Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust=mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the lithosphere. Lateral rheological heterogeneity of the continental lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff lithosphere. On the other hand, rifting may also modify the thermal structure of the lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the continental lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry, and the intrinsic properties (rheological heterogeneity and mechanical anisotropy) of the continental plates.
ISSN: 0040-1951

hal-01389719
http://hal.univ-reunion.fr/hal-01389719
http://hal.univ-reunion.fr/hal-01389719/document
http://hal.univ-reunion.fr/hal-01389719/file/vauchez_etal_rheology_1998_hal.pdf
DOI : 10.1016/S0040-1951(98)00137-1

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The basement of central Madagascar displays two contrasted structural patterns. The first one (D1) is characterized by north-striking foliations that are gently dipping to the west and carry W- to WSW-plunging lineations, whereas the second one (D2) is characterized by steeper foliations that are striking to the NNE and lineations that are either subhorizontal or gently plunging to the SSW. The younger pattern is related to late-Panafrican tectonics along the major Angavo shear zone that is about 1000 km in length and 40 km in width with apparently little offset. Deformation in the Angavo zone induced interference folding on both sides. The D2 event is characterized by low pressures (ca 400 MPa) and high temperatures (up to 790 degrees C) responsible for prograde granulite facies conditions, that resulted from heat transfer due to magma and fluid advection in the Angavo shear zone. The D2 event is pinned at 550 +/- 11 Ma by a new monazite age from a reoriented Andringitrean granite near Ankaramena. A new suite of amphibole and biotite Ar-Ar geochronological data enables to retrace the thermochronogical evolution inside and outside the Angavo shear zone. Combined with new structural results from the western interference zone. these ages yield a better understanding of the late-Panafrican history of central Madagascar. No diachronism is observed along the strike of the Angavo shear zone. Conversely, amphibole and especially biotite ages decrease from West to East, i.e. towards the shear zone. These new ages range from 511 to 469 Ma. A 1-D conductive model constrains the thermal effect in relation with the Angavo shear zone to be restricted to a lateral distance of ca 60 km (in map view) for a maximum heating duration of 20 Myr. This is in agreement with the Ar-Ar data and with the width of the observed interference zone. Following this episode of deformation and heat transfer, the estimated cooling rates of the Angavo shear zone range from to 15 to 6 degrees C/Myr, respectively before and after 515 Ma. A post-collision intracontinental setting is suggested for the Angavo shear zone, which is regarded as a remote effect of the Kuunga Orogeny between India and Antarctica.
ISSN: 0040-1951

hal-00463507
https://hal.archives-ouvertes.fr/hal-00463507
DOI : 10.1016/j.tecto.2009.03.009

Éditeur(s) : HAL CCSD International Phycological Society
Résumé : International audience
We studied a group of monoraphid diatom species (Bacillariophyceae, Achnanthidiaceae) found in the marine coastal environment of tropical islands of the Caribbean Sea, western Atlantic Ocean, Indian Ocean, South Pacific Ocean, the Adriatic Sea and the Black Sea. Based on light and electron microscope examination, Madinithidium was formally described as a genus new to science with the generitype defined as Madinithidium undulatum. The characteristic features of the valve structure are a strongly developed sternum and raphe sternum, transapical striae formed by a single areola (macroareolae) positioned in small depressions, elevated virgae and coaxial internal central raphe endings. Furthermore, the striae of both raphe and sternum valves are closed by finely perforated hymenes. Madinithidium and Achnanthidium species are difficult to identify correctly with light microscopy since their valves are small and finely structured. Four species recently described from the western Indian Ocean and assigned to Achnanthidium sensu lato – Achnanthidium capitatum, A. flexuistriatum, A. pseudodelicatissimum and A. scalariforme – possessed morphological features permitting their placement into Madinithidium gen. nov. The above-mentioned species were formally transferred to the new genus.
ISSN: 2330-2968

hal-01333391
https://hal-univ-perp.archives-ouvertes.fr/hal-01333391
DOI : 10.2216/14-21R2

