HR: 0800h
AN: PP51A-0181    [Abstracts]
TI: Beryllium Isotope Dating of Sediment Cores From the Alpha Ridge, Arctic Ocean
AU: * Sellen, E
EM: emma.sellen@geo.su.se
AF: Department of geology and geochemistry, Stockholm University Svante Arrhenius vag 8C, Stockholm, 106 91, Sweden
AU: Jakobsson, M
EM: martin.jakobsson@geo.su.se
AF: Department of geology and geochemistry, Stockholm University Svante Arrhenius vag 8C, Stockholm, 106 91, Sweden
AU: Kubik, P W
EM: peter.kubik@psi.ch
AF: Paul Scherrer Institute, Villigen c/o Institute for Particle Physics of ETH, Zurich, 5232, Switzerland
AU: Frank, M
EM: mfrank@ifm-geomar.de
AF: IfM-GEOMAR Leibniz Institute for Marine Sciences, University of Kiel Wischhofstrasse 1-3, Kiel, 24148, Germany
AB: Poor preservation of biogenic calcium carbonate and biosilica in Arctic Ocean sediments has led to large problems regarding the establishment of a reliable chronostratigraphy. There are currently two differing sedimentation rate scenarios proposed for the Arctic Ocean. The first suggests sedimentation rates on the order of mm/ka and is based on cores from the Amerasian Basin, whereas the second suggests sedimentation rates on the order of cm/ka mainly derived from Eurasian Basin cores. Here we present dating results from cores HLY0503-09JPC and HLY0503-14JPC retrieved from the Alpha Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). These cores have been analyzed for seawater-derived beryllium (Be) isotopes in order to establish a chronostratigraphy. The isotopes ¹⁰Be and ⁹Be were extracted simultaneously from sample aliquots by using a leaching procedure. The decrease of 10Be concentration (half-life = 1.51 Million years) with depth in core provides first order sedimentation rates for the sampled cores. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope ⁹Be. The preliminary results show low downcore ¹⁰Be concentrations in both cores from the Alpha Ridge. Plotting ¹⁰Be against depth suggests an average sedimentation rate of ~2.9 mm/ka for core HLY0503-09JPC and ~2.3 mm/ka for HLY0503- 14JPC. The calculated ¹⁰Be/⁹Be ratios point to even lower average sedimentation rates of ~1.9 mm/ka for core HLY0503-09JPC and ~1.6 mm/ka for HLY0503-14JPC. However, core HLY0503-14JPC shows a pronounced variability of the ¹⁰Be concentration as well as for the ¹⁰Be/⁹Be ratio, which results in a large uncertainty of the calculated sedimentation rates. The ¹⁰Be concentrations for this core will be compared with the grain size record in order to reduce the scatter of the data. The preliminary beryllium isotope chronostratigraphy supports lower sedimentation rates in the Amerasian Basin compared to the Eurasian Basin. A long-term solid sea ice cover in the Beaufort Gyre may explain the low ¹⁰Be concentrations, but does not explain the calculated low sedimentation rates.
DE: 3022 Marine sediments: processes and transport
DE: 4918 Cosmogenic isotopes (1150)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting