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Bottom trawling significantly impacts benthic communities, reducing habitat complexity and biodiversity. The distribution and abundance of key species in the northeastern Gulf of Cádiz, Spanish waters of Atlantic Ocean, such as soft-bottom octocorals and burrowing megafauna, were examined using video observations and Spatial Distribution Models developed with Random Forest. The study was conducted in the Site of Community Importance “Volcanes de fango del golfo de Cádiz" focusing on depths between 300 and 950 metres depth. The effects of environmental variables and bottom trawling on octocoral distribution and abundance were assessed, and management strategies for habitat protection were proposed. Bottom trawling was found to decrease habitat suitability for large octocoral species while the abundance of Norway lobster was positively correlated with certain values of bottom trawling effort. The study suggests that bottom trawling causes significant reduction in octocoral distributions, substrate homogenization, and habitat differentiation. A 200 km area is recommended for a specific bottom trawling regulation to protect soft-bottom octocorals and support the recovery of commercial burrowing megafauna.

The Spanish Institute of Oceanography has realized nineteen oceanographic cruises in order to monitor the geomorphological changes during the submarine eruption of the Tagoro volcano and later evolution. The major geomorphological features were achieved fundamentally by the use of Multibeam EM710 echosounder data. Eruption was characterized by two main phases, the first one alternate stages of vertical growth and denudation by development of basal and southern flank collapses of the main edifice took place; the second phase was characterized by a fissure growth with a NNW-SSE trend. The eruption produced a main volcanic edifice rising from 400 to 88 m water depth. The edifice consists of four attached cones extended and at least fifteen emission vents. This edifice has a quasi-circular base and its final morphology was modulated by the activity of emission vents during the second phase which produced a NNW-SSE elongated summit line. Both vertical growth and instability phases were conditioned by preexistent southwestwards gradient of the seafloor slope and its initial location into a gully on the southern submarine island flank. In the proximal area, morphology is also characterized in by four ridges that correspond to semi-buried residual scars of different collapse phases. On the SW flank an apron of mixed lavas, pyroclastic and debris flows were deposited along more than 5 km length. These deposits were channeled throughout the previous gully and three parts are differentiated: proximal apron from the cone to an intermediate ravine located at 2.5 km away from the base of the main edifice where its maximum thickness occur in an accumulation front, the intermediated ravine and the distal apron fan deposits from the mouth of the ravine to 1800 m depth. The Tagoro volcano was built during a monogenetic eruption dominated by pyroclastic and lava balloon emissions, with lava emissions in the deepest vents. Its evolution alternating constructive and destructive stages a

Remains of molluscs were collected from the seafloor on the north-eastern margin of the Gulf of Cadiz, between 300 and 1000 m water depth, using different sampling methods (e.g. dredging, trawling and box-coring), during several deep-sea expeditions. Samples contained a suite of species which nowadays mostly occur northwards of the English Channel, together with other widespread species. Species now locally extinct in the Gulf of Cadiz and restricted to northern latitudes, which unequivocally indicate a faunal shift, include the gastropods Buccinum undatum, Colus gracilis, Liomesus ovum and Neptunea antiqua, the bivalves Arctica islandica, Chlamys islandica, Modiolus modiolus, Mya truncata and Nuculana pernula and the scaphopod Antalis entalis. These species represent “Boreal Guests” of marked palaeoclimatic significance, some of which are reported for the first time in the Gulf of Cadiz. The boreal species collected were mostly large (>5 cm) whereas smaller boreal species were extremely scarce, probably winnowed away by strong bottom currents. The pteropod Limacina retroversa, at present restricted to water masses northwards of the Iberian Peninsula but widespread in Mediterranean sediments of the last glaciation, was also recorded. Accelerator mass spectrometry (AMS) C dates obtained from nine specimens of molluscs ranged between 26.1 and 14.6 kyr B.P., thus confirming their attribution to a last glacial assemblage. The abundance of these molluscan remains in the present Mediterranean Outflow Water pathway could be explained if this outflow was reduced in intensity or more likely shifted to a deeper level, leaving the upper slope in contact with suitable Atlantic intermediate waters. The findings of Boreal Guests in the Gulf of Cadiz document the continuity of the faunal shift which is well-known in the Mediterranean basin. Species still living in the Gulf of Cadiz and the Alboran Sea nevertheless account for 84.6% of specimens among the larger species.

Contourite depositional systems (CDS) represent the sedimentary records of paleoceanographic circulation and paleoclimatic changes throughout the geological timescale. These records offer expanded but contingent information relative to their adjacent marine gateways, documenting changes in the intensity and the direction of modern-day and paleo-current pathways on multicentennial, millennial and million-year timescales. This study investigates the late Miocene to Quaternary CDSs from the Gulf of Cadiz towards the West Iberian margin after the exit of the past Betic and Rifian corridors and most recent Strait of Gibraltar, the key gateways for the Mediterranean – Atlantic exchange trough time. A summary of the key results is presented as a representative study case for decoding the long- and short-term behaviour of oceanographic processes related to gateways and their associated overflows.

[EN] The formation and development of a small Mediterranean deltaic system are investigated through a primary seismic stratigraphic interpretation of a high-resolution seismic profile network, combined with multiple bathymetric data (including multibeam bathymetric imagery) and collated with shallow sediment cores collected with a vibro-corer device. The submarine delta of the Adra River is divided into a basal patchy seismic unit and five wedge-shaped younger seismic units that are related to the Holocene highstand stabilization. Limited age control indicates that the two uppermost seismic units are very recent, most likely related to a dearth of fluvial fluxes led by channel deviations and by sediment retention. The formation of the three older seismic units is correlated to three humid periods during the middle Holocene, late Holocene and Little Ice Age, under a general context of progressive aridification of southeastern Iberia. The stacking patterns and spatial distribution of individual seismic units document a history of episodic progradation of successive prodeltaic lobes, with a long-term evolution mediated by climatically-induced changes in the river basin and more recent anthropogenic interventions. Overall, the prodeltaic system registers the complete modification of a deltaic system that evolves from a fluvial-dominated delta to recent wave-dominated wedges. In between, the deltaic system exhibits a progressive asymmetric character, due to the instauration of Atlantic waters on the shelf and their subsequent eastward redistribution. The Adra deltaic system is proposed as an outstanding example of a small deltaic system that reacts almost immediately to the complex interaction between natural changes in the system and anthropogenic interventions in the drainage basin., [ES] La formación y la evolución de un pequeño sistema deltaico mediterráneo se ha estudiado mediante la interpretación estratigráfica de una red de perfiles sísmicos de alta resolución, combinada con múltiples datos batimétricos (incluidas datos de batimetria multihaz) y cotejada con testigos de sedimentos someros recogidos con vibro-corer. En el delta submarino del río Adra se diferencia una unidad sísmica basal y cinco unidades sísmicas más jóvenes en forma de cuña que están relacionadas con la estabilización del alto nivel del Holoceno. A partir de las dataciones realizadas se observa que las dos unidades sísmicas superiores son muy recientes, muy probablemente relacionadas con una disminución en los aportes fluviales provocada por las desviaciones del cauce y por la retención de sedimentos. La formación de las tres unidades sísmicas más antiguas se correlaciona con tres periodos húmedos durante el Holoceno medio, el Holoceno tardío y la Pequeña Edad de Hielo, en un contexto general de progresiva aridificación del sureste de Iberia. Los patrones de sedimentación y la distribución espacial de las unidades sísmicas indican una progradación episódica de sucesivos lóbulos prodeltaicos , con una evolución a largo plazo en la cuenca fluvial mediada por cambios climáticos y más recientemente por intervenciones antropogénicass. En conjunto, el sistema prodeltaico registra la modificación de un sistema deltaico que evoluciona en principio como un delta dominado por flujos fluviales hasta cuñas recientes dominadas por el oleaje. Entre medias, el sistema deltaico muestra un carácter asimétrico progresivo, debido a la influencia de las aguas atlánticas en la plataforma y su posterior redistribución hacia el este. El sistema deltaico del río Adra se propone como ejemplo de un pequeño sistema deltaico que reacciona de forma casi inmediata a la compleja interacción entre los cambios naturales del sistema y las intervenciones antropogénicas en la cuenca de drenaje.

Since Tagoro volcano erupted in 2011, several impacts have been associated to the volcano formation process, some of which are still present to date. This chapter is a review of the marine environmental perturbations caused by Tagoro volcano as a new geological structure, but thoroughly onto the partly annihilated benthic and demersal pre-existing biota, and the colonizing dynamics during the recovery process. Shallow recent volcanic activity in the NE Atlantic is uncommon, thus, Tagoro provides a unique opportunity to study, from the very beginning, the evolution of the unusual shallow hydrothermal systems, and the establishment of new marine habitats and associated biota. Distinct habitat types, with different associated deposit products (volcaniclastic aprons, lava balloons, lava ponds, etc.), have been described, and a description of the colonizing biota has been made from the available published works as well as from underwater imagery and benthic dredge samples taken during several field expeditions (Vulcano0313, 1013, 0314 and Vulcana0417). Those habitats included hard (rocky) and mixed (loose) substrate habitats, but also extreme habitats with hydrothermal vents and bacterial mats, accompanied by significant physical and chemical anomalies. Habitat preference by the observed taxa among the volcanic edifice has been explored through nMDS analyses, and a comparative analysis with published data of the typical fauna of the region (La Restinga, Mar de Las Calmas, Marine Reserve, El Hierro Island), permitted to foresee the very first steps and direction of the recovery of the benthic and demersal communities. The impact caused by Tagoro onto the nearest littoral benthic communities, the ichthyofauna and the local fisheries have been described as well. Finally, some recommendations and further steps are given in order to adequately monitor the successional trend and environmental status of the benthic and demersal communities

[EN] The Strait of Gibraltar is a first-order physiographic feature between southern Iberia and northern Africa. It has been excavated over the Arc of Gibraltar in favor of a conjugated ENE-WSW and WNW-ESE fault system that have acted as weakness structures. The Strait was generated by erosive processes of the water masses coming from the Atlantic Ocean in the lower Pliocene, due to the rude and rapid flooding of the Alboran Sea basin. Once the flood stabilized the exchange and interaction of the Atlantic and Mediterranean water masses began as we know it today; the Atlantic water that circulates on the surface of the Strait towards the Alborán Sea, and the Mediterranean water masses that circulate in depth towards the Atlantic Ocean. The acceleration of the Atlantic and Mediterranean water masses in the Strait corridor has favored the development of erosive processes.These processeshave allowed the outcrops of the rocky substratum, the development of sedimentary instabilities and the generation of paleochannels, carbonate crusts and cold-water coral formations during the Pliocene and Quaternary. Likewise, the acceleration of the Mediterranean water masses on their way in and out of the Strait and their interaction with the sea floor have controlled sedimentation both in the Alborán Sea basin and in the Gulf of Cádiz, forming contouritic depositional systems, [ES] El estrecho de Gibraltar es un rasgo fisiográfico de primer orden entre el sur de Iberia y el norte de África. Ha sido excavado sobre el Arco de Gibraltar a favor de un sistema de fallas conjugadas de direcciones ENE-OSO y ONO-ESE que han actuado como estructuras de debilidad. El Estrecho fue generado por procesos erosivos de las masas de agua procedentes del océano Atlántico en el Plioceno inferior, al producirse de forma brusca y rápida la inundación de la cuenca del mar de Alborán. Una vez estabilizada la inundación comenzó el intercambio y la interacción de las masas de agua atlántica y mediterránea tal y como hoy la conocemos: el agua atlántica que circula en la superficie del Estrecho hacia el mar de Alborán, y las masas de agua mediterráneas que transitan en profundidad hacia el océano Atlántico. La aceleración de las masas de agua atlántica y mediterránea en el corredor del Estrecho ha favorecido el desarrollo de procesos erosivos. Estos procesos han permitido los afloramientos del substrato rocoso, el desarrollo de inestabilidades sedimentarias, generación de paleocanales, costras carbonatas y formaciones coralígenas de aguas frías durante el Plioceno y el Cuaternario.Asimismo, la aceleración de las masas de agua mediterráneas en su camino de entrada y salida del Estrecho y su interacción con el suelo marino han controlado la sedimentación tanto en la cuenca del mar de Alborán como en el golfo de Cádiz, formando sistemas deposicionales contorníticos

The invasive seaweed Rugulopteryx okamurae has recently arrived in Europe from the western Pacific. Its explosive spread on coastal areas of the Gulf of Cádiz (GoC), Strait of Gibraltar and Alboran Sea is spoiling native coastal ecosystems and inflicting heavy losses on ecosystem services. We discovered for the first time large amounts (up to 17 g m) of detached R. okamurae thalli on deep-sea bottoms of the GoC that are being dragged from the Strait of Gibraltar shores into the NE Atlantic by the Mediterranean Outflow Water (MOW). Laboratory experiments revealed that collected unattached macroalgae from deep-sea locations were alive and healthy and maintained intact photosynthetic capacity after long dark periods, suggesting a tremendous resilience and invasive potential. Given the rapid transport of healthy thalli by the MOW and massive accumulation of them in the GoC basin, R. okamurae could represent a major threat to NE Atlantic ecosystems, affecting not only coastal but also deep-sea habitats.

[EN] This work presents a compilation of the place names in the Spanish marine subdivisions (North Atlantic, South Atlantic, Estrecho and Alborán, Levantine-Balearic and Canary). By systematically identifying these features across the subdivisions, an extensive bibliographic and database research was conducted to assign appropriate place names to each element. Ten main toponym types have been recognized: geographic, personal, shape description, commemorative, cultural, fisher name, vessels and expeditions, others and unknows. The most common names are geographic locations followed by names of historical personalities. This work evidences the variability of the types depending on the marine subdivisions. This new database is open allowing modifications and new names could be added in the future., [ES] Este trabajo presenta una recopilación de los topónimos en las subdivisiones marinas españolas (Atlántico Norte, Atlántico Sur, Estrecho y Alborán, Levantino-Balear y Canarias). Mediante la identificación sistemática de estas características en las subdivisiones, se llevó a cabo una extensa investigación bibliográfica y de bases de datos para asignar nombres de lugar adecuados a cada elemento. Se han reconocido diez tipos principales de topónimos: geográficos, personales, descripciones de forma, conmemorativos, culturales, nombres de pescadores, nombres de embarcaciones y expediciones, otros y desconocidos. Los nombres más comunes son ubicaciones geográficas, seguidos de nombres de personalidades históricas. Este trabajo evidencia la variabilidad de los tipos según las subdivisiones marinas. Esta nueva base de datos está abierta a modificaciones y nuevos nombres que podrían agregarse en el futuro.

Multibeam bathymetry, sub-bottom parametric profiler, multichannel seismic reflection data and sediment cores were used to detail the nature, morpho-sedimentary and internal structure of five newly discovered submarine mud volcanoes (MVs) in the Moroccan margin of the Gulf of Cadiz. The Henriet and Subvent MVs are located at 300–400 m water depth, while Chueca, Demetrio de Armas and Puerto Real MVs are at 1100–1800 m water depth. Two main types of morphologies are identified: regular cone-shaped edifices (Subvent MV) with a pronounced crater (Henriet MV) in the eastern province; and ridge-attached oval-shaped conical edifices (Chueca, Demetrio de Armas and Puerto Real MVs) in the western province. The overall seismic architecture of these MVs is the result of successive events of mud extrusion and outbuilding alternating with periods of dormancy. The Henriet and Subvent MV system is composed of stacked bicones and intrusive complexes, which penetrated upper Miocene-Quaternary sedimentary units rooted in the Gulf of Cadiz wedge. Major phases of mud extrusion and outbuilding took place since the Late Pliocene with re-activation during mid-Pleistocene. Mud breccias interbedded with hemipelagic/contourite sediments were collected for all MVs. Cores attest to recent periods of mud outflows lasting from the Late Pleistocene (180 ky) whereas the end of MV extrusion could date back to historic times (the last 0.6 ky), giving rise to the onset of a new quiescent activity. The most active MV points out to the Subvent MV. These new MVs are formed in response to the extensional and compressional system within the Gibraltar Arc. In the eastern side, MVs are related to extensional faults forming deep sedimentary basins and forcing overpressured fluids to migrate upwards coeval with thick contourite deposits. On the western side, MVs are related to compressional ridges at the front of fold-thrust systems which act, as pathways to deep-seated fluids to ascent to seafloor.

Although the effects of tidal dynamics have been studied in shallow marine environments and morphologically restricted straits, the impact of these processes on deep-water marine environments remains to be studied in depth. This study highlights the influence of tides on the seafloor morphology of the eastern Gulf of Cádiz, near the exit of the Strait of Gibraltar. Two moorings, one with an Acoustic Doppler current profiler (ACDP) and another one with a thermistor chain, and local and regional profiles of salinity, temperature, and ADCP reveal the water mass distribution in the study area and associated oceanographic processes. The intermediate water masses flowing along the continental slope are the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Water (MOW), bound by an interface located regionally at depths greater than 300 m, but identified locally at much shallower depths (up to 150 m) in the studied upper slope. The hydrodynamics of the area are governed by barotropic tidal currents, the MOW upper core, and the internal tides, which act at different time and spatial scales shaping the local terraced sea-floor morphology and determining the dominant sedimentary processes. The obtained results allow a better understanding of how secondary oceanographic processes are modulating the water mass circulation in this particular hot spot and their importance in explaining the formation and evolution of morphological depositional and erosional features.

Narrow continental shelves such as those surrounding the Mediterranean basin are usually dominated by active depositional features such as major prodeltaic wedges located off major rivers (e.g. the Gulf of Lions, the northern Adriatic Sea), or by infralittoral wedges in settings where fluvial supply is more limited and hydrodynamic regimes are more energetic. However, the knowledge of the geomorphological patterns of undernourished shelves remains much less documented. In this contribution, we aim to characterize the submarine geomorphology and the sub-surface sedimentary bodies of a shelf sector located west of the Guadalfeo River, a major regional source in the northern margin of the Alboran Sea, where fluvial supply is provided by small seasonal rivers. To reach those goals, we analysed a data base comprising multibeam bathymetric and backscatter data, seafloor video images and Parasound acoustic sections. The studied shelf exhibits a distinctive zonation, where three major domains could be characterised. In the inner shelf, the most significant depositional bodies are composed by wedge-shaped deposits with limited lateral extent. Over the surface, several geomorphic indicators reveal the occurrence of high-energy processes in relation to the seasonal inputs of the Verde and Seco rivers. Recent to modern sedimentation seems to be much reduced distally. The middle shelf is marked by two main breaks of slopes, the surficial expression of highly reflective depositional bodies, likely marking the location of ancient paleo-shorelines and extensive development of paleo-coastal plains. The outer shelf is a flat domain covered by several elongated sedimentary bodies, which are disposed oblique to the middle shelf paleo-shorelines. Below those bodies, sub-surface architectures exhibit several unconformity-bounded regressive wedges. We discuss the shelf zonation observed in the study area considering the confinement of recent infralittoral and prodeltaic wedges to the inne

This paper explains the current seafloor morphology and processes that affect the formation and evolution of three mud volcanoes and one mud volcano/mud diapir complex in the deepest sector of the Spanish margin of the Gulf of Cádiz. The present study provides novel results and interpretations based on an extensive multidisciplinary data set. New high resolution bathymetric and backscatter data from multibeam echosounders enabled a detailed geomorphological analysis aimed at identifying diverse seafloor features in the different edifices studied and their adjacent bottoms. These features are mainly related to fluid escape (e.g., mud volcanoes, mud flows and depressions), gravitational (e.g., slide deposits and scars), and tectonic (e.g., faults and uplifted antiforms) processes. Very high-resolution parametric profiles and single channel seismic reflection profiles were interpreted for further analysis of the internal structures, demonstrating their important interplay with diapiric processes. Box-corer and gravity-corer have been used to identify different sediment types that have been correlated with backscatter values. The dominant benthic species associated with fluid venting and also with different types of substrates (hard and soft) were characterized using submarine images obtained with an underwater camera deep-towed sled. The benthic species observed were contrasted, and added to those collected with beam trawl and box-corer for characterisation of the benthic and demersal communities. Different geological and biological indicators have been used as proxies of the interaction of these features with the geological processes (such as fluid-escape-related, gravitational, or structural) to characterise the environmental conditions that determine the geomorphology, substrates, habitats and their associated biota. Multivariate analyses combining faunistic and environmental data resulted in the presence of 3 main faunistic assemblages linked to different levels of

El Cañón de Algeciras se localiza en el eje de una bahía en forma de herradura (Bahía de Algeciras),está excavado sobre un sustrato rocoso (Unidades del Flysch del Campo de Gibraltar) y afectado por la dinámica de intercambio de masas de agua en el Estrecho de Gibraltar.Por sus características geomorfológicas y el contexto oceanográfico en el que se encuentra, este cañón es un excelente ejemplo para comprender mejor los procesos sedimentarios mixtos. Esta zona se ha estudiado en base a un mosaico de batimetría multihaz (EM710) y perfiles del subsuelo con sonda paramétrica(TOPASPS18). El cañón discurre a lo largo de 19 km de longitud en dirección NNO-SSE,estando constituido por segmentos menores de dirección NNE-SSO, ENE-WSWy NNO-SSE, su anchura varía de 1,2 a 3,6 km y los flancos tienen desniveles comprendidos entre90y560 m. En las paredes del cañón se han caracterizado elementos morfosedimentarios gravitacionales y contorníticos. Los gravitacionales comprenden deslizamientos y cárcavas en las paredes del cañón, así como un talweg turbidítico; los contorníticos incluyen parches de sedimentos adosados en sus paredes que localmente llegan a extenderse hasta el talweg, así como escarpes y superficies erosivas.La variabilidad espacial de estos elementos indica la coexistencia de procesos gravitacionales y contorníticos en los sectores proximal (cabecera, 60-390 m de profundidad) y medio(390-550 de profundidad), mientras que en el sector distal(550-890 de profundidad)se observa únicamente la acción de procesos gravitacionales. Asimismo, indican una sedimentación contornítica preferencial tanto en el flanco oriental del sector proximal como en el flanco occidental en el sector medio.Estos datos sugieren que el factor de control principal de los procesos mixtos es la interacción entre la propia morfología del cañón y la dinámica de avance y retroceso a lo largo del mismo de las masas de agua Atlántica superficial y la Mediterránea profunda, en función de la marea

