Numéro |
J. Phys. IV France
Volume 107, May 2003
|
|
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Page(s) | 61 - 64 | |
DOI | https://doi.org/10.1051/jp4:20030243 |
J. Phys. IV France 107 (2003) 61
DOI: 10.1051/jp4:20030243
Lead fall-out isotopic signal over French northern Alps: Timing and sources constraints from distant lake sediment records
F. Arnaud1, M. Revel2, T. Winiarski3, D. Bosch4, E. Chapron5, M. Desmet6 and N. Tribovillard11 UMR PBDS, UST Lille 1, bâtiment SN5, 59655 Villeneuve-d'Ascq, France
2 UMR LGCA, OSUG, Université J. Fourier-Grenoble 1, 38400 Saint-Martin-d'Hères, France
3 LES, ENTPE, 69518 Vaulx-en-Velin, France
4 Laboratoire Tectonophysique, UMR 5568 du CNRS, Université de Montpellier II, 34095 Montpellier, France
5 Geological Institute, ETH Zurich, Switzerland
6 UMR LGCA, Université de Savoie, Technolac, 73373 Le Bourget du Lac, France
Abstract
We present time-series of lead concentration and isotopic ratio in sediments from two French alpine lakes: Lac du
Bourget
, a suburban lake, and Lac d'Anterne, a mountain lake nearby the Mont-Blanc Range. This approach aims at
differentiating "local" from "regional" inputs by comparing distant sedimentary records.
210Pb and
137Cs dating methods were
validated by historical events recognition [1-2] providing confident age-depth models spanning the last 250 years. In both
lakes the sediment is lead-enriched compared to upper continental crust over the whole records. The human impact reached
its maximum around 1970 AD, and then presents a rapid decline. Lead concentration and isotopic composition are correlated.
When compared to data from a Mont Blanc ice core [3], Lac d'Anterne time-series yields excellent correlation over the last
250 years, confirming the accuracy of both dating process and record of atmospheric lead fall-out. Record from Lac du
Bourget
presents a similar pattern until 1985 AD when the signal from the high elevation sites ones, both in concentrations
and isotopic ratio. Our data confirm the date of 1970 as the maximum of atmospheric lead fall-out over Western Europe.
Today, Lac d'Anterne still records a weak airborne contamination, while Lac du Bourget is mostly influenced by local
sources.
© EDP Sciences 2003