Modelling of atmospheric CO2 consumption by chemical weathering of rocks: Application to the Garonne, Congo and Amazon basins (original) (raw)
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Global Biogeochemical Cycles, 2003
1] The silicate rock weathering followed by the formation of carbonate rocks in the ocean, transfers CO 2 from the atmosphere to the lithosphere. This CO 2 uptake plays a major role in the regulation of atmospheric CO 2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks. This leads us to develop the first world lithological map with a grid resolution of 1°Â 1°. This paper analyzes the spatial distribution of the six main rock types by latitude, continents, and ocean drainage basins and for 49 large river basins. Coupling our digital map with the GEM-CO2 model, we have also calculated the amount of atmospheric/soil CO 2 consumed by rock weathering and alkalinity river transport to the ocean. Among all silicate rocks, shales and basalts appear to have a significant influence on the amount of CO 2 uptake by chemical weathering.
Global Biogeochemical …, 2003
The silicate rock weathering followed by the formation of carbonate rocks in the ocean, transfers CO 2 from the atmosphere to the lithosphere. This CO 2 uptake plays a major role in the regulation of atmospheric CO 2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks. This leads us to develop the first world lithological map with a grid resolution of 1°Â 1°. This paper analyzes the spatial distribution of the six main rock types by latitude, continents, and ocean drainage basins and for 49 large river basins. Coupling our digital map with the GEM-CO2 model, we have also calculated the amount of atmospheric/soil CO 2 consumed by rock weathering and alkalinity river transport to the ocean. Among all silicate rocks, shales and basalts appear to have a significant influence on the amount of CO 2 uptake by chemical weathering.
We report a water chemistry data set from 13 rivers of the Virunga Volcanic Province (VVP) (Democratic Republic of Congo), sampled between December 2010 and February 2013. Most parameters showed no pronounced seasonal variation, whereas their spatial variation suggests a strong control by lithology, soil type, slope, and vegetation. High total suspended matter (289–1467 mg L 21) was recorded in rivers in the Lake Kivu catchment, indicating high soil erodibility, partly as a consequence of deforestation and farming activities. Dissolved and particulate organic carbon (DOC and POC) were lower in rivers from lava fields, and higher in nonvolcanic subcatchments. Stable carbon isotope signatures (d 13 C) of POC and DOC mean d 13 C of 222.5& and 223.5&, respectively, are the first data to be reported for the highland of the Congo River basin and showed a much higher C4 contribution than in lowland areas. Rivers of the VVP were net sources of CH 4 to the atmosphere (4–5052 nmol L 21). Most rivers show N 2 O concentrations close to equilibrium, but some rivers showed high N 2 O concentrations related to denitrification in groundwaters. d 13 C signatures of dissolved inorganic carbon suggested magmatic CO 2 inputs to aquifers/soil, which could have contributed to increase basalt weathering rates. This magmatic CO 2-mediated basalt weathering strongly contributed to the high major cation concentrations and total alkalinity. Thus, chemical weathering (39.0–2779.9 t km 22 yr 21) and atmospheric CO 2 consumption (0.4–37.0 3 10 6 mol km 22 yr 21) rates were higher than previously reported in the literature for basaltic terrains.
High sensitivity of the continental-weathering carbon dioxide sink to future climate change
Nature Climate Change, 2012
According to future anthropogenic emission scenarios, the atmospheric CO 2 concentration may double before the end of the twenty-first century 1 . This increase is predicted to result in a global warming of more than 6 • C in the worst case 1 . The global temperature increase will promote changes in the hydrologic cycle through redistributions of rainfall patterns and continental vegetation cover 1,2 . All of these changes will impact the chemical weathering of continental rocks. Long considered an inert CO 2 consumption flux at the century timescale, recent works have demonstrated its potential high sensitivity to the ongoing climate and land-use changes 3,4 . Here we show that the CO 2 consumption flux related to weathering processes increases by more than 50% for an atmospheric CO 2 doubling for one of the most important Arctic watersheds: the Mackenzie River Basin. This result has been obtained using a process-based model of the chemical weathering of continental surfaces forced by models describing the atmospheric general circulation and the dynamic of the vegetation 5,6 under increased atmospheric CO 2 . Our study stresses the potential role that weathering may play in the evolution of the global carbon cycle over the next centuries.
Chemical weathering and atmospheric/soil CO 2 uptake in the Andean and Foreland Amazon basins
Chemical Geology, 2011
This study is a geochemical investigation of the Andean and Foreland basins of the Amazon River at high spatial and time resolution, carried out within the framework of the HYBAM research program (Hydro-geodynamics of the Amazon Basin). Monthly sampling was carried out at 27 gauging stations located in the upper tributaries of the Amazon Basin (from north to south: the Napo, Marañon, Ucayali, Madre de Dios-Beni and Mamore Rivers). The aim of this paper is to estimate the present-day chemical weathering rate (CWR), as well as the flux of CO 2 consumption from total and silicate weathering in the Andes and Foreland Amazon basins, and to discuss their distribution as a function of geomorphic and structural parameters. Based on the forward method, the Napo and other Ecuadorian basins present high silicate weathering rates in comparison with the other basins. We confirm that the Marañon and Ucayali Rivers control the Amazon hydrochemistry due to the presence of salt rocks and carbonates in these basins. The Madre de Dios, Beni and Mamore basins do not contribute much to the Amazon dissolved load. This north to south CWR gradient can be explained by the combination of decreasing weatherable lithology surface and decreasing runoff rates from the north to the south. The foreland part of the basins (or Mountain-Lowland transition) accounts for nearly the same proportion of the Amazon silicate chemical weathering and carbonate chemical weathering fluxes as the Andean part. This result demonstrates the importance of the sediment accumulation areas in the Amazon Basin weathering budget and can be explained by the occurrence of a higher temperature, the deposition of fresh sediments from Andean erosion and a higher sediment residence time than in the upper part of the basin. With a total CO 2 consumption rate of 744.10 3 moles km − ² year − 1 and a silicate CO 2 consumption rate of 300.10 3 moles km − ² year − 1 , the Upper Amazon River (Andes + Foreland part) is the most intense part of the Amazon Basin in terms of atmospheric CO 2 consumption by weathering processes. It is an important CO 2 sink by weathering processes but accounts for only somewhat more than half of the CO 2 consumption by silicate weathering of the Amazon Basin. This result points out the importance of the Lowland part of the basin in the inorganic C silicate budget. The Upper Amazon accounts for 2-4% of the world's silicate CO 2 consumption, which is the same proportion as for the southern and southern-east Himalaya and Tibetan plateau.
