PHYSICAL OCEANOGRAPHY OP THE GULF OF MAINE 
815 
to be expected there in spring. In 1915, however, the surface freshened by only 
about 0.5 per mille at that locality from May to June; and while salinity may have 
fallen somewhat lower that July (when no observations were taken), it was about 
the same there at the end of August (32.5 per mille at station 10307) as it had been 
in June. 
The available data 19 show the surface freshest here in July or August, or three 
months later than at the mouth of Massachusetts Bay (p. 811), and not saltest until 
May (p. 745), when the coastwise belt is least saline, a seasonal difference associated 
with the geographic location. 
It is not possible to follow the seasonal progression of salinity in the deeper 
strata of the basin from the data at hand because the annual variations outrange 
the seasonal variations even at as small a depth as 40 meters. I can only point out 
that the 40-meter salinity decreased from 33.15 per mille on May 5, in 1915, to 33 
per mille on June 26 and to 32.75 per mille on August 31, suggesting that vernal 
freshening culminates later at this depth than at the surface, as, indeed, is to be 
expected. At 100 meters the values for May, June, and August, 1915, all fell 
close together (33.08 to 33.17 per mille); and the extreme range of variation so far 
recorded at this level, for all years and seasons, has only been from about 32.5 per 
mille to about 33.2 per mille in this part of the basin. 
Pulses in the indraft of banks water govern the salinity of the deeps of the gulf 
(p. 848) ; and these are reflected in fluctuations from a minimum of about 33.5 per 
mille to a maximum of about 34.1 per mille at the 200-meter level in the basin off 
Cape Ann. However, as pointed out (p. 852), it is not yet known how regularly 
periodic these fluctuations are, and if periodic, their exact seasonal schedule. 
ANNUAL SURVEY OF SALINITY ON THE BOTTOM 
The salinity of the bottom water of the gulf (interesting chiefly for its biologic 
bearing) is determined in part by the depth and in part by proximity, on the one 
hand, to the Eastern Channel and on the other to the coastline, with the outflow 
from its rivers. It is also influenced by the Nova Scotian current and by the general 
anticlockwise eddy that occupies the basin of the gulf. In inclosed sinks and bowls 
the degree of isolation is the determining factor. 
In summer and autumn the whole bottom of the open basin deeper than 175 
meters has invariably proved salter than 33.5 per mille — sa'lter than 34 per mille at 
most places and on most occasions. In 1914 a maximum of about 35 per mille was 
recorded for the southeastern part, out through the Eastern Channel (p. 785) , but this 
may have been a somewhat higher value than is usual for that situation. The state 
of the gulf in the midwinter of 1920-1921 and in the spring of 1920, with the fact 
that all but two out of 31 records of the salinity of the two arms of the trough 
deeper that 175 meters have fallen between 33.8 and 34.5 per mille, irrespective of 
the time of year, make it unlikely that its bottom normally experiences a variation 
wider than about 0.5 per mille in salinity during the year, or from year to year, in 
depths greater than 150 meters. Animals living on bottom in deep water in the gulf 
19 Thirteen stations for the months of February, March, April, May, June, July, August, November, and December in var- 
ious years. 
