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We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]

The acoustic properties of seafloor sediments on continental slopes play a crucial role in underwater acoustic propagation, communication, and detection. To investigate the acoustic characteristics and spatial distribution patterns of sediments on the continental slope, a geoacoustic experiment was conducted in the northwestern South China Sea. The experiment covered two sections: one crossing the shelf and slope in the downslope direction, and the other near the shelf break in the along-slope direction. In situ techniques, sediment sampling, and laboratory measurements were used to acquire data on sediment acoustic properties (such as sound speed and attenuation) and physical properties (including particle composition, density, porosity, and mean grain size). The experimental findings revealed several key points: (1) Acoustic properties of shallow water coarse-grained sediments and deep-sea sediments were higher when measured in the laboratory compared to in situ measurements. (2) Relationships between measured attenuation and physical properties, as well as between sound speed and mean grain size, showed deviations from previous empirical equations. (3) Sediment acoustic and physical properties exhibited significant variations in the downslope direction, while showing gradual variations in the along-slope direction. These variations can be attributed to sedimentary environmental factors such as material sources, hydrodynamic conditions, and water depth. [ABSTRACT FROM AUTHOR]

This work presents the results of long-term deep-water observations carried out in the southwestern Adriatic margin. Hydrodynamics and thermohaline measurements were carried out in the last 100 m of the water column using two long-term moorings placed at two different locations along the western sector of the Adriatic continental margin (open slope vs. submarine canyon). The observations, carried out over a period of almost 10 years, made it possible to define the intra- and interannual deep-water dynamics, which are mainly influenced by the passage of cold, dense water. The hydrodynamic field is influenced by seasonal behavior and varies from year to year, with no clear temporal trend or periodicity. Thermohaline properties follow hydrodynamics but also show a climatological trend toward higher temperatures and salinity. The combination and variability of preconditioning factors explains the interannual variability in dense water passage at the mooring sites triggering the formation of dense water in the northern Adriatic. The impulsive nature of the dense water flow, which is difficult to capture with sporadic oceanographic surveys, and its linkage with the large-scale atmospheric circulation make continuous monitoring essential to answer open questions about cascading processes and deep-water dynamics under a global change scenario. [ABSTRACT FROM AUTHOR]

Isopycnal eddy mixing across continental slopes profoundly modulates the ocean circulation and biogeochemistry. Yet this process must be parameterized in coarse‐resolution ocean models via an isopycnal eddy diffusivity prescribed with the Redi scheme. In this work, we evaluate the skill of physics‐based and data‐driven Redi variants in predicting the cross‐slope exchanges using a suite of offline‐mode parameterized tracer simulations for wind‐driven upwelling continental slope fronts, which commonly arise around the margins of subtropical gyres. The tested physics‐based Redi variants range from a constant eddy diffusivity to a recently proposed, bathymetry‐aware diffusivity augmented by the artificial neural network (ANN) that infers the mesoscale eddy kinetic energy from the mean flow and topographic quantities. Moreover, a purely data‐driven eddy diffusivity is learned by the ANN from the output data set of an eddy‐resolving model, whose solutions serve as the ground truth against which the parameterized tracer simulations are compared. Among all tested Redi variants, the ANN‐learned diffusivity and the bathymetry‐aware diffusivity outperform others in reproducing the tracer solutions of the eddy‐resolving model. However, a physics‐based Redi variant with local deficiencies can introduce global errors in the predicted tracer distribution, which calls for ongoing efforts in constraining the shelf‐to‐ocean transition of the isopycnal eddy diffusivity. A purely data‐driven diffusivity can nearly reproduce the diagnosed diffusivity from the eddy‐resolving model, which highlights the efficacy of machine learning techniques for parameterizing eddy processes across steep topography. This work serves as a key step toward parameterizing the isopycnal eddy mixing in ocean models with continental slopes. Plain Language Summary: Turbulent eddies across continental slopes drive the exchanges between shelf seas and open oceans, which are essential for coastal ecosystems and the global climate. These eddies are characterized by length scales smaller than the grid spacing of today's ocean climate models, resulting in unresolved eddy‐induced exchanges. This issue is usually remedied by eddy parameterizations that infer eddy fluxes from properties explicitly resolved in climate models. In this work, we evaluate extant parameterizations in constraining cross‐slope exchanges of oceanic tracers (such as salt and nutrients) by comparing simulations that utilize parameterizations with simulations that can explicitly resolve mesoscale eddies. Our results reveal the necessity to adopt more sophisticated parameterizations in non‐eddying simulations for cross‐slope eddy tracer exchanges than those currently used in climate models. Moreover, machine learning techniques are found to be effective in parameterizing cross‐slope eddy exchanges. Key Points: Data‐driven and physics‐based parameterizations of isopycnal eddy diffusivity across continental slopes are tested prognosticallyArtificial neural network‐inferred diffusivities and bathymetry‐aware diffusivities outperform previously tested variants over steep slopesMachine learning techniques effectively augment physics‐based mesoscale eddy parameterizations [ABSTRACT FROM AUTHOR]

Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves. [ABSTRACT FROM AUTHOR]

This study aimed to characterize the spatial distribution and composition of living Benthic Foraminifera (BF) and to comprehend how environmental conditions (e.g., organic matter) can affect communities of these protozoa in the northern and southern sectors of the Santos Basin (SB), in the continental slope and São Paulo Plateau. In this context, 23 stations (65 samples including replicates at each station) were collected between 400 and 2,400 m water depth. Multivariate analyses revealed that the ecological structure of the community changes mainly along the bathymetric gradients. Stations located between 400 and 700 m, both in northern and southern sectors, are characterized by the presence of indicator species of high intensity of currents, such as Globocassidulina subglobosa and Trifarina bradyi. These stations are also mainly marked by the occurrence of Epistominella exigua, a phytodetritivore species. The stations at 1,000 and 1,300 m depth, in both sectors, are characterized by high accumulation of organic matter in the sediments, which favors the development of agglutinated foraminifera species, such as those of the genus Reophax. Finally, the lower slope and the São Paulo Plateau, in both sectors, are oligotrophic regions, with pulses of labile organic carbon, probably low current velocities and the presence of Alabaminella weddellensis. The quantity and quality of food, which are closely related to hydro-sedimentary dynamics and bentho-pelagic coupling in the slope and São Paulo Plateau, are the main factors that influence the distribution of living BF assemblages in the SB. [ABSTRACT FROM AUTHOR]

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks. [ABSTRACT FROM AUTHOR]

An autonomous lander equipped with a video camera (dropcam) was used for in situ observations of the bento-demersal macrofauna on the upper continental slope off Punta Pichalo in northern Chile, an area of permanent coastal upwelling processes, located ~70 km north of Iquique. The lander was deployed at nine stations and between 227 and 798 m of depth. According to morphological characteristics, 34 operational taxonomic units (OTUs) were identified to the lowest taxonomic level; 24 belonged to macroinvertebrates and 10 to fishes. Macroinvertebrates comprised 9 OTUs of crustaceans, seven cnidarians, and six echinoderms. Fishes included 3 OTUs of the order Chondrichthyes, 3 belonging to macrourid. Perciformes, Anguilliformes, and Alepocephaliformes were represented by one OTU each. Also, we observed one species of lanternfish (Myctophidae). Apart from the brachyuran decapod Lophorochinia parabranchia Garth, 1969 and euphausiids, all species were observed at depths greater than 560 m. The presence of one individual identified as the granulate dogfish Centroscyllium granulatum Günther, 1887 extended the known distribution range of this species about 1000 km to the north. Images taken at 795 m showed Bathyraja peruana McEachran & Miyake, 1984. Our study suggests that the upper continental slope of northern Chile harbors nearly undiscovered biodiversity, worth to be studied more intensively to complete the comparable sparse knowledge about marine biodiversity and species distribution at the continental margin in front of Chile. [ABSTRACT FROM AUTHOR]

Modern marine seismic reflection data have allowed for the study of the morphology of submarine channels in a 3D perspective. This study presents a quantitative analysis of continental slope channel complexes morphology within the Canterbury Basin (New Zealand). It aims to characterize the morphology and seismic facies of submarine channels to better understand their formative sedimentary processes, paleoenvironment, and petroleum prospectivity. Submarine channel morphometric parameters are measured at 150 m intervals perpendicular to the axis of channels complexes. Based on the morphology analysis of erosional surfaces and seismic facies of channel complexes filling deposits, four types of continental slope channel complexes are found in the study area. These are vertical migrating channels, lateral migrating channels, V-shaped channels, and U-shaped channels. Furthermore, our work shows that channel morphometry varies over distances of 0.1 to 14 km in this continental slope system. These changes indicate a combination of submarine gravity flow process and channel wall collapse responsible for the development of continental slope channel complexes. Regionally, the evolution of the channels indicated less significant regional plate movement. This quantitative seismic geomorphology approach of characterizing submarine channels system has broader applications for better interpretation of paleoenvironment and petroleum prospectivity within frontier basins. [ABSTRACT FROM AUTHOR]

From the BIOPEARL 1 and 2 Programs to the Amundsen and Scotia Seas a large series of Tanaidacea was collected using an epibenthic sled. We carried out a thorough morphological analysis of 169 individuals and provide a description of 14 pseudotanaid species distributed in three genera. Twelve species of the genus Pseudotanais are represented by three morphogroups: "affinis+longisetosus", "denticulatus+abathagastor", and "forcipatus". We provide a redescription of Akanthinotanais gaussi, supplement the definitions of the genera Akanthinotanais and Beksitanais, and transfer Pseudotanais abyssi to the genus Beksitanais. Based on the literature and new data, we summarize knowledge of the Antarctic Pseudotanaidae and discuss this family's spatial and bathymetric distribution. [ABSTRACT FROM AUTHOR]

