air temperatures after formation of the solid ice cover) has the greatest salinity. It is natural that 

 the Ice in these cracks is weakest and is the first to melt. In this manner the dynamic and thermal 

 cracks which form during the winter become the natural lines of cleavage of the ice in the spring. 



In relation to the cleavage, the drain holes also are an important factor. Actually, the bottom 

 of the thaw water puddles gradually becomes covered with such a large number of drain holes* that 

 the ice becomes like a kitchen skimming spoon. 



LITERATURE: 62, 77, 88. 



Section 113. Influence of Micro-Organisms and Inorganic 

 Inclusions on Destruction of Sea Ice 



Both on the surface and within the ice there accumulate during the course of the winter all 

 sorts of nutritive matter which is freed during melting and thus "fertilizes" the surrounding water. 



In the first place, along with precipitation which falls onto the ice surface, compounds of 

 nitrogen, phosphorous and silica are concentrated. With the subsequent evaporation of the snow and 

 ice this material may remain on the ice surface and thus gradually be further concentrated. 



Secondly, the accumulation of nutritive matter in the ice itself is explained by the peculiarities 

 of the process of ice formation in the sea. We have seen that with sufficient cooling and mixing the 

 initial colloidal ice particles are produced throughout the entire thickness of the layer involved in 

 the vertical circulation. It is possible that these initial formations are produced around the minute 

 particles of organic matter suspended in the sea water and around the turbidity of continental origin 

 which is found even in those regions which are most remote from the continents. 



The lumps of deep ice which are formed as a result of freezing together of the individual col- 

 loidal ice particles, after their size has increased to a certain limit, float up and bring with them to 

 the surface the particles of organic matter and turbidity (muddiness) which later gradually freeze 

 into the surface of the ice. This phenomenon acquires special significance, of course, in those 

 cases where the mixing process reaches the very bottom — i.e. , primarily in shallow regions. 



The formation of deep ice in small fresh-water puddles, as we have seen, ceases with the 

 formation of the solid ice cover. In the sea, however, this process actually continues throu^out 

 the water. In this manner the sea ice sucks in the nutritive matter from the atmosphere on the one 

 hand, and on the other, the turbidity and organic matter from the entire water layer which is 

 involved in the mixing process. 



Along with the dissolved nutritive matter and organic matter, all sorts of planktonic organ- 

 isms and bacteria are frozen into the ice. Certain of these die under the influence of the low 

 temperatures but some few forms (primarily bacteria and spores which can withstand very low 

 temperature) survive and begin to develop intensively with the start of the thawing. These 

 organisms give rise to life both on the ice itself and in the water which results from the melting 

 of the ice. 



*The swinging or rocking movement of the ice is an important factor in increasing the size of 

 drain holes. All of these are round in shape, which appears to be a result of their being washed 

 by the thaw water. 



305 



