PHYSICAL OCEANOGEAPHY OF THE GULF OF MAINE 801 



there in the summer in any year. True, the seasonal succession is not altogether 

 clarified thereby, because of the certainty that annual differences are sometimes 

 wider than the seasonal differences; 1916 may have been a fresh autumn, while 

 the summers of 1913 and 1915 were certainly more saline than those of 1912 or 

 1914. At least there is nothing in this record to suggest an active inward pulse of 

 slope water during the early autumn, but rather the reverse; and the relationship 

 between the salinities for that date, on the one hand, and the curves for July 17, 

 1912, and August 22, 1914, on the other (stations 10007 and 10254), is what might 

 be expected in the normal seasonal succession, with vertical stirring by tidal cur- 

 rents, winds, and waves becoming increasingly more effective through the autumn, 

 when cooling at the surface decreases the vertical stability of the water. 



We have no data for salinity on the offshore banks — Georges or Browns — for 

 October or later in the autumn; but profiles of the continental shelf in the offing of 

 Marthas Vineyard and a few miles farther west, run by the Grampus during the 

 third week of October, 1915 (stations 10331 to 10334), and on November 10 and 11, 

 1916 (fig. 162), show that if slope water had worked in over this sector of the shelf 

 along this line during the preceding summers it had moved out again from the edge 

 of the continent by mid autumn, leaving values lower than 34 per mUle out to the 

 120-meter contour. It is likely, therefore, that such encroachments of high salin- 

 ity over the outer edge of the continental shelf off southern New England as are 

 described above (p. 796) are strictly summer events. For water as saline as 34 per 

 mille to continue on this part of the shelf after the end of September would, it seems, 

 be an unusual event. 



If the inshore ends of these two profiles, in combination, represent the usual 

 October-November state, and if conditions prevailing there in August, 1914 (p. 796, 

 fig. 158), are equally representative of that season, the coastwise water less saline 

 than 32.5 per mille spreads out from the land, seaward, during the autumn, until the 

 isohaline for this value includes the bottom out to the 40 to 60 meter contour and 

 the surface halfway acoss the shelf .^ The relationship between this November pro- 

 file and the profile off New York for that August affords further evidence of similar 

 import, as remarked elsewhere (Bigelow, 1922, p. 125, figs. 23 and 38). 



The most interesting alteration that takes place later in the autumn is that the 

 vertical range of salinity in the upper 100 meters, like that of temperature, decreases 

 as the water loses stability and as tides and winds stir it more and more actively. 



Observations on the salinity of the gulf for the last half of November and first 

 half of December have been confined to the bowl at the mouth of Massachusetts 

 Bay off Gloucester in 1912 (Bigelow, 1914a, p. 416), and to the deep trough of the 

 Bay of Fundy, between Grand Manan and Nova Scotia, in 1916 and 1917 (Mavor, 

 1923, p. 375). 



At the first of these localities and years salinity had become virtually homoge- 

 neous at about 32.5 per mille from the surface down to a depth of about 50 meters 

 by November 20, increasing slightly with increasing depth to 32.66 per mille at bot- 

 tom in 62 meters (fig. 111). However, the fact that virtually no alteration of salin- 

 ity had taken place at the bottom there siuce the precediag August (stations 10045 



•On the August profile (fig. 158) water less saline than 32.5 per mille did not touch the bottom at all at depths greater than 

 20 meters. 



