q J. is the amount of heat in kg-cal released to the atmosphere during the cooling of the layer, and q 

 is the total amount of heat in kg-cal released to the atmosphere during crystallization and cooling. 



During the computations, the salinity of the ice was assumed to be 0, the density of the ice 

 0.9, the density of the water 1.0, the heat of crystallization 80 g-cal and the heat conductivity of 

 ice (which is closest to that observed in nature) was assumed to be 0.003 g-cal/sec degree cm. 

 Finally, it was assumed that there were 4000 freezing degree-days in the investigated region during 

 the winter, after which melting started. 



FREEZING DEGREE-DAYS 



Figure 75. Ice accretion in stratified water. 



The data in columns 4, 5 and 6 are depicted in figure 75, in which the freezing degree-days 

 are plotted on the X-axis and the ice thickness in centimeters on the Y-axis. 



On examining table 73 and figure 75 we see that: 



1. Ice formation occurs sporadically, namely: during the first 959 freezing degree-days, 

 there is constant ice accretion up to 83 cm, during the next 1540 freezing degree-days, the ice 

 thickness remains the same, then, during the next 1237 freezing degree-days, ice accretion is 

 reactivated, and the ice thickness increases to 126 cm, but then, until the end of the winter regime, 

 i.e. , until the end of the 4000 freezing degree-days, the ice again stops growing. Of course, this 

 sporadic accretion of ice cannot help but affect the structure of the ice, and causes its stratifica- 

 tion. Each new layer of ice results from the inclusion of a new layer of water in the vertical 

 circulation. 



Thus, ice stratification can occur not only when floes overturn or when they raft upon each 

 other during hummocking (dynamic stratification) , but also as a result of the thermal interaction 

 of the atmosphere and sea (thermal stratification). Actually, the rate of ice accretion increases 

 with decreasing air temperature and decreases with increasing air temperature . When ice 



217 



