Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Fractionation, Mass Independent and Dependent

  • Francis AlbaredeEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_597-2


Isotope fractionation is referred to as mass dependent when observed isotopic abundances deviate smoothly and monotonically with the masses of the isotopes from those in the reference material. Both kinetic and equilibrium processes are known to account for this most common form of isotope fractionation. Alternate patterns are referred to as mass independent and are known for O and S in some specific environments and are often related to photochemistry in the solar nebula and in planetary atmospheres.


Isotope fractionation varies approximately with the difference of the isotopic masses. Using oxygen isotopes as an example, the mass difference 18O − 16O is +2 and δ18O will therefore be twice the δ17O \( \left(\mathrm{where},\;\mathrm{e}.\mathrm{g}.,\;{\delta}^{18}\mathrm{O}\; is\left[{\left({}^{18}\mathrm{O}/{}^{16}\mathrm{O}\right)}_{\mathrm{sample}}/{\left({}^{18}\mathrm{O}/{}^{16}\mathrm{O}\right)}_{\mathrm{std}}-1\right]\right). \)


Isotope Mass fractionation 
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References and Further Reading

  1. Sharp Z (2007) Principles of stable isotope geochemistry. Prentice Hall, Upper Saddle RiverGoogle Scholar
  2. Thiemens MH (2006) History and applications of mass-independent isotope effects. Annu Rev Earth Planet Sci 34:217–262ADSCrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Ecole Normale Supérieure de LyonLyon Cedex 7France