ИСТИНА

Mercury (Hg) contamination in Arctic ecosystems has wide impacts on wildlife, with amplified effects on top-predators such as seabirds, exhibiting highest concentrations due to Hg biomagnification along the trophic chain. The cycling circulation of Hg in the environment is still an issue despite international regulations, raising the question of the source of contamination for Arctic species, notably through melting sea ice influenced by global changes. Hg stable isotopes have been recently used to provide key evidence about the complex biogeochemical pathways that Hg undergoes before reaching the food web. But isotopic information alone is insufficient to clearly demonstrate the role of sea ice on Hg bioaccumulation and trophic transfer. Highly branched isoprenoids (HBIs) are biomarker tools which allow to evaluate the importance of sea ice-associated preys into the diet of predator species. We therefore combined for the first time the use of Hg stable isotopes and HBIs to provide new insights into the role of sea ice as a source of Hg in seabirds. We analysed blood samples collected on common eiders (Somateria mollissima) in four Arctic regions influenced by contrasting sea ice conditions. Our first results show that birds’ diet partially explains their Hg contamination, which also seems influenced by the presence of sea ice. Sources and levels of Hg contamination also depend on whether Hg inputs were terrestrial or oceanic, in association with sea ice. These results underscore the importance of integrating diverse analytical tools to advance fundamental knowledge and support conservation policies in a global change context.