TABLE 82. THE THERMOMETRIC CONDUCTIVITY OF SEA-ICE 

 COMPUTED FROM THE LAG OF MINIMUM 

 TEMPERATURES 



In the layer: from to 25 cm 0.0029 



from 25 to 75 cm 0.0060 



from 75 to 125 cm 0.0072 



from 125 to 200 cm 0.0026 



In the layer: from to 75 cm 0.0049 



from to 125 cm 0.0053 



from to 200 cm 0.0046 



Malmgren notes quite correctly that formulas for the depth distribution of periodic tempera- 

 ture fluctuations in a uniform medium of infinite thickness should not be applied to sea-ice, which 

 is not uniform and is comparatively thin. Actually, one of the basic assumptions of the theory of 

 the propagation of periodic fluctuations in a homogeneous medium consists of the fact that the av- 

 erage annual temperature at various levels is equal to the average annual temperature at the sur- 

 face of the medium. This assumption, as well as the other assumptions in the theory, is not ap- 

 plicable to sea-ice. Therefore, Malmgren used other methods to determine the heat conductivity. 



LITERATURE: 62, 104. 



Section 90. Ice Accretion Due to Low Ice Temperatures 



We have already seen that under certain conditions the ice which had formed during the win- 

 ter can become thicker during the summer, because ice formed from melt water which had drained 

 beneath the ice freezes to the lower surface of the ice when it comes into contact with the cold sea 

 water . 



However, aside from this, ice accretion can continue even after the air temperature be- 

 comes higher than the temperature of the surface layers of the ice until the temperature of the ice 

 reaches the temperature of the water beneath it (see Section 62). 



Let us try to compute approximately the maximum possible ice accretion at the lower sur- 

 face of the ice, due to the cold reserves which accumulated within the ice during the winter. Let 

 us make the following assumptions: 



1. The heat reserves in the water are so slight that we can ignore them. 



2 . All the cold accumulated in the ice during the winter is expended on summer ice 

 accretion. 



3. The vertical temperature distribution in the ice is linear (in other words, the vertical 

 temperature gradient is constant). 



Under these assumptions, we can write the equation: 



• 



(,_._x)8,c,/=XS,Af, 



(1) 



238 



