Chapter Eleven 



ROLE OF THE THERMOHALINE 

 CIRCULATION 



Although much effort has been directed toward detailed theoretical 

 elucidation of the consequences of the action of wind stress in producing 

 the oceanic circulation, there has not been a parallel development of the 

 theory of the thermohahne process. The distribution of wind stress over the 

 ocean surface is much better known than the distribution of net heating 

 and cooling of the ocean; thus there is httle hope, at present, of constructing 

 as complete and satisfactory a theory of the thermohaline circulation as is 

 possible for the wind-driven circulation. Nevertheless, it does seem desir- 

 able to reconnoiter the problem and to try to construct, on a tentative 

 status, a simple theory of the thermohaline circulation that can be applied 

 to real ocean circulations. 



In this chapter, attention is first drawn to the fact that the now-famihar 

 'wind-curl' equation introduced by Sverdrup (1947) is simply a statement 

 of the fact that at every geographical position in the ocean the integrated 

 horizontal divergence of the Ekman wind drift is compensated by a cor- 

 responding convergence of the integrated geostrophic current. Next, a 

 thermohaline process is specified in terms of a prescribed vertical velocity 

 structure. At some particular mid-depth the vertical velocity has an 

 extreme value; and this same depth is the level of no horizontal divergence. 

 Two vorticity equations are formed by vertical integration over the layers 

 above and below this level. It is shown that the thermohaline circulation 

 appears as a kind of internal mode of motion, and that the level of no 

 horizontal divergence is also the level of no meridional motion and, if 



