Résumé : Les poissons herbivores jouent un rôle écologique majeur face au phénomène de « coral-algal phase-shift », qui sévit depuis le début des années 80 dans les récifs coralliens de la Caraïbe. Dans cette étude, les habitudes alimentaires des principales espèces de poissons herbivores ont été étudiées afin de comprendre comment ces espèces utilisent et se partagent les ressources trophiques en milieu récifal et dans les herbiers. Les niches trophiques de ces espèces ont été décrites par deux méthodes complémentaires: les analyses des contenus des tractus digestifs et les analyses des isotopes stables du carbone C3C/ 12C) et de l'azoteCSN/ '4N). La qualité nutritionnelle des sources alimentaires a été évaluée par leurs concentrations de macronutriments (protéines, lipides, glucides solubles et insolubles) afin d'expliquer en partie le choix des ressources par les herbivores. Parmi les 14 espèces de poissons étudiées, appartenant aux familles des Pomacentridae, des Acanthuridae et des Scaridae, huit types de niches trophiques ont été décrits, indiquant une diversité fonctionnelle de ces espèces. Les niches trophiques décrites sont occupées par une ou plusieurs espèces, indépendamment de leur morphologie et de leurs affinités taxinomiques. Les résultats de cette étude suggèrent une complémentarité entre ces espèces, en terme d'utilisation des ressources, et soulèvent la question de leur conservation afin de préserver leur rôle écologique dans les écosystèmes côtiers de la Caraïbe.
Herbivorous fishes play a major ecological role against the « coral-algal phase-shift » phenomenon in the coral reefs of the Caribbean. In this study, the feeding patterns of the most important species of herbivorous fishes have been studied to understand how these species use and share the trophic resources on reefs and seagrass beds . Trophic niches of these species have been described by two complementary methods: the analyses oftheir digestive contents and the analyses of stable isotopes of carbon C3C/ J2C) and nitrogen (lsN/14N). The nutritional quality of the sources has been evaluated by their concentrations of macronutrients (proteins, lipids, soluble and insoluble carbohydrates) to explain partially the choice of resources by herbivorous fishes . Among the 14 studied species of herbivorous fishes (Pomacentridae, Acanthuridae and Scaridae), eight types of trophic niches have been described, indicating a functional diversity of these species . The trophic niches are occupied by one or several species, independently oftheir morphology or their taxonomie affinities. The results of this study suggest a complementarity among these species and raise the question of their conservation to preserve their ecological role on marine ecosystems of the Caribbean.

http://www.theses.fr/2013AGUY0597/document

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a d13C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low d13C value can not be due to specific ingestion of 13C-depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by d13C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electronmicroscope views revealed the absence of bacterial endosymbionts. Energy-dispersive X-ray spectroscopy analysis detected low levels of sulfur (0.32%+-0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low d13C value of H. ruberrima can not be due to the presence of sulfur-oxidizing symbionts but more probably to the selective and exclusive consumption of free-living, sulfuroxidizing bacteria
ISSN: 0173-9565

hal-01253239
https://hal.archives-ouvertes.fr/hal-01253239
DOI : 10.1111/maec.12296

