816 BULLETIN OF THE BUEEAU OF FISHERIES 



therefore enjoy an environment that is virtually uniform in this respect from years 

 end to years end. The only exception to this rule has been the eastward of Cashes 

 Ledge, where we have found the salinity of the bottom water only 33.2 per mille in 

 May at a depth of 185 meters (station 10269), contrasting with 33.6 to 34 per mille 

 earlier in spring and in summer. 



Certain other regional variations in the state of the bottom water of the trough 

 also can be traced within more narrow limits. Thus, its eastern arm is usually 

 slightly less saline along the western slope than the eastern, independent of depths. 

 In the western arm, however, off Cape Ann, the salinity of the bottom water is more 

 directly a factor of the depth. The salinity on the intervening broken bottom has 

 usually been slightly below 34permUle; once (in March, 1920) as low as 33.4 per 

 mille. A month later, however, it had risen to 34.18 per mille at this same locality; 

 and water of 34 per mUle must overflow the irregular ridge south of Cashes Ledge 

 with some regularity, this being its only route to the basin to the west. An overflow 

 of this sort was, in fact, reflected by an increase in the bottom salinity there from 

 33.4 per mille on March 20, 1920, to 34.18 per mille on AprU 17 at depths of 175 to 

 200 meters (stations 20052 and 20114). 



An unmistakable, if slight, increase in the bottom salinity, depth for depth, is 

 characteristic of the floor of the gulf from the inner parts of its two troughs 

 out to the entrance to the Eastern Channel, probably at all seasons. 



We have found the bottom salinity of the depth zone between the 175 and 150 

 meter contours (narrow everywhere except north of Cashes Ledge) averaging about 

 33.6 per mille, winter and summer, ranging from occasional values close to 35 per 

 mille (or even slightly higher) at the deeper level to a mean of about 33.3 per mille 

 at the shoaler boundary. No definite seasonal variation is demonstrated in water 

 as deep as this, but the recorded variations, station for station, are associated with 

 the pulses in the inflowing bottom current (p. 690). 



This depth zone is interesting, however, because it includes the isolated bowl 

 at the mouth of the Massachusetts Bay, the trough west of Jeffreys Ledge, and the 

 deeper parts of the Bay of Fundy, in all of which the bottom water is considerably 

 less saline than at corresponding depths in the open basin outside. In the most 

 nearly inclosed of the three — off Gloucester— the bottom water at any given time of 

 year is virtually uniform from a depth of about 100 meters (slightly below the level of 

 the inclosing rim) down to 170 meters. 



Regional differences in salinity increase greatly at depths less than 150 meters 

 as the water shoals, depending on the geographic location, with the changes of the 

 seasons also governing the bottom salinity more and more, so that the picture 

 becomes increasingly complex. 



In the coastal zone between Cape Cod and Cape Sable the bottom salinity, at 

 depths of 100 to 150 meters, has been found to vary from 32.38 per mille to 34.11 

 per mille, according to depth, locality, and date. On the whole it averages lowest 

 in the bowl off Gloucester, in the trough west of Jeffreys Ledge, and in the Bay of 

 Fundy (32.2 to 33.2 per mille for this depth zone); highest on the northeastern 

 slope of the open basin near Lurcher Shoal, where we have had one bottom reading 

 as high as 34.11 per mille in water only 120 meters deep (station 10245, August 12, 

 1914), with others of 33.4 to 33.8 per mille. The upper part of this depth zone also 



