The Legent of Sea Monster "Siren"

In Greek mythology the Sirens were sea deities who lived on an island called Sirenum scopuli. In some different traditions they are placed on Cape Pelorum, others in the island of Anthemusa, and still others in the Sirenusian islands near Paestum, or in Capreae (Strab. i. p. 22 ; Eustath. ad Horn. p. 1709 ; Serv. I.e.). All locations were described to be surrounded by cliffs and rocks. Seamen who sailed near were decoyed with the Sirens' enchanting music to shipwreck on the rocky coast.
The Sirens were considered the daughters of Achelous (by Terpsichore, Melpomene, Sterope, Chthon (in Euripides' Helen)) or Phorcys (Virgil. V. 846; Ovid XIV, 88). Homer says nothing of their number, but later writers mention both their names and number ; some state that they were two, Aglaopheme and Thelxiepeia (Eustath. ad Horn. p. 1709) ; and others, that there were three, Peisinoe, Aglaope, and Thelxiepeia (Tzetz. ad LycopL7l2) or Parthenope, Ligeia, and Leucosia (Eustath. /. c.; Strab. v. pp. 246, 252 ; Serv. ad Virg. Georg. iv. 562). Their number is variously reported as between two and five, and their individual names as Thelxiepeia/Thelxiope/Thelxinoe, Molpe, Aglaophonos/Aglaope, Pisinoe/Peisinoë, Parthenope, Ligeia, Leucosia, Raidne, and Teles. According to some versions, they were playmates of young Persephone and were given wings by Demeter to search for Persephone when she was abducted (Ovid V, 551). Their song is continually calling on Persephone. The term "siren song" refers to an appeal that is hard to resist but that, if heeded, will lead to a bad result. Later writers have stated that the Sirens were anthropophagous, but this is not supported by classical writings, nor is there any evidence that the Sirens drowned themselves failing to seduce one of the many heroes that passed their way, though that has also become a fixture in retellings of the story.

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The Legent of Sea Monster "Scylla"

Scylla was one of the many monsters in Greek mythology (one other being Charybdis) that live on either side of a narrow channel of water. The two sides of the strait are within an arrow's range of each other, so close that sailors attempting to avoid Charybdis will pass too close to Scylla and vice versa. The phrase between Scylla and Charybdis has come to mean being in a state where one is between two dangers and moving away from one will cause you to be in danger from the other. Traditionally the aforementioned strait has been associated with the Strait of Messina between Italy and Sicily, but more recently this theory has been challenged, and the alternative location of Cape Skilla in northwest Greece has been suggested.
Scylla is a horribly grotesque sea monster, with six long necks equipped with grisly heads, each of which contained three rows of sharp teeth. Her body consisted of twelve canine legs and a fish's tail. She was one of the children of Phorcys and either Hecate, Crataeis, Lamia or Ceto (where Scylla would also be known as one of the Phorcydes). Some sources cite her parents as Triton and Lamia.
In classical art she was depicted as a fish-tailed mermaid with four to six dog-heads ringing her waist.
In Homer's Odyssey, Odysseus is given advice by a ghost from the land of the dead to sail closer to Scylla, for Charybdis could drown his whole ship. Odysseus then successfully sails his ship past Scylla and Charybdis, but Scylla manages to catch six of his men, devouring them alive. When this happens, Odysseus takes the empty spot on the boat and helps the men row the ship out of harms way.
According to Ovid, Scylla was once a beautiful nymph. The fisherman-turned-sea-god Glaucus fell madly in love with her, but she fled from him onto the land where he could not follow. Despair filled his heart. He went to the sorceress Circe to ask for a love potion to melt Scylla's heart. As he told his tale of love about Scylla to Circe, she herself fell in love with him. She wooed him with her sweetest words and looks, but the sea-god would have none of her. Circe was furiously angry, but with Scylla and not with Glaucus. She prepared a vial of very powerful poison and poured it in the pool where Scylla bathed. As soon as the nymph entered the water she was transformed into a frightful monster with twelve feet and six heads, each with three rows of teeth. Angry, growling wolf heads grew from her waist, and she tried to brush them off. She stood there in utter misery, unable to move, loathing and destroying everything that came into her reach, a peril to all sailors who passed near her. Whenever a ship passed, each of her heads would seize one of the crew.
In a late Greek myth it was said that Heracles encountered Scylla during a journey to Sicily and slew her. Her father, the sea-god Phorcys, then applied flaming torches to her body and restored her to life.
It is said that by the time Aeneas' fleet came through the strait after the fall of Troy, Scylla had been changed into a dangerous rock outcropping which still stands there to this day.
Scylla and Charybdis are believed to have been the entities from which the phrase, "Between a rock and a hard place" originated.
It has been suggested that the myth of Scylla may have been inspired by real life encounters with giant squid (which are normally dying when near the surface), and she has some similar features to the kraken in Norse mythology and lusca in Caribbean mythology.