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We derive a general formulation of the time domain random walk (TDRW) approach to model the hydrodynamic transport of inert solutes in complex geometries and heterogeneous media. We demonstrate its formal equivalence with the discretized advection-dispersion equation and show that the TDRW is equivalent to a continuous time random walk (CTRW) characterized by space-dependent transition times and transition probabilities. The transition times are exponentially distributed. We discuss the implementation of different concentration boundary conditions and initial conditions as well as the occurrence of numerical dispersion. Furthermore, we propose an extension of the TDRW scheme to account for mobile-immobile multirate mass transfer. Finally, the proposed TDRW scheme is validated by comparison to analytical solutions for spatially homogeneous and heterogeneous transport scenarios.
ISSN: 0043-1397

hal-01356319
https://hal.archives-ouvertes.fr/hal-01356319
DOI : 10.1002/2015WR018511

Éditeur(s) : Elsevier
Résumé : The study, which is based on repetitive bathymetric surveys, assesses changes and effects of one of the most important floods recorded in the Rhone Delta area: bottom morphology and sediment distribution in the Rhone outlet after the December 2003 flood are discussed by comparison between Digital Terrain maps (DTMs) of November 2003 and January 2004. The post-flood morphology shows that the whole of the system is active, mainly in the east. The channel of the Rhbne has been hollowed out on the left bank by more than 5 m, the eastern coast of the mouth has retreated 400 m, the mouth-bar has prograded 200 m and the slope of the delta front has increased by 0.19. The overlay of pre- and post-flood DTMs makes it possible to estimate the total volume deposited in the [0 to -20 m] zone as +7.8 X 10(6) m(3) (i.e. 0.88 m(3) m(-2)), which corresponds to 4 X 10(6) t of sediment. These values are compared with the average annual volume of 0.47 X 10(6) m(3) yr(-1) of sediment deposited in this zone between 1995 and 2003, as well as the average sediment load estimated at the Arles station (50 km upstream) for this flood event (3.1 x 10(6) t to 5.3 x 10(6) t). The acquisition of bathymetric measurements immediately before and after a major flood allows more than a simple morphological description; in addition, an analysis of the solid load transfer processes towards the prodelta is achievable. Three mechanisms are highlighted. Most of the material eroded in the channel and supplied to the delta front corresponds to fine sediment that drape homogeneously over the pre-flood morphology of the delta front. The transit of the coarsest sediment (primarily sand) is slowed down in the channel of the Rh6ne: this sediment builds up in relatively small areas, leading to the formation of gullies on the prodelta slope. The gullies have fixed positions and disappear gradually towards the west, following the progressive migration of the active band towards the east. These old features are not reactivated by floods occurring after their formation. During the flood, only a small volume of coarse sediment bypasses through the gullies, and the fine deposits are remobilised rapidly or compacted. Flood input concerns essentially the delta front, which traps 90% of the fluvial solid discharge between 0 and 20 m depth. The coarse prodelta supply is then due mainly to mass movements of unconsolidated material deposited beforehand on the top of the delta front. Consequently, the main nourishment of the prodelta does not occur directly during and/or immediately after a flood event, but is delayed by sediment being temporarily trapped on the delta front.
Marine Geology (0025-3227) (Elsevier), 2006-12 , Vol. 234 , N. 1-4 , P. 159-177

Droits : 2006 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-2304.pdf
DOI:10.1016/j.margeo.2006.09.025
http://archimer.ifremer.fr/doc/00000/2304/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Geochemical studies of primitive basalts have documented the presence of crustal-derived garnet pyroxenite in their mantle sources. The processes whereby melts with the signature of garnet pyroxenite are produced in the mantle are, however, poorly understood and somewhat controversial. Here we investigate a natural example of the interaction between melts of garnet pyroxenite derived from recycled plagioclase-rich crust and surrounding mantle in the Ronda peridotite massif. Melting of garnet pyroxenite at ∼1.5 GPa generated spinel websterite residues with MREE/HREE fractionation and preserved the positive Eu anomaly of their garnet pyroxenite precursor in whole-rock and clinopyroxene. Reaction of melts from garnet pyroxenite with depleted surrounding peridotite generated secondary fertile spinel lherzolite. These secondary lherzolites differ from common spinel lherzolite from Ronda and elsewhere by their lower-Mg# in clinopyroxene, orthopyroxene and olivine, lower-Cr# in spinel and higher whole-rock Al2O3, CaO, Sm/Yb and FeO⁎ at a given SiO2. Remarkably, secondary spinel lherzolite shows the geochemical signature of ghost plagioclase in the form of positive Eu and Sr anomalies in whole-rock and clinopyroxene, reflecting the transfer of a low-pressure crustal imprint from recycled pyroxenite to hybridized peridotite. Garnet pyroxenite melting and melt-peridotite interaction, as shown in the Ronda massif, may explain how the signature of subducted or delaminated crust is transferred to the mantle and how a garnet pyroxenite component is introduced into the source region of basalts. The efficiency of these processes in conveying the geochemical imprint of crustal-derived garnet pyroxenite to extruded lavas depends on the reactivity of pyroxenite melt with peridotite and the mantle permeability, which may be controlled by prior refertilization reactions similar to those documented in the Ronda massif. Highly fertile heterogeneities produced by pyroxenite-peridotite interaction, such as secondary spinel lherzolite in Ronda, may nucleate magmatic channels that remain chemically isolated from the ambient mantle and act as preferential pathways for melts with the signature of recycled crust.
ISSN: 0012-821X

