CHAPTER V 

 PHYSICAL AND CHEMICAL PROPERTIES 



OF SEA ICE 



Section 55. Salinity 



The initial forms of sea ice, as have already been mentioned, are thin needles or disks of 

 pure ice interwoven vifith one another. Because of its greater density, the brine which is separate 

 during this stage seeps through between the crystals and drops to the bottom. However, if ice 

 formation takes place sufficiently rapidly, the spaces between the crystals are filled with new ac- 

 cretions of ice faster than the brine drains off, and thus a part of the brine remains disseminated 

 in the ice in the form of more or less equally distributed salt cells. In addition, a part of the brine 

 appears on the surface of the new ice and forms the so-called "surface brine" when ice crystals 

 which are formed at a certain depth below the sea surface float up and fuse. 



When there are temperature changes, sometimes the brine on the ice surface hardens and 

 sometimes it again reverts to a liquid mass. In the latter case, it seeps downward slowly but 

 steadily. 



Completely anologous phenomena also occur in the salt cells which are disseminated within the 

 ice mass. When there is a decrease in temperature, additional layers of ice also form in them, 

 and with subsequent temperature increase, these layers again revert to the liquid stage. 



It is clear that surface brine plays the main role in thin ice formation. As the ice thickness 

 increases, the brine cells assume a greater importance the more so since (ui the course of time) 

 there is a continuous downward seepage of brine and the surface brine first enters the salt cells 

 and then the water . 



The disseminated salt solution, which is surrounded on all sides by pure ice, determines the 

 structure of sea ice and is the primary cause for many of its physical-chemical properties. 



It follows from the very processes of sea ice formation that the salinity of sea ice, by which 

 it is understood to be the salinity of the water obtained when the ice melts, depends on the following 

 factors: 



1. The salinity of the water from which the ice was formed. Regardless of the rate of ice 

 formation, part of the brine always manages to seep out of the ice. Therefore, the salinity of sea 

 ice is always lower than the salinity of the water from which it was formed. 



2. The rate of ice formation. The faster the ice forms, the less brine manages to seep 

 down between the crystals. And, other conditions being equal, the rate of ice formation is greater 

 the lower the air temperature at which the ice formation takes place. 



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