SUMMARY 



1. Three Ice Patrol cruises, April, May and 

 June-July 1973 were analyzed. During the first 

 cruise the North Atlantic Current was found 

 74 km farther north than usual and it impinged 

 on the Tail-of-the-Bank forcing the Labrador 

 Current up on the Bank. The much stronger 

 North Atlantic Current appeal's to be capable of 

 overwhelming the weaker Labrador Current and 

 turning it eastward or westward. By the time of 

 the second cruise the North Atlantic Current had 

 receded somewhat toward the south and the flow 

 of the Labrador Current at A4 had increased 

 threefold from the previous cruise. The third 

 cruise which included three intensive dynamic 

 surveys between 43°30'N and 45°N showed a 

 continuation of the southward progression of the 

 point of reversal of the Labrador Current. This 

 in turn affected the area enclosed by the dynamic 

 trough separating the two main current systems, 

 and consequently, the drift of icebergs in that 

 region. 



2. During the May cruise the formation of a 

 large cyclonic meander was noted in the North 

 Atlantic Current. The possible production of 

 cold water cyclonic rings to the south of the 

 warm North Atlantic Current by these meanders 

 could explain the presence of icebergs far to the 

 south of this warm water barrier. 



3. Direct current measurements were made at 

 two locations for two separate time intervals. 

 The current meter records exhibited low mean 

 speeds of 2 cm s-^ and 5.3 cm S"^ toward the south- 

 west. Maximum speeds were 14 cm S"^ and 15 

 cm S"^ respectively with a single short period burst 

 of 25 cm S"\ Small reversals in current direction 

 were observed to average 2 cm s"' and 1 cm S"'. 

 The only identifiable periodic component was the 

 lunar semidiurnal tide which appeared to be 

 intermittent and, thus, did not seem to be phase- 

 locked to the equilibrium tide. Comparison of 

 the geostrophically determined surface currents 



with the directly measured currents at depth in- 

 dicates that Labrador Current measurements are 

 probably underestimated by 10-30% by the 

 methods presently used. 



4. Calculations of geostrophic current and 

 volume transports on the shelf and slope of the 

 Intensive Dynamic Surveys indicate that the 

 method of extrapolation of temperature and 

 salinity values into the Bank causes an inherent 

 error in the estimate of cross slope flow in sta- 

 tions shallower than the reference level. The 

 along slope inclination of isosteric surfaces is 

 carried into the Bank by this method and, there- 

 fore results in an apparent flow into or out of the 

 subsediment boundary of the continental slope. 

 The overestimation of on/off slope currents may 

 be compensated for by calculating the component 

 of flow normal to the slope between adjacent 

 sections with level isosteric surfaces below the 

 ocean/sediment interface, and making that the 

 input to the iceberg drift computer program. 



5. A detailed analysis of volume ti'ansport 

 calculations made during the three Intensive 

 Dynamic Surveys in June and July revealed that 

 in a 21 day period there was a simultaneous in- 

 crease in Labrador Current and North Atlantic 

 Current transport which drove the Labrador 

 Current up onto the Bank. This was followed 

 by a recession of the North Atlantic flow, either 

 by reduction in transport or, more likely, a shift 

 in the axis of the stream which allowed a greater 

 portion of the Labrador Current volume trans- 

 port to flow out of the southern end of the survey 

 area. The progression of the crest of a meander 

 through this area would also account for the 

 dynamic conditions described, but could not be 

 supported because of the lack of data to the east 

 of the survey. 



Acknowledgement : R. Schultz, .1. Krezoski, M. Alles, 

 and B. Peters are thanked for their work in processing 

 of the data in this report. 



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