Search

The Gulf of Maine's lunar semidiurnal (M2) ocean tide exhibits spatially coherent amplitude changes of ∼1–3 cm on interannual time scales, though no causative mechanism has been identified. Here we show, using a specially designed numerical modeling framework, that stratification changes account for 32%–48% (Pearson coefficient 0.58–0.69) of the observed M2 variability at tide gauges from 1994 to 2019. Masking experiments and energy diagnoses reveal that the modeled variability is primarily driven by fluctuations in barotropic‐to‐baroclinic energy conversion on the continental slope south of the gulf's mouth, with a 1‐cm amplitude increase at Boston corresponding to a ∼7% (0.30 GW) drop in the area‐integrated conversion rate. Evidence is given for the same process to have caused the decade‐long M2 amplitude decrease in the Gulf of Maine beginning in 1980/81. The study has implications for nuisance flooding predictions and space geodetic analyses seeking highest accuracies. Plain Language Summary: The height of the twice‐daily tide at Boston is about 135 cm, but researchers have long noted that this value fluctuates by about 1–3 cm from year to year. Here we show that the annual tidal height changes—seen in fact throughout the Gulf of Maine—are closely linked to how seawater density is distributed three‐dimensionally in the region. In particular, as tidal currents enter the gulf over steep underwater topography, the vertical distribution of density determines how much of the incoming wave energy is scattered back as internal tides into the deeper Northwest Atlantic. In years where this conversion of wave energy drops by 7% from its nominal value of 4 Gigawatt, the surface tide at Boston typically increases by 1 cm. Climate‐induced changes in ocean temperature and density may strengthen or weaken the conversion effect and thus slightly alter the role of tides in coastal flood events. Key Points: We propagate the M2 tide through realistic, annually varying density structures (1993–2019) in a regional Gulf of Maine modelStratification changes explain 32%–48% of the observed, cm‐level M2 amplitude variability at coastal tide gauges from 1994 to 2019Modeled M2 changes mainly reflect fluctuations in the barotropic‐baroclinic energy conversion rate on the New England continental slope [ABSTRACT FROM AUTHOR]

The Gulf Stream is the only pathway in the subtropical North Atlantic by which warm water flows poleward. This transport of warm water and return of cold water at depth is called the Atlantic Meridional Overturning Circulation (AMOC). The dynamic method is applied to hydrocasts collected since the 1930s to estimate upper‐ocean transport (0–1,000 m) between the U.S. Continental Slope and Bermuda and separately to Africa with focus on the longest directly observable timescale. Calculating transport between the Slope and Bermuda eliminates the Gulf Stream's northern and southern recirculation gyres, while calculations between the Slope and Africa remove all other recirculating geostrophic flow. The net Slope‐Bermuda upper‐ocean transport is estimated to be 41.1 ± 0.4 Sv, decreasing by 2.0 ± 0.8 Sv between 1930 and 2020. The AMOC contribution is 18.4 ± 0.6 Sv, decreasing by 0.4 ± 0.6 Sv between 1930 and 2020. Plain Language Summary: The Gulf Stream is the only pathway by which the ocean transports warm water to high latitudes in the North Atlantic and Nordic Seas where it cools, sinks and flows back south at intermediate depths from the subpolar North Atlantic and at greater depths from the Nordic Seas. This circulation pattern, the Atlantic Meridional Overturning Circulation (AMOC), plays an important role in Earth's climate. But the Gulf Stream is also the wester boundary current to the horizontal circulation driven by the trade winds and westerlies at low and mid‐latitudes. The Gulf Stream also drives large recirculations to its south and north. In this study we use hydrographic data taken since the 1930s to calculate the poleward flow in the Gulf Stream, while canceling out the recirculation and wind‐driven transports to estimate the strength of the north‐flowing portion of the AMOC. There is evidence for a 2.0 Sv Gulf Stream slow‐down between 1930 and 2020. Whether and to what extent this reflects a slowdown of the AMOC or wind‐driven circulation cannot be established with certainty. Our estimate of a 0.4 Sv AMOC decrease is reported with low confidence. Key Points: Direct measurements along the Oleander line (∼37°N) show that the depth of the Atlantic Meridional Overturning Circulation (AMOC) maximum is close to 1,000 mNet northward transport between North America and Bermuda equals 41.1 ± 0.4 Sv of which the AMOC accounts for about 18.4 ± 0.6 SvNet northward transport NW of Bermuda slowed by 2 ± 0.8 Sv between 1930 and 2020 with 0.4 ± 0.6 Sv attributed to an AMOC decline [ABSTRACT FROM AUTHOR]

