Els filtres actuals son: Any inici = 2019, Any final = 2020
1.81 Mb
Garcia-Castellanos D., Micallef A., Estrada F., Camerlenghi A., Ercilla G., Periáñez R., Abril J.M. (2020)
Earth-science reviews, 201, 103061. DOI: 10.1016/j.earscirev.2019.103061. (BibTeX: garciacastellanos.etal.2020a)
Resum: Veure
About six million years ago, the Mediterranean Sea underwent a period of isolation from the ocean and widespread salt deposition known as the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km3 of Miocene sediment and bedrock. Based on the understanding obtained from Pleistocene onshore megaflooding events and using ad-hoc hydrodynamic modeling, here we explore two predictions of the Zanclean outburst flood hypothesis: 1) The formation of similar erosion features at sills communicating sub-basins within the Mediterranean Sea, specifically at the Sicily Sill; and 2) the accumulation of the eroded materials as megaflood deposits in areas of low flow energy. Recent data show a 6-km-wide amphitheater-shaped canyon preserved at the Malta Escarpment that may represent the erosional expression of the Zanclean flood after filling the western Mediterranean and spilling into the Eastern Basin. Next to that canyon, a ~1600 km3 accumulation of chaotic, seismically transparent sediment has been found in the Ionian Sea, compatible in age and facies with megaflood deposits. Another candidate megaflood deposit has been identified in the Alborán Sea in the form of elongated sedimentary bodies that parallel the flooding channel and are seismically characterized by chaotic and discontinuous stratified reflections, that we interpret as equivalent to gravel and boulder megabars described in terrestrial megaflood settings. Numerical model predictions show that sand deposits found at the Miocene/Pliocene (M/P) boundary in ODP sites 974 and 975 (South Balearic and Tyrrhenian seas) are consistent with suspension transport from the Strait of Gibraltar during a flooding event at a peak water discharge of ~108 m3 s−1.
3.49 Mb
Juan C., Ercilla G., Estrada F., Alonso B., Casas D., Vázquez J.T., d'Acremont E., Medialdea T., Hernández-Molina F.J., Gorini C., El Moumni B., Valencia J. (2020)
Marine Geology, 423, 106138. DOI: 10.1016/j.margeo.2020.106138. (BibTeX: juan.etal.2020b)
Resum: Veure
A new basin-scale comprehensive view of contourite features, turbidite systems, and mass-wasting deposits comprising the Spanish and Moroccan margins and basins of the Alboran Sea has been achieved after a new detailed seismic stratigraphic analysis and the construction of sedimentary maps for the Pliocene and Quaternary sedimentary units. Multiple contourite systems were defined in this sea: i) the Intermediate Mediterranean contourite system (IMCS), formed under the action of the LMW on the Spanish continental margin; ii) the Deep Mediterranean contourite system (DMCS), formed under the action of the DMW and made up of contourites mostly found on the Moroccan margin and annex sub-basins; and iii) the Atlantic contourite system (ACS), shaped by the AW and its interfaces with the LMW and DMW on the uppermost continental slopes of both margins. The contourite features (drifts, moats, channels and terraces) coexist during the various stages of the Plio-Quaternary with turbidite systems showing different onsets and cessations in activity, and with mass-wasting deposits. In this work, the temporal and spatial distributions of contourite and turbidite systems can be considered as proxies to deduct the long-term impacts of bottom-current circulations and related processes, and ultimately allowed to decipher past bottom-current dynamics and the multiple factors controlling Plio-Quaternary sedimentation in the Alboran Sea.
Paraules clau: Alboran Sea; Pliocene; Quaternary; Sedimentary systems; Palaeoceanography
880 Kb
Michaud F., Dañobeitia J., Bartolomé R., Carbonell R., Delgado Argote L., Cordoba D., Monfret T. (2020)
Geo-Marine Letters, 20, 3, 168-173. DOI: 10.1007/s003670000050. (BibTeX: michaud.etal.2020a)
Resum: Veure
New data collected between the northernmost tip of the East Pacific rise (18°05′N, 105°35′W) and the Middle America trench provide evidence that the seafloor, which lacks significant sedimentary cover, has a typical spreading-derived abyssal hill topography. The tectonic fabric of this seafloor is concave to the west, as it is today at the tip of the East Pacific rise. Farther to the east, at the outer wall of the trench, the seafloor topography exhibits a north-south trending fabric. We suggest that this fabric originated along the East Pacific rise, as it reached the trench and possibly subducted beneath the North America plate prior to the development of the complex connection of the East Pacific rise with the Rivera transform.
2.62 Mb
Palanques A., Guillén J., Puiga P., (2020)
Journal of Environmental Management, 260, 110028. DOI: 10.1016/j.jenvman.2019.110028. (BibTeX: palanques.etal.2020a)
Resum: Veure
Polluted sediments retained in water reservoirs are potential sources of deleterious materials downstream, especially during floods or flushing flows (FFs). Their interaction with these events is important for determining potential risks and evaluating management actions. In the Ebro River, the Flix Reservoir accumulated a deposit of more than 3 × 105 t of industrial waste with high Hg concentrations. Because suspended particulate matter (SPM) is the main driver of Hg pollution downriver, this study analyses the transport of particulate matter and Hg pollution from the Flix Reservoir to the Ebro Estuary during FFs. Time series of currents, turbidity and downward particulate matter fluxes were obtained by current meters, turbidimeters and sediment traps assembled in benthic tripods. They were deployed in the reservoir and at two locations in the estuary during two recording periods that each captured a flushing flow (FF) event. In addition, SPM samples were collected during the study period at several locations along the river course, from upstream of the Flix Reservoir down to the river mouth, to measure the suspended particulate matter and associated Hg mobilized downstream. A continuous background level of Hg pollution was observed during the deployment periods, but the Hg and particulate matter fluxes increased by between one and two orders of magnitude during FFs. Though the two events reached similar water discharges, the first FF was after the wet season and generated lower particulate matter concentrations and fluxes, but higher Hg contents than the second, which occurred after the dry season. The higher available particulate matter in the second event diluted the polluted Hg particle load more than the first event. Thus, similar FFs may result in different Hg concentration and sediment transport episodes, largely depending on the previous hydrological regime and the river sediment availability. These findings should be considered for FF management.
