Ice in the Sea 



245 



The ice melts in this way from the interior outwards and becomes "putrid". The sur- 

 face takes on the appearance of a honeycomb (cells), and the entire mass of ice soaks 

 through down to a considerable depth. In contrast to the ice formed from pure water, 

 sea ice has no definite melting temperature, but begins to melt as soon as the tempera- 

 ture starts to rise. Putrid ice breaks up easily, exposing a much larger surface to the 

 effects of solar radiation and to warmer sea-water in which it is floating. Most of the 

 winter ice melts in summer, but a large part still remains, especially along the edge 

 of the Siberian Shelf, that survives the summer and then becomes polar ice and in 

 consequence is explosed to a strong annual melting cycle. 



2. Physical and Chemical Properties of Sea Ice 



{a) The Salinity of Sea Ice 



The salinity of sea ice is defined as that quantity of sohd matter (in g) remaining 

 after evaporation of 1000 g of melted sea ice. The limitation that was found essential 

 in the definition of the saUnity of sea-water (see p. 36) thus also applies here. The 

 essential difference between the salinity of sea-water and that of sea ice is that the first 

 is a rather conservative property of sea-water; while the second, in strict contrast, is 

 a very rapid changing quantity for each single piece of ice. Nevertheless, the sahnity 

 of a sample of ice shows only minor variations. This has been shown by the numerous 

 analyses made by the "Maud" Expedition, 1918-25 (Malmgren, 1927). As has been 

 noticed by all polar expeditions the surface of young ice is covered by a surface salt 

 solution, which remains liquid even for low temperatures and keeps the surface of the 

 ice continuously wet. For very low temperatures only this layer also freezes, giving 

 a mixture of ice and salt crystals which isolate themselves in form of snow-white 

 clusters. 



Beneath the surface a part of the salt solution remains enclosed between the ice 

 crystals and determines the salinity of the sea ice. Its amount depends on the processes 

 going on during the ice formation, specifically on three factors: (1) on the salinity of 

 sea-water from which the sea ice was formed; (2) on the rapidity of ice formation; 

 and (3) on the age of the ice. Referring to the first, the salinity of sea ice is less than 

 that of sec-water, since the part of the salt solution between the ice crystals is always 



Table 91 



able to escape. In the analyses of young ice samples made during the "Maud" Expedi- 

 tion the salinity of sea ice reached a maximum value of 14-59%o, but usually the salinity 

 of sea ice was between 3 and 8%o. Referring now to the rapidity of ice formation it 



