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The larvae of many marine species are pelagic drifters in the vast oceans, yet they are the first and, for sessile species, the only way to connect with other populations. Connectivity is of particular interest in designing and assessing marine protected areas (MPAs), as it is considered a factor of renewal and stability.In this study, we focused on larval mixing between MPAs, investigating mixing rates during and at the end of their pelagic life, and how this is affected by the timing of larval release. We used a particle transport model coupled to the climatological hydrodynamics of the northwestern Mediterranean Sea to simulate the trajectories of Nephrops norvegicus larvae. Larvae were released from four no‐take MPAs, where fishery activity is banned, and started mixing between 7 and 12 days old.At settlement time, larval mixing mainly occurred between two pairs of MPAs labelled AxB (49.4% ± 5.8%) and CxD (23.7% ± 10.7%), respectively, located on the northern and southern sides of a thermal front. Percentages of larval mixing between these pairs changed, and other MPA combinations were formed with delayed larval release times. Mixing of larvae released from the same MPA tended to decrease with increasing delays between release times.This variability in mixing was related to the latitudinal distribution of MPAs along the continental slope and the spatiotemporal dynamics of the regional hydrodynamics, with a strong impact from a thermal front.Larval mixing modelling is a useful measure for understanding connectivity in marine environments and can suggest new conservation decisions. It identifies MPAs that are spatially distributed to facilitate the convergence of larvae from various protected areas. It also underlines that recognizing the significance of hydrodynamic variability when designing MPAs is crucial for promoting efficient connectivity among these areas. [ABSTRACT FROM AUTHOR]

Multiwave interference plays a crucial role in shaping the spatial variations of internal tides. Based on a combination of in situ mooring and altimeter data, interference of semidiurnal internal tides was investigated in the northern South China Sea. Mooring observations indicate the observed kinetic-to-potential energy ratio and group speed are both relatively lower than the theoretical values of mode-1 semidiurnal internal tides, indicating the presence of partly-standing waves. This is consistent with the altimeter result that the mooring was located at the antinode within the interference pattern formed by the superposition of the westward and southward semidiurnal internal tides from the Luzon Strait and the continental slope of the southern Taiwan Strait. However, the kinetic-to-potential energy ratio and group velocity were notably changed when an anticyclonic eddy passed by the mooring. By employing the ray-tracing method, we identified that mesoscale processes may induce a phase difference in the semidiurnal internal tides between the Luzon Strait and the continental slope of the southern Taiwan Strait. This alteration further leads to changes in the positions of nodes and antinodes within the interference pattern of the semidiurnal internal tides. [ABSTRACT FROM AUTHOR]

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

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]

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]

Future mass loss from the East Antarctic Ice Sheet represents a major uncertainty in projections of future sea level rise. Recent studies have highlighted the potential vulnerability of the East Antarctic Ice Sheet to atmospheric and oceanic changes, but long-term observations inside the ice shelf cavities are rare, especially in East Antarctica. Here, we present new insights from observations from three oceanic moorings below Fimbulisen Ice Shelf from 2009 to 2021. We examine the characteristics of Warm Deep Water (WDW) intrusions across a sill connecting the cavity to the open ocean, and investigate seasonal variability of the circulation and water masses inside the cavity. In autumn, solar-heated, buoyant Antarctic Surface Water (ASW) reaches below the 350 m deep central part of the ice shelf, separating colder Ice Shelf Water from the ice base and affecting the cavity circulation on seasonal timescales. At depth, the occurrence of WDW is associated with the advection of cyclonic eddies across the sill into the cavity. These eddies reach up to the ice base. The warm intrusions occur favorably from January to March and from September to November, and traces of WDW-derived meltwater close to the ice base imply an overturning of these warm intrusions inside the cavity. We suggest that both the offshore thermocline depth and interactions of the Antarctic Slope Current with the ice shelf topography over the continental slope cause this timing. Our findings provide a better understanding of the interplay between shallow ASW and deep WDW inflows for basal melting at Fimbulisen, with implications for the potential vulnerability of the ice shelf to climate change. [ABSTRACT FROM AUTHOR]

The access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019–2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite‐derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (a) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (b) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub‐ice‐shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice‐shelf‐ ocean interactions in East Antarctica. [ABSTRACT FROM AUTHOR]

Wave‐ and current‐supported gravity flows (WCSGFs) represent a primary mechanism responsible for the transport of sediment along gentle coastal and continental slopes. However, due to limited in situ measurements, the dynamic processes involved in the downslope movement of WCSGFs along such slopes remain poorly understood. Here, tripods were strategically deployed on a muddy coastal slope in central Jiangsu, China. We found that WCSGFs occurred following a wave event, particularly during tidal slack periods. In instances where WCSGF events coincide with low slack water, the observed time lags between break and toe sites align with expectations based on gravity‐driven velocities and distances, thereby corroborating the gravitationally induced sediment transport across the gently sloping coast. Comparatively, WCSGF events during high slack water were suggested to originate from the upper tidal flat of the cross‐shore profile and were unable to reach the toe site. Waves are crucial in supporting the downslope transport of WCSGFs. In addition to sustaining the cross‐shore movement of WCSGFs, currents suspend sediments from the high‐concentration layer, dispersing them into the overlying water column. This suspension helps extinguishing WCSGFs. The local slope at the toe site lacks the necessary gravitational force to propel high‐concentration layers further offshore, as evidenced by the abnormally low drag coefficient (CD) derived from the theoretical WCSGF model. Despite their short‐lived nature and limited travel distance, the WCSGFs examined in this study make a significant contribution to cross‐shore sediment transport. This study contributes to a better understanding of WCSGF dynamics and their importance in coastal sediment transport. [ABSTRACT FROM AUTHOR]

The Gaoping Submarine Canyon (GPSC) off southwest Taiwan has been extensively studied due to its unique geology, its role in transferring terrestrial material to the deep sea, and its 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 a 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 ∼ 2020 mg C m -2 d -1 in the canyon, 84 % of the carbon flux exited the system, while 12 % was buried. On the slope, 84 % of the OC input (∼ 109 mg C m -2 d -1) was buried, and only 7 % 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 throughflow (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" period. 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" period sampling to reveal the effects of typhoons and monsoon rainfalls on OC cycling. [ABSTRACT FROM AUTHOR]

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

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 <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 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]

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 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]

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]

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]

The article presents observations of near-inertial internal waves (NIWs) in the slope waters of the Black Sea in winter and summer. Rotary spectral analysis of a time series of sea current velocity measurements revealed the prevailing anticyclonic component of the motions near the local inertial frequency f. The clockwise rotation of the velocity vector with depth implies that the NIWs propagate downwards. The amplitude of NIWs usually was 0.1–0.2 m s−1. NIWs were observed in the layer of the permanent pycnocline and the seasonal pycnocline, which attenuate below depths of 160 m and 80 m in winter and summer, respectively. The amplitude of the near-inertial kinetic energy (NIKE) showed a close relationship with vertical stratification. During winter, NIKE exhibited maximum values in the layer of the permanent pycnocline, whereas, in summer, it was primarily observed in the seasonal pycnocline layer. The near-inertial oscillations were generally more energetic in winter. [ABSTRACT FROM AUTHOR]

Internal tides are known to be an important source of mixing in the oceans, especially in the bottom boundary layer. The depth of internal-tide generation therefore seems important for benthic life and the formation of cold-water coral mounds, but internal-tide conversion is generally investigated in a depth-integrated sense. Using both idealized and realistic simulations on continental slopes, we found that the depth of internal-tide generation increases with increasing slope steepness and decreases with intensified shallow stratification. The depth of internal-tide generation also shows a typical latitudinal dependency related to Coriolis effects. Using a global database of cold-water corals, we found that, especially in Northern Hemisphere autumn and winter, the global depth pattern of internal-tide generation correlates (rautumn = 0.70, rwinter = 0.65, p < 0.01) with that of cold-water corals: shallowest near the poles and deepest around the Equator, with a decrease in depth around 25° S and N, and shallower north of the Equator than south. We further found that cold-water corals are situated significantly more often on topography that is steeper than the internal-tide beam (i.e. where supercritical reflection of internal tides occurs) than would be expected from a random distribution: in our study, in 66.9 % of all cases, cold-water corals occurred on a topography that is supercritical to the M2 tide whereas globally only 9.4 % of all topography is supercritical. Our findings underline internal-tide generation and the occurrence of supercritical reflection of internal tides as globally important for cold-water coral growth. The energetic dynamics associated with internal-tide generation and the supercritical reflection of internal tides likely increase the food supply towards the reefs in food-limited winter months. With climate change, stratification is expected to increase. Based on our results, this would decrease the depth of internal-tide generation, possibly creating new suitable habitat for cold-water corals shallower on continental slopes. [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]