The northern margin of the South China Sea (SCS) is often regarded as a magmapoor passive continental margin. Magmatic activities occurred after the cessation of seafloor spreading were founded mainly over the Continent-Ocean Transition (COT) zone. Intrusive rocks are observed in the Luzon-Ryukyu Transform Plate Boundary (LRTPB) dividing Southwest Taiwan Basin (SWTB) and Pearl River Mouth Basin (PRMB) north of the COT and their evolution mechanisms are not very well-studied. Here, detailed structural and geophysical features of a large-scale anomaly (LSA) is revealed from high-resolution multi-channel seismic (MCS) profiles over the LRTPB dividing the SWTB and the PRMB. After velocity estimation, AVO analysis, and geological interpretation for the LSA, we suggest that the LSA is an intrusive igneous rock and further classified as a laccolith. The coexistence of the laccolith and surrounding sills over the LRTPB shows that the north limit of magmatism is further north than the COT zone. The elongated shape of the laccolith is accordant to the NW directional LRTPB, indicating that magmatic activities of study region maybe controlled by the faulting. [ABSTRACT FROM AUTHOR]

Intermediate nepheloid layers (INLs) form important pathways for the cross‐slope transport and vertical export of particulate matter, including carbon. While intermediate maxima in particle settling fluxes have been reported in the Eurasian Basin of the Arctic Ocean, direct observations of turbid INLs above the continental slope are still lacking. In this study, we provide the first direct evidence of an INL, coinciding with enhanced mid‐water turbulent dissipation rates, over the Laptev Sea continental slope in summer 2018. Current velocity data show a period of enhanced downslope flow with depressed isopcynals, suggesting that the enhanced turbulent dissipation is probably the consequence of the presence of an unsteady lee wave. Similar events occur mostly during ice free periods, suggesting an increasing frequency of episodic cross‐slope particle transport in the future. The discovery of the INL and the episodic generation mechanism provide new insights into particle transport dynamics in this rapidly changing environment. Plain Language Summary: In the Arctic Ocean deep basins, only a tiny fraction of the algae that grows in the surface layer sinks down to the sea floor. Most of the particles reaching the sea floor originate from the shallower regions closer to the coast. These particles have already settled on the sea floor once, and originate from rivers or algae that grew, died and sank down in shallow regions. Later, these particles are lifted off the ground again by strong turbulent motions and transported toward deeper regions in the middle of the water column. These lift‐off and transport events happen only occasionally, and have not been directly observed in the Eurasian part of the Arctic Ocean yet. Also, we present a new mechanism for the creation of turbulence, which is necessary to lift particles off the sea floor. This mechanism happens mostly during the summer season, when less sea ice is present. Based on this seasonality, it is likely that sediment transport events will become more frequent in the future, when the Arctic sea ice is further declining. Key Points: First direct observation of an intermediate nepheloid layer in the Eurasian part of the Arctic OceanCoinciding strong midwater turbulence is likely caused by a down‐slope current displacing isopycnalsSimilar downslope flow events exhibit a strong seasonality toward the ice free season [ABSTRACT FROM AUTHOR]

Data on the assessment of the dynamics of sedimentary waves over the western slope of the Caspian Sea are presented. The process of formation of the wave structure of sedimentary waves under the influence of hydraulic pressure jumps during the spreading of gravitational turbidity flows downslope is discussed. [ABSTRACT FROM AUTHOR]

Two new species of the order Plectida are described from Chatham Rise, New Zealand. Leptolaimus dififtinus sp. nov. is characterised by the short body 319-420 microns long, truncate labial region slightly offset from body contour and bearing conspicuous outer labial papillae, cephalic setae 1.3-1.4 microns long, amphid located 4-9 microns from anterior end, lateral alae originating from middle of buccal cavity length, female without supplements, male with precloacal and postcloacal pairs of subventral setae, nine tubular supplements (alveolar supplements absent), tubular supplements weakly S-shaped with pointed tip, spicules arcuate 24 microns or 1.4 cloacal body diameters long and dorsal gubernacular apophyses. Lavareda iramscotti sp. nov. is characterised by adult body length 3,023-3,121 microns long, eight longitudinal rows of body pores each with short papilla, cephalic setae 4-5 microns long, tail 146-165 microns long, male with spicules 54 microns long, gubernaculum with triangular apophyses, 20 precloacal supplements with bifid distal tips arranged in 9 + 1 + 10 pattern, female with vulva at 55% of body length from anterior and cuticularisation perpendicular to vagina at level of vulva. The present study provides the first record of a Leptolaimus species from the New Zealand region and the first description of a female specimen of the genus Lavareda. [ABSTRACT FROM AUTHOR]

