Influence of Exchangeable Oxygen on Biogenic Silica Oxygen Isotope Data

Anthony J. Menicucci, Howard J. Spero, Joy Matthews, Sanjai J. Parikh

Research output: Contribution to journalArticlepeer-review

Abstract

<p> <p id="x-x-sp0075"> Application of biogenic <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/opal" title="Learn more about Opal from ScienceDirect's AI-generated Topic Pages"> opal </a> <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/oxygen-18" title="Learn more about Oxygen 18 from ScienceDirect's AI-generated Topic Pages"> oxygen isotope </a> ratios from fossil and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/subfossil" title="Learn more about Subfossil from ScienceDirect's AI-generated Topic Pages"> subfossil </a> <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/diatom" title="Learn more about Diatom from ScienceDirect's AI-generated Topic Pages"> diatoms </a> to paleoceanographic problems has been hampered by analytical and calibration issues in concert with a lack of experimental data to test fundamental assumptions about sample processing techniques. Here we present experiments where we react purified <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sediment-trap" title="Learn more about Sediment Trap from ScienceDirect's AI-generated Topic Pages"> sediment trap </a> and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sediment-core" title="Learn more about Sediment Core from ScienceDirect's AI-generated Topic Pages"> sediment core </a> diatom samples to waters of different oxygen <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/isotopic-composition" title="Learn more about Isotopic Composition from ScienceDirect's AI-generated Topic Pages"> isotopic composition </a> to quantify oxygen isotope exchange between laboratory processing solutions and &delta; <sup> 18 </sup> O <sub> diatom </sub> values. We generate &delta; <sup> 18 </sup> O <sub> diatom </sub> data using a microfluorination technique, and present FTIR data for samples both before and after vacuum <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/dehydroxylation" title="Learn more about Dehydroxylation from ScienceDirect's AI-generated Topic Pages"> dehydroxylation </a> in order to investigate the mineralogic behavior of biogenic <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/silicon-dioxide" title="Learn more about Silicon Dioxide from ScienceDirect's AI-generated Topic Pages"> silica </a> after dehydroxylation occurs. Our data demonstrate that exposure of diatoms to different &delta; <sup> 18 </sup> O <sub> equil. water </sub> solutions during <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sample-preparation" title="Learn more about Sample Preparation from ScienceDirect's AI-generated Topic Pages"> sample preparation </a> alters final &delta; <sup> 18 </sup> O <sub> diatom </sub> values and this alteration occurs during sample dehydroxylation prior to IRMS analysis. In addition, we present data that show structural diatom hydroxyl is persistent in sediment core samples, but the degree of equilibration with surrounding water decreases with sample age and/or core depth increase. Based on FTIR data, we propose that OH <sup> &ndash; </sup> loss from biogenic silica occurs post depositionally and may occur after heating in the laboratory, producing molecular scale reorganization of the silica <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tetrahedron" title="Learn more about Tetrahedron from ScienceDirect's AI-generated Topic Pages"> tetrahedra </a> within the biogenic opaline structure. Finally, we provide preliminary estimates of the time necessary for complete dehydroxylation of diatom silica, which would result in fully mature biogenic opal. These data suggest that <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/polar-region" title="Learn more about Polar Region from ScienceDirect's AI-generated Topic Pages"> high latitude </a> <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/marine-sediment" title="Learn more about Marine Sediment from ScienceDirect's AI-generated Topic Pages"> marine sediments </a> are slow to mature, and that the rate of exchangeable oxygen reduction varies exponentially at the locations we examined. Maturation time estimates require millions of years, and likely vary depending on core location. </p></p>
Original languageAmerican English
JournalChemical Geology
Volume466
DOIs
StatePublished - Sep 5 2017
Externally publishedYes

Keywords

  • Diatoms
  • Biogenic opal
  • Oxygen isotopes
  • Exchangeability
  • Microfluorination
  • Hydroxyl

Disciplines

  • Earth Sciences

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