Tracking mobility in Neolithic Scotland using strontium and sulfur isotope analysis of humans from Orkney and Caithness

We present here the results of strontium (n = 18) and sulfur (n = 10) isotope analysis of 15 individuals from Scottish Neolithic funerary monuments in Orkney and Caithness, undertaken to assess mobility during the Neolithic. We first created two random forest isoscapes using existing modern strontium and sulfur open access data to predict the underlying strontium and sulfur isotope values for this region. We then compared our measured strontium and sulfur results from these individuals with the predictive isoscapes to assess mobility using the AssignR software package. For most of the individuals our results indicate that they were likely to have been raised in the region where they were interred. One individual from Tulach an tÌ 'Sionnaich, Caithness, an adult male, had values from one of his three sampled teeth that suggested he was raised non-locally. Using the strontium isoscape and assignR, we examined the potential regions of origin at two thresholds of probability (25% and 75% quantiles) and suggest that this individual is likely to have come from northern Scotland. Our study shows the utility of random forest generated isoscapes and the possibilities of combining both strontium and sulfur isotopes for mobility studies.