absorb solar radiation, which is intense in this season of the year (on accovint of the polar day) and 

 in turn become centers of melting of the surrounding ice and centers of accumulation of heat. As a 

 result, the surface temperature of coastal Siberian waters in certain regions where the ice disap- 

 pears early often rises to 10 °C and higher. Since the temperature of these waters drops in the 

 winter to the freezing point, it follows that an annual temperature range of 10° to 12° for these 

 waters is not at all surprising. 



We have already seen that in the ice formation process, salinification is directly proportional 

 to the salinity of the water from which the ice is formed, directly proportional to the thickness of 

 the ice, and inversely proportional to the thickness of the surface layer which is involved in verti- 

 cal circulation in the ice formation process. From this it is clear that in connection with the 

 slight thickness of the layer of coastal Siberian waters, the annual range of salinity of coastal 

 Siberian waters reaches 10 o/oo and In shallow regions the value is even larger. Thus in the 

 Laptev Straits at the end of August 1932, the Sibiryakou observed surface salinities from 12.40 

 to 14.28 o/oo. At the end of March 1928, in the same straits with ice thickness up to 189 cm, 

 Khmyznikov observed salinities from 19.43 to 2.63 o/oo. 



Such a combination of considerable annual ranges of temperature and salinity of the coastal 

 Siberian waters is one of their remarkable peculiarities. 



The next peculiarity of the coastal Siberian water, which has already been mentioned, is the 

 sharply defined layer of change of salinity at their lower surface. Thus, for example, on 9 August 

 1932 at 73°55' north, and 81°06' east, the Sibiryakou observed the following: 



atom, 7 = 8.12° and 5 = 13.20 o/oo, 



at 5 m, r = 7. 70° and 5 = 13. 83 o/oo and 



at 10 m, r= 0.41° and 5 = 28.86 o/oo. 



This means that between the levels of 5 m and 10 m the 1 m gradients are: temperature about 1. 5°, 

 salinity 3.00 o/oo, and density about 2.4. 



If we assume that temperature, salinity and density between 5 m and 10 m vary in a linear 

 fashion, it is then evident that the critical depth of vertical winter circulation at this station is 

 equal to about 6 m, while the freezing index is 4.8 kg-cal per square cm. Further, a simple cal- 

 culation shows that in order for the vertical winter circulation to descend to a depth greater than 

 6 m, formation of ice 146 cm thick is necessary. Thus, despite the comparatively high surface 

 temperatures which are evident towards the end of the polar summer, the coastal Siberian waters 

 are very quickly covered over with ice. 



As has already been noted, ice which grows uninterruptedly (with respect to meteorological 

 conditions) in the Kara Sea region of the coastal Siberian waters, reaches a thickness considerably 

 greater than 150 cm only in occasional years. In case of hummocking, the average ice thickness 

 rarely exceeds 300 cm. But at the station under consideration, the vertical circulation extending 

 dovra to 6 m requires formation of ice 146 cm thick, i.e. , approximately the limiting thickness. 

 Simple calculations show that with ice formation of thickness 300 cm, the vertical winter circula- 

 tion descends only to 7 m, causing the surface layers to be salinified to 19. 60 o/oo. At the 

 Sibiryakou station at a depth of 7 m, the interpolated values are: T = 4.78° and 5 = 19.84o/oo. 



404 



