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In a submarine canyon-incised continental slope, the observed bottom simulation reflection (BSR) frequently appears not to match with the predicted base of the gas hydrate stability zone (BGHSZ). However, the mechanism behind this discrepancy is often debated due to the lack of in-situ borehole measurements. In the Shenhu area, a submarine canyon region on the northern continental slope of the South China Sea, a suite of datasets, including 3D seismic data, well logs and in-situ borehole temperature measurements enable us to study the gas hydrate stability zone. In-situ borehole temperature measurements reveal a nonlinear geothermal gradient within shallow 200 m-thick marine sediments. The geothermal gradient fit with the uppermost sediment interval (<50 m) neglected produces a better match between the depths of predicted BGHSZ and observed BSR. The gas hydrate stability zone (GHSZ) modeling using in-situ borehole measurement information at Site W07 shows that the predicted BGHSZ agrees well with the imaged BSR located atop an inter-canyon ridge, demonstrating that the gas hydrate system is in a steady state. Two-dimensional GHSZ modeling along seismic profiles transecting the ridge shows that the observed BSRs along the western margin of the ridge are deeper than the predicted BGHSZ. We interpret this apparent discrepancy to be attributed to topographic effects. Two scales of topographic effects, i.e. an alternating distribution of canyons and inter-canyon ridges, and localized crests and troughs over the crest of inter-canyon ridges, are revealed to influence gas hydrate system in the study area. The curved BGHSZ resulted from the topographic effect could facilitate the concentration of gas hydrate by enlarging the accumulation space and sealing free gas immediately below BGHSZ. • Gas hydrate system in the vicinity of site W07 is in equilibrium. • Topographic effect accounts for the apparent discrepancy between the observed BSR and the predicted BGHSZ. • Two scales of topographic effect impact the gas hydrate system in the study area. • Curved BGHSZ facilitates the concentration of gas hydrate. [ABSTRACT FROM AUTHOR]

Train noise is a kind of green, non‐destructive and strong‐energy artificial seismic sources, which is widely used in railway safety monitoring, near‐surface imaging and urban underground space exploration. Distributed acoustic sensing is a new seismic acquisition technology, which has the advantages of dense sampling, simple deployment and strong anti‐electromagnetic interference ability. In recent years, distributed acoustic sensing has been gradually applied in the fields of urban traffic microseism monitoring, crack detection and underground space imaging. However, previous studies mainly focused on microseism interferometry using train event coda noise, and there is limited research on the workflow of interferometry imaging using distributed acoustic sensing–based heavy train events noise (with short coda windows), which produces an abundant of near‐source interference. Aiming at proving the effectiveness of this idea, we investigated a process workflow to get underground shear‐velocity structure based on distributed acoustic sensing recorded heavy traffic noise near Qinhuangdao train station. A weighted sliding absolute average method is used to weaken the strong amplitude to the coda wave level and reduce the near‐source influence. We demonstrated that the cross‐coherence interferometry method, after spectral whitening, has the best effect on sidelobe suppression in the virtual source surface wave shot gathers, through a comparative analysis of cross‐correlation and cross‐coherence results. For obtaining concentrated energy and strong continuity in phase velocity spectra, we selected the time windows with high spatial coherence and signal‐to‐noise ratio not less than 1.2 for stacking from 720 time windows in F–K domain. When dividing subarrays to extract pseudo‐two‐dimensional profile, we set the overlap rate between adjacent time windows to 80% to increase stacking times, enhancing the precision of phase velocity spectra and reducing the errors of picking dispersion curve. Our results show that heavy traffic train events noise (non‐pure coda) can be used to detect underground velocity structure with clear dispersion and high inversion reliability. This research provides a new processing flow for distributed acoustic sensing train noise imaging and can be applied in future urban underground space exploration. [ABSTRACT FROM AUTHOR]

The Xuande Atoll, with a discontinuous reef rim caused by platform drowning, is a typical ellipse isolated platform on the northern slope of the South China Sea. Based on the data of drilling holes, the analysis of surface sediments and high resolution acoustic data, six sedimentary facies are identified in the Xuande Atoll, including reef outer slope, reef front, reef flat, aeolianite sand island, back-reef slope and lagoon. Facies map shows that the elevated reef-rimmed margins with islands are more noticeable on the windward of the platform. With an elevated and discontinuous reef-rimmed margin as well as coarse-grained sediment in the interior platform, Xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios. The facies architecture of the Xuande Atoll is evidently influenced by complex and interacting parameters including antecedent topography, sea level, wind-driven currents, water depth and tectonic subsidence. Different controlling factors exist in the drowning of the windward and leeward sides of the platform margin. The study of modern depositional settings in the Xuande Atoll will provide insight on predictions for ancient carbonate provinces. • This is the first systematically survey on bathymetry, single channel seismic profile and grab sampler in the lagoon of the Xuande Atoll. • A newly established depositional model in lagoonal settings provides insight on predictions for ancient carbonate provinces. • Facies distribution of Xuande atoll is mainly influenced by theantecedent topographyand wind-driven currents. [ABSTRACT FROM AUTHOR]