Paraules clau: Flushing flow; Mercury transport; Particulate matter; Polluted reservoir; Salt wedge estuary; Ebro river
19.33 Mb
Poort J., Lucazeau F., Le Gala V., Dal Cin M., Leroux E., Bouzi A., Rabineau M., Palomino D., Battani A., Akhmanov G.G., Ferrante G.M., , Si Bachir R., Koptevr A., , Bellucci M., Pellen R., Camerlenghi A., Migeon S., Alonso B., Ercilla G., Yelles-Chaouche A.K., Khlystov O.M. (2020)
Marine Geology, 419, 106064. DOI: 10.1016/j.margeo.2019.106064. (BibTeX: poort.etal.2020b)
Resum: Veure
The Western Mediterranean basin has been formed by Miocene back-arc extension and is underlain by a thin and young lithosphere. This young lithosphere is warm, as testified by an overall elevated offshore heat flow. Heat flow within the Western Mediterranean is, however, highly variable and existing data are unevenly distributed and poorly studied in the central part of the Liguro-Provençal and Algero-Balearic basins. This central part is floored by a young oceanic crust, bordered by different continental margins, cut by transform faults, and filled by up to 8 km of sediments. We present a total of 148 new heat flow data collected during the MedSalt and WestMedFlux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin-scale, but also locally on the margins. A new heat flow map for the Western Mediterranean outlines the following regional features: (1) a higher average heat flow in the Algero-Balearic basin compared to the Liguro-Provençal basin (94 ± 13 mW/m2 and 78 ± 16 mW/m2, respectively), and (2) a regional thermal asymmetry in both basins, but with opposed heat flow trends. Up to 20% of this heat flow difference can be explained by sediment blanketing, but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint. Estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger West Algerian basin (16–23 Ma) compared to the East Algerian basin and the West Sardinia oceanic floor (31–37 Ma). On the margins and ocean-continent transitions of the Western Mediterranean the new heat flow data point out the existence of two types of local anomalies (length scale 5–30 km): (1) locally increased heat flow up to 153 mW/m2 on the Gulf of Lion margin results from thermal refraction of large salt diapirs, and (2) the co-existing of both low (<50 mW/m2) and high (>110 mW/m2) heat flow areas on the South Balearic margin suggests a heat redistribution system. We suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread Plio-Pleistocene volcanism on the South Balearic margin.
Paraules clau: Heat flow; Western Mediterranean Sea; Liguro-Provençal basin; Algero-Balearic basin; Continental margins; Oceanic crust
17.46 Mb
Silva P.F., Roque C., Drago T., Belén A., Henry B., Gemma E., .Lopes A, López-González N., Casas D., Naughtond F., Vázquez J.T. (2020)
Marine Geology, 420, 106086. DOI: 10.1016/j.margeo.2019.106086. (BibTeX: silva.etal.2020)
Resum: Veure
We present a multidisciplinary study of the seismic stratigraphy, sedimentology, geochemistry and magnetism to characterize the Quaternary mass movement deposits (MMD) and the associated deformation in the Portimão Bank (Gulf of Cadiz, offshore SW Iberia). Two scales of approach have been applied. At large-scale (m to km) approach, were recognized and characterized a series of important and subsequent slide scars (tens of meters high) and MMD (the larger one with 10 km length) related to landslides, more prominent at Portimão Bank\'s southern flank. At small-scale (cm) approach, we point out on a piston core collected within a scar affected by MMD, a replication of the sedimentary column as evidenced by geochronological results and corroborated by sedimentology, geochemistry and magnetic data. Magnetic fabric data enabled the identification and characterization of the internal structure and deformation of MMD along the sedimentary column. For last, geochronology and the morphology of Portimão seamount are discussed in order to constraint the factors controlling MMD triggering. The multidisciplinary approach is useful in a better characterization of the MMD at different scales and improved the understanding of its dynamics.
Paraules clau: Mass movement deposits; Bathymetric and seismic profiles; Piston core analyses; Magnetic fabric; Deformed sediments
526 Kb
Villaseñor A., Herrmann R.B., Gaite B., Ugalde A. (2020)
Solid Earth, 11, 63-74. DOI: 10.5194/se-11-63-2020. (BibTeX: villasenor.etal.2020a)
Resum: Veure
During September–October of 2013 an intense swarm of earthquakes occurred off the east coast of Spain associated with the injection of the base gas in an offshore underground gas storage. Two weeks after the end of the injection operations, three moderate-sized earthquakes (Mw 4.0–4.1) occurred near the storage. These events were widely felt by the nearby population, leading to the indefinite shut-down of the facility. Here we investigate the source parameters (focal depth and mechanism) of the largest earthquakes in the sequence in order to identify the faults reactivated by the gas injection and to help understand the processes that caused the earthquakes. Our waveform modeling results indicate that the largest earthquakes occurred at depths of 6–8 km beneath the sea floor, significantly deeper than the injection depth (∼1800 m). Although we cannot undoubtedly discriminate the fault plane from the two nodal planes of the mechanisms, most evidence seems to favor a NW–SE-striking fault plane. We propose that the gas injection reactivated faults in the Paleozoic basement, with regional orientation possibly inherited from the opening of the Valencia Trough
2.67 Mb
Yenes M., Monterrubio S., Nespereira J., Casas D. (2020)
Engineering Geology, 264, 105375. DOI: 10.1016/j.enggeo.2019.105375. (BibTeX: yenes.etal.2020)
Resum: Veure
In recent years, apparent overconsolidation (AOC) has been observed in the most superficial sections of the sedimentary column of the seabed. AOC has been detected in sediment samples taken from deep and shallow waters, independent of the source area. Although the origin of this phenomenon remains controversial, it seems to be linked principally to physical-chemical bonds and ionic changes that cause strong attractions between particles. This work uses an experimental approach based on standardized oedometer tests to study the presence of AOC in surface sediments and its disappearance at depth. The results obtained show that the existence of AOC is related to the formation of a structured sediment generated by both secondary consolidation and aging processes. In addition, the results obtained facilitate a discussion of how AOC influences the potential development of plane translational slides. The development of this type of instability in areas affected by AOC generates a subsequent stabilization of the ocean floor and, consequently, a lower recurrence of large landslides in these areas than would be expected from a sedimentary process with no AOC.
Paraules clau: Apparent overconsolidation; Submarine sediment; Sub-bottom; Submarine landslide
8.23 Mb
Zitellini N., Ranero C.R., F. Loreto M., Ligi M., Pastore M., D’Oriano F., Sallares V., Grevemeyer I., Moeller S., Prada M. (2020)
Geology, 48, 2, 123-127. DOI: 10.1130/G46774.1. (BibTeX: zitellini.etal.2020a)
Resum: Veure
The Tyrrhenian Basin is a region created by Neogene extensional tectonics related to slab rollback of the east-southeast–migrating Apennine subduction system, commonly believed to be actively underthrusting the Calabrian arc. A compilation of >12,000 km of multichannel seismic profiles, much of them recently collected or reprocessed, provided closer scrutiny and the mapping of previously undetected large compressive structures along the Tyrrhenian margin. This new finding suggests that Tyrrhenian Basin extension recently ceased. The ongoing compressional reorganization of the basin indicates a change of the regional stress field in the area, confirming that slab rollback is no longer a driving mechanism for regional kinematics, now dominated by the Africa-Eurasia lithospheric collision
1.94 Mb
Ercilla G., Juana C., Periáñez R., Alonso B., Abril J.M., Estrada F., Casas D., Vázquez J.T., d’Acremont E., Gorini C., El Moumni B., Do Couto D., Valencia J. (2019)
Deep-Sea Research. Part I: Oceanographic Research Papers, 144, 1-16. DOI: 10.1016/j.dsr.2018.12.002. (BibTeX: ercilla.etal.2019a)
Resum: Veure
This is an interdisciplinary study that combines morphoseismics, sedimentology and numerical modelling to elucidate at different scales of resolution the influence of alongslope processes on the turbidite systems (TSs) and canyons in the Alboran Sea (southwestern Mediterranean). Nine TSs are mapped in the Spanish margin (La Linea, Guadiaro, Baños, Torrenueva, Fuengirola, Salobreña, Sacratif, Calahonda and Almeria) and two in the Alboran Ridge (Piedra Escuela and Al-Borani). In the Moroccan margin, there are only two canyons (Ceuta and Nekor). Distinctive morphoseismic and sedimentological signatures from TSs and canyons have enabled three regional models of alongslope influence to be distinguished: a) Alongslope processes are dominant. This scenario characterizes the canyons of the Moroccan margin. The diagnostic signature is the lack of leveed channels and lobes at the Ceuta and Nekor Canyon mouths. b) Different degrees of interplay exist between alongslope and downslope processes. This scenario occurs in the TSs of the western Spanish margin. Here, the alongslope influence on TSs (La Linea, Guadiaro, Baños, Torrenueva and Fuengirola) is evidenced by the lack of overbank deposits in the La Linea and Guadiaro Canyons and an alongslope trend in the morpho-architecture of the channelized lobes and in the textural distribution of canyon/channel deposits (mass-flow deposits and turbidites). Both signatures indicate sandier TSs as well as Bouma turbidite sequences lacking the finest levels towards the Strait of Gibraltar. Local intercalations of contourites are also present in the Guadiaro lobe deposits. c) Downslope processes are dominant. This scenario characterizes the TSs of the eastern and central Spanish margin and Alboran Ridge. There, TSs seem to be controlled solely by the characteristics of the downslope gravity flows that transport sediment. The hydrodynamic and sediment dispersion models confirm that the main oceanographic factors governing the variable alongslope influence in TSs and canyons are the following: a vigorous WMDW flow along the Moroccan margin and the energetic Atlantic Jet, western Atlantic anticyclonic gyre and general acceleration of the Mediterranean waters towards the Strait of Gibraltar, along the western Spanish margin. This study demonstrates the pivotal role that alongslope processes can play in the onset and formation of TSs and canyons at continental margins.
Paraules clau: Turbidite system; Morphoseismic; Sediments; Alongslope processes; Downslope processes; Alboran Sea
16.81 Mb
Ercilla G., Schwenk T., Bozzano G., Spiess V., Violante R., Estrada F., Ianniccheri F., Spoltore D.V., Alonso B. (2019)
Marine Geology, 417, 106028. DOI: 10.1016/j.margeo.2019.106028. (BibTeX: ercilla.etal.2019c)
Resum: Veure
New insights into the Cenozoic depositional architecture based on the seismic stratigraphy of the northern Argentine continental slope, off Bahia Blanca, allow us to reconstruct its sedimentary evolution. Five major seismic boundaries, B1 to B5 (from oldest to youngest) represent the main discontinuities bounding six seismic units: I (Eocene), II (Oligocene to early Miocene), III (middle Miocene), IV (late Miocene), V (Pliocene), and VI (Quaternary). These units comprise deposits and features (mass-flow deposits, (hemi)pelagites and/or low-density turbidites, contourite drifts and moats, sediment waves, and canyon deposits), of which, through time, the contourites are ubiquitous. The depositional stratigraphic architecture reflects the expansion and relocation of the contourites, which are used to divide the sedimentation history into three major periods: Eocene to Early Miocene; Middle Miocene; and Late Miocene to Recent. Each period is interpreted as having occurred in response to palaeoceanographic changes in the Southern Component Deep Water (SCDW). These changes were regulated by palaeogeodynamic variations, regionally related to the Andean orogeny and remotely related to the opening stages of the Drake Passage and Central American Seaway, as well as the consequent increases in deep-water flux to the southern Atlantic. Additionally, we also consider their interplay with local and global sea-level changes. These three main periods reveal changes in the alongslope dynamics of the SCDW on the Argentine continental slope.
