Editing Abyssal plain

{{Short description|Flat area on the deep ocean floor}}
{{Use dmy dates|date=June 2019}}
{{Good article}}
[[File:Oceanic basin.svg|thumb|right|Diagrammatic cross-section of an [[oceanic basin]], showing the relationship of the abyssal plain to a [[Continental shelf#Topography|continental rise]] and an [[oceanic trench]]]]
[[File:Oceanic divisions.svg|thumb|Depiction of the [[abyssal zone]] in relation to other major [[oceanic zone]]s]]
{{aquatic layer topics}}

An '''abyssal plain''' is an underwater [[plain]] on the deep [[ocean floor]], usually found at depths between {{convert|3000|and|6000|m}}. Lying generally between the foot of a [[continental rise]] and a [[mid-ocean ridge]], abyssal plains cover more than 50% of the [[Earth]]'s surface.<ref name=CRS2008>{{Cite journal
|author1=Craig R. Smith
|author2=Fabio C. De Leo
|author3=Angelo F. Bernardino
|author4=Andrew K. Sweetman
|author5=Pedro Martinez Arbizu
|title=Abyssal food limitation, ecosystem structure and climate change
|journal=Trends in Ecology and Evolution
|volume=23
|pages=518–528
|year=2008
|url=http://cmbc.ucsd.edu/Students/Current_Students/SIO277/Smith%20et%20al.%20TREE%202008.pdf
|pmid=18584909
|issue=9
|doi=10.1016/j.tree.2008.05.002
|access-date=18 June 2010
|archive-date=20 July 2011
|archive-url=https://web.archive.org/web/20110720075942/http://cmbc.ucsd.edu/Students/Current_Students/SIO277/Smith%20et%20al.%20TREE%202008.pdf
|url-status=dead
}}</ref><ref name=Vino1997>{{Cite book
|author=N.G. Vinogradova
|title=The Biogeography of the Oceans
|chapter=Zoogeography of the Abyssal and Hadal Zones
|volume=32
|pages=325–387
|year=1997
|doi=10.1016/S0065-2881(08)60019-X
|series=Advances in Marine Biology
|isbn=9780120261321}}</ref> They are among the flattest, smoothest, and least explored regions on Earth.<ref name=Weaver>{{Cite book
 |title       = Geology and Geochemistry of Abyssal Plains
 |author1     = P.P.E. Weaver
 |author2     = J. Thomson
 |author3     = P. M. Hunter
 |year        = 1987
 |publisher   = Blackwell Scientific Publications
 |location    = Oxford
 |page        = x
 |isbn        = 978-0-632-01744-7
 |url         = http://sp.lyellcollection.org/cgi/issue_pdf/frontmatter_pdf/31/1.pdf
 |access-date  = 18 June 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20101224060317/http://sp.lyellcollection.org/cgi/issue_pdf/frontmatter_pdf/31/1.pdf
 |archive-date = 24 December 2010
}}</ref> Abyssal plains are key geologic elements of [[oceanic basin]]s. (the other elements being an elevated mid-ocean ridge and flanking [[abyssal hill]]s)

The creation of the abyssal plain is the result of the spreading of the seafloor (plate tectonics) and the melting of the lower [[oceanic crust]]. Magma rises from above the [[asthenosphere]] (a layer of the upper [[Mantle (geology)|mantle]]), and as this [[basalt]]ic material reaches the surface at mid-ocean ridges, it forms new oceanic crust, which is constantly pulled sideways by spreading of the seafloor. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained [[sediment]]s, mainly [[clay]] and [[silt]]. Much of this sediment is deposited by [[turbidity current]]s that have been channelled from the [[continental margin]]s along [[submarine canyon]]s into deeper water. The rest is composed chiefly of [[pelagic sediments]]. Metallic [[Manganese nodule|nodules]] are common in some areas of the plains, with varying concentrations of metals, including [[manganese]], [[iron]], [[nickel]], [[cobalt]], and [[copper]]. There are also amounts of carbon, nitrogen, phosphorus and silicon, due to material that comes down and decomposes.

Owing in part to their vast size, abyssal plains are believed to be major reservoirs of [[biodiversity]]. They also exert significant influence upon ocean [[Carbon cycle|carbon cycling]], dissolution of [[calcium carbonate]], and [[Carbon dioxide in Earth's atmosphere|atmospheric CO<sub>2</sub> concentrations]] over [[Geologic time scale|time scales]] of a hundred to a thousand years. The structure of abyssal [[ecosystem]]s is strongly influenced by the rate of [[marine snow|flux of food]] to the seafloor and the composition of the material that settles. Factors such as [[climate change]], [[Trawling|fishing practices]], and [[Ocean nourishment|ocean fertilization]] have a substantial effect on patterns of [[primary production]] in the [[photic zone|euphotic zone]].<ref name="CRS2008"/><ref>{{harvnb|Smith|Paterson|Lambshead|Glover|Gooday|Rogers|Sibuet|Kitazato|Galéron|Menot|2008|p=5}}</ref> Animals absorb dissolved oxygen from the oxygen-poor waters. Much dissolved oxygen in abyssal plains came from polar regions that had melted long ago. Due to scarcity of oxygen, abyssal plains are inhospitable for organisms that would flourish in the oxygen-enriched waters above. [[Deep-water coral|Deep sea coral reefs]] are mainly found in depths of 3,000 meters and deeper in the abyssal and [[hadal zone]]s.

Abyssal plains were not recognized as distinct [[physiographic]] features of the [[Seabed|sea floor]] until the late 1940s and, until recently, none had been studied on a systematic basis. They are poorly preserved in the [[Geologic record|sedimentary record]], because they tend to be consumed by the subduction process. Due to darkness and a water pressure that can reach about 750 times atmospheric pressure (76 megapascal), abyssal plains are not well explored.

==Oceanic zones==
{{Main|Oceanic zone}}
[[File:Pelagiczone.svg|thumb|Pelagic zones]]

The ocean can be conceptualized as [[oceanic zone|zones]], depending on depth, and presence or absence of [[sunlight]]. Nearly all [[Organism|life forms]] in the ocean depend on the [[photosynthetic]] activities of [[phytoplankton]] and other marine [[plant]]s to convert [[carbon dioxide]] into [[Total organic carbon|organic carbon]], which is the basic building block of [[organic matter]]. Photosynthesis in turn requires energy from sunlight to drive the chemical reactions that produce organic carbon.<ref name=PNAS2009>{{Cite journal
|author1=K.L. Smith Jr |author2=H.A. Ruhl |author3=B.J. Bett |author4=D.S.M. Billett |author5=R.S. Lampitt |author6=R.S. Kaufmann |title=Climate, carbon cycling, and deep-ocean ecosystems
|journal=PNAS
|volume=106
|issue=46
|pages=19211–19218
|date=17 November 2009
|doi=10.1073/pnas.0908322106
|pmid=19901326
|pmc=2780780
|bibcode = 2009PNAS..10619211S |doi-access=free }}</ref>

The stratum of the [[water column]] nearest the surface of the ocean ([[sea level]]) is referred to as the [[photic zone]]. The photic zone can be subdivided into two different vertical regions. The uppermost portion of the photic zone, where there is adequate light to support photosynthesis by phytoplankton and plants, is referred to as the [[euphotic zone]] (also referred to as the ''[[Pelagic zone#Epipelagic (sunlight)|epipelagic zone]]'', or ''surface zone'').<ref name="Csirke 1997 4">{{harvnb|Csirke|1997|p=4.}}</ref> The lower portion of the photic zone, where the light intensity is insufficient for photosynthesis, is called the [[mesopelagic zone|dysphotic zone]] (dysphotic means "poorly lit" in Greek).<ref name=Britann>{{cite encyclopedia
|author=Encyclopædia Britannica
|year=2010
|url=http://www.britannica.com/EBchecked/topic/457662/photic-zone
|title=Photic zone
|encyclopedia=Encyclopædia Britannica
|access-date=18 June 2010}}</ref> The dysphotic zone is also referred to as the ''mesopelagic zone'', or the ''twilight zone''.<ref name=enchantedlearning>{{Cite web
|author=Jeananda Col
|year=2004
|url=http://www.enchantedlearning.com/biomes/ocean/twilight/
|title=Twilight Ocean (Disphotic) Zone
|publisher=EnchantedLearning.com
|access-date=18 June 2010}}</ref> Its lowermost boundary is at a [[thermocline]] of {{convert|12|C|F}}, which, in the [[tropics]] generally lies between 200 and 1,000&nbsp;metres.<ref name=Buesseler>{{Cite journal
|author1=Ken O. Buesseler |author2=Carl H. Lamborg |author3=Philip W. Boyd |author4=Phoebe J. Lam |title=Revisiting Carbon Flux Through the Ocean's Twilight Zone
|journal=Science
|volume=316
|issue=5824
|pages=567–570
|date=27 April 2007
|doi=10.1126/science.1137959
|pmid=17463282
|bibcode=2007Sci...316..567B|display-authors=etal|citeseerx=10.1.1.501.2668 |s2cid=8423647 }}</ref>

The euphotic zone is somewhat arbitrarily defined as extending from the surface to the depth where the light intensity is approximately 0.1–1% of surface sunlight [[Insolation|irradiance]], depending on [[season]], [[latitude]] and degree of water [[turbidity]].<ref name="Csirke 1997 4"/><ref name=Britann/> In the clearest ocean water, the euphotic zone may extend to a depth of about 150&nbsp;metres,<ref name="Csirke 1997 4"/> or rarely, up to 200&nbsp;metres.<ref name=enchantedlearning/> [[Solution (chemistry)|Dissolved substances]] and [[Suspension (chemistry)|solid particles]] absorb and scatter light, and in coastal regions the high concentration of these substances causes light to be attenuated rapidly with depth. In such areas the euphotic zone may be only a few tens of metres deep or less.<ref name="Csirke 1997 4"/><ref name=enchantedlearning/> The dysphotic zone, where light intensity is considerably less than 1% of surface irradiance, extends from the base of the euphotic zone to about 1,000&nbsp;metres.<ref name=Buesseler/> Extending from the bottom of the photic zone down to the [[seabed]] is the [[aphotic zone]], a region of perpetual darkness.<ref name=enchantedlearning/><ref name=Buesseler/>

