Complex soil mass redistribution along a catena using meteoric and in-situ 10Be as tracers

In hilly and mountainous landscapes, the bedrock is actively converted to a continuous soil mantle. The bedrock-soil interface lowers spatially at the soil production rate, and the soil acts as a layer removing sediment produced locally and transported from upslope. Forested soils of a hummocky ground moraine landscape in Northern Germany exhibit strongly varying soil thicknesses with very shallow soils on crest positions and buried soils at the footslope. We explored the explanatory power of both ¹⁰Be forms (in situ and meteoric) for forest soils on a hillslope to shed light into the complex mass redistribution. Our main research questions were: how do meteoric and in-situ ¹⁰Be compare to each other? What do they really indicate in terms of soil processes (erosion, sedimentation, reworking)? By using both types of ¹⁰Be, the dynamics of soils and related mass transports should be better traceable. Both ¹⁰Be forms were measured along three profiles at different slope positions: Hydro1 (summit), Hydro3 (shoulder), Hydro4 (backslope). Furthermore, a buried horizon was found in the profile Hydro4 at 160 cm depth and ¹⁴C-dated. The distribution pattern of meteoric ¹⁰Be of Hydro4 shows an inverse exponential depth profile, and an almost uniform content of in-situ ¹⁰Be along the profile. Meteoric ¹⁰Be indicates on the one hand that a new soil was put on top of an older, now buried soil. On the other hand, meteoric ¹⁰Be is involved in pedogenetic processes and clearly exhibits clay eluviation in the topsoil and clay illuviation in the subsoil. The uniform content of the in situ ¹⁰Be shows soil mixing that must have occurred during erosion and sedimentation. The¹⁴C dated buried soil horizon indicates a deposition of eroded soil material about 7 ka BP. Consequently, an increase in the in-situ ¹⁰Be content towards the surface should be expect which however was not the case. The reason for this is so far unknown. Radiocarbon dating and ¹⁰Be data demonstrate that strong events of soil mass redistribution in Melzower Forest are mainly a result of ancient natural events. Further measurements of fallout radionuclides (^239+240Pu) showed no erosion for the last few decades in the same catchment.