Abyssal zone

The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. "Abyss" derives from the Greek word ἄβυσσος, meaning bottomless. At depths of 4,000 to 6,000 metres (13,000 to 20,000 ft), this zone remains in perpetual darkness. These regions are also characterized by continuous cold and lack of nutrients. The abyssal zone has temperatures around 2 to 3 °C (36 to 37 °F) through the large majority of its mass.[1] It is the deeper part of the midnight zone which starts in the bathypelagic waters above.[1][2]

The area below the abyssal zone is the sparsely inhabited hadal zone.[3] The zone above is the bathyal zone.[3]

Trenches

Pelagiczone
Layers of the pelagic zone

The deep trenches or fissures that plunge down thousands of metres below the ocean floor (for example, the midoceanic trenches such as the Mariana Trench in the Pacific) are almost unexplored.[2] Previously, only the bathyscaphe Trieste, the remote control submarine Kaikō and the Nereus have been able to descend to these depths.[4][5] However, as of March 25, 2012 one vehicle, the Deepsea Challenger was able to penetrate to a depth of 10,898.4 metres (35,756 ft).

Biology

Overall, the deep sea is a very food-limited environment. In the abyssal zone, biomass is directly related to the amount of food either supplied from transporting ocean currents or from the water column above. The biological pump is thought of as the main driver for cycling organic matter (e.g. particulate organic carbon or dissolved organic carbon) from the atmosphere into the surface ocean, and eventually to the deep ocean.[6]

Spatially, the abundance of organisms in the deep ocean is hypothesized to be highest where the surface productivity is the highest, as long as there is efficient export from surface ocean to deep ocean. This is located at the bottom of the ocean floor Studies have shown that marine snow alone does not supply an adequate amount of nutrients to support the population of benthic organisms. However, population booms of algae or animals near the surface ocean can result in heavy pulses of particulate organic matter that, in a few weeks, will deliver as many nutrients as would normally be delivered over decadal timescales of marine snow transport.[7]

Some sea floor locations, such as mid-ocean ridges, are unique in that they contain hydrothermal vents. These vents emit geothermically reduced sulfur compounds that allow for microbial primary production, sustaining many benthic organisms in absence of the sunlight required for photosynthesis.[8]

See also

References

  1. ^ a b "Deep Sea Biome". Untamed Science. Archived from the original on 31 March 2009. Retrieved 2009-04-27.
  2. ^ a b Nelson, Rob (April 2007). "Abyssal". The Wild Classroom. Archived from the original on 25 March 2009. Retrieved 2009-04-27.
  3. ^ a b "Abyssal". Dictionary.com. Archived from the original on 18 April 2009. Retrieved 2009-04-27.
  4. ^ "History of the Bathyscaph Trieste". Bathyscaphtrieste.com. Retrieved 2009-04-27.
  5. ^ "World's deepest-diving submarine missing". USA Today. Gannett Company Inc. 2003-07-02. Retrieved 2009-04-27.
  6. ^ Glover (2010). "Temporal Change in Deep-Sea Benthic Ecosystems: A Review of the Evidence From Recent Time-Series Studies". Advances in Marine Biology. 58: 10–12. doi:10.1016/S0065-2881(10)58001-5.
  7. ^ "Marine biology: Feast and famine on the abyssal plain". ScienceDaily. Monterey Bay Aquarium Research Institute. November 11, 2013. Retrieved 23 October 2017.
  8. ^ Karl, D.M.; Wirsen, C.O.; Jannasch, H.W. (March 21, 1980). "Deep-sea primary production at the Galapagos hydrothermal vents". Science. 207.
Abyssal plain

An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3,000 metres (9,800 ft) and 6,000 metres (20,000 ft). 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. They are among the flattest, smoothest, and least explored regions on Earth. Abyssal plains are key geologic elements of oceanic basins (the other elements being an elevated mid-ocean ridge and flanking abyssal hills).

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), and as this basaltic 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 sediments, mainly clay and silt. Much of this sediment is deposited by turbidity currents that have been channelled from the continental margins along submarine canyons into deeper water. The rest is composed chiefly of pelagic sediments. Metallic nodules are common in some areas of the plains, with varying concentrations of metals, including manganese, iron, nickel, cobalt, and copper.

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 cycling, dissolution of calcium carbonate, and atmospheric CO2 concentrations over time scales of a hundred to a thousand years. The structure of abyssal ecosystems are strongly influenced by the rate of flux of food to the seafloor and the composition of the material that settles. Factors such as climate change, fishing practices, and ocean fertilization have a substantial effect on patterns of primary production in the euphotic zone.Abyssal plains were not recognized as distinct physiographic features of the sea floor until the late 1940s and, until very recently, none had been studied on a systematic basis. They are poorly preserved in the sedimentary record, because they tend to be consumed by the subduction process.

Aphotic zone

The aphotic zone (aphotic from Greek prefix ἀ- + φῶς "without light") is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates. Consequently, bioluminescence is essentially the only light found in this zone. Most food in this zone comes from dead organisms sinking to the bottom of the lake or ocean from overlying waters.

The depth of the aphotic zone can be greatly affected by such things as turbidity and the season of the year. The aphotic zone underlies the photic zone, which is that portion of a lake or ocean directly affected by sunlight.

Benthic zone

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi) as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

Chondrites (genus)

Chondrites is a trace fossil ichnogenus, preserved as small branching burrows of the same diameter that superficially resemble the roots of a plant. The origin of these structures is currently unknown. Chondrites is found in marine sediments from the Cambrian period of the Paleozoic onwards. It is especially common in sediments that were deposited in reduced-oxygen environments.

Echinoderm

Echinoderm is the common name given to any member of the phylum Echinodermata (from Ancient Greek, ἐχῖνος, echinos – "hedgehog" and δέρμα, derma – "skin") of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone.

The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.

Aside from the hard-to-classify Arkarua (a Precambrian animal with echinoderm-like pentamerous radial symmetry), the first definitive members of the phylum appeared near the start of the Cambrian. One group of Cambrian echinoderms, the cinctans (Homalozoa), which are close to the base of the echinoderm origin, have been found to possess external gills used for filter feeding, similar to those possessed by chordates and hemichordates.The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, it is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution.

Grimpoteuthis challengeri

Grimpoteuthis challengeri is a species of large octopus living in the abyssal zone.

Hadal zone

The hadal zone (named after the realm of Hades, the underworld in Greek mythology), also known as the hadopelagic zone, is the deepest region of the ocean lying within oceanic trenches. The hadal zone is found from a depth of around 6,000 to 11,000 metres (20,000 to 36,000 ft) to the bottom of the ocean, and exists in long but narrow topographic V-shaped depressions.The cumulative area occupied by the 46 individual hadal habitats worldwide is less than 0.25 percent of the world's seafloor, yet trenches account for over 40 percent of the ocean's depth range. Most hadal habitat is found in the Pacific Ocean.

Kaup's arrowtooth eel

The Kaup's arrowtooth eel (Synaphobranchus kaupii, also known as the Kaup's cut-throat eel, the Gray's cutthroat, the Longnosed eel, the Northern cutthroat eel, or the Slatjaw cutthroat eel) is an eel in the family Synaphobranchidae (cutthroat eels). It was described by James Yate Johnson in 1862. It is a marine, deep water-dwelling eel which is known from the Indo-Western Pacific and eastern and western Atlantic Ocean, including the Faroe Islands, Iceland, Cape Verde, the Western Sahara, Nigeria, Namibia, South Africa, Greenland, France, Saint Pierre and Miquelon, the United Kingdom, Ireland, the Philippines, Portugal, Spain, the Bahamas, Brazil, Canada, Cuba, Japan, Australia, Mauritania, Morocco, and Hawaii. It dwells at a depth range of 120 to 4,800 metres (390 to 15,750 ft), most often between 400 to 2,200 metres (1,300 to 7,200 ft), and inhabits the upper abyssal zone on the continental slope. It is intolerant of the temperatures of higher waters. Males can reach a maximum total length of 100 centimetres (39 in).The common name and species epithet "kaupii" refer to naturalist Johann Jakob Kaup. The Kaup's arrowtooth eel is preyed on by Coryphaenoides rupestris. Its own diet consists of benthic crustaceans including decapods and amphipods, planktonic crustaceans including euphausiids and mysids, cephalopods including species of Rossia, and bony fish including Macroramphosus scolopax. It is of no commercial interest to fisheries, but it is sometimes caught as by-catch by bottom longline and baited fish traps.Due to the widespread distribution of the species and its abundance in many regions, the IUCN redlist currently lists the Kaup's arrowtooth eel as Least Concern.

List of echinoderms of South Africa

The list of echinoderms of South Africa is a list of species that form a part of the echinoderm (Phylum Echinodermata) fauna of South Africa, and includes the starfish, feather stars, brittle stars, sea urchins and sea cucumbers. The list follows the SANBI listing on iNaturalist.

Echinoderm is the common name given to any member of the phylum Echinodermata (from Ancient Greek, ἐχῖνος, echinos – "hedgehog" and δέρμα, derma – "skin") of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone.

The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.

Aside from the hard-to-classify Arkarua (a Precambrian animal with echinoderm-like pentamerous radial symmetry), the first definitive members of the phylum appeared near the start of the Cambrian. One group of Cambrian echinoderms, the cinctans (Homalozoa), which are close to the base of the echinoderm origin, have been found to possess external gills used for filter feeding, similar to those possessed by chordates and hemichordates.

The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, it is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution.

Monoplacophora

Monoplacophora, meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell now living at the bottom of the deep sea. Extant representatives were not recognized as such until 1952; previously they were known only from the fossil record.

Although the shell of many monoplacophorans is limpet-like in shape, they are not gastropods, nor do they have any close relation to gastropods.

