HR: 1340h
AN: B23B-1266    [Abstracts]
TI: Response of carbonate weathering to environmental gradients
AU: * Calmels, D
EM: dcal07@esc.cam.ac.uk
AF: Laboratoire de Geochimie et Cosmochimie, UMR CNRS 7579, Institut de Physique du Globe de Paris, Universite Paris VII, 4 place Jussieu, Paris, 75252, France
AU: Gaillardet, J
EM: gaillardet@ipgp.jussieu.fr
AF: Laboratoire de Geochimie et Cosmochimie, UMR CNRS 7579, Institut de Physique du Globe de Paris, Universite Paris VII, 4 place Jussieu, Paris, 75252, France
AU: Francois, L M
EM: francois@astro.ulg.ac.be
AF: Laboratory for Planetary and Atmospheric Physics, University of Liege, 17 allee du Six Aout, Liege, 4000, Belgium
AB: Chemical weathering of rocks and the subsequent carbonate deposition in the Ocean are the most important processes regulating the CO₂ content of the atmosphere on geological timescale. Although research into weathering has mainly focused on silicate weathering, the dynamics of the carbonate reservoir is of prime interest to understand and reconstruct the global carbon cycle. Because of the size of this reservoir, any imbalance between oceanic precipitation and chemical weathering of carbonate will result in CO₂ excursions. In addition, the fast dissolution of carbonate rocks classically leads to calcite-oversaturated river water, suggesting that the weathering of carbonate is limited by environmental conditions. In order to decipher what controls carbonate weathering, we focused on river chemistry in a well-drained pure carbonate area exhibiting strong but coupled altitude, temperature, runoff and vegetation gradients, the Jura Mountains, France. Associated to those gradients, we observe a two-fold decrease in the chemical weathering of carbonate with the increasing elevation. As the climatic variability cannot explain this weathering gradient, we used the ecological and hydrological ASPECTS model (Rasse et al. 2001) to reconstruct the influence of vegetation on weathering reactions through the production of CO₂ in soils. Simulations allowed us to reconstruct the daily soil partial pressure of CO₂ as well as the hydrological cycle. We show that carbonate weathering can be explain by a difference in soil CO₂ productivity directly linked to the change in vegetation species as a function of altitude. In the Jura Mountains, the dissolution of carbonate as well as the weathering rates are mainly controlled by the vegetation which influences both the carbon and water cycle in soils. This study demonstrates that the chemical weathering is strongly sensitive to the ecosystem dynamics and suggests that carbonate weathering could quickly react to global change.
DE: 0428 Carbon cycling (4806)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1030 Geochemical cycles (0330)
DE: 1039 Alteration and weathering processes (3617)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting