702 BULLETIN OF THE BUEEAXJ OF FISHEEIES 



the 1,000-raeter contour. However, even such a range as this is narrow, as com- 

 pared to temperature, for with the mean salinity of the gulf falling close to 32.5 per 

 mille the extreme variation is not more than 20 per cent. Consequently, I must 

 caution the reader that while emphasis is laid on these variations in the following 

 pages, they are actually so small, from season to season and from place to place, 

 that their measurement requires careful chemical or physical tests. They could not 

 be detected by any human sense. To use a homely example, no one, I fancy, could 

 distinguish the saltest water of the gulf from the freshest by its taste, but no one 

 could fail to tell the temperature of winter from that of summer if he dipped his 

 hand in the water or by feeling the spray on his face. 



The gulf is invariably saltest in the eastern side of its trough and in the 

 Eastern Channel, which connects the latter with the open ocean. It is freshest 

 in the coastwise belt along its northern and western shores and along the western 

 shoreline of Nova Scotia, as appears repeatedly on the charts of salinity for various 

 levels and seasons. 



The fact that the water over Georges Bank (the shoal southern rim of the gulf) 

 is not Salter than the basin to the north of it deserves emphasis because its proximity 

 to the oceanic waters of the "Gulf Stream" might lead us to expect high salinities 

 there. 



A wide seasonal variation in the salinity of the surface is characteristic of coast- 

 wise waters in boreal latitudes, the water freshening at the season of the spring fresh- 

 ets and then gradually salting again as this inrush of river water is incorporated by 

 the mixings and churnings caused by the tides, winds, and waves. 



The Gulf of Maine is no exception to this rule. The widest seasonal variations 

 so far actually recorded there at any given station are from about 28 per mUle in 

 AprU to about 32.7 per mille in winter in the Bay of Fundy (fig. 165), and from about 

 28.3 per mille in May to about 32.3 per mille in early March in the opposite side of 

 the gulf, a few miles off the mouth of the Merrimac Eiver (p. 813). Such changes, 

 however, are confined to the superficial stratum of water not over 40 metei's thick. 

 The bottom waters of the gulf deeper than 100 meters see very little alteration in 

 salinity from season to season. The saUnity has also proved unexpectedly constant 

 from year to year in all parts of the gulf at any given season. 



The Gulf of Maine is characterized by a considerable vertical range in saUnity 

 over all but its most tide-stirred portions, contrasting strongly in this respect with 

 the North Sea, across the Atlantic, where the saUnity as a whole is more nearly 

 uniform from the surface downward. The vertical range is widest in spring and 

 summer, when the surface as a whole is freshest, narrowest toward the end of the 

 winter; greatest, too, where the stirring effects of the tides are least, as in the west- 

 ern side of the gulf off Massachussetts Bay, and least where tidal currents keep the 

 water more thoroughly churned, as in the Bay of Fundy in one side of the gulf or 

 on Nantucket Shoals in the other. 



In summer, and in the coastwise zone, the increase in salinity with depth 

 averages most rapid from the surface down to a depth of about 50 to 75 meters; but 

 there are many exceptions, and in the deep basin of the gulf the salinity gradient 

 may be nearly uniform, surface to bottom, or the rise in salinity may be found most 

 rapid as the bottom is approached. 



