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Depth‐averaged eddy buoyancy diffusivities across continental shelves and slopes are investigated using a suite of eddy‐resolving, process‐oriented simulations of prograde frontal currents characterized by isopycnals tilted in the opposite direction to the seafloor, a flow regime commonly found along continental margins under downwelling‐favorable winds or occupied by buoyant boundary currents. The diagnosed cross‐slope eddy diffusivity varies by up to three orders of magnitude, decaying from O104m2/s $\mathcal{O}\left(1{0}^{4}\hspace*{.5em}{\mathrm{m}}^{2}/\mathrm{s}\right)$ in the relatively flat‐bottomed region to O10m2/s $\mathcal{O}\left(10\hspace*{.5em}{\mathrm{m}}^{2}/\mathrm{s}\right)$ over the steep continental slope, consistent with previously reported suppression effects of steep topography on baroclinic eddy fluxes. To theoretically constrain the simulated cross‐slope eddy fluxes, we examine extant scalings for eddy buoyancy diffusivities across prograde shelf/slope fronts and in flat‐bottomed oceans. Among all tested scalings, the GEOMETRIC framework developed by D. P. Marshall et al. (2012, https://doi.org/10.1175/JPO-D-11-048.1) and a parametrically similar Eady scale‐based scaling proposed by Jansen et al. (2015, https://doi.org/10.1016/j.ocemod.2015.05.007) most accurately reproduce the diagnosed eddy diffusivities across the entire shelf‐to‐open‐ocean analysis regions in our simulations. This result relies upon the incorporation of the topographic suppression effects on eddy fluxes, quantified via analytical functions of the slope Burger number, into the scaling prefactor coefficients. The predictive skills of the GEOMETRIC and Eady scale‐based scalings are shown to be insensitive to the presence of along‐slope topographic corrugations. This work lays a foundation for parameterizing eddy buoyancy fluxes across large‐scale prograde shelf/slope fronts in coarse‐resolution ocean models. Plain Language Summary: Understanding the future climate relies on numerical predictions from climate models. However, these models are limited in accuracy because they cannot resolve all crucial processes in the climate system due to computational resource limitations. One such process is the oceanic "mesoscale" turbulence (swirling ocean flows that are tens to hundreds of kilometers wide) across continental margins. These flows impact coastal circulation and ecosystems by mediating material exchanges between coastal and open‐ocean environments. By running computer simulations that can explicitly resolve mesoscale turbulence, we show that heat transport by mesoscale flows becomes less efficient over continental margins than that in the open ocean, due to the presence of the sloping seafloor. After taking this reduced efficiency into account, we are able to predict the heat transport by mesoscale flows across continental margins by adapting established theories for the open‐ocean environment. This work provides a basis for improving the performance of climate models, especially near coastal regions. Key Points: Process simulations of eddy buoyancy fluxes across prograde shelf and slope fronts are conductedThe GEOMETRIC scaling and the Eady scale‐based scaling for eddy buoyancy fluxes are adapted to continental slopesA basis for parameterizing eddy buoyancy fluxes across prograde fronts is presented [ABSTRACT FROM AUTHOR]

The systematics of REE, Sc, Cr, Zr, and Th in silty-pelitic and pelitic surface bottom sediments sampled during cruises 71, 75, 77, and 80 of the R/V Akademik Mstislav Keldysh in the Nordic Seas is considered. It is shown that the geochemical features of silts in a number of regions (the southern part of the Kolbeinsei Ridge, the continental slope of Norway, the northern end of Mona Ridge) indicate the presence in their composition of a significant (30–40%) proportion of erosion products of basic rocks. Other possible source rock assemblages of fine-grained aluminosiliciclastics for the analyzed bottom sediments were apparently similar in their geochemical characteristics to the basement rocks, supracrustal formations, and leucogranites of the Caledonides of East Greenland, the anorthosite–mangerite–charnockite–granite (AMCG) association of the Lofoten Islands, and a number of other objects. [ABSTRACT FROM AUTHOR]

General distribution patterns for japanese sandfish Arctoscopus japonicus in Peter the Great Bay in spring, summer, and fall, which are related to the water structure, are determined from the bottom trawl survey data. When the larval stage is finished, the sandfish underyearlings appear in trawl catches since July and are recorded at the depths of 23–60 m in July–August at water temperature of 8–16°С. Judging from localization of catches at the upper benthic front, they lead a pelagic mode of life in summer, concentrating above the seasonal pycnocline, so belts of high catches by bottom trawl are located along the line of pycnocline contact with the bottom. In the fall season, the underyearlings pass to bottom dwelling below the upper benthic front. The adults dwell permanently at the bottom, in the subsurface shelf waters. Their feeding starts near the coast in May–June, avoiding the remnants of the cold bottom shelf water, and they gradually retreat deeper in July-September. Prespawning aggregations are formed at the shelf edge and on the upper continental slope in October. The spawners migrate to the coastal zone in November for spawning on seaweeds. For wintering, the sandfish adults may leave Peter the Great Bay, moving to the more southern areas. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) in soft tissues of 41 abundant macrobenthic species from the continental slope of the Sea of Okhotsk were determined. The δ15N and δ13С values of invertebrate species and groups studied were highly variable, reflecting the diversity of their ratio compositions. The range of δ 15N values (from 6.8 to 18.3‰) corresponded to four trophic levels: from second (for detritivorous bivalve molluscs) to fifth (for some species of carnivorous gastropods and starfish). [ABSTRACT FROM AUTHOR]

This study analyses data assimilative numerical simulations in an eddy-dominated western boundary current: the East Auckland Current (EAuC). The goal is to assess the impact of assimilating surface and subsurface data into a model of the EAuC. We used the Regional Ocean Modelling System (ROMS) in conjunction with the 4-dimensional variational (4D-Var) data assimilation scheme to incorporate sea surface height (SSH) and temperature (SST), and subsurface temperature, salinity, and velocities from three moorings located at the upper, mid and lower continental slope using a 7-day assimilation window. Assimilation of surface fields (SSH and SST) reduced SSH root mean square deviation (rmsd) in relation to the non-assimilative (NoDA) run. The inclusion of velocity subsurface data reduced SSH rmsd up- and downstream of the moorings. By improving the representation of the mesoscale eddy field, data assimilation increased complex correlation between modelled and observed velocity in all experiments. However, the inclusion of temperature and salinity slightly decreased the velocity complex correlation. The assimilative experiments had smaller SST rmsd in comparison to the NoDA run. The lack of sub-surface temperature for assimilation led to larger errors (>1 °C) around 100 m in relation to the NoDA run. Comparisons to independent Argo data showed similar results. Withholding subsurface temperature forces near-surface average negative temperature increments that are corrected by increased net heat flux at the surface which does not affect waters at 100 m depth. Assimilation of mooring temperature generates increments to the initial conditions that reduces 100 m water temperature rmsd. Larger positive wind stress curl was generated in experiments that assimilated subsurface temperature data. Positive wind stress curl generates convergence and downwelling which is another way of correcting the upper thermocline cold bias. The larger positive wind stress curl might also be responsible for decreased velocity correlation in the experiments that assimilated temperature and salinity. The few moored CTDs (8) had little impact in correcting salinity, however, using doubled decorrelation length scales of tracers and a 2-day assimilation window improved model salinity in comparison to independent Argo data. In addition, the results were similar to the global reanalysis HYCOM-NCODA which assimilates Argo profiles and was used as boundary condition. HYCOM-NCODA had near zero velocity complex correlation on the mid-slope, whereas all reanalyses showed improved results which highlights the benefit of downscaling to a regional model of the EAuC. [ABSTRACT FROM AUTHOR]

Recent studies suggest that the South Brazil Bight (SBB) hosts strong westward propagating mesoscale eddies. We use 28 years of satellite altimetry data and a new Eddy Atlas to estimate how much of the eddy kinetic energy (EKE) observed in the SBB is accounted for by local eddies, generated in the Brazil Current (BC) region, versus remote eddies generated eastward of the BC region. First, we estimate a BC frontal density to obtain a robust definition of BC region. The BC front is well-defined throughout the SBB, occupying the region between the 200-m and 1000-m isobath, except in eddy hotspots downstream of sharp inflections of the continental slope, where the EKE far exceeds the mean kinetic energy (MKE). Compact, closed-contour mesoscale eddies account for 30–50% of the total EKE observed in the SBB, with local eddies accounting for most of the compact EKE in the BC region, defined as the area within 200 km of the 28-year mean BC front. Remote compact eddies account for less than 10% of the EKE observed in the BC region; compact eddies generated at long distances from the SBB, including eddies generated in the Southeastern Atlantic, contribute an insignificant fraction of EKE in the BC region. [ABSTRACT FROM AUTHOR]

The sea surface expressions of Mediterranean Water eddies, known as "meddies," are observed in satellite data, and their main characteristics are measured. Satellite altimeter observations of surface expressions are detected over the meddies observed in situ using the MEDTRANS meddy dataset (1950–2013). In this study 209 observed meddy cores in the North Atlantic Ocean, selected over the period of the 22 years of sea surface height measurements with satellite altimetry (1993–2013), were analyzed. Results show relatively good agreement between the theoretical estimates of the meddy surface signals as reported by Bashmachnikov and Carton and the measured surface expressions. It was found that, on average, the theoretical results underestimate the measured sea surface elevations of the meddy surface expressions by a factor of 2. Although the variability of the measured expressions is reasonably well described by the combination of meddy core and the ocean background parameters of the theoretical expression, we cannot define a single individual parameter of the meddy core, which chiefly shapes the magnitude of the meddy surface signal. Interestingly, the overall distribution of characteristics of meddy surface expressions in the Atlantic shows that the sea level anomalies formed by meddies intensify westward, growing both in magnitude and radius. This opposes the expected theoretical decrease of meddy surface signals due to a known progressive decay of the meddy cores with distance from their generation region at the Iberian continental slope. This observed tendency is attributed to meddy interaction with the upper-ocean currents and other eddies (in particular in the region of the North Atlantic Current and Azores Current) that are not considered by the theory. [ABSTRACT FROM AUTHOR]

The winter–summer transition in the southern South China Sea (SCS) western boundary current (WBC) is studied. Two categories have been identified. In case 1, the southern SCS WBC transition in the lower layer (below the thermocline) lags that in the upper layer (above the thermocline). In case 2, there is no transition lag at full depth. In both categories, the geostrophic balance dominates the transition. In case 1, the upper layer geostrophic balance is dominated by the sea surface height pressure gradient (SSHPG) and Coriolis forcing during southern SCS WBC transition. Therefore, there is no transition lag with depth in the upper layer. Below the thermocline layer, the competition between the SSHPG and the density pressure gradient (DPG) determines the transition. During the transition, the amplitudes of the SSHPG and DPG are basically equivalent. The SSHPG needs time to develop sufficiently larger than the DPG. Therefore, the transition in the deeper layer significantly lags that in the shallower layer. The reversal of the SSHPG is mainly attributed to the change in the basin-scale wind stress curl over the southern SCS. The change in the DPG is mainly associated with the cooling of the water along the western continental slope, which is induced by upwelling. In case 2, there is no cooling along the western continental slope, and then the amplitude of the DPG is always far smaller than that of the SSHPG. Responding to the change in the SSHPG, the southern SCS WBC transition behaves consistently at full depth. Significance Statement: We have a comprehensive understanding of the South China Sea (SCS) circulation patterns in winter and summer. However, their seasonal transitions remain unclear, and a better understanding of them is potentially helpful for improving ocean circulation modeling and prediction. This paper focuses on the winter–summer transition in the SCS western boundary current (WBC). Above the thermocline (∼100 m), the transition behaves consistently in the vertical direction and is controlled by the conversion of the sea surface height–induced pressure gradient. Below the thermocline, the transition in the deeper layer of the WBC significantly lags that in the shallower layer of the WBC, which is associated with the competition between the SSH-induced pressure gradient and the density-induced pressure gradient at the sea surface. [ABSTRACT FROM AUTHOR]

Deep-water fold-and-thrust belt (DWFTB) systems are gravity-driven collapse structures often found in passive margin settings and are comprised of a linked up-dip extensional domain, central transitional/translational domain, and down-dip compressional domain. Many Late Cretaceous DWFTB systems occur along the SW African passive margin with multiple, over-pressurized, seaward-dipping shale detachment surfaces accommodating gravitational slip. In this study we use 3D reflection seismic data to constrain the strato-structural evolution of the translational and compressional domains of a Late Cretaceous DWFTB system and the overlying Cenozoic deposits in the Orange Basin, South Africa. The stratigraphy and structure of the Late Cretaceous DWFTB system is shown to have controlled fundamental sedimentary processes and the stability of the evolving margin. The compressional domain exhibits large-scale landward-dipping DWFTBs with thrust faults detaching the main Turonian shale detachment surface at depth and terminating at the early Campanian surface. A major ∼ 7 km wide seafloor slump scar reflecting margin instability occurs directly above a syncline of the same width from the buried DWFTB system's compressional domain. The translational domain is imaged as a complex region displaying overprinted features of both extensional and compressional tectonics with the downslope translation of sediment comprising listric normal and then thrust and oblique-slip faults distally. Thrust sheets are segmented along strike by extensive oblique-slip faults which extend from the translational domain into the down-dip compressional domain. Smaller, localized fold-and-thrust belts are found directly below the kilometre-scale DWFTB system in the down-dip compressional domain detaching a lower, Albian shale detachment surface which corresponds to an older gravitational collapse. The upward propagation of normal and oblique-slip faults with progressive sedimentation is hindered by the Oligocene or Miocene stratigraphic markers corresponding to mass erosional processes in the Cenozoic. A large (∼ 2.3 km wide), roughly slope-perpendicular Oligocene submarine canyon formed by turbidity currents is attributed to a major sea-level fall at ∼ 30 Ma. Oceanographic circulation is shown to have held a significant control on the deposition of mid-Miocene to present-day sedimentary sequences. Between 1200 to 1500 m water depths along the upper continental slope well-preserved extensive slope-parallel, sinusoidal channel-like features occur on the Miocene stratigraphic marker. The channels are confined within a ∼ 14 km wide zone at the interface of the upper northward-flowing Antarctic Intermediate Water (AAIW) and deeper southward-flowing North Atlantic Deep Water (NADW) currents. The erosive interaction of these oppositely flowing bottom currents combined with the effects of the Benguela Upwelling System (BUS), all of which formed or intensified at ∼ 11 Ma, are responsible for the creation and preservation of the extensive slope-parallel channels. This study shows the difference in structural styles of the translational and compressional domains of a Late Cretaceous DWFTB system and the processes responsible for mass-scale erosion in the Cenozoic. [ABSTRACT FROM AUTHOR]

The global ocean mass has significantly changed during recent decades, which may induce changes in the abyssal ocean circulation. Due to the lack of in situ observations, the response of the abyssal South China Sea (SCS) circulation to ocean mass changes remains unclear. The ocean state estimate, Estimating the Circulation and Climate of the Ocean (ECCO), provides the long‐term ocean mass changes in terms of ocean bottom pressure (OBP). Here we use the ECCO OBP data to quantify decadal changes in the abyssal SCS circulation and reveal a weakening trend. The OBP gradient trend manifests in forms of an anomalous anticyclonic circulation that is intensified by topographic effects along the continental slopes to reduce the existing abyssal circulation. The weakening abyssal circulation corresponds to the weakening Luzon Strait overflow that yields a decreasing vorticity budget in the abyssal SCS. Plain Language Summary: Caused by global warming, ice melt and long‐term atmospheric forcing changes, ocean mass has been increased and redistributed over the past decades. The changes in ocean mass distribution may lead to changes in abyssal ocean circulation. The changes in the abyssal South China Sea (SCS) circulation remains unclear due to the lack of in situ observations. This study uses the Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to quantify decadal changes in the abyssal SCS circulation. Our analysis of the ECCO ocean bottom pressure data reveals a weakening trend in the abyssal SCS circulation that is consistent with the recently ascertained weakening Luzon Strait overflow. Key Points: Trends in the ECCO ocean bottom pressure (OBP) gradients indicate a decadal weakening abyssal South China Sea (SCS) circulationThe weakening circulation coincides with the weakening Luzon Strait overflow that yields a decreasing vorticity budget in the abyssal SCSThe anomalous anticyclonic circulation is dominated by OBP gradient trends and intensified by topographic effects along continental slopes [ABSTRACT FROM AUTHOR]

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

Submarine earthquakes have increased in the southwestern Ulleung Basin adjacent to the Korean Peninsula. This study analyzed the gravitational and magnetic properties of the three earthquake-prone areas (Hupo Bank and offshore regions near Pohang and Ulsan) in the basin. The basin was affected by tensile and compressive stresses during the formation of the East Sea. The southern Hupo Bank and the Pohang offshore exhibited high gravity anomalies and strong magnetic anomalies. Hupo Bank was separated from the peninsula and earthquakes in this region have been influenced by crustal fractures that facilitated igneous activities during the formation of the basin. Dense volcanic rocks and seaward dipping reflectors along the Pohang coast and continental slope suggest magmatic activities during the formation of the East Sea. Comparatively, the Ulsan offshore, with a thick sedimentary layer, exhibited a slightly higher gravity anomaly than the surrounding area, but no significant differences in the magnetic anomaly. Sequential tensile and compressive stresses related to the creation of the basin produced complex tectonic structures in this region. The magnetic tilt derivative results suggest that earthquakes were located near magnetic source boundaries. The results show that it is important to monitor earthquake-prone areas with gravity and magnetic anomalies. [ABSTRACT FROM AUTHOR]

The lithological study of Recent sediments, as well as planktonic foraminiferal tests and macrobenthos therein, within transverse sections of four submarine canyons in the northern sector of the Argentine Patagonia gravitite–contourite system revealed a considerably more complex facies variability within the canyons than on the Perito Moreno Terrace between them. The facies variability in canyons is controlled by a combination of along-slope contour currents and down-canyon gravity flows. Two southern canyons contain the channel facies of terrigenous glauconite-rich sand that separate the flank facies of sand with a high content of foraminiferal tests. Two northern canyons include the facies of mixed sediments with a high content of <0.1 mm fraction, whose analogs are lacking on the surrounding terrace. They were likely deposited from the down-canyon gravity flows of dense suspension in the still-water bottom environment. Attached macrobenthos with calcareous skeletal elements (commonly corals) inhabits the mainly ice- or iceberg-rafted coarse rock fragments in all canyons and on the surrounding Perito Moreno Terrace. [ABSTRACT FROM AUTHOR]

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

The Vp/Vs kinematic parameter for the Kamchatka seismic subduction zone has been long monitored on a regular basis. This has allowed estimating the behavior of the parameter and revealing its features during the precursory period and actual rupturing of the March 25, 2020 earthquake which occurred in the Pacific plate at the contact between the Pacific plate and the continental slope of Kamchatka. The March 25, 2020 earthquake with its high magnitude (ML = 7.6, MW = 7.5) is a rare enough event to occur in the Pacific plate. Knowledge of earth structure in the source region of the earthquake was updated based on the results of deep seismic sounding and continuous seismic profiling which was carried out in the area in the past. It was shown that the earthquake source area is at an inflection in the descending Pacific plate. The source area lies in the layer at the boundary between the asthenosphere and the crust and mantle. The layer is at depths of 30‒60 km and has lower Vp and Vs velocities. The inflection region along Kamchatka shows lower Vp/Vs values, which is a sign of extension along the plate. The source area is in the contact between the Pacific plate, which is subducting under the southern end of Kamchatka, and the North Kuril Islands, as well as the Sea-of-Okhotsk plate. The region shows a distinct change in the anomalous values of the parameter from lower to higher, with the latter being typical for compression. Our study has allowed estimating possible regions of tension and compression in the geological medium. [ABSTRACT FROM AUTHOR]

The distribution map of submarine landslides in the Sea of Okhotsk based on compilation of available data is presented in this work for the first time. This map is indicative of environments and trigger mechanisms of landsliding. All gravitational processes studied in this work occurred in the environments of an open continental slope and submarine canyons. The most obvious trigger mechanisms of landslides on the Eastern Sakhalin slope are seismic activity and gas seeping. The main trigger mechanism of landslides on the northern slope of the Kuril Basin and in the back-arc basin of the Kuril island arc is seismic activity. [ABSTRACT FROM AUTHOR]

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

The mineral and bulk chemical (basic rock-forming oxides) composition of more than 20 samples of surface bottom sediments taken on a number of cruises of R/V Akademik Mstislav Keldysh in the Nordic Seas (the Mona, Knipovich, Kolbeinsey, and Aegir ridges, the basins of the Norwegian and Greenland seas, the continental slope of Svalbard, the western continental margin of the Barents Sea, etc.) is considered. One of the goals of these cruises was a comprehensive study of the sedimentary system of the Nordic Seas. Our data on the distribution of quartz and calcite in the sediments confirm the idea that the composition of surface bottom sediments at coastal stations is affected by the material coming from the land, while the seaward sediments are affected by the relatively warmer Atlantic waters, leading to their dilution with calcium carbonate, which are mainly produced by planktonic foraminifera. The absence of a correlation between /SiO2 and Al2O3/SiO2 indicates the effect of mineralogical sorting is not pronounced in the sediments. The distribution of the data points of surface bottom sediments on the Ti/Al–1000*(Cr/Al) diagram is considered. It is concluded that the source of fine aluminosiliciclastics for most of the studied samples is both acidic and basic igneous rocks (volcanic rocks of Iceland) in different proportions. The value of Strakhov's modulus in the entire sample ranges from 5 to 10. This gives grounds to believe that no products of hydrothermal activity were introduced into the surface bottom sediments of the areas studied by us. [ABSTRACT FROM AUTHOR]

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

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

An autonomous lander equipped with a video camera (dropcam) was used for in situ observations of the bento-demersal macrofauna on the upper continental slope off Punta Pichalo in northern Chile, an area of permanent coastal upwelling processes, located ~70 km north of Iquique. The lander was deployed at nine stations and between 227 and 798 m of depth. According to morphological characteristics, 34 operational taxonomic units (OTUs) were identified to the lowest taxonomic level; 24 belonged to macroinvertebrates and 10 to fishes. Macroinvertebrates comprised 9 OTUs of crustaceans, seven cnidarians, and six echinoderms. Fishes included 3 OTUs of the order Chondrichthyes, 3 belonging to macrourid. Perciformes, Anguilliformes, and Alepocephaliformes were represented by one OTU each. Also, we observed one species of lanternfish (Myctophidae). Apart from the brachyuran decapod Lophorochinia parabranchia Garth, 1969 and euphausiids, all species were observed at depths greater than 560 m. The presence of one individual identified as the granulate dogfish Centroscyllium granulatum Günther, 1887 extended the known distribution range of this species about 1000 km to the north. Images taken at 795 m showed Bathyraja peruana McEachran & Miyake, 1984. Our study suggests that the upper continental slope of northern Chile harbors nearly undiscovered biodiversity, worth to be studied more intensively to complete the comparable sparse knowledge about marine biodiversity and species distribution at the continental margin in front of Chile. [ABSTRACT FROM AUTHOR]

It is this pressure sensor that gives the depth of the ADCP transducer, and the incorrect pressure data implies that the depths of the ADCP bins in the water column above the transducer are erroneous. Since data from BKD7A were not available for more than a month, the data from the 75 kHz ADCP deployed as BKD7B were used during 2016-2017; this ADCP did not yield data in the top ~60 m and, therefore, the current at 48 m could not be estimated off Kakinada for this deployment. Table 3 ADCP mooring details for the mooring on the continental slope of Kakinada. [Extracted from the article]

Western Atlantic bluefin tuna (ABT) undertake long-distance migrations from rich feeding grounds in the North Atlantic to spawn in oligotrophic waters of the Gulf of Mexico (GoM). Stock recruitment is strongly affected by interannual variability in the physical features associated with ABT larvae, but the nutrient sources and food-web structure of preferred habitat, the edges of anticyclonic loop eddies, are unknown. Here, we describe the goals, physical context, design and major findings of an end-to-end process study conducted during peak ABT spawning in May 2017 and 2018. Mesoscale features in the oceanic GoM were surveyed for larvae, and five multi-day Lagrangian experiments measured hydrography and nutrients; plankton biomass and composition from bacteria to zooplankton and fish larvae; phytoplankton nutrient uptake, productivity and taxon-specific growth rates; micro- and mesozooplankton grazing; particle export; and ABT larval feeding and growth rates. We provide a general introduction to the BLOOFINZ-GoM project (Bluefin tuna Larvae in Oligotrophic Ocean Foodwebs, Investigation of Nitrogen to Zooplankton) and highlight the finding, based on backtracking of experimental waters to their positions weeks earlier, that lateral transport from the continental slope region may be more of a key determinant of available habitat utilized by larvae than eddy edges per se. [ABSTRACT FROM AUTHOR]

The 2022 volcanic eruption in Tonga caused an unusually large tsunami around the Pacific. It travels with a faster apparent velocity and has larger amplitudes at long distances than what would be expected from a conventional tsunami from the volcanic source. This tsunami was generated by the moving atmospheric Lamb wave and traveled at the speed of the Lamb wave (0.31 km/s). Japanese data showed the amplitude of this first tsunami becomes small when approaching the coast, due to the weaker air‐sea coupling at the shallow depth. This wave split when passing the continental slope, and traveled at the speed of the ocean gravity wave. Therefore, the tsunami observed at the coast is delayed by thousands of seconds from the passage of the Lamb wave. Tsunamis generated by this atmospheric mechanism have not been previously observed by modern digital recording systems and should be considered in the tsunami warning systems. Plain Language Summary: A tsunami is usually generated by the sudden changes of the water heights, and caused by offshore earthquakes, coastal landslides, and submarine volcanic eruptions. The generated vertical displacement of the water propagates as a very long wave, and the tsunami waves become compressed with increased heights as they approach the coast. The 2022 volcanic eruption in Tonga caused an unusually large tsunami, which cannot be explained by conventional sources. The speed and amplitude are very different from theoretical values: the speed is about 0.31 km/s, whereas the average tsunami speed in the Pacific is 0.2 km/s. These data suggest that the tsunami from the Tonga eruption was excited by a pulse of atmospheric pressure as it traveled from the volcano. This source of the tsunami in the atmosphere needs to be considered for the tsunami warning system in the future. Key Points: Lamb wave produced by the volcanic eruption excites the sea surface as it travels across the Pacific and generates a tsunami pulseThe effect of the air‐sea coupling becomes weaker as the Lamb wave approaches the coastThe tsunami wave splits when passing the continental slope of Japan causing more complex waves [ABSTRACT FROM AUTHOR]

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

Coastal trapped waves (CTWs) transport energy along coastlines and drive coastal currents and upwelling. CTW modes are nonorthogonal when frequency is treated as the eigenvalue, preventing the separation of modal energy fluxes and quantification of longshore topographic scattering. Here, CTW modes are shown to be orthogonal with respect to energy flux (but not energy) when the longshore wavenumber is the eigenvalue. The modal evolution equation is a simple harmonic oscillator forced by longshore bathymetric variability, where downstream distance is treated like time. The energy equation includes an expression for modal topographic scattering. The eigenvalue problem is carefully discretized to produce numerically orthogonal modes, allowing CTW amplitudes, energy fluxes, and generation to be precisely quantified in numerical simulations. First, a spatially uniform K1 longshore velocity is applied to a continental slope with a Gaussian bump in the coastline. Mode-1 CTW generation increases quadratically with the amplitude of the bump and is maximum when the bump's length of coastline matches the natural wavelength of the CTW mode, as predicted by theory. Next, a realistic K1 barotropic tide is applied to the Oregon coast. The forcing generates mode-1 and mode-2 CTWs with energy fluxes of 6 and 2 MW, respectively, which are much smaller than the 80 MW of M2 internal-tide generation in this region. CTWs also produce 1-cm sea surface displacements along the coast, potentially complicating the interpretation of future satellite altimetry. Prospects and challenges for quantifying the global geography of CTWs are discussed. [ABSTRACT FROM AUTHOR]

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

The storm surge and hydrodynamics along the Krishna–Godavari (K–G) basin are examined based on numerical experiments designed from assessing the landfalling cyclones in Bay of Bengal (BoB) over the past 38 years with respect to its highest maximum sustained wind speed and its duration. The model is validated with the observed water levels at the tide gauge stations at Visakhapatnam during 2013 Helen and 2014Hudhud. Effect of gradual and rapid intensification of cyclones on the peak water levels and depth average currents are examined and the vulnerable locations are identified. The duration of intensification of a rapidly intensifying cyclone over the continental shelf contributed to about 10–18% increase in the peak water levels, whereas for the gradually intensifying cyclone the effect is trivial. The inclusion of the wave-setup increased the peak water levels up to 39% compared to those without wave-setup. In the deep water region, only rapidly intensifying cyclones affected the peak MWEs. Intensification over the continental slope region significantly increases the currents along the shelf region and coast. The effect on peak maximum depth averaged current extends up to 400 km from the landfall location. Thus, it is necessary to consider the effect of various combinations of the highest cyclone intensity and duration of intensification for identifying the worst scenarios for impact assessment of coastal processes and sediment transport. The study is quite useful in improving the storm surge prediction, in preparedness, risk evaluation, and vulnerability assessment of the coastal regions in the present changing climate. [ABSTRACT FROM AUTHOR]

