| Results from a recent cruise (June-July 2002) will be presented to reveal thenature and pathways of upper- to mid-column water masses crossing the MascareneRidge in the western Indian Ocean. The ridge system extends from the Seychelles(4 S) to Mauritius (20 S), and presents a barrier to the westward flow of theSouth Equatorial Current (SEC). The SEC appeared as a broad flow between 12-16 S on the eastern side of the ridge, carrying relatively fresh waters between 0-100 m deep. A large part of these were constricted to flow in a narrow rapidjet through a little-known channel in the ridge between 12-13 S, and werethereafter deflected to the southwest. On the southern side of the SEC, a highsalinity water mass was present between 100-500 m, and below this a fresher watermass between 500-1200 m, the two being separated by a potential vorticityminimum. As they approached the ridge from the east, these waters were partiallydrawn northwards through the channel at 12-13 S, and partially through otherdeeper channels near Mauritius. Further analysis indicates that these waters weresubducted in the south- eastern Indian Ocean, and have circulated as part of thesubtropical gyre. Evidence is also presented, including particle tracks from anocean general circulation model, that these waters may also partially transitinto the South Atlantic as Agulhas eddies. Finally, the lowest potentialvorticity waters mentioned above show a robust change (warmer/ saltier onisopycnals) when compared with earlier WOCE data (from 1995) along 20 S. |
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