Mesoscale eddies heterogeneously modulate CO2 fluxes in eddy-rich regions of the Southern Ocean

Abstract

Mesoscale eddies are known to influence the Southern Ocean biogeochemistry. However, the distinct contributions of cyclonic and anticyclonic eddies to air–sea CO2 fluxes, as well as their longer-term effects remain poorly studied. We present results from a 27-year global eddy-resolving ocean-biogeochemical simulation. We used the Okubo-Weiss parameter to classify the modeled flow regimes into cyclonic and anticyclonic eddies, peripheries, and the surrounding background waters. Our results reveal a heterogeneous influence of eddies depending on the region, driven by regional differences in eddy intensity and the gradients in background properties. The factors controlling CO2 fluxes within eddies follow the same degree of importance as in background waters, with 1pCO2 being the dominant factor. This is driven primarily by changes in dissolved inorganic carbon. Our analysis shows that eddies act as a persistent carbon sink on decadal timescales, while their influence on shorter timescales is more variable and strongly shaped by eddy polarity. Overall, mesoscale regimes exhibit higher carbon uptake efficiency, with anticyclonic eddies showing the highest efficiency. The ability of eddies to absorb carbon computed in our results is consistent with recent observational estimates, confirming that the model realistically represents the influence of mesoscale eddies on CO2 fluxes. Above all, the overall contribution of mesoscale eddies to carbon uptake across the Southern Ocean was relatively small, accounting for approximately 10 % of total and 1 % of anomalous carbon uptake. However, the regional influence is more pronounced in eddy-rich regions.