pattern shown in figure 16 and indicated that many of the bergs 

 ended their southward progress in the vicinity of the 44th parahel, 

 being assisted by prevaiUng southwesterly winds in crossing the 

 dynamic isobaths eastvvard into the nortliward moving margins of 

 the Atlantic Current and mixed water which dominated the south- 

 easterly part of the surveyed area. The current chart was inter- 

 preted to mean that bergs continuing in the Labrador Current south- 

 ward of the 44th parallel could, with favorable winds, cross seaward 

 into the Gulf Stream system anywhere from longitude 49° W., to 

 53° W. Those following the dynamic isobath of about 970.98 were 

 considered to represent the greatest threat to steamship traffic fol- 

 lowing the United States-European tracks of the North Atlantic 

 Track Agreement. It was in this region south of the Tail of the 

 Banks between about longitudes 49°30' W., and 51°00' W., that cold 

 mixed water extended southward beyond the limits of the survey. 

 While the possibility of bergs attaining extra southerly positions may 

 have been greater prior to the period of this survey, it was considered 

 that the threat could increase again with any waning or north- 

 easterly shift of the salient of Atlantic Current water which during 

 this survey was pointed toward approximately 45° N., 49° W. 



The d\niamic topographic chart resulting from the second survey is 

 shown in figure 17. By comparison with figure 16 it w^ill be noted that 

 the area southward of the Grand Banks occu])ied by cold mixed water 

 had decreased somewhat, probably through the blocking efl"ect of the 

 Atlantic Current salient. In each of these surveys this salient had the 

 effect of reducing the volume of Labrador Current water reaching the 

 Tail of the Banks and diverting some of this water eastward and north- 

 easterly north of about the 45th parallel. Although the salient had 

 degenerated somewhat at the time of the second survey it was still 

 effective and the western boundary of northward moving w^ater was 

 closer to the banks at the surface than during the first survey. The 

 eastward diversion of Labrador Current water by the salient is con- 

 sidered responsible for the formation of a Labrador Current salient 

 wdiich carried bergs to the area east-southeasterly of 45° N., 45° W., 

 during early May. By the time of this second survey the Labrador 

 Current salient had been somewhat reduced from its earlier maximum 

 southeastward extension. It was considered, however, that this area 

 could again become one of potential hazard to the United States- 

 European Track Agreement tracks if the Labrador Current increased 

 in volume of flow or if it maintained its volume and the Atlantic 

 Current salient strengthened. 



The dynamic topography foimd during the third survey of the 

 Gi-and Banks region (fourth cruise) is shown in figure 18. Here 

 Atlantic Current water was again pressing in toward the edge of the 



66 



