PHYSICAL OCEANOGKAPHY OF THE GULF OF MAINE 967 



Thus, the wind then tends to act as a motive force for the southern and eastern 

 sides of the Gulf of Maine eddy. 



It is obvious, however, that no matter how steadily the wind blew from the 

 southwest it could not drive the entire surface of the gulf eastward unless the water 

 were nearly enough homogeneous to allow a sinking current to develop in the eastern 

 side, with the deeper stratum so fed flovsdng back from east to west, to well up again, 

 in turn, in the western side. Circulation of this sort probably does take place 

 to some extent along the Nova Scotian side of the gulf, in the Bay of Fundy, and 

 along the coast of Maine east of Mount Desert, where active tidal currents keep 

 the water so thoroughly stirred that it has little stability at most times of year. 

 It is certain, also, that offshore winds do cause more or less upwelling along the 

 western shore line, but the basin of the gulf as a whole, with its western and north- 

 western margins, is so stable vertically that hydrostatic forces very strongly oppose 

 any such "jibing," as Sandstrom (1919) terms it. Consequently, any constant 

 movement of the surface water northward toward the Bay of Fundy would tend to 

 cause an "overflow" in the shape of a westerly drift along the coast of Maine — i. e., 

 against the winds prevailing in summer. 



It is obvious that if the water be in stable equilibrium, southwesterly winds 

 might or might not set a closed circulation of this type in motion, depending on 

 their relative strengths and constancy in various parts of the gulf; depending, too, 

 on the balance in various parts of the gulf between the hydrostatic forces opposing 

 jibing and the tendency of the wind to cause that process, as just explained. 

 To value these several factors will require a knowledge of the gulf and of its winds 

 much more intimate than can yet be claimed. It is certain that with winds reversed 

 as often as they are over the gulf the balance varies constantly. However, the 

 preceding analysis does make it clear, I think, that any eddying circulation which 

 the southwesterly winds of summer might set up in the surface stratum of the gulf 

 would shortly assume the anticlockwise character that, by evidence of more direct 

 sorts, does actually dominate its basin. Consequently, the summer winds parallel 

 the hydrostatic forces set in operation by regional inequalities of density in their 

 general effects to this extent. On the other hand, the current flowing southward 

 and out of the gulf past Nantucket Shoals, which forms part of the overflow from 

 the gulf, is at right angles to the potential wind drift, hence holds its dominant set 

 in spite of the prevailing wind. Neither can the wind be held responsible for the 

 westerly drift of slope water along the continental edge in summer, because this 

 current sets directly against the drift which the prevailing southwesterly winds 

 would tend to produce there. 



The wind current, as it extends its effects deeper and deeper below the surface, 

 ^vill turn more and more to the right of the wind (losing, also, in velocity by 

 geometric progression) ; also, with increasing depth the gulf becomes more and more 

 nearly inclosed, so that any currents, however set in motion, are more and more 

 directed by the contour of the bottom. 



The depth to which currents of wind origin do actually penetrate in the Gulf of 

 Maine is therefore of immediate interest. Unfortunately, no mathematical method 

 yet suggested can measure this, even approximately. However, it is certain that 

 the stable state of the water of most parts of the gulf ordinarily confines wind 



