Modelling detrital cosmogenic nuclide concentrations during landscape evolution in CIDRE V2.0

Abstract. The measurement of cosmogenic nuclide (CN) concentrations in riverine sediment has provided breakthroughs in our understanding of landscape evolution. Yet, linking this detrital CN signal and the relief evolution is based on hypotheses that are not easy to verify in the field. A model would help to better understand the statistics of CN concentrations in sediment grains. In this work, we present a coupling between the landscape evolution model Cidre and a model of the CN concentration in distinct grains. These grains are exhumed and detached from the bedrock and then transported in the sediment to the catchment outlet with temporary burials and travel according to the erosion-deposition rates calculated spatially in Cidre. The concentration in the various CN can be tracked in these grains. Because the CN concentrations are calculated in a limited number of grains, they provide an approximation of the whole CN flux. Therefore, this approach is limited by the number of grains that can be handled in a reasonable computing time. Conversely, it becomes possible to record part of the variability in the erosion-deposition processes in the grain-by-grain distribution of the CN concentrations by tracking the CN concentrations in distinct grains using a Lagrangian approach. We illustrate the robustness and limits of this approach by deriving the catchment-mean erosion from the ¹⁰Be mean concentration of grains leaving a synthetic catchment uplifting at different rates and by comparing this derived erosion rate to the actual one calculated by Cidre.