Denudation and Weathering Rates of Carbonate Landscapes From Meteoric 10Be/9Be Ratios

Abstract

Knowledge of the rates of carbonate rock denudation, the relative apportionment of chemical weathering versus physical erosion, and their sensitivity to climate, vegetation, and tectonics is essential for disclosing feedbacks within the carbon cycle and the functioning of karst landscapes that supply important services to humans. Currently, however, for carbonate lithologies, no method exists that allows to simultaneously partition denudation into erosion and weathering fluxes at spatial scales ranging from soil to watersheds. To determine total denudation rates in carbonate landscapes from an individual soil or river sample, we adapted a published framework that combines cosmogenic meteoric 10 Be as an atmospheric flux tracer with stable 9 Be that is released from rocks by weathering, to the limestone‐dominated French Jura Mountains. By analyzing water, soil, sediment, travertine, and bedrock for 10 Be/ 9 Be, major and trace elements, carbon stable isotopes and radiogenic strontium, we quantified contributions of Be from primary versus secondary carbonate phases and its release during weathering from carbonate bedrock versus silicate impurities. We calculated partitioning of Be between solids and solutes, and rates of catchment‐wide (from sediment) and point source (from soil) denudation, weathering and erosion. Our results indicate that average denudation rates are 300–500 t/km 2 /yr. Denudation is dominated by weathering intensity (W/D) ratios of >0.92, and a non‐negligible contribution from deeper (below soil) weathering. Our rates agree to within less than a factor of two with decadal‐scale denudation rates from combined suspended and dissolved fluxes, highlighting the substantial potential of this method for future Earth surface studies.