Bilan des dépérissements forestiers dans les Alpes-de-Haute-Provence

A travers ce témoignage, nous pouvons constater que les effets des changements climatiques sont déjà en uvre sur certains peuplements. Ainsi, les premiers signes de dépérissement des forêts de la zone préalpine des Alpes-de-Haute-Provence, conséquence directe de la canicule de 2003, sont bien visibles. Les répercussions, tant du point de vue des risques liés aux incendies ou à des reprises d'érosion, que du point de vue paysager ou encore de la valeur des bois, sont importantes. Ces événements vont redessiner le paysage des Alpes du Sud et amener les gestionnaires à définir une autre sylviculture

Structural Characterization of Charcoal Exposed to High and Low pH: Implications for 14C Sample Preparation and Charcoal Preservation

Chemical and structural similarities between poorly preserved charcoal and its contaminants, as well as low radiocarbon concentrations in old samples, complicate 14C age determinations. Here, we characterize 4 fossil charcoal samples from the late Middle Paleolithic and early Upper Paleolithic strata of Kebara Cave, Israel, with respect to the structural and chemical changes that occur when they are subjected to the acid-base-acid (ABA) treatment. Differential thermal analysis and TEM show that acid treatment disrupts the structure, whereas alkali treatment results in the reformation of molecular aggregates. The major changes are ascribed to the formation of salt bridges at high pH and the disruption of the graphite-like crystallites at low pH. Weight losses during the treatments are consistently greater for older samples, implying that they are less well preserved. Based on the changes observed in vitro due to pH fluctuations, various methods for removing contamination, as well as a mechanism for preferential preservation of charcoal in nature, are proposed.Anthropolog

New Data on the Origin of Modern Man in the Levant

Anthropolog

Bilan des dépérissements forestiers dans les Alpes-de-Haute-Provence

International audienceA travers ce témoignage, nous pouvons constater que les effets des changements climatiques sont déjà en uvre sur certains peuplements. Ainsi, les premiers signes de dépérissement des forêts de la zone préalpine des Alpes-de-Haute-Provence, conséquence directe de la canicule de 2003, sont bien visibles. Les répercussions, tant du point de vue des risques liés aux incendies ou à des reprises d'érosion, que du point de vue paysager ou encore de la valeur des bois, sont importantes. Ces événements vont redessiner le paysage des Alpes du Sud et amener les gestionnaires à définir une autre sylviculture

Coal used for Fuel at Two Prehistoric Sites in Southern France: Les Canalettes (Mousterian) and Les Usclades (Mesolithic)

International audienceCharcoal analysis—the study of charcoal from archaeological contexts—is designed to reconstruct palaeoenvironment and human use of wood. At two prehistoric sites in the Causse du Larzac (France)—Les Canalettes (Mousterian) and Les Usclades (Mesolithic)—charcoal analysis has revealed specimens whose anatomical structure was abnormally compressed in transverse section. The authors conducted experiments to determine how the compression could have occurred. The result was the first evidence for lignite in Palaeolithic settlements. Lignite fragments in a hearth suggest local Palaeolithic people used it for fuel. The lignite could have come from major coal outcrops within 7 to 15 km of the sites. Coal use is otherwise unknown for Palaeolithic cultures in France, and its use at Les Canalettes during the last glacial is the oldest recorded instance. Coal may have been used for fuel primarily because wood became scarce during the last glacial

Capabilities of MC3D to investigate the coolability of corium debris beds

International audienceA nuclear severe accident progression may lead to the formation of a corium debris bed either in the vessel lower head (in-vessel debris bed) or in the vessel pit (ex-vessel debris bed). For safety analyses it is essential to know if a debris bed is coolable or not, i.e. whether a given water mass flow rate poured into the debris bed – either from its top or from its bottom – will be sufficient to evacuate the residual heat and stop the accident progression. The IRSN code, mostly used for fuel-coolant interaction studies, has been modified with the addition of new friction laws for diphasic flows in porous media. The validation of the code in the case of debris coolability concerns the friction in isothermal configuration in cold and hot situations, the evaluation of critical heat flux and the bottom and top reflooding of debris beds. The results obtained with MC3D are in good agreement with the experimental data and are estimated satisfactory regarding to the nuclear safety issues. © 2017 Elsevier B.V

Modelling of debris bed reflooding in PEARL experimental facility with MC3D code

International audienceA hypothetical severe accident in a nuclear power plant has the potential for causing severe core damage, including a meltdown. To prevent or in the case of an already formed debris bed to limit the in-vessel core degradation, the basic severe accident management strategies consider the in-vessel reflooding to ensure the debris bed coolability. The purpose of our research was to understand the key processes and conditions related to the in-vessel debris bed coolability in the bottom reflooding conditions. Recently, experimental tests in the PEARL facility (IRSN, France) were performed to highlight the behaviour of the steam and water flow in a hot porous medium and to provide experimental data to validate 2-D and 3-D models for the debris bed reflooding. Our aim was to analyse chosen PEARL experiments performed at the atmospheric pressure. The objective was to analyse the importance of the uncertainties in the initial and boundary conditions on the simulation results and to assess the heat transfer modelling approaches. Simulations were performed using the MC3D code (IRSN, France). In general, the performed simulations are in good agreement with the experiments. The general features, in particular the water preferential entrainment in the bypass are recovered and the analysis of calculation gives further information on the mechanisms. In particular, the mechanism of water deviation in the bypass (2-D behaviour) is described. The hypothesis of water dragged by steam coming from the debris bed region cannot be supported. However, the simulation results are indicating a noticeable impact of the actual conditions as the water temperature and the initial support bed and bypass temperature. The simulations, varying the porosity of the test section, showed that this impact affects the flow configuration and is important for cases with the 2-D configuration. The reflooding capabilities in this configuration may depend strongly on the characteristics of the debris bed. Changes in the heat transfer modelling do not have greater effect on the simulation results. © 2018 Elsevier B.V

Apport des datations au problème des origines des hommes modernes au Proche Orient

International audienc

New climatic approaches to the analysis of the middle Paleolithic sequences: Combined taxonomic and isotopic charcoal analyses on a Neanderthal settlement, Les Canalettes (Aveyron, France)

Over the last decade, several studies have indicated the potential for the δ13C isotope signal of charcoals to act as a new local paleoclimatic/paleoenvironmental proxy, complementary to taxonomic analyses. These studies mainly focused on archeological charcoal from the Holocene series, but the potential of the method to be applied Pleistocene sequences is still under debate. Understanding climate-driven variability in stable carbon isotope ratios of modern samples is fundamental for the accurate characterization of past climate information based on the δ13C of charred material. In a previous study, we laid the methodological foundation to apply the method to Pleistocene contexts. Here, we present the δ13C isotopic signal from Pinus spp. charcoal in a well stratified middle Paleolithic site: “Les Canalettes” (Aveyron, France). We demonstrate that the use of isotopic analyses on ancient charcoal of the genus Pinus from the quaternary period could provide a reliable paleoclimatic marker with high resolution and provide data that is complementary to taxonomic studies. A continuous increase in humidity is observed, with a warming episode identified at the top of the sequence. These results place the occupation of the site in a less rigorous phase at the beginning of MIS 4 and underline the importance of the Causses in the mobility system of several generations of Neanderthals