636 
BULLETIN OF THE BUBEAU OF FISHEKIES 
Annual differences in temperature — Continued 
WEST SIDE OF EASTERN BASIN 
Depth, meters 
1912 
10027 
Aug. 14 
1913 
10092 
Aug. 11 
1914 
10249 
Aug. 12 
1915 
10309 
Sept. 1 
0 
15.0 
16.7 
17.5 
15.6 
20 
9.2 
8. 1 
9. 1 
12. 5 
40 
7.8 
6.7 
6.4 
10.3 
60 
7.4 
5.8 
5.7 
8.5 
80 
7.2 
5.6 
5.3 
6.8 
100 
6. 1 
5.9 
5.3 
5.9 
120 
6.6 
6. 1 
5.5 
5.8 
140 — 
6.2 
6.1 
5.9 
5.9 
160 , 
6. 1 
6. 1 
6. 1 
5.9 
180 
6.0 
6. 1 
6.0 
6. 0 
200 
6. 1 
5.9 
6.1 
220 — — — 
6. 1 
5.8 
240.. 
6.1 
OFF LURCHER SHOAL 
Depth, meters 
1912 
10031 
Aug. 15 
1913 
10196 
Aug. 12 
1914 
10245 
Aug. 12 
1915 
10315 
Sept. 7 
0 _ 
13.3 
12. 1 
14.4 
12. 2 
25 . — - 
11.8 
10.5 
10.3 
11.3 
50 _ 
10. 7 
9.4 
9. 2 
10. 1 
75 — — - — 
10. 1 
8.6 
8.8 
9.9 
100 - 
8.5 
7.4 
8.6 
AUTUMNAL COOLING 
SURFACE 
The surface is at its warmest at some time during August in all those parts of the 
Gulf of Maine where the surface temperature rises much above that of the deep 
water in summer. 41 This includes the whole open area, except for the northeastern 
part, and the sites of active tidal mixing on the banks, the precise date of maximum 
surface temperature for any given summer depending on the prevailing weather. Our 
recent studies have not been sufficiently intensive precisely to locate this critical 
date for any one year or for any given locality in the gulf, but the records collected 
by Rathbun (1887) for the years 1881 to 1885 show that it may fall at any time 
between the first and last of August for the western and northern shores of the 
gulf between Nantucket Shoals and Penobscot Bay. After the first of September 
the surface of this subdivision cools as the autumn advances. 
Experience in the summers of 1912, 1913, and 1914 suggests that the temper- 
ature of the upper layers of the western and deeper parts of the gulf generally (i. e., 
where vertical circulation is only moderately active) probably had passed its mid- 
summer maximum, and that autumnal cooling had commenced there by the date of 
our late August and early September cruise of 1915. Thus, the highest reading 
recorded on August 31 and September 2 of that year, on the run eastward from 
Gloucester toward Cape Sable, was only 17.6°, contrasting with a probable maxi- 
mum of about 19° to 20° over the western side of the basin during mid August. 
The seasonal schedule seems to have been about the same in 1925, also, when the 
Halcyon had surface readings of 16.6° a few miles north of Cape Ann, 15.2° on Platts 
Bank, and 14.7 between the latter and Portland on September 3. 
u The temperature of inclosed harbors is highest in July, mirroring the summer maximum for the air (p. 585). 
