The high transparencies found by Bardovskii are extremely interesting. They indicate first, 

 high illumination under the ice, and secondly, a high purity of water during the period of ice forma- 

 tion which forms as a result of a unique purification of the water during winter vertical circulation. 



The observations conducted by Bardovskii in March are presented in full. The June obser- 

 vations made at 10 points are averaged. It is interesting that in spite of the considerable decrease 

 in the thickness of the snow (and of the almost unchanged over-all thickness; snow plus ice), the 

 transparency decreased sharply under the ice. This of course, should be attributed to the spring 

 processes (development of life) both in the ice and in the water which begin in June. 



It should be pointed out that instrument observations (Trofimov's and others) of ice trans- 

 parency do not agree with the illumination of the sea under ice (Nazarov, Bardovskii) . This 

 question should be investigated further. 



LITERATURE: 62, 77, 130. 



Section 71. Color 



The color of ice, like the color of water, is explained by the selective absorption and a 

 scattering of light rays and also by the size and amount of foreign admixtures. Completely pure 

 and fresh ice which is devoid of air bubbles appears as light azure when being observed in large 

 pieces. 



The ice found at sea can be roughly divided according to color: brown, white, green and 

 azure, or even blue. Sailors also distinguish a black ice. This is the ice of frozen fresh water 

 reservoirs which form on ice fields during the summer. It should be emphasized that these colors, 

 or more correctly, hues, are noticeable only in large ice masses. Small pieces of ice almost 

 always seem to be whitish with inner layers of a steel hue. 



Brown ice (sometimes yellowish), more properly ice having a brown hue, is of river, or 

 generally shore origin. Its color is explained by a greater or lesser amount of impurities of humic 

 acids or clay substances. 



White color is characteristic of ice formed from snow and of layers formed from snow be- 

 tween the layers of ice which had formed from sea water. White ice has many large bubbles of air 

 or brine cells. 



Green is characteristic of comparatively young sea ice containing a great amount of air and 

 brine. In small chunks, green ice is usually a whitish, transparent color having interlayers of a 

 steel hue. 



Blue or azure color is characteristic of old sea ice from which almost all extraneous admix- 

 tures have been squeezed out. The blue color is frequently observed in high ropaks and hummocks 

 which can even be of one year origin. Glacier ice from a deep deposit is also noteworthy for its 

 blue color. 



During the summer, when one is searching for fresh-water reservoirs on arctic ice to take 

 water from them, one can be guided by the color of the ice and the color of the water in the reser- 

 voirs on the ice. Brown color indicates that there are many diatoms on the bottom of the reservoir, 

 and that the water in it is salty. Green color indicates very salty water with a salinity close to that 



180 



