oxygen-isotope analysis Method for estimating past ocean temperatures. The ratio of the stable oxygen isotopes, ¹⁸O and ¹⁶O, is temperature dependent in water, ¹⁸O increasing as temperature falls. Oxygen incorporated in the calcium-carbonate shells of marine organisms will reflect the prevailing ¹⁸O: ¹⁶O ratio (see OXYGEN-ISOTOPE RATIO). Acidification (to release oxygen) of fossils of these organisms under carefully controlled conditions can therefore be used, with appropriate calibration, to indicate the record of past ocean temperatures.

oxygen-isotope analysis A method for estimating past ocean temperatures. The ratio of the stable oxygen isotopes, ¹⁸O and ¹⁶O, is temperature-dependent in water, ¹⁸O increasing as temperature falls. Oxygen incorporated in the calcium-carbonate shells of marine organisms reflects the prevailing ¹⁸O:¹⁶O ratio.