PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
817 
shows the seasonal effects of land drainage and of the Nova Scotian current. Thus, we 
have found the bottom of the Northern Channel freshening from about 33.6 per mille 
in March, 1920, to 32.8 per mille in April at 125 to 135 meters, with 32.9 per mille 
in July, 1914. Off Lurcher Shoal, where the bottom salinity has averaged about 
33.7 per mille at the 100-meter contour in August and September, 33.5 per mille, 
March to April, and 33.08 per mille on January 4, 1921, it was only about 32.3 per 
mille at 90 meters on May 10, 1915 (fig. 108). 
The bottom salinity of the northern and western sides of the gulf ranges from 
about 32.3 to 32.5 per mille along the 100-meter contour in August to 32.5 to 33 per 
mille in winter, according to the precise locality; and the 100 to 150 meter zone 
along the northern slopes of Georges Bank (here only a few miles wide) is close to 
33 per mille in spring, summer, and at the end of the winter, with no definite sea- 
sonal variation demonstrable from the observations taken there so far. 
On the seaward slope of Georges Bank these depths include the so-called “warm 
zone” (p. 530), the salinity of which has been sufficiently discussed in the preceding 
pages. I need only add here that it varies from about 34 per mille to upwards of 
35 per mille, hence is considerably more saline than the corresponding depths any- 
where within the gulf. 
The zone included between the 40 and 100 meter contours is especially interest- 
ing because it comprises most of the important fishing grounds, both within the gulf, 
on Browns Bank, on all but the shoalest parts of Georges Bank, the South Channel, 
and the outer part of the continental shelf. 
The bottom readings for July and August at stations so shoal have varied between 
31.8 and 33.2 per mille around the western and northern slopes of the gulf, with 32 
to 33.2 per mille on bottom in 40 to 140 meters at our June to August stations at 
the mouth of Massachusetts Bay. 
Close in to the western shore of Nova Scotia, Vachon’s (1918) record of 31.09 to 
32.33 per mille at 40 to 45 meters off Yarmouth show the bottom averaging some- 
what less saline, depth for depth, than in most other parts of the gulf. Bottom 
salinities are also low off Cape Sable (32 to 32.3 per mille in 50 to 55 meters in July 
and August, 1914). In the open Bay of Fundy, Mavor (1923) had 31.9 to 32.9 per 
mille in depths of 50 to 100 meters in August, 1919, while Vachon (1918) records 
bottom salinities of 31.13 to 32.4 per mille at 45 to 55 meters in St. Marys Bay and 
31.2 to 32.2 per mille in 40 to 70 meters depth in Passamaquoddy Bay in the sum- 
mer of 1916. It is an interesting question, for future solution, whether the bottom 
salinity of Penobscot Bay and Frenchmans Bay is equally low or whether enough 
water drifts inward along their troughs to maintain bottom salinities as high as off 
the open coast. 
Little change seems to take place in the bottom salinity of the 40 to 100 meter 
depth zone along the northern slope of the gulf in autumn, winter, or March. Thus, 
14 stations between Cape Cod and the Bay of Fundy averaged about the same at 25 
to 80 meters in September and October (32.4 per mille) as in summer, with 4 stations 
east of Cape Elizabeth averaging 32.7 per mille (extremes of 32.8 and 32.6 per mille) 
in the midwinter of 1920-21 at 60 to 100 meters. The bottom values for this sector 
in March, in equal depths, have been 32.4 to 32.5 per mille. Close agreement between 
