Tesis doctorals

In the last 52 years, seismic methods have improved with the development of recording instrumentation, and even more in the last 20 years with increased computational power. This has permitted to model larger amounts of data and implementing increasingly accurate numerical models, which has in turn allowed to obtain better constrained, higher- resolution models of physical properties of the Earth’s subsurface. In particular, my PhD work focuses on the development and application of seismic tomography methods to improve seismic images and models of subduction zones and particularly the inter-plate boundary zone. It consists of two parts: the first part presents the application of joint refraction and reflection travel-time tomography (TTT) to model onshore/offshore wide- angle seismic (WAS) data recorded along a profile in the North Chilean subduction zone using the tomo2d code. This work allowed me to get knowledgeable with the subroutines of this code, an experience which was applied in the second part of my work. In this second part, I modified tomo2d to allow to jointly inverting WAS and near-vertical multichannel sesimic reflection (MCS) and I showed the outstanding improvement of the inversion results by combining both types of data into a common inversion strategy. In the field data application of the first part, I have applied TTT to WAS data recorded during the Crustal Investigations off- and on-shore Nazca/Central Andes (CINCA’95) survey along ~21°S in North Chile. Results show that there is a significant change in the overriding plate properties as well as the inter-plate boundary depth along the Chile Trench. The thickness of the plate increases northwards with the deepening of the inter- plate boundary at similar distances from the trench axis. Furthermore, there is a change in surface deformation of the overriding plate visible in the orientation of faults cutting the onshore relief. Fault orientation changes from trench-parallel in the south to trench-perpendicular in the north. The borderline between the areas of different fault orientation support that there is a change in the regional stress of the overriding plate along the North Chile convergent margin. [...]

Bottom trawling fisheries have existed for centuries, mainly occurring on coastal shelf environments. However, the introduction of the steam engine followed by the diesel engine allowed the expansion of bottom trawling grounds to farther and deeper areas. This expansion, together with the general increase in fishing efforts, amplified the impacts associated to this activity at a global scale. Bottom trawling is now considered one of the most harmful anthropogenic activities in the marine environment given its widespread occurrence, high frequency, and intensity. Since bottom trawling gear are in continuous contact with the seafloor, it can modify seabed morphology by erasing natural sedimentary structures and by leaving behind trawl marks. Bottom trawling gear can also resuspend large volumes of sediment, which can be advected from trawling grounds, eroding the seafloor and altering sediment properties. With the global expansion of bottom trawling to deeper fishing grounds since the mid-XXst century, it is expected that the impacts caused by this activity will be intensified, but studies assessing them are still scarce. This dissertation aims to investigate the combined physical and biogeochemical impacts that deep bottom trawling exerts in different areas of the western Mediterranean basin. This PhD thesis was initially inspired by the results of precedent studies conducted in Palamós (also known as La Fonera) Canyon in the NW Mediterranean, where it was observed that bottom trawling erodes the seafloor and mobilizes large amounts of sediment down-canyon, increasing sedimentation rates in its axis. Prior to this thesis, studies were limited to that specific submarine canyon, but whether these impacts were also present in other trawled submarine canyons, and to which degree their fishing grounds were affected, was still unknown. Moreover, the effects of these alterations in sediment biogeochemistry had not been addressed in detail

This Thesis conducts the study of bedform development and dynamics in the inner shelf integrating observations at different spatial and temporal scales. An initial assumption is that different scales of sedimentary processes strongly interact between them and small-scale sedimentary processes intended to foster those of larger scale. The potential contribution of small-scale bedforms to the sediment transport is particularly addressed. The study includes the monitoring and analysis of sand ridges, ripples and near-bottom suspended sediment variations at the Ebro Delta (NW Mediterranean Sea) and Perranporth (Atlantic Ocean) inner shelves. A sand ridge field with maximum ridges heights of 2.5 m and 400 m spaced is located over a retreating lobe in the Ebro Delta. Ridges are mostly symmetric arranging obliquely to the shoreline. The change of the main Ebro River channel led to the progressive abandonment of the former river mouth and to the severe coastal retreatment, providing large amount of sediment available in the coastal zone. NW winds induce strong near-bottom currents flowing towards the SE, which are able to transport sediment and produce ridge formation and migration towards the SE at ~10 m/y. The characteristics of the Ebro sand ridges match well with those of shoreface-connected sand ridges and, particularly, with the initial stages of sand ridge development on storm-dominated continental shelves. Time-scales related to their genesis can be within a few decades. The presence of ripples on the different inner shelves is the most usual situation under low- to moderate-energetic conditions. In the wave-dominated and tideless coast (Ebro Delta) ripples were observed superimposed on sand ridges. Four types were identified: small undulations that were the precursor ripples, 2D wave-ripples, current-dominated 2D-3D-ripples, and combined wave-current 3D-ripples. The wave-ripples were static while the current-dominated ripples migrated. In a macro-tidal sandy beach exposed to high-energetic Atlantic storms (Perranporth), only wave-ripples were developed arranging orthogonal to wave approach and they were static. The size of ripples changed from larger (developed in equilibrium conditions) to smaller ripples, the latter interpreted as degraded ripples in wash-out conditions. The ripple prediction did not well-adjust to neither ripple appearance nor dimension. However, if the observed thresholds of seabed states are applied the model improves ripple appearance forecast. The near-bottom suspended sediment variability from seconds to months in the Ebro Delta is described distinguishing between waves, currents, and combined wave-currents conditions. In general, waves dominated the sediment resuspensions although strong currents also have an important contribution in the suspended sediment concentration (SSC) increases. The time-averaged SSC usually showed redundant structure by forming three layers with different patterns. In the lower and intermediate layers the SSC oscillated at gravity and infragravity wave frequencies. Time-varying and instantaneous profiles exhibit sediment patterns potentially related to ripples. The potential role of ripple migration as an additional long-term mechanism of sediment transport was analysed. In Perranporth, wave ripples are stationary and did not contribute to beach recovery because of wave orbital symmetry. The sediment transport is alongshore during low-energetic regimes and cross-shore during more energetic regimes when ripples are washed-out. In the Ebro Delta, 3D-ripples migration agrees with sand ridges migration direction towards the SE. The respective migration rates and their differences in size, support that a subordinate part of sand ridge migration can be the result of ripple migration contribution under low-, moderate-regimes, suggesting that in specific environments, dynamics of small-scale bedforms can play a subordinate but not negligible role in the evolution of larger bedforms.

This thesis presents the implementation and application of a procedure combining different geophysical techniques to extract high-resolution information that helps characterizing the structure and properties (p-wave velocity, Vp) of the subsurface by using marine multichannel seismic (MCS) data alone. The challenge is overcoming the inherent non-linearity and non-uniqueness of inverse methods, in general, and of fullwaveform inversion (FWI), in particular, which are especially critical for short-offset, band-limited seismic data. I have applied an in-house modelling workflow consisting of three steps: (1) data re-datuming or downward continuation (DC) by back-propagation of the recorded seismograms to the seafloor; (2) travel-time tomography (TTT) using the first arrivals of the re-datumed shot gathers (synthetic data), combined with those of a reflecting boundary in the original data (field data); and (3) FWI of the original shot gathers using the model obtained by TTT as initial reference. This workflow is first tested with synthetic data, and then applied to field data acquired in the Alboran Sea Basin (SE of Iberia). [...]

In this work we present a geophysical study of three Western Mediterranean basins: Valencia Trough, Gulf of Lions and Algero-Balearic Basin. The work aims to define the tectonic structure, nature of the basement, and to discuss the age, kinematics and mechanisms involved in basin formation. To study the basins we have gathered all deep penetrating seismic data available in the region consisting on several academic and industry data reprocessed and interpreted for this work. [...]

In this PhD thesis we present a geophysical study of the westernmost Mediterranean basin: the Alboran Basin. This basin is located between the Iberian Peninsula and North Africa, and it is surrounded by the Betics and Rif orogenic ranges. Along the Alboran basin, runs the plate boundary between Iberia and Africa tectonic plates. The processes that led to the basin formation in this compressive setting, and the later processes that controlled the basin deformation, remain unclear, as well as the deep structure of the basin. This study aims to: 1) characterize the crust and the basement of the basin, 2) define a seismostratigraphy coherent for the entire basin and analyse the basin evolution in the basis of the sedimentary record, 3) characterize the northeaster transition between the Alboran Basin and the Algero-Balearic Basin through the study of the Palomares Margin and 4) characterize the two most prominent tectonic structures in the area, the Yusuf Fault and the Alboran Ridge front fault. The results of this thesis have been integrated in a geodynamic model of the area, and will help to improve the regional seismic and tsunami hazard assessment model. [...]

An interdisciplinary study of the geomorphology, sedimentology, stratigraphy and physical oceanography of the deep-sea environments of the Alboran Sea (south western Mediterranean Sea) has been carried out with the purpose of evidencing and understanding the role of bottom currents in the sedimentary evolution of the Spanish and Moroccan continental margins and adjacent basins during the Pliocene and Quaternary. This study was conducted using swath bathymetry data, more than 1900 profiles consisting of parametric, single- and multi-channel seismic records, scientific and commercial wells, sediment cores, and hydrographic data comprising: Conductivity, Temperature and Depth (CTD) profiles, Acoustic Doppler Current (ADCP) profiles, and EK60 echograms. Here, for the first time, a morphosedimentary scenario with a wide spectrum of depositional (plastered, sheeted, channel-related, mounded confined, elongated and separated drifts) and erosional (terraces, escarpments, moats, channels and furrows) contourite features are described in the Alboran Sea, from the shelf break to the basin floor. Hydrographic data offers new insights into the distribution of the Mediterranean water masses, and reveals that the 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) with the Moroccan slope, Spanish baseof- slope and deep basins. The integration of distinct datasets and approaches allow a new sedimentary model to be proposed for the Alboran Sea that underlines the significance of bottom current processes in shaping deep-sea morphology. This model suggests that the bottom circulation of water masses governs physiography, that the interface positions of water-masses with contrasting densities sculpt terraces at a regional scale, and that morphological obstacles play an essential role in the local control of processes and watermass distribution. An analysis of the seismic stratigraphy from the Pliocene and Quaternary sequences has enabled to update and rename the stratigraphic boundaries and establish a new seismic stratigraphy for the Alboran Sea, after relocating the base of the Quaternary from 1.8 to 2.6Ma. Additionally, the seismic analysis involves the presentation and discussion of the evidence for contourite features reaching the scale of the Alboran Basin. Contourite drifts (plastered, sheeted, elongated separated and confined mounded drifts) and erosive features (terraces, escarpments, moats, channels, furrows) were developed under the continuous influence of Mediterranean water masses after the opening of the Strait of Gibraltar (~5.33Ma). At least two primary factors have controlled the contourite features 12 in this sea: i) tectonics, which has governed the relocation of the main Mediterranean flow pathways and their circulation patterns; and ii) climate, which has influenced both watermass conditions (depth and density contrast of the interfaces) and hinterland sediment sources, conditioning the morphoseismic expression and growth pattern of drifts and terrace formation (dimensions). The distribution of contourite features through time and space allows to propose three main scenarios for ocean circulation since the opening of the Strait of Gibraltar: i) Atlantic Zanclean flooding; ii) the Pliocene sea, with two different stages for the dense circulation and characterised by poorly-defined and unstable interfaces for the Atlantic Waters (AW), light and dense Mediterranean waters and the presence of a strong countercurrent in the Western Basin; and iii) the Quaternary sea, characterised by tabular Mediterranean water masses with multiple current dynamics, increasingly important density contrasts, and climate shifts causing major vertical and horizontal displacement of the interfaces. These stages reflect variability in the bottom current regimes and related alongslope efficiency in terms of transport, deposition and erosion. The detailed seismic analysis of the units making up the Pliocene and Quaternary sequences allows for the first time, to make an in-depth analysis of the contourite features, turbidite systems and mass-movement deposits, and map them through time. These maps are enormously helpful when it comes to understanding the sedimentary architecture of the Spanish and Moroccan continental margins and basins, as well as for decoding the palaeoceanographic processes from a geological perspective. Two main contourite depositional systems are defined: the Intermediate Contourite Depositional System (ICDS), formed under the action of the Light Mediterranean Waters (LMW) on the Spanish margin, and the Deep Contourite Depositional System (DCMW), formed under the action of the Dense Mediterranean Waters (DMW) mainly on the Moroccan margin and basins. The characterisation of the terraces as contourite features that form under the combination of two water masses, has also led to the definition of the Atlantic Contourite Depositional System (ACDS). The occurrence of several contourite depositional systems has led to the suggestion of a new term, not heretofore considered in the literature: Multiple Contourite Depositional System (MCDS), which refers to the set of different CDSs that occurs in the same area and evolving under the action of multiple water masses. In addition, twenty turbidite systems have been characterised, revealing that they are responsible for the different sedimentary architecture of the Spanish margin, where they coexist with contourites, as on the Moroccan margin the turbidite systems are less well developed. The mass-movement deposits are mainly related to the reworking of the contourites draping the highs. Mainly contourites but also turbidites, allowed to define from a geological 13 perspective the basic oceanographic processes and to determine their occurrence, relative magnitude and energy, and time of action. This PhD thesis also explains the uneven development of the turbidite systems in the Alboran Sea, which is interpreted to be conditioned by the interaction of alongslope with downslope processes. Several morphological and sedimentary signatures produced by the interaction between both processes have been identified in the Pliocene and Quaternary records, as well as on the present-day seafloor of the Alboran Sea. The interaction scenarios move between two-end-members: from bottom currents dominating gravity flows to gravity flows dominating contour currents. In between these extreme cases, the alternation and mutual influence of both processes can occur. Two different conceptual models of interaction are proposed for the Spanish and Moroccan margins. i) On the Spanish margin, the alongslope and downslope interaction is especially complex and varied, with both regional and local effects on the turbidite systems. This is because here the turbidite systems are influenced at different water depths by Atlantic and Mediterranean water masses and their interfaces, with current flows that change acrossand downslope. ii) On the Moroccan margin, the vigorous action of the WMDW primarily inhibits the formation of canyons and associated deposits. The findings of this PhD thesis suggest that the relevance of bottom-water processes in deep sea must be reevaluated. It is concluded that understanding the influence of bottom currents is not only essential for reconstructing present and past water mass circulation, but also for recognising sea floor morphologies and decoding the sedimentary stacking pattern and evolution of deposits, as well as global climate and periods of eustatic variation.

