PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
853 
deep stratum that served as the source for the updraft, as demonstrated by the dis- 
tribution of salinity off the coast of Morocco (Schott, 1912, pi. 33). Off the north- 
eastern American seaboard abyssal water would also be betrayed by its precise com- 
bination of salinity and temperature, for while only moderately cold (about 4°) , the 
salinity of the Atlantic abyss is much higher (34.9 to 35 per mille) than that of any 
water on the continental shelf of like temperature. 
The observations taken in 1912, on our first cruise, were enough to prove that 
the inner part of the Gulf of Maine received little if anything from this abyssal 
source, its salinity being too low and its mean temperature too high. 
The rapid warming of the superficial stratum, which takes place all along our 
seaboard in spring from Nova Scotia to Chesapeake Bay (except in limited areas of 
active tidal stirring), is, of itself, incompatible with any widespread upwelling of 
abyssal water, unless this be confined to the deeper strata. So, also, is the wide 
variation in surface temperature from season to season; for any considerable updraft 
from the abyss would necessarily check vernal warming and so narrow the seasonal 
range of temperature. The profiles which the Grampus, Acadia (Bjerkan, 1919), and 
Albatross have run across the continental shelf between Chesapeake Bay and the 
Laurentian Channel have produced a large body of evidence to the same general 
effect; particularly welcome because upwelling had been postulated more on theo- 
retic grounds than from first-hand observation, previous knowledge of subsur- 
face salinity on the continental shelf between Cape Sable and Chesapeake Bay 
being virtually nil. None of these temperature profiles for the summers of 1913, 
1914, 1915, and 1916 (Bigelow, 1915 to 1922) yield any evidence that abyssal water 
ever tends up the slope, much less reaches the continental shelf at that season. To 
the west of Cape Sable, in fact, the coldest water in on the shelf has been separated 
from the low temperatures of the water of the deeps by a somewhat warmer zone 
washing the edge of the continent bottom at intermediate depths in most cases 
(p. 617) . The corresponding salinities have been no more compatible with upwelling 
either at the time of observation or shortly previous, the coldest water on the shelf 
being in every case much less saline (below 33.5 per mille) than the level of equally 
low temperature outside the edge of the continent (34.9 per mille, or higher, at all 
seasons). 
As I have discussed this question in detail in earlier publications (1915, p. 258; 
1922, p. 166), I need only add here that none of the observations taken by the Bache 
off Chesapeake Bay in January, 1914 (Bigelow, 1917a), by the Grampus between 
Marthas Vineyard and Chesapeake Bay in November, 1916 (Bigelow, 1922), or by 
the Albatross off the Gulf of Maine in the spring of 1920, show any more evidence 
of abyssal water reaching the continental shelf than did the earlier observations. 
The only route we need consider, then, by which abyssal water might, perhaps, 
enter the Gulf of Maine, is the Eastern Channel; but the precise combination of 
temperatures and salinities recorded in its trough for the months of March, April, June, 
and July (6.07° to 7.2° and 34.6 to 35.03 per mille), combined with the general 
distribution of salinity and temperature within the gulf, points to quite a different 
source (the slope water) for the intermittent current that drifts inward over the 
bottom of the channel, as is discussed above (p. 842). 