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

Deep-water corals and sponges provide habitat complexity and shelter for many fauna, contributing to the health of deep-sea ecosystems. However, these taxa are vulnerable to anthropogenic disturbances such as fishing and climate change because they grow slowly and have long life spans. This vulnerability has led to the protection of several deep-water coral and sponge aggregations globally, as Vulnerable Marine Ecosystems. On the continental shelf and slope in Atlantic Canada protection targets the gorgonian corals Paragorgia arborea and Primnoa resedaeformis, and the sponge Vazella pourtalesi. Populations of these three species are discontinuous and spatially fragmented, making self-recruitment and population connectivity important factors in regulating population persistence. However, measures of recruitment are lacking. We used a Remotely Operated Vehicle to collect high resolution video of coral and sponge distribution and size frequency at three locations in the Corsair and Georges Canyons Coral Conservation Area and Northeast Channel Coral Conservation Area on 18–24 June 2019. Analysis revealed evidence of high coral recruitment at two locations on the continental slope off Nova Scotia, and high sponge recruitment at one location. To our knowledge, such high natural recruitment of deep-water corals and sponges has not been recorded elsewhere in the deep sea. Size frequency distributions varied with depth, likely because of differences in larval supply, or post-settlement disturbance due to faunal movement and unstable substrate. The results from this study can be incorporated into high resolution hydrodynamic modeling to assess population connectivity between populations of P. arborea, P. resedaeformis and V. pourtalesi and help identify potentially significant larval sources on the Scotian continental margin. Our results also can also inform ecological risk assessments, leading to more effective design of a network of Marine Protected Areas. [ABSTRACT FROM AUTHOR]

We report K–Pg-age deposits in Baja California, Mexico, consisting of terrestrial and shallow-marine materials re-sedimented onto the continental slope, including corals, gastropods, bivalves, shocked quartz grains, an andesitic tuff with a SHRIMP U–Pb age (66.12 ± 0.65 Ma) indistinguishable from that of the K–Pg boundary, and charred tree trunks. The overlying mudstones show an iridium anomaly and fungal and fern spores spikes. We interpret these heterogeneous deposits as a direct result of the Chicxulub impact and a mega-tsunami in response to seismically-induced landsliding. The tsunami backwash carried the megaflora offshore in high-density flows, remobilizing shallow-marine fauna and sediment en route. Charring of the trees at temperatures up to > 1000 °C took place in the interval between impact and arrival of the tsunami, which on the basis of seismic velocities and historic analogues amounted to only tens of minutes at most. This constrains the timing and causes of fires and the minimum distance from the impact site over which fires may be ignited. [ABSTRACT FROM AUTHOR]

This manuscript presents an inventory of the carbonate system from the main water masses comprising the marine current system on Brazil's northeast coast (South Atlantic Ocean). For this purpose, four transects were conducted with an approximate length of 357 km (each one) through the platform and continental slope of the Sergipe–Alagoas sedimentary basin. Water samples were then collected in vertical profiles measuring from 5 to 1,799 meters depth, totaling 34 stations. Total alkalinity, calcium, and total boron were obtained analytically from these samples and by relationships with salinity. Speciation and concentration of the carbonate system were obtained by means of thermodynamic modeling. The results revealed that the empirical models used to calculate the concentrations of TA, calcium and total boron showed relevant variation when compared to the analytical values (TA: 5.0–6.5%; Ca: 0.4–4.8%; BT: 7.0–18.9%). However, the speciation and concentration of the carbonate system (CA, DIC, CO32− , CO2(aq), ΩCalc, and ΩArag) obtained from the empirical values of TA, calcium and total boron did not differ significantly from those obtained analytically (0.0–6.1%). On the other hand, the parameters of pH, HCO3‐ , CO3(aq)2‐ , CO2(aq), ρCO2, ΩCalc, and ΩArag varied significantly within the different water masses (p < 0.05). This study supports and encourages acidification monitoring projects in the South Atlantic Ocean, based on modeling the carbonate system parameters generated in real-time. [ABSTRACT FROM AUTHOR]

Although the continental slope and abyss comprise the largest habitat on earth, the absence of documented fish sounds from deep waters is striking. Fishes with sexually dimorphic muscles attached to their swim bladders suggests that sounds are likely used in male courtship on the upper, mid and lower continental slope. To investigate the effects of environmental extremes on fish sound production, the acoustic behavior of a driven bubble is examined. This study is also relevant to target strength of sonar returns from fish and hearing in auditory specialist fishes. A bubble is a classic, if imperfect, model for swim bladder behavior since the swim-bladder wall is an anisotropic viscoelastic structure responsible for rapid damping. Acoustic properties of bubbles–including far-field resonant frequency, damping factor, and quality factor–are calculated in warm and cold surface conditions and in cold deep-water (depths 1000 m, 2000 m, and 3500 m) conditions using parameters for oxygen and nitrogen, the dominant gases in swim bladders. The far-field resonant frequency and damping factor of a bubble increase with depth, and the scattering cross-section and quality factor decrease with depth. These acoustic properties scale with undamped oscillation frequency of the bubble and do not vary significantly due to gas type or temperature. Bubbles in the deep-water environments are much less efficient radiators of sound than bubbles near the surface because the far-field radiated power for the same excitation decreases with depth. A bubble at depth 3500 m has a 25 dB loss in radiated sound power compared to the same-radius bubble at the surface. This reduction of radiation efficiency in deep water likely contributes to the absence of fish sound recordings in those environments. [ABSTRACT FROM AUTHOR]

This work presents an 8-years long dataset of monitoring activities conducted on the western margin of the Southern Adriatic Sea, where two moorings have been placed since 2012 in sites that are representative of different morpho-dynamic conditions of the continental slope (open slope vs. submarine canyon). The dataset includes measurements conducted with both current meters and CTD probes, and provides information about the hydrodynamics and thermohaline properties of the last 100 m of the water column. The hydrodynamics in both sites is dominated by weak currents (<0.1 ms-1), which undergo yearly to episodic pulsation able to exceed intensity greater than 0.5 ms-1 which are linked to the passage of dense waters. The 8-years records presented here, represents a starting point for the continuous observation activity set up on occasion of the "Operation Dense Water" in 2012, focused on the Southern Adriatic deep-water dynamic. Since then the observatory has been on-going since 2012 and the database is regularly updated. [ABSTRACT FROM AUTHOR]

Simple Summary: Patagonian moray cod is known to inhabit the cold waters near Antarctica, and it belongs to the Muraenolepis genus. This genus has seven species, and five of them are recently reported. The Muraenolepis genus has similar morphological characters, and this is a limitation of taxonomical classification. In this study, a genome survey and microsatellite marker analysis were conducted to characterize the genome profile for classification. As a result, genomic data such as genome size and microsatellite motifs were obtained. The Muraenolepididae family of fishes, known as eel cods, inhabits continental slopes and shelves in the Southern Hemisphere. This family belongs to the Gadiformes order, which constitutes one of the most important commercial fish resources worldwide, but the classification of the fish species in this order is ambiguous because it is only based on the morphological and habitat characteristics of the fishes. Here, the genome of Patagonian moray cod was sequenced using the Illumina HiSeq platform, and screened for microsatellite motifs. The genome was predicted to be 748.97 Mb, with a heterozygosity rate of 0.768%, via K-mer analysis (K = 25). The genome assembly showed that the total size of scaffolds was 711.92 Mb and the N50 scaffold length was 1522 bp. Additionally, 4,447,517 microsatellite motifs were identified from the genome survey assembly, and the most abundant motif type was found to be AC/GT. In summary, these data may facilitate the identification of molecular markers in Patagonian moray cod, which would be a good basis for further whole-genome sequencing with long read sequencing technology and chromosome conformation capture technology, as well as population genetics. [ABSTRACT FROM AUTHOR]

