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In geochemistry, paleoclimatology and paleoceanography ''δ''13C (pronounced "delta thirteen c") is an isotopic signature, a measure of the ratio of stable isotopes 13C : 12C, reported in parts per thousand (per mil, ‰). The definition is, in per mil: : where the standard is an established reference material. ''δ''13C varies in time as a function of productivity, organic carbon burial and vegetation type. ==Reference standard== The standard established for carbon-13 work was the Pee Dee Belemnite (PDB) and was based on a Cretaceous marine fossil, ''Belemnitella americana'', which was from the Pee Dee Formation in South Carolina. This material had an anomalously high 13C:12C ratio (0.0112372), and was established as ''δ''13C value of zero. Use of this standard gives most natural material a negative ''δ''13C.〔http://www.uga.edu/sisbl/stable.html#calib Overview of Stable Isotope Research – The Stable Isotope/Soil Biology Laboratory of the University of Georgia Institute of Ecology〕 A material with a ratio of 0.010743 for example would have a ''δ''13C value of (0.010743/0.0112372 − 1) *1000 = −44. The standards are used for verifying the accuracy of mass spectroscopy; as isotope studies became more common, the demand for the standard exhausted the supply. Other standards calibrated to the same ratio, including one known as VPDB (for "Vienna PDB"), have replaced the original.〔Miller & Wheeler, ''Biological Oceanography'', p. 186.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Δ13C」の詳細全文を読む スポンサード リンク
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