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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]

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]

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]

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]

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]

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]

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]

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 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]

Interbedded contourites, turbidites and pelagites are commonplace in many deep‐water slope environments. However, the distinction between these different facies remains a source of controversy. This detailed study of calcareous contourites and associated deep‐marine facies from an Eocene–Miocene sedimentary succession on Cyprus clearly documents the diagnostic value of microfacies in this debate. In particular, the variability of archetypical bi‐gradational contourite sequences and their internal subdivision (bedding, layering and lamination) are explored. Contourites can be distinguished from turbidites, pelagites and hemipelagites by means of carbonate microfacies in combination with bed‐scale characteristics. Particle composition provides valuable information on sediment provenance. Depositional texture, determined by the ratio between carbonate mud and bioclasts, is crucial for identifying bi‐gradational sequences in both muddy and sandy contourites, and normally‐graded sequences in turbidite beds. Equally important are the type and preservation of traction structures, as well as the temporality and impact of bioturbation. Shell fragmentation under conditions of increased hydrodynamic agitation (textural inversion) is recognized as a carbonate‐specific feature of bioclastic sandy contourites. [ABSTRACT FROM AUTHOR]

Three new species of Microspio were found in collections from a range of depths including shallow water in Bermuda, the continental shelf off Massachusetts, and deep water in the South China Sea off Brunei. Microspio fischeri, new species, is associated with shallow water sponges in Bermuda where it is a prey species of a predatory syllid; it is characterized by the medial placement of the first pair of branchiae as well as unusual notopodial capillaries in anterior chaetigers and enlarged notopodial lobes in posterior chaetigers. Microspio lydonia, new species, from the continental shelf on the east coast of the United States is distinguished from M. pigmentata (Reish, 1959) from the west coast by differences in the structure of the nuchal organs and hooded hooks, pigmentation, and Methyl Green staining patterns. Additions to the description of M. pigmentata include illustration of the nuchal organs and dorsal ciliary bands. Microspio ariena, new species, from deep water in the South China Sea off Brunei has enlarged branchiae with large glands that stain deeply with Methyl Green on a few anterior chaetigers, followed by much smaller branchiae on additional chaetigers. The three new species bring the total of described species in the genus to twenty-one, although some species remain problematic. A table comparing important characteristics of all 21 known species of Microspio is included. [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]

Samples were collected in the area of the St. Anna Trough in the northern Kara Sea in September 2015 and July–August 2016. Based on salinity and temperature distribution, four areas have been distinguished: the shelf adjacent to the St. Anna Trough, the shelf edge, and the upper and lower parts of the continental slope. The variability of the structure of phytoplankton communities has been analyzed in view of environmental conditions in the distinguished areas. It is shown that changes in the species structure of phytoplankton are more associated with seasonal reorganization in the community than with the effect of river runoff and waters of the Barents Sea and Atlantic. In the shelf area, the presence of Barents Sea winter water led to an increase in the number of species of early spring diatoms and an increase in the abundance of early and late spring diatoms. An increase in the abundance and biomass of phytoplankton and changes in their vertical distribution in mid-July–early August occurred against the effect of Barents Sea and Atlantic waters on the area and desalination of the upper layer under the effect of river runoff in early September. [ABSTRACT FROM AUTHOR]

Abstract—The lithological-facies zonality of the Neo- and Eopleistocene sediments from two main areas of the Cordilleran submarine margin is described for the first time. Processing of corresponding maps and isopach schemes using A.B. Ronov's volumetric method made it possible to calculate the quantitative parameters of sedimentation for the distinguished types of Pleistocene sediments. Terrigenous sedimentation predominated and was intensified during the Pleistocene. The accumulation of biogenic opal and carbonates was more intense in the Neopleistocene than in the Eopleistocene. [ABSTRACT FROM AUTHOR]

Abstract—Analysis more of 80 hydrocarbon fields, mainly oil-producing, in the deepwater part of the Santos, Campos and Espirito Santo basins reveal the tendency of these large fields to lie in a productive oil-pay belt extending in the sea depth from range from 400 to 2500 m (possibly 3000 m or more) in a system of external depressions stretching along the lower part of the continental slope. This belt may continued to the north. All the fields in this belt in reserves category are estimated as large and giant. In the last 10–15 years, exploration works have been conducted in this belt already in the presalt formation: in the Santos Basin, 29 fields; in the Campos Basin, 21; and in the Espirito Santo Basin 7. It is noteworthy that 48% of the total hydrocarbon production of the country formed in presalt carbonate deposits of the Aptian Formation on the continental slope, 44% postsalt rocks on the continental slope and shelf, and only 8% is attributed to the mainland. In the world, Brazil's deepwater presalt Aptian Formation (Barremian–Aptian in the Santos Basin) is essentially unique. In recent decades, giant hydrocarbon accumulations have been discovered, thereby doubling the country's oil and gas reserves to total reserves of more than 3 billion t and 4.7 trillion m3, respectively. The geology of the presalt formation is narrowly related to tectonic movements that took place during the breakup of the Gondwana supercontinent into the South American and African continents. This took place 150 Ma ago in the Early Cretaceous. The salt of the Aptian Formation is an excellent caprock, the presalt reservoirs are superior in their characteristics, the oil is light and sweet, and the source rocks are enriched in organic matter. The thickness of the Aptian salt is limited, varying from basin to basin; the main width of the salt is in the Santos Basin 400 km and the thickness is 2000 m; in the north, the thickness and width decrease; in the Sergipi Alagoas Basin, it already reaches 100 m. [ABSTRACT FROM AUTHOR]

Abstract—The large-scale expedition of cruise 76 of the R/V Akademik Mstislav Keldysh was performed by the Shirshov Institute of Oceanology from July 1 to August 6 2019 within the Program "Marine Ecosystems of the Siberian Arctic." Seventy-one scientist from Russian Academy of Sciences institutes, Moscow State University, and VNIRO participated. Coordinated hydrophysical, hydrochemical, biooceanological, geochemical, and radioecological research was carried out over the shelf and continental slope in the Kara Sea, Ob estuary, and in the eastern coastal bays of Novaya Zemlya. [ABSTRACT FROM AUTHOR]

A marine bacterial isolate, Bacillus vietnamensis sp. MSB17 from the sediments collected from the continental slope of the eastern Arabian Sea exhibited good Malachite Green (MG) decolorization ability in mineral medium supplemented with glucose and yeast extract under static conditions. The complete decolorization of dye (50 mg/L) was attained within 4 h of incubation. The activities of enzymes such as tyrosinase (0.62 IU/ml), laccase (12.02 U/ml), and manganese peroxidase (6.23 U/ml) were observed during dye degradation. UV-VIS, FT-IR, and GC-MS analysis of dye samples extracted with ethyl acetate confirmed the biodegradation of MG into methanone, [4-(dimethylamino) phenyl] phenyl- and 2, 6-bis (1, 1-dimethylethyl) phenol. The metabolites obtained from B. vietnamensis sp. MSB17 mediated MG degradation did not exhibit any microbial toxicity and phytotoxicity. The present study indicated the efficiency of Bacillus vietnamensis sp. MSB17 to effectively degrade MG, revealing its potential to be further utilized for bioremediation purposes. [ABSTRACT FROM AUTHOR]

• Life-history parameters indicate Macrourus carinatus is vulnerable to overexploitation. • Maximum age recorded in our sample was 53 years. • Long life-span was matched with late reproduction of 12–14 years. • Our data support dimorphism in this species with females growing larger than males. In light of their life-history characteristics, deep-sea fishes display a higher vulnerability to overfishing than most other groups of fish, and their exploitation may not be sustainable even at low levels. In the Falkland Islands, increasing efforts have been made to target deep-sea species, such as the ridge-scaled grenadier Macrourus carinatus , in the waters off the continental slope. Research findings relating to the age and growth of this species remain conflicting, largely as a result of non-representative sampling of the population, inappropriate ageing methods, and the absence of age validation. We show how M. carinatus display life-history characteristics typical of the deep-water fish community, such as a long life (53 years), late age at maturity (females = 14.00 years; males = 12.28 years), slow growth and low levels of natural mortality (females = 0.104 year−1; males = 0.117 year−1) that highlight the susceptibility of M. carinatus to overfishing. In particular, validated age estimates obtained using improved ageing criteria indicate that longevity is up to 28 years greater than previously reported estimates. M. carinatus were shown to be sexually dimorphic in size, with females growing larger (females = 31.49 cm pre-anal length [PAL]; males = 24.97 cm PAL) compared to males. Updated biological parameter estimates indicate M. carinatus are far more vulnerable to fisheries exploitation than previously thought. A precautionary approach must be followed and conservation measures put in place to ensure sustainable management of a directed fishery or bycatch of M. carinatus and other similar deep-sea species. [ABSTRACT FROM AUTHOR]

