SCIENTIFIC RESULTS 



33 



reworked, possibly several years old pack that has survived several 

 summers.-^ In the north polar ocean the pack ice occupies a belt 

 intermediate between the fast ice and the polar cap ice. The pack 

 on its ort'shore side may add to the i)olar cap or it may remain in the 

 intermediate zone, or it may freeze again in the re<iion of fast ice. 

 Outside the polar basin, however, pack ice never builds into heavier 

 forms, but eitlier drifts southward to melt or remains in the north to 

 survive lon<rer. Pack ice is distinouiylied from the polar cap ice 

 by its liahtness. 



"Outside the Arctic Ocean the qualities that distinguish pack from 

 jiolar cap ice are not so apparent and the farther south we go the 



Summer in the north polar Basin 



Figure 18. — An old field of pack ice in the polar regions showing the disentegratlve 

 effects of the heat that comes from the summer sun. Note the hummocked 

 moutonee contour of the ice surface and also the fresh-water pools in many of the 

 depressions. (I'hotograph from the lUissian hvdrographical expedition, 1910— 

 191.5.) 



smaller is the difference. Pack ice is distributed from the Arctic to 

 lower latitudes in two main streams which reflect not only the ocean 

 currents but also the general trend of the coastal shelves. The fact 

 that these shallow waters are more effectively chilled than deep 

 permits the ice to survive instead of melting near its sources. The 



='A source of limited supply, not often mentioned, is anchor or bottom ice. As its 

 name implies, it forms on the bottom in those regions where swift-running frigid currents 

 prevail, and at depths seldom exceeding 40 to 45 feet. During clear cold winter nights 

 radiation causes a loss of heat even from the bottom, and anchor ice will form. The first 

 '•ays of the morning sun loosens this, allowing it to rise to the surface. Barnes (1928. 

 p. lO.'n states that thi)usands of tons of this tvpe are added each year to the Gulf of 

 ''{•Lawrence, and similar contributions must be signiticant in all northern seas. Rodman 

 (1890. p. 16) relates an instance where anchor ice brought a tool box to the surface in 

 ine vicinity of X.un, Labrador, the box being recognized as one belonging to a ship lost 

 .years before in Iludsi n Strait, several hundred miles to the northward (see fig. 14, p. 27). 



