98 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



practically at the equator, 0° 18' north, the thickness is 

 also very great and may perhaps be taken as almost 150 

 meters. South of the equator the thickness is of the or- 

 der of 50 meters. 



The surface temperatures are above 25° at aP sta- 

 tions. The isotherm of 20° runs at approximately the 

 same depth at the northern and southern stations, but 

 rises toward the surface at station 100. The course of 

 the isotherms between stations 102 and 97 is very simi- 

 lar to the course of the corresponding isotherms in Sec- 

 tion V between stations 150 and 157. Between the levels 

 of 150 and 300 meters the lowest temperatures occur at 

 station 100, but between 300 and 1500 meters we find the 

 highest temperatures at this station. In still greater 

 depths the temperature maximum shifts toward the south 

 as in Section V. The isotherm of 5° rises more rapidly 

 toward the north than toward the south as was the case 

 in Section V. 



The distribution of the salinity is also similar in the 

 two sections, but in Section VIII it is more symmetrical 

 than in Section V. At the surface, values below 34.6 per 

 mille are found between stations 101 and 100. From the 

 region of low surface salinity values we find increasing 

 values both to the northwest and the southeast, but the 

 maximum values are found at some distance from the 

 surface. The tongues of maximum salinity at a depth of 

 about 150 meters indicate a transport of water of high 

 salinity toward the equator, whereas the low surface sa- 

 linities perhaps can be attributed to a transport of water 

 of low salinity away from the region of low salinity to 

 the north of the equator. At intermediate depths we find 

 a layer of low salinity. The salinity minimum is espe- 

 cially well developed to the northwest where the lowest 

 values, less than 34.20 per mille, are found at stations 

 103 ?nd 104 at a depth of about 600 meters. The salinity 

 increases toward the southeast and the axis of the mini- 

 mum values rises in the same direction, following more 

 or less the course of the isotherms, but rising more 

 rapidly than the latter. The temperature at the level of 

 the salinity minimum, therefore, is between 6° and 7° at 

 station 104, but about 8° between stations 101 and 102. 

 Between stations 100 and 101, the layer of minimum sa- 

 linity appears to diverge in two branches, one which 

 penetrates almost to the surface at station 100, and one 

 which is directed downward. This divergence is not very 

 clearly seen in this section but appears better when the 

 stations are plotted as if they were lying on a north and 

 south line (figs. 32 and 33). A corresponding divergence 

 was much more pronounced in Section V. To the south- 

 east we find minimum values of the salinity of between 

 34.40 and 34.50 per mille at stations 94 to 97. The mini- 

 mum is not sharp and the axis of the lowest values, 

 therefore, cannot be determined with any great accuracy. 

 It appears to lie at a level of about 800 meters, and fol- 

 lows the isotherm of 5°. At stations 159 and 162 (Sec- 

 tion V) the minimum salinity was found at nearly the 

 same level and the temperature was again approximately 

 5°. 



The salinity distribution which is shown in this sec- 

 tion agrees well with the section which WUst (1929) has 

 constructed for a region farther west, mainly by means 

 of observations on the Planet. Wiist's section extends 

 from latitude 15° north to 35° south, and shows especial- 

 ly that the current, which at a depth of 150 to 200 meters 

 carries water of high salinity toward the equator, sub- 

 merges between latitudes 25° and 30°. WQst's section 

 reaches to a depth of 600 meters only. Between latitudes 



15° and 10° north the layer of minimum salinity rises 

 from 500 meters to about 350 meters and to the south of 

 10° north it divides into one ascending and one descend- 

 ing branch in agreement with what we have found. The 

 salinity minimum to the south of the equator is not shown 

 in Wust's section because it lies at a greater depth. 



The deep water, as usual, is very uniform. The 

 temperature decreases to the greatest depth from which 

 observations are available, approximately 3000 meters, 

 and at this level is highest in the southeastern part of 

 the section. The salinity is, on the whole, higher than 

 34.60 per mille below a level of about 1700 meters and 

 increases with depth as far as the observations go. 



Section Xm. --Section XIII (stations 101 to 107) in- 

 cludes stations 101 to 104, which were used in Section 

 Vni, and runs mainly in an east and west direction be- 

 tween longitudes 178° and 146° east. The section forms 

 a regular curves toward stations 101 and 107, however, 

 lying in latitudes 13° 23' and 14° 05' north, respectively, 

 whereas station 104 lies in latitude 20° 12' north. This 

 curvature toward the north, as presently will be seen, 

 determines the characteristic vertical distribution of . 

 temperature and salinity which appears in the section. 



The convection layer reaches to at least 50 meters 

 at all stations and at some of them has a thickness which 

 probably approaches 100 meters. The temperature sec- 

 tion shows the greatest accumulation of warm water in 

 the central part of the section, but this circumstance 

 must be attributed to the fact that the central part lies 

 in a higher latitude than the eastern and western parts. 

 The downward curvature of the isotherm of 10° is, 

 therefore, not related to a change in an east and west 

 direction but to a change in a north and south direction. 

 The isotherms of 5° and less, on the other hand, have 

 their highest position in the central part of the section 

 and the curvature of these isotherms must be related to 

 to the fact that at greater depths the temperature in- 

 creases from north to south. 



The courses of the isohalines show a vertical dis- 

 tribution of the salinity, which agrees perfectly with the 

 vertical distribution of temperature. The highest sur- 

 face value of the salinity is found at the most northern 

 station, 104. Below the surface on both sides of this sta- 

 tion we find a layer of higher salinity which must be re- 

 lated to the subsurface transport of water of high salin- 

 ity toward the equator. The intermediate salinity mini- 

 mum is most pronounced and is found at the greatest 

 depth at station 104. The axis of the minimum values 

 rises to both sides, and the values themselves increase. 

 The axis rises more toward the southeast and southwest 

 than do the isotherms. In the central part the axis lies 

 at a depth of 650 meters where the temperature is 6°, 

 but at the most southeastern station the minimum is 

 found at 450 meters where the temperature is 8.°5, and 

 at the most southwestern locality the minimum lies at 

 400 meters where the temperature is 9°. The only con- 

 clusion which can be drawn as to variations in an east 

 and west direction, however, is that the salinity mini- 

 mum layer appears to lie higher and the temperature is 

 higher at the most western station--107--than at the 

 most eastern station--101. 



It is of interest in this connection to point out that at 

 station 149 (Section V), which lies in almost the same 

 latitude as station 104, we found a salinity minimum at a 

 depth of 350 meters where the temperature was 9°. 

 When discussing sections XIV and XV it was shown that 

 the minimum layer apparently sinks toward the west and 



