Anton Dohrn Seamount: Difference between revisions
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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.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=238}} It may be either stretched [[continental crust]] or [[oceanic crust]], and is covered by sediments.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=239}} 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 {{convert|1000|km}} from the plume.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=245}} A {{convert|100|km}} long crustal [[lineament]] known as the Anton Dohrn Lineament crosses through the seamount; it may extend into Scotland and Rockall Bank.<ref name="Roberts2019" /> |
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.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=238}} It may be either stretched [[continental crust]] or [[oceanic crust]], and is covered by sediments.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=239}} 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 {{convert|1000|km}} from the plume.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=245}} A {{convert|100|km}} long crustal [[lineament]] known as the Anton Dohrn Lineament crosses through the seamount; it may extend into Scotland and Rockall Bank.<ref name="Roberts2019" /> |
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Anton Dohrn Seamount is probably formed mostly by [[basalt]]ic [[lava]]{{sfn|Davies|Stewart|Narayanaswamy|Jacobs|2015|p=4}} and [[tuff]]s |
Anton Dohrn Seamount is probably formed mostly by [[basalt]]ic [[lava]]{{sfn|Davies|Stewart|Narayanaswamy|Jacobs|2015|p=4}} and [[tuff]]s{{sfn|Jones|Ramsay|Preston|Smith|1974|p=129}} which define a transitional to alkaline suite.<ref name="Dietrich1980" /> <!-- Reword -->[[Basalt]]ic rocks, including [[breccia]], have been dredged from the seamount. The rocks contain [[feldspar]] and [[olivine]] [[phenocryst]]s as well as [[plagioclase]]. They are covered with [[ferromanganese]] crusts{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=240}} and vesicles contain [[carbonate]]s, [[clay]] and [[Zeolite|zeolites]] which formed through alteration.{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=241}} [[Chalk]]s of [[Maastricht]]ian age,{{sfn|Jones|Siddall|Thirlwall|Chroston|1994|p=240}} [[Eocene]] nearshore conglomerates{{sfn|Stoker|Weering|Svaerdborg|2001|p=411}} and [[Miocene]] muds and sands have also been recovered.{{sfn|Stoker|Weering|Svaerdborg|2001|p=431}} A [[granite]] rock has been dredged as well; it may be a [[dropstone]] from [[iceberg]]s{{sfn|Rogalla|1962|p=62}} and such exotic rocks have been found in other dredge samples.{{sfn|Jones|Ramsay|Preston|Smith|1974|p=129}} |
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== Geologic history == |
== Geologic history == |
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==References== |
==References== |
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{{reflist|refs= |
{{reflist|refs= |
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<ref name="Dietrich1980">{{cite journal |last1=Dietrich |first1=V. J |last2=Jones |first2=E. J. W |title=Volcanic rocks from Rosemary Bank (Rockall Trough, NE Atlantic) |journal=Marine Geology |date=1 April 1980 |volume=35 |issue=4 |page=295 |doi=10.1016/0025-3227(80)90122-X |url=https://www.sciencedirect.com/science/article/abs/pii/002532278090122X |language=en |issn=0025-3227}}</ref> |
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<ref name="Roberts2019">{{cite journal |last1=Roberts |first1=Alan M. |last2=Alvey |first2=Andrew D. |last3=Kusznir |first3=Nick J. |title=Crustal structure and heat-flow history in the UK Rockall Basin, derived from backstripping and gravity-inversion analysis |journal=Petroleum Geoscience |date=1 May 2019 |volume=25 |issue=2 |page=146 |doi=10.1144/petgeo2017-063 |url=https://pubs.geoscienceworld.org/gsa/pg/article/531029/crustal-structure-and-heat-flow-history-in-the-uk |language=en |issn=1354-0793}}</ref> |
