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15 pages, 13 figures, An integrated approach combining swath bathymetry, an extensive dataset of vibrocores and high‐resolution seismic reflection data was used to assess the origin and evolution of offshore sand ridges on a tideless continental shelf (Gulf of Valencia, western Mediterranean). The sand ridges are located in the mid‐outer shelf at 55–85 m water depth, obliquely oriented to the shoreline. They are 1.5 to 7 m high, with a wavelength between 600 and 1,100 m and a mean height‐to‐wavelength ratio of 0.004. The sand ridges are composed of well‐sorted medium sand and are partially covered by a mud layer, evidencing a moribund stage. They overlie an erosion surface that locally crops out at the seafloor and is interpreted as the Holocene wave‐ravinement surface. In the sediment cores, this surface corresponds to an erosional lag composed of coarse sand and gravel with pebbles. Small topographic irregularities on this surface are interpreted as shoreline‐associated features that may act as the precursor for ridge development. Their preservation within the sand ridges could be related to the hardness of these features. Internally, the sand ridges display high‐angle dipping reflections, indicating ridge migration towards the southeast in the direction of the present‐day sediment transport direction. The presence of interbedded mud layers, associated with these reflections, indicates intermittent episodes of mud deposition when active. The internal architecture of some small ridges also provides new insights into their transition from an active to moribund state, as evidenced by a change in the geometry of the internal units from progradational to aggradational, finally being overlain by onlapping finer deposits over the flanks and in the troughs. The Gulf of Valencia sand ridge field constitutes a valuable potential sand resource of 22 million m3 of well‐sorted medium and coarse sand with limited mud content, which must be preserved as a strategic sand reservoir. © 2020 John Wiley & Sons, Ltd, This research was supported by the projects FORMED (CGL2012-33989) and COSTEM (CTM2009-07806). [...] R. Durán is supported by the Ocean and Littoral Sedimentary Process Consolidated http://mc.manuscriptcentral.com/esp Earth Surface Processes and Landforms For Peer Review Research Group by the Generalitat de Catalunya grant (2017 SGR-863), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

The distribution of benthic ecosystems, dominated by filter-feeding communities, is highly influenced by the seabed geomorphology. However, the spatial variation in settlement of these species is also affected by near-bottom currents and any changes in light, nutrient concentration and food quality often associated with increases of suspended sediment concentrations within the water column. Detailed predictions of the geographic distribution of filter-feeder species and a deeper understanding of the physical processes influencing their distribution patterns is key for effective management and conservation. To date, predictive distribution modelling has been derived essentially from geomorphological parameters, mainly using spatially limited observations. In this study, seabed mapping, oceanographic modelling, hydrographic records and biological observations are integrated to provide high-resolution prediction of filter-feeder habitat distribution within Queen Charlotte Sound/Tōtaranui and Tory Channel/Kura Te Au, South Island of New Zealand. The aim is to evaluate potential suitable habitat areas for filter-feeders to inform where habitat restoration management should focus efforts to recover communities such as the horse mussel (Atrina zelandica) or the green-lipped mussel (Perna canaliculus), both of which have high economic impact in New Zealand. To accomplish this, Maximum Entropy (MaxEnt) predictive modelling was used to produce Habitat Suitability (HS) maps, using geomorphological parameters and seafloor classification information. Final HS maps also incorporated oceanographic and sediment dynamic information, showing that filter-feeder habitat distribution is highly influenced by the hydrodynamics and sedimentary processes apart from the seafloor geomorphology. Filter-feeder communities inhabit quiescent areas, limited by depth, slope and sediment type; and coincide with regions presenting low near-bottom currents and low turbidity levels. Additionally, the obtained results reveal the effects of the coastal settlements and major marine traffic routes, limiting the suitable habitats to areas with less human impact. This study demonstrates that a multidisciplinary approach is crucial to better predict the spatial distribution of benthic communities, which is key to improve benthic habitat restoration and recovery assessments.

