Los filtros actuales son: Año inicio = 2017, Año final = 2018
1.35 Mb
Guerrero Q., Guillén J., Durán R., Urgeles R. (2018)
Marine Geology, 395, 219-233. DOI: 10.1016/j.margeo.2017.10.002. (BibTeX: guerrero.etal.2018a)
Resumen: Ver
A sand ridge field located over a retreating deltaic lobe in the Ebro Delta (NW Mediterranean) is characterized using three sets of co-located multibeam bathymetric data acquired in 2004, 2013 and 2015, measurements of near-bottom currents, high-resolution seismic profiles, and aerial photographs. The aim of this study is to illustrate the processes and timing involved in the initial stages of sand ridge development. The sand ridge field extends from the 5 to 15 m isobaths and the ridges have maximum heights and wavelengths of 2.5 and 400 m, respectively; they have straight crests that are arranged obliquely to the shoreline and are composed of fine sand. In general, the sand ridges are symmetric, although asymmetries with the lee side of the ridge facing to the SE and to the NW are also present. The genesis of the sand ridge field is closely related to the contemporary evolution of the Ebro River mouth. The change of the main river channel in the 1940s led to progressive abandonment of the former river mouth and to severe coastal retreatment (~ 37 m·yr− 1), making large amounts of sediment available for ridge formation. The persistent Mistral winds (NW) induce near-bottom currents flowing towards the SE, which are able to rework and transport sandy sediments. The sand ridges are currently active, with mean SE migration rates of ~ 10 m·yr− 1 most likely in pulses, when high-speed currents occur. Wave-storm events induce reverse flows (E-SE), which reshape the ridges to symmetric or opposite asymmetry geometries. The bedform morphologies, the oblique arrangement with respect to the shoreline, the angle between the strongest current and the crestlines and the sediment grain size match well with those of shoreface-connected (attached) sand ridges and, particularly, with the initial stages of sand ridge development on storm-dominated continental shelves. Sediment availability, shoreline retreat, relatively strong near-bottom currents induced by winds, seafloor irregularities and relative sea-level rise on the Ebro Delta combine to provide a suitable transgressive environment for sand ridge development. Time-scales related to sand ridges are usually of hundreds/thousands of years, but here it is demonstrated that the genesis of sand ridges can take place within a few decades. The studied bedforms are unlikely to persist in the absence of rapid sea-level rise, leading to sediment scarcity and wave and current reworking.
Palabras clave: Ebro Delta, Coastal erosion, Shelf processes, Shoreface connected sand ridge, Morphodynamics, Bedform
1.40 Mb
Fernandez-Arcaya U., Ramirez-Llodra E., Aguzzi J., Allcock A.L., Davies J.S., Dissanayake A., Harris P., Howell K., Huvenne V.A.I., Macmillan-Lawler M., Martín J., Menot L., Nizinski M., Puig P., A. Rowden A., Sanchez F., Van den Beld I.M.J. (2017)
Frontiers in Marine Science, 4 DOI: 10.3389/fmars.2017.00005. (BibTeX: fernandezarcaya.etal.2017a)
Resumen: Ver
Submarine canyons are major geomorphic features of continental margins around the world. Several recent multidisciplinary projects focused on the study of canyons have considerably increased our understanding of their ecological role, the goods, and services they provide to human populations, and the impacts that human activities have on their overall ecological condition. Pressures from human activities include fishing, dumping of land-based mine tailings, and oil and gas extraction. Moreover, hydrodynamic processes of canyons enhance the down-canyon transport of litter. The effects of climate change may modify the intensity of currents. This potential hydrographic change is predicted to impact the structure and functioning of canyon communities as well as affect nutrient supply to the deep-ocean ecosystem. This review not only identifies the ecological status of canyons, and current and future issues for canyon conservation, but also highlights the need for a better understanding of anthropogenic impacts on canyon ecosystems and proposes other research required to inform management measures to protect canyon ecosystems.
