Establishing a strontium isotope baseline in New Zealand for future archaeological migration studies: A case study

Abstract

The application of strontium isotopes to migration studies is well-documented and has been successful around the world. The main constraint of this is the need for geological and bioavailable baseline data from the region of interest. In New Zealand, human migration has played a major role during pre-European and post-European colonisation. Currently New Zealand does not have comprehensive strontium isotope baseline data, therefore isotopic interpretation of migration has been limited. This paper presents a method for the formation of a baseline strontium isotope map. Using published geological data, we define different geological groups across the country, but find that a number of these have overlapping 87Sr/86Sr ratios, likely because of the complex formation processes and tectonic activity of New Zealand. Bioavailable (plant) strontium samples from two sites in Otago were collected to test how closely bioavailable strontium aligned with these geologically predicted values. The bioavailable values overlapped with the geological values, but the bioavailable values also displayed a smaller range in 87Sr/86Sr ratios compared with the range of geological values. This study, we hope, will allow us to use this relationship between geological and bioavailable 87Sr/86Sr ratios to start the process of establishing a nationwide baseline to assist with future migration research. Our results will eventually be used to further understand human movement in the past and may aid in establishing provenance of kōiwi tangata (Māori human remains) for repatriation throughout New Zealand.