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Contrasting silicon isotope signatures in rivers from the Congo Basin and the specific behaviour of organic‐rich waters
Author(s) -
Cardinal D.,
Gaillardet J.,
Hughes H. J.,
Opfergelt S.,
André L.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl043413
Subject(s) - tributary , weathering , dissolved organic carbon , drainage basin , geology , hydrology (agriculture) , wetland , total organic carbon , organic matter , structural basin , environmental science , stable isotope ratio , particulates , environmental chemistry , oceanography , geochemistry , geomorphology , chemistry , ecology , geography , physics , cartography , geotechnical engineering , organic chemistry , quantum mechanics , biology
We investigate the dissolved δ 30 Si of the Congo River, the world's second largest riverine source of Si to the ocean. Small tributaries rich in dissolved organic carbon running through wetlands (“Black Rivers”) exhibit the lowest δ 30 Si ever measured in running surface waters (+0.02 ± 0.15‰), whilst the main branch and largest tributaries have higher values (+0.98 ± 0.13‰), well within the average of what has been measured so far. Our data suggest that the contribution of Black Rivers to the total discharge of the basin is 22 ± 10% and that δ 30 Si is mostly controlled by weathering intensity rather than fluxes. We propose both a mass and Si‐isotopic balance model, which suggest that the distribution of Si in the particulate and/or dissolved components in Congo rivers results mainly from mixing between two types of weathering regimes: one where clays are formed and remain stable, and one where they are dissolved under the action of organic matter.