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The southeastern Australian margin hosts a series of submarine canyons. Although the origin and evolution of canyons within the northwestern segment of the margin is relatively well studied, their quantitative morphology, interaction with longshore drift currents and slope failure remain poorly understood in the southeastern region. In this study, high-resolution bathymetry and 3D seismic reflection datasets revealed five main submarine canyons present in the central offshore Otway Basin. The canyons have V-shaped, evolving to U-shaped morphology downslope with sedimentary infill characterized by medium–high amplitudes, recognizable stratal pattern and localized chaotic seismic reflections. Analysis reveals these canyons were initiated by retrogressive slope failure on the continental slope, that once the shelf edge was reached and subsequently incised, development of the canyon heads was influenced by the shelf parallel Zeehan Current, active on the continental shelf of the region. The heads of the shelf-incised canyons preferentially migrate northwestward and were infilled by laterally accreting sedimentary packages characterized by southeast dipping seismic reflections. These indicate an early erosive phase followed by a period of deposition, a result of the prevalent eastward flowing Zeehan Current. These results have important implications for understanding of the mechanisms that control initiation and development of submarine canyons, and their morphology, both offshore southeastern Australia, and similar settings on continental margins worldwide. [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water has been warming in recent decades throughout most of the oceans and freshening in regions close to its Indian and Pacific sector sources. We assess warming rates on isobars in the eastern Pacific sector of the Southern Ocean using CTD data collected from shipboard surveys from the early 1990s through the late 2010s together with CTD data collected from Deep Argo floats deployed in the region in January 2023. We show cooling and freshening in the temperature‐salinity relation for water colder than ∼0.4°C. We further find a recent acceleration in the regional bottom water warming rate vertically averaged for pressures exceeding 3,700 dbar, with the 2017/18 to 2023/24 trend of 7.5 (±0.9) m°C yr−1 nearly triple the 1992/95 to 2023/24 trend of 2.8 (±0.2) m°C yr−1. The 0.2°C isotherm descent rate for these same time periods nearly quadruples from 7.8 to 28 m yr−1. Plain Language Summary: Cold winds blowing over polynyas (areas of ice‐free water) on the Antarctic continental shelf create sea ice, forming very cold and somewhat salty, hence very dense, waters. These dense shelf waters descend the continental slope to the abyss, mixing with adjacent waters to form Antarctic Bottom Water (AABW). AABW spreads northward from there, filling much of the global abyssal ocean as it mixes with warmer, lighter waters above. AABW has been warming on pressure surfaces, freshening and cooling on density surfaces, and reducing in volume (contracting). These changes are likely a result of melting Antarctic ice sheets, which freshen the shelf waters, making them less dense, hence less able to sink to the bottom. We compare profiles of ocean temperature and salinity in the eastern Pacific sector of the Southern Ocean collected in 2023 and 2024 by robotic freely drifting profilers to data collected from ships from the early 1990s to the late 2010s. We find all of the above listed changes, but also acceleration of the warming, with the rate from 2017/18 to 2023/24 being nearly triple the rate from 1992/95 to 2023/24. The contraction rate has nearly quadrupled. This acceleration has been predicted by high‐resolution climate model simulations. Key Points: Antarctic Bottom Water (AABW) changes in the east Pacific sector of the Southern Ocean are assessed using Deep Argo and ship‐based CTD profilesBottom water warming rates from 2017/18 to 2023/24 nearly triple compared to 1992/95 to 2023/24 rates, contraction rates nearly quadrupleAABW cooling and freshening on isopycnals is also observed in the region, relative to older Circumpolar Deep Water [ABSTRACT FROM AUTHOR]

Large and diverse Eocene otolith assemblages have been described from the US Gulf and Atlantic coastal plains, various basins in Europe, and New Zealand. Here we described a highly diverse otolith association from the middle Eocene (Lutetian and Bartonian) strata of southern California, San Diego County, which was retrieved from the heritage of John E. Fitch (1918-1982) in the archives of the Ichthyology Department of the Natural History Museum of Los Angeles County, Los Angeles, Califronia. The collection represents the first Eocene otolith assemblage described from the Northeastern Pacific and stems from two localities: the Ardath Shale at Black’s Beach in the Torrey Pines Park just south of Black’s Canyon Road and north of the Salk Fault on the Pacific shore face, and the MissionValley Formation from the west-facing graded hill just east of the Miramar Water Treatment Plant near the southern shore of Miramar Reservoir. The Ardath Shale was deposited on the deep shelf and continental slope while the Mission Valley Formation represent an inland, nearshore environment during times of the maximum transgression. A total of more than15,000 otoliths were found representing 96 species of which 53 are described as new and 12 remain in open nomenclature. The fauna of the Ardath Shale is distinctly richer containing 88 species while the one from the Miramar Reservoir site yielded 38 species. The low diversity at the Miramar Reservoir site is thought to be related to the shallow-water environment in which it was deposited whereas the high diversity at Black’s Beach reflects a mixture of shelf and bathyal fishes. In addition, 24 new otolith-based genera are established, four of which are in the category “incertae sedis”. Furthermore, five new species are described from a comparative otolith collection from the US Gulf Coast Eocene and one new species from a comparative collection from the Lutetian of Balegem in Belgium. The Eocene otolith-based fish fauna from California is assessed for its paleoecological, paleobiogeographic and evolutionary significance. Particular emphasis is directed towards the elucidation of the evolution of the early Ophidiiformes, which during the early Paleogene were predominantly adapted to warm, clastic shallow-water environments and there were competing in abundance and diversity with other percomorphs (e.g., perciforms s.l.). A warm Eocene paleobioprovince is proposed for the Californian fish fauna which is not related to today’s endemic Northwest Pacific fish fauna along the regime of the cold-water California Current. [ABSTRACT FROM AUTHOR]

