HR: 0800h
AN: PP51A-0180    [Abstracts]
TI: Radiogenic and U-series isotopes in very low sedimentation rate sediments from Mendeleev Ridge (Arctic Ocean): sources, mineral carriers and stratigraphic implications
AU: * HILLAIRE-MARCEL, C
EM: chm@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Darby, D
EM: ddarby@odu.edu
AF: Old Dominion University, 4600 Elkhorn Ave, Norfolk, Va 23539, United States
AU: Francois, R
EM: rfrancoi@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T1Z4, Canada
AU: Helie, J
EM: helie.jean-francois@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Lamziouaq, R
EM: lamziouaq.reda@courrier.uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Not, C
EM: not.christelle@courrier.uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Polyak, L
EM: polyak.1@osu.edu
AF: Byrd Polar Research Center, Ohio State University 1090 Carmack Rd, Columbus, OH 43210, United States
AU: Preda, M
EM: preda.michel@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Satte, Y M
EM: satte.mohammed_yassir@courrier.uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AU: Stevenson, R
EM: stevenson.ross@uqam.ca
AF: GEOTOP - UQAM & McGill, CP 8888, Montreal, Qc H3C3P8, Canada
AB: Sedimentological and geochemical properties, U-series isotopes, radiogenic isotopes and anthropogenic radionuclides contents were determined on two cores from the Mendeleev Ridge. Excesses in 210Pb over 226Ra activities are observed down to 1.25 cm from core-tops, due to shallow mixing by benthic organisms. Below, 210Pb-activity follows 226Ra-activity in turn controlled by parent 230Th-excess fluctuations in the sediment, except for some 226Ra-diffusion towards the water column from core-top and on both sides of 230Thxs peaks below. Thus, estimating 210Pb-excess requires precise knowledge of 226Ra-supported fraction, i.e., of 230Th- excess and Ra-diffusion. Both cores depict identical grain size, mineralogical, geochemical and isotopic distributions, despite bathymetric difference. This suggests negligible impact of bottom currents, limited scavenging of heavy metals in the lower water column, and a net export of particle reactive U-daughter isotopes (Th, Pa, Pb) produced from the overlying water column. Peaks in 230Thxs and 231Paxs (0-7cm, 17 cm and 30 cm sub-bottom) match high contents in clays and fine carbonates (primarily dolomite), and likely indicate interglacial/interstadial conditions and/or occurrence of turbidity events (e.g., during deglaciations). These peaks correspond to maximum illite supplies, minimum Sr-isotope ratios and epsilon-Nd values in the -10 to -12 range. Interlayered sediments, with high sand but low carbonate contents, minimum clay fluxes (low illite relative contents), minimum 230Th and 231Pa excesses, maximum Sr-isotope ratios, possibly indicate full glacial conditions and significantly reduced sedimentation rates.
DE: 1015 Composition of the core
DE: 1040 Radiogenic isotope geochemistry
DE: 4924 Geochemical tracers
DE: 9315 Arctic region (0718, 4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting