304 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



1917. A 40-meter reading by the Albatross of 34.8° 

 some 12 miles off Yarmouth, Nova Scotia, on 

 March 23, 1920, suggests similar temperatures 

 along the west coast of Nova Scotia outside the 

 headlands, except for a brief period in the spring 

 when the cold drift from the east passing Cape 

 Sable mav temporarily chill the surface there to 

 32° (p. 311). 



At the coldest time of the year, the water in the 

 Gulf not only is nearly uniform in temperature 

 vertically to a depth of 100 meters or so, but the 

 underlying strata at equal depths (like the surface) 

 out over the deep east-central basin and over 

 Georges Bank offshore are some 3° to 6° warmer 

 than the water closer in around the periphery of 

 the Gulf — a contrast illustrated by the 40-meter 

 and 100-meter charts for 1920 (Bigelow 1927, figs. 

 12 and 13). Consequently, the temperature of the 

 bottom water is progressively higher passing off- 

 shore along any line normal to the general trend 

 of the coast as the depth increases, reversing the 

 situation characteristic of summer and autumn. 

 Thus, any bottom-dwelling animals capable of 

 active motion need only move a short distance 

 down the slope into deeper water to escape the 

 rigors of winter; and many do just this. 



While any animal at tide line may be in water 

 soupy with ice crystals and at freezing point, as 

 at Sandy Neck, Barnstable, on February 7, 1901, 

 the minimum temperatures on bottom farther out 

 characteristic of winters as severe as those of 1920 

 and 1925 were about 32° F. in Cape Cod Bay and 

 32° to 33° northward and eastward from Boston 

 along the 20-meter zone; about 33° to 36° along 

 the 40- to 50-meter zone; and about 35.4° to 39.7° 

 along the 100-meter zone all around the periphery 

 of the Gulf. The only important exception is the 

 sink off Cape Ann, where interchange with the 

 warmer water of the open basin is barred by the 

 surrounding sill, as evidenced by a 100-meter 

 reading there of 34.7° on March 1, 1920, con- 

 trasted with 37.5° at this same depth on the slope 

 offshore on February 23, and 38.6° a few miles to 

 the southward on March 24. At 150 meters, the 

 usual winter temperature was between 35° and 39° 

 in the Cape Ann sink and between 42° and 43° in 

 the open basin of the Gulf. 



Readings of 36.6° to 37° F. at 70 to 90 meters 

 on the eastern part of Georges Bank, March 11-13, 

 1920, show that the bottom water chills to about 

 as low a value there as at equal depths around the 



basin to the nortiiward. But it is doubtful whether 

 bottom temperatures lower than about 40° ever 

 spread to the southwestern part of the Bank, for 

 the Albatross recorded a bottom reading of 46.5° 

 there at 70 meters on February 22, 1920. 



During the milder winters included in the period 

 1913-25, the surface probably did not chill below 

 35° anywhere along the open coast to the north 

 of Boston, unless close in to tide line, to judge from 

 water temperatures of 35° to 39° F., March 4-5, 

 1921, at stations scattered between the offings of 

 Seguin Island and of Boston; and perhaps the 

 temperature did not fall below 32° to 33° even in 

 Cape Cod Bay. Readings of 35.1° to 35.4° from 

 the 40-meter level downward in the 180-meter sink 

 15 miles off Gloucester on March 1, 1920, when 

 contrasted with readings of 38.8° to 39° taken there 

 on March 5, 1921, illustrate the temperature differ- 

 ence that is to be expected at comparable localities 

 from winter to winter in the western side of the 

 Gulf. 



Yearly maximum. — The surface water is at its 

 warmest sometime in August generally throughout 

 the southern and western parts of the Gulf of 

 Maine (as early as July in some years, particularly 

 in enclosed situations, such as Boston Harbor), but 

 not until sometime in September, or even early 

 October in the northeastern part and in the Bay 

 of Fundy region, where vertical mixing by tidal 

 currents is more active. The regional differences 

 in temperature, also, are much wider in the warm 

 season than in the cold, often within short dis- 

 tances, for reasons the discussion of which would 

 lead us too far afield.' 



Because of regional differences in the rate of 

 vertical mixing of water by tidal currents, the sur- 

 face warms much more rapidly in the southwestern 

 part of the Gulf, where the cold of the preceding 

 winter is preserved in the underlying strata into 

 autumn, than in the northeastern part, where the 

 heat taken in at the surface is distributed more 

 evenly downward as the season advances. As a 

 consequence of this widespread contrast, combined 

 with local differences caused by smaller-scale mix- 

 ings and upwellings, the surface water temperature 

 is some 3.5° to 7° higher in enclosed situations 

 along the western coast of the Gulf, over an iso- 

 lated pool in Cape Cod Bay, and over the western 



I Sci an earlier paper in the Geographical Review (Bigelow 1928), for a 

 general summary and a more extended account of the physical oceanography 

 of the Oulf based on the cruises of 1912-26 (Bigelow 19271. 



