Éditeur(s) : Gauthier-Villars
Résumé : The dissolved Mn distribution on an oceanographic section along 50-degrees-W in the western North Atlantic shows decreasing concentrations in the offshore direction in the surface layer and with depth at the deep water stations. Leachable particulate Mn concentrations are low in the open ocean surface waters and elevated at intermediate depths. Dissolved Al concentrations in the surface layer are higher in the open ocean than on the shelf and the vertical distributions are characterized by surface maxima, a subsurface minimum at almost-equal-to 1 000 m and increasing concentrations in the deep waters. Leachable particulate Al concentrations are elevated on the shelf and in open ocean surface waters compared to the intermediate and deep waters. The Deep Western Boundary Current has high levels of dissolved Al and leachable particulate Mn and Al, and low levels of dissolved Mn. The distribution of dissolved Al is controlled primarily by inputs from atmospheric dust and removal onto biogenic particles. Both fluvial and atmospheric inputs affect dissolved Mn levels with removal occurring primarily by oxidation of Mn2+. The Al distribution is characterized by short residence times in shelf and surface waters and relatively constant distribution coefficients. The Mn distribution is characterized by longer surface water residence times, shorter deep water residence times, and more widely varying distribution coefficients than Al. Removal of Al by a surface adsorption mechanism and Mn by slower oxidation of Mn2+ are consistent with these observations. A model of Mn oxidation kinetics accurately predicts the intermediate depth leachable particulate Mn maximum.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 6 , P. 609-619

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00101/21186/18803.pdf
http://archimer.ifremer.fr/doc/00101/21186/

Éditeur(s) : HAL CCSD Wiley
Résumé : Tank bromeliads form a conspicuous, yet neglected freshwater habitat in Neotropical forests. Recent studies driven by interests in medical entomology, fundamental aspects of bromeliad ecology and experimental research on food webs have, however, prompted increasing interest in bromeliad aquatic ecosystems. As yet, there is nothing in the literature about the life histories and environmental drivers of invertebrate population dynamics in tank bromeliads. Based on fortnightly samples taken over oneyear, size frequency plots and individual dry masses allowed us to establish the life cycles and growth rates of the dominant aquatic invertebrates in a common bromeliad species of French Guiana. Linear mixed-effect models and Mantel tests were used to predict changes in density, biomass, and growth rates in relation to temperature, rainfall, humidity and detrital resources. Annual variations in invertebrate densities and biomasses could be described according to three types of distribution: unimodal, bimodal or almost constant. Despite seasonal variations, precipitation, temperature, relative humidity and detritus concentration accounted significantly for changes in density and biomass, but we found no significant responses in growth rates of most invertebrate species. Species rather displayed non-seasonal life cycles with overlapping cohorts throughout the year. There was also a trend for delayed abundance peaks among congeneric species sharing similar functional traits, suggesting temporal partitioning of available resources. Beyond novel knowledge, quantitative information on life histories is important to predict food-web dynamics under the influence of external forcing and self-organisation. Our results suggest that changes in species distribution that will affect population dynamics through biotic interactions in space and/or time could have greater effects on food webs and ecosystem functioning than changes in environmental factors per se.
ISSN: 0046-5070

hal-01607779
https://hal.archives-ouvertes.fr/hal-01607779
DOI : 10.1111/fwb.12862
PRODINRA : 407311

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx, were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m−3 for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m−3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average ρx across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood.
ISSN: 1726-4170

hal-01032137
https://hal.archives-ouvertes.fr/hal-01032137

Éditeur(s) : HAL CCSD
Résumé : Understanding of the mechanisms driving diversification of species is a significant way to improve the management of ecosystems, predict the impacts of climate change and understand the actual and past biodiversity level. The aim of this thesis is to understand and comprehend genetic mechanisms behind the diversification of species in the presence of gene flow. This thesis is focused on the biological model Symphonia globulifera, which presents two ecotypes: the S.globulifera, specialist of seasonally flooded lowlands and S.sp1, specialist of terra firme. These two ecotypes show low genetic differentiation, despite the presence of two apparent phenotypes. A first part of this thesis was to test the presence of local adaptation of this using reciprocal transplant experiment gardens, allowing the understanding of the ecotypes distributions in their natural habitats. Then, this local adaptation in the presence of gene flow, directed me to the regulation of gene methylation in order to see the role this brand of epigenetics can have in the divergence of the ecotypes. In a third part of the thesis, new generation sequencing of the transcriptome ecotypes in reciprocal gardens transplantations allowed me to show the evidence of gene regulation to differentiate the ecotypes. This work thesis is based on phenotype records data, AFLP genotyping and high-throughput sequencing of the transcriptome, in order to show the important value of gene regulation in the divergence of the locally adapted ecotypes, and a weak role of DNA methylation in the establishment of local adaptation.
Connaitre et appréhender les mécanismes de la diversification des espèces est important pour la gestion des écosystèmes, la prévision des impacts des changements climatiques et la compréhension de la biodiversité actuelle et passée. Le but de cette thèse est de comprendre et de déceler les mécanismes génétiques à l’origine de la diversification des espèces en présence de flux de gènes. Cette thèse se focalise sur le modèle biologique Symphonia globulifera, qui compte deux écotypes : le S.globulifera spécialiste de la terra firme et le S.sp1, spécialiste des bas-fonds. Ces deux écotypes montrent une faible différenciation génétique, malgré la présence de deux phénotypes différents.Une première étape a été de mettre en évidence la présence d’une adaptation locale au sein de cette espèce, par le biais d’une expérimentation de jardins de transplantation réciproques, permettant d’expliquer la répartition des écotypes dans leur habitat naturel. Ensuite, dans le but d’identifier les mécanismes sous-jacent à cette adaptation locale, j’ai testé l’hypothèse que la méthylation des gènes pourrait être une marque de l’épigénétique contribuant à la divergence des écotypes, par l’utilisation d’enzyme sensibles à la méthylation dans un protocole de génotypage AFLP. Enfin, un séquençage haut-débit du transcriptome des écotypes en jardins de transplantation réciproques m’a permis de mettre en évidence une expression différentielle des gènes entre les écotypes, qui pourrait expliquer les différences phénotypiques observées entre les écotypes malgré une faible différentiation génétique. Ces travaux de thèse s’appuie, ainsi, sur des données de traits phénotypiques, de génotypage AFLP et de séquençage à haut débit du transcriptome pour montrer la valeur importante de la régulation des gènes dans la divergence des écotypes adaptés localement, et un faible rôle de la méthylation de l’ADN dans l’établissement cette adaptation locale.
https://tel.archives-ouvertes.fr/tel-01405400

