Role of the Agulhas Current in Indian Ocean circulation and associated heat and freshwater fluxes

Harry L. Bryden, Lisa M. Beal

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

A reduced estimate of Agulhas Current transport provides the motivation to examine the sensitivity of Indian Ocean circulation and meridional heat transport to the strength of the western boundary current. The new transport estimate is 70Sv, much smaller than the previous value of 85Sv. Consideration of three case studies for a large, medium and small Agulhas Current transport demonstrate that the divergence of heat transport over the Indian Ocean north of 32°S has a sensitivity of 0.08 PW per 10 Sv of Agulhas transport, and freshwater convergence has a sensitivity of 0.03 × 109 kgs-1 per 10 Sv of transport. Moreover, a smaller Agulhas Current leads to a better silica balance and a smaller meridional overturning circulation for the Indian Ocean. The mean Agulhas Current transport estimated from time-series current meter measurements is used to constrain the geostrophic transport in the western boundary region in order to re-evaluate the circulation, heat and freshwater transports across 32°S. The Indonesian Throughflow is taken to be 12Sv at an average temperature of 18°C. The constrained circulation exhibits a vertical-meridional circulation with a net northward flow below 2000dbar of 10.1 Sv. The heat transport divergence is estimated to be 0.66 PW, the freshwater convergence to be 0.54 × 109 kgs-1, and the silica convergence to be 335kmols-1. Meridional transports are separated into barotropic, baroclinic and horizontal components, with each component conserving mass. The barotropic component is strongly dependent on the estimated size of the Indonesian Throughflow. Surprisingly, the baroclinic component depends principally on the large-scale density distribution and is nearly invariant to the size of the overturning circulation. The horizontal heat and freshwater flux components are strongly influenced by the size of the Agulhas Current because it is warmer and saltier than the mid-ocean. The horizontal fluxes of heat and salt penetrate down to 1500m depth, suggesting that warm and salty Red Sea Water may be involved in converting the intermediate and upper deep waters which enter the Indian Ocean from the Southern Ocean into warmer and saltier waters before they exit in the Agulhas Current.

Original languageEnglish (US)
Pages (from-to)1821-1845
Number of pages25
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume48
Issue number8
DOIs
StatePublished - Jun 18 2001
Externally publishedYes

Keywords

  • Agulhas current
  • Heat transport
  • Hydrographic sections
  • Indian Ocean circulation
  • Meridional oceanic circulation
  • Meridional overturning circulation
  • Transoceanic
  • Western boundary currents

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science

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