Search

We consider a randomised version of Kleene’s realizability interpretation of intuitionistic arithmetic in which computability is replaced with randomised computability with positive probability. In particular, we show that (i) the set of randomly realizable statements is closed under intuitionistic first-order logic, but (ii) different from the set of realizable statements, that (iii) “realizability with probability 1” is the same as realizability and (iv) that the axioms of bounded Heyting’s arithmetic are randomly realizable, but some instances of the full induction scheme fail to be randomly realizable.

Coarse carbonate sediments of cold-water coral (CWC) mounds are almost exclusively produced by scleractinian corals and associated calcifying organisms. Due to the sensitivity of several species to environmental changes, variations of benthic carbonate associations (BCA) through time can provide important insights on mound development stages. This study focuses on the BCA collected, through box- and gravity cores, from CWC mounds located in the Melilla Mound Field (MMF) and Pen Duick Escarpment (PDE). The main goal of this work is to characterize the composition of modern and fossil BCA and to relate its variation through time to oceanographic changes at regional and/or global scale. Our preliminary results are based on the analysis of samples collected during the MD 194 cruise and previous oceanographic expeditions (MD 169 and Belgica 09/14b). Observations on modern fauna from the PDE mounds have been carried out also on ROV videos collected during the Belgica 07/13 and 09/14b cruises. The modern BCA of the two examined mound areas are rather different. The PDE mound biocoenoses are characterized by scarce and low-diverse calcifying organisms that colonise dense (mostly fossil) dendrophylliid frameworks or rubble sparse in mud-dominated sediment. The modern MMF BCA are more diversified, dominated by Madrepora oculata and particularly rich in molluscs and bryozoans. Similarities found in the faunistic assemblages of the examined sediment cores hint at comparable environmental conditions in the past that favoured the development of Lophelia-dominated communities on both sides of the Gibraltar Strait

Management of geological resources is based, ideally, on information on the quality and quantity of surface and subsurface litho-stratigraphical properties. Increasingly, these data become available for the offshore domain, though the integration into manageable and user-friendly applications is still at its infancy. Building on expertise from on-land data mining, we are now in the phase of creating 3D voxel models allowing for multi criteria resource volume calculations. The underlying data are subdued to uncertainty modelling, a necessary step to produce data products with confidence limits. Anticipating on the dynamic nature of the marine environment, voxel models are coupled to environmental impact models that calculate resource depletion and regeneration under various scenarios, and using geological boundary conditions. In combination with foreseen impacts on fauna and flora, mining thresholds can be defined. Integration into a decision-support system allows for easy querying and online visualizations. Main aim is to provide long-term predictions on resource quantities to ensure future supplies for the benefit of society and next generations.

The monitoring of sand extraction on the Flemish sandbanks of the Belgian continental shelf is based on multiple types of data: statistics derived from the extraction registers, data from the Electronic Monitoring System (EMS = “black-boxes”) on board the dredging vessels (complete records are available since 2003), and regular bathymetric surveys with the multibeam echosounders MBES) EM1002 and EM3002D (installed on the R/V Belgica) across the sandbanks along parallel lines and on specific areas. The analysis of the various types of data provides a 4D (space and time) view of the evolution of the extraction and admits robust and pragmatic conclusions about the real impact of the sand extraction on the marine environment. From 2003 to 2012, the global bathymetric evolution, based on MBES EM1002 and EM3002D measurements along lines across the control zones, confirms thestraightforward relation between the extraction and the bathymetrical evolution. On a larger scale, virtually all ofthe bathymetric variation can be explained by the extraction itself. In areas without any extraction, no significanttrend of the bathymetry is observed.

Dedicated monitoring programmes are needed for the evaluation of the effects of the exploitation of non-living resources on the territorial sea and the continental shelf. Related to physical impacts, hydrodynamics and sediment transport, together with sedimentological and morphological evolution, need investigation. Overall aim is to increase process and system knowledge of both natural and exploited areas, with a particular focus on thecompliancy of extraction activities with respect to European Directives (e.g., European Marine Strategy Framework Directive and Habitat Directive). More specifically assessments are needed of changes in seafloor integrity and hydrographic conditions, two descriptors to define Good Environmental Status within Europe’sMarine Strategy Framework Directive.An important parameter is the bottom shear stress, with knowledge needed on both natural and anthropogenically induced variability. Bottom shear stress measurements are used for the validation of numerical models, necessary for impact quantification in the far field. Extensive data-model integration is critical for adequate assessments of the status of the marine environment, a prerequisite for sustainable use of living, and non-living resources.

