Seabed

Source: Wikipedia, the free encyclopedia.
seafloor sediment
.
Marine habitats
Coastal habitats
Ocean surface
Open ocean
Sea floor

The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'.

The structure of the seabed of the global ocean is governed by

sediment core, is known as the "depth below seafloor". The ecological environment of the seabed and the deepest waters are collectively known, as a habitat for creatures, as the "benthos
".

Most of the seabed throughout the world's oceans is covered in layers of

boulders
.

Features of the seabed are governed by the physics of sediment transport and by the biology of the creatures living in the seabed and in the ocean waters above. Physically, seabed sediments often come from the erosion of material on land and from other rarer sources, such as volcanic ash. Sea currents transport sediments, especially in shallow waters where tidal energy and wave energy cause resuspension of seabed sediments. Biologically, microorganisms living within the seabed sediments change seabed chemistry. Marine organisms create sediments, both within the seabed and in the water above. For example, phytoplankton with silicate or calcium carbonate shells grow in abundance in the upper ocean, and when they die, their shells sink to the seafloor to become seabed sediments.

Human impacts on the seabed are diverse. Examples of human effects on the seabed include exploration, plastic pollution, and exploitation by mining and

hydrothermal vents. Plastic pollution is a global phenomenon, and because the ocean is the ultimate destination for global waterways, much of the world's plastic ends up in the ocean and some sinks to the seabed. Exploitation of the seabed involves extracting valuable minerals from sulfide deposits via deep sea mining, as well as dredging sand from shallow environments for construction and beach nourishment
.

Structure

See also: Seafloor spreading
Bathymetry of the ocean floor showing the continental shelves and oceanic plateaus (red), the mid-ocean ridges (yellow-green) and the abyssal plains (blue to purple). Like land terrain, the ocean floor has mountains including volcanoes, ridges, valleys, and plains.
Drawing showing divisions according to depth and distance from shore
The major oceanic divisions

Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources. The structure of the oceans, starting with the continents, begins usually with a

continental slope – which is a steep descent into the ocean, until reaching the abyssal plain – a topographic plain, the beginning of the seabed, and its main area. The border between the continental slope and the abyssal plain usually has a more gradual descent, and is called the continental rise, which is caused by sediment cascading down the continental slope.[citation needed
]

The

tectonic plate edges there are typically oceanic trenches – deep valleys, created by the mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench.[1]

hydrothermal vents
– releasing high pressure and extremely hot water and chemicals into the typically freezing water around it.

Deep ocean water is divided into layers or zones, each with typical features of salinity, pressure, temperature and marine life, according to their depth. Lying along the top of the abyssal plain is the abyssal zone, whose lower boundary lies at about 6,000 m (20,000 ft). The hadal zone – which includes the oceanic trenches, lies between 6,000 and 11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone.[2][3]

Depth below seafloor

Depth below seafloor is a

ocean drilling
). The acronym "mbsf" (meaning "meters below the seafloor") is a common convention used for depths below the seafloor.[4][5]

  • Different seabeds in the world's oceans
  • gravel seabed in Italy
    gravel seabed in Italy
  • white sand seabed in Mexico
    white sand seabed in Mexico
  • sand seabed in Greece
    sand seabed in Greece
  • hydrothermal vents
    hydrothermal vents

Sediments

Main article: Marine sediment
Total sediment thickness of the world's oceans and continental margins in meters.

Sediments in the seabed vary in origin, from eroded land materials carried into the ocean by rivers or wind flow, waste and decompositions of sea creatures, and precipitation of chemicals within the sea water itself, including some from outer space.[6] There are four basic types of sediment of the sea floor:

  1. Terrigenous (also lithogenous) describes the sediment from continents eroded by rain, rivers, and glaciers, as well as sediment blown into the ocean by the wind, such as dust and volcanic ash.
  2. Biogenous material is the sediment made up of the hard parts of sea creatures, mainly phytoplankton, that accumulate on the bottom of the ocean.
  3. Hydrogenous sediment is material that precipitates in the ocean when oceanic conditions change, or material created in hydrothermal vent systems.
  4. Cosmogenous sediment comes from extraterrestrial sources.[7]

Terrigenous and biogenous

Satellite image of wind-blown mineral dust over the Atlantic. Dust may become terrigenous sediment on the seabed.
diatoms make silicate
shells, which become siliceous ooze.

