732 



BULLETIN OF THE BUEEAU OF FISHEBIES 



surface to bottom, out to the lOO-meter contour. Mavor's (1923) tables show that 

 this is also the case in the Bay of Fundy up to about the middle of April, when so 

 great a volume of fresh water empties into the bay from the St. John River and from 

 its other tributaries that in 1917 the salinity of the surface water of the center of 

 the bay fell to 29.2 per mille at the first of May. 



The effects of the vernal freshening just described do not penetrate deeper than 

 80 to 100 meters anywhere in the open gulf before the end of April, unless in excep- 

 tional years; consequently, the deeper waters either continue virtually unchanged 

 through that month or become slightly more saline by incorporation of the water 

 that moves in through the Eastern Channel. 



During the spring of 1913 the deepest strata of Massachusetts Bay continued 

 to show this comparative constancy up to April 3 (fig. Ill; Bigelow, 1914a, p. 392), 

 although the surface had already freshened by about 0.5 per mille; and while the whole 

 column of water in Massachusetts Bay freshened appreciably from March 10 to April 

 23^in 1925, as just noted (p. 729), the vernal cycle of 1920 paralleled that of 1913 by 



Fig. 110.— Salinity profile running eastward from Massachusetts Bay to the offing of Cape Sable, .^pril 6 to 18, 1920 



an increase in the salinity of the bottom water over the gulf as a whole from mid- 

 Mai'ch to mid-April at depths greater than 100 meters, except in its southeastern 

 parts, where little alteration took place. 



Thus the salinity of the bottom water of the bowl off Gloucester increased by 

 about 0.1 to 0.2 per mille from March 1 to April 9 of that year. While little altera- 

 tion took place in the salinity of the western side of the basin at depths greater than 

 100 meters during the first half of that April (fig. 112), that of the central part rose 

 by 1.1 per mille at 180 meters (fig. 113), with a corresponding increase of 0.2 to I 

 per mille for the whole column of water in the northeastern part of the trough off 

 the mouth of the Bay of Fundy (fig. 114, stations 20081 and 20100). 



As a result of this salting of the deep water, combined with the freshening of 

 the surface, the vertical range of salinity becomes much wider in the western part of 

 the gulf by mid-April than it is during the first half of March. Off northern Cape 

 Cod, for example, the spread between surface and bottom values increased from 



