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Article Dans Une Revue ACS Earth and Space Chemistry Année : 2018

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

Jérémy Masbou
Jeroen E. Sonke
  • Fonction : Auteur
Gaël Guillou
  • Fonction : Auteur
Paul R. Becker
  • Fonction : Auteur
David Point

Résumé

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
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Dates et versions

hal-01814156 , version 1 (12-06-2018)

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Citer

Jérémy Masbou, Jeroen E. Sonke, David Amouroux, Gaël Guillou, Paul R. Becker, et al.. Hg-Stable Isotope Variations in Marine Top Predators of the Western Arctic Ocean. ACS Earth and Space Chemistry, 2018, 2 (5), pp.479 - 490. ⟨10.1021/acsearthspacechem.8b00017⟩. ⟨hal-01814156⟩
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