Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization'' and "acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.
ISSN: 0148-0227

hal-00420883
https://hal.archives-ouvertes.fr/hal-00420883
DOI : 10.1029/2008JF001072

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

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

Éditeur(s) : HAL CCSD Société Géologique de France
Résumé : Based on a High-Resolution 3D seismic block acquired in the Gulf of Lion in 2004–2005 we investigated fluid pipes and pockmarks on the top of the interfluve between the Hérault canyon and the Bourcart canyon both created by turbidity currents and gravity flows from the shelf to the deep basin in the north-western Mediterranean Sea. Combining the geometry of the potential fluid pipes with the induced deformation of surrounding sediments leads then to the ability to differentiate between potential fluid sources (root vs source) and to better estimate the triggering mechanisms (allochtonous vs. autochtonous cause). We linked together a set of derived attributes, such as Chaos and RMS amplitude, to a 3D description of pipes along which fluids may migrate. As previously shown in other basins, the induced deformation, creating cone in cone or V-shaped structures, may develop in response to the fluid pipe propagation in unconsolidated sediments in the near surface. The level at the top of a cone structure is diachronous. It means that stratigraphic levels over this surface are deformed at the end of the migration. They collapse forming a depression called a pockmark. These pipes are the result of repeated cycles of fluid expulsion that might be correlated with rapid sea-level rise instead of sediment loading. The most recent event (MIS 2.2 stage) has led to the formation of a pockmark on the modern seafloor. It has been used as a reference for calculating the effect of a rapid sea-level rise on fluid expulsion. As all physical and geometrical parameters are constrained, we were able to define that a + 34 m of sea level rise may account for triggering fluid expulsion from a very shallow silty-sandy layer at 9 m below seafloor since the last glacial stage. This value is consistent with a sea level rise of about 102 m during this period. This study shows that the episodic nature of fluid release resulted from hydromechanical processes during sea-level rise due to the interactivity between high pressure regimes and principal in situ stresses.
ISSN: 0037-9409

hal-01667241
https://hal.archives-ouvertes.fr/hal-01667241
DOI : 10.1051/bsgf/2017190

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Aryl hydrocarbon receptor-dependent genomic effects of environmental polycyclic aromatic hydrocarbons (PAHs) have been shown to be modulated by non-genomic protein kinase C (PKC)-related pathways. The present study was designed to determine whether PKC activation may also impair estrogenic genomic response triggered by PAHs. Treatment by the PKC activator phorbol 12-myristate 13-acetate (PMA) was found to markedly and differentially impair the up-regulation of estrogenic markers triggered by the estrogenic PAH benzanthracene (BZA) in cultured human mammary cells; BZA-mediated mRNA up-regulation of pS2 and amphiregulin was thus increased, whereas that of progesterone receptor and CXCL12 was repressed. BZA/PMA cotreatment however failed to alter BZA-mediated increase of activity of a luciferase gene reporter construct driven by an estrogen response element, thus discarding any global effect of PMA toward BZA-triggered estrogen receptor activation. Various chemicals inhibiting PKCs or extracellular signal-regulated kinase (ERK) as well as the knock-down of PKCδ expression counteracted the PMA-mediated increase of pS2 mRNA up-regulation triggered by BZA, demonstrating that it was dependent on PKCs, including PKCδ isoform, and ERKs. This non-genomic modulation of estrogenic effects of PAHs by PKC activation may have to be considered when considering the deleterious effects of these environmental contaminants towards the endocrine system.
ISSN: 0887-2333

inserm-00872862
http://www.hal.inserm.fr/inserm-00872862
DOI : 10.1016/j.tiv.2012.05.006
PUBMED : 22643241

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Numerical models show that small-scale convection (SSC) occurring atop a mantle plume is a plausible mechanism to rejuvenate the lithosphere. The triggering of SSC depends on the density contrast and on the rheology of the unstable layer underlying the stagnant upper part of the thermal boundary layer (TBL). Partial melting may change both properties. We analyze, using 2-D numerical simulations, how partial melting influences the dynamics of time-dependent SSC instabilities and the resulting thermo-mechanical rejuvenation of an oceanic plate moving atop of a plume. Our simulations show a complex behavior, with acceleration, no change, or delay of the SSC onset, due to competing effects of the latent heat of partial melting, which cools the plume material, and of the buoyancy increase associated with both melt retention and depletion of residue following melt extraction. The melt-induced viscosity reduction is too localized to affect significantly SSC dynamics. Faster SSC triggering is promoted for low melting degrees (low plume temperature anomalies, thick lithosphere, or fast moving plates), which limit both the temperature reduction due to latent heat of melting and the accumulation of depleted buoyant residue in the upper part of the unstable layer. In contrast, high partial melting degrees lead to a strong temperate decrease due to latent heat of melting and development of a thick depleted layer within the sublithospheric convecting layer, which delay the development of gravitational instabilities. Despite differences in SSC dynamics, the thinning of the lithosphere is not significantly enhanced relatively to simulations that neglect partial melting.
ISSN: 1525-2027

hal-01277175
https://hal.archives-ouvertes.fr/hal-01277175
DOI : 10.1002/2015GC005967

Éditeur(s) : HAL CCSD Federation of American Society of Experimental Biology
Résumé : International audience
Testes of most male mammals present the particularity of being externalized from the body and are consequently slightly cooler than core body temperature (4-8 degrees C below). Although, hypothermia of the testis is known to increase germ cells apoptosis, little is known about the underlying molecular mechanisms, including cold sensors, transduction pathways, and apoptosis triggers. In this study, using a functional knockout mouse model of the cold and menthol receptors, dubbed transient receptor potential melastatine 8 (TRPM8) channels, we found that TRPM8 initiated the cold-shock response by differentially modulating cold- and heat-shock proteins. Besides, apoptosis of germ cells increased in proportion to the cooling level in control mice but was independent of temperature in knockout mice. We also observed that the rate of germ cell death correlated positively with the reactive oxygen species level and negatively with the expression of the detoxifying enzymes. This result suggests that the TRPM8 sensor is a key determinant of germ cell fate under hypothermic stimulation.Borowiec, A.-S., Sion, B., Chalmel, F., Rolland, A. D., Lemonnier, L., De Clerck, T., Bokhobza, A., Derouiche, S., Dewailly, E., Slomianny, C., Mauduit, C., Benahmed, M., Roudbaraki, M., Jegou, B., Prevarskaya, N., Bidaux, G. Cold/menthol TRPM8 receptors initiate the cold-shock response and protect germ cells from cold-shock-induced oxidation.
ISSN: 0892-6638

hal-01390973
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01390973
DOI : 10.1096/fj.201600257R
PUBMED : 27317670

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Analogue and numerical models have shown that the strength of the lithospheric mantle controls the mode of lithosphere deformation. In extension, the presence or absence of a high strength brittle mantle respectively leads to localized or distributed rifting. However, first order geophysical data question the existence of such a brittle mantle. Here we use 2-D finite-element large strain modelling to quantify the impact of a ductile localizing mantle - instead of brittle - in triggering continental rifting. As a novelty, the mantle rheology considers the effect of grain boundary sliding during strain-induced grain size reduction, which may promote a significant strength drop and subsequent strain localization at low mantle temperature (< 700-800 °C). Our results reveal that such ductile localizing mantle implies varying modes of continental rifting that mainly depend on both the amount of weakening in the ductile mantle and the strength of the lower ductile crust. A medium to strong lower crust implies coupling between the upper crust and ductile localizing mantle, yielding to narrow continental rifting. In contrast, a weak lower crust implies decoupling between the upper crust and ductile localizing mantle, giving rise to a switch from distributed faulting at incipient strain to localized faulting at large strain. Ductile strain localization in the lithospheric mantle is therefore sufficient to trigger continental rifting, although a critical amount of weakening is required. Such ductile localizing mantle provides a relevant geological and mechanical alternative to the brittle mantle. It moreover provides a wider variety of modes of upper crustal faulting that are commonly observed in nature.
ISSN: 0040-1951

Droits : info:eu-repo/semantics/OpenAccess
insu-00924254
https://hal-insu.archives-ouvertes.fr/insu-00924254
https://hal-insu.archives-ouvertes.fr/insu-00924254/document
https://hal-insu.archives-ouvertes.fr/insu-00924254/file/Gueydan_precigout_2014_Tectonophysics.pdf
DOI : 10.1016/j.tecto.2013.11.029

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Several epidemiologic studies have shown an interactive effect of heavy smoking and heavy alcohol drinking on the development of hepatocellular carcinoma. It has also been recently described that chronic hepatocyte death can trigger excessive compensatory proliferation resulting later in the formation of tumors in mouse liver. As we previously demonstrated that both benzo[a]pyrene (B[a]P), an environmental agent found in cigarette smoke, and ethanol possess similar targets, especially oxidative stress, to trigger death of liver cells, we decided to study here the cellular and molecular mechanisms of the effects of B[a]P/ethanol coexposure on cell death. After an 18-h incubation with 100nM B[a]P, primary rat hepatocytes were supplemented with 50mM ethanol for 5 or 8h. B[a]P/ethanol coexposure led to a greater apoptotic cell death that could be linked to an increase in lipid peroxidation. Plasma membrane remodeling, as depicted by membrane fluidity elevation and physicochemical alterations in lipid rafts, appeared to play a key role, because both toxicants acted with specific complementary effects. Membrane remodeling was shown to induce an accumulation of lysosomes leading to an important increase in low-molecular-weight iron cellular content. Finally, ethanol metabolism, but not that of B[a]P, by providing reactive oxygen species, induced the ultimate toxic process. Indeed, in lysosomes, ethanol promoted the Fenton reaction, lipid peroxidation, and membrane permeabilization, thereby triggering cell death. To conclude, B[a]P exposure, by depleting hepatocyte membrane cholesterol content, would constitute a favorable ground for a later toxic insult such as ethanol intoxication. Membrane stabilization of both plasma membrane and lysosomes might be a potential target for further investigation considering cytoprotective strategies.
ISSN: 0891-5849

hal-01018147
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018147/file/Cooperative-interaction_final.pdf
PUBMED : 24681337

