Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
The extent to which Marine Protected Areas (MPAs) benefit corals is contentious. On one hand, MPAs could enhance coral growth and survival through increases in herbivory within their borders; on the other, they are unlikely to prevent disturbances, such as terrestrial runoff , that originate outside their boundaries. We examined the effect of spatial protection and terrestrial sediment on the benthic composition of coral reefs in Saint Lucia. In 2011 (10 to 16 years after MPAs were created), we resurveyed 21 reefs that had been surveyed in 2001 and analyzed current benthic assemblages as well as changes in benthic cover over that decade in relation to protection status, terrestrial sediment influence (measured as the proportion of terrigenous material in reef-associated sediment) and depth. The cover of all ben-thic biotic components has changed significantly over the decade, including a decline in coral and increase in macroalgae. Protection status was not a significant predictor of either current benthic composition or changes in composition, but current cover and change in cover of several components were related to terrigenous content of sediment deposited recently. Sites with a higher proportion of terrigenous sediment had lower current coral cover, higher macroalgal cover and greater coral declines. Our results suggest that terrestrial sediment is an important factor in the recent degradation of coral reefs in Saint Lucia and that the current MPA network should be complemented by measures to reduce runoff from land.
ISSN: 1932-6203

hal-01281152
https://hal-univ-perp.archives-ouvertes.fr/hal-01281152
https://hal-univ-perp.archives-ouvertes.fr/hal-01281152/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01281152/file/journal.pone.0146855.PDF
DOI : 10.1371/journal.pone.0146855

Éditeur(s) : HAL CCSD E Schweizerbart Science Publishers
Résumé : International audience
Mass balance calculations have been performed through a comparison of published graphical and statistical approaches applied to two contrasted geological settings: (i) the development of a greenschist-facies ductile shear-zone that recorded a weak volume change but significant mass transfers, and (ii) the formation of exoskarns in metacarbonate xenoliths that recorded a large volume decrease related to huge mass transfers. The comparison of the four mass-balance approaches shows that, if uncertainties are ignored, (1) they yield similar results concerning the mobile vs immobile behaviour of many components; (2) they yield similar mass-change values on bulk rock and on individual chemical elements (bulk-rock mass-change values differ by a maximum of ca. 15 % between graphical and statistical treatments of the metacarbonate xenolith evolution). The main difference concerns the uncertainties on mass changes (for bulk rocks and individual elements), which are much larger with the graphical than with the statistical approaches when uncertainties on chemical elements are taken into account, as they should be.The main advantage of the graphical methods is their rapid implementation and the clarity of the diagrams. Their main disadvantages are that uncertainties on each chemical element and bulk compositions are not taken into account and the difficulty in choosing an accurate immobility field to precisely define errors. Graphical methods need to be completed by a statistical treatment that gives absolute mass transfer results. The statistical approaches have the advantage of taking into account the chemical heterogeneities of the compared populations, in conjunction to a precise data treatment. The statistical treatment is an important and necessary step to decipher and to be pertinent in interpreting mobility/immobility of chemical elements, and, thus, in the absolute quantification of mass and volume changes.
ISSN: 0935-1221

hal-01260258
https://hal.archives-ouvertes.fr/hal-01260258
DOI : 10.1127/ejm/2015/0027-2475

Éditeur(s) : HAL CCSD Elsevier
Résumé : SUBSURF
Statistical sequential analysis was performed on a series of sediment cores collected from the Têt prodelta in the Gulf of Lions, northwestern Mediterranean Sea, between October 2003 and October 2004. Seabed changes during that period were correlated to hydrodynamic conditions (waves and currents) and river discharge. Low sediment supply prevents full preservation of new sediment strata on this low-accumulation prodelta located on a microtidal, storm-dominated inner shelf. Severe meteorological events caused a rapid succession of erosion and deposition phases. For example, the December 2003 flood and storm produced a flood layer deposit that persisted for 2 months with only slight transformations due to early diagenesis and/or bioturbation, until a new storm event eroded this layer. A typical sedimentary sequence was observed for the secular deposits composed of a 10-cm-thick sandy layer overlaying siltyclayey layers. These characteristic features were used to analyse the last millennia sedimentary record of the Têt prodelta. The low preservation of freshly deposited sediments and variable sedimentation rates during the last millennia period yield a sedimentary sequence formed by the outcropping of muddy prodeltaic units intersected by heterogeneous siltysandy units similar to those formed under present day hydrodynamic conditions. No flood layer was found related to catastrophic flooding of the last century in the sedimentary record. The Little Ice Age ( 1550–1850 AD) probably favoured the formation of a well-developed muddy prodelta in the mouth of the Têt River. Later on, the decrease of sediment supply by rivers due to climate change and/or human activities (damming, irrigation), and the increase of the number of high-energy storms reaching the coast, induced a coarsening of the top sediment layer on this prodelta. This modern change of the substrate is also observed in the composition of benthic biota found in the substrate
ISSN: 0025-3227

