Quantum mechanics

Linguistics

Composite number

Philosophy

Isotopes of carbon

Materials science

Mineralogy

Biochemistry

Isotopes of nitrogen

Carbon fibers

Nitrogen

Geology

Oceanography

Biogeochemical cycle

Physics

Organic chemistry

Isotope analysis

Total organic carbon

Environmental chemistry

δ13C

Composite material

Chemistry

Stable isotope ratio

Composition (language)

Biomolecule

Diagenesis

Isotope

Journal of Archaeological Science

The carbon (δ13C) and nitrogen (δ15N) isotopic compositions of bone and tooth collagen provide a powerful tool for studying past biological, environmental, and cultural phenomena. Collagen has a well-understood chemical composition that has enabled the development of invaluable quality control (QC) criteria for isotopic data – something that is extremely rare among biogeochemical research on ancient biomolecules as a whole. The most important of these collagen QC criteria is atomic C:N ratio (ratio of carbon to nitrogen atoms), which provides an indicator of the extent to which the amount of carbon and nitrogen present in a sample matches the known composition of pure collagen, thereby indicating whether contamination or diagenesis may be influencing a sample's isotopic compositions. We present a model describing the relationship between the carbon and nitrogen isotopic and elemental compositions that accounts for the isotopic composition of the endogenous collagen and exogenous contaminants as well as taxon-specific information about the collagen's amino acid composition. In some cases the traditional C:N QC parameters are applicable, while in others they can result in the inclusion of unreliable (altered) isotopic data primarily due to contamination from humic substances. Using new and previously published data on taxa commonly encountered in ancient studies, we further illustrate how using traditional C:N QC parameters may lead to the inclusion of altered isotopic compositions in real archaeological and paleontological scenarios. We argue that the traditional ‘one size fits all’ approach to the C:N QC criterion should be avoided and we outline new collagen QC criteria specific to certain taxa and environments on the basis of the results of our model. These revised criteria will help to improve the interpretation of isotopic data by more accurately identifying samples with isotopic compositions altered by contamination.

Improved quality control criteria for stable carbon and nitrogen isotope measurements of ancient bone collagen