PHYSICAL OCEANOGRAPHY OF THE GULE OF MAINE 923 



inflowiag 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 th« 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, Oalanus hyperhoreus and Metridia Tonga (Bigelow, 1926, figs. 71 and 76), 

 clearly pictures the drift westward into the gulf from the offing of Cape Sable and 

 westward along the oflFshore slope of Georges Bank in the spring; and the records 

 for the more delicate northern visitors — Mertensia, Ptychogena, Oikopleura vanhoffeni, 

 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 

 {EukroJinia Tiamaia, 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. 