The complex interplay between thrust wedge deformation, tectonically-induced fluid overpressures, and the complex phases of wedge-top sedimentary depositional systems in active plate convergent margins presents a formidable challenge. The offshore Makran accretionary wedge (MAW) is the world's largest, formed by the convergence of Arabian plate underneath Eurasian plate in the Early Cretaceous, followed by Middle Miocene renewed subduction. In this research, geological and geophysical constraints derived from seismic and borehole stratigraphy, seismic attributes, depth structural maps, isopach maps and 3D structural geological models reveal that Middle Miocene renewed subduction controls thrust wedge deformation. Additionally, it influences deep fluid overpressure and the deformational pattern of wedge-top sedimentary depositional systems. The seismic data analysis suggested that the basement pre-kinematic Himalayan turbidities depositional system (HTDs) have been tectonically incorporated into the accretionary wedge by Middle Miocene renewed subduction, which gave rise to complex folding and N-dipping imbricate thrusting features. These N-dipping imbricate thrust faults initiated sediment underplating and served as major structural pathways for deep fluid overpressure migration, resulting in the formation of fluid escape pipes. The fluid escape pipes exhibit conical and bifurcating geometries with inclination angles of approximately 73°, 90°, and 100°, signifying the upward migration of deep overpressured fluids. Furthermore, the Middle Miocene to Pliocene syn-kinematic piggyback and growth depositional system (PGDs) show progressive thickening (Max ∼3600 m) towards onshore MAW. It lies unconformable above the pre-kinematic HTDs and carries valuable sedimentation records, growth stratal patterns, onlap terminations, and truncations against growing structures, revealed the timing and spatial deformation of thrust faults in 3D space. In contrast, the Pleistocene to Recent post-kinematic progradational depositional system (PDs) exhibits clinoforms marked by top-lapping, on-lapping, and down-lapping reflection, which are primarily controlled by sediment recycling dynamics and sea level change since Pleistocene. It shows progressive thickening (Max ∼1800m) towards the Makran subduction zone and lies unconformably above the syn-kinematic PGDs. Abridging the analyses, the tectonic reconstruction and deformation mechanisms model shows four phases, e.g. (1) initiation of subduction and accretionary wedge formation in Eocene, (2) N-dipping imbricate thrust faults and deep fluid overpressure triggered by Middle Miocene renewed subduction, (3) development of piggyback basins and growth stratal geometries in Middle Miocene to Pliocene, (4) thrust deformation ceases and development of progradational depositional system. • Pioneer findings on Middle Miocene renewed Arabian-Eurasian plates subduction. • Tectonically induced fluid overpressures, and thick wedge-top sedimentary depositional systems identified.. • Syn-kinematic PGDs preserve valuable sedimentation records, growth stratal patterns, and onlap terminations against developing structures. • Stratigraphic architecture of post-kinematic PDs controlled by sediment recycling and sea-level changes. • Deep fluid overpressure sourced from rapid underplated sediments and high sedimentation rate. [ABSTRACT FROM AUTHOR]

The data collected by ocean‐bottom seismometers are unique compared to that of land seismic stations and require preprocessing before use. In this study, we focus on preprocessing seismic data obtained from a passive‐source experiment in the Mariana subduction zone conducted by the Institute of Deep‐Sea Science and Engineering, Chinese Academy of Sciences from 2018 to 2019. We outline the steps involved in preprocessing the data, including time correction using the ocean background noise cross‐correlation function, tilt correction using a transfer function and orientation correction based on seismic wave polarization. Our results show that the maximum clock drifting was ∼4 s on two stations (K06 and K20), whereas the rest of the station waveforms have clock drifting of less than 2 s. Among stations, only the K06 station is tilted, and the tilt angle is 19.82°. We use the P‐wave and Rayleigh wave polarization methods to determine the orientation. Our results indicate that the error in the result obtained using the P‐wave polarization method is less than that of the Rayleigh wave polarization method. Additionally, we address the advantages and disadvantages of these preprocessing techniques. Our goal is to offer a comprehensive overview of the preprocessing process, to assist beginners in the field and to serve as a foundation for future research in passive‐source ocean‐bottom seismometers. [ABSTRACT FROM AUTHOR]

Hemipelagic calcareous ooze is a mixture of biogenic carbonate ooze and detrital terrigenous materials from continental weathering. Understanding its early diagenetic features is critical for geophysical measurement and geo-hazard assessment. However, the early diagenesis of hemipelagic calcareous ooze has rarely been studied due to a lack of samples and in-situ measurement in shallow strata. During IODP Expedition 368, hemipelagic calcareous oozes, up to hundreds of meters thick, were encountered in the shallow subsurface (< 400 m) at two sites (U1501 and U1505) close to the continent-ocean transition zone in the northern South China Sea margin. Here, we use coring and well logging data to perform rock physics diagnostics to characterize early diagenetic processes in hemipelagic calcareous ooze. The calcareous ooze in the study area is primarily chalky marl with the ratio of carbonate to carbonate plus siliciclastic minerals ranging 30% ~ 70%, according to a mineralogy-based lithofaices classification scheme. In the chalky marl interval, pyrite accounts for around 15% of the total mineral composition and this existence may be related to significant post-rift magmatic activity that produced significant amouts of volcanic material. The porosity reduction with depth in the chalky marl interval has three phases and carbonate content is suggested to be the controlling factor affecting porosity reduction. The varying carbonate content in the oozes can result in contrasting mechanical properties and porosities, potentially serving as weak layers for submarine landslides. Additionally, the interface between calcareous ooze and siliciclastic sediment is also a potential failure plane. Therefore, we propose that the development of hemipelagic calcareous ooze has significant implications for seafloor instability on continental margins. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction of NO with propane has been investigated with iron based monolithic catalysts supported on alumina, silica, and titania. The catalysts were characterized by N 2 -physisorption, XRD, SEM, XPS, H 2 -TPR, Py-FTIR and in situ DRIFTS technologies. The different supports had a significant influence on specific surface area, surface morphology, lattice oxygen, redox properties and the acid sites, which resulted in differences in the catalytic activity of NO reduction. The C 3 H 8 -SCR performance decreased in the order as Fe/Al 2 O 3 /CM > Fe/SiO 2 /CM > Fe/TiO 2 /CM. Fe/Al 2 O 3 /CM showed the highest activity with a nitrogen oxide conversion of 100% in the presence of oxygen at 500 °C,which is mainly attributed to the good redox properties and the abundant Lewis acid sites. Based on in situ DRIFT studies, the increase of Lewis acid sites will enhance the formation of NO 2 /NO 3 − species and acetate/formate species, then promote the catalytic activity. [ABSTRACT FROM AUTHOR]

The paleoceanography of the South China Sea (SCS) is poorly understood, although recent cruises and an ODP expedition (Leg 184) have provided a useful general framework. Here we report previously unrecognized multi-km scale sedimentary structures consisting of coupled ridges and troughs within the Early Miocene strata, using high-resolution 3D seismic data from the northern SCS margin. The troughs are interpreted as linear and/or arcuate erosional features which truncate the underlying strata. They range in orientation from E-W in the southern part of the study area to nearly NE-SW in the northwestern part of the study area. The spacing of erosional troughs varies from less than 0.1 km in the southern part to more than 3 km in the northern part, and they are about 50–1500 m in width, with a relief of 10–90 m. The erosional troughs are parallel to the regional strike of the Early Miocene slope of the northern SCS. From their internal geometry, context, regional distribution and most importantly their orientation relative to the paleo-slope gradient at the time of their formation, it is argued that they formed due to the action of bottom currents linked to the broader paleo-circulation regime in the basin. We infer that the paleo-bottom currents intruding from the Pacific flowed along the northern SCS slope, resulting in the occurrence of localized erosional troughs as deep water masses impinged on and interacted with the sea floor topography. This study provides new insights into the Early Miocene paleoceanography of the SCS and demonstrates the utility of 3D seismic data to enhance our understanding of paleo-bottom current circulation regimes. [ABSTRACT FROM AUTHOR]

The island-arc crustal growth rate (IACGR) is the island-arc magma production volume per 1 km width along the arc strike within one million years, and its variations are highly related to slab dehydration and mantle wedge melting. A novel method that includes Earth density modelling, gravity forward and inversion, and arc crustal growth thickness integration is designed to estimate the IACGR. This method can not only estimate the IACGR along the entire arc length but also assess the crustal growth of both remnant and active arcs. Therefore, the estimation result has high coverage and low uncertainty. Here, the Izu–Bonin–Mariana (IBM) subduction zone is taken as a case study region. The estimated time-averaged IACGR along the IBM arc changes between 16 and 59 km3 km−1 Myr−1, with a mean value of 40 km3 km−1 Myr−1, and this result matches the findings of previous studies well. The uncertainties due to crustal thickness inversion are relatively larger than those from flow line reconstruction. The rate results of the Mariana part have lower uncertainties than those of the Izu–Bonin parts since the arc boundaries can be delineated more accurately. The IACGR of the region where a plateau approaches the trench tends to be overestimated because the collision of the plateau with the island arc thickens the island arc crust and bias the uniform pre-existing crustal thickness assumption. [ABSTRACT FROM AUTHOR]

Recently, drilling wells have encountered rich gas hydrates in fine-grained sediments in the northern South China Sea. Gas hydrate in fine-grained sediments is very heterogeneous, and its physical properties are different from those of oil and gas reservoirs. The reliability of the classical logging saturation evaluation models established for diagenetic reservoirs is questionable. This study used four wells in GMGS3 and GMGS4 to evaluate the effects of the application of three typical methods for evaluating saturation with different principles in the unconsolidated fine-grained sediments: nuclear magnetic logging, sigma logging, and the Archie formula. It was found that the value of the lithologic capture cross-section in sigma logging and the rock's electrical parameters in the Archie formula affect the accuracy of the model. Therefore, to obtain a reliable saturation value for fine-grained sediments, an innovative method for the calculation of resistivity and acoustic time is proposed to estimate gas hydrate saturation based on logging data, which is most consistent with the results of core analysis. The overall relative error of the verification well was 5.87%, whereas that of the density NMR logging method was 56%, showing that the accuracy of the newly proposed resistivity DT logging method's saturation formula was significantly improved. Finally, a new model-based cross chart was developed, which can rapidly differentiate gas saturation during drilling. [ABSTRACT FROM AUTHOR]

Gravity anomalies detected by different measurement platforms have different characteristics and advantages. There are different kinds of gravity data fusion methods for generating single gravity anomaly map with a rich and accurate spectral content. Former studies using wavelet based gravity fusion method which is a newly developed approach did not pay more attention to the fusion uncertainties. In this paper, we firstly introduce the wavelet based gravity fusion method, and then apply this method to one synthetic model and also to the northern margin of the South China Sea. Wavelet type and the decomposition level are two input parameters for this fusion method, and the uncertainty tests show that fusion results are more sensitive to wavelet type than the decomposition level. The optimal application result of the fusion methodology on the synthetic model is closer to the true anomaly field than either of the simulated shipborne anomaly and altimetry-based anomaly grid. The best fusion result on the northern margin of the South China Sea is based on the ‘rbio1.3’ wavelet and four-level decomposition. The fusion result contains more accurate short-wavelength anomalies than the altimetry-based gravity anomalies along ship tracks, and it also has more accurate long wavelength characteristics than the shipborne gravity anomalies between ship tracks. The real application case shows that the fusion result has better correspondences to the seafloor topography variations and sub-surface structures than each of the two input gravity anomaly maps (shipborne based gravity anomaly map and altimetry based gravity anomaly map). Therefore, it is possible to map and detect more precise seafloor topography and geologic structures by the new gravity anomaly map. [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]

Cenozoic extension rates were calculated based on 20 seismic profiles across the Qiongdongnan Basin, South China Sea. The results confirmed that the Cenozoic rifting in the Qiongdongnan Basin exhibited multistage extension and spatiotemporal variation. In terms of the N–S striking seismic profiles, the structural forms of the northern and southern sags of the basin were characterized by narrow half grabens, while the structure at the center sag of the basin was characterized by wide and gentle grabens. The fault strikes in the west of the basin were mainly northeast–southwest trending, whereas those in the east of the basin changed from northeast–southwest trending to nearly east–west trending. The extension rate in the east sag was higher than that in the west area. The extension rate in the middle part was lower relative to the east and west sags. This was because the rifting was controlled by the distribution of the main boundary fault along the basin. Temporally, the Cenozoic extension could be divided into three periods: Eocene, Oligocene, and Miocene. The amount of stretching in the three extension stages was unevenly distributed in the entire basin. The maximum was mainly in the Oligocene Lingshui and Yacheng Formations. The Oligocene extension occurred in the entire basin, and the Eocene extension was limited to the Ledong and Changchang sags. Significant fault activity could be observed during the deposition period of the Yacheng and Lingshui Formations and could be attributed to strong extensional activity. The rifting tectonics controlled the distribution of source rocks and oil-generating window as well as hydrocarbon generation, reservoir formation, and accumulation. [ABSTRACT FROM AUTHOR]

