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The anticyclonic eddies (ACEs) shed from the Kuroshio intrusion often interact with internal waves (IWs). Those interactions are complex but play an important role in the biogeochemical effects in the northern South China Sea (SCS). However, previous studies on these interactions have mainly focused on physical processes, while biological responses to their interactions have been unclear. In this study, results of two field cruises with focus on two sets of high-frequency time-series observations over the continental slope of the SCS during the summers of 2016 and 2017 revealed that phytoplankton in the euphotic zone were affected by both IWs and ACEs shed from the Kuroshio Current. Distinct surface distributions of phytoplankton were attributable to different sources of the water, Kuroshio intrusions and the plume from the Pearl River. However, similarities of phytoplankton biomass and community composition in the subsurface chlorophyll maximum layer in both years could be explained by the similar upward transport of nutrients induced by combinations of small-amplitude IWs and mature ACEs in 2016 and large-amplitude IWs in 2017. The distinct vertical distributions of the phytoplankton community in both years were attributable to the different responses of phytoplankton groups to the direct effects of isopycnal uplifting, bottom-up controls, and top-down controls. Our results showed that the ecological effects of the interactions between IWs and ACEs shed from the Kuroshio water were complex, and those complex effects further influenced the structure of this marginal sea ecosystem. [ABSTRACT FROM AUTHOR]

Submarine geohazards significantly threaten human economic activities and essential infrastructure. Based on multi‐beam data and high‐resolution 2D seismic data, two types of submarine geohazards are identified: direct and indirect geohazards on the northwestern continental slope and the Xisha Uplift of the South China Sea (SCS). Direct geohazards include submarine landslides and active faults, while indirect geohazards include buried channels, submarine canyons, pockmarks, volcanoes and magma diapirs. This study comprehensively analyzes geomorphological features, including their characteristics, genesis and distribution. Statistical analysis reveals that the gradient of the Xisha Uplift slope is steeper than the shelf break, making it a more unstable region. However, assessing disaster potential indicates that submarine geohazards at the shelf break pose a greater threat than those at the Xisha Uplift. Many factors, including tectonic activity, sediment supply and relative sea‐level changes, influence submarine geohazards' formation. These hazards do not occur in isolation but often interact with one another. The research results provide a scientific basis for predicting deep‐sea geohazards near the northern continental margin and Xisha Island in the SCS. [ABSTRACT FROM AUTHOR]

Modern cold-water corals (CWCs) occur in a wide range of water depths, with Desmophyllum pertusum being one of the most common species. Pleistocene, Holocene, and modern coral mound formation by living CWC reefs have previously been described in the Porcupine Seabight from water depths greater than 700 m in the vicinity of the transitional zone between the Eastern North Atlantic Water and Mediterranean Outflow Water. Here we document occurrence of fossil corals retrieved from two cores at 370 m depth in the Macnas Mounds, a relatively shallow occurrence for mounds on the Irish shelf-edge. Both cores feature D. pertusum restricted to the upper two metres, immediately overlying an erosive surface and a coeval major down-core change in grain size from sand to mud. Radiocarbon dating of coral specimens indicates the CWC mounds initiated 7.82 Cal ky BP. Our study unequivocally documents the existence of Holocene shelf-edge coral mounds in the eastern Porcupine Seabight and highlights the possibility of other occurrences of CWCs in similar settings elsewhere in the northeast Atlantic. Given that no living CWCs were encountered in the study area, we suggest that the area previously experienced more favourable conditions for CWC mound initiation and development along the shelf-edge margin, possibly due to differing conditions in the European Slope Current which flows northward along the continental slope from south of the Porcupine Bank to the Faroe-Shetland Channel. [ABSTRACT FROM AUTHOR]

Topographic Rossby waves (TRWs) dominate the low-frequency variability of deep ocean currents and play a crucial role in energy exchange and material mixing. On the continental slope of the southwestern South China Sea, a deep-water mooring was deployed to observe TRWs for a period of ~ 40 days. The TRWs, with a wavelength of 109 km, account for 41.3% of the subinertial variations. A ray-tracing model was applied to investigate the propagation and energy source. The results showed that the TRWs propagated from the northeast of the mooring location and were most likely caused by the mesoscale eddy disturbances off the Vietnam coast. This study provides a new perspective on examining the impact of mesoscale eddies off Vietnam on abyssal currents. [ABSTRACT FROM AUTHOR]

The structure of the Antarctic Slope Current at the continental shelf is crucial in governing the poleward transport of warm water. Canyons on the continental slope may provide a pathway for warm water to cross the slope current and intrude onto the continental shelf underneath ice shelves, which can increase rates of ice shelf melting, leading to reduced buttressing of ice shelves, accelerating glacial flow and hence increased sea level rise. Observations and modeling studies of the Antarctic Slope Current and cross-shelf warm water intrusions are limited, particularly in the East Antarctica region. To explore this topic, an idealized configuration of the Antarctic Slope Current is developed, using an eddy-resolving isopycnal model that emulates the dynamics and topography of the East Antarctic sector. Warm water intrusions via canyons are found to occur in discrete episodes of large onshore flow induced by eddies, even in the absence of any temporal variability in external forcings, demonstrating the intrinsic nature of these intrusions to the slope current system. Canyon width is found to play a key role in modulating cross-shelf exchanges; warm water transport through narrower canyons is more irregular than transport through wider canyons. The intrinsically episodic cross-shelf transport is found to be driven by feedbacks between wind energy input and eddy generation in the Antarctic Slope Current. Improved understanding of the intrinsic variability of warm water intrusions can help guide future observational and modeling studies in the analysis of eddy impacts on Antarctic shelf circulation. [ABSTRACT FROM AUTHOR]

