Oxygen has three naturally occurring stable isotopes (16O, 17O, and 18O). For studies of stable isotope biogeochemistry we measure the ratio of 18O to 16O (17O is not generally measured, because its abundance is so low) in samples of interest (e.g. water, silicate minerals), expressed relative to the ratio in a standard of known isotopic composition, usually "Vienna Standard Mean Ocean Water" as prepared by the International Atomic Energy Agency in Vienna (V-SMOW; 18O/16O = 0.0020052 (1)(2)). The oxygen isotope composition of carbonate minerals is often reported relative to the ratio "Pee Dee Belemnite" standard (PDB; 18O/16O = 0.0020672 (3)(2)).
The d18O values of terrestrial oxygen samples range from about -60 to +40 per mil (parts per thousand) relative to V-SMOW (4).
(1)From Table 9-1, p. 154, of David P. Mattey, 1997, Gas source mass spectrometry: isotopic composition of lighter elements, pages 154-170 in Robin Gill (editor), Modern Analytical Geochemistry, Longman (UK).
(2)The uncertainty in this value is much larger than the precision with which we can measure relative ratios, which is one reason for the use the "delta" notation; page 32 in Robert E. Criss, 1999, Principles of Stable Isotope Distribution, Oxford University Press.
(3)From Table 2-15, p. 93, of Arthur H. Brownlow, 1996, Geochemistry, Prentice-Hall.
(4)From Table 2-17, p. 97, of Arthur H. Brownlow, 1996, Geochemistry, Prentice-Hall.
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