Carbonate platforms form informative archives for paleoclimates and their internal structures can also hold crucial information about the tectonic history and carbonate evolution of the ocean basins. The Zhongsha atoll (Macclesfield Bank) forms the largest atoll system in the South China Sea with a surface area of 23500 km2. However, the internal structure and evolution of this atoll system is completely unknown. 2D multichannel seismic reflection data were acquired in 2017 over the Zhongsha atoll in the South China Sea to unravel the stratigraphy, geomorphology, depositional processes, and seismic facies of one of the world's largest atoll for the first time. This Neogene carbonate platform comprises more than 1 km thick carbonate sequence and overlies a metamorphic basement. The southeastern part of the atoll comprises a fault-controlled graben system, which was formed during the Cenozoic rifting stage of the South China Sea. Most of the faults trend NE-SW and E-W and terminate at or slightly above the top of Middle Miocene strata. Atolls and abundant organic reefs initiated on the positive relief and closely mimicked the underlying topography during the Early Miocene. Shallow-water carbonates continued growing through Middle Miocene to present times. Regional uplift led to subaerial exposure, termination of platform growth and karstification during the Miocene. We also reveal a number of fluid-flow features such as vertical sub-bottom venting features (chimneys and pipes), chaotic reflection zones, which provide the first evidence of active fluid venting in the area of Zhongsha atoll. The Neogene sedimentation history of Zhongsha atoll further provide an important paleoenvironmental context for future scientific drilling to better constrain the evolution of Asia Monsoon. • First documentation of seismic stratigraphy and deposition of Zhongsha atoll (Macclesfield Bank), South China Sea. • Reefs and lagoons developed during the post-rift phase, whose onset is marked by a turning point around the time of the formation of reflector T50. • Three drowning events are identified to tentatively imply three episodes of fast sea floor spreading in the study region. [ABSTRACT FROM AUTHOR]

High-resolution 2D and 3D seismic data are used to investigate the morphology, internal architecture and origin of widespread seafloor undulations in the eastern area of a submarine canyon system, northern South China Sea. The seafloor undulations reveal similar seafloor morphologies, and three different types (Types A, B and C) can be classified based on their relative locations and internal seismic characters. Types A and B are observed in the canyon areas, whereas Type C occurs in the canyon heads. Seismic reflections within Types A and C are continuous and have an upslope migrating trend, while Type B seafloor undulations are separated by listric faults. Our analysis reveals the origins of these three different types of seafloor undulations. Type A seafloor undulations are sediment waves formed by turbidity currents flowing through the submarine canyons. Gravity-driven submarine creep resulted in the formation of Type B seafloor undulations. Type C undulations are sediment waves generated by internal waves interacting with the continental slope. Our results provide information about the origin of widespread seafloor undulations in other submarine canyon systems. It is also of great significance to future risk assessments, as the study area now is one of the most active regions for hydrocarbon exploration in SE Asia. • Widespread seafloor undulations are identified on the South China Sea margin. • Three types of seafloor undulations show different morphology and internal character. • Different processes are responsible for the generation of the seafloor undulations. • Correctly identifying their origin is important for future geohazard assessments. [ABSTRACT FROM AUTHOR]

Abstract Linking deep seismic profiles with regional-scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution. Here we map upper and lower crustal thicknesses of the northern South China Sea (SCS) margin in order to investigate the occurrence of depth-dependent crustal extension from the proximal to the distal margin. By comparing upper and lower crustal stretching factors, we find that the northern margin of the SCS is segmented in three parts: (1) sedimentary basins where upper crust is stretched more than lower crust, (2) distal margin where lower crust is stretched more than upper crust, (3) mostly proximal margin regions where the two layers have similar stretching factors. Our results suggest that sedimentary basins and distal margin prominently feature depth-dependent extension, however accommodated by different processes. While differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow, we suggest the distal margin to be affected by a combination of mantle flow-induced lower crustal shearing and sequential fault activity during crustal hyper-extension. Graphical abstract Unlabelled Image Highlights • Regional stretching factor contrasts between the upper and lower crust are mapped in the northern margin of the SCS. • Pressure variations are the main mechanisms for depth-dependent stretching in the sedimentary basins • Mantle upwelling, basin-ward localization and crustal hyper-extension contribute to depth-depend stretching at distal margin. [ABSTRACT FROM AUTHOR]

Abstract The origin and evolution of magmatism in rifting margins are a fundamental geological subject, and remain the focus of intense studies. Unlike the classical magma-poor and magma-rich rifting margins, the northern margin of the South China Sea (SCS) exhibits a strong post-rift magmatism, but the evolution and mechanism of this behavior are still poorly understood. In this work we investigate the detailed structural features of the post-rift magmatism in the crust of the SCS northern margin. Our analysis is based on wide-angle and multichannel reflection seismic data, combined with previous seismological results. Our results show a wide distribution of shallow igneous sills and intrusions. These features are spatially and tectonically linked to the lower crustal high-velocity bodies (HVBs) and submarine volcanism, indicating a causative connection between the three features. Considering the existence of an obvious low-velocity branch of the Hainan plume in the northern SCS and uplift of the lithosphere-asthenosphere boundary, we propose that the HVBs reflect consolidated mafic intrusions which formed the lower crustal reservoirs feeding the overlying igneous sills and intrusions. In the SCS northern margin where abundant extensional and detachment faults can act as magmatic channels, such a dynamic process might cause post-rift volcanism. Our results suggest that the crustal magmatic system of post-rift volcanism has a multilevel upward migration mode, and the HVBs in the lower crust could be the product of post-rift magmatism, further indicating that the SCS northern margin had a magma-poor property at the rifting phase but has undergone a strong magmatic rejuvenation by the subsequent mantle plume. Highlights • Revealing seismic features of post-rift magmatism in the SCS northern margin • Lower crustal HVBs link to shallow igneous sills/intrusions and submarine volcanism. • The crustal plumbing system has a multilevel magmatic-transport mode. • Magma-poor SCS northern margin was rejuvenated by the Hainan mantle plume. [ABSTRACT FROM AUTHOR]

