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Schematic map showing intrusion of the North Pacific Deep Water (NPDW) through the Bashi Channel into the SCS (arrows). It flows upward southeast of the Dongsha Islands. See text for discussions. Black lines show moat orientation. See color version of this figure in the HTML.
Source publication
Reflection seismic profiles show that drift sediments occur in the depth range of 1200-2800 m on the continental margin off Southeast China. These drift deposits were generated by upward flow near the Dongsha Islands of the North Pacific Deep Water (NPDW), which enters the South China Sea via the Bashi Channel (sill depth >2500 m). This flow result...
Contexts in source publication
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... places, mass wasting deposits such as debris flows may be intercalated (Figure 3b). The sediment drifts are oriented WNW-ESE oblique to the trend of the continental margin (Figure 4), and downslope migra- tion of the drift is perpendicular to the direction of current flow. ...
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... The drift sediments observed on the continental margin of Southeast China are restricted to two limited areas southeast of the Dongsha Islands (Figure 4). The lithostratigraphy of ODP site 1144 shows that the siliciclas- tic fraction of the sediments consists mainly of clay and silt [Boulay et al., 2003]. ...
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... currents confined to moats are presumably respon- sible for the transport and construction of these drift bodies. These currents flow to the WNW upslope (see orientation of moats, Figure 4) because the moats are located on the NE flank of the NW-SE striking depressions. If the currents flow downslope in the ESE direction, it would have been deflected to the right by the Coriolis force, so that the moats would be on the SW depression flank. ...
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... The only source for a current approaching from the east is the Luzon Strait (Figure 4). Here, the Bashi Channel with a sill depth of around 2500 m provides a possible pathway for deep water masses to ventilate into the SCS. ...
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... we conclude that intrusion of deep waters into the SCS can must place through the Bashi Channel. However, because of the NNE-SSW orien- tation of this channel, water inflow can only occur from the north (Figure 4). Direct current measurements at the centre of the Bashi Channel in water depths of about 2500 m show an inflow of cold Pacific deep waters with a volume transport of 1.2 Sv (Figure 4) [Liu and Liu, 1988]. ...
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... because of the NNE-SSW orien- tation of this channel, water inflow can only occur from the north (Figure 4). Direct current measurements at the centre of the Bashi Channel in water depths of about 2500 m show an inflow of cold Pacific deep waters with a volume transport of 1.2 Sv (Figure 4) [Liu and Liu, 1988]. Liu and Liu [1988] suggested a largely tidal origin for this current, which is strong enough (about 14 cm/s) to erode unconsolidated mud and to transport clay and silt in suspension [Nichols, 1998, Figure 4.5]. ...
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... Qu and Lindstrom [2004] postulated an inflow of oxygen-rich Pacific deep water around the sill depth of the Luzon Strait. Additional supporting evidence comes from provenance analyses of rare earth abundances in sediment samples from ODP site 1144 [Shao et al., 2001], which suggest Taiwan as the source area rather than the Pearl River or the Philippines (Figure 4). They speculated that sediments were transported from Taiwan via the Taiwan Strait onto the slope off the Dongsha Islands (Figure 4). ...
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... supporting evidence comes from provenance analyses of rare earth abundances in sediment samples from ODP site 1144 [Shao et al., 2001], which suggest Taiwan as the source area rather than the Pearl River or the Philippines (Figure 4). They speculated that sediments were transported from Taiwan via the Taiwan Strait onto the slope off the Dongsha Islands (Figure 4). However, this scenario is consistent neither with the WNW-ESE trend of the moats nor with the prevailing direction of surface currents in the Taiwan Strait which flow year-round northward, although in winter there is an additional southward flow along the east coast of China, resulting in a zero to slightly northward net flow [Chen, 2003;Liang et al., 2003]. ...
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... surface waters are monsoon-controlled and flow parallel to the continental margin. In our study area, they result in erosion and sediment reworking at water depths of 200 -1000 m around the Dongsha Islands (Figure 4). Lüdmann et al. [2001] demonstrated that in a large area surrounding the Dongsha Islands, Holocene deposits are absent and that fields of sediment waves occur on the upper slope. ...
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Based upon 2D seismic data, this study confirms the presence of a
complex deep-water sedimentary system within the Pliocene-Quaternary
strata on the northwestern lower slope of the Northwest Sub-Basin, South
China Sea. It consists of submarine canyons, mass-wasting deposits,
contourite channels and sheeted drifts. Alongslope aligned erosive
feature...
