262 
.FISHERY BULLETIN OF FISH AND WILDLIFE SERVICE 
Figt ke ').—Vertical teiiiperatnre (° F.) distribution alons 
the P](iuator illustrating the east-west slope of the 
therinocline. 
tlie surface ai'e sliowii. One center near tlie Equa¬ 
tor and similar to that described for the 140° W. 
section (fi^. 4) results from the effects of the 
wind-induced divergence and iipwellin^. At the 
second, neai-4° S., the shallow therinocline, coupled 
with mixinii’ by the wind and by the turbulence at 
the interface of the opposing easterly and westerly 
surface currents, results in cooler water at the 
surface. 
The second meridional section, that alon^ 120° 
W., is shown in figure 6, B. Within the compara¬ 
tively short sjian of the section, 6° N. to 8° S., the 
therinocline approximates a dome with its center 
positioned at the Equator. Near the northern end 
of the section, the isotherms show a reversal in 
slope, decreasing in depth to either side. This 
trough undoubtedly approximates the position 
of the southern boundary of the Countercurrent. 
The domed configuration over the rest of the sec¬ 
tion reflects the flow of the westerly South Equa¬ 
torial Current. 
Near 4° N. latitude, 120° W. longitude, the 
isotherms (70° to 76° F.) abruptly descend from 
the surface. It was nei^r here that the Smith 
crossed a marked front such as that encountered 
during a previous cruise to this area (Cromwell 
and Reid, 1956). A temperature-depth section 
di*awn from BT data taken at and within a few 
miles either side of the front is shown in figure 7. 
One BT (No. 447), taken with vessel underway 
at 2 knots,’ was sufliciently close to the front so 
that the “up” and “down” traces in the first 20 
meters differed by 6° F., and could be used as a 
reference to locate the position of the other BT 
records relative to the front. Following Crom¬ 
well and Reid (1956, figs. and 4), the waters 
which were “nearly isothermal” have been shaded 
in figure 7. 
The Scripps vessel, the Horizon^ observed a sim¬ 
ilar feature 1 month later near 3° N. latitude, 
120° W. longitude (Knauss 1957). Knauss inter¬ 
prets the circulation at the front as “cold water 
overrunning the less dense warm water and then 
plunging downward.” He describes the feature as 
a “cold front” with the cold water to the south 
moving at right angles to the front at speeds in 
excess of 2 knots. 
Along the 140° W. section (fig. 6, C), the de¬ 
crease in temperature per unit of depth through 
the thermocline is less than in the previous two 
sections (110° W. and 120° W.), and the thermo¬ 
cline, 4° N. to 4° S., is 50-75 meters deeper. The 
influence of the Equatorial Undercurrent on the 
vertical temperature distribution is suggested be¬ 
tween 2° N. and 2° S. latitude. With westerly 
surface flow along the Equator, a ridge centered 
near the Equator is expected. North and south of 
2° N. and 2° S., respectively, the thermocline shows 
an upward trend toward the Equator. Between 
these two latitudes is a trough; i.e., warmer waters 
at greater depths. This trough may be interpreted 
as the result of advection of the warmer waters 
from the west into the lower part of the surface 
layer and to an unknown depth into the thermo¬ 
cline (Fofonoff and Montgomery, 1955). A sim¬ 
ilar situation, vertical spreading of the isotherms, 
may be seen (2° N. to 2° S.) on the 120° W. section 
(fig. 6, B) and to a lesser degree on the 110° W. 
section (fig. 6, A). On the latter sectiou, however, 
is a southerly displacement of the trough, undoubt¬ 
edly related to the easterly surface flow south of 
the Equator (1° S. to 4° S.). Further details of 
the 140° W. vertical temperature section were dis¬ 
cussed in connection with figure 4. 
Salinity 
The most prominent feature in the subsurface 
distribution of this variable is the tongue of high 
salinity water south of the Equator at a depth 
of about 150 meters (fig. 8). In comparing the 
salinities in this feature on the three sections, there 
OCEANOGRAPHY OF EAST CENTRAL EQUATORIAL PACIFIC 
263 
300 
•20® 
lO® -/- 
■ (, 
•0®_ 
r 
m 
•10® 
K 
7^ 
le 
0® 15 
1 
0® 140® 12 
-1-1- 
0° 1^0® lip® 
2 ° 
J^L 
0 ° 
10 “= 
14 ° 
16 ° 
18 ° 
2 ° 0 ° 
LATITUDE 
Figure (>.—P.atliytliermograi)!! tenippratnre-depth sections 110° W. longitude (A) : 120° W. longitud(‘ (B), and 140° W 
longitude (C). Contour interval 2° F. (from King et al.. 1057). 
IS a progressive increase, east to west, from 35.30 
V 00 to 35.80 "/oo to a maximum of 36.13 °/oo. From 
east to west there is an increasingly apparent 
lorthward extension of the tonoaie. 
The source of these higher salinity waters at an 
intermediate level is a Southern Hemisphere 
salinity maximum in the surface waters positioned 
near 20° S., extending east to west between ap- 
])roximately 100° W. and 140° W. (Fleming et ah, 
1945, tig. 222). In this region of descending flow 
of air in the atinosjihere above the ocean and asso¬ 
ciated evaporation from the sea surface, more 
saline waters are formed and sink, moving north¬ 
westerly then westerly at subsurface levels. The 