Cold-water corals are widely distributed along the Moroccan margin in the Northeast Atlantic Ocean. Within the Gulf of Cadiz mud volcanoes, submarine ridges and steep fault escarpments occur, which favour the settlement of scleractinians and build up coral mounds. One of these sites is the Pen Duick Escarpment, situated in the El Arraiche mud volcano field, 35 km offshore the city of Larache. Pen Duick Escarpment is a 6 km long, SSE-NNW oriented, 80 to 125 m high wall with a southwest-facing slope of 8 to 12°. Up to now, 15 coral mounds were recognized on top of the escarpment with an average estimated elevation of 15 m. Although cold-water corals are a common feature on the adjacent cliffs, mud volcanoes and seafloor, no actual living coral has been observed.This study is based upon three on-mound gravity cores (Alpha, Beta and Gamma mound) acquired by R/V Marion Dufresne in 2008 (MD169). Each mound was cored at least twice to recover both a core for biogeochemical and microbial studies, and another core for sedimentological purposes, in order to link both processes. The sedimentological cores were analysed using different techniques (medical CT scanning, XRF, U/Th dating, stable isotopes, grain-size analysis) in order to obtain a holistic view on the build-up of a mound. The coring, together with present-day seabed observations, revealed the architectural importance of open coral rubble plates in the role of mound building. These graveyards act not only as sediment trap but also as microhabitat for a wide range of benthic organisms.

The ESF EuroDIVERSITY MiCROSYSTEMS project aimed to turn the cold-water coral (CWC) mounds on the Pen Duick Escarpment (PDE) in the Gulf of Cadiz into a natural laboratory, exploring this highly complex biotope and to characterize its biodiversity. A common point of discussion with all other CWC mound provinces, surpassing its broad range of regional and morphological variability, concerns the driving forces regarding the initiation of these complex deep-water systems. Both oceanographic and geological processes have been proposed to play a significant role in the mound nucleation, growth and decline. During IODP Expedition 307, the importance of biogeochemical processes was already elucidated. Here, we present the preliminary results of the MD169 campaign as an integrated case study of three PDE CWC mounds: Alpha, Beta and Gamma mounds.Although cold-water corals are a common feature on the adjacent cliffs, mud volcanoes and seafloor, no actual living reef has been observed during the many ROV surveys. This multidisciplinary study aims to present a comprehensive and holistic view on the local dynamic geological and oceanographic environment. Coring data suggests (past or present) methane seepage near the Pen Duick Escarpment. Several sources and pathways are proposed, among which a stratigraphic migration through uplifted Miocene series underneath PDE. Its dominant morphology has influenced the local hydrodynamics within the course of the Pliocene, as documented by the emplacement of a sediment drift. Predominantly during post-Middle Pleistocene glacial episodes, favourable conditions were present for mound growth. An additional advantage for CWC mound nucleation near the top of PDE is offered through seepage-related carbonate crusts which might offer elevated colonization positions. Present-day seabed observations also suggested a possible important role of open coral rubble frameworks in the mound building process. These graveyards not only act as sediment trap but also as micro-habitat for a wide range of organisms. The presence of a fluctuating Sulphate-Methane Transition Zone is responsible for diagenesis, affecting both geochemical as physical characteristics, transforming the buried reef into a solid mound. Nevertheless, these seepage fluxes seem to be locally variable. As such, the origin and evolution of the PDE CWC mounds is, probably more than any other NE Atlantic cold-water coral mound province, located on the crossroads of environmental (hydrodynamic) and geological (seepage) pathways.

During the R/V Marion Dufresne 169 ‘MiCROSYSTEMS’ cruise (July 2008) to the El Arraiche mud volcano field in the Gulf of Cadiz cold-water coral mounds were targeted. Four on-mound gravity cores, with a total length of 17.5 m, were obtained for sedimentological and palaeoceanographic analyses in order to unveil the history of the uppermost meters of these cold-water coral build-ups. In parallel, four on-mound cores were taken on approximately the same location for microbiological and biogeochemical analyses. By comparing and correlating both results, more information can be revealed about the processes acting in the dead coral rubble fields which cover these mounds.Computed X-ray tomography (CT) was used for the identification and quantification of the corals inside the gravity cores. Furthermore, this technique is also useful for the investigation of sedimentological features, i.e. bioturbation, porosity, laminations... In this study, cores were scanned using a medical CT scanner on a relative high resolution which allows the three-dimensional visualization of the corals and sedimentological features. Slices were taken every 3 mm with an overlap of 1 mm.Based on these data it was possible to delineate different “CT” facies within the cores. On one hand there are intervals with a high amount of corals and on the other hand zones with a very low amount of corals or even no corals at all. In the first case two different facies can be distinguished: one facies with clearly recognizable, well preserved corals, and the second facies with crushed coral fragments. In both facies the corals are embedded in a homogenous matrix. Different facies could also be defined in the intervals containing little or no corals. For example, a homogenous facies with bioturbations and/or cracks. Also an important observation is the resence of pyrite which appears in all cores at a certain depth. Sometimes the pyrite could be observed in bioturbations or inside the corals.Besides that also the percentage of corals in these gravity cores were quantified using the “Morpho+” software, which was developed at the UGCT (Centre for X-ray Tomography, Ghent University, Belgium). Based on these results, a clear difference can be noticed between the four mounds. On Conger cliff, corals were only observed in the upper 34 cm while in the other locations corals can be found throughout the entire core with significant variations in the amount of corals.Finally, it was possible to identify different species of cold-water corals, namely Lophelia pertusa, Madrepora oculata, Desmophyllum cristagalli and Dendrophyllia. In conjunction with dating and palaeoenvironmental analyses of the corals and the sediment matrix, this can yield valuable information about the build-up of these cold-water coral mounds in the El Arraiche mud volcano field and the palaeoenvironmental characteristics at the time the corals were living.

