200 200 400 600 800 1000 Ky 



I 1— I I I I :=a 



Figure 171. Computed drift of arctic ice in 1938. 



But the main thing which these maps show is that there can be no question of any simplified 

 diagram of ice movement according to the principle of shortest distances. On the contrary, it 

 must be assumed that in the Central Arctic Basin there is a complex system of circular movement, 

 subject to considerable variations both in time and in the area over which movement occurs. This 

 very complexity of the drift diagram (especially its variability in time) is responsible for the 

 appearance of areas of hummocking and thinning, areas of stagnation and areas of increased drift 

 speed. 



The observed dependence of ice drift in the Arctic Basin on distribution of atmospheric pres- 

 sure permits us to elaborate our conceptions of the nature of currents in this basin. The general 

 scheme of atmospheric circulation over the Arctic Basin is such that it guarantees an ice movement 

 (in the greater part of the basin) in the direction of the Greenland Sea. The ice circulation sets in 

 movement the surface layers of water which lie under the ice. The effect of the wind over the 

 whole area of the Arctic Basin is responsible for a surface current which is strengthened in the 

 Greenland Sea by the prevailing north winds. 



The water deficit in the Arctic Basin (which arises in connection with the northerly winds) 

 intensifies the deep Atlantic current, which is formed as a convection current and a drift current, 

 and apparently transforms it to a considerable degree into a compensation current. 



As may be seen from figures 162 to 166, the nature of the atmospheric circulation may vary 

 from season to season in such a way that intensification of drift may involve only separate scattered 

 area. For example, the increased transfer of ice out of the region adjacent to the Bering Strait 

 may correspondingly increase the amount of water entering the Bering Sea, but may not be reflected 

 on an increased transfer of ice into Greenland Sea and increased entry of Atlantic water. 



436 



