Ice in the Sea 

 Table 95. Latent heat of melting of sea ice 



251 



Table 95 shows values for different salinities and for temperatures equal to 1° and 

 -2°C. 



The coefficient of thermal expansion can be calculated in a similar way; it 

 is made up of the coefficient of thermal expansion of pure water (a = 1-7 x 10"'*) 

 and a term which depends on the amount of ice forming or melting due to the change 

 in temperature in 1 cm^ of sea ice. Since the freezing of 1 g of water at t° is accom- 

 panied by an increase in volume of yr = 0-091, the coefficient of thermal expansion 

 of sea ice will, according to the above discussion, be given by 



dttr S dSr 



Table 96. Coefficient of thermal expansion of sea ice (Ur X 10'*) 



(According to Malmgren) 



From this equation Malmgren has calculated the values given in Table 96, and experi- 

 mental determinations of Ur, on samples of natural ice have fully confirmed the theor- 

 etical values. There is an essential difference between Uj for sea ice and freshwater ice. 



Pure ice always expands with increasing temperature; sea ice expands only to a 

 lesser extent, and then only at very low temperatures and low salinities. Thus the 

 second term in the above equation becomes unimportant. At higher temperatures and 

 salinities the second term predominates; this means that the ice volume increases 

 with decreasing temperature and at very low temperatures and high salinities this 

 increase may be considerable. 



Extensive series of temperature recordings at different depths in sea ice (ice floes) 

 have been made by the "Fram" Expedition 1893-6 and the "Maud" Expedition 

 1918-25. The latter were obtained by using electrical resistance thermometers and are 

 much more reliable. Table 97 gives monthly means for five depths down to 2 m for 

 every month during which the snow cover at the place of measurement was left 

 undisturbed. 



The annual temperature variation at all depths can be approximated closely by a 

 simple sine curve of the form 



Af + a sin 



12 



/ + a 



