A New Estimate of the Southern Ocean Meridional Overturning Circulation from Argo Float Observations

The southern limb of the global meridional overturning circulation plays a critical role in the climate system by impacting ocean heat uptake, regulating the air-sea exchange of carbon dioxide, and driving biological production throughout the tropics and subtropics. However, observations of this region have historically been limited in both space and time. Here we present a direct circumpolar estimate of the overturning circulation in the upper 2000 dbar of the Southern Ocean, produced using absolute geostrophic velocities and eddy thickness fluxes estimated from measurements collected by the Argo array of profiling floats together with satellite-based wind observations. The spatial variability of the overturning and the relative contributions of the mean and eddy components of the flow are both analyzed. Eddies are found to generate significant cross-stream transport of Upper Circumpolar Deep Water, primarily localized to regions just downstream of major topographic features, consistent with predictions based on analytic and numerical models. In addition, our analysis suggests that the eddy component of the overturning circulation is associated with the restratification of deep winter mixed layers and the northward export of mode and intermediate waters.