168 Thermohaline Features 



section, section 1 , goes from shore to shore, and hence should include interior 

 and boundary currents. The 1932 Challenger stations used extended only 

 to a depth of 2000 m. If 2000 m. is used as the depth of no motion there is a 

 net flux above 2000 m. of roughly 30 x 10^ m.^/sec. to the north across 

 section 1. By shifting the level of no motion to about 1500 m., or even 

 shallower, it is possible to obtain a balance of mass flux across the section 

 (as depicted in fig. 79). The flux due to Ekman wind drift across section 1 is 

 showTi, approximately, at the bottom of fig. 79. It is too small to play any 

 important role in the net balance across section 1 . Our reasoning forces us 

 to admit a deep southward flow across section 1 between 1500 m. and the 

 bottom. A similar pattern of flow appears to occur across section 2, but, 

 although the data for this section extend to 3000 m., the section does not 

 extend all the way to the western coast. 



In terms of the foregoing hypotheses, the deep currents, which at sections 

 1 and 2 are distributed over much of the interior, are compressed into a 

 narrow western boundary current at sections 6 and 7 and do not exist in the 

 interior at sections 3, 4, and 5. Because of the shallow sill in the Florida 

 Straits (indeed, even over the Blake Plateau), the deep countercurrent 

 shown below 1600 m. on sections 6 and 7 sphts away (sections 8 and 10) 

 from that part of the surface current (sections 9 and 11) which passes 

 through the Caribbean. Because the curl of the wind stress is nearly uniform 

 between 20 and 40° N., the surface currents across sections 9 and 11 are 

 more properly regarded as wind-driven than are the surface currents across 

 sections 8 and 10. By hjrpothesis, the schematic model of the rectangular 

 ocean described above causes this deep current to be absorbed by vertical 

 motion into the surface layer of the interior of the subtropical North 

 Atlantic. In the real ocean it appears that only part of the deep flow across 

 sections 6, 7, 8, and 10 can be so absorbed, and that most of it must 

 flow across the equator into the South Atlantic Ocean, where it appears on 

 both section 12, beneath the Guiana Current, and section 15, beneath the 

 Brazil Current. The deep currents of the South Atlantic are mostly confined 

 to narrow western boundary currents. Sections 12, 13, and 14 are within 

 10° of the equator, where there is some reason to be slightly suspicious of the 

 geostrophic calculations. Also, the flow of the Ekman wind drift cannot be 

 ignored at these latitudes. It is interesting to note that the flow of Antarctic 

 Intermediate Water appears to be stronger across section 13 than across 

 section 12 ; one wonders whether this indicates vertical velocity near 1000 m. 

 or a surprisingly deep influence of curl of the wind stress. The transport 

 across interior section 14 seems remarkably low, especially when one notes 

 by what a narrow margin the geostrophic transport misses being canceled 

 by the Ekman wind drift. 



We now come to sections 15 and 16, which are the counterpart in the 



