WHOI PO
Ali Exley, WHOI - Patterns and Drivers of Cross-frontal Exchange Diagnosed in the Southeast Indian Ridge Region of the Southern Ocean
| Date |
Time |
Location |
| March 25th, 2025 |
3:05pm-4:05pm |
Clark 507 |
Title: Patternsand Drivers of Cross-frontal Exchange Diagnosed in the Southeast Indian Ridge Regionof the Southern Ocean
Abstract: TheSouthern Ocean plays a fundamental role in the meridional overturningcirculation by ventilating deep, carbon-rich waters to the surface ocean, andthrough the conversion to bottom and intermediate waters, largely compensatessinking in the subpolar North Atlantic. Central to the Southern Ocean overturningcirculation is the role of mesoscale eddies which are the primary mechanism bywhich heat, carbon, nutrients and other properties are transported poleward acrossfronts of the Antarctic Circumpolar Current (ACC), effectively balancing thewind-induced equatorward transport. Satellite altimetry has revealed distinct spatialpatterns in eddy kinetic energy around the ACC, suggesting mesoscale eddy fieldsare largely confined to relatively small regions downstream from topographicridge systems. Despite the outsize importance for meridional heat transporthowever, we lack an accurate estimate of fluxes across the ACC due to thechallenges of observing mesoscale eddy fluctuations on the temporal and spatialscales required. Additionally, the physical mechanisms responsible forinitiating and maintaining these mixing regimes remains poorly constrained.Here, observations from Argo are used together with high-resolution numericalmodel output to investigate horizontal patterns of eddy diffusivity and todiagnose eddy-mean field interactions in the Southeast Indian Ridge system, arelatively under-observed region known to be a hot spot of exchange in theSouthern Ocean. We find a highly localized pattern of diffusivity, peakingbetween the crest and trough of the first standing meander in the lee of theridge system, which correlates with an along-stream increase in eddy kineticenergy. Additionally, by adopting a wave-activity flux framework traditionallyemployed for atmospheric storm track studies, we decompose the role ofbarotropic and baroclinic instabilities as well as the ageostrophic fluxeswhich sustain the growth, flux and decay of energy in the along-streamdirection. This work is an early step towards quantifying the contribution ofthese processes on the large-scale overturning circulation which willultimately be essential for a comprehensive understanding of the system and howit might respond to future change.