818 BULLETIN OF THE BUEEAU OF FISHERIES 



the bottom salinity at 40 meters off Yarmouth on January 4, 1921 (31.3 per mille^ 

 station 10501), and Vachon's summer records for that locality (p. 769) suggest equal 

 constancy as characteristic of the Nova Scotian side from late summer to midwinter. 



Vernal freshening by the rivers and by the Nova Scotian current affects but 

 slightly even the shoaler part of the 40 to 100 meter bottom zone, as described 

 above (p. 750)- — the deeper parts hardly appreciably (p. 752). In Massachusetts Bay 

 this event is reflected in a decrease in salinity by about 0.3 to 0.4 per mille from 

 March to May (p. 813), the Bay of Fundy (p. 809) and the eastern side of the gulf, as 

 exemplified by German Bank (p. 814), freshening somewhat more; but it is doubtful 

 whether any vernal freshening of the bottom water from this source is appreciable 

 along the sector between Cape Elizabeth and Mount Desert at depths greater than 

 100 to 120 meters, except close in to the mouths of rivers (p. 814). 



At the end of the winter and in spring we have found the bottom water at this 

 depth varying from 32.5 per mille to about 33 per mille in salinity on the offshore 

 banks, also; and in some years (1916, for example) bottom salinities no higher than 

 this prevail up to the third week in July — perhaps later still; but in other summers 

 (typified by 1914) when slope waters creep in over the shelf during the first two 

 months of summer it raises the bottom salinity to 34 to 34.9 per mille along the 

 southern (offshore) edge of Georges Bank and on Browns Bank. 



The zone shoaler than 40 meters falls naturally into two divisions, the one 

 including the waters immediately fringing the coast line of the gulf, the other the 

 greater part of Nantucket Shoals and the shoals on Georges Bank. This zone 

 extends right up to tide line within the gulf, including the shoal bays and river 

 mouths; hence, its bottom water ranges in salinity from brackish, on the one hand, 

 to maximum values of about 32.9 per mille toward its lower boundary, on the other, 

 and experiences the full effects of seasonal freshening. Very little attention has 

 yet been paid to the salinity of this zone around the open gulf; but our stations 

 in Massachusetts Bay in August, 1922, with the Canadian data for theBay of Fuudy 

 region, added to such other evidence as is available, point to about 31 to 32.5 per 

 mille as the usual limits to the bottom salinity at 10 to 40 meters depth in summer 

 and autumn all along the open shores from Cape Cod to Cape Sable, including 

 Casco Bay and the Bay of Fundy. Considerably lower bottom sahnities are to be 

 expected over this depth zone in estuaries into which large rivers empty; Vachon 

 (1918), in fact, has recorded values of 28.22 per mille to 31.49 per mille at the 

 mouth of the St. Croix River, varying according to precise locality and stage of the 

 tide, with 31.14 per mille at 20 meters in Kennebecasis Bay and 30.2 to 32.0 per 

 mille at 20 meters at the mouth of the Annapolis River for September, 1916. 



The zone from the surface down to a depth of 20 to 30 meters is the only part 

 of the bottom of the gulf that experiences a wide seasonal fluctuation in salinity 

 from the vernal freshening of the surface stratum from the land and from the vernal 

 expansion of the Nova Scotian current. In this shallow water, however, the change 

 in salinity from autumn and winter (when it is near its maximum) to May (when, 

 generally speaking it falls to its minimum) is so wide that the bottom fauna must 

 either be comparatively indifferent to the salinity of the water or able to carry out 

 bathic migrations sufficiently extensive to escape them. 



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