Late Quaternary climate variations controlled glacial advances and retreats to the shelf edge and therefore the evolution of high latitude continental margins. The variations in ice extension modulated sediment supply to the continental slope resulting in a particular shape and stratigraphy but also exerted a major control on stresses imposed on marine sediments and likely had a major control on fluid flow pattern. This thesis investigates the sedimentary, stratigraphic and hydrogeologic evolution of two Arctic Trough Mouth Fans (TMFs), the Storfjorden and Kveithola TMFs in the NW Barents Sea, from ~2.7 Ma to Present, and identifies how such evolution affected slope instability of the TMFs. The research is carried out by means of sub-bottom and seismic reflection profiles, multibeam bathymetry data and sediment cores on which sedimentological and geotechnical analysis have been performed. Numerical finite elements models allow inferring the detailed stratigraphic architecture and hydrogeological evolution of the TMFs. We found that the Storfjorden and Kveithola TMFs mainly consist of an alternation of rapidly deposited glacigenic debris flows during glacial maxima and a sequence of well-layered plumites and hemipelagic sediments, which were mainly deposited during the deglaciation phase of the adjacent glacial trough. We have identified eight units above regional reflector R1, which indicate that the ice sheet reached the shelf edge within the Storfjorden Trough on at least three occasions during the last ~200 ka. A shallow subsurface unit of glacigenic debris flows suggests that the ice sheet had a short re-advance over the northern and central part of Storfjorden after the Last Glacial Maximum. From stratigraphy, core and literature data, we estimate that ice sheets reached the shelf edge between 19.5 to 22.5 ka, 61 to 65 ka and 135 to 167 ka. [...]

The controlled-source electromagnetics (CSEM) and magnetotellurics (MT) methods are common geophysical tools for imaging the electrical properties of the Earth’s subsurface and are employed independently, jointly, and in combination with other geophysical techniques for this purpose. In order to appreciate measured data, both methods require forward and inverse modeling of the electrically conductive subsurface to the end that the modeled data reasonably fits the observations. Naturally, the potential goodness of this fit not only depends on the error in the measured data but also on the degree of physical approximation inferred by numerical modeling. Therefore, active research focuses on new methods for modeling and inversion to obtain accurate and reliable models of the Earth’s structure in increasingly complex scenarios. [...]

This thesis offers an extensive perspective of the hydrodynamics and sediment transport of the Gulf of Valencia (GoV) continental margin (NW Mediterranean), focussing on the geomorphological and internal structure description of the bedforms observed over the margin. A comprehensive dataset using a wide range of methodologies was used during the project, spanning from hydrographic and hydrodynamic datasets, instrumented moorings, swath bathymetry, sediment sample and seismic profiles. [...]

The Messinian Salinity Crisis (MSC) represents one of the major environmental changes in the recent geological history of the Earth. During this event (5.97-5.33 Ma, Late Miocene), the Mediterranean Sea went into a nearly complete desiccation and more than 1 million km of evaporite deposits accumulated in the Mediterranean basins. Despite the increasing knowledge over the last 40 years, several controversies concerning the mechanisms and timing of the MSC remain currently under discussion. [...]

La circulación oceánica de gran escala se encuentra relacionada con la pequeña escala a través de los procesos turbulentos, los cuales hacen posible el intercambio de energía cinética. En equilibrio, el flujo de energía inyectado por el forzamiento climatológico en el rango de producción (macroescala) debe balancearse por los procesos de mezcla en el rango de disipación (meso- y pequeña escala). Alrededor de la frecuencia de Coriolis, el efecto cinemático dominante es el campo de los giros geostróficos, mientras que a mayores frecuencias y especialmente cerca de la frecuencia inercial, los movimientos están dominados por la dinámica de las ondas internas, cuya propagación en el océano transfiere la energía a menores escalas a través de procesos de dispersión y de interacción onda-onda. Dependiendo de las condiciones oceanográficas, cuando las ondas internas rompen, generando como consecuencia, la transferencia de parte de su energía a las escalas más pequeñas mediante procesos de mezcla irreversible, este proceso se puede generar de diversas maneras. [...]

Les fluctuations du climat et du niveau marin, de plus ou moins grande amplitude, influencent le taux d’érosion sur le continent, le transport de sédiment vers l’océan et sa distribution vers le bassin profond. Les canyons sous-marins, structures érosives de premier abord, sont les zones de transfert privilégiées entre le plateau continental et le bassin profond. Peu d’études se sont concentrées sur la relation entre le remplissage des canyons, l’acheminement des sédiments et les variations du niveau marin. La chronologie de leur mise en place et de leur évolution aux échelles de temps géologiques restent également largement spéculatifs. Ce travail est consacré à la genèse des canyons sous-marins au Plio-Quaternaire sur les marges de l’Ebre et du Golfe du Lion, en Méditerranée occidentale. Cette genèse intervient après la crise de salinité messinienne, qui a conduit au démantèlement par érosion continentale des marges méditerranéennes. Après une initiation par érosion régressive au Pliocène, les canyons sous-marins connaissent un développement majeur lors de la mise en place des cycles climatiques de 100 ka au Quaternaire, en lien avec l’amplification des oscillations du niveau marin pouvant atteindre 150 m. L’utilisation et la comparaison de données sismiques (2D et 3D) de résolution et pénétration différentes, couplées à des calages chrono-stratigraphiques par forages, permettent de mettre en évidence le lien important entre les cycles climatiques de Milankovitch (principalement 100 et 41 ka) et l’architecture des têtes de canyons. Les changements rapides du climat et du niveau marin (cycles de Bond) ont également une influence importante sur le flux sédimentaire et les processus de transport, ainsi que sur la connexion/déconnexion avec les systèmes fluviatiles

Work carried out in this thesis has the purpose to trace the tectonic and stratigraphic features of the Tyrrhenia Sea, and from these characteristics, to define the processes that get involved into the basin formation. The Tyrrhenian is a back-arc basin belonging to the Western Mediterranean realm. Its formation is directly related with the subduction system of the Ionian slab (African plate) below the Mediterranean domain (European plate). The slab retreat causes an stretching of the overriding plate and triggered the opening of the Liguro-Provençal basin, and later on the Tyrrhenian basin (Faccenna et al., 2001; 2007). [...]

This dissertation is devoted to seismic tomography. I have implemented a new modelling tool for 3-D joint refraction and reflection travel-time tomography of wide-angle seismic data (TOMO3D). The reason behind this central objective is the evidence that the information based on 2-D seismic data does not allow to capture the structural complexity of many 3-D targets, and in particular that of the seismogenic zone in subduction margins. The scientific rationale for this statement, which justifies the central part of my thesis work, is based on the analysis of 2-D models obtained in the convergent margin of Nicaragua, a seismically active area where a textbook example of tsunami earthquake took place in 1992. In this application I modelled two perpendicular wide-angle seismic profiles for the characterisation of the overriding plate and the interplate fault. To do this, I applied TOMO2D, a state-of-the-art joint refraction and reflection 2-D travel-time tomography code. The inversion outcomes are two 2-D velocity models along both profiles, together with the 1-D geometry of the interplate boundary. In combination with other geophysical data measurements, namely coincident multichannel seismic profiles and gravity data, these models provide new constraints on the nature and structure of the margin, and in particular add new insights on the nucleation and propagation of the said earthquake and its tsunamigenic behaviour. Ultimately, this case study evidences the aforementioned limitations of 2-D modelling in the investigation of 3-D geological structures and phenomena. Following from this first application and with the idea of increasing the amount of data used in travel-time tomography, I focused on an a priori paradoxical phenomenon related to water-layer multiple phases, that under certain circumstances, is observed on wide-angle record sections. The interest of this study lies in the fact that this phenomenon can provide additional constraints on travel-time tomography models. First, I propose and corroborate the hypothesis explaining the apparent paradox, and then derive the most favourable geological conditions for the phenomenon to occur. Subsequently, the possibility to model this multiple-like phases is introduced in TOMO3D. [...]

In this thesis I present a geophysical study that aims to define the structure and petrological nature of the main geological domains in the Central Tyrrhenian basin, and to investigate the mechanisms involved in their formation. The geophysical data used in this thesis was acquired during the MEDOC (2010) survey within the framework of the MEDOC project, which was designed to improve our understanding of the origin and evolution of rifted margins. The MEDOC survey was focused on the Tyrrhenian back-arc basin, an extraordinary natural laboratory to investigate the structure and evolution of back-arc basins, and hence rifted margins, since 1) extension evolves from north to south [Kastens and Mascle, 1990], 2) the original structure is preserved, and 3) it is small enough to be investigated with a single marine survey. The present work is based on the analysis, processing, modeling, and interpretation of coincident Wide-Angle Seismic (WAS), Multichannel Seismic (MCS), and gravity data corresponding to the two longest transects acquired during the MEDOC survey in the Central Tyrrhenian basin, the southern Line GH/MEDOC-6 (~450 km) and the northern Line EF/MEDOC-4 (~400 km). Both lines run across the Central Tyrrhenian basin from Sardinia to the Campania margin. [...]

Studies have proven that the desired signal for Magnetotellurics (MT) in the electromagnetic (EM) field can be regarded as ’quasi stationary’ (i.e. sufficiently stationary to apply a windowed Fourier transform). However, measured time series often contain environmental noise. Hence, they may not fulfill the stationarity requirement for the application of the Fourier Transform (FT) and therefore may lead to false or unreliable results under methods that rely on the FT. In light of paucity of algorithms of MT data processing in the presence of non stationary noise, it is the goal of this thesis to elaborate a robust, non stationary algorithm, which can compete with sophisticated, state-of-the-art algorithms in terms of accuracy and precision. In addition, I proof mathematically the algorithm’s viability and validate its superiority to other codes processing non stationary, synthetic and real MT data. [...]

In this PhD Thesis I present a new interpretation of: 1) active structures implicating old oceanic lithosphere; 2) the nature of the basement; and 3) the distribution of the basement domains and the geodynamic reconstruction of the SW Iberian margin, a region that hosts the slow convergent boundary between the African and Eurasian plates. This interpretation is based on new geophysical data acquired, processed and modeled in the framework of this PhD work. The main findings of my study are the following ones: [...]

Wave storms and river inputs have been found to be the dominant forcing mechanism of sediment transport in continental shelves dominated by medium to large rivers around the world (e.g. Drake and Cacchione, 1985; Sherwood et al., 1994; Ogston and Stemberg, 1999; Traykovski et al., 2000; Wadman and McNinch, 2008) and in the northwestern Mediterranean Sea (Jiménez et al., 1999; Puig et al., 2001; Guillén et al., 2002, 2006; Palanques et al., 2002, 2011; Ferré et al., 2005; Roussiez et al., 2005; Ulses et al., 2008). However, the contribution of “small” Mediterranean river systems in fine-grained sediment dynamics is not well known. Flood and storm events redistribute not only sediment but also all the associated matter as well, such a heavy metals, which are indicators of the impact of industrial and urban activities. For these reasons, the present thesis project involves studying the dynamics of sediments and associated heavy metals across the inner continental shelf off the Besòs River (Barcelona), and in particular determining the effect of floods and storms in a littoral system affected by industrial and urban activities. To this end, several oceanographic surveys were carried out between 20 and 40 m water depths in the Barcelona continental shelf to obtain a variety of data: to register vertical hydrographical profiles (temperature, salinity and turbidity); to record time series of physical parameters (currents, salinity, temperature, turbidity and seabed variation) by deploying oceanographic equipment; and to take sediment samples (short cores and Van Veen grabs) and suspended and downward particulate matter from water samples and sediment traps for further sedimentological and geochemical analysis. The time period of the present study comprised three seasons, from autumn 2007 to spring 2008, which showed distinct features between them. The purpose of section 3 was to describe the main hydrographic and hydrodynamic conditions during the study period to support the interpretation of sediment transport processes. Three different periods in terms of storm and river activity matched the natural seasons of the year: The period comprised between end of September 2007 and December 2007 (autumn) was characterized by an intense frequency of northeastern-eastern storms mostly coupled with high but short river discharges and a convergence of the across-shelf current between 20 m and 30 m water depths; between January and early March 2008 (winter), the wave and river activity and frequency were reduced significantly with offshore currents dominating the across component; and finally, from March to mid June 2008 (spring), specially between May and June 2008, river discharges lasted more than one month and occurred under low wave energy conditions or in conjunction with S-SE and SW wave storms.

Coasts are subject to erosion and inundation produced by storms, which are very frequent and can produce major damage and economic losses. Storminduced inundation is due to the sum of astronomical tide, surge level and wave runup. The predictability of beach inundation is mainly related to wave runup and most of the formulations that have been developed focus on the hydrodynamics, disregarding the morphological changes caused during storms. For these reasons, the aim of this thesis is to provide more insight into beach inundation processes at embayed and open beaches and to determine how morphological changes can interfere with these processes. To this end, video measurements of beach inundation and the characteristic morphological changes were carried out at two stretches of coast with different wave climates: the stretch comprising La Barceloneta, Somorrostro and Nova Icaria, which are three artificial, tideless embayed beaches located in Barcelona, Spain (NW Mediterranean); and Noordwijk beach, which is an open, microtidal multibarred beach located in Noordwijk, the Netherlands (North Sea).

