SALINITY (•/,.) 



WARM SIDE 

 MIDDLE 

 COOL SIDE 



Figure 19. — Salinity profile and sallnlty-depth curves for the first (B) triplet of hydrocasts at front 5 (22 April 

 1961). The dashed line on the profile is the corresponding 17° C. Isotherm contour (fig. 17), to show the rela- 

 tion of the temperature inversion to the saUnity inversion. Note the salinity maximum (>34.80%o) of eastern 

 tropical Pacific water at about 125 m. c = cool side; m = middle; w = warm side; • = Nansen bottle 

 depths in profile. 



The separation of isopleths between about 

 30 and 45 m. depth in the E series profile 

 (fig. 27) may be related to prior inversion 

 and to mixing, as was suggested for the iso- 

 therms of this triplet of casts (p. 18); the 

 values are higher than on the previous day 

 (compare figs. 26 and 27). The 02-depth curve 

 for the middle station in the E series shows 

 much higher values, relative to those of the 

 other two stations down to about 100 m., than 

 does the "middle" curve in the B series. This 

 may be due to oxygen having been mixed 

 obliquely downward from the surface. 



In both oxygen profiles there is some sug- 

 gestion of a double "oxycline" corresponding 

 to the dual thermocline previously mentioned. 

 The two, at about 70 and 2 5 m. on the warm 

 side (B profile), join at about 45 m. on the 

 cool side. These values agree well with the 

 apparent thermocline topography in the BT- 

 pass temperature profile (fig. 15). Such agree- 

 ment is not so well marked in the E profile. 



Nitrogen as nitrite and nitrate . --Before 

 trying to associate the distributions of phyto- 

 plankton (as chlorophyll a) with that of the 

 zooplankton, some incidental chemical obser- 

 vations will be briefly discussed. 



As noted earlier, phosphate and silicate 

 determinations had to be rejected. 



The nitrite profile of the B series (fig. 28) 

 shows that station maxima correspond roughly 

 to the thermocline and the pycnocline (figs. 

 17 and 21). The profile maximum, on the warm 

 side at about 20 m., is shallower than the 

 salinity maximum (~40 m.) and corresponds 

 to the zone between the middle (5B2) and the 

 warm (5B1) stations and between about 20 and 

 35 m. depth, a zone in which there is a well- 

 developed salinity gradient (fig. 19). 



Much the same is true of the nitrite profile 

 of the E casts (fig. 28), except that the station 

 maxima are a little deeper (as also is the 

 salinity maximum) and, perhaps owing to mix- 

 ing continued from the previous day, more 



26 



