34 



MAEIOX EXPEDITIOX TO DAVIS STEAIT AND BAFFIX BAY 



bathymetrical influence, masked the <2;reater part of the year in pohir 

 seas, becomes more noticeable further south, where in temperate 

 latitudes at the end of winter the boundaries between the warm deep 

 ocean and the cold shallow shelves are very cleai'ly 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 

 heavier floes more compact but with occasional cracks and leads ; and 

 (3) an inner heavy band, possibly polar 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 

 pack it against the coast. In summer a lane of open water often 

 deA^elops adjacent to the shore, the warm drainage from the land 

 overflowing along the coast breaks up the 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 summer and shrink toward their sources 

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

 the heat of summer melting the ice but also tlie absence of the favor- 

 able winds and the strong currents which ]n-evail in spring. Since 

 the supply of j^ack 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 East Greenland ice 

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

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

 Greenland 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 

 througli the tortuous waterways of the Arctic Archipelago, which 

 not only lengthen the journey but 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 ice 

 l)roduction are in the Greenland Sea on the east and Baffin Bay on 

 the west. 



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

 along the two main ice paths to the North Atlantic : 



Ice stream 



East Greenland pack 



Eastern North American pack. 



From- 



75° N., 0° W. 

 74° N., 70° W. 



Approxi- 

 mate 

 time in 

 months 



5M 



The Spitsbergen Pack 



Spitsbergen marks the transition between Arctic and Atlantic 

 influences — to the northeast intense Arctic cold prevails, while on 

 the southwest the coast is warmed bv the Gulf stream drift. This 



