Biogeochemical-Argo (BGC-Argo) acquisitions provide globally distributed, vertically resolved, and sustained observations of marine biogeochemical and bio-optical variability. Chlorophyll-a and underwater light field profiles offer good opportunities to investigate the environmental conditions that regulate phytoplankton dynamics and primary production, also provide an independent observational basis for evaluating the bio-optical relationships used in ocean colour algorithms, ecosystem studies, and operational biogeochemical products.
Here, we present recent and ongoing work that leverages BGC-Argo observations to improve the characterization of upper-ocean bio-optical variability.
First, using measurements from 444 BGC-Argo floats collected between 2012 and 2025, we conducted a global reassessment of widely used bio-optical relationships linking surface chlorophyll-a to diffuse attenuation coefficients Kd and euphotic depth Zeu in open oceans. These quantities describe the underwater light environment available for photosynthesis and are therefore relevant to interpreting phytoplankton and biogeochemical variability. Evaluation with independent model training and testing showed that modelling tailored to different optical water classes across Case 1 waters better represented variations in the relationships among chlorophyll-a, Kd(380), Kd(490), and Zeu. The class-specific refits improved agreement between observed and predicted quantities, demonstrating how BGC-Argo observations can refine bio-optical models across Case 1 optical regimes.
Building on this reassessment, ongoing work within Euro-Argo ONE project (Horizon Europe) investigates how BGC-Argo observations can support the assessment of Copernicus Marine Service ocean colour products. Specifically, daily chlorophyll-a and Kd(490) products are being matched with BGC-Argo observations at global and regional scales. This cross-platform framework quantifies the contribution of autonomous profiling floats to matchup availability since 2012, complements conventional ship-based validation datasets, and reduces observational gaps in poorly sampled regions and seasons. Particular attention is given to Kd(490), for which in situ validation remains limited in several operational products.
Together, these studies demonstrate how BGC-Argo can connect vertically resolved ocean observations with satellite-derived surface products. The resulting framework supports the reassessment of bio-optical parameterizations, the evaluation of operational ocean colour products, and the future integration of autonomous and satellite observations into four-dimensional representations of marine ecosystem and biogeochemical variability.
 

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