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oxygen isotope ratio cycle
Oxygen isotope ratio cycles are cyclical variations in the ratio of the abundance of oxygen with an atomic mass of 18 to the abundance of oxygen with an atomic mass of 16 present in some substances, such as polar ice or calcite in ocean core samples, measured with the isotope fractionation. The ratio is linked to water temperature of ancient oceans, which in turn reflects ancient climates. Cycles in the ratio mirror climate changes in geologic history.
== Isotopes of oxygen ==
Oxygen (chemical symbol O) has three naturally occurring isotopes: 16O, 17O, and 18O, where the 16, 17 and 18 refer to the atomic mass. The most abundant is 16O, with a small percentage of 18O and an even smaller percentage of 17O. Oxygen isotope analysis considers only the ratio of 18O to 16O present in a sample.
The calculated ratio of the masses of each present in the sample is then compared to a standard, which can yield information about the temperature at which the sample was formed - see Proxy (climate) for details.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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