Radiocarbon and 230Th data reveal rapid redistribution and temporal changes in sediment focussing at a North Atlantic drift |
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| Authors: | Gesine Mollenhauer Jerry F McManus Thomas Wagner I Nick McCave Timothy I Eglinton |
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| Institution: | 1. Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany;2. Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;3. School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK;4. Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK;1. Key Laboratory of Marine Sedimentology and Environmental Geology, The First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. College of Marine Geosciences, Ocean University of China; Key Laboratory of Submarine Geosciences and Prospecting, Qingdao 266100, China;4. Phuket Marine Biological Center, Phuket 83000, Thailand;5. Marine and Coastal Resource Research Center, Samut Sakhon Province 74000, Thailand;1. NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, 1790 AB Den Burg (Texel), The Netherlands;2. Utrecht University, Faculty of Geosciences, Budapestlaan 4, 3584 CD Utrecht, The Netherlands;1. Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands;2. Geological Institute, Eidgenössische Technische Hochschule Zürich, Switzerland;3. Department of Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, United States;4. Department of Chemistry, Wellesley College, Wellesley, United States;5. Laboratory for Ion Beam Physics, Eidgenössische Technische Hochschule Zürich, Switzerland;6. Scottish Universities Environmental Research Center, Glasgow, UK;7. Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, United States;8. Department of Earth System Science, University of California at Irvine, Irvine, United States;9. Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden;10. Department of Mathematics, Stockholm University, Stockholm, Sweden;1. Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg (Texel), The Netherlands;2. All-Russian Research Institute for Geology and Mineral Resources of the World Ocean (VNIIOkeangeologia), Ministry of Natural Resources, Russian Academy of Science, St. Petersburg, Russian Federation;3. Utrecht University, Faculty of Geosciences, P.O. Box 80.021, 3508 TA Utrecht, The Netherlands;1. Geological Institute, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland;2. Max Planck Institute for Chemistry, Mainz, Germany;3. Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland;4. Institute of Geochemistry and Petrology, ETH Zurich, Zurich, Switzerland;5. Department of Earth Sciences, University of Cambridge, Cambridge, Cambridgeshire, UK;1. Institute of Arctic and Alpine Research, Department of Geological Sciences, University of Colorado, Boulder, CO, 80303, USA;2. Biogeochemistry Research Centre, School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK;3. LOCEAN, CNRS, Sorbonne Université, Campus Pierre et Marie Curie, 4 Place Jussieu, Paris, France;4. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK |
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| Abstract: | In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (230Thxs) measurements on four sediment cores retrieved in 1649–2879 m water depth from two such high accumulation drift deposits in the Northeast Atlantic, Björn and Gardar Drifts. While 230Thxs inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results show that although focussing factors calculated from bulk sediment 230Thxs inventories may allow useful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing. |
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