266 
FISHERY BULLETIN OF FISH AND WILDLIFE SERVICE 
Fi(;ri{F !).—’’I’cniiperjUnro (° (/.)-salinity (°/oo) (‘lU’ves at selected stations. Southern Hemisphere along 110° W. (A), 
12((° W. (I>). Density (ohliciue lines) in centilitcu's i»er ton. 
tliroii^h tlie tlieriiiocline. Althongli variations in 
salinity, as well as temperature, ali'ect the vertical 
distribution of density of sea water, in tropical 
waters salinity nsnally plays a minor role. To 
illustrate : from east to west (particularly between 
the 120° and the 140° W. sections) there is a 
o’eneral increase in depth of both the thermocline 
and the stable laver. There is a troim-h in each 
* ^ 
at the southern bonndarv of the Countercurrent 
and a marked rid^e near the Equator on 140° and 
120° W., and neai- 4° S. on 110° W. The clian^m 
in temperatni'e and density across the front is re¬ 
flected in the ‘‘bunching” of the density isopleths at 
theii' intersection with the surface near 4° N. on 
120° AV. and 1° N. on 110° AY. 
Oxygen 
The vertical distribution of oxygen is shown in 
figure 11. Selected isopleths foi' 8i ai'e sliown 
on each section. On the foiu’ longitudes, the 
oxygen content in the surface lavers, surface to the 
top of the thermocline, was uniformly high, 4.0 to 
a.;) ml./L., deci'easing thi'ough the thermocline to 
the oxygen minimum, then inci’easing to maximum 
depths sam])led. Near 100° W. and 110° W., the 
minimum with values of less than 0.5 ml./E. was 
continuous from the Southern to the Northern 
Hemisphere. Along the 120° W. and 140° W. 
sections, values less than 0.5 ml./L. Avere observed 
only in the Southern iremisphere. On each sec¬ 
tion a narroAV, vertical tongue of Avater Avitli 
highei’ oxygen (‘ontent Avas centered beneath the 
surface Avaters at the Equator. 
The low oxygen Auilues in the minimum south of 
the Equator (hOO-500 meters) are in Avaters AAddch 
luiAXA moved westerly from the coast of Peru and, 
at least in ]iart, result from the consumption of 
oxygen at subsurface depths by decomposition of 
the oi'ganic material Avhich was in these Avaters 
Avhen they de|)arted from the surface and of the 
organi(‘ detritus sinking fi‘om the euphotic zone. 
North of the Equator in the eastern Pacific is 
a large subsurface body of Avater Avithin Avhich the 
oxygen content is Ioav (0.1 ml./L. or less). As 
described by Sverdiaip et al. (1942, p. 729), this 
body of Avater is found off* the American coast 
between 28° N. and the Equator, extending to the 
Avest as far as 140° W. More recent data (Crom- 
Avell 1951) bring this Avestward extension to at 
least 172° W. The loAvest oxygen concentrations. 
OCEANOGRAPHY OF EAST CENTRAL EQUATORIAL PACIFIC 
267 
100 
a: 
ijj 
I- 
LU 
5 
X 
f— 
Q. 
LlI 
Q 
200 
300 
LATITUDE 
Figure 10.—A^errieal (listribution of density expressed as tlierniosterie anomaly along 110° AV. (A). 120° W. (B). and 
140° W. (C). (’ontonr interval 20 centiliters per ton (from King et al., 10.17). Depths of oh.servations are sliown 
by solid dots; station nnmbers are given along the top of each panel. 
