12 



The bergs, about the liist of April, which failed to drift south of 44° 

 N. were comparatively small ones whose mass was floating entirely 

 in the fairly homogeneous surface layers under the influence of the 

 Avesterly gales, Avhich were prevalent at this time. The}^, therefore, 

 moved to the eastward out of the current into the dead water and 

 there melted. It is possible, also, that during this time there was a 

 slow change in the existing system of currents in this area. After 

 April 10 all the bergs drifted rapidly south in accordance with the 

 successive current maps (figs. 19 to 21). 



In some years the ice menace is brought to an end by the warm 

 Atlantic water pushing northward close to the tail of the Banks and 

 also encroaching from the eastward about in latitude 44°30' N. to- 

 ward the shoal w^ater. Both these movements effectively choke off 

 the cold stream and prevent the further southward movement of ice. 

 As can be seen by the June current map this was not the case this 

 year. (See fig. 21.) At the beginning of the seventh cruise, June 

 4 to 18, all surface conditions, the steady warming of the surface 

 water and even the distribution and movement of the bergs, indicated 

 an early termination of the Patrol. The current chart completed 

 June 10, however, showed a marked southerly current along the 

 eastern slope of the Grand Banks from latitude 46° N. to latitude 

 43° N. A berg entering this current at latitude 45° N. would be 

 carried in 6 days to the tail of the Banks and menace the trans- 

 Atlantic lanes. A small berg sighted on June 9 did, in fact, enter 

 this current and proceeded south at 12 miles per day in exact ac- 

 cordance with the current chart. This berg was, however, too small 

 to survive the journey. This showed how surface conditions may 

 lead to erroneous conclusions as to the true situation and illustrated 

 nicely the inestimable value of these dynamic current maps. With 

 this information at hand, it seemed difficult to explain why, although 

 the area was repeatedly searched, no ice was found in this current, 

 or why, in fact no known ice had drifted south of latitude 44°30' 

 N. since JNIay 12. The solution undoubtedly lies in two important 

 factors: First, the c^n-rent system north of latitude 46° N., as indi- 

 cated by the June current map, was weak and did not tend to carry 

 ice directly to the narrow band of southbound water; second, from 

 June 8 to 18 no bergs were reported north of latitude 46° N. between 

 the Banks and Flemish Cap. The combination of weak currents and 

 lack of ice to the north made it extremely unlikely that any more 

 ice would come south via this route. The Patrol, however, located 

 a medium sized berg on June 18 close to the 100-fathom curve in 

 latitude 45°26' N. on the western edge of the cold current. It seemed 

 that this berg had not come from the north of 46° N. but almost 

 certainly had been blown off the Banks by the westerly gale of June 

 17. The berg was solid and of deep draft and therefore moved 