Éditeur(s) : HAL CCSD
Résumé : International audience
In the context of climate change, this study presents the ability of major/trace elements together with strontiumisotopes to trace back water paths at small scale and to deconvolve the geochemical signal of a small watershedsubject to intense flash floods episodes (Peyne, Hérault, France). Two small sub-basins draining distinct lithologiesin their heads (Plio-Villafranchian conglomerate versus Triassic gypsum-rich marls and dolomites) and the sameMiocene lithology downstream are investigated.Major elements and Ca/Na vs. Mg/Na ratios classically applied at large scale to distinguish carbonate from silicateweathering, allow here discriminating the three main lithologies from the two sub-basins. Trace elements Rband Sr coupled to calcium, also allow this lithological discrimination but in addition the Ca/Rb vs. Sr/Rb tracersappear to be much more discriminant for the various hydrological conditions. Thus, in combination with detailedlithological descriptions, they allow identifying the different facies that imprint the water signature through water-rock interaction according to the hydrological conditions.Strontium isotopes and Rb/Sr ratio, discriminate more precisely the drained lithologies of the 2 sub-basins. Firstly,the 87Sr/86Sr ratios allow identifying the nature of the lithologies and their main component(s) contributing to theSr budget in water and thus imprint the isotopic signature. Secondly, Sr isotopes evidenced two distinct Miocenefacies: the detritric faction (sandy marls), and the marine carbonates.The geochemical signatures of the brook samples draining both compartments were compared to the signatureof the Peyne River outlet just before the confluence into the Hérault River. It appears that the signature of thePeyne River, integrating all the water draining the basin, is relatively stable whatever the hydrological conditionsand mainly marked by the Miocene formations. Sr isotopes further highlight that this signature seems to resultfrom the mixing of both Miocene facies present in the lower part of the Peyne watershed, i.e. the sandy marls andthe carbonates. The typical signatures of the Plio-Villafanchian conglomerates and Triassic gypsiferous marls anddolomites of the headwaters of each sub-basin are completely hidden by the Miocene signatures. This should berelated to the large drainage area of the Miocene compared to other lithologies, despite the high solubility of thegypsum formations releasing large quantities of dissolved elements in solution.Understanding water paths at small scale is even more efficient when the geochemical approach is coupled with adetailed geological description. Indeed, the geochemical tracers are extremely dependent on the facies sequences(morphology) and of the soil nature (mineralogical composition), this is particularly sensitive at small scale.In the context of climate change increasing the intensity of rain events in the Mediterranean region, and resultingin catastrophic floods events (flash floods), tracing the origin of water contributing to the runoff is of primaryimportance and this must be investigated at small scale. Geochemical and isotopic fingerprinting thus constituteexcellent tools which can help to define the area of interest to be monitored in the framework of flood forecast andwarning networks
EGU General Assembly 2015
Vienne, Austria

hal-01118622
https://hal-brgm.archives-ouvertes.fr/hal-01118622

Éditeur(s) : Elsevier
Résumé : The main feature of the Congo-Angola margin in the Gulf of Guinea is the Congo (ex-Zaire) deep-sea fan composed of a submarine canyon directly connected to the Congo River, a channel and a [sediment] lobe area. During the multi-disciplinary programme called BIOZAIRE conducted by Ifremer from 2000 to 2005, two CTD-O2 sections with discrete water column samples were performed (BIOZAIRE3 cruise: 2003-2004) to study the influence of the Congo River discharges, both in the surface layer and in the deep and near-bottom layers. The surface layer water is greatly diluted with river water that has a heavy particle load. The deep layer is affected by episodic turbidity currents that flow in the deep Congo channel and reach deep areas far from the coast. Previous studies revealed deep anomalies in oxygen (deficit) and nutrient (excess) concentrations at not, vert, similar4000 m depth and assumed that they resulted from mineralisation of the particulate organic matter from the Congo River. The BIOZAIRE3 sections were designed to explore these phenomena in more detail near the Congo channel. Oxygen and nutrients were measured as well as additional parameters, including stable isotopes of oxygen and carbon, dissolved inorganic carbon and pH. For the surface layer, the effect of the Congo River was studied with reference to salinity. Deviations from the theoretical dilution of various inorganic solutes suggested the occurrence of mineralisation and consumption processes. For the deep layer, the network of CTD-O2 stations gave a more detailed description of the deep anomalies than in previous studies. From the east-west section, anomalies appeared on the bottom at 4000 m depth and became slightly shallower when they spread to the west. They were also present north and south on the bottom along the 4000 m isobath. In these deep waters, the decrease in the o13C values of dissolved inorganic carbon confirmed that the mineralisation of organic matter plays a role in generating these anomalies. The location of the origin of this deep anomaly is debated. Here, arguments are given in favour of mineralisation of the particulate organic matter input that overflows from the Congo channel at not, vert, similar4000 m depth during turbidity current events. Other authors suggest that this input comes from downslope particle transport. Anomalies of the same origin, but weaker, also occurred deeper on the Congo lobe, where the Congo channel ends, but with a significant pH decrease on the bottom which was not seen at 4000 m depth.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2183-2196

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6737.pdf
DOI:10.1016/j.dsr2.2009.04.002
http://archimer.ifremer.fr/doc/00000/6737/

