Combined influence of meteoric water and protein intake on hydrogen isotope values in archaeological human bone collagen

Publication date: August 2018Source:Journal of Archaeological Science, Volume 96
Author(s): Christine A.M. France, Haiping Qi, Gwénaëlle M. Kavich
Hydrogen isotopes in archaeological human bone collagen are poorly understood, but present an opportunity to add new depth to our understanding of ancient populations. The competing influences of meteoric water versus protein intake on human bone collagen hydrogen isotope values were examined through comparison with the well-understood proxies of hydroxyapatite oxygen and collagen nitrogen isotopes, respectively. Consideration of the data set as individual points compared to averaged pools of individuals in each of 11 archaeological sites suggested the latter partially eliminates inherent variability due to food choice or regional movement. Collagen hydrogen isotopes were moderately correlated with hydroxyapatite oxygen isotopes (R = 0.695, site averages) and collagen nitrogen isotopes (R = 0.562, site averages). Correlation improved with a multiple linear regression including both oxygen and nitrogen (R = 0.745, site averages). Correlation between meteoric water hydrogen and oxygen isotope values converted from hydroxyapatite and collagen values, respectively, yielded a slope well below the expected value of ∼8 observed directly in meteoric water (i.e. the “meteoric water line”). Correlation between converted meteoric water hydrogen and the measured collagen non-exchangeable hydrogen isotope values showed a slope well below the expected value of 1.0. Theoretical meteoric water hydrogen isotope values and theoretical herbivorous collagen hydrogen isotope values were calculated based on previously established equations in order to construct a hypothetical framework free of trophic level influences. Deviations between actual values and these theoretical values correlated weakly with collagen nitrogen isotope values, suggesting that direct trophic level enrichment/depletion is not controlling the disparity between expected and measured values. The deviations are hypothetically caused by non-local food sources, and a decoupling of expected oxygen and hydrogen relationships as individuals consumed more meat and decreased in vivo non-essential amino acid production. This work presents a new model that facilitates understanding of the complex relationship between meteoric water and protein intake controls on hydrogen isotopes in omnivorous human populations that can potentially inform about past meteoric water values and amounts of animal protein consumption.