PHYSICAL OCEANOGKAPHY OF THE GULF OF MAINE 639 
greater depths, resulting, no doubt, from the constant tendency toward vertical equal- 
ization by tidal mixing. 
The profile for this date (fig. 69) shows that cooling had proceeded less rapidly in 
the southern side of the bay next to Cape Cod, which receives warm water from Cape 
Cod Bay, than in the central and northern parts, making the regional variation wider 
than it is in summer (fig. 66) . Temperature of the upper 40 meters of Massachu- 
setts Bay, however, was virtually equalized at 9.5° to 11.5° by the last week of that 
October (stations 10237 to 10239). On the other hand, vertical stirring had been 
active enough to raise the temperature of the 80 to 150 meter stratum of the bowl off 
Cape Ann from 5.8° on August 31, 1915, to 6.8° to 7° on October 1 (stations 10306 
and 10324). 
Fig. 69. — Temperature profile at the mouth of Massachusetts Bay, inside Stellwagen Bank, 
September 29 to October 1, 1915 (stations 10320 to 10322). The broken curve shows the 
contour of the bank 
The thermal cycle was essentially similar in the cold year of 1916, when the 80 
to 90 meter level was nearly 2° warmer at the mouth of the bay on October 31 (sta- 
tion 10399, 5.43° at 90 meters) than it had been on July 19 (station 10341, 3.67° at 
80 meters), although the surface had cooled from 16.4° to 10° during the same inter- 
val, or to about the temperature normal for the outer part of the bay at that season. 
Graphs for temperature off the Isles of Shoals and off Cape Elizabeth on Octo- 
ber 4, 1915 (stations 10225 and 10226), and at various dates in August (fig. 70.) show 
much the same seasonal change as Massachusetts Bay, characterized by consider- 
able cooling at the surface, but at a decreasing rate, down to about 30 to 40 meters, 
contrasted with a slight warming at greater depths down to bottom in 145 to 175 
meters. However, it is impossible to state the precise rate of change for any given 
level for any one year from the data at hand. 
