Modèle stratigraphique et processus sédimentaires au Quaternaire sur deux pentes carbonatées des Bahamas (leeward et windward)
Cette étude présente une reconstruction du fonctionnement sédimentaire au Quaternaire de deux pentes carbonatées des Bahamas (leeward et windward). Elle est basée sur les analyses stratigraphique et sédimentaire de 34 carottes principalement collectées lors de la mission CARAMBAR (2010). Une étude stratigraphique à haute résolution a été développée à partir de plusieurs outils stratigraphiques, dont l’écostratigraphie basée sur les assemblages de foraminifères planctoniques qui a permis de dater l’ensemble des séquences sédimentaires en s’affranchissant des problèmes liés à la diagenèse précoce. L’analyse sédimentaire des carottages a permis de proposer une nouvelle classification des sédiments carbonatés meubles qui caractérise les fractions dominantes du sédiment au moment du dépôt. Elle permet notamment de discriminer les dépôts fins et d’identifier les processus de transport off-bank, les dépôts contouritiques, gravitaires ou légèrement diagenétisés. Les processus de transport off-bank permettent l’accumulation de boue carbonatée de plate-forme (aiguilles d’aragonite et silts) au niveau des pentes des Bahamas lorsque la plate-forme est ennoyée. Les derniers 4ka cal BP, le MIS 5e et le début du MIS 11 sont les principales périodes d’accumulation sédimentaire au cours des derniers cycles climatiques. L’érosion intra-pente, l’action des courants de fond et les processus de diagenèse précoce ont également été mis en évidence. La pente leeward se caractérise par une sédimentation très importante (wackestone) alors que la pente windward a conservés a morphologie pliocène avec localement des accumulations sédimentaires quaternaires de faible épaisseur (wackestone à packstone).
(06/07/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Shoreline response to multi-scale oceanic forcing from video imagery
The aim of this study was to develop a methodology to statistically assess the shorelineresilience to storms at different time scales for a storm-dominated mid-latitude beach(Biscarrosse, France). On a pilot base, storm-free tropical Jamestown beach (Ghana) was alsoanalysed. 6-years (2007-2012) of continuous video-derived shoreline data and hindcastedhydrodynamics were analysed. Wave climate is dominated by storms (Hs>5% exceedancelimit) and their seasonal fluctuations; 75% of storms occur in winter with more than 60identified storms during the study period. A multiple regression on 36 storms shows thatwhereas current and previous storm intensity have predominant role on current storm impact,tide and sandbar play a major role on the post-storm recovery. An ensemble average on poststormrecovery period shows that Biscarrosse beach recovers rapidly (9 days) to individualstorms, and sequences of storms (clusters) have a weak cumulative effect. The results point outthat individual storm recurrence frequency is key. If the interval between two storms is lowcompared to the recovery period, the beach becomes more resilient to the next storms; and thefirst storm in clusters has larger impact than following ones. Shoreline responds in decreasingorder at seasonal, storm frequency and annual timescales at Biscarrosse. The EOF methodshows good skills in separating uniform and non-uniform shoreline dynamics, showing theirdifferent temporal variability: seasonal and short-term scales dominate first EOF (2D) andsecond (3D) modes, respectively.The shoreline at Jamestown was studied on pilot base from 2013-2014. Water level channgesplay a major role on shoreline changes. Waves estimates from video are in good agreement withhindcasts. This study shows the potential of the technique, to be replicated elsewhere in WestAfrica with all its diversity and regional climate variability through a coastal observationnetwork.