En esta Tesis se deriva un nuevo conjunto de ecuaciones tipo Boussinesq para la propagación de oleaje en aguas profundas y someras. Se trata de un nuevo conjunto de ecuaciones totalmente no lineal con propiedades dispersivas mejoradas respecto a los sistemas previos. Las nuevas ecuaciones son exactas hasta O(kh)2. Se emplea un método de optimización para determinar el valor de los coeficientes introducidos en las nuevas ecuaciones propuestas con el objetivo de minimizar las diferencias entre el modelo y las teorías de Airy (dispersión lineal y asomeramiento) y de Stokes (transferencia de energía débilmente no lineal). Se muestra que con la adecuada elección de estos coeficientes el modelo es aplicable hasta valores de kh = 20 con un error relativo menor del 1% en dispersión lineal. En esta Tesis se presenta un nuevo esquema numérico explícito de cuarto orden para resolver y verificar el nuevo conjunto de ecuaciones. Además, se ha llevado a cabo un análisis lineal de estabilidad para obtener una condici´on tipo CFL para el paso de tiempo. La integración temporal se lleva a cabo empleando un esquema Runge-Kutta de 4o orden. El oleaje se genera internamente en el dominio por medio de una función fuente. [...]

La paleosismología trata del estudio de los grandes terremotos prehistóricos con el objetivo de extender el catálogo sísmico atrás en el tiempo. Esto es especialmente importante en regiones donde las tasas de deslizamiento son lentas y los periodos de recurrencia largos, regiones en las cuales el catálogo sísmico no llega a abarcar un ciclo sísmico completo (Santanach y Masana, 2001). Además, la incertidumbre en la localización de terremotos históricos suele ser importante, y más aún cuando el epicentro se localiza en mar, lo cual dificulta la relación entre terremotos históricos y estructuras concretas. Si queremos estar preparados para futuros terremotos, es imprescindible detectar y caracterizar todas las posibles fuentes sísmicas de una región, incluyendo aquellas que no hayan roto durante el periodo histórico. [...]

In the last 60 years air and oceanic temperatures increased in Antarctica above global average (Vaughan et al., 2001; Gille, 2002). As a consequence, the increase of glaciers retreat (Cook et al., 2005) and the thinning of ice shelves (Shepherd et al., 2003; Whingham et al., 2009) have been observed. Furthermore, ice shelf collapses became more frequent in Antarctica, as exemplified by the collapse in 2008 of Wilkins ice shelf and in 2010 of Mertz glacier. In 1995 and 2002, 4200 km2 and 3200 km2 of the sections A and B of the Larsen Ice shelf disintegrated, respectively (Rack and Rott, 2004). [...]

The coastal system is in incessant change, subject to the constant action of waves and tides (in addition to the wind action) that shape its morphology. The mutual interaction and adjustment of the seafloor topography and the fluid dynamics involving the motion of sediment is known as coastal morphodynamics (Voigt, 1998). This interrelation can be explained as follows: in the nearshore region the water motion is influenced by the seafloor topography and is responsible of sediment transport. Gradients in the sediment transport produce morphological changes in the seafloor. The loop is complete as hydrodynamic processes respond to the modified bathymetry. [...]

Gas hydrates have been recently recognized as a key factor affecting a number of global processes such as the climatic change, sea floor stability, etc. In this thesis we present the multidisciplinary study of gas hydrate rich sediments recovered during ODP Leg 204 “Drilling gas hydrates at Hydrate Ridge”. The main objective of this thesis is to study how the textural characteristics of marine sediments can affect the main pathways and intensity of fluid flow and how fluid flow determines the distribution of gas hydrates in the continental margins, as well as the main geochemical processes that occur during early diagenesis. To reach these objectives, a complete sedimentary and geochemical study of 581 sediment samples from southern Hydrate Ridge was carried out. The methods and techniques that were applied include: complete textural analyses (grain size, granulometric distribution curve, statistical parameters, identification of the coarse-grained particles, carbonate content…), mineralogy (bulk sediment and clay minerals), physical properties (magnetic susceptibility) and geochemistry (major and trace elementary composition, total organic carbon). The southern Hydrate Ridge sediments are mainly made up of four lithofacies defined as: hemipelagites, turbidites, ash layers and debrites. Mass-transport deposits such as turbidites and debrites are more abundant in Lithostratigraphic Unit III and II, as well as in Lithostratigraphic Unit IA in the slope basin of southern Hydrate Ridge. Some increasing trends with depth can be observed in the smectite content in the clay mineral assemblages of southern Hydrate Ridge sediments. These features suggests that the transport in suspension of fine sediments through the California Current was more effective during the Pliocene and early Pleistocene period. Bedload transport of coarse material from local and distal areas was more effective during the middle Pleistocene and Holocene due to the tectonic reactivation of the southern Hydrate Ridge uplift. During the Pleistocene and owing to the pervasive fluctuation of sea-level, gas hydrate dissociation together with the seismic movements in the Oregon margin seems a plausible triggering mechanism for mass-movements. Thus, the results presented here confirm that the sedimentation patterns in the Hydrate Ridge region are controlled by climate and tectonic parameters such as the regional intensity of the California Current or the local tectonic movements that lead to the uplift of the Ridge. These parameters mainly control the clay mineral distribution as well as the sedimentary facies that are produced. [...]

