PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 



599 



Meter 



10 



Temperature, Centigrade 



7° 8° 9° 10° W 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),'= 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. 



This also applies off the open coast farther east. 

 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 sHghtly greater average range (2.2°) for the corresponding 

 stratum at three stations haHway 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 ia the following tabulation: 



20 



30 



40 



50 



60 



70 



80 



Fig. 50. — Typical summer temperatures oS 

 Machias, Me. A, August 13, 1913 (station 

 1008S); B, August 12, 1914 (station 10217); 

 C, July 15, 1915 (station 1030)); D, August 

 16, 1912 (station 10033) 



" Forty meters was the deepest reading taken at this station. 



