A Multi-Proxy Isotope Approach to Reconstruct Seawater Oxygenation

Rhodes, Felicity Sarah Amy (2019). A Multi-Proxy Isotope Approach to Reconstruct Seawater Oxygenation. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00011559

Abstract

The isotopic composition of redox sensitive metals in marine sedimentary rocks have been used to provide insights into the degree and extent of oceanic anoxia during environmental changes such as oceanic anoxic events (OAEs). In this study a new method has been developed to determine the isotope composition (δ¹⁸⁷Re = [[(¹⁸⁷Re/¹⁸⁵Re)_sample / (¹⁸⁷Re/¹⁸⁵Re)_{SRM 3143}]-1]*1000) of the redox sensitive element rhenium in sedimentary deposits. The method requires 1.5 – 6.0 ng Re per analysis and utilises a two-stage chromatographic separation and MC-ICP-MS analysis. The accuracy was tested using matrix test samples (δ¹⁸⁷Re = 0) that have an average δ¹⁸⁷Re of -0.035 ± 0.112 ‰; and column processed aliquots of standard SRM 3143 of δ¹⁸⁷Re = -0.042 ± 0.108 ‰. The long-term reproducibility of standard analyses is 0.082 ‰ (2 SD). The reference sample SDO-1 had ¹⁸⁷Re = -0.163 ± 0.113 ‰. The total measured range in δ¹⁸⁷Re was -1.087 ± 0.084 ‰ between a sediment sample from the Baltic Sea and SRM 3143.

The δ¹⁸⁷Re of marine mudrocks from the Toarcian OAE in Yorkshire, UK have a range of 0.699‰ from -0.019 ± 0.080 ‰ to -0.756 ± 0.085 ‰. During the OAE onset δ¹⁸⁷Re increases by 0.219 ‰. The main event is synchronous with a - 0.596 ‰ ¹⁸⁷Re excursion. Minimum δ¹⁸⁷Re values correspond to the maximum global extent of anoxia indicated by other proxies. The ¹⁸⁷Re decrease is interpreted to indicate a decrease in δ¹⁸⁷Re of contemporaneous seawater due to a progressive increase in the global extent of anoxia.

Recent sediments from the Gotland Deep, Baltic Sea have a ¹⁸⁷Re range of 0.826 ‰ from 0.261 ± 0.084 to -1.087 ± 0.084 ‰. The cause of changes in δ¹⁸⁷Re is inconclusive and could include changes in local anoxia, the basin-wide extent of anoxia, anthropogenic Re, runoff variation and diagenesis.

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About

• Item ORO ID
• 71001
• Item Type
• PhD Thesis
• Keywords
• oxidation-reduction reaction; marine sediments; sedimentary rocks; dissolved oxygen; mudstone; seawater
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM)
  Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
• Copyright Holders
• © 2018 The Author
• Depositing User
• ORO Import