Éditeur(s) : Yale University
Résumé : Sea-surface temperature images of the coastal upwelling regions off Northwest Africa show that the core of upwelling is sometimes located far from the coast. This has been documented in three regions that share a common feature, namely a wide and shallow continental shelf. This upwelling feature plays a key role in the ecology of the Canary Current System. It creates an innerfront which provides retention for biological material, e.g. fish eggs and larvae, in the highly productive nearshore environment. An analytical model has been developed based on a two dimensional extension of Ekman's solution. The linear and steady response of a homogeneous ocean forced by an upwelling-favorable wind provides a mechanism for the upwelling separation from the coast. The merging of the surface and bottom Ekman layers induces a very weak cross-shore circulation and a "kinematic barrier" for the Ekman transport divergence. In the case of an alongshore wind, the barrier is located near the isobath h ≈ 0.4D, where D is the thickness of Ekman layers. This yields an upwelling cell which is essentially concentrated in the region 0.5D < h < 1.25D, with upwelling occurring preferentially near the isobath h ≈ 0.6D. It turns out that the cross-shore width of upwelling scales with D/S, the ratio of Ekman depth to bottom topographic slope. The application of this solution to real bathymetric profiles rationalizes, not only the offshore upwelling observations in Northwest Africa, but also the influence of topography on the cross-shelf structure of a wind-driven coastal upwelling. The model also quantifies the effect of the cross-shore wind component showing how it drives the nearshore pressure gradient adjustment and how it affects the upwelling. A linear numerical experiment reproduces the theoretical steady solution, thereby allowing investigation of the transient regime. Relaxation of the hypothesis in the numerical model validates the linear assumption of the theory and then allows investigation of the sensitivity to friction parameterizations and the influence of stratification. The latter leads to an "oscillation" of the upwelling cell with seaward migration driven by outcropping and homogeneization of the water column, and, coastal incursion driven by a "boundary layers splitting" process caused by shoreward advection of the isopycnal dome and stratification of the inner shelf.
Journal of Marine Research (Yale University), 2008-09 , Vol. 66 , N. 5 , P. 589-616

Droits : 2008 Yale University
http://archimer.ifremer.fr/doc/2008/publication-6334.pdf
DOI:10.1357/002224008787536790
http://archimer.ifremer.fr/doc/00000/6334/

Éditeur(s) : HAL CCSD
Résumé : When the upper crust below the mountain ranges shows crustal extension with a direction collinear to the convergence direction, it is generally accepted that it is the result of gravitational collapse. However, recent studies challenge this paradigm by showing that erosion induces uplift and extension in the central part of the low convergent mountain ranges. In this study, we investigate the impact of denudation on the seismotectonic regime of mountain ranges.In order to identify a relationship between seismotectonic regime and erosion, the first part of this work presents a compilation of data in the mountain ranges. Based on these observations, a simple kinematic model is proposed to predict the seismotectonic regime of the study ranges.For low convergence rate and moderate mean elevation ranges, this model predicts an extension regime when the denudation rate is 15% higher than the convergence rate.The second part is devoted to the development of thermomechanical 2D finite element models to study the impact of surface processes on the deformation of the Pyrenees. The results show that the isostatic response to erosion reactivates pre-existing structures. The kinematics of an inherited fault plane can be predicted due to the gradient of the horizontal surface velocity profile. Thus, a plane located in the eroded zone is reactivated in normal fault when near the border of the erosion area, this same plane is reactivated in reverse fault. These results suggest that the current deformation in the North Pyrenean Zone could be the result of surface processes.Given the small number of studies quantifying erosion rates in the Pyrenees, the models developed in the second part suffer from high uncertainty. To remedy this, we study the central Pyrenees through a study that combines two types of data : watershed denudation rates from cosmogenic isotopes concentration, and incision rates from sediments buried in the karst. These results are presented in chapter 3. Denudation profiles obtained are consistent with reactivation of a normal fault plane located in the North Zone of the Central Pyrenees.From our study in the Pyrenees, a good correlation appears between the value of the rate of erosion and the glacier occupation. Given that the glaciers where more developed in the Alps, it raises the question of the impact of the late-würmian deglaciation on the present deformation of this range. A numerical model detailing this relationship is presented in the fourth chapter. Theresults show that deglaciation of the western Alps is controlled by the rheological heterogeneity of the crust. Some of our models predict uplift rates consistent with those highlighted by geodesy.
Lorsque l’extension de la croûte sous les parties hautes des chaînes de montagnes est colinéaire à la direction de convergence, il est traditionnellement admis que le moteur est l’effondrement gravitaire. Pourtant, des études récentes remettent en cause ce paradigme en montrant que l’érosion induit un soulèvement et de l’extension dans la partie centrale des chaînes de montagne à faible taux de convergence. L’objectif de notre étude est d’étudier l’impact de la dénudation de la topographie sur le régime sismo-tectonique des chaînes de montagnes.La première partie de ce travail présente une compilation de données dans les chaînes de montagnes afin de dégager des relations entre régime sismo-tectonique et érosion. Sur la base de ces observations, un modèle cinématique simple permettant de prévoir le régime de la chaîne est proposé. Ainsi, pour les chaînes à faible taux de convergence et d’élévation moyenne, ce modèleprédit de l’extension lorsque le taux de dénudation est 15% plus élevé que le taux de convergence.La deuxième partie est consacrée au développement d’un modèle thermo-mécanique 2D en éléments finis pour étudier l’impact des processus de surface sur la déformation des Pyrénées.Les résultats montrent que la réponse isostatique à l’érosion permet de réactiver des structurespré-existantes. La cinématique d’un plan de faille hérité peut être prédite grâce au gradient du profil des vitesses de surface horizontales. Ainsi, un plan situé dans la zone d’érosion est réactivé en faille normale alors qu’en bordure de cette zone une faille est réactivée en régime inverse. Ces résultats suggèrent que la déformation actuelle des Pyrénées pourrait être la conséquence d’unprocessus d’érosion.Compte tenu du faible nombre d’études quantifiant les taux d’érosion dans les Pyrénées, les modèles développés dans la deuxième partie souffrent d’une forte incertitude. Pour y remédier, nous avons cherché à les quantifier dans les Pyrénées Centrales grâce à une étude qui combine deux types de données : taux de dénudation des bassins versants à partir des isotopes cosmogéniques, et vitesses d’incision à partir des sédiments piégés dans les karsts. Ces résultats sontprésentés dans la troisième partie. Les profils de dénudation obtenus sont compatibles avec unrejeu en faille normale d’un plan situé dans la Zone Nord Pyrénéenne des Pyrénées Centrales.Notre étude dans les Pyrénées, montre une bonne corrélation entre la valeur du taux d’érosion et la cartographie de l’occupation glaciaire. Les glaciers ayant été plus développés dans les Alpes, cela pose la question de l’impact de la déglaciation tardi-Wurmienne sur la déformation actuelle de cette chaîne. Un modèle numérique détaillant cette relation est présenté dans le quatrième chapitre. Les résultats montrent que la déglaciation des Alpes occidentales est contrôléepar l’hétérogénéité rhéologique de la croute. Certains de nos modèles prédisent des vitesses de surrection compatibles avec celles mises en évidence par la géodésie.
https://hal.archives-ouvertes.fr/tel-01262333

tel-01262333
https://hal.archives-ouvertes.fr/tel-01262333
https://hal.archives-ouvertes.fr/tel-01262333/document
https://hal.archives-ouvertes.fr/tel-01262333/file/these-Genti-2015-postjury.pdf

Éditeur(s) : Oxford university press
Résumé : The eastern Baltic cod stock collapsed as a consequence of climate-driven adverse hydrographic conditions and over fishing and has remained at historically low levels. Spatio-temporal fishing closures [Marine Protected Areas (MPAs)] have been implemented since 1995, to protect and restore the spawning stock. However, no signs of recovery have been observed yet, either suggesting that MPAs are an inappropriate management measure or pointing towards suboptimal closure design. We used the spatially explicit fishery simulation model ISIS-Fish to evaluate proposed and implemented fishery closures, combining an age-structured population module with a multifleet exploitation module and a management module in a single model environment. The model is parameterized based on (i) the large amount of biological knowledge available for cod and (ii) an analysis of existing spatially disaggregated fishery data. As the population dynamics of eastern Baltic cod depend strongly on the climate-driven hydrographic regime, we considered two production regimes of the stock. MPAs were only effective for stock recovery when they reduced overall fishing effort. The performance of MPAs needs to be evaluated relative to environmental regimes, especially for stocks facing strong environmental variability.
ICES Journal of Marine Science (1054-3139) (Oxford university press), 2009 , Vol. 66 , N. 1 , P. 109-121

Droits : 2008 ICES/CIEM
http://archimer.ifremer.fr/doc/2009/publication-6094.pdf
DOI:10.1093/icesjms/fsn166
http://archimer.ifremer.fr/doc/00000/6094/

Éditeur(s) : HAL CCSD Lippincott, Williams & Wilkins
Résumé : International audience
Among 103 patients with multidrug-resistant HIV who initiated raltegravir, etravirine, and darunavir/ritonavir-containing regimen in the ANRS 139 TRIO trial, 100 participated in extended follow-up and continued study treatment until week 96. Among them, 87 (87%) received an optimized background therapy including either nucleoside reverse transcriptase inhibitors or enfuvirtide, they were 78 (78%) at week 96. At week 96, 88% achieved durable virologic response (<50 copies/mL). CD4 response was maintained (median change of +150 cells/mm(3)). No major toxicity was reported. This triple drug combination showed sustained efficacy and thus should be strongly considered for patients with multiclass-resistant virus.
ISSN: 1525-4135

hal-00875207
https://hal.archives-ouvertes.fr/hal-00875207
DOI : 10.1097/QAI.0b013e31824bb720
PUBMED : 22293546