Terrigenous sediment is the most abundant sediment found on the seafloor. Terrigenous sediments come from the continents. These materials are eroded from continents and transported by wind and water to the ocean. Fluvial sediments are transported from land by rivers and glaciers, such as clay, silt, mud, and glacial flour. Aeolian sediments are transported by wind, such as dust and volcanic ash.[8]

Biogenous sediment is the next most abundant material on the seafloor. Biogenous sediments are biologically produced by living creatures. Sediments made up of at least 30% biogenous material are called "oozes." There are two types of oozes: Calcareous oozes and Siliceous oozes. Plankton grow in ocean waters and create the materials that become oozes on the seabed. Calcareous oozes are predominantly composed of calcium shells found in phytoplankton such as coccolithophores and zooplankton like the foraminiferans. These calcareous oozes are never found deeper than about 4,000 to 5,000 meters because at further depths the calcium dissolves.[9] Similarly, Siliceous oozes are dominated by the siliceous shells of phytoplankton like diatoms and zooplankton such as radiolarians. Depending on the productivity of these planktonic organisms, the shell material that collects when these organisms die may build up at a rate anywhere from 1 mm to 1 cm every 1000 years.[9]

Hydrogenous and cosmogenous

Hydrothermal vent fluids cause chemical reactions that precipitate out minerals that form sediments on the surrounding seafloor.

Hydrogenous sediments are uncommon. They only occur with changes in oceanic conditions such as temperature and pressure. Rarer still are cosmogenous sediments. Hydrogenous sediments are formed from dissolved chemicals that precipitate from the ocean water, or along the mid-ocean ridges, they can form by metallic elements binding onto rocks that have water of more than 300 °C circulating around them. When these elements mix with the cold sea water they precipitate from the cooling water.[9] Known as manganese nodules, they are composed of layers of different metals like manganese, iron, nickel, cobalt, and copper, and they are always found on the surface of the ocean floor.[9]

Cosmogenous sediments are the remains of space debris such as comets and asteroids, made up of silicates and various metals that have impacted the Earth.[10]

Size classification

Sediment types from the Southern Ocean showing many different grain sizes: A) gravel and sand, B) gravel, C) bioturbated mud and sand, and D) laminated clays and silts.[11]

Another way that sediments are described is through their descriptive classification. These sediments vary in size, anywhere from 1/4096 of a mm to greater than 256 mm. The different types are: boulder, cobble, pebble, granule, sand, silt, and clay, each type becoming finer in grain. The grain size indicates the type of sediment and the environment in which it was created. Larger grains sink faster and can only be pushed by rapid flowing water (high energy environment) whereas small grains sink very slowly and can be suspended by slight water movement, accumulating in conditions where water is not moving so quickly.[12] This means that larger grains of sediment may come together in higher energy conditions and smaller grains in lower energy conditions.

Benthos

This section is an excerpt from Benthos.[edit]
Seaweed and two chitons in a tide pool

tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths
.

Many organisms adapted to deep-water pressure cannot survive in the upper parts of the

atmosphere for every 10 metres of water depth).[14]

Because light is

detritivores
.

The term benthos, coined by
freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams.[17] There is also a redundant synonym, Benton.[18]

Topography

See also: Bathymetry and Ocean surface topography
World map with ocean topography

Seabed topography (ocean topography or marine topography) refers to the shape of the land (topography) when it interfaces with the ocean. These shapes are obvious along coastlines, but they occur also in significant ways underwater. The effectiveness of marine habitats is partially defined by these shapes, including the way they interact with and shape ocean currents, and the way sunlight diminishes when these landforms occupy increasing depths. Tidal networks depend on the balance between sedimentary processes and hydrodynamics however, anthropogenic influences can impact the natural system more than any physical driver.[19]

Marine topographies include

shorelines to continental shelves and coral reefs. Further out in the open ocean, they include underwater and deep sea features such as ocean rises and seamounts. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes,[20] oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains
.

