944 



BULLETIN OF THE BUREAU OF FISHEBIES 



MAY 



Progressive incorporation of river water into the northern and western sides of 

 the gulf, coupled with vernal warming, constantly favors the anticlockwise move- 

 ment of the so-called "spring current" (fig. 194); and with the resultant changes 

 in salinity and temperature affecting chiefly the surface, the site of the chief dynamic 

 impulse toward circulation shifts from the deep strata to the superficial. In May, 

 1915, for example, a difference of about 1.5 units of density was recorded at the 

 surface between the vicinity of the mouth of Massachusetts Bay and the basin in 



Porlland 



Fig. 192. 



-Dynamic gradient at the surface of the gulf, April 6 to 20, 1920, referred to the offing of the Bay of Fundy 

 as base station. Contours for every dynamic centimeter 



its ofBng (fig. 194) in a distance of 30-odd miles, but only about one-seventh as wide 

 a difference at the 50 or 100 meter levels (stations 10266 and 10267). 



As a result, the dynamic chart for May (fig. 195) corresponds closely to the dis- 

 tribution of density at the surface, except for the relationship between the shallows 

 of German Bank and the deep water immediately to the west of the latter. In this 

 region the surface projection, taken by itself, would give a false picture, being con- 

 fused by the strong tides that keep the water thoroughly stirred over the bank, thus 



