Research papers

The current filters are: Starting year = 2016, Ending year = 2017
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)
Abstract: See
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.
Keywords: Trace metals, sediment pollution record, historical evolution of pollution, Barcelona, Mediterranean Sea, environmental regulations
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)
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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.
Keywords: Tsunamis, submarine landslides, submarine tectonics and volcanism, Africa
3.95 Mb
Alonso B., Ercilla G., Casas D., Stow D.A.V., Rodríguez-Tovar F.J., Dorador J., Hernández-Molina F.J. (2016)
Marine Geology, 377, 77-94. DOI: 10.1016/j.margeo.2015.12.016. (BibTeX: alonso.etal.2016c)
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Pleistocene succession at Sites U1386 and U1387 (IODP 339) from palaeo-moat and drift domains of the Faro Drift has been examined to characterize the lithofacies and to identify the most useful criteria for distinguishing between contourite and gravity-flow deposits. Three lithofacies, A, B, and C, are defined based on a combination of sedimentological and mineralogical analyses. The dominant lithofacies A corresponds to contourite deposits; lithofacies B and C comprise turbidites and debrites respectively. Three main criteria have been utilized to distinguish between these deposits: (i) the vertical trend of the grain-size and the sedimentary structures. The contourites show complete sequences (C1 to C5 divisions) and truncate sequences (basecut-out divisions, e.g., C3–C2–C1, and C3). The turbidites display mainly Td–Te divisions, although Tc division is also present to a lesser extent. The debrites display deformational and shearing structures; (ii) the modal frequency distribution. The contourite sequences show similar mode grain-size values in different textures suggesting that the steady conditions of supply are maintained over time. In contrast, turbidite and debrite sequences display different modes, primarily conditioned by mixing of components from allochthonous sources and their downslope gravitational transport; (iii) the sediment composition (clay mineral, bulk mineral and sand fraction) and provenance that reflect long- and short-distance transport modes. Most of the terrigenous components of the contourites come from the Guadalquivir drainage basin, whereas for the turbidites and debrites these are sourced from the neighbouring fluvial drainage basins (Guadiana, Tinto-Odiel). The biogenic components in the latter indicate shallow depositional environments prior to seafloor failure. The spatial and temporal distributions of the lithofacies reflect the different (palaeo) environments of the Faro Drift. Debrite and incomplete turbidite sequences characterize the palaeo-moat domain during the Early Pleistocene. Complete contourite sequences (C1 to C5) and basecut-out sequences (C3–C4–C5, and C3) characterize the proximal palaeo-drift domain during the Early and Middle Pleistocene and the complete contourite sequences represent the distal drift domain during the Late Pleistocene.
Keywords: Gulf of Cadiz, Contourites, Turbidites, Debrites, Grain-size, Bulk mineral, Clay mineral
26.92 Mb
Bartolome R., Górriz E., Dañobeitia J., Cordoba D., Martí D., Cameselle A.L., Núñez-Cornú F., Bandy W.L., Mortera-Gutiérrez C.A., Nuñez D., Castellón A., Alonso J.L. (2016)
Pure and Applied Geophysics, 173, 10, 3575-3594. DOI: 10.1007/s00024-016-1331-y. (BibTeX: bartolome.etal.2016c)
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During the TSUJAL marine geophysical survey, conducted in February and March 2014, Spanish, Mexican and British scientists and technicians explored the western margin of Mexico, considered one of the most active seismic zones in America. This work aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in the offshore part of the Jalisco Block, to link the geodynamic and the recent tectonic deformation occurring there with the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out acquisition, processing and geological interpretation of a multichannel seismic reflection profile running perpendicular to the margin. Crustal images show an oceanic domain, dominated by subduction–accretion along the lower slope of the margin with a subparallel sediment thickness of up to 1.6 s two-way travel time (approx. 2 km) in the Middle American Trench. Further, from these data the region appears to be prone to giant earthquake production. The top of the oceanic crust (intraplate reflector) is very well imaged. It is almost continuous along the profile with a gentle dip (<10°); however, it is disrupted by normal faulting resulting from the bending of the plate during subduction. The continental crust presents a well-developed accretionary prism consisting of highly deformed sediments with prominent slumping towards the trench that may be the result of past tsunamis. Also, a bottom simulating reflector (BSR) is identified in the first half a second (twtt) of the section. High amplitude reflections at around 7–8 s twtt clearly image a discontinuous Moho, defining a very gentle dipping subduction plane.
