oxygen-16

…the ratio of oxygen-18 to oxygen-16. Oxygen-16 is the dominant isotope, making up more than 99 percent of all natural oxygen; oxygen-18 makes up 0.2 percent. However, the exact concentration of oxygen-18 in precipitation, particularly at high latitudes, depends on the temperature. Winter snow has a smaller oxygen-18–oxygen-16 ratio than…

For example, oxygen-16 is enriched relative to the heavier oxygen isotopes in water evaporating from the sea. On the other hand, any precipitate is enriched in the heavy isotope, resulting in a further concentration of oxygen-16 in atmospheric water vapour. Because the processes of evaporation and condensation…

…occurs in three isotopes: ¹⁶O (99.763 percent), ¹⁷O (0.0375 percent), and ¹⁸O (0.1995 percent). Oxygen is found in all organisms and many minerals, including the aragonite and calcite that make up the shells of marine microfossils such as foraminifera. Oxygen isotopes are useful for geologic studies because the rate…