PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 793 



isohalines show a sudden transition from the one to the other (most abrupt at this 

 shoaler levels) and parallel to the edge of the continent. It is especially suggestive 

 that while considerable overflows of water more saline than 33 per mille appear on 

 the profiles in two regions — one from the Eastern Channel across Browns Bank, as 

 just described (p. 788), and the other in the offing of Nantucket Shoals — neither 

 profile (nor the chart for 200 meters, fig. 150) suggests any tendency for this most 

 saline water to enter the Eastern Channel. On the contrary, the isohalines for 

 the highest values at each level cross the latter, leaving the oceanic triangle occupied 

 by the intermediate salinities of the slope water (33 to 35 per mille). 



As to the date when bottom water of high salinity may be expected to drift in 

 over the edge of the continent toward Nantucket Shoals, I can only point out that 

 in 1913 water of 33 to 33.5 per mille and upwards in salinity was encountered at 40 

 meters over the outer edge of that sector of the shelf as early as July 10 (stations 

 10060 to 10062). In 1914 water of this high salinity had encroached on the south- 

 western part of Georges Bank by July 19 and had reached the 40-meter contour off 

 Nantucket Shoals some time prior to the last week in August (fig. 145) ; but in 1916, 

 a backward year (p. 772), the bottom water over this part of the shelf was only 

 32.5 to 33 per mille on July 19 to 25 (stations 10354 to 10355, fig. 159)— i. e., 

 about 1 per mille less saline than at about the same season of 1913 or of 1914, cor- 

 responding almost exactly to the readings obtamed there in May, 1920. 



Water more saline than 35 per mille may be expected to wash, the slope 

 at the 100-m.eter level right across the mouth of the gulf at some time during the 

 summer, and perhaps continuously throughout the summer during some years, for 

 the Canadian Fisheries Expedition had 35.35 per mille at 100 meters on the slope 

 of the La Have Bank in July, 1915 (Bjerkan, 1919; Acadia station 41), where the 

 100-meter salinity on July 28, 1914, was only 34.16 per mille (station 10233; both 

 readings taken over the 450-meter contour line) . 



Only on one occasion have our lines reached water of full oceanic salinity (36 

 per mille) — namely, abreast the western end of Georges Bank on July 21, 1914 

 (p. 780, figs. 1-45 and 156). Failure to find water as saline as this at our outermost 

 stations anywhere else between the offings of Chesapeake Bay and Cape Sable on 

 any other cruise, or ofi' Nova Scotia, suggests that this pure "Gulf Stream water" 

 may be expected to approach the edge of the continent more closely thereabouts, 

 as it moves northward in summer, than either to the west or to the east. 



We have yet to learn whether oceanic water approaches so close to the edge of 

 the continent every summer as it did in 1914. In 1913 and 1916 (the one an early 

 and the other a late season in the sea) it certainly did not do so until well into the 

 summer, if at all. We may assume, therefore, that the situation pictured on the July 

 profile for 1914 (fig. 156) is most likely to be reproduced in August, taking one sum- 

 mer with another. 



Although this highly saline water probably approaches within a few miles of 

 the 200-meter contour at about this longitude (68° to 70°) by the end of every 

 August, it has never been found actually encroaching on the continental shelf abreast 

 of the Gulf of Maine or anywhere else along the North American littoral north of 

 Chesapeake Bay at any season. Bjerkan's (1919) record of 35.9 per mille at 50 

 meters at the Acadia station 44 miles off La Have Bank on July 22, 1915, combines 



