SECT. 3] 



THE SOUTHERN OCEAN 



283 



division into two zones which can be reasonably described as antarctic and snb- 

 antarctic. Surface charts of mean temperature like those of Vowinckel (1957) 

 and U.S.H.O. (1957) based on relatively few observations collected over many 

 years show an inner zone in which the surface temperature increases slowly 

 towards the north and an outer zone where the increase is more rapid but still 

 more or less uniform. Ships fitted with continuously recording thermographs 

 obtain a sharper picture. The surface temperature increases gradually towards 

 the north, away from the continent, till it is about 1 to 2°C in winter or 3 to 4°C 

 in summer, and then rises approximately 2°C in a very short distance. It is 

 shown very clearly in the surface temperature charts which Mackintosh (1946) 

 has based on thermograph recordings. This sharp change of temperature was 



30° 



50° 



1000 m 



2000 m 



3000 m 



Subtropical water 



Antarctic 

 intermediate current 



V* 1 



Antarctic 



40° 



Subtropical Antarctic 



convergence convergence 



Sub-Antarctic zone 



^^~ \ 



V yivlixed- Surface current 

 water region 



Warm 

 deep current 



South 



/ 



Antarctic 

 bottom current 



Fig. 1. The circulation of water in a vertical section from 30° to 60°S in the Atlantic Ocean. 



first described by Meinardus (1923) in the meteorological report of the German 

 South Polar Expedition. He explained it as the line along which the ice-water 

 spreading northwards from the Antarctic sinks below the surface. He gave a 

 table showing its latitude in the Atlantic Ocean and the neighbouring parts of 

 the Pacific and Indian Oceans. It was next described by Schott (1926) who 

 called it the Meinardus Line. Wiist (1928) and Defant (1928) used the name 

 Oceanic Polar Front. The circumpolar voyage made by the Discovery II in 1932 

 gave a clear indication that it was continuous all round the continent, and in 

 subsequent publications, such as Deacon (1937) and Mackintosh (1946), the 

 name Antarctic Convergence has been used. 



Fig. 1 shows the probable circulation of water in a vertical section across 

 the west-wind drift based on temperature and salinity observations in 30°W. 

 The deep current contains some water which has sunk from the surface in 

 the North Atlantic Ocean, in the boundary region between Atlantic and Arctic 



