SCIENTIFIC EESULTS 



25 



XORTII I'OI.AH <-AP ICE 



rolnr cai) \rv is the end product of all the forces wliicji (Icvcloi) a 

 very stroii<:-, massive ice cover in the central north ])oljir sea. This 

 (overiii^^ constitutes about 70 })er cent of tiie pohu- basin: ap|)i-oxi- 

 mately 2,000,000 square miles. Fields and fioes break away from the 

 iiiaiii polar core, either to mix with the inshore ice over" the conti- 

 nental shelves, or to be discharoed thr()u<>:h one of the several ocean 

 straits. The <rreat sea-ice ca]). upon closer examination (see fi^r n 

 p. -20). has the same «:eneral shai)e as the polar basiu. with its mar<rin 

 closely i)arallehn<r the course of the l.OOO-meter isobath. Like the 

 deeper ])art of the polar basin, the elliptical-shaped cap lies nnich 

 closer to the Greenland-North American side than it does to Europe 

 and Asia, with its lon<j: axis runnino; from Spitsbero-en to Point 

 Barrow, its center, often called the pole of inaccessibilitv (see fio- 14 

 p. L'T). offset about 400 miles toward Alaska. '^' ' 



Polar cap Ice 



■m,ii -fl^e polar cap ice at the North Pole on May 11 



jm.iii pdlyiiyas are stated to be toiiiul every 5 to ^ "^ 

 from fh(. dirigible Xorcje by L. EHesworth ) 



l'H:ri(i-: i:;. 



10 miles. 



1!»2G. In summer, 

 (I'botograph taken 



Ihis hub of the permanent sea ice is continuallv fed bv pack ice 

 ''••uuml Its i)eriphery, ami reinforced bv accreti()nal freezin<-- and 

 Miowlall all at a rate durino- the last centurv at least, equal to the 

 '•oiHbined processes of melting, crushin<r, and* discharge through the 

 Mirums exits. Freezing on the underside of the cap progresses 

 tiuonghoiit nine months of the year, most rapidly during the winter, 

 ivxaimnation shows that the underside of an ice "sheet is often rough 

 :"'« brush-like in character. This is the transition zone between ice 

 ■iiKl water. The thickness of the solid sheet depends niainlv upon 

 ;\o tactors, viz, the condition of heat and the ma<:nitude" of the 

 '••rces that raft and i)ile up the ice. Sea water solidities in the 

 -VKtic ()cean to an average depth of Cy. feet.^-' But winds and cur- 

 was ll*'f^f^V?V.';^d'l'*^F"!^^ "* hummoeked ice observed by Nansen in the Arctic Ocean 

 ""■ fntire cm-a- it V "^ '^•^ ^^*^'' tl^«" ^^^'^ of 8 feet ns the estimated mean thickness of 

 Mds frep of n..'p...„!. ^"P°" n<)T2). north of Banks Land, reports the thickness of old 

 i'f-e ot piessure ridges and ratting, as 12 to 14 feet 



