PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
765 
The maximum alteration that took place in the surface salinity at any one of 
these localities during the interval of from three to nine weeks was thus only 0.6 
per mille; in most cases it was less than 0.2 per mille; several times it was too small 
to be measured, a statement covering both sides of the basin of the gulf as well as 
the coastal belt, and applying to one locality or another in three different 
years. Among the islands or off headlands where the tide runs strong the surface 
would not show this uniformity, because the salinity in such situations varies widely 
with the stage of the tide. Even if the observations were taken at the same stage 
of tide, variation would be expected with the varying interaction between current 
and wind. Upwellings, for instance, such as follow offshore winds (p. 588), will bring 
up water appreciably salter, as well as colder, from below, along the western shores 
of the Gulf of Maine, even if the updraft comes from a depth of only a few meters. 
It is probable that the high salinity of the surface stratum recorded near 
Gloucester on July 9, 1912 (station 10001, 32 per mille) is to be explained on this 
basis. The salinity of the whole upper 40 meters, or so, of water may, in fact, be 
expected to vary considerably along the northern shore of the bay within brief periods, 
depending on the direction of the wind as this drives the surface water onshore or 
offshore. Unfortunately, however, our observations do not throw much light on the 
fluctuations in salinity of this sort, except on one occasion at a locality 3 to 5 miles 
off Gloucester, where the surface salinity, as calculated from hydrometer readings, 96 
increased by about 0.7 per mille between July 9 and 11 in 1912, with a correspond- 
ing decrease of 4.5° in surface temperature, the latter usually a sure evidence of 
upwelling thereabouts. In the eastern parts of the gulf, however, where the water 
is more nearly homogeneous vertically, winds and tides affect the surface salinity 
chiefly by the on and off shore interchange of salter and less saline waters. Cope- 
land (1912), for example, found the salinity of Passamaquoddy Bay varying with 
the tide (as well as locally in the bay) according to the relative outflow from the St. 
Croix River. Swirling tidal currents are also partly responsible for the regional 
variations recorded by Vachon (1918) and by Mavor (1923) in the surface salinity 
of Passamaquoddy Bay and of the Bay of Fundy, where, however, they also record 
a general increase in surface salinity during July and August, as follows: 
Locality 
Date 
Salinity 
Locality 
Date 
Salinity 
July 25,1916 
Aug. 2,1916 
Aug. 19,1916 
Aug. 31,1916 
July 24,1916 
Aug. 25,1916 
July 4,1917 
July 31,1917 
Per mille 
31.48 
31.27 
31.73 
31.84 
30.43 
31. 77 
30.61 
31.22 
Bay of Fundy, off Grand Manan, 
Sept. 4, 1917 
July 20,1916 
July 27,1916 
Aug. 3, 1916 
Aug. 10,1916 
Aug. 17,1916 
Aug. 31,1916 
Per mille 
31.92 
30. 36 
28. 97 
30. 27 
30. 19 
30. 58 
30. 77 
Do 
Passamaquoddy Bay, Prince sta- 
tion 4 
Do 
Do 
Do 
Bay of Fundy, off Grand Manan, 
Prince station 3 
Do 
Do 
Do 
Do 
Do 
Do — 
Do - 
In every August of record — 1912 (Bigelow, 1914, pi. 2 ), 1913 (fig. 135), 1914 
(fig. 136), or 1915 (fig. 137) — the surface salinity has been highest over the north- 
“ Both taken with the same instrument 
8951—28 49 