Marine-geophysical evidence on sea-floor morphology and shallow acoustic stratigraphy are used to examine the substrate around the location at which Sir Ernest Shackleton's ship Endurance sank in 1915 and on the continental slope-shelf sedimentary system above this site in the western Weddell Sea. Few signs of turbidity-current and mass-wasting activity are found near or upslope of the wreck site, and any such activity was probably linked to full-glacial higher-energy conditions when ice last advanced across the continental shelf. The wreck is well below the maximum depth of iceberg keels and will not have been damaged by ice-keel ploughing. The wreck has probably been draped by only a few centimetres of fine-grained sediment since it sank in 1915. Severe modern sea-ice conditions hamper access to the wreck site. Accessing and investigating the wreck of Endurance in the Weddell Sea therefore represents a significant challenge. An ice-breaking research vessel is required, and even this would not guarantee that the site could be reached. Heavy sea-ice cover at the wreck site, similar to that encountered by Agulhus II during the Weddell Sea Expedition 2019, would also make the launch and recovery of autonomous underwater vehicles and remotely operated vehicles deployed to investigate the Endurance wreck problematic. [ABSTRACT FROM AUTHOR]

This study uses high‐quality two‐dimensional (2‐D) seismic and well data to analyse seismic stratigraphy and deep‐water Pliocene sediments in the Qiongdongnan Basin (QDNB), South China Sea. Eight major seismic facies were identified based on the amplitude, continuity, configuration, and external geometry of seismic reflections. Among them, sigmoid progradational configurations, oblique progradational configurations, mound‐shaped chaotic configurations, and mound‐shaped hummocky configurations are newly identified seismic facies indicative of provenance and water system significance. They were interpreted as a Pliocene‐aged eastern shelf‐edge delta, a western shelf‐edge delta, and eastern and western submarine fans in QDNB. Consequently, two sets of Pliocene shelf‐edge delta‐continental slope canyon‐submarine fan systems were established in the QDNB. From the approximately NNW–SSE progradation of the shelf‐edge delta, the characteristics of the approximately ENE–WSW distributed continental slope system, and the definition of a source‐to‐sink system, as well as previous heavy mineral research, we conclude the existence of two Pliocene sources from Hainan Island in the northern QDNB, corresponding to the Lingshui River and Wanquan River. Two independent and complete source‐to‐sink systems (S2S‐2, S2S‐3) were distinguished from the northern Hainan Island to the basin area. S2S‐2 is located in the western QDNB, which includes the Lingshui River‐western shelf‐edge delta‐continental slope canyon‐submarine fan. This source‐to‐sink system has more sand‐rich material and better reservoir conditions than S2S‐3 in the eastern basin, predominantly due to a higher quality granite parent rock, abundant provenance, and a large‐scale delta and submarine fan. [ABSTRACT FROM AUTHOR]

The deep-sea crab Chaceon ramosae occurs at 350-1200 m depth in the southeast and south of Brazil. Here we evaluated the latitudinal, bathymetric, and seasonal abundance of C. ramosae in southern Brazil obtained during several research cruises. We also obtained populational data to evaluate the effectiveness of the fishing regulations for C. ramosae. Five sampling cruises were carried out in 2009-2010 and the sampling effort comprised 32 fishing hauls with four pots per mainline. In total, 195 individuals were caught, 128 males and 67 females, of which 17 were ovigerous. The highest catch per unit effort occurred between 29°03' and 29°05'S at 800-1000 m in depth. The highest abundance occurred in winter, and almost all ovigerous females were captured in this season. The size at the onset of sexual maturity was estimated at 120 mm carapace width. Depth was the most critical environmental factor explaining C. ramosae distribution. The largest individuals, as well as the mature ones, were mainly captured in shallower regions (400-600 m). Our results confirm the need for prohibiting the fishing for C. ramosae at depths lesser than 500 m. [ABSTRACT FROM AUTHOR]

Despite being generally located far from contamination sources, deep marine ecosystems are impacted by chemicals like PCB. The PCB contamination in five fish and shark species collected in the continental slope of the Gulf of Lions (NW Mediterranean Sea) was measured, with a special focus on intra- and interspecific variability and on the driving factors. Significant differences occurred between species. Higher values were measured in Scyliorhinus canicula , Galeus melastomus and Helicolenus dactylopterus and lower values in Phycis blennoides and Lepidorhombus boscii . These differences might be explained by specific abilities to accumulate and eliminate contaminant, mostly through cytochrome P450 pathway. Interindividual variation was also high and no correlation was observed between contamination and length, age or trophic level. Despite its major importance, actual bioaccumulation of PCB in deep fish is not as documented as in other marine ecosystems, calling for a better assessment of the factors driving individual bioaccumulation mechanisms and originating high variability in PCB contamination. [ABSTRACT FROM AUTHOR]

Abstract: Little attention has been paid to smaller-scale mass movements on continental slopes, even though they occur much more frequently than their large-scale counterparts. Swath bathymetry, side-scan sonar, sub-bottom profiler and seismic data from the continental slope offshore the Lofoten Islands, northern Norway, reveal evidence of repetitive smaller-scale translational sliding, involving spreading and multi-phase retrogression, in water depths between 1100 and 2500m. Three styles of failure have been identified, occurring in close proximity. Style 1 is characterized by a 4.7km wide and up to 100m deep amphitheater shaped headwall, a relatively deep glide plane (±130mbsf), detached sediment ridges and a run-out area with rafted sediment blocks. Style 2 consists of a staircase pattern of secondary escarpments, caused by the activation of several glide planes between ±30 and 110mbsf. Headwalls and secondary escarpments have a height of up to 30 and 70m, respectively. The run-out area shows an almost complete sediment evacuation. Style 3 is more subtle, as it is only identified on the side-scan sonar data due to its higher spatial resolution. This style shows different phases of on-going evolution, illustrating the gradual disintegration of a slab of sediments moving over a shallow glide plane at ±13mbsf. Zones with sediment slabs are up to several hundreds of meters wide and are sharply delineated by shear margins or escarpments. The spatial variation in the failure style is inferred to have been caused by the activation of different glide planes, which is probably a result of the thinning of contouritic sediments towards the south-west. In the north-east, the mounded contouritic sediments contain more potential glide planes and higher slope angles. The smaller-scale mass movements are suggested to have been triggered by undercutting and removal of support at the foot of the slope due to large-scale mass movements that have occurred immediately south of the study area, such as the Trænadjupet or Nyk slides. The geophysical data indicate that relatively recent mass movement processes have taken place in this area through the formation of shallow cracks and graben structures by the movement of ±13m thick slabs of sediments (Style 3), which could have severe implications for offshore infrastructure. [Copyright &y& Elsevier]

Campbell, N., Neat, F., Burns, F., and Kunzlik, P. 2011. Species richness, taxonomic diversity, and taxonomic distinctness of the deep-water demersal fish community on the Northeast Atlantic continental slope (ICES Subdivision VIa). – ICES Journal of Marine Science, 68: 365–376.The fish community on the Atlantic deep continental shelf and upper slope to the northwest of Scotland has been the subject of biological studies for more than a century, and subject to bottom-trawl fishing for around 25 years. In this work, we examine trends in biodiversity of the deep-water demersal fish community revealed by a decade of trawl surveys by Marine Scotland—Science. The composition and structure of the fish assemblage was described using species richness as well as the descriptors of community interrelatedness: taxonomic diversity (Δ) and taxonomic distinctness (Δ*). Results revealed no temporal trends in community composition. The most significant factor in determining richness and taxonomic diversity of the demersal fish fauna was depth, and to a lesser extent latitude. Diversity and distinctness decreased with increasing depth and showed a complex relationship with latitude, while richness peaked at depths around 1400 m. This study shows taxonomic measures of diversity and distinctness to be sensitive indicators of ecological conditions in the deep-water fish community, with respect to depth and latitude, and the fact that no temporal trends were detected suggests that the structure of the fish community at exploitable depths on the Scottish slope has remained stable over the period 1998–2008. These findings imply that care should be taken when planning spatial measures designed to safeguard deep-water fish biodiversity because the optimal area recommended for protection is strongly dependent on the choice of metric used. [ABSTRACT FROM PUBLISHER]

Trichopeltarion corallinus (Faxon, 1893), a decapod of the family Atelecyclidae, is recorded for the first time in Chile. Seven specimens were captured by bottom trawling at five sites on the continental slope. All the specimens were associated with hard substrates and at least one was associated with a recently discovered methane seep area. The stations were located between 18° and 42°S and at depths from 507 to 922 m. After its original description, the species was reported for Peru from approximately 10° to 17° S and at depths of 860 to 870 m. This first record of the species for Chile extends its geographic distribution about 25° (about 2,775 km) southwards and expands its bathymetric range as well. Moreover, a male specimen of T. hystricosus was collected at an intermediate latitude (∼22°S) in relation to previous records, thereby confirming the presence of this species and the genus Trichopeltarion over deep hard substrates along the continental slope off Chile. [ABSTRACT FROM AUTHOR]

The pedunculate barnacle Scalpellum projectum Nilsson-Cantell, 1930, was described based on benthic material from a telegraph cable recovered from deep waters off Antofagasta (∼23°S). No new records have been reported for this species worldwide since its original description. Six adult females of S. projectum were collected during recent studies of communities associated with methane seeps. The material was taken from three stations located between 34°42' and 36°22'S and at depths of 846 to 922 m. We provide taxonomic information based on the external morphology of the specimens, whose sizes coincide in general terms with those of the original description. No male specimens were observed; these are smaller, aberrant in form, and live within the scuta in the capitulum of the females. With this second finding, the distributional range of this species, previously only reported for the slope off Chile, is extended about 17° latitude southwards (1,800 km) and its bathymetric range is expanded by 200 m. [ABSTRACT FROM AUTHOR]

In this paper, the M2 internal tides (ITs) originating from the continental slope in the South China Sea are studied using the CROCO model. The simulation results show that there are two origins of ITs on the continental slope: at 118°–119.5° E along 22° N near the southern entrance of the Taiwan Strait and at 117°–118° E along 20° N near Dongsha Island. The local generation of ITs is greatly influenced by the ITs that radiate from the Luzon Strait (LS). The integrated conversion at the first generation site is increased by 31% to 0.42 GW compared to the case where the LS is excluded from the simulation region. Its maximum energy flux almost doubles to 2.5 kW/m, which is 10% of the westward component. The existence of the other IT beams from Dongsha Island is attributed to the ITs from the LS. The local generation on the continental slope changes when remotely generated ITs alter the amplitudes and phases of the bottom pressure perturbation. These results indicate that the ITs originating from the LS contribute to the spatial variation of ITs in the SCS by modulating the IT generation on the continental slope. [ABSTRACT FROM AUTHOR]

We observed a distinct drop-off region in the bearing-time record of acoustic reverberation data acquired from the south-western continental margin of the Ulleung Basin, East Sea, in the summer of 2015. 3 kHz continuous waves with pulse lengths of 0.1, 0.3, and 1.0 s were used as source pulses, with an R/V Cheonghae vessel towing a variable depth source and a triplet towed array toward the deep sea from shallow water. The observed pattern changed as the R/V Cheonghae moved across the continental slope further into the sea. This pattern arises as a result of the downward-refracted beams in the 1/2 convergence zone interacting with the soft bottom. In addition, the boundary of the drop-off region was modeled with the two-way maximum travel time of the first bottom-reflected rays using the bathymetry model of the General Bathymetric Chart of the Oceans, 2020. Some discrepancies were observed when comparing the modeled curve to the measured results, and the inaccuracy of the bathymetry model on the continental slope could be the main cause of these discrepancies. This pattern could be useful for bathymetry mapping, as well as estimations of source and receiver configurations. [ABSTRACT FROM AUTHOR]

We present the results of an integrated geomorphological and seismo-stratigraphic study based on high resolution marine data acquired in the north-western Sicilian continental margin. We document for the first time five contourite drifts (marked as EM1a, EM2b, EM2, EM3a, and EM3b), located in the continental slope at depths between ca. 400 and 1500 m. EM1a,b have been interpreted as elongated mounded drifts. EM1a,b are ca. 3 km long, 1.3 km wide, and have a maximum thickness of 36 m in their center that thins northwards, while EM1b is smaller with a thickness up to 24 m. They are internally characterized by mounded seismic packages dominated by continuous and parallel reflectors. EM2 is located in the upper slope at a depth of ca. 1470 m, and it is ca. 9.3 km long, more than 3.9 km wide, and has a maximum thickness of ca. 65 m. It consists of an internal aggradational stacking pattern with elongated mounded packages of continuous, moderate to high amplitude seismic reflectors. EM2 is internally composed by a mix of contourite deposits (Holocene) interbedded with turbiditic and/or mass flow deposits. EM1a,b and EM2 are deposited at the top of an erosional truncation aged at 11.5 ka, so they mostly formed during the Holocene. EM3a,b are ca. 16 km long, more than 6.7 km wide, and have a thickness up to 350 m. Both EM2 and EM3a,b have been interpreted as sheeted drift due to their morphology and seismic features. The spatial distribution of the contourite drifts suggests that the drifts are likely generated by the interaction of the LIW, and deep Tyrrhenian water (TDW) on the seafloor, playing an important role in the shaping this continental margin since the late Pleistocene-Holocene. The results may help to understand the deep oceanic processes affecting the north-western Sicilian continental margin. [ABSTRACT FROM AUTHOR]

Exploited deepwater (>500 m) species generally exhibit clear “K-selected” life-history characteristics markedly different from most shelf species: extreme longevity, late age of maturity, slow growth, and low fecundity. Many also aggregate on restricted topographic features such as seamounts, and as a consequence are notably unproductive, highly vulnerable to overfishing, and have potentially little resilience to overexploitation. Since 1964, deepwater fisheries have contributed 800 000–1 000 000 t annually to global marine fish landings. Underlying this apparent overall stability is the “boom and bust” cycle that has characterized many individual fisheries. The accumulated biomass of previously unfished stocks is typically fished down, often within 5–10 years, to the point of commercial extinction or very low levels. Most deepwater stocks are today overfished or even depleted. Depletion of species from deep-sea environments that dominate mid to upper trophic levels may have long-term ecological implications, but the risks of reduced stock size and age structure to population viability, the potential for species replacement, and the impacts on prey and predator populations are not generally known. However, trawl fisheries have been shown to have potentially severe impacts on the benthic fauna of seamounts, where these fish aggregate. This fauna, dominated by suspension feeders, such as corals, is typically restricted to the seamount environment and is characterized by high levels of endemism, which suggests limited reproductive dispersal. The ability of the benthic community to recover, following its removal by trawling, is not known. [ABSTRACT FROM PUBLISHER]

Based on in situ observations, six episodes of near-inertial internal waves (NIWs) were detected on the East China Sea (ECS) continental slope, and the mechanisms and characteristics of them were examined. The generation mechanisms of the observed NIWs included typhoon, wind burst, lateral propagation, and energy transfer from low-frequency flow. The depth-integrated near-inertial kinetic energy (NIKE) showed no significant seasonal variation, and the annual mean NIKE and near-inertial currents were 400 J/m2 and 3.50 cm/s, respectively. Downward propagation of NIKE was evident in the small wavenumber band according to the rotary vertical wavenumber spectra. The NIKE was subsurface-intensified, and the near-inertial vertical shear reached 0.01 s−1. The vertical phase speeds of the NIWs ranged from 5 to 19 m/h. The frequencies of the NIWs were mostly red-shifted, however, blue-shift also existed. One episode had both blue- and red-shifted frequencies vertically, and had both upward and downward propagating vertical phase speeds. The e-folding times of the observed NIWs ranged from 4 to 11 days, which were influenced by successive wind bursts and background vorticity. On the left-hand side of Kuroshio, the background vorticity is usually positive; however, the NIWs were almost red-shifted, which resulted from the Doppler shift of the Kuroshio. [ABSTRACT FROM AUTHOR]

Living benthic foraminifera (>63 µm) were studied to characterize the continental slope of the Potiguar Basin (SW Atlantic). Foraminifers from the surface (0–2 cm), subsurface (2–5 cm), and integrated (0–5 cm) sediment layers were analyzed to verify their contribution to environmental characterization. It was also estimated if and which changes occur when the subsurface is added. Sampling stations were distributed in five transects in four isobaths (150, 400, 1000, and 2000 m). Sediment samples were fixed with 4% buffered formaldehyde and stained with Bengal rose. Were recorded 396 species in the surface layer, 228 in the subsurface, and 449 in integrating both layers. This study did not include tubular agglutinated species. The assemblages from 150 m isobath indicated the upper slope, from 400 m indicated the middle slope and the ones from the 2000 m indicated the lower slope. The surface layer's assemblage at 1000 m isobath was more similar to the middle slope; in contrast, its subsurface layer's assemblage had more similarity with the lower slope. Rarefaction curves, Permanova, and NMDS routines indicated a high resemblance between surface and integrated layers. Therefore, the first two centimeters were sufficient to characterize this region based on living benthic foraminifera. [ABSTRACT FROM AUTHOR]

Increased ocean heat supply to the Antarctic continental shelves is projected to cause accelerated ice sheet loss and contribute significantly to global sea-level rise over coming decades. Changes in temperature or salinity of dense shelf waters around Antarctica, resulting from increased glacial meltwater input, have the potential to significantly impact the location and structure of the global Meridional Overturning Circulation, with seabed irregularities such as submarine canyons, driving these flows toward the abyss. Submarine canyons also influence the location of intruding warm water currents by acting as preferential routes for rising Circumpolar Deep Water. These global changes have implications for large-scale effects to atmospheric and oceanic circulation. The ability for numerical modellers to predict these future behaviours is dependent upon our ability to understand both modern and past oceanic, sedimentological and glaciological processes. This knowledge allows ocean models to better predict the flux and pathways of Circumpolar Deep Water delivery to the shelf, and consequently to ice shelf cavities where melt is concentrated. Here we seek to understand how dense shelf water and other continental slope processes influence submarine canyon morphology by analysing newly collected geophysical and oceanographic data from a region of significant and prolonged dense shelf water export, the Hillary Canyon in the Ross Sea. We find that cascading flows of dense shelf water do not contribute to significant gully incision at the shelf edge during interglacial periods, however, are strong enough to prevent gully infilling and contribute to canyon-levee aggradation down-slope. We find buried paleo-gullies beneath gullies incising the modern seafloor. Paleo-gullies occur as single gullies and in complexes indicating that gully activity was continuous over multiple glacial cycles and formed an important role in the development of the shelf edge and upper slope. Glacial cycles likely drive large-scale shifts in canyon head processes with periods of intense seafloor erosion and significant gully incision likely occurring when ice grounded near to the shelf edge, during glacial and deglacial periods, when sediment-laden subglacial meltwater was released at the shelf edge. We put slope morphology observed at the Hillary Canyon head into global perspective to show that cascading flows of dense shelf water do not exert consistent patterns of erosion on high-latitude continental margins. Unlabelled Image • New geophysical, sediment and oceanographic data show Antarctic canyon dynamics. • Irregular gully distribution along shelf edge show varying ice extent. • Dense shelf water does not cause significant gully erosion. • Glacial cycles drive large-scale shifts in canyon head processes. [ABSTRACT FROM AUTHOR]

