Hg-Stable Isotope Variations in Marine Top Predators of the Western Arctic Ocean

• Published in: ACS Earth and Space Chemistry
• Main Authors: Masbou, Jérémy, Sonke, Jeroen, E., Amouroux, David, Guillou, Gaël, Becker, Paul, R., Point, David
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux (IPREM), Université de Pau et des Pays de l'Adour (UPPA)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: Arctic; isotopes; mammals; mercury; MIF; [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.ANAL]Chemical Sciences/Analytical chemistry; [CHIM.POLY]Chemical Sciences/Polymers; [CHIM.MATE]Chemical Sciences/Material chemistry; Arctic Ocean; Bering Sea; Gulf of Alaska; Pacific; Beluga; Beluga whale; Beluga*; Delphinapterus leucas; ringed seal; Sea ice; Ursus maritimus; Alaska
• Online Access: https://hal.science/hal-01814156; https://doi.org/10.1021/acsearthspacechem.8b00017

International audience Recent studies on mercury (Hg)-stable isotopes in Alaskan seabird eggs and ringed seal livers illustrated the control of sea ice cover on marine methyl-Hg photochemistry. Here, complementary marine mammal tissues have been analyzed to document variations in Hg-, carbon (C)-, and nitrogen (N)-stable isotope compositions of Arctic marine food webs. Hg-stable isotope ratios were measured in liver samples of 55 beluga whales (Delphinapterus leucas) and 15 polar bears (Ursus maritimus) collected since 1990. Large variations in δ202Hg (≈2.1‰) and Δ199Hg (≈1.7‰) are observed between species and within species stocks covering the Gulf of Alaska-Bering Sea-Arctic Ocean regions. Polar bears, mainly feeding on ringed seal (δ15N shift of 4.2‰), show identical liver Δ199Hg of 0.5‰, confirming the absence of metabolic mass-independent fractionation, and 0.33 ± 0.11‰ enrichment in heavy Hg isotopes. Beluga whale liver total Hg concentrations increase with age, reflecting lifetime bioaccumulation, while Hg speciation shifts to inorganic Hg with age as a result of hepatic methyl-Hg breakdown. Δ200Hg variations in biota show a small, 0.1‰ decrease from North Pacific Ocean to Arctic Ocean habitats, suggesting atmospheric Hg deposition to be important in the Pacific and terrestrial Hg inputs to dominate in the Arctic Ocean. Similar to seabird eggs, a consistent south to north gradient in Δ199Hg baseline is seen in mammal liver tissues, confirming sea ice cover as a control factor on marine Hg photoreduction and Δ199Hg. Arctic Ocean beluga whales have near zero Δ199Hg, indicating that terrestrial Hg and in-situ-produced methyl-Hg are not measurably photoreduced in the Arctic Ocean before entering the marine food web