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The Jan Mayen Channel is located North of the Jan Mayen Island in the Nordic Seas, and is an important gateway for the exchanges of volume, heat and freshwater between the Greenland and the Norwegian basins via the Jan Mayen Current. Based on observations from moored instruments deployed on the shelf and the continental slope of the Jan Mayen Island from August 2017 to August 2018, we document the mean state and the variability of the currents, temperature and salinity and their associated vertical structure. We found that the main feature of circulation is an intense and permanent south‐eastward jet‐like current centered at 150 m depth, located on the 400 m depth slope, with a maximum mean magnitude of 7 cm·s−1. While the velocities recorded on the shelf are largely constant in speed and direction, without any strong seasonal cycle, the moorings located offshore are capturing larger anomalies on short time scales that are likely the signature of eddies passing across the mooring array. Overall, the variability of the transport across the section is correlated with the large‐scale wind pattern over the Nordic Seas, highlighting that the Jan Mayen Current is part of a complex system of currents that operates at larger scale in the region. Plain Language Summary: Located at the junction of the ridges separating the Iceland, Greenland, and Norwegian basins, the Jan Mayen Channel is considered as a route for Greenland Sea water entering into the Norwegian Sea. In 2017–2018, a high‐resolution (6 km spacing mean) mooring array was deployed at the entrance of the Jan Mayen Channel. This array consisting of six moorings progressing onshore to offshore provides a great opportunity to investigate water transport between Greenland and Norwegian Seas via the Jan Mayen Current. We reveal that the Jan Mayen Current presents different behaviors on the shelf and in the channel and we find that the current at the entrance of the channel is characterized by a strong jet‐like structure attached on the shelf with an intensity of about 7 cm·s−1. Thus, over 2017–2018, the Jan Mayen Channel was a regular and direct route for intermediate and deep water from the Greenland Sea to the Norwegian Sea. Key Points: The Jan Mayen Channel was a regular route for the Greenland Sea water to enter the Norwegian Sea in the 2017–2018 periodAn intense and permanent south‐eastward jet‐like current is detected at the entrance of the channel with a maximum magnitude of 7 cm·s−1The variability of Jan Mayen Current at the entrance of the channel is partly correlated with the wind stress curl [ABSTRACT FROM AUTHOR]

The goal of this work is to study the dynamical structure of eddies of the Brazil‐Malvinas Confluence zone (BMC eddies) using direct velocity measurements carried out by Shipborne Acoustic Doppler Current Profiler during five oceanographic cruises performed in 2016–2022. In total, in situ data of 13 BMC eddies, including nine anticyclones and four cyclones are available. These data show that the orbital velocity in such eddies can reach 189 cm/s and their vertical structure is highly barotropic. In several eddies, the velocities exceeding 100 cm/s are observed down to a depth of 560 m and at a depth of 800 m they are still higher than 80 cm/s. The spatial structure of velocity and horizontal shear in the eddies is strongly asymmetric, with higher velocities in the southern part near the intense thermohaline BMC front. Altimetry data show qualitative agreement with in situ data, but underestimate the horizontal velocity shear and the maximum velocities at the periphery of the BMC eddies. We also use satellite altimetry and Argo float measurements to study these eddies, and estimate their impact on the thermohaline structure. The analysis shows that the eddies with orbital velocities exceeding 100 cm/s cause intense temperature and salinity anomalies reaching 7–9°C and 1 psu in anticyclones and −4°C and 0.8 psu in cyclones at 100–300 m depth. Plain Language Summary: The Brazil and Malvinas currents are the main circulation patterns in the Southwest Atlantic. They flow along the South America continental slope toward each other and meet around 38°S generating a thermohaline front known as the Brazil‐Malvinas Confluence zone. Further downstream, both currents retroflect and instabilities generate mesoscale eddies. In this study, we combine new velocity measurements and satellite data for the analysis of the velocity structure and distribution of eddies in the Southwest Atlantic. The velocity observations were carried out across 13 eddies and revealed high velocities exceeding 100 cm/s even at depths greater than 500 m. While direct measurements provide accurate velocity structure in several crossed eddies, satellite altimetry covers the entire region, allowing us to estimate the mean statistical parameters of all eddies over a long period in 1993–2020. The results show that the study area is characterized by the strongest eddies in the western part of the South Atlantic with intense orbital velocities (more than 100 cm/s) reaching 600 m depth. The composite analysis of altimetry and Argo float data shows that such eddies cause very strong temperature and salinity anomalies and significantly affect the salt and heat content in the region. Key Points: The dynamic structure of 13 intense eddies in the Brazil‐Malvinas Confluence zone is investigated using direct Shipborne Acoustic Doppler Current Profiler measurementsThe maximum measured orbital velocity reaches 189 cm/s and the velocities exceeding 100 cm/s are observed down to a depth of 560 mSubsurface temperature and salinity anomalies in the intense eddies can reach 9°C and 1 psu [ABSTRACT FROM AUTHOR]

High-resolution seismic analysis and bathymetry data, used in the Offshore Sinú Fold Belt (OSFB), have revealed seabed and sub-surface anomalies, which were probably caused by the presence of shallow gas within the sedimentary records. Shallow gas is widely detected by the frequent presence of anomalous acoustic reflections including acoustic blanking, enhanced reflections, acoustic plumes, pockmarks, and dome structures. More than 30 anomalies that occur within a subsurface depth of ~65 m were acoustically detected within an area of 1000 km2 on the continental shelf and upper continental slope, in water depths ranging from −20 to −1300 m. Moreover, a map with the spatial distribution of the gas occurrences is shown. A close relationship between the locally elevated seabed (dome structures), pockmarks, and acoustic blanking was found. Most of the active pockmarks may be closely related to the submarine path of the Uramita Fault, indicating that the gas occurrences are controlled by active faulting. The shallow gas occurrence was confirmed by the generation of authigenic carbonate and the occurrence of chemosymbiotic biological communities sampled in the area. Although there is an admixture of biogenic gas, it is believed that many of the features observed relate to thermogenic gas. The identification of these anomalies represents a useful basis for an assessment of marine geohazards and can serve as a hydrocarbon exploration tool. [ABSTRACT FROM AUTHOR]

Against the background of wind-forcing change along with Arctic sea ice retreat, the mesoscale processes undergoing distinct variation in the Beaufort Gyre (BG) region are increasingly important to oceanic transport and energy cascades, and these changes subsequently put oceanic stratification into a new state. Here, the varying number and strength of eddies in the central Canada Basin (CB) and Chukchi–Beaufort continental slope are obtained based on mooring observations (2003–2018), altimetry measurements (1993–2019), and reanalysis data (1980–2020). In this paper, the variability in the BG halocline, representing the adjustment of stratification in the upper layer, is shown in order to analyse how variability occurs under changing mesoscale processes. We find that over almost the last 2 decades the halocline depth has deepened by ∼ 40 m in the south of the central gyre, while that in the north has deepened by ∼ 70 m according to multiple datasets. Surrounding the central gyre, the asymmetry of the halocline, with much steeper and deeper isopycnals over the southern continental slope, reduced after 2014. In the meantime, eddy activities in the upper layer from the southern margin of the BG to the abyssal plain have been enhanced. Moreover, the convergence of the eddy lateral flux has increased as the halocline structures on either side, which is at least 120 km from the central gyre, have reached a nearly identical and stable regime. It has been clarified that long-term dynamic eddy modulation through eddy fluxes, facilitating the freshwater redistribution, affects the meridional asymmetry of the BG halocline. Our results provide a better understanding of the eddy modulation processes and their influence on the halocline structure. [ABSTRACT FROM AUTHOR]

The presence and interannual variability of water masses on the continental shelf surrounding the island of Sardinia are described from three multidisciplinary cruises carried out in September 2019, late August 2020 and September 2021 in the framework of the IDMAR project. A multiparametric probe acquired CTD data along vertical profiles at a total of 166 casts located from the near-shore to the continental slope, between the surface and 300 m depth. The analyses of these observations are for the first time identifying the water mass phenomenology on the Sardinia shelf characterized by the presence of the Atlantic Water at the surface. It shows a mild interannual variability and an unusually low salinity < 37.0 at 35 m on the southwestern approaches, detected during the cruises in 2019 and 2021, and driven by the Algerian eddies. On the southern and eastern shelf, the presence of the Atlantic Water is marked by a salinity of about 38.0, and the water column is affected by the temporal and spatial variability of the South East Sardinia Gyre. These observations are opening new aspects to understand the long-term evolution of the hydrology around Sardinia in the context of the general circulation of the Western Mediterranean basin. [ABSTRACT FROM AUTHOR]

Deep-sea lineages are generally thought to arise from shallow-water ancestors, but this hypothesis is based on a relatively small number of taxonomic groups. Anthozoans, which include corals and sea anemones, are significant contributors to the faunal diversity of the deep sea, but the timing and mechanisms of their invasion into this biome remain elusive. Here, we reconstruct a fully resolved, time-calibrated phylogeny of 83 species in the order Antipatharia (black coral) to investigate their bathymetric evolutionary history. Our reconstruction indicates that extant black coral lineages first diversified in continental slope depths (∼250–3000 m) during the early Silurian (∼437 millions of years ago (Ma)) and subsequently radiated into, and diversified within, both continental shelf (less than 250 m) and abyssal (greater than 3000 m) habitats. Ancestral state reconstruction analysis suggests that the appearance of morphological features that enhanced the ability of black corals to acquire nutrients coincided with their invasion of novel depths. Our findings have important conservation implications for anthozoan lineages, as the loss of 'source' slope lineages could threaten millions of years of evolutionary history and confound future invasion events, thereby warranting protection. [ABSTRACT FROM AUTHOR]

Mapping sediment deposition and erosion by thermohaline ocean bottom currents is important for the development of ocean infrastructure, future geo resources and understanding the sedimentology of contourites and abyssal sediment wavefields. However, only a limited percentage (estimated 20%) of the ocean floor has been mapped directly through seismic or sonar imaging. To better delineate where zones of bottom current deposition and erosion exist, we develop a prediction from numerical model solutions and sedimentological measurements of the ocean floor. This is achieved by integrating three types of data, which include the following: (1) bottom current shear stress from a model run of the HYCOM numerical ocean model; (2) sedimentation rates from ocean lithospheric age and sediment thickness from the GlobSed Model; (3) the measured extents of bottom current deposits from sonar observations. Shear stresses and sedimentation rates inside and outside the mapped extents of bottom current deposits allow us to quantify the conditions that are conducive for bottom current deposition. These conditions are then extrapolated and displayed on a 1/12° arcsecond resolution map of the world's oceans and validated through comparison with known, mapped systems. Based on our prediction, around 12% of the ocean has significant deposition by bottom currents while only 1% has erosion. Most bottom current activity occurs where thermohaline currents impinge upon the ocean floor like on continental slopes or some areas of the abyssal plain. Deposition and erosion also occur where constriction of ocean bottom currents takes place as in straits and seaways. Inland basins (i.e. seas) and continental shelves are mostly disconnected from global‐ocean thermohaline bottom current conveyors and, therefore, have limited bottom current deposition and erosion. Mid‐ocean ridges also have little bottom current deposition due to low sediment supply. [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]

A new mechanism for the renewal of the Sea of Japan intermediate water mass due to the transport of water volumes by mesoscale anticyclonic eddies in the summer season has been established. The structure and dynamics of three eddies over the continental slope east of the Peter the Great Bay are studied in the Sea of Japan based on the data of an autonomous mooring with the Aqualog profiler in June–July 2015. It is shown that the cores of the eddies had an ellipsoidal shape with an elongated lower part. Anticyclones, as isolated dynamic formations, transported water enriched with dissolved oxygen in the western-southwestern direction downstream the Primorye Current along the continental slope. This water based on its thermohaline characteristics corresponded to an intermediate water mass of low salinity in the source of its formation south of the Peter the Great Bay. [ABSTRACT FROM AUTHOR]

Polar and subpolar oceans play a particularly important role in the global climate and its temporal changes, yet these regions are less well sampled than the rest of the global ocean. To better understand the physical or biogeochemical properties and their variabilities in these regions, accurate data mapping is crucial. In this paper, we introduce a mapping methodology that includes a water column shrinking and stretching constraint (SSC) based on the principle of conservation of potential vorticity. To demonstrate the mapping scheme efficiency, we map the ocean temperature in the southern Sea of Okhotsk, where the bottom topography comprises a broad and shallow shelf, a sharp continental slope, and a deep oceanic basin. Such topographic features are typical of polar and subpolar marginal seas. Results reveal that the SSC integrated (SSCI) mapping strongly reduces the mapping error in the broad and shallow shelf compared with a recently introduced topographic constraint integrated (TCI) mapping procedure. We also tested our mapping scheme in the Southern Ocean, which has a comparatively slanted shelf, a wider and gentler slope, and a deep and broad oceanic basin. We found that the SSCI and TCI methods are practically equivalent there. The SSCI mapping is thus an effective method to map the ocean's properties in various topographic environments and should be adequate in all polar and subpolar regions. Importantly, we introduced a standardized procedure for determining the decorrelation length scales—a necessary step prior to implementing any mapping scheme—in any topographic conditions. [ABSTRACT FROM AUTHOR]

This article is devoted to an analysis of double diffusion processes responsible for diapycnal mixing in the zone of the westward Primorye Current in the northern part of the Sea of Japan. This article presents the results of processing and analysis of a long time series of regular measurements of vertical profiles of thermohaline characteristics and current velocity over the upper part of the continental slope between the depths of 60 and 420 m using the Aqualog mooring station from April to October 2015. Efficient heat and salt exchange coefficients and the buoyancy flux are estimated using the Osborne–Cox (1972) and Gregg (1989) parameterizations. The Turner angle for the verification of double diffusion processes is estimated. The contributions of diffusive convection and salt fingers to the buoyancy flux are studied. It is established that, due to differential diffusion, the layer from 80 to 170 m was involved in intense vertical mixing. Moreover, from midspring to early May, diffusive convection penetrates to a depth of 250 m, and then a process like salt fingers plays a leading role. Shear instability, caused, among other processes, by the weakly nonlinear interaction of internal waves, prevails in the underlying layers. [ABSTRACT FROM AUTHOR]

We have analyzed the MZ6 onshore‐offshore wide‐angle seismic profile of the MOZ3‐5 survey to investigate the crustal structure of the South Mozambique passive margin. The NNW‐SSE, 625 km‐long profile runs across the Mozambique coastal plain (MCP), the Continental Shelf and Slope, the Almirante Leite Ridge (ALR), the North Natal Valley (NNV), the Ariel Graben and the Dana Plateau of the Mozambique Ridge. Forward modeling through combined interpretation of the multichannel seismic, the main reflected and refracted phases of the wide‐angle, drill hole data and bathymetric data reveal: (a) a sedimentary cover poorly compacted up to 3 km‐thick, intruded by magmatic dykes that reach the seafloor at the ALR forming 0.5 to 5 km‐wide corrugated mounts, (b) between 2 and 7 km, thick magmatic or volcano‐clastic deposits are observed both at the MCP and NNV, forming a 40 km‐wide terrace at the center of MZ6 and southward‐dipping reflectors in the southern part interpreted as the Pre‐Neocomian Formation contemporary of the Karroo and/or Bombeni‐Movene magmatic events reached in several wells, (c) onshore, the 3‐layered crust reaches 39 km thickness, gradually thinning to ∼27 km at the southern end of MZ6. In the deepest layer, velocities exceed 7.15 km/s, reaching at its base 7.55 km/s at the vertical of the ALR. (d) the seismic Moho is marked by a strong reflection on the wide‐angle data. These results suggests that the basement is composed of slightly thinned and altered continental crust, most likely intruded by several phases of intense magmatism. Plain Language Summary: About 200 Ma ago, the mega‐continent Pangaea broke up. The dispersion of the pieces, linked to the closure and disappearance of the Thetys paleo‐ocean, gave the birth of the Atlantic and Indian Oceans. In detail, the initial position of each piece of this jigsaw is of great importance as it has an impact on our understanding of the genesis of the continental passive margins, the role of tectonic inheritance, the pre‐rift and post‐rift evolution of the topography dynamic (vertical movement) and of the geodynamic of the plates (horizontal movement). Nevertheless, in the Western Indian Ocean, the initial pre‐beak‐up position of Antarctica plate respect to Africa plate is still under debate, mainly due to the lack of deep geophysical data. In 2016, an academic‐industrial collaboration succeeded in acquiring deep information along seven seismic profiles crossing the North Natal Valley (NNV) off the coast of Mozambique. The results falsify the presence of an oceanic crust in that area and thus most of the plate reconstruction models. The NNV presents a thick continental crust intrudedded by several phases of intense magmatism, with at its top, a volcano‐clastic pre‐Neocomian Fm contemporary of the crustal thinning and subsequent spreading between Africa and Patagonia plates. Key Points: The North Natal Valley (NNV) presents a ∼30 km‐thick continental crust, in contrary to what is proposed in most geodynamic modelsVelocity variations in the middle‐lower part of this crust probably represent mantle intrusions during several phases of intense magmatismOn the top of the basement, there is a volcano‐clastic pre‐Neocomian Fm, probably contemporary of the movement of the Patagonia plate [ABSTRACT FROM AUTHOR]

The transfer of nutrients and energy from carcasses to scavengers is an important ecosystem function. In marine ecosystems, mammal carcasses can represent a spatiotemporally restricted but substantial pulse in resource availability, as they are typically only briefly available to scavengers on the surface. Little is understood about how these scavengers respond to such pulses, or how inter-scavenger interactions may influence their behaviour. We describe scavenging interactions of procellariiform seabirds at a fresh and floating New Zealand Fur Seal Arctocephalus forsteri carcass, recently killed by a White Shark Carcharodon carcharias, over the continental slope of southeastern Australia. We highlight potential exclusive and facilitative interactions between the shark and various seabirds, which may play an important role in energy-transfer dynamics in surface pelagic environments. We also provide apparently novel descriptions of scavenging at a marine mammal carcass for six of the seven seabird species that attended the carcass. Further study of sea-surface scavenger behaviour, interactions, and ecology will provide valuable insights into energy-transfer dynamics in pelagic ecosystems. [ABSTRACT FROM AUTHOR]

The reasons for the origin of narrow time-dependent currents formed in the Black Sea in the lower region of the constant pycnocline and deeper are analyzed on the basis of the results of numerical modeling. The prepositions for the generation of deep-water countercurrents in the hydrophysical fields of the Black Sea are studied with reference to the example of its north-east region, where they manifest themselves most frequently. In September 2016 and February 2017 the countercurrents in the region of the North-Caucasian coast were fixed according to the observation data of the ARGO profiling float ID6901833. On the basis of the numerical model of the Marine Hydrophysical Institute (MHI) with a 1 km-resolution and the assimilated data of the hydrological observations of the temperature and salinity the hydrophysical fields of the Black Sea are numerically simulated for the period of 2016–2017. The results of the calculations are used to reproduce the variations in the deep-water flow directions in the above-noted region and to analyze the fields of the main geophysical parameters, together with their derivative parameters. The effect of the mesoscale anticyclonic eddies and the density gradients on the velocity field structure and variability is illustrated. It is established that countercurrents propagated during several days in the anticyclonic direction, along the continental slope on the horizons from 50–100 to 500 m, and their formation took place in the conditions of the attenuation of the cyclonic Black Sea Rim Current in the upper sea layer and the intensification of the Kerch anticyclone. [ABSTRACT FROM AUTHOR]

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The Gaoping Submarine Canyon (GPSC) off Southwest Taiwan has been extensively studied due to its unique geology, the role of transferring terrestrial material to the deep sea, and diverse biological communities. However, there is a lack of understanding of carbon cycling across the sediment--water interface in the canyon. This study aims to fill the gap by utilizing the field data collected between 2014 and 2020 and the Linear Inverse Model (LIM) to reconstruct the benthic food web (i.e., carbon flows through different stocks) in the head of GPSC and the upper Gaoping slope (GS). The biotic and abiotic organic carbon (OC) stocks were significantly higher on the slope than in the canyon, except for the bacteria stock. The sediment oxygen utilization was similar between the two habitats, but the magnitude and distribution of the OC flow in the food web were distinctively different. Despite a significant input flux of ~1400 mg C m-2 d-1 in the canyon, 85% of the carbon flux exited the system, while 14% was buried. On the slope, 75% of the OC input (~105 mg C m-2 d-1) was buried, and only 11% exited the system. Bacteria processes play a major role in the carbon fluxes within the canyon. In contrast, the food web in the upper slope exhibited stronger interactions among metazoans, indicated by higher fluxes between meiofauna and macrofauna compartments. Network indices based on the LIM outputs showed that the canyon head had higher total system throughput (T..) and total system through flow (TST), indicating greater energy flowing through the system. In contrast, the slope had a significantly higher Finn cycling Index (FCI), average mutual information (AMI), and longer OC turnover time, suggesting a relatively more stable ecosystem with higher energy recycling. Due to sampling limitations, the present study only represents the benthic food web during the "dry" season. By integrating the field data into a food web model, this study provides valuable insight into the fates of OC cycling in an active submarine canyon, focusing on the often overlooked benthic communities. Future studies should include "wet" season sampling to reveal the effects of typhoons and monsoon rainfalls on OC cycling. [ABSTRACT FROM AUTHOR]

We investigate interaction between an anticyclonic eddy (AE) and semidiurnal internal tide (SIT) on the continental slope of the northeastern South China Sea (SCS), using a high spatiotemporal resolution numerical model. Two key findings are as follows. First, the AE promotes energy conversion from low-mode to higher-mode SIT; additionally, production terms indicate that the energy is also transferred from the SIT field to the eddy field at an average rate of -3.0 mW m-2. Second, the AE can modify the spatial distribution of tidal-induced dissipation by both refracting and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a shift of the internal tidal rays to the north or south. These findings deepen our understanding of complex interactions between AE and SIT and of their impacts on energy conversion, wave propagation, and coastal processes. [ABSTRACT FROM AUTHOR]

We investigate interaction between an anticyclonic eddy (AE) and semidiurnal internal tide (SIT) on the continental slope of the northeastern South China Sea (SCS), using a high spatiotemporal resolution numerical model. Two key findings are as follows. First, the AE promotes energy conversion from low-mode to higher-mode SIT; additionally, production terms indicate that the energy is also transferred from the SIT field to the eddy field at an average rate of -3.0 mW m-2. Second, the AE can modify the spatial distribution of tidal-induced dissipation by both refracting and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a shift of the internal tidal rays to the north or south. These findings deepen our understanding of complex interactions between AE and SIT and of their impacts on energy conversion, wave propagation, and coastal processes. [ABSTRACT FROM AUTHOR]

Pore pressure (PP) prediction from the downhole response is challenging due to the complex relationship between PP and the underlying variability of downhole response at continental slope setting. Conventional methods are mostly deterministic, and they do not usually take into account the underlying variability and uncertainty in the prediction. Here, we implement statistical machine learning (ML) augmented interpretation techniques for the prediction of PP of well 1344A located at the slope setting of sites IODP 323. Within this framework, we quantify the relative influence of each downhole response and hydrostatic pressure (HP) on PP prediction by taking, (i) downhole responses as input and PP as a target, and (ii) downhole responses + HP as input and PP as target and to fix input parameter lag by examining partial auto-correlation function (PACF) analysis results for ML model development. Comparative performance evaluation shows Gaussian process-based GPRN model is superior to the other three ML models such as ANFIS, ARD-BNN, and SVM based on R2 value between the target via Eaton's and porosity methods and predicted via ML models. Uncertainty analysis shows that GPRN-based prediction falls within the 95% confidence interval (CI) at most of the depths. Further, the derivation of ML-based polynomial equations can be an interesting step towards the development of data-driven prediction of PP that potentially would be exploited for data-driven PP prediction studies in other complex geological settings of the world. [ABSTRACT FROM AUTHOR]

Liang, Z.; Ji, D.; Zhang, X.; Lingyun, W.; Zhang, T.; Li, S.; Yong, J.; Luo, J.; Liu, Y., and Zeng, J., 2023. Carboniferous oceanic basin sediment-gravity flows in the margin of the Junggar Basin, NW China: Characterisation and implications for hydrocarbon potential and evolution pacing. Journal of Coastal Research, 39(5), 890–906. Charlotte (North Carolina), ISSN 0749-0208. Several Carboniferous deep-marine-sandstone reservoirs have recently been discovered in the Junggar Basin, NW China. These reservoir sandstones were deposited by sediment-gravity flows that occurred on the continental slope of the Junggar Basin, and they have high hydrocarbon exploration potential. In this study, careful observations and petrological and geochemical analyses of samples from outcrop sections of Carboniferous rocks from the Junggar Basin were conducted to establish the deep-marine sedimentary characteristics, depositional environments, and mechanism of these gravity-flow deposits, as well as a sedimentary model for their occurrence. The deep-marine, gravity-flow deposit types include those of turbidity currents, debris flows, and slumps. The debris-flow deposits can be divided into pebbly debris-flow deposits and sandy debris-flow deposits. Results allow the relationship between the type and nature of gravity flows and ocean basin evolution to be established. During the early Carboniferous, the ocean basin had sufficient space to accommodate incoming sediment, and the sediment transport distance was long. The gravity-flow sediments of this period are dominated by sandy debris-flow deposits and turbidity-flow deposits characterised by thin individual layers but thick accumulations of multiple deposits. With continuous narrowing of the oceanic basin during the late Carboniferous, the basin had a smaller accommodation space. The main types of gravity-flow deposition during this period were pebbly and sandy debris flows, with rare thin turbidity-flow deposits. These deposits were coarser grained than their early Carboniferous equivalents, and their cumulative thicknesses were smaller. The results of the study provide insights into the prediction of deep-marine reservoir sandstones and the distribution of hydrocarbons in the Junggar Basin. [ABSTRACT FROM AUTHOR]

