Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Criss, R. E. Articles by Farquhar, J. Search for Related Content GeoRef GeoRef Citation

Abundance, Notation, and Fractionation of Light Stable Isotopes

Washington University, St. Louis, Missouri 63130, U.S.A., criss{at}wustl.edu

James Farquhar

University of Maryland, College Park, Maryland 20742, U.S.A., jfarquha{at}essic.umd.edu

Stable isotopes have become an essential tool to characterize and understand terrestrial and extraterrestrial matter. This chapter will briefly review the abundances of important light stable isotopes, demonstrate the link between abundance and atomic weight, introduce the notations and diagrams that are commonly used to report isotopic measurements, describe and partially explain the types of fractionation effects known to occur in nature, and direct the reader to more comprehensive sources of information on each subject. The special techniques needed to make accurate isotopic measurements gave rise to special notation for reporting stable isotope data, and these notations in turn gave rise to special diagrams that emphasize compositional differences and facilitate interpretation. Fundamental definitions are the isotope ratio R, representing the ratio of the abundance of a heavy isotope to that of a lighter, typically much more common isotope, and the isotopic fractionation factor , representing the quotient R_A/R_B of the isotope ratios of two substances A and B. Under equilibrium conditions, ln can theoretically vary linearly with 1/T at low temperatures or with 1/T² at high temperatures, forming the basis for a standard graph. For practical reasons the ratio R is difficult to measure and inconvenient to report, so stable isotope abundances are usually reported as delta values (-values) that describe their deviations from a defined "standard" material. Thus, the most important diagram for data interpretation is the "- plot" where the -values of two coexisting phases are simply plotted against each other. In systems where two different heavy isotopes exist, two different delta values may be defined, each normalizing the abundance of one of the heavy isotopes to the common light isotope. In such cases, a very important diagram called the "three isotope" plot involves simply plotting these two different -values against each other for a given material, and the slopes of data arrays on such graphs can be used to distinguish ordinary "mass-dependent" fractionation (MDF) effects from "non-mass-dependent" fractionations (NMF). Numerous algebraic convolutions of the above definitions have been made, providing special definitions that can elucidate different phenomena. The processes that govern isotope distribution have become progressively better understood, yet recent studies show that these processes are more diverse than anticipated only ten years ago.

This article has been cited by other articles:

				B. S. Meyer, L. R. Nittler, A. N. Nguyen, and S. Messenger Nucleosynthesis and Chemical Evolution of Oxygen Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 31 - 53. [Abstract] [Full Text] [PDF]

				H. Yurimoto, A. N. Krot, B.-G. Choi, J. Aleon, T. Kunihiro, and A. J. Brearley Oxygen Isotopes of Chondritic Components Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 141 - 186. [Abstract] [Full Text] [PDF]

				E. D. Young, K. Kuramoto, R. A. Marcus, H. Yurimoto, and S. B. Jacobsen Mass-independent Oxygen Isotope Variation in the Solar Nebula Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 187 - 218. [Abstract] [Full Text] [PDF]

				T. H. Burbine, A. S. Rivkin, S. K. Noble, T. Mothe-Diniz, W. F. Bottke, T. J. McCoy, M. D. Dyar, and C. A. Thomas Oxygen and Asteroids Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 273 - 343. [Abstract] [Full Text] [PDF]

				I. A. Franchi Oxygen Isotopes in Asteroidal Materials Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 345 - 397. [Abstract] [Full Text] [PDF]

				R. E. Criss Terrestrial Oxygen Isotope Variations and Their Implications for Planetary Lithospheres Reviews in Mineralogy and Geochemistry, January 1, 2008; 68(1): 511 - 526. [Abstract] [Full Text] [PDF]