Ventilation by Submesoscale Motions in the Southern Ocean: Integrated Glider and Float Observations

Lilian Dove, California Institute of Technology, Pasadena, CA, United States, Andrew F Thompson, California Institute of Technology, Pasadena, United States, Alison R Gray, University of Washington, School of Oceanography, Seattle, WA, United States, Dhruv Balwada, Lamont -Doherty Earth Observatory, Palisades, NY, United States, Curtis A. Deutsch, University of Washington Seattle Campus, School of Oceanography, Seattle, United States, Lia Siegelman, UBO, Physical Oceanography, Brest, France and Katy Christensen, University of Washington, Seattle, WA, United States
Abstract:
The Southern Ocean is characterized by weak stratification, energetic frontal currents, and strong surface forcing, and is therefore susceptible to a range of submesoscale motions that influence vertical tracer transport, air-sea exchange, and mixed layer depth. Although the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) float array has provided unprecedented observations of physical and biogeochemical properties in this region, the array’s spatial resolution does not resolve submesoscale processes that help set these tracer distributions. Here, we present results from the Southern Ocean Glider Observations of the Submesoscale (SOGOS) project, in which two Seagliders were deployed with a SOCCOM semi-Lagrangian Biogeochemical-Argo float near the Polar Front in the Indian sector of the Southern Ocean. The initial phase of the experiment was carried out in one of the strongest eddy kinetic energy (EKE) and strain regions of the Southern Ocean; during the latter half, the gliders targeted several coherent mesoscale eddies while tracking the float. Early results show coherent variability of physical and biogeochemical properties on short spatial (~1 km) and temporal (~hours) scales, consistent with an active submesoscale velocity field. In particular, variability is enhanced at the periphery of coherent mesoscale eddies where waters from the base of the mixed layer are injected towards the surface, highlighting an efficient pathway for the exchange of biogeochemical tracers between the ocean interior and the mixed layer. Comparisons between the high-strain/EKE region and the low-strain/EKE downstream region also underscore the importance of vigorous eddies in the production of deep-reaching lateral buoyancy gradients that are associated with vertical transport via cross-frontal secondary ageostrophic circulation. Overall, these results suggest that submesoscale variability that is not resolved by large-scale models or current observing arrays likely plays a crucial role in ventilation and air-sea exchange in the Southern Ocean.