Three new marine tardigrade species from the deep-sea genus Coronarctus are described from the South-Western Atlantic Ocean: Coronarctusdissimilis sp. nov., C. neptunus sp. nov., and C. yurupari sp. nov. These, and C. laubieri Renaud-Mornant, 1987, are the first records of deep-sea tardigrades from this marine region. Specimens of those species were collected from two localities of the Brazilian continental slope (Potiguar and Campos basins) at depths comprised between 150 and 3000 m. Specimens of the three new species have short cephalic appendages and heteromorphic claws, belonging to the, here designated, C. tenellus group of species. Each of the new species can be distinguished from all the other species of the group by their peculiar-shaped secondary clavae and claws. The most relevant morphological characters used for the taxonomy of the genus: shape of cephalic cirri, shape of secondary-clavae, size and number of accessory spines on claws, and shape of seminal receptacles, are discussed and an identification key to all ten known Coronarctus species is provided. [ABSTRACT FROM AUTHOR]

This study presents an exploration into identifying the interactions between ocean waves and the continental margin in the origination of double-frequency (DF, 0.1–0.5 Hz) microseisms recorded at 33 stations across East Coast of USA (ECUSA) during a 10-day period of ordinary ocean wave climate. Daily primary vibration directions are calculated in three frequency bands and projected as great circles passing through each station. In each band, the great circles from all stations exhibit largest spatial density primarily near the continental slope in the western North Atlantic Ocean. Generation mechanisms of three DF microseism events are explored by comparing temporal and spatial variations of the DF microseisms with the migration patterns of ocean wave fronts in Wavewatch III hindcasts. Correlation analyses are conducted by comparing the frequency compositions of and calculating the Pearson correlation coefficients between the DF microseisms and the ocean waves recorded at selected buoys. The observations and analyses lead to a hypothesis that the continental slope causes wave reflection, generating low frequency DF energy and that the continental shelf is where high frequency DF energy is mainly generated in ECUSA. The hypothesis is supported by the primary vibration directions being mainly perpendicular to the strike of the continental slope. [ABSTRACT FROM AUTHOR]

The meridional coherence, connectivity, and regional inhomogeneity in long‐term sea surface temperature (SST) variability over the Northwest Atlantic continental shelf and slope from 1982–2018 are investigated using observational data sets. A meridionally concurrent large SST warming trend is identified as the dominant signal over the length of the continental shelf and slope between Cape Hatteras in North Carolina and Cape Chidley, Newfoundland and Labrador, Canada. The linear trends are 0.37 ± 0.06 and 0.39 ± 0.06 °C/decade for the shelf and slope regions, respectively. These meridionally averaged SST time series over the shelf and slope are consistent with each other and across multiple longer observational data sets with records dating back to 1900. The coherence between the long‐term meridionally averaged time series over the shelf and slope and basin‐wide averaged SST in the North Atlantic implies approximately two thirds of the warming trend during 1982–2018 may be attributed to natural climate variability and the rest to externally forced change including anthropogenic warming. Plain Language Summary: This study investigates long‐term changes in the sea surface temperature (SST) since 1982 over the Northwest Atlantic continental shelf and slope. In particular, we focus on the changes consistently found from Cape Hatteras, North Carolina, United States, to Cape Chidley, Newfoundland and Labrador, Canada. The SST warming rates concurrently found over this large latitudinal range are 0.37 ± 0.06 and 0.39 ± 0.06 °C/decade for the shelf and slope regions, respectively. Analysis indicates that approximately two thirds of the warming trend during 1982–2018 may be attributed to natural climate variability and the rest to externally forced change including anthropogenic warming. Our findings are further confirmed by comparing with multiple other observational data sets. Key Points: Meridionally coherent surface warming is observed over the Northwest Atlantic continental shelf and slopeThe linear trends in SST exhibit distinct spatial maxima in the slope region off Georges Bank and Cape HatterasLong‐term variations in the meridional means of SST are highly correlated with basin‐averaged values [ABSTRACT FROM AUTHOR]