title: Mercury Stable Isotopes in Ornithogenic Deposits As Tracers of Historical Cycling of Mercury in Ross Sea, Antarctica.
abstract: Production of methylmercury (MeHg) in ocean waters and its bioaccumulation in marine organisms are critical processes controlling the fate and toxicity of mercury (Hg). However, these processes are not well understood in the Antarctic, where high levels of MeHg are observed in the subsurface ocean (100-1000 m). We explored the use of Hg stable isotope compositions in historical and modern biological deposits as a new approach for discerning Hg sources and tracing MeHg cycling in the ocean and bioaccumulation in marine biota. We found similar mass independent isotope fractionation (MIF) of Hg between a sediment profile containing historical penguin and seal feces deposits from coastal Antarctica and modern penguin and seal feces, suggesting that penguin and seal feces were the dominant sources of Hg to the sediments at different time periods. Furthermore, sediments dominated by seal feces displayed a significantly lower MIF slope (Δ(199)Hg/Δ(201)Hg) than those dominated by penguin feces despite similar extents of MIF. Since seals forage at greater depths (>400 m) than penguins (<100 m), the high MIF values and lower Δ(199)Hg/Δ(201)Hg in seal feces suggest that a significant fraction of MeHg accumulated by seals was produced in situ in the subsurface ocean from residual inorganic Hg(II) that sank from the euphotic zone after partial photoreduction. Our results suggest that in situ Hg methylation can be an important source of MeHg for marine biota, and Hg isotope compositions in biological archives can be valuable tracers of MeHg cycling.
authors.affiliation: †Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada.
authors.forename: Wang
authors.initials: W
authors.lastname: Zheng
authors.affiliation: ‡Institute of Polar Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Zhouqing
authors.initials: Z
authors.lastname: Xie
authors.affiliation: †Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada.
authors.forename: Bridget A
authors.initials: BA
authors.lastname: Bergquist
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D059001:Aquatic Organisms; D010872:Caniformia / Q000378:metabolism; D005591:Chemical Fractionation / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods*; D005243:Feces; D008628:Mercury / Q000032:analysis; D008629:Mercury Isotopes / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D046429:Spheniscidae / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury