86 



OBSERVATIONS AhfD RESULTS IN PHYSICAL OCEANOGRAPHY 



For comparison we add table 6 which shows the 

 mean potential temperature and the salinity at an ap- 

 proximate depth of 4500 meters according to the obser- 

 vations of Challenger. Dana , and Carnegi e. 



Table 6. Mean potential temperature and salinity, 

 Atlantic deep water, Carnegie. 1928 



Source 



Western deep 



e 



Eastern deep 



e 



The nuTnber of observations are shown in parenthesis 



The temperatures of the Challenger appear to be 

 about 0.°1 too high. The Dana and Carnegie tempera- 

 tures agree well, but the Dana salinities are 0.035 per 

 mille higher on an average. 



Temper atur e -Salinity Relation 



The temperature-salinity (tS) diagrams, which were 

 introduced by Helland-Hansen (1918), have proved very 

 helpful in the discussion of the origin and the mixing of 

 the different types of water in the oceans. The tS dia- 

 grams therefore have been plotted for each station. 



Jacobsen (1929) has discussed the character of the 

 waters of the North Atlantic by means of the tS dia- 

 grams from the Dana expeditions. A comparison shows 

 that the data from the Carnegie are, on the whole, in 

 good agreement with the data which Jacobsen discusses. 

 A similar discussion therefore would not lead to any new 

 conclusions. We have seen (pp.30, 31)that we found rather 

 different conditions at the neighboring stations 3, 5, 15, 

 and 16, and it is of interest to examine the extent to 

 which water of a similar character is met with at these 

 stations. 



In figure 1 the tS curves for these four stations 

 have been plotted. It is seen that they all agree quite 

 well and that no considerable deviations from an average 

 normal tS relation occur. Below a depth of 700 meters, 

 however, where the discrepancies between the stations 

 are found, we find agreement between the conditions at 

 stations 3 and 16, and from 1000 and 1500 meters we 

 find agreement at stations 5 and 15. Therefore, it can 

 hardly be doubted that the water of high salinity and high 

 temperature which is found between 700 and 1500 meters 

 at station 5 comes from the west. On the other hand, it 

 is not very probable that we can trace a continuous flow 

 of this water from the region of station 15 to the region 

 of station 5, because station 3 falls between the two lo- 

 calities. It is more probable that in both localities we 

 deal with whirls which develop at the boundary of the 

 strong Atlantic Current. 



For comparison the tS diagram for station 6 has 

 been shown in the same figure. This curve has a widely 

 different course and at the depth of 1000 meters the de- 

 viation from the normal tS relation is very great. Ac- 

 cording to Helland-Hansen and Hansen this deviation in 

 the region of station 6 must be ascribed to the influence 

 of the Mediterranean water. When discussing the data 



from this station, it was pointed out that the high tem- 

 peratures and salinities are, as a rule, found between 

 700 and 1500 meters in the region where the station was 

 occupied. 



We shall not enter any more into detail as to the tS 

 relations, but shall draw attention to some major fea- 

 tures. When discussing the vertical sections we saw 

 that a marked difference exists between the Carnegie 

 stations north and south of latitude 20° north. To the 

 south of this latitude the characteristic salinity minimum 

 of the intermediate Antarctic Current is found at all sta- 

 tions, but to the north of this latitude the salinity de- 

 creases toward the bottom without any intermediate 

 minimum. The tS relation therefore is quite different 

 at the stations north and south of latitude 20° north. In 

 figure 2 the data for observations at stations north of 

 20° north and below a level of 100 meters have been 

 plotted, using different designations for observations in 

 the depth intervals 100 to 500, 500 to 1500, and below 

 1500 meters. It is seen that all values fall nearly on a 

 mean curve. This agrees well with the corresponding 

 curves which Helland-Hansen has derived from the ob- 

 servations on board the Michael Sars and the Armauer 

 Hansen which are also shown in the diagram. A few 

 values fall above the lines, and these originate from re- 

 gions where the Mediterranean water is found. 



Another feature of considerable interest is that in 

 the northern Atlantic the occurrence of water of a cer- 

 tain tS relation is not restricted to certain intervals of 

 depth. Water of high temperature and high salinity is 

 found in the upper layers only, but in other localities in 

 the upper layers one finds water which has the proper- 

 ties of the water between 500 and 1500 meters at other 

 stations, or even the properties of the deep water. This 

 feature indicates that a considerable vertical circulation 

 exists within the area of the North Atlantic where the 

 observations have been made and that the deep water 

 may be mixed with water which has been at the surface. 



To the south of latitude 20° the salinity minimum 

 is plainly seen in the tS diagram in figure 3, which 

 shows a much more pronounced stratification of the 

 water. Water of a temperature above 12° is never found 

 below 500 meters, of a temperature below 7° never 

 above 500 meters, and of a temperature below 4° never 

 above 1500 meters. Therefore, a direct transport of 

 surface water down to the greitest depth does not take 

 place in the region from which these observations orig- 

 inate. This result is self-evident because all the obser- 

 vations were taken in the tropics, but the stratification 

 has been pointed out here because it will be shown that 

 the corresponding stratification is more pronounced in 

 the Pacific. Figure 4 shows the tS relation on a more 

 open scale for depths below 1400 meters. Short vertical 

 lines on the various curves designate the approximate 

 limiting depths within which the respective temperature 

 and salinity values were obtained. Such designation was 

 not made in figure 3 on the curve for the North Atlantic 

 (stations 1 to 19) because of the varying characteristics 

 of the water and the relative meagerness of data for 

 depths below 1000 meters. 



The temperature-salinity diagrams for each station 

 are shown in figures 201 to 209, I-B. Because of insuf- 

 ficient data, no further detailed discussion of the char- 

 acteristic properties of the water at different levels and 

 in different regions of the North Atlantic will be at- 

 tempted. 



