VERTICAL CIRCULATION IN THE OCEAN 



149 



shown. Both surfaces are inchned from north to south and the current is directed 

 towards the east both within the sub-Antarctic and the Antarctic water. The incHnation 

 is much greater to the north of the convergence and, therefore, the easterly current is 

 much stronger on the northern side. These features are in agreement with the theoretical 

 conclusions as to the character of the distribution of density and the flow of the water 

 within two neighbouring water masses of different density (see Defant, 1929, p. 103), 

 but they do not explain why such a boundary surface exists within the easterly circum- 

 polar current. It seems obvious that no discontinuity in the variation of the density would 



Fig. I. Vertical distribution of density (a,) and inclination of the sea surface and the 



1000 decibar surface, relative to the 3000 decibar surface, between latitudes 42° and 58° S 



in the Atlantic Ocean along the meridian 30° W. 



exist if the direction of the current were due east in all latitudes and the occurrence of the 

 convergence must, therefore, be associated with the presence of north-south components. 



Two factors may contribute to the development of a component towards the north 

 within the Antarctic water: in the first place the prevailing westerly winds, and in the 

 second place the supply of water of low salinity owing to the melting of the pack-ice. 

 The pack-ice is, however, carried towards the north by the wind, and thus the action 

 of the wind seems to be the principal factor which causes a flow of the surface layers to 

 the north. 



Westerly winds prevail within the regions of both the sub-Antarctic and the Antarctic 

 waters. The wind is not blowing permanently from the west, but when considering the 

 effect of the wind it is, as already mentioned, sufficient to take the wind resultant into 

 account. Between latitudes 40 and 65° S the wind resultant is generally from the west, 

 and between these latitudes a pure drift current must exist which transports the surface 

 layers towards the north. The question arises whether the wind resultant from the west 



