PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
599 
Temperature, Centigrade 
7 ° 8 ° 9 ° 10 ° 11 ° 12 ° 
bottom temperature (depth for depth) progressively higher and higher, around the 
margin of the gulf from Cape Cod to the Bay of Fundy, with the average vertical 
range of temperature decreasing from about 12° off Cape Ann to virtually nil in the 
Grand Manan Channel. 
Thus, the difference of temperature between the surface and the 50-meter level 
(never less than about 10° at the mouth of Massachusetts Bay in summer) was only 
about 5° to 8° off Casco Bay (stations 10019 and 10103), 4° to 5° near Monhegan 
Island on August 4, 1915 (station 10303), and about 4° at the west entrance to Penob- 
scot Bay on August 22, 1912 (station 10039). Near Mount Desert Island the vertical 
range for the corresponding column of water was only 2° on August 18, 1915 (station 
10305), about 4° on August 13, 1912 (station 10099), 25 about 4.5° on the 5th 
of the month in the very cold year 1923, or an average of 3° to 4°. The water is 
kept even more nearly homogeneous in temperature among the islands of the Mount 
Desert region by strong tides, so that the surface was only 1.5° to 0.1° warmer than 
the bottom a couple of miles off Little Duck Island 
on August 8 to 11, 1925, in depths of 25 to 30 
meters. Meter 0 
This also applies off the open coast farther east. 10 
Off Machias, for example, the surface reading was 
only about 1° higher than the bottom reading on 
August 16, 1912 (station 10033), 1.2° higher on 
August 13, 1913 (station 10098), 1.5° higher on 
August 12, 1914 (station 10247), 1.7° higher on 
July 15, 1915 (station 10301), and 0.33° higher on 
September 11 (station 10316) in 60 to 70 meters 
(fig. 50) . 
We found the surface at the two ends of the 
Grand Manan Channel, through which the tidal 
currents run with great velocity, only fractionally 
warmer (10° to 10.6°) than the bottom (9.6° to 
9.7°) in 80 to 100 meters on August 17 and 19, 
1912 (stations 10034 and 10035). Vertical stirring 
is thus complete at this locality. 
The temperature gradient that develops within the Bay of Fundy by the end 
of the summer differs regionally, depending on local variations in the tidal circula- 
tion. At the mouth, between Grand Manan and Brier Island, where tidal disturb- 
ances are proverbially strong, Mavor (1923, p. 6, Sec. IV) records a maximum 
difference of only 0.7° to 1.3° between the surface and 50 meters for August 27, 1919; 
but his Section I shows a slightly greater average range (2.2°) for the corresponding 
stratum at three stations halfway up the bay. This thermal difference, which de- 
velops between the Bay of Fundy and the western side of the gulf during the summer, 
is summarized in the following tabulation: 
20 
30 
40 
50 
60 
70 
80 
c- 
/ 
i 
J 
7 
l 
L 
r 
/ 
/ E 
ft 
c 
1 
/ 
L 1 
/ 
1 
1 
1 
fy 
Fig. 50.— Typical summer temperatures off 
Machias, Me. A, August 13, 1913 (station 
10098); B, August 12, 1914 (station 10247); 
C, July 15, 1915 (station 10301); D, August 
10, 1912 (station 10033) 
1 Forty meters was the deepest reading taken at this station. 
