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International audience; U-series age patterns obtained on reef framework-forming cold-water corals collected over a nearly 6000-km-long continental margin sector, extending from off Mauritania (17 degrees N; northwest Africa) to the southwestern Barents Sea (70 degrees N; northeastern Europe), reveal strong climate influences on the geographical distribution and sustained development of these ecosystems. Over the past three glacial-interglacial cycles, framework-forming cold-water corals (Lophelia pertusa and Madrepora oculata) seem to have predominantly populated reefs, canyons, and patches in the temperate East Atlantic and the Mediterranean Sea. Above 50 degrees N corals colonize reefs in the northern East Atlantic primarily during warm climate periods with the biogeographic limit advancing from similar to 50 degrees N to similar to 70 degrees N. We propose that north-south oscillations of the biogeographic limit of reef developments are paced by ice ages and may occur synchronously with north-south displacement of cold nutrient-rich intermediate waters and surface productivity related to changes of the polar front.

Anaerobic oxidation of methane coupled to sulphate reduction (SR-AOM) prevents oceanic methane emissions and is considered as a major environmental process in the deep-sea sediments. To stimulate in vitro SR-AOM activity, we designed a (continuous) high-pressure bioreactor system. Fed-batch mode incubations showed that the elevated methane pressure stimulated SR-AOM activity: when the methane pressure increased from 1 to 4.5 to 8 MPa, the initial SR-AOM activity increased from 3.46 to 8.64 to 9.22 micromol sulphide production/g(dw)/day; the apparent affinity (K(m)) for methane was 37 mM. However, in each fed-batch mode incubation, there was an inhibitory effect observed after 2 days, probably due to the accumulation of sulphide and the increase of pH. When the reactor was operated in a continuous mode, the SR-AOM activity was constantly increasing within 18 days at both 1 and 8 MPa pressures.

Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold-water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore-water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment-water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate-rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds.

Reefs of the tube-building polychaete Lattice conchilega are known to represent hotspots of biodiversity, within inter- and subtidal soft sediments of the North Sea. However, because of their patchy distribution, point sampling does not appropriately map their subtidal spatial distribution. This study evaluated the feasibility to detect L. conchilega reefs by very-high resolution side-scan sonar imagery. A subtidal very-high resolution (410 kHz) side-scan survey, combined with grab sampling, revealed high densities of L. conchilega (up to 1979 ind. m(-2)) to coincide with a higher reflectivity, patchy and grainy acoustic facies. From the side-scan sonar imagery, individual reefs were estimated to reach a maximum size of 15 m(2). To ground truth the acoustic facies, the distribution of intertidal L. conchilega reefs was mapped at low tide and side-scan sonar imagery was recorded during the following high tide. Intertidal L. conchilega reefs had a patch size of 0.8 m(2) up to 11.6 m(2), elevated 7.5 to 11.5 cm above the surrounding seafloor and covered approximately 10% of the selected area. The very-high (445 kHz) resolution side-scan sonar imagery revealed a similar acoustic facies as in the subtidal. Lower-resolution (132 kHz) side-scan sonar imagery was less efficient to detect physically less developed L. conchilega reefs. We conclude that (1) there are no major technical restrictions to map L. conchilega reefs using side-scan sonar, (2) the developmental stage of L. conchilega reefs impacts the detectability of the reefs, and (3) very-high resolution side-scan sonar imagery is considered a necessity when mapping small-scale structures, such as L. conchilega reefs. (C) 2008 Elsevier Inc. All rights reserved.

A look at the sedimentary record in northern Ethiopia tells the story of oceans past—and maybe future.

The El Arraiche field is a new mud volcano field discovered near the Moroccan shelf edge in the Gulf of Cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m. The largest mud volcano in the field (Al Idrissi mud volcano) is 255 m high and 5.4 km wide. The cluster was discovered during a survey with the RV Belgica and studied further during Leg 2 of the TTR 12 survey onboard the R/V Prof Logachev. The 2002 surveys yielded detailed multibeam bathymetry over a 700 km2 study area, dense grids of high-resolution seismic data, deep-tow sub bottom profiles, sidescan sonar mosaics over the major structures. Selected video imagery lines, video guided grab samples, dredge samples, gravity cores, and box cores were collected for groundtruthing purposes. Eight mud volcanoes in water depths from 200 to 700 m cluster around two, sub-parallel anticlines and associated active extensional faults. Rock clasts and regional seismic data locate the El Arraiche field over a Late Miocene–Pliocene extensional basin. The onset of mud volcanic activity is estimated at about 2.4 Ma and probably roots in the Cretaceous–Miocene accretionary wedge. Stacked outflows are visible up to a depth of about 500 m below the sea floor. The occurrence of long-lived mud volcanoes bear witness to continued overpressure generation at depth, either by in situ oil and gas generation or by focussed flow and accumulation in the area. Geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes. The activity of the mud volcanoes is indicated by the thickness of hemi-pelagic sediments covering extruded mud breccia, the occurrence of seep-typical fauna, the degree of mixing between thermogenic and biogenic hydrocarbon processes, or the depth to the base of the sulphate reduction zone. Given its structural setting and the evidence of thermogenic and biogenic hydrocarbons, the area has promising hydrocarbon potential but remains untested.

The north-western corner of Lake Le Bourget is situated along an active fault zone and accommodated a large sediment supply from the Rhone River until the end of the Late Glacial period. On the delta slope, the Holocene sheet drape that covers the largest buried mass wasting deposit (the HDU) shows undulations, small fractures and discontinuities that are attributed to downslope creep. Evidence for episodes of vigorous fluid expulsion is found in association with these discontinuities. All these features are rooted at the top of the HDU and occur along two specific isobaths. These observations indicate a close link between fractures and focused fluid flow. We suggest that focused fluid flow triggered by earthquakes facilitates the formation of small-scale faults that accommodate part of the downslope movement and eventually link up to form a headscarp of a large slide (c .1 0 7 m 3 ).

The Boulonnais is a dome incised by a former marine gulf inset into a zone of tectonic inversion from the Middle Eocene, which was already partly excavated at least at the Upper Eocene. New sedimentological and paleopedological data obtained within the Boulonnais, completed with old seismic profiles, allow a better understanding of the inversion process which developed step by step. The initial breaching probably took place in the late Eocene. The Dover Strait was probably opened during the Lutetian, a part of the Oligocene and the late Neogene. Oligocene and Pliocene faunal assemblages are identical on both sides of the Strait. It was closed again for tectonic and eustatic reasons in the early Quaternary and reopen subsequently just before the Last Interglacial. The opening is related to the evolution of the Western Channel and of its paleovalley system. The inversion of the Variscan front accommodates most of the shortening induced by the Pyrenean Orogen on the western border of the European plate. The inversion of the Dover Strait region is almost synchronous with those of other basins of the Channel and North Sea areas. Tectonic, geomorphologic and climatic implications of this dynamic are discussed within the western European context.

An industrial 3D seismic data volume, supplemented by high-resolution 2D seismics, was used to study part of a province of buried mound structures in the Porcupine Basin, southwest of Ireland. These ‘Magellan’ mounds and their associated moat structures, interpreted as scour marks, were mapped semi-automatically from time-structure and isopach maps. Image analysis techniques such as a tophat transformation (mathematical morphology) were applied for feature extraction. Size measures of both mounds and moats were derived from the resulting maps and summarised by means of some descriptive statistics. Spatial variability in mound occurrence and characteristics was investigated. Comparison with other mound structures in the area allowed the Magellan mounds to be identified as ‘coral banks’, associated with the growth of cold-water deep-sea coral species such as Lophelia pertusa (L.) and Madrepora oculata (L.). Mound growth clearly started in a single ‘event’, confined in time and space. Bottom currents and oceanographic characteristics of the surrounding water masses influenced this sudden process and the further mound development. However, the analysis of the 3D seismic data set did not allow us to identify unambiguously the actual cause for the sudden mound start-up. The mounds appear to have formed a dense cluster of structures of moderate size, which are significantly elongated in a N–S direction. They are associated with even more elongated moats, implying a periodically reversing N–S-directed current influence. A spatial density of one mound per km2 was measured, which remains more or less constant over the area investigated. Mound width and cross-sectional area and moat shape gradually change across the mound province, due to spatially changing environmental conditions at the initial growth stages of the mounds and during their further development (interplay between current regime and sedimentation).

Tectonically active structures prone to cause devastating earthquakes and tsunamis, e.g. the Lisbon 1755 earthquake, were investigated during the UNESCO/IOC Training Through Research-10 (TTR-10) cruise on the southwest Portuguese Continental Margin using single channel seismic profiles, a 3.5-kHz hull-mounted sea-bottom profiler, 10-kHz OKEAN long range side-scan sonar, 30-kHz ORETECH deep-towed side-scan sonar, and a high-resolution deep-towed sea-bottom profiler. These data allowed the definition of new active faults and the establishment of morphological criteria for the classification of active faults in the study area. Landslides associated with the activity of a major tectonic structure, the Marques de Pombal Fault, and other areas with clear signs of mass wasting phenomena were mapped. A slope-to-basin sedimentary system comprising 21 sedimentary ridges up to 20 km long was mapped and described. It was found that the sediments are mainly transported into the deep basins by mass transport processes across the steepest fault scarps forming a channel–levee system, while gravitational slides/slumps dominate the shallower slopes. The sedimentary ridges with an elevation of 40–50 m (50–60 ms TWT) above the seafloor are imaged on the high-resolution seismic profiles as an alternation of high and low amplitude reflectors. It is shown that the Pereira de Sousa Fault, its plateau and the Principes de Avis Plateau are experiencing uplift according to sedimentary and morphological criteria.

The Porcupine Basin, southwest of Ireland, was one of the earliest sites from where the deep-water corals Lophelia sp. and Madrepora sp. were recovered. These deep-water corals have since been found all along the Atlantic margins of Europe, in water depths ranging from 50 to more than 2000 m. Recent geophysical studies have demonstrated the mound-building potential of deep-water corals. Available data indicate that three major provinces of coral bank occurrences can be identified in the Porcupine Basin: (1) high-relief surface mounds which have a dimension of 1 by 5 km and a height up to 200 m (‘Hovland’ mounds), flanked to the north by (2) a swarm of buried mounds, somewhat smaller (up to 90 m), and with more irregular shapes than those recognised in area 1 (‘Magellan’ mounds), and (3) outcropping or buried, conical mounds (single or in elongated clusters, up to 150 m high) occurring on the southeastern slope of the basin (‘Belgica’ mounds). As far as can be inferred from shallow cores, the surface lithology predominantly consists of an upper layer rich in foraminiferal sand and terrigenous silty clay with intercalations of biogenic rubble. The banks host a remarkable number of colonies of living and dead Lophelia pertusa and Madrepora oculata. The living and dead assemblages are underlain by a significant layer of coral debris in a muddy matrix. Deep-water coral debris together with a living association of the same species covers the surface of the ‘Belgica’ and ‘Hovland’ mounds, which may suggest that these corals have played a significant role in the development of the mound structures. The capacity for mound formation by scleractinian corals in the aphotic zone has been known for some time. Examples are found at different locations along the shelves and the continental margins of the North Atlantic. The role of the corals in these deep-water build-ups is still a point of debate. Though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps, it appears that the major development of the Porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply.

The combined analysis of high-resolution 2D seismics and an industrial 3D seismic data volume from the western Porcupine Basin, offshore SW Ireland, revealed an unusual picture of a buried sediment collapse and slope failure. A proportionally thin (??85?m) but vast (>?750?km2) slab of consolidated sediments started to slide downslope, in the meantime breaking into hundreds of vertically undisturbed blocks, up to 500?m in diameter. The most probably overpressured underlying horizon seems to have liquefied and acted as a slide plane until the excess pore pressure had dissipated. Then?–?still very early in the slide development?–?the process stopped, freezing the failure at its initial stage.

Very high-resolution seismic data have been obtained recently, in the framework of the research programme PNEC (French National Programme of Coastal Environment), on the shoreline area of Sete (Mediterranean coast, South East France). These data provide an accurate picture of the internal structure of the shoreline body. Seismic results combined with data about the morphosedimentary evolution of the study area, vibrocore data and results from archaeological investigations yield clues to the historical evolution of the study area. Especially, it is pointed out that the functioning of the present-day shoreline, by comparison with the system built in classical times, is characterized by a severe reduction in sediment supply and in volumes of sand involved in the shoreline dynamics.

A fine-scale seismic stratigraphic model has been developed for the Palaeogene of the southern North Sea on the basis of interpretation of a dense high-resolution reflection seismic grid, covering the Belgian sector of the continental shelf and the adjacent parts of the Dutch, French and UK sectors. Classical seismic stratigraphic criteria have allowed up to 13 major units to be defined; the geometry and seismic facies characteristics of each have been analysed in detail. The seismic stratigraphy has been compared with the results of four offshore boreholes. ‘Events and trends’ identified on seismic sections and in outcrops in northern Belgium have been correlated, and offshore seismic facies have been tentatively matched with onshore lithofacies. The geological history of the study area is discussed in terms of eustatic sea level changes and regional tectonic events, and the main characteristics of the offshore Palaeogene deposits are evaluated in a sequence stratigraphic context.