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
Background: Despite intensive research over several decades, the etiology of multiple sclerosis (MS) remains poorly understood, although environmental factors are supposedly implicated. Our goal was to identify spatial clusters of MS incident cases at the small-area level to provide clues to local environmental risk factors that might cause or trigger the disease. Methods: A population-based and multi-stage study was performed in the French Brittany region to accurately ascertain the clinical onset of disease during the 2000-2004 period. The municipality of residence at the time of clinical onset was geocoded. To test for the presence of MS incidence clusters and to identify their approximate locations, we used a spatial scan statistic. We adjusted for socioeconomic deprivation, known to be strongly associated with increased MS incident rates, and scanned simultaneously for areas with either high or low rates. Sensitivity analyses (focusing on relapsing-remitting forms and/or places of residence available within the year following clinical onset) were performed. Results: A total of 848 incident cases of MS were registered in Brittany, corresponding to a crude annual incidence rate of 5.8 per 100,000 inhabitants. The spatial scan statistic did not find a significant cluster of MS incidence in either the primary analysis (p value >= 0.56) or in the sensitivity analyses (p value >= 0.16). Conclusion: The findings of this study indicate that MS incidence is not markedly affected across space, suggesting that in the years preceding the first clinical expression of the disease, no environmental trigger is operative at the small-area population level in the French Brittany region.
ISSN: 1476-072X

hal-01616063
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01616063
DOI : 10.1186/s12942-017-0108-6
PUBMED : 28934989

Éditeur(s) : Elsevier
Résumé : The Danube Canyon is a large shelf-indenting canyon that has developed seaward of the late Pleistocene paleo-Danube valley. Mechanisms of canyon evolution and factors that controlled it are revealed by analyzing the morphology and the sedimentary structure of the canyon, as well as the main features of the continental margin around the canyon. This is based on investigation by swath bathymetry in the canyon area combined with different types of seismic data. The canyon is a major erosional trough with a flat bottom cut by an entrenched axial thalweg. The thalweg path varies from highly meandering to fairly straight in relation to the local gradient. Segments of the canyon are characterized by specific morphology, orientation and gradient along the axial thalweg. We interpret these segments in terms of canyon maturity. The sedimentary structure of the canyon documents an older phase of erosion followed by partial infilling, and thus attests for repeated cycles of canyon development. Canyon morphology is interpreted as a result of erosive sediment flows along the entrenched axial thalweg that caused downcutting into the canyon bottom and instability of the canyon walls, and hence enlargement of the canyon and expansion by headward erosion. During the last lowstand level of the Black Sea the canyon was located in an area of high sediment supply close to the paleo-Danube River mouths. This is indicated by buried fluvial channels on the shelf and by a wave-cut terrace associated with a water level situated about - 90 m below the present level. We infer that erosive flows in the canyon resulted from hyperpycnal currents at the river mouths, probably favored by the low salinity environment that characterized the Black Sea during lowstand times. Other mechanisms could have contributed to trigger sediment failure along the canyon, such as instability related to the presence of shallow gas, or the effect of a deep fault.
Marine Geology (0025-3227) (Elsevier), 2004-05 , Vol. 206 , N. 1-4 , P. 249-265

Droits : 2004 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2004/publication-476.pdf
DOI:10.1016/j.margeo.2004.03.003
http://archimer.ifremer.fr/doc/00000/476/

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
The formation of ovarian follicles is a finely tuned process that takes place within a narrow time-window in rodents. Multiple factors and pathways have been proposed to contribute to the mechanisms triggering this process but the role of endocrine factors, especially estrogens, remains elusive. It is currently hypothesized that removal from the maternal hormonal environment permits follicle formation at birth. However, experimentally-induced maintenance of high 17β-estradiol (E2) levels leads to subtle, distinct, immediate effects on follicle formation and oocyte survival depending on the species and dose. In this study, we examined the immediate effects of neonatal E2 exposure from post-natal day (PND) 0 to PND2 on the whole organism and on ovarian follicle formation in rats. Measurements of plasma E2, estrone and their sulfate conjugates after E2 exposure showed that neonatal female rats rapidly acquire the capability to metabolize and clear excessive E2 levels. Concomitant modifications to the mRNA content of genes encoding selected E2 metabolism enzymes in the liver and the ovary in response to E2 exposure indicate that E2 may modify the neonatal maturation of these organs. In the liver, E2 treatment was associated with lower acquisition of the capability to metabolize E2. In the ovary, E2 depleted the oocyte pool in a dose dependent manner by PND3. In 10 µg/day E2-treated ovaries, apoptotic oocytes were observed in newly formed follicles in addition to areas of ovarian cord remodeling. At PND6, follicles without any visible oocyte were present and multi-oocyte follicles were not observed. Our study reveals a major species-difference. Indeed, neonatal exposure to E2 depletes the oocyte pool in the rat ovary, whereas in the mouse it is well known to increase oocyte survival.
ISSN: 1932-6203

hal-00936582
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00936582
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00936582/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00936582/file/Systemic_Compensatory_Response-accepted.pdf
DOI : 10.1371/journal.pone.0082175

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present Contact Dynamics discrete element simulations of the earthquake-triggered Jiufengershan avalanche, which mobilized a 60 m thick, 1.5 km long sedimentary layer, dipping similar to 22 degrees SE toward a valley. The dynamic behavior of the avalanche is simulated under different assumptions about rock behavior, water table height, and boundary shear strength. Additionally, seismic shaking is introduced using strong motion records from nearby stations. We assume that seismic shaking generates shearing and frictional heating along the surface of rupture, which, in turn, may induce dynamic weakening and avalanche triggering; a simple "slip-weakening'' criterion was adopted to simulate shear strength drop along the rupture surface. We investigate the mechanical processes occurring during triggering and propagation of an avalanche mobilizing shallowly dipping layers. Incipient deformation forms a pop-up structure at the toe of the dip slope. As the avalanche propagates, the pop-up deforms into an overturned fold, which overrides the surface of separation along a decollement. Simultaneously, uphill layers slide at high velocity (125 km/h) and are folded and disrupted as they reach the toe of the dip slope. The avalanche foot forms a wedge that is pushed forward as deformed rocks accrete at its rear. We simulated five cross sections across the Jiufengershan avalanche, which differ in the geometry of the surface of separation. Topographic and simulated surface profiles are similar. The friction coefficient at the surface of separation determined from back analysis is abnormally low (mu(SS) = 0.2), possibly due to lubrication by liquefied soils. The granular deposits of simulated earthquake- and rain-triggered avalanches are similar.
ISSN: 0148-0227

hal-00420882
https://hal.archives-ouvertes.fr/hal-00420882
DOI : 10.1029/2008JF001075

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
High sea surface temperature accompanied by high levels of solar irradiance is responsible for the disruption of the symbiosis between cnidarians and their symbiotic dinoflagellates from the genus Symbiodinium. This phenomenon, known as coral bleaching, is one of the major threats affecting coral reefs around the world. Because an important molecular trigger to bleaching appears related to the production of reactive oxygen species (ROS), it is critical to understand the function of the antioxidant network of Symbiodinium species. In this study we investigated the response of two Symbiodinium species, from contrasting environments, to a chemically induced oxidative stress. ROS produced during this oxidative burst reduced photosynthesis by 30 to 50% and significantly decreased the activity of superoxide dismutase. Lipid peroxidation levels and carotenoid concentrations, especially diatoxanthin, confirm that these molecules act as antioxidants and contribute to the stabilization of membrane lipids. The comparative analysis between the two Symbiodinium species allowed us to highlight that Symbiodinium sp. clade A temperate was more tolerant to oxidative stress than the tropical S. kawagutii clade F. These differences are very likely a consequence of adaptation to their natural environment, with the temperate species experiencing conditions of temperature and irradiance much more variable and extreme.
ISSN: 0140-7791

hal-01546161
https://hal.archives-ouvertes.fr/hal-01546161
DOI : 10.1111/pce.12825

Éditeur(s) : HAL CCSD
Résumé : The presence of biological matter (biofilms) in deep geological sites for storage of, for instance, toxic elements or groundwater in aquifers was clearly proved. That biomass triggers physical and chemical processes which greatly modify the durability and the sustainability of the sites. These processes, mainly from oxidative/reductive reactions, are poorly understood. This is mainly due to the fact that former studies were done at the macroscopic level far away from the micrometric scale where relevant processes induced by bacteria take place. Investigations at microscopic level are needed. Thus, we developed an experimental set-up based on the combined use of optical microscopy (transmission), atomic force microscopy (AFM) and electrical and electro-chemical AFM microscopy (EC_AFM) in order to get simultaneous information on topographic and electro-chemical processes. The first highly sensitive step was to use AFM with biological samples in liquid environment: wepresent here a study about AFM imaging of living, moving or self-immobilized bacteria, in their genuine physiological liquid medium and in true in vivo conditions. No external immobilization protocol, neither chemical nor mechanical was needed. For the first time, the native gliding movements of Gram negative Nostoc cyanobacteria upon the surface were studied by AFM. AFM height and mechanical stiffness data were simultaneously acquired. From these, mechanical parameters, inner turgor pressure and Young modulus, were derived for different bacterial species (Anabaenopsis circularis, Rhodococcus wratislaviensis). Our study revealed that AFM imaging is thus possible on moving living species. These results open a large window on new studies of both dynamical phenomena of practical and fundamental interests such as the formation of biofilms and dynamic properties of bacteria in real physiological conditions. The second delicate step was to combine AFM and optical measurements with electrical ones. We mounted a new experimental set-up coupling real-time (i) monitoring of optical properties as the optical density (OD) evolution related to bulk bacterial growth in liquid or as the counting of number of bacteria adhering on the surface of the sample as well and (ii) electrical and electrochemical measurements. Furthermore, these results will shortly be applied to the optimized monitoring of the in-situ activity of bacteria consuming oil pollutants, following this way, in real-time, the bioremediation of an oilcontaminated soil (ANR ECOTECH_BIOPHY program).
La présence de matière biologique (biofilms) dans les sites de stockage géologique profond, d'éléments toxiques ou encore de l'eau potable des aquifères est maintenant clairement démontrée. Cette biomasse est à l'origine de processus physiques et chimiques qui modifient considérablement la durabilité et la pérennité des sites concernés. Ces processus, principalement de type oxydo-réductif, sont encore mal compris. Ceci est principalement dû aux méthodes d'investigation, principalement macroscopiques, loin de l'échelle micrométrique caractéristique des bactéries. Seules des études, basées sur des méthodes d'investigation locale, peuvent apporter les informations requises. Ainsi, nous avons développé un dispositif expérimental basé sur l'utilisation combinée de la microscopie optique (en transmission), la microscopie à force atomique (AFM) et la microscopie AFM en mode électrique et électrochimique (EC_AFM) afin d'obtenir des informations simultanées sur la topographie de l'échantillon et sur les processus électrochimiques à l'échelle des bactéries. La première étape sensible consistait à utiliser l'AFM sur des échantillons biologiques en milieu liquide: nous présentons ici les résultats de l'imagerie AFM en milieu liquide de plusieurs types de bactéries dans leurs conditions physiologiques naturelles (conditions in vivo). Aucun protocole d'immobilisation, ni chimique ni mécanique, n'a été nécessaire; et pour la première fois, les mouvements de reptation de cyanobactéries Nostoc ont été étudiés par l'AFM. Les études AFM ont permis d'acquérir des données topographiques mais aussi mécaniques : nous avons pu ainsi mesurer le module d'Young, la pression de turgescence de différentes souches bactériennes (Anabaenopsis circularis, Rhodococcus wratislaviensis). Cette étude complète, a révélé que l'imagerie AFM est donc possible sur des espèces vivantes en mouvement. Ces résultats ouvrent une grande fenêtre sur de nouvelles études d'intérêts tels que la formation de biofilms et les propriétés dynamiques de bactéries dans des conditions physiologiques réelles. La deuxième étape délicate était de combiner l'AFM aux mesures optiques et électriques. Nous avons développé un nouveau dispositif expérimental permettant (i) le suivi de l'évolution de la croissance bactérienne par la mesure des propriétés optiques comme la densité optique DO (pour le développement bactérien en volume - milieu planctonique) , ou l'analyse de l'image du substrat par comptage du nombre de bactéries sur la surface de l'échantillon (biofilm), et (ii) les mesures électriques et électrochimiques. L'ensemble de ces résultats sera prochainement appliqué au développement de nouveaux outils de surveillance d'une biodépollution de terrain contaminé par les hydrocarbures, par le suivi in situ et en temps réel de l'activité de bactéries dépolluantes (ECOTECH_BIOPHY ANR).
https://tel.archives-ouvertes.fr/tel-01044714

tel-01044714
https://tel.archives-ouvertes.fr/tel-01044714
https://tel.archives-ouvertes.fr/tel-01044714/document
https://tel.archives-ouvertes.fr/tel-01044714/file/theseDhahri2013.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Major and trace element signatures and Sr-Nd-Pb isotope data for muscovite (Ms)-bearing amphibolite blocks and associated muscovite-bearing trondhjemite and quartz-muscovite rocks from the Sierra del Convento melange (eastern Cuba) indicate that Proto-Caribbean oceanic crust underwent wet partial melting processes during Mesozoic subduction and after accretion to the upper plate. Trace element normalized patterns of Ms-bearing amphibolites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE) and evidence variable trace element transfer from the Proto-Caribbean subducting slab to the mantle wedge. Ms-bearing trondhjemites show LREE enrichment and HREE depletion and have geochemical features similar to adakites, including SiO2>56 wt.%, high Na2O contents (5.5-9.0 wt.%) and high Sr/Y (16-644). We consider that the trondhjemites represent primary and natural melts formed by deep partial melting of the subducting slab which did not significantly react with the mantle wedge before intrusion in the subduction channel. The Ms-bearing trondhjemites show different geochemical and petrological signatures compared with the Ms-free tonalites-trondhjemites from Sierra del Convent, that are interpreted as primary slab melts. These differences support the idea that partial melting processes in the Sierra del Convento subduction channel were triggered by the infiltration of fluids derived from three distinct subducted sources: sediments, altered mid-ocean ridge basalts (MORB), and serpentinites. In this scenario, the pegmatitic quartz-muscovite rocks, which are highly enriched in LILE, probably represent the crystallization products of fluids derived by differentiation of the trondhjemitic melts.
ISSN: 0024-4937

hal-00669881
https://hal.archives-ouvertes.fr/hal-00669881
DOI : 10.1016/j.lithos.2011.07.011

Éditeur(s) : Amer Soc Limnology Oceanography
Résumé : A new benthic station equipped with oxygen microelectrodes and environmental sensors was developed by Laboratoire des Sciences du Climat et de L’Environnement (LSCE) and Division Technique of the Institut National des Sciences de L’Univers (DT-INSU) to perform in situ time series monitoring of sediment oxygen demand, linked to the mineralization of organic matter. The time series typically cover periods of 2-3 months, with a base frequency of 1 set of oxygen profiles per day. The profiling head assessed the lateral heterogeneity of the sediment oxygen demand at the beginning of the time series over a 0.8-m long rectangle to discriminate spatial and temporal variability. A continuous recalibration is performed using a moored oxygen optode anchored to the benthic station together with a set of environmental sensors. These sensors (turbidity, temperature, salinity, and oxygen) can trigger a high-frequency profiling mode to investigate the fate of particulate organic matter delivered during floods, resuspension, and deposition events. Deployments of the benthic station were performed in the Rhone River subaqueous delta (Mediterranean Sea). We show that “stable” periods (when neither floods nor storms occur) were characterized by a stable oxygen demand. In the case of resuspension events, an increase of the sediment oxygen demand by a factor of 2-3 with a relaxation time of 1 day was observed, indicating that the new benthic station can adequately capture the impact of resuspension events on the oxygen demand in deltaic sediments.
Limnology And Oceanography-methods (1541-5856) (Amer Soc Limnology Oceanography), 2014-11 , Vol. 12 , P. 729-741

Droits : 2014, by the American Society of Limnology and Oceanography, Inc.
http://archimer.ifremer.fr/doc/00230/34126/32597.pdf
http://archimer.ifremer.fr/doc/00230/34126/36349.pdf
DOI:10.4319/lom.2014.12.729
http://archimer.ifremer.fr/doc/00230/34126/

Éditeur(s) : Gauthier-Villars
Résumé : This review provides a brief update of the occurrence and adaptive significance of asexual reproduction in echinoderms. It then focuses on the state of knowledge of biotic and abiotic factors that influence asexual processes in this group, particularly factors that may play a role in regulating the expression and relative proportion of asexual versus sexual phenotypes within populations of species, as well as factors modulating and triggering asexual processes. The information presented in the review is synthesized into the form of a basic model depicting how environmental factors may interact with physiological factors to regulate asexual reproduction in echinoderms, and to show how such regulatory processes may parallel in some ways those known to regulate sexual reproduction. Since the model is based mainly on correlational evidence derived from comparative field observations, a number of experimental approaches for testing the predictions of the model are discussed briefly.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1996 , Vol. 19 , N. 3-4 , P. 227-235

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00094/20481/18151.pdf
http://archimer.ifremer.fr/doc/00094/20481/

