Articles

Els filtres actuals son: Any inici = 2017, Any final = 2018
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Brackenridge R.E., Stow D.A.V., Hernández‐Molina F.J., Jones C., Mena A., Alejo I., Ducassou E., Llave E., Ercilla G., Nombela M.A. (2018)
Sedimentology, 65, 7, 2223-2252. DOI: 10.1111/sed.12463. (BibTeX: brackenridge.etal.2018a)
Resum: Veure
This work presents a detailed study of CONTOURIBER and Integrated Ocean Drilling Program 339 sediment data targeting sand‐rich contourites in the Eastern Gulf of Cadiz. All of the collected sediments are interpreted as contourites (deposited or reworked by bottom currents) on the basis of oceanographic setting, seismic and morphometric features, and facies characteristics. A variety of sandy and associated facies are found across the study area including: (i) bioturbated muddy contourites; (ii) mottled silty contourites; (iii) very fine mottled and fine‐grained bioturbated sandy contourites; (iv) massive and laminated sandy contourites; and (v) coarse sandy/gravel contourites. The thickest sands occur within contourite channels and there is a marked reduction in sand content laterally away from channels. Complementary to the facies descriptions, grain‐size analysis of 675 samples reveals distinctive trends in textural properties linked to depositional processes under the action of bottom currents. The finest muddy contourites (<20 μm) show normal grain‐size distributions, poor to very poor sorting, and zero or low skewness. These are deposited by settling from weak bottom currents with a fine suspension load. Muddy to fine sandy contourites (20 to 200 μm) trend towards better sorting and initially finer and then coarser skew. These are typical depositional trends for contourites. As current velocity and carrying capacity increase, more of the finest fraction remains in suspension and bedload transport becomes more important. Clean sandy contourites (>200 μm) are better sorted. They result from the action of dominant bedload transport and winnowing at high current speeds. The results highlight the importance of bottom current velocity, sediment supply and bioturbational mixing in controlling contourite facies. Despite growing interest in their hydrocarbon exploration potential, contourite sands have remained poorly understood. This research therefore has important implications for developing current understanding of these deposits and aiding the correct interpretation of deep marine sands and depositional processes.
Paraules clau: Contourites; Deep-water sands; Grain size; Gulf of Cadiz; Sediment facies model
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Casas D., Pimentel A., Pacheco J., Martorelli E., Sposato A., Ercilla G., Alonso B., Chiocci F. (2018)
Journal of Volcanology and Geothermal Research, 356, 127-140. DOI: 10.1016/j.jvolgeores.2018.02.017. (BibTeX: casas.etal.2018a)
Resum: Veure
High-resolution bathymetric data and seafloor sampling were used to characterize the most recent volcanic eruption in the Azores region, the 1998–2001 Serreta submarine eruption. The vent of the eruption is proposed to be an asymmetric topographic high, composed of two coalescing volcanic cones, underlying the location where lava balloons had been observed at the sea surface during the eruption. The volcanic products related to the 1998–2001 eruption are constrained to an area of ~0.5 km2 around the proposed vent position. A submarine Strombolian-style eruption producing basaltic lava balloons, ash and coarse scoriaceous materials with limited lateral dispersion led to the buildup of the cones. The 1998–2001 Serreta eruption shares many similarities with other intermediate-depth lava balloon-forming eruptions (e.g., the 1891 eruption offshore Pantelleria and the 2011–2012 eruption south of El Hierro), revealing the particular conditions needed for the production of this unusual and scarcely documented volcanic product.
Paraules clau: Submarine volcanism; Lava balloons; Multibeam bathymetry; Terceira; Serreta Ridge; Cone formation
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Druet M., Muñoz‐Martín A., Granja‐Bruña J.L., Carbó‐Gorosabel A., Acosta J., Llanes P., Ercilla G. (2018)
Tectonics, 37, 5, 1576-1604. DOI: 10.1029/2017TC004903. (BibTeX: druet.etal.2018c)
Resum: Veure
The magma‐poor rifted continental margin of Galicia has an extremely complex structure. Its formation involved several rifting episodes that occurred ultimately during the early Cretaceous near a ridge triple junction, which produced a change in the orientation of the main structures in its transition to the north Iberia margin. In addition, there is a superimposed partial tectonic inversion along its northwest and northern border which developed from the Late Cretaceous to at least Oligocene times. The present study integrates a large volume of new geophysical information (mainly marine gravity data and 2D seismic reflection profiles) to provide insights on the formation of this rift system and on the development of its later inversion. The combined interpretation and modeling of this data enable the presentation of a new crustal and structural domains map for the whole Galicia margin. This includes the rift domains related to the extreme thinning of the crust and the lithospheric mantle (stretched, necking, and hyperextension and mantle exhumation (HME) domains), as well as a domain of intense compressional deformation. New constraints arise on the origin, the deep structure, and the characterization of the along‐ and across‐strike variation of the continent‐ocean transition of the margin, where a progressive change from hyperextension to partial inversion is observed. The development of both rifting and later partial tectonic inversion is influenced by the existence of former first‐order tectonic features. Most of the tectonic inversion is focused on the HME domain, which in some areas of the northwestern margin is completely overprinted by compressional deformation
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Estrada F., Galindo‐Zaldívar J., Vázquez J.T., Ercilla G., D\'Acremont E., Alonso B., Gorini C. (2018)
Terra nova, 30, 1, 24-33. DOI: 10.1111/ter.12304. (BibTeX: estrada.etal.2018a)
Resum: Veure
The Alboran Sea constitutes a Neogene-Quaternary basin of the Betic-Rif Cordillera, which has been deformed since the Late Miocene during the collision between the Eurasian and African plates in the westernmost Mediterranean. NNE-SSW sinistral and WNW-ESE dextral conjugate fault sets forming a 75° angle surround a rigid basement spur of the African plate, and are the origin of most of the shallow seismicity of the central Alboran Sea. Northward, the faults decrease their transcurrent slip, becoming normal close to the tip point, while NNW-SSE normal and sparse ENE-WSW reverse to transcurrent faults are developed. The uplifting of the Alboran Ridge ENE-WSW antiform above a detachment level was favoured by the crustal layering. Despite the recent anticlockwise rotation of the Eurasian-African convergence trend in the westernmost Mediterranean, these recent deformations -consistent with indenter tectonics characterised by a N164°E trend of maximum compression- entail the highest seismic hazard of the Alboran Sea.
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Galindo‐Zaldivar J., Ercilla G., Estrada F., Catalán M., d\'Acremont E., Azzouz O., Casas D., Chourak M., Vazquez J.T., Chalouan A., Sanz de Galdeano C., Benmakhlouf M., Gorini C., Alonso B., Palomino D., Rengel J.A., Gil A.J. (2018)
Tectonics, 37, 8, 2513-2530. DOI: 10.1029/2017TC004941. (BibTeX: galindozaldivar.etal.2018c)
Resum: Veure
The Eurasian‐African NW‐SE oblique plate convergence produces shortening and orthogonal extension in the Alboran Sea Basin (westernmost Mediterranean), located between the Betic and Rif Cordilleras. A NNE‐SSW broadband of deformation and seismicity affects the Alboran central part. After the 1993–1994 and 2004 seismic series, an earthquake sequence struck mainly its southern sector in 2016–2017 (main event Mw = 6.3, 25 January 2016). The near‐surface deformation is investigated using seismic profiles, multibeam bathymetry, gravity and seismicity data. Epicenters can be grouped into two main alignments. The northern WSW‐ENE alignment has reverse earthquake focal mechanisms, and in its epicentral region recent mass transport deposits occur. The southern alignment consists of a NNE‐SSW vertical sinistral deformation zone, with early epicenters of higher‐magnitude earthquakes located along a narrow band 5 to 10‐km offset westward of the Al Idrisi Fault. Here near‐surface deformation includes active NW‐SE vertical and normal faults, unmapped until now. Later, epicenters spread eastward, reaching the Al Idrisi Fault, characterized by discontinuous active NNE‐SSW vertical fractures. Seismicity and tectonic structures suggest a westward propagation of deformation and the growth at depth of incipient faults, comprising a NNE‐SSW sinistral fault zone in depth that is connected upward with NW‐SE vertical and normal faults. This recent fault zone is segmented and responsible for the seismicity in 1993–1994 in the coastal area, in 2004 onshore, and in 2016–2017 offshore. Insights for seismic hazard assessment point to the growth of recent faults that could produce potentially higher magnitude earthquakes than the already formed faults.
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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)
Resum: Veure
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.