<ref name="Roberts2019">{{cite journal |last1=Roberts |first1=Alan M. |last2=Alvey |first2=Andrew D. |last3=Kusznir |first3=Nick J. |title=Crustal structure and heat-flow history in the UK Rockall Basin, derived from backstripping and gravity-inversion analysis |journal=Petroleum Geoscience |date=1 May 2019 |volume=25 |issue=2 |page=146 |doi=10.1144/petgeo2017-063 |url=https://pubs.geoscienceworld.org/gsa/pg/article/531029/crustal-structure-and-heat-flow-history-in-the-uk |language=en |issn=1354-0793}}</ref> |
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<ref name="HenryRoberts2014">{{cite journal |last1=Henry |first1=Lea-Anne |last2=Roberts |first2=J. Murray |title=Recommendations for best practice in deep-sea habitat classification: Bullimore et al. as a case study |journal=ICES Journal of Marine Science |date=1 June 2014 |volume=71 |issue=4 |pages=896-897 |doi=10.1093/icesjms/fst175 |url=https://academic.oup.com/icesjms/article/71/4/895/666861 |language=en |issn=1054-3139}}</ref> |
<ref name="HenryRoberts2014">{{cite journal |last1=Henry |first1=Lea-Anne |last2=Roberts |first2=J. Murray |title=Recommendations for best practice in deep-sea habitat classification: Bullimore et al. as a case study |journal=ICES Journal of Marine Science |date=1 June 2014 |volume=71 |issue=4 |pages=896-897 |doi=10.1093/icesjms/fst175 |url=https://academic.oup.com/icesjms/article/71/4/895/666861 |language=en |issn=1054-3139}}</ref> |
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Revision as of 16:51, 22 February 2020
| Anton Dohrn Seamount | |
|---|---|
 | |
  Anton Dohrn Seamount (North Atlantic) | |
| Summit depth | 600 metres |
| Height | 1,500 m |
| Location | |
| Location | North Atlantic Ocean |
| Coordinates | 57°30′N 11°00′W / 57.500°N 11.000°W[1] |
| Country | United Kingdom (EEZ) |
| Geology | |
| Type | Guyot |
| 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] 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.[5]
Geography and geomorphology
Anton Dohrn Seamount is located in the northeast Atlantic Ocean west of Scotland,[6] approximately halfway between St Kilda (Hebrides) and Rockall,[7] about 155 kilometres (96 mi) west of the former.[8] 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.[7] The seamount is located inside the exclusive economic zone of the United Kingdom.[9]
Anton Dohrn Seamount is a 1.8 kilometres (1.1 mi) high[10] and about 45 kilometres (28 mi)[11]-40 kilometres (25 mi) wide circular[10] guyot[7] with a flat top at 1,100–530 kilometres (680–330 mi) depth.[12] Flat-topped seamounts are unusual in the North Atlantic.[13] The shallowest point of the seamount lies at about 530 metres (1,740 ft) depth[10] and is formed by a pinnacle that protrudes from the c. 600 metres (2,000 ft) deep summit platform.[11] A 100 metres (330 ft) thick layer of sediment covers the flat top[14] and appears to be reworked by storms and sea currents.[10] Mounds,[15] slope breaks and volcanic pinnacles are located on the flat top.[16] The seamount tilts southeastward.[17]
Beyond the margin of the flat top, the slopes of Anton Dohrn Seamount drop down to 2,400 metres (7,900 ft) depth.[18] The steep slopes have been variously described as either lacking a sediment cover[1] or featuring gravelly sediments along with outcropping bedrock.[8] There are cliffs, ridges[12] and rockfalls[15] but no gullies or canyons.[9] Parasitic cones lie on the northwestern slope. A moat surrounds the seamount[16] and reaches depths of about 2,300 metres (7,500 ft).[11] Roberts et al. 1974 explained its formation by erosion through sea currents which are excited by the seamount.[19]
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.[7] 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.[20] 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.[21]
Anton Dohrn Seamount is probably formed mostly by basaltic lava[11] and tuffs[13] which define a transitional to alkaline suite.[22] 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[23] and vesicles contain carbonates, clay and zeolites which formed through alteration.[24] Chalks of Maastrichtian age,[23] Eocene nearshore conglomerates[25] and Miocene muds and sands have also been recovered.[26] A granite rock has been dredged as well; it may be a dropstone from icebergs[27] and such exotic rocks have been found in other dredge samples.[13]
Geologic history
Anton Dohrn Seamount is a former volcano. It was episodically active over 29 million years.[10] Radiometric dating of volcanic rocks dredged from it has yielded ages of 70 ± 1, 62 ± 1, 47 ± 1 and 41 ± 1 million years ago;[28] similarly aged pulses of volcanic activity have been identified at other volcanoes in the region and may reflect fluctuations of the Iceland plume.[29] The onset of volcanic activity may have been the consequence of crustal extension in the region.[13]
During the Cretaceous the seamount was about 2 kilometres (1.2 mi) higher than present,[20] perhaps even reaching 2,000 metres (6,600 ft) height above sea level;[17] 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.[20] An episode of crustal subsidence in the Cretaceous-Oligocene also played a role in lowering Anton Dohrn Seamount.[30] The pinnacles on the seamount may be leftover volcanic conduits that resisted erosion.[13] Sedimentation covered the seamount and its flanks in the Eocene and continued afterwards.[10]
Ocean currents
Ocean currents around Anton Dohrn Seamount are complicated and formed by various water masses.[11] Internal tides at the seamount appear to be important for its ecosystem.[31]
Ecology
Seamounts are considered to be biodiversity hotspots,[32] and there are proposals to make Anton Dohrn Seamount a Special Area of Conservation.[9]
The region is considered to be "the cradle of deep-sea biology" as Victorian-era scientists sampled the regional fauna.[9]
Barnacles and brachiopods grow on the top of the seamount, and echinoderms also occur.[33] On the sandy or gravelly substrate serpulids and sponges are found.[9]
A number of ecosystems have been found on Anton Dohrn Seamount, including coral gardens, cold water coral reefs and sponge and xenophyophore communities;[34][35] this seamount is the first place in the United Kingdom where coral gardens have been discovered.[36] They mostly occur on the sides of the seamount, on mounds on the flat top[37] and its margin,[9] perhaps for hydrodynamic reasons or because substrates favourable for the development of the reefs are found there.[38] The sandy and cobbly terrain of the slopes with occasional bedrock outcrops is populated by reefs that grow on bedrock or on cobbles.[39] There is a vertical stratification, with Lophelia found at shallower depths than Solenosmilia.[40]
Dropframe camera surveys[35] have seen anemones, anthozoans, ascidians, the asteroid (starfish) Henricia sp., bamboo corals, caryophyllids, cerianthids, variously formed antipatharian corals, the corals 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.[39][41]
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.[8] The cold water coral cover can become so thick that the underground disappears underneath it.[42]
The seamount has been impacted by deep water fishing.[9] Lost fishing gear and trawl marks have been found on Anton Dohrn Seamount,[43] and animals found at its foot have ingested microplastics.[44]
References
- ^ a b c Jones et al. 1994, p. 239.
- ^ 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.
- ^ "New discovery of deep-water coral reefs in UK waters". British Geological Survey. 2010. Retrieved October 20, 2019.
- ^ Rogalla 1962, p. 60.
- ^ Rogalla 1962, p. 59.
- ^ Stewart et al. 2009, p. 10.
- ^ a b c d Jones et al. 1994, p. 238.
- ^ a b c Stewart et al. 2009, p. 9.
- ^ 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) - ^ a b c d e f Stewart et al. 2009, p. 12.
- ^ a b c d e Davies et al. 2015, p. 4.
- ^ a b Stewart et al. 2009, p. 31.
- ^ a b c d e Jones et al. 1974, p. 129.
- ^ Jones et al. 1994, p. 244.
- ^ a b Stewart et al. 2009, p. 34.
- ^ a b Stewart et al. 2009, p. 14.
- ^ a b Jones et al. 1974, p. 130.
- ^ Stewart et al. 2009, p. 130.
- ^ Howe, J. A.; Stoker, M. S.; Masson, D. G.; Pudsey, C. J.; Morris, P.; Larter, R. D.; Bulat, J. (1 February 2006). "Seabed morphology and the bottom-current pathways around Rosemary Bank seamount, northern Rockall Trough, North Atlantic". Marine and Petroleum Geology. 23 (2): 165. doi:10.1016/j.marpetgeo.2005.08.003. ISSN 0264-8172.
- ^ a b c Jones et al. 1994, p. 245.
- ^ 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.
- ^ 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.
- ^ a b Jones et al. 1994, p. 240.
- ^ Jones et al. 1994, p. 241.
- ^ Stoker, Weering & Svaerdborg 2001, p. 411.
