On the premises of mixing models to define local bioavailable 87Sr/86Sr ranges in archaeological contexts

In archaeological mobility studies, non-local humans and animals can be identified by means of stable strontium isotope analysis. However, defining the range of local Sr-87/Sr-86 ratios is prerequisite. To achieve this goal, proxybased mixing models have recently been proposed using Sr-87/Sr-86 ratios measured in modern local vegetation, water and soil samples. Our study complements earlier efforts by introducing archaeological animal bones as an additional proxy. We then evaluate the different modelling approaches by contrasting proxy-results generated for the county of Erding (Upper Bavaria, Germany) with a comprehensive set of strontium measurements obtained from tooth enamel of late antique and early medieval human individuals (n = 49) from the same micro-region. We conclude that current mixing models based on environmental proxies dearly underestimate the locally bioavailable Sr-87/Sr-86 ratios due to the limited sample size of modern environmental specimens and a suit of imponderables inherent to e fforts modelling complex geobiological processes. In sum, currently available mixing models are deemed inadequate and can therefore not be recommended. (C) 2020 Published by Elsevier B.V.