Δ13C

In geochemistry, paleoclimatology, archaeology, and paleoceanography, δ C (pronounced "delta carbon thirteen") is a normalized ratio of the two stable isotopes of carbon— C and C—reported in parts per thousand (per mille, ‰). The definition is, in per mille: : \delta \ce{^{13}C} = \left( \frac{(\ce{^{13}C}/\ce{^{12}C})_\mathrm{sample}}{(\ce{^{13}C}/\ce{^{12}C})_\mathrm{standard}} - 1 \right) \times 1000 where the standard is an established reference material. The δ C of a given compound can vary based on the sources of the precursor material and the biogeochemical processes it has undergone. For example, carbon dioxide derived from ecosystem respiration can be differentiated from carbon dioxide formed from the combustion of fossil fuels using δ C, as the precursor materials (modern organic matter and petroleum, respectively) have different isotopic values—the basis of the "Suess effect". In the case of photosynthesis, two plants grown adjacently with the same source of carbon dioxide may be isotopically distinguishable due to differing biochemical mechanisms and physiologies preferentially selecting for a given isotope—a process known as "isotopic fractionation".

In geochemistry, paleoclimatology, archaeology, and paleoceanography, δ C (pronounced "delta carbon thirteen") is a normalized ratio of the two stable isotopes of carbon— C and C—reported in parts per thousand (per mille, ‰). The definition is, in per mille: \delta \ce{^{13}C} = \left( \frac{(\ce{^{13}C}/\ce{^{12}C})_\mathrm{sample}}{(\ce{^{13}C}/\ce{^{12}C})_\mathrm{standard}} - 1 \right) \times 1000 where the standard is an established reference material. The δ C of a given compound can vary based on the sources of the precursor material and the biogeochemical processes it has undergone. For example, carbon dioxide derived from ecosystem respiration can be differentiated from carbon dioxide formed from the combustion of fossil fuels using δ C, as the precursor materials (modern organic matter and petroleum, respectively) have different isotopic values—the basis of the "Suess effect". In the case of photosynthesis, two plants grown adjacently with the same source of carbon dioxide may be isotopically distinguishable due to differing biochemical mechanisms and physiologies preferentially selecting for a given isotope—a process known as "isotopic fractionation". To prevent the depletion of the supply of VPDB, secondary reference materials with isotope ratios determined in direct comparison to VPDB, such as NBS-19 (available from the National Institute of Standards and Technology, δ C VPDB = 1.95‰), are commonly used in the laboratory setting for standardizing measurements.

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