190 MAEIOX EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



limits of the shelf waters is the reason for the areas of accmmilatioii 

 and dissipation being- practically one and the same. The meltin<>- area, 

 it will be seen, includes not only the Avaters inshore of the continental 

 edge, but a marginal mixing zone. This strip naturally varies in 

 width depending to a great extent on the particular contour of the 

 slope, the direction of the current, and like factors at any given 

 locality. For example, off the Tail of the Grand Bank the belt of 

 mixed waters spreads out sometimes 60 to 100 miles or more in 

 width ; a zone much broader than is found farther north in Lalnador. 

 A conservative estimate of the average width of the mixed water 

 zone along the North American shelf is 30 miles. The greater 

 size of the melting area over that of the ice area is balanced, 

 however, by an area along the east coast of Baffin Land which 

 extends from BarroAv Strait to Cumberland Gulf. Pack ice is 

 never absent from this region except for a week or two the first 

 part of September, and then seldom more often than once in four 

 or five years. It is safe to designate this region as one in which no 

 melting prevails. The fact that it is in size just about equal to that 

 of the mixing zone causes ice area and melting area to be approxi- 

 mately equal, viz, 467,300 square miles. 



The estimate of 467,300 square miles of pack ice as the annual crop 

 is believed to be somewhat high, but it adds conservatism to our 

 figures on the magnitude of the ice-chilling effect to be introduced 

 later. It should be also remarked that the pack ice area does not 

 present a solid, unbroken surface, since leads and polynyas prevail 

 in the pack just the same, or to a greater degree, as they do in the 

 polar ocean. The figure of 10 per cent of open water for the polar 

 cap ice is believed to be also fairly representative for the pack ice 

 of Davis Strait and Baffin Bay. The 10 per cent value of open 

 water in the pack does not. however, materially effect, for purposes 

 of comparison, the roughly equivalent size of melting area and ice 

 area. 



In order to compare the annual amount of sea ice and glacial ice 

 in this interesting arm of the northwestern North Atlantic we have 

 assumed the average thickness of the pack ice to be 6 feet. Naturally 

 the floes and fields are thicker at the northern extremity of Baffin 

 Bay than they are much farther south near the melting end off 

 New^foundland. Also where rafting and hummocking has occurred 

 the pack will be thicker than where young ice lies. But an average 

 of 6 feet is believed to be a fairly close approximation. The total 

 volume of sea ice melted annually is therefore 467 cubic miles. 

 Since over a long period of years there has been no tendency toward a 

 persistent increase or decrease in the geographical position of the ice 

 boundaries, it follows that during the course of a normal year 467 

 cubic miles of water are frozen into ice and a like amount of ice is 

 melting into water.*- Compare this figure of 467 cubic miles of sea 

 ice Avith that of 7 to 10 cubic miles as the annual output of glacial 

 ice for Davis Strait and Baffin Bay. Though our figures may only 

 be approximate, they unmistakably reveal, nevertheless, that sea ice 

 annually greatly exceeds glacial ice in volume^ the latter equaling 

 only 0.015 to 0.020 of the former. In fact evaporation of the melting 



*- Speerschneider (1026, p 74) estimates an annual discharge from the polar sea of 

 20,000,000,000 cubic yards. This is far too small since, if fi feet thick, it would amount 

 to an area covering only 1° of longitude and 3° of latitude off northeast Greenland. 



