{"id":1688,"date":"2015-04-29T11:37:21","date_gmt":"2015-04-29T11:37:21","guid":{"rendered":"http:\/\/www.bluehabitats.org\/?page_id=1688"},"modified":"2015-05-06T10:26:51","modified_gmt":"2015-05-06T10:26:51","slug":"trenches","status":"publish","type":"page","link":"https:\/\/bluehabitats.org\/?page_id=1688","title":{"rendered":"Trenches"},"content":{"rendered":"
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Trenches <\/em>\u00a0– Trenches are \u201ca long narrow, characteristically very deep and asymmetrical depression of the sea floor, with relatively steep sides\u201d (IHO, 2008).\u00a0 Trenches are generally distinguished from troughs by their \u201cV\u201d shape in cross section (in contrast with flat-bottomed troughs). \u00a0The upwelling of basaltic lava on the mid-ocean ridges gives rise to the formation and lateral spreading outwards of ocean crust.\u00a0 The tectonic movement (or \u201cdrift\u201d) of continents, driven by seafloor spreading, results in two fundamentally different kinds of junction where ocean and continental crust are in direct contact: active and passive plate margins.\u00a0 Along active plate margins, the ocean crust collides with and is over-ridden by continental crust (or in some cases by less-dense ocean crust) in a region called the subduction zone<\/em>, where ridge and trench complexes are created.\u00a0 This occurs because the denser ocean crust is subducted beneath the lighter continental crust (forming a \u201cV\u201d shaped trench) and the lateral pressure pushes the continental crust upwards (forming a ridge).\u00a0 In some locations, ocean crust is subducted beneath other ocean crust, so not all subduction involves continental crust.<\/p>\n

Ocean trenches are the deepest parts of the ocean, commonly 6 to 10 km in depth[1]<\/a> and have a highly specialised fauna.\u00a0 Trenches are separated from each other by comparatively shallow ocean floor over which any trench-associated animal would have to pass, and so trenches are isolated from each other.\u00a0 This isolation has given rise to a high degree of endemism for trench fauna.\u00a0 Oceanographic conditions vary between trenches, but generally species diversity decreases with increasing depth, with a high percentage of species endemic to individual trenches (Gage and Tyler, 1991).\u00a0 Most of what we know about ocean trench fauna was derived from Danish and Russian expeditions carried out in the 1950\u2019s and 60\u2019s, during the \u201cheroic\u201d era of deep sea exploration (Gage and Tyler, 1991), that culminated in the 10,911 m decent of Jacque Piccard and Don Walsh aboard the bathyscaphe Trieste<\/em> on 23 January, 1960 to the bottom of the Challenger Deep in the Mariana Trench.\u00a0 Looking out of the Trieste\u2019s<\/em> porthole, Piccard observed a solitary flat bottom fish[2]<\/a>, confirming the existence of life at even the greatest ocean depths.\u00a0 Species most common in the hadal community are molluscs, polychaete worms and particularly holothurians (Jamieson et al., 2010).<\/p>\n

Sediment that is eroded from areas of surrounding seafloor slumps down into the trench as debris flows or turbidity currents.\u00a0 Over time, sediment may partially infill the valley to form a flat-floored trough<\/em>.\u00a0 Along passive plate margins there is no subduction zone (or trench) and the oceanic and continental crusts simply abut one another; there are thus no trenches or troughs along passive margins.<\/p>\n

[1]<\/a> The Mariana Trench in the Pacific Ocean is the deepest place in the world ocean at -11,034 m water depth.<\/p>\n

[2]<\/a> Wolff (1960) suggested Piccard\u2019s \u201cfish\u201d was more likely to have been a holothurian since flatfish are uncommon below ~2,000 m depth.<\/p>\n

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Statistics of trenches (from Harris et al., 2014).\u00a0 The percentage areas refer to fraction of ocean regions that is trench.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n

[vc_table vc_table_theme=”classic_blue” allow_html=””]Ocean,Area%20km2,Trench%20area%25,Number%20of%20Trenches,Average%20Trench%20Size%20km2,Maximum%20depth%20(m)|Arctic%20Ocean,0,0,0,0,-|Indian%20Ocean,166%2C580,0.234,9,18%2C510,7%2C318|Mediterranean%20%26%20Black%20Sea%20,14%2C970,0.495,5,2%2C990,4%2C393|North%20Atlantic%20Ocean,116%2C350,0.260,3,38%2C780,8%2C620|North%20Pacific%20Ocean,824%2C720,1.01,21,39%2C270,10%2C941|South%20Atlantic%20Ocean,91%2C240,0.226,2,45%2C620,8%2C188|South%20Pacific%20Ocean,745%2C810,0.856,19,39%2C250,10%2C803|Southern%20Ocean,7%2C690,0.0378,1,7%2C690,7%2C325|All%20Oceans,1%2C967%2C350,0.543,56,35%2C130,10%2C941[\/vc_table]\n\t
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3D view of the Caribbean looking west from the Atlantic Ocean showing the Puerto Rico Trench in the foreground in dark purple.\u00a0 Canyons are shown in reddish-orange, ridges in purple, seamounts in the foreground in orange, shelf in green, slope in light blue, rise in blue, fans in light purple.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div>

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3D view of the Caribbean looking west from the Atlantic Ocean<\/div><\/a><\/div><\/div><\/div><\/div><\/div>
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References<\/h5>\n

Gage, J.D., Tyler, P.A., 1991. Deep-sea biology: a natural history of organisms at the deep-sea floor. Cambridge University Press, Cambridge.<\/p>\n

Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4-24.<\/p>\n

Jamieson, A.J., Fujii, T., Mayor, D.J., Solan, M., Priede, I.G., 2010. Hadal trenches: the ecology of the deepest places on Earth. Trends in Ecology & Evolution 25, 190-197.<\/p>\n

Wolff, T., 1960. The Hadal community, an introduction. Deep Sea Research 6, 95-124.<\/p>\n

Macdonald, K.S., Scheirer, D.S., Carbotte, S.M., 1991. Mid-ocean ridges: discontinuities, segments and giant cracks. Science 253, 986-994.<\/p>\n

Muller, R.D., Roest, W.R., Royer, J.Y., Gahagan, L.M., Sclater, J.G., 1997. Digital Isochrons of the World’s Ocean Floor. Journal of Geophysical Research 102, 3211-3214.<\/p>\n

Tunnicliffe, V., Fowler, M.R., 1996. Influence of sea-floor spreading on the global hydrothermal vent fauna. Nature 379, 531 – 533.<\/p>\n

Van Dover, C., 2000. The ecology of deep-sea hydrothermal vents. Princeton University Press, Princeton, New Jersey.<\/p>\n\n\t\t<\/div>\n\t<\/div>\n<\/div><\/div><\/div><\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

Trenches \u00a0– Trenches are \u201ca long narrow, characteristically very deep and asymmetrical depression of the sea floor, with relatively steep sides\u201d (IHO, 2008).\u00a0 Trenches are generally distinguished from troughs by their \u201cV\u201d shape in cross section (in contrast with flat-bottomed troughs). \u00a0The upwelling of basaltic lava on the mid-ocean ridges gives rise to the formation…<\/p>\n","protected":false},"author":3,"featured_media":0,"parent":1646,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-1688","page","type-page","status-publish","hentry","description-off"],"acf":[],"_links":{"self":[{"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/pages\/1688","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/bluehabitats.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1688"}],"version-history":[{"count":4,"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/pages\/1688\/revisions"}],"predecessor-version":[{"id":1851,"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/pages\/1688\/revisions\/1851"}],"up":[{"embeddable":true,"href":"https:\/\/bluehabitats.org\/index.php?rest_route=\/wp\/v2\/pages\/1646"}],"wp:attachment":[{"href":"https:\/\/bluehabitats.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1688"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}