87 



considerable gain to tlie northeast in the western part of the area. 

 This was not simply a case of only the northern edge of the Gulf 

 Stream spreading out to the' north for its northward migration was 

 backed up by the major portion of the current as is borne out by the 

 fact that the volume of flow computed between stations 2983 and 

 2993 with reference to the 1,500-decibar surface was 49.0 million cubic 

 meters per second. This advance of the Gulf Sti^eam was not caused 

 by any decrease in the amount of cold mixed water supplied by the 

 Labrador Current but instead the advance took place in spite of the 

 continued growth of the quantity of cold water. This is evidenced 

 by that part of the map eastward of about longitude 50° W. Here 

 we see the northward hump in the isobaths displaced eastward from 

 about longitude 49°45' W., to about longitude 49°00' W. Eastward 

 of this northward hump in the isobaths the further southeastward 

 extension of the cold mixed water compensates for the reduction in 

 area covered by this type of water in the western part of the map, 

 the isobath of 971.04 dynamic meters having been extended south- 

 eastward some 60 miles. The second part of this survey was probably 

 made at about the time of the extreme southeastward extension of 

 the area of cold mixed water. 



The current map resulting from the fourth survey is shown in 

 figure 23. Although following its seasonal diminution the Labrador 

 Current was stUl flowing with strength and south of the Banks reached 

 a western limit of about longitude 51°30' W. No comparison with 

 earlier conditions can be made in the area north of latitude 44°N., since 

 this region was not covered in the previous survey. The large quan- 

 tity of cold mixed water whose pronounced southeastward extension 

 had characterized the entire season had begun its northward retreat. 

 The southern extreme of the isobath of 97 LI dynamic meters which 

 had been well south of latitude 41° N., and outside the limits of the 

 surveys since early April had moved northward to about latitude 

 41°20' N., and the end of the tongue of cold mixed water had inter- 

 twined cyclonically with a tongue of Atlantic Current water between 

 latitudes 42° N., and 43° N. This intertwining pattern is considered 

 to be a transitonal stage in the assimilation of the cold mixed water. 

 The next stage is probably the establishment of a closed whorl. The 

 current pattern of mtertwining tongues shown in figure 23 was veri- 

 fied by the drift of a berg in this vicinity. Attention is called to this 

 feature of the map because, although the existence of such current 

 patterns as transitory phenomena has long been suspected, this is the 

 first time that such a clearly defined and unmistakable pattern of 

 this type has been mapped in the vicinity of the Grand Banks. 



In continuation of an investigation of the seasonal variations in the 

 volume of flow of the Labrador Current in the Grand Banks sector, 

 an analysis was made of all the occupations of sections T, U, and W 