Since the average depth of the ocean is about 4,300&nbsp;metres,<ref name=NOAA2008>{{Cite web
|author1=[[National Oceanic and Atmospheric Administration]]
|date=2 December 2008
|url=http://oceanservice.noaa.gov/facts/oceandepth.html
|title=How deep is the ocean?
|publisher=[[National Oceanic and Atmospheric Administration]]
|location=Washington, DC
|access-date=19 June 2010| archive-url= https://web.archive.org/web/20100623180747/http://oceanservice.noaa.gov/facts/oceandepth.html| archive-date= 23 June 2010 | url-status= live}}</ref> the photic zone represents only a tiny fraction of the ocean's total volume. However, due to its capacity for photosynthesis, the photic zone has the greatest biodiversity and [[Biomass (ecology)|biomass]] of all oceanic zones. Nearly all primary production in the ocean occurs here. Life forms which inhabit the aphotic zone are often capable of [[Diel vertical migration|movement upwards through the water column]] into the photic zone for feeding. Otherwise, they must rely on [[marine snow|material sinking from above]],<ref name=CRS2008/> or find another source of energy and nutrition, such as occurs in [[chemosynthetic]] [[archaea]] found near [[hydrothermal vent]]s and [[cold seep]]s.

The aphotic zone can be subdivided into three different vertical regions, based on depth and temperature. First is the [[bathyal zone]], extending from a depth of 1,000&nbsp;metres down to 3,000&nbsp;metres, with water temperature decreasing from {{convert|12|°C|°F|abbr=on}} to {{convert|4|°C|°F|abbr=on}} as depth increases.<ref name=Morelle2008>{{cite news
|author=Rebecca Morelle
|author-link=Rebecca Morelle
|date=7 October 2008
|url=http://news.bbc.co.uk/2/hi/science/nature/7655358.stm
|title='Deepest ever' living fish filmed
|publisher=BBC News
|access-date=18 June 2010| archive-url= https://web.archive.org/web/20100730022055/http://news.bbc.co.uk/2/hi/science/nature/7655358.stm| archive-date= 30 July 2010 | url-status= live}}</ref> Next is the [[abyssal zone]], extending from a depth of 3,000&nbsp;metres down to 6,000&nbsp;metres.<ref name=Morelle2008/> The final zone includes the deep oceanic trenches, and is known as the [[hadal zone]]. This, the deepest oceanic zone, extends from a depth of 6,000&nbsp;metres down to approximately 11,034 meters, at the very bottom of the Mariana Trench, the deepest point on planet Earth.<ref name=Vino1997/><ref name=Morelle2008/> Abyssal plains are typically in the abyssal zone, at depths from 3,000 to 6,000&nbsp;metres.<ref name=CRS2008/>

The table below illustrates the classification of oceanic zones:
{|class="wikitable"
|-
!Zone
!Subzone (common name)
!Depth of zone
!Water temperature
!Comments
|-
|rowspan="2"| [[Photic zone|photic]]
| [[Photic zone|euphotic]] (epipelagic zone)
| 0–200&nbsp;metres
| highly variable
|
|-
| [[Mesopelagic zone|disphotic]] (mesopelagic zone, or twilight zone)
| 200–1,000&nbsp;metres
| {{convert|4|°C|°F|abbr=on|disp=or}} – highly variable
|
|-
|rowspan="3"| [[Aphotic zone|aphotic]]
| [[Bathyal zone|bathyal]]
| 1,000–3,000&nbsp;metres
| {{convert|4|-|12|°C|°F|abbr=on|disp=or}}
|
|-
| [[Abyssal zone|abyssal]]
| 3,000–6,000&nbsp;metres
| {{convert|0|-|4|°C|°F|0|abbr=on|disp=or}}<ref>[http://www.britannica.com/EBchecked/topic/2489/abyssal-zone Britannica]</ref>
| water temperature may reach as high as {{convert|464|°C|°F|abbr=on}} near [[hydrothermal vent]]s<ref name=Haas2007>{{Cite journal
|author=Haase, K. M.
|title=Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge
|journal=Geochem. Geophys. Geosyst.
|volume=8
|issue=Q11002
|pages=17
|date=13 November 2007
|doi=10.1029/2006GC001509
|bibcode=2007GGG.....811002H
|display-authors=etal
|doi-access=free
}}</ref><ref name=Andrea2008>{{Cite journal
|author1=Andrea Koschinsky |author2=Dieter Garbe-Schönberg |author3=Sylvia Sander |author4=Katja Schmidt |author5=Hans-Hermann Gennerich |author6=Harald Strauss |title=Hydrothermal venting at pressure-temperature conditions above the critical point of seawater, 5°S on the Mid-Atlantic Ridge
|journal=Geology
|volume=36
|issue=8
|pages=615–618
|date = August 2008
|doi=10.1130/G24726A.1
|bibcode = 2008Geo....36..615K }}</ref><ref name=Kosch2008>{{cite magazine
|author=Catherine Brahic
|date=4 August 2008
|url=https://www.newscientist.com/article/dn14456-found-the-hottest-water-on-earth.html
|title=Found: The hottest water on Earth
|magazine=New Scientist
|access-date=18 June 2010}}</ref><ref name=Hill2008>{{Cite web
|author=Josh Hill
|date=5 August 2008
|url=http://www.dailygalaxy.com/my_weblog/2008/08/extreme-water-f.html
|title='Extreme Water' Found at Atlantic Ocean Abyss
|publisher=The Daily Galaxy
|access-date=18 June 2010
|archive-date=7 November 2017
|archive-url=https://web.archive.org/web/20171107004546/http://www.dailygalaxy.com/my_weblog/2008/08/extreme-water-f.html
|url-status=dead
}}</ref><ref name=Karst2009>{{Cite journal
|author1=Karsten M. Haase |author2=Sven Petersen |author3=Andrea Koschinsky |author4=Richard Seifert |author5=Colin W. Devey |title=Fluid compositions and mineralogy of precipitates from Mid Atlantic Ridge hydrothermal vents at 4°48'S
|year=2009
|publisher=Publishing Network for Geoscientific & Environmental Data (PANGAEA)
|location=Germany
|doi=10.1594/PANGAEA.727454
|journal=[[PANGAEA (data library)|PANGAEA]]
|display-authors=etal}}</ref>
|-
| [[Hadal zone|hadal]]
| below 6,000&nbsp;metres<ref name=Jame>{{Cite journal
|author1=Alan J. Jamieson
|author2=Toyonobu Fujii
|author3=Daniel J. Mayor
|author4=Martin Solan
|author5=Imants G. Priede
|title=Hadal trenches: the ecology of the deepest places on Earth
|journal=Trends in Ecology and Evolution
|volume=25
|issue=3
|pages=190–197
|date=March 2010
|doi=10.1016/j.tree.2009.09.009
|url=http://cmbc.ucsd.edu/Students/Current_Students/SIO277/jamieson.Trenches.pdf
|pmid=19846236
|access-date=18 June 2010
|archive-date=20 July 2011
|archive-url=https://web.archive.org/web/20110720080131/http://cmbc.ucsd.edu/Students/Current_Students/SIO277/jamieson.Trenches.pdf
|url-status=dead
}}</ref>
| {{convert|1|-|2.5|°C|°F|0|abbr=on|disp=or}}<ref name=ucsd>{{Cite web
|author1=Center for Marine Biodiversity and Conservation
|url=http://cmbc.ucsd.edu/Students/Current_Students/SIO277/Trenches.pdf
|title=The Hadal Zone: ''Deep-sea Trenches''
|publisher=[[Scripps Institution of Oceanography]]
|location=[[University of California, San Diego]]
|access-date=18 June 2010
|archive-date=20 July 2011
|archive-url=https://web.archive.org/web/20110720080126/http://cmbc.ucsd.edu/Students/Current_Students/SIO277/Trenches.pdf
|url-status=dead
}}</ref>
| ambient water temperature increases below 4000&nbsp;metres due to [[Adiabatic heating#Adiabatic heating and cooling|adiabatic heating]]<ref name=ucsd />
|-
|}

==Formation==
{{See also|Plate tectonics|Mantle convection}}
[[File:Tectonic plate boundaries.png|thumb|[[Oceanic crust]] is formed at a [[mid-ocean ridge]], while the [[lithosphere]] is [[subducted]] back into the [[asthenosphere]] at [[oceanic trench]]es]]
[[File:Earth seafloor crust age 1996 - 2.png|thumb|Age of oceanic crust (red is youngest, and blue is oldest)]]