In western boundary current systems, strong currents transport oligotrophic oceanic waters towards the coast. Thaliaceans may have an advantage in these systems due their ability to filter small particles such as the bacterioplankton, typically responsible for the primary production in oligotrophic waters. Here, we evaluated the structure of the thaliacean community present in the tropical South Atlantic Ocean western boundary current system to test the hypothesis that species distribution and abundance are structured by the circulation and thermohaline features. For that purpose, we used data collected though 40 mm mesopelagic trawls above the slope and around oceanic seamounts and islands. Results reveal distinct patterns in the thaliacean community structure. Over the continental slope, under the influence of the strong North Brazilian Undercurrent, Pyrosoma atlanticum was highly abundant. Soestia zonaria was also present but in a lesser amount. Offshore, around oceanic islands and Seamounts under the influence of the central branch of South Equatorial Current, Doliolida spp. were the dominant thaliacean, co-occurring with P. atlanticum in lower abundance. Mesh selectivity is a potential drawback in these results since the coarse aperture may have lost smaller species and early life stages. [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 conductivity, temperature and depth (CTD) probes, and it provides information about the hydrodynamics and thermohaline properties of the last 100 m of the water column. The hydrodynamics in both sites are 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 represent a starting point for the continuous observation activity set up on occasion of the "Operation Dense Water" in 2012 focussed on the southern Adriatic deep-water dynamics. Since then, the observatory has been ongoing since 2012 and the database is regularly updated. All the data described here are made publicly available from 10.5281/zenodo.6770201 (Paladini de Mendoza et al., 2022) and are compliant with the FAIR principles (findable, accessible, interoperable and reusable). [ABSTRACT FROM AUTHOR]

The features of the distribution of the 226Ra, 232Th, 238U concentrations in the surface layer of bottom sediments in the northern part of the Laptev Sea are considered. Data are obtained for the bottom sediments of the shelf zone of the sea, the continental slope, and abyssal depths. The concentrations of 226Ra and 232Th varied in the range 17–36.3 and 28.7–38.1 Bq/kg, respectively, and the 238U concentration, within 12.5–38.7 Bq/kg. It is assumed that the enrichment of sediments in 226Ra and 238U with depth is due to the reduction of part of the carbonates containing 226Ra and 238U, followed by the sorption of 226Ra from sea water and the sedimentation of hydrolysis forms of 238U to the bottom. An increase in the 226Ra and 238U concentrations in the sediment with depth in the eastern section, as the concentration of inorganic carbon decreases, is consistent with this assumption. In this case, the correlation of the 226Ra and 238U concentrations with the concentration of inorganic carbon is negative (R = –0.98 and –0.94, respectively). The 232Th concentration correlates with the concentration of organic carbon (R = 0.85). In the area of the outer shelf and in the Vilkitsky Strait, the 226Ra, 232Th, and 238U concentrations in the surface layer of sediments depend on the fractional composition of the sediment and change with a change in the fractional ratio. The concentrations of 238U and 232Th correlate with each other (R = 0.84) and with the concentration of inorganic carbon (R = 0.75 and 0.87, respectively). [ABSTRACT FROM AUTHOR]

Climate change and human activities have increased avalanche risks in alpine mountains. Therefore, strengthening the research on mitigating and controlling avalanche disasters is indispensable for sustainable socio-economic development in mountainous areas. Early avalanche warning is an essential means of avalanche disaster prevention. However, the theoretical development and application of avalanche warning strategies remain limited due to the lack of systematic understanding of the triggering mechanisms of avalanches. Based on observational data (2015–2019) of avalanches, snowpack, meteorological parameters, surface soil temperature and moisture, and topography in avalanche-prone areas in the central Tianshan Mountains, we analyzed the characteristics of different types of avalanches under a continental snow climate and the environmental factors (such as meteorological conditions and snowpack) that trigger avalanches, as well as the triggering mechanisms for different types of avalanches under the continental snow climate in terms of snow-layer shear fracture modes. We found that the snowpack parameters, weather conditions, and soil temperature and moisture varied significantly among the stages of snow accumulation, stabilization, and melting, resulting in different avalanches prevailing in different stages of snowpack evolution. Moreover, the snow-layer fractures were driven by single external factors or the combined multiple factors under the continental snow climate. Fifty-four percent of the avalanche events in the study area occurred during or after a snowfall, with 36% related to sudden increases in temperature. Then considering different triggering scenarios, snowpack evolution stages, and the coupling of intrinsic and extrinsic drivers of triggering snow-layer shear failure, we constructed five snow-layer shear fracture modes and twelve avalanche-triggering modes on mountain slopes under a continental snow climate. [ABSTRACT FROM AUTHOR]

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

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]

Evaluation of the representative cartographic techniques demonstrated that there are still considerable challenges facing the methods of marine geodetic, geophysical and bathymetric data visualisation. In an oceanic seafloor formation, the interaction between the geological structural elements and topographical relief can be analysed by advanced mapping. In present study, a correlation between geodesy, geophysics and topography has been examined including the following variables: geological structure, coastal topography and bathymetry, geophysical fields, free-air gravity anomalies and geoid undulation, sediment thickness, bathymetric patterns, and extension of the transform faults. The variables were visualised on the high-resolution raster grids using Generic Mapping Tools (GMT) scripting toolset. The study area is located in the Seychelles and the Somali Sea segment of the Indian Ocean. The data incorporates satellite-derived gravity grid, EGM-2008, geological structures, topography from GEBCO grid and GlobSed sediment thickness, processed by GMT scripts. The results demonstrated that western continental slope of Somalia is wide, gently declining to the seafloor at depths exceeding -5000 m. Kenya and Tanzania present a wide continental foot with depths ranging from -3500 to -5000 m. The Somali Sea basin shows low sedimentation lower than 500 m, while ridges and island chains have higher sediment influx (1,000-2,000 m). The Mozambique Channel has dominating values at 2,500-3,500 m. Higher values are noted near the Reunion and Mauritius islands until the Seychelles via the Mascarene Plateau (500-1,000 m) against the <500 m in the areas of the Mid-Indian Ridge, Carlsberg Ridge and open water. [ABSTRACT FROM AUTHOR]

