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Title: Iron isotope fractionation during pyrite formation in a sulfidic Precambrian ocean analogue

Journal Article · · Earth and Planetary Science Letters
 [1];  [1]; ORCiD logo [2];  [3];  [1];  [4]
  1. University of Otago, Dunedin (New Zealand). Department of Chemistry and Centre for Trace Element Analysis
  2. University of Otago, Dunedin (New Zealand). Department of Chemistry ; Royal Netherlands Institute for Sea Research, Texel (The Netherlands). Department of Ocean Systems (OCS); Utrecht Univeristy, Texel (The Netherlands)
  3. University of Otago, Dunedin (New Zealand). Department of Chemistry and Centre for Trace Element Analysis; Univ. of Tasmania, Hobart, TAS (Australia). Antarctic Climate and Ecosystems CRC
  4. Royal Netherlands Institute for Sea Research, Texel (The Netherlands). Department of Ocean Systems (OCS); Utrecht Univeristy, Texel (The Netherlands)

We present that the chemical response of the Precambrian oceans to rising atmospheric O2 levels remains controversial. The iron isotope signature of sedimentary pyrite is widely used to trace the microbial and redox states of the ocean, yet the iron isotope fractionation accompanying pyrite formation in nature is difficult to constrain due to the complexity of the pyrite formation process, difficulties in translating the iron isotope systematics of experimental studies to natural settings, and insufficient iron isotope datasets for natural euxinic (i.e. anoxic and sulfidic) marine basins where pyrite formation occurs. Herein we demonstrate, that a large, permil-level shift in the isotope composition of dissolved iron occurs in the Black Sea euxinic water column during syngenetic pyrite formation. Specifically, iron removal to syngenetic pyrite gives rise to an iron isotope fractionation factor between Fe(II) and FeS2 of 2.75 permil (‰), the largest yet reported for reactions under natural conditions that do not involve iron redox chemistry. These iron isotope systematics offer the potential to generate permil-level shifts in the sedimentary pyrite iron isotope record due to partial drawdown of the oceanic iron inventory. The implication is that the iron stable isotope signatures of sedimentary pyrites may record fundamental regime shifts between pyrite formation under sulfur-limited conditions and pyrite formation under iron-limited conditions. To this end, the iron isotope signatures of sedimentary pyrite may best represent the extent of euxinia in the past global ocean, rather than its oxygenation state. On this basis, the reinterpreted sedimentary pyrite Fe isotope record suggests a fundamental shift towards more sulfidic oceanic conditions coincident with the ‘Great Oxidation Event’ around 2.3 billion years ago. Importantly, this does not require the chemical state of the ocean to shift from mainly de-oxygenated to predominantly oxygenated in parallel with the permanent rise in atmospheric oxygen, contrary to other interpretations based on iron isotope systematics.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1424114
Report Number(s):
LLNL-JRNL-725981; TRN: US1801909
Journal Information:
Earth and Planetary Science Letters, Vol. 488, Issue C; ISSN 0012-821X
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 30 works
Citation information provided by
Web of Science

References (47)

A Whiff of Oxygen Before the Great Oxidation Event? journal September 2007
Coupled Fe and S isotope evidence for Archean microbial Fe(III) and sulfate reduction journal January 2006
Fe Isotope Variations in the Modern and Ancient Earth and Other Planetary Bodies journal January 2004
Iron Isotope Biosignatures journal September 1999
Iron isotopes in an Archean ocean analogue journal May 2014
Fe isotope fractionation on FeS formation in ambient aqueous solution journal July 2005
A new model for Proterozoic ocean chemistry journal December 1998
A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry journal September 2013
Atmospheric oxygenation three billion years ago journal September 2013
The cycling of particulate carbon, nitrogen, sulfur, and sulfur species (iron monosulfide, greigite, pyrite, and organic sulfur) in the water columns of Framvaren Fjord and the Black Sea journal November 1999
Abiotic Pyrite Formation Produces a Large Fe Isotope Fractionation journal June 2011
Calibration of Sulfate Levels in the Archean Ocean journal December 2002
Volcanic gases, black smokers, and the great oxidation event journal November 2002
100th Anniversary Special Paper: Sedimentary Mineral Deposits and the Evolution of Earth's Near-Surface Environments journal December 2005
Optimizing sample and spike concentrations for isotopic analysis by double-spike ICPMS journal January 2012
The flux of iron and iron isotopes from San Pedro Basin sediments journal September 2012
The Iron Isotope Fingerprints of Redox and Biogeochemical Cycling in Modern and Ancient Earth journal May 2008
Processes controlling the redox budget for the oxic/anoxic water column of the Black Sea journal August 2006
Linking crenarchaeal and bacterial nitrification to anammox in the Black Sea journal April 2007
The biogeochemistry of manganese and iron in the Black Sea journal January 1991
Sulfur isotopic trends and pathways of iron sulfide formation in upper Holocene sediments of the anoxic Black Sea journal August 1997
Tracking Euxinia in the Ancient Ocean: A Multiproxy Perspective and Proterozoic Case Study journal May 2009
The rise of oxygen in Earth’s early ocean and atmosphere journal February 2014
A critical look at iron paleoredox proxies: New insights from modern euxinic marine basins journal December 2006
Sulfur, iron and organic carbon fluxes in the Black Sea: sulfur isotopic evidence for origin of sulfur fluxes journal January 1991
Unexpected changes in the oxic/anoxic interface in the Black Sea journal March 1989
Iron isotope composition of some Archean and Proterozoic iron formations journal March 2012
Evidence for oxygenic photosynthesis half a billion years before the Great Oxidation Event journal March 2014
Widespread iron-rich conditions in the mid-Proterozoic ocean journal September 2011
Ferruginous Conditions: A Dominant Feature of the Ocean through Earth's History journal April 2011
Sources of iron for pyrite formation in marine sediments journal March 1998
A Late Archean Sulfidic Sea Stimulated by Early Oxidative Weathering of the Continents journal October 2009
Chemistry of Iron Sulfides journal February 2007
Uranium stable isotope fractionation in the Black Sea: Modern calibration of the 238U/235U paleo-redox proxy journal April 2017
Iron Isotope Constraints on the Archean and Paleoproterozoic Ocean Redox State journal February 2005
Manganese(II) oxidation driven by lateral oxygen intrusions in the western Black Sea journal May 2005
Beyond the Black Sea paradigm: The sedimentary fingerprint of an open-marine iron shuttle journal February 2014
Modern iron isotope perspective on the benthic iron shuttle and the redox evolution of ancient oceans journal January 2008
Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(III) and hematite journal September 2002
Vertical advection diffusion and redox potentials as controls on the distribution of manganese and other trace metals Dissolved in waters of the Black Sea journal August 1971
Isotope fractionation between dissolved and suspended particulate Fe in the oxic and anoxic water column of the Baltic Sea journal January 2013
Large iron isotope fractionation at the oxic–anoxic boundary in Lake Nyos journal July 2009
Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(II) and Fe(III) journal November 2003
Reactive iron in Black Sea Sediments: implications for iron cycling journal February 2001
Experimental determination of iron isotope fractionations among Feaq2+–FeSaq–Mackinawite at low temperatures: Implications for the rock record journal July 2012
Biogeochemical cycling of iron in the Archean–Paleoproterozoic Earth: Constraints from iron isotope variations in sedimentary rocks from the Kaapvaal and Pilbara Cratons journal May 2005
Trace metal composition of suspended particulate matter in the water column of the Black Sea journal September 2011

Figures / Tables (7)