Hughes H. J., Sondag Francis, Santos R. V., André L., Cardinal D. (2013). The riverine silicon isotope composition of the Amazon Basin. Geochimica et Cosmochimica Acta, 121, p. 637-651. ISSN 0016-7037.
Titre du document
The riverine silicon isotope composition of the Amazon Basin
Hughes H. J., Sondag Francis, Santos R. V., André L., Cardinal D.
Source
Geochimica et Cosmochimica Acta, 2013,
121, p. 637-651 ISSN 0016-7037
We present here the first large-scale study of riverine silicon isotope signatures in the Amazon Basin. The Amazon and five of its main tributaries were studied at different seasons of the annual hydrological cycle. The delta Si-30 signature of the dissolved silicon (DSi) exported to the estuary (weighted for DSi flux) for the period considered is estimated at +0.92 parts per thousand. A river cross-section shows the homogeneity of the Amazon River regarding DSi concentration and isotope ratio. The biogenic silica (BSi) concentration measured in surface water from all rivers is generally small compared to the DSi reservoir but large variations exist between rivers. Very low isotope signatures were measured in the upper Rio Negro (delta Si-30 = +0.05 +/- 0.06 parts per thousand), which we explain both by an equilibrium between clay formation and dissolution and by gibbsite formation. The Si isotope fractionation in the Andean tributaries and the Amazon main stem can be explained by clay formation and follow either a Rayleigh or a batch equilibrium fractionation model. Our results also suggest that the formation of 2:1 clays induces a fractionation factor similar to that of kaolinite formation.
Plan de classement
Hydrologie [062]
Description Géographique
AMAZONE BASSIN ; AMAZONE ; RIO NEGRO ; ANDES ; AMAZONIE