In current practices of determining continental shelf area, the measured sediment thickness data do not effectively reflect the distribution of sediments across the area due to its dispersed nature. This issue raises potential limitations in unknown optimal survey line layout strategies for maximizing the posterior determination area. This paper adopts the binary search algorithm, relies on existing sediment thickness grid data, and uses geodetic formulas to build an ellipsoidal surface grid distance calculation model. This model quickly screens potential areas for the 1% sediment thickness line candidate points set. By constraining the azimuth parameter values during the construction process of the ellipsoidal point feature buffer zones, efficiently select the candidate points set for the 1% sediment thickness line. Furthermore, by elucidating the essential meanings of points on the formula limit and combining the candidate points set of the foot of the continental slope (FOS)+60 n mile line, the polygon minimal convex hull construction technique and a baseline points optimization algorithm with a length threshold are used to efficiently select points on formula limit. Experimental results demonstrate that this method can effectively assist coastal states in optimizing the determination of continental shelf area to the fullest extent under the length threshold requirements of the United Nations Convention on the Law of the Sea. Experiments have proven that compared to the traditional intersection method, the method presented in this paper can help coastal countries delineate a larger continental shelf area. In typical application scenarios, the gain in area can reach 77,278,427 m2 accounting for 0.51% of the total area. [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]

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 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]

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]

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]

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 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]

Around most of Antarctica, the Circumpolar Deep Water (CDW) shows a warming trend. At the same time, the thermocline is shoaling, thereby increasing the potential for CDW to enter the shallow continental shelves and ultimately increase basal melt in the ice shelf cavities that line the coast. Similar trends, on the order of 0.05 ∘ C and 3 m per decade, have been observed in the Warm Deep Water (WDW), the slightly cooled CDW derivative found at depth in the Weddell Sea. Here, we report on a sudden, local increase in the temperature maximum of the WDW above the continental slope north of the Filchner Trough (74 ∘ S, 25–40 ∘ W), a region identified as a hotspot for both Antarctic Bottom Water formation (AABW) and potential changes in the flow of WDW towards the large Filchner–Ronne Ice Shelf. New conductivity–temperature–depth profiles, obtained in summer 2021, and recent (2017–2021) mooring records show that the temperature of the warm-water core increased by about 0.1 ∘ C over the upper part of the slope (700–2750 m depth) compared with historical (1973–2018) measurements. The temperature increase occurred relatively suddenly in late 2019 and was accompanied by an unprecedented (in observations) freshening of the overlying winter water. The AABW descending down the continental slope from Filchner Trough is sourced by dense ice shelf water and consists to a large degree (60 %) of entrained WDW. The observed temperature increase can hence be expected to imprint directly on deep-water properties, increasing the temperature of newly produced bottom water (by up to 0.06 ∘ C) and reducing its density. [ABSTRACT FROM AUTHOR]

Nepheloid layers are widely distributed in the marine environment, and their formation and evolution pose many challenges to the current understanding of ocean dynamics and marine sedimentology. In sediment transport processes, nepheloid layers significantly contribute to the exchange of sediment between the continental shelf and the slope. In this paper, we summarize the global research trends on nepheloid layers. In total, 689 publications from 1990 to 2022 were collected from the Web of Science and analyzed using bibliographic software, including Bibliometrix, VOSviewer, CiteSpace, and CorText. Based on these publications, past and present popular research on nepheloid layers is examined and evaluated. The trends in nepheloid layer research are summarized by analyzing keywords, article references, countries, institutions, and authors. Finally, prospects and several key questions related to nepheloid layers are concluded, which can potentially guide future studies. The bibliographic analysis can provide new insights into the history of nepheloid layers. The results also provide valuable information for other researchers and programs investigating geological, geophysical, and biogeochemical processes. [ABSTRACT FROM AUTHOR]

Fluctuations in prey abundance, composition, and distribution can impact predators, and when predators and fisheries target the same species, predators become essential to ecosystem‐based management. Because of the difficulty in collecting concomitant predator–prey data at appropriate scales in patchy environments, few studies have identified strong linkages between cetaceans and prey, especially across large geographic areas. During summer 2018, a line‐transect survey for cetaceans and coastal pelagic species was conducted over the continental shelf and slope of British Columbia, Canada, and the US West Coast, allowing for a large‐scale investigation of predator–prey spatial relationships. We report on a case study of humpback whales (Megaptera novaeangliae) and their primary prey—Pacific herring (Clupea pallasii), northern anchovy (Engraulis mordax), and krill—using generalized additive models to explore the relationships between whale abundance on 10‐km transect segments and prey metrics. Prey metrics included direct measures of biomass densities on segments and an original hotspot metric. For each prey species, segments in the upper fifth percentile for biomass density (across all segments) were designated hotspots, and whale counts on a segment were evaluated for their relationship to number of hotspot segments (species‐specific and multispecies) within 25, 50, or 100 km. Whale abundance was not strongly related to direct measures of biomass densities, whereas models using hotspot metrics were more effective at describing variation in whale abundance, underscoring that evaluating prey at relevant and measurable scales is critical in patchy, dynamic marine environments. Our analysis highlighted differences in the distribution and prey availability for three humpback whale distinct population segments (DPSs) as defined under the US Endangered Species Act, including threatened and endangered DPSs that forage within the California Current Large Marine Ecosystem. These linkages provide insights into which prey species whales may be targeting in different regions and across multiple scales and, consequently, how climatic variability and anthropogenic risks may differentially impact these distinct predator–prey assemblages. By identifying scale‐appropriate prey hotspots that co‐occur with humpback whale aggregations, and with targeted, consistent prey sampling and estimations of potential consumption rates by whales, these findings can help inform the conservation and management of humpback whales within an ecosystem‐based management framework. [ABSTRACT FROM AUTHOR]

Barotropic and baroclinic tides were simulated for the Coral and Tasman Seas off eastern Australia and compared to a simulation without tides. Both simulations included geostrophic currents and replicated a current analogous to the East Australian Current (EAC). Tides and tidal currents in most of this region are weak, generally 1–2 cm s−1, with the exception of the far northwest portion of the Coral Sea. Even these weak tides were found to impact the mean EAC-like current transport, enhancing it by 1–4 Sv in some areas. Southward flow increased over the continental shelf. Tides did not appear to impact eddy formation, size, or rotational speed; however, they affected eddy propagation. Cyclonic eddies propagated northward faster with tides than without tides. Tides impacted cross-shelf transport of colder water, with significantly more on-shore transport occurring with tides, particularly equatorward of the diurnal critical latitudes. Cross-shelf transport of nutrient rich water onto the shelf is important in this oligotrophic region. Although the prime source of vertical shear and mixing were mean currents and eddies, tides played a secondary role. Tides influenced mixing by increasing vertical temperature diffusivities to 10−4 to 10−3 m2 s−1 over portions of the continental slope and over rough topography, particularly in regions near the diurnal critical latitudes (27°–30°). In conclusion, even small tides can significantly impact the circulation through their effects on the mean currents, eddy rotation velocities, eddy propagation, and mixing. [ABSTRACT FROM AUTHOR]

The extensive coverage of 3-D seismic data on the Santos Basin deep water offered an integrated vision of the local physiography and medium- to small-scale geomorphological features, which enhances the understanding of its constructive/deconstructive natural processes and their interrelations. The Santos Basin is a divergent marginal basin composed of three main physiographic provinces: its continental shelf, continental slope, and the São Paulo Plateau, whose dimensions, orientation, gradients, and relief interact with oceanographic, biological, and geological processes. This study geologically contextualized environmental data related to the Regional Environmental Characterization Project of the Santos Basin (hereinafter referred to as PCR-BS), especially regarding the regional physiographical architecture and deep-water geomorphological provinces as a background for the benthic communities and the distribution of several of its geochemical parameters. The integrated analysis of 3-D seismic and multibeam bathymetric data and its derivatives (gradient and edge maps) -- calibrated by 108 piston cores -- aimed to evaluate its seafloor physiographic features and geological processes. Edge detection seismic attributes enhance gradient contrast, which, in turn, can map innumerous medium- to small- scale geomorphic features (features solved in maps at a 1:1,000,000 scale or larger), such as canyons, channels, ravines, pockmark units, pockmark fields, lineaments, carbonate and coral mounds, salt-related features (crests, minibasins, and crestal grabens), scars and rugous relief associated with mass-transport deposits, and bottom current-related features (depressions and furrows). The slope and the gently dipping plateau (São Paulo Plateau) that follow it eastward show four geomorphological domains based on their direction, profile, average gradient, shelf break isobath, distribution of its medium-small scale geomorphic features, and the presence or absence of evaporites at subsurface. The central-northern São Paulo Plateau contains salt-related topographic elevations (salt diapirs and walls) and depressions (minibasins) that give a rough aspect to the seafloor relief. [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]

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]

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks. [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]

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]

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]

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]