hal-00814010
https://hal.archives-ouvertes.fr/hal-00814010
DOI : 10.1016/j.epsl.2012.11.047

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Coastal aquifers often display seawater intrusion resulting in the formation of a salty water wedge progressing inland. This study investigates the mass transfers in the mixing zone at the freshwater-seawater interface where the water is out of equilibrium with the rock-forming carbonates. Investigations were conducted in two boreholes, separated by 5 m, at the Ses Sitjoles test site (Mallorca Island, Spain) where repeated electrical conductivity logs of the formation and the saturating fluid, as well as regular pore-water sampling and permanent downhole multi-parameter monitoring of the water were performed over a period of 9 a. In the mixing zone, the significant acidification, the calcite saturation index profile and the Ca concentration profile cannot be explained by conservative mixing nor by dissolution-precipitation reactions only. Conversely, the analysis of organic C content and of the distinctly different time-resolved pH profiles measured in the two boreholes suggests the development of perennial biomass that triggers calcite dissolution. Moreover, the presence of biomass seems to be correlated with the permeability and vertical connectivity at the meter-scale. It is speculated that the mechanism could be self-activated because the microbiological activity induces calcite dissolution and tends to increase porosity and permeability that favors biomass development.
ISSN: 0883-2927

hal-00937665
https://hal.archives-ouvertes.fr/hal-00937665
DOI : 10.1016/j.apgeochem.2013.09.011

Éditeur(s) : HAL CCSD National Academy of Sciences
Résumé : International audience
All evolutionary biologists are familiar with evolutionary units that evolve by vertical descent in a tree-like fashion in single lineages. However, many other kinds of processes contribute to evolutionary diversity. In vertical descent, the genetic material of a particular evolutionary unit is propagated by replication inside its own lineage. In what we call introgressive descent, the genetic material of a particular evolutionary unit propagates into different host structures and is replicated within these host structures. Thus, introgressive descent generates a variety of evolutionary units and leaves recognizable patterns in resemblance networks. We characterize six kinds of evolutionary units, of which five involve mosaic lineages generated by introgressive descent. To facilitate detection of these units in resemblance networks, we introduce terminology based on two notions, P3s (subgraphs of three nodes: A, B, and C) and mosaic P3s, and suggest an apparatus for systematic detection of introgressive descent. Mosaic P3s correspond to a distinct type of evolutionary bond that is orthogonal to the bonds of kinship and genealogy usually examined by evolutionary biologists. We argue that recognition of these evolutionary bonds stimulates radical rethinking of key questions in evolutionary biology (e.g., the relations among evolutionary players in very early phases of evolutionary history, the origin and emergence of novelties, and the production of new lineages). This line of research will expand the study of biological complexity beyond the usual genealogical bonds, revealing additional sources of biodiversity. It provides an important step to a more realistic pluralist treatment of evolutionary complexity.
ISSN: 0027-8424

hal-01544803
https://hal.archives-ouvertes.fr/hal-01544803
DOI : 10.1073/pnas.1206541109

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7 km to 8 km around the main segment of the fault zone.
ISSN: 0278-7407

hal-01172221
https://hal.archives-ouvertes.fr/hal-01172221
DOI : 10.1002/2014TC003749

