644 



BULLETIN OF THE BUREAU OF FISHEEIES 



Meter 



10 



go ,Qo ,,0 ,2» 13° 14° 15° 16° 17° 18° 19° 20° 21° 22° 



We again found the superficial stratum over this part of the shelf equally homoge- 

 neous in temperature in November, 1916. While the bottom water then showed 

 slight vertical cooling at depths greater than 30 to 40 meters, it was considerably 

 warmer then than it had been there in August — a state obtaining as far southward 

 as Chesapeake Bay (Bigelow, 1922, p. 123). 



Thus, the coast water off southern New England corresponds to the Gulf of 

 Maine in the fact that the temperature tends to become uniformly homogeneous 

 during September and October, though the change takes place at a temperature 3° 

 to 4° higher than is the case to the northward of Cape Cod. "A seasonal change 

 of this sort was, of course, to be expected in the absence of disturbances by extra- 

 limital currents, as the first step in the vertical equalization of temperature so 

 characteristic of northern coastal waters in late autumn and winter." (Bigelow, 

 1922, p. 123.) 



In 1916 the surface temperature near land a few miles west of Marthas Vineyard 

 had fallen fractionally below that of the 30-meter level by November 10 to 11 (sta- 

 tions 10405 to 10408) ; 



Temperature, Centigrade ^^^ although this pro- 



file lies a few miles 

 west of the geographic 

 limits covered by this 

 report, it is repro- 

 duced here (fig. 74) 

 because the readings 

 would have been 

 nearly the same had 

 it been run out from 

 Marthas Vineyard on 

 the same date. Its 

 most instructive 

 feature is its demon- 

 stration of the fact, 

 now sufficiently es- 

 tablished, that 

 autumnal cooling in 

 the coastal waters off 

 the northeastern 

 United States proceeds from the land seaward. In 1916, as I have earlier remarked 

 (Bigelow, 1922, p. 123), this process had progressed so far by that date as to nearly 

 obliterate the preexisting stability of the water on the inner half of the shelf. 

 Farther offshore, however, where the immediate surface alone had yet been chilled 

 by the cool land winds, the underlying water at 20 to 50 meters still continued 1° 

 to 2° warmer than the superficial stratum above or the bottom water below. As a 

 result the curves for 12° and 13° might suggest a landward intrusion of water from 

 offshore if taken by themselves. However, the salinities forbid this interpretation, 

 proving this apparent tongue merely reminiscent of the maximum temperature to 

 which this level had warmed during the preceding summer (Bigelow, 1922, p. 123). 



tT Tt — i 1 1 1 1 



^^A 



C B .^^ 



_c 



20 



30 



40 



50 



60 



70 



80 



90 



100 



Fig. 73.— Vertical distribution ot temperature off Marthas Vineyard to show autumnal cooling. 

 A, August 25, 1914 (station 10259); B, October 22, 1915 (station 10333); C, November 1, 1916 

 (station 10406) 



