854 BULLETIN OF THE BUEEAU OF FISHERIES 



The distribution of density must, in fact, strongly resist any force, such as 

 offshore winds driving the siu-face water out to sea, which would tend to draw abyssal 

 water upward over the continental slope abreast the Gulf of Maine; for in every 

 case we have found a decidedly stable state of equilibrium prevailing there. In fact, 

 most of our cross sections of the outer part of the continental shelf abreast the gulf 

 and to the eastward show a general dynamic tendency of quite a different sort — 

 namely, one leading to the development of a drift of the inner slope water toward 

 the west (p. 847), while a counter drift of the outer slope water (or "inner edge of the 

 Gulf Stream") toward the east has often been recorded. 



In short, continued observation has not adduced any evidence that water from 

 the ocean deeps ever wells far enough up the continental slope to reach the Eastern 

 Channel, much less to overflow the offshore rim of the gulf. 



This conclusion does not imply that upwelling may not take place over the 

 lower part of the continental slope from the Atlantic abyss. On the contrary, much 

 evidence has accumulated to the effect that some such process is of wide occurrence 

 along the lower part of the slope, below, say, the 500 to 1,000 meter level, westward 

 and southward from Georges Bank. Perhaps the clearest evidence of this is afforded 

 by a profile run from Chesapeake Bay to Bermuda by the Bache in January and 

 February, 1914, when the uniform abyssal water (about 4° in temperature and 34.9 

 to 35 per mille in saUnity) was banked up against the slope to within 1,100 to 1,200 

 meters (Bigelow, 1917a, figs. 11 and 12). This also appears on a profile run by the 

 i>ano from Bermuda to Norfolk, Va.,in May, 1922 (Nielsen, 1925, fig. 4) . But no direct 

 evidence has yet come to hand that water from this deep source ever reaches the con- 

 tinental shelf of eastern North America in volume sufficient to affect the temperature 

 or salinity of the coast waters.^' 



In denying the occurrence of abyssal upwelling as a cause of low temperature 

 in the Gulf of Maine, I do not refer to upwelling from shallow water along shore — 

 a common event, which often exerts an immediate effect on the temperature and 

 salinity of the surface water in the vicinity in spring and summer, as described in an 

 earlier chapter (p. 550). 



RECAPITULATION 



The Gulf of Maine incloses a sector of the typical coastwise water of the north- 

 western Atlantic, receiving its most important accessions periodically from the 

 following sources: Slope water of high salinity (close to 35 per mille) and close to 6°-8° 

 in temperature flows intermittently into the gulf as a bottom current, as it does 

 also into the Gulf of St. Lawrence and into other smaller depressions on the conti- 

 nental shelf. There is strong evidence that the slope water that reaches the Gulf 

 of Maine has its source along the Nova Scotian slope to the eastward. The cold Nova 

 Scotian current brings a large volume of water of low salinity into the gulf from 

 the eastward, past Cape Sable, in spring, as a surface drift; but this current slackens 

 or ceases altogether at other times of year. The gulf also receives a surface drift 

 from the offing of Cape Sable, into the composition of which cold banks water from the 

 east, slope water from the Scotian eddy, and tropic water all enter in proportions 

 that can not yet be stated. 



"For further discussion of tliis subject as it concerns the Gulf of Maine, see Bigelow, 1915, p. 255, and 1917, p. 239. 



