CIRCULATION EAST OF THE GRAND BANKS 



First Cruise (7-21 April 1973) 



The first cruise revealed a current regime (fig. 

 2) in which the North Athmtic Current was 

 about 74 km farther north than usual (fig. 3) 

 and was running directly against the Tail-of-the- 

 Bank. This in turn forced a portion of the 

 Labrador Current up on the Banks proper. The 

 volume transport of the Labrador Current was 

 reduced to 0.3xl0**m'^s-' on section A-t from a 

 value of 3.5xl0''m^s-i on A3B. This dynamic 

 topography presented in Figure 2 indicates that 

 the excess Labrador flow had been incorporated 

 into a broad, flat dynamic trough. This trough 

 was the dynamic low region separating the 

 Labrador Current to the west and the North 

 Atlantic Current to the south and east. Extend- 

 ing from the Tail-of-the-Bank to the west and 

 approximately 47°'\V to the east and north to 

 approximately 45°N (fig. 2), this region con- 

 tained the dense water resulting from the mixing 

 of waters from the Labrador Current and those 

 from the North Atlantic Current. The eastward 

 limits of the dynamic low region were ill-defined 

 because operational considerations precluded ad- 

 ditional stations to the east. The conjecture at 

 the time was that this region extended a consid- 

 erable distance to the east. This situation was 

 confirmed by the presence, during this time 

 period, of large numbers of icebergs near 43°N, 

 48°W which did not appear to be moving farther 

 southward. An anticyclonic ring, with a tangen- 

 tial velocity of 28 cm s % was located at 43°40'N 

 and 47°.50'W, near the center of tlie trough. At 

 the northern end of this dynamically flat region, 

 at 45°40'N, was an area where a large portion of 

 the Labrador Current branched from the main 

 flow and moved eastward, south of Flemish Cap. 



Second Cruise (18-24 May 1973) 



By the 18th of May the situation had dra- 

 matically changed (fig. 4). The North Atlantic 

 Current had receded somewhat toward the south 

 but continued to keep the surface strata of the 



Labrador Current up on the Banks. The May 

 flow of the Labrador had increased from the 

 April cruise period at section A4 to l.OxlO^m^s"'. 

 In the same period the flow upstream at section 

 A3C was 2.0xlO<^m''s-S or more than 1.5xlO«m^s-^ 

 less than in April. The most visible change was 

 the appearance of a meander of the North At- 

 lantic Current which had an amplitude of 220 km 

 and a wave length of 165-185 km. Just to the 

 north of the anticyclonic lobe of this meander 

 was an anticyclonic ring, centered at 44°15'N 

 and 47°35'W, which had nearly the same dynamic 

 characteristics as the one seen in April. Its sur- 

 face tangential speed was 23 cm s-^ It was tempt- 

 ing to say that they were one and the same. The 

 latter had a thermohaline structure a full 2°C 

 higher and 0.4°/„„ more saline. The movement 

 toward the southwest was not inconsistent with 

 the probable motion of anticyclonic rings. The 

 higher temperature and higher salinity could be 

 accounted for by seasonal warming and mixing. 

 The unknown factors here were the speed with 

 which these anticyclonic rings move through this 

 area and in what area or areas were they gen- 

 erated. It is possible that the large anticyclonic 

 meander in Figure 4 was either the anticyclonic 

 ring seen during the April cruise or a new anti- 

 cyclonic ring being formed. 



Directly to the east of the large anticyclonic 

 meander in the North Atlantic Current was a 

 cyclonic meander of comparable size. This 

 meander occupied an area not surveyed com- 

 pletely during the April cruise. What was de- 

 veloping here was a situation favorable to the 

 transport of icebergs accompanied by their own 

 cold water pool across an oceanic frontal system. 

 If cyclonic meanders become cold water cyclonic 

 rings south of the warm North Atlantic Current, 

 then an explanation is available for the presence 

 of the southernmost icebergs, in late May 1973, 

 at 40°40'N, 49°W, well south of the North At- 

 lantic Current. 



