96 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



Section V. --Section V, comprising stations 130 to 

 134 and 148 to 162, runs from San Francisco toward the 

 southwest to Samoa. It passes through regions of dif- 

 ferent character and we shall, therefore, first discuss 

 the part of the section which lies between latitudes 20° 

 north and 20° south, namely, stations 149 to 162. 



At the most northern (station 149) of these stations 

 the convection layer has a thickness of about 50 meters, 

 but at station 151 in latitude 12° 40' north the thickness 

 is not much greater than 10 meters. Proceeding toward 

 the south the thickness again increases more or less 

 regularly and at station 160 has a value of about 100 me- 

 ters. The highest temperatures at the surface are found 

 at stations 150 and 158 to 162. The temperature de- 

 creases rapidly with increasing depth below the convec- 

 tion layer, and this decrease is especially rapid at sta- 

 tions 151 and 152, where all isotherms showing a tem- 

 perature of 10° and more are curved toward the surface. 

 At stations 151 and 152 we thus find r.n accupiulation of 

 water of relatively low temperature, but this accumula- 

 tion only reaches a depth of about 400 meters. Below 

 this depth the highest temperatures are found at stations 

 151 and 152 down to a depth of 1000 meters, but at still 

 greater depths the temperature maximum wanders to- 

 ward the south and at a level of 2500 meters is found 

 below station 155 in latitude 4° 51' north. It should be 

 noted especially that the isotherm of 5° rises from its 

 lowest position more rapidly to the north than to the 

 south. The temperature distribution thus shows an ac- 

 cumulation of cold water at stations 151 and 152 down to 

 a depth of less than 400 meters, and below this depth an 

 accumulation of warm water is shown. These accumu- 

 lations indicate an ascending vertical movement above a 

 level of 400 meters and a descending movement below 

 this level. The latter appears to be more pronounced to 

 the north than to the south. 



The salinity distribution in this section shows a 

 number of remarkable features. At stations 151 and 152 

 the surface salinity is below 34.00 per mille and these 

 very low values probably must be attributed to the effect 

 of precipitation. Both to the north and to the south of 

 these two stations the surface salinities are considerably 

 higher, but the maximum values are found about 100 me- 

 ters below the surface. The subsurface maximum is 

 well developed especially to the south of the equator 

 where the distribution indicates that at a level of about 

 100 meters a considerable transport of water of high sa- 

 linity takes place toward the north. At station 150 to the 

 north of the equator, we find a slight indication of a sim- 

 ilar transport toward the south. The very low surface 

 salinities which were observed between stations 159 and 

 162 are difficult to explain. It is possible that the flow 

 of water of high salinity at a level of 100 meters is inter- 

 mittent, and that water of low salinity may reach the sur- 

 face in some localities and spread out. It is also possi- 

 ble that the water of low salinity, which is found to the 

 north of the equator, occasionally spreads toward the 

 south. 



Below the layers of high salinity we find a region of 

 low salinities between 500 and 1500 meters. To the 

 north of station 151 water of low salinity, representing 

 the subarctic current, penetrates toward the south. As 

 will be shown later, it is probable that the major part of 

 this water flows toward the east in the region with which 

 we are dealing, but from the section it is evident that 

 part of the water continues toward the south. This cur- 

 rent divides into two branches, one ascending above a 



level of about 400 meters and the other descending below 

 this level. The vertical distribution of the salinity thus 

 confirms the conclusions which were drawn from the 

 course of the isotherms as to the vertical movement. In 

 the most southern part of the section water of a salinity 

 below 34.5 per mille penetrates toward the north at a 

 level of about 750 meters where the temperature is 5.°5. 

 Between stations 151 and 158 we find water of a uniform 

 salinity a little below or a little above 34.5 per mille. 



The deep water is again of a uniform character. The 

 temperature decreases to values below lf5 and at sta- 

 tion 149 it again increases slightly when approaching 

 the bottom. Later we shall discuss the temperature at 

 the greatest depths. The salinity of the deep water is 

 practically the same within the whole section. 



Turning next to the northern part of the section from 

 San Francisco to station 149 we find in this region a thin 

 convection layer, which at all stations has a vertical ex- 

 tension of less than 50 meters. The lowest surface tem- 

 peratures are found off the coast and here the isotherms 

 rise rapidly when approaching the coast. This rise, 

 however, is found only down to a depth of 400 meters, 

 which indicates that an accumulation of cold water is 

 confined to the upper layers. The salinities of the upper 

 layers are very low in the vicinity of the coast where a 

 rapid increase takes place at about 200 meters. In the 

 section it appears as if the low salinities, which at 

 greater distances from the coast are found at a depth of 

 400 meters, form a direct continuation of the low values 

 near the surface at the coast. It will tie shown later on, 

 however, that this cannot be the case and that the water 

 of low salinity at the coast, and the intermediate water 

 at 400 meters belong to distinctly different currents. 



Section VII. --Section VII (stations 139 to 143) repre- 

 sents a north and south section in the central part of the 

 Pacific, and follows approximately the meridian of 160° 

 between latitudes 34° and 22°. In this section the con- 

 vection layer for the most part has a thickness of about 

 50 meters, varying from about 40 meters at station 143 

 to about 70 meters at station 140. At the last-named 

 station the greatest accumulation of warm water is 

 found, and the isotherms of the upper layers rise both 

 to the north and to the south of the station. At greater 

 depths the highest temperatures are found more to the 

 north. 



A small accumulation of water of high salinity is 

 shown with its center at station 140 where the salinity 

 reaches 35.3 per mille at about 200 meters; but the most 

 conspicuous feature is represented by the tongue of 

 water of salinity below 34.00 per mille extending almost 

 to station 140. Even at station 139 a minimum below 

 34.1 per mille is found. The axis of the lowest values 

 sinks toward the south in the most northern part of the 

 section and rises continuously in the southern part. In 

 the northern part it follows the isotherm of 6° at a level 

 of about 600 meters, but to the south of station 141 the 

 axis rises more rapidly than the isotherms and lies at 

 a depth of 400 meters at station 139 where the tempera- 

 ture is 8°. 



In the deep water both the temperature and the sa- 

 linity appear to decrease toward the nofth. The de- 

 crease of the temperature is undoubtedly a real feature, 

 but the decrease of the salinity toward the north below 

 the 2000-meter level is so small that it lies within the 

 limits of accuracy of the observations. 



Section XIV. --Section XIV (stations 130 to 140) runs 

 from San Francisco to the Hawaiianlslands in adirection 



