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

Seabed data acquired from the Dongsha Region in the northern South China Sea (SCS) revealed the detailed morphology of sand dune fields on the upper continental slope, at depths between 230 and 1240 m. High-resolution multibeam echosounder bathymetry and multichannel seismic reflection data were used to describe and interpret the distribution, characteristics, and migration of these sand dunes. The sand dunes were distributed as patches on a generally gentle continental slope (gradients≤0.58°), on a seafloor mainly covered by silty and coarse sand. The dunes exhibited distinctly different distribution patterns, geometries, and migration behavior. The trough-to-trough wavelength ranged from 47 to 555 m, the height was 0.1 to 19.8 m, the crest length was 100 m to 10s of km, and the dominant orientation was NE-SW. Based on their distribution and characteristics, the sand dunes were further categorized into (i) sinuous, (ii) barchan, (iii) reticular, (iv) restricted, and (v) superimposed types. Most sand dunes migrated to both NW and SE directions. We infer that, in the Dongsha Region, northern SCS, sand dunes formed and migrated due the world's largest observed internal solitary waves (ISWs). Wave-wave and wave-topography interactions occur as ISWs propagate and undergo polarity conversion during shoaling process, reflection, refraction, diffraction at the Dongsha Atoll. These processes bring about variable and complex local hydrodynamic conditions in the Dongsha Region, dissipate vast amounts of energy, erode the seafloor, and supply the sediment and energy required to sustain the formation and migration of very large sand dunes. Our findings not only enhance our understanding of the intricate relationships between topographic and geomorphologic evolution, sedimentary dynamics and mesoscale motions, but also hold significant importance for various hydrographic applications, such as navigation and submarine pipeline installation. • Sand dunes occur at depths of 230–1240 m on the South China Sea continental slope. • These dunes vary in distribution, geometry, and migration. • Dune formation and migration is due to very large internal solitary waves (ISWs). • ISWs induce variable hydrodynamic conditions as they interact with the Dongsha Atoll. • Our findings have important implications for submarine engineering. [ABSTRACT FROM AUTHOR]

The circulation and water properties of Cape Darnley Bottom Water (CDBW), which is a component of Antarctic Bottom Water (AABW) produced in the Cape Darnley polynya, were investigated using results of mooring measurements and hydrographic data collected by a ship-based conductivity-temperature-depth (CTD) profiler and instrumented elephant seals. CDBW was transported northwestward on the western flank of a gully located in Wild Canyon. As CDBW descended down the slope, its thickness increased from ∼ 100 m to ∼ 600 m. The basic properties of CDBW were determined near the Antarctic Slope Front (ASF), where modified shelf water (mSW) intrudes below the dense part of Circumpolar Deep Water (CDW) and mixes with the overlying CDW to produce CDBW. mSW is shown to be the mixture of 40–45 % CDW, 30–40 % winter water (WW), and 20–25 % shelf water (SW) produced in the Cape Darnley polynya. Compared with CDBW produced in 2008, CDBW produced in 2018 and 2019 was colder and less saline. The enhanced influence of dense WW, which is locally produced on the shelf, is suggested to drive the year-to-year variability of CDBW's salinity, at least in these three years. Water properties indicate that CDBW basically corresponds to a water mass in a transition layer between mSW and CDW. The annual mean transport of mSW contained in CDBW was estimated to be 0.26– 1. 2 × 1 0 6 m 3 s−1 • The basic properties of Cape Darnley Bottom Water are determined near the Antarctic Slope Front. • Cape Darnley Bottom Water is the mixture of Circumpolar Deep Water, Winter Water, and Shelf Water produced in the Cape Darnley polynya. • The enhanced influence of Winter Water is suggested to drive the year-to-year variability of salinity of Cape Darnley Bottom Water. • The annual mean transport of Cape Darnley Bottom Water was estimated to be 0. 26 – 1. 2 × 1 0 6 m 3 / s. [ABSTRACT FROM AUTHOR]

Chemosynthetic ecosystems host unique geological, biogeochemical, microbial and faunistic settings, which provide key ecosystem services for human wellbeing. In the Argentine continental margin, the existence of chemosynthetic ecosystems is still unknown. We present the first finding of chemosynthetic ecosystems in the Argentine deep sea. We assessed and compared biological and geological settings for cold seeps at Malvinas Basin and Colorado Basin and a control site (no gas) at Colorado Basin. We found two cold seeps with crater-like geomorphic features (pockmarks) of 500-m and 1000-m diameter at depths of ⁓500 m. Both cold seeps exhibited methane gas bubbles trapped at the surface of the seafloor, one exhibited seepage into the water column. Cold seeps hosted dense benthic macroinvertebrates (≥300 μm) assemblages consisting mainly of polychaetes, peracarid crustaceans and mollusks. The fauna from Argentinean seeps exhibited δ13C and δ15N stable isotope signatures indicative of multiple trophic levels, supported by both chemosynthetic and photosynthetic sources of energy. The difference in bubbling to the water column was not associated with different trophic input of chemosynthetically-derived sources of energy, suggesting that gas input is mediated by the bubbles trapped in the seafloor sediments. The presence of gas bubbles trapped in the surface sediments of the ocean floor allowed the detection of ecological and trophic characteristics of active chemosynthetic ecosystems. Integration of the sub-bottom dimension can help improve our understanding of the interactions of chemosynthetic ecosystems with seafloor fluid flow in a more reliable manner than the gas plumes. These cold seeps host significant biodiversity and ecosystem functions of the deep ocean. They fall within areas tendered for oil and gas industry development, but have not been a focus of conservation efforts to date. Information provided here can inform effective conservation actions and improve our understanding of the distribution of chemosynthetic ecosystems worldwide. • At the continental slope of Argentina, we described two new active pockmarks with different levels of fluid flux. • Pockmarks affected the community structure of the infauna compared to background sediments. • Stable isotope signatures of δ13C and δ15N indicate the use of chemosynthetic sources of carbon and nitrogen by seep infauna. • We found indicators of local nitrogen fixation associated with the active pockmarks. [ABSTRACT FROM AUTHOR]

Ischia Island is an active volcano representing the emerged sector of an E -W trending volcanic ridge largely extending undersea. Its collapsing behaviour, mainly in the form of fast-moving, terrestrial and submarine debris avalanches, has been recognized during the Holocene, but much less is known about previous gravity-driven processes. Using high-resolution multibeam bathymetric data and seismic reflection profiles, we provide evidence that the Island's southwestern flank has been involved in a slow-moving, deep-seated slope deformation that has displaced large volumes of its apron since the Late Pleistocene and until very recent or contemporary times. A long tongue of deformed seafloor, spreading up to 45 km from the Island over an area of 330 km2, between 500 and 1300 m water depths, has been detected along its southwestern slope. Different types of mass movements, genetically associated with each other, characterize this landslide: 1) a basal slump anticline, corresponding to a bulge on the bathymetry detaching at about 400 m sub-bottom depth; 2) an intermediate-mass movement chiefly consisting of debris avalanches and debris/turbiditic flows; 3) an upper mass movement consisting of hundred-metre size slumps detaching at relatively shallow depths. Conservative estimates indicate that at least 50 km3 of volcano-clastic and hemipelagic deposits have been mobilized, most of which comprise the basal slump anticline. This submarine landslide can be explained as a gravity failure of the continental slope unrelated to volcanism or rather as a process related to the dynamics of the volcanic edifice, which would imply volcano-spreading. • Oceanic and continental volcanic edifices may undergo slow collapse, named spreading • Ischia is an active volcano suspected to undergo long-term subsidence along with seismicity • Its southern, undersea section is affected by fast and long-term landslide phenomena • This long-term gravity instability can be viewed within the concept of volcano-spreading. [ABSTRACT FROM AUTHOR]

The lower part of the Mount Messenger Formation, which crops out along the North Taranaki coast (North Island, New Zealand), is widely regarded to display classic examples of exhumed basin floor fan strata. This interpretation is supported by numerous publications on the sedimentary facies and depositional environments inferred for these strata, which are exposed in coastal cliff exposures about 20 m high with limited lateral extent. Consequently, for almost three decades, this succession has served as an analogue and training ground for geoscientists investigating the features of basin floor fan deposits and their reservoir characteristics. Here, we bring together seismic stratigraphy and seismic geomorphology of 2D and 3D seismic reflection datasets, as well as photogrammetric models based on images collected using uncrewed aerial vehicle (UAV) drones from selected locations along the outcrop belt to challenge this paradigm. We analyzed seismic reflection data in an area immediately offshore and down-dip of the strata exposed in the coastal outcrop and found no objective criteria for submarine fan depositional elements based on accepted seismic stratigraphic criteria. Furthermore, mapping of seismic reflectors revealed large submarine channel systems (up to 3 km wide and up to 200 m deep) within the lower part of the Mount Messenger Formation. Submarine channel depositional elements (less than 250 m wide and 25 m thick) are also observed to incise through the outcrops, but they are generally below seismic resolution. In the context of the regional geology, we conclude that the lower Mount Messenger Formation accumulated as continental slope sediments cross-cut by channels rather than as basin floor fans. This study issues a cautionary tale about applying facies analysis to outcrop with limited 3D exposure to interpret sedimentary environments. The spatial distribution of facies and architectural elements viewed in seismic data are invaluable for testing the veracity of facies interpretations. • Facies interpretations of lower Mount Messenger Formation outcrops on the North Taranaki coastal section are challenged. • Combined seismic stratigraphy and seismic geomorphology of seismic reflection data with photogrammetric models of outcrop. • No objective seismic stratal patterns of submarine fans were observed. Instead, seismic mapping reveals channelform dominance. • Photogrammetric outcrop models are used to identify channel-element margins and bedset parameters. • Lower Mount Messenger Formation was deposited on a continental slope. [ABSTRACT FROM AUTHOR]

Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined 210Pb measurements from 409 cores, AMS14C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 106 t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 106 t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 106 t/a) compared to the deep-water basin (∼16.5–20.1 × 106 t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas. • Distribution of modern sedimentation rates in the South China Sea was illustrated at the basin scale. • The sediment budget and mass balance from a source–to–sink perspective was constructed. • Comparison of sedimentation rates and sediment budgets of the South China Sea and east China seas was conducted. [ABSTRACT FROM AUTHOR]

Planktic foraminifera in biogenic sediments are widely applied as palaeoceanographic tools and the abundances of Globorotalia truncatulinoides have been used over the past few decades as indicators of upper water column changes over geologic time. The two morphological coiling directions of this species (sinistral and dextral) can provide valuable insight into how the upper water masses of the South Atlantic vary in response to climate change. This study aims to document and analyse the abundances of the planktic foraminiferal species G. truncatulinoides and its two morphological coiling directions in two cores from the continental slope of western South Africa at >3500 m water depth to assess the response of upper water masses to Quaternary climate change. The relative abundances of total G. truncatulinoides in the >125 μm size fraction, abundances of the dextral and sinistral forms in the >212 μm fraction and the division into further size fractions (212 μm, 250 μm, 300 μm, 355 μm, >400 μm) were analysed and considered to determine whether these abundances can be related to oceanographic regime shifts in the eastern South Atlantic during the late Pleistocene from MIS 6 to MIS 1. It was found that the Subtropical Convergence was located at a more southern location during MIS 5 and MIS 1, which allows for warmer subtropical species to increase in abundance with increasing Agulhas leakage around the southwestern margin. The thermocline is interpreted to have deepened during glacial terminations and interglacial periods when productivity was relatively lower and temperatures increased. The size fraction of the sinistral form in the >355 μm is dominant in MIS 5, MIS 3 and MIS1, indicating implications for the use of this species at certain size ranges. This study therefore indicates that G. truncatulinoides is a useful tracer of past Quaternary oceanographic changes along the western margin of South Africa, particularly when the coiling directions at the larger size fraction is taken into account. • Globorotalia truncatulinoides is indicative of glacial-interglacial cycles along the western margin of South Africa. • The Subtropical Convergence migrates southwards during interglacial periods. • The sinistral form of G. truncatulinoides increases during interglacial periods. • Globorotalia truncatulinoides abundances vary with the shift in polar fronts and regional sea surface temperatures. • The thermocline deepens during interglacial periods. [ABSTRACT FROM AUTHOR]

The dynamics of the Antarctic ice sheet (AIS) have profound implications for the evolution of the Antarctic continental margin, global ocean currents, and climate changes. Marine sediments from the Antarctic continental margins recorded the history of the advance and retreat of the AIS. In this study, we present an integrated analysis of the sedimentary characteristics of the Early Miocene to Late Miocene of the Ross Sea by using 2D seismic reflection data and cores from International Ocean Discovery Program (IODP) Expedition 374 Sites U1521, U1522, and U1524. The characteristics of the seismic facies and sediments show that the expansion and grounding of the ice sheets across the continental shelf significantly influenced the depositional processes, leading to increased glacial erosion, the formation of prograding wedges, mass transport deposits (MTDs), and mixed (turbidite-contourite) depositional systems since the Early Miocene. The seaward migration of the continental shelf edge and the steepening of the continental slope were mainly influenced by the glaciation of extreme expansion of the AIS. Marked increases in the prograding wedge and MTD are associated with extensive sediment reworking and deposition at the grounding zones and along the continental slope as a result of ice sheet expansion. The development of the mixed (turbidite-contourite) depositional systems was the result of extensive sediment reworking and deposition by gravity flows and bottom currents on the continental slope and the rise. This research provides new insights into the complexity of the ice sheet and the sensibility of marginal sediments in responding to the past climate changes in Antarctica. • Ice sheet dynamics are the main factor of the sedimentary processes on the continental margin. • From the Middle Miocene to the Pliocene, the ice sheet expanded several times to the continental shelf edge. • Expansion of the ice sheet resulted in seaward migration of the continental shelf. • Gravity flows and bottom currents formed a mixed (turbidite-contourite) depositional system. [ABSTRACT FROM AUTHOR]

Submarine canyons are the key structures of the transitional area between the deep ocean floor and continental shelf known as the continental slope. They are important submarine features with high ecological, economic, and scientific value. With continual improvements to global and regional marine bathymetry products, digital bathymetric analysis (DBA) techniques must evolve to support ongoing marine geological research and to advance international bathymetric feature catalogs and mapping products. This study aims to further advance the delineation of submarine canyons and associated sea channels using DBA and the recent open-access GEBCO_2019 global bathymetry grid with 15 arc-second resolution, for a small study region in the southern Celtic Sea. A modified semi-automated delineation method is presented based on combining hydrological network analysis and the topographic position index (TPI), a commonly used parameter available in conventional digital terrain analysis toolsets. For the case-study area of interest, 96 submarine canyons were identified, with higher morphological detail than the previous ETOPO1 and SRTM30_PLUS based studies, which identified 81 and 52 submarine canyons, respectively for the same area of interest. The improvements include an increased number of vertices and limbs per canyon, increased positional precision for canyon starting points and endpoints, and the ability to identify associated sea channels. The results also highlight the importance of pre-processing and parameter localization to effectively exploit higher-resolution bathymetric data, which should also improve scale adaptability for application in different types of continental margins and with high-resolution bathymetry products. Future studies will benefit from the TPI-based identification process proposed in this study to identify submarine canyons and channels on other continental slopes, and to delineate different types of linear depressions from high-resolution digital bathymetry. • A method for extracting submarine canyons and associated sea channels from ocean bathymetry is presented. • The scale-adaptive, TPI-weighted flow accumulation method is adaptable to different types of continental margins. • New global bathymetry is used to extract features with the highest level of details to-date for a case-study region. • The method has potential to be used to map submarine canyons and associated sea channels globally. [ABSTRACT FROM AUTHOR]

The Colorado basin in the SW Atlantic is one of the key exploratory frontier basins along the Argentine shelf. The stratigraphy shows a typical rift basin, divided into two major seismic successions, a Jurassic-Lower Cretaceous synrift followed by an Upper Cretaceous to Cenozoic postrift. They represent, respectively, the breakup of Gondwana and passive margin evolution. While the synrift basin formation was associated with the development of structural grabens, the preservation of thick (thousands of meters) postrift sequences are still debated because they cannot be accounted for only by thermal subsidence. In this work, we conducted a multimethodological subsidence analysis across the Colorado basin, including part of the continental slope. We performed a 1D backstripping analysis on 10 hydrocarbon exploration wells and 32 pseudo-wells, covering the whole basin area and a uniform stretching model, which were supported using dynamic topography data from the study region. From the backstripping analyses, considering the six major postrift sedimentary successions described in the literature, we could recognize three subsidence stages. An initial rapid subsidence stage during the post-rift (125–83 Ma), which is restricted to the main depocenters, followed by a stage of generalized and low subsidence focused on the main axis of the basin (83–33 Ma), with an increase in the last 33 my (33–0 Ma). The stretching models exhibit a typical asymptotic curve, depicting significant subsidence at the onset of the postrift stage, gradually diminishing to minimal values within a few tens of millions of years. Upon comparing the backstripping curves with the stretching subsidence models, particularly during the final flat segments, a residual negative value emerges over time (locally exceeding −500 m), indicating considerable residual subsidence during the Cenozoic postrift evolution along the Colorado Basin. This could be interpreted as dynamic subsidence. This residual sinking in the Argentina shelf matches with dynamic topography numerical models in the study region as well as the occurrence of accumulated slabs in the mantle detected by seismic tomography studies. We propose that the accumulation of slabs along this segment of the South American subduction zone might be the drivers of dynamic subsidence, which assisted to the preservation of a large thickness of post-rift strata along the SW Atlantic margin. • Colorado Basin's post-rifting phase revealed three distinct subsidence stages. • Cenozoic residual subsidence linked to dynamic topography detected. • Dynamic topography unveils mantle slab accumulation from South American subduction. • Atlantic post-rift subsidence differs notably from Africa, influenced by dynamic topography from subducted slabs. [ABSTRACT FROM AUTHOR]

Submarine landslide deposits have been recognized in the downslope of a mega-splay fault of the Kumano-nada continental slope. A sediment core was recovered in the mega-splay fault area to find recent slope failures. The youngest mass transport deposit was identified 1.7 m below the seafloor in the study area based on physical properties, radiocarbon dating, and sedimentary and deformation structures. Kinematic analysis of the ductile deformation structure suggests that the mass transport deposit layer came from the steep slope of the hanging wall of the mega-splay fault. This observation agrees with the major scarp collapse being limited mainly to the source area. However, the mega-splay fault in the source area is considered to be currently inactive. Based on the subseafloor structure in the study area, ridge subduction appears to be indirectly destabilizing the slope sediment on the accretionary prism, creating the conditions for submarine landslides on the forearc slope. • A mass transport deposit was identified at a mega-splay fault zone in the Nankai Trough, which is currently inactive. • Transportation of the mass transport deposit the underlying sediment layer. • The uplifting of the accretionary prism due to the ridge subduction possibly induced the slope failure. [ABSTRACT FROM AUTHOR]

Debris avalanche deposits are developed on slopes in various environments, including submarine volcanoes, continental volcanoes, continental slopes, and mountain ranges. In contrast, research is relatively scarce on the coarse-grained subaqueous debris avalanche deposits formed by the collapse of steep basin margins in continental small rift basins, which are controlled by tectonics. Through the interpretation of satellite imagery, field investigations, and the study of the morphological characteristics and internal structures of sediments, a massive debris avalanche event during the Early Cretaceous, Xiguayuan Formation of the Luanping Basin at the northern edge of the Yanshan tectonic belt on the North China Block, named the Wangying Debris Avalanche Deposit (WYDAD), has been identified and analyzed for its kinematics, dynamics, and long-runout mechanisms. The study reveals that based on sedimentology, internal structures, and basal characteristics, five different types of sedimentary morphologies can be identified from the source zone to the distal zone: convergent ridges and grooves (longitudinal expansion and lateral compression), transverse ridges and grooves (compression), longitudinal ridges and grooves (shearing and stretching), arcuate ridges and grooves (compression), and mixed sediments (radial extension). The grain size of coarse-grained debris avalanche deposits decreases with increasing transport distance and fragmentation due to jigsaw cracking, while matrix content increases. Additionally, the entrainment of fine-grained substrate and the mixing of lake waters during the transport of debris avalanches often evolve into secondary debris flows or high-density turbidity currents. Debris avalanches are likely primarily controlled by regional tectonic activity and volcanic action. Compared to subaerial debris avalanche deposits, the subaqueous WYDAD exhibits characteristics such as low fragmentation, smooth underwater terrain due to water resistance and buoyancy, and higher fluidity. The mechanism for the long-distance, high-speed transport of the WYDAD is explained by "hydroplaning" and high pore pressure generated by non-draining shear. This study provides insights into the transport processes of coarse-grained subaqueous debris avalanche deposits in continental rift basins. It verifies whether such sediments can serve as a primary sedimentary system for CCUS or potential resource storage. [ABSTRACT FROM AUTHOR]

Here we present a record of coccolith variation over the past 14 kyr BP from core KF-02 (25.84°S, 45.2°W; 827 m water depth) collected from the continental slope of the São Paulo Bight (SPB), located in the subtropical western South Atlantic. Additionally, we estimated primary productivity based on Florisphaera profunda nannoliths and compared it with other published investigations on the productivity based on different proxies. The coccolith assemblages varied and agreed with the main regional oceanic and atmospheric changes since the latest deglaciation, likely in response to the terrestrial influence and nutricline depth variations. Among eutrophic species, Gephyrocapsa oceanica was more abundant during times with enhanced productivity promoted by the input of terrestrial material. Emiliania huxleyi and small Gephyrocapsa dominated the middle Holocene samples and probably benefitted from the more stable oceanic conditions and the enhanced light availability promoted by the Brazil Current. The paleoproductivity estimates indicated that moderate levels of productivity persisted since the latest deglaciation with a decreasing trend after the middle Holocene, delaying the productivity reduction that was indicated by other regional studies based on planktonic foraminifera. Apparently, seasonal regional hydrographic conditions were responsible for changing coccolith assemblages, and these were not reflected by the planktonic foraminifera G. bulloides variations. • Paleoproductivity in the subtropical Brazilian margin based on Florisphaera profunda. • Higher levels of primary productivity during late deglaciation in the São Paulo Bight. • Primary productivity declined since the middle Holocene in western South Atlantic. • Late Holocene productivity tends to oligotrophy at the subtropical Brazilian margin. • Seasonal hydrographic variability potentially influenced the coccolith assemblages. [ABSTRACT FROM AUTHOR]

• The poleward shift of SB was concurrent with AABW volume reduction. • Reduction in westward ASC (>10 Sv) accompanied by a partial offshore shift of the 0 °C isotherm at 400 dbar. • CDW temperature increased near the shelf break (∼0.4 °C) beneath partial subsurface freshening. • Dense shelf water was found to the east of Mertz Polynya. Full-depth hydrographic sections of the BROKE experiment in 1996 (across the Antarctic margin from 80 to 150°E; Bindoff et al., 2000) were revisited for the first time during the 2018/2019 austral summer. We describe the subsurface physical oceanography in 2019 and the hydrographic changes between 1996 and 2019 not documented in earlier studies. The survey captured decadal changes in ocean structure from the southern flank of the Antarctic Circumpolar Current (ACC) to the continental shelves. In five cross-slope meridional sections, where 1996 and 2019 measurements are comparable (112, 120, 128, 140, and 150°E), the poleward shift of the southern boundary of the ACC (50–120 km) prevailed near the continental rise. The simultaneous displacement of barotropic ACC fronts and poleward migration of deep water contributed to full-depth warming (0.1–1.6 °C) and potentially to a reduction in the bottom water volume. Freshening was widely observed from the deep to bottom layers (∼0.02 g/kg), with the signal extending from the upper continental slope. Bottom-intensified freshening was accompanied by an oxygenation of 10–20 μmol/kg, indicating that freshening-driven oxygenation of bottom layers counteracted the deoxygenation effect of the poleward barotropic frontal shift. Westward transport of the Antarctic Slope Current decreased by more than 10 Sv from 1996 to 2019 in the five cross-slope sections; its frontal features and current axis shifted offshore by more than 20 km in 112–140°E. Additionally, subsurface warming along modified Circumpolar Deep Water by up to 0.4 °C was commonly detected across the upper continental slope. For the 2019 hydrography, shelf water sufficiently dense to form bottom water (>28.35 kg/m3) was found to the east of Mertz Polynya (142–148°E), implying a pathway for dense shelf water export from the eastern margin of Mertz Polynya. Our findings underscore the importance of sustained efforts for in-situ observations that widely cover the East Antarctic margin. [ABSTRACT FROM AUTHOR]

