15 

 The Sea of Okhotsk 



I. PHYSICAL GEOGRAPHY 



The Sea of Okhotsk is separated from the Pacific Ocean by the Kuril 

 Islands. Numerous deep straits, but none deeper than 2,318 m (Boussole), 

 run between them. The great Kuril range, which rises above sea-level as a 

 chain of islands, forms a submarine barrier — the 'Vityaz ridge' — with its 

 eastern slopes sinking down to 10-3 km into the depths of the Kuril-Kam- 

 chatka trench. This geosyncline zone, of the Tertiary or pre-Tertiary Period, 

 runs from southwest to northeast comprising the south Okhotsk trench, the 

 two Kuril ranges divided by a trench, the deep-water Kuril-Kamchatka 

 trench and the bank which borders its southeastern side. 



The process of the formation of the geosyncline zone of the Kuril-Kam- 

 chatka arch is not yet complete, and it is particularly active in its northern 

 part; it is connected with the phenomenon of the overthrust of the Con- 

 tinental block of Eastern Asia on to the bed of the Pacific Ocean (G. Udintzev, 

 1955). 



The area of the Sea of Okhotsk is 1,590,000 km 2 , the volume of its waters 

 1,365,000 km 3 , its maximum depth 3,657 m, and its average depth 859 m. In 

 area the Sea of Okhotsk occupies second place after the Bering Sea among 

 the seas washing the shores of the u.s.s.r., while in volume it is fourth, after 

 the Bering, Japan and Black Seas. Its area is 42 times greater than that of the 

 Sea of Azov and its volume 4,500 times greater. The bottom topography 

 of the Sea of Okhotsk is rich in features (Fig. 388). To the south a deep 

 trench stretches in a latitudinal direction, south of 48° N, demarcated from 

 the northern part of the Sea by the 3,000 m isobath and a steep slope down to 

 the 15,000 m isobath. Its central part is 1,000 to 1,500 m. deep forming, how- 

 ever, some terraced elevations : two at a depth of approximately 1 ,000 m cut- 

 ting the central hollow of the Sea into two parts, and a northern ledge at a 

 depth of about 200 m bordering the northern shallows (the shelf proper) on the 

 southern side. The circulation of sea-water (Fig. 389) is greatly influenced 

 by the two terraced elevations, and the distribution of bottom deposits is 

 determined by them (Fig. 391). 



Small streams of warm Pacific Ocean surface waters penetrate into the Sea 

 of Okhotsk through the northern Kuril Straits, warming the western shores of 

 Kamchatka, some even reaching Shelekhov Bay in small amounts. The main 

 masses of these warm waters, partly under the effect of the general system of 

 cyclonic rotation, turn westward and break up in a fanlike manner in the 

 central part of the Sea. Warm surface waters can be traced by the presence of 

 the crustacean Calanus tonsus (Fig. 390). 



Deep Pacific Ocean waters, entering the Sea of Okhotsk mainly through the 

 Kruzenshtern Strait, fill the central hollow of the Sea and, moving north- 

 ward under the influence of the bottom topography, turn westward at each 



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