Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10388d&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10388
Other
Scientific paper
In the general attempt to link erosion and climate, the study of riverine erosion in basaltic provinces provides important information. Indeed, we have recently shown (Dessert et al., 2001) that basaltic weathering is a major CO_2 sink on timescales of several million years because basaltic rocks dissolve easily. Our study attempts to characterise the chemical weathering of basalts and to quantify more precisely the flux of carbon transferred from the atmosphere to the ocean during this major process at the surface of the Earth. To this aim, we have compiled different data (published and unpublished) on small rivers draining basalts. Each river selected in this study can be characterised by elemental ratios determined from chemical composition of the dissolved load, corrected for atmospheric and hydrothermal inputs. It appears from this database that the concentrations of Ca, Mg and HCO_3 relative to Na are relatively high in comparison with the usually observed values for small streams draining granitoid rocks. As it has been invoked for granitic watershed, these high Na-normalized molar ratios could prove the dissolution of disseminated calcite present in basaltic rocks. These ratios could also be interpreted as the result of chemical weathering of volcanic rocks having more Ca and Mg rich chemistries. Indeed, the relatively low Ca/Mg ratios of Ca- and Mg-rich rivers (0.7 to 1.8) are consistent with those of basaltic rocks (0.9 to 3) while calcite is caracterised by higher Ca/Mg ratios. We thus favour the idea that the chemical signature of rivers results principaly from chemical weathering of basalts. It is noteworthy that the chemical signatures of rivers draining basalts differ from those of rivers draining other silicate rocks. Then, it cannot be neglected when attempting to characterise the silicate end member and to determine the global CO_2 consumption flux coming from silicate weathering. References: Dessert et al., (2001), Earth Planet. Sci. Lett. 188, 459-474. Gaillardet et al., (1999), Chem. Geol. 159, 3-30.
Dessert Céline
Dupré Bernard
Gaillardet Jérôme
Schott Jacques
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