HR: 11:20h
AN: H42B-05    [Abstracts]
TI: Climate Does Matter: Quantifying Rates and Processes for a Southern California Climate Gradient
AU: * Dixon, J L
EM: jean.dixon@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Heimsath, A M
EM: arjun.heimsath@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Kaste, J M
EM: james.kaste@dartmouth.edu
AF: Dartmouth College, Dept. of Earth Sciences, Hanover, NH 03755 United States
AU: Amundson, R
EM: earthy@nature.berkeley.edu
AF: Division of Ecosytem Sciences, Univ. of California, Berkeley, CA 94720 United States
AB: Climate impacts Earth surface evolution by helping to set erosional processes. Despite the critical link between climate forcing and landscape change, field-based studies quantifying the connection are rare. Here, we use four independent, field-based methodologies to examine rates and mechanisms of erosion and provide a mechanistic connection between climate forcing and landscape response. We focus on a well-studied climate gradient for the southwestern Sierra Nevada, California, using four climate zones from the low elevation oak grasslands to the high, periglacial crest of the range. Catchment-averaged, hillslope and bare rock erosion rates are quantified using in situ produced cosmogenic 10-Be. Nuclide-determined denudation rates range from about 30 to 300 m/Ma, depending on erosional process. We also analyzed the fallout-delivered short-lived nuclides, 210-Pb and 137-Cs, in soils, as well as the bulk and trace chemistry of soils and saprolite for the climatic end-members (high and low elevation field sites) to quantify dominant transport processes and chemical weathering rates. Results show three orders of magnitude differences in soil zirconium percent depletion between the extremes, quantifying higher intensities of chemical weathering at lower elevations. Chemical weathering rates range from about 3 m/Ma at the high elevation site to about 70 m/Ma at the low elevation site, accounting for 12 to 70 % of the total denudation, respectively. Additionally, activity profiles for fallout 210-Pb and 137-Cs differ markedly between sites. Deeper profiles and subsurface activity maxima at the low elevation site indicate the dominance of soil transport by mammal burrowing, while depth depletion of nuclides at the high elevation site suggests surface sediment removal by overland flow. When combined, our results from these independent methodologies quantify how climate helps drive land surface evolution.
DE: 1815 Erosion
DE: 1824 Geomorphology: general (1625)
DE: 1854 Precipitation (3354)
DE: 1860 Streamflow
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: Fall Meeting 2005