Flow of bottom and deep water in the Amirante Passage and Mascarene Basin

In the Indian Ocean the Amirante Passage is the sill through which relative ly cold, fresh, oxygen-rich, and nutrient-poor bottom water spreads northwa rd into the Somali Basin from the Mascarene Basin. The passage is also a co nduit through which relatively warm, salty, oxygen-poor, and nutrient-rich deep water spreads south. Previous estimates for northward transport of bot tom water in the passage have been made from station pairs and sections wit hout benefit of tracer measurements. Previous estimates of southward transp ort of deep water are scarce. Three hydrographic sections were made across the passage in 1995 and 1996 as part of the World Ocean Circulation Experim ent (WOCE). Two WOCE sections were also made perpendicular to the western b oundary in the Mascarene Basin, just south of the passage. The geostrophic shear field is used with the salinity, dissolved oxygen, and silica distrib utions to select a range of zero-velocity surfaces (ZVSs) on potential isot herms from 1.0 degrees to 1.1 degrees C (hence a range of geostrophic trans ports) for which the flow direction is consistent with the tracer distribut ions. Objective mapping is used to obtain flux estimates below the deepest common level of station pairs. Estimates in the Mascarene Basin result in a bottom water volume transport from 2.5 to 3.8 x 10(6) m(3) s(-1) northward toward the passage below the ZVSs and a deep-water transport between the Z VSs and 2.5 degrees C from 11.6 to 6.4 x 10(6) m(3) S-1 southward. Estimate s within the passage result in transports from 1.0 to 1.7 x 10(6) m(3) s(-1 ) northward for the bottom water and from 8.6 to 3.8 x 10(6) m(3) s(-1) sou thward for the deep water.