The convergence of different water masses on the shelf and along the shelfbreak, and cross‐isobath shelf‐open ocean exchanges contribute to the complex circulation near Cape Hatteras. We examine the mean and variability of these circulations using data from nine bottom‐mounted acoustic Doppler current profilers, deployed over the mid‐ to outer‐continental shelf north and south of Cape Hatteras as part of the Processes driving Exchange At Cape Hatteras program. The 18‐month‐mean depth‐averaged shelf flows are mostly aligned with isobaths and oriented toward Cape Hatteras. At two sites just north of Cape Hatteras, mean flows have a strong cross‐shelf component. Two dominant spatial patterns in the velocity field are obtained from an empirical orthogonal function analysis. The two leading modes contain 61% of the total variance. The spatial variation of Mode 1 exhibits an along‐shelf flow pattern, while that of Mode 2 shows a convergent flow pattern. The principal component (PC) series of Mode 1 is significantly correlated with the local wind stress, confirming that the along‐shelf flow is wind‐driven as expected. The PC of Mode 2 is highly correlated with the Gulf Stream lateral position as inferred from the current‐ and pressure‐sensor‐equipped inverted echo sounders over the slope south of Cape Hatteras, which indicates that Gulf Stream movement drives time‐varying shelf flow convergence. Conditionally averaged sea‐surface temperature and high‐frequency radar‐measured surface currents based on PC1 and PC2 confirm these relationships and further illustrate how the wind and Gulf Stream forcing work together to influence the flow regime in this region. Plain Language Summary: Several oceanographic processes occur within a small geographic area east of Cape Hatteras. Cool and warm ocean currents meet and collide on the continental shelf, resulting in complex exchange between the shelf and the adjacent open ocean. To better characterize the complicated circulation and understand the processes driving exchanges in this region, we analyze 18‐month current velocity data from an observational array deployed near Cape Hatteras on the shelf and the neighboring continental slope. The time‐mean circulation is characterized as converging flows both on the shelf and along the shelfbreak. We find two dominant spatial patterns in the current velocity: a wind‐driven along‐shelf flow pattern and a Gulf Stream‐driven convergent flow pattern. Additionally, the combined effect of the wind and Gulf Stream forcings mainly drives the shelf and open ocean exchanges. Key Points: The time‐mean depth‐averaged shelf and shelfbreak currents are mostly aligned with isobaths and oriented toward Cape HatterasOn average, the open‐ocean water intrudes on the shelf south of The Point while the shelf water exports to the open ocean north of The PointWind‐driven along‐shelf flow pattern and Gulf Stream‐driven convergent flow pattern are predominant in the shelf velocity field [ABSTRACT FROM AUTHOR]

The Subpolar North Atlantic plays a critical role in the formation of the deep water masses which drive Atlantic Meridional Overturning Circulation (AMOC). Labrador Sea Water (LSW) is formed in the Labrador Sea and exported predominantly via the Deep Western Boundary Current (DWBC). The DWBC is an essential component of the AMOC advecting deep waters southward, flowing at depth along the continental slope of the western Atlantic. By combining sustained hydrographic observations from the Labrador Sea to 26.5°N, we investigate the signal propagation and advective timescales of LSW via the DWBC from its source region to the Tropical Atlantic through various approaches using robust neutral density classifications. Two individually defined LSW classes are observed to advect on timescales that support a new plausible hydrographically observed advective pathway. We find each LSW class to advect on independent timescales, and validate a hypothesized alternative‐interior advection pathway branching from the DWBC by observing the arrival of LSW outside of the DWBC in the Bermuda basin on timescales similar to arriving at 26.5°N, 10–15 yr after leaving the source region. Advective timescales estimated herein indicate that this interior pathway is likely the main advective pathway; it remains uncertain whether a direct pathway plays a significant advective role. Using LSW convective signals as advective tracers along the DWBC permits the estimation of advective timescales from the subpolar to tropical latitudes, illuminating deep water advection pathways across the North Atlantic and the lower‐limb of AMOC as a whole. Plain Language Summary: The Deep Western Boundary Current (DWBC) exports cold and dense deep waters formed in the Subpolar North Atlantic to the tropics, and therefore plays a primary role in global ocean circulation and heat balance. We focus here on Labrador Sea Water (LSW), a water mass formed through wintertime mixing events within the Subpolar North Atlantic characterized by distinctive low‐temperature and low‐salinity signatures. By following the passage of these signatures through several locations, we investigate the pathways and spreading timescales of LSW from its source region toward the subtropical North Atlantic by the DWBC. We find two distinct LSW masses to reach the same location on independent timescales, and observe LSW in the Central Atlantic just prior to or on the same timescale as being observed in the Tropical Atlantic. These findings indicate that an alternative‐interior export pathway branching from the DWBC is likely to exist, exporting LSW away from the continental slope and into the Atlantic interior rather than following a direct equatorward route. Estimating advective timescales and pathways of the DWBC using LSW aid in the present understanding and future prediction of overturning circulation in the Atlantic Ocean. Key Points: Advection timescales of the Deep Western Boundary Current (DWBC) are inferred from Labrador Sea Water (LSW) convective minima in the North AtlanticThe two LSW classes examined are observed to advect on different timescales, likely due to varying advective pathwaysAn alternative interior‐advective pathway observed as a bifurcation in the DWBC advects water to the interior [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 buoyancy 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 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]

