624 



BULLETIN OF THE BL'EEAU OF FISHEKIES 





would have occupied the upper 10 meters i'roiu end to end, instead of showing the 

 chilling effect of the strong tides, which actually characterize its Cape Cod end. 



In the Juty profile (fig. 65) the cold bottom water is banked up against the 

 southern side of the bay, but against the northern side on the profile for August 

 (fig. 66). A difference of this sort probably reflects a corresponding difference in 

 the movements of the deep water around Stellwagen Bank. Judging from experi- 

 ence in other years, the state illustrated by these August stations is the more usual 

 in summer. 



BOTTOM TEMPERATURE 



The bottom temperature of the gulf in summer is governed chiefly by the 

 depths, but also to some extent by locality. At this season the bottom is coldest 



(3° to 5°) in the 



Meter 



troughs off the west- 

 ern shore of the gulf, 

 u'respective of depth, 

 and in the offing of 

 Cape Sable in the 

 opposite side, with 

 the whole deep basin 

 1° to 3° warmer out- 

 side the 150-meter 

 contour (5° to 8°). 

 For example, an ani- 

 mal living in the 

 trough off the Isles 

 of Shoals might actu- 

 ally suffer lower tem- 

 peratures during 

 some summers than 

 in some winters or 

 springs, according as 

 the years be cold or 

 warm in the gulf. 

 The annual differ- 

 ences iu the basins at depths greater than 175 to 200 meters consequent on irreg- 

 ular pulses in the bottom current may so overshadow the regular seasonal cycle as 

 to make the latter neghgible, biologically, up to the end of the summer. Bottom 

 dwellers in the coastal zone, however, must be inured to a wade range of temperature 

 if they are to survive; as, indeed, they must in shallow boreal waters in general. 



Cape Cod Bay experiences a wider fluctuation in bottom temperature, with the 

 succession of the seasons, than any other part of the open gulf outside the estuaries 

 and islands. In order to exist there, without bathic migration, in water shoaler 

 than 5 to 10 meters, any animal must be indifferent to temperatures as high as 18° 

 to 19° in midsummer (p. 623). A bottom temperature of 17.9° was even recorded 

 as deep as 13 meters off Barnstable on August 24, 1922 (station 10644) — an extreme 



Fig. 65.— Temperature profile crossing the mouth of Massachusetts Bay just west of Stellwagen 

 Bank, July 19, 1916 (stations 10310 to 10342). The contour of the bank is represented by the 

 broken curve 



