702 
BULLETIN OF THE BUREAU OF FISHERIES 
the 1,000-meter contour. However, even such a range as this is narrow, as com- 
pared to temperature, for with the mean salinity of the gulf falling close to 32.5 per 
mille the extreme variation is not more than 20 per cent. Consequently, I must 
caution the reader that while emphasis is laid on these variations in the following 
pages, they are actually so small, from season to season and from place to place, 
that their measurement requires careful chemical or physical tests. They could not 
be detected by any human sense. To use a homely example, no one, I fancy, could 
distinguish the saltest water of the gulf from the freshest by its taste, but no one 
could fail to tell the temperature of winter from that of summer if he dipped his 
hand in the water or by feeling the spray on his face. 
The gulf is invariably saltest in the eastern side of its trough and in the 
Eastern Channel, which connects the latter with the open ocean. It is freshest 
in the coastwise belt along its northern and western shores and along the western 
shoreline of Nova Scotia, as appears repeatedly on the charts of salinity for various 
levels and seasons. 
The fact that the water over Georges Bank (the shoal southern rim of the gulf) 
is not sal ter than the basin to the north of it deserves emphasis because its proximity 
to the oceanic waters of the “ Gulf Stream ” might lead us to expect high salinities 
there. 
A wide seasonal variation in the salinity of the surface is characteristic of coast- 
wise waters in boreal latitudes, the water freshening at the season of the spring fresh- 
ets and then gradually salting again as this inrush of river water is incorporated by 
the mixings and churnings caused by the tides, winds, and waves. 
The Gulf of Maine is no exception to this rule. The widest seasonal variations 
so far actually recorded there at any given station are from about 28 per mille in 
April to about 32.7 per mille in winter in the Bay of Fundy (fig. 165), and from about 
28.3 per mille in May to about 32.3 per mille in early March in the opposite side of 
the gulf, a few miles off the mouth of the Merrimac River (p. 813). Such changes, 
however, are confined to the superficial stratum of water not over 40 meters thick. 
The bottom waters of the gulf deeper than 100 meters see very little alteration in 
salinity from season to season. The salinity has also proved unexpectedly constant 
from year to year in all parts of the gulf at any given season. 
The Gulf of Maine is characterized by a considerable vertical range in salinity 
over all but its most tide-stirred portions, contrasting strongly in this respect with 
the North Sea, across the Atlantic, where the salinity as a whole is more nearly 
uniform from the surface downward. The vertical range is widest in spring and 
summer, when the surface as a whole is freshest, narrowest toward the end of the 
winter; greatest, too, where the stirring effects of the tides are least, as in the west- 
ern side of the gulf off Massachussetts Bay, and least where tidal currents keep the 
water more thoroughly churned, as in the Bay of Fundy in one side of the gulf or 
on Nantucket Shoals in the other. 
In summer, and in the coastwise zone, the increase in salinity with depth 
averages most rapid from the surface down to a depth of about 50 to 75 meters; but 
there are many exceptions, and in the deep basin of the gulf the salinity gradient 
may be nearly uniform, surface to bottom, or the rise in salinity may be found most 
rapid as the bottom is approached. 
