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Framework-forming cold-water corals provide a refuge for numerous organisms and, consequently, the ecosystems formed by these corals can be considered as impressive deep-sea biodiversity hotspots. If suitable environmental conditions for coral growth persist over sufficiently long periods of time in equilibrium with continuous sediment input, substantial accumulations of coral mound deposits consisting of coral fragments and baffled sediments can form. Although this conceptual approach is widely accepted, little is known about the prevailing hydrodynamics in their close proximity, which potentially affect sedimentation patterns. In order to refine the current understanding about the hydrodynamic mechanisms in the direct vicinity of a model cold-water coral colony, a twofold approach of a laboratory flume experiment and a numerical model was set up. In both approaches the flow dynamics around a simplified cold-water coral colony used as current obstacle were investigated. The flow measurements of the flume provided a dataset that served as the basis for validation of the numerical model. The numerical model revealed data from the vicinity of the simplified cold-water coral, such as the pressure field, velocity field, or the turbulent kinetic energy (TKE) in high resolution. Features of the flow like the turbulent wake and streamlines were also processed to provide a more complete picture of the flow that passes the simplified cold-water coral colony. The results show that a cold-water coral colony strongly affects the flow field and eventually the sediment dynamics. The observed decrease in flow velocities around the cold water-coral hints to a decrease in the sediment carrying potential of the flowing water with consequences for sediment deposition.

Although subaqueous slopes on active continental margins are subject to a variety of failure styles, their movement mechanisms during earthquakes remain poorly constrained. A primary explanation is that few submarine landslides have been directly sampled for detailed investigation. We have conducted a series of dynamic shear experiments on samples recovered from the base of the Tuaheni Landslide Complex, located off the east coast of the North Island of New Zealand, to explore its behaviour during earthquakes. Our experiments suggest that whilst the basal landslide sediments can be prone to liquefaction in certain conditions, this is not a likely failure mechanism at the stress states operating in the low angled shear zone at the base of this landslide system. Instead, episodic landslide movement can occur through basal sliding when pore water pressures increase sufficiently to lower the shear zone effective stress to the material failure envelope. These low effective stress conditions are most likely to be reached during earthquakes that produce large amplitude, long duration ground shaking. The observed behaviour provides a credible mechanism through which subaqueous landslides moving on low angled shear zones in similar materials may be subject to episodic movement during earthquakes without undergoing catastrophic failure.

Despite intense research by both academia and industry, the parameters controlling slope stability at continental margins are often speculated upon. Lack of core recovery and age control on failed sediments prevent the assessment of failure timing/frequency and the role of prefailure architecture as shaped by paleoenvironmental changes. This study uses an integrated chronological framework from two boreholes and complementary ultrahigh-resolution acoustic profiling in order to assess (1) the frequency of submarine landsliding at the continental margin of NE Gela Basin and (2) the associated mechanisms of failure. Accurate age control was achieved through absolute radiocarbon dating and indirect dating relying on isotope stratigraphic and micropaleontological reconstructions. A total of nine major slope failure events have been recognized that occurred within the last 87 kyr (~10 kyr return frequency), though there is evidence for additional syndepositional, small-scaled transport processes of lower volume. Preferential failure involves translational movement of mudflows along subhorizontal surfaces that are induced by sedimentological changes relating to prefailure stratal architecture. Along with sequence-stratigraphic boundaries reflecting paleoenvironmental fluctuations, recovered core material suggests that intercalated volcaniclastic layers are key to the basal confinement and lateral movement of these events in the study area. Another major predisposing factor is given by rapid loading of fine-grained homogenous strata and successive generation of excess pore pressure, as expressed by several fluid escape structures. Recurrent failure, however, requires repeated generation of favorable conditions, and seismic activity, though low if compared to many other Mediterranean settings, is shown to represent a legitimate trigger mechanism.

Der interozeanische Austausch der Wassermassen südlich von Südafrika ist für die globale thermohaline Zirkulation von zentraler Bedeutung. Zunahme oder Abschwächung dieses Wassermassenaustausches führen zur Verstärkung oder Abschwächung der atlantischen Umwälzbewegung sowie zu einer entsprechenden Veränderung der Tiefenwasserbildung im Nordatlantik. Während der FS SONNE Fahrt SO-182 im April-Mai 2005 wurden mehr als 2800 Kilometer hoch auflösende refexionsseismische Daten im Transkei Becken südöstlich von Südafrika gemessen. Die Analyse zeigt, dass Nordatlantisches Tiefenwasser (NADW) und Antarktisches Bodenwasser (AABW) die Sedimentbildung in dieser Region stark beeinflussen. Die Beobachtungen zeigen weiter, dass die Ströme in dieser Region sehr variabel waren: Eine Nord-Süd-Strömung von AABW beherrschte Sedimenttransport und -absetzung im Transkei Becken vom mittlerem Miozän bis zum frühen Pliozän, gefolgt von einem Haupttransport in W-E Richtung durch NADW. Um die Sedimentanordnung und die Entwicklung der Paläozirkulation südlich von Südafrika besser zu verstehen, wird ein Ozeanzirkulationsmodell benutzt, das mit einem Sedimentmodell gekoppelt ist.Das eingesetzte Modell ist das Regional Ocean Modeling System (ROMS), das auf hydrostatischen, primitiven Gleichungen basiert. Es nutzt terrainfolgende Koordinaten in der Vertikalen und orthogonal gekrümmte Koordinaten in der Horizontalen, die je nach Fragestellung unterschiedliche Auflösung haben. Das Modell simuliert das gegenwärtige Strömungssystem in der Region südlich von Südafrika. Basierend auf dem Modell wird die Simulation der regionalen Verteilung von Sand und Silt weiterentwickelt.

