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As the interface between seawater and the seabed, superficial sediments on the seabed are an important part of the marine acoustic field environment and are indispensable for marine resource investigations. Studying sediments several meters to hundreds of meters below the seafloor is highly valuable and important. This study processes and analyses the water depth, topography and bottom data and obtains the shallow bottom profile and topographic map of the northern continental slope of the South China Sea (SCS). The study analyzes the influence of physical parameter (including density, porosity, and grain size) on the acoustic velocity in sediments. Single-parameter and dual-parameter models are established to further examine this influence. The results show that porosity and density have greater influences on the acoustic velocity of sediments than does grain size. Finally, the acoustic properties of several typical stations with water depths are tested to analyze the variations in the acoustic properties of the shallow sediments in the northern SCS. The results show that the influence of each parameter on the prediction of the acoustic velocity of the sediment is in the following order: porosity>density>grain size. This study analyses and reveals the reason why the seafloor sediments in the local area cause the acoustic properties to change greatly. It may be caused by changes in the sediment type, lithology along with the depth. And the other reason is the development of interlayer in the land slope of the northern SCS. [ABSTRACT FROM AUTHOR]

The sources of supply and transformation of organic matter (OM) as it transitions from dissolved form to particulate matter, fluffy layer, and bottom sediments were investigated along a meridional transect from the Lena River delta to the continental slope (in the depth range of 10 to 2390 meters, cruise 63 of the R/V Akademik Mstislav Keldysh, September 2015). The study of OM molecular markers showed that dissolved and particulate organic matter of marine and terrigenous origin biodegrades in the water column and accumulates insignificantly in bottom sediments. Thus, OM from Lena River runoff does not contribute to the formation of OM in bottom sediments in summer. An area of influence of under-ice blooms on the sedimentation process was identified on the outer shelf. [ABSTRACT FROM AUTHOR]

Wave‐ and current‐supported gravity flows (WCSGFs) represent a primary mechanism responsible for the transport of sediment along gentle coastal and continental slopes. However, due to limited in situ measurements, the dynamic processes involved in the downslope movement of WCSGFs along such slopes remain poorly understood. Here, tripods were strategically deployed on a muddy coastal slope in central Jiangsu, China. We found that WCSGFs occurred following a wave event, particularly during tidal slack periods. In instances where WCSGF events coincide with low slack water, the observed time lags between break and toe sites align with expectations based on gravity‐driven velocities and distances, thereby corroborating the gravitationally induced sediment transport across the gently sloping coast. Comparatively, WCSGF events during high slack water were suggested to originate from the upper tidal flat of the cross‐shore profile and were unable to reach the toe site. Waves are crucial in supporting the downslope transport of WCSGFs. In addition to sustaining the cross‐shore movement of WCSGFs, currents suspend sediments from the high‐concentration layer, dispersing them into the overlying water column. This suspension helps extinguishing WCSGFs. The local slope at the toe site lacks the necessary gravitational force to propel high‐concentration layers further offshore, as evidenced by the abnormally low drag coefficient (CD) derived from the theoretical WCSGF model. Despite their short‐lived nature and limited travel distance, the WCSGFs examined in this study make a significant contribution to cross‐shore sediment transport. This study contributes to a better understanding of WCSGF dynamics and their importance in coastal sediment transport. [ABSTRACT FROM AUTHOR]

The acoustic properties of seafloor sediments on continental slopes play a crucial role in underwater acoustic propagation, communication, and detection. To investigate the acoustic characteristics and spatial distribution patterns of sediments on the continental slope, a geoacoustic experiment was conducted in the northwestern South China Sea. The experiment covered two sections: one crossing the shelf and slope in the downslope direction, and the other near the shelf break in the along-slope direction. In situ techniques, sediment sampling, and laboratory measurements were used to acquire data on sediment acoustic properties (such as sound speed and attenuation) and physical properties (including particle composition, density, porosity, and mean grain size). The experimental findings revealed several key points: (1) Acoustic properties of shallow water coarse-grained sediments and deep-sea sediments were higher when measured in the laboratory compared to in situ measurements. (2) Relationships between measured attenuation and physical properties, as well as between sound speed and mean grain size, showed deviations from previous empirical equations. (3) Sediment acoustic and physical properties exhibited significant variations in the downslope direction, while showing gradual variations in the along-slope direction. These variations can be attributed to sedimentary environmental factors such as material sources, hydrodynamic conditions, and water depth. [ABSTRACT FROM AUTHOR]