- ^ Stoker, Weering & Svaerdborg 2001, p. 431.
- ^ Rogalla 1962, p. 62.
- ^ O'Connor et al. 2000, p. 955.
- ^ O'Connor et al. 2000, p. 957.
- ^ Jones et al. 1974, pp. 130–131.
- ^ Henry et al. 2014, p. 5.
- ^ Davies et al. 2015, p. 2.
- ^ Stewart et al. 2009, p. 13.
- ^ Davies et al. 2015, pp. 14–15.
- ^ a b Henry et al. 2014, p. 1.
- ^ Davies et al. 2015, p. 24.
- ^ Davies et al. 2015, p. 16.
- ^ Davies et al. 2015, pp. 26–27.
- ^ a b Stewart et al. 2009, pp. 38–46.
- ^ 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.
- ^ Davies et al. 2015, pp. 12–13.
- ^ Stewart et al. 2009, p. 30.
- ^ Stewart et al. 2009, p. 74.
- ^ 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
- Davies, Jaime S.; Stewart, Heather A.; Narayanaswamy, Bhavani E.; Jacobs, Colin; Spicer, John; Golding, Neil; Howell, Kerry L. (18 May 2015). "Benthic Assemblages of the Anton Dohrn Seamount (NE Atlantic): Defining Deep-Sea Biotopes to Support Habitat Mapping and Management Efforts with a Focus on Vulnerable Marine Ecosystems". PLOS ONE. 10 (5): e0124815. doi:10.1371/journal.pone.0124815. ISSN 1932-6203.
{{cite journal}}: Invalid|ref=harv(help)CS1 maint: unflagged free DOI (link) - Henry, Lea-Anne; Vad, Johanne; Findlay, Helen S.; Murillo, Javier; Milligan, Rosanna; Roberts, J. Murray (7 July 2014). "Environmental variability and biodiversity of megabenthos on the Hebrides Terrace Seamount (Northeast Atlantic)". Scientific Reports. 4 (1): 1–10. doi:10.1038/srep05589. ISSN 2045-2322.
{{cite journal}}: Invalid|ref=harv(help) - Jones, Ejw; Siddall, R.; Thirlwall, Mf; Chroston, Pn; Lloyd, Aj (1994-01-01). "Seamount,anton,dohrn and the evolution of the rockall trough". Oceanologica Acta. 17 (3): 237–247. ISSN 0399-1784.
{{cite journal}}: Invalid|ref=harv(help) - Jones, E. J. W.; Ramsay, A. T. S.; Preston, N. J.; Smith, A. C. S. (September 1974). "A Cretaceous guyot in the Rockall Trough". Nature. 251 (5471): 129–131. doi:10.1038/251129a0. ISSN 1476-4687.
{{cite journal}}: Invalid|ref=harv(help) - O'Connor, J. M.; Stoffers, P.; Wijbrans, J. R.; Shannon, P. M.; Morrissey, T. (December 2000). "Evidence from episodic seamount volcanism for pulsing of the Iceland plume in the past 70 Myr". Nature. 408 (6815): 954–958. doi:10.1038/35050066. ISSN 1476-4687.
{{cite journal}}: Invalid|ref=harv(help) - Rogalla, E. H. (1962). "Survey of the Anton Dohrn Seamount". The International Hydrographic Review. ISSN 0020-6946.
{{cite journal}}: Invalid|ref=harv(help) - Stewart, Heather; Davies, Jaime; Long, David; Strömberg, Helena; Hitchen, Ken (2009-09-21). JNCC Offshore Natura Survey : Anton Dohrn Seamount and East Rockall Bank areas of search : 2009/03-JNCC Cruise Report (PDF) (Report). Joint Nature Conservation Committee. Retrieved 2020-02-22.
{{cite report}}: Invalid|ref=harv(help) - Stoker, M. S.; Weering, T. C. E. Van; Svaerdborg, T. (1 January 2001). "A Mid- to Late Cenozoic tectonostratigraphic framework for the Rockall Trough". Geological Society, London, Special Publications. 188 (1): 411–438. doi:10.1144/GSL.SP.2001.188.01.26. ISSN 0305-8719.
{{cite journal}}: Invalid|ref=harv(help)