Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers

The main problem associated with the study of silicate weathering using riv er dissolved load is that the main control of solute chemistry is lithology and that all rivers are influenced by carbonate and evaporite weathering. In this paper, newly compiled data on the 60 largest rivers of the world ar e used to calculate the contribution of main lithologies, rain and atmosphe re to river dissolved loads. Technically, an inverse method is used to solv e a model containing of a series of mass budget equations relating river co ncentrations to chemical weathering products and atmospheric inputs. New es timates of global silicate weathering fluxes and associated CO2 consumption fluxes are given. The role of basalt weathering on oceanic islands and vol canic arcs is emphasized. For each large river, an attempt is made to calcu late chemical weathering rates of silicates per unit area. Only relative ch emical weathering rates can be calculated. The relationships between the ch emical weathering rates of silicates and the possible controlling parameter s are explored. A combined effect of runoff-temperature and physical denuda tion seems to explain the variability of modern silicate chemical weatherin g rates. The results of this study highlight the coupling between the physi cal and the chemical processes of silicate weathering. Only an active physi cal denudation of continental rocks seems to be able to maintain high chemi cal weathering rates and significant CO2 consumption rates, (C) 1999 Elsevi er Science B.V. All rights reserved.