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
1] Recent statistical analysis by Lallemand et al. (2008) of subduction zone parameters revealed that the back-arc deformation mode depends on the combination between the subducting (nu(sub)) and upper (nu(up)) plate velocities. No significant strain is recorded in the arc area if plate kinematics verifies nu(up) = 0.5 vsub - 2.3 (cm/a) in the HS3 reference frame. Arc spreading ( shortening) occurs if nu(up) is greater ( lower) than the preceding relationship. We test this statistical law with numerical models of subduction, by applying constant plate velocities far away from the subduction zone. The subducting lithosphere is free to deform at all depths. We quantify the force applied on the two converging plates to sustain constant surface velocities. The simulated rheology combined viscous (non-Newtonian) and brittle behaviors, and depends on water content. The influence of subduction rate vs is first studied for a fixed upper plate. After 950 km of convergence ( steady state slab pull), the transition from extensional to compressive stresses in the upper plate occurs for vs similar to 1.4 cm/a. The effect of upper plate velocity is then tested at constant subduction rate. Upper plate retreat ( advance) with respect to the trench increases extension ( compression) in the arc lithosphere and increases ( decreases) the subducting plate dip. Our modeling confirms the statistical kinematic relationship between vsub and nu(up) that describes the transition from extensional to compressive stresses in the arc lithosphere, even if the modeled law is shifted toward higher rates of upper plate retreat, using our set of physical parameters ( e. g., 100 km thick subducting oceanic plate) and short- term simulations. Our results make valid the choice of the HS3 reference frame for assessing plate velocity influence on arc tectonic regime. The subduction model suggests that friction along the interplate contact and the mantle Stokes reaction could be the two main forces competing against slab pull for upper mantle subductions. Besides, our simulations show that the arc deformation mode is strongly time dependent.
ISSN: 1525-2027

hal-00412328
https://hal.archives-ouvertes.fr/hal-00412328
https://hal.archives-ouvertes.fr/hal-00412328/document
https://hal.archives-ouvertes.fr/hal-00412328/file/arcayG32008.pdf
DOI : 10.1029/2007GC001875

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We propose a new geometric approach to describe the qualitative dynamics of chemical reactions networks. By this method we identify metastable regimes, defined as low dimensional regions of the phase space close to which the dynamics is much slower compared to the rest of the phase space. These metastable regimes depend on the network topology and on the orders of magnitude of the kinetic parameters. Benchmarking of the method on a computational biology model repository suggests that the number of metastable regimes is sub-exponential in the number of variables and equations. The dynamics of the network can be described as a sequence of jumps from one metastable regime to another. We show that a geometrically computed con-nectivity graph restricts the set of possible jumps. We also provide finite state machine (Markov chain) models for such dynamic changes. Applied to signal transduction models, our approach unravels dynamical and functional * corresponding author capacities of signalling pathways, as well as parameters responsible for speci-ficity of the pathway response. In particular, for a model of TGFβ signalling, we find that the ratio of TGFBR2 to TGFBR1 receptors concentrations can be used to discriminate between metastable regimes. Using expression data from the NCI60 panel of human tumor cell lines, we show that aggressive and non-aggressive tumour cell lines function in different metastable regimes and can be distinguished by measuring the relative concentrations of receptors of the two types.
ISSN: 0303-2647

hal-01379033
https://hal.inria.fr/hal-01379033
https://hal.inria.fr/hal-01379033/document
https://hal.inria.fr/hal-01379033/file/Samal_et_al_Biosystems_final.pdf
DOI : 10.1016/j.biosystems.2016.07.004

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé :  
Modeling soil water availability for tropical trees is a prerequisite to predicting the future impact of climate change on tropical forests. In this paper we develop a discrete-time deterministic water balance model adapted to tropical rainforest climates, and we validate it on a large dataset that includes micrometeorological and soil parameters along a topographic gradient in a lowland forest of French Guiana. The model computes daily water fluxes (rainfall interception, drainage, tree transpiration and soil plus understorey evapotranspiration) and soil water content using three input variables: daily precipitation, potential evapotranspiration and solar radiation. A novel statistical approach is employed that uses Time Domain Reflectometer (TDR) soil moisture data to estimate water content at permanent wilting point and at field capacity, and root distribution. Inaccuracy of the TDR probes and other sources of uncertainty are taken into account by model calibration through a Bayesian framework. Model daily output includes relative extractable water, REW, i.e. the daily available water standardized by potential available water. The model succeeds in capturing temporal variations in REW regardless of topographic context. The low Root Mean Square Error of Predictions suggests that the model captures the most important drivers of soil water dynamics, i.e. water refilling and root water extraction. Our model thus provides a useful tool to explore the response of tropical forests to climate scenarios of changing rainfall regime and intensity.
ISSN: 0168-1923

hal-01032181
https://hal.archives-ouvertes.fr/hal-01032181
DOI : 10.1016/j.agrformet.2011.04.012

Éditeur(s) : HAL CCSD
Résumé : This study is designed to improve the understanding of structural, mechanical and petrophysical characteristics of deformation bands in porous sandstone such as their potential influence on fluid storage or migration in reservoir setting. Structural and petrophysical analysis of band networks from Provence show that permeability of band is mainly controlled by the degree of cataclasis and diagenetic processes at depth. Map-scale analysis of band networks underlines the major influence of tectonic regime on band distribution, organization and permeability. Band associated to normal-fault regime (cataclasis and low-permeability) are located around map-sclae-fault whereas band associated to thurst-fault regime (moderate cataclasis and permeability) are pervasively distributed in all the area. Reverse-sense band are cataclastic and low-permeabiilty around the Roquemaure thrust, which show the potential role of large-scale fault on structural and petrophysical characteristics of bands. This analysis also shows the influence of fault propagation on formation of low permeability catacastic bands. This analysis suggests also granulometry as factor controlling organization of band networks.A mechanical analysis of deformation bands is realized based on results from Provence. Yield envelopes of these materials are calculated from analytical solution. Triaxial tests done on sandstone (L'Etang quarry, Orange) confirm the shape of yield envelope theoretically calculated. Triaxial tests done on the poorly-lithified sands (Boncavaï quarry, Uchaux) show grain size, sorting and packing influencing yield envelope and cataclastic band localization at shallow burial depth. Stress paths are calculated for burial and tectonic event (extension and contraction) using the relationship between main stress and secondary stresses (K0) calibrated from well data. These different results are integrated into a model which allows to estimate type and structural characteristics of bands susceptible to form for a known geological setting.A structural, mechanical and petrophysical model is established form these results. This model is calibrated by permeability data from deformation bands of Provence and results from the mechanical model of strain localization. This model is also confronted to a synthesis of permeability data from literature, which confirms the influence of the different controlling parameters integrated to the model. This model is applied for two sites of uranium exploration/exploitation in porous sandstone reservoirs and validated by field observations.
Cette étude est destinée à améliorer la compréhension des caractéristiques structurales, pétrophysiques et mécaniques des bandes de déformation dans les grès poreux ainsi que de leur rôle potentiel sur la migration ou le piégeage des fluides en milieu réservoir. L'analyse structurale et pétrophysique des réseaux de bandes de Provence montre que leur perméabilité découle principalement de l'intensité de la cataclase dans leur microstructure et des processus diagénétiques qui peuvent s'y localiser avec la profondeur. L'analyse régionale de ces réseaux de bandes souligne l'influence majeure du régime tectonique sur leur distribution, leur organisation et leur perméabilité. Les bandes associées au régime normal (cataclactiques et peu perméables) sont localisées autour des failles cartographiques, tandis que les bandes associées au régime inverse (modérement cataclastiques et perméables) sont distribuées dans toute la région. Les bandes inverses sont fortement cataclastiques et imperméables uniquement autour du chevauchement de Roquemaure ce qui montre le rôle potentiel de la présence de grande faille sur les caractéristiques structurales et pétrophysiques de ces bandes. D'autre part, cette analyse suggère que la granulométrie de l'encaissant peut influencer l'initiation et l'organisation des réseaux. L'analyse mécanique des bandes de déformation a ensuite été réalisée à partir des résultats obtenus en Provence. L'enveloppe de plasticité de ces matériaux est calculée à l'aide d'une solution analytique. Les essais triaxiaux menés sur le grès de la carrière de l'Etang (orange) confirment la forme de ces enveloppes estimées théoriquement. Les essais réalisés sur les sables de Boncavaï (Uchaux) montrent que la taille des grains, le tri et de la compaction dans ces matériaux peu lithifiés influent sur leurs enveloppes de plasticité et la localisation des bandes cataclastiques à faibles profondeurs. Les trajets de contraintes sont estimés pour les phases d'enfouissement et de chargement tectonique (extension et compression) à partir de la relation entre contrainte principale et contraintes secondaires (K0), calibrée à partir de données de forage. Ces résultats sont intégrés à un modèle permettant d'estimer la nature et les caractéristiques structurales des bandes susceptibles de se former dans un contexte géologique donné. Un modèle structural, mécanique et pétrophysique a été établir à partir de ces différents résultats. Ce modèle est calibré à partir des données de perméabilité mesurées sur les bandes de Provence et des résultats du modèle mécanique de localisation cité précédemment. Ce modèle a ensuite été confronté à une synthèse des données de perméabilité disponibles dans la littérature et confirme l'influence des différents paramètres de contrôle pris en compte dans le modèle. Ce modèle a enfin pu être appliqué sur deux sites d'explorations/exploitations d'uranium en réservoir gréseux poreux et validé par les résultats obtenus, en concordance avec les observations de terrain.
https://tel.archives-ouvertes.fr/tel-01001389

NNT : 2013MON20067
tel-01001389
https://tel.archives-ouvertes.fr/tel-01001389
https://tel.archives-ouvertes.fr/tel-01001389/document
https://tel.archives-ouvertes.fr/tel-01001389/file/36072_BALLAS_2013_archivage-1_cor.pdf