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Inflow of warm modified Circumpolar Deep Water (CDW) onto the Antarctic continental shelf and into ice shelf cavities is a key driver of Antarctic ice shelf mass loss. While recent research has advanced understanding of CDW heat transport onto the continental shelf, the fate of CDW on the shelf is less understood. Here, we use Lagrangian particle tracking in an ocean‐sea ice model without ice shelf cavities to map the residence time of CDW on the Antarctic continental shelf. Mean residence times vary from <1 month in the East Antarctic to >1 year in the West Antarctic. In regions of dense water formation, transformation of CDW on the shelf limits access of CDW to ice shelves, despite strong onshore CDW heat transport. Elsewhere transformation of CDW on the shelf is weak, implying that temperature on the shelf is limited by heat transport onto the shelf or the offshore heat reservoir. Plain Language Summary: Antarctic ice shelf melt is accelerating and is linked to the inflow of warm ocean waters that melt ice shelves from below. Multiple processes regulate the amount of warm water that reaches the Antarctic ice shelves, and the relative importance of these processes in different regions is not well known. Here, we conduct a virtual particle tracking experiment in a state‐of‐the‐art ocean model to trace the pathways and timescales of warm water on the Antarctic continental shelf. We find that there is a large regional variation in how long warm waters spend on the continental shelf from less than a month to well over a year. In the regions along the continental slope where very dense water formed near the coast flows off the shelf to the abyssal ocean, this is balanced by a strong inflow of warm water onto the continental shelf, which is rapidly converted to denser water, limiting the heat from reaching the ice shelves. Elsewhere warm water can remain on the continental shelf unmodified for a long time, so the heat available for ice shelf melt is instead limited by the strength of the flow of warm water onto the continental shelf. Key Points: Particle tracking in an ocean model shows Circumpolar Deep Water (CDW) residence times on the Antarctic shelf range from a month to several yearsWater mass transformation limits CDW access to ice shelves in Dense Shelf Water formation regions, despite strong onshore CDW transportIn warm shelf regions, long residence times of CDW are associated with weak water mass transformation [ABSTRACT FROM AUTHOR]

In this paper we present geomorphological hazard mapping of the San Vito Peninsula offshore (Sicilian margin of Tyrrhenian Sea), characterised by a very narrow continental shelf and a very dipping, tectonically active continental slope, no far from a seismogenic belt. The data set consists of morpho-bathymetric models achieved by means of multibeam survey and scattered high resolution seismic profiles. The morpho-bathymetric study highlighted some potential sites of geomorphological hazards, the most representative of which are: (i) two canyons developing from the upper slope off San Vito Cape down to the Erice basin; (ii) a dense network of small incisions across the upper slope; (iii) a very active landslide, developed onland and extending in the continental shelf close to the Scopello village. The geomorphological features that can generate submarine hazard are represented by: unstable sediment packages into canyon heads or along the upper slope; submarine canyons with regressive erosion; coastal landslides. [ABSTRACT FROM AUTHOR]

Climatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid-Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low-nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ~50 m) were associated with water mass properties characteristic of GS water (~100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems. Plain Language Summary As the climate has warmed, the changing large-scale circulation of the northwest Atlantic has resulted in increasing western boundary current instability. As a consequence, onshore intrusions of Gulf Stream (GS) water into the Northeast U.S. continental shelf have become increasingly frequent. The impacts of this shift on marine ecosystems have yet to be resolved. While these intrusions of low-nutrient GS water have been thought to potentially diminish biological productivity, we present evidence of an unexpectedly productive subsurface diatom bloom resulting from the direct intrusion of a GS meander toward the continental shelf. These results suggest that changing large-scale circulation has consequences for regional productivity that are not detectable by satellites by virtue of their occurrence well below the surface. [ABSTRACT FROM AUTHOR]

Large scale studies of underwater noise during rain are important for assessing the ocean environment and enabling remote sensing of rain rates over the open ocean. In this study, approximately 3.5 yrs of acoustical and meteorological data recorded at the northeast Pacific continental margin are evaluated. The acoustic data are recorded at a sampling rate of 64 kHz and depths of 81 and 581 m at the continental shelf and slope, respectively. Rain rates and wind speeds are provided by surface buoys located in the vicinity of each hydrophone. Average power spectra have been computed for different rain rates and wind speeds, and linear and nonlinear regression have been performed. The main findings are (1) the linear regression slopes highly depends on the frequency range, rain rate, wind speed, and measurement depth; (2) noise levels during rain between 200 Hz and 10 kHz significantly increase with increasing wind speed; and (3) the highest correlation between the spectral level and rain rate occurs at 13 kHz, thus, coinciding with the spectral peak due to small raindrops. The results of this study indicate that previously proposed algorithms for estimating rain rates from acoustic data are not universally applicable but rather have to be adapted for different locations. [ABSTRACT FROM AUTHOR]

Background and aims: Planktonic dinoflagellates have a great ecological significance in marine environments. While some dinoflagellate species commonly reach bloom concentrations and are thus conspicuous components of marine phytoplankton, others occur in very low abundances which make them difficult to detect in field studies. Here we analyzed dinoflagellate composition and abundance in five oceanographic expeditions carried out in continental shelf and slope waters of the Argentine Sea. M&M: Plankton abundance was estimated by the Utermöhl method, using inverted microscopy, whereas further optical and scanning electron microscopy was applied for the identification of dinoflagellate species. Results: We focused on the occurrence of seven dinoflagellates that have been previously poorly documented or overlooked in marine environments worldwide: Dinophysis microstrigiliformis; Gyrodinium sp.; Karlodinium elegans; Oxytoxum laticeps; Peridiniella danica; Peridiniella globosa and Prorocentrum nux. The latest and K. elegans are observed for the first time in field conditions after their original descriptions based on cell cultures. While most species were detected in low or moderate abundances, P. nux, which is the smallest Prorocentrum species, reached 82,000 cells L-1 in slope waters. Very small Gyrodinium cells (11.5 μm long; 8.7 μm wide) with a distribution restricted to slope waters during spring, were not possible to be accurately assigned to a species. Conclusions: This study contributes to the understanding of dinoflagellate diversity in the Argentine Sea and the worldwide distribution of little known species. [ABSTRACT FROM AUTHOR]

