796 BULLETIN OF THE BUREAU OF FISHERIES 



"Gulf Stream" water more saline than 36 per mille will be met if the profile runs 

 out far enough. 



Farther east (fig. 157) a rather different picture results from the homogeneous 

 state of the water maintained on the bank by active tidal stirring, as described above 

 (p. 770) ; but the contrast between the comparatively low salinity there and the much 

 higher values on the continental slope to the south, on the one hand, as well as in 

 the basin of the gulf to the north, on the other (34 per mille) , affords a graphic 

 illustration of the extent to which the contour of the bottom controls the relationship 

 of water masses that differ in salinity because of different origins. Note also the 

 abrupt transition from the thick layer of 35 per mille water in the bottom of the basin 

 to the very much lower salinity (about 32.2 per mille) at the surface on this profile, 

 reflecting the considerable difference in density that exists in summer between the 

 slope water and the surface stratum beneath which this intrudes. 



All three summer profiles of the continental shelf for 1914 (figs. 156, 157, and 

 158) show extremely uniform salinities of 35.2 to 35.4 per mille bathing the bottom 

 at about 100 to 200 meters depth all along the slope abreast the gulf; and as the 

 Canadian Fisheries Expedition also had 35.4 per mille at 200 meters just outside the 

 continental edge in the offing of Shelburne, Nova Scotia, on July 22, 1916 (Bjerkau, 

 1919; Acadia station 41), this may be taken as normal for the summer. 



In February and March, the reader will recall, only the western sector of this 

 zone was as salt as this; in July, 1916, the values were slightly below 35 per mille 

 (fig. 159) — differences that apparently reflect the normal seasonal succession in 

 the inshore and offshore movements of oceanic water. On this assumption the 

 maximum salinity of the eastern sector of the warm zone for the year is not far from 

 35.5 per mille, and the minimum certainly is as low as 34.5 to 34.7 per mille. 



At depths greater than 400 meters the bottom water on this sector of the con- 

 tinental slope is always close to 34.9 to 35 per mUle in sahnity, perhaps never vary- 

 ing more than 0.2 per mille from this mean value at any time of year. 



Lower salinities off Marthas Vineyard in July, 1916 (fig. 159), than in August, 

 1914 (fig. 158), no doubt reflect the normal seasonal succession in this part of the sea, 

 suggesting that values less than 32 per mille will seldom be recorded on this line 

 after July, and that water more saline than 33 per mille may be expected to move 

 inshore over the bottom during that month and August (p. 793). The fact that the 

 water over the median sector of the shelf was nearly homogeneous in salinity, sur- 

 face to bottom, at that time (fig. 158), contrasting with pronounced stratification 

 closer into the land, on the one hand, and farther out at sea, on the other, is unmis- 

 takable evidence of active circulation. The abrupt transition from low salinities to 

 high ones over the edge of the continent, made evident on the profile by the isoha- 

 lines for 34, 34.5, and 35 per mille, also marks this as the zone of contact between 

 two distinct masses of water at the time (p. 795) . The rather unusual vertical distri- 

 bution of salinity about one-third the way out from the land where the mid stratum 

 was less saUne than either the surface above it or the bottom, has been commented 

 on (p. 779). 



These two profiles (figs. 158 and 159) are also of interest from a more general 

 viewpoint as illustrations of the general increase in salinity from the land seaward, 

 which is characteristic of the whole continental shelf between Cape Cod and Chesa- 

 peake Bay. 