Publisher Summary The Pen Duick Escarpment is a 6 km long, NW-SE oriented, 80–125 m high escarpment with a southwest-facing slope of 8–12°. It is located within the El Arraiche mud volcano field on the Moroccan continental margin (southern Gulf of Cadiz) in water depths of 550–650 m. This chapter provides acase study about habitat mapping of cold-water coral mound, Beta Mound, using a multibeam echosounder, ROV observations, and boxcore sampling. This habitat mapping revealed the presence of four different habitats: soft (bioturbated) sediment, soft sediment with patchy coral rubble, dense cold-water coral rubble fields, and rock slabs. All cold-water corals are dead except for one living Dendrophyllia cornigera . The coral rubble consists mainly of dead Dendrophyllia , Lophelia pertusa , and Madrepora oculata . On top of the coral rubble, numerous crinoids were observed, while the soft sediment is mostly colonized by several species of soft corals. Sponges, squat lobsters, echinoids, and holothurians were also observed. Cold-water corals provide hard-bottom substrate, refuge, and nursery for a large variety of species and are therefore considered important biodiversity hotspots. On Beta Mound, several invertebrate and fish species are living in the three-dimensional framework formed by the dead cold-water coral rubble. The megafauna of the coral rubble patches or fields is dominated by crinoids (Echinodermata, Crinoidea), which cover most of the surface of the rubble. Poriferans and crustaceans such as squat lobsters (Decapoda, Galatheidae) are also commonly found on the coral rubble areas. The fish Helicolenus dactylopterus was found in all the four habitats.

Special Issue on COld-water CArbonate Reservoir systems in Deep Environments - COCARDEOver a decade of research on recent cold-water coral mounds in various oceans has set the stage for comparative studies between recent and ancient carbonate mound systems, with the aim to unravel generic processes and reveal the “red thread” in a fundamental strategy of Life building Geology — a strategy nearly as ancient as Life itself. Natural laboratories have been identified in the present ocean, which provide new insights in oceanographic controls on species migration and settlement, in the interaction of currents and carbonate build-up, in the earliest diagenesis which overprints environmental signals and shapes the template of compartmentalization of carbonate build-ups, and in so many other processes and factors ultimately shaping carbonate bodies, comparable in size and properties to the large-scale carbonate hydrocarbon reservoirs in the geological record. Ocean drilling and coring is an essential component of this research.Ideally, this process is a two- way avenue between Shallow and Deep Time, where fundamental and industrial knowledge about fossil carbonate mounds can drive further investigations and even experimentation in the present seas, while the discoveries and process studies on “live” systems can yield new insights in the architecture and evolution of ancient reservoir systems. This bridging exercise is the quintessence of COCARDE (Cold- Water Carbonate Reservoir Systems in Deep Environments), an international network under the auspices of IOC-UNESCO (http://www.cocarde.eu). COCARDE has organised two workshops in 2009, with a significant support of European programmes (e.g. ESF Magellan workshop series) and partner projects (e.g. ESF EuroDIVERSITY project MiCROSYSTEMS). This special issue groups 12 papers, all addressing observations which by their nature have the potential to provide keys to generic processes, of relevance for past carbonate systems. As COCARDE proceeds, it is the objective to “reciprocate” in near future with an equivalent grouping of contributions from the study of fossil studies, to guide further research in the present ocean. It is the purpose of COCARDE to strengthen such a reflux from the studies of fossil systems by stimulating relevant continental drilling exercises, with comparable sampling protocols, resolution and analytical procedures – where relevant – to allow direct comparisons with records from ocean drilling.The papers in this special issue have been structured in four themes: (i) keys to palaeoenvironmental control, (ii) mound initiation, growth and demise, (iii) of microbes and mounds, and (iv) tracking organominerals — Recent and Ancient.

International audience; In the nineties, cold-water coral mounds were discovered in the Porcupine Seabight (NE Atlantic. west of Ireland). A decade later, this discovery led to the drilling of the entire Challenger cold-water coral mound (Eastern slope, Porcupine Seabight) during IODP Expedition 307. As more than 50% of the sediment within Challenger Mound consists of terrigenous material, the terrigenous component is equally important for the build-up of the mound as the framework-building corals. Moreover, the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development. In this study, the first in-depth investigation of the terrigenous sediment fraction of a cold-water coral mound is performed, combining clay mineralogy, sedimentology, petrography and Sr-Nd-isotopic analysis on a gravity core (MD01-2451G) collected at the top of Challenger Mound. Sr- and Nd-isotopic fingerprinting identifies Ireland as the main contributor of terrigenous material in Challenger Mound. Besides this, a variable input of volcanic material from the northern volcanic provinces (Iceland and/or the NW British Isles) is recognized in most of the samples. This volcanic material was most likely transported to Challenger Mound during cold climatic stages. In three samples, the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on Greenland, Scandinavia or Canada. The grain-size distributions of glacial sediments demonstrate that ice-rafted debris was deposited with little or no sorting, indicating a slow bottom-current regime. In contrast, interglacial intervals contain strongly current-sorted sediments, including reworked glacio-marine grains. The micro textures of the quartz-sand grains confirm the presence of grains transported by icebergs in interglacial intervals. These observations highlight the role of ice-rafting as an important transport mechanism of terrigenous material towards the mound during the Late Quaternary. Furthermore, elevated smectite content in the siliciclastic, glaciomarine sediment intervals is linked to the deglaciation history of the British-Irish Ice Sheet (BIIS). The increase of smectite is attributed to the initial stage of chemical weathering processes, which became activated following glacial retreat and the onset of warmer climatic conditions. During these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed. Therefore, we postulate that the deglaciation of the BUS has an important effect on mound growth. It can seriously alter the hydrography, nutrient supply and sedimentation processes, thereby affecting both sediment input and coral growth and hence, coral mound development. (C) 2011 Elsevier B.V. All rights reserved.

