PHYSICAL OCEANOGEAPHY OF 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 o£E Cape Cod to German Bank, for Maj' 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 

 later than in the inner waters of the Gulf of Alaine. 



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 



