Density-driven Southern Hemisphere subpolar gyres in coupled climate models

We investigate the representation of Southern Hemisphere subpolar gyres in 20 IPCC AR4 climate models. The models reproduce three southern subpolar gyres: the Weddell Gyre, Ross Gyre, and Australian-Antarctic Gyre, in agreement with observations. Some models simulate the presence of a subpolar “supergyre”, with strong connectivity between the three gyres. The gyre strengths and structures show a great range across the models. It is found that the link between the gyre strengths and wind stress curls is weak, indicating that the Sverdrup balance does not hold for the modelled southern subpolar gyres; instead, the simulated gyre strengths are mainly determined by upper layer meridional density gradients, which are themselves determined predominantly by the salinity gradients. These findings suggest that a correct simulation of salinity is crucial in the simulation of southern subpolar ocean circulation.