HR: 09:45h
AN: H41H-08 INVITED     [Abstracts]
TI: Validity of the Steady State Approach of Erosion in Large River Systems
AU: * GAILLARDET, J
EM: gaillardet@ipgp.jussieu.fr
AF: Institut de Physique du Globe, 4 Place Jussieu, 75252, PARIS France
AU: DOSSETO, A
EM: tonydoss@noos.fr
AF: Institut de Physique du Globe, 4 Place Jussieu, 75252, PARIS France
AU: BOURDON, B
EM: bourdon@ipgp.jussieu.fr
AF: Institut de Physique du Globe, 4 Place Jussieu, 75252, PARIS France
AU: METIVIER, F
EM: metivier@ipg.jussieu.fr
AF: Institut de Physique du Globe, 4 Place Jussieu, 75252, PARIS France
AB: At the scale of a drainage basin, secondary products of chemical weathering reactions accumulate in soils and reservoirs. They are periodically removed by physical erosion processes and exported to the ocean. The question to known whether the flux of exported material equals the flux of newly formed material by chemical reactions is that of the "steady state" of erosion. This question is typical a matter of time scale at which the mass budget of erosion is considered: are erosion processes in equilibrium at the scale of a hydrological cycle? Of tens of years? At a geological time scale? To address this issue, we will review the use of geochemical mass budgets based on elemental ratios or isotopic ratios. The largest rivers will be considered with special emphasis on the Congo, Amazon and Mackenzie rivers. Different hypothesis on the mean composition of the upper crust have to be made when elemental ratios are used. Using uranium series disequilibrium, bedrock composition is much more constrained and theoretical suspended sediments concentrations can be predicted. It appears that most of the largest drainage basin are not in steady state and export more sediments than predicted based on a geochemical mass budget approach. If the storage of suspended sediments that occur in most of the largest rivers is taken into account, the discrepancy between predicted and measured sediment yields is even greater. What is the cause of this disequilibrium? Is there a global explanation or is there a specific reason for each drainage basin? We will address this question in terms of response time of physical erosion to climatic or tectonic events in large river basins.
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting