PHYSICAL OCEANOGRAPHY OP THE GULP OP MAINE 



691 



this connection by governing the Archimedian force that tends to pump the slope 

 water westward to the Eastern Channel and so into the Gulf of Maine. This works 

 most effectively in spring and early summer, but fluctuates so narrowly from season 

 to season that only very narrow variations are to be expected in the temperature or 

 salinity of any part of the gulf deeper than about 150 meters, from season to season 

 or from year to year, or have actually been recorded there. 



This uniformity in the physical state of the bottom water on the floor of the 

 deep trough of the gulf proves that the effects of the alternate seasonal warming 

 and chilling of the surface do not penetrate deep enough to obscure the dominance 

 of the slope water there; but the slight seasonal rise and fall of temperature that 

 has been recorded at the bottom of the deep sink off Gloucester and between 

 Jeffreys Ledge and the mainland (from which the slope water is barred by inclosing 

 rims too shoal for it to overflow) is evidence that sHght (but measureable) winter 

 cooling and summer warming from above may be detected down to 200 meters, so 

 far as the depth alone is concerned. 



It is because the slope water is warm, by comparison with the water with which 

 it mixes within the gulf, that the bottom of the latter is usually warmest in the 

 eastern side of the basin, at depths greater than 150 meters, where the inflowing cur- 

 rent is chiefly localized (p. 921), coldest in the "sinks" in the inner parts of the gulf, 

 from which the slope water is more or less effectually barred by submarine rims. 



The following difi"erential table shows that the slope water has little effect on 

 the deep temperature in such situations, as exemplified by the sink off Gloucester 

 and by the trough between Jeffreys Ledge and the Isles of Shoals. This generaliza- 

 tion applies also to the Bay of Fundy, from which most of the slope water is deflected 

 by the topography of the bottom. In summer and autumn, it is true, the 175 to 

 200 meter level may be as warm within the bay (6° to 7°) as without; but low salin- 

 ity proves that this high bottom temperature chiefly reflects the active convectional 

 currents of the bay by which solar heat received at the surface is dispersed more 

 evenly downward there than it is anywhere else in the gulf in water equally deep. 



1 Tlie table shows only the differential existing on the given dates between the deepest level, where a reading was taken 

 within the bowl, and the corresponding level in the t)asin outside. It does not represent the seasonal cycle for the latter because 

 of the difference in levels from station to station. 



' 150-meter reading not taken. 



3 130 meters. 