Photic zone

The photic zone, euphotic zone (Greek for "well lit": εὖ "well" + φῶς "light"), or sunlight (or sunlit) zone is the uppermost layer of water in a lake or ocean that is exposed to intense sunlight. It corresponds roughly to the layer above the compensation point, i.e. depth where the rate of carbon dioxide uptake, or equivalently, the rate of photosynthetic oxygen production, is equal to the rate of carbon dioxide production, equivalent to the rate of respiratory oxygen consumption, i.e. the depth where net carbon dioxide assimilation is zero.

It extends from the surface down to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth. Accordingly, its thickness depends on the extent of light attenuation in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 meters in the open ocean. It also varies with seasonal changes in turbidity.

Since the photic zone is where almost all of the photosynthesis occurs, the depth of the photic zone is generally proportional to the level of primary production that occurs in that area of the ocean. About 90% of all marine life lives in the photic zone. A small amount of primary production is generated deep in the abyssal zone around the hydrothermal vents which exist along some mid-oceanic ridges.

The zone which extends from the base of the euphotic zone to about 200 metres is sometimes called the disphotic zone. While there is some light, it is insufficient for photosynthesis, or at least insufficient for photosynthesis at a rate greater than respiration. The euphotic zone together with the disphotic zone coincides with the epipelagic zone. The bottommost zone, below the euphotic zone, is called the aphotic zone. Most deep ocean waters belong to this zone.

The transparency of the water, which determines the depth of the photic zone, is measured simply with a Secchi disk. It may also be measured with a photometer lowered into the water.

Psychrolutes microporos

Psychrolutes microporos is a species of deepwater marine fish in the family Psychrolutidae, commonly known as a blobfish or fathead. It is found in the abyssal zone in waters around Australia and New Zealand.

Psychropotes longicauda

Psychropotes longicauda is a species of sea cucumber in the family Psychropotidae. It inhabits the deep sea where the adult is found on the seabed. The larva is pelagic and has an appendage shaped like a sail on its back which may enable it to move through the water.The animal is sometimes called the "gummy squirrel" because it looks like a squirrel-shaped gummy bear.

Thaumatichthys axeli

Thaumatichthys axeli is a bottom-dwelling deep-sea anglerfish of the family Thaumatichthyidae. Thaumatichthys axeli lives at a depth of around 3,600 meters (in the abyssal zone), deeper than any other member of the genus Thaumatichthys. As with other members of the family, they possess a distinctive forked light organ inside their mouth, which they use to lure prey. Large, curved teeth "fringe the upper jaw like a comb". Specimens have been founding measuring up to about 50 cm.

Trenchia argentinae

Trenchia argentinae is a species of sea snail, a marine gastropod mollusk, unassigned in the superfamily Seguenzioidea.

Whale fall

A whale fall is the carcass of a cetacean that has fallen into the bathyal or abyssal zone (i.e. deeper than 1,000 m, or 3,300 ft) on the ocean floor. They can create complex localized ecosystems that supply sustenance to deep-sea organisms for decades. This is unlike in shallower waters, where a whale carcass will be consumed by scavengers over a relatively short period of time. It was with the development of deep-sea robotic exploration that whale falls were first observed in the late 1970s.Organisms that have been observed at deep-sea whale falls include giant isopods, squat lobsters, bristleworms, prawns, shrimp, lobsters, hagfish, Osedax, crabs, sea cucumbers, and sleeper sharks.

Whale falls are able to occur in the deep open ocean due to cold temperatures and high hydrostatic pressures. In the coastal ocean, a higher incidence of predators as well as warmer waters hasten the decomposition of whale carcasses. Carcasses may also float due to decompositional gases, keeping the carcass at the surface. In the deep-sea, cold temperatures slow decomposition rates, and high hydrostatic pressures increase gas solubility, allowing food falls to remain intact and sink to great depths.

Yelovichnus

Yelovichnus is an "enigmatic" genus known from fossils of the Ediacaran period. Yelovichnus was originally believed to be an ichnotaxon: its fossils, because of their "meandering nature", were initially thought to be feeding trails left by other life forms, such as annelids or mollusks. Better-preserved specimens later demonstrated that the fossils were not true feeding trails, as there was no evidence of turning by the life form that supposedly left them. The fossils are now recognized as belonging to an organism taking the form of "collapsed, segmented tubes", possibly an alga or a protist. It has also been argued that Yelovichnus and similar organisms are xenophyophores, large but single-cellular organisms that exist today in the abyssal zone. Due to similar structures found in their fossils, it is theorized that Yelovichnus may be related to Palaeopascichnus, as well as Aspidella and Neonereites. The main difference between Yelovichnus and Palaeopasicichnus is the shape of their segments: the segments of Yelovichnus took the shape of "closed, ovate-shaped loops", whereas the segments of Palaeopascichnus were quite varied in shape.The genus and species was described by Mikhail A. Fedonkin in 1985 from the Ediacaran (Vendian) deposits of the White Sea area, Russia. Yelovichnus was named after the Yeloviy Creek near the locality.

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