800 BULLETIN OF THE BUREAU OF FISHEEIES 



31 than at a locality a few miles to the south on August 29 (station 10398), with 

 almost precisely the same values at depths greater than 50 meters as in August and 

 October, 1915. Increasing salinity in the upper strata, contrasted with constancy 

 in the deep water, is thus a regular accompaniment of advancing autumn in this 

 locality. 



Tidal currents being comparatively weak here, autumnal salting at the mouth 

 of Massachusetts Bay reflects some widespread change of the same sort, not simply 

 vertical mixing in situ. The extent to which the inner waters of the bay share in 

 this alteration during the early autumn is therefore interesting. Unfortunately, this 

 can not be stated, for want of data at successive dates throughout any given season; 

 but the fact that the surface of the northern side of the bay had virtually the same 

 salinity on October 26 and 27, 1915 (stations 10338 and 10339), as a month earlier 

 (stations 10320 and 10321), but had become about 0.5 per mille more saline near 

 Cape Cod during this same interval (station 10322, 31.4 per mille; station 10337, 

 31.9 per mille), is evidence that salinity increases more rapidly at the mouth of the 

 bay in autumn than near the head, as might be expected. 



Passamaquoddy Bay, across the gulf, is also somewhat more saline in October 

 than in August, by Vachon's (1918) observations, notwithstanding irregularities in 

 the mid depths, caused, no doubt, by the strong tides. As Passamaquoddy Bay 

 receives the discharge of a large river, while the land drainage into Massachusetts 

 Bay is trifling, it is probable that a corresponding increase in salinity takes place in 

 estuarine situations and along the shore generally all around the coast line of the 

 gulf as well as in the Bay of Fundy, where Mavor (1923) records a considerable 

 increase in the salinity of the upper 80 meters of water between Grand Manan and 

 Nova Scotia^ from August 25, 1916, to November 6. 



Such data as are available for October make it Ukely that this general salting 

 brings the surface salinity above 32 per mille all along the coastal belt to the north 

 and east of Cape Ann (outside the outer islands) by the first week of the month in 

 most years. As a result the area less saUne than 32 per mille which skirts the whole 

 coast line of the gulf from Cape Cod to the Bay of Fundy in July and August (p. 769) , 

 contracts to include Massachusetts Bay alone by mid autumn. A similar relation- 

 ship between the salinities of late summer and of mid autumn prevails down to a 

 depth of 40 to 50 meters. 



Some increase in the salinity of the upper stratum of water was naturally to be 

 expected along this sector of the coast line in autumn as the effects of the vernal 

 discharges from the rivers are gradually dissipated. If this process of mixture is 

 accompanied by an active indraft of highly saline water into the bottom of the gulf 

 the increase will involve the whole column right down to the deepest stratum of the 

 basin; otherwise the intermingling of comparatively low salinities from above with 

 higher salinities from below must result in lowering the salinity of the deeper strata 

 while raising that of the shoaler. The vertical distribution of salinity is therefore 

 an index to the strength of the bottom drift in autumn. 



Unfortunately, no deep stations were occupied during the autumn of 1915; but 

 on November 1, 1916, observations taken in the basin off Cape Ann (station 10401) 

 yielded decidedly lower salinities in the deepest stratum than we have ever found 



< Prince station 3 (Mavor, 1923, p. 375). ' 



