118 results on '"Garlan, Thierry"'
Search Results
2. Wave variability along the world’s continental shelves and coasts: Monitoring opportunities from satellite Earth observation
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Bergsma, Erwin W.J., Almar, Rafael, Anthony, Edward J., Garlan, Thierry, and Kestenare, Elodie
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- 2022
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3. Sediment migrations drive the dynamic of macrobenthic ecosystems in subtidal sandy bedforms
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Robert, Alexandre Elie, Quillien, Nolwenn, Bacha, Mahmoud, Caulle, Clémence, Nexer, Maëlle, Parent, Briz, Garlan, Thierry, and Desroy, Nicolas
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- 2021
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4. 3D variability of Sediment Granulometry in Two Tropical Environments : Nha Trang (Vietnam) and Saint-Louis (Sénégal)
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Garlan, Thierry, Almar, Rafael, Gauduin, Hermann, Gosselin, Maxime, Morio, Olivier, and Labarthe, Carla
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- 2020
5. Sand-spit Evolution and Inlet Dynamics derived from Space-borne Optical Imagery : Is the Senegal-river Inlet Closing?
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Bergsma, Erwin W.J., Sadio, Mamadou, Sakho, Issa, Almar, Rafael, Garlan, Thierry, Gosselin, Maxime, and Gauduin, Hermann
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- 2020
6. Bottom trawling contribution to the spatio-temporal variability of sediment fluxes on the continental shelf of the Bay of Biscay (France)
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Mengual, Baptiste, Le Hir, Pierre, Cayocca, Florence, and Garlan, Thierry
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- 2019
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7. Circular Sedimentary Figures of Anthropic Origin in a Sediment Stability Context
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Garlan, Thierry, Mathias, Xavier, Brenon, Emeric, Favretto-Cristini, Nathalie, Deschamps, Anne, Beucler, Eric, Guyomard, Patrick, and Morio, Olivier
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- 2018
8. Satellite-derived bathymetry from correlation of Sentinel-2 spectral bands to derive wave kinematics: Qualification of Sentinel-2 S2Shores estimates with hydrographic standards
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Almar, Rafael, Bergsma, Erwin W.J., Thoumyre, Grégoire, Solange, Lemai-Chenevier, Loyer, Sophie, Artigues, Stephanie, Salles, Grégoire, Garlan, Thierry, and Lifermann, Anne
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- 2024
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9. Deep-sea terrigenous organic carbon transfer and accumulation: Impact of sea-level variations and sedimentation processes off the Ogooue River (Gabon)
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Mignard, Salomé Lou-Andréa, Mulder, Thierry, Martinez, Philippe, Charlier, Karine, Rossignol, Linda, and Garlan, Thierry
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- 2017
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10. Control factors of Holocene sedimentary infilling in a semi-closed tidal estuarine-like system: the bay of Brest (France)
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Gregoire, Gwendoline, Le Roy, Pascal, Ehrhold, Axel, Jouet, Gwenael, and Garlan, Thierry
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- 2017
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11. Observation and numerical modeling of tidal dune dynamics
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Doré, Arnaud, Bonneton, Philippe, Marieu, Vincent, and Garlan, Thierry
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- 2018
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12. Extraction of sandy bedforms features through geodesic morphometry
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Debese, Nathalie, Jacq, Jean-José, and Garlan, Thierry
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- 2016
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13. Short-Range Recordings of Shallow Underwater Explosions with Short-Period and Broadband Seismometers in the Bay of Hyères, France.
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Bonnin, Mickaël, Mercerat, E. Diego, Beucler, Éric, Favretto-Cristini, Nathalie, Deschamps, Anne, Ambrois, David, and Garlan, Thierry
- Abstract
This study presents the analysis of the seismic records of eight underwater explosions triggered by the French Navy Mine Warfare Office in December 2018 in the Bay of Hyères, southeast France. The explosions (charges of 80-680 kg TNT-equivalent) were recorded by 17 temporary stations composed of medium-to-broadband velocimeters and accelerometers and of microelectromechanical systems accelerometers with sampling rates of 250 or 500 samples per second, installed at less than 10 km from the sources. The relatively high sampling rates used in this study allow us to observe, at the same time, seismic, hydroacoustic, and acoustic signals at the shore. This experiment offers a unique opportunity to investigate the impact at the shore, and in the water, of relatively large-charge weight detonations as well as of the amplification effects of the sedimentary cover. We notably see that the hydroacoustic signal is, at the rocky sites, the most energetic wavepacket recorded, and that its observation seems to be conditioned by the bathymetry and the seabed sedimentary cover. We also show that the hydroacoustic phase can be advantageously used to precisely estimate the location and origin time of the explosions. Finally, analyses of the spectrum and site response along the shore and at a bell tower on the Porquerolles Island provide interesting insights on the mitigation of the possible nuisance caused at the shore by the disposal of unexploded historical ordnance. [ABSTRACT FROM AUTHOR]
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- 2023
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14. Analysis of Seismic, Hydroacoustic and Acoustic Waves Recorded on the Shoreline in the Vicinity of Shallow Underwater Explosions
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Beucler, Éric, Bonnin, Mickael, Diego Mercerat, E., Favretto-Cristini, Nathalie, Deschamps, Anne, Ambrois, David, Garlan, Thierry, Laboratoire de Planétologie et Géosciences [UMR_C 6112] (LPG), Université d'Angers (UA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Nantes université - UFR des Sciences et des Techniques (Nantes univ - UFR ST), Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ), Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement - Equipe-projet MOUVGS (Cerema Equipe-projet MOUVGS), Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (Cerema), Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement - Equipe-projet Repsody (Equipe-projet Repsody), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de Mécanique et d'Acoustique [Marseille] (LMA ), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, ANR-15-ASTR-0001,POSA,Caractérisation de la Propagation des Ondes Sismiques d'origine Anthropique(2015), Deschamps, Anne, and Caractérisation de la Propagation des Ondes Sismiques d'origine Anthropique - - POSA2015 - ANR-15-ASTR-0001 - ASTRID - VALID
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[SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,[SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] ,underwater explosions ,seismic records - Abstract
International audience; The French Navy Mine Warfare Office conducted a series of 8 calibrated underwater explosions in December 2018 in the Bay of Hyères, SE France. The charges were ranging from 80 to 680 kg TNT-equivalent weights and the generated mechanical waves have been recorded at 17 seismic stations (composed of velocimeters, accelerometers and/or Microelectomechanical system accelerometers) temporarily deployed within 10 km of the sources. The large sampling rate recordings (> 250 Hz) allow to clearly identify both seismic, hydroacoustic and acoustic waves on the shoreline. The hydroacoustic phases, mostly observed at the rocky sites, rapidly attenuate when propagating on land and seem to be conditioned by the bathymetry and the seabed sedimentary cover. The hydroacoustic onset times can be used very efficiently to infer explosion locations and origin times. The spectrum analyses and site response along the shore and inside a building (church) provide insights on the mitigation of the possible nuisance caused by the disposal of unexploded historical ordnance.
