Southern Ocean overturning across streamlines in an eddying simulation of the Antarctic Circumpolar Current

[摘要] An eddying global model is used to study the characteristics of the AntarcticCircumpolar Current (ACC) in a streamline-following framework. Previousmodel-based estimates of the meridional circulation were calculated usingzonal averages: this method leads to a counter-intuitive poleward circulationof the less dense waters, and underestimates the eddy effects. We show thaton the contrary, the upper ocean circulation across streamlines agrees withthe theoretical view: an equatorward mean flow partially cancelled by apoleward eddy mass flux. Two model simulations, in which the buoyancy forcingabove the ACC changes from positive to negative, suggest that therelationship between the residual meridional circulation and the surfacebuoyancy flux is not as straightforward as assumed by the simplesttheoretical models: the sign of the residual circulation cannot be inferredfrom the surface buoyancy forcing only. Among the other processes that likelyplay a part in setting the meridional circulation, our model resultsemphasize the complex three-dimensional structure of the ACC (probably notwell accounted for in streamline-averaged, two-dimensional models) and thedistinct role of temperature and salinity in the definition of the densityfield. Heat and salt transports by the time-mean flow are important evenacross time-mean streamlines. Heat and salt are balanced in the ACC, themodel drift being small, but the nonlinearity of the equation of state cannotbe ignored in the density balance.

[学科分类] 海洋学与技术