PERCENT 
BOTTOM - WATER TEMP °C 
Autumn — 
GEORGES BANK 
1963 64 65 66 
Figure 18.—Observed and adjusted bottom-water temperatures on 
Georges Bank in the autumn, 1963-75. 
=) 
1968 
1972 
414 
50 b 4 
© O12 
°O 4 4 ror 1 8 
i969 1973 
414 O 
50 i Om =f 
412 = 
a aia dio © 
dl eee te 
A 1} to et 
1970 1974 $ 
414% 
eo, = 
50 bE 2 
ie i= 
® 
L ° 
2s 7 | o 8 
° 1 1 | its 
1971 1975 
414 
50 <a 
o odie 
4 __a wall 4 
46 81012141618 46810 i214 1618 
414 TCl USI) 
50 
12 
25 Io 
® 
= 
4 6 8 1012141618 
Tcl 
Figure 19.—Percentages of temperature-class intervals (TCI’s) on 
Georges Bank in the autumn, 1963-75. (Dotted circles represent the 
observed mean bottom-water temperatures.) 
offshore waters entering the Gulf of Maine via the North- 
east Channel principally determine these variations, at 
least in deeper basins of the Gulf. Although salinity ob- 
servations were not analyzed in this study, it can be 
assumed that fluctuations in the volume of slope water 
entering the Gulf through the Northeast Channel were 
mainly responsible for the general temperature trend ob- 
served in much of the Gulf and partially affected tem- 
14 
13 
Eastern Georges 
BOTTOM - WATER TEMP °C 
Autumn, Suboreas — GEORGES BANK 
69 70 71 72 
Figure 20.—Adjusted mean bottom-water temperatures on Georges 
Bank by subareas in the autumn, 1963-75. 
perature changes on Georges Bank. Examination of the 
continuity of the 8°C bottom isotherm for the spring 
cruises supports this assumption. The high spring tem- 
peratures observed in 1972-75 in Subareas IV and V (Fig. 
7) were probably the result of an inflow through the 
Northeast Channel each year as indicated by the 8°C iso- 
therm (Fig. 2). The high mean temperature observed in 
Subarea III in 1970 was the result of one of two rather 
large pockets of water >8°C. 
It seems clear that anomalous temperature conditions 
occurred, commencing in the spring of 1970 and autumn 
of 1971, and persisted through 1975. In order to under- 
stand the dynamics of such changes the National Marine 
Fisheries Service initiated in 1977 a program of con- 
tinuous monitoring of temperature, salinity, and cur- 
rents in the Northeast Channel and contiguous waters. 
As stated by Bigelow (1927) this channel is the most 
striking feature of the Gulf of Maine affecting the hydro- 
graphy of the region. Also, an examination of available 
data on the volume and location of slope waters (such as 
Wright 1976) for waters south of Cape Cod would provide 
a better understanding of the observed conditions in the 
Gulf of Maine and on Georges Bank during this period. 
The trend of increasing spring temperatures since 1968 
is much smoother in the Gulf of Maine (Fig. 6) than on 
Georges Bank (Fig. 10) when each area is analyzed as an 
entire unit, but on Georges Bank the subareas are much 
more similar within a given year (Figs. 8, 12). This is to 
be expected as the waters of Georges Bank are well mixed 
by tides and winds as indicated by the homogeneity of 
TCI’s in years of very comparable mean temperatures 
such as in the spring of 1969 and 1972 (Fig. 11). This con- 
dition was not observed in the autumn because Eastern 
Georges Bank was consistently 2°C or more colder than 
the rest of the Bank. This can partially be explained 
because Eastern Georges Bank, being the deepest of the 
three subareas, is least affected by solar heating and mix- 
ing. Also, a buffering effect is probably from the indraft 
of cooler slope water through the adjacent Northeast 
Channel during the autumn. 
