HR: 11:50h
AN: PP22A-07    [Abstracts]
TI: 55,000 yrs of Environmental Change in the Southern Hemisphere: Peat Stratigraphy and Inorganic Geochemistry of Lynch's Crater, NE Queensland, Australia.
AU: * Muller, J
EM: joanne.muller@jcu.edu.au
AF: School of Earth Science, James Cook University, Douglas, Townsville, Qld 4810 Australia
AU: Kylander, M E
EM: malin.kylander@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College, South Kensington, London, SW7 2AZ United Kingdom
AU: Wust, R A
EM: raphael.wust@jcu.edu.au
AF: School of Earth Science, James Cook University, Douglas, Townsville, Qld 4810 Australia
AU: Weiss, D J
EM: d.weiss@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College, South Kensington, London, SW7 2AZ United Kingdom
AB: This study presents one of the first applications of geochemical proxies to define changes in vegetation, hydrology and atmospheric dust recorded in a peat deposit in the Southern Hemisphere. The Lynch's Crater archive has captured local, regional and global environmental changes and reveals dynamic ecosystem changes as a result of climate shifts over the past 55,000 yrs BP. The 13 m peat record consists of 1.5 m of ombrotrophic peat underlain by a minerotrophic peat. The ombrotrophic section consists of low inorganic content ("ash") and low pH, as expected in of an ombrotrophic environment. The minerotrophic section contains several layers, up to a few cm thick, where abundant sponge spicules, diatom fragments and detrital quartz are indicative of high algal and protista productivity. These layers are characterised by high (up to 50%) ash, indicating persistent flooding of the peat deposits of Lynch's Crater and signalling periods of change in precipitation in North Queensland, Australia. Geochemical data are used to differentiate between climatic episodes associated with flooding events and internal and external atmospheric dust fluxes. Lead isotopes with lithogenic and chalcophile elements tell us that two distinctive sources are prevalent in the Lynch's Crater record. Most of the inorganic fractions of the deposits have the same geochemical signatures as the rocks and sediments of the crater wall, with low As concentrations, high Al, Ti and Sc concentrations and a more radiogenic Pb isotope signature. Influence from long-range dust is distinguished in the lower sections of the core (~35,000-55,000 cal yrs BP) where increases in As concentrations and less radiogenic Pb isotopes are found. Leading up to the Holocene (~35,000-10,000) the influence of increased dust influx becomes more significant (increasing lithogenics, chalcophiles and ash content) and where possible long-range sources are still active, but diluted by a prevailing dominance of the local sources. During the Holocene Pb isotope signatures remain similar but lithogenic and chalcophile concentrations decrease significantly and coincide with the lowest ash values (~4%) in the core. The research shows Lynch's Crater is a sensitive record of past atmospheric dust cylces and precipitation regimes leading to an invaluable record of past environmental change in the Southern Hemisphere.
DE: 0429 Climate dynamics (1620)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 1125 Chemical and biological geochronology
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005