NNT : 2015YANE0005
tel-01405400
https://tel.archives-ouvertes.fr/tel-01405400
https://tel.archives-ouvertes.fr/tel-01405400/document
https://tel.archives-ouvertes.fr/tel-01405400/file/these_-_tinaut.pdf

Éditeur(s) : HAL CCSD
Résumé : données, méthodes disponibles auprès de l'auteur
In tropical forest communities, interspecific competition and recruitment limitation by dispersal are two general mecanisms of tree species coexistence. Their role in regeneration remains poorly known, even though it is essential to understand them to better adress the gestion of exploited forests. In this work, environemental conditions and intraspecific relations were taken into account in the analysis of juvenile distribution. Fifteen species were retained according to a gradient of shade-tolerance and various seed dispersal modes. Statistical modelling of local density was used to link the success of installation with environnemental conditions and distances to adults simultaneously. Model prediction evidenced the gradient of shade-tolerance among studied species and revealed different installation curves related to dispersal modes.
Dans les communautés de forêt tropicale humide, la compétition interspécifique et la limitation du recrutement par la dispersion ont généralement invoquées pour expliquer la coexistence de nombreuses espèces d'arbres. Le rôle de ces mécanismes dans la régénération reste peu connu, bien que leur compréhension soit essentielle pour la gestion des forêts exploitées. Dans ce travail, les conditions du milieu et les relations intraspécifiques ont été prises en compte dans l'analyse des distributions de juvéniles. Quinze espèces non pionnières ont été sélectionnées selon un gradient de tolérance à l'ombre et des modes de dispersion variés. La modélisation statistique de la densité locale a permis de relier le succès d'installation des juvéniles aux conditions du milieu et aux distances aux arbres adultes simultanément. Les prédictions des
modèles confirment le gradient de tolérance parmi les espèces étudiées et révèlent des courbes d'installation différentes selon le mode de dispersion.
https://tel.archives-ouvertes.fr/tel-00297707

tel-00297707
https://tel.archives-ouvertes.fr/tel-00297707
https://tel.archives-ouvertes.fr/tel-00297707/document
https://tel.archives-ouvertes.fr/tel-00297707/file/PhD_regeneration_Olivier_Flores.pdf

