546 BULLETIN OF THE BUEEAU OF FISHEKIE3 



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 eft'ected 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 

 stratiim. 



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 



