Bottom ice often forms at the mouths of rivers emptying into seas having strong tidal phe- 

 nomena. Sea water, cooled to a temperature of 1.5° to 1.8° below zero, on entering the mouth of 

 a river when the tide comes in, cools the rocks and the other objects at the bottom of the river. 

 When the tide goes out and fresh water flows over these objects, an ice crust forms around them 

 which, depending on local conditions is either destroyed each time or is gradually increased. 

 Nalivaiko discovered such river-mouth bottom ice while making winter measurements at the mouth 

 of the Onega River. As can be seen from figure 36, which he was kind enough to give to me, the 

 sandy bottom was covered with an ice crust and the sand had frozen through to 10 to 12 cm. 



V^W/?/>^i;/m//;r7^;^ 





ICE 



FROZEN 

 SAND 



SAND 



■'KL' 



Figure 36. The vertical distribution of the 



elements in a column of soil taken 

 on the Onega Bar at a depth of 3 m . 



LITERATURE: 62, 77, 88. 



Section 45. The Classification of Ice According to Origin 



The ice found at sea is divided into three classes according to its origin, which differ sharply 

 from each other according to their physical-chemical characteristics: "river, " "glacial, " and 

 "sea. " 



River ice is carried out from the river to the sea durir^ the spring ice break-up, and during 

 the summer it either melts or, in polar regions, is integrated into the ice of marine origin. River 

 ice is completely fresh and ordinarily it is brown in color, which is conditioned by mixtures of 

 humus materials. Often, river ice contains shore dirt and other inclusions. 



River ice is never found in the South Polar latitudes. In the Arctic Ocean, there is quite a 

 bit of it during the beginning of summer in the areas where the large Siberian rivers drain. Inas- 

 much as this ice is almost completely destroyed during the course of a polar summer, its role in 

 the ice regime of the seas is extremely insignificant. 



Glacier ice gets into the sea when the ends of glaciers break off. Formed from snow which 

 has collected in mountain valleys, glacial ice is fresh and almost completely devoid of foreign 

 material. As a rule, it is bluish in color. 



106 