El análisis morfotectónico del sector central del Promontorio Balear, entre las islas de Ibiza y Mallorca, mediante batimetría multihaz y perfiles sísmicos de muy alta resolución ha permitido diferenciar varios rasgos morfológicos relacionados con la tectónica a dos escalas. Los elementos de gran escala, de dirección NE-SO, son: i) el escarpe Émile Baudot; ii) el monte submarino Émile Baudot, y iii) la alineación de montes submarinos Ausiàs March y Ses Olives. Los elementos de pequeña escala son: i) dos elevaciones longitudinales (ENE-OSO); ii) escarpes rectilíneos (NO-SE a NE-SO); iii) depresiones tectónicas (NNE SSO a NE-SO); y iv) alineaciones rectilíneas de pockmarks (NO-SE a NNE-SSO). Los elementos de mayor tamaño responden a la configuración estructural neógeno-cuaternaria. El escarpe Émile Baudot limita el Promontorio Balear y la cuenca oceánica del Mediterráneo Occidental. La alineación de montes submarinos Ausiàs March y Ses Olives está generada por una fase extensional, y el monte submarino Émile Baudot forma parte de una alineación volcánica NO-SE asociada a la Zona de Fractura de Ibiza. Los elementos de pequeña escala están relacionados con estructuras tectónicas activas que deforman las unidades sedimentarias del Cuaternario y el fondo marino. Las elevaciones longitudinales están generadas por pliegues anticlinales, mientras que el resto de estructuras están asociadas a la actividad de fallas normales de buzamiento alto., A morphotectonic analysis has been carried out between the islands of Ibiza and Majorca in the central sector of the Balearic Promontory using multibeam bathymetry and very high-resolution seismic profiles. Several morphological features related to tectonics at two different scales have been differentiated. The large-scale features have a NE-SW direction, they are: i) the Émile Baudot Escarpment; ii) the Émile Baudot seamount, and iii) the Ausiàs March and Ses Olives seamounts alignment. The differentiated small-scale elements are i) two longitudinal elevations (ENE-WSW); ii) rectilinear scarps (NW-SE to NE-SW); iii) tectonic depressions limited by one or two scarps (NNE-SSW to NE-SW), and iv) rectilinear pockmarks alignments (NW-SE to NNE-SSW). The largest elements respond to the Neogene-Quaternary structural configuration. The Émile Baudot escarpment is the limit between the Balearic Promontory and the Western Mediterranean oceanic basin. The alignment of the Ausiàs March and Ses Olives seamounts respond to the last extensional phase, and the Émile Baudot seamount forms part of a NW-SE volcanic alignment that could be associated with the Ibiza Fracture Zone. The smaller elements are related to active tectonic structures that deform Quaternary sedimentary units and the seafloor. The longitudinal elevations correspond to anticlinal folds, while the rest of the structures are associated to the activity of near vertical normal faults.

The dense and deep water flow that leaves the Mediterranean Sea to the Atlantic flows through the upper and middle slope of the Gulf of Cádiz as a powerful bottom stream that model sand interacts with bathymetry. The detailed analysis of underwater images,obtained with a photogrammetric sled in the central area of the upper and middle slope of the Gulf of Cádiz, together with multibeam bathymetry and oceanographic and sediment types data, has allowed conducting a detailed study of the seafloor microtopography and the predominant oceanographic dynamics in the study area. Different fine-scale spatial bedforms were identified, such as ripples, dunes, burrows, mounds, obstacle marks, rock bottoms, and low-roughness bottoms using underwater images. Besides, a geostatistical study of the different video transects studied was carried out and allowed us to differentiate three types of bottoms depending on the processes that affect their microtopography.

The Gulf of Cadiz and the Alboran Sea are characterized by tectonic activity due to oblique convergence at the boundary between the Eurasian and Nubian plates. This activity has favored a variety of tsunamigenic sources: basically, seismogenic faults and submarine landslides. The main tsunamigenic faults in the Gulf of Cadiz would comprise the thrust systems of Gorringe Ridge, Marquês de Pombal, São Vicente Canyon, and Horseshoe faults with a high susceptibility; meanwhile in the Alboran Sea would be the thrust system of the northern Alboran Ridge with high susceptibility, and the thrust systems of north Xauen and Adra margin, the transpressive segment of Al Idrissi fault, and the Yusuf-Habibas and Averroes faults, with moderate to high susceptibility. The areas with the greatest potential to generate tsunamigenic submarine landslides are in the Gulf of Cadiz, the São Vicente Canyon, Hirondelle Seamount, and Gorringe Ridge; and in the Alboran Sea are the southern and northern flanks of Alboran Ridge. Both sources are likely to generate destructive tsunamis in the Gulf of Cadiz, given its history of bigger earthquakes (>7 Mw) and larger landslides. To fully assess tsunamigenic sources, further work needs to be performed. In the case of seismogenic faults, research focus on geometry, offsets, timing, paleoearthquakes, and recurrence, and in landslides on early post-failure evolution, age, events, and recurrence. In situ measurements, paleotsunami records, and long-term monitoring, in addition to major modeling developments, will be also necessary

