Sheet Drift Research Articles

Distribution and Controlling Factors of the Contourites on the Northern Continental Slope of the South China Sea

ABSTRACTThe northern continental margin of the South China Sea (SCS) is an important component of deep‐water circulation, providing excellent conditions for studying bottom currents in a marginal sea. Seismic data were employed to discern the sedimentary patterns prevalent in the deep‐water continental slope sediments on the northern continental margin of the SCS, encompassing gravity flow, contourite and mixed depositional systems. The contourite depositional system includes various types of deposits (such as separated mounded drifts, patch or channel‐related drifts, deformed sheeted drifts, composite drifts, bottom current sediment waves, plastered contourite drifts) and various morphologic erosional features eroded by the bottom current (such as moats, non‐depositional surfaces, troughs and scarps). These contourite features are related to the continental slope's morphology and its sources. The Dongsha slope exhibits distinctive characteristics marked by intense bottom current erosion and deposition, featuring separated mounded drifts and deformed sheeted drifts along its lower slope. The lower slope of the Pearl River showcases a spectrum of bottom current‐induced features, including sediment wave fields, erosion fields and contourite drifts. The southern flank of the Shenhu slope is characterised by a bottom current erosion field, a non‐depositional surface, a sediment wave field and isolated mounded drifts. On the Yingqiong slope, the contourite drifts are limited to its southern flank where gravity flow action is absent, and the complex geomorphology interacts with the bottom current, forming a complex contourite depositional system. The results of this study serve as a foundational framework for further global research on bottom current circulation and hydrodynamics.

The Maldives, a key location of carbonate drifts

Wind-driven surface currents and deeper water-mass circulation shape carbonate sediment drifts in shallow- to deep-water depositional settings of the Maldives. Drift sediments are located in the platform interior, on top of drowned banks, and around the atolls. They are composed of an admixture of pelagic and shallow-water components. Drift bodies vary in dimension, architecture, and genesis. Small patch drifts and sheeted drifts are present in the platform interior and on top of drowned atolls; large patch drifts preferably form in the current-shadow of large atolls and banks. Small inter-atoll channels and large gateways are dominated by channel-related drifts. The Inner Sea, a large perched basin surrounded by atolls comprises a complex contourite depositional system of giant elongated mounded and sheeted drifts, mixed drifts, as well as delta drifts. This succession of different drift types is organized in sequences, delimited by unconformities caused by changes in the current regime. These may be triggered by a re-configuration of the inter-atoll gateways or by allo-cyclic processes such as climate variability. Effects based on to changes in the global water-mass circulation could not be proven. With exception of the delta drift, carbonate drift types in the Maldives are analogous to their siliciclastic counterparts. By contrast, however, these carbonate drifts are emplaced at a short distance to the shallow-water carbonate factory, which acts as main sediment source. Variability and abundance of drifts in the Maldives emphasize the significant role of current-controlled sediment transport and redistribution in carbonate platform development.

On the origin of the turn-on voltage drop of GaN-based current aperture vertical electron transistors

Non-linear output characteristics and the related turn-on voltages of GaN-based current aperture vertical electron transistors (CAVETs) are investigated experimentally. The resistive components are systematically analyzed in dependence of the device layout to determine the dominant resistances in the devices. Current–voltage (IV) and capacitance–voltage-characteristics (CV) are compared to a proposed planar-doped barrier diode (PDBD) model, and the influence of the bound sheet charge density and drift layer carrier concentration is discussed. The observed CV characteristics are in contrast to the PDBD model as a clearly voltage-dependent capacitance was observed and dopant-diffusion forming a p-type aperture was ruled out. Thermionic emission was verified by temperature-dependent IV characteristics indicating interface states causing a potential barrier. Transient drain current measurements revealed a single dominating trap level with an activation energy of EA = 1.086 ± 0.015 eV. This activation energy was attributed to carbon-related acceptor states present at the regrowth interface and the drift layer. Additional test structures revealed that the interface potential barrier and the space charge in the drift layer limit the initial charge transport causing a turn-on voltage in the devices. The results point out the significance of a precise control of the regrowth interface properties and the effective carrier density in the drift layer to enable efficient, high-power devices based on the CAVET technology.

