Table II 



Volume transport through the east-west 

 leg of standard section A2 in x lO^m.Vsec. 



* (<2.0°C., <34.3%o) 



Standard Section A3 



The three occupations of standard section A3 

 revealed changes of as much as 10 dynamic 

 centimeters in the dynamic topography (fig. 

 17). The two most dramatic changes were the 

 increase in dynamic height on the Grand Banks 

 between 22 April and 24 May and the decrease 

 of 10 dynamic centimeters in height in the dy- 

 namic trough between 24 and 29 May. A similar 

 increase in dynamic height over the banks was 

 observed in 1965 when the dynamic height at 

 the inboard station of section U (nearly the 

 same as standard section A3) increased about 8 

 dynamic centimeters in 9 days (Kollmeyer et al., 

 1966). 



The decrease in dynamic height in the dy- 

 namic trough between 24 and 29 May resulted 

 in an unusually strong gradient of about 2.0 

 dynamic centimeters per nautical mile. This cor- 

 responds to a geostrophic current of over two 

 knots; a geostrophic velocity of 2.5 knots was 

 computed between stations 10748 and 10749. 

 While a current of this strength is unusual, sim- 

 ilar intensifications have been observed on 9-19 

 June 1964 (Kollmeyer et al., 1965) and on 25 

 May-5 June 1961 (Bullard et al., 1963). Adja- 

 cent to the dynamic trough the continental shelf 

 edge rises to within 100 m. of the surface, is 

 slightly concave, and runs in a nearly north- 

 south direction (025°-205°T). Since the conti- 

 nental slope rises from a depth of 3000 m. to 

 100 m. within 35 miles, it forms a boundary for 

 the ocean at this location. 



The eff"ect of the surface wind on the currents 

 at this oceanic boundary was investigated. Ex- 

 amination of six-hourly, surface, hemispheric 

 weather charts for this region revealed that the 

 mean wind direction was 051° true, and the 



mean wind speed was 23 knots during the 96 

 hour period preceding the second occupation of 

 the section. According to Ekman's theory, the 

 wind induced mass transport is 90° to the right 

 of the wind. Thus the water in the surface layer 

 should have been transported toward the con- 

 tinental shelf in a direction within about 25° of 

 perpendicular to the continental slope. This 

 transport would have produced downwelling and 

 intensification of the Labrador Current. 



Comparison of the temperature and salinity 

 profiles for 23 May (fig. 51) with those of 29 

 May (fig. 52) revealed that the contours at the 

 surface moved shoreward while the contours 

 near the continental slope moved downward. 

 Thus, the transport towards the coast did result 

 in downwelling along the continental slope and 

 a change in the distribution of mass. The rela- 

 tively fresh (low density) water in the surface 

 layer (<100 m.) was driven shoreward resulting 

 in an accumulation on the Grand Banks and 

 along the continental slope (figs. 51 and 52). 

 The water of greater density which was dis- 

 placed, moved farther offshore, thus further re- 

 ducing the height of the dynamic trough. This 

 caused, in part, the change of over 10 dynamic 

 centimeters noted earlier. The change in the dis- 

 tribution of mass was apparent in the density 

 profiles for 23 May (fig. 18) and 29 May (fig. 

 19). The sigma-t contours above the continental 

 slope became much steeper on 29 May with the 

 sigma-t contours near the continental shelf mov- 

 ing downward and those further offshore mov- 

 ing upward. Vertical velocities of 8 m. per day 

 (0.009 cm./sec) were inferred from the displace- 

 ment of the sigma-t contours. A similar vertical 

 velocity of 0.007 cm./sec was observed in an up- 

 welling situation off the Oregon coast in May 



