PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 637 



The more tide-swept waters along and among the islands east of Casco Bay 

 where the whole column of water continues nearly homogeneous in temperature 

 through the summer and the surface warms only to about 11° to 13° instead of 16° 

 to 18°, do not commence to chill until a month or more later in the season. In 1925, 

 for example, the surface temperature near the Duck Islands, off Mount Desert, was 

 almost exactly the same on September 9 and 10 (11.1° and 10.8°) as it had been 

 there on August 11 (10.9°), 10° on September 15, and still 10.3° to 10.8° on October 

 15 to 16. Readings of 10.28° off Machias and of 11.6° near Mount Desert on 

 September 15 and 16, 1915, are in line with this. 



This same rule holds good for the Bay of Fundy, where no appreciable cooling 

 takes place until after the first of October — a month later than in Massachusetts 

 Bay or off Cape Ann. Thus, Vachon (1918) had surface readings of 9.21° to 11.07° 

 in the central parts of the bay on September 27 and October 4, 1916, with 9° to 

 10.6° at various localities in Passamaquoddy Bay between October 3 and 17, 

 showing a cooling of only about 1° to 2° from the summer maximum. Mavor 

 (1923) lUiewise records surface temperatures of 11.07° between Grand Manan and 

 the Nova Scotian shore on October 4, 1916, and 9.77° on October 2, 1918. How- 

 ever, the 10-day averages for Lubec Narrows (fig. 31) show that considerable 

 variation is to be expected from year to year in the date after which the surface of 

 this part of the coast water commences to chill, for a steady though slight cooling 

 was recorded through September, 1920, whereas the mean surface temperature at 

 Eastport averaged highest at the last week of September for the 10-year period, 

 1878 to 1887. 



Surface readings of 9.4° on German Bank (station 10311) and 13.3° near Cape 

 Sable (station 10312) on September 2, 1915, suggest that the temperature was then 

 about stationary at its summer maximum in this side of the gulf. 



With the surface along the western shores of the gulf, from Massachusetts Bay 

 northward, chilling rapidly during the early autumn, but with the northeastern and 

 eastern margin of the gulf cooling only very slowly at first, there comes a time when 

 the whole peripheral belt of the gulf outside of the outer headlands is nearly uniform 

 in surface temperature (close to 9.5° to 10.5° in most years), varying only a couple 

 of degrees, at most, from place to place. In 1915 this state was apparently attained 

 sometime between the first and middle of October, the surface of Massachusetts Bay 

 having chilled to 10.5°-13.4° by the last week of September (stations 10320 to 

 10324), with 11.6° off the Isles of Shoals and 11.9° off Cape Elizabeth on October 4 

 (stations 10325 and 10326), 10° at the mouth of Penobscot Bay (station 10329), and 

 9.4° near Mount Desert and off Machias on the 9th (stations 10327 and 10328) . The 

 surface of Massachusetts Bay continued virtually constant at about 11° throughout 

 October. 



The following tabulation (p. 638) of Rathbun's (1887) graphs for the years 1881 

 to 1885 likewise shows extremely uniform averages of 11.67° to 9.44° on October 1 

 for Boon Island, Seguin Island, Matinicus Rock, Mount Desert Rock, and Petit 

 Manan Island, localities where the midsummer temperatures for the same years 

 would show a range of at least 6°.^^ 



«The average surface temperature at Thatchers Island, at the tip of Cape Ann, was somewhat higher (14.17°) for the two 

 years, ISSl and 1882, at the beginning of October. 



37756—27 9 