The study analyzes polycyclic aromatic hydrocarbons (PAHs) isolated from bottom sediments of the Barents and Norwegian seas (2019–2021 cruises of the R/V Akademik Mstislav Keldysh). Elevated PAH concentrations (up to 16 900 ng/g) are recorded in the coastal region of the Svalbard archipelago, and low ones, in the Greenland Basin and the eponymous ridge (up to 80 ng/g), as well as on the continental slope of the Barents Sea (up to 240 ng/g on average). Among cata-condensed PAHs, 2–3 ring polyarenes are the most common: naphthalene, 1- and 2-methylnaphthalenes, and phenanthrene, while among peri-condensed PAHs, 4–6 ring polyarenes are the most typical: fluoranthene, pyrene, and benz(a)anthracene. Anthropogenic sources in the bottom sediments of the study area are of subordinate importance compared to their natural input from the sedimentary stratum with fluid fluxes and erosion. [ABSTRACT FROM AUTHOR]

The features of the concentration distribution of 238U, 232Th, and 226Ra in the surface layer in the bottom sediments of the shelf and continental slope of Svalbard are considered. The content of 226Ra, 232Th, and 238U varied in the range 22–134.3, 22.4–50.9, and 10.9–37.7 Bq/kg, respectively. The amount of 226Ra nonequilibrium with 238U (226Raex) ranged from 23 to 73% of the total 226Ra content in sediments. The maximum concentrations of 226Ra, 238U, 232Th, and 226Raex (134.3, 37.7, 50.9, and 98.2 Bq/kg, respectively) were obtained in the area of increased bioproductivity (Eagle Trough). In this zone, the relationship between the concentrations of 226Ra and 226Raex with the content of organic matter in sediment is well expressed, the correlation coefficients are R = 0.94 and 0.92, respectively, which indicates a significant contribution of the biological community to the accumulation of 226Ra in bottom sediments. The 226Ra concentration and the 226Ra excess value are negatively related to the redox potential of the sediment (R = –0.88). This pattern is also true in other areas of the Svalbard waters. In general, for the entire array of observations, the concentrations of 238U and 232Th increase with increasing content of organic carbon in the sediment (R = 0.72 and 0.7, respectively). The concentrations of 238U and 232Th decrease with increasing Ccarb content in the sediment (R = –0.79 and –0.81, respectively). The data obtained indicate the need to take into account the 226Ra excess when assessing the total natural radioactivity of marine sediments, the value of which may exceed the radioactivity of 238U and 232Th. [ABSTRACT FROM AUTHOR]

In the Mesozoic succession of the Anyui–Chukotka fold system (North‐East Russia), five stratigraphic intervals were recognised that have an abundance of gravity flow deposits. These are the Olenekian (Lower Triassic), Upper Carnian, Upper Norian, Oxfordian–Kimmeridgian and Valanginian. The Triassic gravity flow deposits formed on the south‐facing, passive margin of the Chukotka microplate and consist of greywackes and lithic arenites. Palaeocurrent data indicate that the flows were directed towards the south‐east. The Olenekian gravity flow units consist of clast‐rich sandstone deposited on the continental slope, and clast‐poor sandstone deposited at the base of the slope. Upper Carnian mud‐poor sandstones were deposited at the base of the slope and the Norian thin‐bedded turbidites were upper to mid‐slope deposits. The continental margin was affected by tectonism and was uplifted in the latest Triassic–earliest Jurassic, possibly due to the initiation of the southward translation of the Arctic Alaska–Chukotka microplate. Following an Early–Middle Jurassic uplift of the area, sedimentation resumed in the Late Jurassic and earliest Cretaceous. Several syn‐orogenic depressions (Rauchua, Pegtymel, Pevek, Myrgovaam and Kytepveem) developed on the south‐western margin of the Chukotka microplate, and deposition in these basins included gravity flow deposits at various times. In both the Oxfordian–Kimmeridgian and Valanginian successions, gravity flow deposits included arkosic and subarkosic sandstones with a northern source area of granitoid complexes and deformed Triassic strata. The intervening Tithonian–Berriasian gravity flow deposits consisted mainly of thin‐bedded turbidites. These sediments had a southern source, which included a volcanic arc that had accreted to the southern margin of the Chukotka microplate. [ABSTRACT FROM AUTHOR]

