THE PACIFIC OCEAN 



General 



Prior to the last cruise of the Carnegie the knowledge 

 of the physical oceanography of the Pacific Ocean was 

 based on results of expeditions which had been under- 

 taken before 1910, the major part of these expeditions 

 having been in the last decades of the nineteenth century. 

 Only the expeditions in the early part of the twentieth 

 century were equipped with accurate thermometers and 

 carried out determinations of the salinity with the pre- 

 cision which now is regarded as necessary. None of 

 the expeditions which have obtained reliable information, 

 however, have operated at great distances from land or 

 in the central part of the ocean. Our knowledge of the 

 conditions of the open ocean is, therefore, primarily 

 based on measurements which do not meet the present 

 requirements as to accuracy. This applies especially to 

 the observed salinities but the temperatures are also 

 inaccurate, as will be shown later when discussing the 

 Carnegie data in detail. 



The older observations from the Pacific, however, 

 have given a general view of the thermal and haline 

 characteristics of the waters in the different regions and 

 especially have thrown light over the major features of 

 the stratification of the waters. It has been possible to 

 draw conclusions as to the circulation of the upper strata 

 of the ocean but it has not been possible to disclose the 

 character of the deep-water circulation. 



The woeful lack of knowledge concerning the temper- 

 ature and salinity of tne deep water of the Pacific prior 

 to the Carnegie observations is illustrated in figure 7 

 which shows the location of stations at which observations 

 of temperature and salinity for depths greater than 3000 

 meters had been made by earlier expeditions (according 

 to Wust), as compared with those of the Carnegie . 



Schott and Schu (1910) have discussed the tempera- 

 ture of the Pacific waters on the basis of the entire mat- 

 erial which was available at that time. The isothermal 

 maps which these authors have drawn for the different 

 levels give a good general view of the distribution of 

 temperature, and the major features in their maps are 

 undoubtedly correct. 



Conclusions as to the circulation can hardly be drawn 

 on the basis of temperature maps only. Wust (1929) made 

 use of the observations of density and salinity which had 

 been made on earlier expeditions for the construction of 

 two salinity sections, one representing the salinities in 

 the western part of the Pacific and the other the salini- 

 ties in the central part. He also constructed temperature 

 sections. The sections through the western Pacific are 

 based, to a considerable extent, on the later observations 

 of the Planet expedition and therefore are more trust- 

 worthy than the sections from the central Pacific which 

 are based only on the Challenger's observations, except 

 for the most northern and southern regions. It will be 

 shown later that the temperatures of the Challenger can- 

 not be regarded as having the accuracy which Wiist as- 

 sumed, and that the salinities which were used for con- 

 structing the sections are Inaccurate in spite of the great 

 improvements which Wust introduced by his methods. 

 But, notwithstanding the deficiencies in material, the 

 sections give a correct representation of the more con- 

 spicuous features of the stratification of the waters. We 

 shall, therefore, briefly discuss these sections in order 

 to obtain a general view of the conditions in the region 



which later will be treated more in detail by means of 

 the Carnegie observations. Since it is possible to con- 

 struct a new section from the Carnegie data, however, 

 we shall use this as representative of the central Pacif- 

 ic and use the section by Wust for the western Pacific. 

 The Carnegie section for the central Pacific deviates in 

 important details from the corresponding section by 

 Wust, but the major features in which we now are inter- 

 ested are the same. The four sections with which we 

 are dealing are represented in figures 8 to 11. 



The temperature distribution (figures 8 and 10) in 

 the Pacific Ocean is almost symmetrical as to the equa- 

 tor in contrast with the temperature distribution in the 

 Atlantic. In the Pacific we find accumulations of warm 

 water both in the Northern and Southern hemispheres. 

 In the central Pacific the warm water reaches almost to 

 the same latitude in both hemispheres, but in the west- 

 ern Pacific the extension toward the south is greater 

 than the extension toward the north. In both sections the 

 warm water reaches deeper in the Southern Hemisphere 

 and here we have, therefore, the greater accumulation 

 of warm water. In both sections, at about latitude 10° • 

 north we find only a very thin layer of warm water, but 

 the highest temperatures for 1000-meter depths are 

 found in this latitude. In both sections the temperature 

 decreases rapidly down to a depth of a few hundred me- 

 ters. From this depth the decrease continues slowly and 

 regularly to the bottom. The isotherms in the western 

 section show several bends but in the central section 

 they have a smooth course. There we find none of the 

 temperature inversions so characteristic of the corre- 

 sponding sections from the Atlantic and Indian oceans. 



The salinity distribution (figures 9 and 11) does not 

 show such a pronoimced symmetry as the temperature 

 distribution. The accumulation of water oT high salinity 

 is more conspicuous in the Southern Hemisphere where 

 the vertical extension is greater and where it reaches a 

 greater distance from the equator. This accumulation is 

 more developed in the western than in the central section. 

 The accumulation in each hemisphere is separated from 

 the other by a belt of water of low salinity which follows 

 approximately the parallel of 10", the same latitude in 

 which the isotherm of 20" approaches the surface. 



Below the accumulations of water of high salinity in 

 both hemispheres we find water of very low salinity 

 which appears to penetrate toward the equator from the 

 subarctic and subantarctic regions, representing the in- 

 termediate subpolar currents. In the Atlantic this inter- 

 mediate current is developed only in the Southern Hem- 

 isphere but reaches across the equator up to about lati- 

 tude 20°. In the Pacific the intermediate current appears 

 to be developed almost to the same extent in both hemi- 

 spheres. In the Northern Hemisphere it penetrates to 

 almost 15° in both the central and western sections; in 

 the Southern Hemisphere it penetrates to almost 20 in 

 the central section and to 30° in the western section. In 

 these sections, however, the salinity curve 34.4 per 

 mille has been used as representing the last traces of 

 the intermediate water, but if 34.5 per mille had been 

 used, we would have found that the intermediate water 

 penetrates to between latitudes 15° and 10°^ in the North- 

 ern Hemisphere and to between latitudes 0° and 10° in 

 the Southern Hemisphere. 



Between the last traces of the intermediate water, 

 in the equatorial part of both sections, we find water of 



88 



