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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L14611, doi:10.1029/2007GL030380, 2007

Anthropogenic aerosol forcing and the structure of temperature trends in the southern Indian Ocean

Wenju Cai

CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Wealth from Oceans National Research Flagship, CSIRO, North Ryde, New South Wales, Australia


Tim Cowan

CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Wealth from Oceans National Research Flagship, CSIRO, North Ryde, New South Wales, Australia


Martin Dix

CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia


Leon Rotstayn

CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia


Joachim Ribbe

Department of Biological and Physical Sciences, University of Southern Queensland, Toowoomba, Queensland, Australia


Ge Shi

Department of Biological and Physical Sciences, University of Southern Queensland, Toowoomba, Queensland, Australia


Susan Wijffels

CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia


Abstract

Over the past decades surface warming in the southern subtropical Indian Ocean (IO) has been greater than that in other oceans. The warming penetrates to a depth of 800 m, in contrast to the off-equatorial surface warming which co-exists with subsurface cooling. We examine the dynamics for this rich structure. Results from the 20th century experiments of the Intergovernmental Panel on Climate Change (IPCC) confirm that the southern subtropical IO surface-to-800 m warming is greater than that in the Pacific and Atlantic Oceans. Outputs from two targeted ensemble sets of coupled model experiments, one with and one without increasing anthropogenic aerosols, show that increasing aerosols strengthen the global Conveyor, and generate a greater poleward shift and intensification of the Agulhas outflow and its retroflection; the process increases the warming rate in the subtropics, and takes heat out of the off-equatorial region generating a cooling.

Received 16 April 2007; accepted 18 June 2007; published 31 July 2007.

Keywords: climate change; ocean warming; aerosols.

Index Terms: 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 1635 Global Change: Oceans (1616, 3305, 4215, 4513); 3050 Marine Geology and Geophysics: Ocean observatories and experiments; 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504).

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Citation: Cai, W., T. Cowan, M. Dix, L. Rotstayn, J. Ribbe, G. Shi, and S. Wijffels (2007), Anthropogenic aerosol forcing and the structure of temperature trends in the southern Indian Ocean, Geophys. Res. Lett., 34, L14611, doi:10.1029/2007GL030380.