193 DISCOVERY REPORTS 



surface water to move eastwards across the convergence. According to the evidence 

 which has been obtained so far, the position of the convergence does not vary very 

 much, certainly not more than 60 miles between its extreme positions, although the 

 temperature and salinity of the water sinking into the sub-Antarctic layer vary con- 

 siderably. The position of the Antarctic convergence shown in Fig. 1 1 has been obtained 

 from the position of the sudden change in surface temperature or from the position at 

 which the temperature minimum in the cold stratum of the Antarctic surface layer sinks 

 below 200 m. The two positions are usually about the same ; but in the two bends of the 

 convergence which have just been mentioned, a strong flow of sub- Antarctic water is 

 sometimes found at the surface, whilst the cold stratum of the Antarctic surface layer 

 has not sunk. The surface conditions in these places are thus sub-Antarctic, and are 

 probably only temporary, whilst only about 100 m. below the surface there is still 

 Antarctic water and its presence is permanent. The latitude of the Antarctic convergence 

 for longitudes between 80° W and 30° E is shown in the following table. 



Table I 



Latitude 80° W 75° W 70° W 65° W 60° W^ 55° W^ ^ 



Longitude of Antarctic convergence 62° 40' S 60° 30' S 59° 30' S 58° 40' S 58° 20' S 55° 50' S 



Latitude 50° W 48° W 45° W 40° W 35° W 30° W^ ^ 



Longitude of Antarctic convergence 55° 50' S 55° 30' 50° 30' S 51° 00' S 49° 30' S 50° 10' S 



53 10' 



51 10 



Latitude 25° W 20° W 15° W^ 10° W^ 5° W^ 0° 



Longitude of Antarctic convergence 50° 30' S 49° 40' S 48° 40' 48° 00' 47° 40' 47° 40' 



Latitude 5°E 10° E 15° E 20° E 25° E 30° E 



Longitude of Antarctic convergence 48° 00' 48' 30' 48° 50' 49" 10' 49° 40' S 50° 10' S 



The sudden rise in surface temperature was first noticed by Meinardus (1923, p. 531 

 et seq.), who explained the convergence as the line along which the ice water spreading 

 northwards sinks below the surface. He gave a table (p. 544) showing the latitude of 

 the convergence from 105° W to 80° E which is not much different from Table I. The 

 convergence was next described by Schott (1926, p. 241) in the South Atlantic Ocean, 

 who called it the " Meinardus Line ". It has since been described by Wiist (1928, p. 518) 

 and Defant (1928, p. 475). Both authors call it the " Oceanic Polar Front ", and base its 

 position on a chart of the surface currents in the Atlantic by H. H. F. Meyer (1923). They 

 give its position correctly between 50° W and 10° E, but between 40 and 60° W they 

 have confused it with the sub-tropical convergence between the Falkland current and 

 the Brazil current. We have used the name antarctic convergence, which means the 

 line of the convergence of Antarctic and sub-Antarctic waters. 



The Antarctic Zone extends northwards from the Antarctic Continent to the Antarctic 

 convergence, and includes islands which have been considered from climatic reasons to 

 be sub-Antarctic. The only logical subdivision of the zone on hydrological grounds is 

 into two regions. In the first of these the surface water is part of the westerly drift south 

 of 66 ' S, or has its origin in this drift and is not far removed from it: in the second it 



