| 14 Aug 2025
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 (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).
This manuscript presents a global dataset of long-lived mesoscale eddies (1993–2022) that includes coincident environmental variables, neural-network–based estimates of surface ocean fugacity of CO₂ (fCO₂(sw)), and derived air–sea CO₂ fluxes with comprehensive uncertainty budgets. The dataset builds on the authors’ earlier regional work by integrating a satellite-derived global eddy atlas, reanalysis products, and a refined neural-network methodology (UExO-FNN-U) for estimating fCO₂(sw). Using this global dataset, the authors investigate how long-lived eddies modulate global air–sea CO₂ fluxes and compare their results with other recent estimates obtained using different methods. The findings suggest that anticyclonic eddies tend to enhance the CO₂ sink, while cyclonic eddies slightly reduce it, although the underlying mechanisms remain unclear. Overall, this dataset represents a valuable contribution to the community by improving our understanding of how coherent mesoscale eddies influence air–sea CO₂ exchange. I recommend publication after the following concerns are addressed: