12 octobre 11h. En ligne.
Titre: 'Southern Ocean mesoscale eddies - Their impact on the uptake and transport of CO2, and their interaction with sea ice'
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Mesoscale eddies are a ubiquitous feature of the Southern Ocean circulation as the Antarctic Circumpolar Current and various fronts continuously generate them. The crucial role of these eddies for large-scale circulation and ocean ventilation has long been recognized. Additionally, they interact with the atmosphere, biogeochemistry, and cryosphere. I will introduce two of these cases of interaction in this presentation: The eddies' impact on uptake and transport of CO2, and their interaction with sea ice.To address the former, we developed a new ocean-sea ice-biogeochemical configuration based on the NEMO modeling platform with a global horizontal resolution of 1/2°, refined to 1/10° between 68°S-30°S. Mesoscale eddies are detected based on their dynamical properties, an inventory of individual eddies is built, and the eddies are then tracked to investigate their pathways and property changes. It is found that the anomalous outgassing of CO2 over anticyclones (or uptake of CO2 for cyclones) is driven by the carbon anomaly within the ocean's mixed layer.The same methodological framework for the detection and tracking of eddies is used to investigate the impact of mesoscale eddies on compact sea ice. Eddies are generated using an idealized, reentrant channel configuration of the MITgcm at 10 km horizontal resolution. The simulation shows that anticyclones trap water from further equatorward in their core and, as a result, transport warm anomalies towards the sea ice, while the cyclones have anomalously cold water at their core. The integrated effect of the lateral and vertical processes on sea ice is a reduced thickness over anticyclones (or enhanced thickness for cyclones).