750 
BULLETIN OP THE BUREAU OP FISHERIES 
If the contrast between the salinities for the early spring of 1920 and for May, 
1915, represents the succession normal for this time of year, a very considerable 
freshening also takes place at greater depths in the eastern side of the basin from 
March and April to May, the graphs (figs. 114 and 124) suggesting an average 
decrease of about 0.6 to 0.8 per mille at 100 meters and deeper. Such a reduction 
of the salinity back to about the March values naturally would follow any slackening 
of the inflowing bottom current, but would be less and less apparent the farther from 
its source of supply. A regional relationship of this sort does, in fact, result from our 
station data, which show the salinity of the bottom water of the western side of the 
basin only slightly lower in May and June, 1915, than in March or April, 1920 
(fig. 112). 
The upwelling of water more saline than 33 per mille in the western side of the 
basin, which follows or accompanies the incorporation of river water into the one side 
of the gulf and of the Nova Scotian current into the other, causes a much more 
abrupt transition in salinity between coastal belt and basin at 40 meters in May 
(fig. 125) than in April (fig. 115) ; still wider than in March, and a regional distribu- 
tion more nearly paralleling the surface (fig. 120). The gradation from 31.7 to 31.9 
per mille next the land to 32.8 to 33 per mille in the west-central parts of the basin, 
shown on this May chart, is probably typical for the month, though no doubt the 
precise spread between inshore and offshore values varies somewhat from year to 
year and would probably have proved somewhat narrower in 1925, when the 40-meter 
values for Massachusetts Bay in May averaged slightly higher (32 to 32.6 per mille) 
than was the case in 1915 or in 1920. 
Up to May the decrease in salinity attributable to vernal freshening is 
confined to even a narrower coastal belt at 40 meters than at the surface, 
hardly any change being indicated more than 10 miles out from that contour 
line in the western side of the gulf 93 or farther south than the offing of Cape Cod, 
where the 40-meter values were somewhat higher on May 16 to 17, 1920 (32.3 to 
32.5 per mille at stations 20125 and 20126), than they had been a month earlier 
(32.1 to 32.2 per mille at stations 20116 and 20117 on April 18). The salin- 
ity at this depth was also about the same in the southwest part of the basin and on 
Georges Bank in that May (32.5 per mille) as it had been at the end of February. 
In spite of this apparent agreement, however, the water less saline than 33 per 
mille must actually have increased considerably in volume in the offing of Cape Cod 
during the interval to account for its expansion out from the bank to the seaward 
slope of the latter, where salinity decreased by about 1 per mille at 40 meters between 
February 22 (station 20045, about 33.8 per mille) and May 17 (station 20129, 
about 32.9 per mille). 
It is probable that the salinity of the 40-meter level falls below 32 per mille every 
May over a considerable area out from the Nova Scotian shore of the gulf, where 
the Nova Scotian current then holds sway; and if 1915 was a typical spring in these 
waters (which I see no reason to doubt) the drift of this water of low salinity from 
its more eastern source is directed more definitely westward toward the center of the 
gulf at this depth than it is at the surface, with less evidence of any dispersion north- 
ward toward the Bay of Fundy (p. 745). Reduced to terms of distance, the seasonal 
15 This follows an extremely irregular course. 