Éditeur(s) : HAL CCSD
Résumé : Carbon isotopic signature has been measured at the different stages of the soil CO2 efflux production in trenched and control plots to improve the knowledge about the physical and biochemical processes of the soil respiration. All the measurements of d13C have been performed using a mass-spectrometer. We have compared the isotopic signatures of the CO2 going out of the soil, the CO2 of the soil atmosphere, the organic carbon in the material that could be considered as the main soil respiration sources (live and dead roots, soil organic matter, aerial litter) and the CO2 produced by these sources in incubation jars. The aims of this study were to evaluate the possibilities to combine these different data sets to estimate the partitioning of soil respiration between its autotrophic and heterotrophic components, and to get more insight into potential fractionation during biochemical or diffusion processes. Measurements were conducted in a beech forest located at Hesse in the North East of France (site equipped with a flux tower and belonging to the CarboEurope network) and in a neotropical primary rainforest located at Paracou (French Guiana). Preliminary results show first a very tenuous difference between CO2 isotopic signatures of efflux coming from the trenched and control plots and, secondly, d13C significant divergences between bulk organic material and CO2 produced in the corresponding incubation jars. Our ability to use this kind of data for partitioning soil respiration into its main components will be discussed.
AGU Fall Meeting
San Francisco, United States

hal-01032042
https://hal.archives-ouvertes.fr/hal-01032042

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Brecciated and fractured peridotites with a carbonate matrix, referred to as ophicalcites, are common features of mantle rocks exhumed in passive margins and mid-oceanic ridges. Ophicalcites have been found in close association with massive peridotites, which form the numerous ultramafic bodies scattered along the North Pyrenean Zone (NPZ), on the northern flank of the Pyrenean belt. We present the first field, textural and stable isotopic characterization of these rocks. Our observations show that Pyrenean ophicalcites belong to three main types: (1) a wide variety of breccias composed of sorted or unsorted millimeter- to meter-sized clasts of fresh or oxidized ultramafic material, in a fine-grained calcitic matrix; (2) calcitic veins penetrating into fractured serpentine and fresh peridotite; and (3) pervasive substitution of serpentine minerals by calcite. Stable isotopic analyses (O, C) have been conducted on the carbonate matrix, veins and clasts of samples from 12 Pyrenean ultramafic bodies. We show that the Pyrenean ophicalcites are the product of three distinct genetic processes: (1) pervasive ophicalcite resulting from relatively deep and hot hydrothermal activity; (2) ophicalcites in veins resulting from tectonic fracturing and cooler hydrothermal activity; and (3) polymictic breccias resulting from sedimentary processes occurring after the exposure of subcontinental mantle as portions of the floor of basins which opened during the mid-Cretaceous. We highlight a major difference between the eastern and western Pyrenean ophicalcites belonging, respectively, to the sedimentary and to the hydrothermal types. Our data set points to a possible origin of the sedimentary ophicalcites in continental endorheic basins, but a post-depositional evolution by circulation of metamorphic fluids or an origin from relatively warm marine waters cannot be ruled out. Finally, we discuss the significance of such discrepancy in the characteristics of the NPZ ophicalcites in the frame of the variable exhumation history of the peridotites all along the Pyrenean realm.
ISSN: 1437-3254

insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405
https://hal-insu.archives-ouvertes.fr/insu-00944405/document
https://hal-insu.archives-ouvertes.fr/insu-00944405/file/clerc-etal-IJES-Review.pdf
DOI : 10.1007/s00531-013-0927-z