Éditeur(s) : EDP Sciences
Résumé : Marine Protected Areas (MPA) are often contemplated as a tool for the sustainable management of exploited resources and ecosystem conservation. This paper proposes an approach to establish a statistical diagnostic of the effects of MPAs on fish assemblages, and define corresponding ecological indicators. This requires choosing relevant variables (abundance, diversity, demographic parameters..) and appropriate statistical methods. The study was based on data from the Abore reef Reserve in New Caledonia. Two sets of methods: 1-inferential linear models (ANOVA, GLM): 2- Partial Least Squares (PLS) methods of regression, were used to test the effects of this MPA. PLS enabled us to test simultaneously within a model, density, species richness, biomass and mean size variables of fish community to retain the most sensitive and relevant ones. Habitat variability was also taken into account in these models. Species were grouped according to several criteria: 1-feeding habit; 2- taxonomy; 3-mobility; 4-adult size; 5-demographic strategy. No significant effect of the opening of the Abore reef to fishing was found for mobility. Feeding habit was the only criterion for which the results from the inferential models and PLS showed a significant effect of reserve status for all variables. Species richness, density, and to a lesser extent mean size, were sensitive to the removal of reserve status. but not biomass. Results from ANOVA and PLS regression were consistent but the latter allows a more holistic approach as it integrates all variables within a single model.
Les Aires Marines Protégées (AMP) sont de plus en plus considérées comme des mesures de gestion alternative permettant à la fois une gestion durable des ressources exploitées et la conservation des écosystèmes. Nous proposons une approche pour définir des indicateurs synthétiques et permettre un diagnostic statistique de l'effet des AMP sur les peuplements. Ce travail passe par le choix de variables pertinentes (abondance, richesse spécifique, paramètres démographiques, etc.) et de méthodes statistiques appropriées. Cette étude a été réalisée sur la réserve du récif Aboré en Nouvelle-Calédonie. Les données issues de deux campagnes scientifiques menées sur ce récif sont utilisées pour tester globalement l'effet des AMP grâce à des modèles linéaires inférentiels (ANOVA, GLM), et par des méthodes de régression PLS (Partial Least Squares). Ces dernières permettent de confronter dans un même modèle quatre variables (densité, richesse, biomasse et taille moyenne des poissons), afin de retenir les plus sensibles et les plus pertinentes pour l'évaluation de l'impact de la réserve. La variabilité de l'habitat est également prise en compte dans la modélisation. Les espèces sont regroupées selon plusieurs critères: 1- le régime alimentaire; 2- la taxonomie; 3- la mobilité; 4- des caractéristiques démographiques; 5- des caractéristiques de taille. Les espèces, quel que soit leur mobilité, n'apparaissent pas affectées par l'ouverture à la pêche du récif Aboré, qu'elles soient sédentaires ou très mobiles. Seul le critère trophique révèle un effet du changement de statut Réserve/Non Réserve pour toutes les variables, à la fois d'après les modèles inférentiels et les régressions PLS. Les résultats des modèles inférentiels et des régressions PLS montrent que la richesse spécifique et la densité sont les variables les plus sensibles à l'impact de l'ouverture à la pêche. La taille moyenne est également bien modélisée sur l'ensemble des résultats mais pas la biomasse. Les résultats d'ANOVA et de régression PLS sont cohérents mais la régression PLS permet d'intégrer toutes les variables dans un même modèle
Aquatic Living Resources (0990-7440) (EDP Sciences), 2004-04 , Vol. 17 , N. 2 , P. 139-149

Droits : EDP Sciences, IFREMER, IRD 2004
http://archimer.ifremer.fr/doc/2004/publication-398.pdf
DOI:10.1051/alr:2004022
http://archimer.ifremer.fr/doc/00000/398/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
OBJECTIVES: To compare virological effectiveness in patients who continued on a virologically successful first-line boosted protease inhibitor (PI)-containing combination antiretroviral therapy (cART) regimen or who switched to a PI-free cART including efavirenz, nevirapine or abacavir. METHODS: From the French Hospital Database on HIV, we selected 439 patients with undetectable viral load (VL) on a first-line boosted PI-containing cART regimen who switched to a PI-free combination including efavirenz, nevirapine or abacavir. Each of these patients was matched with three patients who continued to take their first-line cART regimen, on the basis of gender, age, CD4 cell count, VL, date of cART initiation and the duration of VL undetectability. Time to virological failure (VF) was analysed with Kaplan-Meier curves and Cox models. RESULTS: The 12 month probabilities of VF were 3.7% and 5.7% in non-switch and switch patients, respectively, and 3.9%, 7.2% and 9.0% in patients switching to efavirenz-, nevirapine- and abacavir-containing cART, respectively. After adjustment, only patients switching to abacavir-containing cART had a higher risk of VF than non-switch patients (adjusted hazard ratio, 1.99; 95% confidence interval, 1.05-3.79). CONCLUSIONS: Switching from a virologically successful first-line boosted PI-containing cART regimen to a non-nucleoside reverse transcriptase inhibitor-containing cART regimen containing either efavirenz or nevirapine is virologically safe, while switching to abacavir-containing cART should be avoided.
ISSN: 0305-7453

hal-00875284
https://hal.archives-ouvertes.fr/hal-00875284
DOI : 10.1093/jac/dkr208
PUBMED : 21636583

