Strontium in Portugal: merging datasets to create a robust strontium baseline

The creation of bioavailable strontium baseline maps are critical for interpreting bioarchaeological data. With the increasing production of local archaeological site-specific, regional or national maps, devising an approach for combining these datasets to create larger or higher density isoscapes is crucial. Using Portugal as a case study, this presentation will discuss how combining different archives and scales of strontium isotope data can provide a robust baseline for archaeological mobility studies. The presentation will introduce the first country-wide bioavailable strontium baseline for Portugal, created using paired plant and soil leachate measurements from 151 sampling sites. Our dataset will be used as a foundation, with additional data from published archaeological site baselines (using modern plant, human bones and faunal remains), our recently collected regional plant samples, and published European and global datasets (on agricultural soils and mineral waters) compared. Plant samples provide the majority of strontium data in Portugal, and are a solid base for archaeological studies. This approach provides an opportunity to compare different archives to this plant base to highlight the variability in the archives used for strontium mapping and to highlight inadequacies in our current sampling strategies. Comparing datasets also allows for an evaluation of isotopic variation on varying scales; wide-scale sampling highlights how the diverse geological, geographical, and climatic regions of Portugal lead to an interesting spatial distribution of 87Sr/86Sr across the country. Furthermore, regional and site-specific sampling allows for the assessment of residential mobility and the range of landscapes used by past human populations. Reconstructing palaeomobility patterns requires a full picture of isotopic diversity at both the local, regional and broader level, combining datasets of varying scales moves us one step closer to creating the robust baselines required.