Éditeur(s) : Université de Bretagne Occidentale
Résumé : The negative impact of the man on the environment unquestionably increases. The coastal environment as a whole is the maritime environment which is the most exposed to man-made eutrophication. For instance, nitrate loads to coastal waters off Brittany (France) have increased 10 times (from 3 to s 30mg L-1NO3) during the four last decades. Eutrophication of this coastal zone is now a recurrent problem, more and more worrying. This eutrophication exhibits two main forms : " green tides ", which are caused by local proliferations and stranding of green macro-algae (particularly the Ulva species) in nitrogen-enriched areas ; phytoplanktonic blooms, which are responsible for coloured water events, toxic species can be present (Pseudo-Nitzschia, Alexandrium, Dinophysis), and induce banning of shellfish consumption. The objectives of this study are to assess the respective role of various rivers (especially the Loire and the Vilaine) in the eutrophication of the Brittany shelf ecosystem and test the impact of nitrogen enrichment in the triggering of Pseudo-Nitzchia toxicity. For these purposes, a coupled hydrodynamical/ biogeochemical 3D model has been developed and validated against past measured time-series and satellite images. After a brief analysis of primary production over the Brittany shelf under different conditions, we show a description of the real time adaptation of this model. Daily results are currently presented in real time on www.previmer.org web site. The inability of the model to correctly simulate near shore phytoplankton is worsened in this model by the fact that the turbidity field used is a climatological one, made by satellite images averaged on a decadal basis. First, near shore pixels of satellite images are scarcely reliable, secondly a climatological mean cannot represent the sudden bursts or drops of the real turbidity, highly dependent on the actual sea-state : this can explain also why the model at this moment fails to reproduce a sudden bloom occurring in a short period of sunny and calm weather. The simulated Pseudo-Nitzschia biomass and induced risk of toxicity in the water column cannot really be validated offshore, because monitoring measurements are available only near the coast, and deal only with toxicity in benthic filter feeders. To get temporarily rid of that problem, an interesting improvement would be to add to the operational model the bio-accumulation of toxin in the shellfishes : simulated concentrations in shellfish fresh would become directly comparable with usual measurements of the monitoring networks. Our model points out the important impact of Loire river loads on the primary production on the western and southern Brittany. This result is crucial for administrations in charge of reducing the terrestrial loadings responsible for eutrophication, because it can delay reduction programs on small tributaries until the main input from the Loire has been significantly reduced. A question arises, about the reliability of the haline stratification in the model, because the horizontal extent of the Loire plume will be enhanced by a stronger stratification.
L'eutrophisation des milieux marins côtiers, de plus en plus importante, représente un des impacts majeurs des activités humaines sur l'environnement. Les phénomènes d'eutrophisation sont en constante augmentation ; ces dernières décennies ont vu le nombre de sites touchés augmenter de par le monde. La bande côtière bretonne est particulièrement concernée par ce phénomène. L'eutrophisation s'y manifeste de deux façons : "Des phénomènes de marée vertes, très localisées, qui sont provoqués par la croissance excessive et l'échouage de macro-algues du genre Ulva dans ces zones riches en azote ; Des blooms de phytoplancton à l'origine des phénomènes d'eaux colorées, qui peuvent aussi provoquer des interdictions de consommation de coquillages lorsque les espèces mises en jeu sont toxiques (Pseudo-Nitzschia, Alexandrium, Dinophysis). L'objectif de ce travail est multiple : il vise à mettre en évidence et à comprendre l'impact et le rôle des apports en nutriments sur la production primaire et l'eutrophisation des milieux côtiers. Ce travail a aussi pour ambition l'identification et la compréhension des causes des phénomènes d'eutrophisation et permettre ainsi d'apporter des solutions ou des pistes d'amélioration. En n, il a aussi un objectif de prévision à court terme de l'état biologique sur la zone. Pour atteindre ces objectifs, un modèle en temps réel a été mis en oeuvre. Les résultats de simulations numériques et de mesures satellitaires sont présentés sur internet : www.previmer.org. L'outil principal de ce travail est un modèle couplé physique/biogéochimie. La partie hydrodynamique est fournie par le code Mars3D (3D hydrodynamical Model for Application at Regional Scale) développé à IFREMER. Au code hydrodynamique Mars3D est couplé le modèle des cycles de l'azote, du phosphore et du silicium d'IFREMER. Le modèle couplé permet de simuler en 3 dimensions et de manière dynamique les courants, le brassage horizontal et vertical, les champs de température et de salinité, mais aussi les principaux cycles de nutriments, reproduisant ainsi les conditions déterminantes de la production primaire. La croissance des algues est modélisée, et nous permet de voir l'influence des panaches de dilution des principales rivières bretonnes sur leur croissance. Les diffcultés du modèle à correctement simuler les concentrations en phytoplancton près des zones côtières, sont probablement dues à l'utilisation d'une climatologie de concentration en matière en suspension fondée sur des données satellitaires. Tout d'abord, les pixels côtiers des images satellitaires sont entachés d'erreurs, ensuite une climatologie n'est pas capable de représenter les apports soudains des fleuves lors des crues. Cela peut expliquer l'incapacité du modèle a représenter certains blooms liés à des périodes ensoleilées et calmes. A ce modèle de base nous avons ajouté un genre spécifique de phytoplancton : le genre Pseudo-Nitzschia. Certaines espèces de Pseudo-Nitzschia sont réputées toxiques. En effet, ce phytoplancton a la capacité de synthétiser une toxine : l'acide domoïque. Cette toxine est responsable du syndrome ASP (Amnesic Shellfish Poisoning). Le modèle reproduit globalement les mêmes zones de toxicité que les mesures du REPHY, et donne des résultats encourageants. L'étude montre que la Loire influence une large partie de la bande côtière bretonne ; son panache remonte jusqu'au nord de la mer d'Iroise, et contribue pour une grande part à l'enrichissement du sud et de l'ouest de la Bretagne. Le traçage de l'azote en provenance de la Loire au sein des cycles biogéochimiques nous a permis de quantifier cet enrichissement.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00015/12603/9481.pdf
http://archimer.ifremer.fr/doc/00015/12603/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The Nile delta sedimentation constitutes a continuous high resolution (1.6 mm/year) record of Ethiopian African monsoon regime intensity. Multiproxy analyses performed on core MS27PT recovered in hemipelagic Nile sediment margin (<90 km outward of the Rosetta mouth of the Nile) allow the quantification of the Saharan aeolian dust and the Blue/White Nile River suspended matter frequency fluctuations during the last 21 cal. ka BP. The radiogenic Sr and Nd isotopes, clay mineralogy, bulk elemental composition and palynological analyses reveal large changes in source components, oscillating between a dominant aeolian Saharan contribution during the LGM and the Late Holocene (~4 to 2 cal. ka BP), a dominant Blue/Atbara Nile River contribution during the early Holocene (15 to 8.4 cal. ka BP) and a probable White Nile River contribution during the Middle Holocene (8.4 to 4 cal. ka BP). The following main features are highlighted: 1. The rapid shift from the LGM arid conditions to the African Humid Period (AHP) started at about 15 cal. ka BP. AHP extends until 8.4 cal. ka BP, and we suggest that the Ethiopian African Monsoon maximum between 12 and 8 cal. ka BP is responsible for a larger Blue/Atbara Nile sediment load and freshwater input into the Eastern Mediterranean Sea. 2. The transition between the AHP and the arid Late Holocene is gradual and occurs in two main phases between 8.4 and 6.5 cal. ka BP and 6.5 to 3.2 cal. ka BP. We suggest that the main rain belt shifted southward from 8.4 to ~4 cal. ka BP and was responsible for progressively reduced sediment load and freshwater input into the eastern Mediterranean Sea. 3. The aridification along the Nile catchments occurred from ~4 to 2 cal. ka BP. A dry period, which culminates at 3.2 cal. ka BP, and seems to coincide with a re-establishment of increased oceanic primary productivity in the western Mediterranean Sea. We postulate that the decrease in thermo-haline water Mediterranean circulation could be part of a response to huge volumes of fresh-water delivered principally by the Nile River from 12 to 8.4 cal. ka BP in the eastern Mediterranean. We propose that the large hydrological change in Ethiopian latitude could be a trigger for the 8.2 ka cooling event recorded in high latitude. Revel R., Colin C., Bernasconi S., Combourieu-Nebout N., Ducassou E., Grousset F.E., Rolland Y., Migeon S., Brunet P., Zhaa Y., Bosch D., Mascle J.,. "21,000 years of Ethiopian African moonsoon variability recorded in sediments of the western Nile deep sea fan", Regional Environmental Change,
ISSN: 1436-3798

