References of "Goddéris, Yves"
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See detailCan accurate kinetic laws be created to describe chemical weathering ?
Schott, Jacques; Oelkers, Eric H.; Bénézeth, Pascale et al

in Comptes Rendus Geoscience (2012), 344

Knowledge of the mechanisms and rates of mineral dissolution and growth, especially close to equilibrium, is essential for describing the temporal and spatial evolution of natural processes like ... [more ▼]

Knowledge of the mechanisms and rates of mineral dissolution and growth, especially close to equilibrium, is essential for describing the temporal and spatial evolution of natural processes like weathering and its impact on CO2 budget and climate. The Surface Complexation approach (SC) combined with Transition State Theory (TST) provides an efficient framework for describing mineral dissolution over wide ranges of solution composition, chemical affinity, and temperature. There has been a large debate for several years, however, about the comparative merits of SC/TS versus classical growth theories for describing mineral dissolution and growth at near-to-equilibrium conditions. This study considers recent results obtained in our laboratory on oxides, hydroxides, silicates, and carbonates on near-equilibrium dissolution and growth via the combination of complementary microscopic and macroscopic techniques including hydrothermal atomic force microscopy, hydrogen-electrode concentration cell, mixed flow and batch reactors. Results show that the dissolution and precipitation of hydroxides, kaolinite, and hydromagnesite powders of relatively high BET surface area closely follow SC/TST rate laws with a linear dependence of both dissolution and growth rates on fluid saturation state (V) even at very close to equilibrium conditions (jDGj < 500 J/mol). This occurs because sufficient reactive sites (e.g. at kink, steps, and edges) are available at the exposed faces for dissolution and/or growth, allowing reactions to proceed via the direct and reversible detachment/attachment of reactants at the surface. In contrast, for magnesite and quartz, which have low surface areas, fewer active sites are available for growth and dissolution. Such minerals exhibit rates dependencies on V at near equilibrium conditions ranging from linear to highly non-linear functions of V, depending on the treatment of the crystals before the reaction. It follows that the form of the f(DG) function describing the growth and dissolution of minerals with low surface areas depends on the availability of reactive sites at the exposed faces and thus on the history of the mineral-fluid interaction and the hydrodynamic conditions under which the crystals are reacted. It is advocated that the crystal surface roughness could serve as a proxy of the density of reactive sites. The consequences of the different rate laws on the quantification of loess weathering along the Mississippi valley for the next one hundred years are examined. [less ▲]

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See detailTowards an Integrated Model of Weathering, Climate, and Biospheric Processes
Godderis, Yves; Roelandt, Caroline; Schott, Jacques et al

in Reviews in Mineralogy and geochemistry (2009), 70

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See detailCoupled modeling of global carbon cycle and climate in the Neoproterozoic: links between Rodinia breakup and major glaciations
Godderis, Yves; Donnadieu, Yannick; Dessert, Celine et al

in Comptes Rendus Geoscience (2007), 339(3-4), 212-222

A coupled climate-geochemical model of new generation (GEOCLIM) is used to investigate the possible causes of the initiation of snowball glaciations during Neoproterozoic times. This model allows the ... [more ▼]

A coupled climate-geochemical model of new generation (GEOCLIM) is used to investigate the possible causes of the initiation of snowball glaciations during Neoproterozoic times. This model allows the calculation of the partial pressure of atmospheric CO2 simultaneously with the climate at the continental surface with a rough 2D spatial resolution (10 degrees lat. x 50 degrees long.). We calculate that the breakup of the Rodinia supercontinent, starting 800 Myr ago, results in a global climatic cooling of about 8 degrees C triggered by enhanced consumption of atmospheric CO2 resulting from increased runoff over continental surfaces. This increase in runoff is driven by the opening of oceanic basins resulting in an increase of soil moisture sources close to continental masses. This climatic effect of the supercontinent breakup is particularly strong within the 800-700 Ma interval since all continents are located in the equatorial area, where temperature and runoff conditions optimize the consumption of CO2 through weathering processes. However, this effect alone is insufficient to trigger snowball. We propose that the efficient weathering of fresh basaltic surfaces that erupted during the Rodinia breakup, and were transported to the humid equatorial area through continental plate motion, contributed the necessary CO2 sink that triggered the ca. 730-Ma Sturtian glacial event. Simulations of the GEOCLIM model for the ca 580-Ma Gaskiers ice age, where all continents are centered on the South Pole, shows that no snowball glaciation can be initiated. The calculated CO2 partial pressure remains above 1000 ppmv, while a threshold of less than 80 ppmv is required to initiate a snowball glaciation. At that time, a polar configuration does not allow the onset of total glaciation. Nevertheless, a regional glaciation is simulated by the GEOCLIM when the climatic and geochemical (i.e. weathering related) effects of the Pan-African orogeny (similar to 600 Ma) are taken into account. Finally, the question of the role of the paleogeographic setting in the Marinoan snowball event (similar to 635 Ma) is still an open question, since no reliable Marinoan paleogeographic reconstruction exists due to the paucity of paleomagnetic data. [less ▲]

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See detailAtmospheric Carbon Dioxide and Climate Over Phanerozoic Times
François, Louis ULg; Lefèbvre, Vincent; Goddéris, Yves et al

Conference (2006, December)

The atmospheric CO2 mixing ratio has fluctuated widely over the Phanerozoic, according to the estimates from available proxy records. Because atmospheric CO2 is a major greenhouse gas, these fluctuations ... [more ▼]

The atmospheric CO2 mixing ratio has fluctuated widely over the Phanerozoic, according to the estimates from available proxy records. Because atmospheric CO2 is a major greenhouse gas, these fluctuations should have led to significant climatic variations. The "classical" view is indeed that atmospheric CO2 has been the main driver of the Earth's climate history. On long-term time scales, the atmospheric CO2 level is the result of the balance between CO2 inputs from volcanoes or oxidation of old organic carbon (kerogen) in exposed rocks and outputs through silicate weathering or organic carbon deposition. Existing model reconstructions of the Phanerozoic history of atmospheric CO2 are based on such budgets. Recent data and model experiments currently challenge these models. First, the carbon cycle may be more complex than represented in the earliest models. In particular, silicate weathering depends on numerous factors, which are not obvious to model or are poorly known over the Phanerozoic. Mountain uplift is one such factor, which has been much debated in the last decade. Lithology is another example: basalts weather much more rapidly than other silicate rocks and the emplacement of large basaltic areas on the continents may trigger glaciations. Continental configuration is also more important than previously thought, as indicated by recent model experiments on super-continent fragmentation coupling geochemical and climate models. Problems of "classical" Phanerozoic CO2 models are also well illustrated by the fact that the most recent estimates of CO2 degassing show very little variation between the Cretaceous and the present, a period when large changes in CO2 have occurred, whereas degassing is the most important forcing of CO2 evolution in long-term carbon cycle models. Second, CO2 is not the only driver of climate evolution. This obvious fact has largely been forgotten in Phanerozoic studies. What the proxies tell us on paleo-atmospheric CO2 is not always in line with what we know about paleoclimatic records. For instance, the proxies suggest relatively high CO2 levels during the Late Ordovician glaciations. Similarly, the Late Jurassic now appears to be colder than earlier thought, while again proxies suggest high atmospheric CO2 at that time. The mid-Miocene climate warming, which occurs simultaneously with a drop in CO2, provides another example. This latter change in CO2 is unanimously reflected in all proxies and, so, this decoupling between CO2 and climate cannot arise from uncertainties on the reconstructed CO2 levels or from dating problems, as might be the case of the former two examples. Other climatic drivers than CO2 clearly need to be considered. In this respect, vegetation- climate feedbacks have been completely disregarded in long-term climatic studies. Cenozoic cooling is, however, accompanied by a progressive transition from closed forests to more widespread grasslands and deserts on the continental areas, a change which must have had major impacts on the surface albedo and the water cycle. [less ▲]

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See detailModelling the Global Riverine U Fluxes to the Oceans
Riotte, Jean; Goddéris, Yves; Chabaux, François et al

Conference (2005, May 21)

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17 ... [more ▼]

Mean U isotopic ratio of the ocean has remained roughly constant since about 600 kyrs (Henderson, 2001). This 1.14 value cannot be explained considering the present day value of the U riverine ratio (1.17, Chabaux et al., 2001). However, the mean riverine ratio was calculated on half of the total continental runoff. Is this partial mean value really representative of the mean value? If yes, might this value have changed over a glacial-interglacial cycle ? We build up a numerical model calculating the flux of U transfer to the ocean through weathering. The spatial resolution of the model reaches 0.5°lat x0.5°long. Lithology is modified from Amiotte-Suchet et al. (2003). Weathering fluxes are estimated from simple parametric laws, calculating the flux of total dissolved solids from mean annual temperature and runoff. Soil PCO2 is used to estimate carbonate dissolution rates, and is calculated from a simulation of the Caraib model. Uranium fluxes are estimated proportional to the TDS flux, weighted by its abundance in the source rock. CO2 consumption through weathering is simultaneously computed. The 234U/238U ratio of the river is calculated according to a correlation existing between the measured 234U/238U and runoff, showing a decrease of this ratio with increasing runoff. The model is first validated over several large watersheds, including the Amazon, the Ganges-Brahmapoutra, the Mississippi, and the Congo rivers. Global runs are then performed, showing that the modelled mean global value is close to the measured partial mean of 1.17. We explore then possible variations of the modelled ratio at the last glacial maximum. Temperature and runoff fields are taken from LGM simulations of the ECHAM GCM. Extension of ice sheets is assumed to cut off part of the weathering fluxes, producing possible fluctuations in the riverine U isotopic ratio, as well as changes in the regional runoff pattern. [less ▲]

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See detailModelling atmospheric CO2 changes at geological timescales
François, Louis ULg; Grard, Aline ULg; Goddéris, Yves

in Carnets de Géologie = Notebooks on Geology (2005), M02/02(Memoir 2005/02), 11-14

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See detailPaleo-oceanography: Cenozoic oceans – carbon cycle models
François, Louis ULg; Goddéris, Yves

in Steele, J. H.; Thorpe, S. A.; Turekian, K. K. (Eds.) Encyclopedia of Ocean Sciences (2001)

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