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FISHERY BULLETIN OF FISH AND WILDLIFE SERVICE 
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Figure 13.— Vertical distrit)ution of phosphate expressed In micrograni-atonis per liter (/ig. at./L.) along sections near 
110° W. (A) and 120° W. (B). Contour interval 0.2 /ig. at./L. (from King et al., 1957). Depths o o serva ions 
are shown by dots; station numbers are given along the top of each panel. 
Surface Temperature 
The surface temperatures, as measured in the 
bucket samples taken at each BT lowering (gtiu- 
erally at 2-hour intervals, 15 to 20 miles apart) 
are shown by the black contours in figure 14. 
Mean surface temperature distribution for the 
month of November, as published in an atlas pre¬ 
pared by the British Air Ministry (1950), is 
shown by the red contours. 
In tlie ( V)imtercurrent (5° N. to 10° N. latitude) 
tliere is general agreement between the Eastropic 
surface-temperatures and the mean. Over most of 
tlie area the 80° F. isotlierms in each case straddle 
the somewhat warmer waters in the center of the 
current, but swing northerly from the latitude of 
the axis in the eastern part of the survey area. 
Tliis northerly shift in position of the isotherms re¬ 
flects the influence of the warmer waters moving to 
the west away from the coast of Central America. 
A similar configuration of the surface isotheims is 
evident in the report by Jerlov (1956, fig. 3) de¬ 
scribing the results of the Swedish A-Tbtttvoss ex¬ 
pedition to the same area and during the same 
montlis (October-November 1948). 
The distribution of surface temperatures (also 
salinity and phosphate) suggests that there was a 
southerly bulge in the Countercurrent centered 
OCEANOGRAPHY OF EAST CENTRAL EQUATORIAL PACIFIC 
271 
Figure 14.—Surface temperature (° F.) distribution from temperatures of bucket samples taken at position of BT 
lowerings in black; mean temperatures from British Air Ministry Atlas (1950) in red. Tbe arrows denote 
current direction as determined from geostropbic calculations. 
near 132° W. longitude. Although this feature 
appears to be real, there is the possibility that it is 
an artifact resulting from the V-shape of the vessel 
track in this area. There is an acceptable com¬ 
parability, however, in the shape of the contours 
defining the bulge among all the surface variables 
measured. Similar variations were reported by 
Crom^vell (1956, p. 29) during expedition 
Eastropic. 
The cooler surface temperatures in the South 
Equatorial Current, particularly along the Equa¬ 
tor, are strikingly evident. In fact, those observed 
near the Equator during the period of Eastropic 
were from 2° to 4° F. cooler than the mean. At 
any point along the Equator, these cooler waters 
reflect both the mixing of the deeper waiters with 
those at the su rface and, in varying degrees, advec- 
tion from the east. The mixing involves at least 
two separate physical processes, one rehled to the 
divergence of the surface waters under the in¬ 
fluence of winds with an easterly component, the 
other, mixing by the wind which is more effective 
in the east because of the west-to-east shoaling of 
the thermocline. At present, quantitative esti¬ 
mates of the relative roles of each of these two 
processes are not available. 
The oceanic front described in earlier sections 
was evident near 4° N. latitude on 120° lY. longi¬ 
tude, across which there was an abrupt change in 
surface temperature of nearly 4° F. (fig. 14). 
This circulation feature Avas discernible in vary¬ 
ing degrees near 4° N., 135° W. and 2° N., 112° lY. 
That it may be a semipermanent feature in this 
region of the Pacific is evidenced by the fact that 
during expedition Eastropic the Scripps vessel, 
the Horizon^ observed it 1 month later than did the 
Smith (Knauss 1957), and a similar feature Avas 
previously detected by the Smith near 1° N., 120° 
W. on October 27, 1952 (CroniAA^ell and Keid, 
1956). HoAvever, a front Avas not detected by the 
Alhatroxs during October-NoA^ember 1947 Avhen 
she crossed the Equator at 137° W. (Jerlov 1956, 
p. 150), nor by the Baird which AA’as Avorking dur¬ 
ing expedition Eastropic only 300 miles to the east 
of the Horizon (Knauss 1957). 
Depth of Thermocline 
From the preceding discussion of the distribu¬ 
tion of temperature, it is evident that there Avas 
considerable A'ariation in depth of the thermocline 
throughout the area surveyed by the Smith. The 
