Hodel F. auteur aut IRD Macouin M. auteur aut IRD Trindade R. I. F. auteur aut IRD Triantafyllou A. auteur aut IRD Ganne Jérôme auteur aut IRD Chavagnac V. auteur aut IRD Berger J. auteur aut IRD Rospabe M. auteur aut IRD Destrigneville C. auteur aut IRD Carlut J. auteur aut IRD Ennih N. auteur aut IRD Agrinier P. auteur aut IRD text journalArticle eng text/pdf reformatted digital access The evolution of the seawater oxygen isotopic composition (delta O-18) through geological time remains controversial. Yet, the past delta O-18(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 delta O-18 value of -1.33 +/- 0.98% for the Neoproterozoic bottom seawater supporting a constant oxygen isotope composition through time. We demonstrate that the Ait 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 delta O-18(seawater) and submarine hydrothermal processes were likely similar to present day, Neoproterozoic oceans were 15-30 degrees C warmer on the eve of the Sturtian glaciation and the major life diversification that followed. specialized MAROC 064 032 9 art. 1453 [7 p.] 2018 2041-1723 https://www.documentation.ird.fr/hor/fdi:010072752 10.1038/s41467-018-03890-w 2041-1723 [F B010072752] https://www.documentation.ird.fr/hor/fdi:010072752 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers18-05/010072752.pdf IRD - Base Horizon / Pleins textes 2018-06-01 2023-07-11 fdi:010072752 fre