Figure 57. Isolines of air bubble content In a cm'^/kg in the upper 

 layer of an ice floe in the Gulf of Finland. 



Sometimes the amount of air in the ice is expressed in cubic cm per kg of ice. Piotrovich 

 made interesting observations of air content in the ice of the Chuckchee Sea during the voyage of the 

 Krasin in 1935. 



In the very thin discs (about 2 cm) of young ice, the air content fluctuated within the limits of 

 3. 7 to 12 cm^ Ag- In the same ice 10 cm thick, the amount of air increased to 31.0 cm^/kg. Blue 

 ice proved to contain considerably more air (from 55 to 130 cm"' /kg) than did the greenish (from 9 

 to 102 cm^/kg), the yellowish (about 24 cm^/kg) and snow (firn) ice (about 66 cm /kg). On the 

 other hand, the air bubbles in blue ice differed by their small size (up to 1 to 2 mm) whereas the 

 size of the roimded bubbles in greenish ice attained 2 to 3 cm, according to Piotrovich's 

 observations. 



According to Savelev's observations of fast ice near Uedineniya Island conducted February 

 through May, 1939, the porosity of ice increases from February to May and is always greater at 

 the upper and lower surface of the ice than in the middle parts. 



Its values at the following levels in May were: 

 cm"^/kg. 



10 cm -35.0, 80 cm - 8.0 and 170 cm - 44.0 



The data presented and discussions indicate that the hollows determining the porosity of sea 

 ice are explained first of all by the fact that the upper layers of the ice are formed from snow, and 

 second by the fact that the brine draining from the cells and capillaries is replaced with atmos- 

 pheric air. 



The origin of air bubbles in snow and glacial ice is somewhat different. In firn ice which 

 forms from long-lying snow, air occupies 30 to 50 per cent of the volume. In the course of time 

 with a gradual transformation of firn ice, the air bubbles are partially forced out into the atmos- 

 phere through the tiny cracks and canals and are partially compressed and preserved under pres- 

 sure. This pressure has been indicated by the research of the Koch and Wegener Expedition in 

 Greenland in 1912 - 1913, and in separate instances can reach 10 to 12 atmospheres. 



Barnes expressed the thought that by Investigating the air enclosed in the ice of icebergs, it 

 is possible to judge the composition of the atmosphere at the time when the formation of a given 

 ice glacier occurred. The conducted investigations of the air in the bubbles, however, did not 

 disclose any differences from the contemporary composition of the atmosphere. 



168 



