As the T-S characteristics found in the Grand Banks region fluctuate 

 slightly from year to year figure 23 has been prepared to show the amount 

 of this fluctuation as it affects the density at the different levels in the 

 Labrador Current water. The densities shown are the values of a t 

 corresponding to the average temperature and average salinity for the 

 particular level and year. It is of interest to note the degree of fluctua- 

 tion within the 10-year period 1948-57 used for the normal curve shown 

 in figure 22. Similar yearly averages for some of the levels are available 

 for the 8-year period 1934-41 and are also shown in figure 23 to show 

 the changes which have occurred over the longer period. Thus it 

 appears that in recent years the Labrador Current water has been 

 increasing in density in the upper 200 meters and decreasing in density 

 at levels below that. The net effect of these density changes on the 

 average dynamic height of the 50-decibar surface relative to the 1,000- 

 decibar surface shows no consistent trend. 



The position of the steep horizontal temperature gradient at the sea 

 surface which occurs near the outer margins of the Atlantic Current in 

 the Grand Banks region is of great practical importance in determining 

 the southern limits of berg drifts. This steep gradient is called the cold 

 wall. Since it is not always vertical and since we are concerned with 

 its location in a layer whose thickness is commensurate with the draft 

 of an iceberg, in studies of its fluctuations its position has been taken as 

 the horizontal projection of the line along which water of 34.95 °/ 00 

 salinity corresponds to a temperature of 6° C. The position of the cold 

 wall has been delineated thus for each survey which has included this 

 area. To enable the numerical expression of its position, or its retreat 

 from or advance toward the Grand Banks, the area between it and 

 certain fixed rhumb lines has been used. These rhumb lines are the 

 45th parallel from the cold wall westward to the 49th meridian, the 49th 

 meridian from 45° N. to 43° N. and a line from 43° X. 49° W. through 

 42° N. 47° W. extended to the cold wall. 



It is presumed that the position of the cold wall is determined by the 

 relative strengths of the Labrador Current and the Atlantic Current. 

 For each survey for which the position of the cold wall can be delineated, 

 the salinity, temperature and velocity distributions, as well as the 

 volume and heat transports are available for the Labrador Current 

 entering the area from the northward past the 45th parallel. Using 

 what are believed to be realistic values of average velocity distribution, 

 it has been further assumed that each million cubic meters per second 

 of volume transport of the Labrador Current entering the area will 

 require a sea surface area of 10,000 sq. kilometers. The area between 

 the cold wall and the rhumb lines has therefore been reduced by such a 

 proportionate amount to give a remaining adjusted area, A, whose size, 

 it was expected, would be related to forces associated with the North 

 Atlantic eddy and consequently with the Atlantic Current which makes 

 up the outer margin of the eddy in the Grand Banks sector. 



93 



