PHYSICAL OCEANOGRAPHY OP THE GULP OF MAINE 



717 



bank, where salinity increased so rapidly with depth that a greater range was com- 

 pressed into the upper 40 meters than characterized the whole column of water 

 (280 meters) in the basin. 



Both the profiles (figs. 96 and 97) also show a contrast of the reverse order in 

 the deeps between the oceanic slope to the south (nearly homogeneous in salinity 

 below the zone of most rapid vertical transition at 50 to 140 meters) and the gulf 

 basin to the north, where salinity increased from the 100-meter level down to the 

 bottom. Undulations in the thickness of the salt bottom waters or submarine waves 

 also appear on both profiles, evidence of rather an active state of vertical circulation 

 at the time, with the isohalines for 32.5 per mille and 33 permille suggesting a tend- 

 ency toward upwelling in the northeastern part of the basin. 



The rather marked contrast in the salinity of the bottom water of the eastern 

 profile (fig. 97), between 34 per mille to the northward of the ridge that divides this 

 side of the basin into a northern and southern bowl, and upwards of 34.5 per mille 



FiG.S 



-Salinity profile running eastward from Massachusetts Bay, across the gulf toward Cape Sable, March 1 to 23, 1920 



at an equal depth to the south of it, illustrates the very important f61e that such an 

 irregularity of the bottom may play in directing the circulation of the water. In 

 the present instance the bottom is to some extent divided by the ridge, as the charts 

 for the 100 and 150 meter levels (figs. 94 and 95) also show, water from its left-hand 

 side being responsible for the high bottom salinities in the southern side of the basin 

 on this profile (stations 20053 and 20064), whereas its eastern branch drifts north- 

 ward chiefly to the eastward of station 20054. 



This control which the conformation of the bottom exercises over the salinities 

 of the deeper strata of the gulf is made still more evident on a west-east profile (fig. 

 98) by the contrast between the bottom water of the open basin, on the one hand, 

 and of the deep bowl off Gloucester, on the other, just commented on (p. 712), where 

 the barrier rim of the bowl (station 20050) is so effective an inclosure at this season 