Intermediate nepheloid layers (INLs) form important pathways for the cross‐slope transport and vertical export of particulate matter, including carbon. While intermediate maxima in particle settling fluxes have been reported in the Eurasian Basin of the Arctic Ocean, direct observations of turbid INLs above the continental slope are still lacking. In this study, we provide the first direct evidence of an INL, coinciding with enhanced mid‐water turbulent dissipation rates, over the Laptev Sea continental slope in summer 2018. Current velocity data show a period of enhanced downslope flow with depressed isopcynals, suggesting that the enhanced turbulent dissipation is probably the consequence of the presence of an unsteady lee wave. Similar events occur mostly during ice free periods, suggesting an increasing frequency of episodic cross‐slope particle transport in the future. The discovery of the INL and the episodic generation mechanism provide new insights into particle transport dynamics in this rapidly changing environment. Plain Language Summary: In the Arctic Ocean deep basins, only a tiny fraction of the algae that grows in the surface layer sinks down to the sea floor. Most of the particles reaching the sea floor originate from the shallower regions closer to the coast. These particles have already settled on the sea floor once, and originate from rivers or algae that grew, died and sank down in shallow regions. Later, these particles are lifted off the ground again by strong turbulent motions and transported toward deeper regions in the middle of the water column. These lift‐off and transport events happen only occasionally, and have not been directly observed in the Eurasian part of the Arctic Ocean yet. Also, we present a new mechanism for the creation of turbulence, which is necessary to lift particles off the sea floor. This mechanism happens mostly during the summer season, when less sea ice is present. Based on this seasonality, it is likely that sediment transport events will become more frequent in the future, when the Arctic sea ice is further declining. Key Points: First direct observation of an intermediate nepheloid layer in the Eurasian part of the Arctic OceanCoinciding strong midwater turbulence is likely caused by a down‐slope current displacing isopycnalsSimilar downslope flow events exhibit a strong seasonality toward the ice free season [ABSTRACT FROM AUTHOR]

Basal melting of Antarctic ice shelves accounts for more than half of the mass loss from the Antarctic ice sheet. Many studies have focused on active basal melting at ice shelves in the Amundsen–Bellingshausen seas and the Totten ice shelf, East Antarctica. In these regions, the intrusion of Circumpolar Deep Water (CDW) onto the continental shelf is a key component for the localized intensive basal melting. Both regions have a common oceanographic feature: southward deflection of the Antarctic Circumpolar Current brings CDW toward the continental shelves. The physical setting of the Shirase Glacier tongue (SGT) in Lützow-Holm Bay corresponds to a similar configuration on the southeastern side of the Weddell Gyre in the Atlantic sector. Here, we conduct a 2–3 km resolution simulation of an ocean–sea ice–ice shelf model using a recently compiled bottom-topography dataset in the bay. The model can reproduce the observed CDW intrusion along the deep trough. The modeled SGT basal melting reaches a peak in summer and a minimum in autumn and winter, consistent with the wind-driven seasonality of the CDW thickness in the bay. The model results suggest the existence of an eastward-flowing undercurrent on the upper continental slope in summer, and the undercurrent contributes to the seasonal-to-interannual variability in the warm water intrusion into the bay. Furthermore, numerical experiments with and without fast-ice cover in the bay demonstrate that fast ice plays a role as an effective thermal insulator and reduces local sea ice formation, resulting in much warmer water intrusion into the SGT cavity. [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]

A total of 69 specimens of Fedorov's lumpsucker (Eumicrotremus fedorovi) caught on the continental shelf and slope of Simushir Island in the northwest Pacific Ocean were dissected and studied for stomach contents. The Fedorov's lumpsucker was found to feed mainly on the young of fish species, including the walleye pollock (Gadus chalcogrammus), northern lampfish (Stenobrachius leucopsarus), and northern smoothtongue (Leuroglossus schmidti), crustaceans, such as Themisto pacifica, Primno macropa, calanoids, gammarids, mysids, and caprellids, and squid. Histological analyses of ovaries revealed iteroparity, determinate fecundity, group-synchronous ovarian development, and total spawning. Testes were of an unrestricted lobular type. Chorion and thick zona radiata of Fedorov's lumpsucker correspond to the condition of eggs in specimens of other fish species that release demersal eggs. Absolute fecundity values of Fedorov's lumpsucker in our study were significantly less than those that have been reported for other species of Cyclopteridae. The results of this study provide the first data on this little known species of this family. [ABSTRACT FROM AUTHOR]

Antarctic krill (Euphausia superba) larval production and overwinter survival drive recruitment variability, which in turn determines abundance trends. The Antarctic Peninsula has been described as a recruitment hot spot and as a potentially important source region for larval and juvenile krill dispersal. However, there has been no analysis to spatially resolve regional-scale krill population dynamics across life stages. We assessed spatiotemporal patterns in krill demography using two decades of austral summer data collected along the North and West Antarctic Peninsula since 1993. We identified persistent spatial segregation in the summer distribution of euphausiid larvae (E. superba plus other species), which were concentrated in oceanic waters along the continental slope, and E. superba recruits, which were concentrated in shelf and coastal waters. Mature females of E. superba were more abundant over the continental shelf than the slope or coast. Euphausiid larval abundance was relatively localized and weakly correlated between the North and West Antarctic Peninsula, while E. superba recruitment was generally synchronized throughout the entire region. Euphausiid larval abundance along the West Antarctic Peninsula slope explained E. superba recruitment in shelf and coastal waters the next year. Given the localized nature of krill productivity, it is critical to evaluate the connectivity between upstream and downstream areas of the Antarctic Peninsula and beyond. Krill fishery catch distributions and population projections in the context of a changing climate should account for ontogenetic habitat partitioning, regional population connectivity, and highly variable recruitment. [ABSTRACT FROM AUTHOR]

