A combined vacuum crushing and sieving (CVCS) system designed to determine noble gas palaeo-temperatures from stalagmite samples

This paper presents a novel extraction device for water and noble gases from speleothem samples for noble gas paleotemperature determination. The “combined vacuum crushing and sieving (CVCS) system” was designed to reduce the atmospheric noble gas contents from air inclusions in speleothem samples by up to 2 orders of magnitude without adsorbing atmospheric noble gases onto the freshly produced grain surfaces, a process that had often hampered noble gas temperature (NGT) determination in the past. We also present the results from first performance tests of the CVCS system processing stalagmite samples grown at a known temperature. This temperature is reliably reproduced by the NGTs derived from Ar, Kr, and Xe extracted from the samples. The CVCS system is, therefore, suitable for routine determinations of accurate NGTs. In combination with stalagmite dating, these NGTs will allow reconstructing past regional temperature evolutions, and also support the interpretation of the often complex stable isotope records preserved in the stalagmites' calcite.

Accurate analysis of noble gas concentrations in small water samples and its application to fluid inclusions in stalagmites

The concentrations of dissolved noble gases in water are widely used as a climate proxy to determine noble gas temperatures (NGTs); i.e., the temperature of the water when gas exchange last occurred. In this paper we make a step forward to apply this principle to fluid inclusions in stalagmites in order to reconstruct the cave temperature prevailing at the time when the inclusion was formed. We present an analytical protocol that allows us accurately to determine noble gas concentrations and isotope ratios in stalagmites, and which includes a precise manometrical determination of the mass of water liberated from fluid inclusions. Most important for NGT determination is to reduce the amount of noble gases liberated from air inclusions, as they mask the temperature-dependent noble gas signal from the water inclusions. We demonstrate that offline pre-crushing in air to subsequently extract noble gases and water from the samples by heating is appropriate to separate gases released from air and water inclusions. Although a large fraction of recent samples analysed by this technique yields NGTs close to present-day cave temperatures, the interpretation of measured noble gas concentrations in terms of NGTs is not yet feasible using the available least squares fitting models. This is because the noble gas concentrations in stalagmites are not only composed of the two components air and air saturated water (ASW), which these models are able to account for. The observed enrichments in heavy noble gases are interpreted as being due to adsorption during sample preparation in air, whereas the excess in He and Ne is interpreted as an additional noble gas component that is bound in voids in the crystallographic structure of the calcite crystals. As a consequence of our study's findings, NGTs will have to be determined in the future using the concentrations of Ar, Kr and Xe only. This needs to be achieved by further optimizing the sample preparation to minimize atmospheric contamination and to further reduce the amount of noble gases released from air inclusions.

Surviving without leading: Jacques Chirac

The presidency of Jacques Chirac in France (1995-2007) was scarred by two crushing defeats: the parliamentary elections of 25 May and 1 June 1997, and the referendum on the European Constitution of 29 May 2005. As both were highly personal setbacks, since both votes were taken at Chirac’s initiative they suggest that a dominant presidential position, twice won, was twice squandered owing to a failure of leadership. This chapter argues, firstly, that the weaknesses of the presidency arose chiefly from the three decades of Chirac’s career before the 1995 election – and, secondly, that Chirac’s record of presidential leadership, though limited, is more substantial than these two major failures suggest.

Non-concordance between genetic profiles of olive oil and fruit: a cautionary note to the use of DNA markers for provenance testing.

To investigate the contribution of paternal alleles to the DNA content of olive oil, genetic analyses of olive DNA samples from fruits, leaves, and oil derived from the same tree (cv. Leccino) were carried out. DNA extracted from maternal tissues--leaves and flesh--from different fruits showed identical genetic profiles using a set of DNA markers. Additional simple sequence repeat (SSR) alleles, not found in the maternal samples, were amplified in the embryos (stone), and they were also detected in DNA extracted from the paste obtained by crushing whole fruits and from the oil pressed from this material. These results demonstrate that the DNA profile obtained from olive oil is likely to represent a composite profile of the maternal alleles juxtaposed with alleles contributed by various pollen donors. Therefore, care needs to be taken in the interpretation of DNA profiles obtained from DNA extracted from oil for resolving provenance and authenticity issues.

Modelling the rheology of sea ice as a collection of diamond-shaped floes

In polar oceans, seawater freezes to form a layer of sea ice of several metres thickness that can cover up to 8% of the Earth’s surface. The modelled sea ice cover state is described by thickness and orientational distribution of interlocking, anisotropic diamond-shaped ice floes delineated by slip lines, as supported by observation. The purpose of this study is to develop a set of equations describing the mean-field sea ice stresses that result from interactions between the ice floes and the evolution of the ice floe orientation, which are simple enough to be incorporated into a climate model. The sea ice stress caused by a deformation of the ice cover is determined by employing an existing kinematic model of ice floe motion, which enables us to calculate the forces acting on the ice floes due to crushing into and sliding past each other, and then by averaging over all possible floe orientations. We describe the orientational floe distribution with a structure tensor and propose an evolution equation for this tensor that accounts for rigid body rotation of the floes, their apparent re-orientation due to new slip line formation, and change of shape of the floes due to freezing and melting. The form of the evolution equation proposed is motivated by laboratory observations of sea ice failure under controlled conditions. Finally, we present simulations of the evolution of sea ice stress and floe orientation for several imposed flow types. Although evidence to test the simulations against is lacking, the simulations seem physically reasonable.

Travail des enfants et droit à l’éducation au Burkina Faso: L’exemple de la carrière de Pissy

Cet article décrit et analyse le travail des enfants dans une carrière de granit d’un quartier de la ville de Ouagadougou, interroge le rapport entre l’école et le travail du point de vue des acteurs du site pour apprécier l’argument de la scolarisation comme solution alternative au travail des enfants. Les données proviennent d’une enquête réalisée dans le cadre de notre recherche doctorale au Burkina Faso, de février à avril 2009, dont la carrière de Pissy a été un des terrains d’enquête1. Les enquêtés sont constitués de parents et de leurs enfants âgés de moins de 16 ans ayant des trajectoires différentes : non scolarisés,scolarisés, déscolarisés et à la fois écoliers et travailleurs. Les personnes ont été choisies aléatoirement selon leur accord et disponibilité, en variant leur emplacement. L’approche choisie privilégie le point de vue des différents acteurs du site,l’analyse de leurs discours et l’observation de leurs pratiques de travail. La prise en compte du point de vue des enfants s’appuie sur la perspective théorique développée par James & Prout (1997), où les enfants sont des acteurs compétents dans la sphère du travail et de la vie sociale. L’article présente d’abord le processus d’institutionnalisation de l’école et la situation du travail des enfants au Burkina Faso, puis décrit les logiques autour du travail des enfants dans la carrière en montrant que celui-ci n’est pas seulement lié à la nécessité économique. Enfin, il confronte les alternatives au travaildes enfants invoquées par les enfants et leurs parents aux solutions d’éducation proposées par l’état et la société civile. This article is about a particular case of children in working situation: children crushing the granite in the quarry of Pissy. Their working conditions are considered as dangerous by national and international legal texts. This article aims to grasp the experience of children who work in this frame in order to test the hypothesis according to which schooling would be an effective tool of struggle against child labour. The fieldwork reveals that child labour in the quarry is not only guided by economic aspects. The wish of the parents (and of some children and teenagers) to find another job for working children reopen the debate on “the right to work” for children.