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Modelling the Global Riverine U Fluxes to the Oceans
Riotte, Jean; Goddéris, Yves; Chabaux, François et al.
200515th Annual Goldschmidt Conference
 

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Keywords :
Uranium cycle
Abstract :
[en] 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.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Riotte, Jean
Goddéris, Yves
Chabaux, François
Munhoven, Guy ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP) - Pétrologie, géochimie endogènes et pétrophysique
François, Louis  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Modélisation du climat et des cycles biogéochimiques
Lorenz, Stefan
Language :
English
Title :
Modelling the Global Riverine U Fluxes to the Oceans
Publication date :
21 May 2005
Event name :
15th Annual Goldschmidt Conference
Event place :
Moscow, United States - Idaho
Event date :
from 20-05-2005 to 24-05-2005
Audience :
International
Funders :
CNRS - Centre National de la Recherche Scientifique [FR]
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
MPG - Max-Planck-Gesellschaft zur Förderung der Wissenschaften [DE]
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since 28 May 2010

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