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Restricted Oxygen‐Deficient Basins on the Northern European Epicontinental Shelf Across the Toarcian Carbon Isotope Excursion Interval

Wang, YunfengORCIDiD
Ossa, Frantz OssaORCIDiD
Spangenberg, Jorge E.ORCIDiD
Wille, Martin
Schoenberg, RonnyORCIDiD
DOI: https://doi.org/10.1029/2020PA004207
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9565
Wang, Yunfeng; Ossa, Frantz Ossa; Spangenberg, Jorge E.; Wille, Martin; Schoenberg, Ronny, 2021: Restricted Oxygen‐Deficient Basins on the Northern European Epicontinental Shelf Across the Toarcian Carbon Isotope Excursion Interval. In: Paleoceanography and Paleoclimatology, Band 36, 6, DOI: 10.1029/2020PA004207.
 
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  • Abstract
The worldwide recognition of the Toarcian carbon isotope excursion (T‐CIE) in organic‐rich sedimentary rocks has been linked to an oceanic anoxic event (OAE) which implies the world's deep oceans were anoxic ∼183 Ma. The majority of independent redox observations used to build this argument were mainly obtained from T‐CIE organic‐rich sediments deposited on northern European epicontinental shelf. However, increasing evidence has shown that this shelf had limited connection with the open ocean, making it unsuitable for reconstructing the T‐CIE ocean redox structure. To unveil such controversy, we present integrated δ15Nbulk and δ15Nker from Dotternhausen profile, Germany, combined with literature data from other T‐CIE profiles. Both δ15Nbulk and δ15Nker values are predominantly between +0.3 and +2.5‰. These positive near‐zero δ15N values imply enhanced N2 fixation by cyanobacteria using molybdenum (Mo)‐based nitrogenase to compensate bioavailable N loss following quantitative denitrification and/or anammox in a strongly redox‐stratified marine setting. Such N isotope composition contradicts the typical sedimentary δ15N values (>3‰) induced by partial water‐column denitrification and/or anammox in modern‐ocean oxygen minimum zones. We rather propose the existence of local oxygen‐deficient basins on northern European epicontinental shelf where dissolved N underwent extensive denitrification and/or anammox causing bioavailable N deficiency. Mo‐based diazotrophy thus played a critical role in discriminating N isotope compositions among multiple hydrographically restricted T‐CIE marginal basins. Restricted oxygen‐depleted environments on the northern European epicontinental shelf unlikely represent the open‐ocean redox landscape. The existence of the global OAE thus needs comprehensive redox investigations on Tethys and/or Panthalassa deep‐sea T‐CIE successions to validate.
 
Key Points: Molybdenum‐based nitrogen fixation was prevalent in the northern European epicontinental shelf during the Toarcian carbon isotope excursion. Quantitative denitrification and/or anammox caused nitrogen famine in strongly redox‐stratified environments during the early Toarcian. Oxygen‐deficient basins on the northern European epicontinental shelf across the Toarcian carbon isotope excursion.
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  • Geochemie, Mineralogie, Petrologie [395]
Subjects:
Toarcian
carbon isotope excursion
ocean anoxic event
Dotternhausen
nitrogen fixation
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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