708 
BULLETIN OF THE BUREAU OF FISHERIES 
outflow from the Merrimac produced a slightly greater vertical range of salinity 
(average difference of 1.5 per mille between surface and 40 meters) in the region 
between Cape Ann and the Isles of Shoals by March 12 ( Fish Hawk cruise 9, stations 
20 to 28), though its full effect was not felt until a month later (p. 725). 
Unfortunately, the water samples for these Fish Hawk stations and for the Alba- 
tross station off Boothbay for March 4, 1920 (station 20058), were not taken at vert- 
ical intervals close enough to show whether the river water was then pouring into 
the gulf in volume great enough to maintain a sharply defined stratum of low salin- 
ity at the surface. It is more likely that vertical stirring by tides and waves still 
continued active enough to produce a more even gradation from the surface down- 
ward. However, its effect was certainly greatest close to the surface and perhaps 
not appreciably deeper than 20 to 40 meters until later on in the season. 
40 METERS 
Thanks to the homogeneous state that characterizes the superficial stratum of 
the whole gulf (with the exceptions just noted) during the late winter and early 
spring, the regional distribution of salinity for February and March is much the same 
down to a depth of 40 to 50 meters as it is at the surface (fig. 91). The agree- 
ment is especially close for the isohaline for 32.5 per mille, which shows the same con- 
trast at 40 meters (fig. 93) between fresher water near land and salter offshore all 
around the gulf as at the surface, and with the same expansions of low salinity out 
over the western half of Georges Bank, southward into the central part of the basin 
off the Penobscot Bay region, and out from Nova Scotia across the Northern 
Channel to Browns Bank. 
The isohalines for the 40-meter level (fig. 93) likewise parallel those for the sur- 
face in locating the axis of the freshest band on the Shelburne profile (< 32 per 
mille) as lying over the outer part of the shelf, not close in to that coast as we have 
found it later in the season (fig. 132) . However the rather abrupt east- west transition 
in salinity from this tongue to higher values over Browns Bank and in the Eastern 
Channel (32.86 per mille, station 20071) is sufficient evidence that the Nova Scotian 
current had not appreciably affected the salinity so deep as this farther west than 
longitude 65° up to this date, though some slight movement of water may already 
have taken place in this direction at the surface (p. 703). 
The distribution of water salter than 32.5 per mille is also very nearly the same 
at 40 meters as at the surface in March, with the same gradation lengthwise of 
Georges Bank from lo wer values (about 32.4 per mille) at the western end to higher 
values (about 32.6 to 32.7 per mille) at the eastern, and to slightly more saline water 
(32.8 to 33 per mille) in the Eastern Channel and in the southeastern part of the 
basin. 
It is interesting to find a circumscribed pool of very high salinity ( >33 per mille) 
in the eastern side of the basin at this level, which could have resulted only from 
some local upwelling. 
In winter and early spring, when the water has little vertical stability to resist 
vertical currents, events of this sort are to be expected locally over small areas as 
the result of tidal churnings, or caused by the wind. The distribution of salinity at 
different seasons shows that the basin is most subject to them in its eastern side, and 
