Response of the antarctic circumpolar current transport to global warming in a coupled model

The transient and long-term adjustment process of the Antarctic Circumpolar Current (ACC) in response to global warming in the CSIRO climate model is examined in an integration, which is run under increasing atmospheric CO2 following the IPCC/IS92a scenario to stabilisation at triple the initial CO2 concentration (3 × CO2). The ACC transport through Drake Passage shows an evident strengthening along with the CO2 increase and, in the subsequent period with stabilised 3 × CO2, it keeps increasing steadily after CO2 tripling for a few centuries until a maximum (151 Sv, 17% larger than the initial state) is reached. The strengthening of the ACC transport results from the warming-induced enhancement of the meridional density gradient in the ocean interior across the ACC: it leads to a speedup of the upper layer zonal flow which outweights the deceleration in the underlying layer caused by the weakening of the deep overturning off Antarctica.