but the location and density of the dynamic 

 height isopleths indicates that the North Atlantic 

 Current as it passes across section A4 to 40-60 

 nautical miles north of its average position. 



The full dynamic topography survey provided 

 an opportunity to study the variation of the 

 transport and minimum temperature in the 

 Labrador Current as it flowed southward. Both 

 the total southerly transport and the Cold Core 

 transport (less than 2°C and 34.3°/ 00 ) have been 

 calculated (Figure 28). Only about half of the 

 Labrador Current at section A1B turned south- 

 ward to follow the eastern slope of the Grand 

 Banks. This southward flow remained relatively 

 constant between sections A2 and A3B at about 

 2.5 Sv. The transport values computed for these 

 sections are comparable in volume to the Labra- 

 dor Current transports measured in recent years, 

 but was below the long-term average of about 

 3.5 Sv (Bullard, et ul.. 1961). At sections A3B 

 MOD and A3C the transport inexplicably in- 

 creased. "When the flow had reached section A4. 

 the volume transport had decreased almost to 

 zero because of the unusually northerly location 

 of the North Atlantic Current. This had a dam- 

 ming effect on the Labrador Current prevent- 

 ing its usual turn to the west around the Tail 

 of the Bank. The ' minimum temperatures 

 measured in the Labrador Current were nearly 

 the same with the northernmost section showing 

 the coldest water and the southernmost section 

 having the warmest water as expected. Average 

 minimum temperature was about 1.2°C (Bullard, 

 et al. 1961). 



Although the effect on the Labrador Current 

 of the impingement by the North Atlantic Cur- 

 rent on the Tail of the Bank can easily be seen 

 in the contoured dynamic height field (Figure 

 •27), a temperature-salinity (T-S) graphical 

 analysis was made to confirm and explore the 

 presence of the blockade (Figures 29a and 29b). 

 From the T-S cuives it is evident that very little 

 volume with Labrador water properties reaches 

 section A4. The small volume of Labrador water 

 present on section A4 (all of which is below 

 approximately 25 meters in the three northern- 

 most stations) represents a volume transport 

 only 4% of that found on the next section, A3C. 

 Furthermore, whereas the minimum temperatures 

 of the upstream section. A3C, are -0.41°C, 

 -1.2°, and -1.4°C for stations 12112 to 12114, 

 the minimum temperatures for the comparable 

 stations 12089-12091 on section A4 are +1.2°C, 

 0.0°C. and -1.0°C. The salinity is quite similar 

 for all six stations at about 33.0%o to 33.2%o- 

 On A3C water with Labrador properties is seen 

 out to station 12106. 



Since the continental slope rises sharply to the 

 west, little of the volume transport from the 

 blocked Labrador Current can be transported 

 onto the shelf. Consequently, most of the volume 

 flow must be turned eastward to flow along with 

 the North Atlantic Current. This northward 

 migration of the North Atlantic Current on sec- 

 tion A4 is very similar to the conditions observed 

 during the 1973 Ice Patrol Season (Hayes and 

 Robe, 1978). 



31 