We report the northernmost and deepest known occurrence of deep-water pycnodontine oysters based on two surveys along the French Atlantic continental margin to the La Chapelle continental slope (2006) and the Guilvinec Canyon (2008) The combined use of multibeam bathymetry seismic profiling CTD casts and a remotely operated vehicle (ROV) made it possible to describe the physical habitat and to assess the oceanographic control for the recently described species Neopycnodonte zibrowii These oysters have been observed in vivo in depths from 540 to 846 m colonizing overhanging banks or escarpments protruding from steep canyon flanks Especially in the Bay of Biscay such physical habitats may only be observed within canyons where they are created by both long-term turbiditic and contouritic processes Frequent observations of sand ripples on the seabed indicate the presence of a steady but enhanced bottom current of about 40 cm/s The occurrence of oysters also coincides with the Interface between the Eastern North Atlantic Water and the Mediterranean Outflow Water A combination of this water mass mixing internal tide generation and a strong primary surface productivity may generate an enhanced nutrient flux which is funnelled through the canyon When the ideal environmental conditions are met up to 100 individuals per m(2) may be observed These deep-water oysters require a vertical habitat which is often incompatible with the requirements of other sessile organisms and are only sparsely distributed along the continental margins The discovery of these giant oyster banks illustrates the rich biodiversity of deep-sea canyons and their underestimation as true ecosystem hotspots (C) 2010 Elsevier Ltd All rights reserved

During the ‘New Vents’ SO191 cruise in 2007, the activity and distribution of seep sites on the gas-hydrate-bearing Hikurangi Margin, off northeastern New Zealand, were subjected to a highly detailed interdisciplinary study. Here we report on the visual observations and in situ measurements of physical properties performed with a ROV (remotely operated vehicle) and other video-guided platforms at two seep sites in the Rock Garden area; Faure Site and LM-3. The ROV allowed first ever visual observations of bubble-releasing methane seeps at the Hikurangi Margin. At Faure Site, bubble release was monitored during 4 dives, up to periods of 20 min. During the first dive, this resulted in the observation of six violent outbursts, each lasting 1 min over a three minute interval. These outbursts were accompanied by the displacement and resuspension of sediment grains, and the formation of small depressions, with a maximum diameter of 50 cm and depth of 15 cm, showing what is possibly an initial stage of pockmark formation. During subsequent dives at this bubble site, bubble release rates were rather constant and the previously observed outbursts could no longer be witnessed. At LM-3, the strongest manifestation of seep activity was a large platform (100 m2), consisting of fresh authigenic carbonates, which was covered by seep fauna (live Bathymodiolus sp. mussels, Calyptogena sp. shells and live Lamellibrachia sp. tubeworms). Bubble activity near this platform was less prominent than at Faure Site. Our observations suggest that the two seep environments result from different types of methane release; mainly by bubble release at Faure Site and rather diffusive at LM-3. We propose a conceptual model where the different ways of methane release and seep environments may be explained by the depth of underlying hydrate occurrences and different tectonic histories of both seep sites.

The use of magnetism in the study of marine sediments started over a century ago. In their “Report on the Scientific Results of the voyage of the Challenger: Reports on Deep-Sea Deposits" (1891), John Murray and Alphonse-Francois Renard described already in detail the presence of magnetic particles in deep-sea sediments. Opdyke (1972) found that sediments of various lithologies cored from most parts of the deep ocean floor contain a record of the past behaviour of the earth’s magnetic field, especially the sequence of reversals over at least the past 5 million years. Kent (1973) indicated that detrital remanent magnetization and post-depositional remanent magnetization are viable mechanisms of magnetization of deep-sea sediments. Detrital magnetic particles can align themselves in the direction of an applied earth magnetic field while falling through the water column, leading to a “detrital remanent magnetization".

Over the past three decades, major technical and scientific advances have been made towards real-time physical and chemical characterization of deep-sea sediments (Ortiz and Rack 1999). To infer palaeoceanographic and palaeoclimatological information from physical and chemical characteristics of sediments, it is necessary to obtain the most continuous and accurate measurements possible (Rohl and Abrams 2000). Various types of core-logging systems have been developed during the last years and are able to measure continuous physical and chemical data sets down to millimetre-scale. Such a high resolution can never be obtained by standard analytical methods for discrete samples which are in addition time-consuming and expensive. Moreover, logging methods are non-destructive. Ortiz and Rack (1999) give an overview, summarize the historical details and point out the growing advantages of different geochemical and geophysical logging tools which were available at the end of the twentieth century.

The genesis and evolution of cold-water coral banks along the Northeastern Atlantic margin is known to be influenced by several factors, among which the palaeotopography and nature of the coral settling surface, the presence of bottom currents and sediment supply. In this paper, a case study is presented of the Enya mound cluster, located in the southernmost tip of the Belgica mound province, west of Ireland. Below this mound cluster, seismic stratigraphy revealed a yet unmapped local unconformity RD1b, being part of a composite erosion event (RD1). As such, from the Late Miocene to Late Pliocene, at least two erosional events have incised the margin, ending with the final RD1a "moundbase" unconformity, acting as a base for the Enya mounds. During the Quaternary the mounds became outgrown and were covered by a mounded contourite drift. In addition, they are closely associated with a cluster of seabed pockmarks. The bottom current regime which became active since the Middle Pleistocene has certainly influenced the fate of this mound cluster. The occurrence of the pockmarks seems to be related to relatively recent fluid migration processes, however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks.

The presence of giant carbonate mounds along the NE Atlantic continental margin is already known since 1994 (Hovland et al. 1994; Henriet et al. 1998; De Mol et al. 2002; Kenyon et al. 2003; van Weering et al. 2003). These mound structures have been the target of several cruises during the last decade, resulting in extensive data sets placing the carbonate mounds in their environmental and geological context. However, none of these cruises unveiled the internal structure of a carbonate mound and only the upper few metres could be sampled by gravity coring.

During the last 15 years, occurrences of large mound clusters have increasingly been reported along the northeastern Atlantic margins. These mound structures are in many cases covered with cold-water corals, suggesting an enigmatic relationship between cold-water coral growth and the development of such mounds. The growth of cold-water corals and the origin of recent deep-water carbonate mounds was a heavily debated subject during the last decade. Different theories were invoked concerning cold-water coral growth and the development of carbonate mounds. Two main schools developed to explain the origin of recent cold-water coral reefs and carbonate mounds. One school is mainly based on internal controls whereby light hydrocarbon seepage would play an important role in the initial phase of reef and mound growth (Hovland 1990, 1994, 1998; Hovland and Thomsen 1997; Henriet et al. 1998, 2001). The second school relies on the impact of external and environmental controls, such as favourable oceanographic conditions, on cold-water coral growth and so mound build-up (Freiwald et al. 1997, 1999; Freiwald and Wilson 1998; Mortensen 2000; De Mol et al. 2002; Duineveld et al. 2004).

Before the R/V JOIDES Resolution ever entered the Porcupine Seabight to drill Challenger Mound, the top of different mounds and their surrounding environments were already subjected to many detailed studies to unveil the top of their secrets. A systematic sampling of the top of different on-mound and off-mound records was carried out with the Calypso piston corer and the gravity corer aboard the R/V Marion Dufresne during the MD123-Geosciences campaign in September 2001. Within the EC FP5 programmes GEOMOUND and ECOMOUND these cores have been extensively studied.

An exploratory cruise of R/V Belgica in 2002 off Larache (Morocco) has led to the discovery of small mounds topping ridges and structural heights (respectively on Pen Duick Escarpment, Renard Ridge, Vernadsky Ridge and Al Idrisi Ridge). These mounds are found amidst 9 giant mud volcanoes: the El Arraiche mud volcano field (Van Rensbergen et al. 2005a). They occur in a setting where focused fluid seepage is observed (Baraza and Ercilla 1996; Pinheiro et al. 2003; Somoza et al. 2003; Van Rooij et al. 2005). Because of its unique setting, the carbonate mound site on the Moroccan margin became rapidly involved in a developing stage of focused multidisciplinary research. In May 2004, a 9m-long Kasten core was recovered with R/V Marion Dufresne on top of one of the largest build-ups – 60 m high. It contained cold-water corals over its whole length, a striking similarity with the Porcupine mound cores (Foubert et al. 2007) but a very strong smell of hydrogen sulphide was reported on deck. The core featured a well-delineated zone of heavily dissolved cold-water corals and a zone of diagenetic carbonate precipitation. Pore water analyses gave evidence of a sharp sulphate-methane transition (SMT) zone at 3.5 m below the mound top. Cruises in summer 2004 and 2005 have confirmed these observations, and have expanded the exploration of this cluster of mounds.

This paper presents a new cluster of carbonate mounds discovered in 2002 in the Gulf of Cadiz off Morocco (R/V Belgica 2002) in water depths of 500 to 600 m amidst a field of giant mud volcanoes. Multibeam bathymetry, side scan sonar imagery and 2D seismics are analyzed to present four mound provinces: (1) the Pen Duick Mound Province on the Pen Duick Escarpment, (2) the Renard Mound Province on the Renard Ridge, (3) the Vernadsky Mound Province on the Vernadsky Ridge and the Al Idrisi Mound Province on the gas-blanked sediments above the buried Al Idrisi Ridge. Video imagery and surface samples are described to ground-truth the different mound areas. The paradox is that nearly no live corals are presently being observed at the surface of the mounds, while the mound cores display throughout a high number of reef-forming cold-water coral fragments (scleractinians) in association with numerous associated fauna formerly inhabiting the econiches provided by the coral framework. Environmental and oceanographic conditions during the recent past (glacials/stadials) were probably more favourable for cold-water coral growth. Pore water analyses in on-mound cores at the south-eastern edge of Pen Duick Escarpment give evidence of focused, higher methane fluxes and sulphate reduction rates on mounds than in the surrounding sediments. Cores from several mounds display horizons of strong corrosion and dissolution of the coral fragments. A three-phase model for carbonate mound evolution in these settings is proposed. (1) In a first stage external controls (positive oceanographic and environmental conditions, the presence of an active planktonic food chain, based on a high primary production, and a suitable substrate) are responsible for the initiation of cold-water coral growth. (2) Once the cold-water corals established an initial framework, sedimentation becomes an important factor controlling mound growth: the cold-water corals baffle the sediments. (3) Throughout mound growth, the mound may episodically be affected by diagenetic processes responsible for aragonite dissolution and probably carbonate precipitation.

Airborne imaging spectroscopy data (AISA Eagle and HyMap) were applied to classify the sediments of a sandy beach in seven sand type classes. On the AISA-Eagle data, several classification strategies were tried out and compared with each other. The best classification results were obtained applying a linear discriminant classifier (LDC) in combination with feature selection based on sequential floating forward search (SFFS). The statistical LDC was used in a multiple binary approach. In the first step, the original bands were used in the classification, but transformation of the bands to wavelet coefficients enhanced the accuracy obtained. The combination of LDC with SFFS resulted in an overall accuracy of 82% (using three wavelet coefficients). Replacing the LDC with the non-statistical SAM algorithm reduced the overall accuracy to 74% (using all bands or wavelet coefficients). When applying LDC, the optimal number of bands/wavelet coefficients to be used was defined: using more than two bands or three wavelet coefficients did not result in a higher classification accuracy. Finally, the HyMap data, featuring 126 bands in the VNIR-SWIR range, were used to demonstrate that the VNIR range outperforms the SWIR range for this application.

International audience; Studies on the distribution of scleractinian corals in the Bay of Biscay were relatively numerous during the nineteenth and the first half of the twentieth century. Yet, recent reports are scattered, sometimes unpublished, and therefore knowledge about the current coral occurrence in the area is limited. This study aims at compiling the available historical and more recently collected information on the occurrence of scleractinian corals in the Bay of Biscay. Data from two recent cruises are included and compared with previous explored coral sites from as early as 1830 up to 1995. A database of 347 records including 34 described species of scleractinians highlights that the slope of the Bay of Biscay is an important habitat for scleractinians. This could be expected due to the high topographic relief providing the necessary hard substrate and accelerated bottom current flow that corals require. Further exploration of the occurrence and ecology of corals in the area is recommended to support the conservation of cold-water coral reefs along the European margin.

High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime.

Three provinces, characterized by the presence of carbonate mounds interpreted as cold-water coral banks have been reported in Porcupine Seabight, SW of Ireland and were recently subjected to many detailed studies. This contribution discusses the use of X-ray imagery and physical properties in deciphering palaeoceanographic, sedimentological and biological processes. Physical property core logging and X-ray imagery are used to identify and describe sedimentation regimes and so their respective palaeoceanographic and palaeoclimatological settings in two mound provinces, respectively the Belgica mound province and the Magellan mound province. Both provinces show at present time clear differences in the hydrodynamic environment. This study confirms that also during the past the oceanographic and sedimentological environment of both provinces differ clearly. Impacts of glacial–interglacial variations and locally derived ice rafting events (IRE), comparable with the North Atlantic Heinrich events (HE) have been recognized in both provinces. Moreover, the combination of X-ray imagery, magnetic susceptibility, gamma density and P-wave velocity makes it possible to estimate the coral content and coral distribution in unopened cores localized on top of carbonate mounds. A comparison between on-mound and off-mound cores in both provinces allowed revealing some mechanisms of mound evolution and coral growth versus time.

The Magellan mound province is one of the three known provinces of carbonate mounds or cold-water coral banks in the Porcupine Seabight, west of Ireland. It has been studied in detail using a large and varied data set: 2D and 3D seismic data, sidescan sonar imagery and video data collected during ROV deployment have been used to describe the mounds in terms of origin, growth processes and burial. The aim of this paper is to present the Magellan mounds and their setting in an integrated, holistic way. More than 1,000 densely spaced and mainly buried mounds have been identified in the area. They all seem to be rooted on one seismic reflection, suggesting a sudden mound start-up. Their size and spatial distribution characteristics are presented, together with the present-day appearance of the few mounds that reach the seabed. The underlying geology has been studied by means of fault analysis and numerical basin modelling in an attempt to identify possible hydrocarbon migration pathways below or in the surroundings of the Magellan mounds. Although conclusive evidence concerning the processes of mound initiation proves to be elusive, the results of both fault analysis and 2D numerical modelling failed to identify, with confidence, any direct pathways for focused hydrocarbon flow to the Magellan province. Diffuse seepage however may have taken place, as drainage area modelling suggests a possible link between mound position and structural features in the Hovland-Magellan area. During mound development and growth, the interplay of currents and sedimentation seems to have been the most important control. Mounds which could not keep pace with the sedimentation rates were buried, and on the few mounds which maintained growth, only a few corals survive at present.

Numerous studies on sediment drifts have demonstrated a close interaction between sea-bed morphology, palaeoceanography, sediment supply and climate. Contourites have been reported in areas along continental margins directly influenced by the effect of intensive deepwater currents from the global conveyor belt. In this paper, we report the occurrence of a small-scale confined contourite drift from Porcupine Seabight, SW of Ireland, and its association with a province of coral banks. The Porcupine Basin is a relatively shallow, semi-enclosed basin characterized by the presence of cold-water coral bank provinces. These coral banks are often associated to a strong northward-flowing bottom current, created and steered by a complex interaction of the water mass characteristics, tidal influences and sea-bed morphology. Very highresolution seismic stratigraphy allowed the identification of a small mounded drift, located between a depression created by (1) an irregular palaeotopography caused by a vigorous Late Pliocene erosion event and (2) a north–south alignment of coral banks. Core MD99-2327, taken on the flank of this drift mound, shows the variability of the bottom currents. Sortable silt data show several periods of bottom-current enhancement, which may be linked with warmer periods and an inferred influx of Mediterranean Outflow Water. The glacial part of the core has been interpreted as a muddy contourite with a high content of ice-rafted debris. The lower part of the core is a deep-water massive contourite sand resembling the present-day sea-floor sediments. The Porcupine Seabight (PSB) is a shallow to deep-water, amphitheatre-shaped basin SW of Ireland, forming a small bight along the North Atlantic margin (Fig. 1). It is the surface expression of the underlying deep sedimentary Porcupine Basin, which is a failed rift of the proto-North Atlantic Ocean, filled with a 10 km thick series of Mesozoic and Cenozoic sediments (Moore & Shannon 1991). The PSB has gained interest because of the presence of special deep-water habitats (Henriet et al. 1998; De Mol et al. 2002; Huvenne et al. 2003), consisting of a province of coral banks, discovered on the eastern slope and described as the Belgica mound province (BMP). Earlier studies (De Mol et al. 2002; Huvenne et al. 2002; Van Rooij et al. 2003) suggested that the geometry of the most recent deposits in this province seemed to be under the influence of bottom currents of variable intensity. This paper will illustrate the importance of such a relatively small basin as the Porcupine Seabight for the study of bottom-current deposits. Until now, only the large sediment drift systems in the Northern Atlantic Ocean have been extensively studied. High-resolution seismic surveys have allowed description of the details of smaller depositional systems, which were ignored or not observed in earlier studies. In this way, smaller-scale varieties of current-driven deposits were recognized, adding to the complexity of the contourite paradigm (Faugeres et al. 1999; Rebesco & Stow 2001). Moreover, the local hydrodynamic environment of these deposits may be very complex. Because they mostly are located out of reach of the typical thermohaline deep-sea bottom-current circulation, the driving current process needs to be better understood. Here, we present and discuss high-resolution seismic and core data. More specifically, this paper highlights the special present and past hydrodynamic environments of the BMP. The role of palaeoceanographic turnovers is discussed in view of the creation of a specific hydrodynamic, morphological and sedimentary environment, ready to host the development of a contourite drift. In addition, the presence of the deep-water coral bank and its interaction with the sedimentary environment is discussed as a controlling key factor. Ultimately, a link between the sedimentary record and past climate changes is proposed. From: VIANA, A. R. & REBESCO, M. (eds) Economic and Palaeoceanographic Significance of Contourite Deposits. Geological Society, London, Special Publications, 276, 225–244. 0305-8719/07/$15.00 # The Geological Society of London 2007. Material and methods Very high-resolution seismic profiles From 1997 to 2003, about 1500 km of singlechannel seismic reflection data were collected over the eastern flank of the PSB. These data were acquired with an SIG surface sparker source and recorded with a single-channel surface streamer (vertical resolution between 0.4 and 1 m). These data were recorded digitally using the ELICS Delph 2 system. The basic data processing involved a first, broad-window Butterworth bandpass filter (200 Hz with a 24 dB per octave slope and 2000 Hz with a 36 dB per octave slope), minimum phase predictive deconvolution (with a 20 ms window), followed by a second Butterworth bandpass filter (250 Hz with a 24 dB per octave slope and 700 Hz with a 36 dB per octave slope). Additionally, a true amplitude recovery or an automatic gain control was applied. The obtained network of profiles is organized in a general N608 orientation, running perpendicular to the slope. The distance between adjacent profiles was about 3 km. Only a limited number of long, along-slope (N1558) profiles have been acquired.

This paper addresses the possibilities of the combined use of airborne hyperspectral data and airborne laserscanning data to study sand dynamics on the Belgian backshore and foreshore. In August 2000, August 2001, and October 2002, airborne hyperspectral imagery was acquired with a CASI-2 sensor from the entire Belgian beach at low tide. Hyperspectral images contain a reflectance spectrum for each pixel. The characteristics of this spectrum are influenced by the state, the composition, and the structure of the topsoil of the beach. After radiometric, geometric, and atmospheric correction of the images, a normalization of the spectral signatures was necessary to allow comparison of wet and dry pixels. Consequently, the first derivative of the normalized spectra was taken, followed by a spectral angle mapper algorithm that was used to perform a supervised classification. The beach was classified into eight sand classes. Almost simultaneous with the first two CASI campaigns (in September 2000 and September 2001), a laserscan survey was performed to generate digital terrain models with a mean vertical accuracy of 5 cm. By differencing both digital terrain models, a map with sedimentation and erosion zones could be extracted. The combined interpretation of the erosion/sedimentation map with the classified hyperspectral data yields an appropriate method for studying the processes of sand transport along the Belgian coastline. The method was tried out with success on the Belgian east coast.

The discovery of mounds and reefs hosting cold-water coral ecosystems along the northeastern Atlantic continental margins has propelled a vigorous effort over the past decade to study the distribution of the mounds, surface sediments, the ecosystems they host, and their environments [Hovland et al., 1994; Freiwald and Roberts, 2005].This effort has involved swath bathymetry, remotely operated vehicle deployments, shallow coring, and seismic surveys. Global coverage is difficult to gauge, but studies indicate that cold-water corals may cover as large an area as the better known warm-water corals that form shallow reefs (284,300 square kilometers) [Freiwald et al., 2005]. Cold-water corals occur in a variety of forms and settings, from small isolated colonies or patch reefs to giant mound structures such as those found west of Ireland.

Lophelia pertusa is a deep-sea scleractinian coral (azooxanthellate) found on the continental margins of the major world oceans. Built of aragonite it can be precisely dated and measured for stable isotope composition (C–O) to reconstruct past oceanic conditions. However, the relation between stable isotope and skeleton microstructures, i.e. centres of calcification and surrounding fibres, is crucial for understanding the isotopic patterns. Values for δ18O and δ13C in Lophelia pertusa were determined at a micrometer scale using an ion microprobe (SIMS - Secondary Ion Mass Spectrometry). In this coral species, centres of calcification are large (50 µm) and arranged in lines. The centres of calcification have a restricted range of variation in δ18O (−2.8 ± 0.3 ‰ (V-PDB)), and a larger range in δ13C (14.3 to 10.9 ‰ (V-PDB)). Surrounding skeletal fibres exhibit large isotopic variation both for C and O (up to 12 ‰) and δ13C and δ18O are positively correlated. The C and O isotopic composition of the centres of calcification deviate from this linear trend at the lightest δ18O values of the surrounding fibres. The fine-scaled variation of δ18O is probably the result of two processes: (1) isotopic equilibrium calcification with at least 1 pH unit variation in the calcification fluid and (2) kinetic fractionation. The apparent δ13C disequilibrium in Lophelia pertusa may be the result of mixing between depleted δ13C metabolic CO2 (respiration) and DIC coming directly from seawater. This study underlines the close relationship between microstructure and stable isotopes in corals. This relationship must also be taken into consideration for major elements like Mg and trace elements (U-Sr-Ba) increasing the reliability of the geochemical tools used in paleoceanography.

This paper presents an overview of the spatial distribution and morphology of coral banks in the Porcupine Seabight in relation to their environmental settings. The study area is characterised by well-delimited clusters of coral banks, each featuring typical bank morphology and environmental setting. In the central part of the basin, two mound provinces can be identified: a set of complex fl at topped seafloor mounds in the Hovland Mound province is flanked to the north by a crescent of numerous north-south elongated buried coral banks in the Magellan Mound province, along the eastern margin of the basin partly buried and seabed coral banks represent the Belgica Mound province. The banks are mound-shaped elevations, many of them hosting living deep-water corals (Lophelia pertusa, Madrepora oculata, Desmophyllum cristagalli, Dendrophyllia sp.) and associated fauna. This active biological layer covers a dead assemblage of corals clogged with mud. All coral banks, buried or seabed, occur in association with current-induced features (e.g., scouring features, dunes) and steep palaeo- and present-seabed slopes. Only a few banks have a present-day seabed expression, which suggests that environmental conditions have been more favourable for bank development in the past. The depth range of the seabed coral banks coincides with the Mediterranean Outflow Water which may control indirectly the coral distribution. The distribution of corals in the southern part of the North Atlantic and the actual link with Mediterranean water suggest a possible migration of corals within the Mediterranean water along the NE Atlantic margin. The start-up phase of the coral bank development in the basin has taken place simultaneously for all provinces, and tentatively framed in times subsequent to a Late Pliocene period of erosion and non-deposition. It is considered that the sedimentary load of the currents plays an important role in the bank development. Coral banks accrete by the active baffling of sediment by the biological framework and growth of the biological cap. When sedimentation and biological growth get out of balance, the framework will progressively be clogged with sediment. Once sediment dominates the structure the coral banks get buried and draped by sediment.

The Belgica Mound province is one of three provinces where carbonate mounds are associated with cold-water coral species in Porcupine Seabight, west of Ireland. Building upon extensive existing datasets, the Polarstern ARK XIX/3a cruise, deploying the robotic submersible VICTOR6000 (ROV), was undertaken in June 2003. This paper presents an overview of preliminary results from a reconnaissance video survey over and between several steep-flanked Belgica Mounds (giant mounds) and from a microbathymetric survey over some smaller mounds (Moira Mounds). Visual evidence for a strong hydrodynamic regime in the vicinity of the carbonate mounds is found with the interaction between currents and sedimentation having an important role in mound growth and development. Only some mounds show a high percentage of live coral coverage although there is a clear increase of megafaunal concentrations and species on mounds. One area of the province (the eastern ridge of aligned mounds) revealed very little live coral cover, asymmetrical drift accumulations burying the eastern sides and sediment-clogged dead coral frameworks at the western sides. This is in contrast to other areas (e.g., the western alignment of mounds) that show abundant live coral cover at present. In nearly all parts of the survey area the impact of fisheries, especially demersal trawling, is noted.

The El Arraiche mud volcano field was discovered in May 2002 in the Moroccan Atlantic margin in the Gulf of Cadiz. It consists of 8 mud volcanoes of varying size and shape just below the shelf edge (figure 2). The largest mud volcano in the field (Al Idrissi mud volcano) is 255 m high and 5.4 km wide, the smallest we observed is only 500 m wide and 25 m high. The morphology of the mud volcanoes consist of, from base to top: a moat around part of the base of the mud volcano cone, an irregular slope characterized by radial outward sediment flows, terraces and/or depositional sediment flow escarpments (lobe fronts), a crater depression or a flat top, and a central dome.The 2002 surveys by the RV Belgica and the RV Logachev yielded detailed swath bathymetry over the entire area, dense grids of high-resolution seismic data, very high-resolution deep-tow sub bottom profiles, side scan sonar mosaics over the major structures, selected video lines, TV-grabs, dredge samples and gravity cores.The large amount of sea floor data and the clear shape of the larger mud volcanoes prompted us to focus on the morphology of the mud volcano cones. Although mud volcanoes are prominent features in the submarine sea-scape little attention has yet been given to their small-scale morphology. Mud volcanoes in their broadest sense refer to any extrusion of mobilized sediment. Mud volcanoes sensu strictu are cone-shaped with central vents. They are often considered as a sedimentary analog of stratovolcanoes, built by stacked sediment flows issued from a central crater or subsidiary vents at the flanks. The morphology of mud volcanoes sensu stricto is thus largely attributed to extrusion processes whereas the effect of intrusive processes remains unclear. Highresolution seismic profiles provide little information about the internal structure of a large mud cone, due to acoustic blanking. We can in this case only deduce formation processes from the information available at the surface.On basis of the observations we conclude that these large cone-shaped mud volcanoes result from a combination of intrusive and extrusive processes. Sediment flow deposits on the slopes range between two end-members. Flows with low yield strength (type I) extend to the base of the slope and create a steepening convex slope profile with a low overall slope angle (5° - 6°). Flows with a high yield strength (type II) freeze on the steep slope and create an irregular slope profile with almost constant slope angle (8° - 10°). Within the crater, several vents issue fluidised sand and small debris flows that consist of mud breccia with cm to m-sized clasts in a mud matrix. The extrusive sediment flows shape the surface of the mud volcano but in this study we also observemorphological elements that do not appear to correspond solely to extruded sediment deposits and may be partly result from sediment intrusion processes. The central dome and the concentric pattern of continuous terraces and steps on the slope are interpreted to result from different phases of uplift by sediment intrusion, each possibly followed by collapse due to degassing or dewatering. Intrusive processes may involve shallowseated diapirism caused by density re-equilibration within the thick pile of remoulded mud volcano sediments or uplift and volumetric expansion by injection of sedimentary dykes.

We present combined 230Th/U and 14C dating on deep-water corals from the northeastern North Atlantic in order to investigate coral growth and sedimentation on carbonate mounds, as well as past changes of intermediate water ventilation. Within European projects GEOMOUND and ECOMOUND reef forming Lophelia pertusa deep-water corals were raised from intermediate depth (∼610 to 888 m bsl) from top of carbonate mounds at southeast Rockall Bank and at Porcupine Seabight. XRD analyses, δ234U, and 230Th/232Th indicate negligible alteration of the investigated corals, i.e. open system U-series behavior. 230Th/U ages from coral specimens of the uppermost coral sequence of the investigated mounds range from today to 10,950 CAL yr BP, i.e. coral growth during the Holocene. A modern Lophelia gave a 230Th/U age of 1983±6 AD, close to the date of collection in 2001 AD. Deep-water coral growth is the driving process of sediment accumulation on the summit of carbonate mounds, with sediment accumulation rates in the order of ∼0.3 mm yr−1. However, coral growth is discontinuous and irregular, and complete coral sequences are frequently altered (dissolved) likely due to organic matter consumption by oxidizing pore fluids. Mound top sediments indicate the presence of corals over several glacial/interglacial cycles, but corals of glacial origin could not be identified on the investigated mounds.

Carbonate mounds, identified as deep-water coral banks, have been reported recently from three provinces in the Porcupine Seabight, SW of Ireland. As yet, the mechanisms behind their formation and development are only partly understood. This contribution discusses their seabed appearance and present-day sedimentary environment, based on a large-scale TOBI sidescan sonar mapping carried out in 2002, and on detailed ROV video records from specific sites within the three mound provinces, collected in 2001. The study of the present-day characteristics and variability of these mounds can help to understand their development history in the past.

[1] Gas hydrates inside mud volcanoes have been observed in several locations but are generally found at water depths of 1000 m and deeper. We present the first observation of the base of a gas hydrate stability zone within a shallow mud volcano in the El Arraiche mud volcano field on the Moroccan Atlantic margin. The mud volcano base is located at about 475 m and is over 125 m high. On high-resolution seismics we observed an anomalous but coherent reflection under the slopes of the mud volcano. The event was interpreted as the base of a gas hydrate stability zone because of its inverse polarity and its morphology. Far from the crater, the event is nearly parallel to the seafloor. Closer toward the crater, the event shallows. Inside the mud volcano crater, no event is observed. A stability model using thermogenic gas compositions is applied to local P-T conditions, indicating that thermogenic gas hydrates can be stable at this depth. The high modeled heat flow in the crater of the mud volcano indicates a focused flow of warm fluids. Below the slopes of the mud volcano, the inferred heat flow is also elevated but less high. In areas of thermogenic gas production, gas hydrates can occur at shallow water depths, even in areas with high heat flow. This also suggests that dewatering of the accretionary wedge complex is mainly focused along fault surfaces and through seafloor structures, such as mud volcanoes.

Paired 230Th/U and 14C dating were performed on deep-sea corals (Lophelia pertusa and Madrepora oculata) from the northeastern North Atlantic at ∼730 m bsl to investigate past changes of the thermohaline circulation. These were estimated using the Δ14C value of the upper intermediate waters, based on the 14C ages of the top and base of each coral, where possible, and the 230Th/U dating. The reliability of these estimates was checked by dating two very young corals of the species L. pertusa. One of these corals, collected alive in 1999 AD, gave a 230Th/U age of 1995±4 AD after correction for non-radiogenic 230Th. Another coral, the top of which dated to 1969±6 AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 1960s. The calculated Δ14C values from these two corals agree with those measured at GEOSECS Station 23 in 1972–1973 [Ostlund et al., Earth Planet. Sci. Lett. 23 (1974) 69–86] and 1991–1992 [Nydal and Gisfelos, Radiocarbon 38 (1996) 389–406]. This, together with the 100% aragonite content and the δ234U and 230Th/232Th values of all the dated corals, indicates that none of the corals behaved as open systems with respect to their U-series nuclides and that they closely represent the water mass properties in which they lived. The pre-anthropogenic Δ14C value of the North Atlantic intermediate waters was estimated at −69±4‰. The reservoir age varies from ∼400 years to ∼600 years, and this variation is due to atmospheric 14C/12C changes. A reservoir age of 610±80 years, close to the pre-anthropogenic value, was determined from one coral dated at 10 430±120 cal yr BP, when the global sea level was approximately at −35 m [Bard et al., Nature 382 (1996) 241–244]. This suggests a modern-like pattern of the oceanic circulation prevailed in the Northeast Atlantic Ocean at this time although the deglaciation was not completely achieved.