Abstract The great mantle plume debate (GPD) has been going on for ∼15 years (Foulger and Natland, 2003; Anderson, 2004; Niu, 2005; Davies, 2005; Foulger, 2005; Campbell, 2005; Campbell and Davies, 2006), centered on whether mantle plumes exist as a result of Earth's cooling or whether their existence is purely required for convenience in explaining certain Earth phenomena (Niu, 2005). Despite the mounting evidence that many of the so-called plumes may be localized melting anomalies, the debate is likely to continue. We recognize that the slow progress of the debate results from communication difficulties. Many debaters may not truly appreciate (1) what the mantle plume hypothesis actually is, and (2) none of the petrological, geochemical and geophysical methods widely used can actually provide smoking-gun evidence for or against mantle plume hypothesis. In this short paper, we clarify these issues, and elaborate a geologically effective approach to test the hypothesis. According to the mantle plume hypothesis, a thermal mantle plume must originate from the thermal boundary layer at the core-mantle boundary (CMB), and a large mantle plume head is required to carry the material from the deep mantle to the surface. The plume head product in ocean basins is the oceanic plateau, which is a lithospheric terrane that is large (1000's km across), thick (>200 km), shallow (2–4 km high above the surrounding seafloors), buoyant (∼1% less dense than the surrounding lithosphere), and thus must be preserved in the surface geology (Niu et al., 2003). The Hawaiian volcanism has been considered as the surface expression of a type mantle plume, but it does not seem to have a (known) plume head product. If this is true, the Hawaiian mantle plume in particular and the mantle plume hypothesis in general must be questioned. Therefore, whether there is an oceanic plateau-like product for the Hawaiian volcanism is key to testing the mantle plume hypothesis, and the Kamchatka-Okhotsk Sea basement is the best candidate to find out if it is indeed the Hawaiian mantle plume head product or not (Niu et al., 2003; Niu, 2004). [ABSTRACT FROM AUTHOR]

The magma volume flux is reduced by a fracture zone (FZ) crossing the Laccadives-Maldives-Chagos Bank-Mascarene Plateau chain in the Indian Ocean and is negatively correlated with the plate motion rate along the Ninetyeast Ridge (NER). Whether the FZs in the Pacific decrease the crustal magma volume flux and whether the flux along the Hawaii-Emperor seamount chain (HESC) is also negatively correlated with the plate motion rate are both unclear. Focusing on these two issues, we estimate the variations in crustal magma volume flux along the HESC and discussed plume–lithosphere interactions. The present-day crustal thickness is mapped via gravity inversion based on Earth interior density modeling. The accretionary thickness is isolated by filtering the present-day crustal thickness. Then, according to the seamount age variation trend inferred from ages by rock dating, the crustal magma volume flux along the whole HESC is derived. All the FZs correspond well to flux peaks because these weak lithospheric zones provided potential conduits for magma upwelling and promoted magma accretion. However, for the Indian Ocean case, the Reunion plume was captured by the mid-ocean ridge before and after reaching the low-flux transform fault, so the transform fault represented a relatively stronger lithosphere than the nearby mid-ocean ridge. The crustal magma volume flux along the HESC does not correlate with the motion rate of the Pacific Plate because the lithosphere was old during seamount loading, which contrasts with the inverse correlation between these two parameters along the NER, which had a young lithosphere during seamount loading. • Variations in high-resolution crustal magma volume flux along the whole Hawaii-Emperor seamount chain are mapped. • Transform faults increase magma flux when they are far from mid-ocean ridges. • The flux is not affected by the plate motion rate when the overlying lithosphere is old during seamount loading. [ABSTRACT FROM AUTHOR]

Mass transport deposits and geological features related to fluid flow such as gas chimneys, mud diapirs and volcanos, pockmarks and gas hydrates are pervasive on the canyon dominated northern slope of the Pearl River Mouth basin of the South China Sea. These deposits and structures are linked to serious geohazards and are considered risk factors for seabed installations. Based on high resolution three dimensional seismic surveys, seismic characteristics, distributions and origins of these features are analyzed. A distribution map is presented and geometrical parameters and spatial distribution patterns are summarized. Results show that various groups of the mapped features are closely tied to local or regional tectonism and sedimentary processes. Mass transport complexes are classified as slides near the shelf break, initially deformed slumps on the flanks of canyons and highly deformed slumps on the lower slope downslope of the mouth of canyons. We propose them to be preconditioned by pore pressure changes related to sea level fluctuations, steep topography, and fluid and fault activities. Gas chimneys are mainly located in the vicinity of gas reservoirs, while bottom-simulating reflectors are observed within the gas chimney regions, suggesting gas chimneys serve as conduits for thermogenic gas. Mud diapirs/volcanos and pockmarks are observed in small numbers and the formation of pockmarks is related to underlying gas chimneys and faults. This study aims at reducing risks for deep-water engineering on the northern slope of South China Sea. [ABSTRACT FROM AUTHOR]

In this work, Cu 2 O–reduced graphene oxide (rGO) composites were synthesized with tunable Cu 2 O crystal facets ({1 1 1}, {1 1 0} and {1 0 0} facets). The degradation performance of methylene blue under visible light was ranked: o-Cu 2 O{1 1 1}–rGO > d-Cu 2 O{1 1 0}–rGO > c-Cu 2 O{1 0 0}–rGO. UV–vis diffuse reflectance and photoluminescence spectra showed that o-Cu 2 O–rGO exhibited the enhanced visible-light absorption and the faster charge-transfer rate. Furthermore, X-ray photoelectron spectroscopy and Raman characterizations showed that o-Cu 2 O–rGO was beneficial for the stabilization of Cu + species and the formation of oxygen defects. With the help of in-situ electron spin resonance (ESR), more superoxide radicals were detected over o-Cu 2 O–rGO, which promoted organic pollutants degradation. The above results confirmed that the catalytic behaviors of three Cu 2 O–rGO composites were related to the electronic structures and interfacial connections. The o-Cu 2 O{1 1 1}–rGO displayed the superior performance, for the highly-active coordinated unsaturated Cu and the intensive interfacial connection, which was beneficial for the rapid the photo-generated electron transfer and the formed active superoxide species. This study showed that engineering the interfacial structures could provide a scientific basis for the design of efficient photo-catalysts. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sn4+ can be incorporated into the lattice of CeO2 to form uniform Ce x Sn1–x O2 solid solution when the mole ratio of Ce:Sn is not less than 2:1. [•] The incorporation of Sn4+ into the lattice of CeO2 is conducive to the decrease of crystallite size, the increase of lattice strain and the improvement of reduction behavior, which further promote the enhancement of catalytic performance. [•] The catalytic domain (CD, -Ce3+-□-Sn2+- species) in these Ce x Sn1–x O2 mixed oxides plays a key role in NO reduction by CO model reaction. [ABSTRACT FROM AUTHOR]

