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Anton Dohrn Seamount

Coordinates: 57°30′N 11°00′W / 57.500°N 11.000°W / 57.500; -11.000[1]
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Anton Dohrn Seamount
Anton Dohrn Seamount is located in Oceans around British Isles
Anton Dohrn Seamount
Anton Dohrn Seamount is located in North Atlantic
Anton Dohrn Seamount
Anton Dohrn Seamount (North Atlantic)
Summit depth600 metres
Height1,500 m
Location
LocationNorth Atlantic Ocean
Coordinates57°30′N 11°00′W / 57.500°N 11.000°W / 57.500; -11.000[1]
CountryUnited Kingdom (EEZ)
Geology
TypeGuyot
Last eruption~40 million years

The Anton Dohrn Seamount is a guyot in the Rockall Trough in the northeast Atlantic. It was named after the German fishery research vessel which discovered it at the end of the 1950s which, in turn, had been named after the 19th-century biologist Anton Dohrn.

The feature rises from approximately 2,100 metres to 600 metres below sea level and has a sedimentary layer approximately 100 metres thick. It arose through episodic volcanic activity between 70 and 40 million years ago.[2][3]

Around the base of the seamount is a slight "moat" where the sea-bottom is at a lower depth than the surrounding terrain.

Releasing their findings in August 2016, the Deep Links project team, a collaboration between Plymouth University, the University of Oxford, the Joint Nature Conservation Committee and the British Geological Survey, spent six weeks at sea on board the RSS James Cook deploying robot submersibles to film, photograph and collect samples from an exceptionally diverse coral reef environment now revealed on the top of the plateau-like seamount.

Name and research history

Anton Dohrn Seamount is also known as Anton Dohrn Kuppe, a name used by German charts,[4] and as Anton Dohrn bank.[5] It was discovered in 22 September 1958 by the survey vessel Gauss during the Polarfront programme and later surveyed in 18-19 April 1959 by the fishery research vessel FFS Anton Dohrn.[6]

Geography and geomorphology

Anton Dohrn Seamount is located in the northeast Atlantic Ocean west of Scotland,[7] approximately halfway between St Kilda (Hebrides) and Rockall,[8] about 155 kilometres (96 mi) west of the former.[9] It lies in the Rockall Trough, an over 2,000 metres (6,600 ft) submarine depression of unclear origin. North-northeast lies the Rosemary Bank and Hebrides Terrace Seamount is found south-southeast from the seamount.[8] The seamount is located inside the exclusive economic zone of the United Kingdom.[10]

Anton Dohrn Seamount is a 1.8 kilometres (1.1 mi) high[11] and about 45 kilometres (28 mi)[12]-40 kilometres (25 mi) wide circular[11] guyot[8] with a flat top at 1,100–530 kilometres (680–330 mi) depth.[13] Flat-topped seamounts are unusual in the North Atlantic.[14] The shallowest point of the seamount lies at about 530 metres (1,740 ft) depth[11] and is formed by a pinnacle that protrudes from the c. 600 metres (2,000 ft) deep summit platform.[12] A 100 metres (330 ft) thick layer of sediment covers the flat top[15] and appears to be reworked by storms and sea currents.[11] Mounds,[16] slope breaks and volcanic pinnacles are located on the flat top.[17] The seamount tilts southeastward.[18]

Beyond the margin of the flat top, the slopes of Anton Dohrn Seamount drop down to 2,400 metres (7,900 ft) depth.[19] The steep slopes have been variously described as either lacking a sediment cover[1] or featuring gravelly sediments along with outcropping bedrock.[9] There are cliffs, ridges[13] and rockfalls[16] but no gullies or canyons.[10] Parasitic cones lie on the northwestern slope. A moat surrounds the seamount[17] and reaches depths of about 2,300 metres (7,500 ft).[12] It might have formed either through erosion of surrounding sediments by ocean currents or through isostatic subsidence.[20]

Geology

The crust underneath Anton Dohrn Seamount is much thinner than underneath the British Isles and the Rockall Plateau east and west of the seamount, respectively, and the Mohorovičić discontinuity is located at a shallower depth.[8] It may be either stretched continental crust or oceanic crust, and is covered by sediments.[1] At Anton Dohrn Seamount it appears to be unusually shallow, perhaps due to the Iceland plume's buoyancy. The Iceland plume has uplifted terrain as far as 1,000 kilometres (620 mi) from the plume.[21] A 100 kilometres (62 mi) long crustal lineament known as the Anton Dohrn Lineament crosses through the seamount; it may extend into Scotland and Rockall Bank.[22]

Anton Dohrn Seamount is probably formed mostly by basaltic lava[12] and tuffs[14] which define a transitional to alkaline suite.[23] Basaltic rocks, including breccia, have been dredged from the seamount. The rocks contain feldspar and olivine phenocrysts as well as plagioclase. They are covered with ferromanganese crusts[24] and vesicles contain carbonates, clay and zeolites which formed through alteration.[25] Chalks of Maastrichtian age,[24] Eocene nearshore conglomerates[26] and Miocene muds and sands have also been recovered.[27] A granite rock has been dredged as well; it may be a dropstone from icebergs[28] and such exotic rocks have been found in other dredge samples.[14]

Geologic history

Anton Dohrn Seamount is a former volcano. It was episodically active over 29 million years.[11] Radiometric dating of volcanic rocks dredged from it has yielded ages of 70 ± 1, 62 ± 1, 47 ± 1 and 41 ± 1 million years ago;[29] similarly aged pulses of volcanic activity have been identified at other volcanoes in the region and may reflect fluctuations of the Iceland plume.[30] The onset of volcanic activity may have been the consequence of crustal extension in the region.[14] The onset of volcanic activity already during the Cretaceous implies that rifting in the North Atlantic was already underway at that time.[31]

Xenoliths found in volcanic rocks indicate that at Anton Dohrn volcanic activity involved interactions between magma and sediments, resulting in phreatomagmatic eruptions that could have dispersed volcanic ash in the region.[32] This volcanic ash erupted by Anton Dohrn may be the source of post-Cenomanian bentonites of the British Isles[33] but the age and composition of the bentonites do not support this theory.[34] The seamount was once proposed to be the source of Turonian tephra deposits in Western Europe before its Maastrichtian age was established.[35]

During the Cretaceous the seamount was about 2 kilometres (1.2 mi) higher than present,[21] perhaps even reaching 2,000 metres (6,600 ft) height above sea level;[18] presumably it was then eroded during the Paleocene when a wave of erosion took place in western Britain and stripped much of the volcanic centres of northwest Scotland.[21] An episode of crustal subsidence in the Cretaceous-Oligocene also played a role in lowering Anton Dohrn Seamount.[36] The pinnacles on the seamount may be leftover volcanic conduits that resisted erosion.[14] Sedimentation covered the seamount and its flanks in the Eocene and continued afterwards.[11]

Ocean currents

Ocean currents around Anton Dohrn Seamount are complicated and formed by various water masses.[12] Internal tides at the seamount appear to be important for its ecosystem.[37]

Ecology

Seamounts are considered to be biodiversity hotspots,[38] and there are proposals to make Anton Dohrn Seamount a Special Area of Conservation.[10]

The region is considered to be "the cradle of deep-sea biology" as Victorian-era scientists sampled the regional fauna.[10]

Barnacles and brachiopods grow on the top of the seamount, and echinoderms[39] and cirripedes also occur.[40] On the sandy or gravelly substrate serpulids and sponges are found.[10]

A number of ecosystems have been found on Anton Dohrn Seamount, including coral gardens, cold water coral reefs and sponge and xenophyophore communities;[41][42] this seamount is the first place in the United Kingdom where coral gardens have been discovered.[43] They mostly occur on the sides of the seamount, on mounds on the flat top[44] and its margin,[10] perhaps for hydrodynamic reasons or because substrates favourable for the development of the reefs are found there.[45] The sandy and cobbly terrain of the slopes with occasional bedrock outcrops is populated by reefs that grow on bedrock or on cobbles.[46] There is a vertical stratification, with Lophelia found at shallower depths than Solenosmilia.[47]

Dropframe camera surveys[42] have seen anemones, anthozoans, ascidians, the asteroid (starfish) Henricia sp., bamboo corals, caryophyllids, cerianthids, variously formed antipatharian corals, the corals Desmophyllum dianthus, Lophelia pertusa and Solenosmilia variabilis, echinoderms including brisingids and crinoids, glass sponges, gorgonians, holothurians, the ophiuroids Ophiactis balli and Ophiomusium lymani, the pencil urchin Cidaris cidaris, pycnogonids, the scleractinian Madrepora oculata, the seapen Pennatula phosphorea, sea urchins, sea whips, serpulids, soft corals such as Gersemia sp. and Anthomastus sp., lobose, large and encrusting sponges, stylasterids and xenophyophores. Decapods, Fish including the eel Synaphobranchus kaupi and Lepidion eques and squat lobsters Munida sp. have also been encountered.[46][48][49]

Corals such as antipatharians like Leiopathes sp., small bamboo corals, large gorgonians and soft corals like as Anthomastus sp. have also been found at parasitic vents.[9] The cold water coral cover can become so thick that the underground disappears underneath it.[50]

The seamount has been impacted by deep water fishing.[10] Lost fishing gear and trawl marks have been found on Anton Dohrn Seamount,[51] and animals found at its foot have ingested microplastics.[52]

