PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 743 



regional uniformity of the inner parts of the bay, where the surface values varied 

 only from 31.3 to 31.8 per mille at 16 stations, also shows how little the discharge 

 from the small streams that empty along the coast line of the bay affects its salinity. 



This drift past Cape Ann seems to have hugged the shore of the bay more closely 

 in 1915, because the surface value was much higher at the standard station off Glouces- 

 ter on May 4 of that year (station 10266, 32.32 per mille), than any other surface 

 reading for the bay in May or in April. Considerable variations are therefore to be 

 expected in the salinity of Massachusetts Bay from one May to the next, both in the 

 precise value and in the date when the water is freshest, reflecting the considerable 

 distance from the freshening sources — the rivers to the northward of Cape Ann. 

 Even in years when the discharge of these rivers is up to normal, and when the 

 freshets fall at the usual season, the southerly drift need only be turned slightly more 

 offshore than usual, by the jutting promontory of Cape Ann, to pass by Massachu- 

 setts Bay altogether. In this case the bay would be a sort of backwater, with its 

 surface changing little in salinity from winter through spring. It is probable, there- 

 fore, that Massachusetts Bay experiences a wider annual variation in the salinity of 

 its surface waters in spring than any other coast sector of the Gulf of Maine. 



The Bay of Fundy illustrates the seasonal cycle where the salinity of the surface 

 reflects the discharge from a large river (here the St. John) close by. Thus, Mavor 

 (1923, p. 375, table 8) records a very sudden decrease in the salinity of the surface, 

 from 32.5 per mille in the middle of April, 1917, to 27.9 per mille on the 4th of 

 May, at a locality between Grand Manan and Nova Scotia, followed, however, by 

 an increase equally rapid to 31.5 per mille by the middle of June. While 1917 is 

 the only spring (and this the only locality) for which the vernal cycle of the open 

 Bay of Fundy has been followed, month by month, it is probable that the seasonal 

 fluctuation outlined by Mavor represents the normal course of events, the surface 

 freshening suddenly when the St. John and the Nova Scotian rivers come mto flood, 

 and salting again after the freshets subside as the land water becomes mixed into 

 the bay by the strong tides. 



The lowest value to which the surface salinity of the open Gulf of Maine ever 

 falls can not be stated, lacking data near the mouths of the other large rivers at 

 the critical dates in early May. In the Bay of Fundy, 27.9 per mUle, just men- 

 tioned, is the lowest so far recorded; and salinities equally low are to be expected 

 close along the coast line, thence westward to the Merrimac, though only for a few 

 miles out from the strand, and perhaps hardly, outside the outer islands. 



The combined chart of surface salinity for the offshore waters of the Gulf for 

 May (fig. 120) shows the freshest water (< 32 per miUe) continuing to hug the coast, 

 much as in April (fig. 101) ; but the great volume of river water that is poured into 

 the gulf at this season so freshens the surface next the shore that the transition to 

 the more saline water offshore is far more abrupt in May than in April; especially 

 off the coast sector between Portland and Cape Ann, where a change of as much as 

 '2 to 3 per mille may be expected at the surface in a distance of 5 to 10 miles, as one 

 runs offshore from the 100-meter contour in May. The development of so fresh a 

 band next the coast admits of but one interpretation — namely, that the non-tidal 

 drift then parallels and closely hugs this part of the shoreline southward as far as 