The seafloor of the Alboran Sea reflects its complex tectonic, sedimentary, and oceanography dynamics as a consequence of the geological context, involving interaction between the Eurasian and African plates, and oceanographic context, as it is where the Atlantic and Mediterranean waters meet. Their physiography has a semi-enclosed configuration characterized by two margins (the Spanish Iberian and North Africa—mostly Moroccan margins) enclosing deep basins. Tectonic activity is mainly attested by folds and faults that predominantly affect the central and eastern seafloor sectors, as well as numerous seamounts and fluid-flow features (pockmarks, mud volcanoes, and diapirs) that dot the seafloor. The sedimentary and oceanographic processes allow us to distinctly define two principal environments in the Alboran Sea: the shallow proximal margin (continental shelf); and the deep distal margin (continental slope and base of the slope) with the adjacent sub-basins. The shelf mostly comprises prodeltaic and infralittoral prograding wedges, with local bedform fields, submarine valleys, and wave-cut terraces. Coastal and fluvio-marine sedimentary processes, acting since the last glacial period, are responsible for these features. The deep marine environment is characterised by the ubiquity of contourites, whose continuity is interrupted by turbidite systems, canyons, and landslides. The alongslope action of the Mediterranean waters and their interfaces with the Atlantic water has been the main process governing transport, seafloor reworking, and sedimentation of contourites. Mass-movement processes are responsible for the formation of: (1) turbidite systems—turbidity flows and mass flows were dominant during the last glacial sea-level lowstand, evolving to dilute gravity flows during present interglacial high stand; and (2) landslides—the main triggering factors comprising over-steepening, seismicity, under consolidation due to overpressure by interstitial fluids, stratigrap

In this work, we integrate five case studies harboring vulnerable deep-sea benthic habitats in different geological settings from mid latitude NE Atlantic Ocean (24–42° N). Data and images of specific deep-sea habitats were acquired with Remoted Operated Vehicle (ROV) sensors (temperature, salinity, potential density, O2, CO2, and CH4). Besides documenting some key vulnerable deep-sea habitats, this study shows that the distribution of some deep-sea coral aggregations (including scleractinians, gorgonians, and antipatharians), deep-sea sponge aggregations and other deep-sea habitats are influenced by water masses’ properties. Our data support that the distribution of scleractinian reefs and aggregations of other deep-sea corals, from subtropical to north Atlantic could be dependent of the latitudinal extents of the Antarctic Intermediate Waters (AAIW) and the Mediterranean Outflow Waters (MOW). Otherwise, the distribution of some vulnerable deep-sea habitats is influenced, at the local scale, by active hydrocarbon seeps (Gulf of Cádiz) and hydrothermal vents (El Hierro, Canary Island). The co-occurrence of deep-sea corals and chemosynthesis-based communities has been identified in methane seeps of the Gulf of Cádiz. Extensive beds of living deep-sea mussels (Bathymodiolus mauritanicus) and other chemosymbiotic bivalves occur closely to deep-sea coral aggregations (e.g., gorgonians, black corals) that colonize methane-derived authigenic carbonates.

Extensive beds of the deep-sea mussel Bathymodiolus mauritanicus (currently also known as Gigantidas mauritanicus) linked to active cold seeps related to fissure-like activity on Al Gacel mud volcano, Gulf of Cádiz, were filmed and sampled for the first time during the oceanographic expedition SUBVENT-2 aboard R/V Sarmiento de Gamboa. Al Gacel mud volcano is one of up to 80 fluid venting submarine structures (mud volcanoes and mud volcano/diapir complexes) identified in the Gulf of Cádiz as result of explosive venting of hydrocarbon-enriched fluids sourced from deep seated reservoirs. This mud volcano is a cone-shaped edifice, 107 m high, 944 m in diameter constituted by mud breccias and, partially covered by pavements of seep carbonates. Extensive beds of this deep-sea mussel were detected at the northern flank at 810–815 m water depth associated with bacterial mats around intermittent buoyant vertical bubble methane plumes. High methane concentrations were measured in the water column above living mussel beds. Other chemosymbiotic species (Siboglinum sp., Solemya elarraichensis, Isorropodon sp., Thyasira vulcolutre and Lucinoma asapheus) were also found in different parts of Al Gacel mud volcano. Al Gacel mud volcano may currently represent one of the most active mud volcanoes in the Gulf of Cádiz, delivering significant amounts of thermogenic hydrocarbon fluids which contribute to foster the extensive chemosynthesis-based communities detected. This finding is of paramount importance for linking extremophile bivalve populations along the North Atlantic, including cold seeps of the Gulf of México, hydrothermal vents of the Mid-Atlantic Ridge and now, detailed documented at the Gulf of Cádiz.

