Coupled modeling of biospheric and chemical weathering processes at the continental scale

Abstract

[1] In this contribution, a reactive-transport model describing weathering in soil profiles and at the watershed scale is coupled to a dynamic global vegetation model to calculate the dissolved load of continental waters on a 0.5°latitude × 0.5°longitude grid. The so-called Biosphere-Weathering at the Catchment Scale (B-WITCH) model is applied to the Orinoco watershed (South America). We show that B-WITCH is able to reproduce the main cation composition of the surface waters over the watershed. Sensitivity tests demonstrate that clay mineral reactivities are key factors controlling the calculated discharge of dissolved species. More specifically, our simulations show that the dissolution and precipitation rates of clay minerals in the weathering profiles are strongly intertwined, and that this coupling must be accurately described when modeling the weathering fluxes at the continental scale. A second set of sensitivity tests show that, for the tropical environment, land plants control the total base cation discharge through their impact on the soil hydrology, rather than through enhanced soil CO 2 pressures. Indeed, the complete removal of the continental vegetation leads to an increase in the dissolved fluxes to the ocean by 80% because of the collapse in the evapotranspiration, resulting in a more efficient drainage of the weathering profiles. On the other hand, neglecting the root respiration and setting the soil CO 2 pressure to the atmospheric level forces the total base cation discharge to decrease by only 20%.

Evaluating the effects of terrestrial ecosystems, climate and carbon dioxide on weathering over geological time: a global-scale process-based approach

“…It further indicates that our numerical representation of biological and abiotic weathering processes are probably realistic and therefore have some utility when extrapolated into the past. This view is supported by the similarity between our [25].…”

“…Roelandt et al [25] coupled a DGVM into a sophisticated n-layer mechanistic weathering model [26] requiring detailed information about soil characteristics for each grid point, that accounts for both evapotranspiration and root respiration effects on weathering via hydrology and soil pCO 2 . Unlike the simpler one-layer box model of Taylor et al [10], it takes no account of the actions of mycorrhizal fungi on the biological proton cycle that control mineral weathering [16].…”

The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust

“…A spatial representation of the geochemical (or mineralogical) composition of the terrestrial surface can also contribute additional information for Earth system models focusing on the climate system, e.g. to better distinguish CO 2 -consumption by silicate and carbonate chemical weathering or to estimate the phosphorus-release by chemical weathering to soils and ecosystems (Berner 2006;Hartmann et al 2009;Hartmann 2009;Godderis et al 2009;Hartmann and Moosdorf 2010;Roelandt et al 2010).…”

Rates of consumption of atmospheric CO<sub>2</sub> through the weathering of loess during the next 100 yr of climate change

“…Here, a globally validated classification of plant functional types (PFT) is used (updated from François et al, 2011). Finally, the WITCH weathering model has been used to simulate water-mineral interactions in various environments, from polar to tropical settings (Goddéris et al, 2006;Roelandt et al, 2010;Violette et al, 2010;Beaulieu et al, 2011). WITCH was able to reproduce the concentration in base cations and silica in soil solutions and at the outlet of the simulated catchments.…”