HR: 16:15h
AN: GP34A-02    [Abstracts]
TI: Dust and Nutrients in Modern and Late Quaternary Ecosystems of Central Colorado Plateau Drylands
AU: * Reynolds, R L
EM: rreynolds@usgs.gov
AF: U.S. Geological Survey, Box 25046, MS 980, Denver, CO 80225 United States
AU: Reheis, M C
EM: mreheis@usgs.gov
AF: U.S. Geological Survey, Box 25046, MS 980, Denver, CO 80225 United States
AU: Yount, J
EM: yount@usgs.gov
AF: U.S. Geological Survey, Box 25046, MS 980, Denver, CO 80225 United States
AU: Goldstein, H
EM: hgoldstein@usgs.gov
AF: U.S. Geological Survey, Box 25046, MS 980, Denver, CO 80225 United States
AU: Roberts, H M
EM: hmr@aber.ac.uk
AF: University of Wales, Inst. of Geography and Earth Sciences, Aberystwyth, SY23 3DB United Kingdom
AU: Neff, J C
EM: jason.c.neff@colorado.edu
AF: University of Colorado, Dept. of Geological Sciences, Boulder, CO 80309 United States
AB: The inputs of rock-derived nutrients to ecosystems, along with pedogenic and geomorphic processes that distribute nutrients in substrates, are critical aspects of ecosystem dynamics. Stratigraphic, geochronologic, magnetic, chemical, biogeochemical, and textural studies of late Quaternary surficial deposits (including modern and buried soils) on the central Colorado Plateau reveal important ecological roles for far-traveled dust and document the redistribution of deposited dust across the landscape through geomorphic processes. In vast upland settings underlain by nutrient-poor Paleozoic and Mesozoic eolian sandstone, alternating episodes of dune activity and soil formation during the late Pleistocene and Holocene have produced dominantly sandy deposits that support grass and shrub communities. In these deposits, isothermal remanent magnetization (IRM) acquired at 0.3 Tesla provides a measure of eolian dust abundance. Magnetic and petrographic studies indicate that IRM is carried by silt-size Ti-magnetite and is unaffected by pedogenic growth or destruction of iron oxides. Such magnetite is absent in local bedrock, and it thus represents far-traveled dust. Magnetite (dust) abundance, redistributed by modern slope processes, increases systematically down shallow-gradient hillslopes, and it correlates strongly with potential nutrients (e.g., K, Na, P, Mn, Zn). Magnetite and potential nutrients also covary with depth in auger holes (2-3 m) and soil pits in dune-crest, dune-swale, and other geomorphic settings. Magnetite abundance further correlates strongly with elements (e.g., Ti, Li, As, Co, Ni, Th, La, Sc) that are geochemically stable in these environments. Amounts of magnetite and associated potential nutrients vary greatly (as much as 5x) in deposits accumulated over the past ~20-30 ka. Magnetite abundance and its relations to particle-size distribution, hematite abundance, and elemental abundances change sharply in sediment corresponding to 15-10 ka and 5-4 ka, and to deposition over the last century. These changes likely reflect shifts in source regions, the most recent one perhaps in response to human activity in and beyond the Colorado Plateau. Changes in dust accumulation in these surficial deposits during the late Quaternary are important to modern ecosystem dynamics because some plants today tap nutrients deposited as long ago as about 12-15 ka and because eolian dust at depth influences soil-moisture capacity.
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1615 Biogeochemical processes (4805)
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 0305 Aerosols and particles (0345, 4801)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting