Marco Donnini [1,4], Jean-Luc Probst [2,3], Anne Probst [2,3], Francesco Frondini [1], Ivan Marchesini [4] Fausto Guzzetti [4], 2013, Alpine weathering and carbon cycle, Goldschmidt 2013, Firenze, 25-30 Agosto 2013,
URL: http://www.cnr.it/prodotto/i/308412

On geological time-scales the fluxes from atmosphere to solid Earth depend on weathering of silicates and carbonates, biogenic precipitation and removal of CaCO3 in the oceans and volcanic gases - seawater interactions. Here we estimate the atmospheric CO2 uptake by weathering in the Alps, using the dissolved loads of 33 Alpine rivers sampled during dry and flood seasons. The dissolved load of streams originates from atmospheric input, pollution, evaporite dissolution, and weathering of carbonate and silicate rocks. We applied the MEGA (Major Element Geochemical Approach) geochemical code [1, 2] to the chemical compositions of the selected rivers in order to quantify the atmospheric CO2 consumed by weathering. The steps were_ (1) subtracion of the rain contribution, (2) the remaining (Na+K) cames from silicate weathering. The average molar ratio Rsil = (Na+K)/(Ca+Mg) was estimated for each basin following well known lithological classification [2, 3], (3) lastly we estimated the (Ca+Mg) originating from carbonate weathering. Depending on time-scales we considered different equations for the quantification of the atmospheric CO2 consumed by weathering [5]. The results show the net predominance of carbonate weathering on fixing atmospheric CO2 and that, considering different time scales, there is about one order of magnitude of difference on the atmospheric CO2 fixed by weathering. [1] Amiotte-Suchet (1995) Sci. Géol. Mém. Strasbourg 97. [2] Amiotte-Suchet and Probst (1996) Sci. Géologiques Bull. Strasbourg 49, 101-126. [3] Meybeck (1996) Bullettin De La Société Géologique 39, 3-77. [4] Meybeck (1987) Am. J. Sci 287, 401-428. [5] Huh (2010) Society of London, Special Publications 342.

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