UEx-L-Eddies: Decadal and global long-lived mesoscale eddy trajectories with coincident air-sea CO ₂ 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 (fCO2 (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).