Potential vorticity and across ACC eddy transport in the Upper Circumpolar Deep Waters

Eddy transport processes are of first order importance for the meridional transport of the Upper Circumpolar Deep Waters (UCDW) in the Southern Ocean, as the transport due to the geostrophic mean flow integrated along a closed PV contour on an isopycnal vanishes. In this study we quantify this eddy mass transport using a downgradient PV diffusivity parameterization, where the PV gradients are calculated using a climatology produced using ARGO float profile data, and eddy diffusivities quantified using ARGO float trajectories.

The results show a southward transport of approximately 10-15SV along the neutral density layer centered at 27.8 (UCDW). Significant portions of the transport are localized around topographic features encountered by the ACC, primarily due to greater diffusivities associated with these energetic regions.

We also discuss the large scale PV structure of the ACC, addressing the primary question that what is creating and controlling the large scale PV gradients? This is done by calculating the PV budgets, using the flux form of the PV equation, for both ARGO climatology and SOSE model output. The structure is set locally by the interactions of the ACC with topography and non-locally by sources and sinks of PV in individual ocean basins and at outcropping sites.