684 BULLETIN OF THE BUEEAU OF FISHERIES 



St. Marys Bay on September 2 (9.8° in 48 meters), and in 40 and 45 meters off 

 Yarmouth Harbor, Nova Scotia, on September 7 and 9" (9.2° and 9.8° in 40 and 45 

 meters) as off Cape Cod on August 29 (9° at station 10398). Much lower summer 

 temperatures prevail to the eastward of Cape Sable, a dislocation illustrated for 1914 

 by mean values of 10.9° on the northeastern part of Georges Bank and of about 9° 

 on Browns Bank, contrasting with only about 5° at the 50-meter contour off Cape 

 Sable (station 10230) during the last week of July. 



These data may bo summarized as follows: No definite tendency is shown toward 

 lower mean values for the upper stratum in the one side of the basin of the gulf than 

 in the other, outside the 100-meter contour, in years neither unusually warm nor un- 

 usually cold. When we take into account the sharp temperature gradient that char- 

 acterizes most parts of the Gulf of Maine in summer, as a result of which even sUght 

 upwellings from the mid-depths (at, say, 75 to 100 meters) would considerably lower 

 the mean temperature of the shoaler stratum, the most striking result of the 

 calculation is the imiformity of the gulf made evident. 



In the coastal belt the mean temperature is usually, though not invariably, a 

 degree or so lower in the northeastern corner of the gulf in summer than in the 

 southwestern side; and it is possible that in years when the movement of water 

 westward along Nova Scotia persists late into the season (1924, for example, p. 834) 

 this regional difference in temperature is wider than has actually been recorded in 

 the summers when our general surveys of the gulf have been carried out. In evalu- 

 ating it, not only must the possible effect of this cold current be taken into account, 

 but also the difference in latitude between the different stations of observation, 

 which, per se, corresponds to some difference in temperature. The most interesting 

 regional comparison which the available records afford from this point of view is 

 between the waters on Nantucket Shoals, on the one hand, and Passamaquoddy Bay, 

 on the other, both being subject to tidal stirring so active that the water remains 

 comparatively homogeneous from surface to bottom throughout the year, and both 

 experiencing about the same amount of fog during the spring and summer.'^ The 

 difference in latitude between these two localities is about 3^/2° ■ The mean temper- 

 ature of the upper 30 to 40 meters of Passamaquoddy Bay is usually between 8.5° 

 and 10.5° in August, when it is at or close to its maximum for the year, differing 1° 

 or 2° in either direction at different stages of the tide and from year to year. On 

 Nantucket Shoals mean temperatures of 10° to 13° have been recorded in summer, 

 so that a difference of about 2° is to be expected between these two regions. Accord- 

 ing to Krummel's (1907, pp. 400 and 401) tabulation and diagram this about equals 

 the average difference in surface temperature between the latitudes of the shoals 

 (41°) and of Passamaquoddy Bay (44° 30'), whether for the oceans as a whole or for 

 the North Atlantic alone. 



The differences in latitude between Massachusetts Bay (lat. about 42°) and the 

 northeastern shores of the gulf generally (lat. 44° to 44° 30') corresponds to a 

 difference of between 1° and 2° in mean annual surface temperature for the North 

 Atlantic as a whole. 



•' Calculated from Vachou's (1918) tables. 



■ According to the pilot chart (United States Hydrographic Office), Nantucket Shoals is somewhat the foggier region of the 

 two in Juno (40 to 45 per cent of foggy days; 30 to 40 per cent in the Bay of Fundy); but in July about half the days see some 

 fog in the eastern side of the gulf, only 30 to 40 per cent on the shoals. 