Citations
... Cyclonic circulation in the deep SCS was predicted by the Stommel-Arons abyssal circulation theory (Stommel 1958;Stommel and Arons 1960a,b) and was further confirmed by historical water properties (Li and Qu 2006;Qu et al. 2006), historical sediment distributions (Lüdmann et al. 2005;Zheng and Yan 2012;Chen et al. 2013;Xu et al. 2021), temperature and salinity from reanalysis data (Wang et al. 2011;Zhu et al. 2017), and in situ current observations (Zhou et al. 2017;Zhou et al. 2020;Zheng et al. 2021Zheng et al. , 2022a. Modeling studies have indicated that the penetration of NPDW through the Luzon Strait controls the formation and seasonal variation in abyssal circulation in the SCS (Lan et al. 2013(Lan et al. , 2015. ...
Abyssal vorticity balance in the northeast South China Sea was assessed for over a year based on observations from 28 current- and pressure-recording inverted echo sounders distributed west of the Luzon Strait. The regional first-order balance was dominated by the planetary vorticity flux and bottom pressure torque, which reflect the external and internal dynamics of abyssal circulation. Vertical motion considerably contributed to the planetary vorticity flux, whereas the contribution of horizontal motion was negligible. Positive and negative planetary vorticity fluxes dominate the areas along the eastern and western boundaries, indicating upward and downward vertical transport, respectively. The opposite planetary vorticity fluxes in the different areas were accompanied by different current patterns; regional anticyclonic and cyclonic characteristics appeared near the western and eastern boundaries, respectively, owing to the deep topography as the abyssal current followed the boundary. The planetary vorticity flux near the eastern boundary was substantial in spring and autumn; in contrast, along the western boundary it was enhanced only in spring. Deep eddies played important roles in planetary vorticity flux and regional vorticity balance. The results of this study reveal the formation dynamics of abyssal circulation in the South China Sea as well as its spatiotemporal distributions, providing a more detailed description of abyssal circulation.
Significance Statement
The deep South China Sea (SCS) is a nearly enclosed basin characterized by cyclonic abyssal circulation. Based on the observations from 28 current- and pressure-recording inverted echo sounders distributed west of the Luzon Strait, the vorticity balance in the deep SCS was clarified. The planetary vorticity flux and bottom pressure torque maintain a first-order balance of vorticity, which acts as the external and internal dynamics of the abyssal circulation. The study describes the temporal variability and spatial distribution of vorticity terms in the deep ocean west of the Luzon Strait, which may contribute to a more detailed understanding of abyssal circulation formation and its evolution.
... A moat of 300-m deep is formed between the contourite drift and the seamount to its north. This contourite drift has been investigated previously using the seismic reflection profiles and several deep-sea sediment cores have been collected on the drift (Sarnthein et al., 1994;Wong et al., 1994;Shao et al., 2001;Lüdmann et al., 2005;Laj et al., 2005;Shao et al., 2007). The sedimentation rate on the ridge adjacent to the moat of this drift has reached~100 cm/kyr since the Holocene (Shao et al., 2007), which is much higher than the average sedimentation rate in the northern South China Sea, indicating its active sedimentation activity. ...
Ocean dynamic processes in the bottom boundary layer (BBL) are crucial for sedimentation, such as deposition and resuspension of marine sediments. In this study, we conducted in-situ tripod observations of the sediment ridge of a contourite drift in the northern South China Sea to understand the main dynamic processes affecting sedimentation on the contourite drifts. It was found that the diurnal tidal current was the strongest current at the study site, thus acting as the main dynamic affecting sedimentation processes. Periodic events of elevated suspended sediment concentration (SSC) were observed, some of which occurred only within 15 m above the seafloor and were termed near-bottom high SSC events, while others covered the entire range of the observed water column and were termed full-depth high SSC events. In-situ sediment resuspension at the sediment ridge is not an important factor affecting the formation of high SSC events. Rather, these high SSC events were mainly caused by lateral transport of sediments from the main body of the contourite drift by the northwestward diurnal tidal currents. The seafloor sediments at the main drift body are resuspened owing to the near-critical reflection of diurnal tidal currents on the slope topography of the drift. During periods when diurnal tidal currents were weak, locally generated internal waves could also induce burst-like full-depth high SSC events. This study highlights the diurnal tidal current as the main dynamic regulating the sedimentary processes of the contourite drifts in regions where the near-critical reflection prone to occur, implying the complexity of sediment dynamics of contourite drifts.
... The SCS is the largest marginal sea of the western Pacific and has an area of active methane seepage (Tong et al., 2013;Han et al., 2014). The northern SCS exchanges intermediate and deep waters from the Pacific through the Luzon Strait, with a sill depth of ∼2600 m (Lüdmann et al., 2005). The vertical section of the net flow through the Luzon Strait shows a vertical structure: water enters from the deep layer (>1500 m) into the SCS, and then flows out of the SCS into the Pacific in the intermediate layer (500-1500 m). ...
Methane hydrates are widely distributed along continental margins, representing a potential source of methane to the ocean and atmosphere, possibly influencing Earth’s climate. Yet, little is known about the response of methane hydrates to global climate change, especially at the timescale of glacial-interglacial cycles. Here we present a chronology of methane seepage from seep carbonates derived from a series of tens to hundreds of meters long hydrate-bearing sediment records from the South China Sea, drilled at water depths of 664−871 m. We find that six out of seven episodes of intense methane seepage during the last 440,000 years were related to hydrate dissociation, all coinciding with major interglacials, the so-called Marine Isotope Stages 1, 5e, 7c, 9c, and 11c. Using numerical modeling, we show that these events of methane hydrate instability were possibly triggered by the rapid warming of intermediate waters by ∼2.5−3.5 °C in the South China Sea. This finding provides direct evidence for the sensitivity of the deep marine methane hydrate reservoir to glacial-interglacial climatic and oceanographic cyclicity.
... Water masses in the South China Sea comprise a seasonally influenced surface water and permanent intermediate and deep waters (Chen et al., 2014;Gan et al., 2016). Surface water occurs up to a depth of 350 m, and its flow is governed by the East Asia monsoon system (Lüdmann et al., 2005). Due to bi-annual monsoon changes, surface water masses flow counterclockwise during winter, but clockwise in the summer (Zhu et al., 2010). ...
... In detail, the northwestern Yongle Atoll belongs to the escarpment (bypass) margins whereas the southeastern atoll is more likely to erosional (escarpment) margins ( Figure 8B). Gravity-flow, bottom current (contour current), and prevailing wind have been proposed to interpret the morphological differences of the carbonate platform slopes (Schlager and Ginsburg, 1981;Mullins, 1983;Lüdmann et al., 2005;Playton et al., 2010;Vandorpe et al., 2016;Ma et al., 2021;Qin et al., 2022). Gravity-flows are commonly developed in the Xisha Islands (Ma et al., 2021). ...
This study presented recently reprocessed multi-channel seismic data and multi-beam bathymetric map to reveal the geomorphology and stratigraphic architecture of the Yongle isolated carbonate platform in the Xisha Archipelago, northwestern South China Sea. Our results show that the upper slope angles of Yongle carbonate platform exceed 10° and even reach to ∼32.5° whereas the lower slope angles vary from .5° to 5.3°. The variations of slope angles show that margins of Yongle Atoll belong to escarpment (bypass) margins to erosional (escarpment) margins. The interior of carbonate platform is characterized by sub-parallel to parallel, semi-continuous to continuous reflectors with medium-to high-amplitude and low-to medium-frequency. The platform shows a sub-flat to flat-topped shape in its geometry with aggradation and backstepping occurring on the platform margins. According to our seismic-well correlation, the isolated carbonate platform started forming in Early Miocene, grew during Early to Middle Miocene, and subsequently underwent drowning in Late Miocene, Pliocene and Quaternary. Large-scale submarine mass transport deposits are observed in the southeastern and southern slopes of Yongle Atoll to reshape the slopes since Late Miocene. The magmatism and hydrothermal fluid flow pipes around the Yongle Atoll have been active during 10.5–2.6 Ma. Their activity might intensify dolomitization of the Xisha isolated carbonate platforms during Late Miocene to Pliocene. Our results further suggest that the Yongle carbonate platform is situated upon a pre-existing fault-bounded block with a flat pre-Cenozoic basement rather than a large scale volcano as previously known and the depth of the basement likely reached to 1400 m, which is deeper than the well CK-2 suggested.
... Although seismic imaging of drowned or buried isolated carbonate platforms has been conducted in the Gulf of Papua New Guinea, Northeast Australia, Great Bahama Bank, and Southeast Asia (Ludmann et al., 2005;Tcherepanov et al., 2008;Wu et al., 2014), only a few high-resolution seismic surveys of the shallow lagoon and reef flat have been performed. In particular, few multi-channel seismic (MCS) surveys have been performed on most modern carbonate platforms, which are common in the Xisha archipelago in the South China Sea (SCS) (Wu et al., 2014;Shao et al., 2017). ...
