DECONSTRUCTING THE CLIMATE-EROSION CONNECTION

Climate influences the evolution of Earth's Surface by controlling erosion and weathering processes. The fundamental nature of this relationship remains poorly quantified, despite broad interest both in landscape evolution and climate dynamics. Here, we examine both rates and processes of weathering and erosion, using a robust field-based approach to examine the mechanistic links between climate forcing and landscape response. Our study focuses on a climate gradient along the western slope of the Sierra Nevada, California. The 64 km elevation transect extends over 2600 m in elevation across uniform, unglaciated granodiorite bedrock, maximizing the influence of climate on surface processes. We examined zero to second order catchments within five climatically distinct zones. Total denudation was measured using cosmogenic ¹⁰Be for hillslopes, bare rock, and catchment average rates. We show little variation in total denudation rates across climate zones. Physical and chemical components of denudation vary widely, though not systematically, across the climate gradient. Chemical weathering rates range from ~ 1 m/Ma at the high elevation site to ~20 m/Ma at the low elevation site, accounting for ~ 1 to 90 % of the total denudation, respectively. Trends in chemical indices of alteration (CIA), calculated using immobile and mobile oxides, vary markedly from those of zirconium measurements at middle elevations, suggesting a decoupling of chemical weathering intensity and rates. Specifically, while mid elevation saprolites show the highest extent of weathering, they are weathering at the lowest rates. Finally, we use depth profiles of fallout nuclides, ²¹⁰Pb and ¹³⁷Cs, to quantify sediment transport processes. Combining these results from independent methodologies shows a tradeoff between chemical and physical processes across the climate zones, and provides unique insight into how landscapes respond to climate forcing.