Two surveys using a combination of midwater trawl and acoustics were undertaken in October 2014 and June 2015 to investigate species composition and biomass density of mesopelagic nekton over the continental slope of the South China Sea (CSSCS). In two surveys, diversity and dominant species of nektons (Chondrichthyes, Osteichthyes and Cephalopoda) showed obviously diel and depth–dependent difference. In 2014, in general species richness and diversity of nektons in the 0–100 m at night were greater than that in the 350–650 m during the day and 350–650 m at night. In Jun. 2015, species richness and diversity of nektons in the 350–650 m during the day were much greater than that in the 350–650 m at night and 0–100 m at night. Myctophidae and Diaphus are the most common fishes in the CSSCS mesopelagic zone. Jellyfishes could cause the nautical area scattering coefficient (NASC) to increase, but the effect of jellyfishes on NASC could vary over the light–night cycle and trawl depth. Catch rates of different nektonic categories varied by time of day and depth. Night–time catch rate at trawl depths < 100 m were greatest, with Myctophidae the most abundant category. In 2014, from 350 to 650 m, day and night mean catch rates of mytophids were similar, however, in 2015, mean day catch rates were 64.1% night values. Cephalopoda are an important component of mesopelagic nekton. At escape rates of 0.95 and 0.99, daytime trawl–based biomass densities in the 350–650 m depth range in 2015 were 0.339 g m−2 and 1.693 g m−2, respectively. Mean daytime NASC from 200 to 1000 was 3163 ± 1223 m2 nmi−2 (2014) and 2503 ± 698 m2 nmi−2 (2015); corresponding acoustic and trawling data produced mesopelagic nekton biomass density estimates of 9.80 g m−2 (2014) and 28.45 g m−2 (2015). More fishes with swimbladders (mainly small sized lanternfishes of light weight) dominated catch in 2014 than in 2015. [ABSTRACT FROM AUTHOR]

Within the East Canadian continental margin, three oil and gas bearing regions have been identified from north to south: the Labrador Sea shelf, the margin of the Grand Banks of Newfoundland, and the Nova Scotia continental margin. In each of these regions, a number of sedimentary basins are distinguished and completely submerged. The following large sedimentary basins are distinguished on the Labrador Sea shelf: the Saglek, Hopdale, and Havke; on the margin of the Grand Banks of Newfoundland, the following basins are known: the Jeanne d'Arc, Flemish Pass, and Orphan. The Scotian Shelf distinguishes the Nova Scotia and Sable basins. It is noteworthy that at high latitudes, such as the Labrador Sea region, the age of productive sediments begins with more ancient rocks (since the Paleozoic) than in the basins to the low latitude (since the Mesozoic), due to which the stratigraphic range of oil and gas bearing in the high latitude basins is much wider. The oil and gas bearing potential in the entire region is mainly related to the continental slopes and turbidite deposits occurring within them. Late Jurassic and Early Cretaceous reservoirs will be the target sediments during deep drilling. Widespread Late Cretaceous and Early Tertiary formations with oil and gas potential are quite realistic, since they do not lie at deep horizons. The oil and gas bearing potential on the margins of basins is associated with Late Cretaceous and Tertiary sediments, alluvial fan deposits, and salt diapirs. [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]

Cruise 81 of the R/V Akademik Mstislav Keldysh was organized by Shirshov Institute of Oceanology and took place from August 27 to September 25, 2020 under the Program "Marine Ecosystems of the Siberian Arctic." Participants included 76 scientists from the institutes of Russian Academy of Sciences, Moscow State University, VNIRO, and the NRC Kurchatov Institute and specialists from the Emergency Situations Ministry. Coordinated hydrophysical, hydrochemical, biooceanological, geochemical, and radioecological research was carried out over the Kara Sea, on the shelf near the St. Anna Trough, the continental slope, the Novaya Zemlya depression, and bays of the eastern coast of Novaya Zemlya. The condition of disposed radioactive waste in bays of the archipelago was assessed. [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]

Catchments provide water and sediment to downstream sedimentary systems, and these form individual source-to-sink systems. Source-to-sink systems comprise adjacent linked segments, commonly hinterland catchments, alluvial- and coastal plains, the continental shelf, continental slope and submarine fan. The dimensions of the catchment and how it scales to downstream segments provides insight into the sedimentary and tectonic controls that influence the morphology and sedimentation patterns in a basins evolution. In ancient sedimentary successions, where the sedimentary routing system is buried and inaccessible for study, or fragmented due to uplift and erosion, using scaling relationships can provide a powerful tool to understand the complete sedimentary system. Observational data from modern sedimentary systems provide an opportunity to create morphological and sedimentological scaling relationships of segments on the entire source-to-sink system. However, previous studies on global modern source-to-sink systems have typically been based on a limited number of examples restricted by the data available at the time and the methodology used to analyze large datasets. In the last decade, the volume and quality of remotely sensed information has significantly improved so that it is now timely to revisit scaling relationships of modern source-to-sink systems' segment morphologies, and discuss the implications of those r esults for sedimentological parameters and applicability to ancient source-to-sink systems. The results of this reanalysis show that dimensions of the catchment and submarine fan segments scale internally in terms of fan width, length and area. In addition, fan area scales to its largest hinterland catchment area in agreement with previous studies, however, it is important to consider all catchments that contribute sediment to a basin floor region. In paleogeographic settings, where individual submarine fans are difficult to tie to a single catchment, and where basin floor systems are amalgamated, the contributing sediment discharge of all catchments may be significant and likely influence the scale of its submarine fan. Accommodation versus sediment supply in relation to relative sea level change are important controls on the position of the shoreline which vary considerably from system to system over time and space, thus influencing morphological relationships between source-to-sink segments. The continental shelf should therefore be viewed as a transient geomorphic feature rather than a segment of a source-to-sink system. Furthermore, the continental slope length should not be used to scale other segments of the source-to-sink system, which contradicts previous research. The underlying tectonic and sedimentological control on the continental shelf and slope segments, in addition to the subjective interpretation of their basinward boundaries, may render those segments unsuitable for scaling the morphology of other segments. The study highlights both the temporal variability and complexity of controls that influence the morphology and scaling relationships of internal and adjacent linked source-to-sink segments, and the need to place this in a framework of both tectonic and sedimentological history. [ABSTRACT FROM AUTHOR]

Quaternary architectural evolution and sedimentary processes on the mid-Norwegian continental slope are investigated using margin-wide three- and two-dimensional seismic datasets. Of ∼100,000 km 3 sediments delivered to the mid-Norwegian shelf and slope over the Quaternary, ∼75,000 km 3 comprise the slope succession. The structural high of the Vøring Plateau, characterised by initially low (∼1–2°) slope gradients and reduced accommodation space, exerted a strong control over the long-term architectural evolution of the margin. Slope sediment fluxes were higher on the Vøring Plateau area, increasing up to ∼32 km 3 ka −1 during the middle Pleistocene, when fast-flowing ice streams advanced to the palaeo-shelf edge. Resulted in a more rapid slope progradation on the Vøring Plateau, these rates of sediment delivery are high compared to the maximum of ∼7 km 3 ka −1 in the adjacent sectors of the slope, characterised by steeper slope (∼3–5°), more available accommodation space and smaller or no palaeo-ice streams on the adjacent shelves. In addition to the broad-scale architectural evolution, identification of more than 300 buried slope landforms provides an unprecedented level of detailed, process-based palaeoenvironmental reconstruction. Channels dominate the Early Pleistocene record (∼2.7–0.8 Ma), during which glacimarine sedimentation on the slope was influenced by dense bottom-water flow and turbidity currents. Morphologic signature of glacigenic debris-flows appear within the Middle-Late Pleistocene (∼0.8–0 Ma) succession. Their abundance increases towards Late Pleistocene, marking a decreasing role for channelized turbidity currents and dense water flows. This broad-scale palaeo-environmental shift coincides with the intensification of Northern Hemispheric glaciations, highlighting first-order climate control on the sedimentary processes in high-latitude continental slopes. [ABSTRACT FROM AUTHOR]

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

Understanding responses of benthic ecosystems to cumulative impacts of natural stressors, long-term ocean change and increasing resource exploitation is an emerging area of interest for marine ecologists and environmental managers. Few, if any, studies have quantitatively addressed cumulative effects in the deep sea. We report here on a study from the continental slope off Vancouver Island (Canada) in the northeast Pacific Ocean, where the Oxygen Minimum Zone impinges on seabed habitats that are subjected to widespread bottom trawling, primarily by the fishery for thornyhead ( Sebastolobus ssp.). We examined how the benthic megafauna in this area was influenced by varying levels of dissolved oxygen and trawling activity, along a depth gradient that was also likely to shape community composition. Continuous video and sonar records from two ROV surveys (50 linear km total; depth range 300–1400 m) respectively provided data on faunal attributes (composition, abundance and diversity) and the frequency of trawl door marks on the seabed. Faunal and trawl data were compiled in a geo-referenced database along with corresponding dissolved oxygen data, and pooled into 500 m segments for statistical analysis. Trawl mark occurrence peaked between 500 and 1100 m, corresponding to areas of slope subjected to hypoxia (<1.4 ml l -1 ) and severe hypoxia (<0.5 ml l -1 ). A combined total of 266,251 megafauna organisms from 87 taxa were enumerated in the two transects. Significant megafaunal assemblages according to depth, trawling intensity and bottom water dissolved oxygen concentration were identified by PERMANOVA analyses, with characterizing taxa identified for all three factors. Depth, dissolved oxygen and trawl mark density accounted for 21% to 52% of the variability in benthic community structure according to multiple regression (DISTLM) models. Species richness was highest at intermediate depths and in areas subject to intermediate levels of trawling, and higher under hypoxia than under severe hypoxia. These statistically significant trends demonstrate that the structuring influences of bottom trawling on deep-sea benthic communities can be observed even where communities are being shaped by strong environmental gradients. [ABSTRACT FROM AUTHOR]

We document upper slope sedimentary process and strata on the passive margin of the north-western South China Sea (SCS) using multibeam bathymetry and high-resolution seismic data. The upper slope can be divided into two segments based on geomorphology, strata, and sediment supply. (1) The east segment is characterised by deep incised canyons and gullies, and slope failure. Submarine canyons with both U- and V-shaped morphology (13-28 km long × 2-4 km wide) are oriented NNE-SSW or NNW-SSE and are approximately perpendicular to the slope. Erosion is dominant, with escarpments, slumps, and several mass transport deposits (MTDs). Shelf-margin clinoforms show strongly upward vertical aggradation with time and are strongly aggradational in style. Since 5.5 Ma, the shelf break line migrated southwards and then retreated to its present position. The segment is classified as erosion-dominated due to insufficient sediment supply. (2) The west segment has a smooth surface, gentle gradient, and a strongly progradational style, with MTDs triggered by high sedimentation rates. Shelf-margin clinoforms display a combination of progradational and aggradational stacking patterns. The shelf break line migrated southwards with time. The segment is classified as deposition-dominated, resulting from plentiful sediment supply. Depositional models have been constructed for each segment: a constant shelf break model with insufficient sediment supply in the east, and a migration shelf break model with plenty sediment supply in the west. This case study contributes to the understanding of the upper slope sedimentary process and stratigraphic style under different sediment supply conditions. [ABSTRACT FROM AUTHOR]

A giant submarine creep zone exceeding 800 km 2 on the continental slope offshore the Dongsha Islands, South China Sea, is investigated using bathymetric and 3D seismic data tied to borehole information. The submarine creep zone is identified as a wide area of seafloor undulations with ridges and troughs. The troughs form NW- and WNW-trending elongated depressions separating distinct seafloor ridges, which are parallel or sub-parallel to the continental slope. The troughs are 0.8–4.7 km-long and 0.4 to 2.1 km-wide. The ridges have wavelengths of 1–4 km and vertical relief of 10–30 m. Slope strata are characterised by the presence of vertically stacked ridges and troughs at different stratigraphic depths, but remaining relatively stationary in their position. The interpreted ridges and troughs are associated with large-scale submarine creep, and the troughs can be divided into three types based on their different internal characters and formation processes. The large-scale listric faults trending downslope below MTD 1 and horizon T 0 may be the potential glide planes for the submarine creep movement. High sedimentation rates, local fault activity and the frequent earthquakes recorded on the margin are considered as the main factors controlling the formation of this giant submarine creep zone. Our results are important to the understanding of sediment instability on continental slopes as: a) the interpreted submarine creep is young, or even active at present, and b) areas of creeping may evolve into large-scale slope instabilities, as recorded by similar large-scale events in the past. [ABSTRACT FROM AUTHOR]

Time-series bathymetric data acquired from 1967 to 2011 are used to evaluate the morphological evolution of the continental shelf and upper continental slope off the city of Nice (SE France, Ligurian Sea). Mapping in water depths of 0–300 m was undertaken to identify the changing morphology of landslide scars and their erosive chutes. Quantitative Digital Terrain Model (DTM) comparisons reveal areas of erosion and deposition over intervals of 5–8 years. Sediment remobilization events on the upper slope (above depths of 200 m) are frequent and significant; landslide scars with volumes > 25,000 m 3 can occur with frequencies of < 8 years. Shelf break retreat toward the coastline can reach 60 m over 7–8 years where the continental shelf is wider (> 200 m). Periods of quiescence (1980–1990 and 2006–2011) are seen to alternate with periods when rapid retrogressive failure increase sediment volumes eroded from the upper slope-shelf transition by an order of magnitude (1999–2006). Temporal variations in landslide activity were correlated to several potential triggering factors that individually would not induce failures, including earthquake activity, rapid deposition of fine-grained sediments on a steep slope, and rainfall leading to fresh groundwater circulation below the shelf. This 4D bathymetric study suggests that over the last 50 years the most important factor triggering landslides offshore Nice is overpressure due to freshwater outflows. [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]

This study examines the mesoscale and submesoscale circulations along the continental slope in the northern Gulf of Mexico at depths greater than 1000 m. The investigation is performed using a regional model run at two horizontal grid resolutions, 5 km and 1.6 km, over a 3 year period, from January 2010 to December 2012. Ageostrophic submesoscale eddies and vorticity filaments populate the continental slope, and they are stronger and more abundant in the simulation at higher resolution, as to be expected. They are formed from horizontal shear layers at the edges of highly intermittent, bottom-intensified, along-slope boundary currents and in the cores of those currents where they are confined to steep slopes. Two different flow regimes are identified. The first applies to the De Soto Canyon that is characterized by weak mean currents and, in the high-resolution run, by intense but few submesoscale eddies that form near preferentially along the Florida continental slope. The second is found in the remainder of the domain, where the mean currents are stronger and the circulation is highly variable in both space and time, and the vorticity field is populated, in the high-resolution case, by numerous vorticity filaments and short-lived eddies. Lagrangian tracers are deployed at different times along the continental shelf below 1000 m depth to quantify the impact of the submesoscale currents on transport and mixing. The modeled absolute dispersion is, on average, independent of horizontal resolution, while mixing, quantified by finite-size Lyapunov exponents and vertical relative dispersion, increases when submesoscale processes are present. Dispersion in the De Soto Canyon is smaller than in the rest of the model domain and less affected by resolution. This is further confirmed comparing the evolution of passive dye fields deployed in De Soto Canyon near the Macondo Prospect, where the Deepwater Horizon rig exploded in 2010, and at the largest known natural hydrocarbon seep in the northern Gulf, known as GC600, located a few hundred kilometers to the west of the rig wellhead. [ABSTRACT FROM AUTHOR]

Sessile animals living on continental shelves or slopes may adjust their growth and reproduction according to temporally and spatially variable food availability, but little information is available on these animals to date. We collected the pedunculate barnacle Heteralepas canci on a continental slope at a depth of 229 m off Cape Nomamisaki in southern Japan. We developed a rearing method for the barnacles and studied their growth and reproduction at different food levels in the laboratory. A total of 136 individual H. canci were fed with Artemia salina larvae and brewer's yeast at three different food levels for 100 days. Both the growth and the ovary development were delayed when food availability was low, whereas the survival rate was lower at the high food level. In addition, an individual survived under complete starvation for 167 days. We concluded that H. canci has plastic life history traits that are adaptive for variable food availability. [ABSTRACT FROM AUTHOR]

New insights into equatorial slope morphology were acquired through analysis of the continental margin of the Potiguar Basin (NE Brazil). In this paper, we present the first full data coverage of the seafloor between the upper and middle continental slopes (100–1300 m) adjacent to the Brazilian equatorial margin, developed using multibeam bathymetric data. Some of the submarine canyons mapped in this study have wall gradients greater than 35°. Wide (∼1700 km) and deep (∼250 m) incisions are present on the continental slope and can be linked to incised valleys that are underfilled or incised only on the outer shelf at depths up to 60 m. Two different types of canyons were identified. Canyons of one type are characterized by heads that indent the shelf edge, association with incised valleys and large fluvial systems, high sinuosity, ‘V’ shapes, and terraces along margins, in addition to erosive features such as landslides and gullies. These characteristics suggest that canyons of this type are associated with the deposition of submarine fan systems, which are considered permeable hydrocarbon reservoirs, on the base of the continental slope. The presence of gullies and sediment waves illustrates the role of bottom currents in the shaping of the slope. The enlargement of the canyons in the study area and the changes in their courses where they cross an important fault suggest that tectonic activity has probably also influenced the morphology of the deep-water environments of the Potiguar Basin. The results of this study constitute initial steps in describing and understanding submarine canyons as part of the equatorial continental Brazilian margin. [ABSTRACT FROM AUTHOR]

High-resolution multi-beam bathymetry, 3D and 2D seismic reflection profiles from the South China Sea are used to investigate the morphology, characteristics, origin and implications to petroleum systems of recurrent slope failure in the Qiongdongnan Basin, northern South China Sea. Seven Late Miocene-Holocene mass-transport deposits (MTDs) and numerous submarine canyons were identified on the continental slope and rise, providing new insights on the evolution of an enigmatic region of the South China Sea. This paper defends that the interpreted MTDs were triggered by a combination of high sedimentation rates and local tectonic uplift. By comparing the stratigraphy of the study area with local sea-level curves, we show that a significant portion of shelf-edge deposits effectively bypassed most of the continental slope during the Miocene-Quaternary to accumulate as large MTDs on its lower part (i.e. on the 'basin-floor'), independently of sea-level changes. Our work has implications to the current sequence stratigraphic models for continental margins, and sheds new light on the reservoir potential of Miocene units in the South China Sea. Hence, regions where base-of-slope fans are expected to occur are, in the study area, occupied by large-scale recurrent MTDs sourced from the shelf edge. Stratigraphically, recurrent slope instability resulted: a) in abrupt episodes of accommodation space creation on the shelf-edge, b) on a moderate reduction in accommodation space at the base of the continental slope, and c) in a complete separation between shelf and distal slope depositional systems, with most stratigraphic markers on 3D seismic data being diachronous across the continental margin. As MTDs also comprise the bulk of channel-fill deposits in large submarine canyons, we propose that the reservoir potential of channel-fill deposits in the South China Sea is closely dependent on the nature of the sediment (i.e. net-to-gross ratio) eroded and transported by these same MTDs. [ABSTRACT FROM AUTHOR]