hal-00407662
https://hal.archives-ouvertes.fr/hal-00407662
DOI : 10.1016/j.margeo.2007.04.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We report chlorine (Cl) and fluorine (F) abundances in minerals, interstitial glasses, and melt inclusions in 12 andesite-hosted, spinel harzburgite xenoliths and crosscutting pyroxenite veins exhumed from the sub-arc lithospheric mantle beneath Avacha volcano in the Kamchatka Arc (NE Russia). The data are used to calculate equilibrium mineral-melt partition coefficients (Dmineral/meltDmineral/melt) for Cl and F relevant to subduction-zone processes and unravel the history of volatile depletion and enrichment mechanisms in an arc setting.Chlorine is ∼100 times more incompatible in pyroxenes (View the MathML sourceDClmineral/melt = 0.005–0.008 [±0.002–0.003]) than F (View the MathML sourceDFmineral/melt = 0.50–0.57 [±0.21–0.24]), which indicates that partial melting of mantle sources leads to strong depletions in Cl relative to F in the residues. The data set in this study suggests a strong control of melt composition on View the MathML sourceDCl,Fpyroxene/melt, in particular H2O contents and Al/(Al + Si), which is in line with recent experiments. Fluorine is compatible in Ca-amphibole in the ‘wet’ sub-arc mantle (View the MathML sourceDFamphibole/melt = 3.5–3.7 [±1.5]) but not Cl (View the MathML sourceDClamphibole/melt = 0.03–0.05 [±0.01–0.03]), indicating that amphibole may fractionate F from Cl in the mantle wedge. The inter-mineral partition coefficients for Cl and F in this study are consistent amongst different harzburgite samples, whether they contain glass or not. In particular, disseminated amphibole hosts much of the Cl and F bulk rock budgets of spinel harzburgites (View the MathML sourceDClamphibole/pyroxene up to 14 and View the MathML sourceDFamphibole/pyroxene up to 40). Chlorine and fluorine are variably enriched (up to 1500 ppm Cl and 750 ppm F) in the parental arc picrite and boninite melts of primitive pyroxenite veins (and related melt inclusions) crosscutting spinel harzburgites.Based on the data in this study, the main inferences on the behaviour of Cl and F during melting and metasomatic processes in the sub-arc mantle are as follow:(i) Melting models show that most depleted mantle protoliths of intra-oceanic arc sources can have extremely low Cl/F (0.002–0.007) before being overprinted by subduction-derived components.(ii) Chlorine has a higher percolation distance in the mantle than F. Even for small fluid or melt volumes, Cl and F signatures of partial melting are overprinted by those of pervasive percolation, which increases Cl/F in percolating agents and bulk peridotites during chromatographic interaction and/or amphibole-forming metasomatic reactions. These processes ultimately control the bulk Cl and F compositions of the residual mantle lithosphere beneath arcs, and likely in other tectonic settings.(iii) Fluxed melting models suggest that Cl enrichment in arc picrite and boninite melts in this study, and in many arc melt inclusions reported in the literature, could be related to the infiltration of high Cl/F fluids derived from subducted serpentinite or altered crust in mantle wedge sources. However, these high Cl/F signatures should be re-evaluated with new models in light of the possible overprint of pervasive percolation effects in the mantle. The breakdown of amphibole (and/or mica) in the deep metasomatised mantle at higher pressure and temperature conditions than in the slab may explain, at least in part, the positive correlations between F abundances and Cl/F in primitive arc melt inclusions and slab depth.
ISSN: 0016-7037

hal-01553610
https://hal.archives-ouvertes.fr/hal-01553610
DOI : 10.1016/j.gca.2016.10.035

Éditeur(s) : HAL CCSD
Résumé : This PhD work is based on field, petrographic, and geochemical observations of rocks originated at the base of the sheeted dike complex, in the Oman ophiolite and at IODP Site 1256, coupled with an experimental study. It provides new constrains on processes that occur at the magma / hydrothermal system transition in oceanic crust formed at fast spreading ridges. The base of the sheeted dike complex is truncated by intrusive isotropic gabbros, and therefore reheated and recrystallized to the "granoblastic dikes" under temperatures up to 1030°C. Xenoliths of granoblastic microgabbros and microgabbronorites derived from the granoblastic dikes are commonly observed in the about 100 meters thick horizon of isotropic gabbro that underlies the sheeted dike complex. These features can be explained by upward migrations of the melt lens that is present at fast spreading centers. The occurrence of several assimilation features (xenoliths and granoblastic patches) in the isotropic gabbro horizon supports the hypothesis that this horizon represents the fossilization of the upper melt lens. The experimental study was designed to simulate experimentally the effect of partial melting of hydrothermally altered sheeted dikes. The results show that melting starts at 850°C, confirm the residual origin of granoblastic dikes and xenoliths, and attest to the anatectic origin of the oceanic plagiogranites that are commonly present close to the base of the sheeted dike complex. The major and trace element composition of the experimental anatectic melt that represents the main contaminant for primitive MORBs at fast spreading ridges has been determined. The upper axial melt lens at fast spreading mid-ocean ridges is herein described as a dynamic system that can migrate vertically, and which fossilizes when moving off-axis.
Ce travail de thèse est basé sur des observations de terrain, sur une étude pétrographique et géochimique des roches formées à la base du complexe filonien dans l'ophiolite d'Oman et au niveau du Site IODP 1256, ainsi que sur une étude expérimentale. De nouvelles contraintes sont apportées sur les processus se produisant à la transition magma / système hydrothermal dans la croute océanique formée au niveau des dorsales à expansion rapide. L'intrusion de gabbros isotropes dans la base du complexe filonien a provoqué son réchauffement et sa recrystallization en « dikes granoblastiques » jusqu'à des températures de 1030°C. Des xénolites de microgabbro à orthopyroxene dérivées des dikes granoblastiques sont souvent observées dans le niveau de gabbros isotropes épais de 100 mètres environ qui est présent à la base du complexe filonien. Ces différentes caractéristiques sont à relier à des migrations verticales vers le haut du sommet de la lentille magmatique supérieure qui est observée aux dorsales rapides. Les nombreuses évidences d'assimilation (xénolites et patchs granoblastiques) dans le niveau des gabbros isotropes appuient l'hypothèse que ce niveau représente la fossilisation de la lentille magmatique supérieure. L'étude expérimentale a consisté à tester l'effet de la fusion partielle du complexe filonien préalablement hydrothermalisé. Les résultats montrent que la fusion commence à 850°C, confirment l'origine résiduelle des dikes granoblastiques et des xénolites associées, et attestent de l'origine anatectique des plagiogranites océaniques qui sont couramment observés à proximité de la base du complexe filonien. La composition en éléments majeurs et traces du liquide anatectique a été déterminée. Ce liquide représente le principal contaminant pour les MORBs primitifs émis au niveau des dorsales rapides. La lentille magmatique supérieure présente au niveau des dorsales médio-océaniques à expansion rapide est ici décrite comme un système dynamique qui peut migrer verticalement, et qui est fossilisée lorsqu'elle se déplace hors axe.
https://tel.archives-ouvertes.fr/tel-00448699

tel-00448699
https://tel.archives-ouvertes.fr/tel-00448699
https://tel.archives-ouvertes.fr/tel-00448699/document
https://tel.archives-ouvertes.fr/tel-00448699/file/France_2009_PhD.pdf

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : Ants have evolved venoms rich in peptides and proteins used for predation, defense, and communication. However, they remain extremely understudied due to the minimal amount of venom secreted by each ant. The present study investigated the differences in the proteome and peptidome of the venom from the bullet ant, Paraponera clavata. Venom samples were collected from a single colony either by manual venom gland dissection or by electrical stimulation and were compared using proteomic methods. Venom proteins were separated by 2D-PAGE and identified by nanoLC-ESI-QTOF MS/MS. Venom peptides were initially separated using C18 reversed-phase high-performance liquid chromatography, then analyzed by MALDI-TOF MS. The proteomic analysis revealed numerous proteins that could be assigned a biological function (total 94), mainly as toxins, or roles in cell regulation and transport. This investigation found that ca. 73% of the proteins were common to venoms collected by the two methods. The peptidomic analysis revealed a large number of peptides (total 309) but with <20% shared by the two collection methods. There was also a marked difference between venoms obtained by venom gland dissection from different ant colonies. These findings demonstrate the rich composition and variability of P. clavata venom.
ISSN: 1535-3893

hal-01603415
https://hal.archives-ouvertes.fr/hal-01603415
DOI : 10.1021/acs.jproteome.6b00948
PRODINRA : 406775
PUBMED : 28118015

Éditeur(s) : Public Library Science
Résumé : The diversity of deep-water corals in the Caribbean Sea was studied using records from oceanographic expeditions performed by the R/V Pillsbury. Sampled stations were sorted according to broad depth ranges and ecoregions and were analyzed in terms of species accumulation curves, variance in the species composition and contributions to alpha, beta and gamma diversity. According to the analysis of species accumulation curves using the Chao2 estimator, more diversity occurs on the continental slope (200–2000 m depth) than on the upper continental shelf (60–200 m depth). In addition to the effect of depth sampling, differences in species composition related to depth ranges were detected. However, the differences between ecoregions are dependent on depth ranges, there were fewer differences among ecoregions on the continental slope than on the upper continental shelf. Indicator species for distinctness of ecoregions were, in general, Alcyonaria and Antipatharia for the upper continental shelf, but also the scleractinians Madracis myriabilis and Cladocora debilis. In the continental slope, the alcyonarian Placogorgia and the scleractinians Stephanocyathus and Fungiacyathus were important for the distinction of ecoregions. Beta diversity was the most important component of gamma diversity in the Caribbean Basin. The contribution of ecoregions to alpha, beta and gamma diversity differed with depth range. On the upper continental shelf, the Southern Caribbean ecoregion contributed substantially to all components of diversity. In contrast, the northern ecoregions contributed substantially to the diversity of the Continental Slope. Strategies for the conservation of deep-water coral diversity in the Caribbean Basin must consider the variation between ecoregions and depth ranges.
Plos One (1932-6203) (Public Library Science), 2014-03 , Vol. 9 , N. 3 , P. -

Droits : 2014 Ivan Hernandez-Avila. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Research visit to RSMAS was partially supported by Comisio´n de Investigacio´ n, Universidad de Oriente. No additional
http://archimer.ifremer.fr/doc/00187/29868/28326.pdf
DOI:10.1371/journal.pone.0092834
http://archimer.ifremer.fr/doc/00187/29868/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Four fibers from banana-trees (leaf, trunk) and coconut-tree (husk, fabric) were examined before their incorporation in cementitious matrices, in order to prepare insulating material for construction. Their botanical compositions have been determined following a method described previously. Thermal degradation of these fibers were studied between 200 and 700 °C under nitrogen gas flow. Temperature of pyrolysis was the experimental parameter investigated. The solid residues obtained were analyzed by classical elemental analysis, Fourier Transform Infra Red (FTIR) spectroscopy and were observed by Scanning Electron Microscopy (SEM). This study has shown (1) the relation between botanical, chemical composition with both localization of fibers in the tree and type of tree; (2) the rapid and preferential decomposition of banana fibers with increasing temperature of pyrolysis and (3) the rough samples are made of hollow fibers.
ISSN: 0960-8524

hal-00809780
https://hal.univ-antilles.fr/hal-00809780
DOI : 10.1016/j.biortech.2005.11.030

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
The South Pacific region is characterized by a broadly elevated seafloor known as the South Pacific superswell. This region has a concentration of midplate volcanoes that experienced massive eruptions in the mid-Cretaceous period (90-120 Ma). These characteristics suggest the presence of a large-scale mantle plume beneath the South Pacific, called the South Pacific superplume. The geometry, origin depth, temperature, and composition of the superplume remain controversial, however, mainly due to the lack of seismological data that documents the mantle structure beneath the South Pacific. Seismic stations are sparse in the area due to its remote ocean environment. To obtain a better seismic image of the superplume, we deployed temporary broadband seismographs on oceanic islands and the seafloor in the South Pacific, which made possible the highest spatial resolution that has ever been achieved for the mantle structure beneath the region. The seismic image obtained from this new seismic data indicates that large-scale low-velocity anomalies (on the order of 1000 km in diameter), indicative of the superplume, are located from the bottom of the mantle to a depth of 1000 km, and small-scale low-velocity anomalies (on the order of 100 km in diameter) are present above it. A comparison of the seismic image with recent mantle convection studies based upon laboratory and numerical experiments suggests that the superplume may be a hot and chemically distinct mantle dome, and that the small-scale anomalies may be narrow plumes generated from the top of the dome. This model may explain various characteristics of hot spots in the South Pacific, such as the seafloor swell, short-lived hot spot chains, and the periodicity of massive eruptions.
ISSN: 1525-2027

hal-00443845
https://hal.archives-ouvertes.fr/hal-00443845
https://hal.archives-ouvertes.fr/hal-00443845/document
https://hal.archives-ouvertes.fr/hal-00443845/file/Suetsugu_PLUME_tomo_G32009_hal.pdf
DOI : 10.1029/2009GC002533

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : Tropical plant diversity is extraordinarily high at both local and regional scales. Many studies have demonstrated that natural enemies maintain local diversity via negative density dependence, but we know little about how natural enemies influence beta-diversity across habitats and/or regions. One way herbivores could influence plant beta-diversity is by driving allocation trade-offs that promote habitat specialization across resource gradients. We therefore predicted that increasing resource availability should be accompanied by increasing herbivory rates and decreasing plant allocation to defense. Second, relative abundances within plant lineages are predicted to reflect patterns of habitat specialization and allocation trade-offs. A phylogenetic context is vital not only to compare homologous plant traits (including defense strategies) across habitat types, but also to connect evolutionary trade-offs to patterns of species diversification in each phylogenetic lineage. We tested these predictions for trees in white-sand, clay terra firme, and seasonally flooded forests in Peru and French Guiana that represent the range of soil fertility, forest structure, and floristic compositions found throughout the Amazon region. We established 74 0.5-ha plots in these habitats and sampled all trees. Within 12 representative plots we marked newly expanding leaves of 394 saplings representing 68 species, including the most abundant species in each plot in addition to species from five focal lineages: Swartzia and Inga (Fabaceae), Protieae (Burseracaeae), Bombacoideae (Malvaceae), and Micropholis (Sapotaceae). We measured total leaf production rates for each sapling and calculated relative herbivory impact as the ratio between herbivory rate and leaf production rate. Herbivory rates averaged 2.1% per month, did not correlate with leaf production rate, and were similar across habitats. Relative herbivore impacts exceeded leaf production rates for most species. Leaf production rate averaged 2.8%, was significantly higher in seasonally flooded forests than the other two habitats, and exhibited significant correlations with specific leaf area. Species with high herbivory rates exhibited significantly lower relative abundances in terra firme forests. Overall, focal species within lineages present contrasting patterns regarding their herbivory rates and leaf production rate within habitats. These results highlight why a lineage-based approach is necessary when attempting to connect hypotheses regarding evolutionary trade-offs to community assembly patterns.
ISSN: 0012-9658

hal-01032418
https://hal.archives-ouvertes.fr/hal-01032418

Éditeur(s) : HAL CCSD
Résumé : International audience
Vulnerability–resilience indexes fail to grasp all dimensions of sustainability, whereas sustainable development has gained momentum. We fill this gap with a hierarchical multimetric composite index (Net Vulnerability Resilience Index: NVRI) whose robustness relies on a mathematical algorithm based on graph theory. A worldwide application shows that (i) both vulnerability and resilience are policy-responsive and that (ii) there is no determinism for a country to remain vulnerable or resilient. The NVRI enables us to identify a country’s strengths and weaknesses and determine the policy orientations that should be implemented to achieve sustainability.
World Development

hal-01291345
https://hal.archives-ouvertes.fr/hal-01291345
DOI : 10.1016/j.worlddev.2015.02.011

Éditeur(s) : The 11th Pacific Science Inter-Congress : Pacific Countries and their Ocean: Facing Local and Global Changes. March 2 - 6, 2009 Tahiti, French Polynesia
Résumé : New Caledonian shrimp farming feasibility studies started in the mid-seventies. Today ca. 2000 tons of Litopenaeus stylirostris, introduced in 1978, are semi-intensively produced each year. Since fifteen years, production has been impacted by two seasonal vibriosis, the “Summer” syndrome caused by Vibrio nigripulchritudo in relation to pond bottom and water column quality, and the “Winter Syndrome” caused by Vibrio penaeicida in relation to drastic temperature drops . With the ambition of elucidating processes possibly leading to mortality outbreaks in ponds, Ifremer has been conducting a research program since 2003 under the DESANS project (2003-2006) and the present DEDUCTION project, equally funded by the South and North Provinces and by the Government of New Caledonia. This program has been designed in a multidisciplinary approach integrating the suspected multifactorial origin of shrimp mortalities. Environment quality in ponds (either sediment or water column) plays a major role in the shrimp ecophysiological status, influencing sensitivity to pathogens . DEDUCTION focuses on a better knowledge of phytoplankton composition and biogeochemical fluxes at the sediment-water interface in ponds. Impact of farm discharges is also investigated. In addition, a more fundamental work is conducted to understand the pathogenicity mechanisms of these two Vibrio species but also to prevent the occurrence of viral infections through a RNA interference approach. Markers of the ecophysiological status of broodstock, larvae, post-larvae and reared animals, such as enzymes testifying from an oxidative stress, are developed. Gain of performance (resistance to pathogens and growth) were obtained on hybrids of the New Caledonian and introduced Hawaiian strains. Finally the database Stylog is exploited in view of discriminating “good” from “bad” rearings on the basis of relevant indicators.
Les études de faisabilité de l'aquaculture de crevettes ont débuté en Nouvelle-Calédonie dans les années soixante dix. Aujourd'hui environ 2000 tonnes de Litopenaeus stylirostris, introduite en 1978, sont produites chaque année de façon semi-intensive. Depuis quinze ans la production a été impactée par deux vibrioses : le syndrome d'été provoqué par Vibrio nigripulchritudo en relation avec la qualité de la tranche d'eau et des fonds de bassins et le syndrome d'hiver provoqué par Vibrio penaeicida en relation avec des chutes rapides de température. Dans le but d'élucider les processus entrainant des mortalités dans les élevages, Ifremer a conduit un programme de recherche depuis 2003 dans le cadre du projet DESANS (2003-2006) puis du présent projet DEDUCTION co-financé par les provinces Nord et Sud et le Gouvernement de la Nouvelle-Calédonie. Ce programme se construit dans une démarche multidisciplinaire intégrant les origines supposées multifactorielles des mortalités de crevettes. La qualité environnementale dans les bassins (les fonds et la colonne d'eau) joue un rôle majeur dans l'état physiologique des animaux, influençant leur sensibilité aux pathogènes. DEDUCTION se focalise sur une meilleure compréhension de la composition phytoplanctonique et des flux bio-géochimiques à l'interface eau/sédiment dans les bassins.L'impact des rejets des fermes est également étudié. En outre, un travail plus fondamental est conduit pour connaître les mécanismes de pathogénicité de ces deux espèces de Vibrio mais aussi pour prévenir les occurences d'infections virales par des approches ARN Interférence. Des marqueurs de l'état physiologique des oeufs, larves, post-larves et animaux en élevage, tels que les enzymes du stress oxydant sont utilisés.Les gains de performance (résistance aux pathogènes et croissance) sont obtenus sur des hybrides issus du croisement de la souche locale avec une souche hawaienne. Finalement la base de données STYLOG est exploitée dans le but de distinguer les bonnes des mauvaises pratiques sur la base d'indicateurs fiables.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00143/25438/23591.pdf
http://archimer.ifremer.fr/doc/00143/25438/

Éditeur(s) : Aix-Marseille II
Résumé : Les caractères texturaux et granulométriques, la fraction terrigène et la couleur sont étudiés sur 206 échantillons de sédiments meubles prélevés à la benne Neyrpic dans le Grand Lagon Nord de la Nouvelle-Calédonie (8 400 km²), selon un plan d'échantillonnage systématique et une maille de 3 milles nautiques. Sur la base de ces premiers résultats, qui font largement appel à la cartographie, 66 échantillons ont ensuite été sélectionnés pour une étude plus approfondie de leur composition biogène et des variations quantitatives et qualitatives de la biophase sédimentaire dans l'espace. Six environnements de dépôt, dont la différenciation résulte des interactions entre physiographie, hydrodyamisme et nature des peuplements benthiques, ont été identifiés et caractérisés : les zones de passes, les zones d'arrière-récif, la plaine lagonaire, les aires de décantation centrales de la plaine, le domaine côtier et les fonds de baies côtières. Sur l'ensemble du lagon, l'hydrodynamisme, plutôt faible, n'a qu'une action limitée sur les sédiments. La sédimentation fine est nettement prépondérante sur la sédimentation grossière. L'influence terrigène, cantonnée pour l'essentiel au domaine côtier est réduite et n'est décellable qu'au niveau de la phase fine des sédiments. La sédimentation organogène carbonatée domine très largement. La couleur des sédiments apparaît comme un bon indicateur de l'influence continentale et s'avère intéressante dans la distinction des environnements de dépôt. LeS Mollusques, les foraminifères, les Halimeda et les Scléractiniaires jouent un rôle majeur dans l'élaboration de la biophase sédimentaire. Toutefois la répartition des débris coralliens reste étroitement limitée à la proximité des édifices récifaux et la contribution directe du système récifal à la sédimentogénèse de la plaine lagonaire est très réduite. La tendance général est à une sédimentation biogène autochtone ou para-autocthone dont la nature reflèterait directement la distribution et la composition des peuplements générateurs actuellement en place.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00104/21566/19146.pdf
http://archimer.ifremer.fr/doc/00104/21566/

Éditeur(s) : HAL CCSD Ecole nationale du génie rural
Résumé :  
La forte diversité d'espèces arborescentes observées en forêts tropicales représente à la fois une source permanente de questionnements scientifiques et une contrainte forte pour améliorer les connaissances du fonctionnement de l'écosystème forestier. Les hypothèses avancées pour expliquer le maintien de cette diversité sont légion. Elles s'opposent sur la nature déterministe ou stochastique des mécanismes maintenant cette forte diversité. En pratique et pour mieux aborder les problèmes posés, cette diversité peut être simplifiée en regroupant les espèces présentant des similitudes dans leur comportement écologique. L'article présente quelques-unes des théories du maintien de la diversité et une synthèse des approches utilisées pour regrouper les espèces en illustrant chacun de ces thèmes par des travaux réalisés en Guyane.
ISSN: 0035-2829

hal-01032095
https://hal.archives-ouvertes.fr/hal-01032095

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cratons represent the oldest preserved lithospheric domains. Their lithosphere (lithospheric mantle welded to overlying Precambrian crystalline basement) is considered to be particularly robust and long-lived due to the protecting presence of buoyant and rigid “keels” made up of residual harzburgites. Although the cratons are mostly assumed to form in the Archaean, the timing of their formation remains poorly constrained. In particular, there are very few datasets describing concurrently the age of both the crustal and mantle portions of the lithosphere. In this study, we report new U–Pb ages and Hf isotope compositions for zircons in crustal xenoliths from the Udachnaya kimberlite in the central Siberian craton; this dataset includes samples from both the upper and lower portions of the crust. The zircon ages agree well with model melt-extraction Re–Os ages on refractory peridotite xenoliths from the same pipe; taken together they allow an integrated view of lithosphere formation. Our data reveal that the present day upper crust is Archaean, whereas both the lower crust and the lithospheric mantle yield Paleoproterozoic ages. We infer that the deep lithosphere beneath the Siberian craton was not formed in a single Archaean event, but grew in at least two distinct events, one in the late Archaean and the other in the Paleoproterozoic. Importantly, a complete or large-scale delamination and rejuvenation of the Archaean lower lithosphere (lower crust and lithospheric mantle) took place in the Paleoproterozoic. This further demonstrates that craton formation can be a protracted, multi-stage process, and that the present day crust and mantle may not represent complementary reservoirs formed through the same tectono-magmatic event. Further, deep cratonic lithosphere may be less robust and long living than often assumed, with rejuvenation and replacement events throughout its history.
ISSN: 0012-821X

hal-01467648
https://hal.archives-ouvertes.fr/hal-01467648
DOI : 10.1016/j.epsl.2016.09.046

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Plant litter diversity effects on decomposition rates are frequently reported, but with a strong bias towards temperate ecosystems. Altered decomposition and nutrient recycling with changing litter diversity may be particularly important in tree species-rich tropical rainforests on nutrient-poor soils. Using 28 different mixtures of leaf litter from 16 Amazonian rainforest tree species, we tested the hypothesis that litter mixture effects on decomposition increase with increasing functional litter diversity. Litter mixtures and all single litter species were exposed in the field for 9 months using custom-made microcosms with soil fauna access. In order to test the hypothesis that the long-term presence of tree species contributing to the litter mixtures increases mixture effects on decomposition, microcosms were installed in a plantation at sites including the respective tree species composition and in a nearby natural forest where these tree species are absent. We found that mixture decomposition deviated from predictions based on single species, with predominantly synergistic effects. Functional litter diversity, defined as either richness, evenness, or divergence based on a wide range of chemical traits, did not explain the observed litter mixture effects. However, synergistic effects in litter mixtures increased with the long-term presence of tree species contributing to these mixtures as the home field advantage hypothesis assumes. Our data suggest that complementarity effects on mixed litter decomposition may emerge through long-term interactions between aboveground and belowground biota.
ISSN: 0029-8549

hal-01032393
https://hal.archives-ouvertes.fr/hal-01032393
DOI : 10.1007/s00442-011-1966-4

