Fossil black smoker yields oxygen isotopic composition of Neoproterozoic seawater

F. Hodel (1, 2) , M. Macouin (3) , R I F Trindade (2) , A. Triantafyllou (4) , J. Ganne (1) , V. Chavagnac (1) , J. Berger (1) , M. Rospabé (1) , C. Destrigneville (1) , J. Carlut (5) , N. Ennih (6) , P. Agrinier (5)

1 GET - Géosciences Environnement Toulouse
2 IAG - Instituto de Astronomia, Geofísica e Ciências Atmosféricas [São Paulo]
3 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
4 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
5 IPGP - Institut de Physique du Globe de Paris
6 UCD - Université Chouaib Doukkali

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.

Domaines: Géochimie; Océan, Atmosphère

F. Hodel, M. Macouin, R I F Trindade, A. Triantafyllou, J. Ganne, et al.. Fossil black smoker yields oxygen isotopic composition of Neoproterozoic seawater. Nature Communications, 2018, 9, pp.1453. ⟨10.1038/s41467-018-03890-w⟩. ⟨insu-02178803⟩