GENERAL CHARACTERISTICS OF THE NORTHERN SEAS 29 



and the edge of the continental 



to the north precise boundaries do not exist, 

 shelf is taken to be the boundary. 



Huge European and Siberian rivers — the 

 Yenisei, Khatanga, Lena, Yana, Indigirka, 

 basin large masses of river water (up to 3,000 

 of the adjoining areas of sea water, especially 

 Laptev and East Siberian Seas, and likewise 

 Arctic Basin. 



Northern Dvina, Pechora, Ob, 

 Kolyma — bring into the Arctic 

 km 3 a year) lowering the salinity 

 that of the White Sea and of the 

 the surface waters of the whole 



ПЛ ./> 



Fig. 1b. Course of Fram and Sedov and Soviet drifting observation stations NP-1 



to NP-7. 



Size 



The total area of the Arctic Ocean is about 13 x 10 6 km 2 , while its central part 

 is 4-891 X 10 6 km 2 . This latter is in the main more than 2,000 m deep, i.e. it con- 

 sists of an abyssal zone (70 per cent), while only a third of it (30 per cent) is 

 composed by the continental shelf (200 to 2,000 m). The expedition on board 

 the Sedov in 1939 established that the greatest depth of the Arctic Ocean — 

 5,180 m — lies to the north of Franz Joseph Land. 



Ice-floes 



The climatic conditions of our northern seas, except for the southwestern half 

 of the Barents Sea and the southern half of the Chukotsk Sea, are very severe. 

 Even during the warmest season of the year — in August — a great part of the 

 sea surface is usually covered with ice-floes (Fig. 1в). Polar ice can, perhaps, be 

 considered the most characteristic feature of the Arctic basin, determining 

 many aspects of its hydrological and biological conditions. 



