PHYSICAL OCEANOGEAPHY OF TH:E GULF OF MAINE 943 



of a corresponding coastwise belt of low-surface density by April, grading abruptly 

 to considerably higher values a few miles out in the basin (fig. 191). This develop- 

 ment adds both velocity and volume to the longshore drift west and south, which 

 was foreshadowed on the March chart (fig. 188). 



In 1920, according to the dynamic contours at the surface (fig. 192), this spring 

 current had come to dominate the entire coastal belt of the gulf from the neighbor- 

 hood of Mount Desert Island (probably from the Grand Manan Channel) to Cape 

 Cod, by the middle of April, and probably it does so every year by this date — earlier 

 in years when vernal progression in the sea is more forward. During the period 

 covered by this April cruise the average calculated rate of this current, referred to 

 the "low" in the offing of the Bay of Fundy (assumed stationary), was about 0.3 

 knot abreast of Mount Desert, about 0.18 knot abreast of Cape Cod, or an average 

 drift of about 5^ miles per 24 hours along this coast sector as a whole. In spite of 

 the sources of unavoidable error this calculation falls at least within the order of 

 magnitudes suggested by other lines of evidence. 



In Massachusetts Bay, also, a continuation of this longshore drift is indicated 

 by the dynamic contours from the north shore around toward Cape Cod. This, 

 again, agrees with the drifts of bottles that were set out a few miles north of Cape 

 Ann in April, 1925 (p. 890; fig. 177); and evidently this is the characteristic state 

 during that month, for salinities and temperatures taken in the bay by the FisTi 

 Hawk on April 21 to 23, 1925, show a drift of low density (fig. 193) southward past 

 Cape Ann and across the mouth of the bay to Cape Cod as the water from the 

 Merrimac and other rivers to the north floods southward. 



Surface projection (fig. 191) and dynamic contours (fig. 192) for April unite in 

 locating the low in the offing of the Bay of Fundy some 60 miles off Mount Desert 

 Island for that month, the whole east-central part of the basin out through the 

 Eastern Channel being virtually dead dynamically, contrasting with a weak 

 northerly set along the western shores of Nova Scotia. In the southern side of the 

 area the dynamic contours point to a persistence of the drift out of the gulf to the 

 south around the eastern end of Georges Bank, just described for March (p. 938; fig. 

 188), though at a lower velocity; but as a result of the equalization of temperature 

 and salinity from the Eastern Channel in across Browns Bank (p. 553) only a very 

 slow movement into the gulf along this side of the channel is suggested by the April 

 chart (fig. 192). 



The general result of the lightening of the northern and western margins of the 

 gulf, combined with the shift of the cyclonal low northward across the basin, 

 which follows a slackening in the indraft of slope water, is to give the anticlockwise 

 circulation more definitely the character of a great eddy in April than in March, 

 centering off the Bay of Fundy and with its western side traveling southward with 

 greater velocity than its eastern side drifts north. 



It is probable that in April the gradient currents are given an easterly direction 

 along the northern slopes of Georges Bank, just as in March (p. 938), by the contour 

 of the bottom, with a separation off Cape Cod between this easterly drift and a 

 southerly drift past the cape and past Nantucket Shoals. This suggestion is cor- 

 roborated by the fact that bottles followed both these routes from Massachusetts 

 and Ipswich Bays in April, 1925. 