Palabras clave: Submarine canyons, ecosystem service, anthropogenic impacts, conservation, management
9.91 Mb
Gasser M., Pelegrí J.L., Emelianov M., Bruno M., Gràcia E., Pastor M., Peters H., Rodríguez-Santana A., Salvador J., Sánchez-Leal R.F. (2017)
Progress in Oceanography, 157, 47-71. DOI: 10.1016/j.pocean.2017.05.015. (BibTeX: gasser.etal.2017)
Resumen: Ver
The Mediterranean Water leaves the western end of the Strait of Gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope. The salinity of the onset Mediterranean Outflow Water (MOW) is so high that leads to water much denser (initially in excess of 1.5 kg m 3) than the overlying central waters. During much of its initial descent, the MOW retains large salinity anomalies – causing density anomalies that induce its gravity current character – and relatively high westward speeds – caus- ing a substantial Coriolis force over long portions of its course. We use hydrographic data from six cruises (a total of 1176 stations) plus velocity data from two cruises, together with high-resolution bathymetric data, to track the preferential MOW pathways from the Strait of Gibraltar into the western Gulf of Cadiz and to examine the relation of these pathways to the bottom topography. A methodology for tributary systems in drainage basins, modified to account for the Coriolis force, emphasizes the good agreement between the observed trajectories and those expected from a topographically-constrained flow. Both contour avenues and cross-slope channels are important and have complementary roles steering the MOW along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western Gulf of Cadiz. Our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern MOW. Furthermore, they support the hypoth- esis that, as a result of the high erosive power of the bottom flow and changes in bottom-water speed, the MOW pathways and mixing rates have changed in the geological past.
Palabras clave: Mediterranean outflow water Strait of Gibraltar Gulf of Cadiz Topographic steering Bottom drainage system Along-slope contour avenues Down-slope erosional channels
3.26 Mb
Grinyó J., Isla E., Peral L., Gili J.M. (2017)
Progress in Oceanography, 159, 323-339. DOI: 10.1016/j.pocean.2017.11.005. (BibTeX: grinyo.etal.2017a)
2.10 Mb
van Haren H., Puig P. (2017)
Marine Geology, 388, 1-11. DOI: 10.1016/j.margeo.2017.04.008. (BibTeX: vanharen.puig.2017a)
Resumen: Ver
An array of 76 high-resolution temperature sensors at 0.5 m intervals between 5 and 42.5 m off the bottom was moored near the Barcelona harbor buoy in 81 m water depth, between October 2013 and April 2014. The mooring was located just seaward of an extensive sediment wave area developed in the Llobregat River prodelta, with 1 m high crests parallel to the coast and 50–100 m wavelengths. In the NW-Mediterranean, the thermal stratification reaches its maximum penetration through the water column in autumn until it is broken by winter convection. Such a deep stratification affects large-scale sub-inertial slope currents, which are mostly confined to the upper half of the water column, by the hampered vertical exchange of frictional turbulence, and supports near-bottom internal waves between the inertial and buoyancy frequencies. Observed onshelf propagating frontal bores most likely interact with the sediment waves and contribute to their generation, as they are trailed by considerable shear-induced turbulence and high-frequency internal waves close to the buoyancy frequency that have wavelengths matching those of the sediment waves. The bores are either driven by near-inertial or 3–7 day periodic sub-inertial motions just following a brief period of large convective instability at the end of the offshelf flow phase.
1.38 Mb
Palanques A., Lopez L., Guillén J., Puig P., Masqué P. (2017)
Science of The Total Environment, 579, 755-767. DOI: 10.1016/j.scitotenv.2016.11.031. (BibTeX: palanques.etal.2017a)
Resumen: Ver
The evolution of trace metal pollution on the Barcelona city continental shelf during the last few decades was studied by analyzing the historical records of trace metals in sediment cores and surface sediment samples taken at the same locations in 1987 and in 2008. Polluted surface samples taken in 1987 reached enrichment factors of up to 490 for Hg, about 40 for Pb and Cd, and about 17 for Zn, Cr and Cu. The data show a decline of up to one order of magnitude in the trace metal content of surface sediments during the last few decades, with maximum enrichment factors of between 20 and 30 for Hg and Cd and between 5 and 12 for Zn, Cr, Pb and Cu. Although present-day pollution is still significant, it is evident that environmental regulations that are in place, including the operation since 1979 of wastewater treatment plants built in the Besòs River watershed, have drastically reduced the pollution levels in this highly populated and industrialized Mediterranean area. However, water discharge during heavy rain events exceeds the treatment capacity of the existing facilities, leading to the maintenance of still high levels of metals in sediments of the Barcelona city shelf.
