PHYSICAL OCEANOGRAPHY OF THE GULP OP MAINE 699 



THERMAL EFFECT OF THE RIVER WATER 



The great volume of river water that pours into the gulf every spring, at a 

 temperature only a few degrees above the freezing point, when the ice goes out of 

 the lakes and the snow melts, must tend at first to delay the vernal warming of the 

 gulf. However, no attempt has yet been made to estimate its actual effect. 



SUMMARY OF THERMAL DETERMINANTS 



The interaction of the several major factors that govern the temperature of the 

 gulf is so complex that a summary of them may be useful. 



It is definitely established that the gulf owes the particular temperatures 

 proper to it, and especially the wide seasonal range of temperature, chiefly to its 

 geographic location to leeward of the continent and to the rigorous land climate. 

 Only in a much smaller degree is it influenced by warm or cold currents flowing 

 into it. 



Our successive cruises and the observations taken in the Bay of Fundy by the 

 Biological Board of Canada, therefore, corroborate the view long ago advanced by 

 Verrill (1874) that the waters of the Gulf of Maine are not abnormally cold, con- 

 sidering their geographic location and the rigorous climate of the neighboring land 

 mass; that, in short, to describe its temperature as "Arctic," as has so often been 

 done, is entirely a misnomer. 



The chief source of warmth for the superficial stratum of the gulf is the solar 

 heat absorbed by the water in situ. Vernal warming is therefore chiefly of local 

 origin. The rapidity with which solar heat is dispersed downward in the water 

 and the depth to which it penetrates depend on the activity of vertical circulation, 

 whether by tides, winds, storm waves, or dynamic overturnings; and the regional 

 differences in the temperature gradient, which develop in the gulf in summer (Mas- 

 sachusetts Bay at the one extreme, the Bay of Fundy and Nantucket Shoals at the 

 other), result chiefly from differences in the thoroughness with which the tides 

 churn the water. 



The low surface temperature that prevails along the eastern coast of Maine and 

 in the Bay of Fundy in summer, as contrasted with the Massachusetts Bay region, 

 is chiefly due, therefore, to local causes and not to the "Arctic current" that has so 

 commonly been invoked to account for it. 



The surface stratum of the gulf likewise receives heat from warm winds blowing 

 over its surface, from surface water drifting into its eastern side from the region of 

 Browns Bank and the Cape Sable dead water, and also, at long intervals, from over- 

 flows from the tropic water outside the edge of the continent. 



Vernal warming is opposed by the Nova Scotian current flowing from the east- 

 ward, past Cape Sable, into the gulf. During the brief period when at its maxi- 

 mum, this current may lower the surface temperature by a couple of degrees right 

 across to the western side of the basia, thus temporarily producing a regional differ- 

 entiation; and it considerably delays vernal warming in the eastern side probably 

 every year. However, this cold drift is so thoroughly incorporated into the water of 

 the gulf soon after the actual flow past the cape slackens that no regional differenti- 

 ation from this source can be traced definitely in the gulf after midsummer. Neither 



