PHYSICAL OCEANOGRAPHY OF 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'° 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 imlle 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 

 mUle 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 — Salter 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 falien between 33.8 and 34.5 per mille, irrespective of 

 the time of year, make it unlilce y that it^ 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 



'• Thirteen stations for the months of February, Marc i, v ri , .lay, June, July, August, November, and December in var- 

 ious years. 



