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 δS, along with other commonly used stable isotope signatures (δN and δC), 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 δS (R = 0.72). When the combined effects of δS and δN were considered in mixed-effects models, both δS and δN together described Hg patterns in Arctic food webs better than either isotope alone. Our results demonstrate the usefulness of δS 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.