PHYSICAL OCEANOGKAPHY OF THE GULP OF MAINE 853 



deep stratum that served as the source for the updraft, as demonstrated by the dis- 

 tribution of sahnity 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 stu-ring), 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 Grampiis 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) . 



