Summary of Abstract Submission

Abstract Submission No. IO50-04-0015PresentationOral

THE SHALLOW CIRCULATION IN THE UPPER LAYER OF THE SOUTH INDIAN OCEAN

Will P.M. de Ruijter*1

1 Utrecht University, Netherlands

ABSTRACT :

The circulation of the South Indian Ocean is unique in several respects. The Leeuwin Current is a unique poleward eastern boundary current. In the Mozambique Channel and south of Madagascar the western boundary layer breaks up in eddies and dipolar vortices. They propagate into the Agulhas Retroflection where a small part 'leaks' into the Atlantic overturning. Zonal flows establish the connection between these western and eastern boundary regimes. The Pacific-Indian throughflow via the Indonesian passages continues westward across the basin. Between Madagascar and Australia the recently identified 'South Indian Ocean Counter Current' (SICC) flows eastward against the direction of the wind-driven 'Sverdrup' gyre. The SICC is a shallow frontal flow driven by the convergence of Ekman transport combined with differential buoyancy forcing. It impignes into the Leeuwin Current and is probably one of its controls. The SICC seems connected to the subduction region south-west of Australia. The subducted waters return westward as 'intra-thermocline' eddies in an as yet unquantified amount. We present evidence that the SICC is a connector in a large scale shallow circulation system that involves the Indonesian Throughflow, Mozambique and Agulhas Currents, the SICC and the Leeuwin Current. A preliminary modelling study confirms such a large scale coherent shallow system. Associated with these frontal dynamics the SICC is expected to play a role in the Madagascar Bloom that intermittently pops up at a large scale.