PHYSICAL OCEANOGRAPHY OP THE GULF OF MAINE 
571 
ing freshening at the bottom, this cooling is clear evidence that the warm, highly 
saline oceanic water that bathed this part of the slope in February, as it usually 
does in summer (p. 617), had receded offshore by May. Lacking data farther east- 
ward along the slope for this season, it is impossible to state the precise cause of this 
event further than that it probably represented a dynamic alteration (p. 936) rather 
than a direct extension of Nova Scotian water in this direction (p. 825). 
Whatever its cause, however, the fact that so great a chilling of the bottom 
water undoubtedly did occur in just this location in 1920 (and may, perhaps, every 
spring) is of great interest biologically, as events of this sort necessarily limit the per- 
manent bottom dwellers of the eastern part of the so-called “warm zone” to such 
Fig. 37.— Temperature profile from a point a few miles off Cape Cod to German Bank, for May 29 and 30, 1919 (ice patrol 
stations 35 to 38) 
animals as can survive temperatures as low as 7° to 8°. Unfortunately no readings 
were taken there during the only spring (that of 1884) when a serious mortality is 
known to have taken place among its inhabitants — invertebrates as well as fishes 
(notably the tilefish) — but in very cold years the temperature there may fall several 
degrees lower, perhaps, than happened in 1920. Tentatively, mid May may be set 
as the coldest season on bottom along this part of the continental slope — three months 
ater than in the inner waters of the Gulf of Maine. 
JUNE 
I am not able to present as satisfactory a thermal picture of the gulf for June as 
for the spring, no measurements of temperature having been made in the western 
side of the basin, along shore between Cape Ann and Cape Elizabeth, nor on Georges 
Bank during that month. On the other hand, our June cruise of 1915 led far enough 
east past Cape Sable to cross-cut the Nova Scotian current before it passes that 