Éditeur(s) : HAL CCSD
Résumé : In order to identify and quantify the Rif (Morocco) present-day deformation, especially those related to active faults (location, geometry, kinematic), we perform a morphotectonic study. The studied area and faults are located in the Northern part (conjugate faults of Al-Hoceima Bay: Trougout, Boujibar and Rouadi), the Eastern part (Nekor fault) and the Southern part of the chain (Rif frontal thrust between Fes and Meknes cities).Morphotectonic tools (DEMs at different scales, satellite and aerial pictures), field studies and Quaternary dating methods (U/Th, OSL, 14C and in-situ cosmogenic isotopes 10Be, 3He, 36Cl) allow us to characterize transtensional deformation in the Northern Rif. Horizontal and vertical slip rates along the N-S-oriented Trougout major fault are ~1.6 mm/yr and ~2 mm/yr respectively. In the Southern part, the Rif frontal thrust shows a shortening rate of ~1.8 mm/yr into Fes and Meknes area. In the Eastern part, the deformation is focused on the Nekor left-lateral strike-slip major fault with ~1.5 mm/yr. Incision features and raised marine terraces involve an uplift of the chain about ~0.2 mm/yr. The overall deformation in the Rif seems to be continuous since the Messinian-Pliocene time.These new morphotectonic constraints are consistent with the GPS measurements showing southwestward overall motion of most of the Rif belt with respect to stable Africa, associated to clockwise rotation. Finally, we propose a geodynamic model in which the Rif, the Alboran sea and the Betics belong to a single microplate bounded by the strike-slip faults of the Betics on the North, the Rif frontal thrust on the South, the Nekor and TASZ (Trans Alboran Shear Zone) strike-slip faults on the East and North-East, and the western Rif folded structures on the West.
L'objectif de cette étude est d'identifier et de quantifier les déformations actuelles dans la chaine du Rif (Maroc), notamment celles associées aux failles actives (localisation, géométrie, cinématique). Pour ce faire, nous mettons en œuvre pour la première fois dans cette région, une approche morphotectonique. Les sites et failles sélectionnés et étudiés se situent dans la partie Nord (les failles conjuguées de la baie d'Al-Hoceima: Trougout, Boujibar et Rouadi), l'Est (la faille de Nékor) et le Sud (front chevauchant sud rifain entre Fes et Meknes).A partir des outils de la morphotectonique (MNTs à différentes résolutions, images satellitaires, photographies aériennes), d'analyses de terrain et grâce aux méthodes de datation du Quaternaire (U/Th, OSL, 14C et isotopes cosmogéniques produits in-situ 10Be, 3He, 36Cl), cette étude met en évidence et quantifie une déformation transtensive dans la partie Nord de la chaine. Les vitesses de glissement horizontales et verticales le long de la faille principale d'orientation méridienne de Trougout sont de ~1.6 mm/an et ~2 mm/an, respectivement. Dans la partie Sud, nous montrons que le front rifain entre Fez et Meknes est actif avec une vitesse de raccourcissement de ~1.8 mm/an. La déformation dans la région Est se localise principalement sur la faille du Nékor avec une vitesse décrochante senestre de ~1.5 mm/an. Par ailleurs, la présence de nombreuses figures d'incision et de surfaces marines soulevées au niveau du littoral Nord témoignent d'une surrection généralisée de la chaine de l'ordre de ~0.2 mm/an. L'ensemble de cette déformation semble être constante depuis la période du Messino-Pliocène. Ces résultats sont cohérents avec les données GPS qui montrent un déplacement de ~5mm/an vers le SW de l'ensemble du Rif associé à un mouvement rotatif horaire, dans le référentiel Afrique stable. D'un point de vue géodynamique, nous proposons que le Rif, la mer d'Alboran et les Bétiques appartiennent à une même microplaque limitée au Nord par les failles décrochantes des Bétiques, au Sud par le chevauchement rifain, à l'Est et au Nord-Est par les failles décrochantes de Nékor et de la TASZ (Trans Alboran Shear Zone) et à l'Ouest par les structures plissées bordières du Rif.
https://tel.archives-ouvertes.fr/tel-01170466

NNT : 2014MON20105
tel-01170466
https://tel.archives-ouvertes.fr/tel-01170466
https://tel.archives-ouvertes.fr/tel-01170466v2/document
https://tel.archives-ouvertes.fr/tel-01170466/file/41875_POUJOL_2014_archivage_cor.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The coastal sediments of Rhodes in the eastern Mediterranean have recorded transgression-regression cycles that took place during the early Pleistocene. The sedimentary deposits from the Kritika Member of the Rhodes Formation consist in conglomerates, sandstones, siltstones and clays deposited in brackish to shallow marine environments. Faunal associations are dominated by molluscs and reveal rapid ecological changes. Carbon and oxygen isotope ratios of aquatic skeletal carbonates show that these ecological changes were most likely driven by large salinity changes while water temperature remained rather constant at about 22.0 ± 1.5 °C. The tectonic activity of the island rather than glacio-eustatic variations of climatic origin is advocated to be responsible for the ecological and salinity changes and sea-level variations recorded in the sedimentary sequence.
ISSN: 0031-0182

hal-00767568
https://hal.archives-ouvertes.fr/hal-00767568
DOI : 10.1016/j.palaeo.2012.06.009

