PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
923 
inflowing current, than on that to the left (p. 785). The circulation in each may 
therefore be described as “estuarine,” subsidiary to the estuarine circulation of the 
basin of the gulf as a whole, inward along the right-hand (eastern and northern) 
sides and eddying to the left. The regional difference between the right and left 
sides being widest in the eastern trough, with the maximum values of salinity and 
temperature both higher there than in the western, a greater volume of slope water 
continues northward over the bottom toward the Bay of Fundy (and at a greater 
velocity) than is diverted to the westward by the ridge that culminates in Cashes 
Ledge. 
CIRCULATION AS INDICATED BY THE PLANKTON 
The tracks which immigrant members of the planktonic community follow into 
the gulf and in their further wanderings within it are discussed in such detail in 
the preceding number of this volume (Bigelow, 1926, p. 51), to which the reader is 
referred for details, that the briefest of summaries will suffice here. Immigrants 
of this category, whether from tropic or from northern sources, enter the gulf in the 
eastern side; seldom or never across its offshore rim farther west. (Bigelow, 1926, 
figs. 31 32, 33, 69, 71, and 72.) The relative regional abundance of our northern 
copepods, Calanus hyperloreus and Metridia longa (Bigelow, 1926, figs. 71 and 76), 
clearly pictures the drift westward into the gulf from the offing of Cape Sable and 
westward along the offshore slope of Georges Bank in the spring; and the records 
for the more delicate northern visitors — Mertensia, Ptychogena, Oilcopleura vanhujfeni, 
and Limacina helicina — are chiefly confined to the area on the eastern side, where the 
water is most chilled by the Nova Scotian current. 
Clearest evidence of the drift within the gulf is afforded, of course, by such 
species as are comparatively short lived there and can not reproduce in its low (or 
high) temperature. The records for these in the upper 40 meters or so have been 
constantly confined to a rather definite belt paralleling the coast around from the 
Nova Scotian side to the offing of Massachusetts Bay, leaving the central and 
southern parts of the gulf bare (Bigelow, 1926, fig. 31). A distribution of this 
sort is reconcilable with an eddying drift inward, anticlockwise around the gulf; in 
fact, it is explicable on no other reasonable assumption, and this corroborates the 
drift-bottle experiments. A drift of this same sort from the coast of Maine west- 
ward and southward toward Cape Cod is also made probable by the relative dis- 
tribution of buoyant fish eggs and of larval fishes (Bigelow, 1926, figs. 34 and 35). 
Planktonic animals that enter the gulf in the mid levels via the Eastern Channel 
( Eukrohnia hamata, for example) parallel the surface communities in their general 
drift northward, westward, and southwestward, except that they are held farther 
out in the basin by the contour of the bottom; but visitors characteristic of the 
deepest water of the gulf (e. g., Sagitta maxima ) follow the two arms of the Y-shaped 
trough, just as might be expected from the drift of the slope water, as indicated by 
the salinity (p. 922). 
The comparative scarcity of animals of coastwise or shoal-water origin over the 
deep basin of the gulf (Bigelow, 1926, p. 32), like the distribution of salinity, is evi- 
dence of a circulatory system paralleling the coast, not fanning out in the offing of 
the river mouths. 