Mooring observations of nearly the full water column on the continental slope in the South China Sea revealed the ocean's response to Typhoon Mangkhut (2018). Mangkhut induced sea surface cooling ∼4°C that was biased to the right side of its track, which recovered with an e‐folding time after approximately 1 week. Mangkhut was a relatively fast‐moving typhoon and caused a fast near‐inertial response throughout the entire depth in its lee. The typhoon‐induced upper ocean (deep‐water) near‐inertial current velocities were >1.5 m/s (∼0.08 m/s), with an e‐folding time of approximately a week (2 weeks) and frequency of 1.04f (1.08f, where f is the local inertial frequency). The near‐inertial currents were near‐circular polarized in the upper ocean and near‐rectilinear polarized with the main axis in the across‐slope direction in deep water. The deep‐water near‐inertial waves amplified the vertical excursions of isotherms from ∼120 to ∼200 m, reduced the stratification, elevated vertical current shears, and enhanced turbulent dissipation rate, especially during 14–17 September when the effects of near‐inertial waves and diurnal spring tides overlapped. A net cooling ∼0.15°C and salinity increase ∼0.05 psu were observed in the deep ocean after Mangkhut. Typhoon‐induced near‐inertial waves may further contribute to the intensification of southwestward along‐slope mean near‐bottom currents. This study indicates the immediate influence of typhoon in deep‐water through near‐inertial waves and their contribution to the bottom mixing on the continental slope. Plain Language Summary: In 2018, Typhoon Mangkhut traveled over a moored observation station on the continental slope in the South China Sea. Mangkhut caused rightward biased sea surface cooling ∼4°C and recovered nearly a week. Mangkhut was a relatively fast‐moving typhoon, generating near‐inertial waves throughout the entire water depth, with the maximum current speed >1.5 m/s (∼0.08 m/s) in upper ocean (deep water). These waves recovered in almost a week (2 weeks). The near‐inertial currents were similar in all the horizontal directions in upper ocean, while the across‐slope currents were much greater than the along‐slope currents in deep water. The deep‐water near‐inertial waves increased the vertical variation of temperature and salinity isolines from ∼120 to ∼200 m, made near‐bottom water more homogeneous, elevated vertical current difference and enhanced the turbulence, especially when near‐inertial waves and diurnal tides were both affected. A net cooling of ∼0.15°C and salinity increase of ∼0.05 psu were observed in the deep ocean after Mangkhut. Typhoon‐induced near‐inertial waves may further contribute to the intensification of southwestward along‐slope near‐bottom mean flow. This study indicates that the typhoon immediately influence deep water through generating near‐inertial waves and enhancing the bottom mixing on the continental slope. Key Points: Near‐inertial currents were observed in the whole water column on a continental slope in the South China Sea after Typhoon Mangkhut (2018)The near‐inertial waves were near‐circular polarized in upper ocean and near‐rectilinear polarized in deep oceanLarge vertical isotherm excursions and enhancement of bottom turbulent dissipation rates induced by deep‐water near‐inertial waves [ABSTRACT FROM AUTHOR]

Outputs of the regional ocean circulation model are analyzed to demonstrate the measurable impact of the El Niño remote oceanic forcing mechanism along the US West Coast during the major heat wave period of 2014–2016. The 2‐km horizontal resolution model, based on the Regional Ocean Modeling System (ROMS), was run for the period of 2009–2018. Though the model does not assimilate observations, it performs well by comparison with time series data explaining observed variability on temporal scales from several days to seasonal and interannual. The El Niño‐related oceanic anomalies provided by a global state estimate are introduced in the regional model at the southern boundary at 24N. These propagate alongshore with coastally trapped waves (CTWs) and influence the variability off Oregon (41°–46°N). In particular, CTWs are evident in the subsurface along‐slope current, vs, and in the depth of the 26.5 kg m−3 isopycnal surface over the slope, z26.5. In summer 2014 and 2015, vs anomalies are positive (northward) and z26.5 anomalies are negative (deeper) along the US West Coast. In addition to the CTW patterns, z26.5 anomalies also exhibit slow‐moving features associated with undercurrent widening, separation, and subsurface eddy variability. Over the Oregon shelf, El Niño conditions contributed to the sharp weakening of the southward alongshore current throughout the water column in July 2014 and 2015, despite the near‐average southward, upwelling‐favorable winds. Plain Language Summary: El Niño is a large‐scale anomalous pattern that originates in the atmosphere and the ocean in the equatorial Pacific ocean. It occurs once every several years at irregular time intervals and impacts the weather and ocean variability at great distances, in particular reaching the Pacific coast of the United States. In this study, a high‐resolution, three‐dimensional computer ocean circulation model is utilized to track the El Niño‐related signal propagating as very long oceanic waves along the continental slope from Mexico to the United States and Canada in 2014 and 2015. This propagation is best seen in the subsurface alongshore currents and in the depression of the surfaces of constant density over the continental slope. The model compares well to satellite and in‐situ observations. Carefully designed numerical models can be utilized for multiyear simulations to aid scientific discoveries. Key Points: El Niño anomalies propagating with coastally trapped waves (CTWs) impact the coastal ocean variability off Oregon 2014–2016In summers 2014 and 2015, the subsurface along‐slope velocity anomalies are poleward, propagating as CTWOn the shelf, alongshore southward currents are sharply reduced in July 2014 and 2015 despite the upwelling winds are strong [ABSTRACT FROM AUTHOR]

