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

Nature Geoscience volume 4, pages 188194 (2011) | Download Citation

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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.

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Change history

  • 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.


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The samples used in this study were obtained from the Marine Environmental Specimen Bank (MESB) through the Seabird Tissue Archival and Monitoring Project (STAMP), a long-term collaborative effort by the Alaska Maritime National Wildlife Refuge (AMNWR), the National Institute of Standards and Technology (NIST), the US Geological Survey Biological Resources Division (USGS-BRD) and the Bureau of Indian Affairs Alaska Region Subsistence Branch (BIA-ARSB). We thank AMNWR and University of Alaska—Fairbanks (UAF) biologists, members of the St George Traditional Council, the Native Village of Point Hope IRA Council and residents of St George, Savoonga and Point Hope for collecting the eggs.

We also thank K. S. Simac (USGS-BRD) for processing the eggs, M. B. Ellisor (NIST) for cryohomogenizing and banking the eggs and F. Poitrasson and Y. Godderis for providing helpful comments on the manuscript. This work is part of International Polar Year (IPY) Research Activity No. 439 ‘MERSAM’ (MERcury Seabird Arctic Monitoring). Financial support for this research was provided by NIST, the French Centre National de la Recherche Scientifique, and Research Grant ANR-09-JCJC-0035-01 from the French Agence Nationale de Recherche.

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


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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.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to D. Point.

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