Publications

The amount of sediment transport and storage in large basins is an important factor in the continental erosional cycle that controls atmospheric CO2 levels. Therefore, longer-term sediment budgets are necessary that are insensitive to anthropogenic changes in erosion in order to link fluxes eroded from mountainous source areas to those intermittently stored and finally exported to the oceans. Cosmogenic nuclides (CN) are well suited for tracing erosion and weathering processes and operate over longer time scales than sediment gauging. Under certain prerequisites that are summarized in Wittmann et al. (2009)a, CN-derived denudation rates provide a measure of sediment production in a basin. In the Amazon basin, measurements of nuclide concentrations of all areas contributing sediment (Andes, Shields) are compared with those measured at the outlet of the basin. Integrating over a time scale of a few kiloyears, we find that ~610 Mt/yr of sediment are exported to the Atlantic Ocean, and ~460 Mt/yr are added to the basin from erosion of the Andes, whereas only ~45 Mt/yr are eroded from the cratonic Shields. A comparison with published modern sediment fluxes (that integrate over a few decades) shows similarities within a factor of ~2 with an average load of ~1000 Mt/yr at the Amazon basin outlet b,c. This similar trend in fluxes derived from both methods is a surprising finding, given the considerable differences in methodology and integration time scale. We attribute this to the absence of long-term deposition within the basin and to the buffering capability of the large Amazon floodplain. The buffering capability dampens short-term high amplitude fluctuations by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin.

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Wittmann, H.; von Blanckenburg, F.; Maurice, L.; Guyot, J. L.; Filizola, N.; Kubik, P. (2011): Sediment in the Amazon Basin: How much in and out?. International Conference on the Status and Future of the World’s Large Rivers (Vienna 2011).