This is the second part of our study on the resistivity curve responses of marine shale gas reservoirs. The characteristics of the effects of low-porosity systems on electrical conductivity have been explored previously. However, the effects of the pore system and reservoir type should also be carefully considered. The features of the pore system that have the greatest impact on resistivity must be identified so that they can be considered in subsequent studies. This paper shows that the pore type has the most direct effect on the rock resistivity. The relationship between the porosity and resistivity of each pore type is very close. The pore types must be distinguished when considering the application of shale conductivity features. Among the reservoir classification methods considered, those based on reservoir quality characteristics and clustering have the best correspondence with the resistivity curve. In addition, this paper shows that the existing common saturation models are insufficient to evaluate the saturation of shale gas reservoirs. Subsequent research, including the derivation of conductivity models or the performance of shale resistivity experiments and simulations, should fully consider the characteristics of the mineral composition, organic matter and pore types of the rock. This series of analyses paves the way for research on shale gas electrical conduction mechanisms and saturation models, which are for the study of shale gas reservoir petrophysics. This study helps to address the lack of deep rock geophysical research on the large shale gas reserves that have been discovered. • The pore type is the pore system factor that has the greatest influence on the resistivity. • The pore classification method based on pore genesis have the closest relationship with the changes in rock resistivity. • Deriving a conductivity model consider 3 main aspects, the pore type, mineral composition, organic matter content. • Existing saturation models are still difficult to accurately predict the saturation of marine shale. [ABSTRACT FROM AUTHOR]

Submarine canyons are observed along both passive and active continental margins, but the factors controlling their complex morphology are still poorly understood. Here, we use high-resolution multibeam bathymetric and 2D seismic data to investigate an area of the northwest South China Sea in which 48 submarine canyons are identified. These previously unstudied submarine canyons incise the continental shelf, being located at a water depth between 200 m and 2200 m. Canyon morphology varies from southwest to northeast, namely in what their length and incision depth are concerned. We therefore divide these canyons into four main types: a) Types A, B and C showing a predominant NW-SE direction, and b) Type D canyons striking to the north. By analysing their internal architectures, we propose that submarine canyons along the northwest South China Sea margin were initiated in the Late Miocene by retrogressive slope failure in response to the gradual build-up of sediment on the continental slope. Differences in sediment supply and fault activity are recognised here as the main factors controlling the morphology of the investigated submarine canyons. In addition, recurrent mass-transport deposits (MTDs) fed sediment from the northwest South China Sea margin into the study area, accelerating the filling of the Central Canyon system, a giant submarine canyon located to the south of the investigated continental slope. The discovery of gas fields (LS22–1, LS17–2) and a gas hydrate drilling zone (GMGS5) in the Central Canyon system proves that MTDs comprise good reservoir intervals. Our results contribute to a better understanding of the origin and development of submarine canyons and highlight the role of sediment supply and tectonic events in controlling canyon morphology. • Forty-eight (48) submarine canyons are investigated in the northwest South China Sea. • Submarine canyons were initiated by retrogressive slope failure in the Late Miocene. • Sediment supply and fault activity control submarine-canyon morphology. [ABSTRACT FROM AUTHOR]

The complicated response mechanism of shale gas requires that a systematic pilot study is conducted on the influences of resistivity log responses to help with subsequent experimental design, physical derivations and resistivity simulations. The purpose of this research is to clarify the main controlling factors of the resistivity log responses and their semi-quantitative relationship in certain marine shale gas formations. Comprehensive analyses on large core test datasets, including mineralogical, petrological, geochemical and other data, from the Longmaxi-Wufeng Formation and the corresponding resistivity logging curves are carried out in 4 shale gas areas. This research indicates that in low-porosity systems, the mineral composition directly impacts the resistivity. Carbonates with large intergranular pores and even intragranular pores increase the resistivity. The hydrophilic nature of clay decreases the resistivity. When organic matter is not carbonized, the organic matter and biosilica will further increase the resistivity. Pyrite layers will cause a large drop in resistivity (to less than 5 Ω m). The resistivity is lower where organic matter carbonization has occurred in the studied reservoir. Mineral components, especially clay minerals and organic matter, are the main controlling factors of the conductivity of low-porosity systems. In addition, we propose that elemental logging can be used to characterize the comprehensive effect of low-porosity s systems on the resistivity of the reservoir and can accurately reflect the resistivity. These results will help to develop future studies on the relationship between the electrical conductivity and saturation of shale gas rocks, which is of great significance. • Combining the data of 14 wells in four shale gas blocks, the resistivity characteristics of marine shale are systematically and quantitatively analysed. • Shale mineral composition is the non-porous factor that mainly affects resistivity, among which carbonate minerals and combinations of biosilica and (uncarbonized) organic matter will increase the resistivity. • The layered pyrite greatly reduces the resistivity, but the dispersed pyrite has little effect on the resistivity of marine shale. • A semi-quantitative characterization technology for non-porous systems is proposed (ER curve), and the effect of mineral composition on resistivity is semi-quantitatively characterized. [ABSTRACT FROM AUTHOR]

