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Seven new species of Scalibregmatidae are described from deep waters off the east coast of Australia. Samples were collected as part of the RV Investigator voyage IN2017_V03 in May/June 2017 using a Brenke sledge and 0.25 m² box core. Sample depths reported in the present study were from the lower continental slope of about 2450 m to abyssal depths up to 4280 m. These collections provide the first scalibregmatid polychaetes to be described from deep water off Australia. The new species of Scalibregmatidae are in the genera Asclerocheilus (1), Axiokebuita (1), Oligobregma (4), and Pseudoscalibregma (1). Each of the new species is compared and contrasted with their known congeners. Asclerocheilus and Oligobregma are the largest genera of the family in terms of numbers of species; the known species of each of these genera are tabulated and compared. The Scalibregmatidae known from abyssal depths of about 3000 m and greater are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Seven new species of Cirratulidae are described from deep waters off the east coast of Australia. Samples were collected as part of the RV Investigator voyage IN2017_V03 in May/June 2017 using a Brenke sledge and 0.25 m² box core. Sample depths reported in the present study were from the lower continental slope of about 2100 m to abyssal depths up to 4170 m. These collections provide the first cirratulid polychaetes to be described from deep water off Australia. The new species of Cirratulidae are in the genera Aphelochaeta (2), Chaetocirratulus (2), Chaetozone (2), and Kirkegaardia (1). Each of the new species is compared and contrasted with their known congeners. The bitentaculate Cirratulidae known from abyssal depths of 3000 m and greater are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Thiosulfate is a sulfur species in an intermediate oxidation state between sulfate and sulfide. It appears during bacterial and chemical sulfide oxidation processes. Thiosulfate plays a prominent role in sulfide oxidation and its presence may clarify the mechanism of redox reactions in the biogeochemical cycles of sulfur and carbon. This study presents the thiosulfate distribution, determined by the derivatization technique with the reagent 2,2'-Dithiobis(5-nitropyridine), in the upper part of the anoxic water column of Black Sea in 2018–2021. The studies were carried out annually at the station located seaward of Gelendzhik in the area of continental slope. Independently of observation time, the thiosulfate concentration increases with depth simultaneously with increasing sulfide. Thiosulfate concentration above the detection limit of 0.01 µM is found at water depths with a density (σθ) of 16.3 kg/m3 and sulfide concentration of 8–11 µM. Thiosulfate reaches its maxima of 0.30 µM at the maximal studied depth of 600 m. We suggest that in the absence of oxidants in anoxic waters, the appearance of thiosulfate is attributed to the sulfate reduction process in the reductive part of the sulfur cycle. Thiosulfate disappears in the upper part of anoxic water column before sulfide. [ABSTRACT FROM AUTHOR]

We analyze 15‐year of observational data and a 5‐year Southern Ocean model simulation to quantify the transformation rates of Circumpolar Deep Water (CDW) and the associated heat loss to the surface. This study finds that over the continental shelves of East Antarctica and the Weddell and Ross Seas, surface buoyancy fluxes transform ∼4.4 Sv of surface waters into CDW, providing a path for CDW to lose heat to the surface. In addition, ∼6.6 Sv of CDW are mixed with surface waters in the Weddell and Ross subpolar gyres. In contrast, enhanced stratification inhibits the outcropping of CDW isopycnals, reducing their transformation rates by a factor of ∼8 over the continental shelf and by a factor of ∼3 over the deeper ocean in the Amundsen and Bellingshausen Seas. The CDW retains its offshore warm properties as it intrudes over the continental shelves, resulting in elevated bottom temperatures there. This analysis demonstrates the importance of processes in subpolar gyres to erode CDW and to facilitate further transformation on the continental shelves, significantly reducing the heat able to access ice shelf fronts. This sheltering effect is strongest in the western Weddell Sea and tends to diminish toward the east, which helps explain the large zonal differences in continental‐shelf bottom temperatures and the melt rates of Antarctic ice shelves. Plain Language Summary: The continental slope around Antarctica acts as a barrier to deep and warmer offshore waters that can bring heat to the glaciers along the coastline, enhancing their melt rate and contributing to global sea level rise. Around the Antarctic continent these offshore waters, the so‐called Circumpolar Deep Waters, differ in their ability to cross this barrier while retaining their heat, explaining to a large extent why West Antarctic glaciers melt much faster than other Antarctic ice sheets. We study the properties of the warm waters over the continental shelf and offshore regions and contrast them across regions. We show that in East Antarctica, the Ross Sea, and the Weddell Sea, deep warm waters are brought to the surface where they lose heat and mix with surface waters. However, in the Amundsen and Bellingshausen Seas, the warm water is insulated from the surface by land run‐off of fresher and lighter waters that occupy the surface. These results highlight the importance of the subpolar gyres in sheltering Antarctic glaciers. Key Points: Intense Circumpolar Deep Water (CDW) transformation in subpolar gyres (∼−6.6 Sv) reduces heat content on adjacent shelvesMean CDW transformation rates are ∼8 times smaller on the Amundsen and Bellingshausen continental shelves than on othersLocal stratification around Antarctica correlates with CDW layer depth and bottom temperatures on the shelf [ABSTRACT FROM AUTHOR]

Over the continental slope off Oregon at the US West Coast, at 44.6°N, vertical stratification is found to be anomalously weak in July–August of 2014 and 2015 both in a regional ocean circulation model and conductivity–temperature–depth (CTD) profile observations. To understand the responsible mechanism, we focus on the layer between the isopycnal surfaces σθ = 26.5 and 26.25 kg m−3 that is found between depths 100 and 300 m and represents material properties characteristic of the slope poleward undercurrent and shelf‐slope exchange. This layer thickness, about 50 m on average, can be twice as large during the above‐mentioned periods. In the 2009–2018 model analysis, this anomaly is revealed over the continental slope only in summers 2014 and 2015 and only off the Oregon and Washington coasts (40°–47°N). The stratification anomaly is explained as the effect of advection of the seasonal along‐slope potential vorticity (PV) gradient by an anomalously strong poleward slope current. In the annual cycle, the zone of strong along‐slope PV gradient is found between 40° and 47°N, supported by the local upwelling that results in the injection of the large PV in the bottom boundary layer over the shelf followed by its offshore transport in the slope region. The positive along‐slope current anomaly propagates to Oregon with coastally trapped waves as part of the El Niño oceanic response and can be up to 0.1 m s−1. Advection by this anomalous poleward current results in transporting the seasonal PV gradient earlier in the season than on average. Plain Language Summary: Understanding the oceanic dynamics along the continental slopes is important for understanding material exchanges between the coastal and interior ocean and biological diversity. Analysis of a high‐resolution, three‐dimensional ocean circulation model helps explain observed variability over the slope. Associated with the global anomaly pattern called El Niño, the along‐slope poleward current off Oregon was anomalously strong in summers 2014 and 2015. This anomalous transport caused alongshore displacement of the water masses from the south resulting in the vertical spreading of the subsurface oceanic layers. Key Points: In summer 2014 and 2015, the model and data reveal episodes of anomalously weak stratification over the continental slope off OregonAdvection of the seasonal potential vorticity gradient by the anomalously strong slope current drives the weaker stratification anomalyThe poleward along‐slope current anomaly is part of the El Niño oceanic response propagated with coastally trapped waves [ABSTRACT FROM AUTHOR]

The TEX86 paleothermometer has been extensively used to reconstruct past sea water temperatures, but it remains unclear which export depths the proxy represents. Here we used a novel approach to better constrain the proxy recording depths by investigating paleotemperature proxies (TEX86, U37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$, RI−OH and RI−OH′) from two pairs of proximal (<12 km apart) cores from Chilean and Angola margins, respectively. These cores are from steep continental slopes and lower shelves, which leads to a substantial difference in water depth between them despite being closely located. Surprisingly, the deep and the shallow U37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$ records at the Chilean margin show dissimilarities, in contrast to the similar records from the Angola margin, which may be due to post‐depositional alteration at the former sites. In contrast, the TEX86 records were statistically indistinguishable between the sites at both the locations, even though the GDGT [2]/[3] ratio suggests GDGTs derived from potentially different archaeal communities residing at different depths. A short‐lived difference between the TEX86 records is observed during the last glacial period at the Angola margin, possibly due to a contribution of Antarctic Intermediate Waters to the deep site. Modelling suggests that the TEX86 source signal at our core sites reaches its peak abundance at water depths shallower than 350 m. The RI−OH and RI−OH′ records show similar variability as the TEX86 records, although regional differences in their absolute temperature estimates exist. Our approach using proximal sediment cores at steep slopes appears useful to constrain the export depth of organic proxy signals for paleo‐reconstructions. Key Points: Source signal of TEX86 proxy is likely derived from depths shallower than 350 m at Chilean and Angola marginsOH‐GDGT based proxies show similar variability as TEX86 records, but show regional differences in their absolute temperature estimatesU37K′ ${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$ proxy signal may be impacted by post‐depositional changes or lateral transport even for closely located cores [ABSTRACT FROM AUTHOR]

Internal tides are known to be an important source of mixing in the oceans, especially in the bottom boundary layer. The depth of internal-tide generation therefore seems important for benthic life and the formation of cold-water coral mounds, but internal-tidal conversion is generally investigated in a depth-integrated sense. Using both idealized and realistic simulations on continental slopes, we found that the depth of internal-tide generation increases with increasing slope steepness and decreases with intensified shallow stratification. The depth of internal-tide generation also shows a typical latitudinal dependency. Using a global database of cold-water corals, we found that the depth-pattern of internal-tide generation is remarkably similar to the depth-pattern of cold-water corals globally: shallowest near the poles and deepest around the equator with a shoaling around 25 degrees South and North and shallower north of the equator than south of the equator. We further found that cold-water corals are, more than what would be expected by chance, associated to the (super)critical reflection of internal tides (i.e., situated on topography that is steeper than the internal tidal beam) and to trapped internal tides i.e., above the critical latitude of 70 degrees for semidiurnal tides and 30 degrees for diurnal tides). The (super)critical reflection of internal tides and trapped internal tides therefore provide an interesting new angle of food supply mechanisms that has not yet been considered in cold-water coral studies. With climate change, stratification is expected to increase. Based on our results, this would cause a shoaling of internal-tide generation, possibly creating new shallower suitable habitat for cold-water corals on continental slopes. [ABSTRACT FROM AUTHOR]

Dissolved (<0.2 μm) trace metals (dTMs) including iron (Fe), manganese (Mn), and cobalt (Co) are micronutrients that (co-) limit phytoplankton growth in many ocean regions. Here, we present the spatial and seasonal distributions of dFe, dMn, and dCo on the Northeast Atlantic continental margin (Celtic Sea), along a transect across the shelf and two off-shelf transects along a canyon and a spur. Waters on the continental shelf showed much higher dTM concentrations (dFe 0.07–6.50 nmol L−1, average 1.41 ± 0.96 nmol L−1, n = 138; dMn 0.868–14.8 nmol L−1, 2.75 ± 2.37 nmol L−1, n = 148; dCo 54.8–217 pmol L−1, 109 ± 32 pmol L−1, n = 144) than on the slope (dFe 0.03–1.90 nmol L−1, 0.65 ± 0.43 nmol L−1, n = 454; dMn 0.223–1.14 nmol L−1, 0.58 ± 0.20 nmol L−1, n = 458; dCo 27.3–122 pmol L−1, 71.7 ± 11.7 pmol L−1, n = 441), attributed to strong dTM contributions from a low-salinity endmember, i.e., riverine discharge. Benthic sedimentary input via reductive dissolution (especially for dFe and dMn), delineated by short-lived radium (Ra) isotopic activities (223Ra xs and 224Ra xs), was only prominent at a station (Site A) characterized by fine sediments. On the continental slope, dMn levels at depth were mainly determined by the formation of insoluble Mn oxides and the intrusion of Mediterranean Outflow Waters. In contrast, dFe and dCo concentrations at depth were balanced by the regeneration from remineralization of sinking organic particles and scavenging removal. In addition, bottom and intermediate nepheloid layers along the slope illustrated both elevated dTM concentrations and Ra isotopic activities. The presence of nepheloid layers is especially significant along the canyon transect relative to the spur transect, demonstrating the importance of slope topography on the off-shelf transport of dTMs into the Northeast Atlantic Ocean. As a seasonal stratified shelf sea, dTMs and nutrients showed synchronized seasonal variations on the shelf, indicating the influence of biological processes in addition to source effects. Surface dFe and dCo were depleted in summer due to enhanced biological uptake, while sub-surface dFe and dCo were elevated in summer and autumn ascribed to the remineralization of sinking organic particles. In contrast, surface dMn levels were predominantly controlled by the seasonal variations in photoreduction, while sub-surface dMn concentrations were relatively constant throughout the year. The combined effects of fluvial and benthic sources, topographical controls, and biological processes shape the seasonal variations of dTM distributions. Such seasonal variations in dTMs and biological activities can affect the biological carbon pump on the Northeast Atlantic continental margin, and may further influence the carbon cycle in the Atlantic Ocean via the dynamic dTM exchange between continental margins and the open ocean. [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]

Using observed data and results from a numerical model, we investigate the coupled physical‐biogeochemical processes that result from water exchanges between the South China Sea (SCS) and the western Pacific Ocean (WPO) and between the shelf and deep basin along the biophysically active continental slope. We study the nutrient transport and dynamics over the northern slope of the SCS where the main branch of the SCS basin circulation facilitates water exchange between the SCS and the WPO. Our results show that the nutrient flux consistently flows year‐round into the slope region from the WPO and that the along‐slope and cross‐slope transports regulate the nutrient budget in the region. The nutrient transport concentrates mainly in the upper 1,000 m and exhibits significant seasonality. We found that cross‐isobath motion is key to fueling nutrients for biological production along the slope and throughout the SCS. When the persistent westward slope current interacts with the variable sloping topography, a unique upslope/downslope nutrient transport occurs along convex/concave isobaths. Vertical turbulent mixing becomes the main nutrient source in the upper mixed layer, and vertical advection becomes the major contributor of nutrients to the subsurface layer. Biological production dominates the nutrient sink in both layers. Horizontal advection is also an important sink in winter when the slope current is the strongest due to the enhanced northeasterly monsoon and the Kuroshio intrusion. Our findings provide an insightful understanding on the critical role of nutrient transport over the slope in the overall ecosystem dynamics of the marginal SCS. Plain Language Summary: The transport of the northern continental slope of the South China Sea (SCS) connects the nutrient exchanges not only between western Pacific Ocean (WPO) and the SCS, but also between the shelf and deep basin. Based on a three‐dimensional model and observational data, we analyze the exchanges and the underlying biogeochemical processes to illustrate its role on the nutrient budget and ecosystem in the SCS. Our findings indicate that nutrient flow from the WPO to the SCS slope affects the nutrient budget of the SCS (including both the northern shelf and basin). Most nutrient transport is concentrated in the upper 1,000 m with strong seasonality. The upslope cross‐isobath nutrient transport is strong due to interaction between slope current and variable slope topography and is key to providing nutrients for the biological production of the SCS. Vertical mixing and vertical advection are the main source of nutrients in the upper mixed layer and the lower layer, respectively. Biological production dominates the nutrient sink in both layers, while horizontal advection is also an important sink when the slope current and intrusion of lower nutrient concentration water from the WPO are strongest. Key Points: Upslope transport of nutrient is key to fueling nutrients for biological production along the slope and ambient seasInteraction between slope current and topography results in strong upslope/downslope nutrient transport along the meandering slopeVertical mixing and vertical advection are the major nutrient sources in the upper and lower layer, respectively [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]

The geodynamic response of continental margins to erosion may reveal current and past changes in the location of the continental slope. We model the three‐dimensional isostatic response to erosion along the retreating Beringian Margin to test the hypothesis that the margin and its canyons were dominantly eroded during the Pleistocene. Our results predict 900 m of flexural uplift, though evidence for this magnitude of uplift is not observed in Pleistocene and younger deposits, suggesting a substantial amount of margin erosion occurred pre‐Pleistocene. Uplift of this magnitude may be represented by a Late Miocene unconformity across the Bering Shelf and upwarped subsurface units at the base of the Beringian Margin. The distribution of uplift from varying canyon incision and margin retreat scenarios has implications for the extent of geodynamic response during erosional periods. Plain Language Summary: Reconstructing the balance between erosion and deposition along continental margins necessitates constraining multiple variables such as sedimentation rates, tectonic subsidence, isostatic compensation, and compaction. However, reconstructing this balance along erosion‐dominated margins is hindered by the inherent removal (from eroding areas) and access challenges (deep‐water, where eroded materials deposit) to geologic records of erosion. We use geodynamics to link erosion and the resulting rebound of the crust to constrain the magnitude and timing of continental margin retreat. We model the isostatic response to a range of submarine erosion scenarios along the Beringian Margin, which are hypothesized to have formed primarily during the Pleistocene. Our results show that the magnitude of uplift predicted by the mass of sediment removed along the Beringian is too substantial to have entirely occurred since the Pleistocene, suggesting the canyons are older than previously thought. Geophysical subsurface data may instead favor isostatic upwarping that began as early as the Miocene suggesting that margin retreat and canyon incision along the deeply incised Beringian Margin has been ongoing for several millions of years. Key Points: Flexural isostatic modeling of the Beringian margin canyons suggests their erosion predates the PleistoceneSlope retreat has a greater impact than canyon enlargement on geodynamic responses to continental margin erosion, even for very large canyonsCumulative erosion of multiple incising canyons predicts a flexural response beyond the flexural wavelength of an individual canyon [ABSTRACT FROM AUTHOR]

Deep-marine two-part strata consisting of a sand-rich basal part overlain sharply by a mud-rich upper part have been termed linked debrites, hybrid event beds, transitional flow deposits, and bipartite facies. In continental slope and proximal basin floor strata of the Neoproterozoic Windermere Supergroup (western North America) and distal basin-floor strata of the Ordovician Cloridorme Formation (eastern North America), bipartite facies form the middle of a depositional continuum hundreds of meters long consisting upflow of thick-bedded, matrix-poor sandstone (<20% detrital mud matrix) to thin-bedded, sandy mudstone (50%–90% mud matrix). This consistent lithofacies change is interpreted to reflect particle settling in a rapidly but systematically evolving, negligibly sheared sand-mud suspension developed along the margins (Windermere) and downflow terminus (Cloridorme) of a high-energy, mud-enriched avulsion jet. In both study areas, beds of similar lithofacies type succeed one another vertically and transform to the next facies in the depositional continuum at about the same along-strike position, forming stratal units two to nine beds thick whose grain-size distribution gradually decreases upward. This spatial and temporal regularity is interpreted to be caused by multiple surges of a single, progressively waning turbidity current, with sufficient lag between successive surges for the deposition of a traction-structured sandstone overlain by mudstone cap. Furthermore, the systematic back-stepping or side-stepping recognized at the stratal unit scale is interpreted to have been driven by a combination of knickpoint migration and local topographic steering of the flows, which continued until the supply of mud from local seafloor erosion became exhausted, the main channel avulsed elsewhere, or a new stratal element developed. [ABSTRACT FROM AUTHOR]

Isopycnal eddy mixing across continental slopes profoundly modulates the ocean circulation and biogeochemistry. Yet this process must be parameterized in coarse‐resolution ocean models via an isopycnal eddy diffusivity prescribed with the Redi scheme. In this work, we evaluate the skill of physics‐based and data‐driven Redi variants in predicting the cross‐slope exchanges using a suite of offline‐mode parameterized tracer simulations for wind‐driven upwelling continental slope fronts, which commonly arise around the margins of subtropical gyres. The tested physics‐based Redi variants range from a constant eddy diffusivity to a recently proposed, bathymetry‐aware diffusivity augmented by the artificial neural network (ANN) that infers the mesoscale eddy kinetic energy from the mean flow and topographic quantities. Moreover, a purely data‐driven eddy diffusivity is learned by the ANN from the output data set of an eddy‐resolving model, whose solutions serve as the ground truth against which the parameterized tracer simulations are compared. Among all tested Redi variants, the ANN‐learned diffusivity and the bathymetry‐aware diffusivity outperform others in reproducing the tracer solutions of the eddy‐resolving model. However, a physics‐based Redi variant with local deficiencies can introduce global errors in the predicted tracer distribution, which calls for ongoing efforts in constraining the shelf‐to‐ocean transition of the isopycnal eddy diffusivity. A purely data‐driven diffusivity can nearly reproduce the diagnosed diffusivity from the eddy‐resolving model, which highlights the efficacy of machine learning techniques for parameterizing eddy processes across steep topography. This work serves as a key step toward parameterizing the isopycnal eddy mixing in ocean models with continental slopes. Plain Language Summary: Turbulent eddies across continental slopes drive the exchanges between shelf seas and open oceans, which are essential for coastal ecosystems and the global climate. These eddies are characterized by length scales smaller than the grid spacing of today's ocean climate models, resulting in unresolved eddy‐induced exchanges. This issue is usually remedied by eddy parameterizations that infer eddy fluxes from properties explicitly resolved in climate models. In this work, we evaluate extant parameterizations in constraining cross‐slope exchanges of oceanic tracers (such as salt and nutrients) by comparing simulations that utilize parameterizations with simulations that can explicitly resolve mesoscale eddies. Our results reveal the necessity to adopt more sophisticated parameterizations in non‐eddying simulations for cross‐slope eddy tracer exchanges than those currently used in climate models. Moreover, machine learning techniques are found to be effective in parameterizing cross‐slope eddy exchanges. Key Points: Data‐driven and physics‐based parameterizations of isopycnal eddy diffusivity across continental slopes are tested prognosticallyArtificial neural network‐inferred diffusivities and bathymetry‐aware diffusivities outperform previously tested variants over steep slopesMachine learning techniques effectively augment physics‐based mesoscale eddy parameterizations [ABSTRACT FROM AUTHOR]

