Department of Biology

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Mark Lever

Oxygen isotope fractionation in the siderite-water system between 8.5 and 62 °C

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  • Joep van Dijk, Swiss Federal Institute of Technology Zurich
  • ,
  • Alvaro Fernandez, Swiss Federal Institute of Technology Zurich
  • ,
  • Inigo A. Müller, Swiss Federal Institute of Technology Zurich
  • ,
  • Mark Lever
  • Stefano M. Bernasconi, Swiss Federal Institute of Technology Zurich

The oxygen isotope composition of siderites can be used to deduce the temperature and/or oxygen isotope composition of the fluids from which they precipitated. Previous siderite-water oxygen isotope fractionation calibrations are not well constrained at temperatures below 33 °C where most of the siderite forms at the Earth's surface. Moreover, the few experimental low temperature calibration points available are possibly inaccurate as the corresponding siderites may not have formed in equilibrium with the solution. In this study, we synthesized siderite in the laboratory from 8.5 to 62 °C, using both active-degassing experiments and microbial cultures. We used the enzyme carbonic anhydrase, which significantly reduces the equilibration time of oxygen isotopes among all dissolved inorganic carbon (DIC) species and water to minimize siderite formation out of equilibrium. Our calibration is based on many more data points than previous calibrations and significantly reduces the uncertainty in siderite-water oxygen isotope fractionation in natural siderites formed at low temperatures. The best fit equation is 1000∗lnα=19.67±0.42[formula ommited]-36.27±1.34where α (1000 + δ18Osiderite/1000 + δ18Owater) is the fractionation factor and T is the temperature in Kelvin.

Original languageEnglish
JournalGeochimica et Cosmochimica Acta
Volume220
Pages (from-to)535-551
Number of pages17
ISSN0016-7037
DOIs
Publication statusPublished - 1 Jan 2018
Externally publishedYes

Bibliographical note

Funding Information:
We thank Dr. J. Zhou of the University of Oklahoma, Norman, USA for providing the used strain. We are grateful for the expert assistance during isotope measurements of Stewart Bishop and Madalina Jaggi. We furthermore thank Lorenzo Lagostina and Philip Eickenbusch for their help with culturing and Annika Fiskal for her help with the Fe 2+ measurements. This manuscript has greatly benefitted from three anonymous reviews. This study was funded by the Swiss National Science Foundation projects No. 160046 and 156408 and ETH Project no. ETH-3314-1.

Publisher Copyright:
© 2017 Elsevier Ltd

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

    Research areas

  • Ambient temperature, Oxygen isotope fractionation, Siderite

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