Éditeur(s) : Elsevier
Résumé : Analysis of new high-resolution seismic-reflection profiles, chirp profiles and previously published sidescan data, together with piston cores on the Danube Fan provide new insight into the recent sedimentation processes in the deep northwestern Black Sea.The latest channel-levee system on the Danube Fan developed probably during the Neoeuxinian lowstand (oxygene isotope stage 2) in a semi-freshwater basin with a water level about 100 m lower than today. Sediment supplied by the Danube was transported to the deep basin through the Viteaz Canyon, which was directly connected to the leveed channel of this system on the middle slope. Channel avulsion was common in the middle fan, as indicated by four main phases of bifurcation. Each phase developed after the same pattern: breaching of the lower and narrower left levee by turbidity currents, building of a unit of High Amplitude Reflection Packets (HARP) by the unchannelized flow while the former channel was abandoned, followed by initiation of a new meandering leveed channel. The northward migration through successive bifurcations is influenced by the asymmetry between levees, hence by the Coriolis effect. In the lower fan where the levees became too low to maintain a stable pathway for the turbiditic flows, channel migration occurred. Locations of HARPs and channels after bifurcation are controlled by the pre-existing bathymetry. Sedimentary deposits are confined between the high levees of unit 0 (the initial phase of the youngest channel-levee system) to the south, and the steep relief of the Dniepr Fan to the north.The HARPs of the most recent phase of avulsion are the most severely constrained by local topography and form a very narrow elongate structure that is at most half as thick as the previous HARPs. Their distal part is not covered by channel-levee systems and is visible both on sidescan mosaics and on chirp profiles and was sampled in core BLKS 98-20.Sea level controlled fan activity but the evolution of the last channel-levee system with several bifurcations during a single sea level lowstand suggests that the primary control of channel avulsion and sand delivery is probably autocyclic.The presence of important HARP sand bodies in the mud-rich Danube Fan is presumed by analogy with a similar seismic facies on the Amazon Fan and indicated by the sands cored in BLKS98-20. However, only drilling of the HARP units could verify this interpretation.
Marine Geology (0025-3227) (Elsevier), 2001-09 , Vol. 179 , N. 1-2 , P. 25-37

Droits : 2001 Elsevier Science B.V. All rights reserved
http://archimer.ifremer.fr/doc/2001/publication-474.pdf
DOI:10.1016/S0025-3227(01)00197-9
http://archimer.ifremer.fr/doc/00000/474/

Éditeur(s) : Gauthier-Villars
Résumé : Samples of recent sediments and marine organisms from seven coastal lagoons along the Mexican coast of the Gulf of Mexico were analyzed by gas chromatography and GC-MS coupled system to determine the present levels of fossil hydrocarbons. Results show that the highest concentrations of fossil hydrocarbons are present in organisms and sediments located near petrochemical plants and oil refineries, indicating that petroleum hydrocarbons are being released into the coastal lagoons. Stable carbon isotope ratios (12C/13C) of sedimentary organic carbon in sediment and organism samples were also determined. For most of the lagoons, the delta 13C ratios for sediments ranged from -19.0 to -23.9%, anomalous ratios ranging from -26.8 to -29.3% were shown for sediments and organisms (oysters) of two of the studied areas, probably because of the presence of organic carbon from anthropogenic terrestrial sources.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1982

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35713/34222.pdf
http://archimer.ifremer.fr/doc/00246/35713/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Nitrogen (N) transfer from legume trees to associated crops is a key factor for the N economy of low-input agroforestry systems. In this work, we presented a new approach to estimate N transfer based on the 15N content of root exudates and N released by root turnover of the donor plant (Gliricidia sepium) and the temporal change of the 15N content of the receiver plant (Dichanthium aristatum). The study was carried out in greenhouse using two isotopic methods: 15N leaf feeding (LF) and the natural 15N abundance (NA). Measurements of exudate 15N were made at several dates before and after tree pruning. A time-dependent box model was devised to quantify N transfer in time and to make comparisons between the isotopic methods. In NA, although tree roots and exudates presented a similar 15N signature before tree pruning, exudates were strongly depleted in 15N after pruning. In LF, exudates were always depleted in 15N in relation to tree roots. Hence, the current assumption used in N transfer studies concerning the equal 15N/14N distribution in tissues of the donor plant and in its excreted N was not confirmed in our study. Before pruning, N transfer functioned as a two-N-source system (soil N and exudates N) and both isotopic methods provided similar estimates: 11–12% for LF and 10–15% for NA. Calculations performed with the model indicated that N transfer occurred with small or nil fractionation of 15N in exudates. After pruning, there was a third N source associated with N released from tree root turnover. During this period, the isotopic signature of the receiver plant showed a transient state due to the progressive decrease of 15N content of that N source. The amount of N derived from the tree represented 65% of the total N content of the grass at the end of the experiments.
ISSN: 1161-0301

hal-01082183
https://hal-agroparistech.archives-ouvertes.fr/hal-01082183
DOI : 10.1016/j.eja.2007.03.003

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Abstract Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in these flowing rivers and is mainly represented by scarce filamentous green algae and an abundant epilithic biofilm growing on wet stones in the river bed. Stable isotope analysis was used to quantify the relative importance of biofilm and other riverine allochthonous and autochthonous food sources in the diet of tropical shrimps (Palaemonidae, Atyidae and Xiphocarididae) and fishes (Gobiidae and Eleotridae) consumed by the local people. The epilithic biofilm was exploited by most species, constituted an important source of autochthonous carbon and was an important source of organic matter production at the base of freshwater food webs in Caribbean rivers. Biofilm percentages in the diet reached 32% for molluscs, 85% for atyid shrimps, 29% for xiphocaridid shrimps, 14% for palaemonid shrimps and 13% for fish. Assessment of biofilm in nine rivers showed that blue and red cyanobacteria were quantitatively dominant with a moderately rich diatom flora. These results address the interactions between river biofilm and Caribbean freshwater fauna where trophic links between consumers and their potential resources have poorly been documented.
ISSN: 0969-997X

hal-00744809
https://hal.univ-antilles.fr/hal-00744809
DOI : 10.1111/j.1365-2400.2010.00767.x

Éditeur(s) : Elsevier
Résumé : The aim of this study was to distinguish between sources of the complex variety of Marennes-Oléron Bay suspended particulate organic matter (SPOM) contributing to the tropho-dynamics of the Marennes-Oléron oyster farming bay. Basic biomarkers (Chl a, C/N and POC/Chl a ratios), carbon and nitrogen stable isotopes from SPOM were analyzed and the microalgae community was characterized. The sampling strategy was bimonthly from March 2002 to December 2003; samples were taken from an intertidal mudflat. Four main sources contributed to the SPOM pool: terrigenous input from rivers, neritic phytoplankton, resuspended microphytobenthos and periodic inputs from intertidal Zostera noltii meadows. Seasonal fluctuations were observed in both years of the study period: (1) SPOM collected in the spring of 2002 (δ13C = −250/00 to −230/00) was mainly composed of fresh estuarine inputs; (2) SPOM from the summer and fall of 2002 and 2003 was predominantly neritic phytoplankton (δ13C = − 220/00 to −190/00); (3) SPOM from the winter of 2002, spring of 2003 and winter of 2003 (δ13C = −21 to −230/00) was composed of a mixture of decayed terrigenous river inputs and pelagic phytoplankton, which was predominantly resuspended microphytobenthos. In the summer of 2003—the warmest summer on record in southern France and Europe—SPOM was particularly enriched for 13C, with δ13C values ranging from −140/00 to −120/00. Pulses in δ13C values, indicative of 13C-enriched decaying materials, extended into the fall. These were attributed to benthic intertidal inputs, including both resuspended microphytobenthos and Z. noltii detritus. Changes in SPOM sources in Marennes-Oléron Bay may lead to differences in the quality of the trophic environment available for reared oysters.
Estuarine, Coastal and Shelf Science (0272-7714) (Elsevier), 2008-07 , Vol. 78 , N. 3 , P. 576-586

Droits : 2008 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2008/publication-4313.pdf
DOI:10.1016/j.ecss.2007.11.001
http://archimer.ifremer.fr/doc/00000/4313/

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

Éditeur(s) : American Geophysical Union
Résumé : [1] A multiproxy integrated chronological framework, based on oxygen and carbon stable isotope stratigraphy, biostratigraphy (foraminifera and nannoplankton bioevents and foraminifer assemblage-based climate cyclicity), magnetostratigraphy, sapropel stratigraphy, and C-14 AMS radiometric dates, has been achieved for borehole PRAD1-2, collected in 185.5 m water depth in the central Adriatic. This work was carried out within the European Community project Profiles across Mediterranean Sedimentary Systems (PROMESS1). The 71.2 m long borehole spans a time interval between late MIS 11 and MIS 1 (the last 370 ka), showing a chronological resolution of 500 and 250 years per cm during interglacial and glacial intervals, respectively. At present, this record is the most expanded and continuous marine record available for the Adriatic Basin. Several orbital cycles can be recognized in the PRAD1-2 record: the 100 ka glacial-interglacial fluctuations and the 23 ka precession-related cycles, which in turn control the deposition of sapropel layers. An integrated analysis of short-term oscillations within the Last Glaciation interval (MIS 4-MIS 2) allowed the identification of the Adriatic signature of Dansgaard-Oeschger events, showing the potential to achieve a more refined chronostratigraphic framework for the top part of the PRAD1-2 record. Finally, the age model obtained by this study allowed the chronological integration of the main foraminifera bioevents detected in the borehole as well as of the volcanoclastic layers present in the upper part of the record. Despite its proximal location, PRAD1-2 presents a continuous record and shows the potential to be consistently correlated both with deep-sea and continental records in the Mediterranean region and beyond.
Geochemistry Geophysics Geosystems (1525-2027) (American Geophysical Union), 2008 , Vol. 9 , P. NIL_107-NIL_127

