Geochemistry

Strontium isotope baseline mapping

The IRHUM (Isotopic Reconstruction of Human Migration) database is a web platform to access, explore and map isotope data to investigate migration. It is maintained at the Research School of Earth Sciences, ANU.

Citation: M. Willmes, L. McMorrow, L. Kinsley, R. Armstrong, M. Aubert, S. Eggins, C. Falguères, B. Maureille, I. Moffat, R. Grün (2014), The IRHUM (Isotopic Reconstruction of Human Migration) database – bioavailable strontium isotope ratios for geochemical fingerprinting in France. Earth System Science Data 6, 117–122. doi: doi:10.5194/essd-6-117-2014

Archaeological provenance studies in France are currently limited due to the lack of baseline strontium isotope maps. This online database allows the user to explore and map isotopic datasets and exchange data in a variety of formats. It is based on the open source software GeoNode (Boundless) and all modifications are tracked in GitHub, to allow future developments. To ensure the longevity of the dataset it is deposited in the Pangaea data repository (doi:10.1594/PANGAEA.819142). Since strontium isotope ratios are used as a geochemical tracer in a wide range of fields outside of archaeology, including ecology, soil, food and forensic sciences, the IRHUM database will hopefully prove to be a useful tool for the wider science community and encourage collaboration between the different fields of science for geochemical fingerprinting. The data found in the IRHUM database can be used to create bioavailable 87Sr/86Sr isotope maps of France for archaeological provenance studies. A manuscript outlining this mapping is currently is preparation.

Funding was provided by ARC DP110101415 (Grün, Spriggs, Armstrong, Maureille and Falguères) Understanding the migrations of prehistoric populations through direct dating and isotopic tracking of their mobility patterns. Part of this research was supported by the Australian French Association for Science & Technology through the ACT Science Fellowship program (2013).

Advances in laser ablation analysis of fish hardparts

Strontium isotope ratios (87Sr/86Sr) in otoliths are a well-established tool to determine origins and movement patterns of fish. However, otolith extraction requires sacrificing fish, and when working with protected or endangered species the use non-lethal samples such as scales, spines, and fin rays, is preferred. Unlike otoliths that are predominantly aragonite, these tissues are comprised of biological apatite. Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analysis of biological apatite can induce significant interference on mass 87, causing inaccurate 87Sr/86Sr measurements. To quantify this interference, we applied LA-MC-ICP-MS to three marine samples (white seabass, Atroctoscion nobilis, otolith; green sturgeon, Acipenser medirostris, pectoral fin ray; salmon shark, Lamna distropis, tooth) and freshwater walleye (Sander vitreus) otoliths, scales, and spines. Instrument conditions that maximize signal intensity resulted in elevated 87Sr/86Sr isotope ratios in the bioapatite samples, related to a polyatomic interference (40Ca31P16O,40Ar31P16O). Retuning instrument conditions to reduce oxide levels removed this interference, resulting in accurate 87Sr/86Sr ratios across all tissue samples. This method provides a novel, non-lethal alternative to otolith analysis to reconstruct fish life histories.