Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems

Journal name:
Nature Geoscience
Year published:
Published online
Corrected online


Atmospheric deposition of mercury to remote areas has increased threefold since pre-industrial times. Mercury deposition is particularly pronounced in the Arctic. Following deposition to surface oceans and sea ice, mercury can be converted into methylmercury, a biologically accessible form of the toxin, which biomagnifies along the marine food chain. Mass-independent fractionation of mercury isotopes accompanies the photochemical breakdown of methylmercury to less bioavailable forms in surface waters. Here we examine the isotopic composition of mercury in seabird eggs collected from colonies in the North Pacific Ocean, the Bering Sea and the western Arctic Ocean, to determine geographical variations in methylmercury breakdown at northern latitudes. We find evidence for mass-independent fractionation of mercury isotopes. The degree of mass-independent fractionation declines with latitude. Foraging behaviour and geographic variations in mercury sources and solar radiation fluxes were unable to explain the latitudinal gradient. However, mass-independent fractionation was negatively correlated with sea-ice cover. We conclude that sea-ice cover impedes the photochemical breakdown of methylmercury in surface waters, and suggest that further loss of Arctic sea ice this century will accelerate sunlight-induced breakdown of methylmercury in northern surface waters.

At a glance


  1. Common and thick-billed murre colony locations and sea-ice conditions at the beginning of the 2002 breeding season.
    Figure 1: Common and thick-billed murre colony locations and sea-ice conditions at the beginning of the 2002 breeding season.

    a, The colonies include Cape Lisburne (CLIS) in the Chukchi Sea; St Lawrence (STLW), St George (STGE) and Bogoslof islands (BOGO) in the Bering Sea; and East Amatuli (EAAM) and St Lazaria islands (STLA) in the Gulf of Alaska (see Supplementary Table S1). Numbers of samples analysed from the colonies are shown in parentheses, and the dashed circles show the maximum 170km foraging range around them. Sea-ice concentrations (%) show the relative amounts of ice in 25km by 25km blocks in late March 2002. b, Murres breeding at northern latitudes stage and forage in the open lead systems shown in the inset pictures.

  2. Mercury three-isotope diagrams illustrating variations in mercury MDF and MIF in murre eggs.
    Figure 2: Mercury three-isotope diagrams illustrating variations in mercury MDF and MIF in murre eggs.

    ac, δ202Hg plotted against δ200Hg (a), δ201Hg (b) and Δ201Hg (c). See Fig. 1 for legend. The dashed lines in a and b represent the theoretically predicted MDF based on the δ202Hg values35. Mercury δ199Hg and Δ199Hg information is shown in Supplementary Fig. S1. The dotted lines in b and c show the regression trends for the birds breeding at northern latitudes (eastern Chukchi Sea) and southern latitudes (southern Bering Sea and Gulf of Alaska). The uncertainties reported for the samples are the external reproducibility (n = 7) of the method used for NIST Murre Egg Control Material QC04-ERM1 (±0.26‰, 2σ, s.d. for δ202Hg, and ±0.10‰, 2σ, s.d. for Δ201Hg).

  3. Ecological effects on mercury MDF and MIF in murre eggs.
    Figure 3: Ecological effects on mercury MDF and MIF in murre eggs.

    ac, Influence of trophic levels (colony mean ± σ, s.d.) on Hg concentrations (colony mean ± σ, s.d.) (a), Hg MDF (δ202Hg, colony mean ± σ, s.d.) (b) and Hg MIF (Δ201Hg, colony mean ± σ, s.d.) (c) for murre egg sampling events (see Supplementary Table S1 for details and Fig. 1 for legend). The trophic levels of the eggs were estimated from δ15N measurements made on the samples using the method reported by Hobson and co-workers39 and corrected for δ15N baseline shifts (see Supplementary Method S1). Solid lines show the regression trends for the southern Bering Sea and Gulf of Alaska eggs, and dashed lines show the regression trends for all colonies.

  4. Effect of latitude on mercury MIF.
    Figure 4: Effect of latitude on mercury MIF.

    Colony mean Δ201Hg (±σ, s.d.) for common and thick-billed murre eggs collected at different latitudes in the Gulf of Alaska and Bering and Chukchi seas (see Fig. 1 for legend).

