ISO DISCOVERY REPORTS 



and, therefore, the transport varies with latitude. The wind observations from the 

 southern part of the South Atlantic are too scanty to allow a definite answer, but the 

 available data point in the direction that in summer the strongest westerly winds are 

 met with between 50 and 60° S. This is, for instance, evident from Koppen's chart 

 which has been reproduced in Shaw's Maniiol of Meteorology, Vol. 11. This would mean 

 that we have a great transport of water to the north between 60 and 50° S and a smaller 

 transport north of 50° S and that, therefore, a convergence in the northward transport 

 exists at about 50° S. This convergence must take place over a wide belt, since the change 

 in the wind resultant must be gradual, but it may give rise to the development of a 

 discontinuity in the ocean. Two factors may contribute to such a development: the 

 tendency to the conservation of the angular momentum, and the tendency to a minimum 

 consumption of eddy energy. 



Thus, it seems possible that the Antarctic Convergence in the South Atlantic Ocean, 

 which in summer is found in about 50° S, is due to a convergence in the pure drift 

 current. Similar conditions may exist in the southern Indian and Pacific Oceans, but 

 in the Drake Passage, where the convergence is met with in about 60° S, the location 

 must depend upon other circumstances. This great displacement to the south may be 

 due to the fact that the easterly current, which carries both the sub-Antarctic and the 

 Antarctic waters, is forced through the relatively narrow passage. 



All these questions deserve a closer examination, but for the present purpose it is 

 sufficient to state that the convergence exists and that within the Antarctic water the 

 surface layers must be transported to the north by a pure drift current. Since the 

 westerly winds are dominant around the Antarctic Continent, the transport must take 

 place in all longitudes. If, however, this is the case, a compensation current must carry 

 water back to the south at some deeper level. The level at which this return flow takes 

 place can be found only by examining the hydrographic conditions in the area in question. 



An examination can now be undertaken thanks to the work of the Discovery Ex- 

 peditions which have accumulated a great number of observations from the Drake 

 Passage, the Scotia Sea and the South Atlantic Ocean. By means of the published data 

 (1930, 1932) it is possible to construct vertical sections in these areas, and through the 

 courtesy of Dr Kemp unpublished observations from a section along meridian 75° W, 

 in the Pacific Ocean, have also been placed at my disposal. Six temperature and salinity 

 sections have been constructed, and in addition sections showing the vertical distribution 

 of oxygen and phosphate have been prepared when observations have been available. 

 The positions of the sections are shown in Fig. 2 in which they are numbered I-VI. 



In considering these sections we shall begin with the most westerly, section I (Figs. 3 

 and 4) along the meridian 75° W in the Pacific Ocean, to the west of Drake Passage. 

 The observations were taken by the 'Discovery II' in November, 1931. The Antarctic 

 Convergence is found at the surface in about 60° S. The downwards bend of the iso- 

 therms to the north of 60° S indicates sinking motion of the water, and the salinity 

 section shows that there the origin of the Antarctic intermediate current must be sought. 

 From the salinity diagram it seems as if the water which has left the surface continues 