Picophytoplankton are a ubiquitous component of marine plankton communities and are expected to be favored by global increases in seawater temperature and stratification associated with climate change. Eukaryotic and prokaryotic picophytoplankton have distinct ecology, and global models predict that the two groups will respond differently to future climate scenarios. At a nearshore observatory on the Northeast US Shelf, however, decades of year‐round monitoring have shown these two groups to be highly synchronized in their responses to environmental variability. To reconcile the differences between regional and global predictions for picophytoplankton dynamics, we here investigate the picophytoplankton community across the continental shelf gradient from the nearshore observatory to the continental slope. We analyze flow cytometry data from 22 research cruises, comparing the response of picoeukaryote and Synechococcus communities to environmental variability across time and space. We find that the mechanisms controlling picophytoplankton abundance differ across taxa, season, and distance from shore. Like the prokaryote, Synechococcus, picoeukaryote division rates are limited nearshore by low temperatures in winter and spring, and higher temperatures offshore lead to an earlier spring bloom. Unlike Synechococcus, picoeukaryote concentration in summer decreases dramatically in offshore surface waters and exhibits deeper subsurface maxima. The offshore picoeukaryote community appears to be nutrient limited in the summer and subject to much greater loss rates than Synechococcus. This work both produces and demonstrates the necessity of taxon‐ and site‐specific knowledge for accurately predicting the responses of picophytoplankton to ongoing environmental change. [ABSTRACT FROM AUTHOR]

Widespread hypoxia occurs seasonally across the Oregon continental shelf, and the duration, intensity, and frequency of hypoxic events have increased in recent years. In hypoxic regions, iron reduction can liberate dissolved Fe(II) from continental shelf sediments. Fe(II) was measured in the water column across the continental shelf and slope on the Oregon coast during summer 2022 using both a trace metal clean rosette and a high‐resolution benthic gradient sampler. In the summer, Fe(II) concentrations were exceptionally high (40–60 nM) within bottom waters and ubiquitous across the Oregon shelf, reflecting the low oxygen condition (40–70 μM) at that time. The observed inverse correlation between Fe(II) and bottom water oxygen concentrations is in agreement with expectations based on previous work that demonstrates oxygen is a major determinant of benthic Fe fluxes. Rapid attenuation of Fe(II) from the benthic boundary layer (within 1 m of the seafloor) probably reflects efficient cross‐shelf advection. One region, centered around Heceta Bank (~ 44°N) acts a hotspot for Fe release on the Oregon continental shelf, likely due to its semi‐retentive nature and high percent mud content in sediment. The results suggest that hypoxia is an important determinant of the inventory of iron is Oregon shelf waters and thus ultimately controls the importance of continental margin‐derived iron to the interior of the North Pacific Basin. [ABSTRACT FROM AUTHOR]

Elemental sulfur and its derivatives, polysulfides, play a key role in hydrogen sulfide oxidation processes in anoxic basins. Having low solubility, elemental sulfur is mainly represented by suspended forms. However, in sulfide waters, it forms highly soluble polysulfides. This article studies elemental sulfur and polysulfides in the upper part of the Black Sea anoxic water column in 2017–2019 and 2022 at stations located on the continental slope off the coast of the Caucasus and Crimea. Sulfur was sampled, filtered, and determined under strictly anoxic conditions in an argon atmosphere. The concentration of elemental sulfur (zero-valent sulfur (ZVS)–elemental sulfur together with polysulfides) increases with depth and hydrogen sulfide content from 0.01 µmol/kg at the redox interface to 0.67 µmol/kg at a depth of 600 m. The elemental sulfur fraction in the composition of ZVS is 23 ± 5%. Based on thermodynamic data, calculation of the polysulfide concentration in equilibrium with suspended sulfur shows that deeper than 20–25 m of the upper boundary of the anoxic zone, their concentration was higher than ZVS and at a depth of 600 m they differed about threefold. The predominance of elemental sulfur over sulfide sulfur in the composition of polysulfides in the anoxic zone at depths of 450 and 600 m may be the reason for the fractionation of its isotopic composition by 2.2‰ with respect to dissolved sulfide sulfur (–41.0‰ VCDT). [ABSTRACT FROM AUTHOR]

The sources of supply and transformation of organic matter (OM) as it transitions from dissolved form to particulate matter, fluffy layer, and bottom sediments were investigated along a meridional transect from the Lena River delta to the continental slope (in the depth range of 10 to 2390 meters, cruise 63 of the R/V Akademik Mstislav Keldysh, September 2015). The study of OM molecular markers showed that dissolved and particulate organic matter of marine and terrigenous origin biodegrades in the water column and accumulates insignificantly in bottom sediments. Thus, OM from Lena River runoff does not contribute to the formation of OM in bottom sediments in summer. An area of influence of under-ice blooms on the sedimentation process was identified on the outer shelf. [ABSTRACT FROM AUTHOR]

The storage potential of hydrocarbon reservoirs in the central Gulf of Mexico (GOM) makes future development of CO2 storage projects in those areas promising for secure, large-scale, and long-term storage purposes. Focusing on the producing and depleted hydrocarbon fields in the continental slope of the central GOM, this paper analyzed, assessed, and screened the producing sands and evaluated their CO2 storage potential. A live interactive CO2 storage site screening system was built in the SAS® Viya system with a broad range of screening criteria combined from published studies. This offers the users a real-time assessment of the storage sites and enables them to adjust the filters and visualize the results to determine the most suitable filter range. The CO2 storage resources of the sands were estimated using a volumetric equation and the correlation developed by the National Energy Technology Laboratory (NETL). The results of this study indicate that 1.05 gigatons of CO2 storage resources are available in the developed reservoirs at the upper slope area of the central GOM. The Mississippi Canyon and Green Canyon protraction areas contain the fields with the largest storage resources. [ABSTRACT FROM AUTHOR]

The study analyzes polycyclic aromatic hydrocarbons (PAHs) isolated from bottom sediments of the Barents and Norwegian seas (2019–2021 cruises of the R/V Akademik Mstislav Keldysh). Elevated PAH concentrations (up to 16 900 ng/g) are recorded in the coastal region of the Svalbard archipelago, and low ones, in the Greenland Basin and the eponymous ridge (up to 80 ng/g), as well as on the continental slope of the Barents Sea (up to 240 ng/g on average). Among cata-condensed PAHs, 2–3 ring polyarenes are the most common: naphthalene, 1- and 2-methylnaphthalenes, and phenanthrene, while among peri-condensed PAHs, 4–6 ring polyarenes are the most typical: fluoranthene, pyrene, and benz(a)anthracene. Anthropogenic sources in the bottom sediments of the study area are of subordinate importance compared to their natural input from the sedimentary stratum with fluid fluxes and erosion. [ABSTRACT FROM AUTHOR]

