Ice in the Sea 



253 



00. 



^025 



2 00 



1 n E Ez: Y 3a ^zasnux x xixn 

 Fig. 112. Annual temperature variation at different depths in sea ice. 



Gi, Gz are the thermal conductivity coefficients and the temperature gradients at the 

 upper and the lower surface of the cylinder. However, if the mean temperature changes 

 from Tj to T2, then the following relation holds: 



(ArjCi — koG^t = hco{r^ — Tg), 



where h is the height of the cylinder, c the mean specific heat and a the mean density. 

 From observations of temperature in ice it is possible to find cases where the mean 

 temperature of a layer is constant for a certain time, and cases where it undergoes large 

 rapid changes. The above equation can then be used to calculate A^ and k^. Table 98 

 shows numerical values for k determined for the winter periods 1922-3 and 1923-4. 

 They are of the same order of magnitude as the mean values obtained by Stefan but 

 have a marked dependence on the depth (Fig. 113). 



Table 98. Thermal conductivity of sea ice at dijferent depths 

 (According to Malmgren) 



There is a rapid decrease in the thermal conductivity in the top layers of sea ice 

 which must be due to the numerous air bubbles in these layers (density about 0-88). 



