SECT. 3J 



THE SOUTHERN OCEAN 



285 



change abruptly in 40° to 50°S. In the Atlantic Ocean, Wiist (1936) shows that 

 the percentage of North Atlantic water in the high -salinity layer decreases 

 rapidly where the deep current turns eastwards into the Southern Ocean. In 40° 

 to 50°S it is probably not more than 10%. We shall be far from a complete 

 understanding of the general circulation of the Southern Ocean till we know 

 more about the relative transports of the zonal and meridional movements and 

 about the exchanges between the intermediate deep and bottom layers in the 

 oceans outside. Till then we must think of a more or less circumpolar flow, 

 probably lessened by the Drake Passage and the adjoining submarine arc, 

 and fed by deep water from the oceans outside, especially from the Atlantic 



150° 



West 180° East 



Fig. 2. Chart showing the maximum temperature of the warm deep layer in the Antarctic 

 zone. 



Ocean. In most of the circumpolar region of east winds, close to the continent, 

 the slope of the isotherms and isohalines suggests that the deep water moves 

 east in spite of the wind, but in the Atlantic sector and in the eastern approaches 

 to the Ross Sea there is clear evidence that it flows west (see Fig. 2). In the 

 Greenwich meridian the maximum temperature in the warm deep layer falls 

 to less than 0.5°C between 58° and 63°S but rises again to more than 1°C in 64° 

 to 66°S. The cold region coincides more or less with the trough of low atmos- 

 pheric pressure and the divergence between the west- and east-wind drifts. 

 The warm deep layer to the south must be supplied to a large extent from the 

 west Indian Ocean sector. Its temperature and salinity fall as it flows round 

 the south and west sides of the Weddell Sea, and, as is shown on page 287, it 



