Bioavailable soil and rock strontium isotope data from Israel

Strontium isotope ratios (87Sr = 86Sr) of biogenic material such as bones and teeth reflect the local sources of strontium ingested as food and drink during their formation. This has led to the use of strontium isotope ratios as a geochemical tracer in a wide range of fields including archaeology, ecology, food studies and forensic sciences. In order to utilise strontium as a geochemical tracer, baseline data of bioavailable 87Sr = 86Sr in the region of interest are required, and a growing number of studies have developed reference maps for this purpose in various geographic regions, and over varying scales. This study presents a new data set of bioavailable strontium isotope ratios from rock and soil samples across Israel, as well as from sediment layers from seven key archaeological sites. This data set may be viewed and accessed both in an Open Science Framework repository (https://doi.org/10.17605/OSF.IO/XKJ5Y, Moffat et al., 2020) or via the IRHUM (Isotopic Reconstruction of Human Migration) database.

Spatially resolved LA-MC-ICPMS strontium isotope microanalysis of archaeological fauna

The analysis of the strontium isotope composition of archaeological materials can provide important information about the mobility of a range of mammals, including humans. The basis of this method is that, prior to any postburial diagenesis, the Sr87/Sr86 ratio of bone and teeth reflects the geological environment from which food and water were sourced while these biominerals were forming. Teeth are particularly amenable to tracing the geographic origins of humans as they mineralize during the first 12–13 years of life (White and Folkens, 2005) and do not subsequently change strontium composition after this time (Schweissing and Grupe, 2003). Strontium isotope analysis can be used to determine if individuals are local or nonlocal by comparison to the isotopic composition in and around their burial location (i.e., Schweissing and Grupe, 2000; Bentley et al., 2007; Conlee et al., 2009). In order to quantify the extent of faunal mobility, the strontium isotope composition of biominerals from fossil samples needs to be compared with a regional map of values obtained either from local faunal material (Price et al., 2002) or from analysis of the bioavailable component of strontium from plants, regolith, or bedrock (Capo et al., 1998).Strontium isotope analysis has been extensively applied to the determination of archaeological mobility, as reviewed by Price et al. (2002), Budd et al. (2004), Bentley (2006), and Montgomery (2010). Although studies of Paleolithic or older archeological material are rare, some have been undertaken on hominins (Sillen et al., 1995, 1998; Richards et al., 2008; Copeland et al., 2011) and faunal material (Horn et al., 1994; Copeland et al., 2010; Britton et al., 2011).Enamel has been shown to be the most favorable material for strontium isotope analysis based on its ability to resist postburial alteration far better than dentine, cement, or bone (Trickett et al., 2003). Enamel of some species grows over extended periods and, when analyzed with microprofiling or laser ablation analysis, can be used to reconstruct comprehensive life histories. This approach demonstrated the seasonal mobility of cattle in Iron Age Britain (Horstwood et al., 2008), Neolithic Germany (Bentley and Knipper, 2005), and England (Viner et al., 2010).

The IRHUM (Isotopic Reconstruction of Human Migration) database – bioavailable strontium isotope ratios for geochemical fingerprinting in France

Strontium isotope ratios (87Sr / 86Sr) are a key geochemical tracer used in a wide range of fields including archaeology, ecology, food and forensic sciences. These applications are based on the principle that the Sr isotopic ratios of natural materials reflect the sources of strontium available during their formation. A major constraint for current studies is the lack of robust reference maps to evaluate the source of strontium isotope ratios measured in the samples. Here we provide a new data set of bioavailable Sr isotope ratios for the major geologic units of France, based on plant and soil samples (Pangaea data repository doi:10.1594/PANGAEA.819142). The IRHUM (Isotopic Reconstruction of Human Migration) database is a web platform to access, explore and map our data set. The database provides the spatial context and metadata for each sample, allowing the user to evaluate the suitability of the sample for their specific study. In addition, it allows users to upload and share their own data sets and data products, which will enhance collaboration across the different research fields. This article describes the sampling and analytical methods used to generate the data set and how to use and access the data set through the IRHUM database. Any interpretation of the isotope data set is outside the scope of this publication.

Mapping of bioavailable strontium isotope ratios in France for archaeological provenance studies

Strontium isotope ratios (87Sr/86Sr) of archaeological samples (teeth and bones) can be used to track mobility and migration across geologically distinct landscapes. However, traditional interpolation algorithms and classification approaches used to generate Sr isoscapes are often limited in predicting multiscale 87Sr/86Sr patterning. Here we investigate the suitability of plant samples and soil leachates from the IRHUM database (www. irhumdatabase.com) to create a bioavailable 87Sr/86Sr map using a novel geostatistical framework. First, we generated an 87Sr/86Sr map by classifying 87Sr/86Sr values into five geologically representative isotope groups using cluster analysis. The isotope groups were then used as a covariate in kriging to integrate prior geological knowledge of Sr cycling with the information contained in the bioavailable dataset and enhance 87Sr/86Sr predictions. Our approach couples the strengths of classification and geostatistical methods to generate more accurate 87Sr/86Sr predictions (Root Mean Squared Error=0.0029) with an estimate of spatial uncertainty based on lithology and sample density. This bioavailable Sr isoscape is applicable for provenance studies in France, and the method is transferable to other areas with high sampling density. While our method is a step forward in generating accurate 87Sr/86Sr isoscapes, the remaining uncertainty also demonstrates that finemodelling of 87Sr/86Sr variability is challenging and requires more than geological maps for accurately predicting 87Sr/86Sr variations across the landscape. Future efforts should focus on increasing sampling density and developing predictive models to further quantify and predict the processes that lead to 87Sr/86Sr variability.

Strontium Isotope Investigation of Human Mobility Based on Teeth from Cave T1

Seven adult human teeth from Cave T1 were analysed for trace element concentrations using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) and strontium isotope compositions using Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS). The aim of this study was to examine whether the people buried in Cave T1 were of local or foreign origin, given the known connection of Philistine Tell es-Safi/ Gath with the Aegean, Cyprus and Anatolia (e.g., Maeir 2012). The results for the burial cave specimens were compared to bioavailable 87Sr/86Sr values obtained from soil and rock samples from key geological units throughout Israel. This comparison shows that at least four of the individuals have 87Sr/86Sr values that correspond to the area immediately surrounding the site. The remaining samples analysed in this study have 87Sr/86Sr values that do not correspond to any mapped samples from Israel. This result is explained not by mobility, but as an artifact of the very low strontium concentration in these teeth, which precludes an effective correction for isobaric interferences during laser ablation analysis.