Éditeur(s) : HAL CCSD
Résumé : International audience
Despite their dynamic nature, certain chromatin marks must be maintained over the long term. This is particulary true for histone 3 lysine 9 (H3K9) trimethylation, that is involved in the maintenance of healthy differentiated cellular states by preventing inappropriate gene expression, and has been recently identified as the most efficient barrier to cellular reprogramming in nuclear transfer experiments. We propose that the capacity of the enzymes SUV39H1/2 to rebind to a minor fraction of their products, either directly or via HP1α/β, contributes to the solidity of this mark through (i) a positive feedback involved in its establishment by the mutual enforcement of H3K9me3 and SUV39H1/2 and then (ii) a negative feedback sufficient to strongly stabilize H3K9me3 heterochromatin in post-mitotic cells by generating local enzyme concentrations capable of counteracting transient bursts of demethylation. This model does not require direct molecular interactions with adjacent nucleosomes and is favoured by a series of additional mechanisms including (i) the protection of chromatin-bound SUV39H1/2 from the turnovers of soluble proteins, which can explain the uncoupling between the cellular contents in SUV39H1 mRNA and protein; (ii) the cooperative dependence on the local density of the H3K9me3 of HP1α/β-dependent heterochomatin condensation and, dispensably (iii) restricted enzyme exchanges with chromocenters confining the reactive bursts of SUV39H1/2 in heterochromatin. This mechanism illustrates how seemingly static epigenetic states can be firmly maintained by dynamic and reversible modifications. © 2016 Elsevier B.V.
Biochimica et Biophysica Acta - Gene Regulatory Mechanisms

hal-01467548
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01467548
DOI : 10.1016/j.bbagrm.2016.11.006
PUBMED : 27876670

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The tree model and tree-based methods have played a major, fruitful role in evolutionary studies. However, with the increasing realization of the quantitative and qualitative importance of reticulate evolutionary processes, affecting all levels of biological organization, complementary network-based models and methods are now flourishing, inviting evolutionary biology to experience a network-thinking era. We show how relatively recent comers in this field of study, that is, sequence-similarity networks, genome networks, and gene families–genomes bipartite graphs, already allow for a significantly enhanced usage of molecular datasets in comparative studies. Analyses of these networks provide tools for tackling a multitude of complex phenomena, including the evolution of gene transfer, composite genes and genomes, evolutionary transitions, and holobionts.
ISSN: 0966-842X

Droits : http://creativecommons.org/licenses/by-nc-nd/
hal-01300043
http://hal.upmc.fr/hal-01300043
http://hal.upmc.fr/hal-01300043/document
http://hal.upmc.fr/hal-01300043/file/Network-Thinking.pdf
DOI : 10.1016/j.tim.2015.12.003

Éditeur(s) : HAL CCSD
Résumé : International audience
The purpose of our study is to model a geothermal reservoir. When geothermal reservoir are assumed to be composed of pure water, the transfer of mass and energy is classically described by two balance equations: mass balance equation and the energy balance equation. In addition to those equations, fluid velocity ist classically given by the Darcy law while thermodynamic properties, inferred from theoretical or empirical equations of state, are used to close the mathematical system. Once this system is closed, there exist different solutions. The first one is to solve for pressure and temperature with a variable switch to saturation in the two-phase region (e.g. TOUGH2). The second one is to solve for pressure and enthalpy to increase stability of phase transition between single and two-phase states (e.g. Hydrotherm). We adopted the second option and chose te use a splitting method to get rid of the complexity of coupling equations and a finite volume method for the spatial discretization. Selecting object-oriented languages, we developed a multi-language framework, combining Python, Fortran and a C++ implementation of IAPWS (from the freesteam project) including the supercritical equations, in porous media velocity is given by Darcy law and to close the system physical properties are determined by the IAPWS-IF97 thermodynamic formulation. We resolve the equations in pressure and enthalpy instead of pressure and temperature in order to increase stability and to handle easier the passage from a single-phase to a two-phase system. We solve the system by using a splitting method - to get rid of the complexity of coupling equations - and a finite volume method. We offer some freedom to users thanks to the implementation of several methods like explicit or implicit Euler, Runge-Kutta or BDF2 for time solvers or GMRES and BICGSTAB for the linear solver. We can handle several boundary conditions like no-flow - describing a boundary which can not exchange matter with the exterior - or like a mixed-therm condition - a Dirichlet condition to the pressure and a Dirichlet or an outflow condition to the temperature in order to describe a recharge or a discharge zone - ... We're developing a multi-language framework, combining Python, Fortran and the C++ implementation of IAPWS (from the freesteam project). All these languages are object-oriented. We've applied this simulation model to the dogger in Paris, France, to several one-dimensional systems and a two-dimensional one made by Coumou with the CSMP++ platform. The dogger is a reservoir exploited to produce heat by pumping water at 70 and reinjecting it in the reservoir at 40. In the one-dimensional systems we wanted to observe the process of heat transfer from a higher temperature boundary to a smaller one in a high-energy domain. The last simulation shows the natural convection of water in a fault. For every simulation we compared the solutions we found with an other code (TOUGH2 or CSMP++) and they agreed. The next step will be to model the geothermal plant in Guadeloupe, West Indies. It's the only place in France - and in the West Indies so far - producing electricity with the earth power. The temperature can reach up to 1000 and the pressure range is around a few hundreds MPa. In some surface zones we can see two-phase water at atmospheric pressure. In the 1980s Bouillante was a laboratory for France. Since 1995 Bouillante has given 30GWh electricity a year to the Guadeloupeans.
PROCEEDINGS, Thirty-Ninth Workshop on Geothermal Reservoir Engineering
Stanford, United States