The flow and descent of dense water masses formed in shallow regions of the ocean is an important leg in the global overturning circulation. The dense overflow waters tend to flow along the continental slopes as geostrophically balanced gravity plumes, but may be steered downslope by canyons and ridges cross-cutting the slopes. In that process, entrainment and mixing will be greatly enhanced. Ilicak et al. (Ocean Model 38:71–84, 2011) propose a parameterization to include the effects of corrugations in large scale models by increasing the vertical mixing locally. We re-visit the problem using the terrain-following Bergen Ocean Model and a DOME-inspired idealized topography. It is shown that the applied corrugations can move the core of the plume 800 m down the slope, while enhanced mixing raises the center of gravity by only 1–200 m. The overall effect of a corrugation is hence to lower the center of gravity, suggesting that the parameterization proposed by Ilicak et al. (Ocean Model 38:71–84) will act in the wrong vertical direction, if used on its own. A comparison of two bottom drag parameterizations, show that a parameterization consistent with a no-slip boundary condition is needed to correctly represent Ekman drainage, and that the Ekman drainage contribution to plume descent is comparable to that of the corrugation. Ridges are more effective in steering dense water downward than canyons, and we compare the dynamics between the two settings to explain the difference. [ABSTRACT FROM AUTHOR]

We investigate statistical properties of surface currents as well as coherent mesoscale eddies in the seasonally ice‐covered Southern Ocean. Based on a recent regional Sea Level Anomaly satellite altimetry data set, we compute Eddy Kinetic Energy (EKE) and detect mesoscale eddies. EKE is about one order of magnitude higher in the northern sector of the subpolar basin and over the continental slope, as compared to the middle of the subpolar gyres. An eddy detection methodology reveals that eddies are distributed evenly in the subpolar Southern Ocean, and their amplitude follows the spatial pattern of EKE. In addition to regional circulation variations, sea ice concentration arises as an important driver of eddy properties. Eddies have low amplitude and density in the pack ice, in particular in the middle of the gyres where the background circulation is unfavorable for instabilities. In contrast, the northern part of the Marginal Ice Zone is favorable for mesoscale eddies, especially cyclonic. There, eddies are stronger and their density is higher than in any other region of the ice‐covered or ice‐free subpolar Southern Ocean. This region is expected to be a site of frontogenesis due to sea ice melt and upwelling generated from interactions between the wind and the sea ice. While many mesoscale eddies will fall below detection level due to the small Rossby radius at high latitudes, these results contribute to understanding the interactions between mesoscale eddies, sea ice, and the background circulation in the subpolar region. Plain Language Summary: Ocean eddies are spatially coherent vortices, ubiquitous in the global oceans, and are central structures contributing to shaping the global ocean circulation. In the Southern Ocean, they have been shown to play a potentially important role in the cross‐front transport of heat and nutrients at mid and high latitudes. Recent improvements in satellite altimetry capabilities in the ice‐covered regions allow for a first description of mesoscale eddies in the ice‐covered Southern Ocean, and the investigation of their interactions with sea ice. The location of the detected eddies is consistent with the main large‐scale circulation features. In addition to the background circulation, the sea ice cover has a strong impact on the size of eddies. While weaker eddies are found in the highly concentrated sea ice areas, the marginal ice zone seems to be a region with enhanced eddy activity, with more and stronger eddies detected. Key Points: A new satellite altimetry data set allows the detection of mesoscale eddies in the ice‐covered Southern OceanEddy generation and strength are primarily impacted by sea ice concentration and the background circulationWhile the eddy strength is damped under high sea‐ice concentration, the northern edge of the sea‐ice region is a hotspot of large eddies [ABSTRACT FROM AUTHOR]

Features and mechanism of intraseasonal cyclonic and anticyclonic eddy generation in the northeastern Bay of Bengal (NE‐BoB) are investigated using satellite observations, ocean reanalysis, and related wind forcing data. Our results suggest that the intraseasonal cyclonic (anticyclonic) eddies generated in the NE‐BoB can be primarily attributed to intraseasonal easterly (westerly) wind anomalies in the equatorial Indian Ocean, which provokes the upwelling (downwelling) Kelvin wave (KW) traveling along the equator and subsequently the eastern boundary through the Preparis Channel into the NE‐BoB. Anomalous equatorial zonal wind can result in a strong intraseasonal subsurface flow along the KW waveguide located on the continental slope, and this KW‐associated subsurface flow is essential to the formation process of both anticyclonic and cyclonic eddies in the NE‐BoB. A seasonal difference in the response of sea level anomaly (SLA) to the KW‐associated subsurface flow is revealed, which can be explained by the seasonal variability of stratification along the waveguide. The eddy related SLA shows a considerable correlation coefficient of −0.58 with the accumulated transport caused by KW‐associated subsurface flows through the Preparis Channel when it lags 18 days, indicating a possible eddy generation mechanism that the KW‐associated subsurface flow dominated net horizontal inflow (outflow) causes vertical stretching (shrinking) of the subsurface layer, which in turn triggers an anticyclonic (cyclonic) eddy. Plain Language Summary: Some processes that happen in the equatorial ocean can remotely affect the oceans at higher latitudes through the propagation of equatorial and coastal Kelvin waves. In the northeastern Bay of Bengal, coastal Kelvin waves from the equatorial Indian Ocean trigger intraseasonal cyclonic and anticyclonic eddies in a specific region, the west slope of the Irrawaddy Delta off Myanmar. According to our research, an anomalous easterly (westerly) event in the equatorial Indian Ocean may form a cyclonic (anticyclonic) eddy in the northeastern Bay of Bengal approximately 2 months later. The major dynamic of eddy generation occurs at about 100 m depth in the subsurface where coastal Kelvin waves are accompanied by strong current anomalies. The sea surface response to subsurface current anomalies is influenced by the vertical structure of seawater density and shows seasonal variability. Notably, surface observed eddies in the northeastern Bay of Bengal are primarily determined by the accumulated effect caused by these strong subsurface current anomalies. After the eddy is formed, it is also reflected in the sea level anomaly, and hence, can be observed by satellites. Moreover, satellite observations show that these intraseasonal eddies can continue to travel southwestward, affecting the central Bay of Bengal. Key Points: Equatorial wind anomalies lead to strong intraseasonal subsurface flows cross the Preparis Channel by Kelvin wave (KW) propagationThe seasonality of surface response to the KW‐associated subsurface flow is affected by the stratificationThe accumulated transport caused by the KW‐associated subsurface flow plays a vital role in the eddy generation [ABSTRACT FROM AUTHOR]

Under the background of wind forcing change along with Arctic sea ice retreat, the mesoscale processes undergoing distinct variation in Beaufort Gyre (BG) region are more and more significant to oceanic transport and energic cascade, and then these changes put oceanic stratification into a new state. Here the varying eddies and eddy kinetic energy (EKE) in the central Canada Basin (CB) and Chukchi–Beaufort continental slope are obtained based on mooring observations (2003–2018), altimetry measurements (1993–2019) and reanalysis data (1980–2021). In this paper, the variability of halocline in BG representing adjustment of stratification in the upper layer is shown so as to analyze how it occurs under significantly changing mesoscale processes. We find that the halocline depth has deepened by ~40 m while that in the north has deepened by ~70 m in the in the last nearly two decades by multiple data sets. The halocline depth lifting to the north initially was shifted to a final nearly symmetric structure. Eddy strength and Eddy induced low salinity water transportations have been continuously increasing toward the central basin at the mean time the halocline depth and strength among the southern and northern parts in the basin have reached a nearly identical and stable regime. It is clearly clarified that the long-term dynamical eddy modulation through eddy fluxes facilitating the freshwater redistribution inhibited the meridional asymmetry of halocline of the BG. Further research into high-resolution observations and data simulations can helps us to better understand the eddy modulation processes and its influence on large-scale circulation. [ABSTRACT FROM AUTHOR]

Under the background of wind forcing change along with Arctic sea ice retreat, the mesoscale processes undergoing distinct variation in Beaufort Gyre (BG) region are more and more significant to oceanic transport and energic cascade, and then these changes put oceanic stratification into a new state. Here the varying eddies and eddy kinetic energy (EKE) in the central Canada Basin (CB) and Chukchi-Beaufort continental slope are obtained based on mooring observations (2003-2018), altimetry measurements (1993-2019) and reanalysis data (1980-2021). In this paper, the variability of halocline in BG representing adjustment of stratification in the upper layer is shown so as to analyze how it occurs under significantly changing mesoscale processes. We find that the halocline depth has deepened by ~40 m while that in the north has deepened by ~70 m in the in the last nearly two decades by multiple data sets. The halocline depth lifting to the north initially was shifted to a final nearly symmetric structure. Eddy strength and Eddy induced low salinity water transportations have been continuously increasing toward the central basin at the mean time the halocline depth and strength among the southern and northern parts in the basin have reached a nearly identical and stable regime. It is clearly clarified that the long-term dynamical eddy modulation through eddy fluxes facilitating the freshwater redistribution inhibited the meridional asymmetry of halocline of the BG. Further research into high-resolution observations and data simulations can helps us to better understand the eddy modulation processes and its influence on large-scale circulation. [ABSTRACT FROM AUTHOR]

Seafloor methane emissions can affect Earth's climate and ocean chemistry. Vast quantities of methane formed by microbial decomposition of organic matter are locked within gas hydrate and free gas on continental slopes, particularly in large areas with high sediment accumulations such as deep-sea fans. The release of methane in slope environments has frequently been associated with dissociation of gas hydrates near the edge of the gas hydrate stability zone on the upper slope, with discharges in greater water depths less understood. Here we show, using data from the Rio Grande Cone (western South Atlantic), that the intrinsic, gravity-induced downslope collapse of thick slope sediment accumulations creates structures that serve as pathways for gas migration, unlocking methane and causing seafloor emissions via giant gas flares in the water column. The observed emissions in the study region (up to 310 Mg year−1) are three times greater than estimates for the entire US North Atlantic margin and reveal the importance of collapsing sediment accumulations for ocean carbon cycling. Similar outgassing systems on the Amazon and Niger fans suggest that gravity tectonics on passive margins is a common yet overlooked mechanism driving massive seafloor methane emissions in sediment-laden continental slopes. [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]

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m−1 toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km. [ABSTRACT FROM AUTHOR]

The transport of oceanic heat towards the Antarctic continental margin is central to the mass balance of the Antarctic Ice Sheet. Recent modeling efforts challenge our view on where and how the on-shelf heat flux occurs, suggesting that it is largest where dense shelf waters cascade down the continental slope. Here we provide observational evidence supporting this claim. Using records from moored instruments, we link the downslope flow of dense water from the Filchner overflow to upslope and on-shelf flow of warm water. Recent modeling challenges our view on where the on-shelf heat flux in Antarctica occurs, suggesting it to be large where dense waters descend the continental slope. The authors provide observational evidence from the Weddell Sea supporting this claim. [ABSTRACT FROM AUTHOR]

Reducing multiple contaminations in reflection seismic data remains one of the primary challenges in marine seismic data processing. Besides geological settings, its effectiveness is also dependent on the multiple removal methods. In this study, we undertook two legacy 2D multi-channel seismic data crossing the accretionary wedge off SW Taiwan to test the efficiency of various multiple-attenuation scenarios. The tectonic domain has resulted from the incipient arc-continent collision between the northern rifted margin of the South China Sea and the Luzon volcanic arc. The wedge extends from shallow water to deep water bathymetries, hence promoting both short-period and long-period multiples within the seismic records. A cascade of de-multiple methods was tested to attenuate multiple energy under various seafloor bathymetry and tectonic areas. The first step relies on the periodicity nature of multiples. Spatial dependent predictive deconvolution in the x-t domain was performed to attenuate reverberations and improve temporal resolution in the time domain. Wave-equation multiple attenuation (WEMA) was applied to suppress the water layer multiples based on a combination of numerical wave extrapolation in the shot domain through water layer and water bottom reflectivity. Surface-related multiple elimination (SRME) aimed to attenuate the residual water bottom multiple and peg-leg multiple by assuming surface-related multiples can be kinematically predicted via convolution of pre-stack seismic traces at possible surface multiple reflection locations. The second step exploits the spatial move-out difference behavior between primaries and multiples. Parabolic Radon transforms far-offset multiples by subtracting noise energy in the τ-p domain, whereas the frequency-wave number (F-K) filter aimed to eliminate any residual multiples energy in the F-K domain. Predictive deconvolution improved seismic resolution and suppressed sea-bottom reverberation energy in the continental and lower wedge slopes, but not in the upper wedge slope. WEMA, Radon filter, and F-K filter reduced multiples energy both at the continental slope and wedge slope; whereas SRME made minimal impact on both areas. Since the reflection seismic datasets stretch diverse tectonic environments and water depth, there was no single multiple attenuation method capable to suppress multiples in all tectonic environments and bathymetry. [ABSTRACT FROM AUTHOR]

Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km2 area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km2 area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic. [ABSTRACT FROM AUTHOR]

Submarine canyons commonly occur on virtually all continental slopes. Their varied origins are widely studied but still debatable. Eastward (along-slope)–migrating submarine canyons, with nearly regular spacing, are well developed at the northern South China Sea. High-resolution three-dimensional seismic data show that these canyons are localized in the troughs between sediment waves. The waves were present on the slope since before ca. 10.5 Ma and were especially well developed during the late Miocene (ca. 10.5–5.5 Ma). This interval can be divided into two units, of which the upper unit (SU II) has larger sediment waves and much better-developed canyons compared to the lower unit (SU I). Submarine fans developed at the canyon mouths within SU II at the downdip termination of the confinement caused by the sediment waves. Gravity currents were captured between the waves, resulting in erosion mainly along the troughs between them. The canyons were forced to migrate eastward by the migration of the confining sediment waves. In this study, we present a new mechanism for the origin of such regularly spaced submarine canyons for the first time, which we attribute to the formation of regularly spaced sediment waves generated by contour currents. [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]

Significant current velocity near the sea bottom can be induced by internal waves, even for water a few hundred meters in depth. In this study, a nonhydrostatic ocean model was applied to simulate the generation and propagation of internal waves on the continental slope of the northern SCS. Based on the analyses of the vertical profiles of the currents, the propagation of internal waves along the continental slope can be categorized into six modes. The bed shear stress and the bedload transport were calculated to analyze the general characteristics of sediment transport along the continental slope of the northern SCS. Generally, there was no sediment transport on the sea bottom induced by the internal waves when the water depth was deeper than 650 m or shallower than 80 m. The downslope sediment transport dominated the slope at a water depth range of 200~650 m, while the upslope sediment transport dominated the slope at a water depth range of 80~200 m. The predicted directions of the bedload transport are coincident with the field observations of sand wave migration on the continental slope, which further confirms that the main cause of the generation and formation of sand waves on the continental slope of the northern SCS is the strong bottom current induced by the shoaling process of internal waves. [ABSTRACT FROM AUTHOR]

The Chukchi Slope Current is a westward-flowing current along the Chukchi slope, which carries Pacific-origin water from the Chukchi shelf into the Canada Basin and helps set the regional hydrographic structure and ecosystem. Using a set of experiments with an idealized primitive equation numerical model, we investigate the energetics of the slope current during the ice-covered period. Numerical calculations show that the growth of surface eddies is suppressed by the ice friction, while perturbations at mid-depths can grow into eddies, consistent with linear instability analysis. However, because the ice stress is spatially variable, it is able to drive Ekman pumping to decrease the available potential energy (APE) and kinetic energy of both the mean flow and mesoscale eddies over a vertical scale of 100 m, well outside the frictional Ekman layer. The rate at which the APE changes is determined by the vertical density flux, which is negative as the ice-induced Ekman pumping advects lighter (denser) water upward (downward). A scaling analysis shows that Ekman pumping will dominate the release of APE for large-scale flows, but the effect of baroclinic instability is also important when the horizontal scale of the mean flow is the baroclinic deformation radius and the eddy velocity is comparable to the mean flow velocity. Our numerical results highlight the importance of ice friction in the energetics of the slope current and eddies, and this may be relevant to other ice-covered regions. [ABSTRACT FROM AUTHOR]

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10−10 to 4.18 × 10−7 W·kg−1. In the surface mixed layer, high values of ε (10−9∼10−8 W·kg−1) were observed toward the water surface. In the thermocline, ε was 10−9.5∼10−9 W·kg−1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations. [ABSTRACT FROM AUTHOR]

The morphology and development of several submarine canyons offshore southeast South Australia and western Victoria are described. The existence of three of those canyons had been foreshadowed in 1963 by N. Boutakoff, who thought them to be linked to ancient courses of the Glenelg River. These canyons occur on the outer continental shelf where their heads are situated in depths shallower than 1000 m. Sinuous channels are visible within two of the canyon heads, indicating that water and sediment may still travel downslope and cause erosion, and thus are geologically recent. Several other canyons are also documented and named. Two canyons are confined to depths below 3000 m; they may be much older and seem not to be linked to ancient river courses. They are also oblique to the upper canyons. The other characteristic feature of the area is the presence of numerous undersea slides. These occur at three specific depths (∼1200, ∼1500 and ∼1800 m) and are coincident with stratigraphic horizons in which continental groundwater flows have been identified in adjacent exploratory oil and gas wells drilled into the continental shelf. Sapping of groundwater may likely have occurred during very wet periods inland. We suggest that these undersea slides could be the first step in the formation of deep-sea canyons that are not necessarily linked to ancient river courses. We also postulate that the 'sliding' of large piles of sediment down the continental slope has tsunamigenic potential and may have occurred during significant wet climate on land. Several deep-sea canyons and numerous submarine slides are documented along the continental shelf offshore the coastline of western Victoria and southeast South Australia in the Otway Basin. Some of these canyons are linked to previous courses of the Glenelg River, which changed over time in response to regional tectonic changes such as faulting and significant upwarping. The orientation of most of these canyons tends to align with ancient terrestrial lineaments that likely extend offshore. Sinuous channels within the upper canyon reaches are clearly visible and not infilled with sediment; they are likely active and linked to ongoing groundwater seepage. It is proposed that the underwater slides are generated by the submarine discharge of continental groundwater on the continental slope, at three specific water depths with discharge associated with particular lithologies. These slides may still be active. Superimposed slides may engender the formation of new canyons. The volume of some of these undersea slides is of tsunamigenic scale. [ABSTRACT FROM AUTHOR]

Continental shelves are key to societal interactions with the oceans, supporting >90% of the world's fisheries through highly productive ecosystems. Previous research has shown that phytoplankton biomass is generally higher on the inner continental shelves, often due to increased nutrient inputs from upwelling or coastal run‐off. However, consistency in observed vertical and horizontal gradients (in abundance, biomass or size) of larger particulates, including zooplankton, on continental shelves has not been established. Using an optical plankton counter and CTD mounted on an undulating towed body, we present high‐resolution vertically resolved profiles of pelagic particle size structure across a continental shelf. Biomass was highest inshore, declining with distance from shore and with depth in the top 100 m of the water column, although the presence of frontal zones can alter this pattern. In the region adjacent to the East Australian Current (EAC), uplift generated by either the EAC interacting with the continental slope or upwelling‐favorable winds, correlated with smaller geometric mean sizes and steeper size spectrum slopes, particularly in the presence of frontal features. South of the EAC separation, the continental shelf water mass was more homogenous but still displayed the same horizontal and vertical patterns in particulate biomass and mean size. By combining our observations in a global comparison, we demonstrate consistent particulate distributions on continental shelves where the inner shelf has higher biomass with a steeper size spectrum slope compared to offshore. The highly productive inner shelf supports zooplankton communities vital to temperate ecosystems and coastal fisheries, through their consistently high biomass. Plain Language Summary: It is commonly accepted that chlorophyll a and phytoplankton are more abundant on continental shelves compared to the open ocean due to nutrient enrichment from either upwelling or terrestrial inputs. Little is known about the consistency in larger particulates, including zooplankton. We present the first depth resolved cross‐shelf transects of zooplankton sized particulates. We show globally consistent patterns where close to the coast there is higher abundance and biomass, smaller geometric mean size and a steeper size spectrum slope representing a more productive community. Key Points: We present the first depth resolved cross‐shelf transects of the abundance, biomass, and geometric mean size of particulate matterHigher biomass and abundance were generally found close to the coast likely representing a more productive communityThese patterns were consistent globally but can show significant small‐scale variation around frontal zones [ABSTRACT FROM AUTHOR]

The escape structure in southwest Taiwan has long been discussed. The counterclockwise rotation in GPS ground motion is argued to be evidence of tectonic escape. However, tectonic escape events worldwide are always bounded by lithosphere-cutting strike-slip faults at the boundary of the lithospheric-scale rotating block, and these have not observed in Taiwan. In this study, we propose that the escape structure in southwest Taiwan is a thin-skinned deformation due to the open boundary in the continental slope, the ramp, and the shallow décollements. We tested this shallow escape hypothesis using a 3D numerical simulation with elastoplastic rheology. We found that a conjugate pair of forethrust and backthrust developed above the ramp. The strike and location of the forethrust mainly follow the ramp. However, the strike of the forethrust rotates perpendicular to the open boundary when in proximity. From north to south, the strike of the forethrust transfers from NNE to NE, and the deformation transfers from thrust to dextral thrust. This leads to a counterclockwise rotation in ground motion, which matches the GPS observation. This research provides a different explanation of the mechanism for the escape structure in southwest Taiwan. [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 rapid ongoing changes in the Central Arctic Ocean call for baseline information on the pelagic fauna. However, sampling for motile organisms which easily escape vertically towed nets is challenging. Here, we report the species composition and catch weight of pelagic fishes and larger zooplankton from 12 trawl hauls conducted in ice covered waters in the Central Arctic Ocean beyond the continental slopes in late summer. Combined trawl catches with acoustics data revealed low amounts of fish and zooplankton from the advective influenced slope region in the Nansen Basin in the south to the ice-covered deep Amundsen Basin in the north. Both arctic and subarctic-boreal species, including the ones considered as Atlantic expatriate species were found all the way to 87.5o N. We found three fish species (Boreogadus saida, Benthosema glaciale and Reinhardtius hippoglossoides), but the catch was limited to only seven individuals. Euphausiids, amphipods and gelatinous zooplankton dominated the catch weight in the Nansen Basin in the mesopelagic communities. Euphausiids were almost absent in the Amundsen Basin with copepods, amphipods, chaetognaths and gelatinous zooplankton dominating. We postulate asymmetric conditions in the pelagic ecosystems of the western and eastern Eurasian Basin caused by ice and ocean circulation regimes. [ABSTRACT FROM AUTHOR]

