Geochemistry of the peat bog at Etang de la Gruere, Jura Mountains, Switzerland, and its record of atmospheric Pb and lithogenic trace metals (Sc, Ti, Y, Zr, and REE) since 12,370 C-14 yr BP

Citation
W. Shotyk et al., Geochemistry of the peat bog at Etang de la Gruere, Jura Mountains, Switzerland, and its record of atmospheric Pb and lithogenic trace metals (Sc, Ti, Y, Zr, and REE) since 12,370 C-14 yr BP, GEOCH COS A, 65(14), 2001, pp. 2337-2360
Citations number
121
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Earth Sciences
Journal title
GEOCHIMICA ET COSMOCHIMICA ACTA
ISSN journal
0016-7037 → ACNP
Volume
65
Issue
14
Year of publication
2001
Pages
2337 - 2360
Database
ISI
SICI code
0016-7037(200107)65:14<2337:GOTPBA>2.0.ZU;2-K
Abstract
A 650 cm core from a Swiss bog represents 12,370 C-14 years of peat accumul ation and provides the first complete record of atmospheric Pb deposition f or the entire Holocene. Excess, non-atmospheric Sr in the peat was calculat ed by normalizing Sr/Sc to crustal abundance; this was used to differentiat e between the ombrogenic section of the bog in which inorganic solids are s upplied exclusively by atmospheric deposition and the minerogenic zone wher e mineral-water interactions contribute metals to the peat. While sediment dissolution contributes significantly to the Sr inventory of the minerogeni c section of the peat profile, there is no measurable effect of this proces s on the Ph burden. Isotopic analyses (Pb-204, Pb-206, Pb-207, Pb-208) show that effectively all of the Pb in the peat profile was supplied exclusivel y from the atmosphere. To separate natural and anthropogenic Pb, Sc was sel ected over Ti, Y, Zr, Hf and REE as a conservative, reference element which is supplied by soil dust aerosols derived from rock weathering. Enrichment factors (EF) were calculated using the Pb/Sc ratio in the peat samples, no rmalized to the "natural, background" Pb/Sc which is found in peats dating from 8030 to 5320 C-14 yr BP. The results show that anthropogenic source ha ve dominated the supply of atmospheric Pb to the peat core continuously sin ce 3000 C-14 yr BP. The aerosols supplied to the bog can be divided into 3 classes: a) Pre-Anthropogenic (older than 3000 C-14 yr BP with Pb EF < 2 an d Pb-206/Pb-207 > 1.194); b) Pre-Industrial (dating from 3000-240 C-14 yr B P, with Pb EF greater than or equal to 2 but < 20 and Pb-206/Pb-207 1.193-1 .179); c) Industrial (more recent than 240 C-14 yr BP, with Pb EF > 20 and Pb-206/Pb-207 < 1.179). Elevated soil dust fluxes are observed at 5320, 823 0 and 10,590 C-14 yr BP; the latter corresponds to the Younger Dryas. Alumi num, Zr, Hf, and REE/Sc ratios also are elevated at the same depths, sugges ting differences in particle size, wind strength, or source regions. Pre-An thropogenic aerosols deposited since 8230 C-14 yr BP reveal Pb/Sc which is significantly higher, and Pb-206/Pb-207 which is less radiogenic, than duri ng the early Holocene. While the trend toward increasing Pb/Sc could be due to chemical weathering and soil development, this could not explain the sh ift in Pb isotopic composition. The changes which took place at 8230 C-14 B P, therefore, may be related to a large scale climatic reorganization which , at present, is poorly understood. Copyright (C) 2001 Elsevier Science Ltd .