Das Ziel dieser Arbeit ist es, die Mechanik im Bereich des forearcs der Makran Subduktionszone zu untersuchen. Zu diesem Zweck kommen drei verschiedene Simulationstechniken zum Einsatz. Dies sind die Finite und die Diskrete Elemente Methode als zwei numerische Verfahren, sowie analoge Sandexperimente. Durch die Kombination dieser drei Methoden, die sich ergänzende und vergleichende Ergebnisse liefern, wird ein umfassendes Bild der Deformations- und Massentransferprozesse des forearcs in Makran gewonnen. Zudem ermöglichen alle drei Verfahren die Untersuchung des Deformationsverhaltens in einem Material, welches einer Mohr-Coulomb Rheologie mit strain hardening/strain softening bzw. einem work hardening gehorcht.

Swath bathymetry images and 3.5 kHz data acquired during RV Sonne cruise 123 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge Makran accretionary wedge. The continental slope off Pakistan is characterised by three morphological provinces: (a) The lower slope is built of a sequence of imbricate thrust slices which form long and narrow accretionary ridges with flanks locally as steep as 20° and between 10° and 20° on average, while the regional slope is only 1–2°, (b) the nearly flat mid-slope terrace is present in the central east part of the margin, narrows significantly towards the east, and is absent east of 63° 45' and (c) the upper slope up to the shelf has a regionally uniform slope as steep as about 8° and comprises a very rough topography with many gullies and canyons and evidence for mass wasting. Two meandering canyons crossing the entire margin down to the abyssal plain at about 63° 15'–63° 30', can be correlated with onshore rivers. They have been formed by episodic erosion through turbidity flows and are characterised by erosional and depositional portions. Sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obstacles for flow to be directly downhill. Application of Coulomb rheology to the frontal part of the Makran Wedge implies that the mid-level décollement is intrinsically extraordinary weak with a great strength contrast to the overlying sediments. Comparison with Nankai, Cascadia, and the Western Mediterranean Ridge reveals new insights in the parameters controlling the shape of an accretionary wedge and the role of a mid-level décollement.

Although submarine landslides have been studied for decades, a persistent challenge is the integration of diverse geoscientific datasets to characterize failure processes. We present a core‐log‐seismic integration study of the Tuaheni Landslide Complex to investigate intact sediments beneath the undeformed seafloor as well as post‐failure landslide deposits. Beneath the undeformed seafloor are coherent reflections underlain by a weakly‐reflective and chaotic seismic unit. This chaotic unit is characterized by variable shear strength that correlates with density fluctuations. The basal shear zone of the Tuaheni landslide likely exploited one (or more) of the low shear strength intervals. Within the landslide deposits is a widespread “Intra‐debris Reflector”, previously interpreted as the landslide's basal shear zone. This reflector is a subtle impedance drop around the boundary between upper and lower landslide units. However, there is no pronounced shear strength change across this horizon. Rather, there is a pronounced reduction in shear strength ∼10–15 m above the Intra‐debris Reflector that presumably represents an induced weak layer that developed during failure. Free gas accumulates beneath some regions of the landslide and is widespread deeper in the sedimentary sequence, suggesting that free gas may have played a role in pre‐conditioning the slope to failure. Additional pre‐conditioning or failure triggers could have been seismic shaking and associated transient fluid pressure. Our study underscores the importance of detailed core‐log‐seismic integration approaches for investigating basal shear zone development in submarine landslides., Plain Language Summary: Submarine landslides move enormous amounts of sediment across the seafloor and have the potential to generate damaging tsunamis. To understand how submarine landslides develop, we need to be able to image and sample beneath the seafloor in regions where landslides have occurred. To image beneath the seafloor we generate sound waves in the ocean and record reflections from those waves, enabling us to produce “seismic images” of sediment layers and structures beneath the seafloor. We then use scientific drilling to sample the sediment layers and measure physical properties. In this study, we combine seismic images and drilling results to investigate a submarine landslide east of New Zealand's North Island. Drilling next to the landslide revealed a ∼25 m‐thick layer of sediment (from ∼75–95 m below the seafloor) that has strong variations in sediment strength and density. We infer that intervals of relatively low strength within this layer developed into the main sliding surface of the landslide. Additionally, results from within the landslide suggest that the process of landslide emplacement has induced a zone of weak sediments closer to the seafloor. Our study demonstrates how combining seismic images and drilling data helps to understand submarine landslide processes., Key Points: We integrate scientific drilling data with seismic reflection data to investigate the submarine Tuaheni Landslide Complex. Basal shear zone of the landslide likely exploited a relatively low shear strength interval within an older (buried) mass transport deposit. Landslide emplacement seems to have induced an additional weak zone that is shallower than the interpreted base of the landslide deposit., Marsden Fund (Royal Society of New Zealand Marsden Fund) http://dx.doi.org/10.13039/501100009193, European Consortium for Ocean Research Drilling, International Ocean Drilling Program, Science Support Program, New Zealand Ministry for Business Innovation and Employment, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, https://doi.pangaea.de/10.1594/PANGAEA.928073