CLIMATE AND THE DISTRIBUTION OF MARINE ANIMALS 



305 



sido of the gciipral basin of the Gulf tliaii it is dose 

 in along the western coastline; 14° to 15° higher 

 tlian in the northeastern part of the Gulf in gen- 

 eral; and 7° to 1 1° higher than over the shoaler and 

 most tideswept parts of Georges Bank and of Nan- 

 tucket Shoals. In the western part of the Gulf 

 the 20- to 40-meter level is not at its warmest 

 until well into September, the 50- to 70-meter 

 level not until November, the 100-meter level 

 not until late Novertiber or early December, and 

 the 150-meter level not until December or even 

 later. On the other hand, in the northeastern 

 part of the Gulf the entire column of water warms 

 at an almost uniform rate, down to at least 100 

 meters. 



In August, when the surface is at its warmest in 

 the western part of the Gulf, the 40-meter level is 

 5° to 6° colder and the 100-meter level about 4° 

 colder there than in the northeastern part of the 

 Gulf (Bigelow 1927, figs. 53 and 56), reversing the 

 temperature relationship at the surface that is 

 characteristic of that time of year. Since the 

 surface begins to cool in early September in 

 the western part of the Gulf, but not until a 

 month or more later in the eastern, the regional 

 differences in surface temperature decrease as the 

 season advances, until by midautumn the surface 

 is nearly uniform in temperature throughout the 

 Gulf (varying only a degree or two from place to 

 place); and so it continues until the following 

 spring. 



At the warmest season during the summers cov- 

 ered by the cruises of 1912 to 1926, surface temper- 

 atures ranged from about 64° to 68° F. (occasion- 

 ally 1° to 2° higher) in Cape Cod Bay and over the 

 western part of the basin; from 61° to 64° close in 

 along the western coastline; from 50° to 53.5° in 

 the northeastern part of tlie open Gulf in general 

 and in the lower part of the Bay of Fundy; from 

 53° to 57° over the parts of Georges Bank where 

 tides run the strongest; and from 57° to 61° over 

 the shallower parts of Nantucket Shoals. 



The seasonal maxima at deeper levels were as 

 follows in the western part of the Gulf in general 

 and in the lower Bay of Fundy, which cover the 

 regional extremes (table 3). 



Depths greater than 150 meters 



In the 180-meter sink oft' Cape Ann, tlie sill 

 depth of which is about 75 meters, the alternate 

 processes of vernal warming and of autumnal 



414171 0—57. ;! 



Table 3. — Seasonal temperature maxima in the western 

 Gulf of Maine, 1912-26, and in lower Bay of Fundy, 

 1916-17 



[Temperatures In °F.] 



1 Scaled from Mavor (1923, p. 375, table 8). 



2 Xo November data for 1917. 



cooling affect the entire column of water from 

 surface to bottom, though in lessening degree at 

 increasing depths. During the winter of 1920-21, 

 for example, the temperature at 150 meters fell 

 from 44.6° F. on December 29, which could not 

 have been much below the maximum for the year, 

 to 39° on March 5, which certainly was close to 

 the minimum for that winter. In the same year, 

 almost as great a seasonal range (4.7°) was regis- 

 tered at 150 meters, between December 30 (44.5°) 

 and March 5 (39.8°) in the 180- to 190-meter 

 trench between Jeffreys Ledge and the coast, 

 where free interchange over the bottom is hindered 

 by an enclosing sill rising to within 120 to 125 

 meters of the surface. The seasonal difference 

 was about twice as great as this (8.8°) between 

 December 2, 1916 (43.9°) and April 9, 1917 (35°) 

 at 175 meters in the 180- to 208-meter bowl at 

 the mouth of the Bay of Fundy, where the depth 

 of the sill is about 128 to 140 meters (Mavor 1923, 

 p. 375, table 8). 



The picture is not so clear for the deep bottom 

 water of the open basin of the Gulf. The changes 

 in temperature that take place there from time to 

 time at depths greater than 150 meters are the 

 combined result of such slight influence as the 

 climatic cycle may exert from above modified or 

 intensified, according to the season, by indrafts 

 of water from the continental slope that enter via 

 the deep channel between Georges and Browns 

 Banks. (For a discussion of this general matter, 

 see Bigelow 1927, p. 690.) High salinities, for 

 example, made it clear that the higher mean 

 temperatures recorded in late summer and autumn 

 than were recorded in late winter or spring near 

 the bottom in the eastern part of the basin during 

 our caily cruises (table 4) were the direct result 

 of recent indrafts of this water from offshore. 

 Reatlings of 47.1° F. at 200 meters and of 46.3° at 