The stability of the West Antarctic Ice Sheet (WAIS) depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction. The Antarctic Slope Current (ASC), a major boundary current of the ocean's global circulation, serves as a dynamic gateway for heat transport toward Antarctica. Here, we use observations collected from the Bellingshausen Sea to propose a mechanistic explanation for the initiation of the westward‐flowing ASC. Waters modified throughout the Bellingshausen Sea by ocean‐sea‐ice and ocean‐ice‐shelf interactions are exported to the continental slope in a narrow, topographically steered western boundary current. This focused outflow produces a localized front at the shelf break that supports the emerging ASC. This mechanism emphasizes the importance of buoyancy forcing, integrated over the continental shelf, as opposed to local wind forcing, in the generation mechanism and suggests the potential for remote control of melt rates of WAIS' largest ice shelves. Plain Language Summary: The Antarctic Slope Current (ASC) is an ocean current that separates warmer, offshore water from colder waters over the continental shelf. The ASC helps to control the movement of warm water on to the continental shelf and ultimately under floating ice shelves. Warm ocean water has contributed to the melting and thinning of West Antarctic ice shelves in recent decades. This study describes where and how the ASC first forms in West Antarctica. Previous studies have suggested that the ASC responds primarily to atmospheric winds blowing over the current itself, whereas here it is argued that processes occurring over a much larger region of the west Antarctic continental shelf may determine the strength and structure of the ASC. These results contribute to our understanding of the long‐term, for example, decades or longer, evolution of the West Antarctic Ice Sheet. Key Points: The initiation of a westward Antarctic Slope Current (ASC) occurs in the western Bellingshausen SeaThe ASC arises from the export of waters, modified by ocean‐ice interactions, to the shelf break, rather than from local wind forcingThis mechanism suggests the potential for remote control of shelf properties as well as West Antarctic ice shelf melt rates [ABSTRACT FROM AUTHOR]

Marine-geophysical evidence on sea-floor morphology and shallow acoustic stratigraphy are used to examine the substrate around the location at which Sir Ernest Shackleton's ship Endurance sank in 1915 and on the continental slope-shelf sedimentary system above this site in the western Weddell Sea. Few signs of turbidity-current and mass-wasting activity are found near or upslope of the wreck site, and any such activity was probably linked to full-glacial higher-energy conditions when ice last advanced across the continental shelf. The wreck is well below the maximum depth of iceberg keels and will not have been damaged by ice-keel ploughing. The wreck has probably been draped by only a few centimetres of fine-grained sediment since it sank in 1915. Severe modern sea-ice conditions hamper access to the wreck site. Accessing and investigating the wreck of Endurance in the Weddell Sea therefore represents a significant challenge. An ice-breaking research vessel is required, and even this would not guarantee that the site could be reached. Heavy sea-ice cover at the wreck site, similar to that encountered by Agulhus II during the Weddell Sea Expedition 2019, would also make the launch and recovery of autonomous underwater vehicles and remotely operated vehicles deployed to investigate the Endurance wreck problematic. [ABSTRACT FROM AUTHOR]

The Lagrangian characteristics of the surface flow field arising when an idealized, anticyclonic, mesoscale, isolated deep-ocean eddy collides with continental slope and shelf topography are explored. In addition to fluid parcel trajectories, we consider the trajectories of biological organisms that are able to navigate and swim, and for which shallow water is a destination. Of particular interest is the movement of organisms initially located in the offshore eddy, the manner in which the eddy influences the ability of the organisms to reach the shelf break, and the spatial and temporal distributions of organisms that do so. For nonswimmers or very slow swimmers, the organisms arrive at the shelf break in distinct pulses, with different pulses occurring at different locations along the shelf break. This phenomenon is closely related to the episodic formation of trailing vortices that are formed after the eddy collides with the continental slope, turns, and travels parallel to the coast. Analysis based on finite-time Lyapunov exponents reveals initial locations of all successful trajectories reaching the shoreline, and provides maps of the transport pathways showing that much of the crossshelf- break transport occurs in the lee of the eddy as it moves parallel to the shore. The same analysis shows that the onshore transport is interrupted after a trailing vortex detaches. As the swimming speeds are increased, the organisms are influenced less by the eddy and tend to show up en mass and in a single pulse. [ABSTRACT FROM AUTHOR]

Using modern physicochemical methods, the colloidal, nanochemical, and nanostructural transformations of suspensions of iron–aluminosilicate compositions are investigated in model geomechanochemical biocolloid processes. Mechanisms of catastrophic processes and their effect on highly dispersed nanostructured deep marine pelitic sediments in combination with coarsedispersed carbonate–iron–aluminosilicate sand (turbidites) are considered. Model conditions for displacement of marine turbidite–pelitic compositions in the composition of coastal shelf silt with a depth of up to 200 m and underwater continental slopes at depths of 200–2000 m as well as their behaviour at depths of 2–8 km and interaction in deep water (under 8–10 km) intercontinental trenches and dips with magmatic semi-molten iron–aluminosilicate materials are also considered. The mechanisms of complex processes of formation, displacement, flow as well as coagulation–condensation nanostructuring and compaction of iron–aluminosilicate compositions with the preservation of the developed nano- and microporous state are first considered and substantiated according to the laws of physicochemical geomechanics and colloidal nanoscience. The role of the wind and thermal influences as well as their superficial turbulent and underwater laminar (thermophilic) waves on the flowing of iron–aluminosilicate sediments during catastrophic phenomena is considered. The important role and influence on such phenomena of effects of hyperanomaly and ultraanomaly of viscosity of iron–aluminosilicate dispersions during their transition from elastic state to plastic one is mentioned. The corresponding models of the mentioned phenomena and the accompanying rheological processes are given. [ABSTRACT FROM AUTHOR]

Risso's dolphin occurs in tropical and temperate waters worldwide, and is one of the most common cetacean species in Taiwanese waters. This study attempted to reveal its distribution in water-depth ranges and variations in group size and composition (with or without mother-calf pairs). Based on sighting records from experienced whale-watching guides on board whale-watching boats operated in eastern Taiwan, 1630 sightings of Risso's dolphin were recorded from 3939 touring trips near Hualien County from 1998 to 2014. Comparing the frequency distribution of water depths between ship tracks and dolphin sightings, we found that Risso's dolphin commonly occurred on the continental shelf and slope, and mainly stayed in waters of 300~1500 m in depth, with a mean of 862.1 ± 12.3 m (standard error). The frequency distribution of water depths showed a significant difference between sites (deeper in the Shirti area than in the Hualien area), but no significant difference was detected among various group sizes. Nevertheless, the spatial distribution significantly varied with group composition, but not with group size. Groups with mother-calf pairs stayed in significantly shallower water, which was proposed to be related to predator avoidance. In addition, the large fluctuation in annual sighting ratios of Risso's dolphin that ranged 0.1~0.7 sightings per trip during the 17-year period may be related to variations in prey abundances, the confirmation of which requires future investigation. [ABSTRACT FROM AUTHOR]

The Antarctic Slope Front (ASF) is located along much of the Antarctic continental shelf break and helps to maintain a barrier to the movement of Circumpolar Deep Water (CDW) onto the continental shelf. The stability of the ASF has a major control on cross-shelf heat transport and ocean-driven basal melting of Antarctic ice shelves. Here, the ASF dynamics are investigated for continental shelves with weak dense shelf water (DSW) formation, which are thought to have a stable ASF, common for regions in East Antarctica. Using an ocean process model, this study demonstrates how offshore bottom Ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope, and subsequently determines an intrinsic variability of the ASF. The ASF variability is characterized by instability events that affect the entire water column and occur every 5-10 years and last for approximately half a year. During these instability events, the cross-shelf density gradient weakens and CDW moves closer to the continent. Stronger winds increase the formation rate of the bottom mixed layer, which causes a subsequent increase of instability events. If the observed freshening trend of continental shelf waters leads to weaker DSW formation, more regions might be vulnerable for the ASF variability to develop in the future. [ABSTRACT FROM AUTHOR]

Variability in the heat delivery by Circumpolar Deep Water (CDW) is responsible for modulating the basal melting of the Amundsen Sea ice shelves. However, the mechanisms controlling the CDW inflow to the region's continental shelf remain little understood. Here, a high-resolution regional model is used to assess the processes governing heat delivery to the Amundsen Sea. The key mechanisms are identified by decomposing CDW temperature variability into two components associated with 1) changes in the depth of isopycnals [heave (HVE)], and 2) changes in the temperature of isopycnals [water mass property changes (WMP)]. In the Dotson--Getz trough, CDW temperature variability is primarily associated with WMP. The deeper thermocline and shallower shelf break hinder CDW access to that trough, and CDW inflow is regulated by the uplift of isopycnals at the shelf break--which is itself controlled by wind-driven variations in the speed of an undercurrent flowing eastward along the continental slope. In contrast, CDW temperature variability in the Pine Island--Thwaites trough is mainly linked to HVE. The shallower thermocline and deeper shelf break there permit CDW to persistently access the continental shelf. CDW temperature in the area responds to wind-driven modulation of the water mass on-shelf volume by changes in the rate of inflow across the shelf break and in Ekman pumping-induced vertical displacement of isopycnals within the shelf. The western and eastern Amundsen Sea thus represent distinct regimes, in which wind forcing governs CDW-mediated heat delivery via different dynamics. [ABSTRACT FROM AUTHOR]

