A mass balance inventory of mercury in the Arctic Ocean

P. M. Outridge; R. W. Macdonald; F. Wang; G. A. Stern; A. P. Dastoor

doi:10.1071/EN08002

RESEARCH FRONT

Previous Next Contents Vol 5(2)

A mass balance inventory of mercury in the Arctic Ocean

P. M. Outridge ^A ^E , R. W. Macdonald ^B ^E ^G , F. Wang ^C ^E , G. A. Stern ^D ^E and A. P. Dastoor ^F

+ Author Affiliations

- Author Affiliations

^A Geological Survey of Canada, 601 Booth St, Ottawa, ON, K1A 0E8, Canada.

^B Department of Fisheries and Oceans, Institute of Ocean Sciences, PO Box 6000, Sidney, BC, V8L 4B2, Canada.

^C Department of Chemistry, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.

^D Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, MB, R3T 2N6, Canada.

^E Department of Environment and Geography, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.

^F Air Quality Research Division, Science and Technology Branch, Environment Canada, 2121 Trans Canada Highway, Dorval, QC, H9P 1J3, Canada.

^G Corresponding author. Email: robie.macdonald@dfo-mpo.gc.ca

Environmental Chemistry 5(2) 89-111 https://doi.org/10.1071/EN08002
Submitted: 21 December 2007 Accepted: 21 February 2008 Published: 17 April 2008

Environmental context. Mercury (Hg) occurs at high concentrations in Arctic marine wildlife, posing a possible health risk to northern peoples who use these animals for food. We find that although the dramatic Hg increases in Arctic Ocean animals since pre-industrial times can be explained by sustained small annual inputs, recent rapid increases probably cannot, because of the existing large oceanic Hg reservoir (the ‘flywheel’ effect). Climate change is a possible alternative force underpinning recent trends.

Abstract. The present mercury (Hg) mass balance was developed to gain insights into the sources, sinks and processes regulating biological Hg trends in the Arctic Ocean. Annual total Hg inputs (mainly wet deposition, coastal erosion, seawater import, and ‘excess’ deposition due to atmospheric Hg depletion events) are nearly in balance with outputs (mainly shelf sedimentation and seawater export), with a net 0.3% year^–1 increase in total mass. Marine biota represent a small fraction of the ocean’s existing total Hg and methyl-Hg (MeHg) inventories. The inertia associated with these large non-biological reservoirs means that ‘bottom-up’ processes (control of bioavailable Hg concentrations by mass inputs or Hg speciation) are probably incapable of explaining recent biotic Hg trends, contrary to prevailing opinion. Instead, varying rates of bioaccumulation and trophic transfer from the abiotic MeHg reservoir may be key, and are susceptible to ecological, climatic and biogeochemical influences. Deep and sustained cuts to global anthropogenic Hg emissions are required to return biotic Hg levels to their natural state. However, because of mass inertia and the less dominant role of atmospheric inputs, the decline of seawater and biotic Hg concentrations in the Arctic Ocean will be more gradual than the rate of emission reduction and slower than in other oceans and freshwaters. Climate warming has likely already influenced Arctic Hg dynamics, with shrinking sea-ice cover one of the defining variables. Future warming will probably force more Hg out of the ocean’s euphotic zone through greater evasion to air and faster Hg sedimentation driven by higher primary productivity; these losses will be countered by enhanced inputs from coastal erosion and rivers.

Acknowledgements

The new Arctic seawater Hg results incorporated here were made possible by multi-year funding from the ArcticNET Network of Centres of Excellence to R.M., G.S. and F.W. We also acknowledge past support from the Geological Survey of Canada (P.O.), the Science Subvention Program of the Department of Fisheries and Oceans and the Fisheries Joint Management Committee (F.W., G.S.), the Polar Continental Shelf Project (F.W., G.S.), the Canadian Arctic Shelf Exchange Study (CASES; G.S., R.M.), and the Natural Science and Engineering Research Council of Canada (F.W.). P.O. thanks Prof. Bill Shotyk and the Institute for Environmental Geochemistry, University of Heidelberg, Germany, for hosting him during the preparation of the present article. We also thank Dr Alison Green for the invitation to prepare the present review for Environmental Chemistry, and to the Arctic Monitoring and Assessment Program (AMAP) for permission to adapt Fig. 2 (taken from ^[ ²⁵ ^]). Two anonymous reviewers provided numerous suggestions that have helped to improve the presentation.

