836 BULLETIN OF THE BUREAU OF FISHERIES 



finally northward toward the Gulf of Maine, via Browns Bank and the Cape Sable 

 dead water. 



In years such as those just described the region in the offing of Cape Sable, 

 out to Browns Bank, between the two major circulatory eddies (Scotian and Gidf 

 of Maine) but not directly within the sweep of either, is evidently the site of a very 

 active mixing of waters of diverse origins. Under such conditions a very abrupt 

 east-west transition in temperature and salinity develops off the cape, proving that 

 the westerly (inshore) component of the Scotian eddy is not the motive power for 

 such water as does then flood into this side of the Gulf of Maine. This eddy, on 

 the contrary, is clearly outlined by the surface sahnity for July and August, 1914 

 (Bigelow, 1917, fig. 18), and for June, 1915, as swinging offshore toward La Have 

 Bank, which prevents it from flooding westward through the Northern Channel, 

 toward which the rotation of the earth would direct it, did the contour of the bottom 

 allow. 



The strong tidal currents oft' southern Nova Scotia must tend, however, to 

 pump water from the Cape Sable deadwater into the gulf, because the flood, running 

 westward at a mean velocity of 1.4 knots (Dawson, 1908, station R; a journey of 

 something like 8J4 miles for any given particle of water), must follow westward and 

 northward around Cape Sable as it is forced to the right against the shore by the 

 effect of the earth's rotation. With the ebb similarly deflected to the right, a clock- 

 wise movement around the rounded outline of southwestern Nova Scotia naturally 

 results, such as eddies around any submerged shoal in high northern latitudes. 



TROPIC WATER 



We may next consider the possibility that overflows of the surface stratum of 

 tropical or "Gulf Stream" water, the inner edge of which always lies within a few 

 miles of the edge of the continent, may enter the Gulf of Maine from time to time; 

 also possible movements of the coast water from west to east past Cape Cod into 

 the gulf, either via Vineyard Sound or around Nantucket Island. Water from either 

 of these sources would reach the gulf as warm currents, contrasting with the cold 

 Nova Scotian current, the former high in salinity, the latter low. 



As pointed out above (p. 700), events of the first category undoubtedly do occur 

 on occasion. Small amounts of "Gulf Stream " water have long been known to drift 

 inward, toward the sector of coast line bounded on the east by Marthas Vineyard 

 and on the west by Narragansett Bay, during most summers, bringing with them a 

 typically tropical fauna of fishes, planlctonic invertebrates, and Gulf weed (Sargassum) . 



Were it not for the peculiar distribution of densities off the slopes of Georges and 

 Browns Banks, shortly to be described (p. 843), which produce more or less constant 

 dynamic tendency for the surface stratum to move out, seaward, from the edge of 

 the continent (a tendency altered rato a long shore current to the westward by the 

 deflective effect of the earth's rotation; p. 846), tropic water might similarly be 

 expected to drive in over the surface right across the banks under the propulsion of 

 high and prolonged southerly winds. Under most conditions, however, the distri- 

 bution of density imposes an impassible barrier to surface drifts from the southward 

 into the gulf (p. 939). It is fortunate for the fisheries of New England that such is 



