The silicon isotopic composition of the Ganges and its tributaries

Fontorbe, Guillaume and De La Rocha, Christina L. and Chapman, Hazel J. and Bickle, Michael J. (2013) The silicon isotopic composition of the Ganges and its tributaries. Earth and Planetary Science Letters, 381. pp. 21-30. ISSN 0012-821X DOI 10.1016/j.epsl.2013.08.026

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Abstract

The silicon isotopic composition (View the MathML source) of the headwaters of the Ganges River, in the Himalaya, ranged from +0.49±0.01‰ to +2.17±0.04‰ at dissolved silicon (DSi) concentrations of 38 to 239 μM. Both the concentration and isotopic composition of DSi in the tributaries increased between the highest elevations to where the Ganges leaves the Himalayas at Rishikesh. The tributaries exhibit a linear correlation between View the MathML source and DSi that may represent mixing between a low DSi, low View the MathML source (e.g., 40 μM, +0.5‰) component potentially reflecting fractionation during adsorption of a small fraction of silicon onto iron oxides and a high DSi, high View the MathML source component (e.g., 240 μM, +1.7‰) produced during higher intensity weathering with a greater proportional sequestration of weathered silicon into secondary minerals or biogenic silica. On the Ganges alluvial plain, in the Ganges and the Yamuna, Gomati, and their tributaries, DSi ranged from 122 to 218 μM while View the MathML source ranged from +1.03±0.03‰ to +2.46±0.06‰. Highest values of View the MathML source occurred in the Gomati and its tributaries. In general, the lower DSi and higher View the MathML source of DSi in these rivers suggests control of both by removal of DSi by secondary mineral formation and/or biogenic silica production. A simple 1-dimensional model with flow through a porous medium is introduced and provides a useful framework for understanding these results.

Item Type:	Article
Additional Information:	Copyright © 2013 The Authors.
Uncontrolled Keywords:	2013AREP; IA66; OA
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics 07 - Gold Open Access
Journal or Publication Title:	Earth and Planetary Science Letters
Volume:	381
Page Range:	pp. 21-30
Identification Number:	10.1016/j.epsl.2013.08.026
Depositing User:	Sarah Humbert
Date Deposited:	09 Nov 2013 16:14
Last Modified:	13 Jul 2014 21:46
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2899

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