PHYSICAL OCEANOGRAPHY OP THE GULF OF MAINE 921 
CIRCULATION IN THE DEEP STRATA AS INDICATED BY TEMPERATURE 
AND SALINITY 
Dawson’s (1905) observations made it known that the tidal currents of the 
eastern side of the gulf run about as strongly down to a depth of 55 meters as they 
do at the surface, and measurements taken at 5 stations by the Grampus in the 
summer of 1912 showed bottom currents varying in velocity from 0.1 to 0.25 knot 
per hour in depths of 100 to 265 meters (Bigelow, 1914, p. 86). Evidently, then, 
the basin of the gulf is constantly in a state of active circulation right down to the 
bottom, its whole mass of water oscillating to and fro with the tides, though with 
velocities somewhat lower in the deep water than at the surface. 
Up to the present time no attempt has been made to determine the nontidal 
movement of the bottom water of the gulf with current meters or by the use of deep 
drift bottles, such as have proved so instructive in the North Sea, but the regional 
differences in temperature and salinity outline the major movements over the bottom. 
At depths greater than 100 meters the gulf of Maine is an inclosed basin with 
the narrow Eastern and Northern Channels as the only possible entrances or exits 
through which water can flow in or out of its basin. It follows from this that any 
deep current into the gulf can enter only in its eastern side. Such entrance might be 
via either of the two channels or through both, so far as the contour of the bottom 
is concerned. Actually, however, salinity and temperature show that the indraft of 
slope water over the bottom is restricted to the Eastern Channel, the abrupt west- 
east transition in salinity and in temperature, which characterizes the Northern 
Channel, being incompatible with any large transference of bottom water through 
the latter in either direction. 
The dominant drift in the eastern side of the Eastern Channel is clearly northerly 
(into the gulf) at all times of year, but a considerable difference between high values 
of temperature and salinity in the eastern side of the channel and lower values in its 
western side in March, April, and July (pp. 770, 789) point to an outflowing current 
via the latter, continuing southward and westward around the slope of Georges 
Bank. 
Slope water is betrayed in the deep strata of the gulf by its high salinity 
(33.5-34 per mille, p. 849) and moderately high temperature (4.5° to 8°). At the 100- 
meter level the isotherms and isohalines show the inflowing current hugging the eastern 
slope of the basin in March as a rather definite tongue of high temperature and 
salinity (figs. 13 and 94), veering westward around the northern side of the basin, 
with a countermovement of cooler and less saline water setting southward and 
eastward around the southern side of the basin. In fact, physical evidence could 
hardly be clearer that the general Gulf of Maine eddy was effective to a depth of at 
least 100 meters in this particular month, though complicated by an indraft through 
the Eastern Channel in the deeper levels, which did not directly affect the surface 
(p. 704). 
An anticlockwise circulation is also indicated on the 100-meter charts for April 
(figs. 25 and 116), though less clearly, by concentration of the highest salinities and 
temperatures in the eastern and northern parts of the basin, the lowest in the west- 
ern and southern parts. In this case, however, the westerly component involved a 
broader and less definite band off the coast of Maine than in March, and the easterly 
