VERTICAL CIRCULATION IN THE OCEAN 169 



be mentioned. Since the general wind direction is westerly on both sides of the con- 

 vergence a transport to the north must take place on both sides. We have assumed that 

 the transport is greater on the southern side and that, therefore, part of the water must 

 sink near the convergence. It seems to follow that another part continues across the 

 convergence, but the abrupt change in temperature when crossing the convergence is 

 decidedly against such a view. The convergence seems to represent a narrow zone of 

 mixing, but no continuous flow across takes place. A possible motion near the con- 

 vergence is indicated in Fig. 23 by dashed lines. It is supposed that a return flow to- 

 wards the south exists also on the northern side of the convergence, but this return 

 flow takes place near the surface and at the convergence part of the water bends up 

 towards the surface and is carried north, while another part bends down and joins with 

 the Antarctic water and forms one constituent of the Antarctic intermediate current. 



Another difficulty is met with in the southern part of the Antarctic current where re- 

 turning water is supposed to reach the surface again. The observations show that the 

 water of the intermediate return current approaches the surface in high southerly 

 latitudes, but at no station is water of this type met with above 150-200 m. If our con- 

 ception is correct, it must be assumed that the factors which influence the temperature 

 and the salinity of the upper layers are so efi'ective that the properties of the inter- 

 mediate return water are changed when this approaches the surface. This assumption 

 is not unreasonable, since the ascending motion is very slow. 



The questions which have been mentioned here can perhaps be cleared up, partly by 

 means of theoretical considerations, partly by means of new observations or by a closer 

 study of the existing data. At present the above representation of the vertical circulation 

 within the Antarctic circumpolar current must be regarded as hypothetical, but it is 

 hoped that the consideration of vertical circulations which are maintained by the action 

 of the prevaiUng wind may be helpful when studying the structure of other currents. 



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