Browsing by Author "Evrard, Olivier"

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    ²⁴⁰Pu/²³⁹Pu signatures allow refining the chronology of radionuclide fallout in South America
    (Elsevier, 2022-10-15) Chaboche, Pierre-Alexis; Pointurier, Fabien; Sabatier, Pierre; Foucher, Anthony; Tiecher, Tales; Minella, Jean P.G.; Tassano, Marcos; Hubert, Amélie; Morera Julca, Sergio Byron; Guédron, Stéphane; Ardois, Christophe; Boulet, Béatrice; Cossonnet, Catherine; Cabral, Pablo; Cabrera, Mirel; Chalar, Guillermo; Evrard, Olivier
    Atmospheric nuclear tests (1945–1980) have led to radioactive fallout across the globe. French tests in Polynesia (1966–1974) may influence the signature of fallout in South America in addition to those conducted by USA and former USSR until 1963 in the Northern hemisphere. Here, we compiled the ²⁴⁰Pu/²³⁹Pu atom ratios reported for soils of South America and conducted additional measurements to examine their latitudinal distributions across this continent. Significantly lower ratio values were found in the 20–45° latitudinal band (0.04 to 0.13) compared to the rest of the continent (up to 0.20) and attributed to the contribution of the French atmospheric tests to the ultra-trace plutonium levels found in these soils. Based on sediment cores collected in lakes of Chile and Uruguay, we show the added value of measuring ²⁴⁰Pu/²³⁹Pu atom ratios to refine the age models of environmental archives in this region of the world.
    Palabras clave:Plutonium isotopesNuclear weapon testsGeochronology
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    Quantifying the sources and the transit times of sediment using fallout radionuclides (7Be, 137Cs, 210Pbxs) in contrasted cultivated catchments across the world
    (American Geophysical Union, 2017-12-15) Evrard, Olivier; Le Gall, Marion; Laceby, J. Patrick; Foucher, Anthony; Lefèvre, Irène; Salvador-Blanes, Sébastien; Morera Julca, Sergio Byron; Ribolzi, Olivier
    Soil erosion and fine sediment supply to rivers are exacerbated in intensively cultivated catchments. Information on the sediment sources and transit times in rivers is required to improve our understanding of these processes and to guide the implementation of effective conservation measures. Accordingly, natural (7Be, 210Pb) and artificial (137Cs) fallout radionuclide concentrations were measured in overland flow and suspended sediment collected during the erosive season in contrasted cultivated catchments. In Laos, samples were collected in a steep catchment (Houay Pano, 12 km²) covered with cropland and teak plantations during the first flood of the monsoon in 2014. Cropland surface sources dominated the supply of sediment at the upstream sampling location (55%), whereas subsurface sources (channel, landslides) contributed the majority of material at the outlet (60%). Furthermore, the material exported from the catchment mainly consisted of re-suspended sediment.
    Palabras clave:Sediment transportMonsoonsFlood routes