Keywords: Jalisco Block, Mexico, Rivera plate, crustal structure, seismic imaging, subduction, earthquake, tsunami, BSR, gas hydrate, trench infill
1.45 Mb
Casas D., Chiocci F., Casalbore D., Ercilla G., Ortiz de Urbina J. (2016)
Geo-Marine Letters, 36, 6, 405-414. DOI: 10.1007/s00367-016-0458-2. (BibTeX: casas.etal.2016b)
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Regional inventories and magnitude-frequency relationships provide critical information about landslides and represent a first step in landslide hazard assessment. Despite this, the availability of accurate inventories in the marine environment remains poor because of the commonly low accessibility of high-resolution data at regional scales. Evaluating high-resolution bathymetric data spanning the time interval 2007–2011 for the Gioa Basin of the southern Tyrrhenian Sea yielded a landslide inventory of 428 events affecting an area of >85 km2 and mobilizing approximately 1.4 km3 of sediment. This is the first time that this area is studied in such detail, justifying comparison with other areas both onland and offshore. Statistical analyses revealed that the cumulative distribution of the dataset is characterized by two right-skewed probability distributions with a heavy tail. Moreover, evidence of a rollover for smaller landslide volumes is consistent with similar trends reported in other settings worldwide. This may reflect an observational limitation and the site-specific geologic factors that influence landslide occurrence. The robust validation of both power-law and log-normal probability distributions enables the quantification of a range of probabilities for new extreme events far from the background landslide sizes defined in the area. This is a useful tool at regional scales, especially in geologically active areas where submarine landslides can occur frequently, such as the Gioia Basin.
3.50 Mb
Conti D., Orfila A., Mason E., Sayol J.M., Simarro G., Balle S. (2016)
Ocean Dynamics, 66, 11 DOI: 10.1007/s10236-016-0990-7. (BibTeX: conti.etal.2016c)
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This work introduces a new method for ocean eddy detection that applies concepts from stationary dynamical systems theory. The method is composed of three steps: first, the centers of eddies are obtained from fixed points and their linear stability analysis; second, the size of the eddies is estimated from the vorticity between the eddy center and its neighboring fixed points, and, third, a tracking algorithm connects the different time frames. The tracking algorithm has been designed to avoid mismatching connections between eddies at different frames. Eddies are detected for the period between 1992 and 2012 using geostrophic velocities derived from AVISO altimetry and a new database is provided for the global ocean.
Keywords: Coherent structures, Global ocean, Mesoscale eddies, Dynamical systems theory, Stability analysis of fixed points, Tracking algorithm
26.80 Mb
Dañobeitia J., Bartolomé R., Prada M., Nuñez-Cornú F., Córdoba D., Bandy W.L., Estrada F., Cameselle A.L., Nuñez D., Castellón A., Alonso J.L., Mortera C., Ortiz M. (2016)
Pure and Applied Geophysics, 173, 10, 3553-3573. DOI: 10.1007/s00024-016-1388-7. (BibTeX: danobeitia.etal.2016a)
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Processing and analysis of new multichannel seismic records, coincident with wide-angle seismic profiles, acquired in the framework of the TsuJal project allow us to investigate in detail the complex structure of the oceanic domain in the collision zone between Rivera Plate and Block Jalisco at its northern termination. The subducting Rivera Plate, which is overridden by the North American Plate–Jalisco Block, is clearly identified up to 21.5°N (just south of Maria Magdalena Island) as a two clear reflections that we interpret as the interplate and Moho discontinuities. North of the Tres Marias Islands the seismic images display a different tectonic scenario with structures that are consistent with large faulting and rifted margin. A two-dimensional velocity approach for the crustal geometry is achieved using joint refraction/reflection travel time tomography, the uncertainty of the results is assessed by means of Monte Carlo analysis. Our results show an average oceanic crustal thickness of 6–7 km with a moderate increase towards the Jalisco Block, an anomalous thick layers (~3.0 km) displaying a relatively low velocity (~5.5 km/s) underneath Maria Magdalena Rise, and an estimated Moho depth deeper than 15 km in the collision zone between Rivera Plate and Jalisco Block. We have also determined an anomalous crust on the western flank of the Tres Marias Islands, which may be related to the initial phases of continental breakup of the Baja California Peninsula and Mexico mainland. High-resolution bathymetry provides remarkable images of intensive slope instabilities marked by relatively large slides scars of more than 40 km2 extent, and mass-wasting deposits probably triggered by the intense seismicity in the area.
1.82 Mb
Ercilla Gemma, Juan C., Hernández-Molina F.J., Bruno M., Estrada F., Alonso B., Casas D., Farran M., Llave E., García M., Vázquez J.T., D\'Acremont E., Gorini C., Palomino D., Valencia J., El Moumni B., Ammari A. (2016)
Marine Geology, 378, 157-170. DOI: 10.1016/j.margeo.2015.09.007. (BibTeX: ercilla.etal.2016a)
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We present an interdisciplinary study of the geomorphology, sedimentology and physical oceanography of the Alboran Sea (south-western Mediterranean Sea) to evaluate the potential role of bottom currents in shaping the Spanish and Moroccan continental margins and adjacent basins. Bathymetric and seismic data have allowed the recognition of the contourite deposits, including depositional (plastered, sheeted, channel-related, mounded confined, elongated and separated drifts), erosive (moats, channels and furrows) and mixed (terraces and scarps) features. Hydrographic data offer new insights into the distribution of the Mediterranean water masses, and reveal that bottom circulation of the Western Intermediate Water (WIW) and the Levantine Intermediate Water (LIW) interact with the Spanish slope, and the Western Mediterranean Deep Water (WMDW) on the Moroccan slope, Spanish base-of-slope and deep basins. The integration of distinct datasets and approaches allows a proposal of a new sedimentary model for the Alboran Sea that details the significance of bottom current processes in shaping deep-sea morphology. This model considers the bottom circulation of water masses governs physiography, that interface positions of water-masses with contrasting densities sculpt terraces on a regional scale, and that the morphologic obstacles play an essential role in the local control of processes and water-mass distributions. Our findings demonstrate the pivotal role of bottom water circulation in seafloor shaping and sedimentary stacking patterns for continental margins, establishing a new outlook for future studies of deep marine sedimentation.
Keywords: Geomorphology, contourites, bottom currents, continental margin, water-masses interfaces, Alboran Sea
4.50 Mb
García M., Hernández-Molina F.J., Alonso B., Vázquez J.T., Ercilla G., Llave E., Casas D. (2016)
Marine Geology, 378, 5-19. DOI: 10.1016/j.margeo.2015.10.004. (BibTeX: garcia.etal.2016b)
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Morphological features (escarpments, depressions and valleys) identified on the Guadalquivir Bank, within the middle slope of the Gulf of Cadiz, have been investigated based on high- and mid-resolution geophysical datasets. The morphological and seismic stratigraphic analyses allowed their interpretation as the result of the interaction between oceanographic, mass-wasting and tectonic processes. A phase of enhanced tectonic activity occurred during the Mid-Pleistocene related to the activity of diapiric structures, the front of the allochthonous units, and/or basement uplift or adjustments. This event seems crucial for the origin of widespread mass-wasting events along middle slope sheeted drift plateaus that have been further reworked by the Mediterranean Outflow Water. This resulted in the erosion of a marginal valley to the north of the Guadalquivir Bank, while fluid escape processes also have a minor role in the creation of crescent-shaped depressions. The Diego Cao channel is the result of a complex evolution, from a contourite moat associated to a separated drift to a multi-crested drift and moat system during the Pliocene and Early Quaternary. During the Mid-Pleistocene, the mass-wasting phase produced a prominent erosive surface that opened a deep gateway into the Guadalquivir Bank uplifted basement, allowing the onset of the Mediterranean Intermediate Branch to flow towards the N-NW. The system evolved into a contourite system composed of the present-day channel and an associated deposit on its western side (Bartolomeu Dias sheeted drift plateau) that forms a particularly complex separated drift. This drift displays a series of circular depressions that are similar in morphology to collapse features or pockmarks, but are in contrast, the result of the interaction between the bottom current and the irregular mass-wasting-related scars.