High-resolution seismic and borehole data were used to investigate the sedimentological characteristics of carbonate accumulations in the Pearl River Mouth Basin (PRMB) of the South China Sea. Based on seismic morphologies and petrologic analysis, three scale types of oligo-mesophotic ICBs were identified to have developed ephemerally in the early Early Miocene. The first ICB type is represented by small ICBs with lateral extension in the kilometer range, characterized by mounded geometry, complex internal architectures and a high-frequency alternation of carbonates and volcaniclastics. The second ICB type has lateral extensions of tens of kilometers and convex-up reflections, featuring obvious vertical thickening compared to the surrounding siliciclastic deposits. The third ICB type consist of extensive platforms with hundreds of kilometers of lateral extension, onlapped by surrounding siliciclastic deposits. The correlation of seismic and well data allows us to reconstruct the evolutionary history of the three types of ICBs in the PRMB: All the ICBs built by large benthic foraminifera and/or coralline algae biota, occurred on or around submarine topographic highs such as volcanic edifices or inherited from basement rises, developed under stable subsidence rates between 120 m/Myr and 180 m/Myr, and extinguished suddenly in the late Early Miocene with an abrupt decrease in the subsidence rate or a change from subsidence to tectonic uplift. It is proposed that post-rift subsidence of the study area controlled the evolution of the ICBs. Except for ICBs, mixed carbonate-siliciclastic deposits are identified in well succession, characterized by two types of mixing, namely, compositional mixing (core-plug scale) and strata mixing (stratigraphic scale). These mixed systems generated high-frequency alternations of carbonate, siliciclastic and/or mixed deposits sequence stratigraphy. This work reveals in detail the typical features of seismic morphologies, lithofacies, internal architectures and evolutionary mechanism of ICBs and mixed systems in the PRMB, and thus has implications for predicting reservoirs in hydrocarbon exploration and understanding carbonate sedimentology in a siliciclastic-dominated passive marginal basin. • Describe in detail the typical features of seismic morphologies, lithofacies and internal architectures of the carbonate accumulations in the PRMB. • Establish the evolutionary history of carbonate accumulations in a siliciclastic-dominated basin. • Reveal abrupt decrease in basin subsidence or a change to tectonic uplift triggered the drowning of the ICBs in a siliciclastic basin. [ABSTRACT FROM AUTHOR]

The theoretical model of turbidite bedform evolution has been verified based on laboratory tests and outcrop surveys. However, the evolution of the bedforms associated with flow regime variation within the channel–lobe transition zone (CLTZ) is poorly documented and generally extremely poorly understood. In this study, a combination of seismic sedimentological and topographic analyses, based on high-resolution 3D seismic data within the Qiongdongnan Basin of the South China Sea, was used. Continuous bedforms varied with the depositional elements within the CLTZ of the Huaguang leveed channel system along the flow direction. The depositional elements within the CLTZ change from the main channel to the distributary channels as well as to the sub-distributary channels. Numerous bifurcation and confluence points of gravity flows illustrated the complexity of the drainage network within the CLTZ. The average asymmetry index of the bedforms increased from 0.8 to 1.6, with the average wavelength increasing from 803 m to 1545 m along the thalweg of the channels. Crevasse splays at the starting reach of the CLTZ are likely to form the initial state of the new CLTZ in the future, because the slope gradient starting from the avulsion point was higher than that inside the channel. The deep scours at the bifurcation points and high steps at the confluence points demonstrate the critical roles of supercritical flows and hydraulic jumps in reworking the bedforms of the CLTZ. The high steps at confluence points were simultaneously formed along the margin and thalweg of the main channel. The acceleration mechanisms of flow velocity forming the high steps were the increase of the elevation difference along the internal slope of the main channel margin and promotion of discharge along the main channel thalweg. This paper presents newly completed deepwater observations of the present seafloor bedforms based on the turbidity currents within the CLTZ. These observations update the evolution model of local supercritical flows and hydraulic jumps under the global decreasing trend of the Froude numbers within CLTZs. [ABSTRACT FROM AUTHOR]

Island arc magmatism is considered a major mechanism of continental crustal growth; hence, the variation in island arc magma production rates and its influencing factors are of great importance. The along-arc strike variation in the island arc magma production rate is important for elucidating whether the subduction zone temperature is a controlling factor on arc magmatism. No back-arc spreading or ridge subduction is occurring in the intraoceanic subduction region of the Aleutian subduction zone, and the along-arc temperatures vary due to differences in the subducting plate age, convergence rate, and slab dip. Therefore, this is an ideal region to study the correlation between magma production rates and subduction zone temperatures. However, previous studies estimated the magma production rates at only a few locations due to the insufficient coverage of seismic data. Here, we employ the gravity inversion method based on density modelling and seismic data constraints to calculate the present-day arc crustal thickness and then obtain the magmatic thickness by removing the pre-existing crustal thickness from the present-day arc crustal thickness. Finally, the magma production rates along the main intraoceanic subduction region of the Aleutian Arc are mapped by estimating the island arc magmatic thickness and the most recent subduction inception dating result. In addition, the subduction zone temperatures and mantle melt amounts along five profiles across the Aleutian Arc are calculated. The magma production rate variation is highly correlated with the mantle melt amount. The slab temperature controls the extent of the slab dehydration, which is essential for mantle wedge melting, and the mantle wedge temperature controls the size of the hydrated mantle melting region and the melting fraction therein. Therefore, as the subduction zone temperature controls the mantle melt amount, we suggest that the subduction zone temperature is the first-order controlling factor on the magma production rate. • The magma production rates along the main intraoceanic subduction region of the Aleutian Arc are mapped. • The slab temperature controls the extent of the slab dehydration. • The mantle wedge temperature controls the size of the hydrated mantle melting region and the melting fraction therein. • The subduction zone temperature is the first-order controlling factor on the magma production rate. [ABSTRACT FROM AUTHOR]

The Prydz Bay region of Antarctica is the immediate recipient of ice and sediments transported by the Lambert Glacier, the single largest outflow from the East Antarctic Ice Sheet. The continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information. Marine geological and geophysical data collected from the continental shelf and adjacent slope of Prydz Bay, Antarctica, including seismic reflection data, bathymetry, and core records from ODP drilling sites, reveal the history of glacial sediment transport and deposition since the early Pliocene times. Seismic facies are interpreted in terms of episodes of slope progradation, contourite, turbidite, trough-mouth fan, and mass transport deposition. Two seismic units with estimated age of early to late Pliocene and late Pliocene to recent have been analyzed in detail for the area immediately offshore the Lambert Glacier and Prydz Bay and the adjacent Mac. Robertson margin. The upper slope is dominated by episodic mass transport deposits, many of which accumulated to form a trough mouth fan since Early Pliocene times. The trough mouth fan contrasts with the adjacent steep (4–6°) continental slope of the Mac. Robertson margin, where glacigenic sediments have been transported down slope as high-velocity turbidity currents via submarine channels. The distal region exhibits evidence for contrasting effects of high-energy, traction-dominated versus lower-energy, fallout-dominated suspension flows. The counter-clockwise Coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel-levee architecture. Since the early Pliocene, turbidite sedimentation surpassed the amount of sediment reworked and transported by westward-flowing contour currents along the base of slope. On the continental rise, contourites and sediment waves were deposited in response to enhanced bottom-water formation, which is consistent with climatic cooling since late Pliocene times. This study, based on existing seismic reflection and ODP data, highlights the need for a future scientific ocean drilling proposal on the Prydz Bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin. • The geomorphologic setting of Prydz Bay and its marginal architecture of the Pliocene and their linkage to the paleoclimate change. • The role of Wild Canyon on the Mac. Robertson Land margin and its associated depositional and erosional features. • The observation of drift deposits and long-lived sediment waves indicate a vigorous ocean circulation in the late Pliocene. [ABSTRACT FROM AUTHOR]

The symmetry of conjugate rifted margins is a first-order observable feature reflecting the geodynamic processes acting during and after continental rifting. The symmetry of the South China Sea (SCS) rifted margins can be deduced from comprehensive geophysical datasets on a continental-margin scale. Here, we combine three key approaches: (1) lateral fault distributions are delineated according to free-air gravity anomalies, (2) crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles, and (3) total extension of conjugate margins is estimated according to margin restorations and tectonic settings. We infer a predominantly symmetric rifting style caused by pure shear extension, with only narrow domains of asymmetric deformation in continent-ocean transition (COT) regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup. However, our analysis also suggests that this symmetry has been modified by post-rift geodynamic processes. Southward lower crustal flow, which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting Proto-SCS plate during seafloor spreading, shifted the crustal stretching styles from symmetric to asymmetric. The collision between the southern margin and Borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin. This event had a large impact on the SE margin but a small impact on the SW margin. We conclude that (1) for the SE and NE margins, the crustal stretching styles shifted from asymmetric to approximately symmetric, and the total extension shifted from symmetric to asymmetric; (2) for the SW and NW margins, the crustal stretching and total extension remained asymmetric and symmetric, respectively. • The total extensions are asymmetric in the eastern margins, but symmetric in the western margins. • The crustal stretching styles of the eastern margins are approximately symmetric, but asymmetric in the western margins. • Post-rifting lower crust flow and collision modified margin symmetry. [ABSTRACT FROM AUTHOR]

High-resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon (West Penghu Canyon) on the northeastern South China Sea margin, where twenty-three (23) scours are observed along the canyon thalweg. These scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross-section. The identified scours can be further divided into two groups (Types A and B) based on their sizes and relative locations. They are separated by a slope break at a water depth of ~2850 m. Type A scours (S1-S18) occur upslope from the slope break, whereas Type B scours (S19-S23) lie downslope from this same break. The scours are interpreted as net-erosional cyclic steps associated with turbidity currents flowing through the West Penghu Canyon; the currents that form Type A scours reflect higher V, Q, and Δ el compared to the currents forming Type B scours. A change in slope gradient and loss of lateral confinement are proposed to control the change from Type A to Type B scours. Furthermore, Coriolis force influences the flow direction of turbidity currents, leading to the preferential development and larger incision depths of scours towards the southwestern flank of the West Penghu Canyon. Our results contribute to a better understanding on the origin of scours in submarine canyons across the world. • Scours along the West Penghu Canyon relate to net-erosional cyclic steps. • Slope gradient and loss of lateral confinement control the morphology of scours. • Coriolis force affects the distribution and development of scours within the canyon. [ABSTRACT FROM AUTHOR]

The Baiyun Slide Complex is one of the largest submarine landslides on the northern margin of the South China Sea. Newly acquired high-resolution bathymetric data, 2D and 3D seismic data permitted the systematic investigation of the Baiyun Slide Complex in terms of its seafloor morphology and associated sedimentary processes. The headwall region of the Baiyun Slide Complex, located at a water depth between 1000 m and 1700 m, is U-shaped and opens towards the east. It was efficiently and almost completely evacuated, generating pronounced headwall and sidewall scarps. Submarine channels, sediment waves, migrating channels, sediment drifts and moats are observed within and around the headwall region, illustrating the effects of both downslope and along-slope sedimentary processes. Submarine channels are 16–37 km-long 800-1500 m-wide, and 20 to 50 m-deep. As a modern example of the interplay between slope instability and subsequent incision, submarine channels were generated after the formation of the Baiyun Slide scar to suggest intensified downslope sedimentary processes after the slope collapsed. The initiation and formation of these submarine channels result from the evacuation of the Baiyun Slide scar, which provided the necessary space of the continental slope to accommodate subsequent turbidity and mass wasting flows. Our results are an important example of how submarine landslides can influence erosional and depositional processes on continental margins. • Downslope and along-slope processes controlled the morphology of headwall region. • Erosive channels were initiated after the formation of the Baiyun Slide scar. • Downslope sedimentary processes were intensified after the slide scar formation. [ABSTRACT FROM AUTHOR]

Hadal trenches are extreme environments situated over 6000 m below sea surface, where enormous hydrostatic pressure affects the biochemical cycling of elements. Recent studies have indicated that hadal trenches may represent a previously overlooked source of fixed nitrogen loss; however, the mechanisms and role of hydrostatic pressure in this process are still being debated. To this end, we investigate the effects of hydrostatic pressure (0.1 to 115 MPa) on the chemical profile, microbial community structure and functions of surface sediments from the Mariana Trench using a Deep Ocean Experimental Simulator supplied with nitrate and oxygen. We observe enhanced denitrification activity at high hydrostatic pressure under oxic conditions, while the anaerobic ammonium oxidation - a previously recognized dominant nitrogen loss pathway - is not detected. Additionally, we further confirm the simultaneous occurrence of nitrate reduction and aerobic respiration using a metatranscriptomic dataset from in situ RNA-fixed sediments in the Mariana Trench. Taken together, our findings demonstrate that hydrostatic pressure can influence microbial contributions to nitrogen cycling and that the hadal trenches are a potential nitrogen loss hotspot. Knowledge of the influence of hydrostatic pressure on anaerobic processes in oxygenated surface sediments can greatly broaden our understanding of element cycling in hadal trenches., (© 2024. The Author(s).)