Geochemistry of organic-rich river waters in Amazonia: Insights on weathering processes of intertropical cratonic terrain |
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| Institution: | 1. Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Brasília, 70910-900, Brazil;2. Programa de pós-graduação em Geociências, Universidade Federal do Amazonas, Av. Gal. Rodrigo O. J. Ramos 3000, Manaus, 69077-000, Brazil;3. Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562 – Cidade Universitária, São Paulo, 05508-080, Brazil;4. GET-OMP, IRD-CNRS-Université Toulouse 3, 14 avenue Edouard Belin, 31400 Toulouse, France;5. ORE-HYBAM – GET (Géosciences Environnement Toulouse), UR234 IRD-Observatoire Midi-Pyrénées (OMP), France;1. Ruprecht-Karls-Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany;2. Karlsruher Institut für Technologie, Institut für Nukleare Entsorgung, P.O. Box 3640, 76021 Karlsruhe, Germany;1. Vinogradov Institute of Geochemistry, SB RAS, Irkutsk, Russia;2. Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, Russia;3. Novosibirsk State University, Russia;4. Institute of Diamond and Precious Metals, SB RAS, Yakutsk, Russia;5. Larionov Institute of Physical and Technical Problems of the North, SB RAS, Yakutsk, Russia;1. Chemical Engineering and Analytical Chemistry Department, Universitat de Barcelona, 08028 Barcelona, Spain;2. Laboratory for Waste Management, Paul Scherrer Institut, CH-5232 Villigen, Switzerland;1. A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov St. 28, 119991, Moscow, Russian Federation;2. N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St. 4, 119991, Moscow, Russian Federation |
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| Abstract: | In this study, eight organic-rich rivers that flow through the Brazilian craton in the southwestern Amazon rainforest are investigated. This investigation is the first of its type in this area and focuses on the effects of lithology, long-term weathering, thick soils, forest cover and hydrological period on the dissolved load compositions in rivers draining cratonic terrain. The major dissolved ion concentrations, alkalinity (TAlk), SiO2, trace element concentrations, and Sr isotope contents in the water were determined between April 2009 and January 2010. In addition, the isotopic values of oxygen and hydrogen were determined between 2011 and 2013. Overall, the river water is highly dilute and dominated by the major dissolved elements TAlk, SiO2 and K+ and the major dissolved trace elements Al, Fe, Ba, Mn, P, Zn and Sr, which exhibit large temporal and spatial variability and are closely correlated with the silicatic bedrock and hydrology. Additionally, rainwater and recycled water vapor and the size of the basin contribute to the geochemistry of the waters. The total weathering flux estimated from our results is 2–4 t km?2.yr?1, which is one of the lowest fluxes in the world. The CO2 consumption rate is approximately 21–61 103 mol km?2 yr?1, which is higher than expected given the stability of the felsic to basic igneous and metamorphic to siliciclastic basement rocks and the thick tropical soil cover. Thus, weathering of the cratonic terrain under intertropical humid conditions is still an important consumer of CO2. |
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| Keywords: | Trace elements Sr isotopes O and D isotopes Weathering rates |
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