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Efficient extraction of past seawater Pb and Nd isotope signatures from Southern Ocean sediments
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  • Huang Huang,
  • Marcus Gutjahr,
  • Gerhard Kuhn,
  • Ed Hathorne,
  • Anton Eisenhauer
Huang Huang
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel

Corresponding Author:[email protected]

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Marcus Gutjahr
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
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Gerhard Kuhn
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
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Ed Hathorne
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
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Anton Eisenhauer
GEOMAR Helmholtz Centre for Ocean Research Kiel, GEOMAR Helmholtz Centre for Ocean Research Kiel
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Abstract

Radiogenic lead (Pb) and neodymium (Nd) isotope compositions extracted from authigenic phases in marine sediments are sensitive tracers to reconstruct past ocean circulation and water mass mixing. Chemical reductive leaching of hydrogenetic ferromanganese oxyhydroxides from bulk sediments is the most practical way to recover past seawater Pb and Nd isotope signatures in the Southern Ocean, due to the scarcity of alternative archives. However, the leached signal could be compromised if substantial quantities of Pb and Nd were released from non-hydrogenetic sediment fractions during chemical extraction. Here we developed a very short 10-seconds leaching method to extract reliable seawater Pb and Nd isotope signals from sediments in the Atlantic sector of Southern Ocean. The effect of a previously recommended MgCl prewash, the role of chelate ligands in the leaching solution and length of leaching time were investigated. The results show that 10 seconds exposure time of sediments to reductive leaching extracted sufficient and more reliable hydrogenetic Pb and Nd compared with the commonly used 30-minute leaching approaches. The robustness of our improved leaching method was validated via direct comparison of Pb and Nd isotope signatures with actual seawater, porewater and corresponding sediment leachates from three stations in front of the Antarctic Filchner-Rønne Ice Shelf. Our findings suggest that in contrast previously studied sites on the West Antarctic continental shelf, the southern Weddell Sea shelf is not a location of pronounced benthic Nd fluxes to the water column.
Mar 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 3. 10.1029/2020GC009287