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- 2022
15. Seismo-acoustic wave propagation generated by the detonation of UXOs of large charge weights in a shallow water environment
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Favretto-Cristini, Nathalie, Deschamps, Anne, Ambrois, David, Bonnin, Mickaël, Beucler, Éric, Diego Mercerat, E., Wang, Fang, Garlan, Thierry, Demoulin, Xavier, Arrigoni, M., Cristini, Paul, Morio, Olivier, Laboratoire de Mécanique et d'Acoustique [Marseille] (LMA ), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Laboratoire de Planétologie et Géosciences [UMR_C 6112] (LPG), Université d'Angers (UA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Nantes université - UFR des Sciences et des Techniques (Nantes univ - UFR ST), Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ)-Nantes Université - pôle Sciences et technologie, Nantes Université (Nantes Univ)-Nantes Université (Nantes Univ), Observatoire des Sciences de l'Univers Nantes Atlantique (OSUNA), Université d'Angers (UA)-Institut national des sciences de l'Univers (INSU - CNRS)-Conservatoire National des Arts et Métiers [CNAM] (CNAM), HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université Gustave Eiffel-Nantes Université (Nantes Univ), Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (Cerema), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Institut de Recherche Dupuy de Lôme (IRDL), and École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Centre National de la Recherche Scientifique (CNRS)
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[SPI.ACOU]Engineering Sciences [physics]/Acoustics [physics.class-ph] ,Acoustic waves ,Seismic waves ,Detonation ,Underwater explosions ,Military operations ,Acoustic wave propagation ,Seismology - Abstract
International audience; Unexploded historical ordnance (UXO) from World War II, that is discovered almost every week close to the French coast, must be destroyed quickly after discovery to ensure the safety of divers and ships. The favored destruction method is countermining, i.e., the use of a high-order detonation conducted by exploding an additional donor charge placed adjacent to the UXO. In the framework of a UXO countermining campaign conducted in the Rade d'Hyères (Mediterranean Sea, France) in December 2018, hydro-acoustic and seismic recording systems have been deployed to record the explosion-induced waves in water and the seismic signals on the shore, respectively (POSA project). In this expanded abstract, we present the main observations and focus on the impact of the shallow water environment (whose water depth is less than 50 m), and more specifically on the impact of the unconsolidated sedimentary layer, on the recorded signals induced by the detonation of charges with weights ranging from 80 to 680 kg TNT-equivalent. We also discuss the acoustic-to-seismic wave conversions.
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- 2022
16. Influence of bottom trawling on sediment resuspension in the ‘Grande-Vasière’ area (Bay of Biscay, France)
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Mengual, Baptiste, Cayocca, Florence, Le Hir, Pierre, Draye, Robin, Laffargue, Pascal, Vincent, Benoit, and Garlan, Thierry
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- 2016
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17. Morphological evolution of Cap Lopez Canyon (Gabon): Illustration of lateral migration processes of a submarine canyon
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Biscara, Laurie, Mulder, Thierry, Hanquiez, Vincent, Marieu, Vincent, Crespin, Jean-Pierre, Braccini, Eric, and Garlan, Thierry
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- 2013
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18. Observations of waves’ impact on currents in a mixed-energy tidal inlet : Arcachon on the southern French Atlantic coast
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Senechal, Nadia, Sottolichio, Aldo, Bertrand, Frédéric, Goeldner-Gianella, Lydie, and Garlan, Thierry
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- 2013
19. Wave variability along the world's continental shelves and coasts: Monitoring opportunities from satellite Earth observation
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Bergsma, Erwin W. J., Almar, Rafael, Anthony, Edward, Garlan, Thierry, Kestenare, Elodie, Centre National d’Études Spatiales [Paris] (CNES), Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS NOUMEA), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR065-Centre National de la Recherche Scientifique (CNRS), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Service Hydrographique et Océanographique de la Marine (SHOM), and Ministère de la Défense
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Satellite monitoring ,[SDU]Sciences of the Universe [physics] ,Coastal observations ,Seasonality ,Wave variability - Abstract
International audience; Insight on wave regimes along the world's coastlines is important for virtually all coastal and nearshore marine activities, installations, planning and protection. Waves are pervasive and the dominant source of energy driving extreme sea levels, the transport of pollutants and sediments, erosion, and a major contributor to risks of flooding. We quantify the global spatio-temporal wave conditions along the world's coasts and evaluate the needs for coastal Earth Observation strategies, with the aim, notably, that the derived scales of change can contribute to optimisation of these strategies. A global dominant timescale of 30 days is found in coastal wave variability that is, on average, spatially correlated just over the synoptic 5 degrees' regional scale (≈ 550 km at the equator). This regional-scale dimension suggests that the timing and design of traditional field surveys and observations relevant to a vast array of coastal activities, and which may be expensive in terms of human resources, may be complemented by information gained from satellite Earth Observation that throws light on spatio-temporal scales of wave-energy change along the world's coastlines.
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- 2022
20. Observation and Modeling of the Equilibrium Slope Response of a High-Energy Meso-Macrotidal Sandy Beach.
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Labarthe, Carla, Castelle, Bruno, Marieu, Vincent, Garlan, Thierry, and Bujan, Stéphane
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BEACHES ,LITTORAL drift ,SEA level ,AUTUMN - Abstract
Beach slope is a critical parameter to, e.g., beach safety, wave reflection at the coast and longshore transport rate. However, it is usually considered as a time-invariant and profile-average parameter. Here, we apply a state-of-the-art equilibrium model to hindcast beach slope variability from the time scales of days to years at the high-energy meso-macrotidal sandy beach of Truc Vert, southwest France. We use 9 years of bimonthly beach surveys to compute beach slope time series at different elevations. Results show that beach slope exhibits an equilibrium response with contrasting behaviors along two distinct areas of the beach profile. From 0 to 2 m above mean sea level, which is located under the berm crest, a slope response predominantly at the storm time scale is observed. The beach slope steepens under low energy waves, with the equilibrium model explaining up to 40% of the observed beach slope variability. In contrast, from 2.5 to 4 m above mean sea level, which is above the berm crest, the beach slope steepens under high-energy waves. Within this region of the beach profile, the response time scale increases upwards from seasonal (~2.5 m) to seasonal (~4 m), with the model explaining up to 65% of the observed beach slope variability. Such behaviors are found to be enforced by the berm dynamics developing from the end of the winter to early autumn, providing new perspectives to model and predict beach slope on sandy beaches. [ABSTRACT FROM AUTHOR]
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- 2023
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21. Transport of terrestrial organic matter in the Ogooué deep sea turbidite system (Gabon)
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Biscara, Laurie, Mulder, Thierry, Martinez, Philippe, Baudin, François, Etcheber, Henri, Jouanneau, Jean-Marie, and Garlan, Thierry
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- 2011
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22. Seismo-acoustic wave propagation in the Rade of Hyères (France) generated by counter-mining of explosive devices : risk assessment from the comparison between numerical simulations and real experiments
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Favretto-Cristini, Nathalie, Wang, Fang, Garlan, Thierry, Morio, Olivier, Deschamps, Anne, Ambrois, David, Mercerat, Diego, Demoulin, Xavier, Beucler, Éric, Bonnin, Mickaël, Cristini, Paul, Monteiller, Vadim, Laboratoire de Mécanique et d'Acoustique [Marseille] (LMA ), Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM), Shenzhen University [Shenzhen], Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement - Equipe-projet Repsody (Equipe-projet Repsody), Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (Cerema), Auteur indépendant, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Observatoire des Sciences de l'Univers Nantes Atlantiques (OSUNA), Université d'Angers (UA)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Conservatoire National des Arts et Métiers [CNAM] (CNAM)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Université Gustave Eiffel, Ondes et Imagerie (O&I), Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Université d'Angers (UA)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Conservatoire National des Arts et Métiers [CNAM] (CNAM), HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-Centre National de la Recherche Scientifique (CNRS)-IMT Atlantique (IMT Atlantique), and Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)
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[PHYS.MECA.VIBR]Physics [physics]/Mechanics [physics]/Vibrations [physics.class-ph] ,underwater acoustics ,interface waves ,seismics ,13. Climate action ,counter-mining ,14. Life underwater ,[PHYS.MECA.ACOU]Physics [physics]/Mechanics [physics]/Acoustics [physics.class-ph] - Abstract
International audience; Explosive devices from World War II are discovered almost every week on the French coasts and they must be destroyed by the French Navy Mine Warfare Office. The consequences of the counter-mining on the marine environment are complex to evaluate. Depending on the environment geology, the explosive charges and their localization, the seismo-acoustic waves generated by the explosion may cause damage to infrastructures located on the coast, and under specific conditions small submarine landslides. The ANR ASTRID POSA project proposed to address the risk assessment issue on the Mediterranean coast. The main originality of this project lied in the approach used that combines geological measurements, acoustic data recorded within the sea coastal zone and seismic data recorded on the coast, together with numerical simulations of seismo-acoustic wave propagation. We propose here to present the results of such a methodology applied to the counter-mining campaign that occurred in the Rade of Hyères (France) in December 2018. We focus more specifically on the numerical simulations of seismo-acoustic wave propagation from the location of the device explosion to several seismometers deployed on the coast of Hyères. From topographical and sedimentary measurements performed in the Rade of Hyères, physical and geometrical characteristics of the marine seabed have been carefully selected as input data for numerical simulations. In addition, a particular attention has been paid to the measured characteristics of the device explosion (source). The numerical simulations have then been conducted using a spectral-element method. The impact of the explosive device charge and its location (on the seabed or in the water column), together with the impact of the marine environment properties, on the simulated signals have been studied. Finally, the numerical results have been compared with the real signals recorded by the seismometers. The risks of land degradation have been evaluated afterwards.
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- 2020
23. The ECORS-Truc Vert’08 nearshore field experiment: presentation of a three-dimensional morphologic system in a macro-tidal environment during consecutive extreme storm conditions
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Senechal, Nadia, Abadie, Stéphane, Gallagher, Edith, MacMahan, Jamie, Masselink, Gerd, Michallet, Hervé, Reniers, Ad, Ruessink, Gerben, Russell, Paul, Sous, Damien, Turner, Ian, Ardhuin, Fabrice, Bonneton, Philippe, Bujan, Stéphane, Capo, Sylvain, Certain, Raphael, Pedreros, Rodrigo, and Garlan, Thierry
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- 2011
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24. Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part I: Real Case Study.
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Favretto-Cristini, Nathalie, Garlan, Thierry, Morio, Olivier, Demoulin, Xavier, Arrigoni, Michel, Deschamps, Anne, Bonnin, Mickael, Beucler, Eric, Mercerat, E. Diego, Ambrois, David, Schwab, Romain, Cristini, Paul, and Wang, Fang
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RISK assessment ,ORDNANCE ,OCEAN bottom ,UNDERWATER explosions ,SONAR equipment ,ACOUSTIC emission testing ,WATER depth - Abstract
The goal of the work presented in a two-companion paper is to pave the way for reliably assessing the risks of damage to buildings on the shore, induced by the detonation of unexploded historical ordnance (UXO) of large weights in variable shallow water environments with a water depth less than 50 m. The risk assessment is quantified through the seismic magnitude on the Richter scale, induced by the detonation of charges of different weights (between 80- and 680-kg TNT-equivalent). This metric is investigated experimentally using a coupled seismo-acoustic approach within the framework of a UXO clearance (countermining) campaign in the Mediterranean Sea. Analysis of real acoustic and seismic data shows that, compared to a charge detonation in water, a similar detonation on the seabed generates seismic signals of lower frequencies and higher amplitudes that propagate in the seabed. The larger the charge weight, the higher the seismic amplitude. Besides the explosion-coast distance, the ground properties also affect the signals. The sediments favor a longer signal duration and the presence of late dispersive and very low-frequency signals with a large amplitude, whereas the rocky grounds better preserve the high-frequency energy propagation. For the local environment considered in this study, a charge detonation on the seafloor generates seismic events of higher magnitudes compared to a detonation in water. However, these magnitudes are likely low enough to prevent any large damage in the nearby inland infrastructures. [ABSTRACT FROM AUTHOR]
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- 2022
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25. Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part II: Modeling of Seismo-Acoustic Wave Propagation.
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Favretto-Cristini, Nathalie, Wang, Fang, Cristini, Paul, Garlan, Thierry, Morio, Olivier, Mercerat, E. Diego, Monteiller, Vadim, Deschamps, Anne, and Beucler, Eric
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WATER depth ,THEORY of wave motion ,RISK assessment ,ORDNANCE ,SEDIMENTARY basins ,ACOUSTIC wave propagation ,DETONATION waves ,GEOLOGICAL surveys - Abstract
The goal of this work presented in a two-companion paper is to pave the way for reliably assessing the risks of damage to buildings on the shore, induced by the detonation of large-charge historical ordnance (i.e., countermining) in variable shallow water environments. Here, we focus on the impact of the marine environment, more specifically the unconsolidated sedimentary layer, on detonation-induced seismo-acoustic wave propagation. We rely on a multidisciplinary cross-study including real data obtained within the framework of a countermining campaign, and numerical simulations of the seismo-acoustic propagation using a spectral-element method. We first develop a strategy relying on physical insights into the different kind of waves that can propagate in a coastal environment, to provide clues for a computational cost reduction. The geological surveys and the hydroacoustic measurements provide input data for the 3-D axisymmetric modeling of wave propagation. The numerical simulations, obtained for one specific source–receiver path with a variable sedimentary facies, are compared with the real seismic data induced by the detonation of a charge either on the seabed, or in the water column, and recorded on the coast. Numerical analysis sheds light on the strong interaction between surface waves and the sedimentary facies. The short-scale and deep sedimentary basins favor a local wave-amplitude amplification and a frequency shift toward the low-frequency domain. However, the seismo-acoustic waves are globally attenuated during their propagation because of intrinsic attenuation and geometrical spreading, which generally prevents any large damage to nearby buildings on the shore. [ABSTRACT FROM AUTHOR]
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- 2022
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26. Origin of rippled scour depressions associated with cohesive sediments in a shoreface setting (eastern Bay of Seine, France)
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Garnaud, Sébastien, Lesueur, Patrick, and Garlan, Thierry
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- 2005
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27. Dune morphology and hysteresis in alluvial channels during long-duration floods revealed using high temporal-resolution MBES bathymetry
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Cisneros, Julia, Best, Jim, van Dijk, Thaiënne A G P, Mosselman, E., Lefebvre, Alice, Garlan, Thierry, and Winter, Christian
- Abstract
In natural rivers, flow discharge may fluctuate across a range of time scales – from diurnal to seasonal - but is often most pronounced during hydrographs that may encompass long-duration floods. Under these varying flows, bedforms can be created and modified by the flow without achieving any ‘equilibrium’ state. A lag between changes in flow and the morphological response of the bedforms, termed bedform hysteresis, is commonly present. Importantly for channel management and navigation, since dunes may grow larger during floods, but often experience a lagged decay in size during lowering water levels, critical water depths may be reached for inland shipping. There is also a consensus that dunes possess a more flattened shape, and lower leeside angle, than previously assumed in large rivers and that such dunes do not exhibit a region of permanent flow separation downstream of the dune. This different leeside shape thus questions traditional ideas of flow interactions with dunes, where flow separation in the steep dune lee side leads to energy loss (form drag) that increases flow resistance and energy expenditure within the flow. This paper quantifies dune hysteresis in the River Waal, Netherlands, by investigating how dune morphology changes through flood hydrographs, using high spatial- and temporal- resolution bathymetric data and robust computational analysis methods to produce probability density functions of dune morphology. This quantification aims to provide a better understanding of dune hysteresis in large rivers. The analysis examines several large data sets of river bathymetry from a 13 km reach of the River Waal, Netherlands, in a time series of bi-weekly multibeam echo sounder surveys over the last 12 years. Parameterization includes dune height, wavelength, leeside angle and leeside shape, to assess dune kinematics and hysteresis during different flood hydrographs.
- Published
- 2019
28. Modelling the past evolution of observed tidal sand waves: the role of boundary conditions
- Author
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Krabbendam, Janneke M., Nnafie, Abdel, Perk, L., Borsje, Bastiaan Wijnand, de Swart, Huib E., Lefebvre, Alice, Garlan, Thierry, and Winter, Christian
- Published
- 2019
29. Architecture and morphology of the outer segment of a mixed tide and wave-dominated-incised valley, revealed by HR seismic reflection profiling: the paleo-Charente River, France
- Author
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Weber, Nicolas, Chaumillon, Eric, Tesson, Michel, and Garlan, Thierry
- Published
- 2004
- Full Text
- View/download PDF
30. Data heterogeneity and oldness, two difficulties to overcome for the world seabed sediment mapping.
- Author
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Garlan, Thierry, Gabelotaud, Isabelle, Marchès, Elodie, Le Borgne, Edith, and Lucas, Sylvain
- Subjects
- *
SEDIMENTS , *OCEANOGRAPHIC maps , *HETEROGENEITY , *SEDIMENTOLOGY , *BATHYMETRIC maps - Abstract
A global seabed sediment map has been developed since 1995 to provide a necessary tool for different needs. This project is not completely original since it had already been done in 1912 when the French hydrographic Office and the University of Nancy produced sedimentary maps of the European and North American coasts. Seabed sediments is one of the last geographical domains which can't benefit of satellite data. Without this contribution, sediment maps need to use very old data mixed with the new ones to be able to reach the goal of a global map. In general, sediment maps are made with the latest available techniques and are replaced after a few decades, thus generating new cartographic works as if all the previous efforts had become useless. Such approach underestimates the quality of past works and prevents to have maps covering large areas. The present work suggests to standardize all kind of sedimentary data from different periods and from very different acquisition systems and integrate them into a single product. This process has already been done for bathymetric data of marine charts, we discuss in this article of the application of this method at a global scale for sediment data. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
31. An Observing System Simulation Experiment (OSSE) in Deriving Suspended Sediment Concentrations in the Ocean From MTG/FCI Satellite Sensor.