hal-00836300
https://hal.archives-ouvertes.fr/hal-00836300

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Understanding how communities respond to natural disturbances is fundamental to assess the mechanisms of ecosystem resistance and resilience. However, ecosystem responses to natural disturbances are rarely monitored both through space and time, while the factors promoting ecosystem stability act at various temporal and spatial scales. Hence, assessing both the spatial and temporal variations in species composition is important to comprehensively explore the effects of natural disturbances. Here, we suggest a framework to better scrutinize the mechanisms underlying community responses to disturbances through both time and space. Our analytical approach is based on beta diversity decomposition into two components, replacement and biomass difference. We illustrate this approach using a 9-year monitoring of coral reef fish communities off Moorea Island (French Polynesia), which encompassed two severe natural disturbances: a crown-of-thorns starfish outbreak and a hurricane. These disturbances triggered a fast logistic decline in coral cover, which suffered a 90% decrease on all reefs. However, we found that the coral reef fish composition remained largely stable through time and space whereas compensatory changes in bio-mass among species were responsible for most of the temporal fluctuations, as outlined by the overall high contribution of the replacement component to total beta diversity. This suggests that, despite the severity of the two disturbances, fish communities exhibited high resistance and the ability to reorganize their compositions to maintain the same level of total community biomass as before the disturbances. We further investigated the spatial congruence of this pattern and showed that temporal dynamics involved different species across sites; yet, herbivores controlling the proliferation of algae that compete with coral communities were consistently favored. These results suggest that compensatory changes in bio-mass among species and spatial heterogeneity in species responses can provide further
ISSN: 1932-6203

hal-01212344
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01212344/file/journal.pone.0138696.pdf
DOI : 10.1371/journal.pone.0138696