All exchanges between the open ocean and the Antarctic continental shelf must cross the Antarctic Slope Current (ASC). Previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability, yet the mechanisms responsible for setting the ASC's transport and structure have received relatively little attention. In this study the roles of winds, eddies, and tides in accelerating the ASC are investigated using a global ocean–sea ice simulation with very high resolution (1/48° grid spacing). It is found that the circulation along the continental slope is accelerated both by surface stresses, ultimately sourced from the easterly winds, and by mesoscale eddy vorticity fluxes. At the continental shelf break, the ASC exhibits a narrow (~30–50 km), swift (>0.2 m s−1) jet, consistent with in situ observations. In this jet the surface stress is substantially reduced, and may even vanish or be directed eastward, because the ocean surface speed matches or exceeds that of the sea ice. The shelfbreak jet is shown to be accelerated by tidal momentum advection, consistent with the phenomenon of tidal rectification. Consequently, the shoreward Ekman transport vanishes and thus the mean overturning circulation that steepens the Antarctic Slope Front (ASF) is primarily due to tidal acceleration. These findings imply that the circulation and mean overturning of the ASC are not only determined by near-Antarctic winds, but also depend crucially on sea ice cover, regionally-dependent mesoscale eddy activity over the continental slope, and the amplitude of tidal flows across the continental shelf break. [ABSTRACT FROM AUTHOR]

Circumpolar Deep Water (CDW) transport across the Antarctic continental slope regulates the delivery of heat to the shelf and its availability to melt floating ice shelves. The cross‐slope density field, calculated from profiles collected by conductivity‐temperature‐depth‐tagged marine mammals on the East Antarctic slope (0–160°E, above 1,000‐ to 3,000‐m isobaths), indicates eddy‐driven overturning: onshore transport of CDW and offshore transport of shallower Antarctic Surface Water. Enhanced eddy activity, determined by a spice standard deviation threshold in the CDW layer, is present over about a third of the East Antarctic slope analyzed. Significantly stronger CDW transport in regions of elevated spice variability produces subsurface temperature anomalies of 0.2–0.25 °C relative to the East Antarctic average. Estimating eddy diffusivity from the hydrography yields about 0.8 m2/s of warm CDW transport to the shelf break in high‐variability regions. Variability of eddy‐induced CDW transport influences the reservoir of heat available for transport across the shelf break. Plain Language Summary: The transport of warm water from the open ocean to the Antarctic continental shelf has global significance, as it regulates the melt of ice shelves and dense water formation. We quantify the strength of eddy‐driven transport of relatively warm Circumpolar Deep Water (CDW) across the continental slope of East Antarctica from the observed cross‐slope density structure. We find that, in general, there is an eddy‐driven overturning: deeper CDW is transported onshore while shallower Antarctic Surface Water is transported offshore. Upon closer inspection, we find that regions with elevated temperature and salinity variability on density surfaces are associated with significantly stronger onshore transport of CDW by eddies. These hot spots of eddy transport produce warm and salty anomalies at the shelf break, impacting the reservoir of heat available to the shelf. Key Points: Cross‐slope eddy transport is inferred from observed density‐layer thickness gradients in East Antarctica between 0°E and 160°EEnhanced onshore transport (≈1.5 × East Antarctic mean) of warm, salty Circumpolar Deep Water occurs in regions of high isopycnal spice variabilityEddy‐induced overturning carries ≈0.8 m2/s of CDW poleward to produce warm, salty anomalies at the shelf break in eddying regions [ABSTRACT FROM AUTHOR]

The fin whale (Balaenoptera physalus) is a cosmopolitan species with a resident population in the Mediterranean Sea. Due to its habitat, open seas often far from ports and airfields, and its long-distance migratory behaviour, studying and monitoring its distribution is costly. Currently, many opportunistic sightings (OS) reports are available, which provide a source of potentially useful, low-cost information about the spatio-temporal distribution of this species. Since 1993, the Spanish Institute of Oceanography has compiled a dataset comprising 874 records of OS of nine species of cetaceans in the western Mediterranean Sea and adjacent waters. The aim of this study was to use this dataset to investigate the differential use of these waters by the fin whale when compared with other cetaceans. We compared the presence of fin whales with the presence of any other cetacean species in the dataset. Binary logistic regression was then used to model these occurrences according to several spatio-temporal variables expected to reflect their habitat use. Several significant models reveal that fin whales are more prone than other cetaceans to use the waters over the slope of the Gulf of Lion in summer. This finding confirms that the Gulf of Lion is an area of importance for this species and suggests that the slope of the continental shelf could be particularly important. Our study shows how OS can be a source of useful information when appropriately analyzed. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments are performed to investigate the scattering of low-mode internal tides at a continental shelf by varying the criticality parameter and normalized topographic height independently. A wide-range synchronized particle image velocimetery (PIV) measures the velocity fields of the internal tides. Beams radiate from both the shelf break and the bottom of the slope, indicating that energy transfers from low modes to higher modes, which is verified by the modal decomposition. Energy is also transferred to higher harmonics, whose amplitude is less than a quarter of that of the first harmonic. The fraction of energy transmitted onshore and dissipated on the topography is determined by both the criticality parameter and the normalized topographic height, while the fraction of energy reflected offshore is dependent only on the criticality parameter. Mean flow with a shear structure induced by internal tides is observed along the continental slope, with horizontal velocity generally half of the amplitude of the incident waves. A net onshore transport along the slope is caused by the onshore current with larger thickness. The strength of the mean flow is dependent on both the criticality parameter and the normalized topographic height, and a linear relationship between the energy of the mean flow and the vertical shear of internal tides is revealed. [ABSTRACT FROM AUTHOR]