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
This study investigates three-dimensional flow modes of orogenic plateaus by means of physical modeling. Experiments consist of shortening two contiguous lithospheres of contrasting strength, one being a weak plateau-type lithosphere and the other a strong craton-type lithosphere. The lateral boundaries are either totally confined or allow escape toward a lateral foreland on one side. Two synconvergence flow regimes are distinguished, which are governed by the balance between the gravity potential and the strength of the plateau crust and the resistance of its lateral foreland. The first regime implies transversal (orogen-normal) injection of plateau lower crust into the collision zone as a result of confinement of the plateau by an increasingly stiffer lateral boundary. As a precursor mechanism to channel flow, transversal injection responds to downward thickening of the plateau crust that is forcedly extruded into the orogenic wedge. The second regime is that of collapse-driven lateral escape of the plateau. This regime is established after a threshold is attained in the interplate coupling in the collision zone, which allows the gravity potential of the plateau to overcome the resistance of its lateral boundary. Under the collapse-driven escape regime (orogen parallel), such as that governing Tibet during the last 13 Ma, most of the convergence in the plateau and the top and rear of the collisional wedge is transformed into lateral flow and extension.
ISSN: 0148-0227

hal-01229107
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/file/2015JB012110_revised.pdf
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01229107/file/SupplementaryMaterial_final.pdf

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : Production rates in horizontal shale gas wells display declines that are controlled by the low permeability and the intrinsic heterogeneity of the shale matrix. We present an original multi-continuum approach that yields a physical model able to reproduce the complexity of the decreasing gas rates. The model describes the dynamics of gas rate as function of the physical reservoir parameters and geometry, while the shale matrix heterogeneity is accounted for by a stochastic description of transmissivity field. From the 3D (Dimensional) problem setting, including the heterogeneous shale matrix, the fractures generated by the hydrofracking operations, as well as the production well characteristics, we establish an effective upscaled 1D model for the gas pressures in fracture and matrix as well as the volumetric flux. We analyse the decline curves behaviour, and we identify the time scales that characterize the dynamics of the gas rate decline using explicit analytical Laplace space solutions of the upscaled process model. Asymptotically, the flux curves decrease exponentially, while in an intermediate regime we find a power-law behaviour, in which the flux scales with a power law in time as (t^{-beta }), where (beta ) reflects the medium heterogeneity. We use this solution to fit a set of real data displaying distinctly different decline trends and study the sensitivity of the model to the reservoir parameters in order to identify their respective controls at the different stages of the decline curve dynamics. Results indicate that the initial value of the gas rate is determined by the transmissivity of the fractures and the initial pressure of the gas in the shale matrix. The latter causes mainly a shift in the entire decline curve. The early time of decline curve shape is primarily controlled by the fracture properties (compressibility and transmissivity). During the main part of the economically valuable production times, i.e. before the production rate drops exponentially, the decline curve is strongly controlled by the properties of the shale rocks including their heterogeneity, which is modelled by two parameters describing the non-Fickian pressure diffusion effects in a stochastic framework.
ISSN: 0169-3913

hal-01217247
https://hal.archives-ouvertes.fr/hal-01217247
DOI : 10.1007/s11242-015-0504-y

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The association of experimental data showing that the plastic deformation of olivine, the main constituent of the upper mantle, is highly anisotropic and the ubiquitous seismic anisotropy in the upper mantle, which indicates that olivine crystals show coherent orientations over scales of tens to hundreds of kilometers, implies that the long-term deformation in the upper mantle is anisotropic. We propose a multiscale approach, based on a combination of finite element and homogenization techniques, to model the deformation of a lithospheric plate while fully considering the mechanical anisotropy stemming from a strain-induced orientation of olivine crystals in the mantle. This multiscale model explicitly takes into account the evolution of crystal preferred orientations (CPO) of olivine and of the mechanical anisotropy during the deformation. We performed a series of numerical experiments simulating the uniaxial extension of a homogeneous (100% olivine) but anisotropic plate to test the role of the olivine CPO on the plate mechanical behavior and the link between CPO and mechanical anisotropy evolution. Even for this simple solicitation, different orientations and intensity of the initial olivine CPO result in variable plate strengths and deformation regimes. A plate with an initial CPO where the olivine [100] and [010] axes are concentrated at 45 degrees to the extension direction has high resolved shear stresses on the easy (010)[100] and (001)[100] slip systems of olivine. This results in low strength and in deformation by transtension. Plates with an initial CPO where the maximum of [100] axes is parallel or normal to the extension direction show a high initial strength. Isotropic plates have an intermediate behavior. The progressive rotation of olivine [100] axes toward the imposed stretching direction results in hardening in all models, except in those characterized by an initial concentration of olivine [100] axes normal to the imposed extension, in which softening is followed by hardening.
ISSN: 1525-2027

hal-00420063
https://hal.archives-ouvertes.fr/hal-00420063
DOI : 10.1029/2009GC002423