Properties of the abyssal current of Antarctic Bottom Water (AABW) from the Vema Channel are studied based on temperature, salinity, and velocity profiler (CTD/LADCP) data. Previous studies over a period of almost 30 years revealed that very intense current of AABW exists in the Vema Channel. Later, it was found that this current consists of two branches. One branch spreads over the bottom of the channel; the other branch is elevated over the western wall of the channel. The deepest branch decays after it passes approximately 100 km while the upper one continues further to the North Atlantic and is the source of abyssal waters in the Canary and Cabo Verde basins of the North Atlantic. Data analysis suggested that the upper jet splits into two. One of these descends down a canyon at 24°30′ S, while the other (the third one) remains on the continental slope, and indications of its existence are also found at 24°00′ S. This research analyzes the existence and pathway of this third branch that can be traced up to latitude 24° S. Velocity measurements in 2022 allowed us to confirm the existence of this third branch. [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]

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

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]

Multi‐directional propagating nonlinear internal waves (NLIWs) create complex spatial patterns, often making it difficult to quantitatively estimate the reflection and dissipation processes of NLIW energy over a slope. To identify the onshore‐ and offshore‐going wave signals in a regional model, we apply a directional Fourier filter (DFF) method to clarify wave dynamics over varying slopes. First, a series of two‐dimensional analytical solutions of either solitons or NLIW packets are utilized. Next, two‐dimensional numerical experiments indicate that the rate of reflection (dissipation) of energy for the shoaling NLIWs is much lower (higher) than that for the shoaling internal tides over a slope, regardless of varying slope criticality and height. Finally, we apply the DFF method in a three‐dimensional non‐hydrostatic regional model (MITgcm) to directionally decompose the onshore‐ and offshore‐going internal waves (IWs) on the Australian North West Shelf. The model results show that mode‐1 incoming internal tides gradually steepen into NLIWs during the shoaling processes over the slope, and then the reflecting IWs are propagate offshore in the main form of linear IW beams. In addition, the reflectivity of IWs around the Imperieuse Reef is 60% and the offshore‐reflecting IWs quickly dissipate accompanied by an e‐folding length scale of ∼22 km. Plain Language Summary: Nonlinear internal waves (NLIWs) play a crucial role in mass transport and ocean mixing on continental slopes. Therefore, various physical processes, for example, reflection and dissipation, of NLIWs over a slope are of interest to understanding spatial features of wave energy along the sloping boundaries of the world's oceans. Numerical modeling is one of the most important investigation approaches to give a full‐scale picture of NLIW dynamics in a slope region. The Australian North West Shelf (NWS) is well known to be a physiographic hotspot of NLIWs in numerous studies since the last century. Here, we first propose a directional decomposition method (DFF) to separate onshore‐ and offshore‐going internal waves over a continental slope, then apply it to quantitatively identify the reflection, transmission and dissipation processes of NLIWs on the Australian NWS. It is found that the DFF method is capable of simplifying the complicated wave fields by decomposing NLIWs propagating in multiple directions in a regional model with specific spatial and temporal sampling rates. Moreover, the wave energies during the reflection and diffraction processes, due to the blocking effects of the Imperieuse Reef, are quantified. Key Points: A directional decomposition method is proposed to estimate the reflection, transmission, and dissipation of nonlinear internal waves (NLIWs) over a slope in numerical simulationsThe rate of reflection (dissipation) of energy for the shoaling NLIWs is much lower (higher) than that for the shoaling internal tides over the same slopeAbout 60% of shoaling IW energy is reflected due to the blocking effect of the Imperieuse Reef around the Rowley Shoals [ABSTRACT FROM AUTHOR]

This study proposes new insights for the interpretation of GEOVIDE particle measurements. Potential resuspension sites due to internal tides (ITs) have been identified along the western Iberian shelf slope using a tidal regional model. Iberian shelf is mainly a source of lithogenic material whereas Galicia Bank is a source of biogenic matter. The potential pathways for particles from the resuspension sites toward the GEOVIDE stations are identified using IBIRYS reanalysis to infer their transport by the ocean circulation. It appears that each station is influenced by a specific pathway and mixed particles from several resuspension sites. This methodology reveals that the criticality of the bathymetry slope, commonly used to track resuspension sites from internal waves, is not sufficient to investigate ITs. An explicit resolution of ITs using a numerical tidal model is required for an exhaustive identification of the resuspension sites. Plain Language Summary: Internal tides (ITs) are waves with a tidal period generated when tides cross a steep slope of the sea floor. ITs then propagate in every stratified layer of the open ocean over hundreds to thousands of kilometers. The encounter of ITs with underwater relief, either at the generation site or after propagation, results in high bottom friction that enhances sediment resuspension. Evidence of lithogenic particles was found at various depths during the GEOVIDE cruise, from the Iberian continental slope to thousands of kilometers away. The present study identifies the sites where ITs are responsible for sediment resuspension. Additionally, the oceanic circulation is investigated to establish the trajectories of the resuspended sediment that could explain the GEOVIDE measurements. Key Points: Sites of high bottom tidal velocity along the Iberian continental slope were identified using a semi‐realistic internal tides modelSediment resuspension was confirmed on five sites based on earlier sediment surveys and Shields criterion thresholdParticle trajectories were proposed based on circulation modeling to improve the interpretation of geochemical tracers measurements [ABSTRACT FROM AUTHOR]

Hadal trenches are considered to act as depocenters for organic material, although pathways for the material transport and deposition rates are poorly constrained. Here we assess focusing, deposition and accumulation of material and organic carbon in four hadal trench systems underlying different surface ocean productivities; the eutrophic Atacama and Kuril‐Kamchatka trenches, the mesotrophic Kermadec trench and the oligotrophic Mariana Trench. The study is based on the distributions of naturally occurring 210Pbex, 137Cs and total organic carbon from recovered sediment cores and by applying previously quantified benthic mineralization rates. Periods of steady deposition and discreet mass‐wasting deposits were identified from the profiles and the latter were associated with historic recorded seismic events in the respective regions. During periods without mass wasting, the estimated focusing factors along trench axes were elevated, suggesting more or less continuous downslope focusing of material toward the interior of the trenches. The estimated organic carbon deposition rates during these periods exhibited extensive site‐specific variability, but were generally similar to values encountered at much shallower settings such as continental slopes and margins. Organic carbon deposition rates during periods of steady deposition were not mirrored by surface ocean productivity, but appeared confounded by local bathymetry. The inclusion of deposition mediated by mass‐wasting events enhanced the sediment and organic carbon accumulations for the past ∼150 years by up to a factor of ∼4. Thus, due to intensified downslope material focusing and infrequent mass‐wasting events, hadal trenches are important sites for deposition and sequestration of organic carbon in the deep sea. Plain Language Summary: Hadal trenches (>6,000 m water depth) occupy ∼1% of the world's ocean floor yet are largely underexplored, but recent studies have shown that these environments are depocenters for organic material and microbial activity is intensified when compared to shallower abyssal plains. However, transport and accumulation of sediment material to these hadal trenches is poorly understood. This study investigates sedimentation and accumulation dynamics of organic carbon in trenches using results of radionuclide analysis (in sediment from the Atacama, Kuril‐Kamchatka, Kermadec, and Mariana trenches). The analysis shows that trench sediments consist of discreet layers representing both periods of continuous deposition and sudden mass‐wasting events often triggered by historic earthquakes. Down slope focusing of material, intensified the deposition along the trench axes. However, the deposition rates exhibited extensive site‐specific variations that were partly related to mass‐wasting events which greatly enhanced not only mass accumulation but also organic carbon accumulation at the trench axes. Our results illustrate that mass‐wasting events play an important role on supplying organic carbon to hadal communities and suggest that hadal trenches might be quantitatively important for sediment and organic carbon sequestration in the deep sea. Key Points: Hadal trench systems act as important hot spots for accumulation and retention of organic material in the deep seaThe sediment and organic carbon accumulation in trench systems is partly mediated by ongoing material focusingInfrequent mass‐wasting events triggered by earthquakes play a significant role on mass accumulation and organic carbon deposition [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 global supply of Antarctic Bottom Water (AABW) is sourced from a handful of dense overflows. Observations from the Weddell Sea indicate that the overflow there exhibits prominent oscillations accompanied by dense eddies, while the Ross Sea overflow shows no significant oscillations other than tides, yet the genesis of these oscillations and their role in mediating AABW export remain poorly understood. Here idealized model simulations are used to investigate the dynamics of these oscillations. It is shown that the dominant oscillations result from the formation of Topographic Rossby waves (TRWs) associated with baroclinic instability of the dense overflow. A key finding is that the TRWs can feed back onto the dense overflow, producing coherent subsurface eddies of the same frequency. A series of sensitivity experiments reveal that these behaviors depend strongly on the local environment: steep topographic slopes suppress the baroclinic growth of TRWs, while strong downstream along‐slope flows suppress the upstream propagation of TRW energy and genesis of subsurface eddies. These results explain the varying prevalence of different oscillatory phenomena observed across different dense overflow regimes. Plain Language Summary: Antarctic Bottom Water (AABW) comprises the densest water in the major ocean basins, filling more than one‐third of the ocean. AABW is sourced from dense water spilling into the deep ocean at several specific sites around the Antarctic coast, referred to as "overflows." These overflows have been observed to coincide with energetic fluctuations of water across the Antarctic continental slope, which separates the relatively shallow waters around the Antarctic continent from the deep waters of the open ocean. However, the mechanism via which these fluctuations are generated, and their interaction with the overflows of dense waters, remain poorly understood. This study identifies a range of behaviors over the continental slope, ranging from no fluctuations at all, to wave‐like fluctuations across the continental slope, to the formation of horizontal vortices. The transitions between these behaviors are shown to depend on the local environmental conditions, notably the steepness of the continental slope and the speed of the ambient flow along the continental slope. These findings are in good agreement with in‐situ observations and help to explain the range of behaviors observed in overflows in nature. Key Points: Baroclinic instability of dense overflows energizes coupled Topographic Rossby waves (TRWs), which oscillate throughout the water columnFor small topographic slopes, TRWs can feed back to the outflow and instigate the formation of coherent, dense eddiesSteep slopes can suppress the formation of TRWs and eddies, decreasing the amplitude of dense overflow variability [ABSTRACT FROM AUTHOR]

