Imprints of wave climate and mean sea level variations in the dynamics of a coastal spit over the last 250 years: Cap Ferret,SW France     

Alphonse Nahon  Déborah Idier  Nadia Sénéchal  Hugues Féniès  Cyril Mallet  Julie Mugica 《地球表面变化过程与地形》2019,44(11):2112-2125

In coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit–inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large-scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability. © 2019 John Wiley & Sons, Ltd.  相似文献   

Intertidal clay-drape couplets (Gironde estuary, France)     

Hugues Fenies  Amaury De Resseguier  & Jean-Pierre Tastet 《Sedimentology》1999,46(1):1-15

Clay-drape couplets on subaqueous dunes have been regarded as a diagnostic feature of the subtidal environment since Visser's seminal paper (1980). The new observation of clay-drape couplets in the intertidal zone on a present day tidal bar of the Gironde estuary shows that they are not restricted to the subtidal zone.
In the intertidal zone, low-tide slack-water clay drapes are deposited in the bottomsets of the dominant current dunes when the muddy water retained in the troughs is absorbed into the sand during the emergence of the intertidal bar. They drape emergence run-off ripples generated by the drainage currents in the bottomsets. High-tide slack-water clay drapes are deposited over the entire dune surface and are preserved on the lee side of the dunes and in the bottomsets. They drape the subordinate current ripples. Low-tide and high-tide slack-water clay drapes enclose one thin rippled sand layer (the subordinate current bundle) and are isolated from other adjacent clay-drape couplets by the dominant current bundle.
The clay-drape couplets deposited in the intertidal zone can be distinguished from their subtidal counterparts on the basis of two morphological differences:
1. In the intertidal zone, the low-tide clay drape is only present in the bottomsets of the dunes, whereas in the subtidal zone equivalent clay drapes are also present on the lower part of the lee side of the dunes.
2. In the intertidal zone, low-tide clay drapes are deposited in the bottomsets of the dunes over emergence run-off ripples oriented in the direction of the drainage currents (i.e. in a direction normal to the tidal currents). Conversely, in the subtidal zone, the equivalent clay drapes are typically deposited over ripples oriented in the tidal-current direction (ebb or flood). There is a difference of polarity of 90° between the intertidal and subtidal small-scale bedforms draped by the low-tide slack-water drapes.  相似文献   

Facies and geometry of tidal channel-fill deposits (Arcachon Lagoon, SW France)     

Hugues Fenies  Jean-Claude Faugres 《Marine Geology》1998,150(1-4):131-148

The Arcachon Lagoon has an important network of tidal channels and well developed tidal flats covered by the marine grass Zostera marina. Based on 66 piston cores taken from the Graveyron tidal channel, and observations on the neighbouring channels, this paper documents the facies and geometry of the channel-fill deposits. In the inner lagoon (studied area) the tidal channels are 80 to 150 m wide and have a meandering morphology with sandy point bars 2 to 5 m thick. The channel-fill does not consist of the classic inclined heterolithic bedding typical of many channel-fills (Reineck, 1958), but of cross-stratified sandy deposits characterized by the absence of slack-water clay-drapes. These unusual facies characteristics are due to the low turbidity of the lagoonal waters which is caused by the lack of significant river inflow and the dense coverage of Zostera marina on the tidal flats. The overall geometry of the channel-fill deposits is characterized by a narrow sand-ribbon shape, a few kilometres long, 80 to 150 m wide and 1 to 5 m thick. This sand ribbon is made of elliptical sand bodies, deposited as point bars, that coalesce longitudinally along the channel axis. This narrow shape is due to the fact that the lateral migration of the channel is virtually nil (reduced to a few metres). In spite of their characteristic meandering morphology, these channels do not deposit extensive tabular sand sheets of amalgamated point bars like the tidal creeks on the North Sea tidal flats. Two factors are thought to control this lack of channel migration. (1) The tidal flats adjacent to the tidal channels are made of 3- to 5-m-thick cohesive muddy sediments covered by Zostera marina that prevents the erosion of the channel banks. This first mechanism is supported by the observation that the tidal creeks that drain the muddy tidal flats covered by Zostera marina do not migrate laterally, whereas those that drain the sandy tidal flats devoid of a dense coverage of marine grass do have active lateral migration. (2) The tidal channels are not fed by any river and therefore do not receive any fluvial sand influx during the winter floods. Their morphology is in equilibrium with the tidal discharge and represents a stable stage in the development of the channel. This second mechanism is supported by the fact that the only tidal channels that actively migrate laterally in the lagoon receive sandy fluvial influx from the River Leyre located in the southeastern corner of the lagoon.  相似文献   

Facies and architecture of an estuarine tidal bar (the Trompeloup bar, Gironde Estuary, SW France)   总被引：1，自引：0，他引：1  

Hugues Fenies  Jean-Pierre Tastet 《Marine Geology》1998,150(1-4):149-169

This study describes the sedimentary facies and internal architecture of a modern estuarine tidal bar present in the bay-head delta of a wave- and tide-dominated estuary, the Gironde Estuary, in southwest France. Based on 51 cores (2 to 5 m long), this work demonstrates that such bars are composite sedimentary bodies made up of individual sigmoidal sand units isolated from one another by thick muddy layers. The bar appeared in the study area around 1874. Since then, its evolution has been characterized by phases of rapid downstream bar migration alternating with periods of bar abandonment. During the periods of active bar progradation, which commonly last between 10 and 20 years, the bar progrades up to 7 km seaward and forms a narrow (200–800 m wide) sand ridge up to 6 m thick. During abandonment phases which also last around 10–20 years, the bar is starved of sand and a mud layer (1 to 3 m thick) is deposited. The vertical succession formed by the seaward progradation of the tidal bar records these alternating phases of growth and abandonment. A typical vertical succession in the bar system is 8 m thick and comprises several superimposed, upward-coarsening units of cross-stratified sand, deposited during phases of seaward progradation, separated by a thick layer of thinner-bedded mud and sand laminae deposited during phases of bar abandonment. When a tidal bar builds up to the supratidal zone, marshes accumulate and the bar becomes a permanent island in the estuary. The large-scale architecture of the bar is thus made of an alternation of potential sandy reservoir units and muddy internal seals. The reservoir units are characterized by a sigmoidal shape. The muddy layer, which is deposited between the two sigmoidal units, is a thick, continuous potential internal seal. This complex internal architecture is due to the fact that there is a considerable amount of mud present in the bay-head delta of the Gironde Estuary. It is thought to be representative of the architecture of tidal bars in the inner part of wave- and tide-dominated estuaries.  相似文献   

The effect of dynamic–thermodynamic icebergs on the Southern Ocean climate in a three-dimensional model     

Jochem I. Jongma  Emmanuelle Driesschaert  Thierry Fichefet  Hugues Goosse  Hans Renssen 《Ocean Modelling》2009,26(1-2):104-113

Melting icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of icebergs in the coupled climate system. However, icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical icebergs on the upper Southern Ocean and we compare these dynamic iceberg results to the effects of an equivalent parameterized iceberg flux.In our model without interactive icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic icebergs are found to be concentrated closer to shore except for a plume of icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution.Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters.  相似文献   

Nickeliferous pyrite tracks pervasive hydrothermal alteration in Martian regolith breccia: A study in NWA 7533          下载免费PDF全文

Jean‐Pierre Lorand  Roger H. Hewins  Laurent Remusat  Brigitte Zanda  Sylvain Pont  Hugues Leroux  Maya Marinova  Damien Jacob  Munir Humayun  Alexander Nemchin  Marion Grange  Allen Kennedy  Christa Göpel 《Meteoritics & planetary science》2015,50(12):2099-2120

Martian regolith breccia NWA 7533 (and the seven paired samples) is unique among Martian meteorites in showing accessory pyrite (up to 1% by weight). Pyrite is a late mineral, crystallized after the final assembly of the breccia. It is present in all of the lithologies, i.e., the fine‐grained matrix (ICM), clast‐laden impact melt rocks (CLIMR), melt spherules, microbasalts, lithic clasts, and mineral clasts, all lacking magmatic sulfides due to degassing. Pyrite crystals show combinations of cubes, truncated cubes, and octahedra. Polycrystalline clusters can reach 200 μm in maximum dimensions. Regardless of their shape, pyrite crystals display evidence of very weak shock metamorphism such as planar features, fracture networks, and disruption into subgrains. The late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration. The distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just‐saturated near neutral (6 < pH<10), H₂S‐HS‐rich fluids at minimum log fO₂ of >FMQ + 2 log units. It is inferred from the maximum Ni contents (4.5 wt%) that pyrite started crystallizing at 400–500 °C, during or shortly after a short‐duration, relatively low temperature, thermal event that lithified and sintered the regolith breccias, 1.4 Ga ago as deduced from disturbance in several isotope systematics.  相似文献   

Limited Consequences of Seagrass Decline on Benthic Macrofauna and Associated Biotic Indicators     

V. Tu Do  Hugues Blanchet  Xavier de Montaudouin  Nicolas Lavesque 《Estuaries and Coasts》2013,36(4):795-807

Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.  相似文献   

Low‐temperature crystallization of MgSiO3 glasses under electron irradiation: Possible implications for silicate dust evolution in circumstellar environments     

Philippe CARREZ  Karine DEMYK  Hugues LEROUX  Patrick CORDIER  Anthony P. JONES  Louis D'HENDECOURT 《Meteoritics & planetary science》2002,37(11):1615-1622

Abstract— Synthetic MgSiO₃ glasses were irradiated at room temperature by 300 keV electrons in a transmission electron microscope (TEM). One of the samples had been previously irradiated by 50 keV He+ ions. Electron irradiation induces the nucleation and growth of randomly oriented nanometer‐sized crystallites. The crystallites first consist of MgO and subsequently of forsterite (Mg₂SiO₄). Both are seen to form within an amorphous SiO₂ matrix. The rate of crystallization of the samples has been monitored by conventional TEM imaging and electron diffraction. The sample that had been pre‐irradiated with He+ ions is found to transform faster than the as‐quenched glass. The crystallization of metastable MgSiO₃ glasses is explained by ionizing radiation‐induced elemental diffusion that allows the reorganization of matter into a more favourable thermodynamic state. These results show that ionizing radiation interactions could account for crystal formation as observed in infrared spectroscopy in some young stellar environments.  相似文献   

A multiproxy reconstruction of the palaeoenvironment and palaeoclimate of the Late Pleistocene in northeastern Iberia: Cova dels Xaragalls,Vimbodí‐Poblet,Paratge Natural de Poblet,Catalonia     

Juan Manuel López‐García  Hugues‐Alexandre Blain  Maria Bennàsar  Itxaso Euba  Sandra Bañuls  James Bischoff  Esther López‐Ortega  Palmira Saladié  Paloma Uzquiano  Josep Vallverdú 《Boreas: An International Journal of Quaternary Research》2012,41(2):235-249

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Zero-difference GPS ambiguity resolution at CNES–CLS IGS Analysis Center     

Sylvain Loyer  Félix Perosanz  Flavien Mercier  Hugues Capdeville  Jean-Charles Marty 《Journal of Geodesy》2012,86(11):991-1003

CNES (Centre National d’Etudes Spatiales) and CLS (Collecte Localisation Satellites) became an International GNSS Service (IGS) Analysis Center (AC) the 20th of May 2010. Since 2009, we are using the integer ambiguity fixing at the zero-difference level strategy in our software package (GINS/Dynamo) as an alternative to classical differential approaches. This method played a key role among all the improvements in the GPS processing we made during this period. This paper provides to the users the theoretical background, the strategies and the models used to compute the products (GPS orbits and clocks, weekly station coordinate estimates and Earth orientation parameters) that are submitted weekly to the IGS. The practical realization of the two-step, ambiguity-fixing scheme (wide-lane and narrow-lane) is described in detail. The ambiguity fixing improved our orbit overlaps from 6 to 3?cm WRMS in the tangential and normal directions. Since 2008, our products have been also regularly compared to the IGS final solutions by the IGS Analysis Center Coordinator. The joint effects of ambiguity fixing and dynamical model changes (satellite solar radiation pressure and albedo force) improved the consistency with IGS orbits from 35 to 18?mm 3D-WRMS. Our innovative strategy also gives additional powerful properties to the GPS satellite phase clock solutions. Single receiver (zero-difference) ambiguity resolution becomes possible. An overview of the applications is given.  相似文献