Regards croisés

En ces temps d’interrogation sur le réchauffement climatique est parue l’enquête d’Emmanuel Le Roy Ladurie : Histoire humaine et comparée du climat, qui fait suite à son premier livre sur la question publié en 1967. Guy Lemarchand (Université de Rouen), qui a associé Karine Rance (Université de Clermont-Ferrand) à son projet, a eu l’idée de demander à l’auteur des célèbres Paysans de Languedoc (1966) ce qui l’a amené à une démarche qui remet au premier plan, dans une synthèse large, l’orienta..

Globalisation, accounting and developing countries

Accounting is an instrument and an object in globalisation but its impact and manifestation is not uniform across Northern developed countries and Southern developing countries (DCs). This paper reviews contributions on globalisation and its influence on accounting in DCs, and identifies important research gaps. It examines the role of accounting in changing development policies, from state capitalism through neo-liberal market-based to good-governance policies. It then considers specific accounting issues, namely the diffusion of International Accounting Standards (now International Financial Reporting Standards) and how they promote global neo-liberalism; the development of the accounting profession in DCs in the face of competition from Northern global accounting firms and professional associations; accounting issues in state-owned organisations, and privatised and multinational corporations; government accounting reforms and the resurrection of the state in DCs; social and environmental accounting issues; and the rise of non-governmental organisations and their accounting and accountability. The discussion and conclusions reflect on achievements to date and important areas requiring further development

Etude des mécanismes de fractionnement isotopique du bore lors de son interaction avec les acides humiques et les oxydes de fer et de manganèse.

Boron complexation with organic ligands, floculated humic acids, iron oxyhydroxydes (goethite) and manganese oxides (birnessite) has been characterized using potentiometry, adsorption measurements, DRIFT and 11B NMR spectroscopy. Resulting B isotopic fractionation was measured (TIMS). This work shows that boron is strongly complexed by both organic compounds and metal oxides, with, generally, a preferential enrichment of its light isotope (10B) and heavy isotope (11B) at solid surface and in solution, respectively. Adsorption and isotopic fractionation data were successfully modelled, indicating a strong steric control on the isotopic composition of boron surface complexes. This study shows that boron-soil interactions during weathering are likely to have a strong impact on the isotopic composition of surface waters and oceans.La complexation du bore par des acides organiques dissous, un acide humique floculé, et des oxydes métalliques (goethite et birnessite) a été caractérisé expérimentalement par potentiométrie, mesure des taux d'adsorption, spectroscopie infrarouge et RMN de 11B, tandis que les fractionnements isotopiques du bore associés ont été mesurés par spectrométrie de masse à source solide. Il ressort de cette étude que le bore est fortement complexé par les composés étudiés et que l'isotope léger (10B) est généralement (sauf dans le cas de la birnessite) préférentiellement adsorbé sur les surfaces solides entraînant un enrichissement en isotope lourd (11B) des eaux superficielles. La modélisation de l'adsorption et du fractionnement isotopique du bore révèle le rôle prépondérant de la structure surfacique dubore sur les valeurs des facteurs de fractionnement isotopique. Ce travail montre que l'interaction du bore avec les sols lors de l'altération peut influencer fortement la composition isotopique des eaux de surface et des océans

How surface complexes impact boron isotope fractionation: Evidence from Fe and Mn oxides sorption experiments

International audienceAlthough the pH-dependence of boron isotope fractionation between solution and precipitating minerals has been widely used in Earth Sciences, especially for reconstructing ancient seawater pH, the mechanisms by which boron adsorbs on solids or coprecipitates in minerals are still poorly known. Here we have investigated boron isotopic fractionation during its adsorption on goethite (α-FeOOH) and birnessite (K0.1MnO2.2,0.9H2O) as a function of solution pH at T = 25 °C and I = 0.1 M. Maximum partition coefficients (Kd) between adsorbed and aqueous boron, equal to 39 and 34 for goethite and birnessite, respectively, are observed at pH = 8–9. B adsorption at the surface of goethite induces its strong pH-dependent isotopic fractionation ranging from Δ = − 40‰ (10B enrichment on goethite) at pH 10. During adsorption on birnessite at acid and neutral pH, boron isotopic fractionation is lower than during its sorption on goethite (Δ = − 15‰), decreases (α increases) with increasing pH above pH = 8, and reverses at pH > 9: 11B enrichment (+ 23‰ at pH = 10.8) is observed at birnessite surface. Based on combined infrared (DRIFT) spectroscopic analysis and modeling of B speciation at oxides–solution interfaces, the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral boron inner-sphere complexes on goethite surface, and tetrahedral inner-sphere and trigonal outer-sphere and inner-sphere complexes on birnessite surface. B isotopic fractionation is strongly dependent on the structure of surface complexes formed: the high steric strain induced by the formation of trigonal boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation (isotopically lighter sorbed boron) than that following the formation of tetrahedral bidendate binuclear complexes. Conversely, the formation at birnessite surface of trigonal complexes, having almost the same isotopic composition than aqueous boric acid, accounts for the heavier isotopic composition of birnessite than goethite boron, both at acid and alkaline pH. These results show that, in nature, 11B enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of pH that changes boron speciation in solution and at solid surfaces. This is typically the case for soil solution in Fe- and Mn-rich environments and in seawater. In addition, the markedly different isotopic fractionation factor, at the same pH, of boron sorbed on goethite and birnessite (at pH = 8.2, α is equal to 0.967 and 0.986 for goethite and birnessite, respectively) may be used to determine past ocean pH values without requiring knowledge of past isotopic composition

Boron isotopic fractionation related to boron sorption on humic acid and the structure of surface complexes formed

International audienceBoron isotopic fractionation during adsorption onto Ca-flocculated Aldrich humic acid (HA) has been investigated experimentally as a function of solution pH at 25°C and I = 0.15 M. Boron aqueous concentration and isotopic composition were determined by Cs2BO2+ Positive Thermal Ionization Mass Spectrometry analysis, while the structure of B surface complexes on HA was characterized using 11B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). Significant B sorption on HA was observed at 6 9. The measured isotope fractionation cannot be modeled assuming that the isotopic composition of the sorbed borate species is identical to that of B(OH)4- species in the parent solution. It is shown that the extent of isotopic fractionation depends not only on B aqueous speciation but also on the distribution and structure of the borate surface complexes formed. In agreement with energetic constrains, calculation of the isotope fractionation factors between aqueous boric acid and boron surface complexes suggests that the formation of the strained six-membered ring 1,3-diol complex yields a much higher fractionation (?BLP1?III = 0.954 0.960, ? = ?41/-47?) than that of the very stable five-membered ring 1,2-diol (?BLP2?III = 0.983, ? = ?18?). The results of this study open new perspectives to understand and model boron biogeochemical cycle. It is predicted that boron sorption onto organic matter can have important consequences for the boron isotopic composition of surface water reservoirs (seawater, groundwater, soil waters) in which either abundant organic surfaces or significant boron concentrations are available. In addition, the large isotope fractionation between aqueous boric acid and surface boron-organic complexes found in the present work makes boron a promising tracer of biologic activity

Historiens et révolutions. Vers une « paix des braves » ?

Lemarchand Guy, Le Roy Ladurie Emmanuel, Rance Karine. Historiens et révolutions. Vers une « paix des braves » ?. In: Annales historiques de la Révolution française, n°351, 2008. pp. 177-195

Lithium isotope systematics in a forested granitic catchment (Strengbach, Vosges Mountains, France)

International audienceOver the last decade it has become apparent that Li isotopes may be a good proxy to trace silicate weathering. However, the exact mechanisms which drive the behaviour of Li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy. In this study, we analysed the Li concentrations and isotopic compositions in the various surface reservoirs (soils, rocks, waters and plants) of a small forested granitic catchment located in the Vosges Mountains (Strengbach catchment, France, OHGE http://ohge.u-strasbg.fr). Li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin, atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals (which together represent a minimum of 70% of dissolved Li). Li isotope ratios in soil pore waters show large depth dependent variations. Average dissolved d7Li decreases from _1.1&to _14.4& between 0 and _30 cm, but is +30.7&at _60 cm. This range of Li isotopic compositions is very large and it encompasses almost the entire range of terrestrial Li isotope compositions that have been previously reported. We interpret these variations to result from both the dissolution and precipitation of secondary phases. Large isotopic variations were also measured in the springs and stream waters, with d7Li varying from +5.3& to +19.6&. d7Li increases from the top to the bottom of the basin and also covaries with discharge at the outlet. These variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks. We suggest that the dissolved d7Li increases with increasing residence time of waters through the rocks, and so with increasing time of interaction between waters and solids. A dissolution precipitation model was used to fit the dissolved Li isotopic compositions. It was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of _5&to _14& (best fit _10.8&), in agreement with Li incorporation into clay. In soil solutions, it was found that isotopic fractionation during secondary precipitation is larger (at least _23&), suggesting a major role for different secondary phases, such as iron oxides that maybe incorporate Li with a higher isotope fractionation