34 



MARIOX EXPEDITIOX TO DAVIS STRAIT AND BAFFIN BAY 



bathTmetiical influence, inasked the <rreater i)art of the year in polar 

 seas, becomes more noticeal)le furtlier south, where in temperate 

 hititudes at the end of winter the bouiuUiries between the warm deep 

 ocean and the cold shallow shelves are very clearly marked. 



Most all pack-ice streams show the following features in cross sec- 

 tion: (1) An outer zone of scattered loose glacons; (2) a mid zone of 

 heaviei- floes more compact but with occasional cracks and leads: and 

 (:5) an inner heavy band, possibly ]K)lar cap ice. pressed closely 

 against the shore ice. Offshore winds broaden the stream, and 

 scatter the outer floes, while on-shore breezes narrow the ice and 

 ])ack it against the coast. In summer a lane of open water often 

 develops adjacent to the shore, the warm drainage from the land 

 overflowing along the coast breaks up tlie fast ice and speeds the 

 forward movement of the pack. 



The ice streams are most voluminous and extend farthest south- 

 ward during spring or early summei" and shrink toward their sources 

 during late summer or early fall. This recession is due not only to 

 the iieat of summer melting the ice but also the absence of the favor- 

 able winds and the strong currents which ])revail in spring. Since 

 the sup])ly of pack does not immediately increase on the resumption 

 of freezing air temperatures, due to the specific heat of the water, 

 there is consequently a lag in the swelling of the ice streams, and 

 this interval marks the minimum of pack. The seasonal variations 

 in the limits of pack ice are also dependent upon the amount of fast 

 ice that is contributed. 



Pack ice invades the North Atlantic along two main routes, 

 (a) along the eastern side of (ireenland and (h) along the eastern 

 side of North America. (See fig. 11, p. 20.) The P^ast (ireenland ice 

 stream in its upper reaches is split by Spitsbergen. Its nuiin trunk, 

 bearing the heaviest of all sea-ice forms, pours directly through the 

 (xreenland Sea, while an eastern arm from the cachments of the 

 Barents and Kara Seas moves toward Greenland roughly along the 

 seventy-fifth parallel. The ice stream to the western Atlantic is fed 

 thi-ough the tortuous waterways of the Arctic Archipelago, which 

 not only lengthen the journey l)ut materially reduce the volume of 

 contribution. Neither ice stream depends solely on its Arctic Ocean 

 connections for its supply, as two of the most prolific- regions of iee 

 production are in the (ireenland Sea on the east and Baffin Hay on 

 the west. 



The following table gives the approximate length, velocity, etc. 

 along the two main ice paths to the North Atlantic: 



itii 



f 



THK Sl'irSI'.KlUiKN I'ACK 



Spitsbei'gen uiai'ks the transition between Arctic and Atlantic 

 influences — to the northeast intense Arctic cold pivvails. whilf <>ii 

 llie southwest the coast is warmed by the (iiilf stream (h'ift. I his 



