Testing theories of the Antarctic Circumpolar Current against observations

Recent theoretical models of the Antarctic Circumpolar Current (ACC) which invoke transfer by baroclinic eddies as a fundamental player in its large-scale buoyancy, potential vorticity and momentum budgets, are tested against the available observations. Hydrographic observations and mooring data (to give vertical structure), altimteric data (to make inferences about the eddy statistics, eddy diffusivities and eddy transfer) and climatological air-sea flux data, are examined in the framework provide by the 'Transformed Eulerian mean'.

We find that the theoretical assumptions and governing balances previously discussed in the context of laboratory and numerical models, find support in the observations. Combining the theory with observations, we describe the role the ACC plays in the meridional transport of heat, salinity, and tracers. The net transport of heat and salinity is seen to be accomplished by the 'residual circulation', the difference between the wind driven overturning and the eddy induced advection. The residual circulation establishes `diabatic Deacon cells' that bring high (low) buoyancy waters to the surface to lose (gain) buoyancy from the atmosphere. Thus, the residual circulation can be directly diagnosed from the surface buoyancy flux. Not only does the residual circulation govern the formation of deep water, it also governs the redistribution of tracers, and is thus essential in understanding the dynamical nature of the ACC.