Palabras clave: Trace metals, sediment pollution record, historical evolution of pollution, Barcelona, Mediterranean Sea, environmental regulations
1.28 Mb
Paradis S., Puig P., Masqué P., Juan-Díaz X., Martín J., (2017)
Scientific Reports, 7, 43332. DOI: 10.1038/srep43332. (BibTeX: paradis.etal.2017a)
Resumen: Ver
Many studies highlight that fish trawling activities cause seafloor erosion, but the assessment of the remobilization of surface sediments and its relocation is still not well documented. These impacts were examined along the flanks and axes of three headless submarine canyons incised on the Barcelona continental margin, where trawling fleets have been operating for decades. Trawled grounds along canyon flanks presented eroded and highly reworked surface sediments resulting from the passage of heavy trawling gear. Sedimentation rates on the upper canyon axes tripled and quadrupled its natural (i.e. pre-industrialization) values after a substantial increase in total horsepower of the operating trawling fleets between 1960 s and 1970 s. These impacts affected the upper canyon reaches next to fishing grounds, where sediment resuspended by trawling can be transported towards the canyon axes. This study highlights that bottom trawling has the capacity to alter natural sedimentary environments by promoting sediment-starved canyon flanks, and by enhancing sedimentation rates along the contiguous axes, independently of canyons’ morphology. Considering the global mechanisation and offshore expansion of bottom trawling fisheries since the mid-20th century, these sedimentary alterations may occur in many trawled canyons worldwide, with further ecological impacts on the trophic status of these non-resilient benthic communities.
3.93 Mb
Payo-Payo M., Jacinto R.S., Lastras G., Rabineau M., Puig P., Martín J., Canals M., Sultan N. (2017)
Marine Geology, 386, 107-125. DOI: 10.1016/j.margeo.2017.02.015. (BibTeX: payopayo.etal.2017a)
Resumen: Ver
Bottom trawling leads to recurrent sediment resuspension events over fishing grounds. Recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons, which subsequently impacts deep-sea ecosystems. Present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed. The present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in La Fonera submarine canyon, northwestern Mediterranean Sea, thus contributing to an improved assessment of trawling impacts. Based on mooring data within a canyon gully, we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds. This resuspension is later used as forcing for the direct problem: we simulate trawling-induced flows through the canyon and provide a 3D visualization of potential trawling impacts on sediment dynamics, including the identification of the propagation patterns of sediments resuspended by trawling. Flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis, with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope. Trawling-induced sediment flows promote sediment accumulation beyond the canyon mouth. Given the wide geographical distribution of bottom trawling, our results have far-reaching implications that go much beyond La Fonera submarine canyon. Our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins.
Palabras clave: Bottom trawling, inverse model, modeling, sediment transport, submarine canyon, turbidity currents
3.38 Mb
Puig P., Durán R., Muñoz A., Elvira E., Guillén J. (2017)
Marine Geology, 393, 21-34. DOI: 10.1016/j.margeo.2017.02.009. (BibTeX: puig.etal.2017a)
Resumen: Ver
Canyon head regions are key areas for understanding the shelf-to-canyon sedimentary dynamics and assessing the predominant hydrodynamic and sedimentary processes shaping their morphology. High-resolution multibeam bathymetry surveys conducted on the shelf, upper slope and along the main thalwegs of the Alías-Almanzora submarine canyon system were used to recognize the specific morphological features of the various canyon heads and infer the main sediment transport mechanism operating through them. Off the Almanzora River, different canyon head morphologies were observed at 65–90 m water depth, incising the outer prodeltaic deposits. A direct connection from the river supply is evidenced by the presence of a large radial field of sediment waves on the prodelta, presumably related to hyperpycnal flows during flash flood events, and their continuation towards trains of cyclic steps that merge into the Almanzora canyon head. Processes linked to seepage and groundwater sapping also seems apparent in the prodeltaic deposits, which results in pockmark alignments and formation of elongated narrow canyon heads. At the southern limit of the Almanzora prodelta, another type of canyon head results from the formation and merging of linear gullies. These have been interpreted as the morphological expression of the distal off-shelf transport of flood-related hyperycnal flows. However, most of the canyon heads of the main tributaries of this canyon system (i.e., Garrucha, Cabrera and Alías) are found at much shallower water depths (7–20 m). They generally show a continuation in land with rivers or intermittent creeks (known as “ramblas”) that also experience flash flood events, but some of them are disconnected from any river source. These canyon heads cut into the infralittoral prograding wedge, displaying feeder channels that tend to oriented against the direction of the prevalent long-shore current. Some canyon head tributaries show sediment waves along their axis interpreted as the result of hyperpycnal flood events or storm-induced turbidity flows. This study focusses on the diversity of sediment transport processes that can co-exist in the various canyon tributaries of a given submarine canyon system, stressing on the importance of the canyon heads location with respect to the principal sedimentary source, which ultimately determines their main geomorphological traits.
