On the periphery of the Arctic Basin, in regions where the warm Atlantic water hardly pene- 

 trates, the lower boundary of arctic surface water descends even deeper, sometimes to the very 

 bottom. For example, at the northernmost observation point of the Sibiryakov in 1932, at81°28' 

 north, 96°54' east, at a depth of 200 m there was observed T = 1. 38° andl <S'= 34. 67 o/oo. Accord- 

 ingto our observations on the Knipovich in 1932, in the region of Franz Joseph Land at 81°34' 

 north, 52°05' east this boundary limit descended to the bottom, i.e. , to 520 m. In the regions of 

 penetration of warm Atlantic water into the Barents and Kara Seas, where there is sufficiently in- 

 tense summer heating, and where the seasonal variations of temperature and salinity of the topmost 

 layers are not significant, the arctic surface water forms a cold intermediate layer in the summer. 

 In the central part of the Arctic basin the seasonal variations of temperature and salinity, accord- 

 ing to Nansen, do not extend deeper than 60 m and are extremely slight. 



The near freezing-point temperatures of arctic surface water and the vertical distribution of 

 salinity in it indicates that extremely complicated processes are involved in its formation. In par- 

 ticular they are wind-caused mixing, a more intensive salinification during the winter over the 

 shoals, but mainly, the melting process as a result of interaction of water and ice. 



Nansen established that the arctic surface water moves toward the straits between Greenland 

 and Spitzbergen and the speed of this current increases as it approaches the straits, reaching a 

 speed of 1. to 1. 5 miles per day right at the straits. It was established also that the Atlantic 

 water moves in at subsurface depths in approximately the opposite direction, with speed decreasing 

 from these straits, where its speed is also about 1.0 mile per day. It follows that between the 

 levels of and 400 m there is a level where the speed of the current is equal to zero. Evidently the 

 depth of this level lies between 75 and 100 m. 



In addition, the ice, being subjected to wind action, moves in diverse directions and with di- 

 verse speeds, amounting in some instances to 15 miles per day. In this process the ice naturally 

 carries along in its movement the surface water down to a certain depth. For example, the instru- 

 mental observations of Shirshov and Pedorov showed that such a wind-caused current in the Arctic 

 Basin as a rule is clearly defined to a depth of 25 to 30 m and only in rare instances does it em- 

 brace a layer deeper than 50 m. Usually, after a certain interval of time, a wind-caused counter- 

 current is set up somewhat deeper (at depth of 50 to 74 m) and this again will embrace the layer 

 from 35 to 125 m only in case of prolonged and rapid drift. Thus we see that in the upper layer of 

 the Arctic Basin there exist extremely large current velocity gradients which, however, are not 

 sufficient for elimination of their great stability. 



Nansen considered that the low salinity of the surface layers in the drift region of the Fram 

 was due to the fact that these layers are formed as a result of mixing of Atlantic water for the most 

 part with water of the Siberian rivers. This explanation is correct, but the influence of the river 

 water in this phenomenon is not basic and decisive. 



Let us assume that wind-caused mixing is completely absent in a certain region. Let us 

 assume further that a layer of ice is formed in this region. The entire layer which is involved in 

 vertical winter circulation is of course salinified. During the summer, after the ice has com- 

 pletely or partially melted away, the extreme upper layer becomes entirely fresh. Now, if we 

 assume that there exists in the given region even a slight mixing due to wind, then as a result, the 

 layer of thaw water mixes with the lower layers and gradients of salinity are formed. But the thick- 

 ness of ice which forms during the winter and melts away during the summer varies from year to 

 year and in different regions. Masses of ice are constantly carried away from the regions of their 

 formation and melting and they move faster than the water at the lower boundary of the vertical 

 winter circulation. If we recall that the eddy heat-conductivity is greater than the eddy diffusion, 



408 