Droits : info:eu-repo/semantics/OpenAccess
hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133/document
https://hal-brgm.archives-ouvertes.fr/hal-00944133/file/Copol.pdf

Éditeur(s) : Office Int Epizooties
Résumé : The tremendous development of penaeid shrimp culture across the world over the past twenty years has led to international trade in eggs, larvae and spawners of the best shrimp species for aquaculture. Trade has involved, in particular, the following species: - Penaeus japonicus from Japan to Europe, the Pacific Islands and South America - P. monodon from South-East Asia to almost all tropical countries - P. vannamei and P. stylirostris from countries along the Pacific coast of South and Central America to the United States of America, the islands of the South Pacific, countries along the Atlantic coast of the Americas and certain countries in Africa. In the 1980s, research conducted by American and French teams enabled the breeding of stocks of spawners in captivity. This resulted in the establishment of lines of captive broodstock outside natural areas of distribution, and the development of new breeding farms in previously unproductive regions. Trade related to movements of these species is facilitated by the absence of legislation in most countries; even when such legislation does exist, it is not always applied These practices have led to the rapid development of world shrimp production, but have also contributed to the dissemination of pathogens. In recent years, the occurrence of serious epizootics - occasioning heavy losses world-wide - has led to a more cautious approach involving trade of post-larvae obtained from captive broodstock in which thorough control measures have been implemented for known diseases. Trade in wild shrimp will probably be abandoned progressively, to avoid the risk of introducing new pathogens. The main challenges for research in the near future are the development of diagnostic tools, to enable continuous control of captive broodstock, and the selection of strains which are resistant to the principal pathogens affecting these species.
Revue Scientifique Et Technique-office International Des Epizooties (0253-1933) (Office Int Epizooties), 1996-06 , Vol. 15 , N. 2 , P. 499-515

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00091/20231/17883.pdf
http://archimer.ifremer.fr/doc/00091/20231/