(06/07/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Origin of the large Pliocene and Pleistocene debris flows on the Algarve margin
The base of the Faro contouritic drift (IODP Site U1386) on the northern margin of the Gulf of Cádiz (Algarve margin) is characterized by two sequences of frequent gravity deposits with different ages and compositions. Among these gravity deposits, several relatively thick debrites (up to 12 m) have been observed and studied in detail. Sedimentological analyses have been performed and because of non-turbulent behavior of debris flows, detailed micropaleontological studies could be realized. Planktonic foraminifera thus allowed establishing a detailed biostratigraphy of these deposits. Benthic foraminifer and ostracod assemblages were used to evaluate the origin of the sediment composing these debris flows and estimate their run-out distance. These debrites are dated from Early Pliocene and early Pleistocene, and were deposited in a mesobathyal environment. They comprise silty mud clasts and matrixes with sand content up to 34%. The Early Pliocene debrites are bioclast-rich whereas the Early Pleistocene debrite is enriched in terrigenous particles. The data indicates that these debrites were triggered on the continental shelf and traveled less than 100 km, eroding the seafloor all along their path for the Early Pliocene debrites and only the first part of their path for the early Pleistocene debrite. Matrixes originate from failure areas whereas eroded sediments along the flow pathway are incorporated into the flow as clasts. High abundance of shelf fauna during the Early Pliocene and great supply of terrigenous particles from rivers during the early Pleistocene in the south-western Iberian margin have favored gravity flows from the continental shelf to the slope. The contouritic paleo-moat of the Faro drift has been a determining channeling feature for gravity flows along the Algarve margin during the early Pleistocene, testifying of the strong interaction between MOW circulation and down-slope processes. Tectonic and diapiric activities were significant during Early Pliocene and early Pleistocene on the Algarve margin and could have been triggering parameters of failures related to these debris flows.
(Marine Geology. vol. 377, n° 0025-3227, pp. 58-76, 01/07/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, TAMU, INSU - CNRS, UM, CNRS, UA, IPMA
Quaternary chronostratigraphic framework and sedimentary processes for the Gulf of Cadiz and Portuguese Contourite Depositional Systems derived from Natural Gamma Ray records
The Contourite Depositional Systems (CDS) in the Gulf of Cádiz and on the West Iberian margin preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 5.3 Ma. These CDS have been recently drilled in several places during the IODP Expedition 339. These drill sites now offer a new window to the internal Pliocene and Quaternary architecture of the CDS. In this study, we use downhole and core Gamma Ray (GR) data acquired from 5 sites drilled in the CDS along the middle slope and 1 site drilled in the deeper setting of the lower slope, out of the MOW path. The GR data primarily tracks the clay content in the sediment and is the expression of sediment supply and, for sites drilled in the CDS, of the bottom current processes. Both appear astronomically controlled as shown by spectral analysis performed on the GR data. Results also reveal that the GR log patterns correlate well across the sites over the last 1.4 My. Several GR horizons corresponding to drops in GR values were identified, most of which fit with coarse-grained deposits observed in cores and interpreted as contourite beds. The GR horizons are interpreted as isochronous horizons, providing a regional scale chronostratigraphic framework for the CDS depositional records with an accuracy of ~ 20 ky. We further assess the spatial and temporal variability of the CDS hiatuses at the regional scale.
(Marine Geology. vol. 377, n° 0025-3227, pp. 40-57, 01/07/2016)
INSU - CNRS, UM, CNRS, UA, UAlg, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CRIGEN, GDF Suez, TAMU
The antidepressant venlafaxine may act as a neurodevelopmental toxicant in cuttlefish (Sepia officinalis)
The Serotonin/Norepinephrine Reuptake Inhibitor (SNRI) antidepressant venlafaxine (VEN, Effexor (R)) has become one of the most common antidepressants detected in North American and European streams. Mammalian research has established that VEN exposure is associated with a range of structural, neurochemical, and functional alterations of the brain in adults and newborns. However, the neurodevelopmental effects of VEN on non-target organisms have never been investigated. The aim of our research was to decrease this gap in knowledge by characterizing the effects of VEN exposure on a cephalopod mollusk, the common cuttlefish Sepia officinalis. This species inhabits VEN-contaminated waters and possesses an unusually sophisticated brain. These characteristics render it a unique invertebrate species for studying the neurodevelopmental effects of VEN. Cuttlefish were exposed to environmentally-relevant concentrations of VEN (Measured concentrations approximate to 5 and 100 ng L-1) or to filtered natural seawater (control) in a closed-loop system with regular water changes during the first 20 days after hatching. We evaluated brain maturation as well as neurochemical changes and behavioral performances during this critical period of development. Our results show that both VEN-exposed groups exhibited a decrease in norepinephrine levels, along with a reduction in the relative number of glutamate NMDA-like receptors binding sites in the group exposed to 5 ng L-1 of VEN after 20 days of exposure. Brain regional changes in cellular proliferation were observed in VEN-exposed groups in the vertical lobe (i.e. a key structure involved in cognitive processes) and in the optic lobes (i.e. main visual processing centers) in the absence of significant change in their volume. Along with these neurodevelopmental changes, 20 days of exposure to 100 ng L-1 of VEN was associated with a decrease in camouflage ability. Overall, our study suggests that VEN is a neurodevelopmental toxicant in non-target aquatic organisms at environmentally-relevant concentrations. (C) 2016 Elsevier B.V. All rights reserved.
(NeuroToxicology. vol. 55, n° 0161-813X, pp. 142--153, 01/07/2016)
GMPc, UNICAEN, NU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The fate of C 4 and C 3 macrophyte carbon in central Amazon floodplain waters: insights from a batch experiment
The central Amazon floodplains are particularly productive ecosystems, where a large diversity of organic carbon sources are available for aquatic organisms. Despite the fact that C4 macrophytes generally produce larger biomasses than C3 macrophytes, food webs in the central Amazon floodplains appear dominantly based on a C3 carbon source.In order to investigate the respective fate and degradation patterns of C4 and C3 aquatic plant-derived material in central Amazon floodplains, we developed a 23-days batch experiment. Fatty acid and carbon concentrations as well as stable isotope compositions were monitored over time in 60 L tanks. These tanks contained Amazon water, with different biomasses of C3 and C4 macrophyte, representative of in situ densities occurring in central Amazon floodplains.In the C4Paspalum repens treatments, organic (POC, DOC) and inorganic carbon (DIC) got rapidly enriched in 13C, whereas in the C3Salvinia auriculata treatments, POC and DOC showed little change in concentration and isotopic composition, and DIC got depleted in 13C. The contribution of P. repens to POC and DOC was estimated to reach up to 94.2 and 70.7%, respectively. In contrast, no differences were reported between the C3S. auriculata and control treatments, an observation attributed to the lower C3 biomass encountered in the field, to a slower degradation rate of C3 compared to C4 compounds, and to similar isotopic compositions for river POC and DOC, and C3 compounds.The 13C enrichments of POC, DOC, and DIC from P. repens treatments were attributed to an enhanced bacterially-mediated hydrolysis and mineralization of C4 material. Evolutions of bacterial abundance and branched fatty acid concentrations confirmed the role of heterotrophic microbial communities in the high P. repens decomposition rate. Our experiment highlights the predominant role of C4 aquatic plants, as a large source of almost entirely biodegradable organic matter available for heterotrophic activity and CO2 outgassing to the atmosphere.
(Limnologica. vol. 59, n° 0075-9511, pp. 90-98, 01/07/2016)
BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, UFF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MNHN, DGD.REVE, MNHN, ISTO, BRGM, INSU - CNRS, UO, CNRS, ISTO, BRGM, INSU - CNRS, UO, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO, IPG Paris, IRD [Burkina Faso], UFJF
ROULÉPUR: Evaluating innovative solutions for the source control of micropollutants associated with road and parking lot runoff
(28/06/2016)
LEESU, ENPC, UPEC UP12, TEAM, Cerema, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LCPP
Les monuments mégalithiques submergés de la côte léonarde
Les sociétés néolithiques et de l’âge du Bronze ancien installées en Bretagne ont érigé de nombreux monuments mégalithiques (tombes, pierres dressées) en bord de mer. Aujourd’hui plusieurs d’entre eux, ensevelis sous les dunes ou submergés par la mer, sont des témoins spectaculaires de l’évolution du littoral qui s’est opéré durant ces derniers millénaires. Cette étude s’intéresse à trois monuments mégalithiques submergés, situés sur la côte nord de l’ancien pays du Léon. Il s’agit de deux allées couvertes situées respectivement dans l’anse de Kernic (Plouescat) et dans l’anse de Tréssény (Kerlouan) ainsi que d’un ensemble mégalithique (un menhir et probablement une enceinte mégalithique) se trouvant dans l’anse de Saint-Cava à Plouguerneau. Afin d'apporter une lumière nouvelle sur ces sites, une approche pluridisciplinaire relevant à la fois de l’archéologie, de la géologie et de la géographie est mise en œuvre. L’étude a d’abord pour but d’établir une méthodologie spécifique d’étude, applicable au contexte difficile qu’est l’estran et en utilisant des nouvelles technologies de relevés en trois dimensions. En effet, ces monuments subissent une submersion biquotidienne par la mer et ne sont donc accessibles aux observations uniquement durant des brefs instants. Ensuite, un soin particulier est apporté à l’observation des blocs constituants les monuments. Ces derniers sont étudiés tant d’un point de vue de la technologie, apportant des informations sur les modes de mise en œuvre des blocs, que d’un point de vue de la pétrographie afin d’identifier les roches utilisées lors de leur construction. Enfin, nous essayons de reconstituer l’environnement dans lequel chacun de ces sites a été construit et occupé.
(10/06/2016)
LDO, INSU - CNRS, UBO EPE, CNRS, LETG - Brest, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN
A survey of the summer coccolithophore community in the western Barents Sea
The Barents Sea is particularly vulnerable to large-scale hydro-climatic changes associated with the polar amplification of climate change. Key oceanographical variables in this region are the seasonal development of sea-ice and the location and strength of physico-chemical gradients in the surface and subsurface water layers induced by the convergence of Arctic-and Atlantic-derived water masses. Remote sensing imagery have highlighted the increasing success of calcifying haptophytes (coccolithophores) in the summer phytoplankton production of the Barents Sea over the last 20 years, as a response to an overall larger contribution of Atlantic waters to surface and sub-surface waters, as well as to enhanced sea-ice melt-induced summer stratification of the photic layer. The present study provides a first thorough description of coccolithophore standing stocks and diversity over the shelf and slope of the western Barents Sea from two sets of surface and water column samples collected during August-September 2014 from northern Norway to southern Svalbard. The abundance and composition of coccolithophore cells and skeletal remains (coccoliths) are discussed in view of the physical-chemical-biological status of the surface waters and water column based on in-situ (temperature, salinity, fluorescence) and shore-based (microscope enumerations, chemotaxonomy) measurements, as well as satellite-derived data (Chl a and particulate inorganic carbon contents). The coccolithophore population is characterized by a low species diversity and the overwhelming dominance of Emiliania huxleyi. Coccolithophores are abundant both within the well stratified, Norwegian coastal water-influenced shallow mixed layer off northern Norway, as well as within well-mixed cool Atlantic water in close vicinity of the Polar Front. Bloom concentrations with standing stocks larger than 4 million cells/l are recorded in the latter area north of 75°N. Our limited set of chemotaxonomic data suggests that coccolithophores contribute substantially (ca. 20% of the total Chl a) to the summer phytoplankton community which is made essentially of small-sized algal groups. Excluding the bloom area, coccolith calcite accounts for an average of 20% to the bulk particulate inorganic carbon content in the surface waters, and explains to some extent the satellite-derived spatial distribution of this parameter. Deep water living coccolithophore species thriving below the pycnocline as well as populations present in well-mixed cool Atlantic water are rapidly transferred to depth in the form of intact coccospheres down to at least 200 m. High amplitude internal waves which, according to our observations, affect a wide range of water depth up to the lower photic zone, might strengthen the vertical transfer of this sinking population.
(Journal of Marine Systems. vol. 158, n° 0924-7963, pp. 93-105, 01/06/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CAIRN, Inria, IRISA-D3, IRISA, UR, INSA Rennes, UBS, ENS Rennes, Inria, CNRS, BIAF, UA, SHOM
Selection of an appropriate aqueous nano-fullerene (nC60) preparation protocol for studying its environmental fate and behavior
The inevitable future environmental release of fullerene nanoparticles (nC60) requires the development of specific analytical methodologies that are able to identify, characterize and quantify these new nanomaterial species. As is well detailed in the literature, the characterization of nanoscale materials requires the consideration of several physical and chemical parameters, such as size, size distribution, shape, charge surface, and surface chemistry. All of these parameters must be determined to assess the representative impact of manufactured nanoparticles in environmental media. Nevertheless, appropriate and environmentally representative nanoparticles standards are not currently available for the development of such analytical strategy and validating measurements. This tentative critical review presents a different pathway for the preparation of fullerene nanoparticles in aqueous media for environmental studies (characterization, fate and behavior determination). The principal drawbacks and bias measurement are presented as well as the consequences of this new pathway for our understanding of environmental implications.
(Trends in Analytical Chemistry. vol. 80, n° 0165-9936, pp. 1-11, 01/06/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS