Southern Ocean overturning across streamlines in an eddying simulation of the Antarctic Circumpolar Current
1Laboratoire de Physique de Oceans, CNRS-IFREMER-UBO, Plouzané, France
2Climate Change Research Centre (CCRC), University of New South Wales, Sydney, Australia
3CSIRO Wealth from Oceans National Research Flagship and Antarctic Climate and Ecosystems CRC, Hobart, Australia
4Laboratoire d'Océanographie et du Climat: Experimentations et Approches Numériques, Pierre and Marie Curie University, Paris, France
5Laboratoire des Ecoulements Geophysiques et Industriels, Joseph Fourier University, Grenoble, France
Abstract. An eddying global model is used to study the characteristics of the Antarctic Circumpolar Current (ACC) in a streamline-following framework. Previous model-based estimates of the meridional circulation were calculated using zonal averages: this method leads to a counter-intuitive poleward circulation of the less dense waters, and underestimates the eddy effects. We show that on the contrary, the upper ocean circulation across streamlines agrees with the theoretical view: an equatorward mean flow partially cancelled by a poleward eddy mass flux. Two model simulations, in which the buoyancy forcing above the ACC changes from positive to negative, suggest that the relationship between the residual meridional circulation and the surface buoyancy flux is not as straightforward as assumed by the simplest theoretical models: the sign of the residual circulation cannot be inferred from the surface buoyancy forcing only. Among the other processes that likely play a part in setting the meridional circulation, our model results emphasize the complex three-dimensional structure of the ACC (probably not well accounted for in streamline-averaged, two-dimensional models) and the distinct role of temperature and salinity in the definition of the density field. Heat and salt transports by the time-mean flow are important even across time-mean streamlines. Heat and salt are balanced in the ACC, the model drift being small, but the nonlinearity of the equation of state cannot be ignored in the density balance.
Treguier, A. M., England, M. H., Rintoul, S. R., Madec, G., Le Sommer, J., and Molines, J.-M.: Southern Ocean overturning across streamlines in an eddying simulation of the Antarctic Circumpolar Current, Ocean Sci., 3, 491-507, doi:10.5194/os-3-491-2007, 2007.