  5. Influence of sea ice on egg mercury MIF.
    Figure 5: Influence of sea ice on egg mercury MIF.

    Influence of 2002 sea-ice concentrations on Hg MIF Δ201Hg (colony mean ± σ, s.d.) in common and thick-billed murre eggs (see Fig. 1 for legend). Seasonal ice concentration values represent the three-month mean condition (±σ, s.d.) from the arrival at the breeding grounds in early April until most eggs were laid in late June. Sea-ice values for the colonies integrate the 170km foraging distance around the nesting locations (that is, the maximum foraging range shown by the dashed circles in Fig. 1a).

  6. Odd-isotope anomalies in [Delta]201Hg versus [Delta]199Hg space.
    Figure 6: Odd-isotope anomalies in Δ201Hg versus Δ199Hg space.

    The solid and dashed lines show the Δ199/201Hg slopes associated with natural iHg and MeHg photoreduction respectively, based on experiments18 and a literature survey14 (see Fig. 1 for legend). The dash–dot line represents the York regression trend for all samples. The uncertainties reported for the samples are the external reproducibility (n = 7) of the method used for NIST Murre Egg Control Material QC04-ERM1 (±0.11‰, 2σ, s.d. for Δ199Hg, and ±0.10‰, 2σ, s.d. for Δ201Hg; see Supplementary Table S2b).

Change history

Corrected online 21 January 2011
In the version of this Article originally published online, 'Arctic sea' should have read 'Arctic sea ice' in the last sentence of the abstract. This error has now been corrected in all versions of the text.


