Opaque minerals,magnetic properties,and paleomagnetism of the Tissint Martian meteorite     

Jérôme Gattacceca  Roger H. Hewins  Jean‐Pierre Lorand  Pierre Rochette  France Lagroix  Cécile Cournède  Minoru Uehara  Sylvain Pont  Violaine Sautter  Rosa. B. Scorzelli  Chrystel Hombourger  Pablo Munayco  Brigitte Zanda  Hasnaa Chennaoui  Ludovic Ferrière 《Meteoritics & planetary science》2013,48(10):1919-1936

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Volatile transport on inhomogeneous surfaces: I – Analytic expressions,with application to Pluto’s day     

Olivier Mousis  Jonathan I. Lunine  Eric Chassefière  Franck Montmessin  Azzedine Lakhlifi  Sylvain Picaud  Jean-Marc Petit  Daniel Cordier 《Icarus》2012,218(1):80-87

The two orders of magnitude drop between the measured atmospheric abundances of non-radiogenic argon, krypton and xenon in Earth versus Mars is striking. Here, in order to account for this difference, we explore the hypothesis that clathrate deposits incorporated into the current martian cryosphere have sequestered significant amounts of these noble gases assuming they were initially present in the paleoatmosphere in quantities similar to those measured on Earth (in mass of noble gas per unit mass of the planet). To do so, we use a statistical-thermodynamic model that predicts the clathrate composition formed from a carbon dioxide-dominated paleoatmosphere whose surface pressure ranges up to 3 bars. The influence of the presence of atmospheric sulfur dioxide on clathrate composition is investigated and we find that it does not alter the trapping efficiencies of other minor species. Assuming nominal structural parameters for the clathrate cages, we find that a carbon dioxide equivalent pressure of 0.03 and 0.9 bar is sufficient to trap masses of xenon and krypton, respectively, equivalent to those found on Earth in the clathrate deposits of the cryosphere. In this case, the amount of trapped argon is not sufficient to explain the measured Earth/Mars argon abundance ratio in the considered pressure range. In contrast, with a 2% contraction of the clathrate cages, masses of xenon, krypton and argon at least equivalent to those found on Earth can be incorporated into clathrates if one assumes the trapping of carbon dioxide at equivalent atmospheric pressures of ～2.3 bar. The proposed clathrate trapping mechanism could have then played an important role in the shaping of the current martian atmosphere.  相似文献   

Large-Scale Mapping of Hard-Rock Aquifer Properties Applied to Burkina Faso     

Nathalie Courtois  Patrick Lachassagne  Robert Wyns  Raymonde Blanchin  Francis D. Bougaïré  Sylvain Somé  Aïssata Tapsoba 《Ground water》2010,48(2):269-283

A country-scale (1:1,000,000) methodology has been developed for hydrogeologic mapping of hard-rock aquifers (granitic and metamorphic rocks) of the type that underlie a large part of the African continent. The method is based on quantifying the “useful thickness” and hydrodynamic properties of such aquifers and uses a recent conceptual model developed for this hydrogeologic context. This model links hydrodynamic parameters (transmissivity, storativity) to lithology and the geometry of the various layers constituting a weathering profile. The country-scale hydrogeological mapping was implemented in Burkina Faso, where a recent 1:1,000,000-scale digital geological map and a database of some 16,000 water wells were used to evaluate the methodology.  相似文献   

Fate and tidal transport of butyltin and mercury compounds in the waters of the tropical Bach Dang Estuary (Haiphong, Vietnam)     

Navarro P  Amouroux D  Thanh ND  Rochelle-Newall E  Ouillon S  Arfi R  Van TC  Mari X  Torréton JP 《Marine pollution bulletin》2012,64(9):1789-1798

In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (～3kgTBT/day) and dry (～3gMMHg/day) seasons.  相似文献   

The geological evolution of Merapi volcano, Central Java, Indonesia   总被引：1，自引：0，他引：1  

Ralf Gertisser  Sylvain J. Charbonnier  J?rg Keller  Xavier Quidelleur 《Bulletin of Volcanology》2012,74(5):1213-1233

Merapi is an almost persistently active basalt to basaltic andesite volcanic complex in Central Java (Indonesia) and often referred to as the type volcano for small-volume pyroclastic flows generated by gravitational lava dome failures (Merapi-type nuées ardentes). Stratigraphic field data, published and new radiocarbon ages in conjunction with a new set of ⁴⁰K–⁴⁰Ar and ⁴⁰Ar–³⁹Ar ages, and whole-rock geochemical data allow a reassessment of the geological and geochemical evolution of the volcanic complex. An adapted version of the published geological map of Merapi [(Wirakusumah et al. 1989), Peta Geologi Gunungapi Merapi, Jawa Tengah (Geologic map of Merapi volcano, Central Java), 1:50,000] is presented, in which eight main volcano stratigraphic units are distinguished, linked to three main evolutionary stages of the volcanic complex—Proto-Merapi, Old Merapi and New Merapi. Construction of the Merapi volcanic complex began after 170?ka. The two earliest (Proto-Merapi) volcanic edifices, Gunung Bibi (109?±?60?ka), a small basaltic andesite volcanic structure on Merapi’s north-east flank, and Gunung Turgo and Gunung Plawangan (138?±?3?ka; 135?±?3?ka), two basaltic hills in the southern sector of the volcano, predate the Merapi cone sensu stricto. Old Merapi started to grow at ~30?ka, building a stratovolcano of basaltic andesite lavas and intercalated pyroclastic rocks. This older Merapi edifice was destroyed by one or, possibly, several flank failures, the latest of which occurred after 4.8?±?1.5?ka and marks the end of the Old Merapi stage. The construction of the recent Merapi cone (New Merapi) began afterwards. Mostly basaltic andesite pyroclastic and epiclastic deposits of both Old and New Merapi (<11,792?±?90 ¹⁴C years BP) cover the lower flanks of the edifice. A shift from medium-K to high-K character of the eruptive products occurred at ~1,900 ¹⁴C years BP, with all younger products having high-K affinity. The radiocarbon record points towards an almost continuous activity of Merapi since this time, with periods of high eruption frequency interrupted by shorter intervals of apparently lower eruption rates, which is reflected in the geochemical composition of the eruptive products. The Holocene stratigraphic record reveals that fountain collapse pyroclastic flows are a common phenomenon at Merapi. The distribution and run-out distances of these flows have frequently exceeded those of the classic Merapi-type nuées ardentes of the recent activity. Widespread pumiceous fallout deposits testify the occurrence of moderate to large (subplinian) eruptions (VEI 3–4) during the mid to late Holocene. VEI 4 eruptions, as identified in the stratigraphic record, are an order of magnitude larger than any recorded historical eruption of Merapi, except for the 1872?AD and, possibly, the October–November 2010 events. Both types of eruptive and volcanic phenomena require careful consideration in long-term hazard assessment at Merapi.  相似文献   

Sampling strategies based on sets of behavioural parameters. Application to a simple pesticide fate model     

Thierry Leviandier  Stéphanie Madier  Sylvain Payraudeau 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(4):557-568

Sampling strategies are necessary to minimise the cost of data acquisition. We consider the case when several samples must be analysed at the same time, knowing rainfall data, optionally discharge data. We assume also that a rainfall-runoff and pesticide transfer model is available. Three methods are presented based on behavioural sets calculated on prior events, which provide optimal sampling times with respect to different statistical criteria, for a fixed number of samples. A methodology to compare these strategies, adapted to a context of data scarcity is proposed for proper validation. We consider that the combination of a model and a strategy is efficient if it does better than a strategy without a model based on equal volumes. Even with a simple and relatively poor model, it can be concluded that the different strategies are efficient and show similar efficiency in spite of their different levels of conceptual and algorithmic complexity.  相似文献   

