Geographical variability in northern European sheep wool isotopic composition (δ ¹³ C, δ ¹⁵ N, δ ² H values)

Rationale Light stable isotopic analysis of herbivore proteinaceous tissues (hair, muscle, milk) is critical for authenticating the point of origin of finished agricultural or industrial products in both ancient and modern economies. This study examined the distribution of light stable isotopes in herbivores in northern Europe (Iceland to Finland), which is expected to depend on regional-level environmental inputs (precipitation, temperature) and local variables (vegetation type, fodder type, soil type). Methods Sheep wool was obtained from animals managed using traditional methods and located across a gradient of northern European environments. Defatted whole-year samples were analysed by isotope ratio mass spectrometry (IRMS) for carbon (δ¹³C values), nitrogen (δ¹⁵N values) and un-exchangeable hydrogen (δ²H values) isotopic composition. Results Wool δ¹³C, δ¹⁵N and δ²H values showed the same correlations to local mean annual precipitation and temperature as were expected for graze plants. Wool δ²H values were correlated with local modelled meteoric water δ²H values, mediated by plant solid tissue and leaf water fractionations. Cluster analysis distinguished wool from Sweden and the Baltic region from more western material. Local variation in vegetation or soil type did not disrupt dependence on climatic variables but did affect geospatial discrimination. Conclusions Wool isotopic composition in northern Europe is controlled by the effects of local precipitation and temperature on graze plant inputs, and is only weakly affected by pasture type.