Sedimentary processes in the Discovery Gap (Central–NE Atlantic): An example of a deep marine gateway

Paleoceanographic studies of abyssal bottom currents are often complicated by low current speeds and sedimentation rates, resulting in sediment condensation or erosion. However, increased rates of erosion and deposition may occur where bottom current velocities change as they pass through deep marine gaps and gateways. Despite this, the depositional processes in these gateways and their paleoceanographic implications remain poorly understood. Based on new sedimentological, hydrological and geophysical (high resolution seismic and bathymetry) data from Discovery Gap (Azores–Gibraltar Fracture Zone) collected during the 43rd cruise of the R/V Akademik Nikolaj Strakhov in 2019, the key sedimentary processes occurring in the Late Quaternary have been determined. Two depressions with depths exceeding 5300 m in the centre and south of Discovery Gap have been identified, the latter filled with contouritic deposits. These depressions are separated by a roughly N–S trending central sill at 4860 m and a sediment filled terrace at 4720 m water depth. Elongated NE–SW trending highs and sills, are present in the north and south of the study area. Their importance in controlling the flow of water through Discovery Gap is determined by the presence of erosion at the base of these highs with adjacent sheeted or mounded contourite drifts. Pelagic, hemipelagic, reworked pelagic/hemipelagic and fine-grained contourite sedimentary facies have been identified. The sedimentary facies associations point to remarkable variability in the Antarctic Bottom Water (AABW), linked to glacial–interglacial changes, and its intermittent influence in Discovery Gap during the Quaternary. During glacial intervals (MIS 6, 4 and 2) and at their terminations there was enhanced bottom current activity coeval with higher terrigenous content, and increased carbonate dissolution. The results of this study improve our understanding of sedimentary processes in abyssal environments and highlight the value of the sedimentary record in deep marine gateways for interpreting the interaction of bottom water with abyssal morphology. Future work in other modern deep gaps is essential to shed more light on how deep gaps form and to fully reconstruct deep-water paleocirculation within oceanic basins.

Trajectory Analysis of Galactic Cosmic Rays Invading into the Heliosphere

Abstract The trajectories of galactic cosmic-ray protons invading the heliosphere are investigated by using numerical simulations. A time stationary global heliosphere is first reproduced by using a high-resolution MHD simulation. Then, motions of a number of test particles (protons) distributed in the virtual heliosphere are numerically solved. When the initial particle Lorentz factor is 10 (∼10 GeV), the motions of particles are strongly affected by small-scale heliospheric structures reflecting the small gyroradii of the particles. Particles can enter the heliosphere from many parts (nose, flank, and tail) of the heliopause. Once they have entered, they expand in the region where the magnetic field is locally weak, such as the heliopause and the heliospheric current sheet. On the other hand, particles have difficulty invading upstream of the termination shock. We found a variety of invading particle trajectory patterns such as current sheet drift, polar drift, spiral motion, shock drift, and Fermi-like acceleration. In the latter two, particles are accelerated. When the initial particle Lorentz factor is 1000 (∼1 TeV), the particles are insensitive to the small-scale structures of the heliosphere due to their large gyroradii. Some particles show eccentric motions due to resonant interaction with the large-scale eddy in the heliotail. Some other particles passing by the heliosphere are mirror reflected due to the bottleneck structure of interstellar magnetic field surrounding the heliosphere and return back to enter the heliosphere.

Inherited morphobathymetric controls over contourite drift deposition: A case study from the late Cenozoic Mentelle Basin, Australia

Deep-sea sedimentary deposits are important archives of the geologic past that preserve the records of past environmental changes in earth’s ocean. The detailed analysis of deep-sea sedimentary archives, in particular of contourite drifts, can help elucidate past changes in ocean circulation and the stratigraphic evolution of continental margins. However, the bathymetric profile of an oceanic basin can shape and modify the architecture of contourite drifts via the interaction between down-slope and along-slope processes. The identification of local bathymetric influence on depositional architectures is therefore important to help decipher local versus regional influences on deep-sea sedimentary signatures. Seismic data from Mentelle Basin in the southeast Indian Ocean integrated with deep-sea core data reveal a calcareous-siliciclastic mixed contourite-turbidite system developed during the late Cenozoic, starting in the middle Miocene. Current winnowing led to the formation of regional hiatuses, ferromanganese crusts, and siliciclastic lag deposits. The main locus of sediment deposition occurred on the shallower parts of the basin, whereas sediment preservation remained low in the deeper areas. Seismic analysis shows that inherited topography influenced the architecture of contourite deposits within the basin, with elongate-mounded and sheeted drifts forming preferentially at shallower depths on the continental slope and the Naturaliste Plateau, while channel incision occurred in the deepest parts of the basin. These results suggest that the intensification of current transport occurred preferentially within the deeper and spatially constrained parts of the basin, whereas current deflection around the slope and plateau enhanced drift deposition and preservation at shallower depths. Therefore, the basin topography at the time of deposition controlled the distribution of deep-sea deposits and drift morphologies within the mixed contourite-turbidite system in the Mentelle Basin.

