692 
BULLETIN OF THE BUREAU OF FISHERIES 
Further evidence that slope water is of little importance in the thermal cycle of 
the Bay of Fundy results from the fact that we found the 200-meter level 1° colder 
(4.3°) within the latter than just outside (5.4°) in March, 1920 (stations 20079 and 
20081), with a corresponding difference in salinity. A reading of 1.71° reported by 
Mavor (1923) at 175 meters in the bay on April 9, 1917, is colder than the coldest 
reading so far obtained anywhere in the open basin of the gulf at this depth. 
The deep readings for different times of year warrant the following generaliza- 
tions: At depths greater than 150 meters the temperature is most nearly uniform 
through the year in those parts of the gulf which the slope water reaches in greatest 
volume, and shows its widest seasonal fluctuation in the partially inclosed bowls that 
receive least water from this source. Were it not for this deep current flowing in, the 
floor of the gulf would be several degrees (perhaps 3° to 4°) cooler in winter than is 
actually the case, and its mean for the year slightly lower. The bowl off Gloucester 
and the trough west of Jeffreys Ledge show the nearest approach to the thermal 
state that would prevail in the gulf were it neither open to the inflowing bottom 
current nor stirred by such strong tides as those that disturb its eastern side. 
The thickness of the bottom stratum where temperature is governed by the volume 
and precise physical characters of the slope water is of interest. Its upper boundary 
in the inner part of the basin of the gulf may be set tentatively at about the 150- 
meter level, rising to within SO to 100 meters of the surface in the southeastern part 
at the entrance to the Eastern Channel. On the other hand, the deep temperature 
is most influenced from above where tidal or other convectional stirring is most active. 
WINTER CHILLING 
Abyssal upwelling, as I have shown (p. 853), is barred out as a possible source of 
autumnal cooling in the Gulf of Maine. It is equally certain that the Nova Scotian 
current usually serves as a cooling agent in the gulf only in the spring, because none of 
our observations for autumn or winter suggest that progression of cooling from east 
to west across the gulf, which would reflect any inflow of cold water past Cape Sable 
at that season. We must therefore credit the very rapid loss of heat which the Gulf 
of Maine suffers in autumn and winter entirely to local causes, chiefly to the radia- 
tion of heat out from the surface to and through the colder air above it; to evapo- 
ration; in less degree to the melting of the snow that falls on the sea; and, locally, 
to the melting of ice. 
The warming effect of the sun’s rays is combatted the year round by local 
influences tending to reduce the temperature of the water or as least to retard ver- 
nal warming. Evaporation from the surface, for one thing, uses up heat, thus cool- 
ing the water (p. 680). Furthermore, the heated surface radiates heat out into the 
air whenever the temperature of the latter drops below that of the water, even in 
spring and summer. 
The solar energy absorbed by the water is more than enough to offset these 
forces up to mid or late August; consequently the temperature of the surface of all 
parts of the gulf continues to rise. However, the amount of solar heat daily absorbed 
by the water, at its maximum when the sun is at its highest declination, is constantly 
decreasing after June 22 to 23; and after a certain date toward the end of summer 
or early in autumn, a date that varies regionally, as described in an earlier chapter 