The vertical variability of the geometric, dynamic, and thermohaline characteristics of Black Sea eddies is studied using three-dimensional identification of closed streamlines based on the results of simulations of the NEMO model in 2006–2016. The vertical extent of eddies depends linearly on their orbital velocity and significantly affects the speed of their translation motion. The influence of the background current on the upper part of the eddy leads to the mean tilt of the vertical axis of anticyclones in the cyclonic direction and this tilt is maximum in the zone of the Black Sea Rim Current. The eddies occupying the upper layer (up to 150 m) move relatively quickly at a speed of 0.08–0.14 m/s, since they are advected by the Rim Current. The most intense eddy dynamics is observed over the continental slope in the upper 20–70 m layer, where the probability of observing eddies exceeds 30%. Several maxima appear in the surface layer on the shallow northwestern shelf near the mouths of the Danube, Southern Bug, and Dnieper rivers. The relationship between the orbital velocity of eddies, their thermohaline structure, and stratification were estimated. Stability decreases in anticyclonic eddies within the layer 40–100 m due to the lowering of the pycnocline, and in cyclones it increases due to its elevation; in the underlying layers a compensating change of the opposite sign is observed. However, as the orbital velocity increases in the eddies of both signs, a decrease in stratification occurs in the upper 0–100 m layer, which is probably associated with an increase in the vertical shear of the current velocity. Three-dimensional identification of eddies makes it possible to track in detail changes in the individual characteristics of an eddy during its evolution. Using the example of an eddy off the Anatolian coast, it is shown that intensification of anticyclones is associated with the processes of entrainment of shelf waters, which can be one of the important sources of potential energy for anticyclones in the Black Sea. [ABSTRACT FROM AUTHOR]

Submarine landslides are significant geohazards, capable of displacing large volumes of sediment from continental margins to deposit mass transport complexes (MTCs) and generate offshore tsunamis. However, the reactivation of MTCs after their initial failure has long been overlooked. By analyzing high-quality three-dimensional seismic reflection data and seismic attribute maps, as well as comparing the geometry of different MTCs, we investigate the development of long-term slope instability and its hazardous consequences on the northwest flank of the Storegga Slide on the Norwegian margin. Our results demonstrate that the reactivation of MTCs can deform both their inner structure and overlying strata, promoting the formation of sinuous channels and local slope failures on the seafloor. These findings further reveal the MTCs that are underconsolidated or comprise slide blocks may remain unstable for a long time after their initial failure, particularly when affected by slope undercutting and a corresponding reduction in lateral support. This study shows that MTCprone sequences are more likely to comprise regions of continental slopes with long-term instability and recurring marine geohazards. [ABSTRACT FROM AUTHOR]

The <3% dissimilar Amplicon Sequence Variant (ASV) clusters of the 18S‐V4 barcode were used as species‐proxies for the evaluation of ASV composition and ASV diversity indices characterizing the hitherto poorly investigated meiofaunal communities of the south‐eastern part of the Levantine basin. Accompanied by abundance measurements, the relationships of these characteristics with sedimentary and bottom terrain parameters were interpreted. The construction of community composition profiles, namely ASVs' list and their estimated abundances, was done using our previously established procedure (Harbuzov et al., 2022, Marine Genomics 65, 100980), combining metabarcoding with sample reads normalization by the abundance of hard‐bodied meiofaunal taxa. The study province included the 54–1418 m depth range, across vertical sub‐bottom horizons ranging 0–17 cm. Oxygen, hydrogen sulfide and methane concentrations in the pore water, as well as sediment grain size spectra and sedimentary protein and carbohydrate levels, were measured, followed by an evaluation of their involvement in the shaping of the meiofaunal communities' characteristics. Community composition was generally site‐and‐horizon dependent and its abundance decreased with increasing bottom depth and across sub‐bottom horizons, typical to benthic habitats which are nourished by organic carbon from the euphotic zone. The relatively sharply inclined continental slope bottom located in the northern part of the Israeli coast was an exception. Its meiofaunal community characteristics were speculated to be affected by intensive sediment mixing and lateral transport of food from the shelf, in addition to the effect of the euphotic zone‐originated food sources. [ABSTRACT FROM AUTHOR]

The Ross Sea region Marine Protected Area (RSR MPA) is one of the most productive regions in the Southern Ocean. Mesozooplankton intermediates the primary product to the higher predators, such as penguins and seals, in this ecosystem. In this study, the mesozooplankton community structure and spatial pattern in the RSR MPA in January were investigated by using 505 μm-mesh-size bongo net samples. As a result, 37 mesozooplankton taxa with a total mean abundance of 35.26 ind./m3, ranging from 2.94 to 139.17 ind./m3, were confirmed. Of the 37 taxa, 7 occupied almost 84% of the total abundance, with copepods being the main dominant taxa. As shown by our hierarchical analysis, the mesozooplankton community was divided into four groups, each associated with a specific geographical distribution. Group A was composed of stations around Terra Nova Bay and showed relatively low abundance. Group B included stations around the continental slope region. Group D was composed of the Ross Sea continental shelf stations, while group C consisted of stations geographically located between those of groups B and D. These four groups were influenced by various environmental factors, such as water temperature, salinity, and nutrients. In summary, the mesozooplankton community can be separated according to geographical pattern. This pattern is related to several environmental factors. [ABSTRACT FROM AUTHOR]

Microbial communities of the Arctic Ocean are poorly described in comparison to aquatic environments of other regions regarding their patterns of distribution and change. The present work aims to investigate free-living bacterial communities (size fraction 0.22–1.5 μm) of different Arctic seas regions, from the river discharge area to the continental slope. Illumina MiSeq metabarcoding analysis using V3–V4 region of 16S rRNA gene was employed to study the microbial diversity of 11 Arctic seawater samples, collected from the surface and near-bottom layers in the Kara and Laptev Seas in August–September 2018. Additionally, we determined environmental parameters, bacterial abundance, biomass, and respiratory activity. Redundancy analysis, Spearman's rank correlation, and multiple linear regression analysis were used to reveal environmental factors that modulate the bacterial community structure. The differences in the free-living bacterial community composition were associated with environmental characteristics of water layers (salinity and temperature) rather than with geographical area. Although the communities from all examined sites were dominated by Gammaproteobacteria and Alphaproteobacteria followed by Flavobacteriia and Actinobacteria, they showed distinct variations in the distribution at all taxonomical levels. No archaeal taxa were observed. The distribution patterns of the quantitative parameters of total bacterial community were not associated with defined environmental characteristics. [ABSTRACT FROM AUTHOR]

