156 MAKION EXPEDITIOX TO DAVIS STRAIT AXD BAFFIN" BAY 



Many direct observations on the rate of movement of icebergs 

 south of Newfoiindhmd have been made by the ice patrol, and, siip- 

 j)orted by niimei'ous current surveys run simultaneously, furnish us 

 with accurate information. Any student interested in examining 

 this matter in detail is referred to the tile of annual reports of the 

 l)atrol. (See p. 150.) The records may be summarized as follows: 

 During March the average rate is to 7 miles per day, and 10 to 17 

 miles per day from April to June around the soutliern parts of the 

 bank. The bergs on the northern edge of the Gulf Stream move 

 fastest of all, i. e., at rates of 19 to :^>() miles per day. In late summer 

 the ice drifts more slowly, but at all seasons the rates are subje;-t to 

 considerable variations from week to week or even from day to day. 

 The velocities of ocean currents, especially at this junction region, are 

 constantly changing, changes reflected by the drifts of the iceljergs. 

 For examj)le. on one occasion a group of bergs on the east side of the 

 (xrand Bank just north of the Tail suddenly increased their rate of 

 drift overnight from 7 miles to 28 miles i)er day. (Smith. 1921, p. 

 7().) If the current can accelerate suddenly to such a high rate off 

 the Grand I^ank. may not such events occur equally along the Lab- 

 rador shelf ( 



The ice patrol's investigations have revealed the following features 

 in the circulation south of Newfoundland affecting the behavior of I 

 icebergs : 



(a) An elliptical depression in the sea surface nuikes a slow 

 cyclonic vortex in the surface layers off the southwest slope of the 

 Grand Bank west of the Tail. This '• low.'" covering an area of over 

 2.000 square miles, was fii-st discovered l)y chance in 1921 by follow- 

 ing an iceberg as it made tlie circuit. 192() the " low," apparently 

 similar in character to an atmosphere cyclonic depression, was accu- 

 rately charted by several successive dynamic surveys (see Smith, 

 1927. pp. 109. 112, and 115) prevailing throughout the season. It 

 was present also in April. 1927. but disappeared early that May. 

 Bei'gs are often carried northwestward along the slope in the north- 

 ern semicircle of this eddv and sometimes a complete circuit of H65° 

 in its pei'iphery. (See fig. 101.) 



(h) Sometimes the counterclockwise eddy is wanting: displaced by 

 the Gulf Stream encroaching toward the Tail of the bank. An 

 earlier series of current maps (Smith 1927b) shows the development 

 of such a phenomenon in the first week in May, 1927. As long as 

 the Gulf Stream maintains this position ice is blocked from pursu- 

 ing a course west of the Tail. (See lower riglit-liand sketch, fig. 

 101. also overlay figs. 105 and 106.) 



{(■) The cold and warm curi-ents after meeting off the Tail of the 

 Grand Bank [)roceed southeastward in a parallel set to tlie vicinity 

 of latitude 41 \ longitude 47°. where the streams bend sharply to the: 

 left. The existence of this cul-de-sac of the current, and occasionally 

 for bergs, 150 miles southeast of the Tail shows evidently tliat the 

 drift is affected bv tlie bottom configui-ation. even to as gi-eat a depth 

 as 4.000 meters. " (Sec Smith 1922. Chart H and lowci- Icft-iiand 

 sketch, fig. 100.) 



{(I) The ice patrol suspected for several years that the (Julf 

 Stream after turning sharjjly northward on the forty-seventh merid 

 ian pressed in toward the baidv up the submarine emliayment between 