Éditeur(s) : HAL CCSD
Résumé : 20 pp
We first analyze some atmospheric parameters measured in 2004 at the top of La Soufrière volcano: wind speed, pressure and temperature. Next, we study the stochastic process of the wind speed modulus which is of interest for prediction of pollution induced by the plume. We fit to the data various models : FARIMA, periodic trend plus multifractional Brownian noise, multifractal continuous cascades. The estimations show that they evoluate during some transition phases in response to environment changes. Thus, we finally suggest, for future works, some settings that should be more appropriate: time series with regime changes and stochastic processes in random environment.
https://hal.archives-ouvertes.fr/hal-00165572

hal-00165572
https://hal.archives-ouvertes.fr/hal-00165572
https://hal.archives-ouvertes.fr/hal-00165572/document
https://hal.archives-ouvertes.fr/hal-00165572/file/Windsouf_v11.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A set of four reactive flow-through experiments at temperature T = 100 degrees C and total pressure P=12 MPa was performed in limestone reservoir samples. By using various ranging from 0.7 to 10 MPa, these experiments mimic mass transfers occurring (1) near the injection well, where the brine is almost saturated with CO2 (i.e. P-CO2 approximate to P), and (2) at increasing distances from the injection well, where the fluid displays lower values and higher divalent cation concentrations due rock dissolution along the fluid pathway. Results for P-CO2 = 10 MPa show non-uniform dissolution features associated with transport-controlled mass transfer, while reaction-controlled uniform dissolution is observed for P-CO2 = 2.5 MPa. The experiment with P-CO2 = 6 MPa allows investigating in detail the transition from transport-to reaction-controlled dissolution. Conversely, the experiment reproducing conditions far from the injection well (P-CO2 = 0.7 MPa), shows a decrease of porosity triggered by the precipitation of Mg-rich calcite. For all the dissolution experiments, the time-resolved porosity phi(t) can be modeled by a simple non-linear equation including parameters that characterise the dissolution regime triggered by the reactivity of the inlet fluid (measured by the Damkohler number, Da). Furthermore, all dissolution experiments display power scaling between permeability (k) and porosity (phi) with distinctly different scaling exponents characterising the reactivity of the fluid percolating the sample, independently from the decrease with time of the reactive surface area. It is shown also that dissolution at moderate positive values of Da seems the most efficient to increase permeability and promote a rapid spreading of the reaction front, while inducing minimal modification of the porosity in the vicinity of the CO2 injection well. These results can be used to parameterize the k-phi function for modeling the earliest dissolution processes occurring in the vicinity of the reaction front.
ISSN: 0009-2541

hal-00445277
https://hal.archives-ouvertes.fr/hal-00445277
DOI : 10.1016/j.chemgeo.2009.03.028

Éditeur(s) : Oxford university press
Résumé : The response of fish assemblages to changes in protection status is a major issue for both biodiversity conservation and fishery management. In New Caledonia, the Abore reef marine reserve harbours more than 500 fish species, and has been subjected to changes in protection status since 1988. The present study investigates the impact of these changes on a wide subset of species (213), based on underwater visual counts collected before the opening and after the closure to fishing of this marine protected area (MPA). We analysed the spatial and temporal variability in fish assemblage attributable to protection status, explicitly considering habitat. To understand the successive responses of fish assemblage to fishing and protection, the assessment models included four criteria de. ning species groups that partition the fish assemblage: trophic regime, adult size, mobility, and interest for fishing. We could therefore identify the negative impact of opening the MPA to fishing on piscivores and highly mobile species. Surprisingly, target species were not affected more than non-target species. Model results were used to identify species groups that respond to fishing and protection. These results utilize fisheries-related criteria to provide new insight into the response of fish assemblages to protection from the perspective of MPA monitoring.
ICES Journal of Marine Science (1054-3139) (Oxford university press), 2009 , Vol. 66 , N. 1 , P. 170-179

Droits : 2009 ICES/CIEM. Oxford Journals
http://archimer.ifremer.fr/doc/2009/publication-6130.pdf
DOI:10.1093/icesjms/fsn204
http://archimer.ifremer.fr/doc/00000/6130/

Éditeur(s) : HAL CCSD
Résumé : 27 pages
Cascade Stochastic Differential Equation (SDE), a continuous time model for energy dissipation in turbulence, is a generalization of the Yaglom discrete cascade model. We extend this SDE to a model in random environment by assuming that its two parameters are switched by a continuous time Markov chain whose states represent the states of the environment. Moreover, a Dirichlet process is placed as a prior on the space of sample paths of this chain. We propose a Bayesian estimation method of this model which is tested both on simulated data and on real data of wind speed measured at the entrance of the mangrove ecosystem in Guadeloupe.
https://hal.archives-ouvertes.fr/hal-00286131

hal-00286131
https://hal.archives-ouvertes.fr/hal-00286131
https://hal.archives-ouvertes.fr/hal-00286131/document
https://hal.archives-ouvertes.fr/hal-00286131/file/Srik11_PhysicaDDspace.pdf

