THE ANTARCTIC CONVERGENCE 21 



towards the east. The current is, however, directed not only to the east, but generally 

 it has a northward component and occasionally one towards the south. 



The eastward movement tends to carry the Antarctic water continuously round the 

 whole of the Southern Ocean, but the northward movement, although it remains at the 

 surface for a great distance, reaches in the end a latitude where it sinks suddenly from 

 the surface to a deeper level. An examination of the temperature and salinity distribu- 

 tion in the sections that have been made across the Southern Ocean shows that the point 

 at which the Antarctic current sinks is determined by the movements of the warm deep 

 water and the Antarctic bottom water. 



In the subtropical region the warm deep water flows southwards at a very great depth, 

 below 2000 m. in 30-35 S, but on the threshold of the Antarctic region, where it meets 

 a large volume of Antarctic bottom water flowing in the opposite direction, it climbs 

 steeply towards the surface ; in the Antarctic Zone it continues its way southwards just 

 below the surface layer and usually extends to within 200 m., or less, of the surface. Its 

 movements are illustrated by the diagram in Fig. 1 (p. 4), based on the temperature 

 and salinity distribution in 30 W. 



The vertical sections across the ocean show that where a large volume of Antarctic 

 bottom water extends far north the upward movement of the warm deep water takes 

 place far north, and at a steep angle, but where the bottom current is smaller the deep 

 water climbs farther south and less steeply. 



This conclusion is illustrated by the diagram in Fig. 5, which shows the temperature 

 distribution in the Southern Ocean at a depth of 2500 m. At this depth the tempera- 

 ture decreases towards the south as the warm deep water climbs above the Antarctic 

 bottom water ; the decrease is gradual at first, but there is an abrupt fall of temperature 

 where the warm deep water climbs most steeply and a further gradual decrease where 

 the layers slope less steeply again farther south. The temperature measurements them- 

 selves are an approximate indication of the strength of the bottom current ; they show 

 that the most abrupt temperature changes, marking the places where the warm deep 

 water climbs most steeply, are found where the low temperatures indicate that the bottom 

 current is strongest. 



A consideration of the circumstances shows that the warm deep water climbs towards 

 the surface because it can only continue its southward movement above the Antarctic 

 bottom water. The locality and the steepness of the upward movement must therefore 

 be determined by factors which govern the flow of the bottom water. This conclusion 

 is justified by observations which show that wherever the northward flow of the 

 bottom water is influenced by the configuration of the sea-floor, the movements of the 

 deep water are altered conformably. 



The sudden upward movement of the deep water is discussed in this section of the 

 report because it determines the latitude at which the Antarctic water sinks below the 

 surface. Earlier in the report (p. 13) it was shown that the great density of the 

 Antarctic water compared with the warmer surface waters farther north tends to set up 

 a circulation in which the Antarctic water sinks and is replaced at the surface by a 



