546 
BULLETIN OF THE BUREAU OF FISHERIES 
The temperature of the upper 100 meters was 2° to 3° lower in the sink off the 
Isles of Shoals on March 5, 1920, than on that same date in 1921, and while the 
bottom readings for the two years differ by only about 0.1° in 175 meters, the bottom 
water was certainly slightly colder there in 1915 than in either 1920 or in 1921, a 
temperature of only 3.7° at 175 meters as late in the season as May 14 of that year 
contrasting with about 4° early in March of 1920 and 1921. 
Essentially this same relationship between the early March temperatures for 
1920 and for 1921 was recorded off Cape Elizabeth and off Seguin Island, 1920 being 
from 0.2° to 2.4° the colder year at all levels down to the bottom in 45 to 100 meters. 
The temperatures of the western basin some 35 miles off Cape Ann for February 
22 and March 24, 1920 (stations 20049 and 20087), and for March 5, 1921, did not 
differ . by more than 1.2° at any level; in all cases the highest reading was at about 
170 meters, with the upper 40 meters coldest, and 2.74° (on March 24, 1920) as 
the absolute minimum. On the whole, however, the readings for 1921 are slightly 
higher and the maximum for the month was recorded on that date (6.45° at 175 
meters). 
Thus 1920 may be described definitely as a cold winter in the coastal zone out 
to the 50-meter contour; 1921 and 1925 as warm ones. There was much less annual 
difference in temperature in the neighboring basin and almost none below the 200- 
meter level. A regional difference of this sort is just what might be expected if the 
winter chilling of the gulf is due chiefly to the severe climate of the neighboring land 
mass to the west (as there is every reason to believe it is), because the icy north- 
west winds, as they blow out over the adjacent sea, necessarily have most effect on 
the temperature of the water near the land. 
VERNAL WARMING 
After the middle or end of February the temperature of the western and northern 
parts of the gulf slowly rises as the heat given to the surface layers by the increasing 
strength of the sun is propagated downward by the vertical circulation of the water, 
but at different rates in different parts of the gulf, depending on the local activity 
of tidal stirring. 
Were solar warming alone responsible for the warming of the gulf in spring, the 
change would, for the first month or two, be confined to the superficial stratum where 
this vertical mixing is most active, except where a deeper column is kept stirred by 
strong tides — the Bay of Fundy, for example, and parts of Georges Bank. Actually, 
however, the gulf also warms from below during the early spring as the slope water, 
comparatively high in temperature and which enters through the trough of the 
Eastern Channel (p. 526), is incorporated by mixture with the colder stratum above, 
any increase in the amount of this from season to season being betrayed by an 
increase in salinity as well as in temperature. During the first weeks of March the 
warming effected from below by this source raises the temperature of the deep 
waters of the inner part of the gulf as rapidly as solar heat warms the surface 
stratum. 
It is interesting to trace the change that vernal warming effects in the level at 
which the gulf is coldest. Probably the inner parts are invariably coldest in the 
upper 40 meters by the end of winter, a state that persisted into the first week of 
