106 



OBSERVATIONS AND RESULTS IN PHYSICAL OCEANOGRAPHY 



eastward direction from the Weddell Sea to the Drake 

 Passage, as would be expected if the flow is directed to 

 the east, but this feature needs to be confirmed. It may 

 be added that great variations may occur, owing to vari- 

 ations in the admixture of water from the shelf, and such 

 variations may be responsible for the different condi- 

 tions in different years. 



The deep water of the Pacific is, as already stated, 

 similar to the deep water of the Antarctic circumpolar 

 current, which is characterized by temperature between 

 0° and 2°, and by salinity between 34.68 and 34.74 per 

 mille. From table 9 it is seen that below 3000 meters 

 the temperature lies between If 2 and l.°9, if we disre- 

 gard Region 6 off Central America. The observed sa- 

 linity lies between the limits 34.62 and 34.68 per mille, 

 but the values are probably consistently about 0.03 per 

 mille too low, and the actual range is therefore 34.65 to 

 34.71 per mille, in good agreement with the salinity of 

 the circumpolar waters. The highest salinities (cor- 

 rected values greater than 34.7) are found in the South 

 Pacific where, according to the few available data, the 

 oxygen content of the deep water appears to be relative- 

 ly high. These features indicate that the deep water of 

 the South Pacific is slowly renewed by addition of water 

 from the circumpolar current. Whether this renewal 

 has the character of the regular inflow in some definite 

 region or takes place by irregular processes of mixture 

 cannot be decided by means of the available data. 



In the North Pacific the salinity of the deep water is 

 slightly lower, and the oxygen content considerably low- 

 er. These features indicate that the renewal of the deep 

 water of the North Pacific by admixture of water from 

 the Antarctic region is much slower than in the South 

 Pacific, 'and, furthermore, it must be assumed that slow 

 admixture of intermediate water of low salinity takes 

 place and reduces the salt content of the deep water. 



The information which is now available strongly 

 points in the direction that no definite flow of deep water 

 exists in the Pacific Ocean and that the renewal of the 

 water is a result of slow and irregular processes of 

 mixing. It cannot be doubted, however, that on an aver- 

 age a transport of deep water takes place from south to 

 north. It is possible that this transport takes place 

 principally along the bottom, and that an outflow of deep 

 water from the Pacific is present at some high level. It 

 is also possible that the outflow from the Pacific takes 

 place within the upper layers and that slow descending 

 motion of the deep water occurs in certain regions. 



Currents 



Surface Currents 



On several occasions we have touched on the prob- 

 lem of the circulation of the waters in the Pacific and 

 especially have discussed to some extent the intermedi- 

 ate currents in the South and the North Pacific. We shall 

 now undertake a more detailed discussion of the circula- 

 tion as far as this is possible by means of the Carnegie 

 data. The discussion will be based principally on the 

 charts showing the topography of the isobaric surfaces 

 0, 100, 200, 300, 400, 500, 700, 1000, and 1500 decibars 

 relative to the topography of the 2000-decibar surface. 

 In these charts, lines of equal relative elevation have 

 been drawn, except off the coast of Japan where the con- 

 ditions are too complicated to be represented by the few 

 observations of the Carnegie in this region. Near the 



equator the course of the lines is also very doubtful for 

 reasons which will be explained when dealing with the 

 Equatorial Counter current. 



The charts represent very nearly the absolute to- 

 pography of the different isobaric surfaces because it 

 can be assumed, on account of the uniform character of 

 the deep water, that the 2000-decibar surface is very 

 nearly horizontal. It must be borne in mind, however, 

 that when constructing the charts we combined the data 

 from stations which in some regions were taken at great 

 intervals of time. This combination may lead to appar- 

 ent irregularities, especially in regions where the cur- 

 rent systems undergo considerable displacement. Fur- 

 thermore, it must be emphasized that from our repre- 

 sentations we can draw conclusions only as to the cur- 

 rents which are maintained by the distribution of densi- 

 ty. The distribution of density is partly maintained by 

 the processes of heating and cooling, evaporation and 

 precipitation, and partly by the effect of the prevailing 

 winds on the surface layers. 



It is clear that differences in heating and cooling in 

 the different latitudes, and differences in evaporation 

 and precipitation, create differences in density which 

 maintain a system of currents independently of the ac- 

 tion of external forces such as the tangential force ex- 

 erted by the prevailing wind. On the other hand, it is 

 not self-evident that the prevailing winds influence the 

 distribution of density in such a manner that part of the 

 effect of the winds is included in the currents which are 

 computed on the basis of the distribution of density, but 

 some evidence that such is the case<can be found. 



Figure 22 shows the currents at the surface, sup- 

 posing the water at a depth of about 2000 meters to be at 

 rest, and supposing that the velocity, v, of the currents 

 can be derived from the map representing the topog- 

 raphy of the surface by means of the formula 



v = (l/L)(c/sin0) 



where L is the distance between two lines of equal dy- 

 namic height (anomaly), and is the geographic latitude, 

 and c is a constant. The current is directed at right 

 angles to the gradient of the isobaric surface, that is, 

 parallel to the lines of equal dynamic height. In the 

 Northern Hemisphere it is directed 90° to the right of 

 the gradient, in the Southern Hemisphere 90° to the left. 



This computation probably gives velocities which 

 are too great in the vicinity of the equator because the 

 friction, which is not considered, probably plays a great- 

 er part in this region. Aside from these restrictions 

 the computed surface currents represent the currents 

 which result from the distribution of density between the 

 surface and a depth of about 2000 meters. 



This map of the surface currents will now be com- 

 pared with the map of the surface currents (figure 23) 

 constructed by Merz and published by WUst (1929). The 

 latter map is based on the observed surface currents as 

 obtained by dead reckoning and astronomic observations 

 o>^ board ship, and thus represents the actual currents 

 as resulting from the combined effect of the prevailing 

 winds and the distribution of density. The agreement 

 between the two maps is remarkable, considering the 

 widely differing material on which they are based. Some 

 discrepancies are found in the northern part of the North 

 Pacific, but it may be noted that: 



1. The line separating the easterly and westerly 

 currents in the North Pacific in figure 22 lies near the 

 line of subtropic convergence as shown by Merz. 