Keywords: Gulf of Cadiz, contourite depositional system, erosional features, morphology, seismic stratigraphy, Mediterranean Outflow Water
562 Kb
Gili J.M., Zapata-Guardiola R., Isla E., Vaqué D., Barbosa A., Gracia-Sancho L., Quesada A. (2016)
Polar Biology, 39, 1-10. DOI: 10.1007/s00300-015-1852-3.. (BibTeX: gili.etal.2016a)
1.47 Mb
Gutt J., David B., Isla E., Piepenburg D. (2016)
Polar Biology, 39, 5, 761-764. DOI: 10.1007/s00300-016-1937-7. (BibTeX: gutt.etal.2016c)
1.24 Mb
Isla E. (2016)
Polar Biology, 39, 5, 819-828. DOI: 10.1007/s00300-015-1833-6. (BibTeX: isla.2016a)
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To assess whether sea floor sediment reflects the characteristics of the upper water column, organic carbon (OC) and biogenic silica (bSi) were measured in seventeen 5-cm-long sediment cores recovered within a climatic gradient from the northwestern Weddell Sea (WS) to the Drake Passage (DP) across the Bransfield Strait (BS). Climate settings in the study area vary from dry and cold (polar) conditions with seasonal sea ice coverage in the WS to a more humid and warm (oceanic) environment where no seasonal sea ice develops in the DP, with the BS as transitional zone undergoing seasonal sea ice coverage. OC varied between 0.2 and 1.7 % and represented more than 90 % of the total carbon, and bSi varied between 2 and 13 %. The profiles of both variables along the sediment cores suggested that the surface mixed layer is at least 5 cm thick. The inventories of the upper 5 cm of the sediment column were calculated for both variables. Regional averages were significantly lower for OC in DP samples and higher for bSi in the BS. These results suggested relatively high bSi export to the seabed in the BS, higher degradation for OC in the DP and lower bSi export from the euphotic zone in the WS. The observations made evident that the biogenic matter contents in the sediment not necessarily replicate their production characteristics at the upper ocean even across strong climatic gradients. The results may provide a useful baseline for paleo-reconstructions in a rapidly changing environment.
Keywords: Antarctic Peninsula, pelagic–benthic, coupling, biogenic silica, organic carbon, sediment
2.26 Mb
Hunt Jr. G.L., Drinkwater K.F., Arrigo K., Berge J., Daly K.L., Danielson S., Daase M., Hop H., Isla E., Karnovsky N., Laidre K., Mueter F.J., Murphy E.J., Renaud P.E., Smith Jr. W.O., Trathan P., Turner J., Wolf-Gladrow D. (2016)
Progress in Oceanography, 149, 40-81. DOI: 10.1016/j.pocean.2016.10.004. (BibTeX: huntjr..etal.2016b)
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We compare and contrast the ecological impacts of atmospheric and oceanic circulation patterns on polar and sub-polar marine ecosystems. Circulation patterns differ strikingly between the north and south. Meridional circulation in the north provides connections between the sub-Arctic and Arctic despite the presence of encircling continental landmasses, whereas annular circulation patterns in the south tend to isolate Antarctic surface waters from those in the north. These differences influence fundamental aspects of the polar ecosystems from the amount, thickness and duration of sea ice, to the types of organisms, and the ecology of zooplankton, fish, seabirds and marine mammals. Meridional flows in both the North Pacific and the North Atlantic oceans transport heat, nutrients, and plankton northward into the Chukchi Sea, the Barents Sea, and the seas off the west coast of Greenland. In the North Atlantic, the advected heat warms the waters of the southern Barents Sea and, with advected nutrients and plankton, supports immense biomasses of fish, seabirds and marine mammals. On the Pacific side of the Arctic, cold waters flowing northward across the northern Bering and Chukchi seas during winter and spring limit the ability of boreal fish species to take advantage of high seasonal production there. Southward flow of cold Arctic waters into sub-Arctic regions of the North Atlantic occurs mainly through Fram Strait with less through the Barents Sea and the Canadian Archipelago. In the Pacific, the transport of Arctic waters and plankton southward through Bering Strait is minimal. In the Southern Ocean, the Antarctic Circumpolar Current and its associated fronts are barriers to the southward dispersal of plankton and pelagic fishes from sub-Antarctic waters, with the consequent evolution of Antarctic zooplankton and fish species largely occurring in isolation from those to the north. The Antarctic Circumpolar Current also disperses biota throughout the Southern Ocean, and as a result, the biota tends to be similar within a given broad latitudinal band. South of the Southern Boundary of the ACC, there is a large-scale divergence that brings nutrient-rich water to the surface. This divergence, along with more localized upwelling regions and deep vertical convection in winter, generates elevated nutrient levels throughout the Antarctic at the end of austral winter. However, such elevated nutrient levels do not support elevated phytoplankton productivity through the entire Southern Ocean, as iron concentrations are rapidly removed to limiting levels by spring blooms in deep waters. However, coastal regions, with the upward mixing of iron, maintain greatly enhanced rates of production, especially in coastal polynyas. In these coastal areas, elevated primary production supports large biomasses of zooplankton, fish, seabirds, and mammals. As climate warming affects these advective processes and their heat content, there will likely be major changes in the distribution and abundance of polar biota, in particular the biota dependent on sea ice.