[EN] The Gulf of Cadiz upper slope in the area close to the Strait of Gibraltar is covered by a plastered drift deposited by the activity of the Mediterranean Outflow Water (MOW) and the North Atlantic Central Water (NACW). A number of small gullies are incised across the plastered drift, due to the interaction between gravitational and contouritic processes. The study of parametric sounder profiles and sedimentological analyses of nine sediment cores obtained from the axes of two gullies and from the undisturbed upper slope, giving a Holocene age frame, has allowed analyzing the recent sedimentary processes and their spatial and temporal variability. The upper slope shows a general increase in grain size towards the NW, suggesting bottom current intensification and/or the occurrence of gravity flows from the continental shelf and shelf-edge. The two studied upper slope gullies display significant differences in their recent activity and dominant processes. The one located to the SE seems to have been inactive since about 5.9 ka, and it has been draped by contouritic deposits. In contrast, the gully located to the NW has been a sediment transport conduit for the entire time span recorded in the sediment cores, [ES] El talud superior del margen Ibérico del Golfo de Cádiz en las proximidades del Estrecho de Gibraltar está ocupado por un depósito contornítico adosado resultado de la circulación del Agua Mediterránea de Salida (Mediterranean Outflow Water, MOW) y de la Masa de Agua Central Noratlántica (North Atlantic Central Water, NACW). En él se encajan pequeños valles submarinos (gullies) debido a la interacción entre los procesos gravitacionales y contorníticos. Mediante el estudio de perfiles de sonda paramétrica y el análisis sedimentológico de nueve testigos obtenidos en el área del talud superior no afectada por gullies y en los ejes de dos gullies, cuya datación corresponde al Holoceno, este estudio analiza los procesos sedimentarios recientes y su variabilidad espacial y temporal. El talud superior muestra un incremento general del tamaño de grano hacia el NO, indicativo de intensificación de las corrientes y/o el aporte sedimentario de origen gravitacional desde la plataforma continental y borde de plataforma. Los dos gullies estudiados muestran una gran variabilidad en los procesos predominantes. El gully más meridional, dominado actualmente por la sedimentación contornítica, parece haber sido inactivo desde unos 5.9 ka. En cambio, el gully localizado más al NW ha canalizado flujos gravitacionales durante todo el intervalo registrado por los testigos

The seafloor of the Alboran Sea reflects its complex tectonic, sedimentary, and oceanography dynamics as a consequence of the geological context, involving interaction between the Eurasian and African plates, and oceanographic context, as it is where the Atlantic and Mediterranean waters meet. Their physiography has a semi-enclosed configuration characterized by two margins (the Spanish Iberian and North Africa—mostly Moroccan margins) enclosing deep basins. Tectonic activity is mainly attested by folds and faults that predominantly affect the central and eastern seafloor sectors, as well as numerous seamounts and fluid-flow features (pockmarks, mud volcanoes, and diapirs) that dot the seafloor. The sedimentary and oceanographic processes allow us to distinctly define two principal environments in the Alboran Sea: the shallow proximal margin (continental shelf); and the deep distal margin (continental slope and base of the slope) with the adjacent sub-basins. The shelf mostly comprises prodeltaic and infralittoral prograding wedges, with local bedform fields, submarine valleys, and wave-cut terraces. Coastal and fluvio-marine sedimentary processes, acting since the last glacial period, are responsible for these features. The deep marine environment is characterised by the ubiquity of contourites, whose continuity is interrupted by turbidite systems, canyons, and landslides. The alongslope action of the Mediterranean waters and their interfaces with the Atlantic water has been the main process governing transport, seafloor reworking, and sedimentation of contourites. Mass-movement processes are responsible for the formation of: (1) turbidite systems—turbidity flows and mass flows were dominant during the last glacial sea-level lowstand, evolving to dilute gravity flows during present interglacial high stand; and (2) landslides—the main triggering factors comprising over-steepening, seismicity, under consolidation due to overpressure by interstitial fluids, stratigrap