Clinoforms are ubiquitous depositional surfaces in sedimentary systems. The quintessential shape, with a flat or gentle topset, sloping foreset, and gentle to flat bottomset, is recognizable in the smallest ripple to the kilometer high edges of the continents. Essentially the shape is one which develops with differential sedimentation away from a sedimentary source. Systematic decay of transport competence and/or sediment amount from a site favouring deposition, generates differential loading of a typically lens-shaped sedimentary body. The lithology, grain size, water depth, hydrodynamic factors, transport mechanisms, antecedent topography, relative sea level and sediment rate all interact to create different sizes, slopes and shapes. Meanwhile there are several fundamental similarities between clinoforms, even with the smallest bedwave features (ripples and dunes), despite forming under very different depositional conditions. All clinoforms are to some extent governed by accommodation and energy limiting factors (water agitation and/or flow regime), which controls their height, and by proxy influences slope angle. Lithology exerts a fundamental control, slopes can build to angle of repose, which is higher for coarser non-cohesive sediment, while cohesive sediment develops gentler slopes, and also fail at lower angles. Sediment at angle of repose create steep linear slopes, or slope segments, but conversely linear slopes on continental margins are extremely low angle, probably reflecting high sediment with little along-slope contrast and mud-dominance. Meanwhile clinothems of similar lithology display a wide range of foreset angles, indicating numerous additional controls. Sedimentation rate appears to exert significant control on slope steepness, with limited sedimentation promoting steeper slopes related to basinward thinning deposits. The observation of steeper slopes with greater depth is a response to deepening environments generating the effect of comparatively less sedimentation. Processes are important in controlling slope angle as tidal and wave reworking, debris flows, and overpressure and slope failure, typically create lower angles. Turbidity currents meanwhile are part of a dynamic depositional system which can both steepen or lower a slope. There are four basic clinoform shapes: concave, linear, convex, and sigmoidal. These develop in response to variations in sedimentation along the profile driven by erosion/bypass/factors limiting deposition/accumulation/waning sediment supply. Curvature tends to be an indication of along-slope contrast, such as between erosional and deposition, sandier and muddier lithology or higher and lower sedimentation. Sigmoidal clinothems, associated with more accommodation and higher trajectories, are typically shorter and steeper than concave clinothems. Decaying shear-zone agitation and/or reworking and erosion shapes the rounded rollover. Decaying sediment amount and carrying capacity shapes the ensuing curvature. Concave slopes, lacking topsets and associated with sharp rollovers and low angle trajectories, are often longer with lower angle than sigmoidal forms. Their formation is likely closely linked to increased lower slope accumulation through slope failure, bypass, and/or turbidity currents, but can also be from increased suspension-dominated deposition in smaller clinoforms. In this ripples differ, as the concave to sigmoidal transition is associated with higher energy and erosion rounding the crest, and unlike larger clinoforms, the concave is often steeper than the sigmoidal. [ABSTRACT FROM AUTHOR]

This paper presents a detailed description of the lithostratigraphy of mostly contouritic deposits from the Piedra Buena Terrace (PBT), collected at water depth of 2–2.5 km. It is based upon a multi-proxy investigation of five gravity cores, including visual description and scanning, grain size distributions, microfossils and sand fraction study, supported by the analysis of high-resolution sub-bottom profiles. Two older seismic units were identified in addition to those previously described in the area. The defined lithostratigraphic units were correlated to the upper seismic units, while the age of the younger units was confirmed using AMS-14C dating. In terms of the sedimentary facies, the dark quartz-glauconitic sands, which seem to be a fingerprint of the Piedra Buena Terrace, were investigated by applying the X-ray diffraction and performing grain SEM - SE images. The sandy facies correspond to sea-level low-stands during cold glacials (MIS 2 and MIS 4), when glauconite and terrigenous material were transported from the emerged shelf down and along the Patagonian continental slope by vigorous bottom currents. The latter is confirmed by an occurrence of parts of bi-gradational sequences reported from the grain-size distributions in lithostratigraphic units 2 and 4. Units 1 and 3, represented by mostly hemipelagic calcareous ooze, were formed during warm high sea-level stages (MIS 1 and 3). Unlike Unit 1, Unit 3 also demonstrates clear contourite features, similar to Units 2 and 4. They include common bioturbation, occurrence of mottles, lenses, irregular thin layers of sand, erosional boundaries and hiatuses between and within the units, good sorting of fine sands, and microfossil reworking. Together with our previous data from canyons on the Perito Moreno Terrace and the Ameghino segment, supported by available publications from the PBT and Mar del Plata areas, this study demonstrates that the Patagonian Continental Margin could be used as a natural laboratory to investigate and better understand contourite systems. • Massive quartz-glauconite sands discovered on the PBT. • Detailed litho- and chronostratigraphy provided for ∼70 ka. • Contourite sediments identified between ∼70 and ∼14ka. • More developped glauconitization phase during glacials. • New seismic units and unconformities identified in the PBT. [ABSTRACT FROM AUTHOR]

The sedimentary record of the western South African continental shelf is condensed compared to the continental slope and contains erosional unconformities, owing to periods of non-deposition, eustatic sea-level fluctuations, episodic uplift and intensified continental aridity. Despite this, the sedimentary record of the continental shelf provides important information on the depositional history and palaeoenvironmental evolution of the region. A core retrieved from the western shelf of South Africa was analysed for its sedimentary composition, lithological variation, foraminiferal content and its relation to the palaeoenvironment of the region. Four depositional facies were identified along the core, namely quartzitic sand, sandy mud, and glauco-phosphatic sand and a glauco-phosphatic gravel. The basal facies consisting of quartzitic sand is interpreted to have been deposited between 15.90 and 14.60 Ma, corresponding to the timing of the Mid-Miocene Climatic Optimum (MMCO). The highly quartzitic nature of the sediments indicate a high terrestrial influence from fluvial sources. The overlying sandy mud facies was deposited between 14.60 and 13.90 Ma based on planktic foraminiferal biostratigraphy. Foraminiferal analyses of these two facies that were deposited in the Langhian stage of the middle Miocene point to subtropical sea surface conditions and mesotrophic benthic environments. Sea level was noticeably higher during the MMCO and part of the cooling period following the MMCO. An erosional surface that spans 10.77 Myr, equal to the late Miocene (13.90 Ma) to early Pliocene (3.13 Ma), marks the boundary between the two Langhian facies and the overlying two Pleistocene facies, consisting of coarser grained glauco-phosphatic gravelly sand units. The Pleistocene environment on the shelf is interpreted to contrast with the Langhian environment, where cooler, shallower conditions and a more eutrophic benthic environment was prevalent, during a time that Benguela upwelling intensified with higher frequency and higher amplitude sea level fluctuations. Palaeobathymetric interpretations indicate that middle Miocene sea-level in the region were up to 77 m higher than present day and 101 m lower in the Pleistocene, in-line with previous global studies. Glauco-phosphatic content that increase up-core also marks the shallowing of the environment under high productivity conditions. • Core stratigraphy reveal a sedimentary record from the middle Miocene to Pleistocene. • Highly quartzitic nature of sediments reveal terrestrial influence. • Glauco-phosphatic content increases up-core supporting shoaling of environment. • Middle Miocene palaeoenvironment interpreted to be warm subtropical and mesotrophic. • Pleistocene palaeoenvironment reflects high upwelling conditions in cooler waters and a eutrophic benthic environment. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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

