PHYSICAL OCEANOGRAPHY OF THE GULP OF MAINE 703 



DETAILED ACCOUNT OF SALINITY 



The detailed account of the sahnity of the gulf may well commence with its 

 state at the end of the winter and during the first days of spring, both because this is 

 the season when variations in salinity, both regional and vertical, are least, and 

 because this choice of a point of beginning will parallel the description of the 

 temperature of the gulf (p. 522). 



FEBRUARY AND MARCH 



At the end of February and during the first week of March the salinity of most 

 parts of the gulf is at or near its maximum for the year, except close to the mouths 

 of the larger rivers. It is also most nearly uniform then regionally, having had a 

 range of only 1.3 per mUle from station to station at the surface in March, 1920. 

 In the offshore parts of the gulf the salinity is then also close to uniform vertically, 

 from the surface down to a depth of 40 to 50 meters, but increases at greater depths 

 down to the bottom of the trough, as is the general rule in all parts of the Gulf of 

 Maine at all seasons. 



SURFACE 



During the last week of February and the month of March of 1920 (which we 

 must, perforce, take as representative, being the only year when we have made a 

 general survey of the gulf at this season) the surface water was freshest (3 1 .3 to 32 

 per mille) along a narrow band fringing the coast between Portland and the eastern 

 boundary of Maine (fig. 91) ; and it is probable that equally low salinities prevailed 

 in the more inclosed bays and in the mouths of harbors all around the coast line of 

 the gulf at that time. The curves for successive values show that this band of 

 water, less saline than 32 per mille, was probably not wider than 20 mUes (measured 

 from the outermost islands or headlands) on any line normal to the coast, with 

 rather an abrupt transition to salinities higher than 32 per mille a few miles to the 

 seaward of the 100-meter contour. In outlining the distribution of salinity farther 

 out from the land, the curve for 32.5 per mille is the most instructive, its undulating 

 course marking an artificial boundary between the fresher and Salter waters. Water 

 fresher than this overspreads the entire northwestern and western portions of the 

 gulf at this season and its eastern side as well, spreading offshore to include the 

 whole western half of Georges Bank, a considerable area off Penobscot Bay, and the 

 whole breadth of the continental shelf (including Browns Bank) to the southward 

 of Cape SableJ' 



The salinity of the surface water in the offing of the cape is especially interest- 

 ing at this season as evidence of the extent to which the icy waters of the Nova 

 Scotian cmrent (characterized equally by low salinity) have begun to flood west- 

 ward past the cape into the Gulf of Maine. In 1920 the situation of the isohaline 

 for 32.2 per mille on this March chart clearly shows that the freshest (also the coldest) 

 core of this drift lay well out from the shore off southern Nova Scotia, directed 

 toward Browns Bank, and that it had not yet passed the longitude of Cape Sable in 

 appreciable volume. The low salinity of the v^aters that then sldrted the western 



" The surface salinity was only 32.16 per mille at ovi outermost station on the Shelburne profile (20077) on March 19. 