We integrate morphological, geological and geophysical observations with oceanographic measurements and modelling results to interpret the processes behind the origin and evolution of sandwaves on the upper continental slope of the southwestern Barents Sea. Seven sandwave fields covering c. 130 km 2 and with a volume of c. 72 × 10 6 m 3 occur in water depths of c. 475–800 m. Individual sandwaves reach heights up to 6 m. The sandwaves are sinusoidal with asymmetric stoss–lee side relationships, and time lapse multibeam bathymetry analysis indicates that some sandwaves have migrated up to 10 m towards the NNW over a 4-year time period. This contour current parallel migration is counteracted by currents in several other directions, and the sand unit is thus not a simple contourite. Measurements show prominent diurnal period oscillations and clear spring-neap variations of current direction and speed with along-slope and cross-slope current velocities up to 75 cm s −1 and 65 cm s −1 , respectively. Numerical ocean modelling results produce eddies travelling along the slope, positionally stable, daily recurring vortices and bottom current velocity up to 100 cm s −1 in the sandwave fields. Sandwave migration towards the SE is also observed, and the cross-slope currents are capable of transporting sand up and down the slope, as evidenced by ripples migrating normal to the sandwaves. Eroded sand accumulates in the sandwave fields along the boundary between North Atlantic Water and Norwegian Sea Arctic Intermediate Water. This is a consequence of the combined effect of the NNW directed along-slope Norwegian Atlantic Current and tidally induced topographic waves. The sandwave fields started to form 11 000–13 000 14 C yrs BP or possibly later by current erosion of glacial sediments on the continental shelf and slope. [ABSTRACT FROM AUTHOR]

The recent (2011) installation of seismic station Zemlya Franca-Iocifa (ZFI) on Alexander Island in the Franz Josef Land Archipelago allows new seismic monitoring of the 'continent-ocean' transition zone of the Barents-Kara Sea region. The region is seismically active, and we hypothesize that the prevailing geodynamic factor responsible for the occurrence of weak earthquakes is isostatic compensation of avalanche sedimentation in the 'continent-ocean' transition zone. The crustal velocity structure beneath ZFI was determined using receiver functions. Crustal thickness is 30 km, based on an observed Moho discontinuity with underlying mantle velocities being Vp = 8.15 km/s and Vs = 4.5 km/s The model indicates a mid-crustal boundary at a depth of about 17 km with a velocity contrast between the upper ( Vp = 6.1 km/s, Vs = 3.6 km/s) and lower ( Vp = 6.8 km/s, Vs = 3.9 km/s) layers. In addition, the upper crustal sedimentary layer is about 4 km thick with Vp = 4.3 km/s and Vs = 2.36 km/s. [ABSTRACT FROM AUTHOR]

Circulation patterns and sediment dynamics were studied over the Gulf of Valencia (GoV) continental slope during spring and winter 2011–2012. Two moorings were deployed at two locations; at 450 m depth from February to May 2011, and at 572 m depth from October 2011 to February 2012. At both mooring sites, observations were made of currents, temperature and near-bottom turbidity within the lowermost 80 m above the seafloor. The temperature measurements allowed distinction of the different water masses and their temporal evolution. The fluctuations of the boundary between the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW) masses were monitored, and several intrusions of Western Mediterranean Intermediate Water (WIW) were observed, generally coinciding with changes in current direction. At both mooring sites, the currents generally maintained low velocities <10 cm s −1 , with several pulses of magnitude increases >20 cm s −1 , and few reaching up to 35 cm s −1 , associated with mesoscale eddies and topographic waves. The current direction was mainly towards the SSE on the first deployment and to the ESE on the second deployment. This second location was affected by a strong bottom offshore veering presumably generated by local topographic effects. Increases in suspended sediment concentrations (SSC) were observed repeatedly throughout the records, reaching values >3 mg l −1 . However, these SSC variations were uncorrelated with changes in velocity magnitude and direction and/or with temperature oscillations. Results presented in this paper highlight the complex relation between the hydrodynamics and sediment transport over the GoV continental slope, and suggest that other potential sediment resuspension mechanism not linked with current fluctuations, might play a key role in the present-day sedimentary dynamics. Resuspension due to bottom trawling appears to be the most plausible mechanism. [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]