712 BULLETIN" OF THE BUREAU OF FISHERIES 



Channel, or had been so flowing shortly previous. The failure of the Nova Scotian 

 current of low sahnity to show at all in the 100-meter salinities for March, 1920, 

 either on the deeper parts off the shelf abreast of Shelburne, Nova Scotia, or in the 

 southeastern part of the Gulf of Maine, also deserves emphasis as evidence that 

 this current is confined strictly to the upper 50 or 75 meters of water at that season, 

 neither creeping westward through the Northern Channel at deeper levels nor cir- 

 cling Browns Bank. 



The regional variation in salinity at 100 meters within the gulf was about 1.86 

 per mille for February and March, 1920. 



SALINITY AT 150 METERS AND DEEPER 



The March chart of salinity at 160 meters (fig. 95) is interesting chiefly as an 

 illustation of the west-east gradation from lower values to higher, which has 

 proved generally characteristic of the deep strata of the gulf, complicated, however, 

 by an extensive pool of very low salinity in the northwestern part of the basin, in 

 the offing of Penobscot Bay (<33 per mille), and extending southward past Cashes 

 Bank (station 20052). This phenomenon probably reflected an offshore drift, 

 associated M'ith the low temperature to which the northern coastal zone of the 

 gulf chills during the winter (p. 651). Whether it develops annually, as its low 

 temperature (station 20052) would suggest, is an interesting question for the future. 



A salinity slightly below 33 per mille in the extreme southwestern corner of 

 the basin at 150 meters on February 23 (station 20048, 32.97 per mille), apparently 

 entirely inclosed by salter water, contrasting with the increase that took place in 

 the 150-meter salinity off Cape Ann from 33.4 per mille on that date (station 20049) 

 to 33.53 per mille on March 24 (station 200S7), illustrates the extent to which the 

 state of the water at this depth is governed by mutual undulations of the shallow 

 (less saline) and deep (more saline) strata. No doubt movements of this sort are 

 constantly in progress, raising or lowering the upper boundary of the bottom stra- 

 tum Salter than 33.5 per mille; but as yet we have not been able to follow these 

 submarine waves in detail. 



The localization of salinities higher than 33.8 per mille along the eastern slope 

 of the basin at 150 meters in March, with a maximum of 34.4 per mille in the 

 Eastern Channel, points to some inflow right down to the bottom of the latter at 

 that date (February 22 to March 24) or shortly previous; but with so gentle a 

 gradation in sahnity from the one side of the basin to the other, this indraft evidently 

 was (or had been) less rapid at the 150-meter level than at 100 metei-s, or in smaller 

 volume. Nor is its course within the gulf so definitely outlined by the curves for 

 successive values of salinity at the deeper level. Very httle Avater of this origin, if 

 any, was then flowing over the rim into the Fimdy Deep because the 150-meter 

 sahnity was considerably lower within the latter (33.01 per miUe, station 20079) than 

 in the neighboring part of the open basin (33.7 to 33.9 per mille). Nor had it 

 recently overflowed the shoal rim into the bowl at the mouth of Massachusetts Bay, 

 where the bottom water (150 meters) was about 1 per mille less saline on March 1^' 

 than equal depths in the neighboring parts of the basin, and the entire column very 

 close to homogeneous, vertically, from surface to bottom. 



" station 20050, 32.39 per mille at 150 meters. 



