HR: 0800h
AN: U31A-0010    [Abstracts]
TI: A Record of Multiple Sea-Level High-Stands for the Last 650 ka Preserved at Henderson Island, a Coral Atoll in the South Pacific
AU: * Andersen, M B
EM: andersen@erdw.ethz.ch
AF: ETH Zurich, Institute for Isotope Mineralogy and Mineral Resources, ETH Zentrum, Zurich, 8092 Switzerland
AU: Stirling, C
EM: stirling@erdw.ethz.ch
AF: ETH Zurich, Institute for Isotope Mineralogy and Mineral Resources, ETH Zentrum, Zurich, 8092 Switzerland
AU: Potter, E
EM: potter@erdw.ethz.ch
AF: ETH Zurich, Institute for Isotope Mineralogy and Mineral Resources, ETH Zentrum, Zurich, 8092 Switzerland
AU: Halliday, A
EM: halliday@erdw.ethz.ch
AF: ETH Zurich, Institute for Isotope Mineralogy and Mineral Resources, ETH Zentrum, Zurich, 8092 Switzerland
AU: Blake, S
EM: steve.Blake@anzlic.org.au
AF: ANZLIC National office, 91 Northbourne Avenue, Turner, ACT 2612 Australia
AU: McCulloch, M
EM: malcolm.McCulloch@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: Ayling, B
EM: bridget.Ayling@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 Australia
AU: O'Leary, M
EM: michael.oleary@jcu.edu.au
AF: School of Earth Sciences, James Cook University, Townsville, Qld 4811 Australia
AB: The U-series chronometer has a wide range of applications in paleoclimatology. Uranium-series dating of fossil coral reefs provides an excellent record of past sea-level high-stands and offers an independent test of the validity of the Milankovitch theory of climate change. However, U-series ages have a number of limitations, as many corals tend to display poorly understood open-system behaviour due to diagenesis, often leading to inaccurate ages. Also, the poor knowledge of the marine $^{234}$U/$^{238}$U in the past limits the accuracy of the method. Fossil corals from the last interglacial warm period, or MIS 5.5 ($\sim$125 ka), have been studied extensively, however data from older interglacial and interstadial periods are limited. This is mainly due to fewer accessible sample sites, and the tendency for older corals to exhibit a larger degree of diagenetic effects compared with younger MIS 5.5 corals. Another important issue for older samples is the necessity for superior measurement precision, in order to obtain precise ages from samples in which the radioactive isotopes have evolved to a state close to equilibrium. We present new U-series ages of corals from Henderson Island, a fossil coral atoll in the southern Pacific. Previous U-series ages for this locality show that reef growth occurred at $\sim$320 and $\sim$630 ka, correlating respectively with the MIS 9.3 and MIS 15 sea-level high-stands (Stirling {\ et al.}, Science 291, 290-93, 2001). Improved analytical techniques have been developed for the purpose of acquiring highly precise ages for old corals, such as those on Henderson Island. Measurements are conducted using a Nu Instruments Nu Plasma MC-ICPMS (Andersen {\ et al.}, Int. J. Mass Spec 237, 107-118, 2004). Our technique obtains superior precision compared to earlier U-series protocols, allowing 300 ka samples to be dated with age uncertainties of better than \pm 1 ky (2\sigma). Our newly acquired U-series ages for Henderson Island correlate with MIS 15, 9.3, 7.3 and 7.1. These data not only offer the possibility to test the validity of the Milankovitch theory for climate episodes occurring before MIS 5.5, but also allow processes of reef diagenesis to be constrained, and provide critical information on the marine $^{234}$U/$^{238}$U over the past 650 kyrs.
DE: 4825 Geochemistry
DE: 4860 Radioactivity and radioisotopes
DE: 4556 Sea level variations
DE: 1035 Geochronology
DE: 1620 Climate dynamics (3309)
SC: Union [U]
MN: 2004 AGU Fall Meeting