Defining the Estonian strontium isoscape for archeological and paleoecological provenance studies

Strontium isotope analysis has been used in archeology for about 40 years to study the prov­enance and mobility of ancient humans and animals. The interpretation of strontium isotope compositions in archeological materials requires a reference isotopic baseline map that delineates the geographical variation of bioavailable strontium. This paper introduces the first full map of bioavailable strontium in Estonia, based on the 87Sr/86Sr ratio of bioavailable strontium collected from 84 rodents and snails across 38 locations. The results were compared with data that also include larger wild and domestic mammals, to see if their data can be used as a reference in future studies. The analysis identified two clearly distinct isotopic areas in relation to Estonia’s bedrock composition: (1) coastal and central Estonia, including the West Estonian archipelago, where bedrock is composed of Ordovician and Silurian carbonate rocks and characterized by bioavailable 87Sr/86Sr ratios between 0.7094 and 0.7147; and (2) southern Estonia, located predominantly on Devonian sandstone bedrock, with 87Sr/86Sr ratios of 0.7147–0.7185. The analysis also showed that when stricter statistical methods were applied, the dataset that included larger wild and domestic mammals gave similar results. Hence, in Estonia, our expanded dataset can be cautiously used to provide context in areas where rodent data are missing. The baseline map refines and expands our current knowledge about the distribution of bioavailable strontium in the Baltic Sea region.