The study analyzes polycyclic aromatic hydrocarbons (PAHs) isolated from bottom sediments of the Barents and Norwegian seas (2019–2021 cruises of the R/V Akademik Mstislav Keldysh). Elevated PAH concentrations (up to 16 900 ng/g) are recorded in the coastal region of the Svalbard archipelago, and low ones, in the Greenland Basin and the eponymous ridge (up to 80 ng/g), as well as on the continental slope of the Barents Sea (up to 240 ng/g on average). Among cata-condensed PAHs, 2–3 ring polyarenes are the most common: naphthalene, 1- and 2-methylnaphthalenes, and phenanthrene, while among peri-condensed PAHs, 4–6 ring polyarenes are the most typical: fluoranthene, pyrene, and benz(a)anthracene. Anthropogenic sources in the bottom sediments of the study area are of subordinate importance compared to their natural input from the sedimentary stratum with fluid fluxes and erosion. [ABSTRACT FROM AUTHOR]

The results of gas geochemical and lithogeochemical studies of bottom sediments in the Tatar Strait trough (Sea of Japan) based on cruise data from the R/V Akademik M.A. Lavrentyev (LV-81 and LV-85) are presented. Anomalies of hydrocarbon gases (HCGs) and chemical elements in the surface bottom sediments were determined. It has been established that sediments with anomalous methane contents are significantly enriched in Mn, Sc, V, Co, Ni, Cu, As, Se, Mo, Cd, Sb, Te, Tl, and U, the coefficients of the concentration (Kc) of which are 1.3–5.9 times higher than similar values at other stations. The data obtained allow us to assume the presence of gas sources of hydrocarbon migration; the continental slope and deep-water area of the Tatar trough are promising for setting up detailed work on the assessment of the oil and gas potential and the gas hydrate content. [ABSTRACT FROM AUTHOR]

Continental slopes can play a significant contribution to marine productivity and carbon cycling. These regions can harbour distinct geological features, such as salt diapirs and pockmarks, in which their depressions may serve as natural sediment traps where different compounds can accumulate. We investigated the prokaryotic communities in surface (0–2 cm) and subsurface (18–20 or 22–24 cm) sediments from a salt diapir and pockmark field in Santos Basin, Southwest Atlantic Ocean. Metabarcoding of 16 samples revealed that surface sediments were dominated by the archaeal class Nitrososphaeria, while the bacterial class Dehalococcoidia was the most prevalent in subsurface samples. Sediment strata were found to be a significant factor explaining 27% of the variability in community composition. However, no significant difference was observed among geomorphological features. We also performed a metagenomic analysis of three surface samples and analysed the highest quality metagenome-assembled genome retrieved, which belonged to the family CSP1–5, phylum Methylomirabilota. This non-methanotrophic methylotroph contains genes encoding for methanol oxidation and Calvin Cycle pathways, along with diverse functions that may contribute to its adaptation to deep-sea habitats and to oscillating environmental conditions. By integrating metabarcoding and metagenomic approaches, we reported that CSP1–5 is prevalent in the sediment samples from Santos Basin slope, indicating the potential importance of methanol metabolism in this region. Finally, using a phylogenetic approach integrating 16S rRNA sequences assigned to Methylomirabilota in this study with those from a public database, we argued that CSP1–5 public sequences might be misclassified as Methylomirabilaceae (the methanotrophic clade) and, therefore, the role of these organisms and the methanol cycling could also be neglected in other environments. [ABSTRACT FROM AUTHOR]

Interest in the study of microplanktonic organisms in the Arctic has increased owing to their direct participation in the process of sedimentation and sensitive response to changes in environmental and climatic factors. This study presents new data on the taxonomic diversity and content of radiolarian skeletons and agglutinated tintinnid ciliate loricae in the Upper Holocene sediments of the Laptev Sea, East Siberian Sea, and the adjacent part of the Arctic Ocean. We traced the spatial distribution of representative microfauna of these groups in surface sediments and sediment cores. Radiolarian skeletons were found in the surface sediments of the continental slope of the Laptev Sea and adjacent parts of the Arctic Ocean. These belong to the following six species: Stylatractus (?) sp., Actinomma leptoderma leptoderma, Actinomma leptoderma longispina, Streblacantha circumtexta, Spongotrochus glacialis, and Cycladophora davisiana. The radiolarian fauna detected was in deep sea and close to the fauna of the Nansen Basin (Central Arctic). Furthermore, we found tintinnid ciliate loricae belonging to the following seven species: Tintinnopsis ventricosoides, Tintinnopsis fimbriata, Tintinnopsis turbo, Tintinnopsis nitida, Tintinnopsis sp. cf. fusus (?), Tintinnopsis sp., and Stenosemella nivalis. In the study area, the tintinnid ciliate loricae of these species were discovered for the first time and traced mainly in the coastal shelf zone, which can be explained by their ecology. The only exception is that of T. nitida, which was found only on the continental slope of the Laptev Sea. Our findings advance knowledge on the biodiversity of Arctic seas and can be used to monitor ecological and paleoceanographic changes in the Arctic region. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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]

This paper reports new data on the composition of hydrocarbon gases in bottom sediments of the Laptev–East Siberian marginal shelf transition zone, the continental slope of the Lomonosov Ridge, and Podvodnikov Basin of the Arctic Ocean. Anomalous concentrations of methane and hydrocarbon gases (up to C5 inclusive) have been established. Gas-geochemical indicators of eight genetic groups of hydrocarbon gases have been determined. The oil-and-gas content of the study area has been predicted based on the data obtained. [ABSTRACT FROM AUTHOR]

This study presents a systematic analysis of double-frequency (DF) microseisms recorded on the unconsolidated sediments in the eastern and southeastern coasts of United States. For all recordings, the site effect parameters (predominant frequency (f0), amplification factor and unconsolidated sediment thickness (UST)) are obtained by Nakamura method and the DF spectra are classified into five groups in terms of the DF peak patterns and the recording locations relative to the coastline. The frequencies and energy levels of the DF peaks in horizontal direction and the amplification factors are associated with the UST which is resulted from seismic site effect. By polarization analysis, the primary vibration directions of the DF peaks are identified and presented as great circles passing through the recording stations intersecting mainly along the continental slope. Correlation analyses of time histories of the DF energy and the ocean wave climate observed at buoys show that the low (<0.2 Hz) and high (>0.2 Hz) frequency DF microseisms are generated in the deep ocean and the continental shelf respectively. It is concluded that the continental slope plays a significant role in the generation of DF microseisms as it causes reflection of waves from the open ocean, initiating standing waves. [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]

[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]

To increase the proxy toolbox for the reconstruction of redox conditions, the transition metal tungsten (W) has been increasingly suggested as a promising new candidate during the last few years. However, compared to other trace metals such as molybdenum (Mo), studies on the redox behavior of W in the brackish/marine environment are relatively rare and mainly limited to euxinic settings. To contribute to our understanding of the behavior of W in modern aquatic ecosystems, we here present a water column W and Mo dataset that follows the salinity gradient of the Pearl River Estuary towards the adjacent coastal and offshore waters of the northern South China Sea (water depths range from 36 m to 3735 m) with the latter also including mostly anoxic porewater and rather oxic sediment surface data. Except for deviations of W in the low-salinity reaches of the Pearl River Estuary, both metals are conservatively introduced to the coastal ocean. The contribution of dissolved W via the Pearl River plume was identified in surface waters along the coastline. In line with previous open ocean studies, the conservative behavior of W proceeds towards the remote parts of the study area with surface waters that are possibly also affected by the South China Sea Warm Current. Within the short core porewater profiles, W concentrations increased with sediment depth and reached the highest levels at the more distal sites. These trends are not linked to the formation of more soluble thiotungstate species as indicated by generally non-sulfidic porewaters. Along with porewater gradients of W, the W concentrations in near-bottom waters suggest effective trapping of W at the sediment/water interface by Mn oxides especially at greater water depths and limited contribution to the open water column W inventory. In contrast to W, Mo concentrations show little variation in the reducing porewaters and remain close to or slightly above the ocean level. Enrichments of W and Mo in the surface sediments from the upper and lower continental slope reflect the known affinity of both trace metals to Mn oxides. Positive correlations of W with the heavy mineral-associated metals titanium (Ti) and zirconium (Zr) in sand-rich deposits of the outer continental shelf subjected to stronger near-bottom currents, further indicate a relation of sedimentary W abundances to the depositional environment. • Except for low-salinity reaches, W behaves conservative in the Pearl River Estuary. • W contribution by the Pearl River plume could be traced only in near-coastal waters. • Non-sulfidic but anoxic porewaters at the shelf and slope show elevated W levels. • Upward diffusing porewater W is efficiently trapped by Mn oxides in surface sediments. • Depositional energy affects solid W contents and its use as redox proxy. [ABSTRACT FROM AUTHOR]

Here we present the mass and carbonate annual fluxes, collected by two sediment traps at 1000 m depth, located on the western and southern deep-water region of the Gulf of Mexico (GM), and compare them with the total mass and carbonate accumulation rates (CAR) from 46 sediment cores retrieved from continental slopes and the abyssal plain of the southern Gulf of Mexico (sGM). CaCO 3 fluxes in the sediment traps located close to 1000 m water depth, range between 15.1 and 22.4 g m−2 yr−1, these values fall on the high-end range of the mean fluxes reported for the global ocean (9–22 g m−2 yr−1). The carbonate fluxes from the water column are remarkably close to the CAR in the lower slope and abyssal sediments of the southern GM, implying that dissolution processes of biogenic carbonate in the sediments below 1000 m are negligible in the sGM. The spatial patterns of CARs in the sediments are mainly linked with surface productivity of calcareous organisms and export to depth over the continental slope and abyssal plain regions, with mean values of 15.7 ± 5.7 g m−2 yr−1 (0.15 ± 0.06 mol m−2 yr−1). However, there are some large areas over the abyssal plain to the north of the Campeche escarpment showing enhanced CAR values most likely as a result from two processes, lateral input from the Yucatan carbonate shelf region and massive collapse events originating at the Campeche escarpment and deposited to the north of the Yucatan Platform. These processes can account for an additional increase in carbonate mass accumulation by approximately 8 g m−2 yr−1 in this area, showing a decreasing gradient towards the N of the escarpment. Lateral transport by turbidity currents of carbonate platform sediments along submarine canyons and probably episodic gravity flows further aid to explain the localized higher carbonate mass accumulation (> 20 g m−2 yr−1) observed at the foot of the continental slopes to the west and south of the southern GM. We estimate total carbonate accumulation estimates for the entire Gulf of Mexico, from the upper slope to the abyssal plain (1000–3750 m), considering the northern deep-water region reported by Giering et al., 2018 , of 0.09 to 0.12 Tmol/yr accounts for 0.8 to 1.8% of all carbonate sedimentation in the ocean below 1000 m. Taking into considerations its small areal extent of <0.3% of the global ocean the GM carbonate accumulation accounts for a factor of 3 to 6 its areal importance, implying that changes in the production and export of carbonate in the GM due to surface ocean warming and acidification processes in this inland sea will have a sensible effect in the global carbon cycle. • Carbonate accumulation rates in the Gulf of Mexico sediments are very similar to sediment traps carbonate fluxes. • Pelagic export of calcareous organisms is the main origin of carbonate in deep-sea sediments of the GoM locally enriched by resedimentation processes. • Carbonate accumulation in the continental margin and abyssal plane of the GM is a factor of 3 to 6 its areal importance of the global ocean. [ABSTRACT FROM AUTHOR]

Okinawa Trough is a transitional zone between the shallow shelf and the deep ocean, which is covered by a large number of terrigenous materials, recording sea-level fluctuations, tectonic activities, and source-sink during the late Quaternary. Based on grain size and trace element analysis of Core S01–10 from the western continental slope area of central Okinawa Trough, high-resolution paleoenvironment records since 14 ka had been obtained. There is a significant positive correlation between the ratio data of Nb, Th, Sc and REE elements of Core S01–10, which reflects the composition characteristics of terrigenous materials. We use REEs and their discrimination plot of Gd/Yb-Yb and La/Yb-Gd/Yb to conclude that the terrigenous materials mainly came from the Yellow River during 14,000–11,500 a. Moreover, grain size parameters and the provenance discriminant function (DF) show that the transportation of terrigenous materials substance from the main rivers in Chinese Mainland (the Yellow and Yangtze Rivers) to the western slope of central Okinawa Trough is affected by the East Asian winter monsoon. This is mainly manifested in two major stages. During 14,000–11,500 a, these indicators fluctuate on the whole, but in the mass, they indicate a strong East Asian winter monsoon stage, which also leads to the formation and enhancement of the low-temperature underflow, leading to the Yellow River as the dominant source. During 11,500–1920 a, these indicators fluctuated more frequently, reflecting the strengthening/weakening of the East Asian winter monsoon in a shorter period. The tendency of East Asian winter monsoon analyzed by using grain size parameters and DF is consistent with the Ti content of Lake Huguang Maar on the whole, which also verifies the feasibility of the results from the side. Overall, the contribution of substance from the relevant source areas is different in different periods, but Paleo-Huanghe remains the main source. According to the study, the analysis of grain size parameters and trace element in the western slope of central Okinawa Trough can indicate changes of provenance, sea level rising and falling and winter monsoon in this area since 14 ka, which is helpful to explore and reconstruct the sediment provenance and Paleoenvironment evolution in this area since the late Pleistocene. • Based on AMS14C ages, grain size and trace elements, high-resolution paleoenvironment records since 14 ka had been obtained. • The terrigenous materials mainly came from the Yellow River between 14,000–11,500 a. • The terrigenous materials to the western slope of central OT is mainly affected by the East Asian winter monsoon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Strong interannual variability of the sediment dynamics in the Gulf of Lion. • Massive sediment accumulation near the Rhone River mouth (∼56 % of the river inputs) • Sediment deficit on the inner shelf due to the long-term reduction of the Rhone inputs. • Storm-induced sediment accumulation in the southwestern Gulf of Lion. • Cold winters mainly impact the southwestern and outer shelf and the submarine canyons. A simulation based on a hydro-sedimentary model was conducted for the period between summer 2010 and spring 2012 in the Gulf of Lion (northwestern Mediterranean Sea) to understand the spatial and temporal variability of sediment transport, erosion and deposition on the continental shelf and slope. Datasets of both simulated and observed current, temperature and suspended matter from the shelf and the Cap de Creus Canyon which is the main export route towards the continental slope, were first compared to assess the reliability of the simulation. The simulation shows the massive sediment accumulation near the Rhone River mouth (∼56 % of the inputs), the accretion along the mid-shelf mud belt, and the impact of dense shelf water cascading on sediment resuspension and erosion inside the Cap de Creus Canyon. The two studied autumn–winter periods were strongly contrasted in terms of meteorological conditions and subsequent impacts on the sediment dynamics. During the first period (2010–2011) dominated by marine storms, the shelf sediment underwent strong changes, the Rhone River sediment load accumulated in a relatively small area, stock of littoral sands moved to the inner shelf (20–40 m) while inner shelf fine particles fed the mid-shelf mud belt and the upper Cap de Creus Canyon. During the second period (2011–2012) with very little marine wind and a particularly cold winter, sediment on the shelf underwent little change except for a southwestward growth of the Rhone River prodeltaic deposit. Sediment from the southwestern end of the shelf as well as from the upper Cap de Creus Canyon was flushed toward deeper reaches by dense shelf water cascading. Cascading also had a more moderate impact in the various canyons incising the continental shelf. Our work supports the view of an unbalanced sedimentary system, with a deficit mainly over the inner shelf, whose main driver is probably the strong and fast reduction of particulate matter inputs from the Rhone River (by a factor of 4 in less than one century). [ABSTRACT FROM AUTHOR]

Geochemical analyses were used to determine the origin and identify the main factors that lead to the metal trace distribution on the surface sediments from the continental slope of Sergipe in Brazil. Sediment samples were collected during the dry and rainy periods, from 36 sampling points distributed at water depths from 400 to 3000 m. In general, no effect of seasonality was observed on the metal concentrations and no significant differences were observed between the depth ranges. The correlation analysis indicated the continental origin as the most predominant, followed by authigenic deposition. Anthropogenic enrichment was not noted, nor was the possibility of adverse aquatic biota effects. The results made it possible to understand the contribution of rivers in the transport and transfer of particulate matter to the coastal region, in addition to providing new information on the content of trace metals in tropical Atlantic sediments. [Display omitted] • The distribution of trace metals did not exhibit any significant difference with depth. • No seasonality effect was noted. • Metal geochemistry was studied in the sediment from the continental slope. • Enrichment factor indicated the non-occurrence of anthropogenic enrichment. • The sediment quality assessed rarely present adverse effects on aquatic biota. [ABSTRACT FROM AUTHOR]

Marine microplastic pollution has become a major global concern in recent years and the fate of microplastics in the ocean is a hot issue of research. We investigated microplastic pollution in surface sediments in the northern South China Sea to explore its distribution characteristics and influencing factors across the continental shelf, continental slope, and deep-sea environments. It was found that the microplastic abundance of surface sediments was 130.56 ± 40.48 items/kg. The average abundance of microplastics in all three topographic areas gradually decreased with increasing distance offshore. However, the differences in microplastic diversity indices between the three areas were not significant and were higher than those in other seas of the world, indicating that the waters of the northern South China Sea are rich in microplastics from complex sources, with more pollution input channels. In the continental shelf, fibrous and low density microplastics accounted for the largest amount, with a low degree of microplastic aging, and were mostly transported by suspended-load. These microplastics were mainly influenced by human activities. In the deep sea, microplastics with higher density were the most abundant and the number of fibrous microplastics was fewer, while the average size was larger, mainly influenced by the bottom currents. These microplastics underwent long-term bedload transport. In the continental slope, the main factors affecting the distribution of microplastics were more complex. In addition to pollution by human activities, the slope also receives microplastic materials carried by bottom currents; therefore, the composition of microplastics in the slope combines those characteristics of microplastics in both the continental shelf and deep-sea areas. The findings of this study indicate that the South China Sea is affected by complex pollution sources under the dual effects of human activities and natural conditions; in particular, the pollution situation in the deep-sea area needs extensive attention. [Display omitted] • Distribution of microplastic and characteristics from the northern SCS are reported. • MPs distribution is mainly affected by human activities and bottom currents. • Continental shelf has higher abundance than continental slope and deep-sea areas. • Deep-sea areas potentially pool large amounts of microplastics. • Prominent MDI in northern SCS reflects the diversity of pollution input channels. [ABSTRACT FROM AUTHOR]

