Identification of Groundwater Parameters Using an Adaptative Multiscale Method     

Samer Majdalani  Philippe Ackerer 《Ground water》2011,49(4):548-559

The identification of groundwater parameters in heterogeneous systems is a major challenge in groundwater modeling. Flexible parameterization methods are needed to assess the complexity of the spatial distributions of these parameters in real aquifers. In this article, we introduce an adaptative parameterization to identify the distribution of hydraulic conductivity within the large‐scale (4400 km²) Upper Rhine aquifer. The method is based on adaptative multiscale triangulation (AMT) coupled with an inverse problem procedure that identifies the parameters' distributions by reducing the error between measured and simulated heads. The AMT method has the advantage of combining both zonation and interpolation approaches. The AMT method uses area‐based interpolation rather than an interpolation based on stochastic features. The method is applied to a standard 2D groundwater model that takes into account the interactions between the aquifer and surface water bodies, groundwater recharge, and pumping wells. The simulation period covers 204 months, from January 1986 to December 2002. Recordings at 109 piezometers are used for model calibration. The simulated heads are globally quite accurate and reproduce the main dynamics of the system. The local hydraulic conductivities resulting from the AMT method agree qualitatively with existing local experimental observations across the Rhine aquifer.  相似文献   

Degradation of natural organic matter: A thermodynamic analysis     

Douglas E. LaRowe  Philippe Van Cappellen 《Geochimica et cosmochimica acta》2011,75(8):2030-16486

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Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France   总被引：2，自引：0，他引：2  

Farid Juillot  Delphine Jouvin  Philipe Telouk  Philippe Ildefonse  Steve Sutton  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2011,75(9):2295-2308

Zinc isotopes have been studied along two smelter-impacted soil profiles sampled near one of the largest Pb and Zn processing plants in Europe located in northern France, about 50 km south of Lille. Mean δ⁶⁶Zn values along these two soil profiles range from +0.22 ± 0.17‰ (2σ) to +0.34 ± 0.17‰ (2σ) at the lowest horizons and from +0.38 ± 0.45‰ (2σ) to +0.76 ± 0.14‰ (2σ) near the surface. The δ⁶⁶Zn values in the lowest horizons of the soils are interpreted as being representative of the local geochemical background (mean value +0.31 ± 0.38‰), whereas heavier δ⁶⁶Zn values near the surface of the two soils are related to anthropogenic Zn. This anthropogenic Zn occurs in the form of franklinite (ZnFe₂O₄)-bearing slag grains originating from processing wastes at the smelter site and exhibiting δ⁶⁶Zn values of +0.81 ± 0.20‰ (2σ). The presence of franklinite is indicated by EXAFS analysis of the topsoil samples from both soil profiles as well as by micro-XANES analysis of the surface horizon of a third smelter-impacted soil from a distant site. These results indicate that naturally occurring Zn and smelter-derived Zn exhibit significantly different δ⁶⁶Zn values, which suggests that zinc isotopes can be used to distinguish between geogenic and anthropogenic sources of Zn in smelter-impacted soils. In addition to a possible influence of additional past sources of light Zn (likely Zn-sulfides and Zn-sulfates directly emitted by the smelter), the light δ⁶⁶Zn values in the surface horizons compared to smelter-derived slag materials are interpreted as resulting mainly from fractionation processes associated with biotic and/or abiotic pedological processes (Zn-bearing mineral precipitation, Zn complexation by organic matter, and plant uptake of Zn). This conclusion emphasizes the need for additional Zn isotopic studies before being able to use Zn isotopes to trace sources and pathways of this element in surface environments.  相似文献   

Fluid migration at the basement/sediment interface along the margin of the Southeast basin (France): implications for Pb–Zn ore formation     

Luc Aquilina  Philippe Boulvais  Jean-Rémi Mossmann 《Mineralium Deposita》2011,46(8):959-979

This study investigates the isotopic composition (C, O, S and Sr) of carbonates, sulphates and sulphide cements in the rock matrix and fracture fillings in geological formations of the Southeast basin of France, using core samples collected during the Deep Geology of France programme (GPF Ardèche theme). The Southeast basin belongs to the Alpine Tethyan margin. It is one of the thickest sedimentary basins in Europe, reaching upwards of 9 km in certain locations. The main fluid transfer from the basin is related to the large Pb–Zn Mississippi Valley-type district along the southern margin of the Massif Central block. A synthesis of the tectonic, mineralogical and petrographic investigations on the GPF boreholes shows that a major fluid circulation event occurred across the Alpine margin of Tethys during the Early Jurassic (Hettangian–Bathonian). It produced a general cementation of the rock porosity through precipitation of dolomite, sulphate and barite. Fracture fillings yield isotopic signatures distinct from the matrix cements. Matrix cements have particular characteristics, i.e. δ³⁴S and δ¹³C that agree with a marine origin. The δ³⁴S values of Permo-Carboniferous to Triassic sulphides from fracture cements are interpreted as resulting from the thermo-chemical reduction of sulphates. Fracture sulphates in the same geological formations yield δ³⁴S values that define a relatively homogeneous end-member, whose composition is similar to sulphates in the Largentière Pb–Zn ore deposit. The source of S is attributed to the Permo-Carboniferous succession. The borehole fracture fillings are attributed to a major fluid circulation stage compatible with the Early Jurassic stage identified from the geological investigation of the boreholes. The formation of the Largentière deposit is considered as resulting from the mixing of this Early Jurassic fluid with continental hydrothermal fluids circulating in a basement horst, along its margin with the sedimentary basin. Other Pb–Zn deposits may also be related to fluid migration along the basement/sedimentary cover interface in the eastern and western parts of the Massif Central. This regional fluid circulation event may represent a geodynamic marker of the Jurassic extensional phase.  相似文献   

Biogenic carbon flows through the planktonic food web of the Amundsen Gulf (Arctic Ocean): A synthesis of field measurements and inverse modeling analyses   总被引：1，自引：0，他引：1  

Alexandre Forest  Jean-Éric Tremblay  Yves Gratton  Johannie Martin  Jonathan Gagnon  Gérald Darnis  Makoto Sampei  Louis Fortier  Mathieu Ardyna  Michel Gosselin  Hiroshi Hattori  Dan Nguyen  Roxane Maranger  Dolors Vaqué  Cèlia Marrasé  Carlos Pedrós-Alió  Amélie Sallon  Christine Michel  Colleen Kellogg  Jody Deming  Elizabeth Shadwick  Helmuth Thomas  Heike Link  Philippe Archambault  Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436

Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m⁻² calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m⁻², which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m⁻², a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m⁻²), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m⁻²). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain.  相似文献   

Structural controls on the formation of BSR over a diapiric anticline from a dense MCS survey offshore southwestern Taiwan   总被引：1，自引：0，他引：1  

Philippe Schnürle  Char-Shine Liu  Andrew T. Lin  Saulwood Lin 《Marine and Petroleum Geology》2011,28(10):1932-1942

A dense seismic reflection survey with up to 250-m line-spacing has been conducted in a 15 × 15 km wide area offshore southwestern Taiwan where Bottom Simulating Reflector is highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north–south trending thrust faults and northwest–southeast oblique ramps exists in this region, leading to the formation of 3 plunging anticlines arranged in a relay pattern. Landward in the slope basin, a north–south trending diapiric fold, accompanied by bright reflections and numerous diffractions on the seismic profiles, extends across the entire survey area. This fold is bounded to the west by a minor east-verging back-thrust and assumes a symmetric shape, except at the northern and southern edges of this area, where it actively overrides the anticlines along a west-verging thrust, forming a duplex structure. A clear BSR is observed along 67% of the acquired profiles. The BSR is almost continuous in the slope basin but poorly imaged near the crest of the anticlines. Local geothermal gradient values estimated from BSR sub-bottom depths are low along the western limb and crest of the anticlines ranging from 40 to 50 °C/km, increase toward 50–60 °C/km in the slope basin and 55–65 °C/km along the diapiric fold, and reach maximum values of 70 °C/km at the southern tip of the Good Weather Ridge. Furthermore, the local dips of BSR and sedimentary strata that crosscut the BSR at intersections of any 2 seismic profiles have been computed. The stratigraphic dips indicated a dominant east–west shortening in the study area, but strata near the crest of the plunging anticlines generally strike to southwest almost perpendicular to the direction of plate convergence. The intensity of the estimated bedding-guided fluid and gas flux into the hydrate stability zone is weaker than 2 in the slope basin and the south-central half of the diapiric fold, increases to 7 in the northern half of the diapiric fold and plunging anticlines, and reaches a maximum of 16 at the western frontal thrust system. Rapid sedimentation, active tectonics and fluid migration paths with significant dissolved gas content impact on the mechanism for BSR formation and gas hydrate accumulation. As we begin to integrate the results from these studies, we are able to outline the regional variations, and discuss the importance of structural controls in the mechanisms leading to the gas hydrate emplacements.  相似文献   

Analyse quantitative du rifting et de la relaxation thermique de la partie occidentale de la marge transformante nord-africaine: le Rif externe (Maroc)     

Philippe Favre 《Geodinamica Acta》2013,26(2):59-81

Résumén

Un résumé de la cinématique du Rif externe central et occidental, de la période de rifting aux événements tectoniques récents, est proposé. L’évolution du Rif externe est abordée sur le plan quantitatif par le biais des principaux mécanismes physiques qui ont pu affecter cette partie de la marge nord-africaine durant le Jurassique, le Crétacé et le Paléocène (processus de dilatation thermique lors du rifting et de contraction thermique lors du refroidissement de la lithosphère, effondrement par flexure de la marge nord-africaine lors de la collision). Les géométries et densités obtenues sont comparées avec les données gravimétriques et de sismique réfraction.