Hydrozoans are recognized as one of the main and most characteristic zoological groups of the Antarctic benthos, despite the fact that there are still large Antarctic areas where the hydrozoan fauna is completely unknown or poorly known (e.g., the Admunsen Sea and Mary Byrd Land, in West Antarctica, and Queen Maud Land and Enderby Land, in East Antarctica). The present study contributes to a better understanding of the Ross Sea benthic hydroid fauna by studying material collected through several New Zealand expeditions mostly with RV Tangaroa. The Ross Sea includes the world's largest marine-protected area (MPA) and is of considerable biological value and importance for scientific research. Although some parts of the Ross Sea shelf have been intensively sampled, others have not, including deeper parts of the continental shelf and the slope. Forty species were found, belonging to 15 families and 19 genera. Six species, including Eudendrium megaloarmatus sp. nov., Nemertesia gelida sp. nov., Schizotricha frigida sp. nov., Symplectoscyphus pseudofrondosus sp. nov. and Symplectoscyphus tortuosus sp. nov., represent new records, bringing the number of known species in the Ross Sea to 84. Leptothecata is dominant, with 35 species, while Anthoathecata is represented by five species. Symplectoscyphidae is the most diversified family with 12 species (30%), and Symplectoscyphus is the most speciose genus with nine species (23%). Three main hydroid assemblages have been found in the studied area, two with a wide bathymetric range and relatively high species diversity, and a third with a narrow and deep bathymetric range and remarkably low hydroid diversity. The hydroid fauna is dominated by species with a wide bathymetric distribution and virtually all species are restricted to Antarctic or Antarctic/sub-Antarctic waters, with 70% endemic to the Antarctic region. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Current is guided by the topographic gradient of the Antarctic continental slope and creates a dynamical barrier between the continental shelf and the open ocean. The current's vertical structure varies around the continent affecting cross‐slope water mass exchange with consequences for Antarctic mass loss, ventilation of the deep ocean, and carbon uptake. The Antarctic Slope Current is surface‐intensified in many regions but bottom‐intensified in regions of dense overflows. This study investigates the role of dense overflows in modifying the dynamics of the bottom‐intensified flow using a 0.1° global ocean‐sea ice model. The occurrence of bottom‐intensification is tightly linked with dense overflows and bottom speeds correlate with dense overflows on interannual time scales. A lack of vertical connectivity between the bottom and surface flow, however, suggests that the along‐slope bottom water flows are coincidentally co‐located with the Antarctic Slope Current, rather than dynamically a part of the current. Plain Language Summary: The Antarctic Slope Current is a narrow ocean current that travels around Antarctica following the continental slope. It separates the shallow and cold continental shelf from much warmer waters in the open ocean. Intrusions of the relatively warm water across the continental slope impacts melting of Antarctic ice shelves and global sea level rise. Understanding what controls the strength and variability of the Antarctic Slope Current is therefore important. The Antarctic Slope Current usually has the largest velocities near the surface, but there are regions where there is also a strong bottom flow. We use a coupled ocean‐sea ice model and show that the bottom flow is controlled by the export of very dense shelf water that flows down the continental slope in a few locations around the continent. However, the bottom and surface flow does not vary together on interannual time scales which tells us that the two components of the Antarctic Slope Current are largely independent. The result is important as the formation of dense shelf water is expected to reduce in the future which will impact the deep flow, but not the surface component. Key Points: Simulations reveal a close spatial relationship between the bottom‐intensified Antarctic Slope Current and Dense Shelf Water exportInterannual variability of Dense Shelf Water is reflected in the bottom speed of the bottom‐intensified Antarctic Slope CurrentThe surface component varies independently from the bottom‐intensified flow implying two distinct, co‐located currents [ABSTRACT FROM AUTHOR]

Proton-pump rhodopsin (PPR) in marine microbes can convert solar energy to bioavailable chemical energy. Whereas bacterial PPR has been extensively studied, counterparts in microeukaryotes are less explored, and the relative importance of the two groups is poorly understood. Here, we sequenced whole-assemblage metatranscriptomes and investigated the diversity and expression dynamics of PPR in microbial eukaryotes and prokaryotes at a continental shelf and a slope site in the northern South China Sea. Data showed the whole PPRs transcript pool was dominated by Proteorhodopsins and Xanthorhodopsins, followed by Bacteriorhodopsin-like proteins, dominantly contributed by prokaryotes both in the number and expression levels of PPR unigenes, although at the continental slope station, microeukaryotes and prokaryotes contributed similarly in transcript abundance. Furthermore, eukaryotic PPRs are mainly contributed by dinoflagellates and showed significant correlation with nutrient concentrations. Green light-absorbing PPRs were mainly distributed in >3 μm organisms (including microeukaryotes and their associated bacteria), especially at surface layer at the shelf station, whereas blue light-absorbing PPRs dominated the <3 μm (mainly bacterial) communities at both study sites, especially at deeper layers at the slope station. Our study portrays a comparative PPR genotype and expression landscape for prokaryotes and eukaryotes in a subtropical marginal sea, suggesting PPR's role in niche differentiation and adaptation among marine microbes. [ABSTRACT FROM AUTHOR]

Continental slopes can play a significant contribution to marine productivity and carbon cycling. These regions can harbour distinct geological features, such as salt diapirs and pockmarks, in which their depressions may serve as natural sediment traps where different compounds can accumulate. We investigated the prokaryotic communities in surface (0–2 cm) and subsurface (18–20 or 22–24 cm) sediments from a salt diapir and pockmark field in Santos Basin, Southwest Atlantic Ocean. Metabarcoding of 16 samples revealed that surface sediments were dominated by the archaeal class Nitrososphaeria, while the bacterial class Dehalococcoidia was the most prevalent in subsurface samples. Sediment strata were found to be a significant factor explaining 27% of the variability in community composition. However, no significant difference was observed among geomorphological features. We also performed a metagenomic analysis of three surface samples and analysed the highest quality metagenome-assembled genome retrieved, which belonged to the family CSP1–5, phylum Methylomirabilota. This non-methanotrophic methylotroph contains genes encoding for methanol oxidation and Calvin Cycle pathways, along with diverse functions that may contribute to its adaptation to deep-sea habitats and to oscillating environmental conditions. By integrating metabarcoding and metagenomic approaches, we reported that CSP1–5 is prevalent in the sediment samples from Santos Basin slope, indicating the potential importance of methanol metabolism in this region. Finally, using a phylogenetic approach integrating 16S rRNA sequences assigned to Methylomirabilota in this study with those from a public database, we argued that CSP1–5 public sequences might be misclassified as Methylomirabilaceae (the methanotrophic clade) and, therefore, the role of these organisms and the methanol cycling could also be neglected in other environments. [ABSTRACT FROM AUTHOR]

Lumbrineriopsis dulcis sp. nov. is morphologically described from the continental shelf and slope of Espírito Santo and the Campos Basin of Rio de Janeiro state, southeastern Brazil, at depths between 14 and 400 m. Lumbrineriopsis mucronata is the only species of the genus recorded until now in Brazil. The new species differs from other congeneric species in its jaw-apparatus morphology with unfused mandibles and a fixed number of simple limbate chaetae and simple, bidentate, hooded hooks in each parapodium. This paper aims to fill the gap in knowledge on the family Lumbrineridae, which has not been studied in Brazil for the last 25 years and provides the first record of the genus from Espírito Santo and Rio de Janeiro states. This record is significant given the damage to the marine ecosystem of the Espírito Santo region due to the 2015 rupture of the Samarco mining company dam, the largest environmental disaster in Brazil's history. In addition, this region has important environmental conservation units such as Costa das Algas Environmental Protection Area, Santa Cruz Wildlife Refuge, and Comboios Biological Reserve. All these preserved areas are of paramount importance for the protection of marine biological diversity. [ABSTRACT FROM AUTHOR]

The structural styles and magnitudes of Alpine tectonic inversion are reviewed for the Atlantic margin of SW Iberia, a region known for its historical earthquakes, tsunamis, and associated geohazards. Reprocessed, high-quality 2D seismic profiles provide new images of 26 faults, which were mapped to a depth exceeding 10 km for the first time in this work. The faults are mostly syn-rift structures accommodating vertical uplift and horizontal advection (shortening) during Alpine tectonics. At a regional scale, tectonic reactivation has been marked by: a) the exhumation of parts of the present-day continental shelf, b) local folding and thrusting of sediment at the foot of the continental slope, and c) oversteepening of synand post-rift strata near reactivated faults (e.g. 'passive uplift'). This work proves, for the first time, that geometric coherence dominated the growth and linkage of offshore faults in SW Iberia; thus, they are prone to reactivate as a kinematically coherent fault network. Importantly, they form 100-250 km long structures, the longest of which may generate earthquakes with a momentum magnitude (Mw) greater than 8.0. Tectonic inversion started in the Late Cretaceous and its magnitude is greater close to where magmatic intrusions are identified at depth. In contrast to previous models, this work postulates that regions where Late Mesozoic magmatism was more intense comprise thickened, harder crust, forming lateral buttresses to NW-SE compression. It shows these structural buttresses to have promoted the development of early stage fold-and-thrust belts - typical of convergent margins - in two sectors of SW Iberia. [ABSTRACT FROM AUTHOR]

Active continental margins are tectonic sites with complex sedimentary processes. Tectono–sedimentary interactions occur over geological time and determine the modern morphology of the margin. However, such interactions have been poorly documented in high‐latitude regions. This study focuses on deep‐water sedimentary systems on the South Shetland convergent margin, which is the only remaining active continental margin in Antarctica. Numerous gullies, 20 canyons and three contourite drifts are identified by interpreting bathymetry, oceanography and reflection seismic data. Heavy mineral contents of a gravity core, located at a downslope elongated mounded drift, show the asynchronous interplay of downslope and alongslope processes. The rest of the margin is dominated by turbidity currents. Variations in the slope gradient control thalweg profiles and sinuosity of canyons. Tectonic‐related morphology restricts the distribution of contourite drifts. Earthquakes triggered by underplating and tectonic compression may induce slope instability at the lower flank of the plastered drift. Tectonic uplift influences the amount of sediments transported by ice sheets and controls the shelf stacking pattern. The mixed turbidite–contourite system transitions to separated canyon and drift systems from passive to active continental margins under the influence of the tectonic‐related morphology. A systematic comparison has been made among several convergent margins with similar tectonic settings. Results suggest that submarine canyons on these shelf‐slope systems have similar morphological features and are comparable in size. Coarse sediment input and steep continental slopes (mean slope 7 to 10°) control the canyon morphology on these margins. Therefore, this research has important implications for furthering the current understanding of sedimentary systems on high‐latitude convergent margins and tectono–sedimentary interactions. [ABSTRACT FROM AUTHOR]

Carbonate nodules were recovered by gravity coring during a complex research expedition conducted in the Sea of Japan aboard the R/V Akademik Oparin (cruise 61), which were identified as pseudomorphs after ikaite (glendonite). This article presents the results of electron-probe analysis and tomography studies of authigenic carbonates and describes gas-geochemical features of host sediments along the continental slope of the Sea of Japan and in the Tatar Strait. [ABSTRACT FROM AUTHOR]

Using observations and theoretical models, a substantial topographic modulation on the quasigeostrophic (QG) dynamics, which results in a primary surface mode distinct from the classic first baroclinic (BC1) mode with a flat bottom, is revealed in the northern South China Sea (NSCS). In contrast to open oceans, the surface-intensified modes decay downward more rapidly over the continental slope of the NSCS, with a mean e-folding scale of approximately 1/5 of water depth. The subinertial flow variability appears to be vertically incoherent, with planetary and topographic Rossby waves dominating in the upper and deep layers, respectively. With a larger deformation radius (Rd), the surface-mode Rossby waves propagate at a phase speed ~1.5 times of that of the BC1 mode. Moreover, the modal structures can be substantially modified by seasonal NSCS circulation, which is significantly enhanced over continental slopes. Analysis of the triad interactions further implies that the short waves tend to transfer energy to larger scales via the inverse cascade and only those with wavelengths larger than Rd ≈ 70 km in the NSCS can persist because of a slower unstable growth rate but a higher fraction of upscale energy transfer. The present theory excludes the bottom-trapped mode, which is closely associated with topographic Rossby waves and is observed to be significant in the abyssal NSCS. Hence, a complete normalmode basis for any QG state is required for a study that focuses on flow variability throughout the water column. Our findings provide an insight into the vertical partition of horizontal kinetic energy for QG motions, as well as the relevant oceanic variation in marginal seas. [ABSTRACT FROM AUTHOR]

This paper presents a significant advancement in the understanding of tsunamigenic landslide hazard across the length of the Makassar Strait in Indonesia. We use statistical emulation across the length of the continental slope to conduct a probabilistic assessment of tsunami hazard on a regional scale, across 14 virtual coastal gauges. Focusing on the potential maximum wave amplitudes (distance between the wave crest and the still‐water level) from possible tsunamigenic landslide events, we generate predictions from Gaussian Process emulators fitted to input‐outputs from 50 training scenarios. We show that the most probable maximum wave amplitudes in the majority of gauges are between 1 and 5 m, with the maximum predicted amplitudes reaching values of up to 10 m on the eastern coast, and up to 50 m on the western coast. We also explore the potential use of Gaussian multivariate copulas to sample emulator prediction input values to create a more realistic distribution of volumes along the continental slope. The novel use of statistical emulation across a whole slope enables the probabilistic assessment of tsunami hazard due to landslides on a regional scale. This area is of key interest to Indonesia since the new capital will be established in the East Kalimantan region on the western side of the Makassar Strait. Plain Language Summary: This work is the first to use statistical models to conduct a landslide‐generated tsunami hazard assessment for the whole of the Makassar Strait in Indonesia. From 50 simulated landslide‐tsunami scenarios, we fit statistical models (known as emulators) to then predict the likelihood and maximum wave height of potential tsunami waves in 14 different locations along the Makassar continental slope. These predictions show that the most likely wave heights were between 1 and 5 m, with the highest predicted waves reaching up to 10 m on the eastern coast and up to 50 m on the western coast. The results of this study are particularly important because Indonesia has announced the relocation of its new capital city to the western side of the Makassar Strait, within the study area. Key Points: This is the first use of emulation for tsunamigenic landslide hazard assessment worldwide integrating both uncertain location and sizeThis is the first tsunamigenic landslide hazard assessment for the whole Makassar Strait regionProbable tsunami wave amplitudes reach up to 50 m on the West coast and around 14 m where the Indonesian capital will be relocated [ABSTRACT FROM AUTHOR]

Parilia alcocki is a deep-sea crab inhabiting the continental shelves and slopes of the eastern Arabian Sea and western Bay of Bengal at a depth of 128–457 m. No published information is available on its population characteristics and sexual dimorphism. The present study provides the first-ever insight into the population differentiation and sexual dimorphism in P. alcocki using Geometric Morphometric Analysis (GMA) of carapace and chela shapes. The Arabian Sea population possessed carapaces with a more pointed anterior and a rounded posterior margin as compared with the Bay of Bengal population. When chela shapes are compared, the Arabian Sea crabs possess an elongated, narrower arm, and shorter pollex. The observed shape variations could be attributed to heterogeneous habitat conditions in these regions which influence feeding and predation. Sexual dimorphism in carapace shapes was indiscernible. However, males exhibited wider intra-specific variations in carapace shape and show a larger average and maximum size for linear carapace measurements. Also, male crabs possess elongated and narrow arms and shorter pollex, whereas the females have a broader and shorter arm and longer pollex, indicative of classical sexual size dimorphism. Our study confirmed the suitability of GMA to understand the ecological and biological characteristics and trait-habitat linkages of P. alcocki. [ABSTRACT FROM AUTHOR]

Observations of temperature, salinity, and oxygen on the southern Vancouver Island shelf show a large‐scale exchange of shelf water with offshore water, just offshore of a semi‐permanent recirculation, often termed the Juan de Fuca Eddy. The Eddy occupies a region where the shelf widens abruptly in the lee of a bank. The water in this Eddy is a mixture of offshore water and water from a buoyant coastal current. This water is well‐mixed along a mixing line in temperature‐salinity space, though it retains stratification, and is either rapidly mixed or has a long residence time. There is a less than 1 km wide temperature‐salinity front on the offshore side of this well‐mixed water that has no sign of instabilities. The clearest evidence of cross‐front transport is found during a tidally resolved survey over a bank. The transport is due to flows in the cross‐bank direction that also drive 50 m tall hydraulic jumps. Upstream of the Eddy, there is an along‐shelf current flowing equatorward. However, the whole current separates from the shelf before reaching the Eddy, in the lee of a bank, and is replaced by water from offshore. The separation event was also seen in sea‐surface temperatures from satellite images as a tongue of cool coastal water that is ejected offshore. Plain Language Summary: The southern Vancouver Island continental shelf is biologically productive due to high nutrient input from the Strait of Juan de Fuca and Salish Sea estuarine system and substantial cross‐shelf transport due to the complicated topography. Here, we present an intensive sampling of the Juan de Fuca Eddy region. The observations show that below the surface mixed layer, the water in the Eddy is low in oxygen, and has undergone substantial vertical and lateral mixing. In contrast to previous literature, we find that the low oxygen in the Eddy is likely because of respiration rather than being pulled from low‐oxygen water in the California Undercurrent. The observations also show a remarkable flow separation of the equatorward shelf current. The current is seen to detach and is pushed offshore. Such events are readily seen in satellite imagery, but our observations indicate that the separation extends the depth of the water column on the shelf, and that this separation may be partially driven by the local bathymetry. The separation is a very strong cross‐shelf exchange event, and transports substantial nutrient‐rich coastal water offshore to drive productivity in the deeper ocean adjacent to the continental slope. Key Points: The shelf break current along Vancouver Island separates downstream of a submarine bankOffshore water is drawn onto the shelf and forms a sharp semi‐persistent front with the Juan de Fuca EddyThe Eddy shows evidence of long residence times, and little evidence of deep‐water origin [ABSTRACT FROM AUTHOR]

The sedimentary dynamics and geological evolution of the Naples canyons during the Late Quaternary have been studied based on sedimentological and seismo-stratigraphic data. Several factors, including the sedimentary environments, tectonic setting, and volcanic eruptions, have controlled the geological evolution of the coastal and marine areas of the Bay of Naples. The main data and methods include the sedimentological data analysis, the seismo-stratigraphic techniques applied in the geological interpretation of seismic profiles, and the integrated analysis of core data that were previously published. The formation of the Dohrn canyon is controlled by fluvial processes, active in correspondence with the palaeo-Schiazzano River system and by the main eruptive events involving the submarine portion of Naples Bay, including the Campanian Ignimbrite (CI; 39 ky B.P.) and the Neapolitan Yellow Tuff (NYT; 15 ky B.P.). The formation of the Magnaghi canyon is controlled by erosional processes on the continental slope of Procida Island, which was active during the last eruptive phases of the island (Solchiaro Formation; 18 ky B.P.), triggering high rates of volcaniclastic supply. [ABSTRACT FROM AUTHOR]

The paper analyzes quasiperiodic upwellings and downwellings on the shelf and upper part of continental slope of the northeastern Black Sea. It is shown that these processes are related to changes in intensity and direction of alongshore current and the following geostrophic adjustment of the density field. The source of such changes is the meandering of the Black Sea Rim Current (RC). It leads to a quasiperiodic change in direction of the alongshore current, from northwestern (cyclonic RC meander) to southeastern (anticyclonic RC meander, or eddy). These cycles, or phases, have an average duration of about 10 days. During the northwestern phase, the permanent Black Sea pycnohalocline (hereafter pycnocline) and seasonal thermocline descend, their thickness increases, and so does the thickness of the upper mixed layer (UML). During the southeastern phase, both the pycnocline and seasonal thermocline ascend and become thinner, along with the UML, which also becomes thinner. In both phases, isopycnals in the pycnocline and isotherms in the thermocline demonstrate quasi-in-phase vertical oscillations, which have a good correlation with the speed and direction of the alongshore current. These correlations allow estimation of the magnitude of upwellings and downwellings in the shelf–slope area of the northeastern Black Sea using data series of current velocity profiles. [ABSTRACT FROM AUTHOR]

The structure and productivity of planktonic microbial communities in the ecosystems of the Siberian Arctic seas are significantly dependent on freshwater input. During the study, we determined the spatial distribution of the abundance, biomass, and production of heterotrophic bacterioplankton in the Western Laptev Sea on the transect from the Khatanga River estuary to the continental slope and assessed the impact of river freshwater discharge. The influence of fresh water on bacterioplankton was restricted mainly to Khatanga Bay (KHAB) and the transitional zone (TZ) and was poorly recognized in the Western shelf (WS) and continental slope (CS) areas. The total bacterial abundance decreased from KHAB to the CS. Particle-attached bacteria constituted on average 63.0% of the total abundance of bacterioplankton in KHAB and 1.0% at the CS. Average bacterial production in the water column was highest in KHAB (10.3 mg C m−3 d−1), decreasing towards the CS (0.7 mg C m−3 d−1). In KHAB and TZ, bacteria were the main component of the planktonic community (44−55%). These results show that at the end of the growing season, bacterial processes prevailed over autotrophic ones and contributed largely to the total biological carbon flux in the coastal ecosystem of the Western Laptev Sea. [ABSTRACT FROM AUTHOR]

Squaliform sharks are relatively vulnerable bycatch in many deepwater fisheries. The diets of two deep-water sharks, Deania calcea and Deania profundorum, on the continental slope and continental shelf (200-1100 m) of the Moroccan coasts (North-East Atlantic) were subjected to an examination of the stomach content using monthly samples collected between February 2018 and March 2021. For investigation, 683 Deania calcea individuals were collected, ranging in size from 55 to 116cm, with 423 females and 267 males. While, 161 Deania profundorum individuals were sampled, with 117 females and 44 males ranging in size from 49 to 100cm. It was observed that, the diet of both Deania calcea and Deania profundorum consisted of four essential prey groups; cephalopods, bony fish, crustaceans and annelids. The main prey species of the two deep-sea sharks studied were the bony fish, cephalopods and crustaceans. This study would provide comprehensive information for the conservation of the species under study and managing a good exploitation. [ABSTRACT FROM AUTHOR]

As one of the main intermediate products of hydrogen sulfide oxidation, elemental sulfur plays an important indicator role in understanding the oxidative cycle of sulfur in the water of anoxic basins. The distribution of elemental sulfur in the water column of the Black Sea at stations located in the area of the continental slope is considered. For the first time, the concentration distributions of two forms of elemental sulfur depending on the depth in the Black Sea water were obtained: suspended elemental sulfur with a fraction of more than 0.45 μm (S0) and zero-valency sulfur (ZVS), which includes the sum of elemental sulfur (suspended and colloidal) and polysulfide sulfur. In the upper anoxic waters, the concentration of S0 noticeably increases (almost 200 times relative to the depth of 400 m) with an increase in the concentration of hydrogen sulfide and the density of water. At depths of more than 250 m, the concentration of both forms of sulfur remains almost constant (ZVS = 0.21 ± 0.03 µmol/kg, S0 = 0.05 ± 0.01 µmol/kg). A sharp increase in the concentration of S0 at the depths of 150–250 m is associated with the oxidation of hydrogen sulfide due to bacterial anoxygenic photosynthesis after sampling. The value of δ34S(ZVS) was determined in the waters of two stations Ash-26 and 149 at the depths of 450 and 600 m, respectively, which turned out to be +2.2‰ higher than δ34S(Н2S) from the same depths, which indicates the bacterial origin of elemental sulfur. [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water is primarily formed via overflows of dense shelf water (DSW) around the Antarctic continental margins. The dynamics of these overflows therefore influence the global abyssal stratification and circulation. Previous studies indicate that dense overflows can be unstable, energizing topographic Rossby waves (TRW) over the continental slope. However, it remains unclear how the wavelength and frequency of the TRWs are related to the properties of the overflowing DSW and other environmental conditions, and how the TRW properties influence the downslope transport of DSW. This study uses idealized high-resolution numerical simulations to investigate the dynamics of overflow-forced TRWs and the associated downslope transport of DSW. It is shown that the propagation of TRWs is constrained by the geostrophic along-slope flow speed of the DSW and by the dynamics of linear plane waves, allowing the wavelength and frequency of the waves to be predicted a priori. The rate of downslope DSW transport depends nonmonotonically on the slope steepness: steep slopes approximately suppress TRW formation, resulting in steady, frictionally dominated DSW descent. For slopes of intermediate steepness, the overflow becomes unstable and generates TRWs, accompanied by interfacial form stresses that drive DSW downslope relatively rapidly. For gentle slopes, the TRWs lead to the formation of coherent eddies that inhibit downslope DSW transport. These findings may explain the variable properties of TRWs observed in oceanic overflows, and they imply that the rate at which DSW descends to the abyssal ocean depends sensitively on the manifestation of TRWs and/or nonlinear eddies over the continental slope. [ABSTRACT FROM AUTHOR]

Core samples from Ilaro BH-7 (51-202m) in the eastern Dahomey basin were subjected to standard foraminiferal biostratigraphic analysis to determine their foraminiferal assemblages, diversity, age and paleoenvironments. The benthic foraminiferal species were subjected to stable isotope analyses to identify possible records of the Paleocene-Eocene Thermal Maximum. The sediments are essentially silicified limestones, sandstones and shales/mudstones, with thin beds of siltstones. Identified foraminiferal assemblages consists of 16 planktic, 12 benthic and 2 agglutinated species belonging to two planktic foraminiferal zones, P4-P7 and P8, defined by Acarinina pentacamerata and the Pseudohastigerina micra, respectively. The planktic/benthic foraminiferal ratios varied between 22 and 84%. The Shannon-Wiener and Fisher Alpha species richness and diversity averages are 1.99 and 1.13, respectively. δ13C in benthic foraminifera showed negative to strong negative chemostratigraphic curve from 0.59 ‰ to -15.66‰, while δ18O showed slightly strong negative shift from -1.81‰ to - 6.76‰. Recovered species exhibited moderate diversity and were almost entirely calcareous assemblages, indicating restricted environmental conditions in the borehole. The sediments were assigned ages of 50.2Ma, 50.5Ma and 57.7Ma corresponding to Late Paleocene to Early Eocene. The depositional environment ranged from inner shelf to upper continental slope. The oxygen isotope revealed a synchronous negative short-term excursion with cyclic fluctuation owing to the changing water temperature in the environment. The temperature may not play significant role in the extinction of the benthic foraminifera because of their adaptation to δ18O depleted environment. However, strong negative shift of carbon isotope revealed Thermal Maximum event in the studied interval. [ABSTRACT FROM AUTHOR]

Benthic samples collected from depths ranging between 686 and 2410 m along the Brazilian continental upper slope from Rio de Janeiro State to Santa Catarina State (23°S to 27°S) yielded a wealth of tanaidacean material, including two new species of Stenotanais. This is the first described species of the family Akanthophoreidae from Brazilian waters. Stenotanais leonardoi sp. nov. has a combination of unique characters including the uropod basal article longer than the pleotelson and the exopod somewhat wider than the endopod, longer than the endopod article-1 (0.7 times endopod length) and supporting two flat and wide terminal setae. Stenotanais uropedon sp. nov. is recognisable by its oar-shaped uropod endopod, with article-2 large, broad and flattened and the short exopod, only 0.3 times the endopod length. An identification key to the species of Stenotanais is given. These two species bring the total number of described akanthophoreids to 56 species and that of all tanaidaceans in Brazilian waters to 66 species. [ABSTRACT FROM AUTHOR]

This study analyses data assimilative numerical simulations in an eddy-dominated western boundary current: the East Auckland Current (EAuC). The goal is to assess the impact of assimilating surface and subsurface data into a model of the EAuC via running observing system experiments (OSEs). We used the Regional Ocean Modeling System (ROMS) in conjunction with the 4-dimensional variational (4D-Var) data assimilation scheme to incorporate sea surface height (SSH) and temperature (SST), as well as subsurface temperature, salinity and velocity from three moorings located at the upper, mid and lower continental slope using a 7 d assimilation window. Assimilation of surface fields (SSH and SST) reduced SSH root mean square deviation (RMSD) by 25 % in relation to the non-assimilative (NoDA) run. The inclusion of velocity subsurface data further reduced SSH RMSD up- and downstream the moorings by 18 %–25 %. By improving the representation of the mesoscale eddy field, data assimilation increased complex correlation between modelled and observed velocity in all experiments by at least three times. However, the inclusion of temperature and salinity slightly decreased the velocity complex correlation. The assimilative experiments reduced the SST RMSD by 36 % in comparison to the NoDA run. The lack of subsurface temperature for assimilation led to larger RMSD (>1 ∘ C) around 100 m in relation to the NoDA run. Comparisons to independent Argo data also showed larger errors at 100 m in experiments that did not assimilate subsurface temperature data. Withholding subsurface temperature forces near-surface average negative temperature increments to the initial conditions that are corrected by increased net heat flux at the surface, but this had limited or no effect on water temperature at 100 m depth. Assimilation of mooring temperature generates mean positive increments to the initial conditions that reduces 100 m water temperature RMSD. In addition, negative heat flux and positive wind stress curl were generated near the moorings in experiments that assimilated subsurface temperature data. Positive wind stress curl generates convergence and downwelling that can correct interior temperature but might also be responsible for decreased velocity correlations. The few moored CTDs (eight) had little impact in correcting salinity in comparison to independent Argo data. However, using doubled decorrelation length scales of tracers and a 2 d assimilation window improved model salinity and temperature in comparison to Argo profiles throughout the domain. This assimilation configuration, however, led to large errors when subsurface temperature data were not assimilated due to incorrect increments to the subsurface. As all reanalyses show improved model-observation skill relative to HYCOM–NCODA (the model boundary conditions), these results highlight the benefit of numerical downscaling to a regional model of the EAuC. [ABSTRACT FROM AUTHOR]

On the southwest cape of the Congo craton, a subtropical carbonate bank the size of Greenland was heavily glaciated during two Cryogenian panglacial episodes spaced 10–20 Myr apart. In NW Namibia, the bank underwent crustal stretching with resultant Aegean Sea-type topography during the older and longer Sturtian glaciation (717–661 Ma). This is indicated by angular discordance between glacial and preglacial strata and diamictites sourced from all older units, including crystalline basement. In contrast, the bank was flat-topped and underwent broad thermal subsidence during Marinoan glaciation (646 ± 5–635 Ma), attested by stratal parallellism and diamictites sourced from ≤100 m stratigraphic depth. However, ≥2.0 km of relief existed on the Marinoan continental slope, where most glacial erosion and accumulation occurred. The average rates of Marinoan erosion (2.55–6.80 m/Myr, n = 190) and accumulation (2.65–7.07 m/Myr, n = 211) are indistinguishable, implying that the location in a continental promontory did not bias erosion over accumulation. The average accumulation rates for the Sturtian and Marinoan, scaled for different averaging times, including Marinoan uncertainty, are 3.95–4.93 m/Myr (n = 183) and 2.65–7.07 m/Myr (n = 190), respectively, suggesting that a Marinoan glacioeustatic coastal escarpment substituted for rift-related Sturtian basin-and-range topography. These slow rates, comparable to long-term pre-Quaternary accumulation rates on existing abyssal plains, reconcile glacial sedimentology with the feeble hydrologic cycle of snowball Earth. [ABSTRACT FROM AUTHOR]