Oceanic crust, which forms the [[bedrock]] of abyssal plains, is continuously being created at mid-ocean ridges (a type of [[divergent boundary]]) by a process known as [[Igneous rock#Decompression|decompression melting]].<ref name=Wilson1993>{{Cite book|isbn=978-0-412-53310-5|author=Marjorie Wilson|year=1993|publisher=Chapman & Hall|location=London|title=Igneous petrogenesis|author-link=Marjorie Wilson}}</ref> [[mantle plume|Plume]]-related decompression melting of solid mantle is responsible for creating ocean islands like the [[Hawaiian islands]], as well as the ocean crust at mid-ocean ridges. This phenomenon is also the most common explanation for [[flood basalt]]s and [[oceanic plateau]]s (two types of [[large igneous province]]s). Decompression melting occurs when the upper [[Mantle (geology)|mantle]] is [[partial melting|partially melted]] into [[magma]] as it moves upwards under mid-ocean ridges.<ref name=White2001>{{Cite journal
|author1=R.S. WHITE |author2=T.A. MINSHULL |author3=M.J. BICKLE |author4=C.J. ROBINSON |title=Melt Generation at Very Slow-Spreading Oceanic Ridges: Constraints from Geochemical and Geophysical Data
|journal=Journal of Petrology
|volume=42
|issue=6
|pages=1171–1196
|year=2001
|doi=10.1093/petrology/42.6.1171
|bibcode=2001JPet...42.1171W|doi-access=free
}}</ref><ref name=Wilson>{{Cite book
|title=Understanding the Earth
|author1=Geoff C. Brown |author2=C. J. Hawkesworth |author3=R. C. L. Wilson |page=93
|url=https://books.google.com/books?id=Kgk4AAAAIAAJ&pg=PA93
|isbn=978-0-521-42740-1
|edition=2nd
|year=1992
|publisher=Cambridge University Press}}</ref> This upwelling magma then cools and solidifies by [[Conduction (heat)|conduction]] and [[convection]] of heat to form new [[oceanic crust]]. [[Accretion (geology)|Accretion]] occurs as mantle is added to the growing edges of a [[Plate tectonics|tectonic plate]], usually associated with [[seafloor spreading]]. The age of oceanic crust is therefore a function of distance from the mid-ocean ridge.<ref>{{harvnb|Condie|1997|p=50.}}</ref> The youngest oceanic crust is at the mid-ocean ridges, and it becomes progressively older, cooler and denser as it migrates outwards from the mid-ocean ridges as part of the process called [[mantle convection]].<ref name="University of Winnipeg">Kobes, Randy and Kunstatter, Gabor.[http://theory.uwinnipeg.ca/mod_tech/node195.html Mantle Convection] {{Webarchive|url=https://web.archive.org/web/20110114151750/http://theory.uwinnipeg.ca/mod_tech/node195.html |date=14 January 2011 }}. Physics Department, University of Winnipeg. Retrieved 23 June 2010.</ref>

The [[lithosphere]], which rides atop the [[asthenosphere]], is divided into a number of tectonic plates that are continuously being created and consumed at their opposite [[Plate boundaries#Types of plate boundaries|plate boundaries]]. Oceanic crust and tectonic plates are formed and move apart at mid-ocean ridges. Abyssal hills are formed by stretching of the oceanic lithosphere.<ref name=Buck1998>{{Cite journal
|author1=W. Roger Buck |author2=Alexei N. B. Poliakov |title=Abyssal hills formed by stretching oceanic lithosphere
|journal=Nature
|volume=392
|pages=272–275
|date=19 March 1998
|doi=10.1038/32636
|issue=6673|bibcode = 1998Natur.392..272B |s2cid=4422877 }}</ref> Consumption or destruction of the oceanic lithosphere occurs at [[oceanic trenches]] (a type of [[convergent boundary]], also known as a destructive plate boundary) by a process known as [[subduction]]. Oceanic trenches are found at places where the oceanic lithospheric slabs of two different plates meet, and the denser (older) slab begins to descend back into the mantle.<ref>{{harvnb|Condie|1997|p=83.}}</ref> At the consumption edge of the plate (the oceanic trench), the oceanic lithosphere has thermally contracted to become quite dense, and it sinks under its own weight in the process of subduction.<ref name=Olson1>
{{Cite book
|title=Mantle convection in the earth and planets
|author1=Gerald Schubert |author2=Donald Lawson Turcotte |author3=Peter Olson |chapter-url=https://books.google.com/books?id=ij4BaFFpYHAC&pg=PA16
|page=16 ''ff''
|chapter=Chapter 2: Plate tectonics
|isbn=978-0-521-79836-5
|year=2001
|publisher=Cambridge University Press}}
</ref> The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old.<ref name=DSDP>{{Cite web
|year=2010
|url=http://www.deepseadrilling.org/about.htm
|title=About the Deep Sea Drilling Project
|publisher=Deep Sea Drilling Project
|location=[[Texas A&M University]], [[College Station, Texas|College Station]], [[Texas]]
|access-date=24 June 2010}}</ref> The overall process of repeated cycles of creation and destruction of oceanic crust is known as the [[Supercontinent cycle]], first proposed by [[Canadians|Canadian]] [[geophysicist]] and [[geologist]] [[John Tuzo Wilson]].

New oceanic crust, closest to the mid-oceanic ridges, is mostly basalt at shallow levels and has a rugged [[topography]]. The roughness of this topography is a function of the rate at which the mid-ocean ridge is spreading (the spreading rate).<ref name=Small1992>{{Cite journal
|author1=Christopher Small |author2=David T. Sandwell |title=An analysis of ridge axis gravity roughness and spreading rate
|journal=Journal of Geophysical Research
|volume=97
|issue=B3
|pages=3235–3245
|date=10 March 1992
|url=http://topex.ucsd.edu/sandwell/publications/49.pdf
|access-date=23 June 2010
|doi=10.1029/91JB02465
|bibcode=1992JGR....97.3235S}}</ref> Magnitudes of spreading rates vary quite significantly. Typical values for fast-spreading ridges are greater than 100&nbsp;mm/yr, while slow-spreading ridges are typically less than 20&nbsp;mm/yr.<ref name=White2001/> Studies have shown that the slower the spreading rate, the rougher the new oceanic crust will be, and vice versa.<ref name=Small1992/> It is thought this phenomenon is due to [[Fault (geology)|faulting]] at the mid-ocean ridge when the new oceanic crust was formed.<ref name=Buck2005>{{Cite journal
|author1=W. Roger Buck |author2=Luc L. Lavier |author3=Alexei N.B. Poliakov |title=Modes of faulting at mid-ocean ridges
|journal=Nature
|volume=434
|pages=719–723
|date=7 April 2005
|doi=10.1038/nature03358
|pmid=15815620
|issue=7034
|bibcode = 2005Natur.434..719B |s2cid=4320966 |url=https://resolver.caltech.edu/CaltechAUTHORS:20150319-085050879 }}</ref> These faults pervading the oceanic crust, along with their bounding abyssal hills, are the most common tectonic and topographic features on the surface of the Earth.<ref name=Buck1998/><ref name=Buck2005/> The process of seafloor spreading helps to explain the concept of [[continental drift]] in the theory of plate tectonics.

The flat appearance of mature abyssal plains results from the blanketing of this originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt. Much of this sediment is deposited from turbidity currents that have been channeled from the continental margins along submarine canyons down into deeper water. The remainder of the sediment comprises chiefly dust (clay particles) blown out to sea from land, and the remains of small [[Phytoplankton|marine plants]] and [[Zooplankton|animals]] which sink from the upper layer of the ocean, known as [[pelagic sediments]]. The total sediment deposition rate in remote areas is estimated at two to three centimeters per thousand years.<ref name=Kuenen1946>{{Cite journal
|author=Philip Henry Kuenen
|title=Rate and mass of deep-sea sedimentation
|journal=American Journal of Science
|volume=244
|pages=563–572
|date = August 1946
|doi=10.2475/ajs.244.8.563|issue=8|bibcode=1946AmJS..244..563K
|doi-access=free
}}</ref><ref name=DSDP1972>{{Cite book
|title=Initial Reports of the Deep Sea Drilling Project, Volume XII (covering Leg 12 of the cruises of the Drilling Vessel Glomar Challenger)
|volume=12 |editor=Laughton, A. S. |editor2=Berggren, W. A.
|author1=T.A. Davies |author2=A.S. Laughton |chapter=Chapter 11. Sedimentary Processes in the North Atlantic
|page=915
|chapter-url=http://www.deepseadrilling.org/12/volume/dsdp12_11.pdf
|issn=1936-7392
|year=1972
|publisher=U.S. Government Printing Office
|location=Washington, D.C.
|doi=10.2973/dsdp.proc.12.111.1972
|access-date=24 June 2010|display-editors=etal}}</ref> Sediment-covered abyssal plains are less common in the Pacific Ocean than in other major ocean basins because sediments from turbidity currents are trapped in oceanic trenches that border the Pacific Ocean.<ref name=Underwood1986>{{Cite journal
|author1=Michael B. Underwood |author2=Charles R. Norville |title=Deposition of sand in a trench-slope basin by unconfined turbidity currents
|journal=Marine Geology
|volume=71
|issue=3–4
|pages=383–392
|date = May 1986
|doi=10.1016/0025-3227(86)90080-0|bibcode=1986MGeol..71..383U}}</ref>

Abyssal plains are typically covered by deep sea, but during parts of the [[Messinian salinity crisis]] much of the [[Mediterranean Sea]]'s abyssal plain was exposed to air as an empty deep hot dry salt-floored sink.<ref name=Krijgsman1996>{{cite journal
|author=Krijgsman W|author2=Garcés M|author3=Langereis CG|author4=Daams R|author5=Van Dam J|title=A new chronology for the middle to late Miocene continental record in Spain
|journal=Earth and Planetary Science Letters
|volume=142
|issue=3–4
|pages=367–380
|year=1996
|doi=10.1016/0012-821X(96)00109-4
|bibcode=1996E&PSL.142..367K|url=http://doc.rero.ch/record/13400/files/PAL_E203.pdf |display-authors=etal}}</ref><ref name=Clauzon1996>{{cite journal
|vauthors=Clauzon G, Suc JP, Gautier F, Berger A, Loutre MF |title=Alternate interpretation of the Messinian salinity crisis: Controversy resolved?
|journal=Geology
|volume=24
|issue=4
|pages=363–6
|year=1996
|doi=10.1130/0091-7613(1996)024<0363:AIOTMS>2.3.CO;2
|bibcode = 1996Geo....24..363C }}</ref><ref name=Vandijk1998>{{cite journal
|vauthors=van Dijk JP, Barberis A, Cantarella G, Massa E |title=Central Mediterranean Messinian basin evolution. Tectono-eustasy or eustato-tectonics?
|journal=Annales Tectonicae
|volume=12
|issue=1–2
|pages=7–27
|year=1998}}</ref><ref>{{cite journal
|vauthors=Bachea F, Olivet JL, Gorini C, Rabineaua M, Baztan J |title=Messinian erosional and salinity crises: View from the Provence Basin (Gulf of Lions, Western Mediterranean)
|journal=Earth and Planetary Science Letters
|volume=286
|issue=1–2
|pages=139–57
|year=2009
|doi=10.1016/j.epsl.2009.06.021
|url=http://archimer.ifremer.fr/doc/2009/publication-6870.pdf
|access-date=1 October 2010
|bibcode=2009E&PSL.286..139B|s2cid=30843908
|display-authors=etal}}</ref>