Land clearance and hydrological change in the Sahel: SW Niger   总被引：1，自引：0，他引：1  

Marc J. Leblanc  Guillaume Favreau  Sylvain Massuel  Sarah O. Tweed  Maud Loireau  Bernard Cappelaere 《Global and Planetary Change》2008,61(3-4):135-150

In the West African semiarid belt of the Sahel, for the second half of the XXth century, lasting droughts (1970s–1980s) and one of the World's highest population growths have resulted in major land cover and hydrological changes that can be quantified using aerial photographs. This paper aims to provide one of the longest combined observations of land cover and hydrological changes for semiarid areas using a time series of normalised mosaics of aerial photographs dating back from 1950, field inquiries, and updated groundwater data. The 500 km² study area in southwest Niger was chosen (i) for its rural environment representative of the rain-fed agriculture belt of the Sahel and (ii) to encompass the main hydrological study sites investigated in this region over the past two decades (Hapex-Sahel and AMMA experiments, 1990–2000s). Results have significant implications for future freshwater availability and food security in the Sahel.Between 1950 and 1992,  80% of the study area has been cleared, firstly to open new areas for agriculture and secondly for firewood supply (59% of the plateaux, 42% of the valley bottoms, and 87% of the hillslopes). Intermediate aerial photograph surveys (1960, 1975) attest an accelerated loss in the woody savannah that could not be recovered on the short term. A strong, indirect impact of land clearance is observed on the water resources. Land clearance has resulted in a modification of the soil properties and infiltration capacity and has led to an increase in Hortonian runoff collected in numerous gullies and ponds. Between 1950 and 1992, aerial photographs show a  2.5 fold increase of the drainage density with the development of large drainage systems and new ponds. Groundwater data also indicate a continuous rise in the water table, mostly noticeable since the 1980s with a mean groundwater level rise of  4 m for the 1963–2005 period (+ 15% in aquifer reserves). The relatively short  30 year time-lag between the onset of land clearance and the beginning of the water table rise is linked to the process of indirect groundwater recharge and is timed with the connectivity of the drainage network and the formation of new ponds. Finally, the sustained increase in surface runoff and groundwater recharge during the past four decades indicates that the indirect impact of land clearance on the terrestrial water balance has been stronger than that of the long-lasting Sahelian drought. As the rate of land clearance increased for the past century in semiarid Africa, its main hydrological effects may not yet be fully perceptible.  相似文献   

Quantitative compositional analysis of martian mafic regions using the MEx/OMEGA reflectance data 1. Methodology, uncertainties and examples of application     

F. Poulet  J.-P. Bibring  J.F. Mustard  M. Vincendon  P. Pinet  B. Platevoet 《Icarus》2009,201(1):69-83

The Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) collected an unprecedented visible and near-infrared hyperspectral dataset covering the low albedo regions of Mars. We investigate the ability to infer modal abundance of surfaces of these regions from a radiative transfer model developed by Shkuratov et al. [Shkuratov, Y., Starukhina, L., Hoffmann, H., Arnold, G., 1999. Icarus 137, 235-246] and adapted to basaltic surfaces by Poulet and Erard [Poulet F., Erard, S., 2004. J. Geophys. Res. 109 (E2), doi:10.1029/2003JE002179]. From OMEGA measurements of mafic surfaces, we develop several sensitivity tests to assess the extent to which the model can be applied to predict pyroxene composition (high-calcium phase and low-calcium phase), abundance of almost neutral components (plagioclase) in the near-infrared wavelength as well as grain sizes, by using a library of selected end-members. Results of the sensitivity tests indicate that the scattering model can estimate both abundances and grain sizes of major basaltic materials of low albedo regions within uncertainties (±5 to 15 vol%). The model is then applied to data from dissected cratered terrains located in Terra Meridiani. The derived grain size including uncertainties is in the 50-500 μm range. This is consistent with the thermal inertia and albedo of this region, which indicates a fine sand-sized surface with little dust. The abundances of plagioclase (43-57%) and pyroxenes (35-45±10%, including 11±5% of low-calcium phase) are in good agreement with previous basalt-like compositions of low albedo regions from thermal infrared spectral measurements. The method presented in this paper will provide a valuable tool for evaluating the modal mineralogy of other mafic regions of Mars observed in the near-infrared wavelength range.  相似文献   