In the Mesozoic succession of the Anyui–Chukotka fold system (North‐East Russia), five stratigraphic intervals were recognised that have an abundance of gravity flow deposits. These are the Olenekian (Lower Triassic), Upper Carnian, Upper Norian, Oxfordian–Kimmeridgian and Valanginian. The Triassic gravity flow deposits formed on the south‐facing, passive margin of the Chukotka microplate and consist of greywackes and lithic arenites. Palaeocurrent data indicate that the flows were directed towards the south‐east. The Olenekian gravity flow units consist of clast‐rich sandstone deposited on the continental slope, and clast‐poor sandstone deposited at the base of the slope. Upper Carnian mud‐poor sandstones were deposited at the base of the slope and the Norian thin‐bedded turbidites were upper to mid‐slope deposits. The continental margin was affected by tectonism and was uplifted in the latest Triassic–earliest Jurassic, possibly due to the initiation of the southward translation of the Arctic Alaska–Chukotka microplate. Following an Early–Middle Jurassic uplift of the area, sedimentation resumed in the Late Jurassic and earliest Cretaceous. Several syn‐orogenic depressions (Rauchua, Pegtymel, Pevek, Myrgovaam and Kytepveem) developed on the south‐western margin of the Chukotka microplate, and deposition in these basins included gravity flow deposits at various times. In both the Oxfordian–Kimmeridgian and Valanginian successions, gravity flow deposits included arkosic and subarkosic sandstones with a northern source area of granitoid complexes and deformed Triassic strata. The intervening Tithonian–Berriasian gravity flow deposits consisted mainly of thin‐bedded turbidites. These sediments had a southern source, which included a volcanic arc that had accreted to the southern margin of the Chukotka microplate. [ABSTRACT FROM AUTHOR]

Marine plastic pollution is currently one of the most serious environmental threats. In this study, based on scenario calculations for a five-year period, we analyzed the possible spread of microplastics carried by Siberian rivers to the Kara Sea shelf. The Lagrangian particle model used daily data from 3D numerical modeling to simulate microplastic transport by ocean currents and sea ice drift. The results of a series of scenario calculations show how the distribution of particles and their subsequent deposition depend on their type (density), size, processes of freezing into the ice, and biofouling (accumulation of microorganisms). The crucial influence of the effects of microplastic embedding in sea ice and particle biofouling on the trajectories of floating particles and their deposition on the seafloor is highlighted. The transport of light particles of microplastics from Siberian rivers by ice can contribute to the pollution of the Barents Sea, in addition to their more active outflow through the Fram Strait. Biofouling is a driver of microplastic deposition on the shelf bottom or transport along the continental slope in a cyclonic direction following the trajectory of the Atlantic waters. [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]

Two post-metamorphic adult females of the sphyriid copepod Lophoura cornuta (C. B. Wilson, 1919) were collected from Kaup's arrowtooth eel Synaphobranchus kaupii Johnson, 1862 (Anguilliformes: Synaphobranchidae) at two deep-sea sites in the western North Pacific off the south coast of Hokkaido, northern Japan. This paper reports on the morphology of L. cornuta based on the adult female specimens collected as the second record of the species from Japan. One of the collection sites is near the type locality of the parasite, and the infected fish were captured at depths of 550 and 620 m on the continental slope. Although the type host of L. cornuta was reported as "Synaphobranchus affinis Günther, 1877", this fish may be S. kaupii because the latter species predominates among synaphobranchid eels in the western North Pacific off Hokkaido. An identification key to the four nominal species of the genus Lophoura Klliker in Gegenbaur, Klliker, and Müller, 1853 reported from Japan is also provided. [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]

Scientific bottom-trawl surveys are ecological observation programs conducted along continental shelves and slopes of seas and oceans that sample marine communities associated with the seafloor. These surveys report taxa occurrence, abundance and/or weight in space and time, and contribute to fisheries management as well as population and biodiversity research. Bottom-trawl surveys are conducted all over the world and represent a unique opportunity to understand ocean biogeography, macroecology, and global change. However, combining these data together for cross-ecosystem analyses remains challenging. Here, we present an integrated dataset of 29 publicly available bottom-trawl surveys conducted in national waters of 18 countries that are standardized and pre-processed, covering a total of 2,170 sampled fish taxa and 216,548 hauls collected from 1963 to 2021. We describe the processing steps to create the dataset, flags, and standardization methods that we developed to assist users in conducting spatio-temporal analyses with stable regional survey footprints. The aim of this dataset is to support research, marine conservation, and management in the context of global change. [ABSTRACT FROM AUTHOR]

