4.7 Article

Controls on the barium isotope compositions of marine sediments

Journal

EARTH AND PLANETARY SCIENCE LETTERS
Volume 481, Issue -, Pages 101-110

Publisher

ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2017.10.019

Keywords

barium isotopes; marine sediments; marine barium cycle; paleo-oceanography; GEOTRACES

Funding

  1. Shell Global Solutions BV
  2. NERC grants [NE/F017197/1, NE/H004394/1]
  3. NERC fellowship [NE/K009532/1]
  4. NERC [NE/H004394/1, NE/K009532/1, NE/F017197/1] Funding Source: UKRI
  5. Natural Environment Research Council [NE/H004394/1, NE/K009532/1, NE/F017197/1] Funding Source: researchfish

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The accumulation of barium (Ba) in marine sediments is considered to be a robust proxy for export production, although this application can be limited by uncertainty in BaSO4 preservation and sediment mass accumulation rates. The Ba isotope compositions of marine sediments could potentially record insights into past changes in the marine Ba cycle, which should be insensitive to these limitations, enabling more robust interpretation of sedimentary Ba as a proxy. To investigate the controls on the Ba isotope compositions of marine sediments and their potential for paleo-oceanographic applications, we present the first Ba isotope compositions results for sediments, as well as overlying seawater depth profiles collected in the South Atlantic. Variations in Ba isotope compositions of the sediments predominantly reflect changes in the relative contributions of detrital and authigenic Ba sources, with open-ocean sediments constraining the isotope composition of authigenic Ba to be delta Ba-138/134 approximate to +0.1%0. This value is consistent with the average isotope composition inferred for sinking particulate Ba using simple mass balance models of Ba in the overlying water column and is hypothesized to reflect the removal of Ba from the upper water column with an associated isotopic fractionation of Delta Ba-138/134(diss-part) approximate to +0.4 to +0.5. Perturbations to upper ocean Ba cycling, due to changes in export production and the supply of Ba via upwelling, should therefore be recorded by the isotope compositions of sedimentary authigenic Ba. Such insights will help to improve the reliable application of Ba accumulation rates in marine sediments as a proxy for past changes in export production. (C) 2017 Elsevier B.V. All rights reserved.

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