References

[1] AMAP, Arctic Pollution 2002: Persistent Organic Pollutants, Heavy Metals, Radioactivity, Human Health, Changing Pathways 2002 (Arctic Monitoring and Assessment Programme: Oslo).

[2] INAC, Human Health, Canadian Arctic Contaminants Assessment Report II 2003 (Department of Indian and Northern Affairs: Ottawa, ON).

[3] AMAP, AMAP Assessment 2002: Heavy Metals in the Arctic 2005 (Arctic Monitoring and Assessment Programme: Oslo).

[4] B. M. Braune , P. M. Outridge , A. T. Fisk , D. C. G. Muir , P. A. Helm , K. Hobbs , P. F. Hoekstra , M. Kwan , R. J. Letcher , W. L. Lockhart , R. J. Norstrom , G. A. Stern , Z. Z. Kuryk , Persistent organic pollutants and mercury in marine biota of the Canadian Arctic: an overview of spatial and temporal trends. Sci. Total Environ. 2005 , 351–352, 4.
        | Crossref | GoogleScholarGoogle Scholar | [Verified 17 March 2008].

[87] C. H. Lamborg , W. F. Fitzgerald , J. O’Donnell , T. Torgerson , A non-steady-state compartmental model of global-scale mercury biogeochemistry with interhemispheric gradients. Geochim. Cosmochim. Acta 2002 , 66, 1105.
        | Crossref | GoogleScholarGoogle Scholar | [Verified 16 March 2008].

[97] ICES, ICES/AMAP Study Group for the Assessment of AMAP POPs and Heavy Metals Data, Vol. ICES CM 2002/ACME:01 2002 (International Council for the Exploration of the Sea: Copenhagen).

[98] G. A. Gill , W. F. Fitzgerald , Vertical mercury distributions in the oceans. Geochim. Cosmochim. Acta 1988 , 52, 1719.
        | Crossref | GoogleScholarGoogle Scholar | [Verified 17 March 2008].

[126] A. Ohmura , N. Reeh , New precipitation and accumulation maps for Greenland. J. Glaciol. 1991 , 37, 125.
        [Verified 17 March 2008].

[140] C. J. Ashjian , R. G. Campbell , H. E. Welch , M. Butler , D. Van Keuren , Annual cycle in abundance, distribution, and size in relation to hydrography of important copepod species in the western Arctic Ocean. Deep-Sea Res. II 2003 , 50, 1235.
        | Crossref | GoogleScholarGoogle Scholar |

[141] K. N. Kosobokova , H. Hanssen , H.-J. Hirche , K. Knickmeier , Composition and distribution of zooklankton in the Laptev Sea and adjacent Nansen Basin during summer, 1993. Polar Biol. 1997 , 19, 63.
        | Crossref | GoogleScholarGoogle Scholar |

[142] M. E. Vinogradov , E. A. Shushkina , L. P. Lebedeva , V. I. Gagarin , Mesoplankton in the eastern part of the Kara Sea and Ob and Yenisei Rivers estuaries. Oceanology (English Translation) 1995 , 34, 716.


[143] P. Dalpadado , R. Ingvldsen , A. Hassel , Zooplankton biomass variation in relation to climate conditions in the Barents Sea. Polar Biol. 2003 , 26, 233.


[144] H.-J. Hirche , W. Hagen , N. Mumm , C. Richter , The north-east water polynya, the Greenland Sea III. Polar Biol. 1994 , 14, 491.
        | Crossref | GoogleScholarGoogle Scholar |