PHYSICAL OCEANOGKAPHY OF THE GULF OF MAINE 847 



Baldly stated, its practical effect on the slope water which dynamic forces tend to 

 drive out to sea from the continental slope, as described above (p. 843), is to swing 

 this drift to the right (i. e., to the west), thus altering into a longshore current what 

 otherwise would be (and potentially is) an offshore set. *' 



In this way a dominant drift from east to west tends to develop along the 

 upper part of the continental slope of La Have and Browns Banks so long as the 

 distribution of density is of the type actually recorded on the Acadia, Albatross, and 

 Grampus cross profiles of this part of the continental shelf for March, 1920, June 

 and July, 1915, and July, 1914. On each of these occasions the dynamic tendency, 

 acting as the propulsion for such a drift, involved the whole mass of bottom water 

 from the crest of La Have Bank down the slope to a depth of at least 200, if not 

 250, meters. An east-west drift of the bottom water seems, then, comparatively 

 constant on just this part of the slope. 



In July, 1915, this drift involved the whole column of water, surface to bottom; 

 again, in July, 1922, when bottles set out near the edge of the shelf in the offing of 

 Cape Sable drifted into the Gulf of Maine (p. 908). Sandstrom's (1919) calculation 

 of a surface current of about 5 miles per day *^ toward the southwest, along the outer 

 part of the shelf, on this line (between Acadia stations 39 and 41) , shows that the 

 surface water may travel with considerable velocity at times when the whole column 

 is involved in this westerly set along the edge of the continent. This is confirmed 

 by the drifts of four bottles set out 48 to 60 miles off Cape Sable in July, 1922, three 

 of which went to the Bay of Fundy at minimum rates of 3 to 4 miles per day, and 

 one to Winter Harbor, near Mount Desert, at a daily rate of at least 2 miles, and 

 probably considerably faster than that (p. 908). However, the obliquity of the sur- 

 faces of equal density, which originates this drift, decreased with increasing depth 

 on the Acadia section, so that Sandstrom's (1919, p. 332) table indicates a mean 

 velocity of only about 1 mile per day for the whole column of water, surface to bot- 

 tom, between the critical stations (from No. 40 out to the 200-meter contour), with 

 the bottom water creeping westward not faster than about one-half mile per day*^ 

 at a depth of 100 to 200 meters. 



The outermost bottle (which is known to have gone to the Gulf of Maine from 

 the line put out off Cape Sable by the Biological Board of Canada in 1922) was set 

 adrift over the 200-meter contour** 59 miles out from the land, the only returns from 

 bottles set adrift farther out coming from Europe. This limitation of the westerly 

 drift to a narrow belt corroborates the Acadia profile of July, 1915, on which it was 

 only about 20 miles wide (and similarly located), giving place farther out to a suc- 

 cession of lighter and heavier bands, indicating a stronger but even narrower counter- 

 current to the eastward; then, outside of that, a second line of drift to the westward.*^ 



Evidently an active mixing of cold and warm waters was taking place at the 

 outer end of this profile at the time, with bands of higher and lower temperature 



" See Smith's (1926) exposition of this important concept. 



" The velocity arrived at by Sandstrom (1919) from hydrodynamic calculation are only relative to the most nearly station- 

 ary stratum of water, not absolute. This does not lessen their significance in the present case, for with the whole column mov- 

 ing in the same direction the actual velocities would be somewhat greater than the calculated. 



" About 1.4 centimeters per second, or 0.025 knot per hour. 



<< Information contributed by Doctor Huntsman. 



"See Sandstrom (1919, pi. 15) tor the calculated velocities of these two lines of drift. 



