Enhancing archaeological mobility studies: Bayesian-modelled isoscapes and high-resolution refinement of the bioavailable strontium baseline in southern Scandinavia

Mapping spatial variability of bioavailable strontium isotopes ( 87 Sr/ 86 Sr) is fundamental to robust analyses of prehistoric human and animal mobility and provenance based on strontium isotope data. A key challenge is how to construct and extrapolate a baseline for specific landscapes to enable meaningful correlation with high-resolution archaeological data. This study presents a regional high-resolution strontium isotope baseline (isoscape) for southern Scandinavia, developed by integrating a dataset consisting of 1293 samples of water, plants, and micromammal teeth. Of these, 248 were newly collected from previously underrepresented areas, with particular attention to minimising modern contamination. Sampling density is high, with approximately 15 sampling locations per 1000 km 2 in Denmark and 5 per 1000 km 2 in southern Sweden. Interpolated maps of bioavailable strontium were generated using Empirical Bayesian Kriging Regression Prediction (EBKRP), incorporating geological and topographic covariates (lithology, geological age, elevation, and gravity anomaly) to enhance predictive precision. The results reveal substantial geographic variation, with pronounced heterogeneity in geologically complex regions such as Blekinge in southeastern Sweden, while Denmark displays a more homogeneous isotopic distribution. A sea spray effect, resulting in lower 87 Sr/ 86 Sr values, is also evident along the Swedish west coast. This refined isoscape facilitates more precise assessments of mobility and provenance by combining multiproxy data (water, plants, fauna) with geostatistical modelling. This is illustrated on a local scale through an example from the Mesolithic site Ageröd I:HC, where the high-resolution model facilitates more detailed interpretations of Mesolithic mobility and hunting territories. The study thereby demonstrates a methodological framework for constructing and applying bioavailable strontium baselines with high regional detail in archaeological research. By integrating new and existing data with targeted sampling, rigorous analytical protocols, and advanced spatial modelling, the study highlights the importance of regional high-resolution, context-sensitive isoscapes and provides an improved framework for interpreting prehistoric mobility. • Bioavailable strontium isotope baseline (isoscape) for southern Scandinavia. • The 87 Sr/ 86 Sr values range from 0.7065 to 0.7382 in the region. • Baseline based on 1293 samples from water, plants, and small mammals. • EBK regression prediction and multiproxy approach yield high spatial precision. • Higher 87 Sr/ 86 Sr in northeast, lower in Denmark/Skåne; large variation in Blekinge.