THE PACIFIC OCEAN 



93 



Alaska, to the south of Bering Sea, and off the coast of 

 Japan, slightly higher temperatures are present. The 

 distribution of the salinity (fig. 232; I-B) at this level is 

 so uniform that no isohalines can be drawn, but a gener- 

 al decrease of the salinity from south to north appears 

 to be characteristic at this level. Values approaching or 

 slightly surpassing 34.7 per mille are found at the most 

 southern stations, whereas in the North Pacific the sa- 

 linity is only slightly above 34.6 per mille. 



Three-thousand-meter level. --The temperature dis- 

 tribution (fig. 221; I-B) here is very uniform. Near Cen- 

 tral America values above 2.°0 are observed, but else- 

 where the temperature varies between l.°85 in the basin 

 off the Peruvian coast to l.°55 in the central part of the 

 North Pacific. The lowest values again appear to be 

 present in the northern part of the North Pacific, where- 

 as high values prevail in the equatorial region. The 

 material is very scanty, but the variations are suffi- 

 ciently systematic to give significance to the isotherms 

 which have been drawn. At this level the salinity (fig. 

 233; I-B) appears to decrease from south to north, vary- 

 ing from 34.68 per mille in latitude 40° south to 34.63 

 per mille in latitude 40° north. In the southern part the 

 values are approximately the same as at 2500 meters, 

 but in the northern part they are slightly higher. 



Concerning the salinities it must be added that these, 

 according to the discussion given on page 72, appear 

 to be about 0.03 per mille too low. This systematic er- 

 ror is of no importance in the upper levels but at great 

 depth it e.xerts an influence on the course of the isoha- 

 lines. 



The warm water of the Pacific. --We have seen that 

 at the 700-meter level the distribution of both tempera- 

 ture and salinity is quite different from the distribution 

 at higher levels. Therefore, we conclude that the warm - 

 water circulation in no locality reaches as far down as 

 the 700-meter level. At the 500-meter level traces of 

 this circulation were seen in the temperature distribu- 

 tion only, and considering that the temperature at 500 

 meters is lower than 10° and that we have previously 

 regarded the isothermal surface of 10° as representing 

 the lower boundary of the troposphere, we conclude that 

 the warm-water circulation practically has disappeared 

 below the 500-meter level. 



Intermediate water of the Pacific. --The intermedi- 

 ate water of low salinity is first clearly seen at the 400- 

 meter level in the eastern part of the North Pacific 

 where the low salinities off the Gulf of Alaska continue 

 toward latitude 25° and bend toward the west somewhat 

 to the north of this latitude. The isotherms show a 

 corresponding but less pronounced bend toward the west. 

 In the Southern Hemisphere the corresponding interme- 

 diate current appears to be present in the region to the 

 west of South America. At the 500-meter level the in- 

 termediate current evidently reaches farther west in the 

 Northern Hemisphere as indicated by the course of the 

 isohalines and also by the characteristic bend of the iso- 

 therms. At the 700-meter level the intermediate cur- 

 rent is less strongly developed in the eastern part of the 

 North Pacific where the salinities now are higher than 

 at the 500-meter level. The lowest salinities are now 

 found farther west. In the Southern Hemisphere the 

 intermediate current can be traced up to about 15°. At 

 the 1000-meter level we are evidently below the inter- 

 ■ mediate current because the salinities are higher here 

 than at 700 meters both north of latitude 20° north and 



south of latitude 20° south. The intermediate current 

 thus appears to be most strongly developed between 

 depths of 400 and 700 meters in the Northern Hemi- 

 sphere, and to lie at a higher level in the eastern part of 

 the ocean. In the Southern Hemisphere it appears from 

 the horizontal charts to be most prominent at a level of 

 700 meters. The last traces of the intermediate cur- 

 rents do not reach to lower latitudes than about 15° and 

 10°. Between these latitudes we find water of a uniform 

 salinity which is higher than the salinity of the interme- 

 diate currents but lower than the salinity of the deep 

 water. 



Deep water of the Pacific. --The deep water of the 

 Pacific is very uniform; the temperature decreases 

 slowly with increasing depth and the salinity increases 

 slowly. In a horizontal direction we find a decrease of 

 salinity from south to north and maximum temperatures 

 at the equator, but the total range of temperature is less 

 than 0?2, except the local conditions near Central Amer- 

 ica. The uniform character ofthe deep water is illus- 

 trated by the following table, which shows average values 

 of temperature and salinity at the depths 2000, 2500, and 

 ^000 meters within stated intervals of latitude. It is seen 

 seen that the range of the average temperatures de- 

 creases slowly with depth whereas the range of the aver- 

 age salinities remains equal to 0.04 per mille, and the 

 absolute values decrease from south to north at each 

 level. But as a result from a general discussion of the 

 salinity values, it seems probable that salinities as tab- 

 ulated and graphed should be increased by 0.03 per 

 mille. The discussion on which this conclusion is based 

 is presented in Physical Oceanography I-B of the "Sci- 

 entific results of cruise VH of the Carnegie ." 



Vertical Distribution 



When discussing the horizontal distribution of tem- 

 perature and salinity we considered the most prominent 

 features of the vertical distribution and especially em- 

 phasized that the waters of the Pacific show a typical 

 stratification both as to temperature and salinity. Turn- 

 ing to a more detailed discussion of the vertical distri- 

 bution, we shall base this on the representations in the 

 vertical sections and shall also make use of the curves 

 which show the observed data at each station. As to the 

 construction of the sections we refer to the explanation 

 of the graphs. 



Section III. --Section in embraces stations 37 to 40 

 and 60 to 72, begins near the Gulf of Panama, follows the 

 coast of South America down to latitude 17° south, and 

 continues south- southwest to latitude 40° south. Two 

 stations in the Gulf of Panama, stations 35 and 36, were 

 not included when constructing the section. 



The topmost layer of the troposphere has been called 

 by Defant the zone of agitation (St(^rungszone), repre- 

 senting the layer within which convection currents can 

 mix the water thoroughly. It is perhaps better to use the 

 term convection layer because this term better express- 

 es the character of this uppermost stratum. 



Off Central America the convection layer is very 

 thin. At station 35 it does not reach to 27 meters and 

 has a salinity of 29.8 per mille and a temperature of 

 about 27.°5. At stations 36, 37, 38, and 39 the thickness 

 of the layer is between 20 and 30 meters. The salinity 

 increases up to 33 per mille at station 39. The temper- 

 ature is about 27° at the previous three stations and 