Droits : 2008 American Geophysical Union
http://archimer.ifremer.fr/doc/2008/publication-3605.pdf
DOI:10.1029/2007GC001713
http://archimer.ifremer.fr/doc/00000/3605/

Éditeur(s) : Université de Bretagne Occidentale
Résumé : The major objectives of this thesis were to study the structure, functioning and dynamics of different faunal assemblages associated with cold seep ecosystems in the eastern Mediterranean Sea. We focused our study on three main sites: the Marmara Sea, the Mediterranean ridge and the Nile deep sea fan. This thesis aims at determining the environmental signature of Mediterranean sites and the characteristics of the associated fauna at European and global scales. The specific objectives were to (1) determine the composition, diversity, density, biomass of invertebrate assemblages, (2) characterize biogeochemical conditions within different microhabitats in the vicinity of organisms, (3) to define the trophic relationships amongst seep fauna using stable isotope analyses (collaboration) and lastly, (4) to compare the spatial distribution and assemblage characteristics at different spatial scales (local, structure-scale, regional). The results show that (1) the Napoli mud volcano is the richest structure in terms of numbers of taxa while the Nile deep-sea fan sites need additional sampling, (2) a high variability is observed both between the different microhabitats but also within a single microhabitat, (3) the methane and oxygen gradients as well as substratum type are the main structuring factors explaining the distribution of the fauna and (4) the characteristics of the microhabitats, rather than the study area, influence the structure of benthic communities associated with Mediterranean cold seeps.
Les objectifs principaux de cette thèse sont d’étudier la structure, le fonctionnement et la dynamique de différents assemblages de faune associée aux émissions de fluides froids de Méditerranée orientale. Trois principaux sites ont été étudiés : la mer de Marmara, la ride méditerranéenne et le delta profond du Nil. Cette thèse tente de déterminer la « signature environnementale » des sites méditerranéens et les caractéristiques de la faune qui y est associée dans un contexte de marges européennes et mondiale. Les objectifs spécifiques sont (1) de déterminer la composition, la diversité, la densité et la biomasse des assemblages d'invertébrés ; (2) de caractériser les conditions biogéochimiques au sein des différents microhabitats à proximité des organismes; (3) de caractériser les relations trophiques sur les différents assemblages de faune par une approche isotopique (en collaboration) et finalement, (4) de comparer la distribution spatiale et les caractéristiques des assemblages à différentes échelles spatiales (locale, à l’échelle d’une structure géologique, régionale). Les résultats montrent que : (1) le volcan de boue Napoli est le site le plus riche en taxons alors que les sites du delta du Nil nécessiteraient un échantillonnage plus approfondi ; (2) il existe une grande variabilité entre les microhabitats ainsi qu’au sein d’un même microhabitat ; (3) les gradients en méthane, en oxygène ainsi que la nature du substrat sont les principaux facteurs abiotiques expliquant la distribution de la faune, (4) les caractéristiques des microhabitats, plutôt que la zone d’étude, influencent la structure des communautés benthiques associées aux écosystèmes de fluides froids méditerranéens.

Droits : 2010 The Author, UBO
http://archimer.ifremer.fr/doc/00020/13138/10178.pdf
http://archimer.ifremer.fr/doc/00020/13138/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé :  
Genetic variation for intrinsic water use efficiency (W i) and related traits was estimated in a full-sib family of Quercus robur L. over 3 years. The genetic linkage map available for this F1 family was used to locate quantitative trait loci (QTL) for W i, as estimated by leaf carbon stable isotope composition (δ 13C) or the ratio of net CO2 assimilation rate (A) to stomatal conductance to water vapour (g w) and related leaf traits. Gas exchange measurements were used to standardize estimates of A and g w and to model the sensitivity of g w to leaf-to-air vapour pressure deficit (sgVPD). δ 13C varied by more than 3‰ among the siblings, which is equivalent to 40% variation of W i. Most of the studied traits exhibited high clonal mean repeatabilities (>50%; proportion of clonal mean variability in global variance). Repeatabilities for δ 13C, leaf mass per area (LMA) and leaf nitrogen content were higher than 70%. For δ 13C, ten QTLs were detected, one of which was detected repeatedly for all 3 years and consistently explained more than 20% of measured variance. Four genomic regions were found in which co-localizing traits linked variation in W i to variations in leaf chlorophyll and nitrogen content, LMA and sgVPD. A positive correlation using clonal means between δ 13C and A/g w, as well as a co-localisation of QTL detected for both traits, can be seen as validation of the theoretical model linking the genetic architecture of these two traits.
ISSN: 1614-2942

hal-01032066
https://hal.archives-ouvertes.fr/hal-01032066
DOI : 10.1007/s11295-007-0107-z

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Plants often rely on external, mutualistic partners to survive and reproduce in resource-limited environments or for protection from enemies. Such interactions, including mycorrhizal symbioses and ant-plant associations, are widespread and play an important role at the ecosystem and community levels. In ant-plant mutualisms, the plants may benefit from both the protection provided by the presence of ants and from the nutrients absorbed from insect debris. However, the role of third partners in plant nutrition, particularly ant-associated fungi, has never before been demonstrated. 2. We investigate this issue in the ant-plant Hirtella physophora. In this model system, Allomerus decemarticulatus ants are involved in two, highly specific interactions: first, with their host plant, and, secondly, with a fungus that they actively manipulate. Moreover, the ants combine both plant trichomes and fungal hyphae to make a trap to capture prey. 3. We empirically demonstrate the existence of a third type of interaction between the fungus and the plant through the use of both experimental enrichments with stable isotopes (15N) and histological approaches. The fungus growing in the galleries plays a role in providing nutrients to the host plant, in addition to the structural role it plays for the ants. Fungus-facilitated nitrogen uptake occurs mainly in old domatia, where abundant hyphae are in close contact with the plant cells. Whether the fungi inside the domatia and those in the galleries are the same is still uncertain. 4. Synthesis. Together, our results show that a fungal partner in an ant-plant mutualism can benefit the plant by improving its nutrient uptake, and they demonstrate the existence of a true tripartite mutualismin this system. Our results add further evidence to the notion that interpretations of some ant-plant symbioses as purely protective mutualisms have overlooked these nutritional aspects.
ISSN: 0022-0477

hal-00818792
https://hal.archives-ouvertes.fr/hal-00818792

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Almost all Red Sea deeps contain metal-rich sediments covered by brine pools. It is generally agreed that these metal-rich deposits precipitated from overlying metal-rich brines that originated from migrating hydrothermal fluids. No brine pool has ever been reported in Thetis Deep, inciting us to evaluate if such a brine layer ever occurred in the deep during the past. In order to address that questioning, a study combining mineralogical, geochemical (major-, minor-, rare-earth elements) and isotopic (Sr. Nd. Pb) approaches was completed on cored sediments and extracted interstitial waters from inside and outside the deep.;The sediments have an overall hydrothermal origin, as shown by the REE concentrations and patterns, metal contents, and Pb-Nd isotopic data, all pointing to a mantle signature. The intensity of the hydrothermal activity varied with time in the deep; the most intense episode resulting in an almost pure Fe-oxi-hydroxide layer. Varied chemical arguments, especially the Zr and REE data of the sediments, favor the fact that the whole sedimentation in Thetis Deep occurred in the absence of a stable, salt-rich and mineralized brine pool, and that no brine layer ever existed. This conclusion is supported by the constant Sr isotope composition of the sediment and its interstitial waters that are almost identical to that of the Red Sea seawater. The study also suggests that hydrothermal activity monitored fluid supplies that interacted differently with seawater in the different Red Sea deeps, resulting in an overall formation of metal-rich sediments, but along varied local conditions. (C) 2009 Elsevier B.V. All rights reserved.
ISSN: 0375-6742

hal-00475646
https://hal.archives-ouvertes.fr/hal-00475646
DOI : 10.1016/j.gexplo.2009.10.001

Éditeur(s) : HAL CCSD Elsevier Masson
Résumé : Reconstruction of Northern African monsoon between 6.2 and 4.9 Ma and possible relationships with Late Miocene events. Mineralogical and geochemical investigations have been realized on ODP Site 659 in order to better understand the detrital sedimentation of the Cap Verde plateau and to reconstruct African monsoon intensity variations between 6.2 and 4.9 Ma. Time intervals corresponding to an intensification of the summer African monsoon rainfall are associated to a reduction of eolian input from the Sahara and an intensification of the African river input. The reflooding of the Mediterranean Sea at the end of the Messinian salinity crisis (MSC) (5.33 Ma) is correlated to a greater aridity in the Sahara.
ISSN: 1631-0713

hal-00412151
https://hal.archives-ouvertes.fr/hal-00412151
DOI : 10.1016/j.crte.2008.07.005