Fig. 4: Hg stable isotope composition in aquatic key species and peat in Greenland, dominating processes in the aquatic environment, internal (tissue-specific) isotopic fractionation in the key species, and trophic level transfer/isotopic fractionation.

a Odd-isotope mass-independent fractionation (Δ¹⁹⁹Hg) versus mass-dependent fractionation (δ²⁰²Hg) in the muscle tissue of all samples included in this study, i.e., land-locked Arctic char (Salvelinus alpinus, n = 32), shorthorn sculpin (Myoxocephalus scorpius, n = 58), glaucous gull (Larus hyperboreus, n = 15), ringed seal (Pusa hispida, n = 239), and polar bear (Ursus maritimus, n = 195) sampled in Greenland in 1983-2024, and peat core samples (down to 25 cm depth, n = 35). b Odd-isotope mass-independent fractionation signatures (Δ²⁰¹Hg and Δ¹⁹⁹Hg) in all muscle tissues of land-locked Arctic char (inserted graph) and marine aquatic key species in this study compared to experimentally measured trendlines for residual methyl-Hg from aqueous photochemical demethylation and residual Hg(II) from aqueous photochemical reduction of Hg(II)¹³. c Boxplot of δ²⁰²Hg in the muscle and liver of land-locked Arctic char, shorthorn sculpin, ringed seal, glaucous gull, and polar bear sampled in 2021-2023. For polar bear, δ²⁰²Hg in hair and kidney is also shown. The middle line in the box represents the median, the box limits indicate the upper and lower quartiles, and the whiskers represent the range up to 1.5 times the interquartile range. d, Δ¹⁹⁹Hg versus δ²⁰²Hg in the muscle tissue of shorthorn sculpin, ringed seal, glaucous gull, and polar bear sampled in 2021-2023 in Central East Greenland (ITT), representing different trophic levels (although food web dynamics are complex as discussed in the text). Abbreviations used: ITT Ittoqqortoormiit, QAA Qaanaaq, QEQ Qeqertarsuaq, ISO Isortoq, ZAC Zackenberg. In all the figures, the bars indicate analytical uncertainty (mean ± 2 SD on replicate standards), and ellipses show 95% confidence intervals.