Identifying locals vs non-locals using 87Sr/86Sr isotope analysis: a multimethod approach in the homogeneous environments of the Arabian Gulf

Abstract

Archaeological strontium isotope investigations of the movement of peoples and animals rely on different methods to characterize a “local” strontium range. In geologically homogenous regions or regions where the creation of isoscapes using proxies is hampered, statistical methods are useful for identifying individuals likely to be local or non-local. We demonstrate how a multi-method approach can be used to evaluate local strontium isotope ranges in Bahrain, an archipelago in the Arabian Gulf. Combining the enamel samples analyzed for this paper (62 human and domesticate herbivore individuals) with previously published faunal 87Sr/86Sr values from Bahrain (20 domesticated herbivores), we found that different statistical methods identified different numbers of individuals as local and were predicated on different assumptions about the distribution of the data. Compared to the standard approach using 2σ of the sample mean, the statistical approaches used in this manuscript identified more potential non-local or securely non-local individuals. Between 18.5 and 44.4% of the non-human animals were identified as non-local, indicating the trade of animals and why using faunal (herbivore) samples alone to characterize a local range is problematic in trading centers. The identification of between 13.7 and 32.9% of the humans as non-local is consistent with other studies of movement in archaeological populations of the Gulf and makes sense given the prominent role of trade in Bahrain from the Early Dilmun to Islamic periods. We argue that statistical approaches to identifying probable non-locals can be used where detailed isoscape data are hard to obtain, but that such results need to be evaluated within the specific archaeological context.