References

  1. ^ a b c Jones et al. 1994, p. 239.
  2. ^ O'Connor, Stofferes, Wijbrans, Shannon and Morrissey (2000). Evidence from episodic seamount volcanism for pulsing of the Iceland plume in the past 70 Myr Archived April 11, 2007, at the Wayback Machine, Nature 408, 954–958.
  3. ^ "New discovery of deep-water coral reefs in UK waters". British Geological Survey. 2010. Retrieved October 20, 2019.
  4. ^ Rogalla 1962, p. 60.
  5. ^ Bott, Martin H. P.; Saxov, Svend; Talwani, Manik; Thiede, Jörn, eds. (1983). Structure and Development of the Greenland-Scotland Ridge. Boston, MA: Springer US. p. 679. doi:10.1007/978-1-4613-3485-9. ISBN 978-1-4613-3487-3.
  6. ^ Rogalla 1962, p. 59.
  7. ^ Stewart et al. 2009, p. 10.
  8. ^ a b c d Jones et al. 1994, p. 238.
  9. ^ a b c Stewart et al. 2009, p. 9.
  10. ^ a b c d e f g Morato, T.; Kvile, K. Ø; Taranto, G. H.; Tempera, F.; Narayanaswamy, B. E.; Hebbeln, D.; Menezes, G. M.; Wienberg, C.; Santos, R. S.; Pitcher, T. J. (6 May 2013). "Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea". Biogeosciences. 10 (5): 3047. doi:10.5194/bg-10-3039-2013. ISSN 1726-4170.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  11. ^ a b c d e f Stewart et al. 2009, p. 12.
  12. ^ a b c d e Davies et al. 2015, p. 4.
  13. ^ a b Stewart et al. 2009, p. 31.
  14. ^ a b c d e Jones et al. 1974, p. 129.
  15. ^ Jones et al. 1994, p. 244.
  16. ^ a b Stewart et al. 2009, p. 34.
  17. ^ a b Stewart et al. 2009, p. 14.
  18. ^ a b Jones et al. 1974, p. 130.
  19. ^ Stewart et al. 2009, p. 130.
  20. ^ Heezen, Bruce C.; Johnson, G. Leonard (1 November 1963). "A moated knoll in the Canary Passage". Deutsche Hydrografische Zeitschrift. 16 (6): 270. doi:10.1007/BF02025932. ISSN 1616-7228.
  21. ^ a b c Jones et al. 1994, p. 245.
  22. ^ Roberts, Alan M.; Alvey, Andrew D.; Kusznir, Nick J. (1 May 2019). "Crustal structure and heat-flow history in the UK Rockall Basin, derived from backstripping and gravity-inversion analysis". Petroleum Geoscience. 25 (2): 146. doi:10.1144/petgeo2017-063. ISSN 1354-0793.
  23. ^ Dietrich, V. J; Jones, E. J. W (1 April 1980). "Volcanic rocks from Rosemary Bank (Rockall Trough, NE Atlantic)". Marine Geology. 35 (4): 295. doi:10.1016/0025-3227(80)90122-X. ISSN 0025-3227.
  24. ^ a b Jones et al. 1994, p. 240.
  25. ^ Jones et al. 1994, p. 241.
  26. ^ Stoker, Weering & Svaerdborg 2001, p. 411.
  27. ^ Stoker, Weering & Svaerdborg 2001, p. 431.
  28. ^ Rogalla 1962, p. 62.
  29. ^ O'Connor et al. 2000, p. 955.
  30. ^ O'Connor et al. 2000, p. 957.
  31. ^ Gordon, John E.; Brooks, Anthony J.; Chaniotis, Peter D.; James, Ben D.; Kenyon, Neil H.; Leslie, Alick B.; Long, David; Rennie, Alistair F. (1 December 2016). "Progress in marine geoconservation in Scotland's seas: assessment of key interests and their contribution to Marine Protected Area network planning". Proceedings of the Geologists' Association. 127 (6): 724. doi:10.1016/j.pgeola.2016.10.002. ISSN 0016-7878.
  32. ^ Pacey 1984, p. 57.
  33. ^ Pacey 1984, p. 58.
  34. ^ Wray, David S. (1999). "Identification and long-range correlation of bentonites in Turonian–Coniacian (Upper Cretaceous) chalks of northwest Europe". Geological Magazine. 136 (4): 367. doi:10.1017/S0016756899002836. ISSN 1469-5081.
  35. ^ Wray, David S.; Wood, Christopher J. (1 May 1998). "Distinction between detrital and volcanogenic clay-rich beds in Turonian–Coniacian chalks of eastern England". Proceedings of the Yorkshire Geological Society. 52 (1): 95. doi:10.1144/pygs.52.1.95. ISSN 0044-0604.
  36. ^ Jones et al. 1974, pp. 130–131.
  37. ^ Henry et al. 2014, p. 5.
  38. ^ Davies et al. 2015, p. 2.
  39. ^ Stewart et al. 2009, p. 13.
  40. ^ Gage, J. D. (1986). "The benthic fauna of the Rockall Trough: regional distribution and bathymetric zonation". Proceedings of the Royal Society of Edinburgh, Section B: Biological Sciences. 88: 169. doi:10.1017/S026972700000453X. ISSN 2053-5910.
  41. ^ Davies et al. 2015, pp. 14–15.
  42. ^ a b Henry et al. 2014, p. 1.
  43. ^ Davies et al. 2015, p. 24.
  44. ^ Davies et al. 2015, p. 16.
  45. ^ Davies et al. 2015, pp. 26–27.
  46. ^ a b Stewart et al. 2009, pp. 38–46.
  47. ^ Henry, Lea-Anne; Roberts, J. Murray (1 June 2014). "Recommendations for best practice in deep-sea habitat classification: Bullimore et al. as a case study". ICES Journal of Marine Science. 71 (4): 896–897. doi:10.1093/icesjms/fst175. ISSN 1054-3139.
  48. ^ Davies et al. 2015, pp. 12–13.
  49. ^ Copard, K.; Colin, C.; Henderson, G. M.; Scholten, J.; Douville, E.; Sicre, M. -A.; Frank, N. (1 January 2012). "Late Holocene intermediate water variability in the northeastern Atlantic as recorded by deep-sea corals". Earth and Planetary Science Letters. 313–314: 35. doi:10.1016/j.epsl.2011.09.047. ISSN 0012-821X.
  50. ^ Stewart et al. 2009, p. 30.
  51. ^ Stewart et al. 2009, p. 74.
  52. ^ Courtene-Jones, Winnie; Quinn, Brian; Gary, Stefan F.; Mogg, Andrew O. M.; Narayanaswamy, Bhavani E. (1 December 2017). "Microplastic pollution identified in deep-sea water and ingested by benthic invertebrates in the Rockall Trough, North Atlantic Ocean". Environmental Pollution. 231: 271–272. doi:10.1016/j.envpol.2017.08.026. ISSN 0269-7491.

Sources

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