754 BULLETIN OF TEE BUEEAXJ OF FISHEEIES 



for the northern side during the first half of May, 1915 — i. e., less than half the 

 regional variation recorded there for March and April of 1920 (32.91 to 34.1 per 

 mille) . 



The locations of the isohalines for 33 per mille from month to month on the 100- 

 meter charts for March (fig. 94), April (fig. 116), and May (fig. 127) illustrate the 

 expansion of water of comparatively high salinity westward across the basin 

 during a strong pulse in the inflowing bottom current, and the recession to be 

 expected when the indraft is weak. Some change of this sort is consistent with the 

 general progress of the vernal cycle. Salinity averaging about 0.6 per mille lower 

 over the basin of the gulf at 175 to 200 meters in May, 1915, than in April, 1920, is 

 probably to be explained on this same basis; but the observations taken by the Ice 

 Patrol cutter in 1919, when the sahnity of the east-central part of the basin 

 increased through May, proves that the indraft continues active right through 

 the month in some years. 



The differences that may be expected in this respect from one May to the next 

 are more graphically illustrated by the west-east profiles of the gulf for that month 

 of 1915 (fig. 126) and 1919 (fig. 121). Note especially the thick band of 34 per 

 miUe water on bottom in the latter year in the eastern side of the gulf, where the 

 value was only shghtly more saline than 33.5 per mille in 1915. The fact that this 

 is the only month when we have found the salinity of the basin lowest, as a whole, 

 in the eastern side, not in the western, deserves emphasis. 



The decrease in salinity that took place from February, 1920, to May over the 

 continental slope to the southwest of Georges Bank has already been mentioned 

 (p. 750). At 100 meters the May value (station 20129, ±34 per mille) was the lower 

 by 1.3 per mille. 



Unfortunately no water samples have been collected in May along the 400-mile 

 sector of the continental edge from the offing of Nantucket eastward to the ofiing of 

 Sable Island, v/here 100-meter values varying from 33.4 to 34.8 per mOle have been 

 reported by the Canadian Fisheries Expedition (Bjerkan, 1919; ^coJw stations 9 

 and 10) and by the Ice PatroP* in the years 1914, 1915, and 1922, evidence of con- 

 siderable fluctuations in the physical state of the slope water. 



With the low values just stated, and values even lower at the same relative 

 location off the eastern slope of Georges Bank in March and April, 1920 (32.8 to 33.46 

 per mille at 100 meters, stations 20068 and 20109), oft' Shelburne, Nova Scotia, on 

 March 19 of that year (33.78 per mille at 100 meters, station 20077), it is evident 

 that water of 35 per mille is usually separated from the slope by lower salinities east- 

 ward from Georges Bank to the tail of the Grand Banks during the third month of 

 the spring. 



Additional information as to the salinity along the seaward slope of the Scotian 

 Banks in May is much to be desired. 



SALINITY IN JUNE 



A tendency toward progressive equalization is recorded from May to June as 

 the overflow of the Nova Scotian current past Cape Sable and the outpourings of river 

 waters are gradually incorporated into the gulf. 



"Ice patrol station 29, May 17, 1914, 34.06 per mille at 200 meters; statian 24, May 19, 1915, 33.66 per mille at about 100 

 meters; station 213, May 28, 1922, 34.79 per mille at 100 meters; see U. S. Coast Guard (1916) and Fries (1923). 