Deep-sea corals are important benthic inhabitants that support the biodiversity and function of the wider faunal community; however, their taxonomy is underdeveloped and their accurate identification is often difficult. In our study, we investigated the utility of a superextended (>3000 bp) barcode and explored the effectiveness of various molecular species delimitation techniques with an aim to put upper and lower bounds on the estimated number of calcaxonian species in Irish waters. We collected 112 calcaxonians (70 Keratoisididae, 22 Primnoidae, 20 Chrysogorgiidae) and one chelidonisid from the Irish continental slope and sequenced a 3390 bp DNA barcode comprising four mitochondrial regions (mtMutS, COI + igr1, 16S rRNA-ND2, and igr4), recovering 38 haplotypes. Individuals that shared a haplotype were often morphologically distinct, and we thus undertook detailed morphological work, including SEM of sclerites, on one representative of each morphotype within each haplotype. GMYC, bGMYC, and mPTP returned incongruent estimates of species numbers. In total, there are between 25 and 40 species, although no definitive number could be assigned, primarily due to poorly defined keratoisidid species boundaries. As expected, the superextended barcode provided greater discrimination power than single markers; bGMYC appeared to be the most effective delimiter. Among the identified species were Chelidonisis aurantiaca, collected deeper than previously known at 1507 m, and Calyptrophora clinata, recorded for the second time from the Northeast Atlantic. A full understanding of the diversity and distribution of calcaxonians requires substantial taxonomic work, but we highlight the Irish continental slope as harbouring significant diversity. [ABSTRACT FROM AUTHOR]

A great earthquake struck the Semidi segment of the plate boundary along the Alaska Peninsula on 29 July 2021, re‐rupturing part of the 1938 rupture zone. The 2021 MW 8.2 Chignik earthquake occurred just northeast of the 22 July 2020 MW 7.8 Simeonof earthquake, with little slip overlap. Analysis of teleseismic P and SH waves, regional Global Navigation Satellite System (GNSS) displacements, and near‐field and far‐field tsunami observations provides a good resolution of the 2021 rupture process. During ∼60‐s long faulting, the slip was nonuniformly distributed along the megathrust over depths from 32 to 40 km, with up to ∼12.9‐m slip in an ∼170‐km‐long patch. The 40–45 km down‐dip limit of slip is well constrained by GNSS observations along the Alaska Peninsula. Tsunami observations preclude significant slip from extending to depths <25 km, confining all coseismic slip to beneath the shallow continental shelf. Most aftershocks locate seaward of the large‐slip zones, with a concentration of activity up‐dip of the deeper southwestern slip zone. Some localized aftershock patches locate beneath the continental slope. The surface‐wave magnitude MS of 8.1 for the 2021 earthquake is smaller than MS = 8.3–8.4 for the 1938 event. Seismic and tsunami data indicate that slip in 1938 was concentrated in the eastern region of its aftershock zone, extending beyond the Semidi Islands, where the 2021 event did not rupture. Plain Language Summary: The Pacific plate underthrusts the North American plate along the Alaska‐Aleutian subduction zone producing great earthquakes along most of the plate boundary. The region, that ruptured in 1938, hosted another great earthquake with magnitude 8.2 on 29 July 2021 offshore of Chignik, adjacent to a magnitude 7.8 event in 2020 beneath the Shumagin Islands. Using seismic wave recordings, Global Navigation Satellite System static displacements, and tsunami wave recordings at regional and distant locations, we determine the space‐time evolution of slip during the 2021 rupture process. The rupture extended northeastward ∼170 km, ending just short of the Semidi Islands. The slip is concentrated on the megathrust, from 32‐km to 40‐km deep. Shallow slip at depths <25 km is precluded by the tsunami observations, confining all rupture to beneath the shallow continental shelf. Most aftershocks are up‐dip of the large‐slip regions with a concentration in the shallow region of the southwestern rupture zone. Comparisons of observations and rupture models with the 1938 event indicate distinct slip distributions and seismic energy release, with the 1938 event being somewhat larger and extending further northeast than the 2021 rupture. This provides strong evidence that the 2021 event is not a simple repeat failure of the 1938 rupture. Key Points: The slip distribution of the 2021 Chignik MW 8.2 earthquake is constrained by joint analysis of seismic, geodetic, and tsunami recordingsDuring the ∼60‐s long rupture, patchy slip of up to 12.9 m occurred at depths of 32–40 km on the megathrust below the continental shelfThe 2021 slip pattern differs from the 1938 MW 8.2 rupture, with larger slip in the west and no slip in the easternmost 1938 rupture zone [ABSTRACT FROM AUTHOR]

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

The Arctic is a climate‐sensitive area, responding rapidly to present changes, but for the past changes, the record is still incomplete. For instance, the Weichselian glacial history of the Svalbard–Barents Sea Ice Sheet (SBIS) has largely been reconstructed based on studies of the fragmentary Spitsbergen terrestrial and shelf records. However, the sediments removed from the land and shelf areas during peak glacials were deposited on trough mouth fans located along the continental slope. By studying the stratigraphy and processes of the trough mouth fans, comprising a more complete sediment archive, our new data have allowed gaps in the Weichselian glacial history of the SBIS to be refined and filled. Here we present new lithological and geochronological data from the Kongsfjorden Trough Mouth Fan, closely linked to the advance and decay of the SBIS. High‐resolution TOPAS seismic profiles reveal three distinct packages of glacigenic debris flows (GDFs) within its upper stratigraphy, each interpreted to represent an advance of the SBIS to the shelf edge. A radiocarbon dated, 12.6‐m‐long core from the southern flank of the Kongsfjorden Trough Mouth Fan penetrates trough sediments directly linked to the youngest GDF package and terminates in the second GDF, allowing us to study the last two Kongsfjorden ice‐stream advances in greater detail than was previously possible. The age model of core GS10‐164‐09PC, based on combining 14C‐, 18O‐stable isotope and magnetic susceptibility data, spans the last ~54 ka. An Early Weichselian glacial advance is tentatively dated to have ended at ~90 ka. A second peak glaciation is estimated at ~70 ka, followed by a deglaciation from ~54 ka. An ice rafted debris‐rich unit (U7) dated between 38 and 34 ka, followed by a plumite (U6), indicates an advance of unknown extent. The Last Glacial Maximum advance is dated to before 24 ka BP, followed by a rapid deglaciation at ~15 ka. The presence of coarser‐grained sorted sediments at the present seafloor is attributed to the influence of the West‐Spitsbergen Current, acting on water depths of at least 846 m, and is thought to have worked in the vicinity of the coring site since ~14 ka BP. [ABSTRACT FROM AUTHOR]

Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic debris flows (GDFs), subglacial meltwater flows, and suspended sediment. Thus, past ice configurations may be interpreted from the sedimentological record. This study links the records in cores, high-resolution seismic profiles, and multibeam swath bathymetry of Hatton Slope and Fan to the changing glaciological history in Hudson Strait, one of the largest ice streams of the late Pleistocene Laurentide Ice Sheet. 14C-AMS dates, X-ray fluorescence geochemical profiles, and oxygen isotopes in sixteen cores document sediment supply during the last glacial cycle, and earlier history is interpreted from seismic data. The Frobisher Bay slope sector has a long record of GDF deposits from severe glacial periods between MIS 6 and 22, with little impact of meltwater discharge. Mass-transport events and aggrading gravel-floored valleys dominate the northern Hatton slope sector. The central slope sector shows the greatest shelf break progradation by till deposition, with kilometre-spaced gullies heading at 700–730 mbsl from the last major grounding of the ice-stream on the upper slope during Heinrich event 3 (H3). The gullies pass downslope into ∼5 km wide valleys, which have been sites of sediment bypass since widespread meltwater flow in MIS 6 and show little aggradation since MIS 16. Intervening >50 m high ridges show alternating levee accretion and erosion by shallow mass-transport events. Downslope on Hatton Fan, GDFs are common and fill wide erosional channels that lead to the sandy braid plain of the central Labrador Sea. The channels of the southern sector and Saglek Slope have channeled turbidity currents down the NAMOC, and stratified contourite deposits accumulated on the fan. Over the MIS 1–3 period widely represented by cores, ice was grounded in Hatton Basin and on the upper slope to 700 m water depth only immediately prior to H3. Older and younger H events had a floating ice-shelf in Hatton Basin, and sedimentation was dominated by the retreat of that ice shelf to Resolution Island. Distal cores show no systematic difference between the H1–top H3 interval and the base H3–H5 interval. Given the supply of carbonate detritus of consistent composition back to at least H5, any MIS 3 deglaciation of Hudson Bay would require improbably high growth rates of ice sheets in the centre of the continent. • First multibeam swath bathymetric and seismic profiling of the Hudson Strait Ice Stream. • Glacigenic debris flows, and mass-transport events were outlined during MIS 6 and 16. • Glacial ice was grounded in Hatton Basin and on the upper slope to 700 m over MIS 1-3. • Lack of a systematic difference between H1–H3 and H4–H5 events raises the question about the deglaciation hypothesis during MIS 3. [ABSTRACT FROM AUTHOR]

The Gulf of Mexico (GoM) is characterized by strong mesoscale eddy activities that have been studied extensively, yet the comprehensive three-dimensional (3-D) kinematic properties of GoM eddies are still not well documented. In this study, the 3-D mesoscale eddy activities in the upper layer (0–800 m) of the GoM are characterized using 14-year (1997–2010) global Hybrid Coordinate Ocean Model (HYCOM) outputs. Most eddies in the upper layer (both cyclonic and anticyclonic) have radii of ∼30–60 km and lifespans shorter than 30 days. The spatial distributions of GoM eddies do not vary much with depth, while their intensity decreases with depth. The size of cyclonic eddies does not vary much with depth, while the size of anticyclonic eddies decreases slightly with depth. Cyclonic eddies are often found to be generated in the eastern GoM (especially in the Loop Current region), the Bay of Campeche, and on the continental slope of the Campeche Bank, while anticyclonic eddies are often generated on the northeastern and northwestern GoM continental slopes, and in the central GoM (near 24°N) and the Bay of Campeche (92–94°W). In addition, long-lived GoM eddies (e.g., lifespan >150 days) tend to have intermediate eddy intensity (e.g., 0.13–0.32 for cyclonic eddies at the 10 m level). Both cyclonic and anticyclonic eddies are found to play an important role in the horizontal and vertical transport of heat and salt, and eddy-induced anomalies of water temperature and salinity at both surface and subsurface are generally more pronounced in the eastern GoM than in the western GoM. • 3-D eddy kinematics in the GoM (0–800 m) are characterized using global HYCOM. • Eddy-induced temperature and salinity anomalies are strongest in the eastern GoM. • Eddies with intermediate intensity tend to have long lifespans (>150 days). [ABSTRACT FROM AUTHOR]

The Andaman Sea Basin, a well-known back-arc spreading centre and a mature petroliferous basin, presents a unique and complex scenario for understanding the interplay of sedimentary processes and fault tectonics on seafloor geomorphology evolution, particularly in the eastern shelf region. This study, using high-resolution 3D seismic data and published exploratory well-seismic interpretation results, aims to establish a comprehensive stratigraphic framework for the Tanintharyi region, spanning the Lower Miocene, Middle Miocene, Upper Miocene, Pliocene, and Quaternary. A submarine canyon system was identified and investigated along the Tanintharyi continental slope within the East Andaman Basin, comprising thirteen slope-confined canyons arranged predominantly in an east-west vertical slope orientation. By analysing seismic reflection features, five distinct seismic facies have been identified, including basal lag (BL), slump and debris-flow deposits (SDFDs), canyon confined sheets (CCSs), laterally inclined packages (LIPs), and channel-levees (CLs). The evolution of this canyon system, a vital focus of this study, can be categorised into three phases based on the morphology and sedimentary structures observed: canyon initiation, canyon extension, and erosion-sedimentation. The findings of this study highlight the critical controlling role of faults in canyon evolution, with the intensity of fault activity displaying a negative correlation with canyon size, indicating the direct impact of faults on geomorphological changes. In addition, the geomorphological changes induced by fault activity have resulted in changes in sediment supply, dispersal, and sedimentation rates, thus significantly impacting the spatial distribution and dimensions of slope-confined canyons within the East Andaman Basin, with far-reaching implications. [Display omitted] • A matured canyon system exists in the Tanintharyi region of the East Andaman Basin. • Thirteen slope-confined canyons show nearly an east-west vertical slope alignment. • The sedimentary characteristics of these canyons display three stages of evolution. • Geomorphological changes induced by fault activity impacted the canyon's evolution. • Intensity of fault activities displays a negative correlation with canyon extent. [ABSTRACT FROM AUTHOR]

The western East Sea (Sea of Japan) is a seismically active region. A major earthquake in the western East Sea may cause damage in the eastern Korean Peninsula. The nature of seismicity in the western East Sea is important information for mitigation of seismic hazards. The seismicity in the western East Sea occur around the paleo-rifting structures where seismic and geophysical properties apparently change. Both reverse faulting and strike slip earthquakes occur in the region. Earthquake locations and focal depths are refined. The maximum focal depth generally increases from ∼ 10 km in the coast to ∼ 32 km in the continental slope of the western East Sea that is located in distance of ∼ 60 km from the coast. Mid to lower crust earthquakes continue around the paleo-rifting structures that may extend to the lower crust and Moho. Offshore earthquakes rarely occur in oceanic basins of bathymetry with > 2 km. Clustered episodic earthquakes occur in four local offshore areas including the stress-induced areas by the 12 September 2016 M L 5.8 M W 5.4 Gyeongju and 15 November 2017 M L 5.4 M W 5.5 Pohang earthquakes. The spatiotemporal clustering of earthquakes suggests stress accumulation at localized paleo-rifting structures and episodic stress release. The mid to lower crustal earthquakes are confirmed from phase arrival time analyses with collocated vertically-separated sensors. The laterally progressive focal depth changes suggest neotectonic evolution of thrust across the crust in the paleo-rifting structure. • Middle to lower crustal earthquakes occur continuously in the western East Sea (Sea of Japan). • Paleo-rifting structures spawn earthquakes as response to the ambient stress. • Neotectonic evolution of lower crustal thrust happens around the paleo-rifting structures. [ABSTRACT FROM AUTHOR]

