The density is less in each water mass level for level in the recent 

 period than in the earlier period. In Labrador Current water the 

 postwar observations show fresher and colder water at the levels 

 above 600 meters and fresher water of about the same tempera- 

 tures at the levels below 600 meters. The postwar mixed water 

 is fresher and warmer at all levels. In Atlantic Current water 

 the postwar observations show saltier and warmer water at levels 

 above 600 meters and fresher and warmer water at 800 meters 

 and below. The prewar salinity inversion with a minimum at 

 about 5.5° is not present in the postwar curve. The salinity differ- 

 ence between the prewar and postwar curves at 1,000 meters is 

 about 0.02 °/oo, being somewhat less in Atlantic Current water 

 and somewhat more in Labrador Current water and mixed water. 

 While it is possible that this may represent a shift in instrument 

 standardization it is considered to be at least partly a real change 

 in salinity of the water. The temperature changes are considered 

 to be real. The differences in the curves for Atlantic Current water 

 are not as significant as those in the curves for the other two 

 water masses since most of the surveys do not get far enough 

 into the Atlantic Current to get a representative sampling of the 

 entire current. 



In figure 17 the T-S relationships found in 1956 are compared 

 with the means for the period 1948-56. It will be seen that in 

 1956 the Labrador Current water was denser, warmer and saltier 

 than the mean at levels above 600 meters and was the same as 

 the mean at levels below 600 meters. The mixed water was denser 

 and saltier than the mean at all levels and colder above about 150 

 meters, warmer from 150 to 800 meters and about the same below 

 800 meters. The Atlantic Current water was denser, saltier and 

 warmer than the mean at all levels. 



The position of the cold wall was estimated for each of the first 

 two surveys, using as a criterion the horizontal projection of the 

 line along which a temperature of 6°C corresponds to a salinity 

 of 34.95°/oo- To permit a simple numerical expression of the posi- 

 tion of this cold wall with respect to its advance toward or retreat 

 from the Grand Banks we have used the area between it and the 

 fixed rhumb lines of the 45th parallel, the 49th meridian from 

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

 42° N., 47° W., extended. This area was 7.7 and 7.5 (x 10 4 square 

 kilometers) for the first and second surveys respectively. Reason- 

 ing that the position of the cold wall is determined by the relative 

 strengths of the Labrador Current and the Atlantic Current the 

 effect of the latter is approximated by adjusting the area by 10 4 

 square kilometers for each 1 - cubic meters per second of Labrador 

 Current entering the area past the 45th parallel. The resulting 



46 



