32 MARION EXPEDITION" TO DAVIS STRAIT AND BAFFIN BAY 



Siberia indicates that the wind is a major factor in keeping the 

 polar cap ice in motion. 



The second famons })olynya was discovered and described by Peary 

 (1907, p. 97) as the '' Bio; Lead '' (see ti«!:. IG, p. 31). It coincides in 

 position very closely with the continental edge rnnning along the 

 eighty-fourth parallel from Grant Land to Cape Bridgeman, Green- 

 land. The " Big Lead '" is smaller than the Siberian ])olynya. being 



A floeberg 



FiotRE 17. — A floeberg (see p. 30) in the northern part of the Hall Basin between 

 Ellesmere Land and Greenland. Its s'eographical position indicates its origin as 

 an old pressure ridge. Floebergs, although from an entirely different source, are 

 often mistaken for icebergs. Some of the bergs drifting in the North Atlantic 

 may well be floebergs from the polar basin. (Photograph by L. Koch, 1929.) 



seldom over a mile or more in width vet having an estimated length 

 of at least WO miles.-'' 



PACK ICE 



Although seamen usually refer to any Hat ice drifting at sea as 

 " field ice," such a practice is not recommended because it tends to 

 confuse one not thoroughly familiar with ice terms. It is better to 

 follow the classification of Priestley (1922, p. 393), wdio defines pack 

 ice as any sea ice Avhich has drifted from its original position under 

 the influence of winds and currents. The word " pack '' does not 

 necessarily mean the ice is tightly packed together, because the pack 

 may have large or small areas of open water, as the case may be, 

 within its bounds. Its northern sources are the fast ice and the 



-"Koch (1926, p. 102) is of the opinion that the "Big Lead" marks the line of shear- 

 ing of the ice cover while the northward part, out in the deep polar basin, drifts east- 

 ward the southern side does not, partly because there is no definite gradient current in 

 over the shelf, but chiefly because it is prevented by the promontory formed b.v the north 

 Greenland coast. This theory is supported not only b.v the .iamming of the ice between 

 Greenland and Grant Land, but also by a marked change in the age of the material. Thus 

 old ice alone was observed by him south of the ■" Big Lead." Koch also observed a west- 

 erly current running in between the ice floes along the northern coast of (Jreenland west 

 of Cape Bridgeman. 



