Abstract: This article reports on high-resolution (60 km) atmospheric general circulation model simulations of the Antarctic climate for the periods 1981–2000 and 2081–2100. The analysis focuses on the surface mass balance change, one of the components of the total ice sheet mass balance, and its impact on global eustatic sea level. Contrary to previous simulations, in which the authors directly used sea surface boundary conditions produced by a coupled ocean–atmosphere model for the last decades of both centuries, an anomaly method was applied here in which the present-day simulations use observed sea surface conditions, while the simulations for the end of the twenty-first century use the change in sea surface conditions taken from the coupled simulations superimposed on the present-day observations. It is shown that the use of observed oceanic boundary conditions clearly improves the simulation of the present-day Antarctic climate, compared to model runs using boundary conditions from a coupled climate model. Moreover, although the spatial patterns of the simulated climate change are similar, the two methods yield significantly different estimates of the amplitude of the future climate and surface mass balance change over the Antarctic continent. These differences are of similar magnitude as the intermodel dispersion in the current Intergovernmental Panel on Climate Change (IPCC) exercise: selecting a method for generating boundary conditions for a high-resolution model may be just as important as selecting the climate model itself. Using the anomaly method, the simulated mean surface mass balance change over the grounded ice sheet from 1981–2000 to 2081–2100 is 43-mm water equivalent per year, corresponding to a eustatic sea level decrease of 1.5 mm yr?1. A further result of this work is that future continental-mean surface mass balance changes are dominated by the coastal regions, and that high-resolution models, which better resolve coastal processes, tend to predict stronger precipitation changes than models with lower spatial resolution.

Abstract: The mechanisms of magma crust accretion at large igneous provinces (LIPs) are questioned using arguments based on the north Atlantic case. Published and new data on the calculated flow vectors within dike swarms feeding the early traps and subsequent seaward-dipping reflector lavas suggest that most of the mafic magmas forming the north Atlantic LIP transited through a small number of igneous centers. The magma was injected centrifugally in dike swarms at some distance away from individual igneous centers along the trend of the maximum horizontal stress acting in the crust, feeding lava piles via dikes intersecting the ground surface. This mechanism is similar to that observed in present-day Iceland and, more generally, in mafic volcano-tectonic systems. The absence of generalized vertical magma transit in a LIP has major geodynamic consequences. We cannot link the surface extent of LIP magmas to the dimensions of the mantle melting zone as proposed in former plume head models. The distribution of LIP magmas at the surface is primarily controlled by the regional stress field acting within the upper crust, but is also affected by magma viscosity. The igneous centers feeding LIPs most likely represent the crustal expression of small-scale convective cells of the buoyant mantle naturally located beneath the mechanical lithosphere.

Abstract: Thèse de Doctorat, Université de Paris VII
Les hydrocarbures non méthaniques (NMHC) légers de deux à six atomes de carbone (C2-C6), en raison de leur réactivité, sont essentiels dans les processus chimiques troposphériques qui contrôlent le bilan d'ozone. La diversité de leurs durées de vie apporte également des informations quantitatives sur les processus dynamiques atmosphériques. L'implication des NMHC ne se limite pas aux régions polluées, mais par un transport à grande échelle, peut également s'étendre aux régions éloignées de leurs sources. Ainsi l'intérêt de la mesure des hydrocarbures concerne tous les compartiments atmosphériques, et repose sur une très bonne spéciation de ces espèces. La méthode de mesure la plus utilisée jusqu'aux années 1990 afin d'effectuer la spéciation des NMHC puis leur quantification, a été basée sur les prélèvements en flacons en acier avec une analyse différée par chromatographie en phase gazeuse (CPG). Cette méthode nous a permis dans le cadre de ce travail d'établir des facteurs d'émission d'hydrocarbures et de monoxyde de carbone de la source automobile (tunnel de Thiais) et d'étudier les variations saisonnières des NMHC dans une station de bruit de fond (Ile Amsterdam). Les limites de ce protocole sont évaluées lors d'une étude de la stabilité des hydrocarbures stockés dans deux types de flacons en acier et en verre. En conséquence, une analyse en continu «in situ» est nécessaire afin de mieux établir la variabilité spatiale des NMHC et notamment leurs distributions verticales et temporelles. La mise au point et les performances d'un instrument de mesure en continu des hydrocarbures légers (C2-C6) par CPG sont présentées ici. Les mesures préliminaires au sol ou lors d'essais aéroportés sont évaluées et permettent de définir de futures optimisations.

Abstract: In endotherms, regulation of the degree of mitochondrial coupling affects cell metabolic efficiency. Thus it may be a key contributor to minimizing metabolic rate during long periods of fasting. The aim of the present study was to investigate whether variation in mitochondrial avian uncoupling proteins (avUCP), as putative regulators of mitochondrial oxidative phosphorylation, may contribute to the ability of king penguins (Aptenodytes patagonicus) to withstand fasting for several weeks. After 20 days of fasting, king penguins showed a reduced rate of whole animal oxygen consumption ([IMG]f1.gif“ ALT=”V“ BORDER=”0“>O2; -33%) at rest, together with a reduced abundance of avUCP and peroxisome proliferator-activated receptor-{gamma} coactivator-1{alpha} (PGC1-{alpha}) mRNA in pectoralis muscle (-54%, -36%, respectively). These parameters were restored after the birds had been refed for 3 days. Furthermore, in recently fed, but not in fasted penguins, isolated muscle mitochondria showed a guanosine diphosphate-inhibited, fatty acid plus superoxide-activated respiration, indicating the presence of a functional UCP. It was calculated that variation in mitochondrial UCP-dependent respiration in vitro may contribute to nearly 20% of the difference in resting [IMG]f1.gif” ALT=“V” BORDER=“0”>O2 between fed or refed penguins and fasted penguins measured in vivo. These results suggest that the lowering of avUCP activity during periods of long-term energetic restriction may contribute to the reduction in metabolic rate and hence the ability of king penguins to face prolonged periods of fasting.