Éditeur(s) : HAL CCSD Annual Reviews
Résumé : International audience
The record of the continental lithosphere is patchy and incomplete; no known rock is older than 4.02 Ga, and less than 5% of the rocks preserved are older than 3 Ga. In addition, there is no recognizable mantle lithosphere from before 3 Ga. We infer that there was lithosphere before 3 Ga and that ∼3 Ga marks the stabilization of blocks of continental lithosphere that have since survived. This was linked to plate tectonics emerging as the dominant tectonic regime in response to thermal cooling, the development of a more rigid lithosphere, and the recycling of water, which may in turn have facilitated plate tectonics. A number of models, using different approaches, suggest that at 3 Ga the volume of continental crust was ∼70% of its present-day volume and that this may be a minimum value. The continental crust before 3 Ga was on average more mafic than that generated subsequently, and this pre-3 Ga mafic new crust had fractionated Lu/Hf and Sm/Nd ratios as inferred for the sources of tonalite-trondhjemite-granodiorite and later granites. The more intermediate composition of new crust generated since 3 Ga is indicated by its higher Rb/Sr ratios. This change in composition was associated with an increase in crustal thickness, which resulted in more emergent crust available for weathering and erosion. This in turn led to an increase in the Sr isotope ratios of seawater and in the drawdown of CO2. Since 3 Ga, the preserved record of the continental crust is marked by global cycles of peaks and troughs of U-Pb crystallization ages, with the peaks of ages appearing to match periods of supercontinent assembly. There is increasing evidence that the peaks of ages represent enhanced preservation of magmatic rocks in periods leading up to and including continental collision in the assembly of supercontinents. These are times of increased crustal growth because more of the crust that is generated is retained within the crust. The rates of generation of continental crust and mantle lithosphere may have remained relatively constant at least since 3 Ga, yet the rates of destruction of continental crust have changed with time. Only relatively small volumes of rock are preserved from before 3 Ga, and so it remains difficult to establish which of these are representative of global processes and the extent to which the rock record before 3 Ga is distorted by particular biases.
ISSN: 0084-6597

hal-01622692
https://hal.archives-ouvertes.fr/hal-01622692
DOI : 10.1146/annurev-earth-063016-020525

Éditeur(s) : Elsevier
Résumé : Clinoforms on modern shelves and slopes, as well as in ancient rock records, are widely recognized as a fundamental building element of continental margin growth. Regardless of their dominant lithology, clinoforms are composed of three geometric elements: topset, foreset and bottomset. Traditionally, much emphasis in the study of clinoforms was put on the geometry of the topset, viewed as the most energetic portion of a clinoform and studied to discern if aggradation was active rather than erosional truncation, and on the foreset, the area with the highest sediment accumulation rates. Here we focus on the factors forcing clinoforms to taper out and on the inferred mechanisms for bottomset creation. We base our analysis on muddy shelf clinoforms, a particular class of clinoforms that is typical of low-gradient settings and is characterized by a substantial component of shore-parallel sediment transport. This paper is based on a large dataset of CHIRP-sonar profiles, bathymetric and isopach maps of the Late Holocene clinoform on the Adriatic shelf, where integrated stratigraphic studies from sediment cores allow a very high (in some cases century-scale) chronological resolution. Knowledge on the dominant oceanographic regime affecting sediment dispersal and, ultimately, clinoform development, has been recently refined during the EuroSTRATAFORM collaboration. Muddy clinoforms are markedly three-dimensional features that cannot be entirely understood solely on two-dimensional shore normal sections. We suggest that this class of clinoform is advection dominated and that an increase in the energy regime at the toe of the foreset may prevent sediment from reaching beyond the transition to the bottomset region.
Continental Shelf Research (0278-4343) (Elsevier), 2007-02 , Vol. 27 , N. 3-4 , P. 506-525

Droits : 2006 Elsevier Ltd All rights reserved
http://archimer.ifremer.fr/doc/2007/publication-2409.pdf
DOI:10.1016/j.csr.2006.11.013
http://archimer.ifremer.fr/doc/00000/2409/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : In the present work, a biophysical dispersal model is used to understand the role of the physical environment in determining reef fish larval dispersal patterns in the South-West Lagoon of New Caledonia. We focus on a reef fish species, the humbug damselfish Dascyllus aruanus, to investigate seasonal variability of simulated larval retention at the scale of a reef patch and at the scale of the lagoon, and to explore links between larval retention and wind variability. The model shows that retention exhibits considerable temporal variability and periodically reaches values much larger than anticipated. Non-zero larval settlement occurs over a large part of the lagoon. Nevertheless, settlement values decrease quickly away from the natal reef and mean dispersal distances are of order 25-35 km. Cross-correlation analyses indicate that weather conditions characterized by strong south east trade winds lead to low retention rates at both local (reef) and regional (lagoon) scales. By contrast, subtropical weather conditions characterized by weak winds result in high retention rates. These results suggest that large-scale weather regimes can be used as proxies for larval retention of the humbug damselfish in the South-West Lagoon of New Caledonia. Nevertheless, relatively small mean dispersal distances suggest that meta-population dynamics occur on relatively small spatial scales.
Progress In Oceanography (0079-6611) (Pergamon-elsevier Science Ltd), 2014-03 , Vol. 122 , P. 105-115

Droits : 2013 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00170/28115/26326.pdf
DOI:10.1016/j.pocean.2013.12.006
http://archimer.ifremer.fr/doc/00170/28115/