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



History of exploration 



The remarkable voyage of Dr F. Nansen's Fram (1896) marked the beginning 

 of the comprehensive exploration of the central part of the Arctic Ocean. The 

 honour of the discovery of the great oceanic depths of the central depression 

 belongs to Dr Nansen, and it was he who first put forward a theory about the 

 stratification of, and the forces exerted by, the waters of the Arctic basin and 

 the causes of these phenomena. 



After an interval of 32 years the intensive exploration of the central areas of 

 the Arctic Ocean was begun and has been brilliantly expanded by a long series 

 of remarkable Soviet expeditions, starting with the voyage of the icebreaker 

 Krasin to the north of Spitsbergen in 1928. 



Substantial results were obtained by the expedition on board the Sadko 

 (1935) which succeeded in navigating between Franz Joseph Land and Sever- 

 naya Zemlya into the central Arctic up to a latitude of 82° 42'. 



The drift expedition of Papanin, Shirshov, Fedorov and Krenkel (1937-38) 

 and the voyage of the Sedov (1937-40), which was remarkably well equipped 

 for scientific purposes, confirmed in the main the data previously obtained by 

 Dr Nansen during his voyage on the Fram about the peculiar stratification of 

 the waters in the central part of the Arctic basin, and collected abundant new 

 material. 



Observations were carried out for more than a year, during 1950-51, from 

 M. Somov's drifting station (NP-2), landed from the air in the region of the 

 'Ice Pole'. Two drifting stations were fitted out in 1954 — the Treshnikov one 

 near the North Pole (NP-3) and the Tolstikov one within the region of the 

 'Pole of Inaccessibility' (NP-4). The existence of a peculiar cyclonic rotation 

 of water masses was observed in the eastern part of the Arctic basin at the 

 Somov and Tolstikov stations. Lately new drifting stations have been set up 

 every year. Rich material (meteorological, hydrological, geological and bio- 

 logical) has been gathered by all these expeditions. In particular they have 

 shown that the central part of the polar basin is divided into two independent 

 depressions by a huge submarine range, which has been named the Lomono- 

 sov range. It stretches from the Novosibirsk Islands to Ellesmere Island, rising 

 from a depth of 4 km to within 1 ,000 m of the surface at its summit. 



Stratification of waters 



Throughout the central part of the Arctic basin (Fig. 2), underneath the shallow 

 surface layer (100 to 150 m) of water with low salinity* (30 to 32% ) and of 

 low temperature (from —1-5 to —1-7°) there is a second layer with normal 

 salinity (34% ) but of low temperature ( — 1 -0°) and beneath it lies a 600 m 

 deep layer of warm (up to 20 to 2-5°) Atlantic water with high salinity (34-7 

 to 34-9%,,). Deeper down and extending to the sea bottom the salinity remains 

 the same as that of the layer immediately above it, but its temperature is low. 

 In the higher levels of the eastern sector of the Arctic basin waters are ob- 

 served which have penetrated from the Bering Sea. 



* Salinity, symbol S, will be quoted in grammes per kilogramme (denoted % ) through- 

 out this text. 



