PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 723 



years were substantially alike off Seguin Island. This also applies to the western 

 basin above the lOO-meter level; but 1920 was the salter year there at greater depths, 

 with an annual spread of 0.5 to 1 per mille at 150 to 200 meters. 



With so little difference in salinity between the two years it is safe to assume 

 neither was unusually fresh or unusually salt, but that the two together may be 

 assumed to represent a typical Gulf of Maine March.^^ 



Judging from one station at the mouth of Massachusetts Bay, with readings of 

 32.85 per mille at the surface, 32.96 per mille at 25 fathoms, and 33.04 per mille at 

 45 fathoms (station 10054), the March salinity was about the same in 1913 as in 

 1921. Again, the salinity of the upper 100 meters of the Fundy Deep was almost 

 precisely the same on March 22, 1920 (station 20079), as on April 9, 1917 (Mavor, 

 1923); the 150-meter level the same as on February 28 of that year, though 1920 

 seems to have been slightly the salter at depths greater than 150 meters. 



Thus, the March saUnity of the gulf showed but little annual variation in the 

 years 1913, 1917, 1920, and 1921, and it is probable that annual differences are 

 smallest at this season. Even in March, however, much wider differences than those 

 just stated are to be expected between springs of heavy or light rainfall and snow- 

 fall, or between years when the freshets occur unusually early or unusually late. 

 Fluctuations in the bottom current flowing into the gulf will also be mirrored by 

 salinity. 



Hydrometer observations taken in Massachusetts Bay and to the northward of 

 Cape Ann from the Fish, Hawk on March 10 to 12, 1925, give a hint of this in bottom 

 readings considerably higher than we had previously obtained there at that season — 

 an average of about 33 per mille at 40 to 60 meters depth contrasting with 32.2 to 

 32.5 per mille for 1920 and 1921. The superficial stratum was likewise slightly more 

 saline in Massachusetts Bay in March, 1925 (32.4 to 32.9 per mille), than in either 

 of the earlier years of record. 



VERNAL FRESHENING 



The great rush of fresh water that annually poura into the gulf from the land, 

 when the snow melts and brings the rivers into freshet, causes a very decided lowering 

 of salinity contemporaneous with the first signs of vernal warming. The effect of 

 this, first apparent along the western and northern shores of the gulf, had consider- 

 ably lowered the surface salinity of the superficial stratum off the Kennebec River 

 by March 4 in 1920, a late year (p. 704). The upper 30 to 40 meters of the coast 

 sector between northern Cape Cod and the neighborhood of Mount Desert Island 

 proved decidedly less saUne by the 9th to 18th of that April (fig. 101), also, than it 

 had been a month earlier (fig. 91). 



Localization of the lowest salinities (in this case < 30 per mille) between Cape 

 Elizabeth to the west and Penobscot Bay to the east, up to this date, is evidence 

 that the Kennebec and the Penobscot combined had continued to affect the salinity 

 more than the Saco and the Merrimac did until mid-April in that particular year; 

 but whether a seasonal relationship of this sort is normal, or whether the freshening 

 effect of these two groups of rivers is more nearly simultaneous in most years than 



»5It will require records for many years to establish the normal state of the waters of the gulf for thatmonth or for any other. 



