Tracking recent climatic and anthropogenic perturbations of surface processes in the French Massif Central from paired 14Cin situ and 10Be analysis

Understanding landscape evolution over Late Quaternary timescales requires quantifying transient erosion responses to climatic and anthropogenic forcings. The paired cosmogenic nuclide system 10 Be– 14 C in situ offers unique insights into surface process variations across 1–10 ka timescales owing to their strongly contrasting half-lives. We present new 14 C in situ measurements in river sediment combined with existing 10 Be data from ten catchments along the southeastern margin of the French Massif Central to investigate recent landscape dynamics. All samples indicate a state of temporal disequilibrium in the 10 Be– 14 C in situ system, with 14 C in situ -derived denudation rates being up to five times higher than 10 Be-derived rates. This pattern suggests recent intensification of surface processes. The magnitude of disequilibrium varies spatially, with the strongest signal in the steep catchments of the Cévennes east of the main drainage divide with the Rhône basin. We employ a novel inversion framework incorporating hilltop curvature measurements and hillslope transport theory to reduce parameter space and account for regional similarities in denudation dynamics. Two transient scenarios can explain the observations: an increase in denudation rate around 15–5 ka BP, possibly associated with the Pleistocene–Holocene transition, or recent soil removal events within the last few centuries linked to historical deforestation, although the available data do not allow us to unambiguously discriminate between the two. Our results demonstrate the sensitivity of the 10 Be– 14 C in situ system to recent landscape perturbations and highlight the complex interplay between climatic transitions and anthropogenic forcing in shaping temperate mid-elevation mountain landscapes.