Palabras clave: Prodeltaic processes, infralittoral prograding wedge, hyperpycnal flows, turbidity currents, crescent shaped sediment waves, cyclic steps
660 Kb
Quirós L., Pedrosa-Pàmies R., Sánchez-Vidal A., Guillén J., Durán R., Cabello P. (2017)
Estuarine, Coastal and Shelf Science, 189, 267-280. DOI: 10.1016/j.ecss.2017.03.004. (BibTeX: quiros.etal.2017a)
Resumen: Ver
Continental shelves are recognized to play a key role in the biogeochemical cycle of carbon, linking terrestrial and marine carbon reservoirs. In this study we investigate the physical and biogeochemical processes that control the source, transport and fate of organic carbon (OC) in the continental shelf off Barcelona city, in the NW Mediterranean Sea. Surface sediment samples were collected from depths of 10–40 m during late summer and autumn 2012. Grain size and biogeochemical parameters such as OC, its stable isotope δ13C, total nitrogen (TN) and OC/TN ratios were analysed in size-fractionated sediments. The influence of environmental factors over the study area was determined using hydrological and oceanographic time series, together with video images of the Barcelona coast line and nearshore region. We have found a wide range of OC contents, from 0.13 to 8.68%, depending on water depth and sediment particle size. The highest OC concentration was always found in the clay fraction (<4 μm), followed by the sand fraction (>63 μm) that contained terrestrial plant debris. Wave activity, discharge of the Besòs River and the “Espigó de Ginebra” outfall were the main mechanisms controlling the sorting of sediments by their grain size and thus the distribution of OC in the inner shelf off Barcelona. In addition, we observed that the organic matter in clay particles was progressively degraded seawards, probably because these particles remain suspended in the water column much more time compared to those that are heavier and, therefore, they are exposed for longer time periods to oxygenated conditions. Both OC/TN ratios and δ13C values found suggest that the organic matter preserved was predominantly land supplied.
Palabras clave: Organic carbon, Carbon isotope ratio, Grain size, Shelf dynamics, NW Mediterranean
8.80 Mb
Rodriguez M., Maleuvre C., Jollivet-Castelot M., d’Acremont E., Rabaute A., Lafosse M., Ercilla G., Vázquez J.T., Alonso B., Ammar A., Gorini C. (2017)
Geophysical Journal International, 209, 1, 266–281. DOI: 10.1093/gji/ggx028. (BibTeX: rodriguez.etal.2017a)
Resumen: Ver
The active Eurasia–Nubia plate boundary runs across the Alboran Sea in the Western Mediterranean Sea, where the connection between the Atlantic and Mediterranean water masses occurs. Earthquakes above magnitude Mw > 6 may favour the occurrence of landslides within contouritic drifts in the Alboran Sea. A compilation of recent multibeam data reveals for the first time the distribution of slope failures along the Xauen–Tofiño banks, in the southern Alboran Sea. Here, we provide a detailed mapping and description of the morphology of eight Holocene landslides, including volume estimations of the failed mass and the related mass transport deposits (MTDs). The most voluminous landslide mobilized ∼0.5 km3 of sediment at the initial stage of slope failure, and formed a ∼2.2–5.6 km3 MTD. A finite-difference numerical model, assimilating the landslide to a granular flow, simulates tsunami generation and propagation for a slide similar to the most voluminous one. Simulations show that the coastline of Al Hoceima may be impacted by a ∼0.5-m-high tsunami wave, whereas the coastline of Al Jebha may be impacted by a ∼1-m-high tsunami wave, only ∼13 min after sediment failure. The 0.2-m-high tsunami waves may impact the southern Spanish coast of the Iberian Peninsula ∼20 min after slide initiation. Although the elevations of the modeled tsunami waves are modest, landslides from the Xauen–Tofiño banks may represent a more dangerous source of tsunami in some parts of the Moroccan coast than earthquakes.
Palabras clave: Tsunamis, submarine landslides, submarine tectonics and volcanism, Africa
447 Kb
Simarro G., Ribas F., Álvarez A., Guillén J., Chic O., Orfila A. (2017)
Journal of Coastal Research, 35, 5, 1217-1227. DOI: 10.2112/JCOASTRES-D-16-00022.1. (BibTeX: simarro.etal.2017a)
Resumen: Ver
Video monitoring systems have become a powerful and low-cost tool in coastal studies. Extrinsic calibration of the cameras is compulsory to get quantitative information from the images. This paper presents an Open Source Software for extrinsic calibration and for the generation of related products such as planviews and time stacks. The methodology employed for extrinsic calibration minimizes errors comprising ground control points, the camera position, and, whenever is available, the horizon line. The dip of the horizon due to Earth curvature is corrected for. Planview generation is performed in such a way that the user can decide the smoothing degree in the transition zone between cameras. Time stack generation has been designed to save the minimum number of pixels in order to obtain the desired transect in the real world. The reader will find a versatile software meant to manage large data sets in a simple way.
Palabras clave: Video monitoring, coastal monitoring, extrinsic calibration, planview generation, beach dynamics