Early medieval reliance on the land and the local: An integrated multi-isotope study (⁸⁷Sr/⁸⁶Sr, δ¹⁸O, δ¹³C, δ¹⁵N) of diet and migration in Co. Meath, Ireland

Three early medieval Irish communities within a 30-km radius in Co. Meath, Ireland, have been examined using multiple isotopes (⁸⁷Sr/⁸⁶Sr, δ¹⁸O, δ¹³C, δ¹⁵N) to elucidate human and domesticated animal subsistence and provenance. Existing ⁸⁷Sr/⁸⁶Sr data from geochemical mapping of contemporary soils, plants and streamwater were compared to human and animal tooth enamel ⁸⁷Sr/⁸⁶Sr to assess potential past human migration, in combination with δ¹⁸O from bone collagen. Oxygen isotope (δ¹⁸O) values of human bone collagen are notably invariable, 10.0 ± 0.6‰ (n = 36), for the three archaeological sites: Collierstown, Johnstown and Raystown. Fauna (sheep, pigs, cats and a dog) δ¹⁸O_collagen from Raystown are distinctly grouped between and among certain species, the first instance to our knowledge of such a result. The aggregate faunal data demonstrate that δ¹⁸O_collagen values of faunal remains should not be used to infer local δ¹⁸O ranges for humans. Nitrogen isotope (δ¹⁵N) values for both domesticated animal (9.8 ± 1.7‰) and adult human (12.0 ± 0.8‰) bone collagen are tightly constrained suggesting a similar source of protein in the diet of humans. A mean carbon isotope (δ¹³C) value of −21.0 ± 0.4‰ for adult humans indicates overwhelming terrestrial sources of foodstuffs. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) from human dental enamel range from 0.7085-0.7110 (n = 25). Two individuals (R841 and R854), both from Raystown, are statistical outliers based on their ⁸⁷Sr/⁸⁶Sr and δ¹³C values and are likely migrants to the locality where they were buried. We note that one of these putative migrants met a particularly violent end.