PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 



729 



In the western side of the gulf the seasonal alteration decreases progressively as 

 the depth increases, to nil at a depth of 80 meters off Cape Cod (fig. 106). If 

 Massachusetts Bay can be taken as representative of this side of the gulf, the freshen- 

 ing effect penetrated somewhat deeper or somewhat more rapidly in 1925, when the 

 bottom water in 70 meters' depth was about 0.5 per mille less saline at one station on 

 April 23 {Fish Hawk station ISA) than it had been on March 10. 



FIQ. 105. — Vertical distribution of salinity ofl Boston Harbor at various seasons. A, Marcb 5, 1020 (station 20062); B, 

 April 6, 1920 (station 20089); C, May 16, 1920 (station 20123); D, August 20, 1913 (station 10106); B, December 29, 

 1920 (station 10488) 



Wide local variation is to be expected in this respect, depending on how actively 

 the water is stirred by waves and tides, in even as small an area as Massachusetts 

 Bay, where a vertical range of about 0.6 per mille developed in the central part by 

 April 22 to 23 in 1925, though the waters of Cape Cod Bay still continued nearly homo- 

 geneous, vertically, but about 1 per mUle less saline than they had been on March 10. 



Fig. 106.— Vertical distribution ot salinity oS northern Cape Cod in various months. A, April 18, 1920 

 (station 20116); B, May 16, 1920 (station 20125); D, July 14 1913 (station 10213) 



The freshening effect of the discharge from the Merrimac and Saco Rivers seems 

 also to have penetrated down to a considerable depth into the gulf during April of 

 1913 (stations 8 and 18, William Welsh; p. 981). In 1920, however, this freshening 

 was confined to the upper 60 meters near Seguin Island and to the upper 35 to 40 

 meters near Mount Desert Island (fig. 107), up to the middle of April. 



The upwellings caused by offshore winds, which temporarily raise the salinity 

 of the surface along the western shores of the gulf (p. 709), exert a correspondmg effect 