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

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

When the internal tides encounter topography during propagation, the scattering effect will induce the baroclinic energy to transfer from the low mode to the higher mode, which may cause the internal tide to become unstable or even enhance dissipation. The characteristics of scattering of mode-1 M 2 internal tide in the northern South China Sea (SCS) and its impact on baroclinic energy dissipation are explored in this study based on numerical simulations. The results show that the energy flux of the mode-1 M 2 internal tide gradually weakens during propagation into the South China Sea. In the northern SCS, which has more complex topography, such as the continental slope, scattering will occur, resulting in a vertical mode increase and shear enhancement, and finally, the baroclinic energy is dissipated. Next, the effect of different topographies on mode-1 M 2 internal tide scattering is analyzed by ideal experiments. The mode-1 M 2 internal tide is scattered by topography, and the propagation as well as dissipation are also modified. The results show that the strong energy flux is mainly distributed on the surface of the continental slope and the area near the slope break. With the increase in criticality, the energy flux around the seamount and on the shelf gradually weakens, and the dissipation rate increases continuously. In addition, the slope topography is more likely to induce internal tide scattering than the seamount topography. • In the SCS, internal tide scattered by topography, vertical mode and shear increased. • Scattering on the slope is stronger than that on the seamount. • Scattering causes internal tide to become unstable or even enhances the dissipation. [ABSTRACT FROM AUTHOR]

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

This work presents the first known application of a new approach to tsunami modelling, by linking a discrete cellular automata (CA) dynamic model of a submarine landslide to an off-the-shelf tsunami modelling package. This has the advantage of simulating the temporal evolution of the submarine landslide rather than as a single rigid sliding mass. We first tested that the coupled model was able to satisfactorily reproduce observed tsunami wave heights resulting from the flank collapse of the Anak Krakatau volcano in the Sunda Strait (Indonesia) in December 2018, before applying it to a speculative area of interest on the North Borneo (Continental) Shelf (NBS). The NBS has one of the thickest near-shore clastic sediment wedges known globally (12 km thickness) and a very long pre-history of submarine landsliding. We modelled a small slide (5 km3 volume) because this is far more likely to occur than a recurrence of the gigantic Brunei slide (1200 km3 volume). Results indicate that a 5 km3 submarine landslide generates multiple tsunami waves, the largest of which reached 8 m at the coast of nearby Balabac Island (The Philippines). Small tsunami waves also arrived on the central Vietnam coast, more than 900 km distant. A larger potential failure on the NBS therefore appears capable of causing a tsunami with greater runup heights, which could pose a risk to much of central and southern Vietnam, northern Borneo (Sabah, Brunei) and Palawan. Finally, we note that the South China Sea is fringed by a necklace of other thick offshore clastic sediment accumulations, most notably on the southern China continental margin, offshore southern Taiwan, and offshore central Vietnam. Given the proof-of-concept of our coupled CA–tsunami modelling approach described here, we recommend this also be applied in these areas to assess the risk posed by a wide range of submarine landslides to coastal populations and infrastructural assets (including nuclear power plants). • This work is a proof-of-concept that cellular automata (CA) can be used to simulate a tsunamigenic submarine landslide. • The CA method for landslide simulation can be coupled with a tsunami generation model. • A small (5 km3) simulated landslide on the Northwest Borneo Shelf produces locally dangerous tsunami waves. • Potential failures on continental slopes surrounding the South China Sea pose significant tsunami risk. [ABSTRACT FROM AUTHOR]

This study examines the variations in relative abundance, test size, and biomass of the species Bolivina ordinaria (Foraminifera) over the last 112 ka BP on the northern slope of the Pelotas Basin, Southern Brazil. The analyses were based on 651 individuals from 42 samples distributed along the cores SIS-249 (Marine Isotope Stage 5 to 3) and SIS-188 (Marine Isotope Stage 3 to 1). Bolivina ordinaria was the most abundant species of the Bolivinitidae family in these cores, particularly during warmer periods (MIS 1 and 5). Nine other species of this family were identified: B. compacta, B. doniezi, B. lowmani, Bolivina sp., B.striatula, Brizalina sp., Brizalina spinescens, Brizalina subaenariensis, and Brizalina subspinescens. Larger test lengths were observed during MIS 3 in the both cores. The summed biomass was higher during MIS 5 in the SIS-249 core and lower during MIS 3 in the SIS-188 core. The fluctuations observed in the relative abundance and summed biomass of B. ordinaria are consistent with the oscillations in total organic carbon flow, and the variations in primary productivity between the interglacial and glacial periods. The results suggest that this infaunal species is favored by the regular supply of refractory organic matter during warmer periods but faces increased competition from shallow infaunal and epifaunal species during glacial periods, when the flow of labile organic matter increases. • The high abundance of bolivinids is associated with meso-eutrophic conditions on the northern slope of the Pelotas Basin. • The biometrics of Bolivina ordinaria offer paleoceanographic insights into glacial and interglacial cycles. • B. ordinaria appears to thrive in response to regular fluxes of refractory organic matter during interglacial periods. [ABSTRACT FROM AUTHOR]

Marine methane hydrates are a huge and dynamic carbon reservoir found mainly at the continental margins, and their stability might be affected by climate-associated pressure and temperature changes on the seafloor. Reconstructing the growth history of cold-seep carbonates, which formed during seafloor methane leakage, could help to constrain methane hydrate stability in the geological past. However, U-Th isotope systematics of these complex carbonate cements have not yet been systematically investigated on the micro-scale, leaving uncertainties in the U-series geochronology which is commonly applied to date the seep carbonates. In this study, we have developed multiple in-situ analytical methods, including U-Th isotope analysis by laser ablation MC-ICPMS, elemental concentration mapping by laser ablation ICPMS, as well as organic distribution mapping by Raman Spectroscopy, to provide insights into the U-series geochemistry and geochronology for the different types of cold-seep carbonates. Our result demonstrates that 238U and 232Th of these carbonates are dominantly derived from seawater and detrital particles, respectively. As the [230Th/232Th] (activity ratio) of micro-domains with high [232Th/238U] is negligibly affected by U decay, we have directly determined the initial [230Th/232Th] of the cold-seep carbonates which is 0.7 ± 0.1 (2 SD, n = 12). In general, U-series isotopes show closed-system behavior within our studied analytical precision in the interior of the seep cements, and the initial [230Th/232Th] derived from the isochron approach is consistent with the in-situ direct determination. A notable exception is a calcitic pipe sample with highly enriched U in its rim which has also experienced post-depositional mobilization. Our method is then applied to a large set of seep carbonate samples from the upper continental slope of the northern South China Sea (SCS). The obtained U-series ages provide evidence that cold seep was likely continuously active since at least ∼72 ka in the northern SCS, but the timing and duration of methane leakage vary between different sites within this region. While the upper continental slope methane hydrates are highly susceptible to destabilization under changing bottom water conditions, our extensive dating on seep carbonates from the SCS further indicates that bottom water P-T conditions could exert contrasting impacts on methane hydrate stability at different depths within the same geological setting. Overall, the in-situ U-series geochronological method developed in our study has the potential to date cold-seep carbonates efficiently and reliably, offering new opportunities to probe into the history of methane leakage in the late Quaternary. [ABSTRACT FROM AUTHOR]