Contourite characterization and its discrimination from other deep‐water deposits in the Gulf of Cadiz contourite depositional system

AbstractDespite numerous efforts to properly differentiate between contourites and other deep‐water deposits in cores and outcrops, reliable diagnostic criteria are still lacking. The co‐occurrence of downslope and along‐slope sedimentary processes makes it particularly difficult to differentiate these relatively homogeneous deposits. The main aim of this paper is to identify differences in deep‐water sediments based on Principal Component Analysis of grain size and geochemistry, sedimentary facies, and reinforced by microfacies and ichnofacies. The sediments studied were obtained from two International Ocean Drilling Program Expedition 339 sites in mounded and sheeted drifts in the Gulf of Cadiz. The statistical approach led to the discernment of hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine‐grained turbidites and debrites over a range of depositional and physiographic elements. These elements are linked to contourite drifts, the drift‐channel transition, the contourite channel and distal upper slope. When bottom currents or gravity‐driven flows are not the dominant depositional process, marine productivity and continental input settling forms the main depositional mechanism in deep‐water environments. This is reflected by a high variability of the first principal component in hemipelagic deposits. The stacked principal component variability of these deposits evidences that the contourite drift and the adjacent contourite channel were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. This interrelation questions the paradigm that a drift is made up solely of muddy sediments. The interrelation of sedimentary processes is a consequence of the precession‐driven changes in the intensity of the Mediterranean Outflow Water related to Mediterranean climate variability, which are punctuated by millennial‐scale variability. Associated vertical and lateral shifts of the Mediterranean Outflow Water, and therefore of its interface with the East North Atlantic Central Water, controlled sediment input and favoured turbulent sediment transport in the middle slope. During the interglacial precession maxima/insolation minima, a more vigorous upper core of the Mediterranean Outflow Water and the enhanced impact of the East North Atlantic Central Water – Mediterranean Outflow Water interface allowed for the development of the sandier contourite deposits.

Geomorphology of Ona Basin, southwestern Scotia Sea (Antarctica): Decoding the spatial variability of bottom-current pathways

Ona Basin, the westernmost oceanic basin in the southern Scotia Sea, is affected by the opposite flows of Circumpolar Deep Water (CDW) and Weddell Sea Deep Water (WSDW); thus, it represents a key location for exploring seafloor morphologies influenced by bottom currents. The present study aims to capture the spatial arrangement of recent subsurface contourite features, assuming a latitudinal influence of water masses and the interactions between along- and downslope processes, in order to contribute to the knowledge of regional deepwater flow pathways and to the sedimentary model of small sediment-starved oceanic basins. To this end, the investigation combines an interpretation of multibeam bathymetry and parametric echo sounder seismic data complemented with hydrological data. The distribution of morpho-sedimentary features in Ona Basin reveals two major domains. The southern margin of the basin can be regarded as a mixed/hybrid system containing abundant sediment drifts with channels and contourite moats and a lateral continuity interrupted by downslope morphologies. In contrast, the northern abyssal setting comprises relatively homogeneous large sheeted drifts with superimposed sediment waves, mounded drifts, and several scattered erosive features, likely reflecting the more distinct influence of deepwater contourite processes. Our work demonstrates that tectonic features in the southern basin control the interaction between deepwater along- and downslope processes, as the westward flow of the WSDW is deflected, channelized, and intensified along its westward route. In the northern region, the study indicates an overall clockwise rotation of the WSDW flow, with the spatial and vertical variability of CDW and WSDW affecting the distribution of bottom-current features around seamounts and/or structural highs. The results underscore the importance of sloping interphases in the water mass vertical structure, the degree of basin confinement, and the influence of local bathymetric elevations in sedimentation models of small sediment-starved oceanic basins.

A multi-disciplinary investigation of the AFEN Slide: the relationship between contourites and submarine landslides

Abstract Contourite drifts are sediment deposits formed by ocean bottom currents on continental slopes worldwide. Although it has become increasingly apparent that contourites are often prone to slope failure, the physical controls on slope instability remain unclear. This study presents high-resolution sedimentological, geochemical and geotechnical analyses of sediments to better understand the physical controls on slope failure that occurred within a sheeted contourite drift within the Faroe–Shetland Channel. We aim to identify and characterize the failure plane of the late Quaternary landslide (the AFEN Slide), and explain its location within the sheeted drift stratigraphy. The analyses reveal abrupt lithological contrasts characterized by distinct changes in physical, geochemical and geotechnical properties. Our findings indicate that the AFEN Slide likely initiated along a distinct lithological interface, between overlying sandy contouritic sediments and softer underlying mud-rich sediments. These lithological contrasts are interpreted to relate to climatically controlled variations in sediment input and bottom current intensity. Similar lithological contrasts are likely to be common within contourite drifts at many other oceanic gateways worldwide; hence our findings are likely to apply more widely. As we demonstrate here, recognition of such contrasts requires multi-disciplinary data over the depth range of stratigraphy that is potentially prone to slope failure.

An Improved Treatment of Neutral Sheet Drift in the Inner Heliosphere

Abstract Drifts due to the curvature and gradients in the heliospheric magnetic field, as well as along the heliospheric current sheet, have long been known to play a significant role in the transport of galactic cosmic rays. Recently, there has been greater interest in the role these drifts play in the transport of solar energetic particles. This study proposes an approach to modeling particle drift velocities in particle transport codes that, while being relatively simple to implement and computationally inexpensive, also models drift effects accurately across a broader range of energies than previous approaches.

Quantitative characterisation of contourite deposits using medical CT

Five sediment cores, retrieved from four different depositional contouritic morphological settings (a sheeted drift, a confined mounded drift, a mounded elongated drift and a plastered drift) from the Northern Gulf of Cadiz and the Alboran Sea have been analysed using medical X-ray computed tomography (medical CT). A quantitative approach has been used, resulting in a workflow that delineates several radio-density ranges based on the Hounsfield Unit (HU) histogram of each core and tracks these ranges throughout the cores. In order to derive the geological significance, the radio-density ranges of all cores have been compared to non-destructive, continuous chemical and physical proxies as well as grain size measurements. The highest correlations occurred between high HU and proxies indicating elevated bottom currents, such as Zr/Al and sortable silt. Additionally, a continuous increase in average HU and inferred bottom current velocities, needed for the creation of the specific contourite setting, could be observed throughout the five cores. Despite imperfections and the requirement of additional research, promising results have been obtained which could improve the detection of diagnostic criteria for contourites. Moreover, the CT data can give more conclusive evidence on the nature of the (contourite) sedimentary sequence boundaries.

Seismic stratigraphy of upper Quaternary shallow-water contourite drifts in the Gulf of Taranto (Ionian Sea, southern Italy)

The occurrence of articulated seafloor morphology over continental shelf-upper slope environments, may result in a significant change in the patterns and intensity of basin-scale thermohaline circulation during eustatic sea-level fluctuations. These changes may cause, in turn, erosion, deposition and/or transport of sediments at the seafloor, to form shallow-water contourite drifts. Here we investigate this process in the NW sector of the Gulf of Taranto (Ionian Sea) during and following the Last Glacial Maximum (LGM), by integrating multibeam bathymetric data, ultra-high resolution seismic-reflection data and gravity core data. Sea level fall caused subaerial exposure of the summit of the Amendolara Bank, forming a short-lived island off the eastern coast of Calabria, and also creating a narrow passageway between the island and the northern Calabria mainland. Integrated seismic-stratigraphic data show that Upper Quaternary shallow-water contourite drifts and associated erosional features locally formed both around the flanks of the Amendolara Bank (AMBK), and the continental shelf and upper slope off the Amendolara village. Contourite drifts are bounded at the bottom and at the top by two major unconformities, indicating that the formation of the sediments drifts occurred between the onset of the LGM and the GS-1/Younger Dryas event. The stratal architecture suggests the occurrence of various types of contourite deposits, mostly represented by: a) Axial and lateral channel-patch drifts, and channel-related drifts along the incision to the NE of the AMBK; b) Sheeted drifts along the northeastern slope of the AMBK; c) Elongated drifts along the continental shelf and upper slope off the coast of Amendolara village. Erosional features also developed on the south-eastern flank of the AMBK, where the Levantine Intermediate Water flows from the central Ionian Sea towards the Gulf of Taranto, until the present-day. Both processes and timing responsible for erosion of the seafloor and the formation of sediment drifts in the Gulf of Taranto may be similar to that occurred in the Tyrrhenian margins during the Late Quaternary.

Solar Energetic Particle Transport Near a Heliospheric Current Sheet

Abstract Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1–800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibit multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.

Unusually large tsunamis frequent a currently creeping part of the Aleutian megathrust

AbstractCurrent models used to assess earthquake and tsunami hazards are inadequate where creep dominates a subduction megathrust. Here we report geological evidence for large tsunamis, occurring on average every 300–340 years, near the source areas of the 1946 and 1957 Aleutian tsunamis. These areas bookend a postulated seismic gap over 200 km long where modern geodetic measurements indicate that the megathrust is currently creeping. At Sedanka Island, evidence for large tsunamis includes six sand sheets that blanket a lowland facing the Pacific Ocean, rise to 15 m above mean sea level, contain marine diatoms, cap terraces, adjoin evidence for scour, and date from the past 1700 years. The youngest sheet and modern drift logs found as far as 800 m inland and >18 m elevation likely record the 1957 tsunami. Previously unrecognized tsunami sources coexist with a presently creeping megathrust along this part of the Aleutian Subduction Zone.

Very Local Interstellar Spectra for Galactic Electrons, Protons and Helium

The local interstellar spectra (LIS) for cosmic rays at energies below ∼30 GeV/nuc are increasingly obscured from view at Earth by solar modulation, the lower the energy becomes. These charged particles encounter significant changes in the heliosphere, over an 11-year cycle, which include processes such as convection, diffusion, adiabatic energy losses and gradient, curvature and current sheet drifts. Particle drifts cause charge-sign-dependent modulation and a 22-year cycle, adding complexity to determining the respective very LIS from observations only at Earth. However, with measurements now made by the Voyager 1 spacecraft in the vicinity of the heliopause, it is possible to determine a very LIS for galactic electrons between ∼5 and ∼120 MeV. At these low energies, also galactic protons observed in the outer heliosphere had been completely obscured by the so-called anomalous component which is accelerated inside the heliosheath. Since August 2012, these anomalous cosmic rays are substantially depleted at Voyager 1 so that for cosmic ray ions, it is now possible to obtain a lower limit to their very LIS. Combining numerical modelling of solar modulation with the accurate measurements by the PAMELA mission and with Voyager observations, the lower limit of the very LIS for electrons, protons and helium and other ions can be determined from ∼5 MeV and above. These spectra are called heliopause spectra which is considered to be the lowest possible very LIS. Also, from an astrophysics point of view, the determination of what can be called a very LIS, not just an averaged galactic spectrum, is encouraging. The mentioned aspects are discussed, focusing on a comparison of recent heliospheric observations and corresponding solar modulation modelling.

THE EFFECT OF DRIFT ON THE EVOLUTION OF THE ELECTRON/POSITRON SPECTRA IN AN AXISYMMETRIC PULSAR WIND NEBULA

Charged particles propagating through a structured magnetic field are subject to drift motion. The primary aim of the present paper is therefore to investigate the effects of gradient, curvature, and neutral sheet drift on the evolution of the electron and positron spectra in a pulsar wind nebula, where the drift motion is a direct result of the magnetic field having an Archimedean spiral structure. In order to investigate the evolution of the spectra, the steady-state, axisymmetric Fokker-Planck transport equation is solved numerically using a finite-difference scheme. Apart from drift motion, the transport processes of convection and diffusion, along with the energy loss processes of adiabatic cooling and synchrotron radiation, are also included in the model. It is found that drift, particularly neutral sheet drift, can lead to a quantitative difference in the evolution of the electron and positron spectra. This difference may be of importance when interpreting the positron excess observed by PAMELA and AMS-02 near Earth.