Paraules clau: Seismic stratigraphy; Contourites; Cenozoic sedimentary history; Argentine continental margin; Ewing Terrace
633 Kb
Evans R.L., Benoit M.H., Long M.D., Elsenbeck J., Ford H.A., Zhu J., Garcia X. (2019)
Earth and Planetary Science Letters, 519, 308-316. DOI: 10.1016/j.epsl.2019.04.046. (BibTeX: evans.etal.2019b)
Resum: Veure
A joint analysis of magnetotelluric and Sp receiver function data, collected along a profile across the central Appalachians, highlights variations in regional lithospheric structure. While the interpretation of each data set by itself is non-unique, we identify three distinct features that are consistent with both the resistivity model and the receiver function image: 1) thin lithosphere beneath the Appalachian Mountains, 2) somewhat thicker lithosphere to the east of the mountains beneath the Coastal Plain, and 3) a lithosphere-asthenosphere boundary that deepens to the west of the mountains. In some regions, the correspondence between seismic velocity discontinuities and resistivity mark the base of the lithosphere, while in other locations we see seismic discontinuities that are contained within the lithosphere. At the western end of our profile a transition from highly resistive lithosphere to more conductive mantle represents the transition across the Grenville front. The thickness of lithosphere beneath the Grenville terrain is ∼140 km. Lithosphere at the eastern end of the profile has a thickness that is not well constrained by our coverage, but is at least 110 km thick. This lithosphere can be associated with a broader region of high resistivity material seen to extend further south. Directly beneath the Appalachian Mountains, lithospheric thickness is inferred to be as thin as ∼80 km, based on observations of elevated mantle conductivities and a westward-dipping seismic converter. Electrical conductivities in the uppermost asthenospheric mantle are sufficiently high (>0.1 S/m) to require the presence of a small volume of partial melt. The location of these elevated conductivities is close (offset ∼50 km to the west) to Eocene volcanic outcrops in and around Harrisonburg, VA. Our observations speak to mechanisms of intraplate volcanism where there is no divergent or convergent plate motion to trigger mantle upwelling or obvious fluid release, either of which can facilitate melting. Instead, we suggest that small scale mantle convection related either to pre-existing lithospheric thickness variations, or to lithospheric loss through delamination, coupled with relative plate motion with respect to the underlying asthenosphere, can trigger small amounts of melting. This melt migrates upslope, along the base of the lithosphere, potentially thermally eroding the lithosphere resulting in further thinning
Paraules clau: Magnetotellurics; Seismic; Receiver function; Lithosphere
1.83 Mb
Garcia X., Julià J., Nemocón A.M., Neukirch M. (2019)
Gondwana Research, 68, 174-184. DOI: 10.1016/ (BibTeX: garcia.etal.2019b)
Resum: Veure
The lithospheric architecture of the western Borborema Province and northern São Francisco craton of NE Brazil has been investigated through analysis of long-period magnetotelluric data acquired along a 700 km long survey, using 12 instruments. The survey samples several tectonic terrains in the Province and penetrates into the adjacent São Francisco craton after crossing the Araripe Basin, an aborted rift basin filled with Mesozoic sediments that peak at ∼1000 m above mean sea level. High conductivities are observed at shallow depths under the main Precambrian shear zones that pervade the Province – consistent with tectonic reactivation – and as a small patch embedded within the high resistivities that characterize the São Francisco craton. High conductivities (∼25 Ωm) are also observed below 120 km depth between the Patos and Pernambuco lineaments – right under the Araripe Basin – flanked by resistive (>120 Ωm) material immediately to the north and south. This deep, highly conductive body is found consistent with the presence of melt and aqueous fluids, and is interpreted as shallow asthenospheric mantle bounded by thicker lithosphere. We propose that extensional stresses in the Mesozoic stretched and thinned the lithosphere under the Araripe Basin, causing passive upwelling of asthenospheric material and lateral flow of the overlying lithosphere, and resulting in thickening of the lithosphere under the flanks and uplift of the Araripe Basin. We also hypothesize that thermal weakening of the lithospheric mantle – perhaps sustained by channeling of asthenospheric flows under the basin – would have caused regional stresses to concentrate in the brittle upper crust and contribute to basin inversion. We thus propose that a combination of localized horizontal stresses and vertical buoyancy from underlying asthenospheric material are ultimately responsible for the actual topography of the Araripe Basin.
Paraules clau: Araripe Basin; Borborema Province; Magnetotellurics; Conductivity; Lithosphere; Asthenosphere; Basin inversion; Partial melt
1.98 Mb
Gràcia E., Grevemeyer I., Bartolomé R., Perea H., Martínez-Loriente S., Gómez de la Peña L., Villaseñor A., Klinger Y., Lo Iacono C., Diez S., Calahorrano A.e, Camafort M., Costa S., d’Acremont E., Rabaute A., Ranero C.R. (2019)
Nature Communications, 10, 3482. DOI: 10.1038/s41467-019-11064-5. (BibTeX: gracia.etal.2019a)
Resum: Veure
Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are associated with prominent topographic features and can produce large earthquakes. Here we show the first evidence of a major tectonic structure in its initial-stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Combining bathymetric and seismic reflection data, together with seismological analyses of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event ever recorded in the area – we unveil a 3D geometry for the AIFS. We report evidence of left-lateral strike-slip displacement, characterise the fault segmentation and demonstrate that AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model of the inception and growth of a young plate boundary fault system.
15.63 Mb
Gras C., Dagnino D., Jiménez-Tejero C.E., Meléndez A., Sallarès V., Ranero C.R. (2019)
Solid Earth, 10, 6, 1833-1855. DOI: 10.5194/se-10-1833-2019. (BibTeX: gras.etal.2019a)
Resum: Veure
We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.
18.84 Mb
Isla E., Gerdes D. (2019)
Progress in Oceanography, 178, 102180. DOI: 10.1016/j.pocean.2019.102180. (BibTeX: isla.gerdes.2019a)
Resum: Veure
Global warming is heating the Antarctic circumpolar deep water (CDW), which comes into direct contact with the diverse and abundant macrobenthic communities thriving on the continental shelf of the Weddell Sea (WS). A set of 16 current meters deployed along more than 3000 km coastline revealed that tidal currents drive CDW intrusions onto the WS continental shelf and they can increase the temperature near the seabed by ~2.7 °C. The ongoing ocean warming trend may expose macrobenthic assemblages to ambient temperatures >2 °C by the end of the century with dramatic consequences for communities which have evolved during millions of years in near geophysical isolation under rather constant environmental conditions with temperatures <0 °C. These stenothermal communities have long generation times (therefore, reduced opportunity to mutate) and require hundreds of years for adaptation. Results from 135 benthic stations along the study area showed that macrobenthic communities in the southeastern section of the WS are the most vulnerable to the increase of temperature near the seabed given their high component of sessile organisms. Besides a dramatic marine biodiversity loss, the eventual demise of these communities, which provide habitat structure for a large number of species that can build up >87 g C m−2, will cause the liberation of thousands of tons of carbon to the environment. Macrobenthic communities colonizing the recently opened shelf in the Larsen A and B bays may not have the chance to reach the type of mature assemblage inhabiting the eastern WS shelf. The highest temperatures derived from CDW intrusions were recorded in the Filchner-Ronne region, suggesting that the consequences of the thermal impact could develop faster here than in the rest of the WS. Thus, these macrobenthic communities may show the effects of warming earlier than those thriving in other regions of the WS shelf. Global warming seriously threats the abundant and highly diverse macrobenthic communities of the Antarctic continental shelf
Paraules clau: Continental shelf; Antarctica; Global warming; Tides; Climate change; Benthic ecosystem; Weddell Sea
3.10 Mb
Liu S., Van Rooij D., Vandorpe T., González-Pola C., Ercilla G., Hernández-Molina F.J. (2019)
Deep-Sea Research. Part I: Oceanographic Research Papers, 149, 103054. DOI: 10.1016/j.dsr.2019.05.014. (BibTeX: liu.etal.2019a)
Resum: Veure
The present-day morphology of the Le Danois Bank region has been investigated based on bathymetric and high to ultra-high resolution seismic reflection data. The involved bottom-current processes are associated with the Eastern North Atlantic Central Water, the Atlantic Mediterranean Water and the Labrador Sea Water. Sediments originating from various canyon systems along the Cantabrian Margin and the Asturias continental shelf are transported by downslope and alongslope processes towards the Le Danois intraslope basin. The background flow velocities of bottom currents are all below the threshold (8–10 cm/s) of generating plastered and mounded geometries of contourite drifts. However, bottom currents are locally accelerated (up to 25 cm/s) due to the presence of the Le Danois Bank and the Vizco High, creating a furrow and three moats and generating six plastered drifts, three elongated mounded and separated drifts at different depth intervals. The extension and distribution of the drifts are controlled by slope morphology and/or bottom current velocities. Unlike contourite drifts along other continental slopes, a single contourite drift (the Gijón Drift) with a lateral variation in drift geometry and internal structure indicates the interaction of bottom currents with different flow dynamics. Additionally, scouring of active bottom currents and rapid sedimentation rate of contourite drifts may be at the origin of slope instability events. Besides contourite drifts, internal waves may have induced the formation of sediment waves. In the Le Danois intraslope basin, multiple sedimentary processes work together and shape the present-day seafloor. Bottom currents are focused due to deflection on complex topographical obstacles within a relatively small basin setting, and create a wide variety of sedimentary features, including contourite drifts. The resulting sedimentary features thus have more frequent lateral variations, a feature typical for topographically constrained small basins.
Paraules clau: Bottom currents; Contourites; Southern Bay of Biscay; Small basin
4.88 Mb
López-González N., Alonso B., Juan C., Ercilla G., Bozzano G., Cacho I., , Palomino D., Vázquez J.-T., Estrada F., Bárcenas P., d’Acremont E., Gorini C., El Moumni B. (2019)
Geosciences, 9, 8, 345. DOI: 10.3390/geosciences9080345. (BibTeX: lopezgonzalez.etal.2019a)
Resum: Veure
The Djibouti Ville Drift is part of a contourite depositional system located on the southern side of the Djibouti Ville Seamount in the Alboran Sea (Western Mediterranean). The sedimentary record of a core located in the drift deposits has been characterized to achieve the possible sediment sources for the Saharan dust supply and the paleocurrent variability related to Mediterranean intermediate waters for the last 133 kyr. Three end-member grain-size distributions characterize the sediment record transported by the bottom current to address the different aeolian populations, i.e., coarse EM1, silty EM2, and fine EM3. For these particles, the most likely source areas are the Saharan sedimentary basins and deserts, as well as the cratonic basins of the Sahara-Sahel Dust Corridor. The prevalence of these main source areas is shown in the core record, where a noticeable change occurs during the MIS 5 to MIS 4 transition. Some punctual sediment inputs from the seamount have been recognized during sea-level lowstand, but there is no evidence of fluvial supply in the drift deposits. The paleocurrent reconstruction allows the characterizing of the stadial and cold periods by large increases in the mean sortable silt fraction and UP10, which point to an enhanced bottom current strength related to intermediate water masses. Conversely, interglacial periods are characterized by weaker bottom current activity, which is associated with denser deep water masses. These proxies also recorded the intensified Saharan wind transport that occurred during interstadial/stadial transitions. All these results point to the importance of combining sediment source areas with major climatic oscillations and paleocurrent variability in palaeoceanographic sedimentary archives, which may help to develop future climate prediction models.
Paraules clau: Contourite drift ;Aeolian sediment sources; Paleocurrent proxies; Mediterranean intermediate water masses; Djibouti ville seamount; Alboran sea
2.32 Mb
Maldonado M., López-Acosta M., Sitjà C., , Galobart C., Ercilla G., Leynaert A. (2019)
Nature Geoscience, 12, 815-822. DOI: 10.1038/s41561-019-0430-7. (BibTeX: maldonado.etal.2019b)
Resum: Veure
Silicon (Si) is a pivotal element in the biogeochemical and ecological functioning of the ocean. The marine Si cycle is thought to be in internal equilibrium, but the recent discovery of Si entries through groundwater and glacial melting have increased the known Si inputs relative to the outputs in the global oceans. Known outputs are due to the burying of diatom skeletons or their conversion into authigenic clay by reverse weathering. Here we show that non-phototrophic organisms, such as sponges and radiolarians, also facilitate significant Si burial through their siliceous skeletons. Microscopic examination and digestion of sediments revealed that most burial occurs through sponge skeletons, which, being unusually resistant to dissolution, had passed unnoticed in the biogeochemical inventories of sediments. The preservation of sponge spicules in sediments was 45.2 ± 27.4%, but only 6.8 ± 10.1% for radiolarian testa and 8% for diatom frustules. Sponges lead to a global burial flux of 1.71 ± 1.61 TmolSi yr−1 and only 0.09 ± 0.05 TmolSi yr−1 occurs through radiolarians. Collectively, these two non-phototrophically produced silicas increase the Si output of the ocean to 12.8 TmolSi yr−1, which accounts for a previously ignored sink that is necessary to adequately assess the global balance of the marine Si cycle.
1.30 Mb
Martínez‐Loriente S., Sallarès V., Ranero C.R., Ruh J.B., Barckhausen U., Grevemeyer I., Bangs N. (2019)
Tectonics, 38, 12, 4360-4377. DOI: 10.1029/2019TC005586. (BibTeX: martinezloriente.etal.2019a)
Resum: Veure
We present a 2‐D P wave velocity model and a coincident multichannel seismic reflection profile characterizing the structure of the southern Costa Rica margin and incoming Cocos Ridge. The seismic profiles image the ocean and overriding plates from the trench across the entire offshore margin, including the structures involved in the 2002 Osa earthquake. The overriding plate consists of three domains: Domain I displays thin‐skinned deformation of an imbricate thrust system composed of fractured rocks. Domain II shows ~15‐km‐long landward dipping reflection packages and active deformation of the shelf sediment. Domain III is little fractured and appears to be dominated by elastic deformation, overlain by ~2‐km‐thick landward dipping strata. The velocity structure supports the argument that the bulk of the margin is highly consolidated rock. Thick‐skinned tectonics probably causes the uplift of Domains II and III. The oceanic plate shows crustal thickness variations from ~14 km at the trench (Cocos Ridge) to 6–7 km beneath the shelf. We combine (1) interplate geometry and fracturing degree, (2) tectonic stresses and brittle strain, and (3) earthquake locations, to investigate relationships between structure and earthquake generation. The 2002 Osa sequence nucleated at the leading flank of subducting seamounts in the area of highest tectonic overpressure. Both estimated rock fracturing and modeled brittle strain steadily increase from the leading flank of the subducting seamounts to their top, reflecting the progressive damage caused by the seamount. Therefore, the seismicity and structural‐mechanical evolution of the upper plate reflect the downward propagation of the leading edge of seamounts.
9.06 Mb
Meléndez A., Jiménez C.E., Sallarès V., Ranero C.R. (2019)
Solid Earth, 10, 6, 1857-1876. DOI: 10.5194/se-10-1857-2019. (BibTeX: melendez.etal.2019a)
Resum: Veure
We present the implementation of Thomsen\'s weak anisotropy approximation for vertical transverse isotropy (VTI) media within TOMO3D, our code for 2-D and 3-D joint refraction and reflection travel-time tomographic inversion. In addition to the inversion of seismic P-wave velocity and reflector depth, the code can now retrieve models of Thomsen\'s parameters (δ and ε). Here, we test this new implementation following four different strategies on a canonical synthetic experiment in ideal conditions with the purpose of estimating the maximum capabilities and potential weak points of our modeling tool and strategies. First, we study the sensitivity of travel times to the presence of a 25 % anomaly in each of the parameters. Next, we invert for two combinations of parameters (v, δ, ε and v, δ, v⊥), following two inversion strategies, simultaneous and sequential, and compare the results to study their performance and discuss their advantages and disadvantages. Simultaneous inversion is the preferred strategy and the parameter combination (v, δ, ε) produces the best overall results. The only advantage of the parameter combination (v, δ, v⊥) is a better recovery of the magnitude of v. In each case, we derive the fourth parameter from the equation relating ε, v⊥ and v. Recovery of v, ε and v⊥ is satisfactory, whereas δ proves to be impossible to recover even in the most favorable scenario. However, this does not hinder the recovery of the other parameters, and we show that it is still possible to obtain a rough approximation of the δ distribution in the medium by sampling a reasonable range of homogeneous initial δ models and averaging the final δ models that are satisfactory in terms of data fit.
1021 Kb
Neukirch M., Rudolf D., Garcia X., Galiana S. (2019)
Geophysics, 84, 5, B299-V302. DOI: 10.1190/geo2018-0352.1. (BibTeX: neukirch.etal.2019b)
Resum: Veure
The introduction of the Phase Tensor marked a breakthrough in the understanding and analysis of electric galvanic distortion effects. It has been used for (distortion free) dimensionality analysis, distortion analysis, mapping and subsurface model inversion. However, the Phase Tensor can only represent half of the information contained in a complete impedance data set. Nevertheless, to avoid uncertainty due to galvanic distortion effects, practitioners often choose to discard half of the measured data and concentrate interpretation efforts on the Phase Tensor part. This work assesses the information loss due to pure Phase Tensor interpretation of a complete impedance data set. To achieve this, a new MT impedance tensor decomposition into the known Phase Tensor and a newly defined Amplitude Tensor is motivated and established. Additionally, the existence and uniqueness of the Amplitude Tensor is proven. Synthetic data is used to illustrate the Amplitude Tensor information content compared to the Phase Tensor. While the Phase Tensor only describes the inductive effects within the subsurface, the Amplitude Tensor holds information about inductive and galvanic effects that can help to identify conductivity or thickness of (conductive) anomalies more accurately than the Phase Tensor. Furthermore, the Amplitude and Phase Tensors sense anomalies at different periods and thus the combination of both provides means to evaluate and differentiate anomaly top depths in the event of data unavailability at extended period ranges, e.g. due to severe noise
10.58 Mb
O’Reilly B.M., Prada M., Lavoué F., Lebedev S. (2019)
Geophysical Journal International, 219, 2, 1421-1430. DOI: 10.1093/gji/ggz378. (BibTeX: oreilly.etal.2019a)
Resum: Veure
Gravitational compaction of thick (2–10 km) sediment accumulations in sedimentary basins is controlled by the interplay of mechanical and chemical processes that operate over many orders of magnitude in spatial scale. The compaction of sediments into rock typically involves a density increase of ≈500 to 1000 kg m−3, occurring over a depth-scale of several kilometres. The volume decrease in the compacting sediments releases vast volumes of water, which plays an important part in the global hydrological cycle and also in tectonic and geochemical processes; including the formation of hydrocarbon and mineral deposits. This study utilizes recently developed tomographic seismic images from the Porcupine Basin, which lies in the deep-water North Atlantic Ocean. A generic method for predicting fluid pressure variations that are driven by gravitational compaction is developed over the scale of the entire sedimentary basin. The methodology is grounded upon both observational evidence and empirically based theories, relying on geophysical measurements and relationships between sediment porosities and densities. The method is based upon physical concepts that are widely used in the petroleum industry and applied extensively in models of overpressure development in sedimentary basins. Geological and geophysical data from exploration wells are used to test the predictions of the method at two locations within the basin and are found to be in good agreement with the theory.
Paraules clau: Permeability and porosity; Europe; Seismic tomography; Sedimentary basin processes
1.97 Mb
Ortuño M., Corominas O., Villamor P., Zúñiga R.F., Lacan P., Aguirre-Díaz G., Perea H., Štěpančíková P., Ramírez-Herrera M.T. (2019)
Geomorphology, 326, 17-37. DOI: 10.1016/j.geomorph.2018.07.010. (BibTeX: ortuno.etal.2019)
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
4.44 Mb
Ramón M., Simarro G., Galimany E., Lleonart J. (2019)
Regional Studies in Marine Science, 31, 100763. DOI: 10.1016/j.rsma.2019.100763. (BibTeX: ramon.etal.2019b)
Resum: Veure
Parastichopus regalis is an epibenthic holothurian common in the Mediterranean Sea and the NE Atlantic, which feeds on the upper layer of the sediment playing a significant role on soft-bottom dynamics. Whether or not P. regalis is able to select the sediment ingested by size is the question of this study. For this purpose, a comparison between grain size distributions of the seabed sediments and the digestive contents of sea cucumbers were carried out. We performed the comparisons among sediment distributions through the median diameter and the granulometric dispersion . The results showed that the size of the sediment within the holothurians was significantly smaller and more uniform than the ones in the seabed. Evidence showed that P. regalis select sediment by particle size during feeding, choosing the smaller particles. This finding reports novel information on the feeding behavior of this species, a fishery resource of local interest and importance in the Western Mediterranean region
Paraules clau: Holothurian; Feeding; Grain size selection; Mediterranean Sea
658 Kb
Rossi S., Isla E., Bosch-Belmar M., Galli G., Gori A., Gristina M., Ingrosso G., Milisenda G., Piraino S., Rizzo L., Schubert N., Soares M., Solidoro C., Thurstan R.H., Viladrich N., Willis T.J., Ziveri P. (2019)
ICES Journal of Marine Science, 76, 7, 2008-2019. DOI: 10.1093/icesjms/fsz147. (BibTeX: rossi.etal.2019b)
Resum: Veure
Climate change is already transforming the seascapes of our oceans by changing the energy availability and the metabolic rates of the organisms. Among the ecosystem-engineering species that structure the seascape, marine animal forests (MAFs) are the most widespread. These habitats, mainly composed of suspension feeding organisms, provide structural complexity to the sea floor, analogous to terrestrial forests. Because primary and secondary productivity is responding to different impacts, in particular to the rapid ongoing environmental changes driven by climate change, this paper presents some directions about what could happen to different MAFs depending on these fast changes. Climate change could modify the resistance or resilience of MAFs, potentially making them more sensitive to impacts from anthropic activities (i.e. fisheries and coastal management), and vice versa, direct impacts may amplify climate change constraints in MAFs. Such changes will have knock-on effects on the energy budgets of active and passive suspension feeding organisms, as well as on their phenology, larval nutritional condition, and population viability. How the future seascape will be shaped by the new energy fluxes is a crucial question that has to be urgently addressed to mitigate and adapt to the diverse impacts on natural systems.
