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

The R.V. Pelagia pre-drilling site survey at the Rockall and Porcupine cold water coral mounds provinces, European Atlantic margin. The CARBONATE project, ESF EuroMARC program

From 30 September to 22 October 2007 a cruise with the Royal NIOZ research vessel Pelagia was carried out within the framework of the ESF (EuroMARC) project CARBONATE. The goal of this cruise was to complete the existing data set of carbonate mounds present at the European Atlantic margin in order to be able to choose suitable coring sites to drill complete top to base sections through the carbonate mounds with the MeBo drilling device. This is a remotely operated drill that is placed at the sea floor and capable of drilling sediment cores with a maximum length of 85 metres. The drilling cruise, with the Irish research vessel Celtic Explorer, is planned to take place in the summer of 2008.During the Pelagia cruise 5 carbonate mound provinces were visited. The mounds were selected based on two main criteria:the mound provinces should represent different stages in mound developmentit must be possible to penetrate the mounds from top to base with the MeBo (expected maximum sequence thickness in the order of 75 m)The first area that was visited is located at the SE Rockall Bank margin. These mounds are characterised by abundant living cold water corals at their top. The second mound province that was visited is located at the SW Rockall Bank. Initially a large mound cluster known as Franken Mound was chosen for detailed studies. This mound, as well as smaller mounds in the vicinity, is dominated by dead corals and it is considered to be in what is often called the retirement stage. At theWand N margin of the Porcupine Bank two areas were visited. Most of the mounds occur as isolated structures. Only limited amounts of living cold water corals are present. The mounds in the last area that was visited are also referred to as the Magellan Mounds. This is a group of small (<100 m) mounds located in the Porcupine Seabight. These mounds are mostly fully buried and thus represent the final stage of mound development.At all sites a multibeam bathymetric survey was carried out. Subsequently a benthic lander was deployed which was equipped for a period of 2 to 4 days to measure near bed hydrography and sediment transport. This was followed by seismic and video surveys.The initial results of the cruise indicate that at all proposed drilling sites carbonate mounds with a total thickness that can be penetrated by the MeBo are present. The video observations did not reveal the presence of any rough terrain that may hamper the positioning of the MeBo at the seabed

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

Cold-Water Coral Ecosystem Functioning through Time in the Deep Sea: The example of cold-water coral carbonate mounds in the northeast Atlantic (from IODP307 to EuroMARC - CARBONATE)

Along the European Atlantic continental margin, recent to young (late Quaternary) fossil carbonate mounds and build-ups by cold-water corals (predominantly the framework forming ahermatypic corals Lophelia pertusa and Madrepora oculata) occur from northern Norway to the Gulf of Cadiz with an emerging global distribution pattern showing a European concentration (see Roberts et al., 2006). These have been the focus of multi-disciplinary European investigations that has moved from the discovery phase (where and what are they) to a more applied stage (how do they function and what do we need to know). One key question is how do these ecosystems function through time and how do they respond to environmental forcing.Investigations so far reveal that all mounds possess different growth histories depending on the environmental setting and the involved faunal associations. Unfortunately, existing cores only penetrated the upper few meters of the mounds thus limiting mound research to the very late stage of mound development. Access to the longer sequences preserved in giant carbonate mounds was overcome in May 2005 when the IODP Expedition 307 (Porcupine Mound Drilling) recovered complete sedimentary records from the 155 m high “Challenger Mound” in the Porcupine Seabight west off Ireland, including the underlying strata and the enigmatic mound base. Shipboard and preliminary shore based investigations of the recovered sediments exposed complex internal mound sedimentary structures and sedimentary fabrics. Coral occurrences throughout the core stressed the biological influence on mound development and construction. The common occurrence of hardgrounds is indicative of harsh environmental controls on mound formation and development with diagenetic effects playing a progressive role in internal mound geochemical environment influencing cementation, dissolution, porosity and permeability.Up to now the carbonate stored in carbonate mounds has not been considered in any global carbonate budget or linked to any global carbon budget involving greenhouse gases. A major challenge exists to quantify the amount and flux of carbon stored by these newly discovered areas of enhanced carbonate accumulation in intermediate water depth (e.g. carbonate mounds). The only existing integrative cold-water coral carbonate budget that has been performed is on short, post-glacial cores relevant to the Norwegian shelf only, which suggests that these small cold-water coral carbonate mounds alone may account for an additional 1% of total marine carbonate production (Lindberg et al., 2005).IODP has delivered one complete record from base to top of one carbonate mound in the Belgica Mound Province, Porcupine Seabight, NE Atlantic. EU FP projects have revealed late stage history of giant mounds in different settings showing that different mounds respond in different ways to environmental forcing factors with no one mound being typical of all. EuroMARC – CARBONATE hopes to study sequences through various mounds in different environmental settings. By understanding how biogeochemical processes control the development of these carbonate mounds and their response to climate change, we will make an important step in quantifying their role as mid-latitude carbonate sinks. In the end, a better understanding of the processes involved in mound formation and development may also result in new views on fossil analogues many of which are less accessible hydrocarbon reservoirs