A multidisciplinary approach, involving geochemical, sedimentological and oceanographic analyses, was employed to examine the distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in a strongly anthropized area of the marginal Adriatic Sea (Mediterranean basin). The investigation into PAH distribution considered the grain size and biogeochemical properties of the sediments, as well as in relation to the main oceanographic processes and river inputs. Both biogeochemical and hydrographical inputs regulated the sedimentation of organic particles, influencing the distribution of PAHs. The results indicated PAH levels in 116 marine surface sediments ranging from 4 to 235 ng g−1 (average 55 ng g−1). The distribution of PAHs in Adriatic Sea surface sediments aligned with a higher clayey sedimentation in the deeper basin areas of the Middle Adriatic Depression. [Display omitted] • A multidisciplinary approach combined geochemical and oceanographic aspects. • Level of PAHs in a large area of central and southern Adriatic Sea was evaluated. • The biogeochemical and hydrographical factors regulated PAH distributions. [ABSTRACT FROM AUTHOR]

Based on hydrographic data from two cruises (June 2010 and May 2012) off Baja California Sur, Mexico, historical in situ measurements from the World Ocean Database 2018, California Cooperative Oceanic Fisheries Investigations, and Investigaciones Mexicanas de la Corriente de California cruise programs, as well as satellite images and data from the Global Reanalysis, this study describes the California Current System off Baja California Sur. The California Current System is characterized by the interaction of four near-surface currents. Far from the coast, the California Current flows within the North Pacific Subtropical Gyre but does not reach the Pacific Tropical-Subtropical Convergence off Mexico. From December to June, an equatorward flow known as the Tropical Branch of California Current emerges along the coast. This flow intensifies from March to June and is closely related to the mass flux induced by coastal upwelling. In July, a new branch of the Tropical Branch of the California Current turns poleward along the Baja California Sur coast. This flow is often referred to as the California Surface Countercurrent because it flows in the opposite direction to the California Current. Additionally, the California Undercurrent is detected, influencing the water column from 100 to 900 m, with a maximum poleward flow between 200 m and 300 m, decreasing toward the surface. The California Undercurrent persists throughout the year over the continental slope, displaying a significant semiannual component around the Gulf of California entrance. The California Current System off Baja California Sur plays a crucial role in the formation of Transitional Waters within the Pacific Tropical-Subtropical Convergence off Mexico. The importance of equatorward flows by the Tropical Branch of California Current in ventilating the Oxygen Minimum Zone waters in the Central Pacific off Mexico is emphasized. [ABSTRACT FROM AUTHOR]

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

The family Polymixiidae is an ancient group of acanthomorph fish, often regarded as living fossils. Currently, there are 11 valid species allocated in the genus Polymixia , and commonly known as beardfish. All species are benthopelagic and can be found at depths between 80 and 800 meters, in the Atlantic, Indian, and Pacific oceans. Traditionally, only two species had been assigned to the Atlantic Ocean, P. lowei , in the western Atlantic, and P. nobilis , in the North Atlantic, including northern South America and Saint Peter and Saint Paul Archipelago; however, recent studies revealed a cryptic species from the Bermudas, described as P. hollisterae , and a yet undescribed species from the Caribbean Sea. Herein, we describe a new species of Polymixia from the western South Atlantic, which was previously confused with P. lowei. The new species is supported by both morphological and molecular evidence and can be distinguished among its congeners by a combination of characters, including counts of gill rakers, pyloric caeca, and dorsal-fin rays, arrangement of scales spines, and the shape of preopercle. The new species is distributed on the upper continental slope in Brazil, from Bahia to Rio Grande do Sul, and Uruguay, between 160 and 600 meters deep. • A new species of the living fossil genus Polymixia is described. • Integrative taxonomy reveals a new beardfish from the western South Atlantic. • The Atlantic Ocean harbors a cryptic diversity of the deep-sea genus Polymixia. • Molecular phylogeny reveals allopatric speciation between North and South Atlantic. • Industrial activities and marine litter are threatening Brazilian deep-sea fish. [ABSTRACT FROM AUTHOR]

The purpose of this paper is (i) to re-assess the presence of submarine fan systems of Middle and Late Miocene age (Moki and Mount Messenger formations) previously mapped on the continental slope in offshore southern and central Taranaki Basin, New Zealand, and (ii), to demonstrate the occurrence of two newly mapped Late Miocene submarine fans in the deep-water part of offshore western Taranaki Basin, based on accepted seismic stratigraphic criteria for submarine fans. In our work we have found that the fans previously mapped amongst canyons and channels in the Moki and Mount Messenger formations on the upper and middle continental slope in southern and central Taranaki Basin do not fulfil established stratal criteria for submarine fan deposits. Moreover, detuning of 3D seismic reflection volumes for the Moki and Mount Messenger formation intervals ahead of amplitude attribute extraction, shows that the strata previously mapped as submarine fans based on amplitude alone, are merely artifacts of bed thickness. The two new fans systems of Late Miocene age that we map here, both attributed to the Mount Messenger Formation, principally comprise mudstone and represent a minor proportion of the Late Miocene succession that accumulated in southern and central parts of the basin. Our remapping of slope canyons and channels in the southern part of the basin and the identification of the two new fan systems in the western part of the basin are embodied in three new paloegeographic maps for the Middle and Late Miocene development of Taranaki Basin. A modern analogue for the two new Late Miocene fans in Taranaki Basin is the Hikurangi Fan at the terminus of the Hikurangi Channel, located outboard of the modern subduction zone of the Hikurangi margin along Eastern North Island. The new Taranaki Basin deep-water fans documented here, may have significance for hydrocarbon exploration in deep water parts of Taranaki Basin, which is largely unexplored. • New seismic geomorphologic mapping of the upper Moki and lower Mount Messenger formations in Taranaki Basin, New Zealand. • Critical reassessment of previously published submarine fan systems in southern and central Taranaki Basin and their dismissal on standard seismic stratigraphic criteria. • Seismic mapping of two new submarine fan systems in western Taranaki Basin. • Updated Taranaki Basin palaeogeographic maps for ∼14 Ma, ∼12 Ma and ∼6 Ma. [ABSTRACT FROM AUTHOR]

New bathymetric and subsurface data from the Santos Basin, offshore southeast Brazil, reveal sharp lateral morphological variations facing the margin-parallel (along-margin) flow of the Antarctic Intermediate Water. The data, derived from 3D Pre-Stack Depth Migrated (PSDM) seismic reflection volumes, show on a ∼100 km long Southern segment slope gullies, mass transport deposits, and scars. These morphologies sharply shift laterally to a ∼50 km long Northern segment, typified by a smooth relief built of plastered contourite drifts with occasional elongated depressions. We examine this sharp lateral shift in the morphology of bottom current indicators in view of the hydrodynamical regime, sediment sources, and their distribution pattern. Results indicate that the sharp lateral morphological shift is attributed to (1) a 30° change in slope orientation, and (2) a northward increase in the across-margin velocity component of the Intermediate Water Boundary Current (IWBC). Subsurface data suggest this flow pattern has persisted since the mid-Miocene. In this case study, the lateral morphological shifts under contemporary hydrodynamic conditions emphasize the importance of understanding the coupling between ocean bottom currents and the seafloor in any marine environment. [Display omitted] • New bathymetric and subsurface data from the Santos Basin, offshore southeast Brazil • Sharp lateral shift from down- to along-slope dominated morphologies. • In between - mega slide tunnels shelf sediments to the deep Atlantic seafloor • Flow of Antarctic Intermediate Water along the slope regulates seafloor morphology. • Extent of coupling between ocean bottom current and seafloor is central for seafloor morphology analysis worldwide. [ABSTRACT FROM AUTHOR]