Paraules clau: Benthic-pelagic coupling; Benthic suspension feeders; Climate change; Energy fluxes; Heterotrophy; Ocean warming; Primary productivity; Secondary productivity; Seston availability; Water stratification
776 Kb
Salazar J., Dominguez-Carrió C., Gili J.-M., Ambroso S., Grinyó J., Vendrell-Simón B. (2019)
Frontiers in Marine Science, 6, 576. DOI: 10.3389/fmars.2019.00576. (BibTeX: salazar.etal.2019a)
Resum: Veure
The deep sea is considered the largest environment on Earth, providing multiple ecosystem services to human societies. Although its relevance has long been recognized, not enough attention and interest is generally given to it by society, and its study is almost non-existent in formal and informal education. Getting the deep sea closer to the general public would considerably benefit from the commitment of scientists involved in deep-sea research, who could generate effective educational tools based on their own personal experiences in research projects. Here we report the development of an immersive workshop that displays video footage and sounds recorded during scientific dives inside a replica of a submarine. The workshop recreates with as much detail as possible the experience of researchers when exploring the deep sea using modern technologies, in this case a manned submersible. The workshop is conducted by scientists from the same research team which carried out the study, aiming to transmit their expertise and personal experience to participants. The workshop is complemented with additional spaces that allow the exchange of knowledge and ideas between scientists and the general public. It also shows other, more intrusive, sampling methodologies traditionally used to prospect and study the deep sea, putting them in contrast with modern techniques, more respectful with the environment. Since its first exhibition in 2010, the workshop has been displayed at over 50 events held in different locations around Spain, including educational fairs, museums, schools and fishermen associations. Over 6,000 participants have taken part in the activity, most of which have expressed their opinions and suggestions about the workshop by voluntarily filling a specific survey, and thus helping to improve it. They also stated which aspects of the deep-sea life were unknown to them. Thanks to its versatility and to its simple operation, this educational workshop opens a wide range of possibilities to significantly improve the current knowledge on marine life (and deep-sea ecosystems in particular) by the general public, also aiming to reduce the distance between academia and citizenship.
Paraules clau: Submarine dive; Ocean literacy; Deep sea; Marine ecosystems; Environmental education
9.21 Mb
Sallarès V., Ranero C.R. (2019)
Nature, 576, 96-101. DOI: 10.1038/s41586-019-1784-0. (BibTeX: sallares.ranero.2019)
Resum: Veure
Seismological data provide evidence of a depth-dependent rupture behaviour of earthquakes occurring at the megathrust fault of subduction zones, also known as megathrust earthquakes1. Relative to deeper events of similar magnitude, shallow earthquake ruptures have larger slip and longer duration, radiate energy that is depleted in high frequencies and have a larger discrepancy between their surface-wave and moment magnitudes1,2,3. These source properties make them prone to generating devastating tsunamis without clear warning signs. The depth-dependent rupture behaviour is usually attributed to variations in fault mechanics4,5,6,7. Conceptual models, however, have so far failed to identify the fundamental physical causes of the contrasting observations and do not provide a quantitative framework with which to predict and link them. Here we demonstrate that the observed differences do not require changes in fault mechanics. We use compressional-wave velocity models from worldwide subduction zones to show that their common underlying cause is a systematic depth variation of the rigidity at the lower part of the upper plate - the rock body overriding the megathrust fault, which deforms by dynamic stress transfer during co-seismic slip. Combining realistic elastic properties with accurate estimates of earthquake focal depth enables us to predict the amount of co-seismic slip (the fault motion at the instant of the earthquake), provides unambiguous estimations of magnitude and offers the potential for early tsunami warnings.
610 Kb
Salvadó J., Grimalt J.O., López J.F., Palanques A., Canals M. (2019)
Science of The Total Environment, 647, 597-605. DOI: 10.1016/j.scitotenv.2018.07.458. (BibTeX: salvado.etal.2019b)
Resum: Veure
The significance of the offshore vertical convection currents in the transport and sinking of water-soluble organic pollutants into marine deep basins has been evaluated. For this purpose, sediment cores were collected in the Gulf of Lion (GoL) at sites between 26 and 2330 m water depth. The top core layers were analyzed for aromatic and aliphatic hydrocarbons and organochlorine compounds. Organic compounds with logKAW (air water partition coefficient) between −2 and −4, e.g. lindane, PCB 28, PCB 52, phenanthrene, methylphenanthrenes, dimethylphenanthrenes, C14–C23n-alkanes, are found in higher concentrations or exhibit relative concentration increases in the sediments deposited in the continental rise as consequence of the open-sea convection processes associated with the formation of Western Mediterranean Deep Water (WMDW). In contrast, the organic pollutants with intermediate air-water distribution coefficients, logKAW between −2 and 0, and high octanol water distribution coefficients (logKow > 6), e.g. highly chlorinated PCBs, DDTs, DDEs, DDDs, C25–C35n-alkanes, and polycyclic aromatic hydrocarbons with molecular weight higher than 200, occur in association to sediment particles, which are mainly transported by the Northern current along the continental shelf forming the mud belt. The Rhône prodelta is therefore the area of the GoL showing the highest concentrations of this group of organic compounds, which are preferentially associated with water particles. Overall, the results show that vertical open-sea convection processes related with offshore formation of WMDW may have an important role in the transport and accumulation of water soluble pollutants to deep marine environments of the GoL (>2000 m water depth).
