Constraining soil formation and development through quantitative analyses of chemical weathering and physical erosion

At the Earth surface, the terrestrial life is supported by a thin soil mantle. Human activities can alter soil physical and chemical properties to the extent that humans are now identified as the sixth soil forming factor. Yet, quantitative data on natural soil development processes are hardly needed to distinguish anthropogenic from natural changes in the soil system. This dissertation aims to provide new insights on soil development on time scales of 103 to 105 years for two critical zone observatories: the Betic Cordillera (southeast Spain) and the Rio Grande Do Sul (southern Brazil). In the first part, the coupling between chemical weathering and physical erosion is analyzed based on chemical depletion and total denudation. In the semi-arid environment of the Betic Cordillera, soil weathering extents increase with soil thickness and decrease with increasing surface denudation rates, consistent with kinetically limited weathering. In the deeply weathered soils of southern Brazil, the soil development is strongly controlled by local topography, with increasing chemical depletion downslope. In the second part, the widely accepted concept of steady state soil thickness is challenged for thin soil profiles based on analytical data from in-situ produced cosmogenic nuclides and U-series disequilibria. In the third part, meteoric 10Be is used as a geochemical tracer for quantifying long-term soil denudation rates. Given the low retention of meteoric 10Be in highly weathered soil profiles, a new laboratory protocol involving sequential extraction of Be from the mineral reactive phases is developed and tested. The dissertation demonstrates the potential of employing multiple geochemical techniques to provide new insights in the rates of soil development, chemical weathering and surface denudation.