Oxygen-18

Oxygen-18 (¹⁸O) is a natural, stable isotope of oxygen and one of the environmental isotopes.

¹⁸O is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharmaceutical industry, enriched water (H₂¹⁸O) is bombarded with hydrogen ions in either a cyclotron or linear accelerator creating fluorine-18. This is then synthesized into FDG and injected into a patient.

Paleoclimatology

In ice cores, mainly Arctic and Antarctic, the ratio O-18/O-16 (δ¹⁸O) can be used to determine the temperature of precipitation through time. Assuming that atmospheric circulation and elevation has not changed significantly over the poles, the temperature of ice formation can be calculated as equilibrium fractionation between phases of water is known for different temperatures. Water molecules are also subject to Rayleigh fractionation as atmospheric water moves from the equator poleward which results in progressive depletion of O-18, or lower δ¹⁸O values. In the 1950s, Harold Urey performed an experiment in which he mixed both normal water and water with oxygen-18 in a barrel, and then partially froze the barrel's contents.
The ratio O-18/O-16 (δ¹⁸O) can also be used to determine paleothermometry in certain types of fossils. The fossils in question have to contain Calcite or Aragonite and show progressive growth in the animal or plant that the fossil represents. For example, a sea shell from a scallop from a prehistoric ocean may be used to determine the changes over time. Each time the scallop grows, an extension is seen on the surface of the shell. A calculation is used to determine the probable sea water temperature in comparison to each growth. The equation for this is:

Where t is temperature in Celsius and A and B are constants.

See also

• Willi Dansgaard - a paleoclimatologist
• Isotopes of oxygen
• Paleothermometry

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