Résumé : in mollusc hatcheries. Consequently, we assessed themost commonly used species to establish their growth and size profiles, their cytomorphological, biochemical, biomolecular identification as well as their cytometer signs, and also their ability to grow under extreme conditions of temperature and salinity. This work aimed at matching the conformity of the strains used in Argenton (dispatched to most of the French commercial hatcheries) to those of a referenced culture collection. A previous screening preceded this study, because of the 45 species and/or clones held originally, Argenton kept no more than 15 species. As most of the latter are also represented in referenced collection, our strains are therefore correctly identified. On the other hand, the combination of several approaches (characteristic of growth and size, cytomorphological description, establishment of biochemical and biomolecular profiles) to discriminate the different species was broadly successful. Nevertheless, flow cytometer measurements were extremely variable from sample to sample, dueto their high sensitivity to the microalga's physiological state. Accordingly, we have developed a method of identification which could be transferred at a national or international level, to the Institutions in charge of microalgae collections. Furthermore, we achieved relevant data to establish an identity card for each of the microalgae suitable for mollusc hatcheries.
La caractérisation des microalgues fourrage constituait l'un des points perfectibles au regard de ce qui est appliquée en microbiologie. Nous avons alors cherché à définir, pour les espèces les plus utilisées en écloserie, leurs profils de croissance et de taille, leur caractéristiques cytomorphologique, cytofluorimétrique, biochimique et biomoléculaire, et enfin, précisé leur aptitude au développement sous des conditions extrêmes de température et de salinité (écotolérance). Ce travail avait pour but de vérifier, d'une part, la conformité des souches utilisées à l'écloserie d'Argenton (auprès de laquelle se fournissent la plupart des écloseries commerciales françaises) en comparant les espèces utilisées à celles issues d'une collection référencée. Un premier balayage avait été réalisé avant la mise en place de cette étude puisque sur les 45 espèces et clones détenus originellement, Argenton ne possédait plus que 15 espèces. La plupart de ces dernières ayant leur équivalent en collection référencée notre souchier est désormais parfaitement identifiée. D'autre part, la confrontation de plusieurs approches, caractéristique de la croissance et de taille, description cytomorphologique, établissement des profils biochimique et biomoléculaire, écotolérance, signature cytofluorimétrique, pour discriminer les différentes espèces de microalgues fourrage a été globalement couronnée de succès. Seule cette dernière technique n'a pas permis de caractériser les espèces entre elles, les paramètres mesurés en cytométrie de flux étant particulièrement sensibles à l'état physiologique des microalgues, très variable d'un échantillon à un autre. Nous disposons dorénavant d'une méthode d'identification qu'il serait souhaitable de transférer, au niveau national voire international, auprès des organismes en charge des collections. De plus, nous disposons dorénavant de données pertinentes pour établir pour chacune des microalgues d'intérêt aquacole une véritable carte d'identité.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2004/rapport-1546.pdf
http://archimer.ifremer.fr/doc/00000/1546/

Éditeur(s) : HAL CCSD Elsevier
Résumé : While most rocks from active volcanoes display ((210)pb/Ra-226) activity ratios lower than or close to the equilibrium value of 1, several other have ratios much higher than 1. Transfer of Rn-222 by magmatic volatiles has often been advocated to explain both Pb-210 deficits and excesses. We develop here a model to account for Pb-210 excesses through Rn-222 accumulation. We show that large Pb-210 excesses can be readily obtained, even for moderate ratios of degassing magma over accumulating magma, in a closed-system model where the Rn-222 atoms produced by decay of Ra-226 in the degassing magma are continuously extracted by a gas phase. For a given duration of volatile transfer, relative Pb-210 excesses are expected to be much larger than Pb-210 deficits. This model is applied to samples from Santorini (Aegean arc) and Surtsey (Iceland) both of which show high ((210)pb/Ra-226) ratios of 6.7 and 2.3 respectively at the time of eruption. The agreement with field data suggests that Rn-222 accumulation leading to Pb-210 excesses might be a rather common process in zoned magma chambers as well as in individual lava flows, and that it can be described by a closed-system model.
ISSN: 0012-821X

hal-00496398
https://hal.archives-ouvertes.fr/hal-00496398
DOI : 10.1016/j.epsl.2010.02.048

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Context: Woodcutting is a very old technology but scientific research is scarce on the subject. In the last 50 years much work on basic mechanisms as well as industrial processes has been done in France. Aims: The specific nature of wood introduces strong differences between wood and metal cutting processes. The paper focuses on French teams' contributions. Results: The basic aspects of the tool–material interaction for different basic modes in woodcutting are highlighted. In primary conversion such as sawing, veneer cutting or green wood chipping, huge progress comes from automation and the possibility of linking the process to log and product quality through new sensors. In secondary processing much has been done on the links between the cutting process, surface qualification and the properties of these surfaces for further processing, such as gluing or coating. Tool wear depends on the cutting process, timber quality, and species. Trade-offs are required in tool technology and coating technologies may improve tool life. Conclusion: A large amount of knowledge and innovation has come from 50 years of worldwide research effort, with France being particularly active in this period. The transfer of skills from metals cutting industry was often a key, but much is needed to move closer to both metal cutting sector and woodcutting skills among craftsmen.
ISSN: 1286-4560

hal-01135156
https://hal.archives-ouvertes.fr/hal-01135156
https://hal.archives-ouvertes.fr/hal-01135156/document
https://hal.archives-ouvertes.fr/hal-01135156/file/Wood_machining_focus_French_research_Thibaut_al_2015.pdf
DOI : 10.1007/s13595-015-0460-2

