Lesson plan
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".
Article summary
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".
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.