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.

中文翻译：

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西冰洋海洋顶级捕食者中汞稳定同位素的变化

最近对阿拉斯加海鸟卵和环状海豹肝脏中汞（Hg）稳定同位素的研究表明，海洋甲基汞光化学对海冰覆盖的控制。在这里，已经对互补的海洋哺乳动物组织进行了分析，以记录北极海洋食物网的汞，碳（C）和氮（N）稳定同位素组成的变化。汞稳定同位素比率的55白鲸（肝样品中测量学名Delphinapterus leucas）和15只北极熊（熊属maritimus自1990年以来大的变化收集）在δ ²⁰²汞柱（≈2.1‰）和Δ ¹⁹⁹汞柱（≈1.7‰）在物种之间以及物种覆盖范围内观察到了阿拉斯加湾-白令海-北冰洋地区。北极熊，主要取食环状密封件（δ ¹⁵N个移位4.2‰），显示相同的肝Δ ¹⁹⁹的Hg 0.5‰，证实不存在代谢质量无关的分馏，和0.33±0.11‰富集重汞柱同位素。白鲸的肝脏总Hg浓度随年龄增长而增加，反映了终生生物积累，而Hg形态因肝甲基Hg分解而随年龄而转变为无机Hg。Δ ²⁰⁰在生物群汞柱的变化示出了小，0.1‰从北太平洋到北冰洋栖息地下降，这表明大气汞沉积是在太平洋和地面汞柱输入主宰北冰洋重要。类似海鸟蛋，一以贯南向北梯度Δ ¹⁹⁹汞柱基线被认为是在哺乳动物肝组织，证实海冰覆盖作为海洋汞柱光还原控制因数和Δ ¹⁹⁹汞柱。北冰洋白鲸接近零Δ ¹⁹⁹汞，表明地面Hg和原位-produced甲基汞不是测量北冰洋进入海洋食物网前光还原。