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Evidence of magnetic isotope effects during thermochemical sulfate reduction

  1. James Farquhara,1
  1. aDepartment of Geology and Earth System Science Interdisciplinary Center (ESSIC), University of Maryland, College Park, MD 20742;
  2. cDepartment of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742;
  3. dGeophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, DC 20015; and
  4. bDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307
  1. Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved August 23, 2011 (received for review May 24, 2011)

Abstract

Thermochemical sulfate reduction experiments with simple amino acid and dilute concentrations of sulfate reveal significant degrees of mass-independent sulfur isotope fractionation. Enrichments of up to 13‰ for 33S are attributed to a magnetic isotope effect (MIE) associated with the formation of thiol-disulfide, ion-radical pairs. Observed 36S depletions in products are explained here by classical (mass-dependent) isotope effects and mixing processes. The experimental data contrasts strongly with multiple sulfur isotope trends in Archean samples, which exhibit significant 36S anomalies. These results support an origin other than thermochemical sulfate reduction for the mass-independent signals observed for early Earth samples.

Footnotes

  • 1To whom correspondence may be addressed. E-mail: hoduro{at}umd.edu, hoduro{at}mit.edu, or jfarquha{at}glue.umd.edu.
  • Author contributions: H.O. and J.F. designed research; H.O. and J.F. performed research; H.O. and J.F. contributed new reagents/analytic tools; H.O., B.H., H.O.S., A.J.K., G.C., and J.F. analyzed data; and H.O., B.H., H.O.S., and J.F. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.danielhellerman.com/lookup/suppl/doi:10.1073/pnas.1108112108/-/DCSupplemental.

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