Current induced seabed features along the eastern Rockall Trough, NE Atlantic – an interpretation of TOBI side-scan sonar imagery

The Rockall Trough, located west of Ireland, bordered by the Rockall Bank in the west and the Porcupine Bank in the east, has been intensively studied during the last decade. Numerous seabed structures were discovered along its eastern and western margin including cold-water coral covered carbonate mounds. The investigations in the Rockall Trough also included TOBI 30 kHz sidescan sonar surveys along its eastern margin.The TOBI data (TOBI stands for ‘Towed Ocean Bottom Instrument’) revealed that this margin is characterised by an inhomogeneous and complex topography. Mound, scarp and hedge structures can be found, often associated with cold-water corals. Furthermore, hardgrounds, outcrops of banked carbonates observed with ROVs and sediment waves occur, indicating erosion and sediment movement. All of the previously mentioned features are the result of, or affected by, strong bottom currents. Maps based on TOBI data display that most of the pronounced features (e.g. scarps and mound chains) strike parallel to the contours thus parallel to the northward oriented shelf edge current.Sediment waves manly strike slope-parallel indicating across-slope currents. In addition, oblique structures can be found which are neither parallel nor perpendicular to the slope. These complex patterns are probably the expression of the interplay of different bottom currents (main flow, tidal currents). As the spatial effects of these currents remain largely unknown, this study interprets the observed seabed features to reconstruct the prevailing relative bottom current velocities (direction and intensity) along the eastern Rockall Trough margin.This publication uses data and survey results acquired during a project undertaken with support of the European Union (EASSS III programme, ‘Improving Human Potential’, contract HPRI-CT-1999-00047) and on behalf of the Porcupine Studies Group (PSG) of the Irish Petroleum Infrastructure Programme Group 3. The PSG comprises: Agip Ireland BV, Chevron UK Ltd, Elf Petroleum Ireland BV, Enterprise Energy Ireland Ltd, Marathon International Hibernia Ltd, Phillips Petroleum Company United Kingdom Ltd, Statoil Exploration (Ireland) Ltd and the Petroleum Affairs Division of the Department of Communication, Marine and Natural Resource

Sea-floor and sea-ice conditions in the western Weddell Sea, Antarctica, around the wreck of Sir Ernest Shackleton's Endurance

AbstractMarine-geophysical evidence on sea-floor morphology and shallow acoustic stratigraphy are used to examine the substrate around the location at which Sir Ernest Shackleton's ship Endurance sank in 1915 and on the continental slope-shelf sedimentary system above this site in the western Weddell Sea. Few signs of turbidity-current and mass-wasting activity are found near or upslope of the wreck site, and any such activity was probably linked to full-glacial higher-energy conditions when ice last advanced across the continental shelf. The wreck is well below the maximum depth of iceberg keels and will not have been damaged by ice-keel ploughing. The wreck has probably been draped by only a few centimetres of fine-grained sediment since it sank in 1915. Severe modern sea-ice conditions hamper access to the wreck site. Accessing and investigating the wreck of Endurance in the Weddell Sea therefore represents a significant challenge. An ice-breaking research vessel is required, and even this would not guarantee that the site could be reached. Heavy sea-ice cover at the wreck site, similar to that encountered by Agulhus II during the Weddell Sea Expedition 2019, would also make the launch and recovery of autonomous underwater vehicles and remotely operated vehicles deployed to investigate the Endurance wreck problematic.The Flotilla Foundation Marine Archaeological Consultants Switzerlan

The southwest Indian Ocean Bathymetric Compilation (swIOBC)

We present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data-constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N-S trending Zambezi Channel could be imaged in the central Mozambique Basin. Maps are crucial not only for orientation but also to set scientific processes and local information in a spatial context. For most parts of the ocean seafloor, maps are derived from satellite data with only kilometer resolution. Acoustic depth measurements from ships provide more detailed seafloor information in tens to hundreds of meters resolution. For the southwest Indian Ocean, all available depth soundings from a variety of sources and institutes are combined in one coherent map. Thus, in areas where depth soundings exist, this map shows the seafloor in so-far unknown detail. This detailed map forms the base for subsequent studies of e.g. the direction of ocean currents, geological and biological processes in the southwest Indian Ocean

Large-scale mass wasting in the western Indian Ocean constrains onset of East African rifting

Faulting and earthquakes occur extensively along the flanks of the East African Rift System, including an offshore branch in the western Indian Ocean, resulting in remobilization of sediment in the form of landslides. To date, constraints on the occurrence of submarine landslides at margin scale are lacking, leaving unanswered a link between rifting and slope instability. Here, we show the first overview of landslide deposits in the post-Eocene stratigraphy of the Tanzania margin and we present the discovery of one of the biggest landslides on Earth: the Mafia mega-slide. The emplacement of multiple landslides, including the Mafia mega-slide, during the early-mid Miocene is coeval with cratonic rifting in Tanzania, indicating that plateau uplift and rifting in East Africa triggered large and potentially tsunamigenic landslides likely through earthquake activity and enhanced sediment supply. This study is a first step to evaluate the risk associated with submarine landslides in the region

Ireland: Submerged Prehistoric Sites and Landscapes

Evidence of Ireland's drowned landscapes and settlements presently comprises 50 sites spread across the entire island. These comprise mainly intertidal find spots or small collections of flint artefacts. A handful of fully subtidal sites are known, generally from nearshore regions and consisting, with one exception, of isolated single finds. Evidence of organic remains is also sparse, with the exception of Mesolithic and Neolithic wooden fish traps buried in estuarine sediments under Dublin. The relatively small number of sites is probably due to lack of research as much as taphonomic issues, and thus the current evidence hints at the potential archaeological record which may be found underwater. Such evidence could contribute to knowledge of the coastal adaptations and seafaring abilities of Ireland's earliest inhabitants. Nonetheless, taphonomic considerations, specifically relating to Ireland's history of glaciation, sea-level change and also modern oceanographic conditions likely limit the preservation of submerged landscapes and their associated archaeology. Realistically, the Irish shelf is likely characterised by pockets of preservation, which makes detection and study of submerged landscapes difficult but not impossible. A range of potential routes of investigation are identifiable, including site-scale archaeological survey, landscape-scale seabed mapping, archival research and community engagement

The International Bathymetric Chart of the Arctic Ocean Version 4.0

Funder: The Nippon Foundation of Japan, grant Seabed 2030Funder: Open access funding provided by Stockholm UniversityAbstract: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet