have been designated A through F and are presented as figures 20 to 25 

 inckisive. Their geographical locations have been indicated by cor- 

 responding letters on figure 19. It will be noted that section F does not 

 show the marked division of the Labrador Current into the two branches 

 shown in section D. As mentioned earlier in the narrative of the cruises, 

 two gales passed through the area between the occupation of sections D 

 and F. Although these gales may have had a tendency toward erasing 

 the complicated temperature pattern found in section D it is considered 

 that the mixing effect of these gales did not extend below about 50 meters 

 and at deeper levels the general conditions shown in figures 23 and 25 

 existed simultaneously. 



The dynamic topographic chart resulting from the June survey is 

 shown in figure 26. From the practical standpoint of Ice Patrol, the most 

 important feature shown in this chart is the diversion eastward of the 

 Labrador Current north of latitude 44° N., by the persistent thrust of the 

 Atlantic Current salient just southward of that latitude. In the area 

 between the 100- and 1,000-fathom curves immediately northward of the 

 44th parallel the dynamic isobaths indicate weak residual currents and a 

 situation where it would be possible but improbable that a shallow draft 

 berg could continue southward to and beyond the Tail of the Banks if it 

 experienced easterly winds and passed through the critical area just north- 

 ward of the 44th parallel near the edge of the banks when the tidal cur- 

 rents were setting southwesterly. At the southwestern edge of the 

 charted area there is to be seen the northern end of the colder mixed 

 water eddy system found in this vicinity in the May survey. The vigor 

 of the Atlantic Current border was greater during the June survey than 

 during the May survey by inference from the greater westward extension 

 of its thrust toward the banks. However, the Labrador Current still 

 maintained sufficient strength to extend its elTect eastward almost to the 

 45th meridian just northward of the 44th parallel. Experience has in- 

 dicated that the persistence of such circulation patterns, once established, 

 is relatively great and that the direction of the progress of eddies of 

 mixed water between the Labrador and Atlantic Currents is similar to 

 that of the latter. These generalities, combined with the seasonal de- 

 crease in the number of bergs immediately upstream available for trans- 

 portation, led to the conclusion that the threat of ice endangering the 

 U. S.-European steamer tracks would, for the rest of the season, be 

 confined to such bergs as had already reached positions south of lati- 

 tude 46°30' N. 



In past years, observations made in the Grand Banks region have 

 been used to determine characteristic temperature-salinity relationships 

 with the result that not only did the Labrador and Atlantic Currents 

 emerge as water masses but the observations from the mixed water showed 

 a small enough scatter from a characteristic T-S curve so that it seemingly 

 approached a water mass. L^nfortunately the numerous winch break- 

 downs experienced in 1948 so seriously limited the extent of the area 



75 



