706 BULLETIN OF THE BUREAU OF FISHERIES 



40-meter level for this whole area was only 0.1 per mille, including the deep water 

 off the southeastern slope of Georges Bank (station 20069) and the continental shelf 

 abreast southern Nova Scotia (stations 20073 to 20077). 



Our several stations in Massachusetts Bay, for various dates in March during 

 the three years of record, have shown the upper 40 meters of water equally homoge- 

 neous there; and it is probable that this generalization would apply to the entire 

 coastal zone of the gulf outside the outer islands during the last half of February, 

 except close to the mouths of the larger rivers. 



In March, 1920, homogeneity characterized the whole column of water in the 

 western part of the basin of the gulf, as limited by a Une running southeastward from 

 Penobscot Bay, down to a depth of 100 to 150 meters, with the difference in salinity 

 between 40 and 100 meters averaging almost exactly the same as between the sur- 

 face and 40 meters (about 0.05° per mille) . In other words, stirring by tides and 

 waves is active enough to keep the water virtually equalized in salinity down to this 

 depth during the late winter and early spring. However, our March stations have 

 all yielded considerably higher salinities at 100 meters' depth than at 40 meters in 

 the Eastern Channel and inward all along the eastern side of the basin of the gulf 

 (not however, in the Bay of Fundy), with an average difference of about 0.6 per 

 mUle (stations 20055, 20056, 20071, 20072, 20081, 20082, and 20086) and a maxi- 

 mum range of 1.43 per mille in the channel between Georges and Browns Banks 

 (station 20071) . 



The presence of this tongue of more saline water at 100 meters combines with a 

 more or less constant tendency toward upwelling from the deeper strata to raise the 

 lower boundary of the stratum, equalized by vertical stirrings, some meters higher 

 there than in any other part of the gulf. An even wider vertical range of salinity 

 between the 40-meter and 100-meter levels, recorded over the shelf south of Nova 

 Scotia that same March (stations 20074 to 20077; range of 0.8 to 2.7 per mille), 

 suggests a drift of the fresher coastal water out over the salter slope water;*" and 

 this, or a reciprocal movement of the slope water in toward the slope on bottom, is 

 also the probable explanation for almost as steep a gradient in the upper 40 meters 

 off the southwest slope of Georges Bank on February 22 (station 20044 and 20045), 

 and off its southeast face on March 12 (station 20069; fig. 92). 



All the March stations in the open basin of the gulf also show a considerable 

 vertical increase in salinity at depths greater than 100 meters, with a maximum 

 difference of 1.26 per mille between 100 meters and 150 (station 20053), a minimum 

 of 0.14 per miUe. 



The homogeneity of the superficial stratum of the gulf, characteristic of the last 

 weeks of winter, gives place to the development of a more stratified state in the 

 coastal belt in March as the increasing volume of fresh water discharged from the 

 rivers lowers the salinity of the surface along the tracks affected by their discharges. 

 In the year 1920 the discharge from the Kennebec, perhaps combined with water from 

 the Penobscot, had reduced the salinity of the surface water off Boothbay fully 1 per 

 mille below that of the 40-meter level by March 4 (station 20058)." In 1925 the 



•» The surface stratum ot low salinity cut by the Sholburne profile tor March is the southoromost extension of the Nova 

 Scotian current (p. 832) . 



81 No observations were taken at the mouth of Penobscot Bay during this month, consequently I can not stale bow far sea- 

 ward the outflow from the Penobscot Eiver may then have influenced the vertical distribution of salinity. 



