[A-CG36] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG36-02] Eddy stirring in a standing meander of the Polar Front near Macquarie Ridge

*Maya Jakes^1,2,3, Helen Phillips^1,2, Annie Foppert^1,3, Nathan Bindoff^1,2,3, Steve Rintoul⁴ (1.Institute of Marine and Antarctic Studies, IMAS, 2.Centre of Excellence for Climate Extremes, CLEX, 3.Australian Antarctic Partnership Program, AAPP, 4.Commonwealth Scientific and Industrial Research Organisation, CSIRO)

Keywords:eddy stirring, standing meander, Antarctic Circumpolar Current, thermohaline variability, topography-flow interactions

Zonal heterogeneities in the Antarctic Circumpolar Current (ACC) occur where the current interacts with major bathymetric features, producing standing meanders and rich eddy fields that alter the baroclinicity of the flow and its ability to act as a barrier to poleward heat transport. These regions – referred to as ‘leaky jets’ – exhibit a breakdown of eddy stirring suppression and thus influence watermass transformation and eddy heat flux across the front. Observations from six EM-APEX floats deployed between 2018 and 2020 reveal the subsurface temperature and velocity structure through an energetic standing meander of the Polar Front near Macquarie Ridge. The floats travelled for 3000-4000 km, collecting 400-500 vertical profiles of temperature, salinity, and velocity over a period of 5-7 months, roughly tracking the frontal position defined by sea surface height streamlines. Spice standard deviation (std), calculated from the temperature and salinity profiles, is used as a proxy for the strength of eddy stirring along the float track. Peaks in spice std suggest elevated local eddy stirring and water mass transformation - characteristics of a 'leaky' jet and weakened zonal barrier. We find peaks in spice std in regions of high depth-averaged eddy kinetic energy (EKE), and along more northern streamlines in a region of eddy generation and shedding within the meander trough. These unique observations will improve our understanding of the physical processes and mechanisms that generate thermohaline variability within standing meanders and facilitate cross-frontal transport, allowing better representation of these dispropotionately important localised dynamics in global climate models.