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Fossil black smoker yields oxygen isotopic composition of Neoproterozoic seawater

Abstract : The evolution of the seawater oxygen isotopic composition (δ 18 O) through geological time remains controversial. Yet, the past δ 18 O seawater is key to assess past seawater temperatures, providing insights into past climate change and life evolution. Here we provide a new and unprecedentedly precise δ 18 O value of −1.33 ± 0.98‰ for the Neoproterozoic bottom seawater supporting a constant oxygen isotope composition through time. We demonstrate that the Aït Ahmane ultramafic unit of the ca. 760 Ma Bou Azzer ophiolite (Morocco) host a fossil black smoker-type hydrothermal system. In this system we analyzed an untapped archive for the ocean oxygen isotopic composition consisting in pure magnetite veins directly precipitated from a Neoproterozoic seawater-derived fluid. Our results suggest that, while δ 18 O seawater and submarine hydrothermal processes were likely similar to present day, Neoproterozoic oceans were 15-30°C warmer on the eve of the Sturtian glaciation and the major life diversification that followed.
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F. Hodel, M. Macouin, R Trindade, A. Triantafyllou, J. Ganne, et al.. Fossil black smoker yields oxygen isotopic composition of Neoproterozoic seawater. Nature Communications, Nature Publishing Group, 2018, 9, pp.1453. ⟨10.1038/s41467-018-03890-w⟩. ⟨insu-02178803⟩

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