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BULLETIN OF THE BUBEAU OF FISHEBIES 
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 4 from August 25, 1916, to November 6. 
Such data as are available for October make it likely 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 saline 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 
1 Prince station 3 (Mavor, 1923, p. 374) 
