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Holtbyrnia anomala is a bathypelagic platytroctid widely distributed in the Atlantic Ocean. In this contribution, we report, for the first time, the occurrence of this species in the tropical southwest Atlantic. A single specimen was collected in 2000 on the continental slope off Rio de Janeiro, Brazil, at an average depth of 1158 m. This report also represents the first record of Holtbyrnia anomala in the Brazilian Economic Exclusive Zone. [ABSTRACT FROM AUTHOR]

Life history characteristics of Watases lanternfish Diaphus watasei from a deep sea fishing ground of the East China Sea were studied. Overall, 452 adult individuals with standard length ranging from 91 to 147 mm were collected in the continental slope during 3 years. The growth pattern and hatching date were inferred from otolith microstructure analysis, and the stomach contents were examined to clarify feeding ecology. Three distinct zones of the otolith microstructure were depicted, the numbers of increments in the central and middle zones of the D. watasei otolith are in the lowest level in myctophid species studied. The maximum number of growth increments indicated a short lifespan of 2 years. The spawning time almost lasted throughout the year, and then two cohorts were separated according to the estimated hatching time. The length–weight relationship revealed a negative allometric pattern and significant difference between the two cohorts, and a significant seasonal difference was also detected in somatic growth pattern. A piscivorous habit dominated by Maurolicus muelleri was revealed across sampling seasons and standard length groups. Overall, D. watasei show distinct life history characteristics compared to coinhabiting myctophids, and such characteristics could reduce interspecific competition. [ABSTRACT FROM AUTHOR]

Submarine canyons are hot spots for topography‐internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf‐break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K1) energy is sub‐inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near‐inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near‐inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M2) energy appears focused near critical shelf‐break and canyon floor topography, due to local and remote baroclinic forcing. The high‐frequency internal wave continuum has enhanced near‐bottom energy at both sites (up to 7 × the Garrett‐Munk spectrum), and inferred dissipation rates, ɛ, reaching 10−7 W kg−1 near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are ε∼M20.8+ $\varepsilon \sim {M}_{2}^{0.8}+$SubK10.6 ${\text{Sub}}_{{K}_{1}}^{0.6}$ on the slope, and ε∼M21.5+ $\varepsilon \sim {M}_{2}^{1.5}+$ NI0.2 in the canyon. There is also a build‐up of "shoulder" energy (PSh) near the buoyancy frequency, with a power law fit to dissipation of PSh ∼ ɛ0.3 at both sites. Plain Language Summary: Internal waves are sub‐surface waves that can mix ocean water, particularly over rough topography such as that found on continental slopes or in submarine canyons. Mixing is important for understanding ocean circulation, climate, and biological productivity. At Barkley Canyon on Canada's west coast, 4 years of current observations are used to study internal waves at both slope and canyon sites. These long‐term data allow for analysis of seasonal and year‐to‐year trends. The currents follow topography, and near‐bottom internal wave energy is generally increased. The observed seasonal patterns change little year‐to‐year. Internal waves occurring once‐a‐day or less are trapped along the slope, and result from once‐a‐day surface tides. Internal waves associated with the Earth's rotation are driven by wind—with only some events reaching the deep canyon. Internal waves occurring twice‐a‐day may be amplified by topography, and result from twice‐a‐day surface tides and internal waves from other underwater sites. Seasonal trends indicate that larger internal waves transfer energy to smaller, turbulent motions near topography, elevating mixing. There is evidence that this transfer of energy may continue to smaller scales than is typically observed. These findings can support models of mixing near topography and improve understanding of internal wave processes. Key Points: Analysis of 4 years of acoustic Doppler current profiler horizontal velocity data from Barkley Canyon and nearby slopeElevated internal wave energy and mixing near topography, with power law relationships to semidiurnal and site‐dependent secondary forcingBuild‐up of energy near the local buoyancy frequency with a power law relationship to dissipation [ABSTRACT FROM AUTHOR]

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]

Within the program "Ecosystems of the Siberian Arctic Seas," carried out by Shirshov Institute of Oceanology, Russian Academy of Sciences since 2007, studies of the water structure and spatial variability of the parameters of the carbonate system have been performed, and the intensity and direction of the carbon dioxide flux over the continental slope of the Laptev Sea and in the Vilkitsky Strait in September 2018 have been calculated. The presence of several main water masses that govern the water structure in the study area is shown. A strong spatial variability of the parameters of the carbonate system of seawater, determined by complexes of physical and chemical–biological processes, has been revealed. The intensity and direction of the carbon dioxide flux at the water–atmosphere boundary were calculated, which range from –12 to 4 mmol m–2 day–1. It was revealed that the investigated area of the outer shelf and continental slope of the Laptev Sea is an emitter of carbon dioxide into the atmosphere as of September 2018. Conversely, the area of the Vilkitsky Strait, is a CO2 sink zone. [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]

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km2 area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km2 area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic. [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]

Based on high‐quality two‐dimensional seismic profiles and well data, the seismic reflection characteristics from the late Pliocene and Pleistocene succession of the Qiongdongnan Basin in the South China Sea have been analysed. The result will help in understanding the sedimentological development of slope areas. Twenty coeval clinothems are recognized and four major clinothem types are distinguished. In addition, three types of shelf‐edge trajectories are recognized. The various parameters of the clinothems are analysed quantitatively and the relationships between the various clinothem types are studied in combination with the controlling roles. It is concluded that: (i) the shelf‐edge trajectories are related to the type of clinothem; (ii) fluctuations in the relative sea level, in combination with variations in sediment supply, result in different clinothem types and geometric parameters; these parameters show interdependencies; (iii) the alternations of progradation and aggradation of clinothems may provide information of the relative sea level and changes in sediment supply; (iv) some lowstand fans could develop at the foot of the slope in the central–eastern part of the basin when the relative sea level started to fall or began to rise. The results of the present study are consequently significant for further quantitative analyses of the characteristics and development of the continental slope, not only in the Qiongdongnan Basin, but also in other basins. [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]

Observational data from the submesoscale hydrological polygon confirm the presence of summer runoff of dense Antarctic shelf water (ASW) on the continental slope in the Commonwealth Sea. It is provided by a huge amount of ASW accumulated in shelf depressions during winter. The ASW overflows the shelf edge in the form of discrete meanders, which are formed as a result of baroclinic instability of a deep ( 150–250 m) ASW front. The estimated instability scale along the dense water front km coincides with the observed spatial discreteness of ASW. At the same time, the distribution of near-bottom density currents affected by the bottom irregularities, is noted on the shelf. The Antarctic Slope Front (ASF) is formed on the slope due to the interaction of ASW with warm Circumpolar Deep Water (CDW). Due to the continuity of motion in the near-slope area, 3D cascading is accompanied by compensatory upwelling of CDW, which complements its large-scale advection. These processes form the intrusive structure of water on the edge of the shelf and on the shelf. Depending on the bathymetric characteristics of the slope in different parts of the polygon, the cascading of ASW has a different regime. [ABSTRACT FROM AUTHOR]

Cruise 89 of the R/V Akademik Mstislav Keldysh was organized by the Shirshov Institute of Oceanology in the framework of the Program "Marine Ecosystems of the Siberian Arctic" and was conducted from September 19 to October 10, 2022. Sixty scientists from institutes of the Russian Academy of Sciences, Moscow State University, Moscow Institute of Physics and Technology, VNIRO, and MES participated in the cruise. Coordinated hydrophysical, hydrochemical, biooceanological, and geochemical research and assessments of greenhouse gas concentrations in the near-surface atmosphere were carried out over the shelf and continental slope of the poorly studied eastern Kara Sea. The ecosystem of Blagopoluchiya Bay (Novaya Zemlya) and the conditions of radioactive waste disposal there were also objectives of the research. [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]

During the evolution of shrimp, essential aspects of their organization have remained unchanged. Approximately the same adaptations that have generated a large number of parallelisms within this relatively small group of arthropods have been used in the process of their adaptive evolution. This evolutionary process is typical telogenesis. The ancient shrimp fauna of both Dendrobranchiata and Pleocyemata may have originated in shallow waters not later than in the Jurassic. This is confirmed by the remains of Dendrobranchiata found in the shallow-water sediments of the Cenomanian (early Upper Cretaceous) and the remains of Pleocyemata as inhabitants of shallow-water refugia and representatives of the most primitive caridean shrimp family Procarididae. The last group is morphologically very similar to fossil shrimp of the Jurassic (for example, Udorella agassizi). Later, due to adaptive radiation at the generic level, shrimp occupied both the continental slope and the pelagic zone. These shallow-water species may have then been ousted by a new shrimp fauna during colonization of the shelf. The previous shrimp fauna may have been displaced to the continental slope, perhaps bordering on it. Some part of the species from various genera could have moved deeper along the slope down to the abyssal zone, whereas some others might have shifted to occupy the pelagic zone. This movement may have been associated with food resources, which were limited on the slope in the places with low levels of terrigenous sedimentogenesis. Numerous species seem to have switched from the detrital food chain to a grazing one. This process was repeated several times; as a result, the surviving representatives of the most ancient and subsequent fauna occurred at even greater depths. It follows from the above information that a pulsing type of telogenesis is characteristic of shrimp. Therefore, the modern shrimp fauna consists of young shelf groups with intensive cladogenesis, groups that have persisted since the Cretaceous (or even Jurassic), and remains of earlier fauna that have survived at great depths or in shallow-water refugia. [ABSTRACT FROM AUTHOR]

This study presents a systematic analysis of double-frequency (DF) microseisms recorded on the unconsolidated sediments in the eastern and southeastern coasts of United States. For all recordings, the site effect parameters (predominant frequency (f0), amplification factor and unconsolidated sediment thickness (UST)) are obtained by Nakamura method and the DF spectra are classified into five groups in terms of the DF peak patterns and the recording locations relative to the coastline. The frequencies and energy levels of the DF peaks in horizontal direction and the amplification factors are associated with the UST which is resulted from seismic site effect. By polarization analysis, the primary vibration directions of the DF peaks are identified and presented as great circles passing through the recording stations intersecting mainly along the continental slope. Correlation analyses of time histories of the DF energy and the ocean wave climate observed at buoys show that the low (<0.2 Hz) and high (>0.2 Hz) frequency DF microseisms are generated in the deep ocean and the continental shelf respectively. It is concluded that the continental slope plays a significant role in the generation of DF microseisms as it causes reflection of waves from the open ocean, initiating standing waves. [ABSTRACT FROM AUTHOR]

The values and direction of carbon dioxide flux in the area of the continental slope in the north of the Kara Sea (St. Anna Trough) are calculated based on field studies in 2020 within the Siberian Arctic Sea Ecosystems program. The existence of a stable frontal zone in this area has been confirmed, which is formed by an alongslope current and limits the northward spread of surface waters freshened by the continental runoff. The simultaneous analysis of the carbonate system in the upper sea layer and the CO2 concentration in the surface air layer shows the CO2 flux with a rate of 0.2 to 22 mmol/m2 day to be directed from the atmosphere into the water in the area of the outer shelf, which is affected by the river runoff, and in the area of the continental slope, which is beyond this effect. The highest rates of CO2 absorption by the sea surface layer are localized above the continental slope. Local processes in the area of the slope frontal zone determine the CO2 emission into the atmosphere with a rate of 0.34 mmol/m2 day. [ABSTRACT FROM AUTHOR]

The family Polymixiidae is an ancient group of acanthomorph fish, often regarded as living fossils. Currently, there are 11 valid species allocated in the genus Polymixia , and commonly known as beardfish. All species are benthopelagic and can be found at depths between 80 and 800 meters, in the Atlantic, Indian, and Pacific oceans. Traditionally, only two species had been assigned to the Atlantic Ocean, P. lowei , in the western Atlantic, and P. nobilis , in the North Atlantic, including northern South America and Saint Peter and Saint Paul Archipelago; however, recent studies revealed a cryptic species from the Bermudas, described as P. hollisterae , and a yet undescribed species from the Caribbean Sea. Herein, we describe a new species of Polymixia from the western South Atlantic, which was previously confused with P. lowei. The new species is supported by both morphological and molecular evidence and can be distinguished among its congeners by a combination of characters, including counts of gill rakers, pyloric caeca, and dorsal-fin rays, arrangement of scales spines, and the shape of preopercle. The new species is distributed on the upper continental slope in Brazil, from Bahia to Rio Grande do Sul, and Uruguay, between 160 and 600 meters deep. • A new species of the living fossil genus Polymixia is described. • Integrative taxonomy reveals a new beardfish from the western South Atlantic. • The Atlantic Ocean harbors a cryptic diversity of the deep-sea genus Polymixia. • Molecular phylogeny reveals allopatric speciation between North and South Atlantic. • Industrial activities and marine litter are threatening Brazilian deep-sea fish. [ABSTRACT FROM AUTHOR]

Cruise 83 of the R/V Akademik Mstislav Keldysh was organized by the Shirshov Institute of Oceanology in the framework of the Program "Marine Ecosystems of the Siberian Arctic" and took place from June 18 to July 08, 2019. Seventy-five scientists from institutes of Russian Academy of Sciences, Moscow State University, Moscow Institute of Physics and Technology, and VNIRO participated in the cruise. Coordinated hydrophysical, hydrochemical, biooceanological, and geochemical research and assessments of greenhouse gas concentrations in the near water atmosphere were carried out over the Kara Sea shelf and the continental slope of the St. Anna Trough in the period of seasonal sea ice melting. [ABSTRACT FROM AUTHOR]

Mesoscale eddies have been reported to have a substantial impact on the distribution of phytoplankton through the regulation of environmental variables in the open ocean. However, the influence of warm eddies on phytoplankton in continental slopes remains largely unknown. To reveal the impact of mesoscale eddies within slope regions, we conducted a field investigation of picophytoplankton on the northern slope of the South China Sea during an anticyclonic warm eddy propagation. We observed different picophytoplankton distribution patterns. Synechococcus dominated the picophytoplankton community in the Kuroshio-affected eddy core rather than the previously reported Prochlorococcus , and Prochlorococcus dominated outside the eddy in the shelf. In addition, through further vertical study of typical layers, we found that the influence of warm eddy varied in different layers. Analysis of the mechanisms indicated that the distributions were attributed to warm eddy-induced nutrients and light variations and the physical processes in it. [Display omitted] • Analysis of warm eddy impacts on picophytoplankton in South China Sea slope area • Different distribution pattern of picophytoplankton was observed. • The warm eddy changed the distribution of nutrients and light intensity. • The warm eddy affected the composition of water masses. • The distribution of picophytoplankton was influenced by physical-chemical variations. [ABSTRACT FROM AUTHOR]

Sediments on continental slopes, which are rich in hydrates and organic matters, may release methane into the overlying seawater and even into the atmosphere. To evaluate the impact of sediment emissions on oceanic methane cycling and greenhouse gas emissions, this study assessed the distribution of methane in surface sediments and water columns and calculated the sea-to-air methane flux in the Dongsha area of the northern South China Sea. Results show that the methane concentrations exhibited large spatio-temporal changes. In May 2019, the methane concentrations and sea-to-air methane flux (4.1 ± 3.7 μmol m−2 d−1) were close to the background values, indicating that in situ aerobic methane production was a weak atmospheric methane source. In contrast, in September 2020, abnormally high methane concentrations up to 26.6 nM were detected in the upper slope with water depths of 600–950 m and to the east of a seamount; the average sea-to-air methane flux increased to 11.3 ± 7.9 μmol m−2 d−1. The consistency of methane distribution throughout the water column and surface sediments, with a generally increasing trend with the increasing depth, indicates that in September 2020, sediment emissions were crucial methane sources in seawater and led to moderate emissions into the atmosphere. The heterogeneities of methane concentrations and sea-to-air methane fluxes were attributed to the uneven distribution of methane in the sediments. Besides, strong internal solitary waves in summer and autumn exacerbates methane release, especially around high terrain areas, such as in continental upper slopes and in the upstream side of seamounts. Our results demonstrate that methane released from the sediments, being perhaps affected by internal solitary waves induced sediments disturbance, substantially impacted the oceanic methane cycling in continental slopes. Thus, this study provides new insights into the methane budget of marginal basins. • Abnormally high methane concentrations were detected in the upper slope and to the east of a seamount. • Sediment emissions were crucial methane sources in seawater in the Dongsha area. • ISWs enhance methane released from sediments into atmosphere near high terrain areas in Autumn. [ABSTRACT FROM AUTHOR]

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

The role of possible controlling factors in influencing the geomorphology of submarine canyons has been investigated using a database of 282 globally distributed modern examples collated from the literature and open-source worldwide bathymetry. Canyon geomorphology has been characterised quantitatively in terms of maximum and average canyon dimensions, canyon sinuosity, average canyon thalweg gradient, and maximum canyon sidewall steepness. An assessment is made of how geomorphological characteristics vary with respect to the position of the canyon apex relative to the shelf break, continental-margin type, terrestrial source-to-sink system setting, oceanographic environment, and latitude. Scaling relationships between canyon morphometric parameters, and correlations between these and attributes of the canyon physiographic settings, terrestrial catchments, and continental shelves and slopes, have been quantified. Key findings are as follows: (i) a number of scaling relationships describing canyon morphometry (e.g. scaling between maximum canyon dimensions, relationships of maximum canyon sidewall steepness with maximum canyon width and depth) can be recognised globally, suggesting their general predictive value; (ii) possible causal links are identified between hydrodynamic processes (e.g. upwelling, longshore- and along-slope currents) and canyon morphology; (iii) potential predictors of aspects of canyon geomorphology include whether a canyon is incised into the shelf or confined to the slope, the continental-margin type, the oceanographic environment, latitude, and shelf-break depth; (iv) similarity in the distributions of maximum width-to-maximum depth ratios across all settings suggests that the relative magnitudes of canyon-margin erosion and intra-canyon deposition do not vary greatly depending on setting or canyon size. The relationships between canyon geomorphology and environmental variables identified in this study may be incorporated into conceptual models describing canyon geomorphology and its relationship both to other elements of deep-water systems, and to its broader source-to-sink context. The results provide a framework for future experimental and numerical studies of canyon geomorphology. • Canyon geomorphology cannot be described by generic models. • Some scaling in canyons can be recognized globally. • Predictive value of environmental settings for canyon geomorphology is variable. • Canyon geomorphology is more complex than in current models. [ABSTRACT FROM AUTHOR]

The pattern of sediment dispersal and the location of sediment depocentres on continental margins can be very complex in both space and time. We aim at investigating how significantly external and internal factors, such as river runoff, bottom current and sliding can deviate the sediment dispersal from a simplistic fully sea-level controlled spreading. In this study we examined the sedimentation at two transects across the Mozambique-Zambezi slope between 17°20S-20°S, where multibeam bathymetry, sub-bottom profiler data and sediment cores were acquired. The period investigated spans the last 40 cal ka BP with a focus on the contrast between the last glacial (lowstand) and the Holocene (highstand) periods. Results show contrasting patterns of sediment dispersal, deposition and preservation. Sea level fluctuation remains the main forcing and most of the sediment from the Zambezi River settled on the inner shelf since the last sea level rise. However, we found that two major depocentres have developed on the upper slope during the Holocene consequent to the interaction of bottom currents with seabed morphologies at the shelf edge and at the upper slope. Early Holocene sliding in the north-east and in the south-west upper slope is a secondary but yet major factor of sediment transfer to the deep domain. Identified preconditioning factors for sliding on the slope are related to lowstand sediment loading and fluid circulation on the upper slope, and erosion at the base of slope of a plastered drift. Triggering must be related to margin wide mechanisms such as changes in hydrostatic pressure and reorganisation of sediment dispersal, subsequent to the post-glacial sea level rise, or maybe a period of regional seismicity. Climatic conditions in the Zambezi River watershed during the Bolling-Allerod and Younger Dryas periods are recorded and imprinted on the upper slope in the form of a detrital rich layer and a prominent slope-wide high-amplitude reflector. All over the continental slope, plastering of sediment deposits by bottom currents is pervasive and shows a morphological continuum from erosional scours at the base of slope to sediment waves on the upper slope and a possible interaction between along and across slope transport processes. We conclude that, in addition to sea level, the interplay of external and internal factors such as oceanic circulation and sliding, together with margin morphology, lead to the development of unexpected depocentres on the continental slopes. Thus, the study of modern marine analogues is crucial to avoid misleading interpretation of fossil deposits in terms of paleo sea level and more generally of paleo-environmental conditions. • Early Holocene sliding occurred in contrasting morphological and sedimentary settings • Expanded Holocene deposits on the upper slope related to interaction between bottom current and the morphology of the margin and of the seabed • Continuum of sediment undulations ranging from scours to sediment waves from base of slope to upper slope • Sedimentation contrast between Bolling-Allerod/Younger Dryas and Early Holocene periods visible as a high amplitude reflector [ABSTRACT FROM AUTHOR]

The Gulf of Cadiz Contourite Depositional System (GCCS) developed due to the interaction of the Mediterranean Outflow Water (MOW) with the middle continental slope of the SW Iberian continental margin. The GCCS evolved in a complex tectonic setting within the foreland of the Betic Orogeny and near the Nubia-Eurasia plate boundary. This study used tectonostratigraphic analysis of an extensive 2D multichannel seismic reflection dataset to investigate how inherited basin configuration and tectonic activity controlled sedimentary stacking pattern and evolution of the GCCS. Three regional tectonostratigraphic units (U1 - U3) were recognised in the margin. The younger seismic unit U3 corresponds to the Miocene-Quaternary foreland basin system where the contourite system is generated. Seismic analysis also detected the dextral strike-slip Gil Eanes Fault Zone (described herein for the first time), the Cadiz Fault, the Albufeira-Guadalquivir-Doñana Basement High and several diapiric structures. Integrated analysis of seismic profiles showing these tectonic structures with thickness and earthquake distribution maps suggest four tectono-sedimentary domains. The distinct characteristics shown by contourite features in the different domains, depends at broad-scale on the tectonic-control of the accommodation space (i.e., subsidence or uplift) and at local-scale on the presence of structural highs and fault-related depressions. Both influence bottom-current circulation and thus the evolution of the contourite deposits through the late Miocene and Quaternary. Three main stages have been recognised in the Gulf of Cadiz evolution: 1) the region was the western continuation of the Betic Corridor until the final re-opening of the Strait of Gibraltar (8–5.3 Ma). In this stage there is a predominance of turbidites or hemipelagic deposits, dependant on tectonic activity; 2) with the final re-opening of the Mediterranean-Atlantic connection there is the onset of the Pliocene- Quaternary contourite depositional system (5.3–2.0 Ma). Short-term changes in sedimentation during this stage, from contourite to turbidite deposits, indicate periods of increased tectonic activity; and 3) after the onset of the transpressive tectonic regime in the area (from 2.0 Ma), sedimentation became more homogeneous suggesting stable conditions (decrease of tectonic activity) with dominant contourite deposition. This work highlights the remarkable influence of structural features and tectonic events in controlling the seafloor relief and in turn in influenced the local oceanic circulation processes that controlling the morphology and sedimentary evolution of contourite systems. • Identified four tectono-stratigraphic domains bound by lithospheric structures • Three tectono-sedimentary evolutionary stages were recognised in the Gulf of Cadiz • A new structure was identified in this study, the strike-slip Gil Eanes Fault Zone • Inherited topography and structural features influenced contourite development • Local bottom-current circulation regulated by tectonic-related seafloor relief [ABSTRACT FROM AUTHOR]

To understand the main environmental factors controlling the benthic foraminiferal distribution along continental slopes, and corroborate paleoenvironmental interpretations, we investigated benthic foraminiferal assemblages (total fauna >63 μm) and sedimentological data along six transects on the continental slope of the Espírito Santo Basin (ESB) between 18°20′ and 21°20′ S. Surface sediment samples (0–2 cm) were collected perpendicularly to the coast, from the upper (400 m) to the lower slope (3000 m). The density, taxonomic diversity and assemblage composition change with depth. The genus Globocassidulina dominates the upper and lower slope, whereas Bolivina is the most abundant taxon in the deepest lower slope. The differences in ecological preferences among the most abundant taxa allowed us to recognize five benthic foraminiferal groups, distributed in three main bathymetric sectors: upper, middle – lower, and lower slope. Group I (upper slope, 400 m) is characterized by the highest mean relative abundances of Globocassidulina rossensis , Trifarina spp. and Trifarina angulosa. Group II (middle – lower slope, 1000–1300 m) shows the highest mean relative abundances of Globocassidulina subglobosa , Bolivina albatrossi , Bulimina aculeata and Uvigerina peregrina. Group III (middle – lower slope, 1000–1300 m) is characterized by the highest mean relative abundances of Globocassidulina crassa , Gavelinopsis versiformis , Epistominella exigua and the unilocular group. Group IV (lower slope, 1900 m) shows the highest mean relative abundances of Alabaminella weddellensis , Bolivina inflata and E. exigua. Group V (lower slope, 2500–3000 m) is dominated by the genus Bolivina (B. lowmani , B. pseudoplicata and Bolivina spp). The most abundant taxa along the ESB slope are ecologically associated to the organic matter flux, bottom water oxygen concentration, and hydrodynamics conditions. The quantity and quality of food supply is the primary factor controlling the distribution of benthic foraminiferal assemblages along depth. Secondary factors include the properties of water masses, and intermediate and deep boundary currents. The increased fragmentation of benthic and planktic foraminifera tests (>125 μm) on the upper and middle – lower slope is related to abrasion during transport from shallower regions to the slope. • Recent benthic foraminiferal assemblages change markedly with depth. • Benthic foraminifera distribution is primarily ruled by the organic matter influx. • The organic flux is high on the upper slope due to the shelf-break upwelling. • Opportunistic species confirms the influence of the Vitoria Eddy in the primary productivity. • The properties of waters masses play a secondary role in the microfauna distribution. [ABSTRACT FROM AUTHOR]

A new species of the rare, deep-sea genus Sciadonus Garman, 1899 (Bythitidae) is described based on two specimens obtained by the Brazilian R/V Alpha Crucis on the continental slope off São Paulo State, Southeastern Brazil, western South Atlantic. It differs from its congeners by the combination of the following characters: body pale lacking dark pigmentation except for on female claspers; a pair of dermal tissue flaps anteriorly on lower jaw; pelvic-fin rays present; precaudal vertebrae 39 or 40 and total vertebrae 74 or 75. The key to the species of Sciadonus is updated. A discussion of the presence and differentiation between troglomorphic and miniature characteristics among the species in the aphyonid clade is provided and compared with other bythitids. • A new species of the rare genus Sciadonus is discovered from Brazilian waters. • Highly specialized reproductive apparatus enables internal fertilization and viviparity in a deep-sea fish. • The depletion of sunlight resulted on convergent evolution of troglomorphic traits in deep-sea fishes and cave fishes. • Human activities of oil and natural gas exploration, fisheries and littering may be impacting rare deep-sea species. [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]