Mobility or diet? The importance of interpretating bioarchaeological strontium data alongside environmental baselines and archaeological information

Strontium isotope analysis is a common tool in archaeological studies, providing invaluable information on past human mobility and diet. The interpretation of these strontium data requires additional sources of information, such as an environmental baseline built from modern plants to confirm the local strontium signature or archaeological evidence to identify or restrict potential origins and food sources.
This presentation will discuss the combination of strontium isotope analysis (87Sr/86Sr and δ88Sr) and concentration ([Sr]) on bioarchaeological samples and highlight the necessity of these avenues of additional information, using a Roman case study from the site of Tongobriga in northern Portugal. A modern plant baseline, consisting of 30 sampling sites within 50km of the site and 78 sampling sites across northern Portugal, has been constructed which identifies the local 87Sr/86Sr, δ88Sr and [Sr] signatures. Strontium analysis on cremated human remains from Tongobriga necropolis (1st century CE) all returned values not consistent with a local origin suggesting either all individuals were non-local or perhaps the consumption of non-local food resources. In this presentation, these two possibilities will be explored. Using the local plant 87Sr/86Sr, δ88Sr and [Sr], and archaeological evidence for food sourcing from the site, the potential sources of Sr in the diet will be modelled. Lastly, implications for interpreting strontium data without these two avenues of information will be explored.