566 



BULLETIN OF THE BUEEAU OF FISHERIES 



of temperature at the 40-meter level alters from April (fig. 24) to mid-May (fig. 34) 

 by a shift of the coldest area (1.58° to 2.1° in April, 1920; 3° to 3.25° in May, 1915) 

 from the western and northwestern sides of the gulf to the eastern side. Similarly, 

 the warmest center shifts from the eastern arm of the basin, where the April read- 

 ings were highest in 1920, to the western, with the coastal sector from Massachusetts 

 Bay to Cape Elizabeth (4.5° to 5.1°, May 4 to 14, 1915), with about equal tempera- 

 tures along the southwestern edge of Georges Bank (5.4° to 5.6° on May 17, 1920, 

 stations 20128 and 20129). 



The mid-stratum of the gulf, as illustrated by the 100-meter level, continues 

 through May as regionally uniform in temperature as it is in April (fig. 25), with an 

 extreme recorded range of only 2.45° within the gulf for the two years 1915 and 1920 

 (2.65°, Massachusetts Bay, station 20124, to 5.1° northeastern part of the basin, sta- 

 tion 10273) and slightly warmer (7.5°) along the southwestern slope of Georges Bank 

 (station 20129). Within the basin of the gulf the 100-meter readings for May have 

 been highest (4.4° to 5.1°) in the central and northeastern parts, lowest in the western 

 (2.6° to 3.5°) and eastern sides (about 4°). This last reading perhaps reflects the 

 chilling effect of the Nova Scotian current from above; but there is no reason to 

 suppose that the latter influences the spring temperature much deeper than this, 

 because the 150-meter readings for March 2 and 23, for April 17, 1920, and for May 

 6, 1915, all fall within 0.2° of one another (about 5° in temperature) in the eastern 

 side, and are nearly as uniform over the gulf, generally, for all the May cruises, as 

 appears from the following table : 



' At 146 meters. 



» At 140 meters. 



Thus the open basin of the gulf may be described as virtually uniform in tem- 

 perature from side to side at the 150-meter level in May, though the precise read- 

 ings may be a degree or so warmer or colder from one year to the next. The read- 

 ings at the four deepest stations for May, 1915, also fall withm 0.2° of one another 

 at 185 to 190 meters (5.6° to 5.9° at stations 10267, 10268, 10269, and 10270). 



The graphs for individual stations (figs. 3 to 11) show that in May (as is the 

 case throughout the spring) the horizontal uniformity in temperature in the deep 

 strata of the gulf usually is associated with a considerable rise in temperatiu-e with 

 increasing depth, from the 50 to 100 meter level downward. As an example, I may 

 cite a station off Cape Ann, occupied on May 4, 1915 (station 10267), when the 130- 

 meter reading was 4.69°, with 6.59° at 260 meters depth. During the month the 

 200-meter level has averaged slightly warmer than the 100-meter level in the open 