We combine forward stratigraphic models with a suite of uncertainty quantification and stochastic model calibration algorithms for the characterization of sedimentary successions in large scale systems. The analysis focuses on the information value provided by a probabilistic approach in the modelling of large-scale sedimentary basins. Stratigraphic forward models (SFMs) require a large number of input parameters usually affected by uncertainty. Thus, model calibration requires considerable time both in terms of human and computational resources, an issue currently limiting the applications of SFMs. Our work tackles this issue through the combination of sensitivity analysis, model reduction techniques and machine learning-based optimization algorithms. We first employ a two-step parameter screening procedure to identify relevant parameters and their assumed probability distributions. After selecting a restricted set of important parameters these are calibrated against available information, i.e., the depth of interpreted stratigraphic surfaces. Because of the large costs associated with SFM simulations, probability distributions of model parameters and outputs are obtained through a data driven reduced complexity model. Our study demonstrates the numerical approaches by considering a portion of the Porcupine Basin, Ireland. Results of the analysis are postprocessed to assess (i) the uncertainty and practical identifiability of model parameters given a set of observations, (ii) spatial distribution of lithologies. We analyse here the occurrences of sand bodies pinching against the continental slope, these systems likely resulting from gravity driven processes in deep sea environment. [ABSTRACT FROM AUTHOR]

Recent progress in understanding Beaufort Gyre (BG) dynamics reveals an important role of ice‐ocean stress in stabilizing BG freshwater content (FWC) over seasonal to interannual timescales. But how the BG's stratification and FWC respond to surface forcing over decadal timescales has not been fully explored. Using a global ocean‐sea ice model, we partition the BG into upper, middle (halocline), and lower (thermocline) layers and perform a volume budget analysis over 1948–2017. We find that the BG's asymmetric geometry (with steep and tight isohalines over continental slopes relative to the deep basin) is key in determining the mean volume transport balance. We further find that a net Ekman suction during 1983–1995 causes the upper and middle layers to deflate isopycnally, while an enhanced Ekman pumping during 1996–2017 causes these layers to inflate both isopycnally and diapycnally, the latter via anomalous flux from the upper to the middle layer. Plain Language Summary: The Beaufort Gyre (BG) has increased its liquid freshwater content (FWC) by 40% in the past two decades. If released and transported downstream to the subpolar North Atlantic Ocean, the excess water might affect the ocean circulation via suppression of deep‐water formation. However, which layer is responsible for BG freshwater accumulations and releases over decadal timescales and the corresponding physical processes remain unclear, hampering our attempts to make future predictions. Here we use an ocean‐sea ice model to explore such changes in its three characteristic layers (upper mixed‐layer water, Pacific Water in the middle layer, and Atlantic Water in the lower layer). We find that the asymmetry of the BG, which has been simplified as a symmetric bowl shape in most previous studies, is important in determining the BG's layered mean state. Over decadal timescales, changes in BG volume are controlled by annual‐mean Ekman pumping/suction resulting from combined wind and ice‐ocean stresses. This study emphasizes the role of asymmetric geometry in determining the BG mean volume balance. It also explores the role of mean flow across the gyre's lateral boundaries in regulating BG's volume and FWC over decadal timescales. Key Points: The Beaufort Gyre's asymmetric geometry is the key to explain a net mean lateral outflow in the upper layer, despite Ekman convergenceIn the mean, the Gyre is fed by a northeast inflow into its middle layer, with outflow to its southwest from both upper and middle layersDeflation/inflation processes are asymmetric in response to anomalous Ekman suction/pumping on decadal timescales [ABSTRACT FROM AUTHOR]

This article presents the findings of a research project conducted in the Santos Basin, Brazil, which aimed to collect comprehensive oceanographic data for future environmental management in offshore oil and gas regions. The study examined various aspects of the benthic and pelagic environments, including physical, chemical, sedimentological, and biological factors. The research findings are categorized into methodological aspects, hydrographic conditions, pelagic ecosystems, and benthic ecosystems. The ultimate goal of the project is to balance sustainable oil and gas exploration with the preservation of regional biodiversity and environmental health. The article also discusses the study of meiofauna and the use of machine learning techniques to identify distinct benthic zones with unique environmental conditions. Additionally, the study highlights differences in macrofauna and foraminifera between the northern and southern sectors of the slope. The implementation of ecosystem-based management (EBM) in the Santos Basin faces challenges such as distinguishing natural variability from human-mediated changes and involving relevant stakeholders. However, it is crucial to base EBM on high-quality scientific data to ensure the long-term preservation of marine ecosystems. [Extracted from the article]

This work describes the circulation over the continental slope and the São Paulo Plateau in the Santos Basin during the SANSED winter 2019 survey. The cruise consisted of four legs in the period between June, 11 and August, 03 2019. The observed circulation is dominated by the Atlantic southwestern boundary current regime and remotely-generated anticyclones and cyclones. The former is composed by the Brazil Current, the Intermediate Western Boundary Current and their mesoscale meanders; the latter are 300km vortical rings with origin in the eastern side of the South Atlantic Basin. A Lagrangian scheme applied over satellite altimeter maps indicate that the origin of these rings is primarily the Cape Basin off South Africa. The interaction between the boundary currents, their cyclonic meanders, and the anticyclonic rings is complex, and varies widely. During the SANSED winter 2019 survey period, three anticyclones interacted with the Brazil Current, instabilizing it, forming dipoles with the current cyclonic meanders, leading to their downstream propagation. Ancienter cyclonic eddies within Santos Basin may interfere with the propagation of the large anticyclones further south. In addition, the continuous arrival of remotely-originated anticyclones, the larger portion over the São Paulo Plateau presented a tendency of counter-clockwise circulation during the whole cruise period. [ABSTRACT FROM AUTHOR]

Continental margins usually have a high degree of environmental heterogeneity, which, in turn, promotes high benthic biodiversity. The South-Southeast regions concentrate the most well-mapped areas of the Brazilian continental margin regarding seafloor geomorphology and physical oceanography. However, the structure of the soft-sediment benthic fauna of the continental slope is still unknown. Characterization and understanding of the Brazilian continental slope biota are imperative since human activities are increasing in the last decades, especially after the discovery of the pre-salt reservoir in Santos Basin. In this study, we aimed to establish a baseline of the spatial distribution of the benthic macrofaunal communities regarding their latitudinal and bathymetric patterns in the Santos Basin to support future environmental monitoring activities in the region. As part of the Santos Project - The Santos Basin Regional Environmental Characterization (PCR-BS) - coordinated by CENPES/PETROBRAS, a benthic oceanographic cruise was carried out in 2019. Sediment samples were collected using a GOMEX-type box corer in 47 stations distributed in eight transects (4002,400 m depth range). In total, 12 additional stations (1,300-2,200 m) were defined to cover an area where oil and gas are exploited. Our results showed that macrofaunal assemblages of the Santos Basin present strong depth zonation related to changes in organic matter input, as well as to temperature, carbonate, and grain size. At local scale, the northern sector stood out for having a higher abundance of macrofauna in the upper slope (400 m) and it probably reflects the oceanographic processes and the organic enrichment caused by the upwelling events that occur at Cabo Frio region. The zonation pattern and the dominance of some polychaete, peracarid crustacean, and bivalve families were similar to other SE Brazilian continental margins. [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]

This study aimed to characterize the spatial distribution and composition of living Benthic Foraminifera (BF) and to comprehend how environmental conditions (e.g., organic matter) can affect communities of these protozoa in the northern and southern sectors of the Santos Basin (SB), in the continental slope and São Paulo Plateau. In this context, 23 stations (65 samples including replicates at each station) were collected between 400 and 2,400 m water depth. Multivariate analyses revealed that the ecological structure of the community changes mainly along the bathymetric gradients. Stations located between 400 and 700 m, both in northern and southern sectors, are characterized by the presence of indicator species of high intensity of currents, such as Globocassidulina subglobosa and Trifarina bradyi. These stations are also mainly marked by the occurrence of Epistominella exigua, a phytodetritivore species. The stations at 1,000 and 1,300 m depth, in both sectors, are characterized by high accumulation of organic matter in the sediments, which favors the development of agglutinated foraminifera species, such as those of the genus Reophax. Finally, the lower slope and the São Paulo Plateau, in both sectors, are oligotrophic regions, with pulses of labile organic carbon, probably low current velocities and the presence of Alabaminella weddellensis. The quantity and quality of food, which are closely related to hydro-sedimentary dynamics and bentho-pelagic coupling in the slope and São Paulo Plateau, are the main factors that influence the distribution of living BF assemblages in the SB. [ABSTRACT FROM AUTHOR]

