Diet or mobility? Multi-isotopic (C, N, and Sr) dietary modeling at Shamanka II, Cis-Baikal, Siberia

Abstract

Dietary reconstructions increasingly rely on Bayesian techniques such as Food Reconstruction Using Isotopic Transferred Signals (FRUITS). These models benefit from the use of additional isotopic proxies (13C, 15N, and 87Sr/86Sr), which help refine proportional contributions of potentially overlapping reference groups. However, each new isotope comes with additional considerations and uncertainties. Strontium isotopes are typically discussed as recording primarily geographic information (place of origin) that can be used to infer the movements of individuals through different phases of their lives. Yet, strontium is incorporated into the body through the foods consume, as are 13C and 15N, raising the question of whether strontium ratios are informing primarily about movement of the individual or changes in the diet. Inferring human movement across landscape thus relies on demonstration that observed values could not have come from local sources and required inputs from other geographic regions. Contemporary biogeochemical records are necessary to resolve these possibilities. Refinements in the developmental age estimates for the specific sampling locations on human teeth enable the integration of additional isotopic data through matching of biochemical signatures obtained from dentin and enamel micro-samples. Using multi-isotopic dietary modeling allows better assessment of relative contributions to overall diet of food groups such as terrestrial large game, lake or riverine fish, seal, and plants (inner bark, willow shoots, mushrooms). Notable variability between human molars and adult bone strontium isotopic ratios has been inferred as representing the presence of non-locals at the Shamanka II cemetery. Dietary reconstruction suggests that plants are the primary variable responsible for this “mobility” indicator.