Challenges in the geochronological interpretation of sedimentary records: examples from the Cantabrian coast (N Spain)

²¹⁰Pb short-lived radionuclide provides a valuable tool for reconstructing depositional histories and environmental changes over the last ~ 110 years. However, the complex environmental dynamics and the numerous anthropogenic processes that characterize coastal areas have the potential to disrupt radionuclide activity profiles in geological archives and, therefore, to hinder the accuracy of geochronological models. In this study, we evaluate the radioisotopic records (²¹⁰Pb, ¹³⁷Cs, and ^239+240Pu) of five case studies representing different environmental conditions in Cantabrian coast estuaries, through a multidisciplinary perspective that combines sedimentological (grain size), micropaleontological (benthic foraminifera), and geochemical (trace metals and Hg) data, alongside documentary records (historical aerial photography). Distinct downcore radionuclide fingerprints were identified and classified into four different profile styles: ideal, smoothed, interrupted, and erosional. The integration of multiproxy evidence allowed the validation of ²¹⁰Pb-derived geochronological frameworks and, in those cases where absolute chronology could not be obtained, to establish relative age models. The study highlights the importance of a critical evaluation of radionuclide profiles within a multiproxy approach to accurately reconstruct the recent environmental transformation of coastal ecosystems.