Résumé : After a period of rapid development of the sites (an increase in both reared surface area and production), tropical shrimp aquaculture is currently being faced with critical problems due to economical and ecological constraints. In many countries with favourable conditions for shrimp aquaculture such as indonesia or Vietnam, sites are often badly selected and/or over-exploited. This conducts to sorne extent to decreases or collapses in the production due to the difficulty in predicting the maximum production capacity of the sites. Furthermore, it appears that production sustainability depends on many factors among which socio-economy and ecolo gy are of prime importance. The STD3 project titled « Assessment of tropical shrimp aquaculture impact on the environment in tropical countries using hydrobiology, ecology and remote sensing as helping tools for diagnosis )) was initiated in 1994, with the aim to study the sustainability of marine shrimp aquaculture in tropical areas, main! y Indonesia and Vietnam, through the following tasks: (i) improve site selection and study the impact of aquaculture on marine environments presenting a variable sensitivity to organic sewage, (ii) analyse the socio-economical aspects and profitability of the aquaculture industry and of common resources (iii) use remote sensing and geographical data bases for diagnosis and monitoring of site degradation (iv) reinforce the capacity of Asian scientists through training. Severa! aquaculture sites have been investigated in the Lampung region (South Sumatra, Indonesia), the Mekong delta (Vietnam) and on the West coast of New-Caledonia, providing a large range of typical ecosystems encountered in Asia and in the Pacifie, from coralline sites to coastal plains with mangrove and deltaic areas. The study concerned the spatial structure and seasonal influence of these ecosystems, the temporal variation during the course of the project (3 years) and the relation between the ecological structure and farm productions. Remote sensing provides a synoptic vision over large land expanses. Severa! scenes were processed for landuse mapping using conventional classification techniques. Concerning water quality assessment, a general relation for the Java sea was found between image and field data in terms of total suspended matter. Applying this relation to a new site in Sumatra has provided an initial approach to water type and, together with land use mapping, a preliminary assessment of the suitability of the area to shrimp aquaculture development. Socio-economic research has been focused on the identification ofneeds for collective action, including public policy, in the perspective of shrimp farming sustainability. The main concern is in the regulation of shrimp farming intensification and extensification at the scale of coastal ecosystemic entities in a common property resource management perspective. The common considered here is coastal water quality. Comparing the local development profiles and the institutional grounds for the design and implementation of collective management rules shows that variables such as land tenure system, farm owner socio-economic profile, social homogeneity or heterogeneity of the farmers are key factors to analyse the potential for sustainability. The defmition of water quality and the possible means to ensure its collective management are discussed. The main conclusion is that the economie incentives to farming development are strong but there is no significant difference among traditional, semi-intensive and intensive systems in terms of economie efficiency or wealth distribution. The description of the functioning of the different kinds of ecosystems make it possible to give an advice concerning the positioning of the activity inside the ecosystem, and furthermore to have a reference state in order to determine the impact of the activity on the coastal environnement. This impact can be summarized as an increase in the concentration of total suspended matt€?r, of particulate organic matter and of sulfate reducing bacterias. This organic ma~.er is either issued from rearing activities or from telluric origine, due to mangrove eradication when building the ponds. An evaluation of the relationship existing between productivity and characteristics of each ecosystem bas been conducted by correlating ecological indicators data (concentration of total suspended matter, particulate organic matter, chlorophyll, percentage of pheopigments in total pigments and cyanobacteria and sulfatereducing bacteria in water and sediments) with the average production of the farms. This comparison lead to the compilation of a scale of observed production integrating the range of these environmental parameters with shrimp production levels, bound to facilitate the positioning of shrimp farming in relation with the confmement leve! of each ecosystem. Lastly, ali geographie data originated from the various compartments of the study have been geo-referenced and loaded into a geographical information system. This allows to display any query made on spatial variables and their related statistical data, including the ir variations over the last few years and to reveal patterns and phenomena otherwise not obvious.
Le programme mis en oeuvre par la DRV (Paris, CREMA-L'Houmeau, DELIAO Brest, COP Tahiti, GIE/RA Nouvelle Calédonie), dans le cadre d'un projet européen STD3 «(Sciences et Technique au Service du Développement», en collaboration avec l'Université de Montpellier II, l'Ecole Nationale d'Agronomie de Rennes, l'ITC (Hollande), l'Institut Océanographique de Nha Trang (Vietnam), le BADC de Jepara et le BPPT de Jakarta (Indonésie), avait pour but la mise au point de méthodes permettant d'améliorer la sélection des sites ainsi que le suivi du développement et de l'impact de l'aquaculture des crevettes Péneides en milieu tropical pour éviter la surexploitation. Quatre axes de recherche ont été défmis : a) identifier la nature et quantifier les rejets de déchets issus de ce type d'aquaculture, b) définir les caractéristiques écologiques des écosystèmes susceptibles d'accueillir l'activité aquacole et suivre leur évolution sous l'influence des rejets, c) déterminer l'influence de la gestion des fermes et des ressources (aspects économiques) sur les performances de productivité, d) déterminer la capacité de la télédétection comme outil de diagnostic d'impact à l'échelle de la région, e) mener un programme de formation d'étudiants et jeunes chercheurs Vietnamiens et Indonésiens.

Droits : 1998 Ifremer
http://archimer.ifremer.fr/doc/00132/24357/22357.pdf
http://archimer.ifremer.fr/doc/00132/24357/

