Presenter: Lilian Dove (Caltech)

Description:
The circulation of the Southern Ocean is strongly influenced by flow-topography interactions along the path of the Antarctic Circumpolar Current (ACC), which generates standing meanders in the lee of topography, modifies frontal structure, and creates hotspots of eddy kinetic energy (EKE). Ventilation, or exchange of waters between the surface and interior ocean, may be enhanced in regions of high EKE due to stirring along isopycnals at the mesoscale and submesoscale. Numerical models suggest these hotspots have consequences for the global ocean circulation and the uptake of heat and carbon. The expanded use of autonomous platforms has enhanced our ability to observe tracer distributions and analyze localized processes across the Southern Ocean.   Here, we use data from Biogeochemical-Argo floats to observe patterns of oxygen ventilation within the ACC by partitioning measurements between low and high EKE regions. Regions of high EKE show reduced apparent oxygen utilization (AOU) values 200-600 meters below the base of the mixed layer, with median values around 50 μmol/kg as compared to 140 μmol/kg in low EKE regions. Probability distributions in temperature-salinity space reveal distinct differences in hydrographic properties between regions. Specifically, high EKE regions have lower salinity and warmer temperatures at depth, consistent with recent subduction of surface-formed intermediate waters. We suggest processes at the submesoscale, shaped by mesoscale stirring, have a defining role in the observed ventilation. This is supported by the distribution of finite-size Lyapunov exponents (FSLEs) that are used as a proxy for lateral buoyancy gradients. Mechanisms driving ventilation of climatologically-important tracers on interannual to decadal timescales remain uncertain; we demonstrate that dynamics in localized regions of the ACC may play a dominant role in influencing such fluxes, emphasizing the importance of zonally-asymmetric dynamics in the Southern Ocean.