- Author
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Jourdin, Frederic, Renosh, Pannimpullath Remanan, Charantonis, Anastase Alexander, Guillou, Nicolas, Thiria, Sylvie, Badran, Fouad, and Garlan, Thierry
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SUSPENDED sediments ,SIMULATION methods & models ,HIDDEN Markov models ,SELF-organizing maps ,PARTICLE dynamics ,OCEAN waves ,SEDIMENT transport - Abstract
The capacity to monitor suspended sediment concentrations (SSCs) in the ocean, from surface to bottom, using data acquired by the future Meteosat Third-Generation (MTG)/flexible combined imager (FCI) satellite sensor has been quantified by observing system simulation experiments (OSSEs). The “true” ocean state for these experiments is based on a 15-month numerical simulation of hydrodynamic and sediment transport, configured to represent the highly dynamical waters of the English Channel under the influences of tides and waves. Simulated MTG/FCI hourly averaged acquisitions at a given location near the Isle of Wight have been processed via hidden Markov model combined with a statistical classification—based on self-organizing maps—of predicted vertical SSC profiles. The resulting experiments demonstrated that MTG/FCI images, despite their high temporal resolution, and because of many gaps due to nights and clouds over the English Channel, still require spatial interpolations to enhance the amount of information available at a given location. For an accurate determination of particle concentrations, time series of the main forcing (wind, tides, and waves) need to be included in the process: 1) as a crucial parameter correlated with the dynamics of large particles (sands) and 2) as an equally important parameter as satellite data themselves in the correlation with the dynamics of fine particles (silts). [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
32. Holocene to modern fine-grained sedimentation on a macrotidal shoreface-to-inner-shelf setting (eastern Bay of the Seine, France)
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Garnaud, Sébastien, Lesueur, Patrick, Clet, Martine, Lesourd, Sandric, Garlan, Thierry, Lafite, Robert, and Brun-Cottan, Jean-Claude
- Published
- 2003
- Full Text
- View/download PDF
33. Global and local forcings on sediment distribution of the SW Gulf of Lions (NW Mediterranean)
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Grenard-Grand, Elise, Berné, Serge, Agin, Grégory, Alonso, Yoann, Bassetti, Maria-Angela, Bourrin, François, Courp, Thierry, Dennielou, Bernard, Garlan, Thierry, Isabelle, Gabelotaud, Labrune, Céline, Simplet, L., Centre de Formation et de Recherche sur les Environnements Méditérranéens (CEFREM), Université de Perpignan Via Domitia (UPVD)-Centre National de la Recherche Scientifique (CNRS), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Agence Française pour la Biodiversité (AFB), Laboratoire Géodynamique et enregistrement Sédimentaire - Geosciences Marines (GM-LGS), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Laboratoire d'Ecogéochimie des environnements benthiques (LECOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Observatoire océanologique de Banyuls (OOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Grenard-Grand, Elise
- Subjects
Sedimentary mapping ,Distribution of surficial sediments ,Golf of Lions ,[SDU.STU.GM] Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,Beachrocks ,[SDU.STU.AG] Sciences of the Universe [physics]/Earth Sciences/Applied geology ,[SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU] Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.ST] Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology ,[SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology ,Seismic stratigraphy - Abstract
International audience; The SW termination of the Gulf of Lions (GoL) is characterized by a narrowing shelf (from 80 km in the central part to ca. 20 km at the French/Spanish border), increased hydrodynamic processes and lowered sediment supply. It has been the target of a relatively large number of high-resolution seismic and acoustic investigations, as well as grab sampling, but few long cores are presently available because relatively low sedimentation rates (compared to the central GoL) did not attract the interest for paleo-environmental studies.In preparation of a map of surficial sediments in this area, a compilation of available data was undergone. In dip section, beyond the littoral prism, 4 distinct morpho-sedimentary units are at the origin of submarine landscapes. From W to E, they include: (1) between -20 and -60 m, a (2) between 60 and -75 m, a relict, 2 to 5 m-thick mud wedge, highly eroded, that can be assigned to the Younger Dryas by analogy with similar, thicker features described and well-dated further to the east; (3) between ca. -75 m and -100 m, a set of stacked thickening seaward forced-regressed Systems Tracts linked to 100 ky and 40 ky glacio-eustatic cycles. They consist of over-consolidated muds from paleo-prodeltas and lower shorefaces, and to sand bodies reworked into large dunes, drapped by a veneer of recent muds. These sands are locallycemented and form elongated reliefs at the position of paleo-shorelines (beachrocks). A characteristic of unit 3 in that part of the GoL is that, because of important reworking by hydrodynamic processes, sequences assigned to Marine Isotope Stages (MIS) 6.2, 6.4 and 7.6 are outcropping at some places, in contrast with the central GoL where they are buried underneath a 20-50 m interval of MIS 3-MIS 2 sediments. (4) between ca. -100 m and the shelf edge (that ranges between -110 and -170 m depending on the distance from canyon heads), normally consolidated offshore muds forming a wedge up to 150 m where accommodation is sufficient (infilled canyon heads).In summary, the distribution of surficial sediments in the GoL is, in general, largely controlled by the history of sea-level changes and the position of point sources. More specifically, the western termination of the GoL exemplifies the major role of hydrodynamic processes in modifying the position and water depth of boundaries between different sedimentary units and sequences.
- Published
- 2017
34. Active tectonics of the Calabrian subduction revealed by new multi-beam bathymetric data and high-resolution seismic profiles in the Ionian Sea (Central Mediterranean)
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Gutscher, Marc-André, Kopp, Heidrun, Krastel, Sebastian, Bohrmann, Gerhard, Garlan, Thierry, Zaragosi, Sebastien, Klaucke, Ingo, Wintersteller, Paul, Loubrieu, Benoit, Le Faou, Yann, San Pedro, Laurine, Dominguez, Stephane, Rovere, Marzia, Mercier de Lepinay, Bernard, Ranero, Cesar, and Sallares, Valenti
- Published
- 2017
- Full Text
- View/download PDF
35. Utilisation of numerical and statistical techniques to describe sedimentary circulation patterns in the mouth of the Gironde estuary
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Mallet, Cyril, Howa, Hélène, Garlan, Thierry, Sottolichio, Aldo, Le Hir, Pierre, and Michel, Denis
- Published
- 2000
- Full Text
- View/download PDF
36. Population dynamics of modern planktonic foraminifera in the western Barents Sea.
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Meilland, Julie, Howa, Hélène, Hulot, Vivien, Demangel, Isaline, Salaün, Joëlle, and Garlan, Thierry
- Subjects
FORAMINIFERA ,POPULATION dynamics ,WATER sampling ,SEAS ,BIOMASS ,SEDIMENTS ,COASTAL sediments ,SOCIAL dominance - Abstract
This study reports on diversity and distribution of planktonic foraminifera (PF) in the Barents Sea Opening (BSO). Populations of PF living in late summer (collected by means of stratified plankton tows) and recently deposited individuals (sampled by interface corer) were compared. High abundances reaching up to 400 ind.m-3 in tow samples and 8000 ind.m-3 in surface sediments were recorded in the centre of the studied area while low abundances were observed in coastal areas, likely due to continental influences. The living and core-top assemblages are mainly composed of the same four species Neogloboquadrina pachyderma, Neogloboquadrina incompta , Turborotalita quinqueloba and Globigerinita uvula. The two species G. uvula and T. quinqueloba dominate the upper water column, whereas surface sediment assemblages display particularly high concentrations of N. pachyderma. The unusual dominance of G. uvula in the water sample assemblages compared to its low proportion in surface sediments might be the signature of (1) a seasonal signal due to summer phytoplankton composition changes at the BSO, linked to the increase in summer temperature at the study site, and/or (2) a signal of a larger timescale and wider geographical reach phenomenon reflecting poleward temperate/subpolar species migration and consecutive foraminiferal assemblage diversification at high latitudes due to global change. Protein concentrations were measured on single specimens and used as a proxy of individual carbon biomass. Specimens of all species show the same trend, a northward decrease in their size-normalized-protein concentration. This suggests that foraminiferal biomass is potentially controlled by different constituents of their organelles (e.g. lipids). The coupling of data from plankton tows, protein measurements and surface sediments allows us to hypothesize that PF dynamics (seasonality and distribution) are decoupled from their metabolism. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
37. Population dynamics of modern planktonic foraminifera in the western Barents Sea.
- Author
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Meilland, Julie, Howa, Hélène, Hulot, Vivien, Demangel, Isaline, Salaün, Joëlle, and Garlan, Thierry
- Subjects
FORAMINIFERA ,POPULATION dynamics ,SPECIES distribution ,SPECIES diversity ,WATER sampling ,BIOMASS ,COASTAL sediments ,SOCIAL dominance - Abstract
This study reports on species diversity and distribution of planktonic foraminifera (PF) at the Barents Sea Opening (BSO). PF populations living in late summer (collected by mean of stratified plankton tows) and recently settled individuals (sampled by interface corer) were studied and compared. High abundances reaching up to 400 ind.m
-3 in tow samples and 8000 ind.cm-3 in surface sediments were recorded in the centre of the studied area while low abundances were observed in coastal areas, likely hampered by continental influences. The living and subfossil (i.e. core-top) assemblages are mainly composed of the four same species Neogloboquadrina pachyderma, Neogloboquadrina incompta, Turborotalita quinqueloba and Globigerinita uvula. The two species G. uvula and T. quinqueloba largely dominate the upper water column whereas surface sediment assemblages display especially high concentrations of N. pachyderma. The unusual dominance of G. uvula in the water sample assemblages compared to its low occurrence in surface sediments might be the signature of (1) a seasonal signal due to summer phytoplankton composition changes at the BSO, linked to the increase of summer temperature at the study site, and/or (2) a signal of a larger time-scale and wide geographical reach phenomenon inducing poleward temperate/subpolar species migration and consecutive foraminiferal assemblage diversification at high latitudes under global climate forcing. Protein concentrations were measured on single specimens and used as a proxy of individual carbon biomass. Specimens of all species show the same trend, i.e. a northward decrease of their size-normalized-protein concentration suggesting foraminiferal biomass to be potentially controlled by different constituents of their organelles (e.g. lipids). The originality of coupling data from plankton tows, protein measurements and surface sediments allows us to hypothesise that PF dynamics (seasonality and distribution) is decoupled from their metabolism. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
38. Detection and description of sand dunes using a geomorphometric approach
- Author
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OGOR, Julien, Debese, Nathalie, Zerr, Benoit, Garlan, Thierry, Lab-STICC_ENSTAB_CID_SFIIS, Laboratoire des sciences et techniques de l'information, de la communication et de la connaissance (Lab-STICC), École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Télécom Bretagne-Institut Brestois du Numérique et des Mathématiques (IBNM), Université de Brest (UBO)-Université européenne de Bretagne - European University of Brittany (UEB)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS)-École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Télécom Bretagne-Institut Brestois du Numérique et des Mathématiques (IBNM), Université de Brest (UBO)-Université européenne de Bretagne - European University of Brittany (UEB)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS), Lab-STICC_ENSTAB_CID_PRASYS, Institut Mines-Télécom [Paris] (IMT)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-École Nationale d'Ingénieurs de Brest (ENIB)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Université Bretagne Loire (UBL)-Institut Mines-Télécom [Paris] (IMT)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-École Nationale d'Ingénieurs de Brest (ENIB)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Université Bretagne Loire (UBL), Lab-STICC_ENSTAB_CID_TOMS, Pôle STIC_OSM, École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, University of Bath, École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS)-Université Bretagne Loire (UBL)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), Institut Mines-Télécom [Paris] (IMT)-École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS)-Université Bretagne Loire (UBL)-IMT Atlantique Bretagne-Pays de la Loire (IMT Atlantique), and Institut Mines-Télécom [Paris] (IMT)
- Subjects
geomorphometry ,seabed feature detection ,MBES ,sand dune ,[SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing - Abstract
International audience; In the last decades, sandbanks and sand dunes of various shapes and sizes have been found anddescribed on continental shelves all over the world. These structures tend to migrate and ourunderstanding of the mechanisms regulating their dynamics is limited. These sandbanks became aconcern due to the fact that they interfere with the human activities at sea. Consequently, theirpresence has economical and environmental impacts. The purpose of this study is to automaticallydetect these dunes in DTMs (Digital Terrain Models) generated from MBES data. So far, automatictechniques aiming at describing marine dune fields have always brought information such as theheight, dune spacing or the orientation at local scale but never went down to a dune scale.Currently, the dunes are still manually digitized and then form parameters are calculated. This task istedious and time-consuming. In addition, the amount of data to process being always bigger, it getsdifficult for operators to keep the pace. To address this issue, we propose a geomorphometricapproach. Attributes such as the slope or curvatures are estimated from DTMs. A combined analysisof the metrics maps enables to extract dunes from their environment. The following step is thedetermination of parameters characterizing the shape and size for each dune. This work providesknowledge about dune fields at a detailed level. Thus, the composition, spatial distribution and otheraspects of sand banks can be obtained. Further research can be conducted in order to learn moreabout the dynamics of dune fields at an individual level.
- Published
- 2015
39. The Ogooue Fan (offshore Gabon): a modern example of deep-sea fan on a complex slope profile.
- Author
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Mignard, Salomé, Mulder, Thierry, Martinez, Philippe, and Garlan, Thierry
- Subjects
SUBMARINE fans ,SEDIMENTATION & deposition ,TURBIDITY currents ,SEDIMENTARY basins ,SEAMOUNTS ,SAND - Abstract
The effects of changes in slope gradient on deposition processes and architecture have been investigated in different deep-sea systems both in modern and ancient environments. However, the impact of subtle gradient changes (< 0.3 ∘) on sedimentary processes along deep-sea fans still needs to be clarified. The Ogooue Fan, located in the northeastern part of the Gulf of Guinea, extends over more than 550 km westwards of the Gabonese shelf and passes through the Cameroon volcanic line. Here, we present the first study of acoustic data (multibeam echosounder and 3.5 kHz, very high-resolution seismic data) and piston cores covering the deep-sea part of this West African system. This study documents the architecture and sedimentary facies distribution along the fan. Detailed mapping of near-seafloor seismic-reflection data reveals the influence of subtle slope gradient changes (< 0.2 ∘) along the fan morphology. The overall system corresponds to a well-developed deep-sea fan, fed by the Ogooue River sedimentary load, with tributary canyons, distributary channel–levee complexes and lobe elements. However, variations in the slope gradient due to inherited salt-related structures and the presence of several seamounts, including volcanic islands, result in a topographically complex slope profile including several ramps and steps. In particular, turbidity currents derived from the Gabonese shelf deposit cross several interconnected intra-slope basins located on the low gradient segments of the margin (< 0.3 ∘). On a higher gradient segment of the slope (0.6 ∘), a large mid-system valley developed connecting an intermediate sedimentary basin to the more distal lobe area. Distribution and thickness of turbidite sands is highly variable along the system. However, turbidite sands are preferentially deposited on the floor of the channel and the most proximal depositional areas. Core description indicates that the upper parts of the turbidity flows, mainly composed of fine-grained sediments, are found in the most distal depocenters. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
40. The Ogooue Fan (Gabon): a modern example of deep-sea system on a complex sea-floor topography.
- Author
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Mignard, Salomé, Mulder, Thierry, Martinez, Philippe, and Garlan, Thierry
- Subjects
SUBMARINE topography ,SEDIMENTATION & deposition ,TURBIDITES - Abstract
The Ogooue deep-sea Fan located in the northeastern part of the Gulf of Guinea expands over more than 550 km westwards of the Gabonese shelf and passes through the Cameroun volcanic line. Here are presented the first study of acoustic data (multibeam echosounder and 3.5 kHz seismic data) and piston cores covering the deep-sea part of this West African system. This study led to the construction of the sedimentary processes map of this area. The overall system corresponds to a well-developed mud-sand rich deep-sea fan, fed by the Ogooue River 'sedimentary load. This system presents the typical morphological elements of clastic slope apron: tributary canyons, distributary channel-levees systems and lobes elements. However, variations on the slope gradient cumulated with the presence of numerous seamounts, including volcanic islands and mud volcanoes, led to a more complex fan architecture and sedimentary facies distribution. In particular, turbidity currents derived from the Gabonese shelf deposit across several interconnected sedimentary sub-basins located on the low gradient segments of the margin. The repeated spill-overs of the most energetic turbidite flows have notably led to the incision of a large distal valley connecting an intermediate sedimentary basin to the more distal lobe area. The sedimentary facies repartition over the fan indicates that pelagic to hemipelagic sedimentation is dominant across the area. Distribution and thickness of turbidite sand beds is highly variable along the system, however turbidite sands preferentially deposit in the bottom of channel-levee systems and on the most proximal depositional areas. The most distal depocenters receive only the upper parts of the flows, which are composed of fine-grained sediments. The Ogooue deep-sea system is predominantly active during periods of low sea-level because canyon heads are separated from terrestrial sediment sources by the broad shelf. However, the northern part of this system appears active during sea-level highstands. This feature is one deeply incised canyon, the Cape Lopez canyon, located on a narrower part of the continental shelf has a different behaviour and receives sediments transported by the longshore drift. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
41. Construction of Multi-Year Time-Series Profiles of Suspended Particulate Inorganic Matter Concentrations Using Machine Learning Approach.
- Author
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Renosh, Pannimpullath R., Jourdin, Frédéric, Charantonis, Anastase A., Yala, Khalil, Rivier, Aurélie, Badran, Fouad, Thiria, Sylvie, Guillou, Nicolas, Leckler, Fabien, Gohin, Francis, and Garlan, Thierry
- Subjects
PARTICULATE matter ,INORGANIC compounds ,MACHINE learning ,HIDDEN Markov models - Abstract
Hydro-sedimentary numerical models have been widely employed to derive suspended particulate matter (SPM) concentrations in coastal and estuarine waters. These hydro-sedimentary models are computationally and technically expensive in nature. Here we have used a computationally less-expensive, well-established methodology of self-organizing maps (SOMs) along with a hidden Markov model (HMM) to derive profiles of suspended particulate inorganic matter (SPIM). The concept of the proposed work is to benefit from all available data sets through the use of fusion methods and machine learning approaches that are able to process a growing amount of available data. This approach is applied to two different data sets entitled "Hidden" and "Observable". The hidden data are composed of 15 months (27 September 2007 to 30 December 2008) of hourly SPIM profiles extracted from the Regional Ocean Modeling System (ROMS). The observable data include forcing parameter variables such as significant wave heights (Hs and Hs50 (50 days)) from the Wavewatch 3-HOMERE database and barotropic currents (Ubar and Vbar) from the Iberian-Biscay-Irish (IBI) reanalysis data. These observable data integrate hourly surface samples from 1 February 2002 to 31 December 2012. The time-series profiles of the SPIM have been derived from four different stations in the English Channel by considering 15 months of output hidden data from the ROMS as a statistical representation of the ocean for ≈11 years. The derived SPIM profiles clearly show seasonal and tidal fluctuations in accordance with the parent numerical model output. The surface SPIM concentrations of the derived model have been validated with satellite remote sensing data. The time series of the modeled SPIM and satellite-derived SPIM show similar seasonal fluctuations. The ranges of concentrations for the four stations are also in good agreement with the corresponding satellite data. The high accuracy of the estimated 25 h average surface SPIM concentrations (normalized root-mean-square error--NRMSE of less than 16%) is the first step in demonstrating the robustness of the method. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
42. Gravity-Driven Deposits in an Active Margin (Ionian Sea) Over the Last 330,000 Years.
- Author
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Köng, Eléonore, Zaragosi, Sébastien, Schneider, Jean-Luc, Garlan, Thierry, Bachèlery, Patrick, Sabine, Marjolaine, and San Pedro, Laurine
- Abstract
In the Ionian Sea, the subduction of the Nubia plate underneath the Eurasia plate leads to an important sediment remobilization on the Calabrian Arc and the Mediterranean Ridge. These events are often associated with earthquakes and tsunamis. In this study, we analyze gravity-driven deposits in order to establish their recurrence time on the Calabrian Arc and the western Mediterranean Ridge. Four gravity cores collected on ridges and slope basins of accretionary prisms record turbidites, megaturbidites, slumping and micro-faults over the last 330,000 years. These turbidites were dated by correlation with a hemipelagic core with a multi-proxy approach: radiometric dating, δ18O, b* colour curve, sapropels and tephrochronology. The origin of the gravity-driven deposits was studied with a sedimentary approach: grain-size, lithology, thin section, geochemistry of volcanic glass. The results suggest three periods of presence/absence of gravity-driven deposits: a first on the western lobe of the Calabrian Arc between 330,000 and 250,000 years, a second between 120,000 years and present day on the eastern lobe of the Calabrian Arc and over the last 60,000 years on the western lobe, and a third on the Mediterranean Ridge over the last 37,000 years. Return times for gravity-driven deposits are around 1,000 years during the most important record periods. The turbidite activity also highlights the presence of volcaniclastic turbidites that seems to be link to the Etna changing morphology over the last 320,000 years. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
43. Influence of tide vs wave on sediment dynamics and dune internal architecture on a macrotidal inner continental shelf (eastern English Channel)
- Author
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Ferret, Y., Le Bot, Sophie, Lafite, R., Blanpain, O., Garlan, Thierry, Morphodynamique Continentale et Côtière (M2C), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS), Service Hydrographique et Océanographique de la Marine (SHOM), and Ministère de la Défense
- Subjects
[SDE.MCG]Environmental Sciences/Global Changes ,[SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment - Abstract
Seabed of continental shelf environments is regularly covered with a multitude of bedforms formed in response to interactions between fluid dynamics and sediment. These mobile sedimentary features have been widely studied in order to prevent damages on human activities and anthropogenic structures. In coastal areas, submarine dune dynamics is mainly controlled by tidal currents and wind and wave forcings (e.g. Le Bot et al., 2004; Idier et al., 2011). However, it is generally not obvious to distinguish which forcing is predominant in dune dynamics.
- Published
- 2012
44. A portative celerimeter for measurement and analysis of compressional speed and attenuation in marine sediments: description and first results
- Author
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Demoulin, Xavier, Guillon, Laurent, Bourdon, Raphaël, Dufrechou, Laurent, Guyomard, Patrick, Garlan, Thierry, System, HAL, and Société Française d'Acoustique
- Subjects
geoacoustic ,[SPI.ACOU] Engineering Sciences [physics]/Acoustics [physics.class-ph] ,tank experiment ,signal processing - Abstract
Geoacoustic parameters of the seafloor are required for accurate sonar prediction and analysis of seismic reflection profiles, especially in shallow water. They are generally established by means of empirical relations. The presented work is part of CARASEDIM, an experimental project devoted to refine these geoacoustical relations in marine sediments, including coarse sands. We focus on the results of the celerimeter prototype that has been developed for that purpose. This portative device is equipped with two emitting probes and two receiving probes allowing to transmit signals between 40kHz and 400kHz. It is designed to both laboratory and in-situ measurements. We discuss about the processing techniques, the protocole of measurement and about the first results. Some laboratory results are presented in both real coarse sands and artificial glass beads. They are compared with theoretical models of sound propagation in sediments based on various assumptions (fluid, visco-elastic, porous...).
- Published
- 2012
45. Seafloor characterization by bathymetric image segmentation.
- Author
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Zarai, Mohamed, Boudraa, Abdel O., Garlan, Thierry, Thibaud, Remy, and Ray, Cyril
- Published
- 2016
- Full Text
- View/download PDF
46. Instrumentation and data management for geoacoustic characterization of shallow water sediments.
- Author
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Demoulin, Xavier, Boudraa, Abdel, Bourdon, Raphael, Durafour, Marine, Garlan, Thierry, Guillon, Laurent, Guyomard, Patrick, Jan, Romain, Ray, Cyril, and Touazi, Ithri
- Published
- 2016
- Full Text
- View/download PDF
47. South Brittany substratum morphology and quaternary fluvial system : contributions to new 2D and 3D views
- Author
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Menier, David, Thinon, Isabelle, Guennoc, Pol, Leroy, P., Guillocheau, François, Proust, Jean-Noël, Garlan, Thierry, Laboratoire Histoire et Sciences Sociales du Littoral et de la mer (SOLITO), Université de Bretagne Sud (UBS), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Université de Liège, Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Service Hydrographique et Océanographique de la Marine (SHOM), and Ministère de la Défense
- Subjects
[SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy ,[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology - Published
- 2005
48. Modelling Fine Sediment Dynamics: Towards a Common Erosion Law for Fine Sand, Mud and Mixtures.
- Author
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Mengual, Baptiste, Le Hir, Pierre, Cayocca, Florence, and Garlan, Thierry
- Subjects
EROSION ,TURBIDITY ,SECCHI disks ,ANALYTICAL mechanics ,SEDIMENTATION & deposition - Abstract
This study describes the building of a common erosion law for fine sand and mud, mixed or not, in the case of a typical continental shelf environment, the Bay of Biscay shelf, characterized by slightly energetic conditions and a seabed mainly composed of fine sand and muddy sediments. A 3D realistic hydro-sedimentary model was used to assess the influence of the erosion law setting on sediment dynamics (turbidity, seabed evolution). A pure sand erosion law was applied when the mud fraction in the surficial sediment was lower than a first critical value, and a pure mud erosion law above a second critical value. Both sand and mud erosion laws are formulated similarly, with different parameters (erodibility parameter, critical shear stress and power of the excess shear stress). Several transition trends (linear or exponential) describing variations in these erosion-related parameters between the two critical mud fractions were tested. Suspended sediment concentrations obtained from simulations were compared to measurements taken on the Bay of Biscay shelf with an acoustic profiler over the entire water column. On the one hand, results show that defining an abrupt exponential transition improves model results regarding measurements. On the other hand, they underline the need to define a first critical mud fraction of 10 to 20%, corresponding to a critical clay content of 3-6%, below which pure sand erosion should be prescribed. Both conclusions agree with results of experimental studies reported in the literature mentioning a drastic change in erosion mode above a critical clay content of 2-10% in the mixture. Results also provide evidence for the importance of considering advection in this kind of validation with in situ observations, which is likely to considerably influence both water column and seabed sediment dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
49. Modern morpho-sedimentological patterns in a tide-dominated estuary system: the Bay of Brest (west Britanny, France).
- Author
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Gregoire, Gwendoline, Ehrhold, Axel, Le Roy, Pascal, Jouet, Gwenael, and Garlan, Thierry
- Subjects
SEDIMENTOLOGY ,GEOMORPHOLOGICAL mapping ,ESTUARIES - Abstract
Long-studied with respect to its sedimentological features (1897), the Bay of Brest (Western Britanny, France) is a textbook example of a tide-dominated estuary. Characterised by macrotidal conditions, this estuary system is sheltered from the open sea (Iroise Sea) by a narrow strait that partitions the wave tide influences and continental/marine inputs. Sediments are supplied to the bay both by rivers (the Aulne and Elorn rivers) and by marine tidal currents. This study presents new analyses of detailed facies and morphological patterns, based on the integration of multisource data compiling seabed sampling, swath and LIDAR bathymetry, and backscatter imagery. TheMain Map, at a scale of 1:90,000, contains (1) a sedimentological distribution using the ‘Code Manche’ classification, (2) a morphological map, and (3) bathymetric mapping which presents the morphology of marine and terrestrial landforms. This work may lay the foundation for a future study on sedimentary transport in a unique and confined coastal environment. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
50. A CLASSIFICATION OF SCOURING MARKS IN MACROTIDAL ENVIRONMENTS FROM ANALYSIS OF LONG TERM WRECK MARKS.
- Author
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GARLAN, THIERRY, MARCHES, ELODIE, and BRENON, EMERIC
- Subjects
SHIPWRECKS ,SAND dunes ,SCOUR (Hydraulic engineering) ,SUBMARINE geology ,SEDIMENTS - Published
- 2015
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