PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 553 



temperature over Nantucket Shoals as that of the western and southwestern parts 

 of the gulf generally at this season . 



In 1920 the surface warmed by about 2° all along the belt from Massachusetts 

 Bay to the Bay of Fundy from mid-March to mid- April; by less than 2° over the 

 basin generally and along western Nova Scotia; by less than 1° on the eastern part 

 of Georges Bank; and there had been no measurable change in surface temperature 

 in the Eastern Channel (stations 20071 and 20107, 3.33°). In other words, where 

 the surface is most chilled in winter it warms most rapidly in early spring. 



The fact that the surface temperature increased over the German Bank-Cape 

 Sable area and out across Browns Bank from March to April, 1920, is proof that the 

 westward flow of Nova Scotian water, chilled by ice melting far to the eastward 

 (p. 832) , did not impress the temperatures of the gulf until still later in that spring, 

 marking 1920 as a "tardy" year in this respect as in others. The opposite extreme 

 is illustrated by a surface reading of 0° in the eastern side of the basin (the lowest 

 yet recorded for the open gulf)'^ on March 28, 1919,'^ explicable only by some 

 movement of cold water from the east, though as so thin a surface layer that neither 

 the temperature nor the salinity were appreciably affected by it more than 20 to 30 

 meters downward. 



In 1920 the mean temperature of the 40-meter level proved about 0.8° warmer 

 in mid-April (fig. 24) than in mid-March, with this change greatest (1° to 1.67°) in 

 the eastern side of the basin and off western Nova Scotia, resulting in a general 

 equalization at 2.2° to 3° for the whole western and northwestern parts of the gulf, 

 with 3° to 3.7° over the southern and eastern parts. In the warmer spring of 1925 

 the Halcyon found the 40-meter level about half a degree warmer — namely, about 

 3.2° — four miles off Cape Ann whistle buoy on April 17; 2.8° close to little Duck 

 Island (off Mount Desert) on the 19th; and 2.9° eight miles out from Duck Island 

 on that same day. 



The progressive change in temperature was not so regular from March to April 

 at depths greater than 40 to 50 meters in 1920, and wherever warming took place in 

 the deep strata during the interval, it was accompanied by a corresponding rise in 

 salinity, proving the source of heat to be warmer bottom water, solar warming not 

 having penetrated more than a few meters downward as yet. 



Thus the inner parts of the gulf north of the Cape Cod-Cape Sable line 

 warmed by about as much (about 1.7°) from mid-March to mid- April at 100 

 meters (fig. 25) as at the surface. Virtually no change took place meantime 

 in the 100-meter readings in the southern part of the basin, while the 100-meter 

 level had cooled by nearly 1° in the southeastern part of the area, a change 

 accompanied by a corresponding decrease in salinity (p. 735) . Thus, it seems that 

 the middle of April is the coldest season of the year in this region at this depth. 

 This regional difference in the rate and order of the seasonal change of temperature 

 tended to equalize the mid-stratum over the gulf as a whole, so instead of the re- 

 gional range of nearly 5° obtaining at 100 meters in March (fig. 13), the highest and 

 lowest readings at this depth were only 3.56° apart in April (fig. 25). While the 

 general distribution of temperature remained the same — lowest (3° to 3.5°) along 



" This reading is corroborated by a con'espondingly low salinity (p. 727). u Ice patro! stations 1 to 3, p. 997. 



