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Several high-resolution 'SES 2000 deep' seismic profiles and a core of bottom sediments were obtained in cruises 33, 35, and 37 of the R/V Akademik Ioffe in the area of the Columbia channel (continental rise of Brazil, South America). The analysis of seismic facies and direct correlation of acoustic and lithological data indicates that sedimentation in this area is mostly controlled by the contour current of the Antarctic Bottom Water (AABW). The gravity flows from seamounts and continental slope only episodically contributed coarser material to the deposition of the muddy contourites. The mixed gravitite-contourite systems consisting of accumulative bodies (drifts) and erosion channels are the results of interaction of these sedimentation processes. [ABSTRACT FROM AUTHOR]

Recent studies suggest that as much as half of the organic carbon (OC) undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering. These estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils, freshwater sediments, and river deltas, and thus only minimally contributes to the extraneously old 14C ages of total organic matter often observed on adjacent shelves. Here we test this paradigm by measuring the Δ14C and δ13C values of individual higher plant wax fatty acids as well as the δ13C values of extractable alkanes isolated from the Eel River margin (California). The isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition. A coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated, with pre-aged terrestrial material instead composing a considerable proportion of all organic matter. If these findings are characteristic of other continental margins proximal to small mountainous rivers, then the importance of petrogenic OC burial in marine sediments may need to be reevaluated. [ABSTRACT FROM AUTHOR]

Echo character recorded on Chirp sub-bottom sonar data from offshore of SW Taiwan was analysed to examine and compare the sedimentary processes of adjacent passive and active continental margin settings. Seafloor echoes in the study area are classified into four types: (1) distinct echoes, (2) indistinct echoes, (3) hyperbolic echoes and (4) irregular echoes. Based on the mapped distribution of the echo types, the sedimentary processes offshore of SW Taiwan are different in the two tectonic settings. On the passive South China Sea (SCS) margin, slope failure is the main process on the upper continental slope, whereas turbidite deposits accumulate in the lower continental slope. In contrast, the submarine Taiwan orogenic wedge is characterized by fill-and-spill processes in intraslope basins on the upper slope, and mass-transport deposits are observed in the canyons and on the lower Kaoping slope. This difference is largely caused by the huge influx of terrigenous sediments into the submarine Taiwan orogenic wedge compared with the passive SCS continental margin. In the latter, loading and movement of the Taiwan orogenic wedge has had a significant effect on the seafloor morphology and has triggered retrogressive failures. Gas hydrate dissociation may have enhanced the slope failure processes at some locations. [ABSTRACT FROM AUTHOR]

We attempt here to quantify and model physiographic features off the central west coast of India in terms of power spectral exponent, amplitude parameter. We demonstrate that statistical analysis of multi-beam echo-sounder grid bathymetry data is able to characterise the outer shelf, upper slope, shelf margin basin and several structural rises in the region. A scatter diagram analysis shows that the seafloor data can be grouped into two distinct clusters. Distinctly different clustering patterns are observed over the structural rises, compared to the shelf, slope and basinal areas. This suggests different modes of formation for the members of these two clusters. In fact, the steep structural rises appear to be part of the NW–SE-trending coast-parallel Mid-Shelf Basement and Prathap ridges. These ridges are rift-induced volcanic emplacements on a stretched and thinned continental crust which probably formed during mid-Cretaceous times. [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]

This study applies detailed seafloor bathymetry data and seafloor images to understand upper slope features and how these influence the distribution of seafloor biota on the East Antarctic margin. The East Antarctic slope on the Sabrina margin has been shaped by diverse processes related to repeated glaciation. Differences in the morphology of gullies on the upper slope enable an understanding of the likely processes that have been active on this margin. Gully morphology varies according to changes in slope gradient, which may have driven variations in sedimentation. Areas of lower slope angles may have led to rapid sediment deposition during glacial expansion to the shelf edge, and subsequent sediment failure. Typically, gullies in these areas are U-shaped, initiate well below the shelf break, are relatively straight and long, and have low incision depths, consistent with formation due to mass wastage. Areas of higher slope angles likely experienced enhanced flow of erosive turbidity currents during glaciations associated with the release of sediment-laden basal meltwaters. Sediment-laden subglacial meltwater flows typically create gullies such as those we observe that initiate at, or near, the shelf break; are V-shaped in profile; and have high sinuosity, deep incision depths and a relatively short downslope extent. The short downslope extent reflects a reduced sediment load associated with increased seawater entrainment as the slope becomes more concave in profile. These differences in gully morphology have important habitat implications associated with differences in the composition and beta-diversity of the seafloor communities. This upper slope region also supports seafloor communities that are distinct from those on the adjacent shelf, highlighting the uniqueness of this environment for biodiversity. Conservation strategies therefore need to consider slope and shelf communities as distinct and equally important components of the Antarctic ecosystem. • Upper slope gullies on this Antarctic margin have distinct morphology. • Upper slope morphology is driven largely by variations in depositional history. • Benthic community structure and beta-diversity is associated with gully morphology. • Upper slope communities are distinct from the adjacent continental shelf. [ABSTRACT FROM AUTHOR]

Internal solitary wave shoaling is the product of the interaction of internal solitary waves (ISWs) with the seafloor. There will be a series of changes in the waveform of the internal solitary wave when water depth decreases, and it affects the flow near the seafloor. These processes are captured by the seismic oceanography(SO) method. We analyze and summarize water-column reflections characteristics in the Dongsha region of South China Sea(SCS). The interior of the ocean is dominated by high/low frequency internal waves, internal solitary waves and high-mode internal waves. The seismic oceanography profiles record 45 internal solitary waves in the study area, and the depression waves are widely distributed in both deep and shallow water area. During their shoaling process in the Dongsha region, the depression waves gradually come into the transition stage under influence of the topography, and finally convert its polarity to elevation waves in the shallow water area. In addition, the energy dissipation during the internal solitary wave shoaling process, has an important impact on the shaping of the upper continental slope in the northern South China Sea.It is proposed that the computational fluid dynamic (CFD) modelling is combined with seismic forward modelling to study seawater seismic facies. Modelling experiments are focused on internal solitary waves shoaling as well as the formation and evolution of seismic facies over sand dunes. Shoaling internal solitary waves propagating westward in the northeastern South China Sea of depression, transition and elevation types are simulated. The temperature, velocity field and seismic reflection events in forward modelling sections are compared with observed SO data. The shape of isothermal curve is analyzed to study the speed of ISWs and the effect of seafloor fiction. Different Iribarren numbers are discussed to study the diverse types of ISW breaking, including surging and plunging breaking.The depression and elevation internal solitary waves bring about the southeast and northwest direction wave-induced currents respectively. On the one hand these near-bed wave-induced currents resuspend sediment particles into water columns to generate nepheloid layers, and on the other hand they contribute to the bed load, which maintains the very large sand dunes formation and migration. Seawater seismic facies over sand dunes are analyzed, including the coupling of seismic events and morphology, the high frequency oscillating seismic events in both edges of ISWs, and hair reflection configuration seismic events over sand dunes on slope. Modelling results show that the coupling of sand dunes and seismic events may be related to unidirection flow over sand dunes. The high frequency oscillating seismic events in both edges of ISWs are related to ISWs propagating over sand dunes. While the shape of the oscillating seismic events is similar to undulation of sand dunes in the beginning, they are reshaped by ISWs and move toward the same direction of ISW propagation. This study may reveal the relationship among multi-scale movements of seawater, bottom topography and sedimentary processes, which can deepen the understanding of the seafloor interface process. [ABSTRACT FROM AUTHOR]