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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]

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 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]

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]

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]

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]

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]

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]

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

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

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

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

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

The use of the Fluidity-ICOM model in a full non-hydrostatic formulation enables the correct investigation of fine-scale water dynamics and water transformations on the Antarctic shelf and the continental slope. A possibility of solving problems with high order of accuracy in models is determined by the use of a three-dimensional adaptive unstructured mesh with automatic refinement to given scales. The modernization of the graphical model output has made it possible to visualize reliably the details of simulated hydrophysical process development, to obtain the numerical estimates of parameters of these processes, and to verify them against unique field observation data. An original three-dimensional numerical experiment was held in the area of a shelf glade with an open water surface. In this case, the real salt (buoyancy) flux is specified, which is caused by the in-water ice formation in the glade and obtained from the actual atmospheric forcing. As a result, the convective circulation was correctly simulated as a process of forming dense water on the shelf, which then flows down the shelf and the continental slope in the form of discrete density currents. Similarity of the model geometric, dynamic, and hydrophysical characteristics of cascading with the characteristics obtained from the analysis of field observations is noted. [ABSTRACT FROM AUTHOR]

Breaking internal tides contribute substantially to small-scale turbulent mixing in the ocean interior and hence to maintaining the large-scale overturning circulation. How much internal tide energy is available for ocean mixing can be estimated by using semianalytical methods based on linear theory. Until recently, a method resolving the horizontal direction of the internal waves generated by conversion of the barotropic tide was lacking. We here present the first global application of such a method to the first vertical mode of the principal lunar semidiurnal internal tide. We also show that the effect of supercritical slopes on the modally decomposed internal tides is different than previously suggested. To deal with this the continental shelf and the shelf slope are masked in the global computation. The global energy conversion obtained agrees roughly with the previous results by Falahat et al. if the mask is applied to their result, which decreases their energy conversion by half. Thus, around half of the energy conversion obtained by their linear calculations occurs at continental slopes and shelves, where linear theory tends to break down. The barotropic-to-baroclinic energy flux at subcritical slopes away from the continental margins is shown to vary substantially with direction depending on the shape and orientation of topographic obstacles and the direction of the local tidal currents. Taking this additional information into account in tidal mixing parameterizations could have important ramifications for vertical mixing and water mass properties in global numerical simulations. [ABSTRACT FROM AUTHOR]

The Newfoundland and Labrador Shelves Bioregion, located on the glaciated continental shelf and adjacent continental slope of eastern Canada, is classified into units that reflect its great physiographic diversity. There are ten shelf units: bedrock zone, fjord systems, major inlet, shelf-crossing troughs, four types of offshore banks, basin, and disturbed (glaciotectonic) terrain. There are three units on the continental slope: channelized areas, trough-mouth areas, and large sedimentary drifts. A series of vignettes illustrates both the distinguishing characteristics of the principal geomorphic units and the morphologic diversity within them. A sediment mobility analysis reveals that wave- and current-generated disturbances are dominant and largely depth-controlled within the shelf units, while the south-flowing Labrador Current impacts sediment transport and mobility along the continental slope. [ABSTRACT FROM AUTHOR]

Simple Summary: The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed species found in all oceans, even if irregularly, inhabiting continental shelves and slopes, islands, and mid-ocean ridges in deep seas. The species is currently classified by the International Union for Conservation of Nature (IUCN) as globally near-threatened, with a decreasing population. Despite some records in Brazil, the known distribution of this species in the Southwestern Atlantic is very patchy and, in some cases, not yet recorded in the world reference literature, such as in northeastern Brazil. This study, therefore, highlights new records for the species in the Tropical Southwestern Atlantic, particularly off the northeastern Brazilian coast. This information is paramount to establishing distribution maps for the species employed in a population status assessment by the IUCN. The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed demersal species found in tropical and temperate waters of the Pacific, Atlantic, and Indian Oceans, inhabiting continental shelves and slopes, islands, and mid-ocean ridges at depths ranging from 200 to 1100 m. In the Southwestern Atlantic, this species has been recorded from northeastern to southern Brazil, Argentina, and Uruguay. Despite this, the known distribution of this species in the Southwestern Atlantic is very patchy and, in some cases, still mostly ignored in the literature, such as in northeastern Brazil. This study, therefore, aimed to report 23 new records of Hexanchus griseus in the Tropical Southwestern Atlantic and highlight the presence of this species off the northeastern Brazilian coast. So far, Hexanchus griseus was officially reported from the Fernando de Noronha Archipelago, Saint Peter and Saint Paul Archipelago, and the state of Ceará along the northeast coast of Brazil. Herein, the known distribution is extended to the continental shelf breaks and upper slopes of other Brazilian states, reinforcing the previously reported occurrence of the species near the Saint Peter and Saint Paul Archipelago. [ABSTRACT FROM AUTHOR]

Interest in the study of microplanktonic organisms in the Arctic has increased owing to their direct participation in the process of sedimentation and sensitive response to changes in environmental and climatic factors. This study presents new data on the taxonomic diversity and content of radiolarian skeletons and agglutinated tintinnid ciliate loricae in the Upper Holocene sediments of the Laptev Sea, East Siberian Sea, and the adjacent part of the Arctic Ocean. We traced the spatial distribution of representative microfauna of these groups in surface sediments and sediment cores. Radiolarian skeletons were found in the surface sediments of the continental slope of the Laptev Sea and adjacent parts of the Arctic Ocean. These belong to the following six species: Stylatractus (?) sp., Actinomma leptoderma leptoderma, Actinomma leptoderma longispina, Streblacantha circumtexta, Spongotrochus glacialis, and Cycladophora davisiana. The radiolarian fauna detected was in deep sea and close to the fauna of the Nansen Basin (Central Arctic). Furthermore, we found tintinnid ciliate loricae belonging to the following seven species: Tintinnopsis ventricosoides, Tintinnopsis fimbriata, Tintinnopsis turbo, Tintinnopsis nitida, Tintinnopsis sp. cf. fusus (?), Tintinnopsis sp., and Stenosemella nivalis. In the study area, the tintinnid ciliate loricae of these species were discovered for the first time and traced mainly in the coastal shelf zone, which can be explained by their ecology. The only exception is that of T. nitida, which was found only on the continental slope of the Laptev Sea. Our findings advance knowledge on the biodiversity of Arctic seas and can be used to monitor ecological and paleoceanographic changes in the Arctic region. [ABSTRACT FROM AUTHOR]

Canada ratified the United Nations Convention on the Law of the Sea (UNCLOS) in 2003. With that ratification is an obligation to submit data and information to the U.N. pertaining to the limits of the country's extended continental shelf (ECS); the portion of the juridical continental shelf that extends beyond 200 nautical miles. A team of Canadian scientists, managers, and legal experts that included representation from three Federal Departments (Natural Resources Canada, Fisheries and Oceans Canada, and Global Affairs Canada) with additional support from other departments, spent 13 years compiling and acquiring data to provide the scientific evidence to support delineation of Canada's seaward most maritime limit. The submission has the potential to provide Canada with 2.4 million km2 of additional submarine landmass in the Atlantic and the Arctic oceans over which Canada exercises sovereign rights for the purpose of exploring and exploiting its natural resources. Specific information such as the tectonic framework of the continental margin, the geomorphology of the margin and in particular the continental slope, the geologic nature of adjoined ridges, rises, and plateaux, and sediment thickness within adjacent basins are examples of fundamental pieces of geoscientific information needed to substantiate Canada's outermost maritime limits. This paper highlights a number of segments of Canada's continental margins to showcase this scientific evidence and how it is applied in the UNCLOS context. In doing so, the paper demonstrates the geologic complexity of Canada's margins as illustrated in scientific publications that have resulted from these new data collections, while at the same time presenting new scientific evidence and interpretations. This collection of data and information provides a wealth of new knowledge in Canada's offshore regions. The massive data compilation in the Atlantic led to conception of continental margins, in a source-to-sink scenario, as having an equilibrium base level or graded form, comparable to river systems. Departures from this shape relate to the interplay of sedimentary processes and in particular to those processes that do not fit the source-to-sink paradigm. For example, a significant part of the Atlantic margin is shown to be heavily influenced by along-slope geostrophic currents that generated massive contourite drift deposits. These deposits reflect lateral transport of sediment that had a significant impact on the morphology of the margin. The role of mass transport processes in shaping continental margins is also highlighted, and in particular the collapses of entire segments of the margin were observed. The prominent role mass failure processes play in delivering sediment to the adjacent abyssal plain is also critical in the ECS context. These observations challenge the entrenched notion of a continental margin comprising a shelf, slope, and rise and in particular the concept of the "continental rise". Prior to 2006, regions of the Arctic Ocean seaward of the Canadian landmass had fewer than 5000 km of seismic reflection data. The massive efforts of Arctic coastal States to map their margins for ECS purposes have led to a leap in technological advances to acquire data in ice-covered seas and have led to a wealth of new geoscientific knowledge. Perhaps foremost amongst this knowledge is demonstration that Canada Basin is indeed a fully developed ocean basin, albeit significantly infilled with sediment. Based on this knowledge and identification of related structures, new realistic tectonic scenarios for opening of the Amerasia Basin are proposed that include a significant component of transform or strike-slip motions. With seismic velocity and rock sample information, the continental nature of Alpha and Mendeleev ridges has been substantiated. Even bathymetric data were lacking in the Arctic and new editions of seafloor maps now support grids of 500 m spacing; although some regions remain sparse. Once thought to be relatively stagnant, sedimentary processes such as found in many ocean basins were discovered in the Arctic Ocean. Evidence of geostrophic currents, sediment mass failures, and deep-sea turbidity current channels were found to be ubiquitous, even in the deepest parts of the Arctic's basins. [ABSTRACT FROM AUTHOR]

Bathymetric study of northwestern Bay of Bengal has great regional importance due to its influence on waves, tides, storm surges, etc., that affect the population and vegetation of the adjacent coastal parts. In this article, the bathymetry of northwestern part of Bay of Bengal has been mapped extensively using gridded bathymetric data set of GEBCO_2020 (15 arc-second interval data of The General Bathymetric Chart of the Oceans). One-dimensional variations of bathymetry along specific latitudes and longitudes adjacent to six popular Indian stations of West Bengal and Odisha have been presented. A number of underwater depressions of the order of 100 km2 each have been identified in the continental shelf between 21.2°N and 21.6°N latitudes, adjacent to Sundarban National Park. Few prominent highs have been marked on the continental slope of Andhra Pradesh coast. One dimensional bathymetry profile of the whole sea bed in north–south direction is presented along 85.83°E and 90.5°E longitudes. A general study of Swatch of No Ground, Bengal Fan, 85°E Ridge and Ninetyeast Ridge is also carried out, and findings are compared with existing literature. The purpose of the study is to model the interaction of shallow-water waves with this part of the seafloor in future. Research highlights: Detailed study of bathymetry of northwestern Bay of Bengal is provided in the article. Recently published gridded 15 arc-second interval bathymetric dataset of GEBCO_2020 is used in this study. Some underwater depressions between 88.5°–89.2°E longitude and 21.2°–21.6°N latitude adjacent to Sundarban National Park and few bathymetric highs along the continental slope of Andhra Pradesh between 83.2°–84.2°E longitude and 17.6°–18°N latitude have been identified from the data. Bathymetry profile of the whole sea bed in N–S direction is presented along 85.83°E and 90.5°E longitude is given. This study will help in future goal of modeling interaction of shallow water waves with bathymetry of the study area. [ABSTRACT FROM AUTHOR]