Coastline stability is a function of the equilibrium between planform geometry and sediment supply for a static sea level and wave climate. In this chapter, sandy coastline configuration is downscaled to a hierarchy of compartments. Sediment transport and exchange between compartments are explored with respect to wave climate, planform embaymentisation, headlands acting as sand valves for bypassing and the time-varying sediment budget. A case study from south-eastern Australia is provided to demonstrate that centennial-scale sediment budgets are required for assessment of past, present and future coastal evolutions. Big data comprising nearshore and onshore LiDAR coverage are producing opportunities to model coastal stability and sediment budgets in response to changing sea levels and wave climate, using a variety of modelling approaches from simple geometric models to three-dimensional (3D) hydrodynamic models and probabilistic model frameworks.

16 pages, 13 figures, 1 table, Detailed analysis of recently acquired swath bathymetry, together with high-resolution seismic profiles and bottom sediment samples, revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. As many other deep-water sediment waves, these features were previously attributed to gravitational slope failure, related to creep-like deformation, and are here reinterpreted as sediment wave fields extending from 250m depth to the continental rise, at ~850m depth. Geometric parameters were computed from the high-resolution multibeam dataset. Sediment wave lengths range between 500 and 1000m, and maximum wave heights of up to 50m are found on the upper slope, decreasing downslope to minimum values of 2m high. Sediment waves on the lower part of the slope are quasi-stationary vertically accreting, whereas they show an upslope migrating pattern from the mid-slope to the upper part of the continental slope. High-resolution seismic profiles show continuous internal reflectors, with sediment waves merging down-section and sediment wave packages decreasing in thickness downslope. These sediment packages are thicker on the crest of each individual sediment wave and thinner on the downslope flank. 210Pb analyses conducted on sediment cores collected over the sediment wave fields also indicate slightly higher sediment accumulation rates on the wave crests. Sediment wave formation processes have been inferred from contemporary hydrodynamic observations, which reveal the presence of near-inertial internal waves interacting with the Gulf of Valencia continental slope. Internal wave activity is suggested to be the preferential mechanism for the transport and deposition of sediment, and the maintenance of the observed sediment wave fields. © 2015 Elsevier B.V., This work was funded by the project COSTEM (CMT2009-07806) and FORMED (CGL2012-33989). [...] The author M. Ribó is supported by a FPI grant (Ref. BES-2010-029949) fromthe Spanish Ministry of Economy and Competitiveness. P. Masqué acknowledges the financial support through the ICREA Academia award and by a Gledden Visiting Fellowship from the Institute of Advanced Studies, The University of Western Australia

13 pages, 8 figures, 2 tables, Large sediment waves have been observed over the Gulf of Roses (GoR) continental slope (NW Mediterranean), developed between ~200 and ~400 m water depth. Geometric parameters computed from the acquired swath bathymetry revealed mean wave lengths of ~2000 m, and maximum wave heights of ~60 m. Single-channel reflection seismic profiles provided information on the sediment wave internal structure and the Quaternary stratigraphic architecture of the GoR outer shelf and slope. Seven main seismic units could be identified, with continuous development of sediment waves over the outer continental shelf and upper slope, showing differences in wave height and length. The seismic units are differentiated by erosional surfaces that can be followed from the outer shelf down the slope, and which have been correlated with Pleistocene eustatic oscillations. Sediment cores were collected over the sediment wave crests and troughs, and grain size distribution and sediment accumulation rates were analysed. Results show a dominant fraction of fine sediments, allowing classifying the observed bedforms as mud waves. Calculated sediment accumulation rates ranged between 0.08 and 0.18 cm/y, with no clear sedimentation pattern (e.g. differential sediment deposition rates) observed between wave crests and troughs. Nevertheless, the presence of thick surface mixed layers and the increase of the sand fraction in the upper sections of the cores indicate that the surface sediments are affected by bottom trawling activities, since the area is highly impacted by this human activity. The sediment waves observed over the GoR slope are most likely to be formed by bottom currents generated by overflows of dense water originated in the Gulf of Lions shelf, which cascade downslope in an oblique angle with respect the main bathymetric contours. This study offers new insights on the role of dense shelf water cascading processes and associated off-shelf sediment transport reshaping the morphology of the open-slope regions, This work was funded by the Spanish grants FORMED (CGL2012-33989) and ABIDES (CTM2015-65142-R) and by the Generalitat de Catalunya supporting grants 2014 SGR-1642 and 2014 SGR-1356

7 pages, 3 figures, Recently acquired swath bathymetry, high-resolution seismic profiles and bottom sediment samples have revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. Like many other deep-water sediment waves, these features were previously attributed to gravitational slope failure related to creep-like deformation, and have now been reinterpreted as sediment wave fields extending from 250 m depth to the continental rise at ~850 m depth. Sediment wave lengths range between 500 and 1000 m and maximum wave heights of up to 50 m are found on the upper slope, decreasing downslope to a minimum height of 2 m. Seismic profiles showed continuous internal reflectors and several sediment wave packages were differentiated, being thicker on the crest of each wave and thinner on the downslope flank, indicating that these sediment waves are upslope-migrating. The sediment wave formation process was inferred from contemporary hydrodynamic observations, and internal wave activity is suggested to be the most probable mechanism for the sediment transport and deposition and subsequent maintenance of the sediment waves over the Gulf of Valencia continental slope

Special issue The contourite log-book: significance for palaeoceanography, ecosystems and slope instability.-- 15 pages, 10 figures, High-resolution single channel sparker reflection seismic data revealed the presence of large-scale sediment waves nearby DSDP Site 548, located on Goban Spur. They developed in a gentle terraced environment which contrasts with the canyon-incised Celtic margin, and the relatively smooth Porcupine Seabight to the north. Based upon the morphological characteristics of the observed seabed and buried sediment waves, energetic alongslope bottom currents are thought to be the driving mechanism for the sediment wave development. These currents are driven on their turn by an enhanced internal tide regime that could be attributed to the introduction of the Mediterranean Outflow Water. The DSDP Site 548 downhole geophysical data and the seismic stratigraphic analysis allowed the differentiation of three sequences that relate to evolutionary stages since the lower Pliocene. The sequences are bounded by local erosional events, associated with mass wasting events, which seem to occur roughly synchronously to major northern hemisphere glaciations, respectively during the Lower Pleistocene (~ 2.5 to 2.15 Ma), and the Middle Pleistocene (~ 0.45 Ma). The lower sequence (from ~ 4.5 to ~ 2.15 Ma) shows no morphological evidence of bottom-current driven sedimentation. It is however settled over a smooth erosional surface which could indicate the introduction of the Mediterranean Outflow Water. The intermediate sequence is characterised by large-scale sediment waves that have gradually developed in close association with palaeo-seafloor irregularities. It is inferred that the sedimentation resumed with a relative bottom current energy increase. The youngest sequence recorded active sediment wave formation, similar to the previous sequence. Although the Goban Spur sediment waves cannot be regarded as contourite drifts as such, their stratigraphic evolution corresponds to other well-documented contourite depositional systems, influenced by the Mediterranean Outflow Water, This study was carried out within the framework of a Ghent University BOF “Starting Grant”. [...] These research cruises were carried out within the framework of the EC FP6 IP HERMES and EC FP7 IP HERMIONE projects

25 pages, 15 figures, 5 tables, Clinoform depositional features along the Iberian Mediterranean margin are investigated in this study, with the aim of establishing the causes of their varied shapes and other characteristics. We have analyzed the broad-scale margin physiography and seismic stratigraphic patterns based on high-resolution bathymetric data and previously interpreted seismic data. In addition, we have evaluated regional supply conditions and the uplift-subsidence regime of the different shelf sectors. The upper Quaternary record is strongly dominated by shelf-margin regressive wedges affected by the prevailing 100 ka cyclicity. However, the margins exhibit considerable lateral variability, as the result of the balance between the amount of sediment supply and the uplift-subsidence relationship. Three major shelf sectors with distinct morpho-sedimentary features have been defined. The relatively narrow northern shelves (Roses, La Planassa and Barcelona) are supplied by discrete river outlets that collectively constitute a linear source and are mainly affected by tectonic tilting. The wide middle shelves (Ebro Shelf, the Gulf of Valencia, and the Northern Arc) receive the sediment supply from the large Ebro River and other medium rivers. Although the tectonic regime changes laterally (strong subsidence in the north and uplift in the south), shelf growth is maintained by lateral advection of sediments. The southern shelves (the Southern Arc and the northern Alboran Shelf) are very abrupt and narrow because of the uplifting Betic Cordillera, and the torrential fluvial regimes that determine a very efficient sediment by-pass toward the deep basin. Submarine canyons deeply incised in the continental margin constitute a key physiographic feature that may enhance the transport of sediment to the deep sea or individualize shelf sectors with specific sedimentation patterns, as occurs in the Catalan margin, This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness projects CGL2011-30302-C02-02, CGL2015-74216-JIN, CTM2015-65142-R and CTM2017-88237-P

16 pages, 14 figures, 1 table, A sand ridge field with crests oriented NE-SW (52°) located between 55 and 85m water depth on the Valencia continental shelf (Spain) was mapped with multibeam swath bathymetry and characterized with seismic profiling and sediment sampling. Boundary-layer hydrodynamic measurements conducted over a sand ridge at 66m depth show evidence of wave and current sediment resuspension during a major storm event with a three-year recurrence period. From the measured intrawave sediment concentration profiles it is shown that the suspended sediment time evolution is related not only to mean currents but also to the wave field. The near-bottom shear stress generated during storm conditions reached around 1N/m2 and was able to resuspend and transport sandy and muddy sediments for more than 32h. The total suspended sediment transport in a layer of 1m above the bottom was around 4000kg per meter width and directed 160°.It is argued that these sand ridges were developed in a shallow environment and there is no evidence of present-day ridge migration or morphological degradation. It is hypothesized that sediment dynamics affecting sand ridges during storms favors the maintenance of their morphology. © 2015 Elsevier B.V., G. Simarro was supported by the Spanish Government through the Ramón y Cajal program. This research was supported by the projects COSTEM (CTM2009-07806), FORMED (CGL2012-33989) and BUS2 (CGL2011–22964). [...] M. Ribó is supported by a FPI grant (Ref. BES-2010-029949) from the Spanish Ministry of Economy and Competitiveness. R. Durán acknowledges a CSIC JAE-Doc contract co-funded by the FSE

13 pages, 13 figures, Circulation patterns and sediment dynamics were studied over the Gulf of Valencia (GoV) continental slope during spring and winter 2011-2012. Two moorings were deployed at two locations; at 450m depth from February to May 2011, and at 572m depth from October 2011 to February 2012. At both mooring sites, observations were made of currents, temperature and near-bottom turbidity within the lowermost 80m above the seafloor. The temperature measurements allowed distinction of the different water masses and their temporal evolution. The fluctuations of the boundary between the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW) masses were monitored, and several intrusions of Western Mediterranean Intermediate Water (WIW) were observed, generally coinciding with changes in current direction. At both mooring sites, the currents generally maintained low velocities 20cms-1, and few reaching up to 35cm s-1, associated with mesoscale eddies and topographic waves. The current direction was mainly towards the SSE on the first deployment and to the ESE on the second deployment. This second location was affected by a strong bottom offshore veering presumably generated by local topographic effects. Increases in suspended sediment concentrations (SSC) were observed repeatedly throughout the records, reaching values >3mgl-1. However, these SSC variations were uncorrelated with changes in velocity magnitude and direction and/or with temperature oscillations. Results presented in this paper highlight the complex relation between the hydrodynamics and sediment transport over the GoV continental slope, and suggest that other potential sediment resuspension mechanism not linked with current fluctuations, might play a key role in the present-day sedimentary dynamics. Resuspension due to bottom trawling appears to be the most plausible mechanism. © 2014 Elsevier Ltd., This research was supported by the project COSTEM (CTM2009–07806). [...] M. Ribó is supported by a FPI grant (Ref. BES-2010-029949) from the Spanish Ministry of Economy and Competitiveness

10 pages, 8 figures, Commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution. In particular, trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves, but the issue is at present poorly documented with direct observations. This paper analyses changes in water turbidity in a tributary valley of the La Fonera (=Palamós) submarine canyon, whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m. A string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years, 2010–2011. The second year, an ADCP profiled the currents 80 m above the seafloor. The results illustrate that near-bottom water turbidity at the study site is heavily dominated, both in its magnitude and temporal patterns, by trawling-induced sediment resuspension at the fishing ground. Resuspended sediments are channelised along the tributary in the form of sediment gravity flows, being recorded only during working days and working hours of the trawling fleet. These sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom, reaching suspended sediment concentrations up to 236 mg l−1 close to the seafloor (5 m above bottom). A few hours after the end of daily trawling activities, water turbidity progressively decreases but resuspended particles remain in suspension for several hours, developing bottom and intermediate nepheloid layers that reach background levels ∼2 mg l−1 before trawling activities resume. The presence of these nepheloid layers was recorded in a CTD+turbidimeter transect conducted across the fishing ground a few hours after the end of a working day. These results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near-bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development, We are grateful to the crew and officers of B/O García del Cid (CSIC) and “Lluerna” (Generalitat de Catalunya) and to the participants in the HERMIONE-I & II surveys for their help at sea. This work is funded by the HERMIONE project (Grant agreement 226354) under the European Commission's 7th framework Programme. J. Martín was funded through a JAE DOC contract within the Program «Junta para la Ampliación de Estudios», granted by Consejo Superior de Investigaciones Científicas and co-financed by the European Social Fund. We thank the two anonymous reviewers who helped to improve the submitted manuscript through their constructive comments

5 pages, 4 figures, High-resolution multibeam swath-bathymetry and sediment samples were collected across the outer shelf region of the Columbretes Islands (southern Ebro continental shelf, western Mediterranean Sea). Bathymetric data from the submerged part of the Columbretes volcanic system revealed the presence of three main relict sand bodies along the outer shelf, at 80-116. m depth range, above which asymmetric and slightly asymmetric large and very large 2D and 3D subaqueous dunes were observed. These bed features were recognized, mapped and quantified with the aim of evaluating their potential formation mechanisms in relation to the local hydrodynamic and morphologic settings of the area. Dunes range from 150 to 760. m in wavelength and from tens of centimeters to 3. m in height, and are among the longest ever recognized in an outer shelf region. These bedforms are mostly composed of medium-sized sandy sediments, presumably coming from the degraded relict sand bodies on top of which they have developed, mixed with fine fractions from the recent draping holocenic sediments. The orientation of the dunes is SSW, progressively turning W towards the southernmost sector of the area, following the trend of the shelf-edge. Contemporary hydrodynamic measurements at the Ebro continental shelf-edge show that recorded currents are insufficient to form the observed bedforms and that stronger currents are required for sediment mobilization and dune formation. Based on their morphology and orientation, it is proposed that these bedforms are produced by the action of the southward-flowing Liguro-Provençal-Catalan (LPC) geostrophic current. The LPC probably reaches high near-bottom currents during energetic hydrodynamic events through interactions with the seafloor morphology of the study area. Subaqueous dunes are expected to be basically inactive features with respect to present-day processes, although they can be reactivated during high-energy events. The small Δh/λ ratio measured in the dune fields of the Columbretes shelf revealed that the dune heights fall below the values predicted by the Flemming (1988) global equation, as observed in other outer shelf settings also dominated by unidirectional flows. This may suggest a different morphodynamic character of large dunes formed on outer shelves in a micro-tidal regime, This research was supported by the Spanish national Projects CASCADES (Ref. CTM2008-01334-E/MAR) and COSTEM (Ref. CTM2009-07806). Additional support was provided by the Secretaría General de Pesca Marítima (MAPA), which provided ship-time to carry out the BALCOM cruise