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71.
Uncertainties in European summer precipitation changes: role of large scale circulation 总被引:2,自引:2,他引:0
Climate models suggest that anthropogenic emissions are likely to induce an important drying during summer over most of Europe in the late 21st century. However, the amplitude of the associated decrease in precipitation strongly varies among the different climate models. In order to reduce this spread, it is first necessary to identify its causes and the associated physical mechanisms. Consequently, the focus of this paper is to better estimate the role of large scale circulation (LSC) in precipitation changes over Europe using a multi-model framework and then to characterize the LSC changes using the weather regime paradigm. We show that LSC changes directly lead to a decrease of precipitation over northwestern Europe. This circulation-driven decrease in rainfall is mainly linked to an increase (decrease) of the occurrence of positive (negative) phase of the North Atlantic Oscillation regime. LSC is also responsible for a significant part of the models spread in precipitation changes over these regions. Over southern Europe, the role of LSC changes on multi-model mean precipitation changes is generally weak. We also show that the precipitation anomalies directly induced by LSC modifications seem to be further amplified through local feedbacks. 相似文献
72.
Harold C. Helgeson Laurent Richard William F. McKenzie Alexandra Schmitt 《Geochimica et cosmochimica acta》2009,73(3):594-7350
Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock at temperatures ?25 but ?100 °C along a typical US Gulf Coast geotherm, immature (reduced) kerogen with a given atomic hydrogen to carbon ratio (H/C) melts incongruently with increasing temperature and depth of burial to produce a metastable equilibrium phase assemblage consisting of naphthenic/biomarker-rich crude oil, a type-II/III kerogen with an atomic hydrogen/carbon ratio (H/C) of ∼1, and water. Hence, this incongruent melting process promotes diagenetic reaction of detritus in the source rock to form authigenic mineral assemblages.However, in the water-absent region of the system CHO (which is extensive), any water initially present or subsequently entering the source rock is consumed by reaction with the most mature kerogen with the lowest H/C it encounters to form CO2 gas and a new kerogen with higher H/C and O/C, both of which are in metastable equilibrium with one another.This hydrolytic disproportionation process progressively increases both the concentration of the solute in the aqueous phase, and the oil generation potential of the source rock; i.e., the new kerogen can then produce more crude oil.Petroleum is generated with increasing temperature and depth of burial of hydrocarbon source rocks in which water is not stable in the system CHO by a series of irreversible disproportionation reactions in which kerogens with higher (H/C)s melt incongruently to produce metastable equilibrium assemblages consisting of crude oil, CO2 gas, and a more mature (oxidized) kerogen with a lower H/C which in turn melts incongruently with further burial to produce more crude oil, CO2 gas, and a kerogen with a lower H/C and so forth.The petroleum generated in the process progresses from heavy naphthenic crude oils at low temperatures to mature petroleum at ∼150 °C. For example, the results of Computer Experiment 27 (see below) indicate that the overall incongruent melting reaction in the water-absent region of the system C-H-O at 150 °C and a depth of ∼4.3 km of an immature type-II/III kerogen with a bulk composition represented by C292H288O12(c) to produce a mature (oxidized) kerogen represented by C128H68O7(c), together with a typical crude oil with an average metastable equilibrium composition corresponding to C8.8H16.9 (C8.8H16.9(l)) and CO2 gas (CO2(g)) can be described by writing
(A) 相似文献
73.
Ccile Gautheron Laurent Tassan-Got Jocelyn Barbarand Maurice Pagel 《Chemical Geology》2009,266(3-4):157-170
Recent data on He diffusion challenge the temperature sensitivity of apatite (U–Th)/He thermochronology: the damage induced by recoil of U and Th decay series during emission of α particles (α-recoil damage) has been proposed to modify He-diffusion properties through time. However, we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly-cooled or reheated basement rocks. To test this hypothesis, we developed a quantitative model including an explicit treatment of α-recoil damage, annealing, and their effect on He-diffusion kinetics, and calibrate it against literature data. Our model is based on two hypotheses: (1) helium is in equilibrium between an apatite crystal and its defects and (2) alpha-recoil damage annealing can be described analogously to fission-track annealing. This model has been embedded into a Monte Carlo simulation of helium production/ejection/diffusion and applied to data from the French Massif Central; a complex slowly-cooled terrain with burial reheating, where the thermal history has been constrained by previous fission-track (FT) data including FT length distributions. (U–Th)/He ages are close to the FT ages from the same samples and are generally reproducible among replicates, but some samples present He-age dispersion that is not correlated with crystal size. Our model reproduces the Massif Central data very well except for three samples where He ages are older than corresponding FT ages. We show that annealing of irradiation damage has an important impact on retentivity of helium and that the He content, [He] is only a rough approximation of the damage level. In particular our results show that independence of He ages on crystal sizes, in case of reheated samples, is a clear indication of the higher He retentivity induced by α-recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of (U–Th)/He ages in such a case. More generally a correlation with the crystal size can bring information on the thermal path only if the age of defects, well represented by the fission-track age, is available, due to the dependence of the partial retention zone on damages. Conversely, in case of rapid cooling or for samples having low U and Th contents, damage effects can be ignored without significant effects on He ages. 相似文献
74.
