Sedimentary processes determining the modern carbonate periplatform drift of Little Bahama Bank
This paper presents an analysis of the combined influence of along-slope sediment transport and off-bank sediment export from the Little Bahama Bank (LBB) to the periplatform sediment wedge of the northwestern part of the slope over the last 424 ka. The LBB northwestern slope is divided in (i) a plateau-like structure (margin) at similar to 40 m water depth over at least 4 km parallel to the edge of the LBB; (ii) the uppermost slope with a mean slope angle of similar to 1.15 degrees from 40 to 300 m water depth; (iii) the upper, slope with slope angle of similar to 0.7 from 300 to 650 m water depth, (iv) the middle slope with slope angle of similar to 1.2, from 650 to 800 m water depth, and (v) the lower slope with slope angle of -6 m) that occurred during interglacial periods, the highest sedimentation rates (10-30 cm/ka) and the finest sediment fades were found on the slope. During interglacial periods when RSL < -6 m, LBB was emerged but bank margins were still flooded and correspond to intermediate sedimentation rates (a few to 10 cm/ka) on the slope. Finally, during glacial periods (RSL < -90 m), LBB was emerged (including its margins), sedimentation rates on the slope dropped to a few mm/ka associated to coarser sediment facies. Off-bank-transported sediment is the main sediment supply during sea-level highstands, occurring preferentially during three major periods of LBB flooding over the last 424 ka: marine isotopic stages 1, 5e and 11. During sea level lowstands, shallow carbonate production was very low but could develop over a 4 km-wide plateau-like structure when RSL was above -40 m. The regional Antilles Current affected the sea floor along the northwestern LBB slope and influenced coral mound distribution as well as sediment facies and sequences along the upper and middle slopes (300-800 m). During glacial periods, the stronger influence of the Antilles Current upon the along-slope sedimentation promoted diagenesis via the development of indurated nodules in the upper slope (similar to 400 m water depth). It also encouraged bi-gradational sequences showing a coarsening-up unit followed by a fining-up unit along the middle slope (similar to 800 m water depth) that is thoroughly bioturbated. The characteristics of these contourite sequences were similar to those described in siliciclastic environments, but in contrast were condensed with low sedimentation rates over long (glacial) periods. (C) 2015 Elsevier B.V. All rights reserved.
(Marine Geology. vol. 378, n° 0025-3227, pp. 213-229, 01/08/2016)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, KFUPM, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, [Total Energies. Anciennement : Total, TotalFina, TotalFinaElf]
Effects of disc asymmetries on astrometric measurements
(Astronomy & Astrophysics - A&A. vol. 592, n° 0004-6361, pp. A39, 01/08/2016)
LESIA (UMR_8109), INSU - CNRS, CNRS, PSL, UPD7, SU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LUTH (UMR_8102), INSU - CNRS, CNRS, PSL, UPD7, CNRS, SYRTE, INSU - CNRS, CNRS, PSL, SU, CNRS
Sedimentary response to sea ice and atmospheric variability over the instrumental period off Adélie Land, East Antarctica
Diatoms account for a large proportion of primary productivity in Antarctic coastal and continental shelf zones. Diatoms, which have been used for a long time to infer past sea surface conditions in the Southern Ocean, have recently been associated with diatom-specific biomark-ers (highly branched isoprenoids, HBI). Our study is one of the few sedimentary research projects on diatom ecology and associated biomarkers in the Antarctic seasonal sea ice zone. To date, the Adélie Land region has received little attention, despite evidence for the presence of high accumulation of laminated sediment, allowing for finer climate reconstructions and sedimentary process studies. Here we provide a sequence of seasonally to annually laminated diatomaceous sediment from a 72.5 cm interface core retrieved on the continental shelf off Adélie Land, covering the 1970–2010 CE period. Investigations through statistical analyses of diatom communities, diatom-specific biomarkers and major element abundances document the relationships between these proxies at an unprecedented resolution. Additionally, comparison of sedimentary records to meteorological data monitored by automatic weather station and satellite derived sea ice concentrations help to refine the relationships between our proxies and environmental conditions over the last decades. Our results suggest a coupled interaction of the atmospheric and sea surface variability on sea ice seasonality, which acts as the proximal forcing of siliceous productivity at that scale.
(Biogeosciences. vol. 13, n° 1726-4170, pp. 4205-4218, 25/07/2016)
LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, ULaval, INSU - CNRS, CNRS, ULaval, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, VOG, LOCEAN, IPSL, ENS-PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS
Enhanced development of lacustrine microbialites on gravity flow deposits, Great Salt Lake, Utah, USA.
The Great Salt Lake, Utah, USA is a shallow, hypersaline, intracontinental lake hosting extensive microbial deposits. At a large spatial scale, the distribution of these deposits is driven by environmental and geodynamical factors (i.e. water-level fluctuations and a fault-related framework). A detailed mapping of the Buffalo Point area, in the north-western part of Antelope Island, indicates the presence of an anomalous concentration of microbial deposits dated ca. 5.8 ka BP and distributed along a lobe-shaped geometry. This uncommon microbial deposit geometry results from an extensive colonization of a conglomerate substrate exhibiting an accumulation of m-sized rounded Cambrian quartzite boulders. We suggest that this conglomerate substrate provides a stable nucleation point that promotes the development and preservation of the lobe-shaped microbial deposits. Microbial deposits may also have protected the conglomerate substrate from erosional processes and thereby increased the preservation potential of the lobe-shaped structure. Based on the characteristics of the conglomerate (e.g. grain size, texture) and its location (i.e. 200 m beyond the average shoreline), this lobe-shaped structure likely results from subaqueous debris or a hyperconcentrated density flow that transports sedimentary material from the Buffalo Point slopes downward to the shore. We estimate the age of the conglomerate deposition to be between 21 and 12 ka BP. The initiation of the flow may have been triggered by various mechanisms, but the existence of a major active normal fault in the vicinity of these deposits suggests that an earthquake could have destabilized the accumulated sediments and resulted in conglomerate emplacement. The catastrophic 15 ka BP Bonneville Flood, which led to a drop in the lake level (approximately 110 m), may also provide an explanation for the initiation of the flow.
(Sedimentary Geology. vol. 341, n° 0037-0738, pp. 1-12, 15/07/2016)
BGS, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Bordeaux INP, UBM, UAM, UAM, CRIGEN, GDF Suez, UCONN
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
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
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