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Abyssal plain
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==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 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 metres,<ref name="Csirke 1997 4"/> or rarely, up to 200 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 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 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 metres down to 3,000 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 metres down to 6,000 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 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 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 metres | highly variable | |- | [[Mesopelagic zone|disphotic]] (mesopelagic zone, or twilight zone) | 200–1,000 metres | {{convert|4|°C|°F|abbr=on|disp=or}} – highly variable | |- |rowspan="3"| [[Aphotic zone|aphotic]] | [[Bathyal zone|bathyal]] | 1,000–3,000 metres | {{convert|4|-|12|°C|°F|abbr=on|disp=or}} | |- | [[Abyssal zone|abyssal]] | 3,000–6,000 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 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 metres due to [[Adiabatic heating#Adiabatic heating and cooling|adiabatic heating]]<ref name=ucsd /> |- |}
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