Silver and lead in high-altitude lake sediments: Proxies for climate changes and human activities |
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| Authors: | Marion Garçon Catherine Chauvel Emmanuel Chapron Xavier Faïn Mingfang Lin Sylvain Campillo Sarah Bureau Marc Desmet Marie-Christine Bailly-Maître Laurent Charlet |
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| Institution: | 1. ISTerre, Université de Grenoble 1, CNRS, BP 53, 38041 Grenoble Cedex 09, France;2. Université d’Orléans, CNRS/INSU, Université François Rabelais-Tours, Institut des Sciences de la Terre d’Orléans (ISTO) – UMR 6113, 1A rue de la Férollerie, 45071 Orléans Cedex 2, France;3. Laboratoire de Glaciologie et Géophysique de l’Environnement, Université de Grenoble 1,CNRS, BP 96, 38402 Saint-Martin d’Hères Cedex, France;4. Université de Lyon – Ecole Nationale des Travaux Publics de l’Etat, rue Maurice Audin, 69518 Vaulx en Velin Cedex, France;5. Laboratoire d’Archéologie Médiévale Méditerranéenne, UMR 6572 CNRS – Université de Provence, Aix en Provence, France |
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| Abstract: | High-altitude lake sediments are often used as archives for environmental changes and their chemical and isotopic compositions provide significant constraints on natural and anthropogenic long-term changes that have occurred in their catchment area. Here, trace-element concentrations and Pb isotopes are presented for two sedimentary cores from Lake Blanc Huez in the French Alps, to trace the impact of climate changes and human activities over the Holocene. Lead and Ag contents are very high and clearly dominated by input from a Pb–Ag vein located a few meters from the lakeshore, a vein that also buffers the Pb isotopes. Mining of this vein in medieval times is recorded in the corresponding lake sediments with high Ag content coupled with high Pb/U ratio. These chemical characteristics can be used to constrain the major Holocene climate changes. Significant advances of glaciers next to the lake produced sediments with Ag and Pb concentration peaks and high Pb/U ratios due to accelerated erosion of the Pb–Ag vein, similar to the effects of the medieval mining. In contrast, reduced glacier activity led to the formation of organic-rich sediments with high U and As contents and low Pb/U ratios. More generally, the observed combination of chemical changes could be used elsewhere to decipher environmental changes over long periods of time. |
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