Éditeur(s) : HAL CCSD
Résumé : International audience
The challenge is to implement research that can estimate the consequences ofclimate changes in terms of impact on terrestrial environments and resources.Emphasis should be placed on regions dependent on natural resources and forwhich demographic pressure is strong. Simulations obtained from climate modelprojections (using different Representative Concentration Pathways (RCPs))predict that the Mediterranean basin and its southern periphery are particularlyvulnerable to water resources and environmental impact (IPCC, AR5, 2013).An annual rainfall decrease by 30% is found for the projection period 2070-2099(IPCC, AR5, 2013) associated with a decrease in water resources by 30 to 50%(Milano, 2012). In addition, several studies using regional atmospheric modelsindicate an increase in the precipitation inter-annual variability with extremeevents and a spatial heterogeneous signature, superimposed on a decrease in thetotal precipitation amount (Giorgi and Lionello, 2008; Raible et al. 2010).Currently, regional climate projections are highly sensitive to the climate modelused. In particular, spatial resolution as well as local climate conditions seemto impact significantly on the simulations (Jacob et al. 2014).The Mediterranean region, at the interface between arid and temperate climateswith several mountainous areas, is a complex climate system affected by theinteractions between mid-latitude and sub-tropical processes. In this context,Morocco, located at the transition between a temperate climate to the North anda tropical climate to the south constitutes a key area for an impact and sensitivitystudy to global climate changes. The climate is influenced by the Atlantic Ocean,the Mediterranean Sea and the Sahara, together with a very steep orography inthe Atlas region. The precipitation distribution is therefore characterised by greatspatial variability, and exhibits a marked seasonality, a strong inter-annualvariability (Ouda et al. 2005) and in general a pronounced gradient from northto south and west to east. At a broader scale, Morocco is located on the subtropicalsubsidence path and between the Acores High and the Saharan Low (Agoussine,2003). Several studies have also identified strong links with inter-annualprecipitation variability and NAO index (Knippertz, 2003) as well as remoteclimate modes (Esper et al. 2007).Continental climate variability at a local/regional scale, if it is to be integratedin climate predictions, needs to be supported by long-term observation.Meteorological stations in Morocco provide climatic data mainly for the last40 years with only a few stations located in the mountainous region (Tramblayet al. 2012; 2013; Driouech et al. 2010). This climate database is also supportedby the IAEA network providing stations for which isotope tracers have beenapplied to daily/monthly rain and water vapour samples over 2 to 3 years between2000 and 2004. Besides the poor coverage of instrumented areas, lacustrinesystems can provide a climatic data set that offers access to short and long-termtime series of climate parameters when knowledge of modern lake water balanceis combined with lacustrine sedimentary-climate records. Lake sediment recordsideally provide high resolution climate/environmental information of the last10,000 years (Magny et al. 2013). This time interval (corresponding to theHolocene) is a key period to investigate short and long-term climate variabilityand to improve prediction in a warming climate.In this study we present an integrated approach focusing on a mountainous lake(Aguelmam Azigza). The modern lake system study is based on site monitoring(2012-2016) and available regional hydro-climatic data. These data show thatlake level changes during the instrumented period were mainly driven byprecipitation following the high inter-annual variability. These data are thencompared with accurately dated short sediment cores retrieved in the same lake.Micro-scale geochemical and sedimentological analyses of these sequencesenable us to identify various sedimentary facies that can be linked with periodsof high (low) lake levels over the past decades.
The Mediterranean Region under Climate ChangeLa méditerranée face au changement climatique

insu-01394690
https://hal-insu.archives-ouvertes.fr/insu-01394690
https://hal-insu.archives-ouvertes.fr/insu-01394690/document
https://hal-insu.archives-ouvertes.fr/insu-01394690/file/Vidaletal.2016-COP22-Chap1.pdf

Résumé : Les forêts tropicales contiennent dans leur biomasse aérienne un stock de carbone important à l’échelle de la planète. Mesurer ce stock et comprendre son fonctionnement permet de mieux saisir les enjeux liés à sa protection, sa destruction ou sa modification, ainsi que son rôle dans le cycle du carbone et les mécanismes climatiques globaux. Dans le cadre des problématiques économiques et écologiques liés au climat, les forêts sont progressivement prises en compte dans les programmes internationaux de mesures visant à réduire l’impact anthropique sur le climat (Protocole de Kyoto, 1998 ; Accord de Copenhague, 2009). L’intégration des forêts dans les mécanismes financiers liés au marché du carbone est clairement envisagée dans les années à venir (marché de carbone « d’origine forestière »).L’estimation de la biomasse aérienne d’une parcelle de forêt inventoriée nécessite l’utilisation successive de plusieurs modèles. Dans ces parcelles, le diamètre et l’espèce de chaque arbre sont renseignés. Ensuite, ces parcelles sont utilisées comme références pour l’extrapolation spatiale des valeurs de biomasse. Cette extrapolation repose souvent sur le traitement de signaux aériens (avions, satellites). Il est aussi possible d’utiliser covariables environnementales (climat, géologie, …).L’incertitude associée à l’estimation de la biomasse d’une région est le résultat de toutes les incertitudes associées à ces différents processus. Les connaissances actuelles ne nous permettent pas de quantifier cette incertitude. L’objectif de la thèse est de développer une méthodologie d’estimation de la biomasse qui permette la propagation des incertitudes ainsi que l’identification des sources de cette incertitude.Modèle de hauteur : Nous proposons un nouveau modèle de hauteur pour les forêts tropicales. Les paramètres de ce modèle ont un sens écologique et peuvent être prédits par des variables décrivant le peuplement sur lequel il est appliqué. Nous avons utilisé les données des projets Amalin et Bridge et sélectionné 42 parcelles réparties en Guyane dans lesquelles le diamètre et la hauteur de chaque arbre ont été mesurés.Modèle de densité de bois : Un modèle à été conçu pour associer à chaque espèce une distribution de densité de bois et non une valeur fixe. Nous avons utilisé les données du projet Bridge dans lequel la densité de bois a été mesurée sur 2504 arbres représentant 466 espèces.Modèle de biomasse: Nous avons montré par une analyse de sensibilité que les incertitudes des prédictions de hauteur et de densité de bois n’avaient qu’une part négligeable dans l’incertitude des prédictions de biomasse. L’amélioration de la précision de ces modèles n’est donc pas une priorité. En revanche, le modèle de hauteur peut être une source de biais.Modélisation spatiale : Les modèles développés ont été appliqués à différents réseaux de parcelles couvrant bien la zone littorale guyanaise : inventaires papetiers de l’ONF, réseau Guyafor, projet Amalin… Les prédictions de biomasse de ces parcelles sont utilisées dans un modèle spatiale. Nous produisons ainsi une carte de biomasse guyanaise associée à une carte de l’incertitude de cette estimation.
Tropical forest yield and important part of the aerial vegetation carbon stock on earth. Measuring and understanding this stock distribution is crucial for the management of the tropical forests facing the actual environmental challenges (REDD+, carbon market).Aerial Biomass estimation of forest census plots requires few models depending on the precision of the inventory: diameter models, height models, wood density models. Spatial extrapolation between census plots relies on aerial data (satellite measurements, images) or ground-based data (geology, altitude).The uncertainty of the estimation of a region’s biomass is the result of the uncertainty brought by all these models. The aim of the thesis is to develop models and methods to estimate the biomass of a region while propagating the uncertainties. This is applied to the neo-tropical forest of French Guiana (South America, Guianas Plateau).

