RRS Charles Darwin Cruise 129, Durban, South Africa to Port Louis, Mauritius 6 Jul - 11 Aug 2001. History of the Deep Western Boundary Current in the Madagascar and Mascarene Basins

Cruise 129 of the RRS Charles Darwin was designed to investigate the history of the Deep Western Boundary Current in the Madagascar and Mascarene Basins and make hydrographic and biological measurements in support of those objectives. Swath bathymetry (10 kHz) and 3.5 kHz sub-bottom profiles were recorded continuously. Kasten (16) and box (29) cores were recovered and one piston core. 16 CTD casts with transmissometer and fluorometer, and plankton net hauls at 9 stations (generally 3 tow depths per station) were also deployed. The topography proved to be quite rugged on the ridges to the north and south of Madagascar, as was the western flank of the Mascarene Ridge. This made it impossible to find coring targets at the depths of AAIW. Furthermore, much of the sediment apron east of Madagascar is made of turbidites and only a few contourite deposits, none forming a significant sediment drift. It appears that the deep Western boundary current is not particularly strong here, and recent work has shown that the dominant current is related to Rossby waves in the basin with a period of 60 days. Nevertheless sufficient material has been obtained in order to examine aspects of the paleoceanography and flow history in this basin, especially from the flow constriction in Amirante Passage.