Éditeur(s) : HAL CCSD Linnean Society of London
Résumé : International audience
Although migratory pelagic fishes generally exhibit little geographic differentiation across oceans, as expected from their life-history (broadcast spawning, pelagic larval life, swimming ability of adults) and the assumed homogeneity of the pelagic habitat, exceptions to the rule deserve scrutiny. One such exception is the narrow-barred Spanish mackerel (Scomberomorus commerson), where strong genetic heterogeneity at the regional scale has been previously reported. We investigated the genetic composition of S. commerson across the Indo-West Pacific range using control-region sequences (including previously published datasets), cytochrome-b gene partial sequences, and eight microsatellite loci, to further explore its phylogeographic structure. All haplotypes sampled from the Indo-Malay-Papua archipelago (IMPA) and the southwestern Pacific coalesced into a clade (Clade II) that was deeply separated (14.5% nucleotide divergence) from a clade grouping all haplotypes from the Persian Gulf and Oman Sea (Clade I). Such a high level of genetic divergence suggested the occurrence of two sister-species. Further phylogeographic partition was evident between the western IMPA and the regions sampled east and south of it, i.e. northern Australia, West Papua, and the Coral Sea. Strong allele-frequency differences were found between local populations in the southwestern Pacific, both at the mitochondrial locus (ΦST=0.282-0.609) and at microsatellite loci (^θ=0.202-0.313). Clade II consisted of four deeply divergent subclades (9.0-11.8% nucleotide divergence for the control region; 0.3-2.5% divergence at the cytochrome b locus). Mitochondrial sub-clades within Clade II generally had narrow geographic distribution, demonstrating further genetic isolation. However, one particular haplogroup within Clade II was present throughout the central Indo-West Pacific; that haplogroup was found to be sister-group to an haplogroup restricted to West Papua and the Coral Sea, yielding evidence of recent secondary westward colonization. Such a complex structure is in sharp contrast with the generally weak phylogeographic patterns uncovered to date in other widely distributed, large pelagic fishes with pelagic eggs and larvae. We hypothesize that in S. commerson and possibly other Scomberomorus species, philopatric migration may play a role in maintaining the geographic isolation of populations by annihilating the potential consequences of passive dispersal.
ISSN: 0024-4066

ird-00759711
http://hal.ird.fr/ird-00759711
http://hal.ird.fr/ird-00759711v2/document
http://hal.ird.fr/ird-00759711/file/FauvelotBorsa_Scomberomorus%20commerson%20p%20HAL.pdf

Résumé : La distribution actuelle des espèces d’arbres des forêts tropicales humides amazoniennes est le résultat de processus dynamiques sur lesquels les perturbations passées, d’origine climatique ou anthropique, peuvent avoir jouées un rôle majeur. Des outils génétiques actuels associés à des méthodes d’analyses puissantes permettent d’inférer et de dater l’empreinte génomique des évènements démographiques subits par les populations naturelles. Le but de cette thèse est de contribuer à une vision d’ensemble de l’évolution démographique de la forêt tropicale humide du plateau des Guyanes pendant le Quaternaire. J’ai d’abord étudié les propriétés des microsatellites (répétitions simple de séquences, SSR) et les limites de leurs applications en tant que marqueurs moléculaires en phylogéographie. Plusieurs allèles SSR contenu dans diverses populations de trois genres d’arbres différents ont été séquencés et le polymorphisme, porté par chaque partie des fragments ADN contenant des SSR, a été étudié. J’ai observé que la quantité de variation génétique était aussi importante dans les régions encadrant le microsatellite que dans le SSR lui-même. Ces régions ont contribué significativement à l’information phylogénétique et ont parfois été la principale source de différenciation entre les individus et les populations. Cette expérience m’a permis de choisir la meilleure stratégie à adopter pour traiter les données de variation génétique des SSR dans des modèles démographiques. J’ai ensuite utilisé ces marqueurs SSR et des méthodes ABC pour étudier l’impact local des occupations humaines précolombiennes sur les forêts en Guyane française. Les changements démographiques subis par des populations de quatre espèces d’arbres ont été comparés entre cinq sites occupés et quatre sites non perturbés. Les perturbations naturelles et induites par l’homme ont contribué à la mise en place de la diversité observée actuellement, comme le suggère des signatures d’effet fondateur détectées sur les sites perturbés ou non. Néanmoins, la taille des populations fondatrices semble être proportionnelle à l’impact humain estimé, indiquant que les perturbations anthropique ont induit un remplacement des populations plus important que les processus écologiques naturels. Pour terminer, j’ai mené une étude de démographie comparative d’espèces d’arbres tropicaux à l’échelle régionale de la Guyane française. Cinq scénarios démographiques ont été testés pour neuf populations de huit espèces en utilisant des microsatellites nucléaires et des séquences chloroplastiques. Les changements démographiques les plus récents détectés convergent vers une signature générale d’expansion de la forêt humide depuis probablement la dernière glaciation. Cela peut suggérer, soit que la composition des forêts du plateau des Guyanes était différente, ou que le couvert forestier était moins étendu. Ce résultat constitue le premier indice de changement passé, probablement d’origine climatique, subi par les communautés forestières du plateau des Guyanes ; qui n’avait jusque-là pas pu être testé avec des méthodes standards en raison d’un manque de fossiles. En conclusion, j’ai recueilli des preuves génétiques que les perturbations, à différents échelles de temps, ont marqué la structure et la composition génétique des forêts du plateau des Guyanes. L’application de ces méthodes à d’autres régions Néotropicales pourrait contribuer, à l’avenir, à reconstruire l’histoire écologique de la forêt amazonienne de façon détaillée.
The current tree species distribution in Amazonian tropical rainforests is the outcome of dynamic processes in which past perturbations, climatic or anthropogenic, may have played a major role. Currently available genetic tools associated with powerful analytical methods allow inferring and dating the genomic imprint of demographic events undergone by natural populations. The aim of my thesis is to contribute to an overview of the demographic evolution of the tropical rainforest in the Guiana shield during the Quaternary. I have first studied the properties of microsatellites or Simple sequence repeat (SSR) and the limits in their applications as molecular markers in phylogeography. Several SSR alleles in multiple populations of three divergent tree genera have been sequenced and the sources of polymorphisms, carried by each portion of SSR-containing DNA amplicons, have been broken apart. I have observed that the amount of variation was as large in flanking regions as in the SSR itself. The former contributed significantly to the phylogenetic information and sometimes was the main source of differentiation among individuals and populations. This experiment allowed me to choose the best strategy to treat SSR variation in demographic modeling. I have subsequently used SSR markers and ABC methods to study the impact of pre-Columbian human settlements at the local level on rainforests in French Guiana. Demographic changes undergone by populations of four tree species were compared between five settled and four undisturbed sites. Both natural turnover and human-induced disturbances appeared as shaping currently observed genetic diversity, with signatures of founder effect both at disturbed and undisturbed sites. Nevertheless, the size of founding populations appeared to be proportional to the estimated human impact, suggesting that human-made disturbance caused deeper population turnover than background ecological processes. Finally, I have conducted a comparative demography study of tropical tree species at the regional level across French Guiana. Five demographic scenarios have been tested for nine populations from eight species using both nuclear microsatellites and chloroplastic sequences. The most recent demographic signals detected converge on a global signature of expansion of the rainforest since probably the last glaciation. This finding can suggest either that the composition of the Guiana shield rainforests was different, or that its global extent was smaller, during earlier epochs of the Pleistocene than today. This result is the first firm indication of changes undergone by the forest communities of the Guiana shield in the distant climatic past – something which could not be tested with standard methods due to almost complete lack of fossil evidence. In conclusion, I have gathered genetic evidence that disturbances, both in historical and geological times, have marked the structure and composition of forests in the Guiana shield.The extensive application of these methods to other regions of the Neotropics maycontribute, in the future, to the detailed reconstruction of the ecological history ofAmazonian forests.