http://www.theses.fr/2012AGUY0567/document

Éditeur(s) : HAL CCSD
Résumé : Aricle soumis à Solar Energy
In order to qualify the fluctuating nature of solar radiation under tropical climate, we classify daily distributions of the clearness index kt by estimating a finite mixture of Dirichlet distributions without assuming any parametric hypothesis on these daily distributions. The method is applied to solar radiation measurements performed in Guadeloupe (16°2 N, 61 W) where important fluctuations can be observed even within a short period of a few minutes. The results put in evidence four distinct classes of distributions corresponding to different types of days. The sequence of such classes can be of interest for prediction.
https://hal.archives-ouvertes.fr/hal-00289567

hal-00289567
https://hal.archives-ouvertes.fr/hal-00289567
https://hal.archives-ouvertes.fr/hal-00289567/document
https://hal.archives-ouvertes.fr/hal-00289567/file/Article_Classif_soumis.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In order to qualify the fluctuating nature of solar radiation under tropical climate, we classify daily distributions of the clearness index kt by estimating a finite mixture of Dirichlet distributions without assuming any parametric hypothesis on these daily distributions. The method is applied to solar radiation measurements performed in Guadeloupe (16°2 N, 61 W) where important fluctuations can be observed even within a short period of a few minutes. The results put in evidence four distinct classes of distributions corresponding to different types of days. The sequence of such classes can be of interest for prediction.
ISSN: 0038-092X

hal-01527878
https://hal.archives-ouvertes.fr/hal-01527878
DOI : 10.1016/j.solener.2009.01.010

Éditeur(s) : HAL CCSD Elsevier
Résumé : The depth of the oceanic lithosphere–asthenosphere boundary (LAB), as inferred from shear wave velocities, increases with lithospheric age, in agreement with models of cooling oceanic lithosphere. On the other hand, the distribution of radial anisotropy under oceanic plates is almost age-independent. In particular, radial anisotropy shows a maximum positive gradient at a depth of ∼70 km, which, if used as a proxy, indicates an age-independent LAB depth. These contrasting observations have fueled a controversy on the seismological signature of the LAB. To better understand the discrepancy between these observations, we model the development of lattice preferred orientation (LPO) in upper mantle crystal aggregates and predict the seismic anisotropy produced by plate-driven mid-ocean ridge flows. The model accounts for the progressive cooling of the lithosphere with age and can incorporate both diffusion and dislocation creep deformation mechanisms. We find that an age-independent distribution of radial anisotropy is the natural consequence of these simple flows. The depth and strength of anisotropy is further controlled by the deformation regime – dislocation or diffusion creep – experienced by crystals during their ascent towards, and subsequent motion away from, the ridge axis. Comparison to surface wave tomography models yield constraints on rheological parameters such as the activation volume. Although not excluded, additional mechanisms proposed to explain some geophysical signatures of the LAB, such as the presence of partial melt or changes in water content, are not required to explain the radial anisotropy proxy. Our prediction, that the age-independent radial anisotropy proxy marks the transition to flow-induced asthenospheric anisotropy, provides a way to reconcile thermal, mechanical and seismological views of the LAB.
ISSN: 0012-821X

hal-01553243
https://hal.archives-ouvertes.fr/hal-01553243
DOI : 10.1016/j.epsl.2016.12.004

