Zinc isotopes from archaeological bones provide reliable trophic level information for marine mammals

In marine ecology, dietary interpretations of faunal assemblages often rely on nitrogen isotopes as the main or only applicable trophic level tracer. We investigate the geographic variability and trophic level isotopic discrimination factors of bone zinc (66)Zn/(64)Zn ratios (δ(66)Zn value) and compared it to collagen nitrogen and carbon stable isotope (δ(15)N and δ(13)C) values. Focusing on ringed seals (Pusa hispida) and polar bears (Ursus maritimus) from multiple Arctic archaeological sites, we investigate trophic interactions between predator and prey over a broad geographic area. All proxies show variability among sites, influenced by the regional food web baselines. However, δ(66)Zn shows a significantly higher homogeneity among different sites. We observe a clear trophic spacing for δ(15)N and δ(66)Zn values in all locations, yet δ(66)Zn analysis allows a more direct dietary comparability between spatially and temporally distinct locations than what is possible by δ(15)N and δ(13)C analysis alone. When combining all three proxies, a more detailed and refined dietary analysis is possible.