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

Evaluating the seismic site effect by the ambient noise based horizontal-to-vertical spectral ratio (HVSR) method is strongly affected by the spatial and temporal variations of the ambient noise sources. Therefore, it is necessary to locate the source regions of ambient noise and investigate the relationships between the source energy and HVSR values at the predominant frequency (HVSRf0) of the site. The generation mechanisms of the single- and double-frequency microseisms (SFMs, 0.05–0.085 Hz and DFMs, 0.1–0.5 Hz) in ambient noise are better understood than the noise in other frequency bands and they are dominantly composed of fundamental Rayleigh (Rg) waves. With this advantage, the recordings of SFMs and DFMs at 30 stations in the east coast region of the United States are used to demonstrate a study on locating their source regions with reasonable certainty and constructing the functional relationship between the HVSRf0 and the source energy of SFMs and DFMs. The recordings are processed in four sub-frequency bands (Fs) of SF and DF bands and a polarization analysis is carried out to select the ellipsoids approximating the particle motions of Rg waves. Then the probability density functions of the back azimuths of the ellipsoids' semi-major axes are computed for each F and station, and are projected on the ocean to determine their possible source regions. These regions are further constrained by (1) the correlation coefficients between the SFMs and the WAVEWATCH III (WWIII) hindcasts of ocean wave spectra in the SF band, or between the DFMs and the modeled DF energy on ocean surface in the selected time windows in the DF band, (2) the energy contribution defined by (i) the average WWIII ocean wave energy and the ocean bottom topographical gradient in the SF band, or (ii) the average modeled DF energy on ocean surface and a frequency and water depth dependent coefficient measuring the conversion efficiency of DF energy from water to solid earth in the DF band, and (3) the percentile retained energy of Rg waves in both the SF and DF bands. Results of source regions reveal that (1) the SFMs recorded in eastern US result from the interactions of low frequency (0.05–0.085 Hz) ocean waves with the continental slope and shelf of western North Atlantic Ocean; (2) the source regions for long- (0.1–0.2 Hz) period DFMs are located in the deep ocean close to the continental slope; and (3) the short- (0.2–0.5 Hz) period DFMs are generated in the continental shelf. Finally, the correlation analyses between the simulated source energy and the HVSRf0values at the stations whose f0s fall in DF band are carried out revealing significant source effect on thick sediments at low frequencies. [ABSTRACT FROM AUTHOR]

The results of modern studies of the lithosphere based on the GOCE satellite gravity data were used for the first time for a comparative metallogenic analysis of the geodynamic settings of the formation of Pb–Zn deposits in the folded frame of the Siberian platform. Sedimentary-exhalative polymetallic deposits (Baikal and Taimyr systems) are most often found in the areas with predominant development of the lower "basalt" layer of the Earth's crust. Pyrite copper and lead–zinc deposits are mainly characteristic of suprasubduction island-arc and accretionary settings on the consolidated crust with the predominant development of the middle "granite" layer (Yenisei Ridge). The MVT-type lead–zinc ores, which are closely associated with pericratonic deep sedimentary petroleum basins on the shelf and the continental slope do not obviously have a spatial relationship with the stratification of the Earth's crust. The similarity between the geodynamic settings of the formation of the silver-polymetallic deposits in Southern Taimyr and Western Verkhoyansk confined to the pericratonic rift troughs on the passive continental margin is revealed, which makes it possible to combine them into single silver-polymetallic Taimyr—Western Verkhoyansk belt. [ABSTRACT FROM AUTHOR]

Geochemical data are presented on the Pleistocene sediments from the central part of the outer shelf of the East Siberian Sea, the continental slope and Podvodnikov Basin of the Arctic Ocean. The studied sediments of the outer shelf and continental slope belong to the aleuropelitic type, while those of the shelf edge and the Podvodnikov Basin, to the pelitoaleuritic type. The contents of the psammitic fraction and stone material do not exceed 10 and 1%, respectively. These features predetermine the distribution of the maximum sediment density and median diameters in the sediments of the outer shelf, and the minimum values in the Podvodnikov Basin. The distribution of Corg and Сcarb contents in the studied sediments is characterized by a similar variability. The average wetness content in the bottom sediments in the study area systematically increases in the "shelf–pelagial" direction. The study of the chemical and gas composition of the bottom sediments in the same direction made it possible to distinguish four main groups of geochemical associations in the Pleistocene sediments of the study area. The bottom sediments of the outer shelf are characterized by the maximum concentrations of the first group of chemical elements (Si, Sr, Ba) and methane (up to 0.102 cm3/kg), those of the shelf edge, by the maximum concentrations of the second group (Cd, Hg, U, K, Ca) and the minimum content of methane (up to 0.002 cm3/kg). The sediments of the continental slope have the maximum concentrations of the third group (Cu, Zn, Ti, Be, Nb, Ag, Tl, Pb, Lu, Tm, Tb, Ho, Eu, Yb, Er, Dy), while those of the Podvodnikov Basin, the fourth group (Mn, Fe, Al, Cr, P, Mg, Mo, Ni, Sb, Sn, As, Th, Co, Ga, W, Hf, Rb, V, Cs, Sc, Li, Gd, Sm, Pr, Nd, La, and Ce) and intermediate contents of methane (up to 0.051 cm3/kg). The maximum total concentration of methane homologues (up to С5 including, 0.006 cm3/kg), δ13С-СН4 (up to –36.0‰), δ13С-С2Н6 (up to –17.2‰), molecular mass of the hydrocarbon fraction (up to 27.5 g/mol), coefficient of transformation and "wetness" of the hydrocarbon fraction were found in the Pleistocene sediments of the continental slope and the foot of the Podvodnikov Basin, while the lowest concentrations of these parameters were determined in the outer shelf. The established isotope-gas-geochemical indicators point to the predominance of epigenetic hydrocarbon gases from various gas sources in the studied sediments. The positive and negative correlations between geochemical and isotopic-gas-geochemical indicators have been established. Obtained data were used to estimate the oil and gas prospects of the study area. [ABSTRACT FROM AUTHOR]