Keywords: Advection, Climate change, Polar and sub-polar biota, Polar marine ecosystems, Sea ice
6.61 Mb
Juan C., Ercilla G., Hernández-Molina F.J., Estrada F., Alonso B., Casas D., García M., Farran M., Llave E., Palomino D., Vázquez J.-T., Medialdea T., Gorini C., D'Acremont E., El Moumni B., Ammar A. (2016)
Marine Geology, 378, 292-311. DOI: 10.1016/j.margeo.2016.01.006. (BibTeX: juan.etal.2016c)
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A seismic analysis of the Pliocene and Quaternary stratigraphy was conducted in the Alboran Sea (westernmost Mediterranean) using more than 1250 profiles consisting of single- and multi-channel seismic records. This allowed for the updating and renaming of the stratigraphic boundaries and the establishment of a new Pliocene and Quaternary seismic stratigraphy for the Alboran Sea, after the relocation of the base of the Quaternary from 1.8 to 2.6 Ma. The boundaries of the stratigraphic division are as follows: the Messinian (M at 5.96 to 5.33 Ma), the intra-lower Pliocene (P0 at ca. 4.5 Ma), the top of the Zanclean (P1 at ca.3.3 Ma), the base of the Quaternary (BQD at ca. 2.6 Ma), the top of the Gelasian (Q0 at ca. 1.8 Ma), the intra-lower Quaternary (Q1 at ca. 1.12 Ma), and the top of the Calabrian (Q2 at ca. 0.7 Ma). Additionally, for the first time, the seismic analysis allowed us to present and discuss the evidence of contourite features reaching the scale of the Alboran Basin. Contourite drifts (plastered, sheeted, elongated separated and confined monticular drifts) and erosive features (terraces, scarps, moats and channels) were developed under the continuous influence of Mediterranean water masses (light and dense), after the opening of the Strait of Gibraltar in the latest Miocene (5.46 Ma). There are at least two primary factors controlling the contourite features, based on the seismic analysis, as follows: i) tectonics, which has governed the relocation of the main Mediterranean flow pathways and their circulation patterns; and ii) climate, which has influenced both water mass conditions (interfaces) and hinterland sediment sources, conditioning the morpho-seismic expression and growth pattern of the drifts and terrace formation (dimensions). The distribution of contourite features through time and space has allowed us to propose the three following main scenarios for ocean circulation since the opening of the Strait of Gibraltar: Atlantic Zanclean flooding; the Pliocene sea, with two different stages for the dense circulation; and the Quaternary sea, with well-defined and stable interfaces for the Atlantic Waters (AW), light and dense Mediterranean waters.
Keywords: Contourites, Alboran Sea, Pliocene and Quaternary, stratigraphy, palaeoceanography
7.74 Mb
Neves M.C., Roque C., Luttrell K.M., Vázquez J.T., Alonso B. (2016)
Geo-Marine Letters, 36, 6, 415 -424. DOI: 10.1007/s00367-016-0459-1. (BibTeX: neves.etal.2016b)
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Earthquakes and submarine landslides are recurrent and widespread manifestations of fault activity offshore SW Iberia. The present work tests the effects of sea-level rise on offshore fault systems using Coulomb stress change calculations across the Alentejo margin. Large-scale faults capable of generating large earthquakes and tsunamis in the region, especially NE–SW trending thrusts and WNW–ESE trending dextral strike-slip faults imaged at basement depths, are either blocked or unaffected by flexural effects related to sea-level changes. Large-magnitude earthquakes occurring along these structures may, therefore, be less frequent during periods of sea-level rise. In contrast, sea-level rise promotes shallow fault ruptures within the sedimentary sequence along the continental slope and upper rise within distances of <100 km from the coast. The results suggest that the occurrence of continental slope failures may either increase (if triggered by shallow fault ruptures) or decrease (if triggered by deep fault ruptures) as a result of sea-level rise. Moreover, observations of slope failures affecting the area of the Sines contourite drift highlight the role of sediment properties as preconditioning factors in this region.