  1. Lindberg, S. et al. A synthesis of progress and uncertainties in attributing the sources of mercury in deposition. Ambio 36, 1932 (2007).
  2. Lockhart, W. L. et al. Concentrations of mercury in tissues of beluga whales (Delphinapterus leucas) from several communities in the Canadian Arctic from 1981 to 2002. Sci. Total Environ. 351, 391412 (2005).
  3. Braune, B. M. et al. Persistent organic pollutants and mercury in marine biota of the Canadian Arctic: An overview of spatial and temporal trends. Sci. Total Environ. 351, 456 (2005).
  4. Campbell, L. M. et al. Mercury and other trace elements in a pelagic Arctic marine food web (Northwater Polynya, Baffin Bay). Sci. Total Environ. 351, 247263 (2005).
  5. Choi, A. L. & Grandjean, P. Methylmercury exposure and health effects in humans. Environ. Chem. 5, 112120 (2008).
  6. Schroeder, W. H. et al. Arctic springtime depletion of mercury. Nature 394, 331332 (1998).
  7. Outridge, P. M., Macdonald, R. W., Wang, F., Stern, G. A. & Dastoor, A. P. A mass balance inventory of mercury in the Arctic Ocean. Environ. Chem. 5, 89111 (2008).
  8. Ebinghaus, R. Mercury cycling in the Arctic—does enhanced deposition flux mean net-input? Environ. Chem. 5, 8788 (2008).
  9. St Louis, V. L. et al. Methylated mercury species in Canadian high arctic marine surface waters and snowpacks. Environ. Sci. Technol. 41, 64336441 (2007).
  10. Cabana, G. & Rasmussen, J. B. Modelling food-chain structure and contaminant bioaccumulation using stable nitrogen isotopes. Nature 372, 255257 (1994).
  11. Loseto, L. L. et al. Linking mercury exposure to habitat and feeding behaviour in Beaufort Sea beluga whales. J. Mar. Syst. 74, 10121024 (2008).
  12. Wilson, S. in AMAP Workshop on Statistical Analysis of Temporal Trends of Mercury in Arctic Biota (AMAP Report Vol. 3, AMAP, 2007).
  13. Macdonald, R. W., Harner, T. & Fyfe, J. Recent climate change in the Arctic and its impact on contaminant pathways and interpretation of temporal trend data. Sci. Total Environ. 342, 586 (2005).
  14. Bergquist, R. A. & Blum, J. D. The odds and evens of mercury isotopes: Applications of mass-dependent and mass-independent isotope fractionation. Elements 5, 353357 (2009).
  15. Kritee, K., Barkay, T. & Blum, J. D. Mass dependent stable isotope fractionation of mercury during mer mediated microbial degradation of monomethylmercury. Geochim. Cosmochim. Acta 73, 12851296 (2009).
  16. Zambardi, T., Sonke, J. E., Toutain, J. P., Sortino, F. & Shinohara, H. Mercury emissions and stable isotopic compositions at Vulcano Island (Italy). Earth Planet. Sci. Lett. 277, 236243 (2009).
  17. Laffont, L. et al. Anomalous mercury isotopic compositions of fish and human hair in the Bolivian Amazon. Environ. Sci. Technol. 43, 89858990 (2009).
  18. Bergquist, B. A. & Blum, J. D. Mass-dependent and -independent fractionation of Hg isotopes by photoreduction in aquatic systems. Science 318, 417420 (2007).
  19. Buchachenko, A. L. et al. Magnetic isotope effect for mercury nuclei in photolysis of bis(p-trifluoromethylbenzyl)mercury. Dokl. Phys. Chem. 413, 3941 (2007).
  20. Thiemens, M. H. & Heidenreich, J. E. The mass-independent fractionation of oxygen—a novel isotope effect and its possible cosmochemical implications. Science 219, 10731075 (1983).
  21. Farquhar, J., Bao, H. M. & Thiemens, M. Atmospheric influence of Earth’s earliest sulphur cycle. Science 289, 756758 (2000).
  22. Jackson, T. A., Whittle, D. M., Evans, M. S. & Muir, D. C. G. Evidence for mass-independent and mass-dependent fractionation of the stable isotopes of mercury by natural processes in aquatic ecosystems. Appl. Geochem. 23, 547571 (2008).
  23. Das, R., Salters, V. J. M. & Odom, A. L. A case for in vivo mass-independent fractionation of mercury isotopes in fish. Geochem. Geophys. Geosyst. 10, Q11012 (2009).
  24. Rodriguez-Gonzalez, P. et al. Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic Bacteria (Desulfobulbus propionicus) under dark conditions. Environ. Sci. Technol. 43, 91839188 (2009).
  25. Kaufman, K. Lives of North American Birds (Houghton Mifflin Harcourt,1996).
  26. Cramp, S. Handbook of the Birds of Europe, the Middle East, and North Africa (Oxford Univ. Press, 1985).
  27. Hatch, S. A., Meyers, P. M., Mulcahy, D. M. & Douglas, D. C. Seasonal movements and pelagic habitat use of murres and puffins determined by satellite telemetry. Condor 102, 145154 (2000).
  28. Ehrlich, P. R., Dobkin, D. S. & Wheye, D. The Birder’s Handbook: A Field Guide to the Natural History of North American Birds (Simon & Schuster, 1988).
  29. Gaston, A. J. & Hipfner, J. M. in The Birds of North America, No. 497 (eds Poole, A. & Gill, F.) (The Birds of North America, 2000).
  30. Braune, B. M., Donaldson, G. M. & Hobson, K. A. Contaminant residues in seabird eggs from the Canadian Arctic. Part I. Temporal trends 1975–1998. Environ. Pollut. 114, 3954 (2001).
  31. Day, R. D. et al. Murre eggs (Uriaaalge and Urialomvia) as indicators of mercury contamination in the Alaskan marine environment. Environ. Sci. Technol. 40, 659665 (2006).
  32. Programme-AMAP, AMAP Report. 2002.
  33. Davis, W. C. et al. An accurate and sensitive method for the determination of methylmercury in biological specimens using GC-ICP-MS with solid phase microextraction. J. Anal. At. Spectrom. 19, 15461551 (2004).
  34. Furness, R. in Birds as Monitors of Environmental Change (eds Furness, R. & Greenwood, J. J. D.) 86143 (Chapman & Hall, 1993).
  35. Blum, J. D. & Bergquist, B. A. Reporting of variations in the natural isotopic composition of mercury. Anal. Bioanalyt. Chem. 388, 353359 (2007).
  36. Ainley, D. G., Nettleship, D. N., Carter, H. R. & Storey, A. E. in The Birds of North America Vol. 666 (eds Poole, A. & Gill, F.) 143 (Academy of Natural Sciences and American Ornithologists’ Union, 2002).
  37. Coyle, K. O., Hunt, G. L., Decker, M. B. & Weingartner, T. J. Murre foraging, epibenthic sound scattering and tidal advection over a shoal near St-George Island, Bering Sea. Mar. Ecol.-Prog. Ser. 83, 114 (1992).
  38. Springer, A. M., Roseneau, D. G., Murphy, E. C. & Springer, M. I. Environmental controls of marine food webs—food-habits of seabirds in the eastern Chukchi Sea. Can. J. Fish. Aquat. Sci. 41, 12021215 (1984).
  39. Hobson, K. A., Piatt, J. F. & Pitocchelli, J. Using stable isotopes to determine seabird trophic relationships. J. Anim. Ecol. 63, 786798 (1994).
  40. Senn, D. B. et al. Stable isotope (N, C, Hg) study of methylmercury sources and trophic transfer in the Northern Gulf of Mexico. Environ. Sci. Technol. 44, 16301637 (2010).
  41. Jaffe, D. & Strode, S. Sources, fate and transport of atmospheric mercury from Asia. Environ. Chem. 5, 121126 (2008).
  42. Sunderland, E. M. & Mason, R. P. Human impacts on open ocean mercury concentrations. Glob. Biogeochem. Cycles 21, GB4022 (2007).
  43. Biswas, A., Blum, J. D., Bergquist, B. A., Keeler, G. J. & Xie, Z. Q. Natural mercury isotope variation in coal deposits and organic soils. Environ. Sci. Technol. 42, 83038309 (2008).
  44. Dissing, D. & Wendler, G. Solar radiation climatology of Alaska. Theor. Appl. Climatol. 61, 161175 (1998).
  45. Andersson, M. E., Sommar, J., Gardfeldt, K. & Lindqvist, O. Enhanced concentrations of dissolved gaseous mercury in the surface waters of the Arctic Ocean. Mar. Chem. 110, 190194 (2008).
  46. Sherman, L. S. et al. Mass-independent fractionation of mercury isotopes in Arctic snow driven by sunlight. Nature Geosci. 3, 173177 (2010).
  47. Gratz, L. E., Keeler, G. J., Blum, J. D. & Sherman, L. S. Isotopic composition and fractionation of mercury in Great Lakes precipitation and ambient air. Environ. Sci. Technol. 44, 77647770 (2010).
  48. Vander Pol, S. S. et al. Development of a murre (Uria spp.) egg control material. Anal. Bioanal. Chem. 387, 23572363 (2007).
  49. Nolin, A. R., Armstrong, R. L. & Maslanik, J. Near-Real-Time SSM/I-SSMIS EASE-Grid Daily Global Ice Concentration and Snow Extent, (March–June 2002). National Snow and Ice Data Center (ed. Digital media, 1998) (updated daily).

