Turbulent mixing in the Amazon River: The isotopic memory of confluences | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  Turbulent mixing in the Amazon River: The isotopic memory of confluences

Type de publication:

Journal Article

Source:

Earth and Planetary Science Letters, Volume 290, Ticket 1-2, p.37-43 (2010)

ISBN:

0012-821X

Numéro d'accès:

ISI:000274844700005

URL:

http://dx.doi.org/10.1016/j.epsl.2009.11.054

Mots-clés:

UMR 7154 ; Dynamique des Fluides Géologiques ; Géochimie et Cosmochimie ; N° Contribution : 2569 ; Amazon River; confluence; Sr isotopes; turbulent mixing; dissolved species; heterogeneities

Résumé:

<p>Rivers continuously discharge dissolved material to the oceans. Dissolved compounds partially result from water-rock interactions, which produce a large range of water chemical and isotopic compositions. These waters are collected by rivers, that are commonly assumed to be well-mixed with regard to their different tributaries, as a result of turbulent dispersion. In this paper, we test this hypothesis on the Solimoes River (at Manacapuru), the largest tributary of the Amazon River, by analyzing the sodium concentration and strontium isotopic composition of river water on a transverse section at different depths. High-precision measurements reveal lateral heterogeneities. This reflects poor mixing between two main river masses, that have distinct chemical and isotopic signatures, a hundred kilometers downstream from their confluence: the Solimoes mainstream and the Purus River. Using sodium concentration data, the transverse dispersion coefficient is estimated for the studied Solimbes reach (the Earth's largest river on which such an estimate now exists), and is found to be 1.8 +/- 0.2 m(2)/s. Comparison with previously reported data highlights the potential role of bed morphology and islands in the efficiency of lateral mixing in large rivers. We finally demonstrate that the characteristic length of lateral mixing downstream from confluences in large rivers is at least of several tens of kilometers. (C) 2009 Elsevier B.V. All rights reserved.</p>

Notes:

Bouchez, Julien Lajeunesse, Eric Gaillardet, Jérôme France-Lanord, Christian Dutra-Maia, Poliana Maurice, Laurence