is separated or forced together by the wind flow. Thus the newly-formed 

 pressure ridges are proportionately weaker than the old floes although 

 much thicker. In early Sept.eraber the warm current from the Bering Sea 

 loses some of its velocity and heatj, and v/ater temperatures fall. Next 

 the land mass, which in spring wanned faster than the water, cools faster 

 than the water, so that near shore the blocks and small floes freeze to- 

 gether into giant floes, which then may become detached by winds and cur- 

 rents, and drift until finally frozen into place. The last portion of 

 the water to freeze is the shore lead, where the relatively warmer and 

 more saline viater cools off very slowly. The pack proper, therefore, 

 extends southward finally joining the shorefast iee spreading northward 

 from the land. The process of growth of the pack is facilitated by the 

 fact that the shore lead is never completely free of ice, and the few 

 remaining floes act as nuclei for the growth of winter ice. Continued 

 low air temperatures cause thick ice to form quickly over the open leads 

 in the pack, so that frozen leads form, the smoothest portion of the ice 

 sheet. In the interval between summer and winter conditions many pres- 

 sure ridges are formed, while cracks and leads form and freeze over, re- 

 form and refreeze, and so on. At the edges of the ice mass there is never 

 complete freezing, since the alternate motion back and forth of the wind- 

 driven pack prevents the forming of thick ice. The elasticity of the ice 

 depends on the rate of freezing. Ice in the newly frozen leads freezes 

 quickly and retains many salt crystals in its contitution, so that it is 

 weaker and more elastic than the older ice. During the winter the older 

 polar floes add some ice from the bottom and are also covered with snow, 

 but the accretion of ice is slow and does not contain much salt. There- 

 fore, the old floes are hard and brittle. 



Currents play an important role in the life cycle of the Arctic ice. 

 The transport of warai water to the north causes semipernHnent zones of 

 weakness where the ice is thinner than in other areas. One such area 

 exists along the coast of Alaska from Bering Strait toward Point Barrow, 

 Other areas of warm-water currents have not yet been delineated because 

 of difficulties of winter reconnaissance. Currents carrying cold water 

 also influence the ice. In the Arctic the cold currents are much weaker 

 than the warm currents, so that the ice is carried slowly in an anti- 

 cyclonic (clockivise) whirl around the basin. By being carried within 

 the basin, the ice has a chance to remain unmelted for some time, and 

 the ice islands in particular must have been floating for many years in 

 the basin. The hard polar ice is thus partly due to the existence of 

 the anticyclonic current whirl. 



The validity of this theory of ice pack development and history can- 

 not be determined without further data, Tvro postulates may be listed: 

 (1) that the gross total, amount of ice in the Arctic basin remains con- 

 stant, and (2) that the total volume of ice varies from year to year. 

 It is possible that the volume of ice remains essentially unchanged from 

 one year to the ne>rt, due to similar wind and current conditions. If 

 this is true, the causes of heavy or light ice years are the wind and 

 current stresses on the ice pack. Wind forces will cause a packing of 

 ice in one area one year and in a different area the next, so that if an 



