Soil production and hillslope transport in mid-latitudes during the last glacial-interglacial cycle: A combined data and modelling approach in northern Ardennes

The relative efficiency of various hillslope processes through Quaternary glacial–interglacial cycles in the midlatitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate-dependent hillslope evolution with an inversion algorithm in order to get deeper insight into
the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a ~ 2500km2 real area under a simple two-stage 120-kyr-long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function
in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges.We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first-order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm–cold and cold–warm transitions, when the mean annual temperature passes through the [0, 5 °C] range. We also point to the overwhelming importance of solifluction
in shaping hillslopes and transporting soil, and the role of depth-dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor.