Rockall trough
The Rockall Trough is a lake basin in the eastern North Atlantic , northwest of Ireland . The trough is named after the Rockall Plateau, which forms its western boundary and is in turn named after the Rockall rock . In the northeast it ends at the Wyville-Thomson Ridge at a depth of about 1000 meters, in the southwest it merges into the deep Atlantic Basin at about 4000 meters.
geology
The basin is an extension of the North Atlantic Basin into the British continental shelf . It probably originated in the Cretaceous , when the Rockall microcontinent, today Rockall Plateau, broke away from the British continental shelf and the trench opened.
In the west the Rockall Plateau borders the basin, in the east the continental shelf and in the north the Wyville-Thomson Ridge rises to a depth of 620 meters, blocks the way to the Faroe-Shetland Canal and thus prevents any further exchange between warm North Atlantic water and colder water Arctic water from the Northern European Sea .
The Rockall trough is about 200 to 300 kilometers wide at the 1000 meter depth line and about 1200 kilometers long from the Wyville-Thomson Ridge to the Porcupine Abyssal Plain in the Atlantic. In the northern and central part it has individual elevations such as the Anton-Dohrn-Kuppe, the Rosemary-Bank or the Hebriden-Terrasse.
The discovery of the Darwin Mounds in 1998 caused a particular stir . There are several hundred elevations in the northern Rockall Trough, up to five meters high and up to 75 meters in diameter, and were first discovered on sonar images of the area. In the vicinity of the Wyville-Thomson Ridge these are higher and occur in denser stands than further south. Above all, they consist of sand, but there are also components of carbon, which presumably can be sediments , but also decayed corals and in some cases still living Lophelia pertusa . Further south, in water depths of 1000 to 1200 meters, there are 3000 km² of craters, mostly circular with a diameter of about 50 meters, which, however, hardly differ in relief and, as far as is known, in fauna and flora no different from the surrounding seabed. Presumably both phenomena are sand volcanoes, which were created by the ejection of liquids from the sediment. The difference between positive and negative relief in north-south direction is probably due to the different composition of the sediment in this area.
Hydrology
The basin is up to 4000 meters deep, with two clearly distinguishable water layers. Atlantic water from the central Atlantic dominates up to 1500 meters. At depths below this, masses of water from the Mediterranean (the so-called Gulf of Gibraltar water (up to about 2000 meters depth)), the Labrador Sea (up to about 3000 meters depth) and north-east Atlantic deep water flow with relatively low flow speeds in a north-westerly direction. Cold, dense arctic water flows into the trench over the Wyville-Thomson Ridge. In general, the currents on the western slopes of the Rockall Plateau are much stronger than on the eastern border with the British continental shelf, which also has a significant impact on fauna and flora.
fauna and Flora
The area from the Rockall Trough to the Bay of Biscay was already considered the best-explored deep sea in the world in the early 1990s . Researchers have been studying the flora and fauna of the Rockall Trough on a regular basis since the 19th century. Nevertheless, research is naturally subject to major restrictions. Even now, in the deep areas, it is largely restricted to species large enough to be recognizable in photos.
Near the ground, the benthic area , in particular, echinoderms often. Overall, researchers found 131 echinoderm species in the basin, 40 of starfish , 36 brittle stars , 33 cucumbers , 18 sea urchins and four crinoid . Of the number of individuals, however, the brittle stars represent almost two thirds of all echinoderms.
Various coral species have settled on the slopes, at a depth of around 150 to 1200 meters , which benefit from the greater transport of nutrients due to the stronger currents. Lophelia pertusa is found relatively widespread in the sections between 600 and 800 meters, in the northern areas also in shallower water. They are particularly common on bumps and benches in the ditch. Madrepora oculata, on the other hand, is more likely to be found in individual locations in the lower sections of this area.
Strong currents also favor other creatures, so especially on the steep slopes on Wyville Thomson Ridge and the Anton Dohrn Seamount barnacles of the species Bathylasma hirsutum and brachiopods of species Dallina sepigera and Macandrevia cranium occur. Deep sea stocks are particularly known from the depths of 2,200 meters and 2,900 meters, as two permanent measuring stations of the Scottish Association for Marine Science are located here. The most common animals there were poly-bristles , which made up 59 percent of the individuals of the animals tracked, followed by scabs (10.3 percent), mussels (10.1 percent) and woodlice (4.4 percent). Comparative measurements at 1800, 2000, 2500 and at other locations at 2900 meters yielded similar results, only woodlice seem to be less frequent at other locations of the trench. They tracked down so far 24 species of deep-sea fishing, three Skates and rays , two black heads , two lizard fish , two eels , two notacanthidae , six grenadiers , two eelpout and individual species from five other families.
Investigations carried out with the help of deep-sea fishermen revealed a similar picture to that prevailing in the Biscay or Porcupine Bay : Echinoderms dominate in all depths, the species that occur mainly differ on the basis of the contour lines, with the greatest changes between 800 and 1200 meters depth occur. There are other drastic changes at 1800 meters, with the composition of the dominant brittle stars in particular changing significantly here. Cnidarians are common, as are crustaceans .
Human use
After oil has been discovered on the Rockall Plateau to the west since 1959, evidence of hydrocarbons was also found in the Rockall trough in 1988 . Both the geological research in the ditch and the political disputes over shelf rights have intensified considerably since then. Because of this, the Rockall Trough is now likely to be the best-researched deep-sea area in the world. Since oil and natural gas are suspected in the basin, like the Rockall Plateau, it is the object of disputes between the neighboring states of Ireland, Great Britain and Denmark / Faroe Islands for sovereign and economic rights. In 1995, however, it was to be used for the opposite purpose, as in that year the Brent Spar was to be sunk in the Rockall trough, which led to worldwide protests.
Individual evidence
- ↑ MS Stocker, TCE van Weering and T. Svaerdborg: A Mid- to Late Cenozoic tectonostratigraphic framework for the Rockall Through , in: Pat Shannon, PDW Haughton, DV Corcoran, Geological Society of London: The Petroleum Exploration of Ireland's Offshore Basins , Geological Society, 2001 ISBN 1-86239-087-8 , pp. 411-435.
- ^ Alan Judd, Martin Hovland: Seabed Fluid Flow: The Impact of Geology, Biology And the Marine Environment , Cambridge University Press, Cambridge 2007, ISBN 0521819504 , pp. 64-66.
- ^ Nigel R. Merrett, RL Haedrich: Deep-sea Demersal Fish and Fisheries , Springer, 1997, ISBN 0412394103 , pp. 17-20.
- ^ A b c Paul A. Tyler: Ecosystems of the Deep Oceans: Ecosystems of the World , Elsevier, 2003, ISBN 044482619X , pp. 134-135.
- ↑ John D. Gage, Paul A. Tyler: Deep-Sea Biology: A Natural History of Organisms at the Deep-Sea Floor , Cambridge University Press, Cambridge 1992, ISBN 0-521-33665-1 , p. 130.
- ↑ a b c d C. Berry, S. Jones: The Rockall Trough / Channel - A Potential MPA. WWF's North-East Atlantic Programs. Bremen 2001 ( PDF ( Memento from September 23, 2006 in the Internet Archive ))
- ↑ Martin White et al .: Deep-water coral development as a function of hydrodynamics and surface productivity around the submarine banks of the Rockall Trough, NE Atlantic , in: André Freiwald, J. Murray Roberts: Cold-water Corals and Ecosystems , Springer , 2005, ISBN 3540241361 , pp. 503-514.
- ↑ Kevin T. Pickering, Lewis A. Owen: An Introduction to Global Environmental Issues , Routledge, London 1997, ISBN 0415140986 , p. 14.
Coordinates: 55 ° N , 14 ° W