What is our goal?
Isotopes are ubiquitous markers of provenance. For example, the ratio of strontium isotopes are very useful to track the provenance of materials (e.g., Fig. 1). Different rocks have different but predictable strontium isotope ratios based on their geology. Those geochemical signatures are transmitted to living things through the ingestion of local water and food. By analyzing the tissues of individuals, we can reconstruct their mobility history. For example, the strontium isotopes along teeth, hair or even tusk record the different locations an individual moved to.
For instance, the geochemistry of my teeth shows that I was born in the Antilles (where the geology is very special), and moved to mainland France during my early childhood. My bones probably still show that I lived in the US for many years. Finally my hair looks like cold and geologically old Canada!
My aim is to apply and predict spatiotemporal isotope variations in a range of substrates to develop novel geolocation tools.
How do we do this?
We analyze isotopes of soil, hair, salmon, human teeth or water depending on the question we are trying to solve using mass spectrometers.
We develop GIS models to predict the isotope patterns on the lanscape of the study area (e.g., Fig. 2)
We use those models and Bayesian statistics to assign the geographic origin of the material studied.
Why should you care?
The spatial models we have developed can be used for many applications of provenance. Many animals are too small and numerous to be tracked with GPS (e.g., insects). Isotopes offer an alternative to track the dispersal/migration of insects that provide essential services to ecosystems but can also carry diseases, seeds or GMOs from other countries (Fig. 3).
Isotopes are also useful when studying animal or human that have been dead for a long time (Fig. 4). For example, isotopes are the only tool we have to ask questions about extinct animals. Why did some animals like the woolly mammoth, become extinct during the last Ice Age? Or why were all these humans buried together in a mass grave? My work combining isotope and statistical modeling answers questions about these individuals.
Fig. 1 Strontium isotopes cycling in ecosystems (from Bataille et al. 2020)
Fig. 2 Global bioavailable strontium isoscape built using machine-learning regression (from Bataille et al. 2020)
Fig. 3 Painted ladies butterfly and their geographic provenance based on the isotopic composition of their wings (from Talavera et al. 2018)
Fig. 4 Bisons in Alaska and their geographic provenance based on the isotopic composition of their teeth (from Funck et al. 2021)