http://www.theses.fr/2012AGUY0568/document

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : Relict dune fields that are found as far south as 14 N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the Late Pleistocene. However, the discontinuous nature of dune records means that abrupt millennial-timescale climate events are not always resolved. High-resolution marine core studies have identified Heinrich stadials as the dustiest periods of the last glacial in West Africa although the spatial evolution of dust export on millennial timescales has so far not been investigated. We use the major-element composition of four high-resolution marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara Sahel boundary. Our records indicate that the Sahara Sahel boundary reached its most southerly position (13 N) during Heinrich stadials and hence suggest that these were the periods when the sand dunes formed at 14 N on the continent. Heinrich stadials are associated with cold North Atlantic sea surface temperatures which appear to have triggered abrupt increases of aridity and wind strength in the Sahel. Our study illustrates the influence of the Atlantic meridional overturning circulation on the position of the Sahara Sahel boundary and on global atmospheric dust loading.
Climate Of The Past (1814-9324) (Copernicus Gesellschaft Mbh), 2013 , Vol. 9 , N. 3 , P. 1181-1191

Droits : Author(s) 2013. CC Attribution 3.0 License. Access Climate of
http://archimer.ifremer.fr/doc/00181/29240/27635.pdf
DOI:10.5194/cp-9-1181-2013
http://archimer.ifremer.fr/doc/00181/29240/

Éditeur(s) : HAL CCSD American Geophysical Union (AGU) American Geophysical Union
Résumé : International audience
Environmental magnetism of speleothems is still in its early stage of development. Here we report on our investigation of the environmental and paleomagnetic information that has been recorded in speleothems, and what are the factors that control its preservation and reliability. To address these issues, we used a multidisciplinary approach, including rock magnetism, petrography, scanning electron microscopy, stable carbon and oxygen isotope compositions, and major and trace element concentrations. We applied this to a set of samples from different stages of speleothem evolution: present-day dripwater (glass plates), a weathered stalactite, a fresh stalagmite, cave sediments, and terra rossa soils. These samples come from the Penico and Excentricas caves, located in two distinct aquifers of the Algarve region, South Portugal. Our results show that the main magnetic carriers of the speleothems under study are primary (detrital) and consist of maghemite (and magnetite?). Similarities in coercivity and temperature dependence of the studied set of samples suggest that iron oxides are inherited from the terra rossa soils that cap the cave and were transported to the speleothems by dripwater. Hence, they represent a regional environmental signature. Interestingly, a stable and probably detrital remanent magnetization could be isolated in the fresh stalagmite, whereas the weathered stalactite yielded chaotic magnetic directions and very low remanent intensities. We propose that these low intensities can be the result from (i) different remanence acquisition mechanisms between stalagmite and stalactite and/or (ii) iron dissolution by fungal activity. We also suggest that magnetic properties and color and the content in detrital elements in the fresh speleothem inform about environmental processes acting on the interface of rock (soil)-atmosphere, while oxygen isotope composition and alkaline-earth element concentrations inform about calcite-water interaction processes. These results provide a better understanding of how environmental information is recorded in speleothems and what the factors are that control the reliability of the paleomagnetic and paleo-environmental signal.
ISSN: 0148-0227

hal-01114953
https://hal.archives-ouvertes.fr/hal-01114953
DOI : 10.1002/2014JB011381