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Laboratory Assessment of the Impact of Chemical Oxidation, Mineral Dissolution, and Heating on the Nitrogen Isotopic Composition of Fossil-bound Organic Matter
  • +9
  • Alfredo Martinez-Garcia,
  • Jonathan Jung,
  • Xuyuan Ellen Ai,
  • Daniel M. Sigman,
  • Alexandra Auderset,
  • Nicolas N. Duprey,
  • Alan Foreman,
  • Francois Fripiat,
  • Jennifer Leichliter,
  • Tina Lüdecke,
  • Simone Moretti,
  • Tanja Wald
Alfredo Martinez-Garcia
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry

Corresponding Author:[email protected]

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Jonathan Jung
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Xuyuan Ellen Ai
Princeton University, Princeton University, Princeton University
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Daniel M. Sigman
Princeton University, Princeton University, Princeton University
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Alexandra Auderset
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Nicolas N. Duprey
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Alan Foreman
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Francois Fripiat
Université Libre de Bruxelles, Université Libre de Bruxelles, Université Libre de Bruxelles
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Jennifer Leichliter
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Tina Lüdecke
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Simone Moretti
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Tanja Wald
Max Planck Institute for Chemistry, Max Planck Institute for Chemistry, Max Planck Institute for Chemistry
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Abstract

Fossil-bound organic material holds great potential for the reconstruction of past changes in nitrogen (N) cycling. Here, with a series of laboratory experiments, we assess the potential effect of oxidative degradation, fossil dissolution, and thermal alteration on the fossil-bound N isotopic composition of different fossil types, including deep and shallow water scleractinian corals, foraminifera, diatoms and tooth enamel. Our experiments show that exposure to different oxidizing reagents does not significantly affect the N isotopic composition or N content of any of the fossil types analyzed, demonstrating that organic matter is well protected from changes in the surrounding environment by the mineral matrix. In addition, we show that partial dissolution (of up to 70-90%) of fossil aragonite, calcite, opal, or enamel matrixes has a negligible effect on the N isotopic composition or N content of the fossils. These results suggest that the isotopic composition of fossil-bound organic material is relatively uniform, and also that N exposed during dissolution is lost without significant isotopic discrimination. Finally, our heating experiments show negligible changes in the N isotopic composition and N content of all fossil types at 100 οC. At 200 οC and hotter, the N loss and associated nitrogen isotope changes appear to be directly linked to the sensitivity of the mineral matrix to thermal stress. These results suggest that, so long as high temperature does not compromise the mineral structure, the biomineral matrix acts as a closed system with respect to N, and the N isotopic composition of the fossil remains unchanged.