Éditeur(s) : HAL CCSD
Résumé : National audience
The Lesser Antilles subduction zone has produced no recent strong thrust earthquakes, making it difficult to quantify the seismic hazard from such events. The Lesser Antilles arc has a low subduction rate and an accretionary wedge that is very wide at its southern end. To investigate the effect of the wedge on seismogenesis, numerical models of forearc thermal structure were constructed along six transects perpendicular to the arc in order to determine the thermally predicted width of the seismogenic zone. The geometry of each section is constrained by published seismic profiles and crustal models derived from gravity and seismic data and by earthquake hypocenters at depth. A major constraint on the deep part of the model is that mantle temperature beneath the volcanic arc should achieve a temperature of 1,100°C to generate partial melts. Predicted surface heat flow is compared to the available heat flow observations. Thermal modeling results indicate a systematic southward increase in the width of the seismogenic zone, more than doubling in width from north to south and corresponding to a dramatic southward increase in forearc width (distance from the arc to the deformation front of the accretionary wedge). The minimum width of the seismogenic zone (distance between the intersections of the subduction interface with the 150°C and 350°C isotherms) increases from about 80 km, north of 16°N, to 230 km, at 13°N. The maximum width (between the 100°C and 450°C isotherms) ranges from about 150 km in the north to up to 320 km in the south. This large variation in the width of the seismogenic zone is a consequence of the increasing width of the accretionary wedge to the south, caused by the increased thickness of sediment on the subducting plate. There is good agreement between the thermally predicted seismogenic limits and the sparse distribution of recorded thrust earthquakes, which are observed only in the northern portion of the arc. Possible scenarios for mega-thrust earthquakes are discussed. Depending on the segment length (along-strike) of the rupture plane, the occurrence of an event of magnitude 8-9 cannot be excluded.
Bulletin Société Géologique de France

insu-00814056
https://hal-insu.archives-ouvertes.fr/insu-00814056
DOI : 10.2113/gssgfbull.184.1-2.47

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Porous thin films considered for applications like separation, sensing and microelectronic have to sustain mechanical stresses during their integration process or in working conditions. Thanks to recent progress in processing methods, it is now possible to precisely control the porosity and combine ordered mesopores with randomly-distributed macropores to achieve hierarchically porous materials. The mechanical properties of thin films containing different types of porosity (ordered meso, random macro and hierarchical) have been investigated by means of nanoindentation. In particular a method recently proposed by Li and Vlassak (H. Li, J.J. Vlassak, Journal of Materials Research 24 (2009) 1114-1126) is applied to account for the substrate effect. Residual indent impressions were imaged by Atomic Force Microscopy (AFM) to provide some insights in the mechanical behavior of the films. In addition, experimental indentation moduli are compared to theoretical predictions obtained via Finite Element (FE) analysis. The different porous structures have been modeled by FE to obtain the effective elastic properties from which the indentation modulus can be inferred. Finally, the experimental-model differences are discussed. © 2010 Elsevier Inc. All rights reserved.
ISSN: 1387-1811

hal-01683194
https://hal.univ-antilles.fr/hal-01683194
DOI : 10.1016/j.micromeso.2010.09.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerical programs for simulating flow and reactive transport in porous media is essential for predicting reservoir properties related to CO2 sequestration performance, subsurface storage and risk assessment. In this paper we solve the Navier Stokes' equation using finite difference method, on a simulated porous rock structure, to study the velocity distribution of fluid flowing through it under a constant pressure gradient. A reactive solute carried through the fluid is allowed to interact with the minerals in the rock. This chemical reaction dissolves the mineral which changes the rock structure thus affecting its flow properties. These changes of flow properties are studied with variation in reactive solute concentration and pressure field. The different mechanisms of dissolution responsible for the variation of flow properties for the different parameters is predicted. Before the onset of homogeneous dissolution, variation in porosity follows a power-law behaviour with change in permeability when the latter is scaled by the concentration of the reactive species. The simulation results are compared with available experimental data and found to give a reasonable match.
ISSN: 0022-1694

hal-00757760
https://hal.archives-ouvertes.fr/hal-00757760
DOI : 10.1016/j.jhydrol.2012.05.024

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We aim at testing and validating a mobile-immobile mass transfer model from a set of single-well injection withdrawal tracer tests in a heterogeneous porous aquifer. By varying the duration of the injection phase, different volumes of aquifer are investigated by the tracer. Hence, we focus the transport model validation not only on reproducing a single breakthrough curve (BTC) but also on the model's capacity to predict the amount of mixing as a function of the volume visited by the tracer. All the BTCs are strongly asymmetric, as expected when dispersion is controlled by diffusive mass transfers between the mobile water and the immobile water part of the porosity. However, the BTC cannot be modeled by a conventional mobile-immobile mass transfer model with a simple power law memory function. To account for that, we implement a continuous time random walk model in which the transition time distribution y (t), which is related to the excursion time probability of the tracer in the immobile domain, is a dual-slope power law distribution. The model best fits the BTC data set with a transitional regime controlled by y(t) t2 and an asymptotic regime characteristic of the conventional double-porosity model with y(t) t1.5 . This work emphasizes that high-resolution concentration measurement and multiple-scale tracer tests are required for assessing solute dispersion models in heterogeneous reservoirs and for subsequently obtaining reliable predictions.
ISSN: 0043-1397

insu-00373698
https://hal-insu.archives-ouvertes.fr/insu-00373698
https://hal-insu.archives-ouvertes.fr/insu-00373698/document
https://hal-insu.archives-ouvertes.fr/insu-00373698/file/Borgne_et_al-2008-Water_Resources_Research.pdf
DOI : 10.1029/2007WR006279

