Regolith production and transport at the Susquehanna Shale Hills Critical Zone Observatory, Part 2: Insights from meteoric 10Be

Regolith-mantled hillslopes are ubiquitous features of most temperate landscapes, and their morphology reflects the climatically, biologically, and tectonically mediated interplay between regolith production and downslope transport. Despite intensive research, few studies have quantified both of these mass fluxes in the same field site. Here we present an analysis of 87 meteoric Be-10 measurements from regolith and bedrock within the Susquehanna Shale Hills Critical Zone Observatory (SSHO), in central Pennsylvania. Meteoric Be-10 concentrations in bulk regolith samples (n=73) decrease with regolith depth. Comparison of hillslope meteoric Be-10 inventories with analyses of rock chip samples (n=14) from a 24m bedrock core confirms that >80% of the total inventory is retained in the regolith. The systematic downslope increase of meteoric Be-10 inventories observed at SSHO is consistent with Be-10 accumulation in slowly creeping regolith (similar to 0.2cmyr(-1)). Regolith flux inferred from meteoric Be-10 varies linearly with topographic gradient (determined from high-resolution light detection and ranging-based topography) along the upper portions of hillslopes at SSHO. However, regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick, near the base of hillslopes. Meteoric Be-10 inventories at the north and south ridgetops indicate minimum regolith residence times of 10.53.7 and 9.12.9 ky, respectively, similar to residence times inferred from U-series isotopes in Ma et al. (2013). The combination of our results with U-series-derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on SSHO hillcrests.