6.46 Mb
Ribó M., Puig P., Urgeles R., Van Rooij D., Muñoz A. (2016)
Marine Geology, 378, 276-291. DOI: 10.1016/j.margeo.2015.11.011. (BibTeX: ribo.etal.2016b)
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Several fields of large-scale sediment waves have been observed along the Gulf of Valencia continental margin (NW Mediterranean). The largest sediment waves develop on the continental slope, extending from 250 to 850 m water depth, with wavelengths ranging between 500 m and 1000 m and wave heights from ~ 2 m to ~ 50 m. On the lower part of the slope, sediment waves are quasi-stationary “vertically accreting”, becoming up-slope migrating towards the mid- and upper part of the slope. A second group of sediment waves have developed over the outer continental shelf, with wavelengths of 400 to 800 m and heights of 2 to 4 m, also displaying an up-slope migrating pattern. Multi-channel seismic lines crossing the continental margin show that the sediment waves over the continental slope region have been continuously developed on the foreset region of the prograding margin clinoform. Several units of sediment waves have been identified in the sedimentary record, evolving in accordance with the margin progradation. Detailed analysis of single-channel (sparker) seismic profiles revealed the presence of several sediment depositional subunits over the outer continental shelf, some of them with successive development of sediment waves being truncated by erosive surfaces, likely related to Quaternary eustatic sea-level oscillations. These erosional surfaces can be followed downslope into paraconformable strata of the sediment waves on the continental slope, where constant bedform growth is observed, without being affected by sea level changes. Based on geophysical data, the thickness of the sediment waves mapped units show that the largest sediment waves (in wave ratio, length and height) develop where sediment deposition rates are the highest, coinciding with the upper part of the continental slope (foreset clinoforms), confined by the presence of structural highs. The development of these sediment waves has been previously explained by the interaction of internal waves over the continental slope. Because sediment waves are preserved in the sedimentary record since the Lower/Pliocene, internal waves activity could have been present in this part of the margin shortly after the Zanclean reflooding of the Mediterranean Basin, following the Messinian desiccation event ~ 5.6 My ago. Deep water hydrodynamic conditions were re-established at that time, modulating sediment transport and deposition over the continental slope and outer continental shelf.
Keywords: Sediment waves; Plio-Quaternary sedimentary record; Internal waves; Gulf of Valencia continental margin; NW Mediterranean
3.14 Mb
Solé J., Emelianov M., Ostrovskii A., Puig P., García-Ladona E. (2016)
Scientia Marina, 80S1, 195-204. DOI: (BibTeX: sole.etal.2016c)
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In this work we report short-term measurements of the thermohaline structure and velocity field inside a narrow submarine canyon by means of a yo-yo–like profiler. An Aqualog profiler was deployed inside the Besòs Canyon in the northwestern Mediterranean continental margin, providing a unique data set on the vertical evolution of water column characteristics with unprecedented fine-scale spatial and temporal resolution. The observations reported here show a very dynamic transient short-term response with a complex vertical structure not observed previously in any submarine canyon of this region. The vertical distribution of water masses was characteristic of the western Mediterranean basin with Atlantic waters (AW) at the surface, Western Intermediate waters (WIW) in the middle and Levantine Intermediate (LIW) waters below. Turner angle and empirical orthogonal functions show that double-diffusive and isopycnal mixing are the main dominant processes at small scales. The interfaces of the three layers exhibit highly vertical excursions in relatively short times. At the surface, deepening of AW was observed, associated with flow intensification events. Deeper in the water column, within the submarine canyon confinement, the WIW-LIW interface uplifts about 100-150 m. These motions are associated with relatively up- and down-canyon–enhanced current events (up to 15-20 cm s–1 at 500 and 800 m depths) along the canyon axis. The time scales of the vertical variability were concentrated in a broad band around the semi-diurnal and local inertial frequencies within the WIW and LIW layers.
Keywords: fine-scale variability; submarine canyon; yo-yo like profiler; thermohaline structure; AW; WIW; LIW.