As mentioned above, a comparison of the Smith and Manning sections indicates the 

 possibility of quite considerable changes in detail in a relatively short time, although the basic 

 features remain distinct. 



Surface temperatures are indicated at the top of each temperature section. These 

 are often influenced by shallow diurnal effects, as at 3°15'N. latitude, 180° longitude (fig. 8); 

 no attempt was made to include these temporary variations in the vertical temperature sections. 



Several of the details of the temperature field, such as the reduction of the vertical 



temperature gradient at the Equator and the presence of stable inversions in the thermocline 



near the Equator, are described in reports of ihis series (Cromwell 1954, Austin MS,), Both 



of these features are seen on each of the Smith cruise 14 temperature sections. A detail not so 



far described is the persistent, relatively "sharp" bottom of the main thermocline at about 2°- 



,o 



^ N. latitude. Figure 17 presents BT traces taken near these latitudes on various longitudes 



during several cruises. The traces best illustrating the phenomenon were chosen from a 



meridional series in each case, demonstrating a rerriarkable consistency in position; it has 



moreover never been completely absent. Figure 18 gives the detailed temperature structure on 



the oblique section nnarked on figure 2. The most evident "sharp" bottom of the thermocline is 



seen at 2°06'N. latitude, 175 04'W. longitude; this particular trace is second from the left in 



figure 17. 



Sigma-t --The distribution of sigma-t is shown in figures 6, 9, and 13. These 

 figures are closely associated with, and share most of the details of, the temperature sections 

 (see procedures). For an exception to this rather general rule, the surface layer decrease in 

 density at the southern end of the 180 longitude line is largely associated with a decrease in 

 salinity. The expected slight east to west thickening of the light surface layer may be seen in 

 a comparison of the sections. 



There is a marked meridional change in the character of the water just beneath the 

 main thermocline in approximately the 2°-3° N. latitude region discussed above; this feature is 

 reflected in the sharp southerly increase in depth of the sigma-t isopleths 26.6 to 27.0 in this 

 area. The effect of this distribution of density is evident in the plot of dynamic heights of iso- 

 baric surfaces, but at these latitudes the interpretation is extremely uncertain. Barnes et al. 

 (1948, p. 872) describe what seems to be a similar case in the Marshall Islands area, with 

 regard to a dip in the 10 C. isotherm. 



Salinity — The vertical sections of the field of salinity are shown in figures 7, 10, 

 and 14. The major features of the distribution are as described previously for the central 

 Pacific (Cromwell 1951, 1953, 1954; Austin 1954; Montgomery 1954; Mao and Yoshida 1953). 

 The similarity fronn section to section of Smith cruise 14 is self-evident. 



The detailed vertical distribution of salinity in the region of 2°-3° N. latitude is of 

 interest and is not readily evident from the sections. Figure 1, illustrating the method of re- 

 presenting the oceanographic stations is taken from Smith cruise 14, station 27 at 2°07'N. 

 latitude, 179 57'W. longitude and shows this distribution. The sharp bottom of the thermocline 

 seems to be a boundary between overlying water associated with a salinity minimum extending 

 from the north, in the thermocline, and deeper water with a temperature-salinity relation 

 identical with that of water to the south. The salinity decreases downward through the thermo- 

 cline, increases sharply across the boundary, then decreases gradually again below; the relative 

 maximum and minimum values lie close together vertically. With the isopleth values used, this 

 feature is most evident on the 180 longitude section. The increase in salinity across the bound- 

 ary is often accompanied by a stable temperature inversion. Farther to the north the vertical 

 transition below the salinity minimum is more gradual; toward the Equator the salinity minimum 

 disappears into the very salty water extending into the area from the south. 



Phosphate phosphorous — The vertical sections of inorganic phosphate for longitudes 

 180 and 169° W. appear in figures U and 15. On the 155° W. longitude line the colorimeter 



