(e) The "wind drying" of the ice, caused by evaporation and convection, which occurs 

 both during the summer and winter, has the greatest effect on the parts of the 

 hummocks which are elevated above the level ice. 



(f) The separate deeper parts of the ice fields, which are sufficiently durable at the 

 beginning due to their low temperature, within time absorb the temperature of the 

 water surrounding them, and because of this, become considerably weaker, and 

 sometimes, if their salinity is low, they simply melt. In this way, all underwater 

 projections of the ice fields are also gradually "wind blown. " This phenomenon 

 assumes particular importance during all the migrations of the ice fields. The pro- 

 truding underwater parts of the ice fields, weakened by a rise in temperature, 

 disintegrate during this time and their pieces float up to the thinner parts of the ice. 



5. Freshening, as a result of a gradual drainage of the more dense (than sea water) brine 

 in the saline cells, is especially intensive during the rise in the temperature of the ice, and also 

 as a result of the expulsion of brine during compression. 



6. A decrease in the porosity of the ice, as a result of the same compressions. 



7. Isostatic phenomena (see Section 103), which consist of the fact that when the above water 

 or underwater projections of the ice fields are destroyed, the corresponding parts of the fields 

 either rise or fall. As we shall see, this phenomenon occurs most intensively during the summer. 



As is known, both the Fram and the Sedo v observed three-year-old ice, but just the same, 

 that was not real pack ice, as was, for example, the field of the "North Pole" station. 



Thus, pack ice in its main mass is old ice, consisting of floes which are powerful, very com- 

 pact, also monolithic, almost fresh, and almost free of air bubbles, and represents in itself large 

 fields of comparatively level ice which form areas sufficient in size for airplane landings. Along 

 the edges, these fields are bordered by young hummocks and criss crossed sloping ice mounds 

 (smoothed ridges of hummocking) *. 



In separate areas, however, pack ice is a chaos of upraised and heaped-upon-each -other 

 chunks of ice, in the distribution of which there is no regulation (hummocking area. ) 



The assumption has been made that not all of the pack ice (in the final summation) drifts to 

 the Greenland Sea, i. e. , the ice field of the "North Pole" station drifted, but a part of it drifts 

 further to the west and enters into the region of constant pressure in the area north of the 

 American mainland. 



Actually, it is just in this region that the greater variety of pack ice is found — the "paleo- 

 crystic ice" (figure 42). Nares introduced this term to designate compact sea-ice formations re- 

 sembling in their size and power fragments of glacier ice, but which had come about as a result 

 of hummocking and rafting of ice of sea origin. Participants in the 2arj/ a expedition evaluated 



*As Libin informed me, in the area where the airplane N-169 landed (beyond the 80th paral- 

 lel on the Wrangel Island meridian) pack ice occupied 80 per cent of the area visible from the 

 airplane. The intervals between them were occupied by ice fields of one to 1.5 years of age and 

 150 to 200 cm thick. Airplane landings (2-28 April 1941) were made on such fields. 



119 