==Discovery==
{{See also|Bathymetry}}
[[File:Marianatrenchmap.png|thumb|right|Location of the [[Challenger Deep]] in the [[Mariana Trench]]]]

The landmark scientific [[Challenger expedition|expedition]] (December 1872 – May 1876) of the British [[Royal Navy]] survey ship [[HMS Challenger (1858)|HMS ''Challenger'']] yielded a tremendous amount of [[Bathymetry|bathymetric]] data, much of which has been confirmed by subsequent researchers. Bathymetric data obtained during the course of the Challenger expedition enabled scientists to draw maps,<ref name=Murray1891>{{Cite book
|author1=John Murray |author2=A.F. Renard |title=Report of the scientific results of the voyage of H.M.S. Challenger during the years 1873 to 1876
|publisher=Her Majesty's Stationery Office
|location=London
|year=1891
|url=http://www.19thcenturyscience.org/HMSC/HMSC-Reports/map-800/b-200.jpg
|access-date=26 June 2010}}{{page needed|date=December 2013}}</ref> which provided a rough outline of certain major submarine terrain features, such as the edge of the [[continental shelves]] and the [[Mid-Atlantic Ridge]]. This discontinuous set of data points was obtained by the simple technique of taking [[Sounding line|soundings]] by lowering long lines from the ship to the seabed.<ref name=Murray_Deepsea>{{Cite book
 |author1      = John Murray
 |author2      = A.F. Renard
 |title        = Report on the Deepsea Deposits based on the Specimens Collected during the Voyage of H.M.S. Challenger in the years 1873 to 1876
 |publisher    = Her Majesty's Stationery Office
 |location     = London
 |year         = 1891
 |url          = http://www.19thcenturyscience.org/HMSC/HMSC-Reports/1891-DeepSeaDeposits/htm/doc.html
 |access-date   = 26 June 2010
 |archive-url  = https://web.archive.org/web/20110724205544/http://www.19thcenturyscience.org/HMSC/HMSC-Reports/1891-DeepSeaDeposits/htm/doc.html
 |archive-date = 24 July 2011
 |url-status     = dead
}}{{page needed|date=December 2013}}</ref>

The Challenger expedition was followed by the 1879–1881 expedition of the [[USS Jeannette (1878)|''Jeannette'']], led by [[United States Navy]] Lieutenant [[George Washington DeLong]]. The team sailed across the [[Chukchi Sea]] and recorded [[meteorological]] and [[astronomical]] data in addition to taking soundings of the seabed. The ship became trapped in the [[Sea ice|ice pack]] near [[Wrangel Island]] in September 1879, and was ultimately crushed and sunk in June 1881.<ref>{{Cite book
 |author=Naval Historical Center 
 |title=Dictionary of American Naval Fighting Ships, Volume 3, G-K 
 |editor=James L. Mooney 
 |chapter=''Jeannette'' 
 |publisher=Defense Department, [[United States Department of the Navy|Department of the Navy]], Naval History Division 
 |location=Washington DC 
 |date=1977 
 |orig-year=First published in 1968 
 |isbn=978-0-16-002019-3 
 |oclc=2794587 
 |chapter-url=http://www.history.navy.mil/danfs/j2/jeannette.htm 
 |access-date=26 June 2010 
 |author-link=Naval History & Heritage Command 
 |archive-url=https://web.archive.org/web/20100708095936/http://www.history.navy.mil/danfs/j2/jeannette.htm 
 |archive-date=8 July 2010 
 |url-status=dead 
}}</ref>

The ''Jeannette'' expedition was followed by the 1893–1896 Arctic [[Nansen's Fram expedition|expedition]] of [[Norwegians|Norwegian]] explorer [[Fridtjof Nansen]] aboard the ''[[Fram (ship)|Fram]]'', which proved that the [[Arctic Ocean]] was a deep oceanic basin, uninterrupted by any significant land masses north of the [[Eurasia]]n continent.<ref name=Aber2006>{{Cite web
|author=James S. Aber
|title=History of Geology: Fridtjof Nansen
|url=http://academic.emporia.edu/aberjame/histgeol/nansen/nansen.htm
|publisher=[[Emporia State University]]
|location=[[Emporia, Kansas]]
|year=2006
|access-date=26 June 2010
|archive-url=https://web.archive.org/web/20090416163515/http://academic.emporia.edu/aberjame/histgeol/nansen/nansen.htm
|archive-date=16 April 2009
|url-status=dead
}}</ref>
<ref name=Krishfield>{{Cite web
|last=Krishfield|first=Rick
|title=Nansen and the Drift of the Fram (1893–1896)
|url=http://www.whoi.edu/beaufortgyre/history/history_fram.html|publisher= [[Woods Hole Oceanographic Institution]]
|work=Beaufort Gyre Exploration Project
|access-date=26 June 2010}}</ref>

Beginning in 1916, Canadian physicist [[Robert William Boyle]] and other scientists of the Anti-Submarine Detection Investigation Committee ([[ASDIC]]) undertook research which ultimately led to the development of [[sonar]] technology. [[Echo sounding|Acoustic sounding]] equipment was developed which could be operated much more rapidly than the sounding lines, thus enabling the [[German Meteor expedition]] aboard the German research vessel [[Meteor (1915)|Meteor]] (1925–27) to take frequent soundings on east-west Atlantic transects. Maps produced from these techniques show the major Atlantic basins, but the depth precision of these early instruments was not sufficient to reveal the flat featureless abyssal plains.<ref name=Maurer1933>{{Cite journal
|author1=Hans Maurer |author2=Theodor Stocks |title=Die Echolotengen des 'Meteor' Deutschen Atlantischen Exped. Meteor, 1925–1927
|journal=Wissenschaftliche Ergebnisse
|volume=2
|pages=458–460
|date=May–June 1933
|issue=5
|jstor=1786634}}</ref><ref name=Stocks1935>{{Cite journal
|author1=Theodor Stocks |author2=Georg Wust |title=Die Tiefenverhaltnisse des offenen Atlantischen Ozeans: Deutsche Atlantischen Exped. Meteor, 1925–1927
|journal=Wissenschaftliche Ergebnisse
|volume=3
|pages=1–31
|year=1935
|url=http://www.photolib.noaa.gov/htmls/map00085.htm
|access-date=26 June 2010}}</ref>

As technology improved, measurement of depth, [[latitude]] and [[longitude]] became more precise and it became possible to collect more or less continuous sets of data points. This allowed researchers to draw accurate and detailed maps of large areas of the ocean floor. Use of a continuously recording [[Fishfinder|fathometer]] enabled Tolstoy & Ewing in the summer of 1947 to identify and describe the first abyssal plain. This plain, south of [[Newfoundland and Labrador|Newfoundland]], is now known as the [[Sohm Abyssal Plain]].<ref name=Tolstoy1949>{{Cite journal
|author1=Ivan Tolstoy |author2=Maurice Ewing |title=North Atlantic hydrography and the mid-Atlantic Ridge
|journal=Geological Society of America Bulletin
|volume=60
|issue=10
|pages=1527–40
|date = October 1949
|doi=10.1130/0016-7606(1949)60[1527:NAHATM]2.0.CO;2
|issn=0016-7606
|bibcode = 1949GSAB...60.1527T }}</ref> Following this discovery many other examples were found in all the oceans.<ref name=Heezen1951>{{Cite journal
|author1=Bruce C. Heezen |author2=Maurice Ewing |author3=D.B. Ericson |title=Submarine topography in the North Atlantic
|journal=Geological Society of America Bulletin
|volume=62
|issue=12
|pages=1407–1417
|date=December 1951
|doi=10.1130/0016-7606(1951)62[1407:STITNA]2.0.CO;2
|issn=0016-7606
|bibcode = 1951GSAB...62.1407H }}</ref><ref name=Heezen1954>{{Cite journal
|author1=Bruce C. Heezen |author2=D.B. Ericson |author3=Maurice Ewing |title=Further evidence for a turbidity current following the 1929 Grand banks earthquake
|journal=Deep-Sea Research
|volume=1
|issue=4
|pages=193–202
|date = July 1954
|doi=10.1016/0146-6313(54)90001-5
|bibcode = 1954DSR.....1..193H }}</ref><ref name=Koczy1954>{{Cite journal
|author=F.F. Koczy
|title=A survey on deep-sea features taken during the Swedish deep-sea expedition
|journal=Deep-Sea Research
|volume=1
|issue=3
|pages=176–184
|year=1954
|doi=10.1016/0146-6313(54)90047-7
|bibcode = 1954DSR.....1..176K }}</ref><ref name=Heezen1962>{{Cite book
|author1=Bruce C. Heezen |title=Heezen, Bruce C., Marie Tharp, and Maurice Ewing: The Floors of the Oceans. I. The North Atlantic. Text to Accompany the Physiographic Diagram of the North Atlantic. With 49 fig., 30 plates. – New York, N.Y.: The Geological Society of America, Special Paper 65, 1959. 122 p. $10.00 |journal=Internationale Revue der Gesamten Hydrobiologie und Hydrographie |author2=Marie Tharp |author3=Maurice Ewing |chapter=The Floors of the Oceans. I. The North Atlantic. Text to Accompany the Physiographic Diagram of the North Atlantic
|editor=H. Caspers
|publisher=WILEY-VCH Verlag GmbH & Company
|location=Weinheim
|volume=47
|issue=3
|pages=487
|year=1962
|doi=10.1002/iroh.19620470311}}</ref><ref name=Heezen1963>{{Cite book
|author1=Bruce C. Heezen |author2=A.S. Laughton |title=The Sea
|chapter=Abyssal plains
|editor=M.N. Hill
|publisher=Wiley-Interscience
|location=New York
|volume=3
|pages=312–64
|year=1963}}</ref>

The [[Challenger Deep]] is the deepest surveyed point of all of Earth's oceans; it is at the south end of the [[Mariana Trench]] near the [[Mariana Islands]] group. The depression is named after HMS ''Challenger'', whose researchers made the first recordings of its depth on 23 March 1875 at [https://web.archive.org/web/20110310200116/http://www.19thcenturyscience.org/HMSC/HMSC-Reports/1895-Summary/htm/doc878.html station 225]. The reported depth was 4,475 [[fathom]]s (8184&nbsp;meters) based on two separate soundings. On 1 June 2009, sonar mapping of the Challenger Deep by the [[Simrad Optronics|Simrad]] EM120 [[Multibeam echosounder|multibeam sonar bathymetry]] system aboard the [[RV Kilo Moana (T-AGOR-26)|R/V ''Kilo Moana'']] indicated a maximum depth of 10971&nbsp;meters (6.82 miles). The sonar system uses [[Phase (waves)|phase]] and [[amplitude]] bottom detection, with an accuracy of better than 0.2% of water depth (this is an error of about 22&nbsp;meters at this depth).<ref name=Moana1>{{Cite web
 |author=University of Hawaii Marine Center 
 |date=4 June 2009 
 |url=http://www.soest.hawaii.edu/UMC/Reports/Archives/KMreportJuneJuly2009.html 
 |title=Daily Reports for R/V KILO MOANA June & July 2009 
 |publisher=University of Hawaii 
 |location=Honolulu, Hawaii 
 |access-date=26 June 2010 
 |url-status=dead 
 |archive-url=https://archive.today/20120524194643/http://www.soest.hawaii.edu/UMC/Reports/Archives/KMreportJuneJuly2009.html 
 |archive-date=24 May 2012 
}}</ref><ref name=Moana2>{{Cite web
 |author=University of Hawaii Marine Center 
 |date=4 June 2009 
 |url=http://www.soest.hawaii.edu/UMC/KM/scienceequipment.htm 
 |title=Inventory of Scientific Equipment aboard the R/V KILO MOANA 
 |publisher=University of Hawaii 
 |location=Honolulu, Hawaii 
 |access-date=26 June 2010 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20100613143513/http://www.soest.hawaii.edu/UMC/KM/scienceequipment.htm 
 |archive-date=13 June 2010 
}}</ref>

==Terrain features==

===Hydrothermal vents===
[[File:Phase-diag2.svg|thumb|In this [[phase diagram]], the green dotted line illustrates the [[Water (molecule)#Density of water and ice|anomalous behavior of water]]. The solid green line marks the [[melting point]] and the blue line the [[boiling point]], showing how they vary with pressure.]]
{{Main|Hydrothermal vent}}

A rare but important terrain feature found in the bathyal, abyssal and hadal zones is the hydrothermal vent. In contrast to the approximately 2&nbsp;°C ambient water temperature at these depths, water emerges from these vents at temperatures ranging from 60&nbsp;°C up to as high as 464&nbsp;°C.<ref name=Haas2007/><ref name=Andrea2008/><ref name=Kosch2008/><ref name=Hill2008/><ref name=Karst2009/> Due to the high [[Atmospheric pressure|barometric pressure]] at these depths, water may exist in either its liquid form or as a [[supercritical fluid]] at such temperatures.

At a barometric pressure of 218 [[Atmosphere (unit)|atmospheres]], the [[Critical point (thermodynamics)|critical point]] of water is 375&nbsp;°C. At a depth of 3,000&nbsp;meters, the barometric pressure of sea water is more than 300&nbsp;atmospheres (as salt water is [[Density|denser]] than fresh water). At this depth and pressure, seawater becomes supercritical at a temperature of 407&nbsp;°C (''see image''). However the increase in salinity at this depth pushes the water closer to its critical point. Thus, water emerging from the hottest parts of some hydrothermal vents, ''[[black smoker]]s'' and [[submarine volcano]]es can be a [[Supercritical fluid#Submarine volcanoes|supercritical fluid]], possessing physical properties between those of a [[gas]] and those of a [[liquid]].<ref name=Haas2007/><ref name=Andrea2008/><ref name=Kosch2008/><ref name=Hill2008/><ref name=Karst2009/>

''Sister Peak'' (Comfortless Cove Hydrothermal Field, {{Coord|4|48|S|12|22|W|}}, elevation −2996&nbsp;m), ''Shrimp Farm'' and ''Mephisto'' (Red Lion Hydrothermal Field, {{Coord|4|48|S|12|23|W|}}, elevation −3047&nbsp;m), are three hydrothermal vents of the black smoker category, on the Mid-Atlantic Ridge near [[Ascension Island]]. They are presumed to have been active since an earthquake shook the region in 2002.<ref name=Haas2007/><ref name=Andrea2008/><ref name=Kosch2008/><ref name=Hill2008/><ref name=Karst2009/> These vents have been observed to vent [[Phase transition|phase-separated]], vapor-type fluids. In 2008, sustained exit temperatures of up to 407&nbsp;°C were recorded at one of these vents, with a peak recorded temperature of up to 464&nbsp;°C. These [[thermodynamics|thermodynamic]] conditions exceed the critical point of seawater, and are the highest temperatures recorded to date from the seafloor. This is the first reported evidence for direct [[magma]]tic-[[Hydrothermal circulation|hydrothermal]] interaction on a slow-spreading mid-ocean ridge.<ref name=Haas2007/><ref name=Andrea2008/><ref name=Kosch2008/><ref name=Hill2008/><ref name=Karst2009/> The initial stages of a vent chimney begin with the deposition of the mineral anhydrite. Sulfides of copper, iron, and zinc then precipitate in the chimney gaps, making it less porous over the course of time. Vent growths on the order of 30&nbsp;cm (1&nbsp;ft) per day have been recorded.[11] An April 2007 exploration of the deep-sea vents off the coast of Fiji found those vents to be a significant source of dissolved iron (see iron cycle).

Hydrothermal vents in the deep ocean typically form along the mid-ocean ridges, such as the East Pacific Rise and the Mid-Atlantic Ridge. These are locations where two tectonic plates are diverging and new crust is being formed.

===Cold seeps===
[[File:cold seep community.jpg|thumb|[[Tube worm (body plan)|Tubeworms]] and [[Alcyonacea|soft corals]] at a [[cold seep]] 3000&nbsp;meters deep on the [[Florida Platform|Florida Escarpment]]. [[Eelpout]]s, a [[Squat lobster|galatheid crab]], and an [[Alvinocarididae|alvinocarid shrimp]] are feeding on chemosynthetic [[Mytilidae|mytilid]] [[mussel]]s.]]
{{Main|Cold seep}}

Another unusual feature found in the abyssal and hadal zones is the [[cold seep]], sometimes called a ''cold vent''. This is an area of the seabed where seepage of [[hydrogen sulfide]], [[methane]] and other [[hydrocarbon]]-rich fluid occurs, often in the form of a deep-sea [[brine pool]]. The first cold seeps were discovered in 1983, at a depth of 3200&nbsp;meters in the [[Gulf of Mexico]].<ref name=Paull1984>{{Cite journal
|author1=Paull, C. K. |author2=Hecker, B. |author3=Commeau, R. |author4=Freeman-Lynde, R. P. |author5=Neumann, C. |author6=Corso, W. P. |author7=Golubic, S. |author8=Hook, J. E. |author9=Sikes, E. |author10=Curray, J. |title=Biological communities at the Florida Escarpment resemble hydrothermal vent taxa
|journal=Science
|volume=226
|issue=4677
|pages=965–967
|date=23 November 1984
|doi=10.1126/science.226.4677.965
|pmid=17737352
|bibcode = 1984Sci...226..965P |s2cid=45699993 }}</ref> Since then, cold seeps have been discovered in many other areas of the [[World Ocean]], including the [[Monterey Canyon|Monterey Submarine Canyon]] just off [[Monterey Bay]], California, the [[Sea of Japan]], off the Pacific coast of [[Costa Rica]], off the Atlantic coast of Africa, off the coast of Alaska, and under an [[ice shelf]] in [[Antarctica]].<ref name=nsf>{{Cite web
|author=Caitlyn H. Kennedy
|date=26 July 2007
|url=https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=109683
|title=Demise of Antarctic Ice Shelf Reveals New Life
|publisher=National Science Foundation
|access-date=19 June 2010}}</ref>

==Biodiversity==
{{ocean habitat topics}}
{{See also|Deep sea communities|Deep sea creature|Deep sea fish|Demersal fish|Benthos}}

