PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
855 
At most times there is no dominant drift into the gulf across Georges Bank, 
but on rare occasions overflows of tropic water take place at the surface, probably 
via that route. 
The discharges of various rivers, added to rainfall, contribute annually to the 
gulf sufficient fresh water to form a layer half a fathom thick over its inner parts 
out to Georges Bank. The gulf also receives annually a blanket of rain water about 
a foot in thickness, in excess of the amount withdrawn by evaporation. 
The gulf discharges water as a surface current around Nantucket Shoals to the 
westward; to some extent around the eastern end of Georges Bank, 50 and so out 
through the Eastern Channel. 
It is not likely that the gulf ever receives water from the oceanic abyss, by 
up welling, or directly from the Labrador current. 
CIRCULATION IN THE GULF OF MAINE 
Study of the circulation that dominates any part of the sea can be attacked in 
two different ways: (1) Directly, by observation with current meters or drift bottles, 
by ships’ log books, and by interpreting the distribution of salinity and temperature, 
or (2) indirectly, by calculation of the hydrostatic forces tending to set the water in 
motion. The second method has greatly concerned oceanographers of late, and its 
value can hardly be overestimated in the study of ocean currents in the open sea; but 
its application to the Gulf of Maine is complicated by the disturbing factors intro- 
duced by the irregular contour of the bottom, the limiting coast line, and the strong 
tides, which not only produce currents of considerable velocity, but are constantly 
altering the slope of the surface. It is fortunate, therefore, that the following account 
can be based on the more direct methods of observation, supported by consideration 
of hydrodynamic forces as causative agents (p. 930). 
TIDAL CURRENTS 
No one can sail the Gulf of Maine without soon learning that its tidal currents 
run so strong that they must always be taken into account in coastwise navigation. 
Their velocities are so great, in fact, in most parts of the gulf, at the strength of ebb 
and flood, that for the ordinary observer they entirely obscure any dominant or 
nontidal drift that may be in progress. 
No attempt has been made to add to the knowledge of the tides during our 
survey; but the following brief statement, condensed from the Coast Pilot, the 
tide tables and current tables of the Atlantic coast published by the United States 
Coast and Geodetic Survey (1923 and 1926), from the investigations of the Tidal 
Survey of Canada (Dawson, 1905 and 1908), and from other scattered sources, may 
be of interest. 61 
The flood, at its strength, runs northerly, the ebb southerly, along the whole line 
between Nantucket Shoals and the Northern Channel and likewise in the basin to 
8a For discussion of the discharge from the gulf see p. 974. 
81 In 1912 the Grampus recorded the velocity of the current near the mid-period of flood or ebb, hoping to learn the approxi- 
mation of the direction and velocity at its strength. The value of these measurements is discussed in an earlier report (Bigelow, 
1914, p. S3). 