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Large earthquakes nucleate at tectonic plate boundaries, and their occurrence within a plate's interior remains rare and poorly documented, especially offshore. The two large earthquakes that struck the northeastern Indian Ocean on 11 April 2012 are an exception: they are the largest strike-slip events reported in historical times1, 2 and triggered large aftershocks worldwide3. Yet they occurred within an intra-oceanic setting along the fossil fabric of the extinct Wharton basin, rather than on a discrete plate boundary4, 5, 6, 7, 8. Here we show that the 11 April 2012 twin earthquakes are part of a continuing boost of the intraplate deformation between India and Australia that followed the Aceh 2004 and Nias 2005 megathrust earthquakes, subsequent to a stress transfer process recognized at other subduction zones9, 10. Using Coulomb stress change calculations, we show that the coseismic slips of the Aceh and Nias earthquakes can promote oceanic left-lateral strike-slip earthquakes on pre-existing meridian-aligned fault planes. We further show that persistent viscous relaxation in the asthenospheric mantle several years after the Aceh megathrust explains the time lag between the 2004 megathrust and the 2012 intraplate events. On a short timescale, the 2012 events provide new evidence for the interplay between megathrusts at the subduction interface and intraplate deformation offshore. On a longer geological timescale, the Australian plate, driven by slab-pull forces at the Sunda trench, is detaching from the Indian plate, which is subjected to resisting forces at the Himalayan front6, 8, 11.
ISSN: 0028-0836

hal-00767569
https://hal.archives-ouvertes.fr/hal-00767569
DOI : 10.1038/nature11520

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The Caribbean bivalves Codakia orbicularis (Linnée, 1758) and C. orbiculata (Montagu, 1808) live in seagrass beds of Thalassia testudinum and harbor intracellular sulfuroxidizing gamma-proteobacteria. These bacterial symbionts fix CO2 via the Calvin Benson cycle and provide organic compounds to the bivalve. During experimentally induced starvation, no reduced sulfur compounds and no organic particle food are available; the symbionts could be considered as the sole nutrient source of the host bivalve. A previous study has shown that the intracellular bacterial population decreased considerably during starvation and that bacterial endosymbionts were not released by the bivalves. In this study, the activity of two lysosomal marker enzymes (acid phosphatase and arylsulfatase) was detected using cytochemical experiments coupled with energy-dispersive X-ray transmission electron microscopy during sulfide and organic particle starvation. The degradation of bacterial endosymbionts began after 2 weeks of starvation in C. orbiculata and after 3 weeks in C. orbicularis. Degradation processes seem to be continuous over several months and could be responsible for the disappearance of the bacterial endosymbionts within the gills during starvation. These data suggest that the host use symbionts as a nutrient source to survive a hunger crisis. The carbon transfer from the symbionts to the host could be flexible and could consist in transfer of organic matter, “milking,” under normal feeding conditions and digestion of the symbionts under starved conditions.
ISSN: 1059-910X

Droits : info:eu-repo/semantics/OpenAccess
hal-01206367
https://hal.univ-antilles.fr/hal-01206367
https://hal.univ-antilles.fr/hal-01206367/document
https://hal.univ-antilles.fr/hal-01206367/file/revised%20version%20to%20be%20submitted%20to%20the%20editor3oct.pdf
DOI : 10.1002/jemt.22458

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Large-scale conical and saucer-shaped sand injectites have been identified in the Upper Miocene sediments of the Lower Congo Basin. These structures are evidenced on the 3D high-resolution seismic data at about 600 ms TWT (two-way traveltime) beneath the seabed. The conical and saucer-shaped anomalies range from 20 to 80 m in height, 50 to 300 m in diameter, and 10 to 20 ms TWT in thickness. They are located within a sedimentary interval of about 100 m in thickness and are aligned over 20 km in dip direction (NE-SW), above the NW margin of an underlying Upper Miocene submarine fan. We have interpreted the conical and saucer-shaped anomalies as upward-emplaced sand injectites sourced from the Upper Miocene fan because of their discordant character, the postsedimentary uplifting of the sediments overlying the cones and saucer-shaped bodies, the alignment with the lateral fringe of the Upper Miocene submarine fan, and the geological context. Sand injection dates from the Miocene-Pliocene transition (approximately 5.3 Ma). The prerequisite overpressure to the sand injection process may be due to the buoyancy effect of hydrocarbons accumulated in the margins of the fan. Additionally, overpressure could have been enhanced by the lateral transfer of fluids operating in the inclined margins of the lobe. The short duration of sand injection and the presence of many sandstone intrusions suggested that the process of injection was triggered by an event, likely due to a nearby fault displacement related to diapiric movements. This is the first time that sand injectites of seismic scale have been described from the Lower Congo Basin. The localized nature of these injectites has led to a change in the migration path of fluids through the sedimentary cover. Consequently, the sand intrusions are both evidence and vectors of fluid migration within the basin fill.
ISSN: 1468-8115