Though the plains were once assumed to be vast, [[desert]]-like habitats, research over the past decade or so shows that they teem with a wide variety of [[microbial]] life.<ref name=Scheck2010>{{Cite journal
|author1=Frank Scheckenbach |author2=Klaus Hausmann |author3=Claudia Wylezich |author4=Markus Weitere |author5=Hartmut Arndt |title=Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor
|journal=Proceedings of the National Academy of Sciences
|volume=107
|issue=1
|pages=115–120
|date=5 January 2010
|pmid=20007768
|pmc=2806785
|doi=10.1073/pnas.0908816106
|bibcode = 2010PNAS..107..115S |doi-access=free }}</ref><ref name=Jorg2007>{{Cite journal
|author1=Jørgensen BB |author2=Boetius A. |title=Feast and famine—microbial life in the deep-sea bed
|journal=Nature Reviews Microbiology 
|volume=5
|issue=10
|pages=770–81
|date = October 2007
|pmid=17828281
|doi=10.1038/nrmicro1745|s2cid=22970703 }}</ref> However, ecosystem structure and function at the deep seafloor have historically been poorly studied because of the size and remoteness of the abyss. Recent [[oceanography|oceanographic]] expeditions conducted by an international group of scientists from the [[Census of Marine Life|Census of Diversity of Abyssal Marine Life]] (CeDAMar) have found an extremely high level of biodiversity on abyssal plains, with up to 2000 species of bacteria, 250 species of [[protozoan]]s, and 500 species of [[invertebrate]]s ([[worm]]s, [[crustacean]]s and [[molluscs]]), typically found at single abyssal sites.<ref name=NOAA>{{Cite web
 |author       = Census of Diversity of Abyssal Marine Life (CeDAMar)
 |url          = http://explore.noaa.gov/abstract-and-bio-census-of-the-diversity-of-abyssal-marine-life-dr-craig-smith
 |title        = Abstract and Bio: Census of the Diversity of Abyssal Marine Life (Dr. Craig Smith)
 |publisher    = Office of Ocean Exploration & Research, National Oceanic and Atmospheric Administration
 |access-date   = 26 June 2010
 |archive-url  = https://web.archive.org/web/20100527223751/http://explore.noaa.gov/abstract-and-bio-census-of-the-diversity-of-abyssal-marine-life-dr-craig-smith/
 |archive-date = 27 May 2010
 |url-status     = dead
}}</ref> New species make up more than 80% of the thousands of seafloor invertebrate species collected at any abyssal station, highlighting our heretofore poor understanding of abyssal diversity and evolution.<ref name=NOAA /><ref name=Glover2002>{{Cite journal
|author=Glover, A.G. |author2=Smith, C.R. |author3=Paterson, G.L.J. |author4=Wilson, G.D.F. |author5=Hawkins, L. |author6=Sheader, M.
|title=Polychaete species diversity in the central Pacific abyss: local and regional patterns and relationships with productivity
|journal=Marine Ecology Progress Series
|volume=240
|pages=157–170
|year=2002
|doi=10.3354/meps240157
|bibcode=2002MEPS..240..157G|doi-access=free
}}</ref><ref name=Martinez2010>{{Cite journal
|author1=Pedro Martínez Arbizu |author2=Horst Kurt Schminke |title=DIVA-1 expedition to the deep sea of the Angola Basin in 2000 and DIVA-1 workshop 2003
|journal=Organisms Diversity & Evolution
|volume=5
|issue=Supplement 1
|pages=1–2
|date=18 February 2005
|doi=10.1016/j.ode.2004.11.009|doi-access=free
}}</ref><ref name=Snelgrove2010>{{Cite journal
|author1=Paul V.R. Snelgrove |author2=Craig R. Smith |title=A riot of species in an environmental calm: the paradox of the species-rich deep-sea floor
|journal=Oceanography and Marine Biology: An Annual Review
|volume=40
|pages=311–342
|year=2002
|id={{INIST|14868518}}}}</ref> Richer biodiversity is associated with areas of known [[phytodetritus]] input and higher organic carbon flux.<ref name=Lambshead2003/>

''[[Abyssobrotula galatheae]]'', a [[species]] of cusk eel in the [[Family (biology)|family]] [[Ophidiidae]], is among the deepest-living species of fish. In 1970, one specimen was [[trawl]]ed from a depth of 8370&nbsp;meters in the [[Puerto Rico Trench]].<ref name="ellis">{{Cite book
|title=Deep Atlantic: Life, Death, and Exploration in the Abyss
|author=Ellis, R.
|publisher=Alfred A. Knopf, Inc
|location=New York
|year=1996
|isbn=978-1-55821-663-1}}</ref><ref name="fishbase">{{FishBase
|genus=Abyssobrotula
|species=galatheae
|date = December 2008|access-date=26 June 2010}}</ref><ref name="nielsen">{{Cite journal
|author=Nielsen, J.G.
|title=The deepest living fish ''Abyssobrotula galatheae'': a new genus and species of oviparous ophidioids (Pisces, Brotulidae)
|journal=Galathea Report
|volume=14
|pages=41–48
|year=1977}}</ref> The animal was dead, however, upon arrival at the surface. In 2008, the [[hadal snailfish]] (''Pseudoliparis amblystomopsis'')<ref name=Pseudoliparis>{{FishBase
|genus=Pseudoliparis
|species=amblystomopsis
|date = March 2009|access-date=26 June 2010}}</ref> was observed and recorded at a depth of 7700&nbsp;meters in the [[Japan Trench]]. In December 2014 a type of snailfish was filmed at a depth of 8145 meters,<ref>{{Cite news |date=2014-12-19 |title=New record for deepest fish |url=https://www.bbc.com/news/science-environment-30541065 |access-date=2024-03-03 |publisher=BBC News |language=en-GB}}</ref> followed in May 2017 by another sailfish filmed at 8178 meters.<ref>{{Cite news |date=Aug 25, 2017 |title=Ghostly fish in Mariana Trench in the Pacific is deepest ever recorded |url=https://www.cbc.ca/news/science/deepest-fish-1.4263003 |access-date=2024-03-02 |work=CBC News}}</ref> These are, to date, the deepest living fish ever recorded.<ref name=Morelle2008/><ref name=Keller2010>{{Cite web
|author=Elizabeth Keller
|year=2010
|url=http://www.extremescience.com/zoom/index.php/life-in-the-deep-ocean/44-deepest-fish
|title=Deepest Fish: Snailfish (''Pseudoliparis amblystomopsis'')
|access-date=26 June 2010| archive-url= https://web.archive.org/web/20100628211038/http://www.extremescience.com/zoom/index.php/life-in-the-deep-ocean/44-deepest-fish| archive-date= 28 June 2010 | url-status= live}}</ref> Other fish of the abyssal zone include the fishes of the family [[Ipnopidae]], which includes the abyssal spiderfish (''[[Bathypterois longipes]]''), tripodfish (''[[Bathypterois grallator]]''), feeler fish (''[[Bathypterois longifilis]]''), and the black lizardfish (''[[Bathysauropsis gracilis]]''). Some members of this family have been recorded from depths of more than 6000&nbsp;meters.<ref name=McGrouther>{{Cite web
|author=Mark McGrouther
|date=22 April 2010
|url=http://australianmuseum.net.au/Spiderfish-Bathypterois-sp/
|title=Spiderfishes, ''Bathypterois spp''
|publisher=Australian Museum
|location=Sydney, NSW
|access-date=26 June 2010}}</ref>

CeDAMar scientists have demonstrated that some abyssal and hadal species have a cosmopolitan distribution. One example of this would be protozoan [[foraminifera]]ns,<ref name=Akimoto>{{Cite journal
|author1=K. Akimoto |author2=M. Hattori |author3=K. Uematsu |author4=C. Kato |title=The deepest living foraminifera, Challenger Deep, Mariana Trench
|journal=Marine Micropaleontology
|volume=42
|issue=1–2
|pages=95–97
|date = May 2001|doi=10.1016/S0377-8398(01)00012-3
|bibcode=2001MarMP..42...95A}}</ref> certain species of which are distributed from the Arctic to the Antarctic. Other faunal groups, such as the [[polychaete]] worms and [[Isopoda|isopod]] crustaceans, appear to be endemic to certain specific plains and basins.<ref name=NOAA /> Many apparently unique [[Taxon|taxa]] of [[nematode]] worms have also been recently discovered on abyssal plains. This suggests that the deep ocean has fostered [[adaptive radiation]]s.<ref name=NOAA /> The taxonomic composition of the nematode fauna in the abyssal Pacific is similar, but not identical to, that of the North Atlantic.<ref name=Lambshead2003/> A list of some of the species that have been discovered or redescribed by CeDAMar can be found [https://web.archive.org/web/20100905112108/http://www.cedamar.org/Species-List here].

Eleven of the 31 described species of ''[[Monoplacophora]]'' (a [[Class (biology)|class]] of [[Mollusca|mollusks]]) live below 2000&nbsp;meters. Of these 11 species, two live exclusively in the hadal zone.<ref name=Schwabe2008>{{Cite book
|author=Enrico Schwab
|title=Bringing light into deep-sea biodiversity (Zootaxa 1866)
|editor1=Pedro Martinez Arbizu |editor2=Saskia Brix |chapter=A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca)
|publisher=Magnolia Press
|location=Auckland, New Zealand
|isbn=978-1-86977-260-4
|year=2008
|pages=205–222
|chapter-url=http://www.mapress.com/zootaxa/2008/f/zt01866p222.pdf
|access-date=26 June 2010}}</ref> The greatest number of monoplacophorans are from the eastern Pacific Ocean along the oceanic trenches. However, no abyssal monoplacophorans have yet been found in the Western Pacific and only one abyssal species has been identified in the Indian Ocean.<ref name=Schwabe2008/> Of the 922 known species of [[chiton]]s (from the ''[[Polyplacophora]]'' class of mollusks), 22 species (2.4%) are reported to live below 2000&nbsp;meters and two of them are restricted to the abyssal plain.<ref name=Schwabe2008/> Although genetic studies are lacking, at least six of these species are thought to be eurybathic (capable of living in a wide range of depths), having been reported as occurring from the [[Littoral zone|sublittoral]] to abyssal depths. A large number of the polyplacophorans from great depths are [[Herbivore|herbivorous]] or [[Xylophagy|xylophagous]], which could explain the difference between the distribution of monoplacophorans and polyplacophorans in the world's oceans.<ref name=Schwabe2008/>

