Fine-scale eddy fluxes in the Southern Ocean with the satellite missions SWOT

– Elisa Carli, Doctotant, Legos –

Résumé :

Understanding small-scale ocean circulation is a significant challenge in oceanography, as it holds key information about the ocean’s ability to store and transport heat, gases, and nutrients. Ocean eddies, which dominate kinetic energy transport, have characteristic scales ranging from hundreds to just a few kilometers. While large eddies (>100 km) are well-studied using in-situ instruments and satellite altimeters, smaller eddies (10–100 km) also play a critical role, especially in driving vertical water movement. These vertical motions facilitate exchanges between the surface and deeper layers, aiding in heat and carbon storage. However, existing satellite altimeters inadequately capture these smaller-scale dynamics, limiting their inclusion in climate and ocean models.
The new NASA/CNES satellite SWOT (Surface Water and Ocean Topography) offers a breakthrough, observing scales as fine as 15 km globally. Our research assesses SWOT’s capability to resolve small-scale dynamics by analyzing a high-resolution numerical model of the Agulhas Current region and surface observations of SWOT south of Tasmania. These finer scales significantly enhance estimates of surface geostrophic kinetic energy, strain rate and improves the representation of the shape of the eddies.
Additionally, SWOT surface observations can estimate vertical velocities and heat fluxes deep into the ocean. Using as effective Surface Quasi-Geostrophic methodology, we captured up to 70% of vertical velocity at 1 km depth for wavelengths of 70 km. Validation against high-resolution temperature data south of Tasmania during the 2023 SURVOSTRAL campaign further highlights SWOT’s ability to consistently map the small scales.
By advancing our understanding of ocean dynamics across scales, SWOT contributes to improving climate models, supporting efforts to safeguard oceans and biodiversity amid the global climate crisis.

Jury :

• Sabrina Speich, Rapportrice, ENS-IPSL
• Jean-Baptiste Sallée, Rapporteur, CNRS
• Isabelle Dadou, Examinatrice, Université Toulouse III – Paul Sabatier
• Ernesto Rodriguez, Examinateur, Jet Propulsion Laboratory
• Rosemary Morrow, Directrice de thèse, Université Toulouse III – Paul Sabatier
• Oscar Vergara, Co-directeur de thèse, Collecte Localisation Satellite (CLS)
• Laura Gomez-Navarro, Membre invité, IMEDEA
• Lia Siegelman, Membre invité, University of California San Diego