UEx-L-Eddies: Decadal and global long-lived mesoscale eddy trajectories with coincident air-sea CO₂ fluxes and biogeochemical conditions

Abstract. Mesoscale eddies are prevalent features within the global ocean that modify the physical, chemical and biological properties as they move and evolve. These modifications can alter the air-sea exchange of CO₂, and therefore these features may be hotspots for enhanced or reduced CO₂ uptake compared to the surrounding environment. The understanding of the global and regional effect of mesoscale eddies on ocean CO₂ uptake is however limited and largely based on single eddies or small regional subsets. Here, we provide a global dataset of 5996 long lived eddies trajectories (lifetimes greater than a year) with corresponding air-sea CO₂ fluxes all tracked using a Lagrangian approach between 1993 to 2022. The trajectories comprise 3244 anticyclonic (‘warm core’) and 2752 cyclonic (‘cold core’) eddies and the dataset provides the biogeochemical conditions, including the CO₂ fluxes, within and outside each eddy. The dataset refines a previous regional methodology with a focus on climate quality environmental parameters and uses a global neural network for estimating the fugacity of CO₂ in seawater (fCO_{2 (sw)}) along with a comprehensive air-sea CO₂ flux uncertainty budget. These refinements provide a robust foundation for studying the modulation of air-sea CO₂ fluxes by mesoscale eddies. As an example use of the dataset, we investigate the role of mesoscale eddies in modifying the global and regional air-sea CO₂ fluxes, by comparing the eddy driven air-sea CO₂ flux to that of the surrounding environment. We find that globally, long-lived anticyclonic eddies enhanced the CO₂ sink by 4.5 ± 2.8 % (95 % confidence), while long-lived cyclonic eddies reduce the CO₂ sink by 0.7 ± 2.6 %. Collectively, the long-lived eddies indicate an enhancement of the ocean CO₂ sink by 2.7 ± 1.1 Tg C yr^-1. Propagating the air-sea CO₂ flux uncertainties was found to be a key component needed to fully understand apparent differences between previous regional and global studies. The long lived eddies (UEx-L-Eddies) dataset is available on Zenodo at https://doi.org/10.5281/ZENODO.16355763 (Ford et al., 2025).