Collapse and reorganisation of the Southern Ocean overturning under globalwarming in a coupled model

This study investigates the long-term behaviour of the thermohaline circula tion (THC) in the CSIRO climate model, under a scenario of transient increa se of atmospheric (equivalent) CO2 concentration followed by a perpetual st abilisation at triple the initial level (3xCO(2)). The North Atlantic Deep Water Formation (NADWF) declines substantially and the Antarctic Bottom Wat er Formation (AABWF) essentially ceases by the time Of CO2 tripling. During the subsequent millennium of stable 3xCO(2), NADWF recovers slightly but t he AABWF shows no sign of returning and the residual deep overturning dies away. Accelerating the convergence to equilibrium of the deep ocean under t he 3XCO2 condition, the global THC eventually reaches a near-stable state w ith the entire ocean warming by about 7 degreesC, NADWF fully recovered and AABWF partly re-established. This result shows a possible new quasiequilib rium of the ocean under long-term global warming induced by the anthropogen ic CO2 increase.