Based on high‐quality two‐dimensional seismic profiles and well data, the seismic reflection characteristics from the late Pliocene and Pleistocene succession of the Qiongdongnan Basin in the South China Sea have been analysed. The result will help in understanding the sedimentological development of slope areas. Twenty coeval clinothems are recognized and four major clinothem types are distinguished. In addition, three types of shelf‐edge trajectories are recognized. The various parameters of the clinothems are analysed quantitatively and the relationships between the various clinothem types are studied in combination with the controlling roles. It is concluded that: (i) the shelf‐edge trajectories are related to the type of clinothem; (ii) fluctuations in the relative sea level, in combination with variations in sediment supply, result in different clinothem types and geometric parameters; these parameters show interdependencies; (iii) the alternations of progradation and aggradation of clinothems may provide information of the relative sea level and changes in sediment supply; (iv) some lowstand fans could develop at the foot of the slope in the central–eastern part of the basin when the relative sea level started to fall or began to rise. The results of the present study are consequently significant for further quantitative analyses of the characteristics and development of the continental slope, not only in the Qiongdongnan Basin, but also in other basins. [ABSTRACT FROM AUTHOR]

The Biophysical and Ecological Overview of the Fundian Channel-Browns Bank Area of Interest (AOI) summarizes what is known about key physical and biological components of the Fundian Channel-Browns Bank ecosystem. These key attributes and description of their ecosystem function can be used to inform the development of Conservation Objectives and management measures, should the study area be established as a Marine Protected Area under Canada's Oceans Act. The Fundian Channel-Browns Bank is an offshore AOI that includes representative portions of the continental slope, Browns Bank, Georges Basin, the Fundian Channel, and Northeast Channel. Diverse assemblages of fishes and invertebrates are associated with the correspondingly diverse topographic features and unique oceanographic processes of the area. Significant concentrations of corals and sponges have been identified within the Northeastern Channel Coral Conservation Area and southern Browns Bank that are encompassed by the proposed boundaries. High productivity within the AOI is linked to the unique oceanographic features including upwelling and circulation gyres, as well as dynamic features of the warm Gulf Stream. The AOI encompasses an area of highly suitable habitat for juvenile Atlantic Halibut, as well as several depleted species and species at risk including Atlantic Cod (Endangered - COSEWIC), Atlantic Wolffish (Special Concern - SARA), Cusk (Endangered - COSEWIC), Spiny Dogfish (Special Concern - COSEWIC), Smooth Skate (Special Concern - COSEWIC), Thorny Skate (Special Concern - COSEWIC), and White Hake (Threatened - COSEWIC). The area also encompasses foraging habitats for cetaceans, sea turtles and large pelagic fishes such as Bluefin Tuna and Swordfish. The Fundian Channel-Browns Bank area is also noted as important foraging ground for most functional guilds of marine birds, including several species listed by SARA and the IUCN. [ABSTRACT FROM AUTHOR]

Turbidity currents commonly bypass sediment in submarine channels on the continental slope, and deposit sediment lobes farther down-dip on the flat and unconfined abyssal plain. Seafloor and outcrop data have shown that the transition from bypass to deposition usually occurs over complex zones referred to as channel–lobe transition zones (CLTZs). Recognition of these zones in cores and outcrop remains challenging due to a lack of characteristic sedimentary facies and structures. This paper focuses on Unit E of the Permian Fort Brown Formation in the Karoo Basin, South Africa, in the Slagtersfontein outcrop complex, which has previously been interpreted as a CLTZ. This study integrates thin-section micrographs, sedimentary facies, bed-set and stratigraphic architecture, and palaeoflow directions to achieve a multiscale analysis of CLTZ features. A novel process-based facies scheme is developed to evaluate deposits in terms of the depositional or erosional tendencies of the flows that formed them. This scheme allows bypass to be distinguished from depositional zones by the spatial distribution of certain sediment facies. Areas of net sediment bypass were predominantly marked by erosive sediment facies and a larger variability in palaeoflow direction while depositional areas showed a lower variability in palaeoflow directions. Metre-scale structures in the bypass-dominated area reveal seafloor erosion and scour formation. Field relations suggest the presence of a ∼500 m long mega-scour in the CLTZ. The characteristic structures documented here are applicable for identifying CLTZs in sparse datasets such as outcrops with limited palaeogeographical context and sediment cores obtained from subsurface systems. [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]

Small copepod genera play an important role in marine food webs and biogeochemical fluxes but have been neglected in many studies. This is the first study determining biomass, carbon consumption and egestion rates of small- (<1 mm prosome length, PL), medium- (1–1.5 mm PL) and large-sized (>2 mm PL) copepods along a cross-shelf transect in the southern Benguela upwelling system. Calanoids contributed on average 55 ± 19% to total copepod abundance and 82 ± 13% to total copepod biomass. Small-sized Oithona spp. (114–119 mg C m−2 d−1) and Clausocalanidae/Paracalanidae (87–263 mg C m−2 d−1) as well as large-sized Calanoides natalis (47–193 mg C m−2 d−1) were the dominant consumers at the most inshore stations. Small- and medium-sized copepodite stages of Metridia lucens were also important, especially towards the continental slope. At offshore stations, Clausocalanidae/Paracalanidae, Oithona spp. Pleuromamma spp. Calanus agulhensis , Acartia spp. C. natalis and M. lucens were dominant consumers. Hence, usually small- and medium-sized copepods dominated total copepod ingestion and egestion, emphasizing that inadequate representation of small copepods will lead to significant underestimations and misinterpretations of the functioning of zooplankton communities and finally to inadequate biogeochemical models. [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]

We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (>0.30 m s−1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s−1 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with‐ and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf‐processes and advection of seasonal‐variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway. Plain Language Summary: We assessed the structure and seasonal variability of the flow and water masses of the Arctic Boundary Current (ABC) in the region north of Severnaya Zemlya. This current is important in the Arctic Ocean as it transports relatively warm and saline waters along the Eurasian Arctic continental slope. We quantified the flow, transport and hydrographic variability of the ABC. Compared to observations from upstream, our results indicate that the water masses away from the shelf break maintained the hydrographic characteristics from upstream. In contrast, the water masses near the shelf break were significantly cooled and freshened due to intrusion of‐ and mixing with shelf waters. The water masses near the shelf break showed a seasonal signal in volume transport and temperature which derives from local shelf processes, advection of seasonal‐variable waters along the ABC pathway and the seasonal cooling of the Barents Sea. If the warming trend in the Barents Sea continues, warmer waters are expected to be advected eastward along the Eurasian continental slope by the ABC. Key Points: We quantify the Arctic Boundary Current (ABC) transport north of Severnaya Zemlya with a 2015–2018 mooring arrayHydrographic changes along the ABC pathway are most prominent at the continental slope due to the interaction with shelf waterSeasonality of water masses from the shelf sea was observed in transport, temperature and off‐shelf excursions within the ABC [ABSTRACT FROM AUTHOR]