HR: 15:10h
AN: V13F-07 INVITED    [Abstracts]
TI: Weathering processes traced with isotopes in a glacial soil chronosequence
AU: * Bourdon, B
EM: bourdon@erdw.ethz.ch
AF: Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstr. 25, Zurich, 8092, Switzerland
AU: Kretzschmar, R
EM: kretzschmar@env.ethz.ch
AF: Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitätstr. 16, Zurich, 8092, Switzerland
AU: Kiczka, M
EM: kiczka@env.ethz.ch
AF: Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitätstr. 16, Zurich, 8092, Switzerland
AU: Wiederhold, J G
EM: wiederhold@env.ethz.ch
AF: Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstr. 25, Zurich, 8092, Switzerland
AU: Wiederhold, J G
EM: wiederhold@env.ethz.ch
AF: Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitätstr. 16, Zurich, 8092, Switzerland
AU: Reynolds, B R
EM: reynolds@erdw.ethz.ch
AF: Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstr. 25, Zurich, 8092, Switzerland
AU: de Souza, G
EM: desouza@erdw.ethz.ch
AF: Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstr. 25, Zurich, 8092, Switzerland
AB: There has been numerous studies of isotope tracers to study the processes involved in chemical weathering. In the context of the BigLink project, we have focused on a recent soil chronosequence in the forefield of a retreating glacier in the central Swiss Alps. The bedrock of the soil chronosequence consists of paleozoic granites and gneisses with metamorphic overprint during the Tertiary. The retreat of the Damma glacier has been carefully documented over the past 150 years by swiss scientists such that we now have a fine-scale chronosequence to investigate the early development of soils in a glacial environment. Remarkably, soil construction is extremely rapid and shows the existence of well- developed soils horizons in the first 100 years. Our approach is to sample comprehensively the bedrock, soil horizons, soil solutions, runoff waters as well as plants and soil organic material. Here, we report initial results for Sr, Fe and U-series but the number of studied isotope systems is currently being extended. Our approach allows the derivation of a full mass balance for understanding the cycling of the elements in the soil. Even in the first 100 years of soil development, the soil data shows strong isotope gradients in the secondary phases with an enrichment in the light Fe isotopes in the clay fraction. Our Fe isotope data shows clear evidence for mobilization of iron from the biotite, while the magnetite, the other Fe-carrier in the granite is little affected. Our data shows that light Fe isotopes are preferentially uptaken by plants. We have also explored the stable Sr isotope fractionation in the same soil chronosequence and the most weathered soil horizons are enriched in the heavy strontium isotopes and the waters enriched in the light isotopes, indicating a fractionation of stable Sr isotope during chemical weathering. Although the minerals in the granite do show distinct stable isotope signatures, preferential weathering of one mineral is not consistent with the data. The combination of stable and radiogenic isotope will provide excellent tools for quantifying individual mineral weathering rates. We are currently investigating the source of this fractionation.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1865 Soils (0486)
DE: 4875 Trace elements (0489)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting