PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 
605 
Such, for example, was the case near the northern edge of the bank on July 23, 
1914 (station 10224), when surface and bottom temperatures (11.11° and 10.78°) 
differed by less than 0.5° in 55 meters depth. This same state prevailed at a station 
on the western end of the bank (10059) on July 9, 1913 (surface 13.3°; bottom 12.6°), 
and again on July 23, 1916. 30 In August, 1896, Doctor Kendall found a maximum 
difference of only about 1° between surface and 18-meter readings at many localities 
along its northern and northwestern sides. 
On the parts of the bank where the water is more than 50 to 60 meters deep, 
and where tidal currents do not run so strong, the surface warms more rapidly during 
the progress of summer, the bottom less so; witness readings of 14.8° to 17.8° at the 
surface and 6° to 9° on bottom in 60 to 70 meters on the northern and eastern parts in 
August, 1926 (stations 20203 to 20208). The temperature gradient likewise differs 
widely from place to place in the Nantucket Shoals region in the late summer, 
depending on the topography of the bottom, with the water most nearly homogeneous 
over the shoal banks and ridges. Thus, the temperature of the entire column of 
water was 10° to 10.5° in 30 meters at a station 12 miles ESE. from Round Shoal 
buoy on July 15, 1924 (station 10655); and in August, 1925, when a greater number 
of serials was taken, the surface was invariably less than 1° warmer than the bottom 
on Rose and Crown Shoal, Round Shoal, and Great Rip in depths ranging from 20 
to 30 meters, the actual temperatures ranging from 11.5° to 15° from station to 
station (p. 595). 
The surface temperature rises high above that of the bottom water by the end 
of the summer over the smoother bottom to the south of the shoals, a regional 
contrast illustrated by two Grampus stations for July 25 and 26, 1916. One of these, 
located on the southern edge of the shoals (station 10355), was only about 1° warmer 
(11.95°) at the surface than at the bottom (10.97° in 30 meters). The other, in 
deeper water 23 miles to the southeast (station 10354), was 5° warmer at the surface 
(13.6°) than at the 30-meter level, and 7.6° warmer than on bottom at a depth of 
70 meters. Readings of 16.1° at the surface, 14.1° at 18 meters, and 10.2° at 46 
meters, near by, show about this same vertical range on July 9, 1913 (station 10060). 
A steep temperature gradient also develops to the west of the shoals by the end of 
August, illustrated by Grampus stations 10258, 10259, and 10263 (p. 987), and by the 
many serials taken off southern New England by Libbey (1891) in 1889. 
TEMPERATURE GRADIENT ALONG THE CONTINENTAL EDGE 
Sudden fluctuations in temperature are to be expected along the edge of the 
continent where the conflict between warm oceanic and cool coastal waters is con- 
stant. The station data do, in fact, show wide variations in the upper 100 meters 
along this zone (fig. 51). The one extreme, which may fairly be described as 
subtropical, is exemplified by stations 10218, southwest of Georges Bank, July 21, 
1919, and station 10261, in the offing of Marthas Vineyard, August 26, 1914. These 
chill, with increasing depth, from a very warm (20° to 24°) surface stratum to 7° 
to 9° at 400 meters and to about 5.25° to 6° at 500 meters. These contrast with 
stations showing a well-marked cold stratum at 40 to 80 meters, as south of Cape 
30 Station 10347, surface 11.39°, bottom 9.61° in 60 meters; station 10348, surface 11.67°, bottom 11.26° in 51 meters. 
8951—28 39 
