Section 109. Initial Phase of Weakening of Ice 



In sea ice, due to its physical and chemical peculiarities, melting commences from the mo- 

 ment when the ice temperature, having reached a certain minimum, starts to rise under the action 

 of one or another factor. These factors are the absorption by the ice of the direct and diffused solar 

 radiation, and of heat from the adjacent air and water layers. 



During the polar winter the reception of radiant energy is zero and therefore the chance in- 

 creases in temperature of the surface layers of ice are caused entirely by absorption of heat from 

 the air. This absorption is by no means slight. Table 86 shows the average positive deviations 

 from the mean monthly ice temperatures observed by Malmgen in January 1924 (author's 

 computations). 



TABLE 86. AVERAGE POSITIVE DEVIATIONS FROM MEAN MONTHLY ICE 

 TEMPERATURES IN JANUARY 1924 



Ice depth in cm 25 75 125 200 



Temperature deviations 



in degrees Centigrade 2.4 1.6 0.6 0.2 



From this table it may be seen that the positive deviation of temperature embraced the ice 

 layer to a depth of 200 cm and raised its temperature on an average of 0. 6'. If we consider that 

 under low temperature conditions, sea ice has a specific heat equal to 0.5, we find that each square 

 centimeter of ice surface in the case under consideration absorbed nearly 64 g/cal from the atmos- 

 phere during the month. * 



The reflecting quality of the snow which covers the sea ice is the basic factor which deter- 

 mines the melting of the sea ice by the action of radiant energy. It is therefore clear that, gener- 

 ally speaking, melting commences earliest wherever the snow surface is solid or dirtied by one 

 means or another. ** 



♦Computations based on the original data published in Malmgren's "On the Properties of Sea 

 Ice" from the Scientific Results of the Norwegian North Pole Expedition with the Maud 1918 to 1925, 

 Vol. 1 and lA, show that the temperature deviations in table 86 at 125 and 200 cm are 0. 5°C and 

 0.4°C instead of 0.2°C and 0. 0°C as given by Zubov. Furthermore, the amount of heat absorbed 

 from the atmosphere per square centimeter of ice surface for the month should be 54 g/cal rather 

 than 64, as shown by the following computation: 



= c p V AT 



where dQ = amount of heat absorbed, 



c = specific heat of ice, 



p = density of ice, 



7 = volume of ice affected, 



AT = increase in temperature. 



Translator. 



**Contrarily, a large amount of dirt or scattered stones on the ice, due to their low heat con- 

 ductivity, will retard the melting of the ice. 



298 