Bathymetry and geological setting of the Drake Passage (Antarctica)

IX Congreso Geológico de España, Huelva, Septiembre 2016The Drake Passage is an oceanic gateway of about 850 km width located between South America and the Antarctic Peninsula that connects the southeastern Pacific and the southwestern Atlantic oceans and is an important gateway for mantle flow, oceanographic water masses, and migrations of biota. This gateway developed within the framework of geological evolution of the Scotia Arc. As a consequence of this and subsequent submarine processes, this region shows a varied physiography. The new detailed map in the Drake Passage region is mainly founded on a compilation of precise multibeam bathymetric data obtained on cruises between 1992 and 2014, and covers the area between parallels 52ºS and 63ºS and meridians 70ºW and 50ºW. The new map that we present is based in a DTM with 200 m cell resolution of the seafloor in Drake Passage that permits identification of the main seafloor features and the map includes additional useful geological information. This work constitutes an international cooperative effort and is part of IBCSO project (International Bathymetric Chart of the Southern Ocean), under the SCAR umbrella.Instituto Geológico y Minero de España, EspañaBritish Antarctic Survey, Reino UnidoDepartamento de Geodinámica, Universidad de Granada, EspañaInstituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, EspañaInstituto Andaluz de Ciencias de la Tierra, Universidad de Granada, EspañaJet Propulsion Laboratory M/S 300-323, Estados UnidosAlfred Wegener Institute, AlemaniaKorea Polar Research Institute, CoreaDepartamento de Geología y Geoquímica, Universidad Autónoma de Madrid, EspañaLamont-Doherty Earth Observatory, Columbia University, Estados Unido

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

Geophysical and geochemical survey of a large marine pockmark on the Malin Shelf, Ireland

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q01011, doi:10.1029/2011GC003787.Marine pockmarks are a specific type of seabed geological setting resembling craters or pits and are considered seabed surface expressions of fluid flow in the subsurface. A large composite pockmark on the Malin Shelf, off the northern coast of Ireland was surveyed and ground truthed to assess its activity and investigate fluid related processes in the subsurface. Geophysical (including acoustic and electromagnetic) data confirmed the subsurface presence of signatures typical of fluids within the sediment. Shallow seismic profiling revealed a large shallow gas pocket and typical gas related indicators such as acoustic blanking and enhanced reflectors present underneath and around the large pockmark. Sulphate profiles indicate that gas from the shallow reservoir has been migrating upwards, at least recently. However, there are no chimney structures observed in the sub-bottom data and the migration pathways are not apparent. Electromagnetic data show slightly elevated electrical conductivity on the edges of the pockmarks and a drop below regional levels within the confines of the pockmark, suggesting changes in physical properties of the sediment. Nuclear Magnetic Resonance (NMR) experiments were employed to characterize the organic component of sediments from selected depths. Very strong microbial signatures were evident in all NMR spectra but microbes outside the pockmark appear to be much more active than inside. These observations coincide with spikes in conductivity and the lateral gas bearing body suggesting that there is an increase in microbial activity and biomass when gas is present.We wish to thank the Geological Survey of Ireland, the INtegrated Mapping FOr the Sustainable Development of Ireland’s MArine Resource (INFOMAR) program, the Irish Environmental Protection Agency, Science Foundation of Ireland, QUESTOR (Queens University Belfast) and the Irish Council for Science, engineering and technology for funding this research. AJS thanks NSERC, (Strategic and Discovery Programs), the Canada Foundation for Innovation (CFI), and the Ministry of Research and Innovation (MRI) for providing Canadian funding. The survey data utilized in the research has been co‐funded by the Geological Survey of Ireland and the Offshore Irish Petroleum Infrastructure Programme (PIP; Ref. No: IS05/16 Malin Basin EM).2012-07-1

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