Triple iron isotope constraints on the role of ocean iron sinks in early atmospheric oxygenation

Type Article
Date 2020-10
Language English
Author(s) Heard Andy W.1, 2, Dauphas Nicolas1, 2, Guilbaud Romain3, Rouxel Olivier4, Butler Ian B.5, Nie Nicole X.1, 2, 6, Bekker AndreyORCID7, 8
Affiliation(s) 1 : Univ Chicago, Dept Geophys Sci, Origins Lab, 5734 S Ellis Ave, Chicago, IL 60637 USA.
2 : Univ Chicago, Enrico Fermi Inst, 5640 S Ellis Ave, Chicago, IL 60637 USA.
3 : CNRS, UMR5563, Geosci Environm Toulouse, F-31400 Toulouse, France.
4 : IFREMER, Unite Geosci Marines, F-29280 Plouzane, France.
5 : Univ Edinburgh, Grant Inst, Sch Geosci, Edinburgh EH9 3JW, Midlothian, Scotland.
6 : Carnegie Inst Sci, Earth & Planets Lab, Washington, DC 20015 USA.
7 : Univ Calif Riverside, Dept Earth & Planetary Sci, Riverside, CA 92521 USA.
8 : Univ Johannesburg, Dept Geol, ZA-2006 Johannesburg, South Africa.
Source Science (0036-8075) (Amer Assoc Advancement Science), 2020-10 , Vol. 370 , N. 6515 , P. 446-449
DOI 10.1126/science.aaz8821
Abstract

The role that iron played in the oxygenation of Earth's surface is equivocal. Iron could have consumed molecular oxygen when Fe3+-oxyhydroxides formed in the oceans, or it could have promoted atmospheric oxidation by means of pyrite burial. Through high-precision iron isotopic measurements of Archean-Paleoproterozoic sediments and laboratory grown pyrites, we show that the triple iron isotopic composition of Neoarchean-Paleoproterozoic pyrites requires both extensive marine iron oxidation and sulfide-limited pyritization. Using an isotopic fractionation model informed by these data, we constrain the relative sizes of sedimentary Fe3+- oxyhydroxide and pyrite sinks for Neoarchean marine iron. We show that pyrite burial could have resulted in molecular oxygen export exceeding local Fe2+ oxidation sinks, thereby contributing to early episodes of transient oxygenation of Archean surface environments.

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