Paraules clau: Ebro Delta, Coastal erosion, Shelf processes, Shoreface connected sand ridge, Morphodynamics, Bedform
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Isla E., Pérez-Albaladejo E., Porte C. (2018)
Scientific Reports, 8, 9154. DOI: 10.1038/s41598-018-27375-4. (BibTeX: isla.etal.2018a)
Resum: Veure
Industrial activity generates harmful substances which can travel via aerial or water currents thousands of kilometers away from the place they were used impacting the local biota where they deposit. The presence of harmful anthropogenic substances in the Antarctic is particularly surprising and striking due to its remoteness and the apparent geophysical isolation developed with the flows of the Antarctic Circumpolar current and the ring of westerly winds surrounding the continent. However, long-range atmospheric transport (LRAT) of pollutants has been detected in the Antarctic since the 70’s along the Antarctic trophic food web from phytoplankton to birds. Still, no information exists on the presence of cytotoxic compounds in marine sediments neither at basin scales (thousands of kilometers) nor in water depths (hundreds of meters) beyond shallow coastal areas near research stations. Our results showed for the first time that there is cytotoxic activity in marine sediment extracts from water depths >1000 m and along thousands of kilometers of Antarctic continental shelf, in some cases comparable to that observed in Mediterranean areas. Ongoing anthropogenic pressure appears as a serious threat to the sessile benthic communities, which have evolved in near isolation for millions of years in these environments.
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Isla E., DeMaster D.J. (2018)
Geochimica et cosmochimica acta, 242, 34-50. DOI: 10.1016/j.gca.2018.08.011. (BibTeX: isla.demaster.2018a)
Resum: Veure
Labile organic carbon (LOC) dynamics (i.e., of recently produced, planktonic material) and sediment dynamics were studied in the seabed using naturally occurring 14Corg and 210Pb measurements in the region where the Larsen Ice Shelves A and B were floating almost two decades ago. A non-steady-state diagenetic model was used to estimate sediment mixing coefficients as well as LOC fluxes to the seabed and LOC turnover times (i.e., mean residence times) in a suite of 14 sediment cores from the continental shelf, including a glacial trough. At four of the stations, cores were collected during 2007 and 2011 cruises, enabling a time-series approach for understanding the evolution of sedimentary processes and LOC dynamics in the deposits below a collapsed ice shelf. Sediment mixing coefficients, based on non-steady-state 210Pb profiles, varied between 0.01 cm2 y−1 and 1.6 cm2 y−1 in these post-ice shelf sediments. These values were similar to those found in polar deep-sea environments, where sedimentary conditions are less dynamic than in shallower provinces. LOC, whose abundance decreased uniformly with depth, was detected to depths ranging from 2 to 16 cm, with LOC seabed inventories varying from 1.5 to 22 mg LOC cm−2. Excess 210Pb and LOC fluxes were relatively uniform across the study area suggesting that similar particle fluxes have taken place within the Larsen system since the disintegration of the various ice shelves. The LOC mean residence time at the different stations varied from 3 y to >60 y. The 14Corg approach, calculating LOC content based on a two-end member model with planktonic 14Corg as the labile carbon end member, most closely correlated with the lipid content of the sediment, which has been considered one of the best descriptors of reactive organic matter readily available to benthic consumers. We suggest that the irregular combination of sea ice coverage, organic matter production and supply to the sea floor introduce scatter in the determination of sediment and LOC dynamics such that short-term temporal (<5 years) and spatial trends could not be readily resolved.
Paraules clau: Antarctica; Ice shelf collapse; Labile organic carbon; Biogeochemistry; Marine sediment; Larsen ice shelves; 14C; 210Pb
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Lafosse M., Gorini C., Le Roy P., Alonso B., d’Acremont E., Ercilla G., Rabineau M., Vázquez J.T., Rabaute A., Ammar A. (2018)
Marine and Petroleum Geology, 97, 370-389. DOI: 10.1016/j.marpetgeo.2018.07.022. (BibTeX: lafosse.etal.2018a)
Resum: Veure
In active basins, tectonics can segment the continental shelf and control its stratigraphic architecture and physiography. Segmentation can explain the local evolution and morphology of the continental shelf because of sea-level variations, local tectonic segmentation and hydrodynamic processes. Here we investigate the tectonically active Morocco continental margin (southern Alboran Sea) using high-resolution seismic profiles and multibeam bathymetric data. The active faults bounding the transtensive Nekor basin triggered the segmentation of the shelf into three sectors showing different subsidence rates: a western sector corresponding to an extensive fault relay, a central sector corresponding to the subsiding Al-Hoceima Bay and an eastern sector corresponding to the footwall of the Trougout senestral normal fault. Results show that the staircase morphology of the shelf corresponds to successive submarine terraces at the shelf edge (ST1), mid-shelf (ST2) and inner-shelf (ST3) around −110 m,-80 m, and −40 to −20 m deep, respectively. The terraces correspond to the top of prograding wedges seaward and are erosive landward. They are correlated with stillstand from the Last Glacial Maximum to the Holocene highstand. Above the terraces, sub-aqueous dune fields are interpreted as degraded and deposited during the post-glacial transgression. In the central sector, typical delta front seafloor undulations on the shelf and crescent shaped bedforms at the head of marine incisions on the upper slope denote a fluvial influence during the Holocene. Seismic stratigraphy analysis revealed the preservation of six seismic units bounded by polygenic regional unconformities (S1, S2, S3, S4 and S5). Based on comparison with other Mediterranean margins, S1 to S5 are attributed to 4th order maximum regressive surface. We discuss the local preservation of the system tracts as a function of the vertical motion and the physiography of this tectonically active domain. This study provides useful clues for future local paleo-seismic analysis and to advance our understanding of sedimentary processes in active areas.
