Denmark Strait is 56 percent of 4,380 cubic km. annually, or 2,350 cubic 

 km. per year. This figure is 20 percent less than Zubov's, 70 percent 

 less than Vize's and 80 to 85 percent less than Weaver's estimate. 



The total mass of ice in the Polar Basin is estimated at 28,000 

 cubic km,, assuming an area of 8 million square km. and an average thick- 

 ness of ice of 3»5 meters. The Oceans , estimates the average thickness 

 of the ice at 3 to 4 meters in winter and 2 to 3 meters in summer. Thus, 

 9.2 percent of the polar ice drifts away each year. 



In order to calculate the average age of the polar ice, it is nec- 

 essary to consider the different melting properties of the polar and 

 winter ice. Due to the hardness of the polar ice and its lack of salt, 

 it melts more slowly than winter ice. Therefore, the percentage of 

 winter ice which melts in the ensuing summer should be much greater 

 than that for polar ice. It is known that about 3 feet of ice are 

 melted annually from the surface of the ice pack (Malmgren, 1927). It 

 is necessary to redefine the melting as referring to the percentage of 

 the area covered which is decreased through melting, rather than the 

 volumetric change of ice. Considering the areal coverage, winter ice 

 should "melt" faster than polar ice, because it is thinner and saltier. 

 If, for example, 10 percent of the polar ice drifts out of the basin 

 ajnnually, and melting of the polar ice amounts to 1 percent in area, 

 and if the total extent of ice is 95 percent in stommertime, composed of 

 85 percent polar ice and 10 percent winter ice, statistically then 28.6 

 percent of the winter ice area is melted and the average age of the polar 

 ice is 8,7 years. Tables 1 and 2 give the melting percentages of winter 

 and polar and the average age of the polar ice for area coverages of 95 

 and 90 percent in summer, thus including the probable range of area 

 coverage and percentage composition of polar and winter ice. Further 

 aerial reconnaissance is necessary to secure better estimates of the sur- 

 face ice coverage and the relative proportions of winter and polar ice 

 during the summer season. Note from the tables that if 10 percent of 

 the ice drifts away each year and if the melting of polar ice amounts 

 to as little as 1 percent of the basin area, no more than 89 percent of 

 the surface of the basin can be covered with polar ice during the summer 

 months, regardless of the formation or melting of winter ice. 



The percentage of winter ice is fairly high, even in the middle of 

 the Polar Basin. On the basis of available surface and aerial reconnais- 

 sance, the areal coverage of the basin is greatest between the North Pole, 

 Spitzbergen, and Greenland, where the constriction due to Incoming and 

 outflowing currents give summer coverages of 98 or 99 percent, v«hereas 

 the section of the basin between the Laptev and Beaufort Seas may have 

 a summer coverage as low as 70 percent in places, and an average of per- 

 haps 90 percent. The proportion of winter ice must therefore be greater 

 in the latter area, but as the ice moves in the slow drift over the Pole 

 and into the East Greenland current, the percentage of winter ice decreases 

 until practically all of the outflow is polar ice. 



