The Rockall Trough is a basin in the eastern North Atlantic Ocean, northwest of Ireland. The trough is named after the Rockall Plateau, which forms its western boundary and is in turn named after the rock Rockall. In the northeast, it ends at the Wyville -Thomson ridge at about 1000 meters depth, in the southwest, he goes at about 4000 meters deep into the deep Atlantic basin.
The basin is an extension of the North Atlantic basin in the British continental shelf inside. It probably originated in the Cretaceous, as the Rockall microcontinent, today Rockall Plateau broke away from the British continental shelf and the trench opened.
In the west the Rockall Plateau bounds the basin, to the east the continental shelf and in the north of the Wyville -Thomson ridge depth rises to 620 meters, blocking the way to the Faroe - Shetland Channel and therefore prevented a more extensive exchange between warm Nordatlatlantikwasser and colder Arctic water from the Norwegian Sea.
The Rockall Trough is the 1,000 -meter isobath about 200 to 300 kilometers wide and the Wyville -Thomson ridge about 1200 kilometers to the Porcupine Abyssal Plain in the Atlantic. In the northern and central parts he has individual increases as the Anton Dohrn - - tip, the Rosemary Bank and the Hebridean Terrace.
Particular caused a stir in 1998 the discovery of the Darwin Mounds. There are hundreds of surveys in the northern Rockall Trough, which have up to five meters high and up to 75 meters in diameter and were first discovered on sonar images of the area. Near the Wyville -Thomson Ridge, these are higher and come in denser stands in front than further south. Above all, they are made of sand, but there are also apparent components of carbon, which may be sediments, but also disintegrated coral and partly Lophelia pertusa probably still living. Further south, in water depths of 1000-1200 meters following 3000 km ² crater, mostly circular with about 50 meters in diameter, but hardly in relief, and, if known, did not differ in fauna and flora from the surrounding seabed. Probably both phenomena sand volcanoes caused by the ejection of fluids 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 the area.
The basin is up to 4000 meters deep, where there are two distinctly different water layers. Up to 1500 meters dominates the Atlantic water from the central Atlantic. At depths below flowing water masses from the Mediterranean Sea ( the so-called Gulf of - Gibraltar - water (up to about 2000 meters depth) ), the Labrador Sea (up to about 3000 meters depth) and northeast Atlantic deep water with relatively low flow velocities in the west. About the Wyville -Thomson Ridge dense cold arctic water flows into the ditch. Generally occur on the western slopes of the Rockall Plateau significantly stronger currents than on the eastern border of the British continental shelf, which also has a significant impact on fauna and flora.
Fauna and Flora
The area of the Rockall Trough to the Bay of Biscay was back in the early 1990s as the best-researched deep sea world. Since the 19th century, researchers regularly the flora and fauna of the Rockall trough. Nevertheless, the research is inherently subject to significant restrictions. Even now it is limited in the low areas to a large extent on species that are large enough to be visible on photos.
Near the ground, the benthic area, especially echinoderms are common. Overall, researchers found 131 echinoderm species in the basin, of which 40 starfish, 36 brittle stars, sea cucumbers, 33, 18 sea urchins and sea lilies and feather stars four. From the number of individuals, however, make the brittle stars, almost two thirds of all echinoderms dar.
On the slopes, at about 150 to 1200 meters depth, different species of corals have settled, the benefit there from the larger nutrient transport through the strong current. Lophelia pertusa is found relatively widespread in sections between 600 and 800 meters, in the northern areas in shallower water. Particularly common are they in surveys and benches in the ditch. Madrepora oculata, however, there is more at individual sites in the lower portions of this area.
Strong currents also favor other living beings, so that especially occur on the steep slopes of the Wyville -Thomson Ridge and the Anton Dohrn Seamount barnacles of the species Bathylasma hirsutum and brachiopods of the species Dallina sepigera and Macandrevia cranium. Deep-sea species are known particularly from the depths of 2,200 meters and 2,900 meters, there are two permanent stations of the Scottish Marine Biological Association / Scottish Association for Marine Science here. Most animals there were polychaetes, who provided 59 per cent of the individuals of the tracked animals, followed by scissors isopods ( 10.3 percent ), mussels ( 10.1 percent ) and isopods ( 4.4 percent ). Comparative measurements at 1800, 2000, 2500, and at other points to 2,900 meters gave similar results, only isopods seem to be less frequent at other points of the trench. They felt so far on 24 species of deep-sea fish, including three Skates and rays, two black heads, two lizard fish, two eels, two Dornrückenaale, six grenadiers, two eelpout and individual species from five other families.
Investigations that have been made with the help of deep-sea fishermen, showed a similar pattern as in the Bay of Biscay or the Porcupine Bay prevails: Echinoderms dominate in all low areas occurring species differ primarily based on the depth contours, with the largest changes between 800 and 1200 meters depth occur. More radical changes, there are at 1800 meters, with particular changes the composition of the dominant brittle stars clear here. Cnidarians are just as crustaceans often.
Once there is already oil discoveries on the westerly Rockall Plateau since 1959, 1988 Notes on hydrocarbons were also found in the Rockall Trough. Both the geological researches in the trench as well as the political disputes over the continental shelf rights have been stepped up considerably since then. Because of the Rockall Trough should now be the best-researched deep-water area worldwide. As in the basin oil and gas is suspected, it is similar to the Rockall Plateau object of disputes between the neighboring countries Ireland, the UK and Denmark / Faroe Islands to the territorial and economic rights. In 1995, he, however, should be used for the opposite purpose, since this year, the Brent Spar should be sunk in the Rockall Trough, which led to worldwide protests.