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Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Pb on the Faroe Islands |
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| Authors: | W Shotyk ME Goodsite F Roos-Barraclough N Givelet G Le Roux AK Cheburkin J Heinemeier SA Norton |
| Institution: | 1 Institute of Environmental Geochemistry, University of Heidelberg, INF 236, D-69120 Heidelberg, Germany 2 Department of Atmospheric Environment, National Environmental Research Institute of Denmark, Frederiksborgvej 399, P. O. Box 358, DK-4000 Roskilde, Denmark 3 Institute of Geological Sciences, University of Berne, Baltzerstrasse 1-3, CH-3012 Berne, Switzerland 4 Earth Science and Engineering, Imperial College, RSM Building, Prince Consort Road, London SW7 2BP England 5 Environmental Chemistry Research Group, Department of Chemistry, University of Southern Denmark, Odense University, Campusvej 55, Odense M, Denmark 6 AMS 14C Dating Laboratory, IFA, Aarhus University, Aarhus, Denmark 7 Institute of Plant Sciences, University of Berne, Altenbergrain 21, CH-3013 Berne, Switzerland 8 Department of Earth Sciences, Bryand Global Sciences Center University of Maine, Orono, Maine 04469-5790 USA |
| Abstract: | A monolith representing 5420 14C yr of peat accumulation was collected from a blanket bog at Myrarnar, Faroe Islands. The maximum Hg concentration (498 ng/g at a depth of 4.5 cm) coincides with the maximum concentration of anthropogenic Pb (111 μg/g). Age dating of recent peat accumulation using 210Pb (CRS model) shows that the maxima in Hg and Pb concentrations occur at AD 1954 ± 2. These results, combined with the isotopic composition of Pb in that sample (206Pb/207Pb = 1.1720 ± 0.0017), suggest that coal burning was the dominant source of both elements. From the onset of peat accumulation (ca. 4286 BC) until AD 1385, the ratios Hg/Br and Hg/Se were constant (2.2 ± 0.5 × 10-4 and 8.5 ± 1.8 × 10-3, respectively). Since then, Hg/Br and Hg/Se values have increased, also reaching their maxima in AD 1954. The age date of the maximum concentrations of anthropogenic Hg and Pb in the Faroe Islands is consistent with a previous study of peat cores from Greenland and Denmark (dated using the atmospheric bomb pulse curve of 14C), which showed maximum concentrations in AD 1953.The average rate of atmospheric Hg accumulation from 1520 BC to AD 1385 was 1.27 ± 0.38 μg/m2/yr. The Br and Se concentrations and the background Hg/Br and Hg/Se ratios were used to calculate the average rate of natural Hg accumulation for the same period, 1.32 ± 0.36 μg/m2/yr and 1.34 ± 0.29 μg/m2/yr, respectively. These fluxes are similar to the preanthropogenic rates obtained using peat cores from Switzerland, southern Greenland, southern Ontario, Canada, and the northeastern United States. Episodic volcanic emissions and the continual supply of marine aerosols to the Faroe Islands, therefore, have not contributed significantly to the Hg inventory or the Hg accumulation rates, relative to these other areas. The maximum rate of Hg accumulation was 34 μg/m2/yr. The greatest fluxes of anthropogenic Hg accumulation calculated using Br and Se, respectively, were 26 and 31 μg/m2/yr. The rate of atmospheric Hg accumulation in 1998 (16 μg/m2/yr) is comparable to the values recently obtained by atmospheric transport modeling for Denmark, the Faroe Islands, and Greenland. |
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