Stable Isotope Analysis as a Geospatial Tool for Identification: Intra-Individual Isotopic Variability

Geo-profiling from stable isotope analysis of human tissues is a powerful technique, providing investigative leads for the nameless. There is an urgent need for such methods, with nearly 12,000 unidentified human remains in the NamUs database. However, as isotopic geo-profiling experiences a surge in use, the science underpinning these techniques must be rigorously proven to be reliable. Until now, no high-spatial resolution studies exist on intra-individual isotopic variability of modern individuals with known residence a key knowledge gap in producing accurate and precise predictions of geographic origins. AIM 1: Constrain the intra-individual oxygen and strontium isotopic variance in bones and teeth of individuals with known residence history. AIM 2: Evaluate the accuracy of geographic predictions of residence for known individuals. The sampled individuals have been donated to decomposition facilities at the University of Tennessee, Texas State University, and Colorado Mesa University. 35 individuals will have 18 skeletal and 2 dental elements analyzed for carbon, nitrogen, oxygen, and strontium isotope composition. These three facilities are located in different geographic regions with different absolute isotopic values and different isotopic gradients. The intra-individual variance may be larger in regions with steeper isotopic gradients, although this has never been previously demonstrated. Samples for light stable isotopes will be prepared at Middle Tennessee State University, while trace elements and radiogenic strontium isotopes will be analyzed at Arizona State University. The assumption of equal variance will be statistically tested between geologic regions and between load-bearing and non-load bearing bones. The assumption of a normal data distribution will be tested before determining confidence intervals for distinguishing local from non-local individuals and thresholds for differentiating between intra-individual variation and residential mobility. This dataset also will improve the estimation of the carbonate oxygen and phosphate oxygen isotopic offset and test whether less destructive sampling of proximal phalanges can provide equivalent isotopic information compared to load-bearing bones such as femurs. Individuals who have had constant residency will be prioritized for study inclusion, but some analyzed individuals will have experienced residential mobility, allowing assessment of the expression of residential mobility in bone and teeth. Products of this research will include data submission to open data warehouses, peer-reviewed papers, conference presentations, and trainings about sample collection and analytical availability to local law enforcement and to students. This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14). CA/NCF