Sigma-t : The four sections for sigma-t are shown in figures 8 through 11. These 

 sections, as is the case with the subsequent sections for salinity and phosphate, are arranged 

 in the following order: southbound, stations 1 through 17; northbound, stations 17 through 31; 

 southbound, stations 31 through 45; and northbound, stations 45 through 60. The sigma-t sur- 

 faces are drawn at 0.2 gm/1 intervals. 



In general, the picture may be considered characteristic for the central Pacific 

 equatorial region. Reading from north to south (right to left on each of the four sections), we 

 see the pronounced, relatively shallow density gradient associated with the northern edge of 

 the Countercurrent; the inclined surfaces in the Countercurrent and domed configuration asso- 

 ciated with the divergence in the South Equatorial Current at or near the Equator. 



The trough at the Equator, first evident in the sigma-t surfaces at 75 to 100 meters 

 below the surface, is similar to that pointed out by Cromwell (1954) as characteristic of this 

 region. 



Salinity: The salinity sections for the four legs of the cruise are shown on figures 

 12 to 15. In their general features, these sections are very similar to those described in pre- 

 vious reports of this series (Cromwell 1951, 1954; Austin 1954) and in the report by Montgomery 

 (1954). The tongue of high salinity water (at 100-150 meters, southern half of sections) and the 

 low salinity surface waters of the Countercurrent are pronounced features and will be subse- 

 quently discussed in the section on the temperature -salinity relationships (T-S curves). 



Inorganic phosphate: The inorganic phosphate sections for each of the four legs are 

 shown in figures 16 to 19. The values for each observation were obtained by nneans of the mo- 

 lybdenum method, using the Automatic Servo Operated Photometer (Snodgrass et al. 1953). 



We can see that in the first two sections the 0.8 jig at/1 isopleth reaches the surface 

 in the region of the equatorial divergence, but is to be found beneath the surface waters in the 

 last two sections. In the region of the northern edge of the Countercurrent there is a well de- 

 veloped "phosphocline" with the values increasing from 0. 8 to 2.4 p.g at/1 in a depth range of 

 10 to 20 meters. 



Attention is called to the trough in the phosphate isopleths at about 100 meters below 

 the surface between 2 N. to 2 S. latitudes. Comparing the first section, figure 16, with the last, 

 figure 19, we see the trough as broadened latitudinally, both to the north and south of the Equator, 

 and the lower limit (2.2 (ig at/1) decreased in depth from about 425 meters to 350 meters. 



Temperature-salinity relationships (T-S curves) : A temperature-salinity curve for 

 each station of cruise 15 is plotted in figure 20. The curves have been grouped according to the 

 latitude of the individual stations, 9°N. to 7°S, Interpolated values were used. 



In discussing the T-S curve, Sverdrup, et al. (1942) point out that "By means of 

 this diagram, characteristic features of the temperature-salinity distribution are conveniently 

 represented and anomalies in the distribution are easily recognized. " In the case of the cruise 

 under discussion, these curves may serve a twofold purpose; they help to classify the zonal 

 currents crossed on the section along 140°W. longitude, sind they suggest the variations with 

 time zmnong the four stations at each latitude. Normally, data for the surface layer (less than 

 200 meters) are omitted, primarily because of seasonal variations and local modifications. In 

 our case, however, these surface layer data, as well as the data from greater depths, have been 

 included in order to show the variations with both tinne and latitude. 



Figure 21 is a "fan" of T-S curves for the first leg of cruise 15. Selected station 

 curves, have been plotted for latitudes between 9°N, to 7°S. (left to right in the figure). 



