QUANTIFYING SOIL PRODUCTION AND TRANSPORT PROCESSES

Soil-covered upland landscapes comprise a critical part of the habitable world. Our understanding of how they evolve as a function of different climatic, tectonic, and geologic regimes is important across a wide range of disciplines and depends, in part, on understanding the links between chemical and physical weathering processes. Our extensive previous work showed that soil production rates decrease with increasing soil column thickness, but did not measure chemical weathering rates, or the underlying strength of the weathered bedrock. Soil production rates also vary extensively with field location. Here we use in situ produced cosmogenic nuclides (10-Be and 26-Al) to determine soil production rates, and show how we couple these measurements with several new methodologies to quantify the underlying material strength, weathered state, and chemical weathering rate. Specifically, we use measurements of the immobile element Zr in soils and saprolite with our rates of total denudation to determine chemical weathering rates. Major and trace element analyses, as well as measurements of pH, quantify the extent of weathering in the saprolite, while measurements of shear strength constrains the competence of the weathered bedrock underlying the soil mantle. In addition, we use the short-lived isotopes (210-Pb and 137-Cs) to quantify soil mixing and transport processes and rates. Field sites include two upland landscapes in northern California, three field sites across the passive margin escarpment of southeastern Australia, and a field site in the Hubbard Brook Experimental Forest of New Hampshire. Results from this multi-pronged approach are extensive, but will be focused here to show how a diverse set of field measurements can significantly improve our understanding of how soil mantled landscapes are eroding.