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

Four new species of buccinoid gastropods from the continental shelf and slope are described. Neptunea flatteryensis Clark, n. sp. and Latisipho ritteri Clark, n. sp. from depths of 134-165 m off the Cape Flattery area of Washington State, Buccinum cascadiense Clark, n. sp. found at bathyal depths of 788-1203 m, off of the coasts of Washington and Oregon, and Golikovia fitchi Clark, n. sp. found at bathyal depths of 722-1240 m off of California. [ABSTRACT FROM AUTHOR]

The offshore area of the Otway Basin (south‐eastern Australia) is dominated by multibranched canyons where mass‐transport complexes are widely distributed. This study integrates high‐resolution multibeam and seismic data to investigate the importance of mass‐transport complexes in dictating the evolution of canyons. The study interprets three regionally distributed mass‐transport complexes that fail retrogressively and affect almost 70% of the study area. Within the mass‐transport complexes, seven canyons that initiated from the continental shelf edge and extended to the lower slope are observed. Although the canyons share common regional tectonics and oceanography, the scales, morphology and distribution are distinctly different. This is linked to the presence of failure‐related scarps that control the initiation and formation of the canyons. The retrogressive failure mechanisms of mass‐transport complexes have created a series of scarps on the continental shelf and slope. In the continental shelf, where terrestrial input is absent, the origin of the canyons is related to local failures and contour current activities, occurring near the pre‐existing larger headwall scarps (ca 120 m high, 3 km long). The occurrence of these local failures has provided the necessary sediment input for subsequent gravity‐driven, downslope sediment flows. In the continental slope, the widespread scarps can capture gravity flows initiated from the continental shelf, developing an area of flow convergence, which greatly widens and deepens the canyons. The gradual diversion and convergence through mass‐transport complex related scarps have facilitated the canyon confluence process, which has fundamentally changed the canyoning process. Thus, this study concludes that the retrogressive failure mechanism of mass‐transport complexes has a direct influence on the initiation, distribution and evolution of the canyons. The scarps associated with mass‐transport complexes have greatly facilitated the delivery of sediments and marine plastics from the shelf edge into the deep oceans, especially in areas where fluvial input is missing. [ABSTRACT FROM AUTHOR]

Shallow seabed depressions attributed to focused fluid seepage, known as pockmarks, have been documented in all continental margins. In this study, we demonstrate how pockmark formation can be the result of a combination of multiple factors—fluid type, overpressures, seafloor sediment type, stratigraphy and bottom currents. We integrate multibeam echosounder and seismic reflection data, sediment cores and pore water samples, with numerical models of groundwater and gas hydrates, from the Canterbury Margin (off New Zealand). More than 6800 surface pockmarks, reaching densities of 100 per km2, and an undefined number of buried pockmarks, are identified in the middle to outer shelf and lower continental slope. Fluid conduits across the shelf and slope include shallow to deep chimneys/pipes. Methane with a biogenic and/or thermogenic origin is the main fluid forming flow and escape features, although saline and freshened groundwaters may also be seeping across the slope. The main drivers of fluid flow and seepage are overpressure across the slope generated by sediment loading and thin sediment overburden above the overpressured interval in the outer shelf. Other processes (e.g. methane generation and flow, a reduction in hydrostatic pressure due to sea‐level lowering) may also account for fluid flow and seepage features, particularly across the shelf. Pockmark occurrence coincides with muddy sediments at the seafloor, whereas their planform is elongated by bottom currents. [ABSTRACT FROM AUTHOR]

The Shumagin seismic gap along the Alaska Peninsula experienced a major, MW 7.8, interplate thrust earthquake on 22 July 2020. Several available finite‐fault inversions indicate patchy slip of up to 4 m at 8–48 km depth. There are differences among the models in peak slip and absolute placement of slip on the plate boundary, resulting from differences in data distributions, model parameterizations, and inversion algorithms. Two representative slip models obtained from inversions of large seismic and geodetic data sets produce very different tsunami predictions at tide gauges and deep‐water pressure sensors (DART stations), despite having only secondary differences in slip distribution. This is found to be the result of the acute sensitivity of the tsunami excitation for rupture below the continental shelf in proximity to an abrupt shelf break. Iteratively perturbing seismic and geodetic inversions by constraining fault model extent along dip and strike, we obtain an optimal rupture model compatible with teleseismic P and SH waves, regional three‐component broadband and strong‐motion seismic recordings, hr‐GNSS time series and static offsets, as well as tsunami recordings at DART stations and regional and remote tide gauges. Slip is tightly bounded between 25 and 40 km depth, the up‐dip limit of slip in the earthquake is resolved to be well‐inland of the shelf break, and the rupture extent along strike is well‐constrained. The coseismic slip increased Coulomb stress on the shallow plate boundary extending to the trench, but the frictional behavior of the megathrust below the continental slope remains uncertain. Plain Language Summary: Several studies on the 22 July 2020 MW 7.8 thrust event have included finite‐fault inversions, yielding generally consistent slip models. However, none of these studies have fully considered the seismic and geodetic data together with the tsunami measurements at tide gauges and deep‐water pressure sensors. We select two representative slip models obtained from prior seismic and geodetic inversions for tsunami modeling and find that they give distinct tsunami predictions despite having only a minor shift of slip by ∼20 km relative to shelf break. Large differences in tsunami excitation occur when seafloor deformation extends to the continental slope under deeper water. We perform iterative inversion of seismic and geodetic observations and forward modeling of tsunami signals to obtain an optimal slip model compatible with teleseismic waves, regional seismic recordings, hr‐GNSS time series and static offsets, along with tsunami recordings at DARTs and tide gauges. Precise placement of the slip distribution beneath the continental shelf controls the strength and timing of seaward tsunamis, with waveforms varying nonlinearly with seafloor deformation extending across the shelf break. The earthquake increased Coulomb stress on the shallow megathrust, but uncertainty in the shallow frictional behavior leaves it unclear whether a future large event can occur there. Key Points: Published finite‐fault models for the 2020 MW 7.8 earthquake predict varying tsunami signals despite having similar slip patternsThe tsunami excitation is very sensitive to the absolute placement of slip relative to the shelf break and along strikeIteration of slip inversion parameters and tsunami predictions optimizes the model to fit all data well with slip only beneath the shelf [ABSTRACT FROM AUTHOR]

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope. • The number of known cold seep sites on the U.S. Atlantic margin has now doubled. • Seeps and clusters are found at ∼275 locations, mostly north of Cape Hatteras. • Most seeps are shallower than the landward limit of gas hydrate stability. • Faulting, erosion, unroofing, and hydrologic sapping dominate seep evolution. • Complex hydrate distribution leads to promontory seeps next to shelf-break canyons. [ABSTRACT FROM AUTHOR]

Fault activities in sea areas always produce devastative marine geohazards. For marine geohazard assessment, it is important to know the location, geometric structure, and activity regularity of active faults. In this study, high-resolution multi-channel seismic and topographic data are used to investigate the exact location, geometric structure and latest activity of the Continental Slope Fault Zone (CSFZ) in the northern South China Sea. The results show that the Qiongdongnan (QDN) segment of the CSFZ is a 194 km long NEE-trending fault zone that developed near the transition of continental shelf and slope. In its geometric structure, the CSFZ (QDN segment) cuts through the Cenozoic basement and breaks upward to near the seafloor with high-angle dip. According to whether it ruptures to the seafloor, it can be divided into eastern and western segments. In the western segment, the fault scarps about 8∼9 m high can clearly be seen on the seafloor. Whereas in the eastern segment, the fault shows a blind characteristic below the seafloor. The analysis of fault throws and expansion indices show that CSFZ (QDN segment) have remained active since the late Pleistocene. Due to the CSFZ is an active fault and geographically adjacent steep slope, which may cause large interpolate landslides, and then leading to destructive tsunamis. As a result, the CSFZ has great seismogenic potential and may produce marine geohazard chain. Thus, it is of great significance to the assessment of marine geohazard chain posed by the CSFZ for improving hazard mitigation. • The exact location, geometric structure and latest activity of the Continental Slope Fault Zone are investigated. • The Continental Slope Fault Zone has been active since the Late Pleistocene. • The Continental Slope Fault Zone has great seismogenic potential and might trigger marine geohazard. [ABSTRACT FROM AUTHOR]

NASA's Suomi National Polar-orbiting Partnership (NPP), Visible Infra-red Imaging Radiometer Suite (VIIRS) data utilized to detect night time lights (NTL) radiances and fishing boat pixels using VIIRS boat detection (VBD) approach. Study attempted for first time in Indian waters to detect night time fishing boats during 2017 along with chlorophyll and sea surface temperature (SST). Night-time fishing observed higher in Arabian Sea (AS) compared to Bay of Bengal (BoB). The reason likely the shallower bathymetry (50–200meters) of AS, broader continental shelf and more biological productivity, compared to BoB's narrow and steep continental slope and less productive water. AS night time fishery observed season-dependent (December–May) with VBD pixels ranging 100–300, wherein BoB distribution is sparse, <30 VBD pixels. In AS, moderate/high chlorophyll (0.2–1.2 mgm−3), moderate SST (27–30.5 °C) and non-cloudy months observed suitable for night time fishing. In BoB, moderate chlorophyll (0.2-0.45 mgm−3) and moderate SST (27-30.5 °C) played positive role for night light fishing. [ABSTRACT FROM AUTHOR]

Warm deep water intrusion over the Antarctic continental shelves threatens the Antarctic ice sheet stability by enhancing the basal melting of ice shelves. In East Antarctica, the Antarctic Slope Current (ASC), along with the Antarctic Slope Front (ASF), acts as a potential vorticity barrier to prevent the warm modified Circumpolar Deep Water (mCDW) from ventilating the cold and fresh shelf. However, mCDW onshore transport is still observed within certain shelf regions, such as submarine troughs running perpendicular to the continental shelf. This study focuses on the dynamic mechanisms governing mCDW intrusion within a submarine trough over the fresh shelf regions, East Antarctica. Based on an idealized eddy-resolving coupled ocean–ice shelf model, two high-resolution process-oriented numerical experiments are conducted to reveal the mechanisms responsible for the mCDW onshore transport. Three dynamic mechanisms governing cross-slope mCDW intrusion are identified: 1) the bottom pressure torque, 2) the topography beta spiral, and 3) the topography Rossby waves. These three mechanisms simultaneously govern the mCDW intrusion together. The bottom pressure torque plays a leading role in driving the time-mean onshore flow whose vertical structure is determined by the topography beta spiral, while the topography Rossby waves contribute to the high-frequency oscillations in the onshore volume and heat transport. The simulated spatial distribution and seasonality of mCDW intrusion qualitatively coincide with the observed mCDW intrusion over fresh shelf regions, East Antarctica. Both the topography beta spiral and the ASC play an important role in governing the seasonality of mCDW intrusion. [ABSTRACT FROM AUTHOR]

The Intergovernmental Panel on Climate Change Fifth Assessment Report lists sea‐level rise as one of the major future climate challenges. Based on pre‐industrial and historical‐and‐future climate simulations with the Community Earth System Model, we analyze the projected sea‐level rise in the Northwest Atlantic Ocean with two sets of simulations at different horizontal resolutions. Compared with observations, the low resolution (LR) model simulated Gulf Stream does not separate from the shore but flows northward along the entire coast, causing large biases in regional dynamic sea level (DSL). The high resolution (HR) model improves the Gulf Stream representation and reduces biases in regional DSL. Under the RCP8.5 future climate scenario, LR projects a DSL trend of 1.5–2 mm/yr along the northeast continental shelf (north of 40° N), which is 2–3 times the trend projected by HR. Along the southeast shelf (south of 35° N), HR projects a DSL trend of 0.5–1 mm/yr while the DSL trend in LR is statistically insignificant. The different spatial patterns of DSL changes are attributable to the different Gulf Stream reductions in response to a weakening Atlantic Meridional Overturning Circulation. Due to its poor representation of the Gulf Stream, LR projects larger (smaller) current decreases along the north (south) east continental slope compared to HR. This leads to larger (smaller) trends of DSL rise along the north (south) east shelf in LR than in HR. The results of this study suggest that the better resolved ocean circulations in HR can have significant impacts on regional DSL simulations and projections. Plain Language Summary: Projecting future sea‐level rise has great socioeconomic value. Based on long‐term global high‐resolution Community Earth System Model simulations, we analyze future sea‐level rise in the Northwest Atlantic Ocean. Two identical sets of simulations were conducted with different horizontal resolutions. Comparisons between the two sets of simulations show different sea‐level rise projections along the US east continental shelf between the low‐resolution (LR) and high‐resolution (HR) models. At the northeast shelf, HR projects a sea‐level rise of 0.8 mm/yr, less than half of the trend (1.7 mm/yr) projected by LR. At the southeast shelf, HR projects a sea‐level rise of 0.6 mm/yr, while the trend in LR is statistically insignificant at only 0.15 mm/yr. We attribute the different sea‐level rise projections to the different ocean circulations simulated in LR and HR. Under global warming, LR projects a decrease in Gulf Stream flow along the entire east continental slope, while the decrease in Gulf Stream strength is confined to the southeast continental slope in HR. This study provides an explanation for the discrepancy in regional sea‐level rise projections between low‐ and high‐resolution climate models and thus improves our understanding of projected future sea‐level rise. Key Points: The high resolution (HR) Community Earth System Model reduces biases in dynamic sea level (DSL) and circulation on US east continental shelfCompared to the low resolution model, the HR projects enhanced (reduced) trends of DSL rise along the US south (north) east continental shelfDifferent DSL rise patterns are related to different Gulf Stream reductions under a weakening Atlantic Meridional Overturning Circulation [ABSTRACT FROM AUTHOR]

Spatial patterns in fish distribution determine most fishing opportunities and tactics learned by fishers. To determine fishing opportunities and recurrent fishing grounds of deepwater fish such as the cardinalfish (Epigonus crassicaudus) in the south‐central zone of Chile, we analyzed records of fishing logs covering the period 1999–2007. Fishing trawls covered from Topocalma (34º06'S) to northwest Corral (39º52'S), and we compared the position of individual fishing hauls (Euclidean distance) applying a hierarchical agglomerative clustering technique. The clusters obtained represented spatially distributed fishing opportunities (n = 28), which were visited occasionally (<10 fishing hauls) or regularly (>50 fishing hauls) to fishing for cardinalfish. The recurrent fishing opportunities (n = 7) were distributed discretely, from Constitución (35°19'S) to northwest Mocha Island (38°23'S) along the continental shelf slope and between 313 and 333 m depth. The species composition in the bycatch and the catch per unit effort trends allow us to identify secondary species and locally depleted fishing opportunities, the last occurring close to main fishing ports. [ABSTRACT FROM AUTHOR]

The shelf-edge and continental slope current off the west coast of Canada has been monitored at a site off West Vancouver Island since 1985. However, observations at this site may not represent the characteristics of the shelf-edge and slope current off the entire west coast of Canada. Here, we use along-track satellite altimetry data over six transects to investigate the characteristics of the surface geostrophic currents over the shelf edge and continental slope off the west coast of Canada from 1992 to 2020. It is shown that along-track satellite altimetry is well suited for monitoring longshore and climatic variations of the near-surface shelf-edge and slope currents off the west coast of Canada. It is found that the surface current over the shelf edge and slope has different features from the south to the north. While the surface current is poleward in winter and equatorward in summer off South Vancouver Island, it is poleward year-round off the rest of the west coast of Canada. The seasonal current anomalies show longshore correlation significant at the 95% confidence level, except at the North Haida Gwaii transect. The first empirical orthogonal function mode of the seasonal current anomalies is correlated with the longshore wind anomalies both off South Vancouver Island and off Oregon. However, this first mode is not correlated with either the Niño 3.4 index or the Pacific Decadal Oscillation index, though they often show large episodic events during strong El Niño and La Niña years. Consistent with previous findings, the present study indicates that the surface currents over the shelf edge and continental slope off the west coast of Canada are related to regional and remote longshore wind forcing. [ABSTRACT FROM AUTHOR]

Meiodorvillea Jumars, 1974 is a little-known genus of Dorvilleidae Chamberlin, 1919, characterized by its small size and reduced appendages and jaw apparatus. A revision of the genus is presented, including analysis of the type material of M. minuta (Hartman, 1965) and M. apalpata Jumars, 1974, as well as specimens collected from shelf and slope continental areas in Brazil. A neotype was designated for M. minuta and its distribution was extended to Brazil. The identity of M. chilensis (Hartmann-Schröder, 1965) is questioned and three new species from 21 to 1,300.7 meters depth are also described. Meiodorvillea penhaesp. nov. has furcate chaeta only in the first anterior chaetigers. In contrast, Meiodorvillea hartmanaesp. nov. has very small palps and asymmetrical thin furcate chaeta and Meiodorvillea jumarsisp. nov. has dorsal cirri and geniculate chaeta only in the first anterior chaetigers. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Current (ASC) circumnavigates the Antarctic continent following the continental slope and separating the waters on the continental shelf from the deeper offshore Southern Ocean. Water mass exchanges across the continental slope are critical for the global climate as they impact the global overturning circulation and the mass balance of the Antarctic ice sheet via basal melting. Despite the ASC's global importance, little is known about its spatial and subannual variability, as direct measurements of the velocity field are sparse. Here, we describe the ASC in a global eddying ocean–sea ice model and reveal its large-scale spatial variability by characterizing the continental slope using three regimes: the surface-intensified ASC, the bottom-intensified ASC, and the reversed ASC. Each ASC regime corresponds to a distinct classification of the density field as previously introduced in the literature, suggesting that the velocity and density fields are governed by the same leading-order dynamics around the Antarctic continental slope. Only the surface-intensified ASC regime has a strong seasonality. However, large temporal variability at a range of other time scales occurs across all regimes, including frequent reversals of the current. We anticipate our description of the ASC's spatial and subannual variability will be helpful to guide future studies of the ASC aiming to advance our understanding of the region's response to a changing climate. [ABSTRACT FROM AUTHOR]