Global carbon sequestration through continental chemical weathering in a climatic change context
2021
Here, we simulate carbon dioxide (CO2) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under both the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historic baseline (1969-1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that global temporal evolution of the CO2 uptake presents a general increase in the annual amount of CO2 consumed from 0.247 Pg C·y-1 to 0.261 and 0.273 Pg C·y-1, respectively for RCP 2.6 and RCP 8.5. Besides, despite showing a general increase for the global daily carbon sequestration, both climate scenarios present a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods.
Atmospheric CO2 sink: Silicate weathering or carbonate weathering?
Applied Geochemistry, 2011
It is widely accepted that chemical weathering of Ca-silicate rocks could potentially control long-term climate change by providing feedback interaction with atmospheric CO 2 drawdown by means of precipitation of carbonate, and that in contrast weathering of carbonate rocks has not an equivalent impact because all of the CO 2 consumed in the weathering process is returned to the atmosphere by the comparatively rapid precipitation of carbonates in the oceans. Here, it is shown that the rapid kinetics of carbonate dissolution and the importance of small amounts of carbonate minerals in controlling the dissolved inorganic C (DIC) of silicate watersheds, coupled with aquatic photosynthetic uptake of the weatheringrelated DIC and burial of some of the resulting organic C, suggest that the atmospheric CO 2 sink from carbonate weathering may previously have been underestimated by a factor of about 3, amounting to 0.477 Pg C/a. This indicates that the contribution of silicate weathering to the atmospheric CO 2 sink may be only 6%, while the other 94% is by carbonate weathering. Therefore, the atmospheric CO 2 sink by carbonate weathering might be significant in controlling both the short-term and long-term climate changes. This questions the traditional point of view that only chemical weathering of Ca-silicate rocks potentially controls long-term climate change.
Impact of atmospheric CO 2 levels on continental silicate weathering
Geochemistry, Geophysics, Geosystems, 2010
1] Anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric CO 2 concentrations since the beginning of the industrial revolution. Here we use the B-WITCH model to quantify the impact of increased CO 2 concentrations on CO 2 consumption by weathering of continental surfaces. B-WITCH couples a dynamic biogeochemistry model (LPJ) and a process-based numerical model of continental weathering (WITCH). It allows simultaneous calculations of the different components of continental weathering fluxes, terrestrial vegetation dynamics, and carbon and water fluxes. The CO 2 consumption rates are estimated at four different atmospheric CO 2 concentrations, from 280 up to 1120 ppmv, for 22 sites characterized by silicate lithologies (basalt, granite, or sandstones). The sensitivity to atmospheric CO 2 variations is explored, while temperature and rainfall are held constant. First, we show that under 355 ppmv of atmospheric CO 2 , B-WITCH is able to reproduce the global pattern of weathering rates as a function of annual runoff, mean annual temperature, or latitude for silicate lithologies. When atmospheric CO 2 increases, evapotranspiration generally decreases due to progressive stomatal closure, and the soil CO 2 pressure increases due to enhanced biospheric productivity. As a result, vertical drainage and soil acidity increase, promoting CO 2 consumption by mineral weathering. We calculate an increase of about 3% of the CO 2 consumption through silicate weathering (mol ha −1 yr −1 ) for 100 ppmv rise in CO 2 . Importantly, the sensitivity of the weathering system to the CO 2 rise is not uniform and heavily depends on the climatic, lithologic, pedologic, and biospheric settings.
Influence of acid rain on CO 2 consumption by rock weathering: local and global scales
1995
Sulphuric and nitric acids, which are supplied by acid precipitation, take over from carbonic acid in weathering reactions, which induced a decrease of the atmospheric/soil COz consumption by weathering (WCO2). In order to quantify this disturbance, one has compared the bicarbonate fluxes determined at the outlet of 2 small catchments (one is substantially disturbed and the other is is weakly disturbed by acid precipitation). Our study shows that, under the influence of acid precipitation, bicarbonate fluxes (i.e. WCO2) are decreased by about 73%. It has also been attempted to simulate at the continental scale, the influence of acid precipitation on WCOz, using a Global Erosion Model (GEM-CO2) recently developed. Several simulations have been performed corresponding to different realistic scenarios of global acid precipitation. In the most pessimistic of these scenarios, the GEM-CO: simulation shows that the global WCO: would be decreased by no more than 10%.