Wednesday 24 August 2005

P4
1050-1230 hours

267
Southward shift of the Eastern Australian Current induced by an upward trend of the Southern Annular Mode
Cai, Wenju¹
1 CSIRO Atmospheric Research, Aspendale, Vic, Australia
Author email: wenju.cai@csiro.au
The response of the Southern Hemisphere ocean circulation to climate change is not as well studied as the Northern Hemisphere counterpart. Observational studies have revealed an upward trend of the Southern Annular Mode (SAM) over the past few decades, although the relative importance of greenhouse, ozone depletion and natural variability in forcing the trend is not fully conclusive. Here we demonstrate, via the Sverdrup relationship, that the associated change in wind stress curl causes a southward shift of the Southern Hemisphere subtropical gyre, particularly the Eastern Australian Current (EAC), leading to an intensification of the southern part of the gyre circulation. Climate models forced by the Intergovernmental Panel for Climate Change scenarios project a continuing upward trend of the SAM into the future. In response, the EAC moves southward by up to 8 degree latitude by year 2070. The southward shift is a part of annular-scale circulation changes that involve all subtropical gyres of the Southern Hemisphere. The changes significantly alter the boundaries of bio-diversity and generate accelerated warming and sea-level rises in regions where the southward flowing current intensifies.

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