Impact of winter dense water formation on shelf sediment erosion (evidence from the Gulf of Lions,NW Mediterranean)     

François Bourrin  Xavier Durrieu de Madron  Serge Heussner  Claude Estournel 《Continental Shelf Research》2008

A 1-year survey of sediment dynamics on the Têt inner-shelf in the south-western part of the Gulf of Lions was conducted as part of the EUROSTRATAFORM program (European Margin Strata Formation) from October 2004 to November 2005. Several bottom instruments (ADCP, wave gauge and altimeters) were deployed at 28 m water depth on the Têt prodelta to measure forcing responsible for sediment erosion and transport on the inner-shelf.  相似文献   

Seasonal and event-controlled export of organic matter from the shelf towards the Gulf of Lions continental slope     

Joan Fabres  Tommaso Tesi  Jose Velez  Fabian Batista  Cindy Lee  Antoni Calafat  Serge Heussner  Albert Palanques  Stefano Miserocchi 《Continental Shelf Research》2008

To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments.  相似文献   

Flow fields and particle trajectories beneath a tidal bore: A numerical study     

Adrien Berchet  Bruno Simon  Anthony Beaudoin  Pierre Lubin  Germain Rousseaux  Serge Huberson 《国际泥沙研究》2018,33(3):351-370

Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomenon is rare but has a strong impact during its short duration: i.e. the river bed is significantly eroded and sediments are then transported. In this paper, the trajectories of suspended particles induced by this flow are numerically studied. Four undular bores with Froude numbers between 1.1 and 1.2 are studied. Despite similar Froude numbers, various initial flow conditions were selected to produce or not an inversion of the flow direction during the bore passage. The particle trajectories associated with each distinct flow configuration are presented and analyzed. These trajectories, estimated by solving the Maxey-Riley equation, appear to be very different even though the Froude numbers of flows are similar. These observations are important because the Froude number is often used to characterize a tidal bore as it describes well the free surface, however, it cannot describe the sediment transport. Finally, Chen's model of wave-current interactions is adapted to fit the cases studied and is applied to the four bores simulated. The results highlight that this latter model can reproduce the observed trajectories and dissociate their different components. From this model, it is shown that the inertial and Basset history effects can be neglected compared to the gravity and flow entrainment effects due to the viscous drag when one wants to determine the long-term trajectories of suspended particles.  相似文献   

Precast industrial buildings in Southern Europe: loss of support at frictional beam-to-column connections under seismic actions     

Cristoforo Demartino  Ivo Vanzi  Giorgio Monti  Concetta Sulpizio 《Bulletin of Earthquake Engineering》2018,16(1):259-294

This paper presents the evaluation of the loss-of-support conditions in frictional beam-to-column connections of industrial precast concrete buildings under seismic actions. This type of connection is widespread throughout Southern Europe in non-seismically designed industrial precast buildings. First, geometric properties of industrial precast buildings and of the frictional beam-to-column connections, together with reference values for the friction coefficient, are reviewed. Then, earthquake time histories taken from the European Strong-Motion sets and recordings of the two major shocks of the 2012 Emilia-Romagna events are presented and discussed showing the importance of the vertical component. Two dynamic models of increasing complexity are used to ascertain loss-of-support conditions under seismic action. The first model is an elastic one, representing a single frame of the industrial buildings. Results are obtained according to: (1) 2D analyses, disregarding the time correlation between the response peaks along the horizontal and vertical directions, (2) 2D analyses taking into account time correlation, and (3) 3D analyses to evaluate also directionality effects. The second model is a 2D non-linear planar frame developed within the OpenSees framework. Results show that simplified (linear) models are a good proxy to more refined (non-linear) ones. However, one must resort to non-linear models if differential displacements between beam and column are of interest. The non-linear numerical investigations show that friction coefficient, horizontal and vertical periods and damping, and column reinforcement ratio are the key variables in estimating the loss-of-support conditions.  相似文献   

Positioning fisheries in a changing world   总被引：1，自引：1，他引：0  

R. Quentin Grafton  Ray Hilborn  Lori Ridgeway  Dale Squires  Meryl Williams  Serge Garcia  Theodore Groves  James Joseph  Kieran Kelleher  Tom Kompas  Gary Libecap  Carl Gustaf Lundin  Mitsutaku Makino  Thorolfur Matthiasson  Richard McLoughlin  Ana Parma  Gustavo San Martin  Ben Satia  Carl-Christian Schmidt  Maree Tait  Lin Xiu Zhang 《Marine Policy》2008,32(4):630-634

Marine capture fisheries face major and complex challenges: habitat degradation, poor economic returns, social hardships from depleted stocks, illegal fishing, and climate change, among others. The key factors that prevent the transition to sustainable fisheries are information failures, transition costs, use and non-use conflicts and capacity constraints. Using the experiences of fisheries successes and failures it is argued only through better governance and institutional change that encompasses the public good of the oceans (biodiversity, ecosystem integrity, sustainability) and societal values (existence, aesthetic and amenity) will fisheries be made sustainable.  相似文献   

Rhythmic pelagic successions and terrestrial orbital variations. The example of the Lower Cretaceous from Angles (SE France)     

Michel Rio  Pierre Cotillon  Serge Ferry 《地学学报》1989,1(5):449-450

An harmonic analysis of limestone bed and marl interbed thicknesses of pelagic Berriasian-Barremian interval from the Angles area (SE France) shows that marly parts of the succession contain frequencies significantly different from calcareous ones. Some of the resulting periods are in the Milankovitch frequency band but many others are different from those predicted by the orbital theory.  相似文献   

Observation and photometry of an outer ring of saturn     

Audouin Dollfus  Serge Brunier 《Icarus》1982,49(2):194-204

A faint outer ring (E ring), which lies outside the classical rings A, B, C, and F, has been detected out to eight Saturn radii. We first observed it on November 1, 1979, and thereby confirmed the 1966 observation by Feibelman. Our plates were taken with a coronographic design and are specially intended for photometry. They are directly scaled in reflectance by reference to the Saturn disk which is properly attenuated. Photometry of the edge-on ring E lineament shows a strong brightness increase at small phase angles, which is compatible with scattering by particles of several microns in radius. The excess reflectivity in blue compared to the B ring implies a significant contribution of small particles in the scattering process. The E ring shows brightness and radial gradient changes, with condensations, which differ between east and west limbs and are not always the same from night to night. The E ring is probably a flat structure with a condensation centered at a distance of 4 R_s, but without a simple axial symmetry. It is probably shaped by segments or lumps and may have streamerlike structures.  相似文献   

The dammed Hikurangi Trough: a channel-fed trench blocked by subducting seamounts and their wake avalanches (New Zealand–France GeodyNZ Project)     

Keith B. Lewis  Jean-Yves Collot  & Serge E. Lallem 《Basin Research》1998,10(4):441-468

The Hikurangi Trough, off eastern New Zealand, is at the southern end of the Tonga–Kermadec–Hikurangi subduction system, which merges into a zone of intracontinental transform. The trough is mainly a turbidite-filled structural trench but includes an oblique-collision, foredeep basin. Its northern end has a sharp boundary with the deep, sediment-starved, Kermadec Trench. Swath-mapping, sampling and seismic surveys show modern sediment input is mainly via Kaikoura Canyon, which intercepts littoral drift at the southern, intracontinental apex of the trough, with minor input from seep gullies. Glacial age input was via many canyons and about an order of magnitude greater. Beyond a narrow, gravelly, intracontinental foredeep, the southern trench-basin is characterized by a channel meandering around the seaward edge of mainly Plio-Pleistocene, overbank deposits that reach 5 km in thickness. The aggrading channel has sandy turbidites, but low-backscatter, and long-wavelength bedforms indicating thick flows. Levées on both sides are capped by tangentially aligned mudwaves on the outsides of bends, indicating centrifugal overflow from heads of dense, fast-moving, autosuspension flows. The higher, left-bank levée also has levée-parallel mudwaves, indicating Coriolis and/or boundary currents effects on dilute flows or tail plumes. In the northern trough, basin-fill is generally less than 2 km thick and includes widespread overbank turbidites, a massive, blocky, avalanche deposit and an extensive, buried, debris flow deposit. A line of low seamounts on the subducting plate acts as a dam preventing modern turbidity currents from reaching the Kermadec Trench. Major margin collapse probably occurred in the wake of a large subducting seamount; this seamount and its wake debris flow probably dammed the trench from 2 Ma to 0.5 Ma. Before this, similar dams may have re-routed turbidity currents across the plateau.  相似文献   

On the Lagrangian and Eulerian Time Scales of Turbulence Within a Two-Dimensional Array of Obstacles     

Di Bernardino  Annalisa  Monti  Paolo  Leuzzi  Giovanni  Querzoli  Giorgio 《Boundary-Layer Meteorology》2022,184(3):375-379

Boundary-Layer Meteorology - Fields of Lagrangian ( $$T^{L}$$ ) and Eulerian ( $$T^{E}$$ ) time scales of the turbulence within a regular array of two-dimensional obstacles of unit aspect ratio...  相似文献   

Giant solution‐subsidence structure in the Western Mediterranean related to deep substratum dissolution     

Johanna Lofi  Serge Berné  Michel Tesson  Michel Seranne  Philippe Pezard 《地学学报》2012,24(3):181-188

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