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

Andy W Heard; Nicolas Dauphas; Romain Guilbaud; Olivier J Rouxel; Ian B Butler; Nicole X Nie; Andrey Bekker

doi:10.1126/science.aaz8821

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

Science. 2020 Oct 23;370(6515):446-449. doi: 10.1126/science.aaz8821.

Authors

Andy W Heard¹, Nicolas Dauphas², Romain Guilbaud³, Olivier J Rouxel⁴, Ian B Butler⁵, Nicole X Nie^{2

6}, Andrey Bekker^{7

8}

Affiliations

¹ Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA. [email protected].
² Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.
³ Géosciences Environnement Toulouse, CNRS, UMR5563, 31400 Toulouse, France.
⁴ Unité Géosciences Marines, IFREMER, Plouzané 29280, France.
⁵ School of Geosciences, University of Edinburgh, Grant Institute, Edinburgh EH9 3JW, UK.
⁶ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA.
⁷ Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA.
⁸ Department of Geology, University of Johannesburg, Johannesburg 2006, South Africa.

PMID: 33093107
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.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.