Stable Carbon and Nitrogen Isotopic Analysis of Skeletal Remains ...

activities (Tykot et al. 2009:160). Studies on marine ecosystems have shown that
on average there is a 3‰ enrichment of 15 N versus the diet between the
different trophic level species in ecosystems (Michener and Kaufman 2007:238).
For example, a carnivore’s δ 15 N values would be approximately 3‰ more
positive than that of a herbivore, with this process continuing through the food
chain (Schoeninger 1985). As well as this, average δ 13 C values of the whole body
of an animal have been found to be approximately 1‰ more positive than that
of the animal’s diet (DeNiro and Epstein 1978.). This fractionation factor can be
accounted for by subtracting the fractionation factor from the stable isotope
ratio of the consumer’s bones, thus giving a more accurate isotope reading of the
diet of the animal (Ambrose 1993:60).
Plants use two photosynthetic pathways in order to create sugars. C₃ plants, such
as temperate shrubs, trees and many grasses living in cooler climates, and C₄
plants such as maize or grasses and herbs found in warmer tropical
environments, both contain carbon isotopes in their tissues (O’Leary 1988:330).
The first of these pathways is the Calvin pathway, where a three-­‐carbon
compound is created, which incorporates C₃ grouped plants. The second
alternative pathway is the Hatch-­‐Slack enzymatic pathway, which produces a
four-­‐carbon compound incorporating C₄ grouped plants (Aufderheide and
Santoro 1999:244; Slack and Hatch 1967). C₃ plants result in more negative
isotope values than do C₄ plants (such as maize and tropical grasses and herbs),
which result in more positive δ 13 C values within the person’s diet (Pate 1994;
Schoeninger and Moore 1992). From these differences in values it is possible to
determine the type of plants, C₃ or C₄, and marine versus terrestrial resources
that a person was consuming throughout their life.
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