m thick horizon 

 is characteristic of a period of lowered temperature ; while the third horizon, 

 lying inside the sediments at a depth of 5 to 1 1 m corresponds to the period 

 of the rise of temperature, the fourth again to a fall in temperature, and the 

 fifth to a rise. 



Therefore this worker assumes also 'that the monoliths examined cover a 

 period of two Ice Ages and two inter-glacial epochs in the northeast of the 

 u.s.s.r.'. The Ice Ages are characterized by sediments with a weak qualitative 

 and quantitative development of diatoms, of predominantly Arctic forms, and 

 a considerable admixture of neritic and fresh-water forms ; the periods of 

 warming up by an increase of oceanic warm-water forms, and a great abund- 

 ance and rich variety of diatoms. The 27 m long core from the Sea of Okhotsk, 

 however, belongs entirely to Quaternary deposits. 



Currents, salinity and temperature 



Cold masses of water (Oyashio) move from the north along the whole of the 

 western coast of the Bering Sea, Kamchatka and the Kuril Islands, while the 

 strong warm current, Kuroshio — the Gulf Stream of the Pacific (Fig. 328) — 

 flows from the south along the shores of Japan to meet them. The warm 

 Pacific waters penetrate into all the three Seas. They enter the Sea of Japan 

 through the Korea Strait, the Sea of Okhotsk through the North Kuril 

 Straits and the Bering Sea through the Aleutian Straits. 



In summer more abundant warm currents move farther north, penetrating 

 deeper into the Far Eastern Seas. In winter the main streams of Kuroshio 

 move northeastward and eastward much farther to the south, and the intensity 

 of the currents is greatly slackened in the northern part of the Ocean. This 

 can be seen even better from the distribution of surface isotherms (Fig. 329). 

 In summer the Aleutian Islands are skirted by the 10° isotherm and in winter 