International conservation goals have been set to mitigate Southern Ocean ecosystem deterioration, with multiple monitoring programs evaluating progress towards those goals. The scale of continuous monitoring through visual observations, however, is challenged by the remoteness of the area and logistical constraints. Given the ecological and economic importance of the Southern Ocean, it is imperative that additional biological monitoring approaches are explored. Recently, marine sponges, which are frequently caught and discarded in Southern Ocean fisheries, have been shown to naturally accumulate environmental DNA (eDNA). Here, we compare fish eDNA signals from marine sponge bycatch specimens to fish catch records for nine locations on the continental shelf (523.5–709 m) and 17 from the continental slope (887.5–1611.5 m) within the Ross Sea, Antarctica. We recorded a total of 20 fishes, with 12 fishes reported as catch, 18 observed by eDNA, and ten detected by both methods. While sampling location was the largest contributor to the variation observed in the dataset, eDNA obtained significantly higher species richness and displayed a significantly different species composition compared to fish catch records. Overall, eDNA read count correlated more strongly with fish abundance over biomass. Species composition correlated on a regional scale between methods, however eDNA signal strength was a low predictor of catch numbers at the species level. Our results highlight the potential of sponge eDNA monitoring in the Southern Ocean by detecting a larger fraction of the fish community compared to catch recordings, thereby increasing our knowledge of this understudied ecosystem and, ultimately, aiding conservation efforts. [ABSTRACT FROM AUTHOR]

To gain a better understanding of the mechanisms underlying spatial heterogeneity in ichthyoplankton communities in the SW Atlantic, we examined for the first time the latitudinal and continental shelf–slope gradients in ichthyoplankton structure and oceanographic features in the Campos Basin during the relaxation phase of coastal upwellings (late autumn to early winter). This region, located on SE Brazil's continental margin, is the most productive offshore oil basin in the country and has ecological relevance owing to the existence of areas that experiences mesoscale (tens to hundreds of kilometers) processes (eddies, filaments, and upwelling) caused by the interaction of continental shelf and slope circulation with deep water masses. The present study collected a total of 3892 fish eggs and 10,030 larvae from 36 sampling stations, averaging 22 eggs per 100 m3 and 56 larvae per 100 m3. A total of 250 taxa (5 for fish eggs and 248 for larvae) were identified, encompassing 80 families and 145 genera. Species distribution exhibited a considerable degree of spatial variability, which was related mostly to hydrological characteristics. In general, greater densities were associated with higher nutrient concentrations areas. Through distance‐based Redundancy Analysis, some discriminating species were found to associate with certain areas of the continental shelf characterized by colder temperatures. The ichthyoplankton distribution patterns suggested a potential influence from mesoscale oceanographic fronts, specifically those that induce upwelling of the cold and nutrient‐rich South Atlantic Central Water. Nonetheless, the methodologies used in this study faced challenges in distinctly identifying these processes. [ABSTRACT FROM AUTHOR]

The features of the concentration distribution of 238U, 232Th, and 226Ra in the surface layer in the bottom sediments of the shelf and continental slope of Svalbard are considered. The content of 226Ra, 232Th, and 238U varied in the range 22–134.3, 22.4–50.9, and 10.9–37.7 Bq/kg, respectively. The amount of 226Ra nonequilibrium with 238U (226Raex) ranged from 23 to 73% of the total 226Ra content in sediments. The maximum concentrations of 226Ra, 238U, 232Th, and 226Raex (134.3, 37.7, 50.9, and 98.2 Bq/kg, respectively) were obtained in the area of increased bioproductivity (Eagle Trough). In this zone, the relationship between the concentrations of 226Ra and 226Raex with the content of organic matter in sediment is well expressed, the correlation coefficients are R = 0.94 and 0.92, respectively, which indicates a significant contribution of the biological community to the accumulation of 226Ra in bottom sediments. The 226Ra concentration and the 226Ra excess value are negatively related to the redox potential of the sediment (R = –0.88). This pattern is also true in other areas of the Svalbard waters. In general, for the entire array of observations, the concentrations of 238U and 232Th increase with increasing content of organic carbon in the sediment (R = 0.72 and 0.7, respectively). The concentrations of 238U and 232Th decrease with increasing Ccarb content in the sediment (R = –0.79 and –0.81, respectively). The data obtained indicate the need to take into account the 226Ra excess when assessing the total natural radioactivity of marine sediments, the value of which may exceed the radioactivity of 238U and 232Th. [ABSTRACT FROM AUTHOR]

Accurate parameterizations of eddy fluxes across prograde, buoyant shelf and slope currents are crucial to faithful predictions of the heat transfer and water mass transformations in high-latitude ocean environments in ocean climate models. In this work we evaluate several parameterization schemes of eddy buoyancy fluxes in predicting the mean state of prograde current systems using a set of coarse-resolution noneddying simulations, the solutions of which are compared against those of fine-resolution eddy-resolving simulations with nearly identical model configurations. It is found that coarse-resolution simulations employing the energetically constrained GEOMETRIC parameterization can accurately reconstruct the prograde mean flow state, provided that the suppression of eddy buoyancy diffusivity over the continental slope is accounted for. The prognostic subgrid-scale eddy energy budget in the GEOMETRIC parameterization scheme effectively captures the varying trend of the domain-wide eddy energy level in response to environmental changes, even though the energy budget is not specifically designed for a sloping-bottomed ocean. Local errors of the predicted eddy energy are present but do not compromise the predictive skill of the GEOMETRIC parameterization for prograde current systems. This work lays a foundation for improving the representation of prograde current systems in coarse-resolution ocean climate models. Significance Statement: The objective of this study is to evaluate different methods for predicting ocean volume transports caused by ocean mesoscale eddies across continental margins. This is important because these transports play a critical role in exchanges between coastal seas and open oceans, but cannot be resolved or well represented in ocean climate simulations. This study emphasizes the importance of accounting for the influence of sloping seafloors in controlling the eddy transport across the continental slope. This study also highlights the necessity of simultaneously predicting the eddy energy for better representation of the cross-slope eddy transport in ocean climate simulations. [ABSTRACT FROM AUTHOR]

The scale-to-scale kinetic energy (KE) cascade induced by the nonlinear interaction among topography, the Kuroshio, and mesoscale eddies is systematically investigated in the coarse-graining framework based on simulated data from the well-validated Regional Ocean Model System. The KE transfer exhibits inhomogeneous spatial and temporal distributions and varies with length scale. During current–topography interaction, the KE transfers downscale across larger scales and reversely across smaller scales with an inherent separation scale of 150 km northeast of Taiwan, resulting in a significant positive net KE flux for mesoscale motions. The transfer around Suao Ridge is consistently downscaled with significant seasonal variation that is stronger in summer and weaker in winter. South of Suao Ridge, the transfer is one order of magnitude weaker and changes greatly with time. The cyclonic (anticyclonic) eddy weakens (enhances) KE transfer in most study areas. In particular, the cyclonic eddy reverses the transfer direction around Suao Ridge. The anticyclonic eddy triggers a significant bidirectional transfer south of Suao Ridge. Analyses show that the special arc-shaped topographic feature and northwestward Kuroshio intrusion current are responsible for the nature of bidirectional KE transfer northeast of Taiwan. The direction of mean current relative to the topography gradient determines the Rossby number magnitude and the KE transfer direction. The large-scale circulation determines the transfer intensity by changing the horizontal shear and barotropic instabilities. The KE transfer caused by nonlinear dynamics contributes significantly to the total anticyclonic eddy-induced net KE flux changes. In particular, the inverse KE cascade plays a key role in net KE flux changes in mesoscale motions east of Taiwan. Significance Statement: In this work, we clarify the scale-to-scale kinetic energy transfer east of Taiwan. Energy transfer varies in different subareas. It is bidirectional northeast of Taiwan, consistently downscale around Suao Ridge, and weak and variable south of Suao Ridge. These transfer characteristics are closely related to the direction of mean flow relative to the topography gradient. Mesoscale eddies can trigger bidirectional transfer and even reverse the transfer direction. The reverse cascade is as important as the forward cascade for the total mesoscale energy change. This study not only shows an example of KE cascade when strong currents pass through continental slope, sea ridge, and open ocean, but also is of great significance for studying the dynamical and ecological environment variation of marginal sea. [ABSTRACT FROM AUTHOR]

Enhanced diapycnal mixing induced by the near-bottom breaking of internal waves is an essential component of the lower meridional overturning circulation. Despite its crucial role in the ocean circulation, tidally driven internal wave breaking is challenging to observe due to its inherently short spatial and temporal scales. We present detailed moored and shipboard observations that resolve the spatiotemporal variability of the tidal response over a small-scale bump embedded in the continental slope of Tasmania. Cross-shore tidal currents drive a nonlinear trapped response over the steep bottom around the bump. The observations are roughly consistent with two-dimensional high-mode tidal lee-wave theory. However, the alongshore tidal velocities are large, suggesting that the alongshore bathymetric variability modulates the tidal response driven by the cross-shore tidal flow. The semidiurnal tide and energy dissipation rate are correlated at subtidal time scales, but with complex temporal variability. Energy dissipation from a simple scattering model shows that the elevated near-bottom turbulence can be sustained by the impinging mode-1 internal tide, where the dissipation over the bump is O(1%) of the incident depth-integrated energy flux. Despite this small fraction, tidal dissipation is enhanced over the bump due to steep topography at a horizontal scale of O(1) km and may locally drive significant diapycnal mixing. Significance Statement: Near-bottom turbulent mixing is a key element of the global abyssal circulation. We present observations of the spatiotemporal variability of tidally driven turbulent processes over a small-scale topographic bump off Tasmania. The semidiurnal tide generates large-amplitude transient lee waves and hydraulic jumps that are unstable and dissipate the tidal energy. These processes are consistent with the scattering of the incident low-mode internal tide on the continental slope of Tasmania. Despite elevated turbulence over the bump, near-bottom energy dissipation is small relative to the incident wave energy flux. [ABSTRACT FROM AUTHOR]

The identification of important habitat and the behavior(s) associated with it is critical to conservation and place‐based management decisions. Behavior also links life‐history requirements and habitat use, which are key to understanding why animals use certain habitats. Animal population studies often use tracking data to quantify space use and habitat selection, but they typically either ignore movement behavior (e.g., foraging, migrating, nesting) or adopt a two‐stage approach that can induce bias and fail to propagate uncertainty. We develop a habitat‐driven Langevin diffusion for animals that exhibit distinct movement behavior states, thereby providing a novel single‐stage statistical method for inferring behavior‐specific habitat selection and utilization distributions in continuous time. Practitioners can customize, fit, assess, and simulate our integrated model using the provided R package. Simulation experiments demonstrated that the model worked well under a range of sampling scenarios as long as observations were of sufficient temporal resolution. Our simulations also demonstrated the importance of accounting for different behaviors and the misleading inferences that can result when these are ignored. We provide case studies using plains zebra (Equus quagga) and Steller sea lion (Eumetopias jubatus) telemetry data. In the zebra example, our model identified distinct "encamped" and "exploratory" states, where the encamped state was characterized by strong selection for grassland and avoidance of other vegetation types, which may represent selection for foraging resources. In the sea lion example, our model identified distinct movement behavior modes typically associated with this marine central‐place forager and, unlike previous analyses, found foraging‐type movements to be associated with steeper offshore slopes characteristic of the continental shelf, submarine canyons, and seamounts that are believed to enhance prey concentrations. This is the first single‐stage approach for inferring behavior‐specific habitat selection and utilization distributions from tracking data that can be readily implemented with user‐friendly software. As certain behaviors are often more relevant to specific conservation or management objectives, practitioners can use our model to help inform the identification and prioritization of important habitats. Moreover, by linking individual‐level movement behaviors to population‐level spatial processes, the multistate Langevin diffusion can advance inferences at the intersection of population, movement, and landscape ecology. [ABSTRACT FROM AUTHOR]

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

Results of modern studies of the earth's crust based on the gravitational data of the GOCE satellite have been used for the first time in a comparative metallogenic analysis of the geodynamic settings of the formation of polymetallic deposits in the folded frame of the Siberian and East European platforms. It is shown that deposits of the sedimentary exhalative deposits (SEDEX) type are more often located in the earth's crust with the dominating development of the lower "basaltic" layer. Pyrite copper and lead–zinc volcanogenic massive sulfide (VMS) deposits, as well as some manifestations of the SEDEX type, occur in supra-subduction island-arc and accretionary settings in the crust with the dominating development of the middle "granitic" layer. Pb-Zn ores of the Mississippi Valley type (MVT) are localized in deep pericratonic sedimentary oil and gas basins on the shelf and continental slope, with no spatial relationship to the stratification of the earth's crust. The Ag polymetallic mineralization of Taimyr and the Western Verkhoyansk region are confined to deep pericratonic rift troughs on the passive continental margin. They have a similar ore-bearing environment and can be combined into a single silver polymetallic Taimyr–Western Verkhoyansk belt. The results confirm the prospects of Pb-Zn deposits in Central and Eastern Taimyr and also in the Saurey ore region (Polar Urals), indicating the need for their further research. [ABSTRACT FROM AUTHOR]

The structure and chemical composition of ferromanganese crusts formed on the sedimentary cover of the underwater volcanoes of the Peter the Great Seamount and the Vasilkovsky Ridge, located near the continental slope of Primorye (Sea of Japan), are studied. The crusts were formed as a result of cementation and precipitation of manganese hydroxides on the sediment surface. The signs of the hydrothermal nature of these formations are very high titanium and low aluminum modules, low contents of nonferrous and rare-earth elements (REEs), and an excess of heavy REE contents over the light ones. An ore substance was probably deposited in the Pleistocene–Holocene from postvolcanic hydrothermal solutions. Unlike the crusts deposited on basalts in the central parts of the Sea of Japan, these crusts do not contain inclusions of fine grains of medium- and high-temperature mineral phases of nonferrous metals. [ABSTRACT FROM AUTHOR]

The study analyzes polycyclic aromatic hydrocarbons (PAHs) isolated from bottom sediments of the Barents and Norwegian seas (2019–2021 cruises of the R/V Akademik Mstislav Keldysh). Elevated PAH concentrations (up to 16 900 ng/g) are recorded in the coastal region of the Svalbard archipelago, and low ones, in the Greenland Basin and the eponymous ridge (up to 80 ng/g), as well as on the continental slope of the Barents Sea (up to 240 ng/g on average). Among cata-condensed PAHs, 2–3 ring polyarenes are the most common: naphthalene, 1- and 2-methylnaphthalenes, and phenanthrene, while among peri-condensed PAHs, 4–6 ring polyarenes are the most typical: fluoranthene, pyrene, and benz(a)anthracene. Anthropogenic sources in the bottom sediments of the study area are of subordinate importance compared to their natural input from the sedimentary stratum with fluid fluxes and erosion. [ABSTRACT FROM AUTHOR]

The vertical variability of the geometric, dynamic, and thermohaline characteristics of Black Sea eddies is studied using three-dimensional identification of closed streamlines based on the results of simulations of the NEMO model in 2006–2016. The vertical extent of eddies depends linearly on their orbital velocity and significantly affects the speed of their translation motion. The influence of the background current on the upper part of the eddy leads to the mean tilt of the vertical axis of anticyclones in the cyclonic direction and this tilt is maximum in the zone of the Black Sea Rim Current. The eddies occupying the upper layer (up to 150 m) move relatively quickly at a speed of 0.08–0.14 m/s, since they are advected by the Rim Current. The most intense eddy dynamics is observed over the continental slope in the upper 20–70 m layer, where the probability of observing eddies exceeds 30%. Several maxima appear in the surface layer on the shallow northwestern shelf near the mouths of the Danube, Southern Bug, and Dnieper rivers. The relationship between the orbital velocity of eddies, their thermohaline structure, and stratification were estimated. Stability decreases in anticyclonic eddies within the layer 40–100 m due to the lowering of the pycnocline, and in cyclones it increases due to its elevation; in the underlying layers a compensating change of the opposite sign is observed. However, as the orbital velocity increases in the eddies of both signs, a decrease in stratification occurs in the upper 0–100 m layer, which is probably associated with an increase in the vertical shear of the current velocity. Three-dimensional identification of eddies makes it possible to track in detail changes in the individual characteristics of an eddy during its evolution. Using the example of an eddy off the Anatolian coast, it is shown that intensification of anticyclones is associated with the processes of entrainment of shelf waters, which can be one of the important sources of potential energy for anticyclones in the Black Sea. [ABSTRACT FROM AUTHOR]

The results of gas geochemical and lithogeochemical studies of bottom sediments in the Tatar Strait trough (Sea of Japan) based on cruise data from the R/V Akademik M.A. Lavrentyev (LV-81 and LV-85) are presented. Anomalies of hydrocarbon gases (HCGs) and chemical elements in the surface bottom sediments were determined. It has been established that sediments with anomalous methane contents are significantly enriched in Mn, Sc, V, Co, Ni, Cu, As, Se, Mo, Cd, Sb, Te, Tl, and U, the coefficients of the concentration (Kc) of which are 1.3–5.9 times higher than similar values at other stations. The data obtained allow us to assume the presence of gas sources of hydrocarbon migration; the continental slope and deep-water area of the Tatar trough are promising for setting up detailed work on the assessment of the oil and gas potential and the gas hydrate content. [ABSTRACT FROM AUTHOR]

The seafloor contains complex ecosystems where habitat heterogeneity influences biodiversity. Natural biological and geological features including vents, seeps and reefs create habitats that select for distinct populations of micro‐ and macrofauna. While largely studied for macrobiological diversity, built habitats may also select distinct microbiomes. Built habitat density on the seafloor is increasing with ocean sprawl expanding in the continental shelf and slope, potentially having widespread effects on benthic communities. This study addresses one type of built habitat, shipwrecks, on microbiomes in surrounding sediment. Using deep‐sea sediment samples (762 total) from the Gulf of Mexico, we report elevated diversity and a predictable core microbiome around nine shipwrecks. We show the sphere of influence of built habitats extends up to 300 m onto the seafloor. Supervised learning made predictions of sample proximity to structures based on frequency of taxa. Strongest predictions occurred in sediments nearest and furthest from sites for archaea and mid‐transect for bacteria. The response of archaea to built habitats was consistent across sites, while bacteria showed greater between site variability. The archaeal core shipwreck microbiome was enriched in taxa (e.g., Bathyarchaeia, Lokiarchaeia, Thermoplasmata) not present in the surrounding seafloor. Shipwrecks shaped microbiomes in expected ways, providing insight on how built habitats impact microbiome biodiversity in the Anthropocene. [ABSTRACT FROM AUTHOR]

For the first time, original results concerning the composition of fluids extracted from glendonite found in Japan (East) Sea continental slope bottom sediment have been obtained. We used the one-act shock-destructive extraction of volatile components from fluid inclusions and made their pyrolysis-free gas chromatography-mass spectrometry analysis, which, despite the limited amount of analytical data, are of scientific and practical interest. According to the data obtained, the fluids in glendonite represent a complex multicomponent mineral-forming system. In addition to water and carbon dioxide, representatives of 13 homologous series of organic compounds were found in the studied fluid inclusions. These include oxygen-free aliphatic and cyclic hydrocarbons (paraffins, olefins, cyclic alkanes and alkenes, arenes, polycyclic aromatic hydrocarbons-PAHs), oxygenated hydrocarbons (alcohols, ethers and esters, furans, aldehydes, ketones, carboxylic acids), nitrogen-, sulfur-, halogenated compounds. An oxidized water-carbon dioxide fluid with a reduced content of hydrocarbons and S–N–F-containing compounds 0.8 rel % is preserved in glendonite. [ABSTRACT FROM AUTHOR]

A new genus and species of Loricifera, Scaberiloricus samba gen. et sp. nov., is described from the continental shelf and slope off Rio de Janeiro, Brazil. Adult morphology remains unknown for the new entity, but information is available from three different Higgins larval instars. The Higgins larva of the new species is characterised by a bulbous head and a slender, elongate trunk, separated by a constriction behind the head. The cuticle of the thorax and the posterior part of the head is characterised by numerous longitudinal zigzag folds. The new species and genus shows greatest morphological resemblance with Wataloricus japonicus, and a phylogenetic analysis based on Higgins larval morphological characters suggests that Scaberiloricus gen. nov., Wataloricus, Tenuiloricus, and Patuloricus form a monophyletic group within Pliciloricidae. The analysis furthermore suggests that the Higgins larvae of Scaberiloricus gen. nov. and Wataloricus represent transitional, evolutionary stages towards the highly aberrant Shira larvae, found in species of Tenuiloricus and Patuloricus. [ABSTRACT FROM AUTHOR]

Compressional velocity (Vp) and bulk density (ρb) logs are essential for characterizing gas hydrates and near-seafloor sediments; however, it is sometimes difficult to acquire these logs due to poor borehole conditions, safety concerns, or cost-related issues. We present a machine learning approach to predict either compressional Vp or ρb logs with high accuracy and low error in near-seafloor sediments within water-saturated intervals, in intervals where hydrate fills fractures, and intervals where hydrate occupies the primary pore space. We use scientific-quality logging-while-drilling well logs, gamma ray, ρb, Vp, and resistivity to train the machine learning model to predict Vp or ρb logs. Of the six machine learning algorithms tested (multilinear regression, polynomial regression, polynomial regression with ridge regularization, K nearest neighbors, random forest, and multilayer perceptron), we find that the random forest and K nearest neighbors algorithms are best suited to predicting Vp and ρb logs based on coefficients of determination (R2) greater than 70% and mean absolute percentage errors less than 4%. Given the high accuracy and low error results for Vp and ρb prediction in both hydrate and water-saturated sediments, we argue that our model can be applied in most LWD wells to predict Vp or ρb logs in near-seafloor siliciclastic sediments on continental slopes irrespective of the presence or absence of gas hydrate. [ABSTRACT FROM AUTHOR]

Mesoscale eddy buoyancy fluxes across continental slopes profoundly modulate the boundary current dynamics and shelf–ocean exchanges but have yet to be appropriately parameterized via the Gent–McWilliams (GM) scheme in predictive ocean models. In this work, we test the prognostic performance of multiple GM variants in noneddying simulations of upwelling slope fronts that are commonly found along the subtropical continental margins. The tested GM variants range from a set of constant eddy buoyancy diffusivities to recently developed energetically constrained, bathymetry-aware diffusivities, whose implementation is augmented by an artificial neural network (ANN) serving to predict the mesoscale eddy energy based on the topographic and mean flow quantities online. In addition, an ANN is employed to parameterize the cross-slope eddy momentum flux (EMF) that maintains a barotropic flow field analogous to that in an eddy-resolving model. Our tests reveal that noneddying simulations employing the bathymetry-aware forms of the Rhines scale–based scheme and GEOMETRIC scheme can most accurately reproduce the heat contents and along-slope baroclinic transports as those in the eddy-resolving simulations. Further analyses reveal certain degrees of physical consistency in the ANN-inferred eddy energy, which tends to grow (decay) as isopycnal slopes are steepened (flattened), and in the parameterized EMF, which exhibits the correct strength of shaping the flow baroclinicity if a bathymetry-aware GM variant is jointly used. These findings provide a recipe of GM variants for use in noneddying simulations with continental slopes and highlight the potential of machine learning techniques to augment physics-based mesoscale eddy parameterization schemes. Significance Statement: This study evaluates the predictive skill of parameterization schemes of water mass transports induced by ocean mesoscale eddies across continental slopes. Correctly parameterizing these transports in noneddying ocean models (e.g., ocean climate models) is crucial for predicting the ocean circulation and shelf–ocean exchanges. This work highlights the importance of bathymetric effects on eddy transports, as parameterization schemes that account for the influence of a sloping seafloor outperform those developed specifically for a flat-bottomed ocean. This work also highlights the efficacy of machine learning techniques to augment physics-based mesoscale eddy parameterization schemes, for instance, by estimating the mesoscale eddy energy online to realize energy-dependent parameterization schemes in noneddying simulations. [ABSTRACT FROM AUTHOR]

Energetic tidal currents in the Arctic play an important role in local mixing processes, but they are primarily confined to the shelves and continental slopes due to topographic trapping north of their critical latitude. Recent studies employing idealized models have suggested that the emergence of higher harmonic tidal waves along these slopes could serve as a conduit for tidal energy transmission into the Arctic Basin. Here we provide observational support from an analysis of yearlong observations from three densely-instrumented oceanographic moorings spanning 30 km across the continental slope north of Svalbard (∼ 81.3 ∘ N). Full-depth current records show strong barotropic diurnal tidal currents, dominated by the K 1 constituent. These sub-inertial currents vary sub-seasonally and are strongest at the 700-m isobath due to the topographic trapping. Coinciding with the diurnal tide peak in summer 2019, we observe strong baroclinic semidiurnal currents exceeding 10 cm s - 1 between 500 m and 1000 m depth about 10 km further offshore at the outer mooring. In this semidiurnal band, we identify super-inertial K 2 waves, and present evidence that their frequency, timing, polarization, propagation direction and depths are consistent with the generation as higher harmonics of the topographically trapped K 1 tide at the continental slope. [ABSTRACT FROM AUTHOR]