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Author information


  1. National Institute of Standards and Technology (NIST), Hollings Marine Laboratory, Charleston, South Carolina 29412, USA

    • D. Point,
    • R. D. Day,
    • S. S. Vander Pol,
    • A. J. Moors,
    • R. S. Pugh &
    • P. R. Becker
  2. Laboratoire des Mécanismes et Transferts en Géologie (LMTG), Observatoire Midi-Pyrénées, UMR CNRS 5563, UMR IRD 154, Université Paul Sabatier, 31400 Toulouse, France

    • D. Point &
    • J. E. Sonke
  3. US Fish and Wildlife Service, Alaska Maritime National Wildlife Refuge, Homer, Alaska 99603, USA

    • D. G. Roseneau
  4. Environment Canada, Saskatoon, Saskatchewan, S7N 0X4, Canada

    • K. A. Hobson
  5. Institut Pluridisciplinaire de Recherche sur l’Environnement et les Materiaux, Equipe de Chimie Analytique BioInorganique et Environnement, UMR CNRS 5254, 64053 Pau, France

    • O. F. X. Donard


P.R.B., O.F.X.D., D.P. and R.D.D. designed the study; D.G.R. obtained the scientific collecting permits, made arrangements to collect the eggs and coordinated field logistics; and S.S.V. managed sample processing and banking. A.J.M. and R.S.P. were responsible for specimen processing, cryogenic banking and cryogenic homogenizations. Mercury isotopes were measured by D.P., R.D.D. and J.E.S. R.D.D. measured total mercury and K.H.H. measured nitrogen stable isotopes. D.P. and J.E.S. prepared the manuscript and all of the authors reviewed it.

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