PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
975 
In some summers, if not in all, the westerly drift just mentioned involves the 
surface water across the whole breadth of the continental shelf in the offing of 
Marthas Vineyard and Nantucket. This, however, can not be regarded as a direct 
continuation of the outdraft from the gulf around the eastern end of Georges Bank. 
On the contrary, the latter probably swings offshore to join in the easterly move- 
ment of the so-called “inner edge of the Gulf Stream.” 
The evidences of temperature, salinity, and of dynamic gradient unite to show 
this “Gulf Stream” current departing from the edge of the continent as it crosses 
the mouth of the gulf from west to east, so that while it may be encountered within 
15 miles of the 200-meter contour line at longitude 69° to 70°, it is usually at least 
40 to 50 miles out at longitude 66°. Farther east, however, it again approaches the 
slope, at least in some summers. 
Our recent cruises have afforded no evidence of any movement across Georges 
Bank from south to north, though the surface water not infrequently drifts northward 
from the edge of the continent to the west of Nantucket Shoals during the late 
summer. 
The chief seasonal variations from the circulatory scheme just outlined result 
during the autumn and winter from a shift in the heavy (“low”) center of anticlock- 
wise circulation to the Eastern Channel, from a speeding up of the coastwise drift 
around the northern and western shores in spring, and from the brief overflow of 
the Nova Scotian current into the eastern side of the gulf at that same season. 
As a result we find the circulation centering chiefly around the Eastern Channel 
in March with velocities greatest as it drifts inward along the eastern side and out- 
ward along the western side of the latter. From March to April, however, the 
center of circulation shifts northward across the basin; the movement slackens in 
the southeastern part of the area, and the coastwise drift gathers strength. Shortly 
thereafter, when the water of the Nova Scotian current floods into the gulf from 
the east, the heavy center is shifted southwestward right across the gulf. At the 
same time (in May) the northeast-southwest drift around the northern and western 
coasts attains its highest velocity and its most definitely long-shore character, and 
is most definitely continued southward past Cape Cod. It also involves Massa- 
chusetts Bay, not only crossing the mouth of the latter, but also skirting its coast- 
line from north to south, and so out again past Cape Cod. Under these circumstances 
flotsam of any kind (buoyant fish eggs, for instance, or the larvae hatched therefrom) 
that may drift from the north into the northern side of Massachusetts Bay, or 
that may be produced there, tends to drift out of its southern side. 
This long-shore movement (involving Massachusetts Bay) may continue, little 
altered, into the summer; but some time between May and July the heavy center 
again shifts eastward, and in some years, at least, this center becomes divided into 
the two lows recorded for the summer of 1914 — the one in the offing of the Bay 
of Fundy, the other in the region of the Eastern Channel. This completes the 
yearly cycle. 
On the bottom the water moves inward along the eastern side of the Eastern 
Channel during the early spring, and at other times of year in pulses not yet under- 
stood, usually outward along the western side. At depths of 150 meters, or deeper, 
the general tendency within the basin is northward along the eastern (Nova Scotian) 
