13 Sep 2022
13 Sep 2022
Status: this preprint is currently under review for the journal BG.

Technical Note: No impact of alkenone extraction on foraminiferal stable isotope, trace element and boron isotope geochemistry

Jessica Georgina Magdalen Crumpton-Banks1,, Thomas Tanner2,, Ivan Hernández Almeida2, James William Buchanan Rae1, and Heather Stoll2 Jessica Georgina Magdalen Crumpton-Banks et al.
  • 1School of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, U.K.
  • 2Geological Institute, ETH Zürich, 8092 Zürich, Switzerland
  • These two authors contributed equally to this project.

Abstract. Recent advances in geochemical techniques mean that several robust proxies now exist to determine the past carbonate chemistry of the oceans. Foraminiferal δ11B and alkenone carbon isotopes allow us to reconstruct sea-surface pH and pCO2 respectively, and the ability to apply both proxies to the same sediment sample would give strongly paired datasets and reduce sample waste. However, no studies to date have examined whether the solvents and extraction techniques used to prepare alkenones for analysis also impact the geochemistry of foraminifera within those sediments. Here we examine six species pairs of planktic foraminifera, with half being taken from non-treated sediments and half being taken from sediments where alkenones have been extracted. We look for visual signs of contrasting preservation and compare analyses of δ18O, δ13C, δ11B and trace elements (Li, B, Na, Mn, Mg, Sr, and U/Ca). We find no consistent geochemical offset between the treatments, and excellent agreement in δ11B measurements between them. Our results show that boron isotope reconstructions of pH in foraminifera from alkenone-extracted sediments can be applied with confidence.

Jessica Georgina Magdalen Crumpton-Banks et al.

Status: open (until 25 Oct 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-187', Anonymous Referee #1, 22 Sep 2022 reply
    • AC1: 'Reply on RC1', Jessica Crumpton-Banks, 24 Sep 2022 reply
  • RC2: 'Comment on bg-2022-187', Anonymous Referee #2, 30 Sep 2022 reply

Jessica Georgina Magdalen Crumpton-Banks et al.

Jessica Georgina Magdalen Crumpton-Banks et al.


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Short summary
Past ocean carbon is reconstructed using proxies, but it is unknown whether preparing ocean sediment for one proxy might damage the data given by another. We have tested whether the extraction of an organic proxy archive from sediment samples impacts the geochemistry of tiny shells also within the sediment. We find no difference in shell geochemistry between samples which come from treated and untreated sediment. This will help us to maximise scientific return from valuable sediment samples.