Evolution of Air-Sea Fluxes in Modeled Long-Lived Mesoscale Eddies in the South Atlantic Ocean

Mesoscale eddies modify physical and biogeochemical properties, facilitating the exchange of heat and CO2 between the surface, mixed-layer and ocean interior. Most state-of-the-art Earth System Models fail to resolve mesoscale processes (10 - 100km) due to computational constraints, thus contributing to uncertainties in current and future projections of ocean heat and CO2 fluxes. While recent advances have shown progress in understanding regional and seasonal mean characteristics of eddies, their impact on air-sea fluxes over the eddy life cycle remains poorly understood. We use a high-resolution (1/12°) ocean physical-biogeochemical (NEMO-PISCES) model to investigate the temporal evolution air-sea heat and CO2 fluxes in long-lived (> 90 days) eddies in the South Atlantic Ocean. These eddies have varying lifespans, different propagation pathways, regional and seasonal dynamics. Examining these features reveals important nuances in their impact on air-sea heat and CO2 fluxes. We find a high occurrence (~30%) of "abnormal eddies", defined as cold surface anticyclonic and warm surface cyclonic eddies, emerging more frequently in longer-lived eddies, which can weaken or reverse the direction of air-sea fluxes. Long-lived anticyclonic eddies sustain heat fluxes to the atmosphere and reduced CO2 uptake throughout the eddy life cycle. In contrast, cyclonic eddies in the South-East Atlantic exhibit declining heat uptake with time, highlighting an asymmetry between eddies of different polarities. This asymmetry extends to other regions of the South Atlantic when considering CO2 fluxes. Understanding these dynamics is necessary to improve air-sea flux projections, inform mesoscale parameterizations that influence the carbon-climate sensitivity of the Southern Ocean.