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

Magmatism and crustal structural characteristics are well-known phenomena that support understanding the marginal sea's tectonic evolution. The South China Sea (SCS) has become a natural laboratory for researchers to investigate the evolution of the marginal sea because of its complex tectonic background and multiple phases of magmatic activities. However, due to limitations in resolution and depth of observations, the evolutionary process of the SCS is still controversial. We use the latest processed multi-channel seismic reflection profile Line AB to evaluate the sedimentary sequences, crustal tectonics, and the Cenozoic magmatism in the southern SCS. The gravity modeling results indicate a reduction in crustal thickness from 18 km in the proximal domain to 7 km in the Continent-Ocean Transition (COT). The COT is roughly 35 km wide, representing a rapid break up process of the SCS. A high-velocity layer (HVL) of about 3 km thickness was formed in the continental slope crust, interpreted as post-spreading magmatic underplating. In addition, four sedimentary sequences, post-spreading magmatic intrusion, and the possible magma conduits were identified in the profile. Combining with previous ocean bottom seismometer (OBS) data, multi-channel seismic data, fault system data, and petrologic observations, we indicate the deep mantle magmatic material upwelled to the crust and further intruded into sediments along the hyper-extended crust or detachment faults during the post-spreading stage. We contend that cooling and heat shrinking within the SCS oceanic lithosphere have the potential to initiate decompression melt deformation in the continental slope. In summary, we construct a model of the origin and migration mechanism of extensive post-spreading magmatism in the SCS. Our research reveals the Cenozoic evolution and the HVL of the southern SCS, and provides a possible genesis for the anomalously young magmatism observed at the continental margin. • A high-velocity layer in lower crust is observed in southern South China Sea. • A narrow COT (∼35 km) was found in the southern continental margin. • The post-spreading magmatic underplating formed the HVL. • The extensional crust and detachment faults promote the post-spreading magmatism. • The cooling and heat shrinking of oceanic lithosphere reactivated the faults. [ABSTRACT FROM AUTHOR]

The frontal emplacement of the submarine and sublacustrine mass-transport complexes (MTCs) are subdivided into the frontally emergent and confined types. However, it remains unclear what factors control the variability of the frontal emplacement of submarine MTCs. High-resolution 2D and 3D seismic data are utilized to investigate the variability of four MTCs_1–4. The results show that (1) Four MTCs_1–4 herein in the lower slope are subdivided into frontally emergent MTCs_1 and 2 and frontally confined MTCs_3 and 4 (2) The magnitude (e.g., length, width, area and volume); of (frontally) emergent MTCs_1 and 2 is larger than that of confined MTCs_3 and 4; (3) Their flow directions and sources are variable; (4) Height drop (HD) and depth of the basal shear surface (DB) of emergent and confined MTCs_1–4 are greatly variable. Their HDs and DBs as controlling factors present/determine their gravitational potential energy, and HD/DB ratio controls their emplacement type (frontal emergence or confinement). High gravitational potential energy (mainly determined by high HD) of the sliding mass enables landslides to ramp out on the coeval seafloor, resulting in the creation of the gentle and/or moderate fontal ramps. Low potential energy (mainly presented by large DB) of the sliding mass prevents landslides from overrunning the undeformed downslope strata, forming the steep frontal ramps. Scales of sedimentation accumulation rate, slope gradient and earthquakes as possible triggering factors affect variability of MTCs_1–4. The sources of emergent MTCs_1 and 2 are from the continental margin slope. Confined MTC_3 comes from the upper slope of the northern flank of the Xisha uplift and confined MTC_4 derives from a point source (local lower slope). The variability of their gravitational potential energy, mainly depending on variable HDs and DBs, predominantly determines the emplacement variability of submarine MTCs and eventually affects their variable evolutions. This study provides new perspectives and enriches the repository of frontally confined and emergent (submarine) MTCs. • Frontally confined and emergent MTCs are studied using 2D and 3D seismic data. • Frontally emergent and confined MTCs are of difference in flow direction and sources. • HD and DB ratio can separate frontally emergent (high ratio) from confined (low ratio) MTCs. • Scales of sediment accumulation rate, slope gradient and earthquake can affect the scale-variability of MTCs. [ABSTRACT FROM AUTHOR]

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

Identifying species assemblages helps understand the relationship between organisms and their environment. Assemblages can be used to predict biological changes caused by environmental perturbations, and are thus essential surrogates to monitor biodiversity. In this study, to identify and describe seabird assemblages, we used 15 at-sea ship-based survey data sets collected over 37°of latitude off eastern Australia, from 2016 to 2021. We fitted seasonal Region of Common Profile (RCP) mixture models, for two types of data (presence–absence and abundance). RCP groups are defined as regions where the probability of encountering a particular species profile is constant within regions, but different amongst them. These groups also vary according to covariates, which in our case included oceanographic, climatic, and physiographic parameters. Results were based on 142,646 seabirds recorded from 80 species, including albatrosses, petrels, prions, shearwaters, boobies, and terns, among other taxa. All models suggested two macro-scale assemblages ('northern' and 'southern'), except for the autumn presence–absence model that identified three groups. The model results consistently show a biogeographic transition at ∼ 34°S, near the latitude at which the East Australian Current (EAC) separates from the Australian continental slope. Sea surface temperatures or sea surface salinities were selected in all final models, further indicating a close relationship between seabird assemblages and water masses. Results from both data types, presence–absence and abundance, resulted in similar spatial and species profile patterns. RCP models clearly identified two seabird assemblages off the east coast of Australia, suggesting the persistence of these groups at seasonal and macro spatial scales. Given the ongoing poleward intensification that the EAC is experiencing, which is projected to continue over the next century, and its importance in influencing the distributions of seabirds, the methods applied in our study could be replicated to assess possible changes in seabird assemblages and how they are affected by changing environmental conditions. • We described seabird assemblages based on the Region of Common Profiles (RCP) method. • Assemblages of seabird species were correlated with the East Australian Current. • Our analysis can be replicated to assess possible changes in seabird distribution. • The RCP method works well at the macro spatial scale for highly mobile animals. [ABSTRACT FROM AUTHOR]

An inflow of warm and salty Atlantic origin waters (AW) from the Nordic Seas to the Arctic Ocean interior is in the list of the major external factors, which control the hydrologic regime of the East-Atlantic sector of the Arctic Ocean. Rapid decay of the sea ice cover in 2000–2010s raised questions on the possible changes in the fate of the inflow under present ice-depleted conditions: whether warm and salty AW will cool and freshen slower (due to less ice to be melted underway), or intensified heat loss to the atmosphere through the open surface will lead to the faster AW cooling on shorter distance? We present rare hydrologic data, collected during the late winter 2019 in the international expedition "Transarktika-2019" in the northern part of the Barents Sea and at the adjoining continental slope of the Nansen Basin. On the basis of field data, supported by the oceanic reanalysis product and numerical modelling we have studied the transformation of AW on its transit between Svalbard and Franz Joseph Land. We show that the observed cooling and desalination of the fraction of AW over the continental slope around this area is controlled by lateral mixing with colder and fresher waters, outflowing from cross-slope canyons, which cut the continental slope: Kvitøya Trough, Franz Victoria Trough and probably, the British Channel. The obtained results demonstrate more intensive transformation of AW on this transit compared to previous studies. Possible explanations of this contrast, which are supported by the earlier studies, may include: the season of the survey when dense water outflow through canyons is at its maximum and gradual "atlantification" of the East-Atlantic sector of the Arctic Ocean, which favours intensification of dense water formation in winter polynyas under conditions of increased seasonality of sea ice. In the latter case, faster cooling and desalination of AW en route in this part of the Arctic Ocean may be considered as a reasonable hypothesis, provided the atlantification of the Nansen Basin is progressing. [ABSTRACT FROM AUTHOR]