The width of shelves and continental slopes of the East Siberian and Laptev seas affected the postglacial transgression. This dependence, in turn, is directly determined by the viscosity of mantle layers. Based on numerical simulations, the sea level on the East Siberian Sea coast was at higher altitudes than on the Laptev Sea 4–6 ky BP. The difference in the transgression rate could be explained by the hydroisostatic mechanism. [ABSTRACT FROM AUTHOR]

The article presents data indicating the relationship of the bathymetric distribution of solitary endemic scleractinian corals inhabiting the Antarctic continental shelf and upper continental slope with the vertical density of the Antarctic Circumpolar Current. The study is based on materials collected by expeditions of the Shirshov Institute of Oceanology (IO RAS) and the literature data. The results show that endemic species that appeared in the Late Neogene and Pleistocene were unable to propagate across other oceans due to the existing horizontal and vertical density of the Arctic Circumpolar Current during that period. [ABSTRACT FROM AUTHOR]

We focus on the ichthyofauna on continental shelves and slopes of the Enshu-nada Sea--an area of the northwest Pacific Ocean off the coast of Southern Japan as one of the essential trawl fishery grounds in Japan. We conducted market samplings of the trawl catches from the Enshu-nada Sea, and trawl surveys of bycatch species by commercial trawlers. As a result, 208 deep-sea fish species (92 families) were recorded, with 46 species first recorded from the Enshu-nada Sea, of which five species were the northernmost record for these species. The results reveal the ichthyofaunal diversity in the continental shelf and upper continental slope of the Enshu-nada Sea, providing biogeographic information on various species based on the vouchers. [ABSTRACT FROM AUTHOR]

Coastal trapped waves (CTWs) are sub-inertial waves with energy confined to the continental shelf and play a crucial role in the coastal dynamics. In this study, we focus on analyzing the seasonal characteristics of CTWs in the South China Sea shelf region by using observations from tide gauges and reanalysis data. Our findings reveal significant seasonal variations in both the phase speed and amplitude of CTWs in the South China Sea. It is shown that phase speed tends to be higher during the winter, followed by spring and autumn, and with less distinct propagation characteristics during the summer. In terms of amplitude, apart from seasonal variations, the CTW amplitudes on the narrower Vietnam shelf are relatively smaller. Drawing on classical theories, we analyze the Kelvin wave mode, the first shelf wave mode, and the second shelf wave mode in CTWs, and investigate the effects of winds, background currents, and stratification. Results indicate that the winds have a significant impact on the generation of CTWs, and the greatest influence of winds occurs upstream relative to the direction of CTW propagation. Background currents can have a significant impact on the phase speed of CTWs, and the seasonal variations of CTWs are closely linked to the background circulations. Additionally, we discuss the influence of seawater stratification on the phase speed of CTWs (measured by Burger number, Bu). Under conditions of strong stratification in the summer, the Bu is larger and leads to higher phase speed of CTWs, particularly when the Bu reaches its maximum on the continental slope. This study provides a better understanding of the CTWs dynamics in the South China Sea shelf region. Our findings can be useful for predicting and managing coastal hazards in the region. • The CTWs in the South China Sea exhibit significant seasonal characteristics. • This study covers a longer period and utilizes historical data from tidal gauges. • We investigate the CTWs' propagation by combining observational data with theoretical solutions. • We investigate the effects of winds, background currents, and stratification on CTWs. [ABSTRACT FROM AUTHOR]

Variability in the Agulhas Current system is dominated by meanders, which constitute cyclonic eddies along the inshore edge of the Current on the southeast coast of South Africa. Few studies have investigated the influence of these meanders on hydrographic variability on the adjacent shelf and slope and to date only a handful have been sampled in situ. This study used available in situ data and GLORYS12v1 model output to investigate the impact of meanders on the distribution of Intermediate waters, namely Red Sea Water (RSW) and Antarctic Intermediate Water (AAIW), as well as mechanisms driving these variations. We focussed on four eddies, sampled in situ during July 1998, April 2010, January–February 2017, and July–August 2017. RSW dominated along the inshore edge of the Agulhas Current in the absence of meanders, but larger proportions of AAIW occurred in the presence of cyclonic eddies. During eddy events, the kinematic steering level was raised above the lower boundary of Intermediate waters, increasing cross-frontal mixing of waters at depths of 800–1800 m. Eddy-induced upwelling of Central and Intermediate waters onto the shelf appeared to be inhibited by bands of strong positive relative vorticity (>0.4 × 10−4 s−1), which likely promoted downwelling conditions inshore of the July 1998, April 2010, and July–August 2017 eddies. Weak positive relative vorticity (<0.2 × 10−4 s−1) inshore of the January–February 2017 eddy was associated with enhanced water mass exchange between the shelf and deeper (>1000 m) ocean. GLORYS12v1 was consistently comparable with satellite and in situ data, and simulated the overall distribution of water masses on the continental shelf and slope despite its inability to reflect the influence of river discharge in nearshore regions during austral summer. The model is thus suitable to investigate the influence of Agulhas Current meanders on the hydrography of South Africa's southeast coast. • Red Sea Water occurs inshore of Agulhas Current in the absence of meandering. • Agulhas Current meanders facilitate cross-frontal mixing of Intermediate waters. • Antarctic Intermediate Water found inshore of Agulhas Current during meandering. • GLORYS simulated the effects of Agulhas Current meanders with reasonable accuracy. [ABSTRACT FROM AUTHOR]

The continental shelf and slope, with upwelling systems, are usually accompanied by the formation of oxygen minimum zones, thereby stimulating marine paleoproductivity and promoting organic matter (OM) enrichment. However, due to a more oxygen-enriched environment, a distinct paleoecological characteristic, and the uncertainty of upwelling effects, it remains ambiguous whether a similar mechanism of OM preservation occurs in the adjacent carbonate platform. Here, limestone–marl alternations (LMAs) that developed in the Yangtze Carbonate Platform (YCP) during the Middle Permian were selected as the research object and compared with the chert–mudstone alternations developed on the Lower Yangtze continental shelf (LYCS). Both sets of rhythmites belong to the contemporaneous products of the Permian Chert Event in South China. Considering that the Middle Permian rhythmites in South China contain the Milankovitch record and that upwelling was controlled by astronomically forced monsoons, this study investigated the impact of upwelling on the carbonate platform by adopting astronomical cycle research. Based on GR data, a framework of astronomical cycles was established. The suboxic to anoxic conditions of the YCP are supported by evidence from syngenetic pyrite framboids, Ce/Ce* ranges, and U EF –Mo EF covariation. Upwelling geochemical indicators and the detection of a pivotal (∼210-kyr) astronomical cycle regarding upwelling indicate that the YCP was affected by upwelling. The paleoproductivity/OM/fossil-related data exhibit this ∼210-kyr astronomical cycle, and the correspondence between the converted AMs determines that upwelling enhanced marine primary paleoproductivity and OM preservation. However, the intensities of short eccentricity cycles exceed those of the ∼210 kyr cycle in the time series analyses of data from the nearshore YCP. Additionally, the covariations between the upwelling proxy and total fossil content confirm the impact of upwelling on biomass of benthic organisms. Therefore, the (monsoon-driven) upwelling system in the continental shelf can extend to the carbonate platform. After reaching the platform, under the control of a (an) (astronomically forced) climatic–oceanic system, limited upwelling can stimulate primary productivity and marine OM preservation; however, upwelling reduces biomass in the bottom water. In the nearshore side of the platform, detrital dilution likely replaces upwelling as the primary stimulus for productivity. Moreover, this study reveals and explains the ∼200-kyr cycles in the Permian strata of South China for the first time. [Display omitted] • The ∼200-kyr cycles are first revealed and explained in the Permian strata of South China. • Limited upwelling increases productivity and OM preservation in the carbonate platform. • Upwelling promotes productivity and thus depletes oxygen, reducing benthic biomass in the platform. • A model for the effect of the upwelling systems along continental shelves on carbonate platforms is proposed. • Milankovitch cycles are the basis of the Maokou LMAs forming a set of source rocks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Global warming drives microeukaryotes to move northward in the coastal sediments. • Microeukaryotic benthos stride over the ecological barrier of 32°N between the ECS and the YS under the global change. • Water depth restricts the connectivity between the continental slope community from the SCS and the continental shelf communities from the ECS and YS. • Higher phylogenetic diversity was detected in SCS than those in ECS and YS. • The depth, temperature and latitude significantly influence the microeukaryotes community in the coastal sediments. The marine flora and fauna along the China seas include the Indo-West Pacific warm-water fauna and the North Pacific temperate fauna. The latitude of 32°N is recognized as the ecological barrier for benthic fauna in the China Seas. However, the ecological barrier on macrobenthos community gradually weakened because of global warming. Microeukaryotes are major components of marine food webs and can quickly response to environmental changes. We hypothesis that microeukaryotic benthos can stride over the ecological barrier of 32°N from the East China Sea (ECS) to the Yellow Sea (YS) under the global change, but their distribution is still limited by depth gradients between the South China Sea (SCS) and the ESC. Therefore, we investigated the distribution of benthic microeukaryotes in the China Seas using RNA metabarcoding. Higher OTU richness and phylogenetic diversity were detected in the SCS than those in the YS and ECS. The YS and ECS communities clustered together firstly and then clustered with the SCS community. Unexpectedly, communities from the 33°N in the YS clustered with those from the ECS. Similar pattern was also detected for Cercozoa, Diatomea, Amoebozoa and Fungi. These findings indicated that microeukaryotic benthos strode over the ecological barrier of 32°N under the global change. Source-sink analyses indicated more than 50% sources of the 33°N community were attributed to the ECS community, while only 12.5% from the YS community. Depth, temperature and latitude showed significant influence on communities in the China Seas. This study highlights the response of active microeukaryotes to the global warming in the coastal sediments. [ABSTRACT FROM AUTHOR]

This study investigates the response of foraminifera and nematodes to different types of methane and other hydrocarbon gases (alkanes, alkins) in bottom sediments of the northwestern shelf and continental slope of the Black Sea. Foraminifera are represented by 39 species from six orders, 13 families, 24 genera. Nematoda are represented by 48 species from six orders, 17 families, 27 genera. Both groups of meiobenthos are characterized by impoverished simple diversity and abundance/density as well as by much smaller sizes of foraminiferal tests compared to those from areas not affected by hydrocarbon gases, indicating stressful conditions for their life in the study areas. Among foraminifera, calcareous hyaline taxa dominate, but agglutinated forms are present as well and occasionally play a dominant role. A significant number of the identified nematode species belong to the tyobiotic type from the families Comesomatidae and Linhomoidae. They are characterized by a long, thin body and a small or completely undeveloped oral cavity, indicating their feeding on small particles of sediment or bacteria. Nine groups of foraminifera and nematodes were identified according to their tolerance and sensitivity to methane (15 species), ethane (five species), propane (eight species), butane (10 species), pentane (11 species), ethylene (20 species), propylene (two species), acetylene (three species), and isobutylene (one species). This study provides evidence for the first time that different types of methane, its homologues, and other hydrocarbon gases affect the reproduction, diversity, abundance, and growth of foraminifera, as well as density and simple diversity of nematodes. • Methane. • Homologues. • Taxonomy and quantitative distribution of meiobenthos. [ABSTRACT FROM AUTHOR]