Structure and development of carbonate mounds along the NE Atlantic margin

Giant carbonate mounds between 500-1200 m water depth along both the SE and SW margins of Rockall Trough rise 5 to 300 m above the surrounding seafloor and have diameters at their basis of up to 5 km. Buried mounds, at relatively shallow depth below the seafloor are also found. Both individual and complex clusters of mounds can be recognized. Smaller and individual, sometimes buried mounds are found at the upper slope. On the SW Rockall Trough margin, higher, steeper and individual mounds are found deeper downslope (900-1100 m). At the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors (600-1000 m depth). These clusters are oriented perpendicular and slightly oblique to the prevailing bathymetry, and show on TOBI profiles as linear ridges. Further results of the TOBI survey in summer 2002 show that the distribution of mounds along the flanks of SW Rockall Trough is considerably more widespread than previously considered, and also that the mounds appear to form constructional elements on a large plateau. Erosional channels between mounds identify the strong interaction between mound shape and strong bottom currents along the slopes of mounds. On the upper flank the mounds are delineated by a field of large gravelly sediment waves of 500m wavelength oriented parallel to the margin in the central part and more curved to the north. On their lower flank slide scars do locally occur

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

Cold-water coral growth under extreme environmental conditions, the Cape Lookout area, NW Atlantic

The Cape Lookout cold-water coral area off thecoast of North Carolina forms the shallowest and northernmostcold-water coral mound area on the Blake Plateau inthe NW Atlantic. Cold-water coral habitats near Cape Lookoutare occasionally bathed in the Gulf Stream, which is characterisedby oligotrophic warm water and strong surface currents.Here, we present the first insights into the mound distributionand morphology, sedimentary environment and coralcover and near-bed environmental conditions as recordedby bottom landers from this coral area. The mounds occurbetween 320 and 550m water depth and are characterisedby high acoustic backscatter indicating the presenceof hard structure. Three distinct mound morphologies wereobserved: (1) a mound with a flattened top at 320 m, (2)multi-summited mounds with a teardrop shape in the middlepart of the area and (3) a single mound at 540m water depth.Echosounder profiles show the presence of a strong reflectorunderneath all mound structures that forms the base of themounds. This reflector cropped out at the downstream side ofthe single mound and consists of carbonate slabs. Video analysisrevealed that all mounds are covered by Lophelia pertusaand that living colonies only occur close to the summitsof the SSW side of the mounds, which is the side that facesthe strongest currents. Off-mound areas were characterisedby low backscatter and sediment ripples, indicating the presenceof relatively strong bottom currents. Two bottom landerswere deployed amidst the coral mounds between December2009 and May 2010. Both landers recorded prominentevents, characterised by large fluctuations in environmentalconditions near the seabed as well as in the overlyingwater column. The period between December and April wascharacterised by several events of increasing temperature andsalinity, coinciding with increased flow and near-bed acousticbackscatter. During these events temperature fluctuatedby up to 9 ?C within a day, which is the largest temperaturevariability as measured so far in a cold-water coral habitat.Warm events, related to Gulf Stream meanders, had the durationof roughly 1 week and the current during these eventswas directed to the NNE. The consequences of such eventsmust be significant given the strong effects of temperature on the metabolism of cold-water corals. Furthermore, elevatedacoustic backscatter values and high mass fluxes werealso recorded during these events, indicating a second stressorthat may affect the corals. The abrasive nature of sand incombination with strong currents might sand blast the corals.We conclude that cold-water corals near Cape Lookout liveunder extreme conditions that limit mound growth at present

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

Late Holocene (0-2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean

Planktonic foraminiferal Mg/Ca ratios and oxygen isotopic compositions of a spliced sediment record from Feni Drift, NE Atlantic Ocean (box core M200309 and piston core ENAM9606) trace late Holocene sea surface temperature (SST) and salinity changes over the past 2400 years. At this location, the variability of SST and oxygen isotopic composition of seawater (

Enhanced short-term sediment deposition within the Nazaré Canyon, North-East Atlantic

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