Theemohaline Features 161 



layer is shown as a function of latitude by the curves on the left-hand side 

 of the diagram. The features of the circulation in this ideaUzed basin, and 

 with this very arbitrary choice of distribution of vertical velocity, cannot, 

 of course, be appUed directly to any real oceanic basin, but they do give an 

 indication of the way in which the introduction of the therm ohaline process 

 modifies the current pattern in the central ocean regions. The broken-line 

 arrows indicate direction and amount of transport in the upper layer due to 

 wind stress alone, which are similar to those given by the Munk theory. 

 They also represent the total transport of both layers in the thermohaline 

 model, because, as we have seen above, the transports of the thermohaline 

 process are an internal mode of motion, in which the transport of one layer 

 is compensated by a counterflow in the other layer. On the left-hand side 

 of the figure the transport of the upper layer due to wind alone, or alter- 

 natively the transport of both layers {G^ + G2) in the thermohaline case, in 

 the western current, is indicated by the broken-line curve. Because of the 

 choice of parameters, the maximum transport, 36 x lO^m.^/sec, matches 

 that computed by Munk (1950) for the Gulf Stream. 



The introduction of vertical mass flux at an arbitrary level of no hori- 

 zontal divergence completely alters the picture of the transports, so far as 

 individual layers are concerned. In the upper layer (heavy soHd arrows and 

 curves), this modification is revealed as: (i) a general strengthening of 

 transport over the southern half of the basin, (ii) a turning toward the north 

 in the northern half, (iii) an increase in the transport in the western current 

 in low latitudes, (iv) an abrupt cutoff of the western current somewhat south 

 of the maximum westerlies, and (v) a reversal of the western current in the 

 northern quarter of the ocean, contrary to the wind-driven current. 



In the lower layer (fight solid arrows and curves) : (i) strong southwest- 

 ward transports occur in the northern half of the basin; (ii) this flow con- 

 centrates toward the west into a powerful countercurrent underneath the 

 surface western current ; (in) at the latitude of no vertical flux there is no 

 meridional transport in the interior of the ocean, and thus the northern half 

 of the lower layer is completely cut off from the southern half over the entire 

 interior region of the ocean, except for the connection through the counter- 

 flow underneath the western current; (iv) the flow in the southern half is 

 northeastward and slow; and (v) the water in the lower layer, in the 

 southern half, is relatively stagnant, and more than 200 years old (that is, 

 since contact with the surface). 



It is interesting to note that the behavior of the thermohaline circulation 

 impfied by this model in the southern half of the interior of the ocean is 

 inverse to the action of a simple Hadley-type convective circulation: 

 warmed water moves equatorward, cold water poleward. The northern half 

 of the interior solution behaves fike a Hadley ceU. 