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The reactivation of faults with near-optimal orientations is commonly considered to control the state of stress in the crust. Near the surface, where a principal stress direction is vertical, the attitude of such faults is explained by Anderson's theory. This raises the questions of how prevalent this type of faulting actually is in current seismicity, down to what depth it frequently occurs, and what range of friction angles explains it best. The Global Centroid Moment Tensor catalog is analyzed to address these questions. Dip-slip and strike-slip mechanisms are dominant, and oblique slips are relatively rare for well-constrained events with depths shallower than 30 km. Preferred Andersonian faulting is the simplest, but not the unique, explanation for this dominance. Isolating reverse, strike- slip, and normal events reveals an asymmetry in the distribution of nodal plane dips and plunges of the P, B, and T axes between reverse and normal faulting. Assuming that the most frequent events correspond to reactivation near optimal orientations yields 40-60 degrees and 0-20 degrees friction angles for reverse and normal faults, respectively. This indicates that reverse and normal faulting mechanics are not symmetrical with respect to stress configuration as predicted by Anderson's theory.
ISSN: 8755-1209

hal-00412159
https://hal.archives-ouvertes.fr/hal-00412159
DOI : 10.1029/2007RG000240

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Precise mapping of above-ground biomass (AGB) is a major challenge for the success of REDD+ processes in tropical rainforest. The usual mapping methods are based on two hypotheses: a large and long-ranged spatial autocorrelation and a strong environment influence at the regional scale. However, there are no studies of the spatial structure of AGB at the landscapes scale to support these assumptions. We studied spatial variation in AGB at various scales using two large forest inventories conducted in French Guiana. The dataset comprised 2507 plots (0.4 to 0.5 ha) of undisturbed rainforest distributed over the whole region. After checking the uncertainties of estimates obtained from these data, we used half of the dataset to develop explicit predictive models including spatial and environmental effects and tested the accuracy of the resulting maps according to their resolution using the rest of the data. Forest inventories provided accurate AGB estimates at the plot scale, for a mean of 325 Mg.ha^-1. They revealed high local variability combined with a weak autocorrelation up to distances of no more than10 km. Environmental variables accounted for a minor part of spatial variation. Accuracy of the best model including spatial effects was 90 Mg.ha^-1 at plot scale but coarse graining up to 2-km resolution allowed mapping AGB with accuracy lower than 50 Mg.ha^-1. Whatever the resolution, no agreement was found with available pan-tropical reference maps at all resolutions. We concluded that the combined weak autocorrelation and weak environmental effect limit AGB maps accuracy in rainforest, and that a trade-off has to be found between spatial resolution and effective accuracy until adequate “wall-to-wall” remote sensing signals provide reliable AGB predictions. Waiting for this, using large forest inventories with low sampling rate (<0.5%) may be an efficient way to increase the global coverage of AGB maps with acceptable accuracy at kilometric resolution
ISSN: 1932-6203

hal-01269305
https://hal.archives-ouvertes.fr/hal-01269305
DOI : 10.1371/journal.pone.0138456
PRODINRA : 326359

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Transport of liquid and gaseous hydrocarbons through focused fluid flow systems is a widespread process in continental margins and sedimentary basins, which is gaining increased attention in the assessment of geohazards, environment conservation, and securing fossil energy resources. Studying the abundance, distribution and drivers for this process is crucial for understanding its role in 1) the dynamics of gas hydrate accumulation and destabilization, 2) submarine slope stability and related tsunamis, 3) the plethora of chemosynthetic benthic ecosystems that develop in deep seep sites, and 4) the input of greenhouse gases (e.g. methane) into the ocean/atmosphere system, which may influence the atmospheric carbon budget and Earth's paleo- and present climate. New ocean exploration tools provide ever more data and improve our understanding of these systems. However, the subject still suffers from a lack of interdisciplinary knowledge dissemination. The ongoing international debate about the timing and the processes that control fluid expulsion in sedimentary basins is fuelled by their implications for structural and petroleum geology. Because fluids expelled at cold seeps originate at depth they represent open windows into the underlying petroleum systems and are valuable indicators for the reservoir systems. They may also help in deciphering past and predicting future climate change because worldwide release of large amounts of fluids may have an impact on the chemistry of the ocean and atmosphere.
ISSN: 0025-3227

hal-00772472
https://hal.archives-ouvertes.fr/hal-00772472
DOI : 10.1016/j.margeo.2012.10.012