Microstructure measurements of velocity shear from the continental slope of the northwest coast of India (NWCI) in the eastern Arabian Sea are used to quantify the relative importance of double diffusion and internal tides induced diapycnal mixing in the different depth layers. It is found that the hydrographic conditions in the NWCI are conducive to the formation of moderately strong salt fingering (Turner angle between 55° and 72°). However, salt finger-induced vertical mixing dominates only in the upper 180 m of the water column, below which intense shear-driven turbulent mixing due to internal tide reduces its significance. As a result of this, the staircase structures, a measure of salt finger dominance in the water column, are frequent, and the mean temperature change across the interface (DT IH ; 0.33 °C) is relatively larger in the upper 180 m compared to sporadic occurrence of steps with a small magnitude of DT IH (0.18 °C) below 180 m. It is also found that in the upper 180 m of the water column in the NWCI, mean diapycnal diffusivity (K ρ) is approximately a factor of eight larger (8.3 ± 1.3 × 10−5 m2s−1) than the estimation in the open ocean region of the eastern Arabian sea (5.4 ± 1.1 × 10−6 m2 s−1). However, due to internal tides, the magnitude of K ρ reaches as large as O (10−2) m2 s−1 below 180 m in the NWCI. The mean downward heat flux estimated in the salt finger-dominated (upper 180 m) layers is ∼ -6.1 Wm-2, and the shear-driven mixing-dominated layers (below 180 m) is ∼ -10.2 Wm-2. • The relative importance of salt finger and internal tide-induced mixing on the northwest coast of India is evaluated. • Salt finger dominates in the upper 180 m of the water column on the northwest coast of India. • Shear-driven turbulence due to internal tides dominates below 180 m on the northwest coast of India. [ABSTRACT FROM AUTHOR]

Living (rose Bengal stained) benthic foraminiferal faunas, grain size, geochemical parameters (total organic matter, chlorophyll-a, pheophytin-a, molecular markers, and vertical flux of particulate organic matter) were investigated in 14 stations in two submarine canyons Almirante Câmara and Grussaí considered mature and immature, respectively, and on the adjacent continental slope, from 400 to 1300 m water depth, in the southwestern Atlantic Ocean. Samples were retrieved during two campaigns, in the austral winter 2008 and the austral summer 2009. The density, richness, and species composition of the benthic foraminiferal fauna decrease with depth in the canyons and along the adjacent slope transects, reflecting the availability and quality of sedimentary organic matter. Both canyons act as traps of labile organic matter, mainly towards the head of the Almirante Câmara canyon, promoting high specimen density, species richness, and the occurrence of species indicative of pulses of phytodetritus (e.g., Bolivina pacifica , Nonionella opima , and Nonionella stella). Towards the deeper regions of Almirante Câmara canyon and in the adjacent slope area, the lower abundance, diversity, and richness reflect more oligotrophic conditions and an adverse environment in terms of easily metabolizable organic matter. This multiproxy study demonstrates that the canyons in the southeastern Brazilian continental margin play an important role in accumulating organic matter. • Response of benthic foraminifera for particulate organic matter flux. • Behavior of benthic foraminifera to organic compounds in canyons. • Canyons as traps of organic matter in an oligotrophic area. • Colonization by benthic foraminifera after events of sediment disturbance. [ABSTRACT FROM AUTHOR]

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

The southern sector of the northern Argentine continental margin (NACM), extending from 40 to 41° S, corresponds to a previously unmapped area of the South Atlantic Ocean in term of high-resolution bathymetry. Newly acquired high resolution data in the slope sector of the NACM between 900 and 5000 m allowed us to carry out a geomorphological analysis by combining novel multibeam data with a very high-resolution 3D seismic-derived bathymetry. The resultant digital elevation model revealed the presence of a wide variety of seafloor features and allowed us to characterize them by a geomorphometric analysis. Along slope processes, produced by the interaction of contour currents with the seafloor, make up a large array of erosional and depositional elements on the slope, including a contourite terrace, scours, drift bodies and sediment waves, that as a whole form part of a Contourite Depositional System (CDS). Additionally, across slope processes are also present, and give origin to four deeply incised submarine canyons that intersect the CDS. Overall, this work reveals the geomorphological complexity of this sector of the NACM and serves as a reference point for further studies regarding the sedimentary processes and oceanographic dynamics acting in the continental slope. • Geomorphology of a previously unmapped sector of the Argentine continental margin. • Combination of multibeam and 3D seismic-derived bathymetry for high resolution morphometric analysis. • Description of diverse seafloor bedforms, current derived features and submarine canyons. [ABSTRACT FROM AUTHOR]

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

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

One of the eddy "hotspots" in the Black Sea is the area of stationary Sevastopol anticyclone. Here this eddy can reside for >3–6 months significantly affecting the cross-shelf exchange and nutrient fluxes in the Black Sea. Detaching from its stationary location, the eddy moves westward, where it finally dissipates. In this article, we use altimetry measurements and a high-resolution (1 km) Nemo numerical model to investigate in detail the physical processes responsible for the observed evolution of the Sevastopol eddies. The main reason for the stationarity of such eddies is the sharp turn of the continental slope, which plays the role of the meridional wall blocking the vortex propagation in the cyclonic direction. Such a wall is situated at depths of 200–500 m and acts only on sufficiently intense eddies with large vertical extensions, while weak eddies with a small thickness do not feel it. The eddy trajectory near the obstacle represents a cyclonic spiral, which displaces to the southeast before the eddy separation. The process of vortex separation from the wall can prolong for several months and can be divided into 4 stages: 1) Movement to the north after the collision with the meridional wall due to the action of the reactive forces; 2) The formation of an attached submesoscale cyclonic lens-like eddy (SCE) at 200–400 m caused by the rise of horizontal shear due to the interaction of currents with the local uplift of the bathymetry near the continental slope; 3) The movement of the formed vortex dipole to the southwest due to self-propelling force; 4) Displacement of the dipole to the south beyond the meridional wall and further movement of the Sevastopol eddy to the west. During the separation process, Sevastopol AE loses a large amount of energy due to leakage of the mass during its interaction with the wall and transfer of a large part of its energy to the attached SCE. This process explains the observed decrease in the intensity of the Black Sea eddies to the west of the places of their stationarity. Modeled (top panels) and schematic (bottom panels) stages of the stationarity and separation of the Sevastopol eddies. [Display omitted] • Meridional "wall" at 200 m causes stationarity of the Sevastopol anticyclone (SA). • Only intense and vertically-elongated eddies became stationary. • Eddy-topographic interaction causes formation of the submesoscale cyclonic eddy. • The vortex dipole displaces southward and SA separates from topographic obstacle. • SA loses large part of the energy during the separation process. [ABSTRACT FROM AUTHOR]

• The internal architecture of seafloor undulations and the initial growth interface are investigated. • Seafloor undulations are interpreted as a result of Quaternary sediment transport processes. • Inherited faults provide preexisting relief, allowing the initial growth of undulations. Sediment undulations are widely distributed along continental shelf and slope worldwide. The driving mechanisms of undulations are crucial for assessing the long-term stability of continental slope, which, however, remain poorly understood. We used high-resolution 3D seismic data to investigate the internal architecture and origin of a field of seafloor and subsurface undulations along the slope of South China Sea (SCS). The undulations have narrow troughs and broad ridges. The reflection geometries in the troughs between undulations tend to be continuous and not offset by faults. These troughs terminate at different subsurface depths, commonly ranging from 50 to 400 ms in two-way travel time (TWTT) below the seafloor, often at locations related to subsurface geological structures, such as buried faults and steps within mass transport deposits (MTDs). These subsurface terminations therefore suggest that the undulations are probably depositional features not linked to creep-related basal detachment. The troughs between undulations display an absence of growth features, while the undulations increase in amplitude from base to top (characteristics that are also incompatible with gravitational deformation). Erosional and depositional features are commonly found in the undulations; thus, we interpret the narrow troughs between undulations to represent the areas where sediment-laden bottom currents undergo passage from supercritical to subcritical conditions. These troughs nucleated mostly from fault scarps and seafloor steps induced by past slope failures. Previous alternative interpretations report that these features originate from subsurface creep; alternatively, the present interpretation as sediment transport structures has significant implications for seafloor management and engineering projects. [ABSTRACT FROM AUTHOR]