Edge Flow and Canopy Structure: A Large-Eddy Simulation Study   总被引：4，自引：4，他引：0  

Sylvain Dupont  Yves Brunet 《Boundary-Layer Meteorology》2008,126(1):51-71

Sharp heterogeneities in forest structure, such as edges, are often responsible for wind damage. In order to better understand the behaviour of turbulent flow through canopy edges, large-eddy simulations (LES) have been performed at very fine scale (2 m) within and above heterogeneous vegetation canopies. A modified version of the Advanced Regional Prediction System (ARPS), previously validated in homogeneous conditions against field and wind-tunnel measurements, has been used for this purpose. Here it is validated in a simple forest-clearing-forest configuration. The model is shown to be able to reproduce accurately the main features observed in turbulent edge flow, especially the “enhanced gust zone” (EGZ) present around the canopy top at a few canopy heights downwind from the edge, and the turbulent region that develops further downstream. The EGZ is characterized by a peak in streamwise velocity skewness, which reflects the presence of intense intermittent wind gusts. A sensitivity study of the edge flow to the forest morphology shows that with increasing canopy density the flow adjusts faster and turbulent features such as the EGZ become more marked. When the canopy is characterized by a sparse trunk space the length of the adjustment region increases significantly due to the formation of a sub-canopy wind jet from the leading edge. It is shown that the position and magnitude of the EGZ are related to the mean upward motion formed around canopy top behind the leading edge, caused by the deceleration in the sub-canopy. Indeed, this mean upward motion advects low turbulence levels from the bottom of the canopy; this emphasises the passage of sudden strong wind gusts from the clearing, thereby increasing the skewness in streamwise velocity as compared with locations further downstream where ambient turbulence is stronger.  相似文献   

Quantitative geochemical mapping of martian elemental provinces     

Olivier Gasnault  G. Jeffrey Taylor  Suniti Karunatillake  James Dohm  Horton Newsom  Olivier Forni  Patrick Pinet  William V. Boynton 《Icarus》2010,207(1):226-341

We present an exploratory approach to the interpretation of the elemental maps produced by the Odyssey Gamma-Ray Spectrometer (GRS). These maps benefit from a direct detection of elemental mass fractions and are used to delineate and characterize elementally homogeneous provinces in the mid-latitudinal martian surface on the basis of chemistry alone. This approach is different from assessing the elemental composition of regions previously defined by their geologic context. Multivariate statistical approaches are discussed and a combination of principal component and clustering analyses is applied on the GRS-based hydrogen, chlorine, potassium, silicon, iron, and calcium maps. At least three principal components must be considered to properly describe the compositional variability seen in the maps. The main component is likely driven by the degree of mantling through a GRS perspective, i.e. by materials enriched in mobile elements (Cl, H) and finer than 10-20 cm, at horizontal and depth scales of hundreds of kilometers and tens of centimeters, respectively. Elemental diversity is found in both mantled and less-mantled provinces, suggesting both local and regional sources for the surficial materials. The less-mantled regions appear to have compositions which include basaltic igneous rocks. Although there is an absence of obvious natural clusters in the data, a solution between five and eight elemental provinces seems optimal and is discussed (Amazonis-Tharsis and Sabaea-Arabia, Tempe and the southern highlands, Chryse and Utopia, Elysium-Tartarus, Acidalia-Arabia). Future investigation of the defined elemental provinces will involve integrating other types of data and geological information.  相似文献