Horizontal distribution of the vertically integrated barotropic‐to‐baroclinic energy conversion has been widely studied to examine the generation of internal tides at steep topography. The vertical structure of the energy conversion that provides insights into the associated dynamics, however, is masked by the often used depth‐integrated approach. Here, we reveal the vertical profile of barotropic‐to‐baroclinic energy conversion by employing an idealized ocean model in a slope‐shelf context forced by M2 barotropic tidal flow. The model shows two vertically separated hotspots of energy conversion, one near the sloping bottom and the other at the thermocline, resulting from the stronger vertical velocity and enhancement of the density perturbation, respectively. Isolation of the hotspots demonstrates that baroclinic energy generated in the bottom layer radiates toward onshore and offshore primarily in the form of internal wave beams, whereas that generated at the thermocline propagates away in the form of internal wave modes. Although energy converted at the thermocline contributes to only a small portion of the total energy conversion, it plays an important role in onshore baroclinic energy radiation and can be significantly affected by the internal wave activity at the bottom layer. With a fixed bottom topography, the percentage of baroclinic energy generated at the thermocline is linearly related to a body force exerted by the barotropic tidal flow over topography that can be estimated analytically. This provides a convenient way to estimate the overall barotropic‐to‐baroclinic energy conversion over a continental slope in the real ocean by measuring the energy conversion in the thermocline only. Plain Language Summary: Internal waves propagating in the interior of the stratified ocean are linked to energy redistribution and mixing. They are often generated when the surface tides flow over sloping topography. In this process, a portion of tidal energy is converted to internal waves. The horizontal distribution of this converted energy has been well‐studied, while its vertical structure has not. Here, we reveal the vertical profile of the energy conversion by employing an idealized ocean model to provide insights into the associated dynamics. The model shows two vertically separated hotspots of energy conversion, one near the seafloor and the other at the thermocline where the temperature and salinity change dramatically in the vertical direction. Although the upper hotspot contributed to only a small portion of the total energy conversion, it plays an important role for the baroclinic energy radiating onto the shallow continental shelf. By isolating the hotspots and comparing the modeled energy conversion with theoretical predictions, we find a linear relation between them. This provides a convenient way for energy conversion estimation in the real ocean that only the parameters in the thermocline need to be measured, instead of the whole water column. Key Points: Vertical structure of barotropic‐to‐baroclinic energy conversion shows two hotspots, near the sloping bottom and at the thermoclineNear thermocline hotspot provides a small portion of the total energy conversion but is essential in onshore baroclinic energy radiationTotal energy conversion can be estimated from a linear relation between the thermocline energy conversion and an analytical prediction [ABSTRACT FROM AUTHOR]

Diapausing populations of Calanus finmarchicus at depth in the Lofoten Basin (LB) return to the continental shelf and slope off the Lofoten‐Vesterålen Islands during the phytoplankton spring bloom to feed and spawn, forming surface swarms with a great abundance. To study how overwintering populations of C. finmarchicus move with the deep currents and return to the shelf, Lagrangian transport characteristics of particles in deep water between 2008 and 2019 were analyzed using Global Ocean Reanalysis and Simulation re‐analysis data and Lagrangian Coherent Structures (LCSs). Our analyses revealed that persistent eastward transport of diapausing C. finmarchicus between LB and continental slope occurred mainly between 600 and 1,100 m in the Arctic Intermediate Water. The consistency of the vertical distributions of C. finmarchicus abundance and salinity further suggests that physical factors control the horizontal distribution of the species. Hovmöller diagrams of kinetic energy indicate that there is an eastward advection of mean current at depth. The co‐occurrence between the eastward transport of LCSs and the eastward advection of the mean current provides direct evidence that the life history of C. finmarchicus is subjected to physical control in the Norwegian Sea. Plain Language Summary: Overwintering populations of the copepod Calanus finmarchicus in the Lofoten Basin (LB) are critical for maintaining its life cycle and food web in the northern Norwegian Sea. Horizontal advection and particle tracking simulation between 2008 and 2019 were performed using reanalysis data. Our analyses revealed that eastward transport between 600 and 1,100 m in the Arctic Intermediate Water below the Atlantic Water was responsible for moving C. finmarchicus from the LB to the continental slope. The consistency of the vertical distributions of C. finmarchicus and salinity further suggests that physical factors control the horizontal distribution of the species. The trend of decreasing abundance of C. finmarchicus from west to east in January results from the eastward transport of the species and its accumulation on the continental slope. Eastward transport from the basin to the slope is a key process in the life cycle of C. finmarchicus and demonstrates the importance of large‐scale physical‐biological interactions in Nordic Seas. Key Points: Lagrangian Coherent Structures reveal persistent eastward transport between 600 and 1,100 m depth in winter in the northern Norwegian SeaThere is a strong similarity between the eastward advection of the mean current and the eastward transport of diapausing Calanus finmarchicusThis process is a part of the potential spatial and temporal closure of C. finmarchicus life histories at the basin‐slope‐shelf [ABSTRACT FROM AUTHOR]

