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 it> offshore side may add to the polar cap or it may remain in the 

 intermediate zone, or it may freeze a<rain in the re<rion of fast ice. 

 Outside the i)olar basin, however, paciv ice never l)uilds into heavier 

 foinis. but eitlier drifts southwai-d to melt or remains in the north to 

 survive lon<;er. Pack ice is distin<;uished from the polar cap ice 

 by its liiihtness. 



Outside the Arctic Ocean the (jualities that distinguish ])ack from 

 ])olar cap ice are not so api)arent and the farther south Ave go the 



Summer in the north polar Basin 



FiciRE 18. — An okl field of pack ice in the polnr resioiis sliowing tlie disentegrative 

 effects of tlie 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 Itussian hvdrographical expedition, 1010— 



irti.-.i 



smaller is the dill'erence. 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 Ixittom in tlmsc regions where swift-funning frigid currents 

 prevail, and at depths seldom exceeding 4(t to 4r> feet. During clear cold winter nights 

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

 rays <if the morning sun loosens this. allr)Wing it to rise to the surface. Barnes (1028, 

 p. l<»."ii states that thousands of tons of this type are added each year to the Gulf of 

 St. Lawrcnci', .ind similar contributions must l)e significant in all northern seas. Rodman 

 (ISOd. p. Ki) relates .in instance whi-re jinclior ice brougtit a tool box to the surface in 

 the vicinity of N.iin. Labrador, the box being re<'iiunized as one lielonging to a ship lost 

 years liefore in Iludsi.n Strait, seveial liundivd miles to the northward (see fig. 14, p. 27). 