The Cantabrian continental margin constitutes a magnificent natural laboratory to investigate submarine sedimentation and the processes of deposition and erosion that operated in a continental margin from the Alpine continental collision up to the recent evolution. More specifically, this research focuses on the sedimentary evolution spanning from the Late Oligocene to the present of the easternmost sector of this margin, that is, from Gijón to Bilbao, comprising also a small sector of the distal Aquitanian continental margin, from Biarritz to Bordeaux. [...]

The Central Bransfield Basin is located at the northernmost tip of the Antarctic Peninsula (West Antarctica). This investigation, focused in the morphology, stratigraphy and near-surface sedimentation, and based on acoustic, seismic and sedimentological methods, reveals the main sedimentary systems and processes involved in the stratigraphic architecture and growth pattern of the basin. Likewise, it provides clues about the interplay of the global and local factors that have controlled the basin sedimentary evolution during the post-rift stage and allows the reconstruction of depositional models. The most striking physiographic characteristic of the Central Bransfield Basin is the presence of slope platforms composing the middle domain of the slope, in both the Antarctic Peninsula and South Shetland Islands margins. This favors the occurrence of glacial and glaciomarine processes on this domain, representing a difference with other high-latitude margins, where these processes are restricted to the continental shelf. The morphologic elements identified on the Central Bransfield Basin may be grouped into four major sedimentary systems (glacial-glaciomarine, slope-basin, seabed fluid outflow and contourite). The development of these systems has occurred during the last glacial cycle and has been controlled by the glacial cyclicity, tectonics, physiography and oceanography. The post-rift seismic stratigraphy of the Antarctic Peninsular margin consists on two seismic sequences, S1 and S2, of glacial and glaciomarine origin, overlying the syn-rift record. S2 was deposited during the post-rift to the Mid-Pleistocene and can be subdivided into four seismic units composed of prograding wedges. S1 was deposited after the Mid-Pleistocene and is composed of prograding/aggrading deposits. This sequence is composed of five seismic units whose distribution was mostly governed by variations in the thermal regimes of the Antarctic Peninsula Ice Sheet. Climate and physiography are interpreted as the major factors controlling the stratigraphic architecture and growth pattern of the margin. The near-surface sedimentary record of the Central Bransfield Basin corresponds to the last glacial cycle and offers a high-resolution definition of sediment sequences, including subglacial diamicton, compound glaciomarine, turbid glacial meltwater, proglacial diamicton, flow-in and contourite sequences, and a characterization of the sedimentary paleoenvironments during the deglaciation and interglacial stage. Likewise, the identification of sedimentary processes allows the establishment of several stratigraphic models (glacial trough, slope platforms, lower slope and basin) in the Central Bransfield Basin, in relation to sedimentary processes that were directly controlled by climatic factors and modulated by the physiography/morphology, sediment source and oceanography. This PhD Thesis has allowed the definition of post-rift sedimentary models by different scale, resolution and temporal approaches. Likewise, the interpretation of the interplay among the different depositional systems has been done considering the margin and deep sea as an entire system, to analyze the inherent sedimentary dynamics and processes that transfer the sediment from the shoreline to the deep basin.

Las inestabilidades submarinas de sedimentos tienen un impacto significativo en la construcción y evolución de los márgenes continentales y en la transferencia de sedimentos hacia las zonas profundas de los océanos. También son un factor de gran importancia económica al poder afectar a estructuras submarinas construidas por el hombre. Todas las provincias fisiográficas del margen continental presentan fenómenos de inestabilidad sedimentaria desde la línea de costa hasta el glacis continental. Pero el número de inestabilidades presentes es significativamente más alto en el talud continental. De entre los diferentes tipos de movimientos de masa submarinos existentes, los deslizamientos, las coladas de derrubios y las corrientes de turbidez son quizás los más abundantes y los que transportan mayores volúmenes de sedimento hacia las zonas más profundas de los océanos. [...]

The present thesis focuses on the transfer and accumulation of particulate matter in the Palamós Canyon, located in the Northwestern Mediterranean. In the context of the CANYONS project, 7 moorings with a total of 7 sediment traps and 18 current meters (some of them equipped with turbidimeters) were deployed in the Palamós submarine canyon and adjacent slope from March to November 2001, during two consecutive deployments. [...]