xygen Isotopes

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⁾.

Isotope	Atomic mass (ma/u)	Natural abundance (atom %)
16O	15.99491463	99.757
17O	16.9991312	0.038
18O	17.9991603	0.205

See the page on the Isotopes of Oxygen.
and the centered on O.

⁽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.