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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–2) 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. [ABSTRACT FROM AUTHOR]

Different datasets have been analyzed to identify the origin of the temperature and salinity seasonal and interannual fluctuations in the surface layer of the eastern North Atlantic Ocean, close to the Gulf of Cadiz. The analysis was motivated by the surprising short-term salinity trend recorded by a monitoring station deployed in the Atlantic layer of the Strait of Gibraltar between years 2003 and 2007, which has been described and investigated by Millot (2007. Geophys. Res. Lett. 34, L21609. doi:10.1029/2007GL031179.). Temperature and salinity display similar annual cycles whose maxima occur by the end of the year, the former leading the latter by one month approximately. Despite their similarities, their origin is not the same. More than 80% of the variability of the temperature seasonal cycle is accounted for by the annual cycle of surface heat flux, while advective fluxes are secondary. This is not true for salinity, which both seasonal and interannual fluctuations are shaped by the advection and the evaporative annual cycle jointly. For the advection contribution, the identified external agent is the wind stress that drives the upwelling season in the eastern mid-latitude boundary of the North Atlantic. Vertical advection of salinity associated with the Ekman pumping and horizontal advection caused by the upwelling jet and the fluctuations of the North Atlantic Subtropical Gyre are behind the local advective changes. The strengthening (weakening) of the seasonal upwelling in summer (winter) decreased (increased) the local salinity in the Gulf of Cadiz, giving rise to the observed cycle in the data recorded at Gibraltar. Short term trends in the wind-inducing upwelling off the Iberian Peninsula during the above mentioned period triggered concomitant changes of the salinity in the waters that fed the inflow and produced the short–term trend observed in the Strait of Gibraltar. [ABSTRACT FROM AUTHOR]

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 km2 area is recommended for a specific bottom trawling regulation to protect soft-bottom octocorals and support the recovery of commercial burrowing megafauna. • Soft-bottom octocorals and Nephrops norvegicus distributions were examined using video and Spatial Distribution Models. • Bottom trawling was found to decrease habitat suitability for large octocoral species. • N. norvegicus exhibit high densities in mud and trawling effort apparently does not significantly impact their density. • N. norvegicus abundance predictions was positively correlated with certain values of fishing effort. • A 200 km2 area is recommended for a specific bottom trawling regulation to protect soft-bottom octocorals. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) is a major component of the organic matter pool, playing a key role in the global ocean functioning. However, studies on DOM in waters of many ocean regions, such as the Gulf of Cadiz (GoC), are poorly known. Advanced aquatic sensors enable autonomous for long-term deployments in situ collection of high frequency DOM data using fluorescent dissolved organic matter (FDOM) as a proxy. The present study evaluates the relevance of FDOM, the estuarine influence and the environmental factors that determine its spatial distribution in the GoC. Our results suggest that the GoC water mass, under the estuarine influence of three main rivers, is receiving large amounts of DOM transported mainly by Guadalquivir and Guadiana rivers and much less from Tinto-Odiel. Salinity is the main factor explaining the FDOM variability within the Guadalquivir and Guadiana rivers and in the inner shelf of the GoC. In the outer shelf of the GoC, plankton-produced DOM could explain the persistent spatial pattern of FDOM, playing an important role in the dynamics of FDOM from the North area of the GoC through the persistent low-salinity Eastern North Atlantic Central Water. The oceanographic dynamics and the spatial pattern of FDOM concentration in the continental shelf of the GoC suggest a net transport of FDOM through the GCC (Gulf of Cadiz Current) to the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

The Mediterranean Water leaves the western end of the Strait of Gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope. The salinity of the onset Mediterranean Outflow Water (MOW) is so high that leads to water much denser (initially in excess of 1.5 kg m −3 ) than the overlying central waters. During much of its initial descent, the MOW retains large salinity anomalies – causing density anomalies that induce its gravity current character – and relatively high westward speeds – causing a substantial Coriolis force over long portions of its course. We use hydrographic data from six cruises (a total of 1176 stations) plus velocity data from two cruises, together with high-resolution bathymetric data, to track the preferential MOW pathways from the Strait of Gibraltar into the western Gulf of Cadiz and to examine the relation of these pathways to the bottom topography. A methodology for tributary systems in drainage basins, modified to account for the Coriolis force, emphasizes the good agreement between the observed trajectories and those expected from a topographically-constrained flow. Both contour avenues and cross-slope channels are important and have complementary roles steering the MOW along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western Gulf of Cadiz. Our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern MOW. Furthermore, they support the hypothesis that, as a result of the high erosive power of the bottom flow and changes in bottom-water speed, the MOW pathways and mixing rates have changed in the geological past. [ABSTRACT FROM AUTHOR]

Our understanding of bottom-currents and associated oceanographic processes (e.g., overflows, barotropic tidal currents) including intermittent processes (e.g., vertical eddies, deep sea storms, horizontal vortices, internal waves and tsunamis) is rapidly evolving. Many deep-water processes remain poorly understood due to limited direct observations, but can generate significant depositional and erosional features on both short and long term time scales. This paper represents a review work, which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the Iberian continental margins. This review explores the implications of the studied processes, given their secondary role relative to other factors such as mass-transport and turbiditic processes, and highlights three major results: a) contourite depositional and erosional features are ubiquitous along the margins, indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation; b) the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient, including the contourite terraces development; and c) contourites deposits exhibit greater variation than the established facies model suggests. Therefore, a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development. An integrated interpretation of these oceanographic processes requires an understanding of contourites, seafloor features, their spatial and temporal evolution, and the near-bottom flows that form them. This approach will synthesize oceanographic data, seafloor morphology, sediments and seismic images to improve our knowledge of permanent and intermittent processes around Iberia, and evaluate their conceptual and regional role in the margin's sedimentary evolution. Given their complexes, three-dimensional and temporally-variable nature, integration of these processes into sedimentary, oceanographic and climatological frameworks will require a multidisciplinary approach that includes Geology, Physical oceanography, Paleoceanography and Benthic Biology. [ABSTRACT FROM AUTHOR]

The seabed morphology, type of sediments, and dominant benthic species on eleven mud volcanoes and diapirs located on the northern sector of the Gulf of Cádiz continental slope have been studied. The morphological characteristics were grouped as: (i) fluid-escape-related features, (ii) bottom current features, (iii) mass movement features, (iv) tectonic features and (v) biogenic-related features. The dominant benthic species associated with fluid escape, hard substrates or soft bottoms, have also been mapped. A bottom current velocity analysis allowed, the morphological features to be correlated with the benthic habitats and the different sedimentary and oceanographic characteristics. The major factors controlling these features and the benthic habitats are mud flows and fluid-escape-related processes, as well as the interaction of deep water masses with the seafloor topography. Mud volcano eruptions give rise to mud flows and/or aqueous fluid seepage. These processes sustain chemosynthesis-based communities, closely associated with fluid seepage. Large depressions in the nearby area are influenced by collapse-related phenomena, where active fluid escape and the erosive effect of bottom currents have been identified. When the extrusion activity of the mud volcano is low and the seepage is diffuse, authigenic carbonates form within the edifice sediments. The bottom current sweeps the seafloor from the SE to the NW. When the velocity is moderate, sedimentary contourite processes take place on both sides of the edifices. At high velocities, the authigenic carbonates may be exhumed and colonised by species associated with hard substrates. Small carbonate mounds are found at the summits of some volcanoes and diapirs. Living corals have been found on the tops of the shallowest mud volcanoes, revealing different oceanographic conditions and strong bottom currents that favour the availability of nutrients and organic particles. The edifices affected by very high current velocities are located in the channels where erosive processes dominate. [ABSTRACT FROM AUTHOR]

The Iberian margin in the Gulf of Cádiz hosts a fluid venting area embedded into a contourite depositional drift and is a natural laboratory to study how multiple interacting processes shape the seafloor. A high-resolution morpho-sedimentary analysis, based on geophysical data, sediment samples and submarine imagery, has been carried out; the onset and evolution of the main geoforms are discussed; and the influence of geological, oceanographic and biogenic processes conditioning substrate types and benthic community distribution are evaluated. The interplay of geological (e.g., salt and shale diapirism, mud volcanism), oceanographic (e.g., water mass circulation, secondary circulation, vertical eddies, internal waves) and biogenic (e.g., methane derived authigenic carbonates formation, coral mound aggradations) processes drive the formation of a large variety of geoforms including, among others, contourite drifts, channels, diapiric ridges, mud volcanoes, pockmarks, and coral mounds. At a smaller scale, the interaction between massive and fluid extrusive, biogenic, and bottom current-related processes (both depositional and erosive) determines the distribution of substrate types and benthic communities, which have been classified as belonging to different biotopes. • A number of geoforms have been mapped and their substrates and fauna described over the Iberian margin of the Gulf of Cádiz. • The onset of the geoforms depends on the interaction of a hierarchy of geological, oceanographic, and biological processes. • Massive and fluid extrusive, biogenic, and bottom current-related processes determine the distribution of biotopes. • Variable Mediterranean Outflow Water intensity reflects substrate types, related to the benthic community that host. • Several coral mounds have been mapped for the first time in the Cádiz contourite depositional systems. • Coral mound construction could be favored by alternating phases of gas migration. [ABSTRACT FROM AUTHOR]

The Gulf of Cádiz represents an area of extensive seepage of the south-western Iberian Peninsula that is located between two continents and basins, where a high geomorphologic, sedimentary and environmental complexity occurs. In the present study, epibenthic communities were investigated in a mud volcano field containing four mud volcanoes (Gazul, Anastasya, Pipoca and Tarsis), one diapir/mud volcano complex (Chica) and several diapirs that are all located in the upper and middle slope of the Spanish margin of the Gulf of Cádiz (300–700 m depth). Faunistic samples were collected in 2010 and 2011 using a beam-trawl in different sectors of the mud volcano field, including fluid venting submarine structures and their adjacent seabeds. Environmental variables from the sediment and water column as well as the commercial bottom trawling activity were also measured in the same sampled areas for studying relationships with the fauna. A total of 325 taxa were found in the samples, including sponges, molluscs, cnidarians and decapods the most diverse groups. The epibenthic communities displayed differences between sectors that were related to depth, sediment features, characteristics of the water masses and the trawling activity. Six different assemblages were found including deep-sea sponge aggregations and cold-water coral banks in Gazul, echinoid and solitary coral aggregations in Gazul, sea-pen communities that were sometimes intermixed with sponge and gorgonian aggregations in Tarsis, Chica and Pipoca, and low density sea-pen communities with components of chemosynthesis-based communities in Anastasya. Species richness was higher in Gazul, Pipoca and Chica due to the presence of complex habitats (e.g. cold-water coral banks, sponge aggregations) and low in Anastasya due to the scarce epifauna, high trawling activity and low near-bottom current speed. Typical cold seep chemosymbiotic bivalves of the Gulf of Cádiz were not detected in beam-trawl samples due to their infaunal habit. The studied mud volcano field was declared a Site of Community Importance due to the presence of habitats and species with a conservation status, but several commercial species are exploited by bottom trawling. Therefore, a sustainable management of this mud volcano field is still needed according to current EU directives for combining fisheries and habitat conservation (Habitats Directive of the European Union, Directive 1992/43/EEC; Marine Strategy Framework, Directive 2008/56/EC). • A high number of taxa was detected in the mud volcano field of the northern Gulf of Cádiz. • Six epibenthic assemblages occur in different sectors and zones with different Mediterranean Outflow Water influence. • Epibenthic communities displayed relationships with depth, sediment features, water masses characteristics and trawling. • The presence of several vulnerable habitats (e.g. cold-water coral banks), may imply trawling restrictions in some sectors. [ABSTRACT FROM AUTHOR]