It is well known that strong low-mode internal tides generated in Luzon Strait propagate westward to impinge continental slopes in the northeastern South China Sea (SCS). The reflection and scattering of these internal tides including diurnal and semidiurnal components on the slopes are quantitatively investigated using two sets of mooring data and a linear internal tide model with realistic topography and stratification. Flux reflections computed from mooring data collected on the continental slopes are consistent with the linear model. Based on the results of the observations and simulations, a map of low-mode internal tide reflection and scattering coefficients along the continental margin in the northeastern SCS is revealed. On average, diurnal internal tides lose 38% of their energy to high modes (≥mode 4) that are assumed to dissipate on the slopes, transmit 28% onto the continental shelf, and reflect 31% back to the deep ocean. On the contrary, most of the semidiurnal energy (89%) transmits onto the continental shelf, and only 11% is scattered to high modes (7%) and reflected back to the deep ocean (4%). For diurnal internal tides, a large fraction of energy that is scattered to high modes and reflected back to the deep sea can be attributed to the critical–supercritical slopes, while the weak reflection for the semidiurnal energy is due to the subcritical slopes. These quantitative descriptions for evolutions of low-mode internal tides incident to the slopes provide an energy budget map on the continental slopes in the northeastern SCS. [ABSTRACT FROM AUTHOR]

Observations from a Seaglider, two pressure-sensor-equipped inverted echo sounders (PIESs), and a thermistor chain (T-chain) mooring were used to determine the waveform and timing of internal solitary waves (ISWs) over the continental slope east of Dongsha Atoll. The Korteweg–de Vries (KdV) and Dubreil–Jacotin–Long (DJL) equations supplemented the data from repeated profiling by the glider at a fixed position (depth ∼1017 m) during 19–24 May 2019. The glider-recorded pressure perturbations were used to compute the rarely measured vertical velocity (w) with a static glider flight model. After removing the internal tide–caused vertical velocity, the w of the eight mode-1 ISWs ranged from −0.35 to 0.36 m s−1 with an uncertainty of ±0.005 m s−1 due to turbulent oscillations and measurement error. The horizontal velocity profiles, wave speeds, and amplitudes of the eight ISWs were further derived from the KdV and DJL equations using the glider-observed w and potential density profiles. The mean speed of the corresponding ISW from the PIES deployed at ∼2000 m depth to the T-chain moored at 500 m depth and the 19°C isotherm displacement computed from the T-chain were used to validate the waveform derived from KdV and DJL. The validation suggests that the DJL equation provides reasonably representative wave speed and amplitude for the eight ISWs compared to the KdV equation. Stand-alone glider data provide near-real-time hydrography and vertical velocities for mode-1 ISWs and are useful for characterizing the anatomy of ISWs and validating numerical simulations of these waves. Significance Statement: Internal solitary waves (ISWs), which vertically displace isotherms by approximately 100 m, considerably affect nutrient pumping, turbulent mixing, acoustic propagation, underwater navigation, bedform generation, and engineering structures in the ocean. A complete understanding of their anatomy and dynamics has many applications, such as predicting the timing and position of mode-1 ISWs and evaluating their environmental impacts. To improve our understanding of these waves and validate the two major theories based on the Korteweg–de Vries (KdV) and Dubreil–Jacotin–Long (DJL) equations, the hydrography data collected from stand-alone, real-time profiling of an autonomous underwater vehicle (Seaglider) have proven to be useful in determining the waveform of these transbasin ISWs in deep water. The solutions to the DJL equation show good agreement with the properties of mode-1 ISWs obtained from the rare in situ data, whereas the solutions to the KdV equation underestimate these properties. Seaglider observations also provide in situ data to evaluate the performance of numerical simulations and forecasting of ISWs in the northern South China Sea. [ABSTRACT FROM AUTHOR]

In natural systems, animal‐mediated nutrient transport can be a major driver of primary productivity, but the role of marine megafauna such as cetaceans in mediating the transfer and recycling of nutrients has been overlooked. Here, we developed a spatially resolved, stochastic, nutrient‐transport model for cetaceans in the oceanic Gulf of Mexico using species−specific foraging depths, distributions, and diets. An estimated 6.4 × 108 mmol N d−1, or 0.06 mt N yr−1 ind−1, is transported to the surface from depths below 100 m by the 19 cetacean species that occur in the oceanic Gulf of Mexico; 75% of this transport occurs seaward of the continental slope, but the per area transported nitrogen is greater on the continental slope (200–1000 m) than in the ocean basin. Benthos to surface transport comprised 6.0 × 107 mmol N d−1 and was much more common on the continental slope than the open basin. Compared to an existing physical‐biogeochemical model, the transported nutrients add 8% N d−1 to the estimated ammonium concentration above the nutricline and could add 16% N d−1 to the surface ammonium concentration if expelled nutrients remain at the surface. Through feeding on diel vertical migrants, cetaceans retain an additional 2.7 × 107 mmol N d−1 in the surface waters that would otherwise return to depth via downward diel vertical migration. Cetaceans contribute to nutrient movements and recycling in the oceanic Gulf of Mexico, and may provide one of the few allochthonous sources of nutrients for primary producers in oligotrophic ecosystems. [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]

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]

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]

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]

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]

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]

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]

Energetic tidal currents in the Arctic play an important role in local mixing processes, but they are primarily confined to the shelves and continental slopes due to topographic trapping north of their critical latitude. Recent studies employing idealized models have suggested that the emergence of higher harmonic tidal waves along these slopes could serve as a conduit for tidal energy transmission into the Arctic Basin. Here we provide observational support from an analysis of yearlong observations from three densely-instrumented oceanographic moorings spanning 30 km across the continental slope north of Svalbard (∼ 81.3 ∘ N). Full-depth current records show strong barotropic diurnal tidal currents, dominated by the K 1 constituent. These sub-inertial currents vary sub-seasonally and are strongest at the 700-m isobath due to the topographic trapping. Coinciding with the diurnal tide peak in summer 2019, we observe strong baroclinic semidiurnal currents exceeding 10 cm s - 1 between 500 m and 1000 m depth about 10 km further offshore at the outer mooring. In this semidiurnal band, we identify super-inertial K 2 waves, and present evidence that their frequency, timing, polarization, propagation direction and depths are consistent with the generation as higher harmonics of the topographically trapped K 1 tide at the continental slope. [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]

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]