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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]

The Capbreton canyon stands out by its deep incision through continental shelf and slope and its present turbidity activity. The head of the canyon is disconnected from the Adour River since 1310 AD but is located close enough to the coast to allow a direct supply by longshore drifting. Gravity processes in the canyon body are well understand, but many questions remain for the head and the upper part of the Capbreton submarine canyon such as: Which kind of gravity processes provide sediment transfer from the head to the canyon? How these processes interact with the canyon floor morphology: floor shaping and feedback? Our study is based on the analysis and comparison of eight multibeam bathymetric surveys acquired between 1998 and 2018 from a depth of 10 to 320 m below sea level. This data set covers the same area of the upper part of the canyon and allows the comparison and morphologic follow-up of this outstanding dynamic area. This proximal dataset is completed by two distal bathymetric surveys on a meander at 1500m water depth acquired in the canyon in 2013 and 2016. The morphological evolutions in these sites over the last 20 years especially affect the canyon floor and the canyon head. Time of flat floor talweg is observed, succeeded by a period of talweg incision (low lateral terraces and axial narrow talweg). The entrenchment of the narrow talweg is induced by retrogressive erosion and is evidenced by upstream-migrating-knickpoints suggesting a return to the equilibrium profile. The construction process of the low terraces observed here appears to be an analog of the fluvial terraces construction, where axial channel entrenchment follow the sediment filling of the valley. Time of flat shaped talweg (1998) suggests a partial filling of the canyon talweg related to a substantial emptying of the canyon head and significant mass transfer to the proximal part of the canyon. Such flat floor talweg has not been observed again so far (since 2010), suggesting a possible quieter working mode of the canyon. In fact, in the light of currentmeter data (ADCP) recorded during winters 2015 and 2016 (at 555, 900 and 1500m water depth in the canyon), periods of talweg entrenchment (2010 to present day) are subject to gravity flows weaker than 40 cm.s-1. However, first accurate volume quantification on the canyon floor has been undertaken. This underlines an alternation of filling and erosive periods in the canyon axis and an unexpected continuous sediment deposition in the canyon head during the last 20 years. At the present time, the canyon head is filling up and we may fear an important head emptying including costal risks during the upcoming violent event. [ABSTRACT FROM AUTHOR]

Submarine mass movements may have profound effects on the morphology and stratigraphic architecture of continental margins. Furthermore, they can represent a threat to human life and infrastructures, and also have implications for hydrocarbon exploration/production. In polar regions, they are one of the predominant sedimentary processes on the continental slope. Exploration seismology has been widely employed to study masstransport deposits (landslides, glacigenic debris flows, mass flows, etc.), which are usually characterized by chaotic reflections. In this study, we analyse a seismic profile acquired in the southern part of the Storfjorden trough mouth fan (NW Barents Sea margin), showing the presence of two submarine mass-transport deposits (MTDs). A giant MTD (PLS-1) is located on the lower continental slope at 2.6–3 km depth, while a more recent MTD (PLS-2) occurs at 1.9–2.4 km depth. Velocity and attenuation seismic tomography, seismic attributes analyses and rock-physics models reveal distinct petrophysical properties for PLS-1 and PLS-2. Despite the known influence of burial depth(s), fluid flow content, and compaction on the internal character of MTDs, the two deposits studied here, in fact, show distinct petrophysical characteristics that reflect lithological variations - more than to any other control. These results suggest different source areas for the two MTDs. The inferred coarser sediment in PLS-1 indicates provenance from areas with abundant glacigenic debris flows, (such as the Bjørnøya Trough-Mouth Fan). Conversely, the finer, relatively fluid-rich sediments of PLS-2 that underwent little translation could have an origin in the area between trough-mouth fans. Here, slow-moving ice resulted in a relatively scarce release of subglacial debris at the shelf edge and the continental slope was subject to enhanced erosion and degradation with a comparatively higher production of relatively fine-grained turbidite flows. [ABSTRACT FROM AUTHOR]