On the role of wind-driven sea ice motion on ocean ventilation

Simulations with a coupled ocean-atmosphere-sea ice model are used to investigate the role of wind-driven sea ice motion on ocean ventilation. Two model experiments are analyzed in detail: one including and the other excluding wind-driven sea ice transport. Model-simulated concentrations of chlorofluorocarbons (CFCs) are compared with observations from the Weddell Sea, the southeastern Pacific, and the North Atlantic. The authors show that the buoyancy fluxes associated with sea ice divergence control the sites and rates of deep- and intermediate-water formation in the Southern Ocean. Divergence of sea ice along the Antarctic perimeter facilitates bottom-water formation in the Weddell and Ross Seas. Neglecting wind-driven sea ice transport results in unrealistic bottom-water formation in Drake Passage and too-strong convection along the Southern Ocean sea ice margin, whereas convection in the Weddell and Ross Seas is suppressed. The freshwater fluxes implicitly associated with sea ice export also determine the intensity of the gyre circulation and the rate of downwelling in the Weddell Sea. In the North Atlantic, the increased sea ice export from the Arctic weakens and shallows the meridional overturning cell. This results in a decreased surface flux of CFCs around 65degreesN by about a factor of 2. At steady state, convection in the North Atlantic is found to be less affected by the buoyancy fluxes associated with sea ice divergence when compared with that in the Southern Ocean.