ter, while the offshore band over the slope pos- 

 sesses warmer (>1°C), more saline (>34.0%o) 

 water, greater velocities, and a greater thick- 

 ness. 



A chart of sea surface dynamic topography 

 relative to 600 decibars was prepared for the 

 survey area to estimate the component of mo- 

 tion of the study iceberg resulting from ocean 

 currents. Defant's method of estimating the 

 level of no motion by comparing the differences 

 in dynamic height between pairs of stations 

 at varying pressures (Defant, 1961) was ap- 

 plied to several of the deeper stations in the 

 area surveyed, and 600 decibars was cho.sen as 

 a reference level. The 600 decibar level al.so was 

 a suitable compromise between the deeper levels 

 previously used and shallower levels desired to 

 reduce errors in the integration procedure in 

 shallow waters. Defant (1961), on a chart of 

 the entire Atlantic Ocean, presented a depth 

 exceeding 1900 meters as a suitable reference 

 level for the survey area. Previous work done 

 by the Oceanographic Unit in the region utilized 

 a reference level of 1500 decibars. 



In the area surveyed, the slope band of the 

 Labrador Current appears on the chart of 

 dynamic topography (fig. 2) as a concentra- 

 tion of contours near the eastern ends of the 

 occupied sections. The shelf band is exhibited 

 most clearly by the presence of negative-tem- 

 perature water centered at about 75 meters 

 (figs. 11, 13, 15, and 17) and appears to be 

 split into several bands. 



The trajectory of the iceberg under study was 

 generally consistent with the dynamic topogra- 

 phy of the sea surface relative to 600 decibars 

 (fig. 2) until 4 August when it began moving 

 westward again.st the geopotential gradient of 

 an anticyclonic gyre. On 6 August the iceberg 

 began moving northwestward against the cir- 

 culation of the gyre. This seemingly anomalous 

 motion probably is the result of a change in the 

 wind observed at this time. The wind shifted 

 from about 320° at approximately 7 knots to 

 170 at approximately 15 knots and continued 

 to blow at this velocity for the next 28 hours. 

 The final part of the trajectory up to 1900Z 

 9 August is difl^cult to explain in terms of the 

 observed winds or dynamic topography. The 

 relationship between this portion of the ice- 

 berg's trajectory and the dynamic topography 

 should be inferred with caution because this 



portion of the trajectory occurred midway be- 

 tween two lines of stations (sections B and C) 

 and two weeks after the completion of the 

 oceanographic survey. 



Because of the complexity of the surface dy- 

 namic topography and the uncertainty of the 

 dynamic method in regions shallower than the 

 reference level, an investigation of the region 

 by i.sentropic analyses was conducted (figs. 

 3-10). It was recognized that in a compara- 

 tively shallow region such as the study area, 

 where vertical mixing probably is extensive, 

 isentropic analysis is not an entirely suitable 

 tool of investigation either, but the analysis 

 was performed to see if it would corroborate 

 the results attained by the dynamic method. 



Comparison of the variation of depth of the 

 27.00 0-, and 27.25 o-, surfaces (figs. 8 and 10) 

 with the sea surface dynamic topography rela- 

 tive to 600 decibars (fig. 2) indicates agreement 

 in the basic features of the current regime. 

 Although this agreement might be expected 

 because the distribution of sea surface dynamic 

 heights and the configuration of density sur- 

 faces are both functions of the mass distribu- 

 tion, it is still encouraging that such agreement 

 was found in view of the approximations used 

 to integrate the dynamic height along the 

 shoaling sea bottom. 



The chart of dynamic topography (fig. 2) in- 

 dicates a weak cyclonic gyre centered on the 

 third station (station 10349) fi-om the western 

 end of section C. That this gyre plays a more im- 

 portant role in the circulation of the area than 

 is apparent from its manifestation at the sea 

 surface may be appreciated after examining the 

 distribution of density along section C (fig. 21). 

 A doming of the density surfaces, with its axis 

 inclined to the west, arises out of a bathymetric 

 depression centered on station 10350. The dome 

 is associated with a cyclonic vortex whose 

 speed of rotation below the pycnocline (located 

 at about 20 meters) decreases with depth. 



The vortex appears to be a direct consequence 

 of a depression in the shelf at 53°N 53.5°W 

 (fig. 1), near .stations 10348-51 (figs. 15, 16, 

 and 21). The bathymetric chart suggests that 

 the sill depth is greater to the east of this 

 depression north of section C. Vertical sections 

 of temperature, salinity, and density through 

 the bathymetric depression (figs. 15, 16, and 

 21) revealed an incursion into the depression 