Jürgen Oberst Valéry Lainey Christophe Le Poncin-Lafitte Veronique Dehant Pascal Rosenblatt Stephan Ulamec Jens Biele J?rn Spurmann Ralph Kahle Volker Klein Ulrich Schreiber Anja Schlicht Nicolas Rambaux Philippe Laurent Beno?t Noyelles Bernard Foulon Alexander Zakharov Leonid Gurvits Denis Uchaev Scott Murchie Cheryl Reed Slava G. Turyshev Jesus Gil Mariella Graziano Konrad Willner Kai Wickhusen Andreas Pasewaldt Marita W?hlisch Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271
GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame. 相似文献
75.
Yveline Lebreton Josefina Montalbán Jørgen Christensen-Dalsgaard Ian W. Roxburgh Achim Weiss 《Astrophysics and Space Science》2008,316(1-4):187-213
We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT. 相似文献
76.
Olivier Witasse Lyle Huber Jean-Pierre Lebreton David Heather John Zarnecki Roland Trautner Piero Leon Stoppato Chuck See Cyril Pennanech Lisa McFarlane Bobby Kazeminejad Brijen Hathi John Haberman Francesca Ferri Lyn Doose Giacomo Colombatti Michael Bird Alessio Aboudan 《Planetary and Space Science》2008,56(5):770-777
77.
Laurent REMUSAT Corentin Le GUILLOU Jean‐Noël ROUZAUD Laurent BINET Sylvie DERENNE François ROBERT 《Meteoritics & planetary science》2008,43(7):1099-1111
Abstract— Kainsaz CO3 insoluble organic matter (IOM) was studied using Curie point pyrolysis, electronic paramagnetic resonance (EPR), and high‐resolution transmission electron microscopy (HRTEM) to determine the effect of thermal metamorphism on molecular chondritic fingerprints. Pyrolysis released a very low amount of products that consist of one‐ and two‐ring aromatic units with methyl, dimethyl, and ethyl substituents. Moreover, Kainsaz IOM contains two orders of magnitude fewer radicals than Orgueil, Murchison, and Tagish Lake IOM. In addition, no diradicaloids were found in Kainsaz, although they are thought to constitute a specific signature for weakly organized extraterrestrial organic compounds in contrast to terrestrial ones. HRTEM reveals a very heterogeneous structure, with microporous disordered carbon, mesoporous graphitic carbons and graphite. Graphitization likely occurs and explains the differences between Kainsaz and CI or CM IOM. Heating stress experienced by Kainsaz IOM, on the parent body and/or prior its accretion, is likely responsible for the differences in molecular and structural organizations compared with those of CI and CM IOM. 相似文献
78.
Van T.H.Phan Fabrizio Bardelli Pierre Le Pape Raoul-Marie Couture Alejandro Fernandez-Martinez Delphine Tisserand Rizlan Bernier-Latmani Laurent Charlet 《地学前缘(英文版)》2019,10(5):1715-1729
The cumulative effects of periodic redox cycling on the mobility of As,Fe,and S from alluvial sediment to groundwater were investigated in bioreactor experiments.Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated:Matrix A(14 m deep)had a higher pyrite concentration than matrix B(7 m deep)sediments.Gypsum was present in matrix B but absent in matrix A.In the reactors,the sediment suspensions were supplemented with As(Ⅲ)and SO_4~(2-),and were subjected to three full-redox cycles entailing phases of nitrogen/CO_2,compressed air sparging,and cellobiose addition.Major differences in As concentration and speciation were observed upon redox cycling.Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles.Indeed,a high pyrite content associated with a low SO_4~(2-)content resulted in an increase in dissolved As concentrations,mainly in the form of As(Ⅲ),after anoxic half-cycles;whereas a decrease in As concentrations mainly in the form of As(Ⅴ),was instead observed after oxic half-cycles.In addition,oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation,increasing the As pool available for mobilization.The same processes seem to occur in sediment with the presence of gypsum,but,in this case,dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe—S system,and by specific physico-chemical condition(e.g.pH).The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work,and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta(Vietnam). 相似文献
79.
Crack nucleation has been the subject of important contributions in the last two last decades. However, it seems that few attention has been granted to the case of saturated porous media. This is the question addressed in the present paper which is devoted to nucleation in traction mode. From a physical point of view, nucleation is a sudden phenomenon, so that the material response is both adiabatic and undrained. In the spirit of the variational approach, the nucleated crack is viewed as the final state of a region of space in which the material undergoes a full damage process. In traction mode, the opening of a saturated crack in undrained condition induces a drop of fluid pressure. In case of low fluid compressibility, the presence of the fluid delays the brittle failure usually associated with nucleation, as long as the fluid pressure remains above the saturation vapor pressure. Nucleation is therefore possible only if a partial vaporization of the fluid takes place. 相似文献
80.
Sébastien Gogo Jean-Baptiste Paroissien Fatima Laggoun-Défarge Jean-Marc Antoine Léonard Bernard-Jannin Guillaume Bertrand Philippe Binet Stéphane Binet Guillaume Bouger Yohann Brossard Thierry Camboulive Jean-Pierre Caudal Stéphane Chevrier Geneviève Chiapiuso Benoît D'Angelo Pilar Durantez Chris Flechard André-Jean Francez Didier Galop Laure Gandois Daniel Gilbert Christophe Guimbaud Louis Hinault Adrien Jacotot Franck Le Moing Emilie Lerigoleur Gaël Le Roux Fabien Leroy Alexandre Lhosmot Qian Li Elodie Machado Da Silva Jean-Sébastien Moquet Juanita Mora-Gomez Laurent Perdereau Thomas Rosset Marie-Laure Toussaint 《水文研究》2021,35(6):e14244
Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ). 相似文献