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We investigated benthic foraminifera in cores GPC03 and GPC04 in the northeast tropical Indian Ocean (TIO) over the past ∼450 ka to evaluate the ballasting effect of particulate organic matter (POM) and the long‐term zonal change during the mid‐Brunhes dissolution interval (MBDI). Today, interannual climate and oceanographic variability in the TIO is governed by the Indian Ocean Dipole (IOD), which manifests as asymmetric zonal oceanographic change. Previous studies have been conducted to uncover such zonal paleoceanographic change and have referred to their climatic pattern as an "IOD‐like mode." In the northeast TIO, after ∼390 ka, contributions of lithogenic matter and %Nuttallides umbonifer were unusually high under the better carbonate preservation conditions during glacial periods. Our findings suggest that the effect of lithogenic matter from the Ganga‐Brahmaputra‐Meghna River system increased significantly under glacial low sea‐level conditions, possibly by lateral transport along the continental slope. As a result, ballasting of POM seemed more efficient during glacial periods by abundant riverine lithogenic particles. In addition, the long‐term (∼320–200 ka) trend of high benthic foraminiferal accumulation rate (BFAR) and several short‐term fluctuations of high BFAR at ∼310, ∼280, ∼260, and ∼240 ka were discernible. We attribute these changes to increased paleoproductivity driven by upwelling, which may be related to the Indian Ocean equatorial westerlies and Indian summer monsoon dynamics via variations arising from precession. We propose that a long‐term mean‐state transition of IOD‐like mode might have occurred during the MBDI, similar to other hypotheses invoking concomitant changes in the El Niño‐Southern Oscillation system. Key Points: Nuttallides umbonifer were commonly observed in the glacial sediments at the Ninetyeast Ridge of the northeast tropical Indian OceanBallasting of particulate organic matter by the riverine lithogenic particles was more efficient during the glacial periods at the Ninetyeast RidgeWe found evidence for a long‐term mean‐state transition in northeast tropical Indian oceanography since the mid‐Brunhes period [ABSTRACT FROM AUTHOR]

We investigate the 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 energy is also transferred from the SIT field to the eddy field at an average rate of 3.0 mW m -2 (accounting for 7 % of the incoming energy flux of SIT when integrated over the eddy diameter). Second, the AE can modify the spatial distribution of tidal-induced dissipation by refracting, scattering, and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a northward or southward shift in the internal tidal rays. These findings deepen our understanding of the complex interactions between AE and SIT, as well as their impacts on energy conversion, wave propagation, and coastal processes. [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 characteristics and mechanism of the southern South China Sea (SCS) Western Boundary Current (WBC) summer-winter transition have been investigated. The transition typically starts in early October and lasts for about two weeks. Above the thermoclines (~100 m), the transition is simultaneous with depth, while below the thermoclines the transition in deeper layer significant lags that in the shallow layers. The geostrophic balance dominates the transition of WBC. Above the thermocline, the transition is determined by the barotropic pressure gradient component. Below the thermocline, the transition is determined by the competition between the barotropic and baroclinic pressures components. When the southern SCS WBC transition above the thermocline starts, the barotropic and baroclinic pressures components offset each other below the thermocline, resulting in the lag of the geostrophic balance. With the depth increases, more time is needed for the barotropic pressures component to enhance enough to dominate a geostrophic balance, which induces the transition lag with depth. Changes in the barotropic pressure gradient component are mainly due to the variations in SCS basin scale wind stress curl, while changes in the baroclinic pressure gradient component below the thermocline are associated with the warming of the deeper water column caused by the downwelling near the continental slope and the disappearing of upwelling off Vietnam. [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 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]

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]

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]

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]

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]

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]

Flow of dense shelf water provide an efficient mechanism for pumping CO2 to the deep ocean along the continental shelf slope, particularly around the Antarctic bottom water (AABW) formation areas where much of the global bottom water is formed. However, the contribution of the formation of AABW to sequestering anthropogenic carbon (Cant) and its consequences remain unclear. Here, we show prominent transport of Cant (25.0 ± 4.7 Tg C yr−1) into the deep ocean (>2,000 m) in four AABW formation regions around Antarctica based on an integrated observational data set (1974–2018). This maintains a lower Cant in the upper waters than that of other open oceans to sustain a stronger CO2 uptake capacity (16.9 ± 3.8 Tg C yr−1). Nevertheless, the accumulation of Cant can further trigger acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr−1. Our findings elucidate the prominent role of AABW in controlling the Southern Ocean carbon uptake and storage to mitigate climate change, whereas its side effects (e.g., acidification) could also spread to other ocean basins via the global ocean conveyor belt. Plain Language Summary: The Southern Ocean is thought to uptake and store a large amount of anthropogenic CO2 (Cant), but little attention has been paid to the Antarctic coastal regions in the south of 60°S, mainly due to the lack of observations. Based on an integrated data set, we discovered the deep penetration of Cant and a visible pattern of relatively high concentration of Cant along the AABW formation pathway, and the concentration of Cant along the shelf‐slope is higher than that of other marginal seas at low‐mid latitudes, implying a highly effective Cant transport in AABW formation areas. We also found strong upper‐layer CO2 uptake and a significant acidification rate in the deep waters of the Southern Ocean due to the AABW‐driven CO2 transport, which is 3 times faster than those in other deep oceans. It is therefore crucial to understand how the Antarctic shelf regions affect the global carbon cycle through the uptake and transport of anthropogenic CO2, which also drives acidification in the other ocean basins. Key Points: We show evidence for the accumulation of Cant along the Antarctic shelf‐slope into the deep oceanThe process of AABW formation drives Cant downward transport at 25.0 ± 4.7 Tg C yr−1, sustaining the CO2 uptake in the surface oceanThis further triggers acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr−1, which is faster than in other deep oceans [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]