[[Peracarid]] crustaceans, including isopods, are known to form a significant part of the macrobenthic community that is responsible for scavenging on large food falls onto the sea floor.<ref name=CRS2008/><ref name=Debroy2004>{{Cite journal
|author=De Broyer, C. |author2=Nyssen, F. |author3=P. Dauby
|title=The crustacean scavenger guild in Antarctic shelf, bathyal and abyssal communities
|journal=Deep-Sea Research Part II: Topical Studies in Oceanography
|volume=51
|issue=14–16
|pages=1733–1752
|date=July–August 2004
|doi=10.1016/j.dsr2.2004.06.032
|bibcode = 2004DSRII..51.1733D |hdl=2268/34147 |url=http://orbi.ulg.ac.be/handle/2268/34147 |hdl-access=free
}}</ref> In 2000, scientists of the ''Diversity of the deep Atlantic benthos'' (DIVA 1) expedition (cruise M48/1 of the German research vessel RV ''Meteor III'') discovered and collected three new species of the [[Asellota]] [[suborder]] of [[benthic]] isopods from the abyssal plains of the [[Angola Basin]] in the South [[Atlantic Ocean]].<ref>{{harvnb|Mursch|Brenke|Wägele|2008|pp=493–539.}}</ref><ref name=Schmid2002>{{Cite journal
|author=Schmid, C. |author2=Brenke, N. |author3=J.W. Wägele
|s2cid=82476475 |title=On abyssal isopods (Crustacea: Isopoda: Asellota) from the Angola Basin: Eurycope tumidicarpus n.sp. and redescription of Acanthocope galathea Wolff, 1962
|journal=Organisms Diversity & Evolution
|volume=2
|issue=1
|pages=87–88
|year=2002
|doi=10.1078/1439-6092-00030|doi-access=free
}}</ref><ref name=Lowry>{{Cite web
|author=J.K. Lowry
|date=2 October 1999
|url=http://www.crustacea.net/crustace/www/asellota.htm
|title=Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval (Asellota)
|publisher=Australian Museum
|access-date=26 June 2010
|archive-url=https://web.archive.org/web/20090120094611/http://crustacea.net/crustace/www/asellota.htm
|archive-date=20 January 2009
|url-status=dead
}}</ref> In 2003, De Broyer et al. collected some 68,000 peracarid crustaceans from 62 species from baited traps deployed in the [[Weddell Sea]], [[Scotia Sea]], and off the [[South Shetland Islands]]. They found that about 98% of the specimens belonged to the [[Amphipoda|amphipod]] [[Taxonomic rank|superfamily]] ''[[Lysianassidae|Lysianassoidea]]'', and 2% to the isopod family [[Cirolanidae]]. Half of these species were collected from depths of greater than 1000&nbsp;meters.<ref name=Debroy2004/>

In 2005, the [[Japan Agency for Marine-Earth Science and Technology]] (JAMSTEC) remotely operated vehicle, [[Kaikō ROV|KAIKO]], collected sediment core from the Challenger Deep. 432 living specimens of soft-walled foraminifera were identified in the sediment samples.<ref name=Todo2005>{{Cite journal
|author1=Yuko Todo |author2=Hiroshi Kitazato |author3=Jun Hashimoto |author4=Andrew J. Gooday |title=Simple Foraminifera Flourish at the Ocean's Deepest Point
|journal=Science
|volume=307
|issue=5710
|pages=689
|date=4 February 2005
|doi=10.1126/science.1105407
|pmid=15692042|s2cid=20003334 }}</ref><ref name=Roach>{{Cite web
|url=http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html
|archive-url=https://web.archive.org/web/20050205041944/http://news.nationalgeographic.com/news/2005/02/0203_050203_deepest.html
|url-status=dead
|archive-date=5 February 2005
|title=Life Is Found Thriving at Ocean's Deepest Point
|author=John Roach
|date=3 February 2005
|publisher=National Geographic News
|access-date=26 June 2010}}</ref> Foraminifera are single-celled [[protist]]s that construct shells. There are an estimated 4,000 species of living foraminifera. Out of the 432 organisms collected, the overwhelming majority of the sample consisted of simple, soft-shelled foraminifera, with others representing species of the complex, multi-chambered genera ''[[Leptohalysis]]'' and ''[[Reophax]]''. Overall, 85% of the specimens consisted of soft-shelled [[allogromiids]]. This is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20% of the total. Small organisms with hard calciferous shells have trouble growing at extreme depths because the water at that depth is severely lacking in calcium carbonate.<ref name=Turekian1975>{{Cite journal
|author1=Karl K. Turekian |author2=J. Kirk Cochran |author3=D.P. Kharkar |author4=Robert M. Cerrato |author5=J. Rimas Vaisnys |author6=Howard L. Sanders |author7=J. Frederick Grassle |author8=John A. Allen |title=Slow growth rate of a deep-sea clam determined by 228Ra chronology
|journal=Proceedings of the National Academy of Sciences of the United States of America
|volume=72
|issue=7
|pages=2829–2832
|date = July 1975|doi=10.1073/pnas.72.7.2829
|pmid=1058499
|pmc=432865
|bibcode = 1975PNAS...72.2829T |doi-access=free }}</ref> The giant (5–20&nbsp;cm) foraminifera known as [[Xenophyophorea|xenophyophores]] are only found at depths of 500–10,000 metres, where they can occur in great numbers and greatly increase animal diversity due to their bioturbation and provision of living habitat for small animals.<ref>{{Cite journal|last1=Levin|first1=Lisa A.|last2=Thomas|first2=Cynthia L.|date=December 1988|title=The ecology of xenophyophores (Protista) on eastern Pacific seamounts|url=https://linkinghub.elsevier.com/retrieve/pii/0198014988901227|journal=Deep Sea Research Part A. Oceanographic Research Papers|language=en|volume=35|issue=12|pages=2003–2027|doi=10.1016/0198-0149(88)90122-7|bibcode=1988DSRA...35.2003L|url-access=subscription}}</ref>

While similar lifeforms have been known to exist in shallower oceanic trenches (>7,000&nbsp;m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep may represent independent taxa from those shallower ecosystems. This preponderance of soft-shelled organisms at the Challenger Deep may be a result of selection pressure. Millions of years ago, the Challenger Deep was shallower than it is now. Over the past six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment of that ancient biosphere were unable to adapt to the increasing water pressure and changing environment. Those species that were able to adapt may have been the ancestors of the organisms currently endemic to the Challenger Deep.<ref name=Todo2005 />

Polychaetes occur throughout the Earth's oceans at all depths, from forms that live as [[plankton]] near the surface, to the deepest oceanic trenches. The robot ocean probe [[Nereus (underwater vehicle)|Nereus]] observed a 2–3&nbsp;cm specimen (still unclassified) of polychaete at the bottom of the Challenger Deep on 31 May 2009.<ref name=Roach /><ref name=Guam>{{Cite web
|author=Bernice Santiago
|date=15 June 2009
|url=http://sciencetech-search.blogspot.com/2009/07/robotic-vehicle-explores-challenger.html
|title=Robotic vehicle explores Challenger Deep
|publisher=Guam Pacific Daily News, Hagatna, Guam
|access-date=26 June 2010}}</ref><ref name=WHOI>{{Cite journal
|author1=Lonny Lippsett |author2=Amy E. Nevala |title=Nereus Soars to the Ocean's Deepest Trench
|journal=Oceanus Magazine
|date=4 June 2009
|url=http://www.whoi.edu/oceanus/viewArticle.do?id=57606
|access-date=26 June 2010
| archive-url= https://web.archive.org/web/20100601172511/http://www.whoi.edu/oceanus/viewArticle.do?id=57606| archive-date= 1 June 2010 | url-status= live}}</ref><ref name=WHOI2>{{Cite web
|author=WHOI Media Relations
|title=Hybrid Remotely Operated Vehicle "Nereus" Reaches Deepest Part of the Ocean
|publisher=[[Woods Hole Oceanographic Institution]]
|date=2 June 2009
|url=http://www.whoi.edu/page.do?pid=24136&tid=282&cid=57586
|access-date=26 June 2010}}</ref> There are more than 10,000 described species of polychaetes; they can be found in nearly every marine environment. Some species live in the coldest ocean temperatures of the hadal zone, while others can be found in the extremely hot waters adjacent to hydrothermal vents.

Within the abyssal and hadal zones, the areas around submarine hydrothermal vents and cold seeps have by far the greatest biomass and biodiversity per unit area. Fueled by the chemicals dissolved in the vent fluids, these areas are often home to large and diverse communities of [[Thermophile|thermophilic]], [[Halophile|halophilic]] and other [[extremophile|extremophilic]] [[prokaryote|prokaryotic]] [[microorganism]]s (such as those of the sulfide-oxidizing genus ''[[Beggiatoa]]''), often arranged in large [[Biofilm|bacterial mats]] near cold seeps. In these locations, chemosynthetic archaea and bacteria typically form the base of the food chain. Although the process of chemosynthesis is entirely microbial, these chemosynthetic microorganisms often support vast ecosystems consisting of complex multicellular organisms through [[symbiosis]].<ref name=MMS3>{{Cite book
 |author1=[[Minerals Management Service]]
 |title=Gulf of Mexico OCS Oil and Gas Lease Sales: 2007–2012. Western Planning Area Sales 204, 207, 210, 215, and 218. Central Planning Area Sales 205, 206, 208, 213, 216, and 222. Draft Environmental Impact Statement. Volume I 
 |editor=Chris C. Oynes 
 |chapter=3: Description of the affected environment 
 |publisher=[[United States Department of the Interior]], [[Minerals Management Service]], Gulf of Mexico OCS Region 
 |location=New Orleans 
 |date=November 2006 
 |pages=3–27–3–31 
 |chapter-url=http://www.gomr.mms.gov/PDFs/2006/2006-062-Vol1.pdf 
 |access-date=20 June 2010 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20090326005638/http://www.gomr.mms.gov/PDFs/2006/2006-062-Vol1.pdf 
 |archive-date=26 March 2009 
}}</ref> These communities are characterized by species such as [[Vesicomyidae|vesicomyid clams]], [[Mytilidae|mytilid]] [[mussel]]s, [[limpet]]s, isopods, [[giant tube worm]]s, [[Alcyonacea|soft corals]], [[eelpout]]s, [[Squat lobster|galatheid crabs]], and [[Alvinocarididae|alvinocarid shrimp]]. The deepest seep community discovered thus far is in the [[Japan Trench]], at a depth of 7700&nbsp;meters.<ref name=Morelle2008/>

