Historical Variations in the Stable Isotope Composition of Mercury in Arctic Lake Sediments
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- 作者：Togwell A. Jackson ; Derek C. G. Muir ; and Warwick F. Vincent
- 刊名：Environmental Science & Technology
- 出版年：2004
- 出版时间：May 15, 2004
- 年：2004
- 卷：38
- 期：10
- 页码：2813 - 2821
- 全文大小：152K
- 年卷期：v.38,no.10(May 15, 2004)
- ISSN：1520-5851
文摘
The stable isotope composition of mercury (Hg) in adated core from the anoxic zone of a saline, meromicticArctic lake was found to vary as a complex function of theage and chemical composition of the sediment. Throughoutthe stratigraphic sequence, which spans the years1899-1997, the ratios 198Hg/202Hg, 199Hg/202Hg, 200Hg/202Hg,201Hg/202Hg, and 204Hg/202Hg expressed as 
-values (per mildeviations relative to a standard) reveal enrichment in198Hg, 199Hg, 200Hg, and 201Hg, with depletion in 204Hg, thedegree of enrichment varying inversely with atomic mass.A plot of 198Hg, 199Hg, 200Hg, and 201Hg againstdepth gave parallel profiles characterized by large, regularundulations superimposed on an overall trend towardincrease with depth (i.e. age), and the 204Hg profile is amirror image of them. The 198Hg, 199Hg, 200Hg, and201Hg values of the oldest (1899-1929) strata vary inverselywith NH2OH·HCl/HNO3-extractable manganese concentration, but those of the youngest (1963-1997) strata give apositive correlation; intermediate (1936-1956) strata showno correlation and negligible variation in -values,possibly signifying a transition phase in which the twoopposite trends offset each other. The -values show similarbut weaker relationships with organic carbon. Theresults strongly suggest fractionation of Hg isotopes bymicrobial activities linked to oxidation-reduction reactionsin the lake, although effects of isotopic signaturesindicative of the sources of the Hg have not been ruledout. The radical change in the nature of the relationshipbetween -values and sediment chemistry over time mayreflect environmental and biotic changes that altered theisotope-fractionating processes. These findings imply thatvariations in the isotopic makeup of Hg, together withrelated physical, chemical, and biological data, could yieldimportant new information about the biogeochemicalcycle of Hg.
-values (per mildeviations relative to a standard) reveal enrichment in198Hg, 199Hg, 200Hg, and 201Hg, with depletion in 204Hg, thedegree of enrichment varying inversely with atomic mass.A plot of 198Hg, 199Hg, 200Hg, and 201Hg againstdepth gave parallel profiles characterized by large, regularundulations superimposed on an overall trend towardincrease with depth (i.e. age), and the 204Hg profile is amirror image of them. The 198Hg, 199Hg, 200Hg, and201Hg values of the oldest (1899-1929) strata vary inverselywith NH2OH·HCl/HNO3-extractable manganese concentration, but those of the youngest (1963-1997) strata give apositive correlation; intermediate (1936-1956) strata showno correlation and negligible variation in -values,possibly signifying a transition phase in which the twoopposite trends offset each other. The -values show similarbut weaker relationships with organic carbon. Theresults strongly suggest fractionation of Hg isotopes bymicrobial activities linked to oxidation-reduction reactionsin the lake, although effects of isotopic signaturesindicative of the sources of the Hg have not been ruledout. The radical change in the nature of the relationshipbetween -values and sediment chemistry over time mayreflect environmental and biotic changes that altered theisotope-fractionating processes. These findings imply thatvariations in the isotopic makeup of Hg, together withrelated physical, chemical, and biological data, could yieldimportant new information about the biogeochemicalcycle of Hg.