Within the framework of the EC projects FP6 IP HERMES and FP5 RTN EURODOM, as well as the ESF Euromargins project MoundForce, Ghent University organised a joint geophysical and biological research cruise to the La Chapelle continental slope with FUV Belgica from 13 to 20 June 2006. This area was targeted for its reported cold-water coral finds (Le Danois, 1948), rugged topography and hydrodynamics in a setting linking the shelf seas to the deep marine realm. The area was first surveyed using FUV Belgica's multibeam echosounder, imaging canyon heads and thalweg channels between prominent spurs where corals had been reported. High-resolution seismic sparker lines provided a geological context and linked into the existing seismic stratigraphy (Bourillet et al., 2003). Here, we present preliminary results of the La Chapelle area, including the geological and biological ROV GENESIS image analysis which revealed a hidden ecosystem of deep-water oyster banks down to 700 m.The ROV GENESIS dives were mainly concentrated along NW-SE ridges alongside the eastern slope of a newly mapped and yet unnamed spur. The hence called "Ostrea Spur" has a main NE SW orientation in water depths from 150 to 1100 m. The slopes of the spur are intersected by a 'herringbone' like pattern of WNW-ESE orientated gullies on the western slope and NNW-SSE orientated gullies on the eastern slope.The 2 successful dives along the "Ostrea" Spur revealed a sandy to muddy bioturbated seabed, curious bedforms and erosion exposing consolidated carbonate-like sedimentary sequences. These are often cut by vertical step-like escarpments or cliffs up to 10 m high. Ripple marks were also observed on the ROV images, indicating the presence of strong bottom currents, possibly originating from internal tides focused along the canyon axis (New, 1987; Pingree & Le Cann, 1989). At the base of the cliffs, fallen blocks provided settlement sites for sessile organisms whilst the cliffs and protruding banks revealed dense communities of giant oysters, forming a 3D assemblage with occasional cold-water corals (Lophelia pertusa). Though deep-water 'oyster banks' of Neopyncodonte cochlear had already been reported in the Bay of Biscay based on dredges, the larger and deeper Neopycnodonte observed during the ROV GENESIS dives likely belongs to a new species, which have remained hidden to the human eye up to now. Unfortunately the lack of living samples does not allow an exact, phylogenetic identification of the oysters involved in the formation of dense and rich 'hotspot' communities on the eastern slope of the "Ostrea" Spur.

Within the framework of the EC FP6 HERMES project, Ghent University organised a joint geophysical and biological research cruise to the Gollum and Whittard Canyon system with R/V Belgica from 23rd to 29th of June 2006. The aim was to study the local ecosystems and their drivers. In combining and integrating various scientific disciplines, it is aimed to get a complete picture on how biodiversity, biological processes and physical factors are linked to each other and how they can control the various ecosystems along the European Margin.During this campaign, special attention was given to the upper slope configuration of the Gollum channel heads, fitting in a framework of multibeam bathymetry ........(Beyer et al., 2003), seismic profiling and TOBI side-scan sonar data ....................(Wheeler et al., 2003) collected during previous campaigns. The main Gollum channel system is characterised by several deeply incised canyons with numerous slide scars on their flanks. Their pathways seem to be influenced by a structural control, creating a bayonet-shaped course. Upstream of this structural feature, the channel floor deposits are characterized by thick acoustically transparent units suggesting ponded turbidites or mass-wasting deposits. A long piston core, acquired with R/V Marion Dufresne in 2001 (MD01-2464), however, only yields a small number of fine-grained turbidites in a muddy hemipelagic host sediment. This suggests that this system has known a relatively low activity during Quaternary times. The high-resolution single-channel sparker geophysical survey on the Whittard canyon system was originally designed to better document its morphology and structure and to assist finding suitable places for biological sampling. During this survey, a set of enigmatic mound-like structures were found in water depths of 300 to 500m, very much alike the coral banks observed in the Porcupine basin, recently drilled by IODP expedition 307 ......................(IODP 307 Expedition Scientists, 2005; De Mol et al., 2002). They are closely associated to a downslope gully of the Whittard canyon and some levee (or even drift) deposits. The presence of coral banks in this canyon location would be a perfect example of the HERMES ecosystem hotspots. However, only few profiles were acquired and no detailed bathymetric data was available at the time of the campaign. Further investigations within the HERMES community will be conducted in order to verify this potentially interesting observation.