650 BULLETIN OF THE BXJEEAU OF FISHERIES 



side of the Gulf of Maine after November, the thermal relation between surface and 

 bottom temperatures may be reversed at different stages of the tide, as warmer 

 water from offshore comes in with the flood and water chilled near shore moves out 

 on the ebb. But whether the flood water will drift in at the surface, or whether it 

 wUl sink to some deeper level as it approaches the coast, depends on the regional 

 distribution of density. Accordingly, the flood tide may either raise the surface 

 temperature slightly above that of the deeper water near land in winter or it may 

 warm the mid stratum temporarily, a state which may persist until the last of the 

 «bb. Both these alternatives are illustrated among the Massachusetts Bay stations 

 for December 16 and 17, 1925 (stations 5, 6, 7, 9, 13, 14, and 17). The fact that the 

 •station off Cohasset (16) was not only coldest at the surface but gave the minimum 

 temperature for the cruise (3.8°), although taken about the middle of the flood, 

 probably results from the general drift discussed below (p. 972). 



The fourth week of December, 1925, saw very wintry weather, with several days 

 of northwest gales, the mLaimum temperature of the air falhng to — 1° F. ( — 18.2° C.) 

 at Boston on the 21st and to about 5° F. (about - 15° C.) on the 22d. This was 

 reflected by an average cooling of about 1° for the waters of the bay between the 

 16th and 17th and the 22d and 23d, which gives a rough measure of the radiation to 

 be expected from the surface during two or three days of low air temperatures and 

 high offshore winds at this time of year. 



Although the entire area was much more uniform in temperature on December 

 22 and 23 than it had been a week earUer (all the readings for that date fell between 

 4.95° and 2.5°), temperatures of 2.5° to 3° near Plymouth, in the one side, and a 

 mile off Gloucester, in the other," on the same day, contrasting with 4.5° to 5° in 

 the central part of thfe bay (station 18; about 7° at station 10049 on December 23, 

 1913), show the thermal gradation usual for the winter season. Thus, 4° to 7° may 

 be taken as normal for the deep parts of the bay during the last week iu December, 

 jand 2° to 4° for its coastal belt. 



The Bay of Fundy, in the opposite side of the gulf, experiences essentially the 

 same cycle of temperature as Massachusetts Bay during December. Thus, Mavor's 

 (1923) tables show the whole column of its deep trough as virtuaUy homogeneous, 

 vertically, by November (fig. 79), and about reproducing Massachusetts Bay in 

 temperature iu December, notwithstanding the difference La latitude. Compare, for 

 instance, 6.4° to 6.9° in the central parts of Massachusetts Bay on December 11, 1925, 

 with 6.18° to 6.6° for the corresponding depth column in the Bay of Fundy on 

 December 2, 1915, and 5.62° to 6.12° on December 5, 1917 (Mavor, 1923, p. 375) .« 



Some variation is to be expected in the vertical distribution of temperature in 

 these bays in December from year to year. In 1913, as noted (p. 645), the water off 

 Gloucester was homogeneous, surface to bottom, throughout that month; but in 

 1920 more rapid chilling had lowered the temperature of the surface (5.56°) about 

 1.5° below that of the 40-meter level (6.94°) at this locality by the end of the month 



" Observation taken by C. Q. Corliss (p. 513.) 



" Mavor (1923) records 6.11° for the surface, 6.42° at 60 meters, and 6.6° at 176 meters on Dec. 2, 1916; 5.62° at the surface, 5.72° 

 at 60 meters, 6.16° at 100 meters, and 6.18° at 176 meters on Deo. 6, 1917. . 



