274 
FISHERY BULLETIN OF FISH AND WILDLIFE SERVICE 
Figure 18.—Distribution of inorganic phosphate (^ug. at./L.) in surface waters. Surface samples were taken at the 
position of the oceanographic stations and at the time of the BT lowerings. The positions at which the samples 
were taken are indicated. The arrows denote current direction as determined from geostrophic calculations. 
centrutions of 1.0 to 2.0 /xg. at./L. near 137° W. 
and 3° N. are difficult to explain. LTnfortunately, 
there are no siilisnrface phosphates available for 
analysis of vertical transport, and no indications 
of such in the temperature fields. There are no 
apparent indications of analytical error. More 
than one sample is involved and the high values 
are consistent among these samples. One expla¬ 
nation is that these Avaters reached the surface 
near the Equator and moved to the position where 
sampled from the A similar situation was 
described by Sette et al. (1954) near 3° N. and 
1()5° AV. Tlie high value near the Marquesas, 7° 
S., 142° may have resulted from some as yet 
undetermined circulation feature(s) associated 
with the islands. Similar concentrations in this 
area wei’e observed during the recent participa¬ 
tion of the in Equapac (Austin 1957). 
DISCUSSION OF RESULTS 
Eastropic was a combined physical and biologi¬ 
cal study of the eastern central equatorial Pacific. 
The 1 ‘esults of POE Ps oceanographic observations 
have been described in the preceding sections of 
this report. The results of the biological sam¬ 
pling program Avill be considered in relation to 
these environmental features. Before this can be 
done Ave must consider the question, “Hoav typical 
Avere the environmental factors '^” It appears that 
the oceanographic conditions Avere someAAdiat 
atypical. 
The surface temperatures along the Equator 
(fig. 14) AATre 2°-4° F. cooler than normal; those 
in the Countercurrent shoAved little variation 
from normal. Waters Avere also cooler than normal 
at four stations in the eastern Pacific (fig. 19) one 
each off (hilifornia, Panama, Peru, and Christmas 
Island (Line Islands group). liodeAvald (1956) 
demonstrates that these beloAv-normal surface 
temperatures Avere typical for the entire eastern 
Pacific during 1955, particularly the latter half 
of the year. North to south, he reports anomalies 
in 1955 of —0.9° F. for Alaskan Avaters, —1.7° F. 
for AA^ashington and Oregon, —1.2° F. for Cali¬ 
fornia, and —0.6° F. for Chile and Peru. These 
temperatures and the cooler water observed by the 
Smith in the South Equatorial Current may be 
considered to be “eastern Pacific temperatures,” 
while the normal temperatures in the easterly 
fioAving Countercurrent more or less reflect con¬ 
ditions farther to the west. In the western Pa¬ 
cific near the Philippines, the anomaly in 1955 
OCEANOGRAPHY OF EAST CENTRAL EQUATORIAL PACIFIC 
275 
Avas +0.2° F., exceeding +1° F. for August 
through November. 
The comparatively high measured and calcu¬ 
lated s])eeds of surface flow in the South Equa¬ 
torial (dirrent, as Avell as the cooler than normal 
Avaters at the surface in the eastern Pacific, suit- 
gest that the circulation during expedition 
Eastropic Avas more vigorous than normally ob¬ 
served. If such Avas the case, this should be re¬ 
flected in the distribution of mass. 
Montgomery and Palmffii (1940), using data 
from one station near 99°07' AAk and the mean of 
three near 135° E., calculated the mean slope of 
the sea surface (0/400 db. reference level) to be 
4.0 X 10'^^, Avith a dilference in level of 0.7 dynamic 
meter. In figure 20, using data from more recent 
cruises, the longitudinal variations in levTl of the 
sea surface oati* the 400-dh. FatI are shoAvn for the 
span between 100° AAh and 140° E. longitude. 
Data from stations betAveen 00°30' N. and 00°30' S. 
Avere used. The 400-db. leATl Avas chosen in order 
to increase the number of aAuiilable stations. The 
slope from Montgomery and Palmen's I’eport is 
also shoAvn. 
Of ])articular interest to this discussion is the 
slo])e betAveen 100° AY. and 140° AAk For com¬ 
parative purposes, the data from Smith cruise 35 
(August-Octoher 1956) and cruise 38 (January- 
Figuke 19. —Surface teiiiperature anomalies (° F.) for 
four stations in the eastern Pacific for October, NoA^ein- 
ber, and December, 1955. 
Figure 20.—Longitudinal slope, sea surface, 0/400 db. 
level. 
March 1957) have been added. It may be seen 
that the slope during Eastropic Avas steeper than 
that for either of these tAvo cruises or for the 
mean. Comparative ATilues, 120° AA^. to 140° AY., 
are: mean, 4.5X10"^; Smith cruise 38, 5.3X10~®; 
and Eastropic, 13.1X10"®. A iwersal in the cal¬ 
culated slope of the sea surface during Eastropic 
is evident near 120° AY. (fig. 20). This reversal 
results from the deepening of the thermocline east 
of 130°-120° AY. (see fig. 5) and the accompany¬ 
ing increase in depth of the Avarmer, less-saline, 
and thus less-dense Avaters of the mixed laver. 
The same features and conclusions can be in¬ 
ferred from the distribution of the depth of the 
70° F. isotherm along the Equator (fig. 21). This 
isotherm is normally found near the center of the 
depth range of the thermocline (Austin 1954a), 
and thus exhibits the same variations in depth as 
the thermocline. 
In figure 21, prepared from all available BT 
data from POFI files and those furnished by 
Scripps Institution of Oceanography, betAveen 2° 
N. to 2° S., the ATIriations in depth of the 70° F. 
Figure 21.—Depth of 70° F. isotberm, 2° N. to 2° S. 