Xuande Atoll is an isolated carbonate platform that has developed since the early Miocene. This study conducted high-resolution seismic surveys and shallow drilling to understand its internal structure and development. Five seismic sequences were observed (from bottom to top): SQ1 (early Miocene), SQ2 (middle Miocene), SQ3 (late Miocene), SQ4 (Pliocene), and SQ5 (Quaternary). The seismic data indicated that the platform formation started in the early Miocene and flourished during the early and middle Miocene. The platform shrank before the isolated platform formed in the middle Miocene. The final shrinking stage occurred in the southern and western parts of the platform at the end of the Miocene, which may reflect rapid tectonic subsidence and increased terrigenous sediment inputs owing to the formation of the semi-marginal sea. The peri-platform contains a falling sea-level sequence that was dominated by mass wasting deposits.
... Station SCS18-10 is located in the northeastern SCS between stations SCS18-25 and SCS18-18. Four seawater samples were collected at station SDA3, close to Dongsha Island, where a series of large drift sediments have been identified (Lüdmann et al., 2005). Physical water properties (A-D) at our sampling stations over the northern and central SCS. ...
Dissolved rare earth elements (REEs) and neodymium isotopes (ϵNd) have been jointly used to evaluate water mass mixing and lithogenic inputs in the ocean. As the largest marginal sea of the West Pacific, the South China Sea (SCS) is an ideal region for reconstructing past hydrological changes. However, its REE and ϵNd distributions and underlying controlling mechanisms remain poorly understood. On the basis of four seawater profiles spread across the SCS, this study presents dissolved REE concentrations and ϵNd data under summer condition to better understand the processes that potentially influence changes in these parameters and their marine cycling. The results show high concentrations of REEs and large variations in ϵNd (−6.7 to −2.8) in surface water, likely caused by the dissolution of riverine and marine particles. Comparison with published data from samples taken during the winter of different years in this and previous studies suggests a possible seasonal variability of middle REE enrichment. The SCS deep water shows a narrow ϵNd range from −4.3 to −3.4, confirming the dominant presence of the North Pacific Deep Water in the deep SCS. The intermediate water in the central SCS is characterized by a more negative ϵNd signal (–4.2 to –3.4) than that found in its counterpart in the West Pacific (–3.5 to –2.8), indicating alterations by deep water through three-dimensional overturning circulation from the northern to southern SCS below ~500 m. The contributions of external sources could be quantitatively estimated for the SCS in terms of Nd. The dissolution of particles from the SCS surrounding rivers (0.26–1.3 tons/yr in summer; 5.6–29 tons/yr in winter) and continental margins (2–12 tons/yr in summer; 23–44 tons/yr in winter) may play an important role in providing additional Nd to the SCS surface water.
... The South China Sea is the largest marginal sea in the western Pacific Ocean, and it is also one of the world's highest microplastic input areas from surrounding countries (~2.65 −7.08 Mt/y or 0.61 Mt/y) (Jambeck et al., 2015;Meijer et al., 2021). The sea has complex and diverse deep-sea geomorphological units, such as submarine canyons, sand dunes, sediment drifts, and seamounts (Lüdmann et al., 2005;Reeder et al., 2011;Wang et al., 2016;Chiang et al., 2020). It develops multiscale hydrodynamic processes, like turbidity currents, internal waves, contour currents, and mesoscale eddies (Xiu et al., 2010;Reeder et al., 2011;Zhang et al., 2014;Zhao et al., 2015). ...
Marine microplastics are widely distributed in deep-sea sedimentary environments and are altering sediment compositions and ecological conditions on the seafloor. However, the relation between the distribution of microplastics in deep-sea sediments and the sedimentary dynamic conditions is poorly understood. In this study, we collected surface sediments from some typical geomorphological units (sand dune, sediment drift, and submarine canyon channel/levee) in the northern South China Sea to study composition and distribution of the deep-sea microplastics and their controlling factors. The results show that the microplastic abundance in surface sediments ranges from 19 to 347 p·kg–1, and the identified microplastics consist of 10 types, including dominant polycarbonate (29%), polyethylene (27%), polyester fiber (16%), polyvinyl chloride (13%), and polypropylene (7%), and minor polyethylene terephthalate resin, acrylonitrile-butadiene-styrene, epoxy resin, hydrocarbon resin, and acrylic. The source analysis shows that the deep-sea microplastics may be influenced by riverine inputs from Taiwan and South China. In addition, the microplastic spatial distribution shows that the sand dune and canyon channel contain the highest abundances (136–347 p·kg–1) and more types (4–6 types) of microplastics, which are dominated by relatively high-density polycarbonate or polyvinyl chloride. The canyon levee contains the lowest abundances (19–132 p·kg–1) and less types (1–3 types) of microplastics, which are dominated by relatively low-density polyester fiber or polyethylene. Nevertheless, the microplastic composition of the sediment drift is between those of the canyon channel and the canyon levee. The abundance and polymer type (density) of microplastics all increase with the increased mean grain size of detrital sediments, which represents the progressively enhanced intensity of sedimentary dynamic conditions. We therefore infer that the sedimentary dynamic conditions control the composition and distribution of microplastics in the deep-sea sediments. This study highlights that some deep-sea environments with stronger sedimentary dynamic conditions may accumulate more microplastics, which is of great significance for evaluating the storage and ecological damage of deep-sea microplastics.
... The water circulation in the northern SCS is complex, with deep currents flowing clockwise in the SSW direction and intermediate currents flowing counterclockwise along the slope in the SSE direction (Qu and Lindstrom, 2004;Wang and Li, 2009;Xu et al., 2014). The depth limit of the intermediate current in the SCS is still controversial, with the upper boundary mainly at 300-500 m below sea level (Lüdmann et al., 2005;Zhao et al., 2009) ments. In contrast, bottom current deposits in the YGHB, which are also located in the western part of the northern SCS, have rarely been reported . ...
The Dongfang1-1 gas field (DF1-1) in the Yinggehai Basin is currently the largest offshore self-developed gas field in China and is rich in oil and gas resources. The second member of the Pliocene Yinggehai Formation (YGHF) is the main gas-producing formation and is composed of various sedimentary types; however, a clear understanding of the sedimentary types and development patterns is lacking. Here, typical lithofacies, logging facies and seismic facies types and characteristics of the YGHF are identified based on high-precision 3D seismic data combined with drilling, logging, analysis and testing data. Based on 3D seismic interpretation and attribute analysis, the origin of high-amplitude reflections is clarified, and the main types and evolution characteristics of sedimentary facies are identified. Taking gas formation upper II (IIU) as an example, the plane distribution of the delta front and bottom current channel is determined; finally, a comprehensive sedimentary model of the YGHF second member is established. This second member is a shallowly buried “bright spot” gas reservoir with weak compaction. The velocity of sandstone is slightly lower than that of mudstone, and the reflection has medium amplitude when there is no gas. The velocity of sandstone decreases considerably after gas accumulation, resulting in an increase in the wave impedance difference and high-amplitude (bright spot) reflection between sandstone and mudstone; the range of high amplitudes is consistent with that of gas-bearing traps. The distribution of gas reservoirs is obviously controlled by dome-shaped diapir structural traps, and diapir faults are channels through which natural gas from underlying Miocene source rocks can enter traps. The study area is a delta front deposit developed on a shallow sea shelf. The lithologies of the reservoir are mainly composed of very fine sand and coarse silt, and a variety of sedimentary structural types reflect a shallow sea delta environment; upward thickening funnel type, strong toothed bell type and toothed funnel type logging facies are developed. In total, 4 stages of delta front sand bodies (corresponding to progradational reflection seismic facies) derived from the Red River and Blue River in Vietnam have developed in the second member of the YGHF; these sand bodies are dated to 1.5 Ma and correspond to four gas formations. During sedimentation, many bottom current channels (corresponding to channel fill seismic facies) formed, which interacted with the superposed progradational reflections. When the provenance supply was strong in the northwest, the area was dominated by a large set of delta front deposits. In the period of relative sea level rise, surface bottom currents parallel to the coastline were dominant, and undercutting erosion was obvious, forming multistage superimposed erosion troughs. Three large bottom current channels that developed in the late sedimentary period of gas formation IIU are the most typical.
... Considering that microplastic color and shape are more susceptible to physicochemical processes than microplastic type, we chose to use a modified microplastic diversity index (MDI) based on Simpson's diversity index (Lou, 2006;Simpson, 1949) to analyze the complexity of microplastic assemblages in different areas using the following Equations (1) and (2): ...
... Models of microplastic transport suggest that some bottom currents have shear stresses close to or exceeding those required to carry fibers and debris, and indicate that previously deposited microplastics may be resuspended . Strong deep-water underflow activity exists throughout the study area (Luedmann et al., 2005;Shao et al., 2007) (Fig. 2b). The bottom currents transport sediment and microplastics along the northern slope of the South China Sea towards the southwest, and eventually enter into the sea's central basin. ...
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.
