674 BULLETIN OF THE BUREAU OF FISHEEIES 



FACTORS GOVERNING THE TEMPERATURE OF THE 



GULF OF MAINE 



The temperature of the gulf, Uke that of other boreal seas, is governed by a 

 complex of factors into which the temperature of the water that enters the gulf from 

 the several sources emmierated below (p. 854), warming by the sun's rays, and cooling 

 by the radiation of heat from the water to the air in autumn and winter, as well as 

 by evaporation from its surface and by the melting of snow (and locally of ice), all 

 enter. Added to all of which the temperature at any given depth, date, and local- 

 ity depends to a large degree on the local activity of vertical circulation, especially 

 of tidal stirring. 



Continued studies confirm the earher generaKzation that the temperature of the 

 superficial stratum of the gulf down to a depth of about 100 meters is governed 

 chiefly by the chilling caused by rigorous winter climate and by the influx of cold 

 water from the Nova Scotian current in spring, on the one hand, balanced against 

 local solar heating in spring and summer, on the other, and against the warming 

 influence of the influx of offshore water which enters its eastern side. As the 

 gulf lies to leeward of the continent, its western and northern sides are the most 

 responsive to climatic changes (Bigelow, 1922, p. 164). 



In evaluating the relative importance of these several processes it is to be 

 observed that all of them are distinctly seasonal in their effects. 



SOLAR WARMING 



In the Gulf of Maine, which very seldom is invaded by warm water from the 

 south or from outside the continental edge — situated, too, at a temperate latitude, 

 with the sun's noon altitude rising to more than 63° above the horizon during the 

 months of May, June, July, and the first half of August — solar heating in situ is the 

 chief and, indeed, almost the sole source of heat. 



The absorption of heat by the water from warm air blowing over its surface 

 exerts much less effect on the sea temperature. This last statement rests on the 

 fact that the capacity of sea water for heat (technically its specific heat '^'') is about 

 3,000 times greater than that of air. 



Such great volumes of warm air must, then, blow over the surface of the sea 

 before the latter is warmed appreciably that heat from this source can be responsi- 

 ble for only a very small part of the vernal rise ia temperature that characterizes 

 the Gulf of Maine. 



Water, fresh or salt, is apparently a transparent fluid when viewed in small 

 volumes. Actually this is far from the truth. Consider, for example, how rapidly 

 any object lowered into even the clearest sea vanishes from sight.^' In fact, sea 

 water is so nearly opaque to such of the sun's rays as convey most of its energy 



"The specific heat of distilled water is usually stated as 3,267 times that of air. Sea water has slightly less capacity for heat, 

 Eriimmel (1907, p. 279) quoting from experiments by Thoulet and Chevalier (1898), giving the specific heat of water of 30 per 

 mille salinity as 0.939 and that of water of 35 per mille salinity as 0.932, both at 17.5° temperature, taking distilled water as 

 unity. 



"See page 822 for actual measurements of the visual transparency of the Gulf of Maine at various times and places. 



