Nitrogen and sulfur isotopes predict variation in mercury levels in Arctic seabird prey

Mercury (Hg) biotransformation and biomagnification are processes that affect Hg burdens in wildlife. To interpret variation in Hg in seabird eggs, used as Hg bioindicators in the Arctic, it is important to understand how Hg biomagnifies through the food web. We evaluated the use of δ³⁴S, along with other commonly used stable isotope signatures (δ¹⁵N and δ¹³C), for the determination of possible sources of Hg in an Arctic food web (56 individuals of 15 species of fish and invertebrates). Hg correlated with δ³⁴S (R² = 0.72). When the combined effects of δ³⁴S and δ¹⁵N were considered in mixed-effects models, both δ³⁴S and δ¹⁵N together described Hg patterns in Arctic food webs better than either isotope alone. Our results demonstrate the usefulness of δ³⁴S to account for variation in Hg among marine animals and to study the possible underlying effects that MeHg production may have on Hg pathways in Arctic ecosystems.