Blum Joel D, Drazen Jeffrey C, Johnson Marcus W, Popp Brian N, Motta Laura C, Jamieson Alan J
Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109;
Department of Oceanography, University of Hawaii at Manoa, Honolulu, HI 96822.
Proc Natl Acad Sci U S A. 2020 Nov 24;117(47):29292-29298. doi: 10.1073/pnas.2012773117. Epub 2020 Nov 16.
Mercury isotopic compositions of amphipods and snailfish from deep-sea trenches reveal information on the sources and transformations of mercury in the deep oceans. Evidence for methyl-mercury subjected to photochemical degradation in the photic zone is provided by odd-mass independent isotope values (ΔHg) in amphipods from the Kermadec Trench, which average 1.57‰ (±0.14, = 12, SD), and amphipods from the Mariana Trench, which average 1.49‰ (±0.28, = 13). These values are close to the average value of 1.48‰ (±0.34, = 10) for methyl-mercury in fish that feed at ∼500-m depth in the central Pacific Ocean. Evidence for variable contributions of mercury from rainfall is provided by even-mass independent isotope values (ΔHg) in amphipods that average 0.03‰ (±0.02, = 12) for the Kermadec and 0.07‰ (±0.01, = 13) for the Mariana Trench compared to the rainfall average of 0.13 (±0.05, = 8) in the central Pacific. Mass-dependent isotope values (δHg) are elevated in amphipods from the Kermadec Trench (0.91 ±0.22‰, = 12) compared to the Mariana Trench (0.26 ±0.23‰, = 13), suggesting a higher level of microbial demethylation of the methyl-mercury pool before incorporation into the base of the foodweb. Our study suggests that mercury in the marine foodweb at ∼500 m, which is predominantly anthropogenic, is transported to deep-sea trenches primarily in carrion, and then incorporated into hadal (6,000-11,000-m) food webs. Anthropogenic Hg added to the surface ocean is, therefore, expected to be rapidly transported to the deepest reaches of the oceans.
来自深海海沟的端足类动物和狮子鱼的汞同位素组成揭示了关于深海中汞的来源和转化的信息。克马德克海沟端足类动物的奇质量非质量依赖同位素值（ΔHg）提供了光化学降解甲基汞的证据，其平均值为1.57‰（±0.14，n = 12，标准差），马里亚纳海沟端足类动物的平均值为1.49‰（±0.28，n = 13）。这些值接近在太平洋中部约500米深度觅食的鱼类中甲基汞的平均值1.48‰（±0.34，n = 10）。与太平洋中部降雨平均值0.13（±0.05，n = 8）相比，克马德克海沟端足类动物的偶质量非质量依赖同位素值（ΔHg）平均值为0.03‰（±0.02，n = 12），马里亚纳海沟为0.07‰（±0.01，n = 13），这提供了降雨中汞贡献变化的证据。与马里亚纳海沟（0.26 ±0.23‰，n = 13）相比，克马德克海沟端足类动物的质量依赖同位素值（δHg）升高（0.91 ±0.22‰，n = 12），这表明在甲基汞库纳入食物网基础之前，微生物对甲基汞的去甲基化水平更高。我们的研究表明，约500米深度海洋食物网中的汞主要来自人为活动，主要通过腐肉被输送到深海海沟，然后纳入超深渊（6000 - 11000米）食物网。因此，添加到海洋表层的人为汞预计会迅速被输送到海洋的最深处。