Between Florida and Cape Hatteras, North Carolina, the Gulf Stream carries warm, salty waters poleward along the continental slope. This strong current abuts the edge of the South Atlantic Bight (SAB) continental shelf and is thought to influence exchange of waters between the open ocean and the shelf. Observations from a pair of instruments deployed for 19 months in the northern SAB are used here to examine the processes by which the Gulf Stream can impact this exchange. The instrument deployed on the SAB shelf edge shows that the time‐averaged along‐slope flow is surface‐intensified with only few flow reversals at low frequencies (>40‐day period). Time‐averaged cross‐slope flow is onto the SAB shelf in a lower layer and off‐shelf above. Consistent with Ekman dynamics, the magnitude of lower‐layer on‐shelf flow is correlated with the along‐slope velocity, which is in turn controlled by the position and/or transport of the Gulf Stream that flows poleward along the SAB continental slope. In the frequency band associated with downstream‐propagating wave‐like meanders of the Gulf Stream jet (2‐15 day period), currents at the shelf‐edge are characterized by surface‐intensified flow in the along‐ and cross‐slope directions. Estimates of maximum upwelling velocities associated with cyclonic frontal eddies between meander crests occasionally reach 100 m/day. Plain Language Summary: Along the southeastern US, the Gulf Stream carries warm, salty waters northward. This strong current flows along the South Atlantic Bight (SAB) continental slope and modulates processes that control movement of waters between the continental shelf and open ocean. This two‐way exchange is important for physical oceanography (controlling temperature and salinity of the SAB shelf) and for the shelf's chemical budgets and ecological systems. This study combines observations from two instruments deployed for 19 months near Cape Hatteras on the edge of the shelf and on the upper continental slope to help characterize two important exchange processes. The first is upwelling associated with Gulf Stream meanders, which are small‐scale undulations of the Gulf Stream path along the SAB shelf edge. Upwelling pumps deep nutrient rich waters from the slope onto the neighboring SAB shelf as cyclonic (counter‐clockwise rotating) cells of circulating waters "ride" along the onshore side of the Gulf Stream between meander crests. A second exchange process occurs within a bottom layer where friction causes water to veer onshore (from the open ocean onto the shelf). Variability in Gulf Stream strength and position along the SAB causes variability in the strength of this Ekman flow. Key Points: Gulf Stream variability drives shelf‐ocean exchange mechanisms in the northern South Atlantic Bight (SAB)Transport pulses onto the SAB shelf in a bottom Ekman layer are driven by low frequency variability in Gulf Stream position and/or strengthUpwelling at the SAB shelf edge associated with intense cyclonic frontal eddies between Gulf Stream meander crests can reach 100 m/day [ABSTRACT FROM AUTHOR]

Turbidite fans, serving as good reservoirs for petroleum accumulation, are typically formed during deep faulting periods in continental basins, particularly in steep slope zones. However, gentle slope zones are also significant and unique for the formation of turbidite fans. These turbidite fans hold immense importance in exploring concealed lithological reservoirs. Taking the Chezhen Depression of Bohai Bay Basin as an example, we conducted a comprehensive study of the turbidite fan deposits in the gentle slope zone. Our results indicate that (1) small-scale distal-source turbidite fans are a common sedimentary type in the Chezhen Depression of the Bohai Bay Basin; (2) the study area is mainly characterized by seven lithofacies; (3) there are incomplete Bouma sequences in the study interval. This study is an important turbidite investigation into continental faulted basins, and it can also provide an important reference value for exploration and development in unconventional reservoirs of the same type. [ABSTRACT FROM AUTHOR]

Submarine landslides in regions enriched with gas hydrates pose a significant threat to submarine pipelines, cables, and offshore platforms. Conducting a comprehensive regional-scale susceptibility assessment is crucial for mitigating the potential risks associated with submarine landslides in gas hydrate enrichment regions. This study conducted a preliminary exploration by presenting a probabilistic assessment framework that integrated database construction, rapid prediction model training, and landslide susceptibility assessment in hydrate enrichment regions. The database was a virtual repository constructed using numerical simulations of hydrate dissociation under various combinations of factors, including water depth, geothermal gradients, seafloor slope gradients, the seafloor temperature's rate of increase, gas hydrate saturation, and the strength and permeability of sediments. The rapid prediction model was trained using machine learning techniques, relying on the virtual database. A probabilistic assessment was performed using Monte Carlo simulations, with the landslide susceptibility determined by the rapid prediction model. The probability of landslide susceptibility exceeding a certain threshold served as an indicator for classifying the susceptibility of the study area. The proposed framework was implemented in the Shenhu area of the South China Sea, which is a representative region known for its substantial hydrate enrichment and well-developed landslides. The trained rapid prediction model for landslide susceptibility exhibited a speed advantage of over 60,000 times compared to traditional numerical calculation methods. The statistical analysis of the results in Monte Carlo simulations suggested that the landslide susceptibility was subjected to a high level of uncertainty due to limited survey data availability. Based on the probability of landslide susceptibility exceeding 0.4 in Monte Carlo simulations, the study area was classified into three zones of susceptibility: low, moderate, and high levels. [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]

The southwestern tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal-tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal-tide field around the New Caledonia islands through energy budgets that quantify the coherent internal-tide generation, propagation, and dissipation. A total of 15.27 GW is converted from the barotropic to the baroclinic M2 tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes, highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy either dissipates in the near field close to the generation sites or loses coherence. The remaining baroclinic energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m -1 toward the open ocean. The New Caledonia site represents a challenge for SWOT (Surface Water and Ocean Topography) observability of balanced motion in the presence of internal tides with sea surface height (SSH) signatures >6 cm at similar wavelengths. We show for our study region that a correction of SSH for the coherent internal tide potentially increases the observability of balanced motion from wavelengths >160 km to well below 100 km. [ABSTRACT FROM AUTHOR]

The Gulf of Mexico supports many seabird species, yet data gaps describing species composition and habitat use are prevalent. We used vessel-based observations from the Gulf of Mexico Marine Assessment Program for Protected Species to identify and characterize distinct seabird assemblages in the northern Gulf of Mexico (within the U.S. Exclusive Economic Zone; nGoM). Using cluster analysis of 17 seabird species, we identified assemblages based on seabird relative density. Vessel-based surveys documented the location, species, and number of seabirds across the nGoM between 2017–2019. For each assemblage, we identified the (co-)dominant species, spatial distribution, and areas of greater relative density. We also assessed the relationship of the total relative density within each assemblage with environmental, spatial, and temporal covariates. Of the species assessed, 76% (n = 13) breed predominantly outside the nGoM basin. We identified four seabird assemblages. Two assemblages, one dominated by black tern and the other co-dominated by northern gannet/laughing gull, occurred on the continental shelf. An assemblage dominated by sooty tern occurred along the continental slope into pelagic waters. The fourth assemblage had no dominant species, was broadly distributed, and was composed of observations with low relative density ('singles' assemblage). Differentiation of assemblages was linked to migratory patterns, residency, and breeding location. The spatial distributions and relationships of the black tern and northern gannet/laughing gull assemblages with environmental covariates indicate associations with river outflows and ports. The sooty tern assemblage overlapped an area prone to mesoscale feature formation. The singles assemblage may reflect commuting and dispersive behaviors. These findings highlight the importance of seasonal migrations and dynamic features across the seascape, shaping seabird assemblages. Considering the potential far-ranging effects of interactions with seabirds in the nGoM, awareness of these unique patterns and potential links with other fauna could inform future monitoring, research, restoration, offshore energy, and aquaculture development in this highly industrialized sea. [ABSTRACT FROM AUTHOR]

Understanding the interactions of submarine channels with seafloor deformations is challenging as these channels more often involve a wide variety of responses relying on both autogenic and allogenic factors. The effect of active growing structures on channel pathways is well documented, but the evolution of lateral migration and the internal architectures along the deflected channel bends around ongoing active structures remain poorly constrained. Here, we use 3D seismic interpretation and quantitative geomorphologic methods to examine the channel bend morphology and the kinematics of lateral migration near gravity‐driven tectonic deformation. Using high‐resolution seismic reflection data acquired from the offshore Niger Delta, two‐channel levee systems (Amaku Major System and Amaku Channel Levee System) have been recognized in the seismic survey. Each system consists of three channel complexes, recording five types of deflected channel bends, defined here as: (i) avulsed bend, (ii) confined bend, (iii) chute cut‐off bend, (iv) blocked bend and (v) kinked bend. Geomorphologic parameters including bend sinuosity, bend amplitude, along‐bend length, straight‐bend length, channel depth and width, were considered within the deflected channels. Lateral migration estimators; channel lateral shift (SH), and channel lateral spacing (CS), were assessed throughout the distances of cross‐sectional channel patterns. The lateral migration estimators (SH and CS) were used to estimate the expression of internal architectures and the evolution of lateral migration around seabed deformation at the scale of the channel complex. The results show that the morphology and internal architecture of the deflected bends, although developing in the same structural context, display varied responses to structural deformation. Unlike previously published models of channel‐fold interactions asserting tectonics as the solitary driver, here we demonstrate that the channel deflections around structures are sensitive to the lateral confinement produced by sediment relief of the outer levees, and the autogenic forcing of channel mechanisms. This study provides new insights into the evolution of submarine channels in active tectonic settings, shows detailed mechanisms of channel bends at a small scale and offers a better understanding of the distribution of sediments in the deep sea. [ABSTRACT FROM AUTHOR]