Hall Factor Calculation for the Characterization of Transport Properties in N-Channel 4H-SiC MOSFETs

For the characterization of n-channel 4H-SiC MOSFETs, current-voltage and Hall-effect measurements were carried out at room temperature. To interpret the Hall-effect measurements, the Hall factor for the electron transport in the channel of SiC MOSFETs was evaluated, for the first time. The method of the Hall factor calculation is based on the interdependence with mobility components via the respective scattering relaxation times. The results of the calculation reveal a strong dependence of the Hall factor on the gate voltage. Depending on the gate voltage applied, the values of the Hall factor vary between 1.3 and 1.5. Sheet carrier density and drift mobility values derived from the Hall-effect measurements using our new gate-voltage-dependent Hall factor show very good agreement with simulations performed with Sentaurus Device of Synopsys.

On the Temperature Dependence of the Hall Factor in n-Channel 4H-SiC MOSFETs

To interpret Hall-effect measurements in a range of temperatures, the Hall factor for the electron transport in the channel of a SiC MOSFETs was evaluated. The method of the Hall factor calculation is based on the interdependence with mobility components via the respective scattering relaxation times. For the first time, the temperature dependence of the Hall factor in n-channel 4H-SiC MOSFETs was calculated. The results of the calculation reveal a strong reduction of the Hall factor with increasing temperature. Depending on gate voltage and temperature, the values of the Hall factor vary between 1.2 and 1.5. In addition, the sheet carrier densities and drift mobilities derived from the Hall-effect measurements using our new temperature-dependent Hall factor show very good agreement with independent simulation results.

AN AB INITIO MODEL FOR COSMIC-RAY MODULATION

A proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays (CRs) is of vital importance for a better understanding of CR modulation in the heliosphere. This study presents an ab initio model for CR modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. This model is solved for solar minimum heliospheric conditions, utilizing boundary values chosen so that model results are in reasonable agreement with spacecraft observations of turbulence quantities in the solar ecliptic plane and along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modeled slab and two-dimensional (2D) turbulence energy spectra. The modeled 2D spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers. There currently exist no models or observations for the wavenumber where this drop-off occurs, and it is considered to be the only free parameter in this study. The modeled spectra are used as inputs for parallel mean free path expressions based on those derived from quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore, the effects of turbulence on CR drifts are modeled in a self-consistent way, also employing a recently developed model for wavy current sheet drift. The resulting diffusion and drift coefficients are applied to the study of galactic CR protons and antiprotons using a 3D, steady-state CR modulation code, and sample solutions in fair to good agreement with multiple spacecraft observations are presented.

Seismic characteristics and processes of the Plio-Quaternary unidirectionally migrating channels and contourites in the northern slope of the South China Sea

The Plio-Quaternary unidirectionally migrating channels (UMCs) and contourites in the northern slope of the South China Sea were investigated in this paper using seismic data. The UMCs include thalweg deposits (TDs) and laterally migrating deposits (LMDs), which result from the interaction between gravity flow and contour current. The LMDs migrating directions are northeast (NE) and west-southwest (WSW) and also display weak seismic reflection and obvious multi-stages. By contrast, the TDs show high seismic reflection and lateral aggradation.Giant elongated, confined, and slope sheeted drifts, as well as sediment waves are widespread in the northern slope of the South China Sea. Helicoidal contour currents can generate giant elongated and confined drifts associated with moats. By contrast, tabular contour currents can develop slope sheeted drifts with rare moats. NE-migrating channels, giant elongated drifts, and a number of sediment waves are exclusively formed at water depths of 200 m–1200 m. Drifts, sediment waves, and few WSW-migrating channels are developed at water depths of 1200 m–3000 m.The intermediate water contour current circulates clockwise, moving from Xisha Islands to Dongsha Islands and extending into the eastern part of Dongsha Islands because of the bathymetry. Deep water contour current may circulate counterclockwise and be transported northeastward through Dongsha Islands to Xisha Islands, bifurcating in the Xisha Islands because of topographical prominences.