Climate Driven Tradeoffs in Chemical and Physical Landscape Denudation

Climate influences the evolution of soil mantled landscapes by altering the pace and patterns of erosion and weathering processes. To help constrain the control of climate forcing on landscape evolution, we quantified cosmogenic nuclide 10Be derived denudation rates for hillslopes and nested catchments along a 64km climate transect across the Sierra Nevada Range of California. The transect spans 2600m in elevation, across uniform granodiorite bedrock, from the grassland foothills to the periglacial crest of the range. Both temperature and precipitation vary systematically with elevation such that the transect of field sites define a clinosequence. Denudation rates are roughly constant across the transect, with a 5-31m/Ma range in hillslope denudation rates and a 25-59m/Ma range in catchment-averaged rates. Physical and chemical components of denudation are calculated using a mass balance approach with immobile zirconium and cosmogenic 10Be, and exhibit strong differences between climate zones. We find a systematic trade off between the relative fractions of chemical and physical erosion as a function of climate zone. At low elevations (~200m), in dry grasslands, chemical weathering accounts for between 70 and 90% of total denudation on hillslopes, while at high elevations (~3000m), physical erosion accounts for the bulk of landscape lowering (60-100%). At low- middle elevations (~1200m) physical erosion dominates denudation, and at upper-middle elevations (~2000m), denudation is balanced between physical and chemical components. These two sites fall within a single vegetative zone. The tradeoff at middle elevations occurs concurrently with strong soil texture differences and likely reflects variable weathering and transport process differences across the long-term averaged permanent snow line for the region. The repeated tradeoffs in chemical weathering and erosion across our climate gradient are a result of how climate affects the unique suite of soil erosion and production processes active on each landscape. Our results attest to the complexity of climate-landscape interactions and emphasize the need for a mechanistic approach towards quantifying the connections between climate forcing and landscape evolution.