Probably the most important ecological characteristic of abyssal ecosystems is energy limitation. Abyssal seafloor communities are considered to be ''food limited'' because [[benthic]] production depends on the input of [[Detritus|detrital]] [[Biotic material|organic material]] produced in the euphotic zone, thousands of meters above.<ref name=Smith2003>Smith, C.R. and Demoupolos, A.W.J. (2003) Ecology of the Pacific ocean floor. In: Ecosystems of the World (Tyler, P.A., ed.), pp. 179–218, Elsevier</ref> Most of the organic flux arrives as an [[marine snow|attenuated rain]] of small particles (typically, only 0.5–2% of net primary production in the euphotic zone), which decreases inversely with water depth.<ref name=Buesseler/> The small particle flux can be augmented by the [[whale fall|fall of larger carcasses]] and downslope transport of organic material near continental margins.<ref name=Smith2003 />

==Exploitation of resources==
{{See also|Deep sea mining|Offshore drilling}}

In addition to their high biodiversity, abyssal plains are of great current and future commercial and strategic interest. For example, they may be used for the legal and illegal disposal of large structures such as ships and [[Oil platform|oil rigs]], [[radioactive waste]] and other [[hazardous waste]], such as [[Ammunition|munitions]]. They may also be attractive sites for [[Fishing|deep-sea fishing]], and [[Hydrocarbon exploration|extraction of oil and gas]] and other [[mining|minerals]]. Future deep-sea [[Waste management|waste disposal]] activities that could be significant by 2025 include [[Sewage treatment|emplacement of sewage and sludge]], [[carbon sequestration]], and disposal of [[Dredging|dredge spoils]].<ref name=Glover2003>{{Cite journal
|author1=Adrian G. Glover |author2=Craig R. Smith |s2cid=53666031 |title=The deep-sea floor ecosystem: current status and prospects of anthropogenic change by the year 2025
|journal=Environmental Conservation
|volume=30
|issue=3
|pages=219–241
|year=2003
|doi=10.1017/S0376892903000225|bibcode=2003EnvCo..30..219G }}</ref>

As [[fish stocks]] dwindle in the upper ocean, deep-sea [[Fishery|fisheries]] are increasingly being targeted for exploitation. Because [[deep sea fish]] are long-lived and slow growing, these deep-sea fisheries are not thought to be sustainable in the long term given current management practices.<ref name=Glover2003/> Changes in primary production in the photic zone are expected to alter the standing stocks in the food-limited aphotic zone.

Hydrocarbon exploration in deep water occasionally results in significant [[environmental degradation]] resulting mainly from accumulation of contaminated [[drill cuttings]], but also from [[oil spill]]s. While the [[Blowout (well drilling)|oil blowout]] involved in the [[Deepwater Horizon oil spill]] in the [[Gulf of Mexico]] originates from a [[wellhead]] only 1500&nbsp;meters below the ocean surface,<ref>{{Cite news|last=Macdonald |first=Ian R. |url=https://www.nytimes.com/2010/05/22/opinion/22macdonald.html |title=The Measure of an Oil Disaster
|author2=John Amos |author3=Timothy Crone |author4=Steve Wereley
|work=The New York Times
|date=21 May 2010
|access-date=18 June 2010| archive-url= https://web.archive.org/web/20100526182228/http://www.nytimes.com/2010/05/22/opinion/22macdonald.html| archive-date= 26 May 2010 | url-status= live}}</ref> it nevertheless illustrates the kind of [[environmental disaster]] that can result from mishaps related to [[offshore drilling]] for oil and gas.

Sediments of certain abyssal plains contain abundant mineral resources, notably [[Manganese nodule|polymetallic nodules]]. These potato-sized [[concretion]]s of manganese, iron, nickel, cobalt, and copper, distributed on the seafloor at depths of greater than 4000&nbsp;meters,<ref name=Glover2003/> are of significant commercial interest. The area of maximum commercial interest for polymetallic nodule mining (called the [[Pacific nodule province]]) lies in [[international waters]] of the Pacific Ocean, stretching from 118°–157°, and from 9°–16°N, an area of more than 3 million km<sup>2</sup>.<ref name="Smith 2008 4">{{harvnb|Smith|Paterson|Lambshead|Glover|Gooday|Rogers|Sibuet|Kitazato|Galéron|Menot|2008|p=4}}</ref> The abyssal [[Clarion-Clipperton fracture zone]] (CCFZ) is an area within the Pacific nodule province that is currently under exploration for its mineral potential.<ref name=Lambshead2003>{{Cite journal
|author1=P John D Lambshead |author2=Caroline J Brown |author3=Timothy J Ferrero |author4=Lawrence E Hawkins |author5=Craig R Smith |author6=Nicola J Mitchell |title=Biodiversity of nematode assemblages from the region of the Clarion-Clipperton Fracture Zone, an area of commercial mining interest
|journal=BMC Ecology
|volume=3
|pages=1
|date=9 January 2003
|pmid=12519466
|doi=10.1186/1472-6785-3-1
|pmc=140317 |doi-access=free }}</ref>

Eight commercial contractors are currently licensed by the [[International Seabed Authority]] (an [[intergovernmental organization]] established to organize and control all mineral-related activities in the international seabed area beyond the limits of [[Territorial waters|national jurisdiction]]) to explore nodule resources and to test mining techniques in eight [[Mineral rights|claim areas]], each covering 150,000&nbsp;km<sup>2</sup>.<ref name="Smith 2008 4"/> When mining ultimately begins, each mining operation is projected to directly disrupt 300–800&nbsp;km<sup>2</sup> of seafloor per year and disturb the [[benthos|benthic fauna]] over an area 5–10 times that size due to redeposition of suspended sediments. Thus, over the 15-year projected duration of a single mining operation, nodule mining might severely damage abyssal seafloor communities over areas of 20,000 to 45,000&nbsp;km<sup>2</sup> (a zone at least the size of [[Massachusetts]]).<ref name="Smith 2008 4"/>

Limited knowledge of the [[Taxonomy (biology)|taxonomy]], [[biogeography]] and [[natural history]] of [[deep sea communities]] prevents accurate assessment of the risk of species [[extinction]]s from large-scale mining. Data acquired from the abyssal North Pacific and North Atlantic suggest that deep-sea ecosystems may be adversely affected by mining operations on decadal time scales.<ref name=Glover2003/> In 1978, a dredge aboard the [[GSF Explorer|Hughes Glomar Explorer]], operated by the American mining [[consortium]] [[GSF Explorer#Leasing|Ocean Minerals Company]] (OMCO), made a mining track at a depth of 5000&nbsp;meters in the nodule fields of the CCFZ. In 2004, the [[France|French]] Research Institute for Exploitation of the Sea ([[Ifremer|IFREMER]]) conducted the ''Nodinaut'' expedition to this mining track (which is still visible on the seabed) to study the long-term effects of this physical disturbance on the sediment and its benthic fauna. Samples taken of the superficial sediment revealed that its physical and chemical properties had not shown any recovery since the disturbance made 26 years earlier. On the other hand, the biological activity measured in the track by instruments aboard the crewed [[submersible]] [[bathyscaphe]] ''[[Nautile]]'' did not differ from a nearby unperturbed site. This data suggests that the benthic fauna and nutrient fluxes at the water–sediment interface has fully recovered.<ref name=Khripounoff2006>{{Cite journal
 |doi         = 10.4319/lo.2006.51.5.2033
 |author1     = Alexis Khripounoff
 |author2     = Jean-Claude Caprais
 |author3     = Philippe Crassous
 |author4     = Joël Etoubleau
 |title       = Geochemical and Biological Recovery of the Disturbed Seafloor in Polymetallic Nodule Fields of the Clipperton-Clarion Fracture Zone (CCFZ) at 5,000-m Depth
 |journal     = Limnology and Oceanography
 |volume      = 51
 |issue       = 5
 |pages       = 2033–2041
 |date        = 1 September 2006
 |url         = http://www.aslo.org/lo/pdf/vol_51/issue_5/2033.pdf
 |access-date  = 19 June 2010
  |url-status     = dead
 |archive-url  = https://web.archive.org/web/20080724132014/http://aslo.org/lo/pdf/vol_51/issue_5/2033.pdf
 |archive-date = 24 July 2008
|bibcode= 2006LimOc..51.2033K
 |s2cid = 16748259
 }}</ref>

==List of abyssal plains==
{{Main|List of submarine topographical features}}

==See also==
{{Portal|Oceans}}
*[[List of landforms#Coastal and oceanic landforms|List of oceanic landforms]]
*[[List of submarine topographical features]]
*[[Mid-ocean ridge|Oceanic ridge]]
*[[Physical oceanography]]

==References==
{{Reflist}}

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|chapter=Results of the DIVA-1 expedition of RV "Meteor" (Cruise M48:1): Three new species of Munnopsidae Sars, 1864 from abyssal depths of the Angola Basin (Crustacea: Isopoda: Asellota)
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|chapter=Biodiversity, species ranges, and gene flow in the abyssal Pacific nodule province: predicting and managing the impacts of deep seabed mining
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{{Refend}}

==External links==
*{{cite web
|author=Monterey Bay Aquarium Research Institute
|date=3 November 2009
|url=https://www.sciencedaily.com/releases/2009/11/091102171559.htm
|title=Deep-sea Ecosystems Affected By Climate Change
|website=ScienceDaily
|access-date=18 June 2010}}
{{GeoGroup}}

{{Physical oceanography|expanded=other}}
{{Tectonic plates}}
{{Earthsinterior}}
{{Authority control}}

{{DEFAULTSORT:Abyssal Plain}}
[[Category:Abyssal plains| ]]
[[Category:Coastal and oceanic landforms]]
[[Category:Submarine topography]]
[[Category:Oceanic plateaus]]
[[Category:Oceanographical terminology]]
[[Category:Physical oceanography]]
[[Category:Aquatic ecology]]