6.08 BULLETIN OF THE BUREAU OF FISHERIES 



this station. Consequently, I have not found it possible to chart the normal 

 isotherms for values between 0° and 10° for the 40-meter level for August, except 

 for the very obvious fact that the whole Gulf of Maine is then 4° to 5° warmer at this 

 level than is the water along the outer coast of Nova Scotia, where the 40-meter 

 temperature was about 1.9° to 3° in July, 1914, warming to about 3.4° off Shelburne 

 by the first week of September in 1915 (stations 10313 and 10314). 



If the gulf north of Georges Bank be arbitrarily divSied into two subdivisions 

 by the meridian of Penobscot Bay (69° W. long.), the average of all the 40-meter 

 readings to the west of it is 7.4° for August, 8.8° in the eastern subdivision (omitting 

 the Bay of Fundy) . 



When the August temperatures for the several years are studied individually, 

 instead of in combination, this separation into a cooler western and a warmer eastern 

 subdivision of the gulf proper, but with much colder water east of Cape Sable, becomes 

 still more apparent (figs. 52 to 54). Although the precise readings vary a degree 

 or two at any given station from year to year, the 40-meter charts agree in locating 

 the coldest area (6° to 8° in 1914; 9° in 1913 and 1915) in the western side of the 

 gulf, extending eastward into the south-central part of the basin in wedgelike outline. 

 Thus a line running from north to south across the gulf in the offing of Penobscot 

 Bay would alternately cross warm water next the coast, fractionally cooler farther out, 

 and warmer agaiii in the southern side. 



In August, 1913 and 1915, the 40-meter level was warmest along the eastern 

 side of the basin; closer in to western Nova Scotia in 1914. 



A detailed temperature survey of Massachusetts Bay, carried out during the 

 last week of August, 1922 (stations 10631 to 10645), gave 40-meter values of 7° to 

 8.5° — lowest close in to the land off Gloucester (where upwelling is so often made 

 evident by low surface temperature) and along the inner edge of Stellwagen Bank 

 (5° at station 10632), where tidal overturnings are to be expected because of the con- 

 tour of the bottom. In other years August readings in the bay at the 40-meter level 

 have ranged from about 6.5° (off Gloucester, August 9, 1913, and August 22, 1914, 

 stations 10087 and 10253) to 8° at that same locality on August 31, 1915 (station 

 10306). 



The 40-meter chart for 1914 (fig. 53) shows a band 1° to 3° cooler than the 

 water on either side of it extending lengthwise of Georges Bank. Our July profile of 

 the western end of the bank, in 1916, also cut across a similar but still cooler baud 

 (p. 629 ; about 4° to 5°) just outside the 100-meter contour (station 10352) . Although 

 nothing in our previous experience foreshadowed summer temperatures there as low 

 as those of that year, the presence near by of a similar cold stratum (10.8°) at about 

 75 meters in July, 1913 (station 10061), and temperature gradients of the same sort 

 recorded in the offing of Marthas Vineyard by Libbey (1891), show that a cool band 

 of this sort may be expected along the oft'shore edge of Georges Bank in most summers. 

 In some years this extends as far west as the longitude of Marthas Vineyard as late 

 as August, but in other years it is obliterated there at an earlier date by encroach- 

 ments of the warm oceanic water from outside the edge of the continent, as happened 

 in 1914 when the 40-meter level had warmed to 12.5° to 13.7° right across the shelf 

 abreast of Marthas Vineyard by the last week of August. 