Éditeur(s) : HAL CCSD BioMed Central
Résumé : [b]Background[/b]: [i]Amblyomma variegatum[/i] and [i]A. hebraeum[/i] are two ticks of veterinary and human health importance in south-east Africa. In Zimbabwe they occupy parapatric (marginally overlapping and juxtaposed) distributions. Understanding the mechanisms behind this parapatry is essential for predicting the spatio-temporal dynamics of Amblyomma spp. and the impacts of associated diseases. It has been hypothesized that exclusive competition between these species results from competition at the levels of male signal reception (attraction-aggregation-attachment pheromones) or sexual competition for mates. This hypothesis predicts that the parapatry described in Zimbabwe could also be present in other countries in the region. [br/][b]Methods[/b]: To explore this competitive exclusion hypothesis we conducted field surveys at the two species' range limits in Mozambique to identify areas of sympatry (overlapping areas) and to study potential interactions (communicative and reproductive interference effects) in those areas. At sympatric sites, hetero-specific mating pairs were collected and inter-specific attractiveness/repellent effects acting at long and short distances were assessed by analyzing species co-occurrences on co-infested herds and co-infested hosts.[br/] [b]Results[/b]: Co-occurrences of both species at sampling sites were infrequent and localized in areas where both tick and host densities were low. At sympatric sites, high percentages of individuals of both species shared attachment sites on hosts and inter-specific mating rates were high. Although cross-mating rates were not significantly different for[i] A. variegatum[/i] and [i]A. hebraeum[/i] females, attraction towards hetero-specific males was greater for [i]A. hebraeum[/i] females than for A. variegatum females and we observed small asymmetrical repellent effects between males at attachment sites.[br/][b]Conclusions[/b]: Our observations suggest near-symmetrical reproductive interference between [i]A. variegatum[/i] and [i]A. hebraeum[/i], despite between-species differences in the strength of reproductive isolation barriers acting at the aggregation, fixation and partner contact levels. Theoretical models predict that sexual competition coupled with hybrid inviability, greatly reduces the probability of one species becoming established in an otherwise suitable location when the other species is already established. This mechanism can explain why the parapatric boundary in Mozambique has formed within an area of low tick densities and relatively infrequent host-mediated dispersal events.
ISSN: 1756-3305

hal-01220744
https://hal.archives-ouvertes.fr/hal-01220744
https://hal.archives-ouvertes.fr/hal-01220744/document
https://hal.archives-ouvertes.fr/hal-01220744/file/2015%20Bournez%20Parasites%20%26%20Vectors_%7B365AAFF5-7041-480B-9B77-9CD0485A9B72%7D.pdf
DOI : 10.1186/s13071-015-1116-7

Éditeur(s) : HAL CCSD
Résumé : Tropical forests are a biodiversity hotspot, with the coexistence of numerous species until a fine spatial scale. Particularly, 16.000 tree species coexist in Amazonia, 1.800 in Frenche Guiana and between 120 and more than 200 tree species per hectare. However, there are some uncertainties in maintaining diversity in regard to global changes. Hence before predicting the diversity evolution face of global changes, fundamental studies are needed to understand which assembly processes are involved in the maintenance of diversity. These fundamental studies still relevant given the lack of consensus on the relative importance of assembly processes. This thesis is a continuation of these fundamental studies, using innovative integrative approach, at multi-scale, to address three types of diversity: taxonomic diversity, functional and phylogenetic. Our results challenge the importance of environmental filtering for hydrological and chemical properties of soils, versus the importance of biotic interactions on community assembly. Furthermore, our results suggest that species distributions could be affected by forest dynamics related to falling trees and therefore by light availability. Finally, we have highlighted the importance of dispersal limitation on community assembly.
Les forêts tropicales représentent un ‘hotspot’ de diversité avec un nombre considérable d’espèces qui coexistent jusqu’à une échelle locale fine. Plus particulièrement, 16 000 espèces d’arbres coexistent en Amazonie, 1 800 en Guyane française et entre 120 et plus de 200 espèces d’arbres par hectare. Cependant, le maintien de cette diversité face aux changements globaux actuels et à venir (qu’ils soient anthropiques ou climatiques…) est incertain. Avant de pouvoir prédire l’évolution de la diversité face aux changements globaux, un travail fondamental est nécessaire afin de comprendre les processus d’assemblage des communautés, processus qui maintiennent cette diversité. Ce travail est réalisé depuis de nombreuses années en écologie et reste d’actualité vu l’absence de consensus quant à l’importance relative des processus d’assemblage. Cette thèse s’inscrit dans la continuité de ce travail fondamental en utilisant une approche intégrative innovante, qui aborde de manière multi-échelle trois types de diversité : diversité taxonomique, fonctionnelle et phylogénétique. Nos résultats questionnent sur l'importance du filtrage environnemental quant aux propriétés hydrologiques et chimiques des sols, et sur celle des interactions biotiques dans l’assemblage de la communauté étudiée. Par ailleurs, nos résultats suggèrent que les distributions d’espèces puissent être influencées par la dynamique forestière en lien avec les chutes d’arbres et donc avec la disponibilité en lumière. Enfin, nous avons mis en évidence l’importance de la limitation de dispersion.
https://tel.archives-ouvertes.fr/tel-01418447

NNT : 2016YANE0003
tel-01418447
https://tel.archives-ouvertes.fr/tel-01418447
https://tel.archives-ouvertes.fr/tel-01418447/document
https://tel.archives-ouvertes.fr/tel-01418447/file/these.pdf