8 



TEMPERATURE OF THE SVRFACE WATERS OF THE ATLANTIC OCEAN 



of temporature from 2.5° to 3.5° at 52° S., the Meteor 

 had to pass again tlu-ough colder water of about 3° 

 before the front was encountered at 50° S. with a rapid 

 rise in temperature to 5°. 



The correspondmg vertical section (fig. 8) hkewise 

 shows this body of water of somewhat higher tempera- 

 ture beyond the real front. 



A consideration of the summary of the average find- 

 ings recorded in table 3, of the individual results from 

 the sections, and of the grouping of the isotherms on 

 the montUy charts establishes the Antarctic polar front 

 A' as it is drawn in figure 4. In an investigation of 

 the subantarctic intermediate current (Volume VI of 



7000. 



Figure 5. — Vertical section of tlie temperatur 



Drake Passage (profile Va.). A' = 



through the 

 polar front. 



the work on the Expedition), G. Wiist found the zone 

 in which the "intermediate water" sinks beneath the 

 surface by another means, namely, calculating the mix- 

 ing proportions {Alischungsverhdlthisse) . Even the 

 boundary discovered in this way (fig. 4) deviates slight- 

 ly, as did Deacon's, from the average position established 

 from the meridional gradients, so that the line indicated 

 on the chart may now be accepted with some certainty 

 as indicating the boundary of antarctic and subantarc- 

 tic water in contrast to the warmer water of the west 

 wind drift — in other words, the polar front. 



The question of whether it is permissible to refer to a 

 pronounced fluctuation of the front cannot be answered 

 with certainty. According to table 3, the front swings 

 about its average position from one to two degrees of 

 latitude in the individual months. This amount results 

 from the fact that, as was previously explained, the one- 

 degree field had to be chosen as a surface unit for the 

 temperature averages. In addition, the unperiodic in- 

 fluences, and especially those of the wind, are very great 

 in these areas and probably obscure the periodic ones. 



Another of these zones of high temperature gradients, 

 which were mentioned previously, lies, as table 4 and 

 figure 4 show, farther north, in fact in the middle of the 

 ocean at about 38° S. to 40° S. Only in the east, south 

 of the Agtilhas Current, and in the west, south of the 

 Brazil Current, does it reach 41° S. Off the mouth of 



the La Plata, it turns north approximately parallel to 

 the coast. In this zone, the temperature reaches 13° to 

 16°. This boundary area, which is to be designated as 

 subtropical boundary, coincides approximately with 

 the line which was discovered by Deacon and called 

 subtropical convergence. In places, however, it is in 

 contradiction to the line C, which is given on the 

 chart by H. H. F. jNIeyer " as subtropical convergence 

 in the month of February. In order to clear up this 

 question, the coiu'se of the currents for all 12 months in 

 this area was investigated. Charts of ctuTcnt displace- 

 ments |in the Dutch atlases^* Avcre used, and the posi- 

 tion of the convergence C for the annual average was 

 determined (fig. 4). The results showed that the sub- 

 tropical boundary established from the temperature 

 B' and the convergence resulting from the current 

 displacements C were in agreement only in the area 

 between the Falldand and the Brazil Current. From 

 40° W. to 5° E. the convergence hes about 10° farther 

 north and in the vicinitj^ of the African Continent 3° to 

 5° more. Greater rises in temperature were not found 

 here in C. Even in the area of the Agulhas Current, 

 with its involved structure, which was rather closely 

 investigated hy G. Dietrich,^' the two boundaries, B' 

 and C can be clearly difl'erentiated, as the following 

 descriptions and figures 9 through 11 also show. 



Thus it is proved that the two boundaries, insofar as 

 their causes are concerned, have nothing to do with 

 each other and that Deacon's conception must be cor- 

 rected. 



There arises the qu.estion regarding the cause of 

 this subtropical boundary. Purely climatic influences 



Figure 6. — Surface temperatures of profile Va according to the 

 hourly values taken from the recording. 



might first be considered, for, according to Angot, the 

 amounts of warmth radiated to the earth ^^ reach their 

 greatest increase precisely between 40° S. and 50° S. 

 In addition, an unportant fact is that the decrease in 



" Cf. footnote 24. 



25 Oceanogr. en Met. Waarnemingen i. d. Atlant. Oc. Koninkl. Nederl. Met. Inst. 

 No. no. 



28 G. Dietrich, Au/bau und Dynamik des sudlichen Agulhas-Stromgebietes. Veroff. d. 

 Inst. f. Meereskde. Berlin. N. F. Roihe A, Heft 27. Berlin, 1935. 



so Hann-Siiring, Lehrbuch der Meteorologie. Leipzig, 1926. 



