746 



BULLETIN OF THE BUREAU OF FISHEEIES 



expected there, raising the surface value from 32.5 to 33 per mille over the western 

 arm of the basin from the one month to the next. An increase of this sort in the 

 surface salinity, takmg place at a season when the waters to the west and to the 

 east freshened, would of itself suggest local upwelling. This explanation is corrob- 

 orated, also, by the fact that the upper 120 to 130 meters proved nearly as homo- 

 geneous there vertically, in salinity, on that occasion as in either March or April, and 

 about 0.6 per mille more saline in absolute value (fig. 112), instead of showing the 

 considerable vertical range of salinity that might otherwise be expected to develop 

 in this region by May. 



West-east profiles of the gulf also give unmistakable evidence that some such 

 circulatory movement did take place in 1919 between the end of April and the end 

 of May (fig. 121), by which date a strong pulse in the inflowing bottom current had 

 raised the upper boundary of water, more saline than 32.5 per mille, to within 20 



yiG. 121.— Salinity profile running eastward from the olBng o[ Cape Cod toward Cape Sable, iVIay 29 to 30, 1919 (ice patrol 



stations 35 to 38) 



meters of the surface in this side of the basin. Some upwelling is therefore to be 

 expected in the western side of the basin from April through May, correlated with 

 the speeding up of the anticloclcwise circulation that follows the freshets from the 

 rivers tributary to the gulf (p. 916). The actual alteration which this effects in the 

 salinity of the surface stratum, however, may not be as wide in any given year as 

 the difference between the April records for 1920 and those for May, 1915, might 

 suggest, because it is possible that these two years illustrate two extremes — the one 

 lower in salinity than is usual, the other higher. 



BELOW THE SURFACE 



The fact that May sees the culmination of vernal freshening from the land, 

 and also the maximum expansion of the Nova Scotian current past Cape Sable, 

 lends interest to the subsurface salinities for the month. 



Perhaps our most instructive illustration of how strictly the decrease in the 

 salinity of the coastal belt is confined to the superficial stratum of water up to this 