Paraules clau: Seismic stratigraphy; Active tectonic; Pleistocene; Continental shelf; Swath bathymetry; Geomorphology; Western Mediterranean
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Ortuño M., Corominas O., Villamor P., Zúñiga R.F., Lacan P., Aguirre-Díaz G., Perea H., Štěpančíková P., Ramírez-Herrera M.T. (2018)
Geomorphology DOI: 10.1016/j.geomorph.2018.07.010. (BibTeX: ortuno.etal.2018a)
Resum: Veure
The Acambay Graben, within the central part of the Trans-Mexican Volcanic Belt, is one of the major sources of continental earthquakes in Mexico. To date, the activity and paleoseismological history of the axial faults of the graben are not well constrained. We provide morphological, structural and sedimentological evidence of the seismogenic nature of two of the axial structures, the Temascalcingo and the Tepuxtepec fault systems. Faults consist of multiple parallel scarps with en echelon and horse-splay patterns. Fault systems extend for 60 km and displace Quaternary to Upper Miocene volcanic edifices and volcano-sedimentary materials. Surface lengths of individual fault traces range between 3 and 25 km, and observed throws reach a minimum of 150–200 m. The long-term and short-term slip rate of the Temascalcingo fault system in the studied section presents similar values, ranging from 0.06 ± 0.02 (minimum long term) to 0.12 ± 0.02 mm y−1 (maximum value of average short-term). Only the long-term slip rate of the Tepuxtepec system could be constrained in 0.01–0.02 mm/y, being a minimum estimate. The Holocene fault rupture history at two sites provided evidence of six ruptures since 12,500–11,195 BCE, among which three ruptures should have occurred between 11,847 ± 652 BCE and 11,425 ± 465 BCE Variable single event displacements (SEDs, between 6 and 77) are interpreted as the result of fault interdependences and/or the interaction with the latest volcanic activity. Also, small displacements triggered by activity on other faults probably contributed to slip variability, i.e., faults display primary and secondary behavior
Paraules clau: Temascalcingo fault system; Tepuxtepec fault system; Paleoseismology; Fault complexity
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Palanques A., Puig P. (2018)
Marine Geology, 406, 119-131. DOI: 10.1016/j.margeo.2018.09.010. (BibTeX: palanques.puig.2018a)
Resum: Veure
The effects of deep dense shelf water cascading and open sea convection on the sediment dynamics of the northwestern Mediterranean basin were studied by near-bottom moored instruments recording trapped particle fluxes, suspended particle fluxes, water properties and hydrodynamics from November 2011 to July 2012. During this period, near-bottom currents induced by winter dense water formation generated benthic storms that caused resuspension at 2450 m water depth, increasing by more than one order of magnitude the ambient suspended sediment concentrations, the trapped particle fluxes and the suspended sediment fluxes. During the preconditioning phase of the open sea convection, from December 2011 to mid-February 2012, currents (1–10 cm s−1), suspended sediment concentrations (<0.1 mg l−1), Chl-a fluorescence values (<0.063 μg l−1), trapped total mass fluxes (10–50 mg m−2 d−1) and trapped organic carbon fluxes (1–4 mg m−2 d−1) were low, and organic matter was mainly undegraded and of marine origin. Open sea convection was observed at the study site in mid-February, at the beginning of the violent mixing phase, increasing current velocities up to 26 cm s−1 and Chl-a fluorescence values up to 0.074 μg l−1, supplying particles with fresh marine organic matter content. During the last fortnight of February, two major dense shelf water cascading pulses generated Chl-a fluorescence increases (up to 0.116 μg l−1) and large suspended sediment concentration peaks (up to19 mg l−1), suspended sediment fluxes (up to 6500 mg m−2 d−1) and trapped total mass flux increases (up to 22,900 mg m−2 d−1), which were associated with benthic storms resuspension. During this phase, trapped organic carbon flux increased almost two orders of magnitude (up to 260 mg m−2 d−1), with pulses of both marine and terrestrial organic matter. The sinking and spreading phase occurred from early March to mid-June. The signal of deep dense shelf water cascading lasted past early April, and the spreading of the newly formed dense water maintained maximum currents of up to 25 cm s−1 and trapped particle fluxes of up to 2000 mg m−2 d−1 until mid-June. At the beginning of this phase, organic matter was terrestrial and several turbidity peaks occurred during current speed increases generated by benthic storms. At the end of this phase, the organic matter became less terrestrial, trapped organic carbon fluxes decreased from about 190 to 10 mg m−2 d−1 and turbidity peaks occurred with low current velocities indicating the arrival of storm tails at the mooring site. The large particle fluxes of fresh or relatively undegraded organic carbon induced by deep dense water formation during winter 2012, contributed to the “fertilization” of the northwestern Mediterranean deep benthic ecosystems.
