PHYSICAL OOEANOGEAPHY OF THE GULP OF MAINE 917 



The most interesting aspect of the seasonal dislocations of the isohalines in the 

 southeastern part of the Gulf of Maine area is the light they throw on the fluctu- 

 ations and lines of dispersal of the Nova Scotian current while this is flowing into 

 the gulf from the eastward. The source of this cold water of low salinity and the 

 chilling effect it exerts on the gulf are discussed in another chapter (p. 825), leaving 

 for present consideration the r61e it plays in the dominant circulation of the gulf. 



No dominant current of any great volume is demonstrable past Cape Sable in 

 either direction from the salinities for August or September (though bottle drifts 

 show the movements of water stated in another chapter — p. 908), nor in March (fig. 

 91) ; but when the Nova Scotian current commences to flood westward into the gulf in 

 spring, its freshening efl'ect is unmistakably reflected by a very noticeable dislocation 

 of the critical isohalines (32 and 32.5 per mille). The seasonal schedule of this 

 event varies from year to year, as described on page 832, 1920 being late in this 

 respect, 1919 early, but experience in those years and in 1915 suggests that as the 

 flow of the Nova Scotian current increases to its greatest head, it may be described 

 as sweeping the isohalines westward before it far out into the gulf. 



Unfortunately, our May cruise of 1915 did not extend to the southeastern part 

 of the gulf, nor did the Canadian Fisheries Expedition take observations west of 

 Halifax during that month, which leaves a wide gap for which I can not attempt 

 to reconstruct the courses of the isohalines. However, the curves for 32 per mille 

 salinity at the surface and at 40 meters (figs. 120 and 125) both outline the current 

 as spreading westward from the cape toward the center of the gulf and somewhat 

 fanlike toward the north. 



This is corroborated by the fact that the Grampus encountered a strong set to 

 the westward, upwards of 2 knots in velocity, on her run from the eastern side of 

 the basin (station 10270) toward Seal Island, off Cape Sable (station 10271), on the 

 7th of that month. In that year, however, which may be taken as representative, 

 the surface isohahne for 32 per mille had again withdrawn a considerable distance 

 eastward toward Cape Sable by the last week in June (fig. 128), evidence that the 

 westerly drift across the basin of the gulf ceased as soon as the flow of the Nova 

 Scotian current slackened. The general distribution of salinity that characterizes 

 the eastern side of the gulf in summer (p. 765) is best explained on the assumption 

 that any water that rounds Cape Sable from the east during the months of July, 

 August, and September veers northward along Nova Scotia toward the bay of 

 Fundy, which is in accord with the drifts of the bottles that have entered the gulf 

 from the east (p. 908). 



It is obvious that the western extension of the Nova Scotian current must pro- 

 foundly affect the nontidal circulation of water in the gulf at the season when it is 

 at its maximum. Comparison of the surface salinity in May (fig. 120) with the 

 currents deduced from bottle drifts m. August suggests that this change consists 

 chiefly in shifting the eastern side of the Gulf of Maine eddy westward — how far, 

 can not yet be stated. 



It is also obvious that if the the anticlockwise eddy persists through spring (as 

 there is ample evidence, theoretic as well as direct) it must constantly draw into its 

 eastern side (and so carry northward toward the Bay of Fundy and the coast of 