Un des aspects du modèle de Wernicke (1985), la dissymétrie du rifting de la marge africaine, semble se vérifier par l’analyse et à la modélisation de la subsidence. Mais celle-ci montre l’existence d’une fusion adiabatique tardive du manteau supérieur dont le modèle de cisaillement simple ne tient pas compte. Le soulèvement de la marge à la fin du rifting ne serait pas dû uniquement à une dilatation thermique car les données de terrain montrent des discordances angulaires importantes sur la marge africaine. Ce soulèvement est attribué localement à la poussée des rides médio-océaniques naissantes de l’Atlantique et du sillon transformant nord-africain.

La modélisation de la subsidence tectonique permet d’expliquer l’absence d’intumescence sous le Rif. Elle est attribuée aux taux d’amincissement crustaux élevés durant les phases d’extension triasico-jurassiques. Cette approche quantitative confirme l’existence d’un bassin intra-continental avorté au sud-ouest et d’une marge continentale sensu stricto au nord-est. Si l’océanisation paraît plus tardive dans la partie rifaine du sillon transformant nord-africain (Callovien) que dans l’Atlantique Central (Bajocien), la subsidence post-rift ne se distingue pas de celle d’une marge passive classique.  相似文献   

On the co-orbital motion of two planets in quasi-circular orbits     

Philippe Robutel  Alexandre Pousse 《Celestial Mechanics and Dynamical Astronomy》2013,117(1):17-40

We develop an analytical Hamiltonian formalism adapted to the study of the motion of two planets in co-orbital resonance. The Hamiltonian, averaged over one of the planetary mean longitudes, is expanded in power series of eccentricities and inclinations. The model, which is valid in the entire co-orbital region, possesses an integrable approximation modeling the planar and quasi-circular motions. First, focusing on the fixed points of this approximation, we highlight relations linking the eigenvectors of the associated linearized differential system and the existence of certain remarkable orbits like the elliptic Eulerian Lagrangian configurations, the anti-Lagrange (Giuppone et al. in MNRAS 407:390–398, 2010) orbits and some second sort orbits discovered by Poincaré. Then, the variational equation is studied in the vicinity of any quasi-circular periodic solution. The fundamental frequencies of the trajectory are deduced and possible occurrence of low order resonances are discussed. Finally, with the help of the construction of a Birkhoff normal form, we prove that the elliptic Lagrangian equilateral configurations and the anti-Lagrange orbits bifurcate from the same fixed point $L_4$ L 4 .  相似文献   

Pb,Hf and Nd isotope compositions of the two Réunion volcanoes (Indian Ocean): A tale of two small-scale mantle “blobs”?     

Delphine Bosch  Janne Blichert-Toft  Frédéric Moynier  Bruce K. Nelson  Philippe Telouk  Pierre-Yves Gillot  Francis Albarède 《Earth and Planetary Science Letters》2008,265(3-4):748-765

Pb, Hf, Nd and Sr isotopes of basaltic lavas from the two Réunion Island volcanoes are reported in order to examine the origin of the sources feeding these volcanoes and to detect possible changes through time. Samples, chosen to cover the whole lifetime of the two volcanoes (from 2 Ma to present), yield a chemically restricted (compared to OIB lavas) but complex distribution. Réunion plume isotopic characteristics have been defined on the basis of the composition of uncontaminated shield-building lavas from the Piton de la Fournaise volcano. The average ?_Nd, ?_Hf, ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb isotope ratios calculated for this component are + 4.4, + 9.1, 0.70411, 18.97, 15.59 and 39.03, respectively. In Pb–Pb isotope space, each volcano defines a distinct linear trend but slight variations are also detected within the various volcanic sequences. The Piton des Neiges volcano yields a distinct and significantly more scattered isotopic distribution than Piton de la Fournaise for both Pb, Hf and Nd isotope tracers. A principal component analysis of the Pb isotope data from Piton de la Fournaise reveals a major contribution of the C and EM-1 components (with a clear Dupal flavor) as main components for the modern Réunion plume. The same components have been identified for Piton des Neiges but with a stronger participation of a depleted mantle component and a weaker EM-1 contribution. The compositional change of the lavas erupted by the Piton des Neiges and Piton de la Fournaise volcanoes is attributed to the impingement of two small-scale blobs of plume material at the base of the Réunion lithosphere. Compared to other hot-spots worldwide, in particular Hawaii and Kerguelen, magmas beneath Réunion are generated from a considerably more homogeneous, compositionally more primitive plume higher in ²⁰⁶Pb. Although shallow-level contamination processes have been locally detected they did not alter significantly the composition of the plume magmas. This is tentatively attributed to mantle dynamics producing small, high-velocity blobs that ascend rapidly through the lithosphere, and to the lack of a well-developed magma chamber at depth in the lithosphere.  相似文献   

Methodology of seasonal morphological modelisation for nourishment strategies on a Mediterranean beach     

Larroudé P 《Marine pollution bulletin》2008,57(1-5):47-52

A modified 2DH morphodynamical model was employed to simulate the evolution of large-scale features with major implications for beach nourishment. The study was focused on modelling the evolution of material artificially placed in different parts of the profile, extracting or adding material to the natural bars, and quantifying how the profile responds to different wave climates and nourishment placements. The simulated results were compared with field data from a Mediterranean beach.  相似文献