Paraules clau: Benthic storms; Open sea convection; Dense shelf water cascading; Deep sea; Sediment transport; Seafloor resuspension
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Purroy A., Najdek M., Isla E., Župan I., Thébault J., Peharda M. (2018)
Marine Environmental Research, 142, 234-249. DOI: 10.1016/j.marenvres.2018.10.011. (BibTeX: purroy.etal.2018a)
Resum: Veure
The trophic ecology of two bivalves, the clam Callista chione and the cockle Glycymeris bimaculata was studied using environmental and biochemical variables of the suspended particulate matter and the sediment. Samples were collected from two shallow sites, Pag and Cetina, in the coastal oligotrophic Mediterranean Sea, during a 17 month period. The temporal variation of the particulate matter reflected a mixture between marine and terrestrial sources throughout the year, with a clear marine influence during summer and fall, and predominance of terrestrial inputs during spring and winter. The digestive gland was a useful rapid turnover tissue, where the carbon isotope signal was species-specific and the nitrogen isotope one was site-specific. FA markers in the digestive gland revealed a mixed diet where Callista chione fed more upon fresh material than G. bimaculata which relied largely on bacteria-derived detritus. Overall, little feeding niche overlap was observed between the two species during the year, indicating resource partitioning, expected for a food-limited system. The present trophic ecology study in co-occurring species allowed identifying species-specific feeding adaptations to environmental variability.
Paraules clau: Feeding ecology; Bivalves; Suspension feeder; Biochemical variables; Stable isotopes; Fatty acids; Adriatic sea; Niche partitioning; Coastal ecosystems
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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)
Resum: Veure
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.
Paraules clau: Submarine canyons, ecosystem service, anthropogenic impacts, conservation, management
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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)
Resum: Veure
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.
Paraules clau: Mediterranean outflow water Strait of Gibraltar Gulf of Cadiz Topographic steering Bottom drainage system Along-slope contour avenues Down-slope erosional channels
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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)
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van Haren H., Puig P. (2017)
Marine Geology, 388, 1-11. DOI: 10.1016/j.margeo.2017.04.008. (BibTeX: vanharen.puig.2017a)
Resum: Veure
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.
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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)
Resum: Veure
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.
Paraules clau: Trace metals, sediment pollution record, historical evolution of pollution, Barcelona, Mediterranean Sea, environmental regulations
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Paradis S., Puig P., Masqué P., Juan-Díaz X., Martín J., (2017)
Scientific Reports, 7, 43332. DOI: 10.1038/srep43332. (BibTeX: paradis.etal.2017a)
Resum: Veure
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.
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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)
Resum: Veure
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.
Paraules clau: Bottom trawling, inverse model, modeling, sediment transport, submarine canyon, turbidity currents
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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)
Resum: Veure
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.
Paraules clau: Prodeltaic processes, infralittoral prograding wedge, hyperpycnal flows, turbidity currents, crescent shaped sediment waves, cyclic steps
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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)
Resum: Veure
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.
Paraules clau: Organic carbon, Carbon isotope ratio, Grain size, Shelf dynamics, NW Mediterranean
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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)
Resum: Veure
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.
Paraules clau: Tsunamis, submarine landslides, submarine tectonics and volcanism, Africa
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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)
Resum: Veure
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.
Paraules clau: Video monitoring, coastal monitoring, extrinsic calibration, planview generation, beach dynamics