Stable oxygen isotopes

Oxygen has three naturally-occuring stable isotopes: ¹⁶O, ¹⁷O, ¹⁸O, with ¹⁶O being the most abundant (99.762%).

Two international reference standards are used to report variations in oxygen isotope standards: PDB and SMOW. The use of the PDB standard in reporting oxygen isotope composition is restricted to carbonates of low-temperature origins (e.g., oceanic, lacustrine ). The conversion between SMOW and PDB scales is given by:

$\delta^{18}O_{SMOW} = 1.03091 (\delta^{18}O_{PDB}) +30.91$

The δ¹⁸O may be measured on:

• the shells of foraminifera