PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 701 
naturally follow any cold winter or spring (cases in point are 1916 and 1923). If 
coupled with unusually low salinity, an unusual extension of the Nova Scotian current 
would be indicated, though this same state might result from a cold winter followed 
by greater river freshets than usual, a combination not unknown. Abnormally low 
summer temperature, coupled with high salinity, would result if more slope water 
than usual was then flowing into the gulf and if it was being incorporated with the 
overlying water more rapidly than usual. 
Temperatures and salinities lower than usual along the outer part of the continen- 
tal slope abreast the gulf in summer would be conclusive evidence of some unusual 
expansion of water from the northeast, such as seems actually to have occurred in 
1916 (p. 848). If combined with very high salinity, very low temperatures along 
the edge of the continent would be good evidence of some upwelling from the abyss; 
and although no upwelling of this sort has come under direct observation off the 
Gulf of Maine region, or seems likely to occur there, events of this sort would have 
such a wide-reaching effect on local hydrography that strict watch should be kept 
for them. 
SALINITY 78 
GENERAL SUMMARY 
The account of the salinity of the gulf may commence, appropriately, with a 
brief summary, both because the general reader may find in it information sufficient 
for his wants and to serve as introductory to the more detailed description. 
The Gulf of Maine falls among the less saline of inclosed seas; the salt content 
of its waters averages very much lower, for instance, than that of the Mediterranean, 
somewhat lower than that of the North Sea, but higher than that of the Baltic. A 
close parallel to the Gulf of Maine, in salinity, is to be found in the Skagerak, con- 
necting the Baltic with the North Sea. This relationship was to have been expected 
because the continental waters along the northwestern margin of the Atlantic are 
decidedly less saline, as a whole, than on the European side. 
Compared with the Gulf of St. Lawrence, the Gulf of Maine shows slightly the 
higher mean salinity at the surface; but the deep waters of these two gulfs agree very 
closely in this respect, as they do also in temperature. 
Perhaps the most notable feature of the gulf, from the present standpoint, is the 
abrupt contrast between the decidedly low salinity (averaging only about 32 to 32.5 
per mille at the surface and 32.8 to 33 per mille at 100 meters’ depth) over and 
within its offshore rim, and the very much salter (>35.5 per mille) water of the so- 
called “Gulf Stream,” always to be found only a few miles to the seaward of the 
edge of the continent. This contrast finds its counterpart in the temperature and 
also in the color of the water. 
The Gulf of Maine is also interesting for the wide regional variations in salinity 
in its inner waters, where, in spite of its small extent, the extremes recorded (about 
27 to 35 per mille) cover a range wider than that of the entire Atlantic basin outside 
78 In modern oceanographic parlance the degree of saltness, or “salinity,” of the sea water is expressed as the total weight, in 
grams, of the solids in a state of solution in 1,000 grams of water. This relationship “per thousand,” or “per mille,” is chosen 
rather than the more familar term “per cent,” merely for convenience to avoid the constant use of small fractional parts. 
8951—28 15 