• Macrofauna taxonomic and functional composition remained seasonally constant. • A sediment "food bank" might be responsible for lack of seasonality in macrofauna. • Seasonality in macrobenthic stocks are highly decoupled from pelagic processes. The Barents Sea has been coined 'the Arctic hotspot' of climate change due to the rapidity with which environmental changes are taking place. This transitional domain from Atlantic to Arctic waters is home to highly productive benthic communities. This system strongly fluctuates on a seasonal basis in its sympagic-pelagic-benthic coupling interactions, with potential effects on benthic standing stocks and production. Recent discoveries have questioned the marked seasonality for several high Arctic seafloor communities in coastal waters of Svalbard. Still, the seasonal variability of benthic process in the extensive Barents Sea open shelf remains poorly understood. Therefore, we studied the seasonality of macrofauna communities along a transect in the northwestern Barents Sea comprising two hydrographic domains (Arctic vs. Atlantic Water, across the Polar Front) and three geomorphological settings (shelf, continental slope and abyssal plain). Overall, we did not find strong signs of seasonal variation in taxonomic community structure and functional diversity. However, we found some weak signs of seasonality when examining each station separately, especially at a station close to the Polar Front, with high seasonal fluctuations in abiotic drivers indicating a stronger pelagic-benthic coupling. The lack of seasonality found both at the shelf stations south and north of the Polar Front could be related to organic matter stored in the sediments, reflected in constant levels of total organic carbon in surface sediment across time for all stations. We did observe, as expected, highly spatially structured environmental regimes and macrofauna communities associated to them from shelf to slope and basin locations. Understanding the underlying spatio-temporal mechanisms by which soft-bottom benthic communities are structured along environmental gradients is necessary to predict future impacts of climate change in this area. Our results indicate that short-term climate driven changes in the phenology of pelagic ecosystem components might not be directly reflected in the Arctic benthic system, as seafloor processes seem to be partially decoupled from those in the overlying water. [ABSTRACT FROM AUTHOR]

For the last half century, studies based on an increasing, diverse data set, have focused on passive continental margin evolution, as a result of a sequence of tectonic processes that occur in crustal scale and in the geological time. Where extensive subsurface data exists, two distinct endmembers of continental margin architectures were first described along specific margins of the North Atlantic: 1) wide continent-ocean transitions or hyper-extended; 2) narrow continent-ocean transitions or hypo-extended. The lateral transition between these endmember margins, which can occur laterally in short distances, is still not fully understood. The same two endmember margin types are observed across passive margins around the world and notably along the South Atlantic margin. In an area known for controversial interpretations about the crustal nature and the limits of thinned continental crust, this investigation integrates crustal thickness, seismic interpretation, and facies analyses across ∼150,000 km of seismic data along the Brazilian southeastern margin. This study has implications for those investigating the crustal geometry variations for basin analysis and results impact hydrocarbon assessments for the southeastern margin of Brazil. We resume continental margin analyses, in a critical moment as hydrocarbon exploration advances from the continental slope to ultra-deep waters. Results indicate a marked change from a narrow, hypo-extended, sub-aerial, Iceland-like, plume-related volcanic crust in the Pelotas Basin, to a hyper-extended, Iberia-like, magma-rich crust in the Santos Basin, which is separated by a pronounced oceanic transform-fault zone. Dextral movement along this NW-oriented fault zone accommodated differential extensional rates between the hypo- and the hyper-extended margins. Lateral variations in magmatic content within these margin types are interpreted as result from the interaction with mantellic plumes. Margin architecture can locally be affected by pre-existing fault zones and be later modified by oceanic transform faults. The interactions between crustal extensional rates, crustal rheology, mantle underplating, and volcanic material exhumed through mantle-derived plumes, are the key controls for the evolution of continental margins. Tectonic framework classification proposed in this study presents an alternative, original model for continental passive margins evolution. • Continental passive margin types change laterally in short distances, with variable magmatic content. • The passive margin architecture analysis is a more consistent margin type classification criterion than magmatism. • Hyper-extended passive margins exhibit wide continent-ocean transition (COT), and may be magma-poor or magma-rich. • Hypo-extended passive margins exhibit narrow COT, and also may be magma-poor or magma-rich. • Regional, integrated studies based on potential methods and seismic are recommended to comprehend passive margin evolution. [ABSTRACT FROM AUTHOR]

The presence of marine litter in the deep ocean (>200 m depth) may represent an invisible threat that has been neglected due to the scarcity of data. Herein, we provide the first report of persistent marine litter on the Southwestern Atlantic continental slope. Marine litter was collected onboard the Brazilian R/V Alpha Crucis , using bottom trawling, in 28 out of 31 sampled stations, between 274 and 1520 m depth, in two distinct areas off the southern Brazilian coast. In total, 603 items and 13.8 kg of litter were collected and classified according to the type of material. Plastic was the most frequent and most abundant material found. Although there was no bathymetric variation along the slope, density of litter was considerably higher off São Paulo than off Santa Catarina State, supposedly due to the heavier presence of oil and gas platforms and large cargo vessels. • The deep ocean is, silently, becoming a dumpster of human trash. • Litter was recovered from the Brazilian continental slope, up to 1520 m depth. • Plastic as a major problem: the most frequent, most abundant, and found in all locations. • Food packages produced over 26 years ago were found deposited on the deep-sea floor. • Highly toxic materials from the marine industry bring extra concern about marine pollution. [ABSTRACT FROM AUTHOR]

The Fram Strait is a key region for investigating the exchange of Atlantic water with the Arctic Ocean. Uranium-236 (236U) from the two European nuclear reprocessing plants (NRPs) at La Hague and Sellafield provides a unique fingerprint in Atlantic water which can be used for studying its circulation patterns in the Arctic Ocean. And NRPs-derived 236U (236U NRPs) can be identified by its 233U/236U signature. In this study, we use colored dissolved organic matter (CDOM) absorption to constrain the selection of three Atlantic branch waters that carried different inputs of 236U NRPs in Fram Strait. This can potentially provide better estimates of transit times of Atlantic waters in the Arctic Ocean. High CDOM levels (a 350 ≥ 0.35 m − 1) in Fram Strait reflect the passage of Atlantic water transported to the Arctic by the Norwegian Coastal Current (NCC) and its extension and subsequently along the Siberian continental slope and shelf where the Ob, Yenisei and Lena rivers supply terrestrial organic matter with significantly high CDOM content. Conversely, low CDOM water represents Atlantic water that has remained off the shelf. Based on CDOM absorption, potential temperature (Θ), potential density (σ Θ) and 236U concentration, the path of a given body of Atlantic water could be inferred and an appropriate NRPs input function constrained so that transit times could be estimated. Our results indicate that Arctic High CDOM Water (a 350 ≥ 0.35 m − 1) sourced from the NCC and Barents Sea Branch Water (BSBW) in the Barents Sea Opening has an average of 7–27 yrs transit time in the upper ∼200 m of the western shelf of the Fram Strait. Atlantic Low CDOM Water (a 350 < 0.35 m − 1 , Θ > 2 °C) sourced from the Fram Strait Branch Water (FSBW) has a short pathway from the eastern Fram Strait. Arctic Low CDOM / High 236U Water (a 350 < 0.35 m − 1 , Θ ≤ 2 °C, σ Θ ≤ 27.97 or 236U concentration ≥15 × 106 atom/L) sourced from the BSBW and the FSBW has an average of 22–28 yrs transit time. These findings demonstrate how combining measurements of CDOM with 236U NRPs can improve the robustness in estimation of transit times of different Atlantic water pathways in the Arctic Ocean. There are limited ways to empirically derive estimates and the values provided offer unique data for comparison with estimates from regional circulation models. • New approach defining water classes by combining CDOM and 236U. • 233U applied to isolate the reprocessing plant signal of 236U in the Fram Strait. • Atlantic water reaching Siberian shelf has 14 yrs transit time in the Arctic Ocean. • Siberian shelf water with longer transit time has higher CDOM content. • Atlantic water remaining off-shelf has a transit time of 22–28 yrs. [ABSTRACT FROM AUTHOR]