Io8 POLAR PROBLEMS 



millimeter in thickness), which loosely freeze together and form "ice 

 gruel"; the water at that time is of gruelly or souplike consistency, 

 and its surface has the appearance of cooling grease, with a peculiar 

 steel-gray or lead tint. Because of this appearance, this primary 

 stage of the freezing of the sea water has been called slush, or sludge 

 (Russian, salo, grease; Fig. lo). 



PANCAKE ICE 



"Owing to various disturbing conditions connected with the 

 slight motion in the upper layers of sea water, the freezing together 

 of the ice needles and plates does not proceed equally on the whole 

 surface of the open sea but starts its development as if from a num- 

 ber of centers of freezing, spreading equally in all directions from 

 these centers. Grouping themselves around these centers the crystals 

 or plates of ice form small areas having the appearance of rather reg- 

 ular disks, from i to 2 or 3 feet in diameter [maximum, 5-6 feet]" 

 (Kolchak). This phenomenon, called pancake ice, is the next stage 

 of ice formation and, like the previous one, develops when the at- 

 mosphere and the sea are calm (Fig. 11). 



YOUNG ICE 



"Gradually growing thicker and stronger, the disks of pancake 

 ice begin to congeal together (thanks to the freezing of crystals in 

 the intervals between the disks) and form more or less large, compact 

 ice areas," which, "starting in motion under the influence of the wind, 

 wave movement, and currents, break up into several pieces; these 

 pieces, colliding with each other, have their edges crumpled up to 

 form narrow rims a few centimeters high ; under favorable conditions 

 the pieces freeze together again into new, more extensive areas; 

 gradually they grow thicker and more and more solid; and finally 

 they form compact young ice consisting of wet ice, saturated with 

 water, which has a coarse crystalline composition of more or less de- 

 veloped ice crystals. The upper surface of this young ice is smooth or 

 more often slightly rough, while the under surface has a coarse, rough 

 appearance, sometimes like a brush of ice crystals. Underneath the 

 under surface of this ice there is a more or less thick layer (about 

 one foot deep) of water saturated with ice crystals, which gradually 

 makes the newly formed ice thicker and thicker. Such young ice is 

 usually 2 or 3 centimeters thick" (Kolchak); it increases continually 

 during the whole winter and in May reaches its full thickness of 

 about 2 meters on the average (maximum thickness of ice observed 

 by Nansen was 3.65 meters). (See Fig. 10). 