• Selective pressurized liquid extraction of organic biomarkers for paleoclimatology. • Fast and reproducible determination of alkenones, n -alkanes, and PAHs. • The method is robust and applicable to both marine and lacustrine sediments. • Reproducible CPI, ACL, and U 37 K' -derived SST values were obtained. The study of different organic biomarker classes is essential to elucidate global Earth dynamics since different biogeochemical processes play a role in regulating environmental and climatic conditions. However, multiproxy analysis generally consists of labor-intensive and time-consuming methodologies, which hamper the study of a large number of samples. Here, we develop and validate a fast analytical method to quantify different classes of organic biomarkers (PAHs, n- alkanes and alkenones) in sediments. This new method sequentally extracts and fractionates the target compounds using a pressure liquid extraction (PLE) system, which allows us to selectively obtain the analytes by reducing the time of analysis, sample handling and solvent usage. We show that our method provides reproducible results and high recoveries (>70%), and can be applied to a wide range of sedimentary environments, such as oceanic basins, continental slope and shelf, and lakes. Moreover, the method provides reproducible estimates of paleoclimatic indices, such as the carbon preference index (CPI), the average chain length (ACL) and the U 37 K' -derived sea-surface temperature (SST). Therefore, this new method enables fast quantitative multiproxy analysis of oceanic, coastal and lake sediments. [ABSTRACT FROM AUTHOR]

The terrigenous sediment source-to-sink processes in continental margins are determined by complex interactions among climate, sediment discharge, sea level and oceanic circulations on various temporal and spatial scales. The northeastern South China Sea (NSCS) margin is a natural laboratory to catch a glimpse of these processes due to large amounts of terrigenous sediment inputs and continuous sedimentations during the late Quaternary. Based on a 35 m-long sedimentary sequence (core MD12-3429) retrieved from the NSCS upper continental slope, we distinguished sediment sources based on geochemical compositions, and then linked sedimentary responses to sea level change and Kuroshio intrusion over the past 244 kyrs via various sedimentary records including mass accumulation rates (MAR), foraminifera data, grain-size end-member modeling (EMM) and spectral analysis. Geochemical proxies including major element ratios and fractionation parameters of rare earth elements suggest that the detrital sediment in the core was derived primarily from the Taiwan. The MAR of terrigenous sediment yields an average 9.6 g/cm2/kyr, and high MAR values are both observed in glacial and interglacial intervals. The results of EMM reveal three end-members with dominant modal grain sizes of 6.6 μm (EM1), 26.3 μm (EM2) and 49 μm (EM3), respectively. The temporal variations of the finest end-member (EM1) and the coarsest end-member (EM3) demonstrate clearly glacial-interglacial cyclicity, and the spectral analysis indicates the dominance of 100-kyr eccentricity, which suggests that sea level changes are the first-order control for the NSCS continental margin sedimentation. In addition, the temporal variations in hydrodynamic sensitive component (EM2) and its MAR display gradually increasing trends with weakening East Asian monsoon. Combing with modern observation and modeling results, we suggest that enhanced Kuroshio intrusion might account for the transport of Taiwan-derived sediment during the late Quaternary. As indicated by a 31 kyr periodicity in EM2, we infer that the development of El Niño-like condition strengthened the intrusion of oligotrophic Kuroshio from the Luzon Strait, resulting in the obvious increase of Taiwan terrigenous MAR but decreases of the primary productivity in the northeastern South China Sea. This study provides deep insight into the complex terrigenous sediment source-to-sink processes in a fast-changing marginal sea environment during the late Quaternary. • Sea-level change was the primary control for terrigenous sediment source-to-sink processes in the NSCS since MIS7. • Strengthened intrusion of Kuroshio dominated Taiwan sediments transport. • Kuroshio intrusion and ENSO forcing were coupled on glacial-interglacial scale. • Grain size end-member modeling provides insights into sedimentary response to changes of sea level and oceanic circulation. [ABSTRACT FROM AUTHOR]

To inform risk assessments, reliable, time efficient and affordable quantification methods are required for creating a microplastic (MP) pollution baseline in the world's oceans. To facilitate this, MP abundance was investigated in sediments of three contrasting areas of the UK continental shelf: North West of Jones Bank, the Canyons in the Celtic Sea and Dogger Bank in the North Sea, utilising the Nile Red tagging method to assess its time efficiency and cost. Average MP abundance in the top 10 cm was 1050–2700 MP kg−1. MP abundance decreased with increasing sediment depth and increased with increasing water depth. The findings emphasise the extent of MP pollution and illustrate the value of Nile Red for large scale mapping at relatively low cost. [Display omitted] • Three different areas of the UK continental-shelf were investigated for microplastics. • Microplastic abundance increases with water depth and decreases with depth into the sediment. • Microplastic abundance in UK sediments could be as high as 2700 MP kg−1. • Nile Red offers a rapid and low-cost approach to monitoring microplastics on a large scale. [ABSTRACT FROM AUTHOR]

Gas hydrate-bearing sediments provide an extreme and unique habitat for bacteria and archaea, but the relationship between the microbial community and gas hydrate formation is poorly known. In the Shenhu area of the northern South China Sea, it was inferred that the gas source is mixed biogenic-thermogenic, and contradictions exist between relatively low total organic carbon content and high saturation of gas hydrates. The synthesized geophysical and geological evidence showed that deep thermogenic fluid could migrate upward through migrating pathways. In this study, samples were collected from Shenhu area from 224 to 271 mbsf (meters below the seafloor), which covered gas hydrate-bearing sediments (GHBS), free gas-bearing sediments (FGBS), and non-gas hydrate-bearing sediments (NGHBS), and 16S rRNA gene sequencing was used to characterize bacterial and archaeal community structure. The results revealed significant differences of microbial community structure among the three sediment types as indicated by alpha (richness and diversity indices) and beta (Bray-Curtis-based non-metric multidimensional scaling) diversity analyses as well as community composition analyses. In bacterial community, abundant genera included Pseudomonas , Halomonas , Alcanivorax , Thiobacillus , Marinobacter , Rhodococcus , and Dietzia , some of which were identified as putative hydrocarbon degraders. Most abundant archaeal genera were potential methanogenic archaea, and the dominant genera between GHBS and FGBS differed. Multiple types of methanogenesis were noted, and the hydrogenotrophic type was inferred to be predominant. Deviations of temperature of methanogens from the geothermal gradient of the study area again suggested the migration of organic matters. Based on the characterization of bacterial and archaeal community structure in the deep subsurface sediments, we proposed a geological model for the gas hydrate formation and accumulation of the gas hydrate reservoir, emphasizing the possibility of microbially-mediated secondary microbial gas formation from deep thermogenic fluid. This study characterized bacterial and archaeal community structure in deep subsurface sediments, which can provide insight into the potential roles of bacteria and archaea including hydrocarbon degradation and methanogenesis in gas hydrate formation and help reevaluate the contribution of deep thermogenic fluid to gas hydrate formation in the Shenhu area of the northern continental slope of the South China Sea. • 16S rRNA gene sequencing was employed to characterize microbial community of deep subsurface sediments in the Shenhu area. • Significant differences in microbial community structure were observed among sediment types (GHBS, FGBS, and NGHBS). • Putative hydrocarbon degraders and potential methanogenic archaea (with hydrogenotrophic type predominant) were detected. • The contribution of deep thermogenic fluid to gas hydrate formation in the Shenhu area should be reevaluated. [ABSTRACT FROM AUTHOR]

The upper continental slope offshore Romania is a complex area hosting turbidite deposits, multiple types and ages of deep-seated faults, gas hydrates, gas-escape features, and numerous Mass Transport Deposits (MTDs). Multi-scale seismic data sets (2D-high-resolution and near-bottom very high-resolution) were used to study the interaction between such disparate geological features and determine their impact on slope stability. At least five main paleo-valleys have been identified in the north of the Viteaz (Danube) canyon/valley. The most recent channelized systems linked to these valleys formed over a basal layer of MTDs. These MTDs are associated with an unconformity corresponding to the Base Neoeuxinian Sequence Boundary formed during the last major sea-level fall. This erosional surface shows scarp alignments that coincide with underlying faults. We argue that gravity-driven fault reactivation, with possible upward gas/fluid migration along these faults, is a determinant factor controlling sedimentary instabilities. Numerous MTDs are also observed during channel-levees building and reveal local sediment instabilities related to localized erosional process in the canyon. Finally, MTDs recorded within the upper draping unit, suggest that sediment instability also occurred during recent sea level highstand. Sediment pulse, seismicity, and gas hydrates dynamics can also play a determinant role in sediment instability throughout the sediment record. • Five main valleys have been successively active in the north of the Viteaz (Danube) canyon. • They have formed channelized systems during the last Lowstand. • These channels overlie Mass Transport Deposits (MTDs) and associated slide scarps. • Most of these scarps are located over faults attributed to gravity-driven deformation. • The channel sidewalls and slide scarps serve as migration pathways for gas. [ABSTRACT FROM AUTHOR]