A new peer-reviewed study led by Daniel Ford has been published in Earth System Science Data, presenting a spatially and temporally complete global surface chlorophyll-a (chl-a) data record spanning 1997–2024.
Chl-a is an essential climate variable widely used to understand marine ecosystems, primary production, and the ocean’s role in the global carbon cycle. While satellite observations have enabled high-quality, long-term chl-a climate data records, they suffer from persistent data gaps caused by cloud cover and the absence of sunlight during the polar winter. These gaps present a major challenge for global climate studies, data assimilation, and machine-learning applications that require spatially complete inputs.
The newly published dataset addresses this challenge by combining satellite ocean-colour observations with biogeochemical Argo (BGC-Argo) float data. Cloud-affected regions were reconstructed using an established spatial kriging approach, while missing polar winter data were filled using relative changes observed in wintertime BGC-Argo chl-a, anchored to satellite observations from the preceding autumn or following spring in each hemisphere. Importantly, uncertainties are retained and explicitly modified to account for the gap-filling process, ensuring consistency with climate data record standards.
Independent validation against in situ measurements shows that the accuracy and precision of the underlying satellite data are maintained, even in the reconstructed wintertime periods. The resulting dataset reveals realistic seasonal cycles driven by light availability, as well as clear interannual and hemispheric variability in polar chl-a.
The 26-year global, monthly chl-a dataset, provided at 0.25° spatial resolution, is openly available and represents a valuable new resource for climate research, model assimilation and ocean carbon studies.
This work was a joint effort between SCOPE, the sister project Ocean Carbon for Climate alongside partially support from the OceanICU project.
Publication details
Ford, D. J., Kulk, G., Sathyendranath, S., and Shutler, J. D. (2026). Decadal and spatially complete global surface chlorophyll-a data record from satellite and BGC-Argo observations. Earth System Science Data, 18, 569–584.
https://doi.org/10.5194/essd-18-569-2026
Data access
The full global dataset is available via Zenodo:
https://doi.org/10.5281/zenodo.15689006