hal-00963594
https://hal.archives-ouvertes.fr/hal-00963594
DOI : 10.1111/gfl.12057

Résumé : In the French West Indies islands, the transfer of chlordecone (kepone) from treated grounds towards the marine environment has been proved since the beginning of 2000s. In 2008, a maximal residue limit (MRL) was set at 20 µg / kg wet weight in fish and seafood, and therefore intensified the concern about the risks of high human exposure to the pesticide due to the consumption of contaminated marine products. To answer this concern, several sampling cruises were carried by public authorities and by Ifremer in order to analyze the contamination of the fish fauna around the Guadeloupe island. The data collected within these surveys improved our knowledge on the characteristics of the contamination of fish fauna and allowed to assess the distribution of this contamination in relation with optional geographical plans of the marine area around the Guadeloupe island. Further, this study was completed by an assessment of the fishery activity in areas which are the more exposed to the chlordecone contamination, taking into account data from a fishery observatory which has been set up in the archipelago since 2007. The results allow to precise two main characteristics of distribution of the contamination: its spatial and specific dimensions. About the spatial aspect, contamination of the fish fauna is centred on marine areas which are closely downstream contaminated watersheds. Concerning the marine fauna, two species groups are particularly exposed: the very coastal ones, particularly those living at or close to the mouth of rivers, and crustaceans wherever they live. Among fishes, the most contaminated species belong to many various groups which are present in the very coastal belt, more or less regularly. Lastly, this study provided orders of magnitude on the relative part of the fishery activity around the archipelagos for which the contamination is of great concern.
Aux Antilles, l’existence d’un transfert de la molécule de chlordécone des sols traités vers le milieu marin est avérée depuis le début des années 2000. L’établissement d’une limite maximale de résidus à 20 µg/kg pf pour tous les produits marins en 2008 y a intensifié la préoccupation vis-à-vis des risques d’exposition des populations humaines par les produits de la pêche. Pour répondre à cette préoccupation, depuis 2008, plusieurs campagnes d’échantillonnage ont été réalisées par les services de l’Etat (DAAF) et par l’Ifremer pour analyser la contamination de la faune halieutique autour de la Guadeloupe. Les données collectées de 2008 à 2011 par ces plans d’observation ont été utilisées pour actualiser les connaissances sur les caractéristiques de la contamination de la faune halieutique autour de la Guadeloupe, et analyser cette distribution en référence à différents schémas de segmentation du domaine marin. L’étude a été complétée par une analyse de l’activité halieutique dans les secteurs les plus sensibles à la contamination, à partir des données du système d’informations halieutiques déployé dans l’archipel depuis 2007. L’analyse a permis de préciser deux traits majeurs de cette distribution : sa dimension spatiale et son caractère spécifique. Sur le plan spatial, la contamination de la faune halieutique est centrée sur les espaces maritimes situées immédiatement en aval des bassins versants contenant des sols contaminés. Sur le plan faunistique, deux groupes apparaissent particulièrement sensibles, les espèces très côtières, en particulier celles fréquentant les embouchures des cours d’eau, et les crustacés, quelque soit leur milieu de vie. Chez les poissons, parmi les espèces contaminées, on trouve un large cortège d’espèces fréquentant plus ou moins régulièrement la bande littorale. Enfin, l’étude a permis de fournir des ordres de grandeur sur la part de l’activité halieutique de l’archipel directement concernée par cette pollution.

Droits : 2013 Ifremer
http://archimer.ifremer.fr/doc/00136/24762/22840.pdf
http://archimer.ifremer.fr/doc/00136/24762/