PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 807 
Island (station 10495), where the salinity increased only from 32.6 per mille at the 
surface to 32.77 per mille at 75 meters. 
Local freshening of the surface, just described (p. 806), was then responsible for 
the very considerable vertical range of 2.6 per mille in water only 30 meters deep 
between Cape Ann and the Merrimac River, with differences of 0.8 to 1.4 per mille 
between the surface and the 75 to 100 meter level off Cape Elizabeth and off Cape 
Ann (stations 10488, 10489, 10492, and 10494). 
It is certain, however, that as the surface continued to cool during that winter 
the decrease in vertical stability was accompanied by a progressive equalization of 
salinity in the upper 100 meters; for the surface and the 100-meter level differed by 
less than 0.2 per mille in salinity at five out of seven of the stations for the follow- 
ing March (stations 10505 to 10511). Thus, the seasonal cycle was fundamentally 
the same in this respect in 1920-21 as in 1912-13, except that it was more tardy in 
its early progression. 
No general survey of the salinity of the gulf has yet been attempted during 
the last half of January or the first half of February— on the whole the coldest 
season (p. 655) . However, periodic observations taken in Massachusetts Bay during 
this period of 1913, hydrometer readings taken at 15 stations by the Fish Hawk in 
its southern side on February 6 and 7, 1925, and Mavor’s (1923) winter records for 
the Bay of Fundy in 1916 and 1917 show that no very wide change is to be expected 
in the salinity of the gulf during the last half of the winter. 
These Fish Hawk determinations ranged from about 32.3 per mille to about 33.3 
per mille, according to the precise locality, averaging lowest in the hook of Cape Cod, 
where the surface was about 32.3 to 32.4 per mille, and highest in the center of the 
bay (whole column close to 33 per mille, surface to bottom). The maximum differ- 
ence in salinity between surface and bottom was then only 0.4 per mille (average 
difference about 0.2 per mille), with the water virtually homogeneous, surface to 
bottom, at the two deepest stations (about 70 meters deep). 
It is interesting to find the salinity of the deeper part of the bay for February 
7, 1925, almost exactly reproducing the values recorded off Gloucester on the 13th 
of the month in 1913 (station 10053, surface 32.83 per mille, bottom 32.84 per mille); 
evidently neither of these winters, as contrasted with the other, can be described as 
"fresh” or "salt” in the bay. In both 1913 and 1925 the water away from the 
immediate influence of the shore line was equally homogeneous in salinity from 
top to bottom by these dates; but the data for the two years combined bring 
out a decided regional difference in this respect, with the surface continuing 0.3 to 
0.4 per mille less saline than the deeper strata along the northern and southern mar- 
gins of the bay, no doubt because of land drainage. 
Although we have made no offshore stations in the gulf between the middle of 
January and the last week of February, some knowledge of the ebb and flow of the 
slope water over that period is obtainable from the seasonal progression from Feb- 
ruary to March in the deeper parts of Massachusetts Bay, and from the salinity of 
the basin off Cape Ann for March 5, 1921 (station 10510), compared with the pre< 
ceding December and January (stations 10490 and 10503). 
In 1913 the salinity rose to about 32.8 per mille at the surface, to 32.9 per mille 
on bottom in 70 meters, at the mouth of the bay by Januarv 16— a mean increase of 
