852 BULLETIN OF THE BUREAU OF FISHEKIES 



With 10 of our 14 August stations as deep as 180 meters (100 fathoms), or deeper, 

 also showing bottom values higher than 34 per mille in 1912, 1913, and 1914, this 

 indraft is evidently characteristic of June or July. No doubt, however, it varies from 

 year to year, both in its seasonal schedule and in its volume and velocity, and the 

 distribution of density (pp. 958, 960) shows that in some summers, at least (as exempU- 

 fied by 1914), a counterdrift develops through the channel, out of the gulf, in 

 July, though perhaps only for a brief period. 



In a summer when this inflowing bottom current is active, slope water may be 

 expected to occupy approximately the area shown in the contour chart for July and 

 August, 1914 (fig. 152), its boundaries, as in March less extensive than in April, 1920 

 (figs. 100 and 118), including only the two arms of the trough and the region of 

 their junction instead of the whole central part of the gulf basin. 



By good fortime our records afford charts of the slope water at its maximum for 

 the respective months ^^ — the one representing a period of active inflow, the other the 

 tendency toward equalization that follows such a period. 



Slope water is thus shown to enter the gulf from midsummer on through autumn 

 and winter — but certainly in varying pulses — and to slacken or cease during the late 

 spring and early summer. It is not possible to outline its fluctuations in the gulf 

 more definitely than this from the data gathered so far. 



ABYSSAL UPWELLINGS 



Upwellings from the oceanic abyss, if such occur, would be a second possible 

 source of water of high salinity and moderate temperature for the deeps of the Gulf 

 of Maine. Upwelhng of this sort, in fact, has often been invoked to explain the low 

 temperature of the so-called "cold wall" (referred to here as "slope water"), as con- 

 trasted with the tropic water on its offshore side (Buchan, 1896). 



Thus, Pettersson (1907 and 1907a), for example, definitely classed the cold wall 

 along the North American littoral as an updrift over the continental slope from the 

 cold abyssal water of the Atlantic, having for its motive power the sinking of cold 

 water off Newfoundland. While this view has not found a very favorable reception, 

 both Schott (1912) and Kriimmel (1911) have believed that more or less upwelling 

 does occur along our coasts, at least in winter; while A. H. Clark (1914) has argued that 

 the cold water off Nova Scotia must receive something from the abyss to account 

 for the geographical distribution of crinoids. 



The criteria by which upwelling from the oceanic abyss would be made recog- 

 nizable may be stated in a few words. 



In temperate zones surface temperature is perhaps the best index of this process 

 in summer, for in regions where the water wells up actively seasonal warming is 

 retarded, causing abnormally low surface temperature . Unless the upwelling extended 

 along the whole east coast of North America (a most improbable supposition) any 

 cold water welling up would be surrounded by a warmer surface to the north and 

 south of it as well as on its offshore side, as is the case off California (McEwen, 1912) 

 and off the northwest coast of Africa (Schott, 1902, pi. 8). At the same time there 

 would be a continuity in salinity between this cold water near the surface and the 



*' 1920 was a salt March, compared with 1921; 1914 a salt summer, compared with 1913. 



