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



of the elevations mentioned, forming part of the total current through the 

 southern Kuril Straits (mainly through the Boussole Strait). Warm waters 

 divide in the north, following bottom topography, into a larger northwestern 

 branch which approaches Iona Island through the Derjugin trench, and a 

 smaller northeastern branch flowing towards Shelekhov Bay through the 

 Tinro trench. 



The southern trench of the Sea of Okhotsk, with depths greater than the 

 maximum depth of the straits, is somewhat isolated both from the Sea itself 

 and from the adjacent parts of the Pacific Ocean. Hence the deep-water masses 

 of the Sea of Okhotsk may be divided into the deep Pacific Ocean waters and 

 the waters of the southern trench (Fig. 402). The wide Shelekhov Bay with 

 its two additional bays — the western Gizhiginskaya Inlet and the eastern 

 Penzhinskaya Inlet — lies in the northwest of the Sea of Okhotsk. 



The northwestern part of the Sea or, more precisely, the western part of 

 the northern half of it, sometimes called the Shantar-More, is situated north- 

 west of the northern end of Sakhalin. The Shantar Islands (the Greater and the 

 Lesser) lie in the westernmost part of the Bay. The cone-shaped Iona Island 

 rises on the outer side of it. Two small islands (Safar'ev and Zav'yalov) are 

 situated at the northern end of the Sea at the entrance into the Tauisk Inlet. 

 The small Tyulenyi Island, with its important seal fishery, lies off the eastern 

 coast of Terpienya Bay, on the southeastern coast of Sakhalin. 



The deposits of the Sea of Okhotsk bed are most varied (P. Bezrukov, 

 1955), sand, rock and cliff soils being found at all depths (Fig. 391). Cliffs 

 and gravel-shingle soils descending to depths of 3,000 m are strongly featured 

 on the slopes of the Kuril ridge and submarine range and off the coast of 

 Kamchatka. Cliff outcrop formations may be due to different causes such as 

 volcanic activity, the abruptness of the slopes, or the rapid currents. Even the 

 floor of the Kuril Straits and the marginal parts of the Ocean are frequently 

 covered by coarsely broken stones, When moving from north to south in the 

 Sea of Okhotsk, zones of hard soils are found occasionally, in conformity 

 with the bottom topography. The first zone is adjacent to the northern coast 

 (Fig. 402) ; the second lies at a depth of 100 to 1 50 m, the third at the Elevation 

 of the Institute of Oceanography, below 1 ,000 m. The fourth and fifth zones 

 lie on the elevation of the sea-bed along the northern and southern slopes of 

 the southern Okhotsk trench (the Elevation of the Academy of Sciences), in 

 Boussole Strait and elsewhere. The southern trench of the Sea of Okhotsk 

 is filled with soft ooze or oozy clay containing a large amount of amorphous 

 silica (diatoms and radiolarians) ; this latter forms a considerable part of all 

 the deposits throughout the Sea of Okhotsk (Fig. 392). Such an abundance of 

 silica as that found in the northwestern part of the Sea of Okhotsk is not 

 known in any other sea. Along the northwestern coast, in the region of Shantar 

 and Iona Islands, and in Shelekhov Bay with its inlets, boulder-gravel- 

 shingle floors are exceptionally abundant. Sands encircle the Sea, forming an 

 especially wide zone along the western coast of Kamchatka, the eastern and 

 northern shores of Sakhalin and along the ocean coast of the Kuril Islands. 



On the mainland side the Sea of Okhotsk is surrounded by mountainous 

 formations, mostly of Mesozoic overthrust. Sakhalin, Kamchatka and the 