Paraules clau: Organochlorine compounds; Aliphatic hydrocarbons; Polycyclic aromatic hydrocarbons; Marine sediments; Western Mediterranean; Deep water formation
6.27 Mb
Sauer W.H.H., Gleadall I.G., Downey-Breedt N., Doubleday Z., Gillespie G., Haimovici M., Ibáñez C.M., Katugin O.N., Leporati S., Lipinski M.R., Markaida U., Ramos J.E., Rosa R., Villanueva R., Arguelles J., Briceño F.A., Carrasco S.A., Che L.J., Chen C., Cisneros R., Conners E., Crespi-Abril A.C., Kulik V.V., Drobyazin E.N., Emery T., Fernández-Álvarez F.A., Furuya H., González L.W., Gough C., Krishnan P., Kumar B., Leite T., Lu C., Mohamed K.S., Nabhitabhata J., Noro K., , Putra D., Rocliffe S., Sajikumar K.K., Sakaguchi H., Samuel D., Sasikumar G., Wada T., Zheng X., Tian ., Pang Y., Yamrungrueng A., Pecl G. (2019)
Reviews in Fisheries Science & Aquaculture DOI: 10.1080/23308249.2019.1680603. (BibTeX: sauer.etal.2019a)
Resum: Veure
Recent studies have shown that coastal and shelf cephalopod populations have increased globally over the last six decades. Although cephalopod landings are dominated by the squid fishery, which represents nearly 80% of the worldwide cephalopod catches, octopuses and cuttlefishes represent ∼10% each. Total reported global production of octopuses over the past three decades indicates a relatively steady increase in catch, almost doubling from 179,042 t in 1980 to 355,239 t in 2014. Octopus fisheries are likely to continue to grow in importance and magnitude as many finfish stocks are either fully or over-exploited. More than twenty described octopus species are harvested from some 90 countries worldwide. The current review describes the major octopus fisheries around the globe, providing an overview of species targeted, ecological and biological features of exploited stocks, catches and the key aspects of management.
Paraules clau: Octopus; Fisheries; Review; Global
3.20 Mb
Teixeira M., Terrinha P., Roque C., Rosa M., Ercilla G., Casas D. (2019)
Marine Geology, 410, 88-108. DOI: 10.1016/j.margeo.2018.12.011. (BibTeX: teixeira.etal.2019b)
Resum: Veure
An integrated analysis of multibeam bathymetry and single- and multichannel seismic records were used to image the morpho-stratigraphy of the Alentejo Margin (Southwest Portuguese Continental Margin). The complex interaction of several alongslope and downslope processes in the area leads to the formation of various bottom current driven depositional and erosive features (moat) as well as gravity-driven features (gullies and landslides) in the Alentejo Margin. These processes feed each other contributing for the active sedimentary pattern on the area. Sines Contourite Drift (SCD) is a ~2311 km2 sedimentary feature with a perimeter of 303.9 km, 98 km length and 35 km width. Landslides occur either on steep and on gentle slopes between ~200 and 3200 mwd (meters water depth) in the study area, which has a total extent of ~85 km × 82 km. Scar concentration is higher in the middle- and lower-slope, whereas the thickest debris deposits are found in the slope basin area - Lebre Basin (LB). Translational landslides, with planar failure planes parallel to the slope surface are the main landslide typology verified in the study area. Several triggering and pre-conditioning factors, resulting from the interaction of alongslope and downslope processes, contribute for varied landslides scar concentration. Steep-slope and high sedimentation rates favour sediments under-consolidation, promoting excess pore water pressure and weak layers formation. In this paper, we show that the interaction of bottom currents with pre-existing tectonic structures promotes the complex interaction of both alongslope and downslope processes thus promoting an active and diversified geomorphological evolution and generalised slope instability.
Paraules clau: Sedimentary processes; Morphosedimentary features; Contourite drift; Bottom currents; Slope instability; Submarine landslides; Triggering and pre-conditioning factors
992 Kb
Ugalde A., Gaite B., Ruiz M., Villaseñor A., Ranero C.R. (2019)
Seismological Research Letters, 90, 4, 1565-1576. DOI: 10.1785/0220180353. (BibTeX: ugalde.etal.2019a)
Resum: Veure
In November 2014, a temporary land and marine seismic network was deployed to monitor the drilling of an exploratory well in the Canary Channel (eastern Canary Islands). This region is characterized by low‐seismic activity; however, because of the increased awareness of the potential seismic hazard caused by hydrocarbon exploitation activities, the drilling operations were monitored with an unprecedented level of detail for an activity of this kind. According to the reported earthquakes, there was not a measurable increase in seismicity in the vicinity of the well. Overall seismic activity was low, which is consistent with the historical seismicity records. Harmonic tremor, explained here as resonances of the instrument‐seafloor system generated by bottom water currents in the area, was commonly detected on the ocean‐bottom seismometer (OBS) recordings. The marine network data also revealed dozens of nonseismic short‐duration signals per day that appear similar to other events on OBS recordings throughout the world. We suggest that they may be caused by direct perturbations on the OBS, mostly induced by ocean currents in the Canary Channel.
3.04 Mb
Vandorpe T., Collart T., Cnudde V., Lebreiro S., Hernández-Molina F.J., Alonso B., Mena A., Antón L., Van Rooij D. (2019)
Marine Geology, 417, 106003. DOI: 10.1016/j.margeo.2019.106003. (BibTeX: vandorpe.etal.2019b)
Resum: Veure
Five sediment cores, retrieved from four different depositional contouritic morphological settings (a sheeted drift, a confined mounded drift, a mounded elongated drift and a plastered drift) from the Northern Gulf of Cadiz and the Alboran Sea have been analysed using medical X-ray computed tomography (medical CT). A quantitative approach has been used, resulting in a workflow that delineates several radio-density ranges based on the Hounsfield Unit (HU) histogram of each core and tracks these ranges throughout the cores. In order to derive the geological significance, the radio-density ranges of all cores have been compared to non-destructive, continuous chemical and physical proxies as well as grain size measurements. The highest correlations occurred between high HU and proxies indicating elevated bottom currents, such as Zr/Al and sortable silt. Additionally, a continuous increase in average HU and inferred bottom current velocities, needed for the creation of the specific contourite setting, could be observed throughout the five cores. Despite imperfections and the requirement of additional research, promising results have been obtained which could improve the detection of diagnostic criteria for contourites. Moreover, the CT data can give more conclusive evidence on the nature of the (contourite) sedimentary sequence boundaries.
Paraules clau: Medical Computed Tomography (CT); Contourites; Grain size; Bottom currents; Gulf of Cadiz; Alboran Sea