436 



General Theory of Ocean Currents in a Homogeneous Sea 



Fig. 186, since this is in the Southern Hemisphere). The extremes do not always coin- 

 cide in position but particularly in the eastern part are in excellent agreement. 



Schumacher (1940, 1943) has indicated further examples. Over the mid- Atlantic 

 Ridge especially, there is often a corresponding bending of the current to observe. 

 The large stationary cum sole vortex off the eastern side of the Azores plateau must also 



Fig. 188. Upper picture: bottom topography and stream lines for the gradient current in 



the disturbance region of the subtropical convergence zone in the South Atlantic Ocean 



(30°-45° S., 50-0 W.). Lower picture: vertical bottom profiles at 30° and 35° S. according 



to the depth chart of the Atlantic Ocean. 



be favoured by the bottom topography. In the Equatorial Counter Current the presence 

 of the Atlantic Ridge shows this very typical effect. If the water masses are stratified, 

 there will be corresponding displacements in the isosteres inside the region of influence 

 of the bottom irregularity (see p. 558). If an isolated submarine ridge lies in the path 

 of a current a cyclonic vortex will be formed above it. An example of a vortex of this 

 type is given in the description of oceanic conditions around the "Altair" submarine 

 volcano in the North Atlantic (Neumann, 1940) (see also, Schott, 1939). 



In discussing the effect of the bottom topography on ocean currents it has always 

 been assumed that the current is more or less uniform from the sea surface down to 

 the sea bottom. In almost all cases, however, the velocity of the current falls off rapidly 

 with depth and in addition there are changes in the direction of the current. In these 

 circumstances it is not so easy to accept a direct effect of the bottom topography on 

 the current in the upper layers of the sea, since these are often separated from the bottom 

 currents by very thick motionless water layers or layers with quite a different type of 

 current. Attention should be drawn to these considerations in any discussion of the 

 effect of the bottom topography on the currents. 



5. Ice Drift 



The wind drift of the ice in the polar regions (see pt. I, Chap. VIII, p. 243), like 

 the ordinary wind-driven ocean currents, is dependent on three forces: wind stress, in- 

 ternal turbulent friction and Coriolis force; in addition to these it is also affected by 