The mass of the oceans is approximately 1.35×1018 

metric tons, or about 1/4400 of the total mass of the Earth. The oceans cover an area of 3.618×108 km2 with a mean depth of 3,682 m, resulting in an estimated volume of 1.332×109 km3.[21]

Features

Layers of the pelagic zone

Each region of the seabed has typical features such as common sediment composition, typical topography, salinity of water layers above it, marine life, magnetic direction of rocks, and sedimentation. Some features of the seabed include flat abyssal plains, mid-ocean ridges, deep trenches, and hydrothermal vents.

Seabed topography is flat where layers of sediments cover the tectonic features. For example, the

sea currents eroding the seabed and transporting sediments to the deeper ocean, and phytoplankton
shell materials.

Where the seafloor is actively spreading and sedimentation is relatively light, such as in the northern and eastern

mid-ocean ridges.[7]

Other seabed environments include hydrothermal vents, cold seeps, and shallow areas. Marine life is abundant in the

vertebrates. This marine life receives its energy both from the extreme temperature difference (typically a drop of 150 degrees) and from chemosynthesis by bacteria. Brine pools are another seabed feature,[24] usually connected to cold seeps. In shallow areas, the seabed can host sediments created by marine life
such as corals, fish, algae, crabs, marine plants and other organisms.

Human impact

Exploration

Main articles: Deep-sea exploration and Oceanography § History
A video describing the operation and use of an autonomous lander in deep sea research.

The seabed has been explored by submersibles such as

maps of the seabed,[25]
and these satellite-derived maps are used extensively in the study and exploration of the ocean floor.

Plastic pollution

In 2020 scientists created what may be the first scientific estimate of how much

seafloor, after investigating six areas of ~3 km depth ~300 km off the Australian coast. They found the highly variable microplastic counts to be proportionate to plastic on the surface and the angle of the seafloor slope. By averaging the microplastic mass per cm3, they estimated that Earth's seafloor contains ~14 million tons of microplastic – about double the amount they estimated based on data from earlier studies – despite calling both estimates "conservative" as coastal areas are known to contain much more microplastic pollution. These estimates are about one to two times the amount of plastic thought – per Jambeck et al., 2015 – to currently enter the oceans annually.[26][27][28]

Exploitation

This section is an excerpt from Deep sea mining.[edit]
Schematic of a polymetallic nodule mining operation. From top to bottom, the three zoom-in panels illustrate the surface operation vessel, the midwater sediment plume, and the nodule collector operating on the seabed. The midwater plume comprises two stages: (i) the dynamic plume, in which the sediment-laden discharge water rapidly descends and dilutes to a neutral buoyancy depth, and (ii) the subsequent ambient plume that is advected by the ocean current and subject to background turbulence and settling.
Schematic of a polymetallic nodule mining operation. From top to bottom, the three zoom-in panels illustrate the surface operation vessel, the midwater sediment plume, and the nodule collector operating on the seabed. The midwater plume comprises two stages: (i) the dynamic plume, in which the sediment-laden discharge water rapidly descends and dilutes to a neutral buoyancy depth, and (ii) the subsequent ambient plume that is advected by the ocean current and subject to background turbulence and settling. [29]

Deep sea mining is the extraction of minerals from the ocean floor at depths of 200 metres (660 ft)[30][31] to 6,500 metres (21,300 ft).[32][33][34]

Deep-sea mining uses hydraulic pumps or bucket systems that carry deposits to the surface for processing.

The environmental impact of deep sea mining is controversial.[35][36] Environmental advocacy groups such as Greenpeace and the Deep Sea Mining Campaign[37] claimed that seabed mining has the potential to damage deep sea ecosystems and spread pollution from heavy metal-laden plumes.[38] Critics have called for moratoria[39][40] or permanent bans.[41] Opposition campaigns enlisted the support of some industry figures, including firms reliant on the target metals. Individual countries with significant deposits within their exclusive economic zones (EEZ's) are exploring the subject.[42][43]

As of 2022, no commercial deep sea mining was underway. However, the

Clarion Clipperton Zone.[44] China has exclusive rights to mine 92,000 square miles (240,000 km2) or 17 percent of the area. Mining is set to begin in 2025.[45] In 2022 the Cook Islands Seabed Minerals Authority (SBMA) granted 3 exploration licenses for polymetallic nodules within their EEZ.[46] Papua New Guinea was the first country to approve a DSM permit, to Solwara 1, even though three independent reviews of the environmental impact statement mine alleged significant gaps and flaws in the underlying science.[47]

Related technologies include robotic mining machines, as surface ships, and offshore and onshore metal refineries.[48][49]

Wind farms, solar energy, electric cars, and battery technologies use many of the deep-sea metals.[48]

As of 2021, the majority of marine mining used dredging operations at depths of about 200 m, where sand, silt and mud for construction purposes is abundant, along with mineral rich sands containing ilmenite and diamonds.[50][51]

In art and culture

Some children's play songs include elements such as "There's a hole at the bottom of the sea", or "A sailor went to sea... but all that he could see was the bottom of the deep blue sea".

On and under the seabed are archaeological sites of historic interest, such as shipwrecks and sunken towns. This underwater cultural heritage is protected by the

UNESCO Convention on the Protection of the Underwater Cultural Heritage. The convention aims at preventing looting and the destruction or loss of historic and cultural information by providing an international legal framework.[52]

See also

References

  1. ISBN 978-0-321-59779-3
    .
  2. ^ "Open Ocean – Oceans, Coasts, and Seashores". National Park Service. U.S. Department of the Interior. Retrieved 13 October 2021.
  3. ^ NOAA. "Ocean floor features". National Oceanic and Atmospheric Administration. Retrieved 13 October 2021.
  4. doi:10.2973/odp.proc.sr.155.200.1997
    . we follow Ocean Drilling Program (ODP) meters below seafloor (mbsf) convention
  5. ISBN 978-0-521-85485-6. Retrieved 11 June 2010. metres below the seafloor (mbsf) {{cite book}}: |work= ignored (help
    )
  6. ^ Murray, Richard W. "Ocean-Floor Sediments," Water Encyclopedia
  7. ^
    ISBN 978-1-4051-8734-3
    .
  8. ISBN 978-1-4051-8734-3
    .
  9. ^ a b c d "The Bottom of the Ocean," Marine Science
  10. ^ "Types of Marine Sediments", Article Myriad
  11. ^ Grobe, Hannes; Kiekmann, Bernhard; Hillenbrand, Claus-Dieter. "The memory of polar oceans" (PDF): 37–45. {{cite journal}}: Cite journal requires |journal= (help)
  12. ^ Tripati, Aradhna, Lab 6-Marine Sediments, Marine Sediments Reading, E&SSCI15-1, UCLA, 2012
  13. ^ a b Benthos from the Census of Antarctic Marine Life website
  14. ^ US Department of Commerce, National Oceanic and Atmospheric Administration. "How does pressure change with ocean depth?". oceanservice.NOAA.gov.
  15. ^ Haeckel, E. 1891. Plankton-Studien. Jenaische Zeitschrift für Naturwissenschaft 25 / (Neue Folge) 18: 232-336. BHL.
  16. Perseus Project
    .
  17. ^ "North American Benthological Society website". Archived from the original on 2008-07-05. Retrieved 2008-08-16.
  18. ^ Nehring, S. & Albrecht, U. (1997). Benthos und das redundant Benton: Neologismen in der deutschsprachigen Limnologie. Lauterbornia 31: 17-30, [1].
  19. ^ Giovanni Coco, Z. Zhou, B. van Maanen, M. Olabarrieta, R. Tinoco, I. Townend. Morphodynamics of tidal networks: Advances and challenges. Marine Geology Journal. 1 December 2013.
  20. ^ Sandwell, D. T.; Smith, W. H. F. (2006-07-07). "Exploring the Ocean Basins with Satellite Altimeter Data". NOAA/NGDC. Retrieved 2007-04-21.
  21. hdl:1912/3862
    .
  22. S2CID 210979539. Retrieved 13 October 2021. {{cite book}}: |website= ignored (help
    )
  23. ^ a b "The Discovery of Hydrothermal Vents". Woods Hole Oceanographic Institution. 11 June 2018. Retrieved 13 October 2021.
  24. ISBN 978-3-662-05127-6
    .
  25. ^ "Ocean Surface Topography". Science Mission Directorate. 31 March 2010. Retrieved 13 October 2021.
  26. ^ May, Tiffany (7 October 2020). "Hidden Beneath the Ocean's Surface, Nearly 16 Million Tons of Microplastic". The New York Times. Retrieved 30 November 2020.
  27. ^ "14 million tonnes of microplastics on sea floor: Australian study". phys.org. Retrieved 9 November 2020.
  28. S2CID 222125532. Available under CC BY 4.0
    .
  29. ISSN 2662-4435
    .
  30. ^ "Seabed Mining". The Ocean Foundation. 2010-08-07. Archived from the original on 2021-02-28. Retrieved 2021-04-02.
  31. ^ "SPC-EU Deep Sea Minerals Project - Publications and Reports". dsm.gsd.spc.int. Archived from the original on 2021-09-06. Retrieved 2021-09-06.
  32. ^ SITNFlash (2019-09-26). "The Next Gold Rush: Mining in the deep sea". Science in the News. Archived from the original on 2022-10-04. Retrieved 2023-02-17.
  33. ^ Poston, Jonathan. "Deeperminers". site name. Archived from the original on 2023-01-19. Retrieved 2023-02-17.
  34. ^ Nascimento, Decio. "Council Post: Could Deep-Sea Mining Rescue The Future Of The Renewable Transition?". Forbes. Archived from the original on 2022-12-06. Retrieved 2023-02-17.
  35. doi:10.1016/j.marpol.2017.05.010
    .
  36. hdl:10261/216646
    .
  37. ^ Rosenbaum, Dr. Helen (November 2011). "Out of Our Depth: Mining the Ocean Floor in Papua New Guinea". Deep Sea Mining Campaign. MiningWatch Canada, CELCoR, Packard Foundation. Archived from the original on 13 December 2019. Retrieved 2 May 2020.
  38. S2CID 128645876
    .
  39. ^ "Collapse of PNG deep-sea mining venture sparks calls for moratorium". the Guardian. 2019-09-15. Archived from the original on 2021-04-11. Retrieved 2021-04-02.
  40. ^ "David Attenborough calls for ban on 'devastating' deep sea mining". the Guardian. 2020-03-12. Archived from the original on 2021-09-06. Retrieved 2021-09-06.
  41. ^ "Google, BMW, Volvo, and Samsung SDI sign up to WWF call for temporary ban on deep-sea mining". Reuters. 2021-03-31. Archived from the original on 2021-09-06. Retrieved 2021-09-06.
  42. ^ "SPC-EU Deep Sea Minerals Project - Home". dsm.gsd.spc.int. Archived from the original on 2021-09-06. Retrieved 2021-09-06.
  43. ^ "The Environmental Protection Authority (EPA) has refused an application by Chatham Rock Phosphate Limited (CRP)". Deepwater group. 2015. Archived from the original on 2016-01-24. Retrieved 6 September 2021.
  44. ^ "Exploration Contracts | International Seabed Authority". isa.org.jm. Archived from the original on 2021-02-05. Retrieved 2021-09-06.
  45. ^ Kuo, Lily (October 19, 2023). "China is set to dominate the deep sea and its wealth of rare metals". Washington Post. Retrieved 2024-02-14.
  46. ^ "Cook Islands Seabed Minerals Authority - Map". Archived from the original on 2022-06-30. Retrieved 2022-07-06.
  47. ^ "Campaign Reports | Deep Sea Mining: Out Of Our Depth". 2011-11-19. Archived from the original on 2019-12-13. Retrieved 2021-09-06.
  48. ^ a b SPC (2013). Deep Sea Minerals: Deep Sea Minerals and the Green Economy Archived 2021-11-04 at the Wayback Machine. Baker, E., and Beaudoin, Y. (Eds.) Vol. 2, Secretariat of the Pacific Community
  49. ^ "Breaking Free From Mining" (PDF). Archived from the original (PDF) on 2021-12-23.
  50. ^ John J. Gurney, Alfred A. Levinson, and H. Stuart Smith (1991) Marine mining of diamonds off the West Coast of Southern Africa, Gems & Gemology, p. 206
  51. ^ "Seabed Mining". The Ocean Foundation. 2010-08-07. Archived from the original on 2021-09-08. Retrieved 2021-09-06.
  52. ^ Safeguarding the Underwater Cultural Heritage UNESCO. Retrieved 12 September 2012.

Further reading

External links

Look up seabed in Wiktionary, the free dictionary.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Seabed&oldid=1219810417"
This page is based on the copyrighted Wikipedia article: Seabed. Articles is available under the CC BY-SA 3.0 license; additional terms may apply.Privacy Policy