Material transport caused by mesoscale eddies has been revealed much in the open ocean; however, it is still unclear how much eddy‐induced mass transport in the slope region of the northern South China Sea (SCS). Using the LASG/IAP Climate System Ocean Model (LICOM) from 2007 to 2017, we identified 47 anticyclonic eddies and 97 cyclonic eddies that intruded onto the continental slope, termed slope intrusion eddies. The slope intrusion eddies are more horizontally asymmetric and energetic than those without entering the slope. These eddies induced cross‐slope heat and salt transport of O (1012) W and O (104) kg s−1 owing to their horizontal asymmetry in both Xisha Islands and Dongsha Islands, where are the intrusion zones of mesoscale eddies. Based on the potential vorticity budget, we found that the horizontal asymmetry of velocity was caused by the asymmetry of potential vorticity, which was mainly generated by eddy‐current nonlinear effect in the Dongsha Islands and topographic beta effect in the Xisha Islands, respectively. This study may promote our understanding on the mesoscale dynamics and oceanic energy redistribution in the continental shelf zone of marginal sea. Plain Language Summary: Mesoscale eddies are numerous in the open ocean, and can transport heat, salt, and carbon around the ocean through their movement and asymmetric structure. However, it is unclear how much heat and salt transport is induced by their asymmetry in the continental shelf zone. Using a numerical model, we investigate the three‐dimensional heat and salt transport process of slope intrusion eddies in the northern South China Sea. We find that the asymmetry of slope intrusion eddies induces a cross‐slope heat and salt transport of O (1012) W and O (104) kg s−1, which is comparable to the transport of mean flow. We suggest that variation in the potential vorticity is dynamically linked to the nonlinear effect near the Dongsha Islands and the topographic beta effect near the Xisha Islands. These results contribute to our understanding of the redistribution of oceanic energy. Key Points: The asymmetry of mesoscale eddy induces O (1012) W onshore heat transport and O (104) kg/s salt transportThe asymmetric flow of mesoscale eddy is mainly caused by the asymmetry of potential vorticityThe asymmetry of potential vorticity is primarily induced by eddy‐current interaction in Dongsha Islands and topographic beta effect in Xisha Islands [ABSTRACT FROM AUTHOR]

The evolution of halocline waters in the Makarov Basin and along the East Siberian continental slope is examined by combining drifting platform observations, shipborne hydrographic data, and simulations from a global operational physical model from 2007 to 2020. From 2012 onwards, relatively shallow and cold Atlantic‐derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian continental slope. Their eastward extent abruptly shifted from 155°E to 170°E in early 2012, stabilized at 170°E until the end of 2015, then gradually advanced to reach the western Chukchi Sea in 2017. Such eastward progression led to a strengthening of the associated boundary current and to the shedding of mesoscale eddies of cold Atlantic‐derived waters into the lower halocline of the Makarov Basin in September 2015 and near the East Siberian continental slope in November 2017. Additionally, active mixing between upwelled Atlantic Water and shelf water formed dense warm water supplying the Makarov Basin lower halocline. The increasing contribution from Atlantic‐derived waters into the lower halocline along the East Siberian continental slope and in the Makarov Basin led to a weakening of the halocline, which is characteristic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime may now extend toward the Amerasian Basin. Plain Language Summary: In the Arctic Ocean, the "halocline" is a cold near‐surface layer where salinity increases rapidly with depth. The halocline isolates the sea ice at the surface from the heat stored in the underlying warm and salty water. Hence, the strength of the halocline is a key feature in the maintenance of the sea ice cover. In this study, we use various ocean measurements and computer models to document recent changes in the halocline in the East‐Amerasian sector of the Arctic. In this region, warm and salty water, usually found about a hundred meters deep, was found to become closer to the surface from 2012 onwards. We show that the shoaling of this warm water contributed to the progressive warming and weakening of the halocline in the East‐Amerasian Arctic Ocean. This weakening of the halocline is emblematic of the emergence of a new Arctic regime, previously observed in the Eurasian sector of the Arctic, a region undergoing the growing influence from the Atlantic Ocean. Our study suggests the progression of this new regime, with shallow warm water and weakened halocline, further into the Arctic. Key Points: Ice‐tethered measurements in 2008, 2015, and 2017 in the Makarov Basin highlight changes in the upper and lower halocline propertiesThe cold Atlantic‐derived lower halocline progressed eastward along the East Siberian slope reaching the Chukchi BorderlandThe Makarov Basin lower halocline was increasingly supplied with warmer water resulting from the mixing of Atlantic water with shelf water [ABSTRACT FROM AUTHOR]

Paleozoic (Silurian and Devonian) cherts from Western Bulgaria occur in three tectonic units: Svoge, Lyubash-Golo Bardo and Morava. The SiO2 content in these rocks varies from 76.06% to 96.02%. The silica source and depositional settings of the cherts have been interpreted based on the received geochemical major element data. The calculated Si/(Si+Fe+Al+Ca) ratio and Al-Fe-Mn diagram plotting at non-hydrothermal field suggest that most of silica in the cherts is biogenic or both biogenic and terrigenous in origin. On the other hand, all studied siliceous samples plot into the field of the continental margin sediment environments on the Fe2O3/TiO2 vs. Al2O3/(Al2O3+Fe2O3) diagram. The calculated MnO/TiO2 ratio also indicates deposition in continental shelf or slope environments. [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]

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]