HR: 11:25h
AN: H52B-05    [Abstracts]
TI: Chemical Weathering Rate and Climate: Measurements in the Idaho Batholith
AU: * Ferrier, K L
EM: ferrier@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, 340 McCone Hall, Berkeley, CA 94720-4767, United States
AU: * Ferrier, K L
EM: ferrier@eps.berkeley.edu
AF: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, P.O. Box 808 L-206, Livermore, CA 94550, United States
AU: Kirchner, J W
EM: kirchner@eps.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, 340 McCone Hall, Berkeley, CA 94720-4767, United States
AU: Kirchner, J W
EM: kirchner@eps.berkeley.edu
AF: Swiss Federal Institute for Forest, Snow and Landscape Research, Zürcherstrasse 111, Birmensdorf, CH-8903, Switzerland
AU: Finkel, R C
EM: finkel1@llnl.gov
AF: Department of Earth and Planetary Science, University of California, Berkeley, 340 McCone Hall, Berkeley, CA 94720-4767, United States
AU: Finkel, R C
EM: finkel1@llnl.gov
AF: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, P.O. Box 808 L-206, Livermore, CA 94550, United States
AB: Many biogeochemical and Earth surface processes depend critically on chemical weathering. Chemical weathering supplies nutrients to soils, accelerates physical erosion by weakening bedrock, and buffers Earth's climate over geologic time by modulating atmospheric carbon dioxide concentrations. Measurements of chemical weathering rates (and of their dependence on external factors such as climate) are thus important for understanding the biogeochemical evolution of the soil-bedrock system and the geomorphological evolution of the Earth's surface. Chemical weathering fluxes can be measured in mountainous terrain using cosmogenic radionuclide measurements of long-term denudation rates, coupled with measurements of the rock-to-soil enrichment of chemically inert tracers. Here we use this method to measure chemical weathering fluxes at a series of sites along a 1500-meter altitudinal transect on Pilot Peak in the granitic Idaho Batholith. Concentrations of cosmogenic ¹⁰Be in soil-borne quartz indicate that total denudation rates range from 61±5 to 201±17 t km^-2 yr^-1 among the sites on this elevation transect. In rock and soil samples from the same sites, concentrations of zirconium --- an element we assume is chemically immobile --- are slightly enriched in soil relative to parent rock, implying that chemical weathering fluxes account for 0-20% of the total denudation rate. When combined, these ¹⁰Be and zirconium data imply that chemical weathering fluxes at these sites range from -5±8 to 30±4 t km^-2 yr^-1, and are fastest at the highest elevations where it is coldest -- contrary to the expectation that chemical weathering rates should decrease as temperature decreases. This suggests that variations in factors other than temperature are the dominant controls on chemical weathering rates at Pilot Peak.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1807 Climate impacts
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting