22 research outputs found

    Breeze influence on waves and vertical current profile in the coastal area based on EOF analysis (Vilanova i la Geltrú, Barcelona)

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    This article presents some preliminary results on the breeze influence on waves and vertical current profiles during eleven months of data recorded by an Acoustic Wave and Current Profiler installed in the OBSEA platform in the coast of Vilanova i la Geltrú (NW Mediterranean). The collected data has been analyzed using Empirical Orthogonal Functions and spectral analysisPostprint (published version

    Ploughing the deep sea floor

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    Bottom trawling is a non-selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor. The direct impact of this technique on fish populations1,2 and benthic communities3,4 has received much attention, but trawling can also modify the physical properties of seafloor sediments, water-sediment chemical exchanges and sediment fluxes5,6. Most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7,8, however, where the capacity of trawling to modify the seafloor morphology coexists with high-energy natural processes driving sediment erosion, transport and deposition9. Here we show that on upper continental slopes, the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales. We found that trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time, reducing its original complexity as shown by high-resolution seafloor relief maps. Our results suggest that in recent decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolution. Given the global dimension of this type of fishery, we anticipate that the morphology of the upper continental slope in many parts of the world's oceans could be altered by intensive bottom trawling, producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

    Efectes de la pesca d'arrossegament en els sediments dels canyons submarins catalans.

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    Bottom trawling is a nonselective commercial fishing technique whereby heavy nets and gear are pulled along the seafloor, modifying the physical properties of seafloor sediments and altering natural sediment fluxes. Most studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments, where the capacity of trawling to modify the seafloor sediments coexists with high-energy natural processes driving sediment erosion, transport and deposition. Recent studies conducted on the Catalan margin have demonstrated that on continental slopes where the sediment dynamics is less energetic the reworking of the deep seafloor by bottom trawling produces periodic resuspension of surface sediments, and ultimately modifies the shape of the submarine landscape over large spatial scales. Trawling-induced sediment displacement and removal from fishing grounds causes the morphology of the deep seafloor to become smoother over time, reducing its original complexity. These results suggest that during the last decades, following the industrialization of fishing fleets, bottom trawling has become an important driver of deep seascape evolutio

    Sediment transport to the deep canyons and open-slope of the western Gulf of Lions during the 2006 intense cascading and open-sea convection period

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    An array of mooring lines deployed between 300 and 1900 m depth along the Lacaze-Duthiers and Cap de Creus canyons and in the adjacent southern open slope was used to study the water and sediment transport on the western Gulf of Lions margin during the 2006 intense cascading period. Deep-reaching cascading pulses occurred in early January, in late January and from early March to mid-April. Dense water and sediment transport to the deep environments occurred not only through submarine canyons, but also along the southern open slope. During the deep cascading pulses, temporary upper and mid-canyon and open slope deposits were an important source of sediment to the deep margin. Significant sediment transport events at the canyon head only occurred in early January because of higher sediment availability on the shelf after the stratified and calm season, and in late February because of the interaction of dense shelf water cascading with a strong E-SE storm. During the January deep cascading pulses, increases in suspended sediment concentration within the canyon were greater and earlier at 1000 m depth than at 300 m depth, whereas during the March-April deep cascading pulses sediment concentration only increased below 300 m depth, indicating resuspension and redistribution of sediments previously deposited at upper and mid-canyon depths. Deeper than 1000 m depth, net fluxes show that most of the suspended sediment left the canyon and flowed along the southern open slope towards the Catalan margin, whereas a small part flowed down-canyon and was exported basinward. Additionally, on the mid- and lower-continental slope there was an increase in the near-bottom currents induced by deep open-sea convection processes and the propagation of eddies. This, combined with the arrival of deep cascading pulses, also generated moderate suspended sediment transport events in the deeper slope regions

    Sediment transport along the Cap de Creus Canyon flank during a mild, wet winter

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    Cap de Creus Canyon (CCC) is known as a preferential conduit for particulate matter leaving the Gulf of Lion continental shelf towards the slope and the basin, particularly in winter when storms and dense shelf water cascading coalesce to enhance the seaward export of shelf waters. During the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) cruise in March 2011, deployments of recording instruments within the canyon and vertical profiling of the water column properties were conducted to study with high spatial-temporal resolution the impact of such processes on particulate matter fluxes. In the context of the mild and wet 2010-2011 winter, no remarkable dense shelf water formation was observed. On the other hand, the experimental setup allowed for the study of the impact of E-SE storms on the hydrographical structure and the particulate matter fluxes in the CCC. The most remarkable feature in terms of sediment transport was a period of dominant E-SE winds from 12 to 16 March, including two moderate storms (maximum significant wave heights = 4.1-4.6 m). During this period, a plume of freshened, relatively cold and turbid water flowed at high speeds along the southern flank of the CCC in an approximate depth range of 150-350 m. The density of this water mass was lighter than the ambient water in the canyon, indicating that it did not cascade off-shelf and that it merely downwelled into the canyon forced by the strong cyclonic circulation induced over the shelf during the storms and by the subsequent accumulation of seawater along the coast. Suspended sediment load in this turbid intrusion recorded along the southern canyon flank oscillated between 10 and 50 mg L−1, and maximum currents speeds reached values up to 90 cm s−1. A rough estimation of 105 tons of sediment was transported through the canyon along its southern wall during a 3-day-long period of storm-induced downwelling. Following the veering of the wind direction (from SE to NW) on 16 March, downwelling ceased, currents inside the canyon reversed from down- to up-canyon, and the turbid shelf plume was evacuated from the canyon, most probably flowing along the southern canyon flank and being entrained by the general SW circulation after leaving the canyon confinement. This study highlights that remarkable sediment transport occurs in the CCC, and particularly along its southern flank, even during mild and wet winters, in absence of cascading and under limited external forcing. The sediment transport associated with eastern storms like the ones described in this paper tends to enter the canyon by its downstream flank, partially affecting the canyon head region. Sediment transport during these events is not constrained near the seafloor but distributed in a depth range of 200-300 m above the bottom. Our paper broadens the understanding of the complex set of atmosphere-driven sediment transport processes acting in this highly dynamic area of the northwestern Mediterranean Sea

    Formación de surcos sedimentarios por cataratas submarinas en el interior del cañón de Cap de Creus.

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    De septiembre de 2004 a septiembre de 2005 se fondearon varios anclajes en el interior del cañón submarino de Cap de Creus para investigar los procesos de transporte de sedimento asociados a las cataratas submarinas de agua densa del Golfo de León. Durante el invierno de 2005 este fenómeno oceanográfico fue excepcionalmente intenso, afectando de forma casi continuada la cabecera del cañón submarino desde finales de enero hasta principios de abril, manteniendo temperaturas bajas, concentraciones de sedimento en suspensión altas y corrientes elevadas (procedentes preferentemente del flanco sur del cañón). El análisis de las partículas atrapadas por una trampa de sedimento fondeada a 30 m sobre el lecho marino evidenció que estas cataratas submarinas son capaces de transportar sedimentos de tamaño grueso en suspensión (hasta un 65 % de fracción arena), dotándose de una gran capacidad erosiva y de generación de formas de fondo. La orientación de un campo de surcos sedimentarios erosivos identificado recientemente en el interior del cañón coincide claramente con las direcciones preferentes de las corrientes de mayor intensidad durante los eventos de cataratas submarinas. Este hecho indica una relación causa-efecto entre los procesos contemporáneos de transporte de sedimento asociados a este proceso oceanográfico y la formación y mantenimiento de los surcos edimentarios en el interior del cañón submarino de Cap de Creus

    Holocene neoglacial events in the Bransfield Strait (Antarctica). Paleogeographic and paleoclimatic significance

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    The morphological characterisation of the western submarine island flanks of El Hierro and La Palma differentiates four type-zones that may give new insights into the evolution of oceanic island slopes. The different type-zones result from the interplay between constructive volcanic processes, hemipelagic settling and volcano collapses. The latter results in massive debris avalanche deposits, which form large volcaniclastic aprons. In most cases, the headwall scarps are clearly exposed on the emerged part of the islands. The events that occurred in the youngest and westernmost islands of El Hierro and La Palma have vertical runouts exceeding 6,000 m and volumes that can reach several hundred km3. The landslide frequency for the entire Canaries is one major event per 90 ka. Triggering mechanisms are closely related to magmatic processes. The increase in the shear stress is directly linked with the forceful intrusion of magma along ridge-rift systems, while in the western Canary Islands it seems that the main process reducing shear resistance may be related to the rise in pore pressure due to hydrothermal circulation

    Formación de surcos sedimentarios por cataratas submarinas en el interior del cañón de Cap de Creus.

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    De septiembre de 2004 a septiembre de 2005 se fondearon varios anclajes en el interior del cañón submarino de Cap de Creus para investigar los procesos de transporte de sedimento asociados a las cataratas submarinas de agua densa del Golfo de León. Durante el invierno de 2005 este fenómeno oceanográfico fue excepcionalmente intenso, afectando de forma casi continuada la cabecera del cañón submarino desde finales de enero hasta principios de abril, manteniendo temperaturas bajas, concentraciones de sedimento en suspensión altas y corrientes elevadas (procedentes preferentemente del flanco sur del cañón). El análisis de las partículas atrapadas por una trampa de sedimento fondeada a 30 m sobre el lecho marino evidenció que estas cataratas submarinas son capaces de transportar sedimentos de tamaño grueso en suspensión (hasta un 65 % de fracción arena), dotándose de una gran capacidad erosiva y de generación de formas de fondo. La orientación de un campo de surcos sedimentarios erosivos identificado recientemente en el interior del cañón coincide claramente con las direcciones preferentes de las corrientes de mayor intensidad durante los eventos de cataratas submarinas. Este hecho indica una relación causa-efecto entre los procesos contemporáneos de transporte de sedimento asociados a este proceso oceanográfico y la formación y mantenimiento de los surcos edimentarios en el interior del cañón submarino de Cap de Creus

    Monitoring sediment dynamics at the boundary between the coastal zone and the continental shelf

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    This article presents some preliminary results of the sedimentary dynamics observed during the first 3 months of data collection obtained with the Acoustic Wave and Current Profiler installed in the OBSEA platform in the coast of Vilanova i la Geltrú (NW Mediterranean)Peer Reviewe

    Monitoring sediment dynamics at the boundary between the coastal zone and the continental shelf

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    This article presents some preliminary results of the sedimentary dynamics observed during the first 3 months of data collection obtained with the Acoustic Wave and Current Profiler installed in the OBSEA platform in the coast of Vilanova i la Geltrú (NW Mediterranean)Peer ReviewedPostprint (published version
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