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The Legent of Sea Mosters "Kraken"

Kraken are legendary sea monsters of gargantuan size, said to have dwelled off the coasts of Norway and Iceland. The sheer size and fearsome appearance attributed to the beasts have made them common ocean-dwelling monsters in various fictional works (see Kraken in popular culture). The legend may actually have originated from sightings of real giant squid that are estimated to grow to 13 metres (46 feet) in length, including the tentacles. These creatures normally live at great depths, but have been sighted at the surface and reportedly have "attacked" small ships.
Kraken is the definite article form of krake, a Scandinavian word designating an unhealthy animal, or something twisted.[1] In modern German, Krake (plural: Kraken) means octopus, but can also refer to the legendary Kraken (Terrell, 1999).
History

Although the name kraken never appears in the Norse sagas, there are similar sea monsters, the hafgufa and lyngbakr, both described in Örvar-Odds saga and the Norwegian text from c. 1250, Konungs skuggsjá.[2] Carolus Linnaeus included kraken as cephalopods with the scientific name Microcosmus in the first edition of his Systema Naturae (1735), a taxonomic classification of living organisms, but excluded the animal in later editions. Kraken were also extensively described by Erik Pontoppidan, bishop of Bergen, in his "Natural History of Norway" (Copenhagen, 1752–3).
Early accounts, including Pontoppidan's, describe the kraken as an animal "the size of a floating island" whose real danger for sailors was not the creature itself, but the whirlpool it created after quickly descending back into the ocean. However, Pontoppidan also described the destructive potential of the giant beast: "It is said that if it grabbed the largest warship, it could manage to pull it down to the bottom of the ocean" (Sjögren, 1980). Kraken were always distinct from sea serpents, also common in Scandinavian lore (Jörmungandr for instance). A representative early description is given by the Swede Jacob Wallenberg in his book Min son på galejan ("My son on the galley") from 1781:
"… Kraken, also called the Crab-fish, which [according to the pilots of Norway] is not that huge, for heads and tails counted, he is no larger than our Öland is wide [i.e. less than 16 km] ... He stays at the sea floor, constantly surrounded by innumerable small fishes, who serve as his food and are fed by him in return: for his meal, if I remember correctly what E. Pontoppidan writes, lasts no longer than three months, and another three are then needed to digest it. His excrements nurture in the following an army of lesser fish, and for this reason, fishermen plumb after his resting place ... Gradually, Kraken ascends to the surface, and when he is at ten to twelve fathoms, the boats had better move out of his vicinity, as he will shortly thereafter burst up, like a floating island, spurting water from his dreadful nostrils and making ring waves around him, which can reach many miles. Could one doubt that this is the Leviathan of Job? "
According to Pontoppidan, Norwegian fishermen often took the risk of trying to fish over kraken, since the catch was so good. If a fisherman had an unusually good catch, they used to say to each other, "You must have fished on Kraken." Pontoppidan also claimed that the monster was sometimes mistaken for an island, and that some maps that included islands that were only sometimes visible were actually indicating kraken. Pontoppidan also proposed that a young specimen of the monster once died and was washed ashore at Alstahaug (Bengt Sjögren, 1980).
Since the late 18th century, kraken have been depicted in a number of ways, primarily as large octopus-like creatures, and it has often been alleged that Pontoppidan's kraken might have been based on sailors' observations of the giant squid. In the earliest descriptions, however, the creatures were more crab- like than octopus-like, and generally possessed traits that are associated with large whales rather than with giant squid. Some traits of kraken resemble undersea volcanic activity occurring in the Iceland region, including bubbles of water; sudden, dangerous currents; and appearance of new islets.
In 1802, the French malacologist Pierre Dénys de Montfort recognized the existence of two kinds of giant octopus in Histoire Naturelle Générale et Particulière des Mollusques, an encyclopedic description of mollusks. Montfort claimed that the first type, the kraken octopus, had been described by Norwegian sailors and American whalers, as well as ancient writers such as Pliny the Elder. The much larger second type, the colossal octopus (depicted in the above image), was reported to have attacked a sailing vessel from Saint-Malo, off the coast of Angola.
Montfort later dared more sensational claims. He proposed that ten British warships that had mysteriously disappeared one night in 1782 must have been attacked and sunk by giant octopuses. Unfortunately for Montfort, the British knew what had happened to the ships, resulting in a disgraceful revelation for Montfort. Pierre Dénys de Montfort's career never recovered and he died starving and poor in Paris around 1820 (Sjögren, 1980). In defence of Pierre Dénys de Montfort, it should be noted that many of his sources for the "kraken octopus" probably described the very real giant squid, proven to exist in 1857.
In 1830, possibly aware of Pierre Dénys de Montfort's work, Alfred Tennyson published his popular poem "The Kraken" (essentially an irregular sonnet), which disseminated Kraken in English forever fixed with its superfluous the. The poem in its last three lines, also bears similarities to the legend of Leviathan, a sea monster, who shall rise to the surface at the end of days.
Tennyson's description apparently influenced Jules Verne's imagined lair of the famous giant squid in Twenty Thousand Leagues Under the Sea from 1870. Verne also makes numerous references to Kraken, and Bishop Pontoppidan in the novel.
Later developments of the Kraken image may be traced at Kraken in popular culture.

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The Legent of Sea Mosters "Charybdis"

In Greek mythology, Charybdis or Kharybdis (in Greek, Χάρυβδις) was a sea monster, daughter of Poseidon and Gaia. She takes form as a monstrous mouth. She swallows huge amounts of water three times a day and then belches them back out again creating whirlpools. Charybdis was originally a naiad, sea-nymph who flooded land to enlarge her father's underwater kingdom, until Zeus turned her into a monster. He was angry that she was taking so much of his land and made it so that she would be incredibly thirsty three times a day and suck in the water.
The myth has Charybdis lying on one side of a narrow channel of water. On the other side of the strait was Scylla, another sea-monster. The two sides of the strait are within an arrow's range of each other, so close that sailors attempting to avoid Charybdis will pass too close to Scylla and vice versa. The phrase between Scylla and Charybdis has come to mean being in a state where one is between two dangers and moving away from one will cause you to be in danger of the other. Between Scylla and Charybdis is the origin of the phrase "between the rock and the whirlpool" (the rock upon which Scylla dwelt and the whirlpool of Charybdis) and may be the genesis of the phrase "between a rock and a hard place".
The Argonauts were able to avoid both dangers because they were guided by Thetis, one of the Nereids. Odysseus was not so fortunate; he chose to risk Scylla at the cost of some of his crew rather than lose the whole ship to Charybdis. (Homer's Odyssey, Book XII). Odysseus successfully navigated the strait, losing only six men to Scylla. However, the men offended Helios by killing the god's sacred cattle, and Zeus retaliated by destroying ship and crew with a thunderbolt.
Stranded on a makeshift raft, Odysseus was swept back through the strait to face Scylla and Charybdis again. This time, Odysseus passed near Charybdis. His raft was sucked into Charybdis' maw, but Odysseus survived by clinging to a fig tree grown on the rock overhanging her lair. On the next outflow of water, his raft was expelled, and Odysseus was able to recover it and paddle away.
Traditionally, the location of Charybdis has been associated with the Strait of Messina off the coast of Sicily, opposite the rock called Scylla. The whirlpool there is caused by the meeting of currents, but is seldom dangerous. Recently scholars have looked again at the location and suggested this association was a misidentification and that a more likely origin for the story could be found close by Cape Skilla in north west Greece.

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The Legent of Sea monster

Sea monsters or leviathans are sea-dwelling, mythical or legendary creatures, often believed to be of immense size.
Marine monsters can take many forms, including sea dragons, sea serpents, or multi-armed beasts; they can be slimy or scaly, often spouting jets of water. Often they are pictured threatening ships.

Sightings and legendsHistorically

Decorative drawings of heraldic dolphins and sea monsters were frequently used to illustrate maps, such as the Carta marina. This practice died away with the advent of modern cartography. Nevertheless, stories of sea monsters and eyewitness accounts which claim to have seen these beasts persist to this day. Such sightings are often catalogued and studied by folklorists and cryptozoologists.
Sea monster accounts are found in virtually all cultures that have contact with the sea. Eyewitness accounts come from all over the world. For example, Avienus relates of Carthaginian explorer Himilco's voyage "...there monsters of the deep, and beasts swim amid the slow and sluggishly crawling ships." (lines 117-29 of Ora Maritima). Sir Humphrey Gilbert claimed to have encountered a lion-like monster with "glaring eyes" on his return voyage after formally claiming St. John's, Newfoundland (1583) for England. Another account of an encounter with a sea monster comes from July 1734. Hans Egede, a Danish/Norwegian missionary reported that on a voyage to Gothaab/Nuuk on the western coast of Greenland:
''[There] appeared a very terrible sea-animal, which raised itself so high above the water, that its head reached above our maintop. It had a long, sharp snout, and blew like a whale, had broad, large flippers, and the body was, as it were, covered with hard skin, and it was very wrinkled and uneven on its skin; moreover, on the lower part it was formed like a snake, and when it went under water again, it cast itself backwards, and in doing so, it raised its tail above the water, a whole ship length from its body. That evening, we had very bad weather.''

Other reports are known from the Pacific, Indian and Southern Oceans (e.g. see Heuvelmans 1968).
A more recent development has been the mysterious "Bloop" picked up by hydrophonic equipment since 1997. While matching the audio characteristics of an animal, it was deemed too large to be a whale. Investigations thus far have been inconclusive.
It is debatable what these modern "monsters" might be. Possibilities include frilled shark, basking shark, oarfish, giant squid, seiches, or whales. For example Ellis (1999) suggested the Egede-rellis-phooba monster might have been a giant squid. Other hypotheses are that modern-day monsters are surviving specimens of giant marine reptiles, such as ichthyosaur or plesiosaur, from the Jurassic and Cretaceous Periods, or extinct whales like Basilosaurus.
In 1892, Anthonid Cornelis Oudemans, then director of the Royal Zoological Gardens at The Hague saw the publication of his The Great Sea Serpent which suggested that many sea serpent reports were best accounted for as a previously unknown giant, long-necked pinniped.
It is likely that many other reports of sea monsters are misinterpreted sightings of shark and whale carcasses (see below), floating kelp, logs or other flotsam such as abandoned rafts, canoes and fishing nets.
Alleged sea monster carcasses

Sea monster corpses have been reported since recent antiquity (Heuvelmans 1968). Unidentified carcasses are often called globsters. The alleged plesiosaur netted by the Japanese trawler Zuiyo Maru off New Zealand caused a sensation in 1977 and was immortalized on a Brazilian postage stamp before it was suggested by the FBI to be the decomposing carcass of a basking shark. Likewise, DNA testing confirmed that an alleged sea monster washed up on Fortune Bay, Newfoundland in August, 2001, was a sperm whale.
Another modern example of a "sea monster" was the strange creature washed up on the Chilean sea shore in July, 2003. It was first described as a "mammoth jellyfish as long as a bus" but was later determined to be another corpse of a sperm whale. Cases of boneless, amorphic globsters are sometimes believed to be gigantic octopuses, but it has now been determined that sperm whales dying at sea decompose in such a way that the blubber detaches from the body, forming featureless whitish masses that sometimes exhibit a hairy texture due to exposed strands of collagen fibers. The analysis of the Zuiyo Maru carcass revealed a comparable phenomenon in decomposing basking shark carcasses, which lose most of the lower head area and the dorsal and caudal fins first, making them resemble a plesiosaur.

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Submarine canyon

A Submarine canyon is a steep-sided valley on the sea floor of the continental slope. Many submarine canyons are found as extensions to large rivers; however there are many that have no such association. Canyons cutting the continental slopes have been found at depths greater than 2 km below sea level. They are formed by powerful turbidity currents, volcanic and earthquake activity. Many submarine canyons continue as submarine channels across continental rise areas and may extend for hundreds of kilometers.

Characteristics

Submarine canyons are more common on steep slopes than on gentle slopes. They show erosion through all substrates, from unlithified sediment to crystalline rock. They are more densely spaced on steep slopes while being rare on gentle slopes. The walls are generally very steep and can be near vertical. The walls are subject to erosion by turbidity currents, bioerosion, or slumping
Examples of submarine canyons:

Congo canyon, the largest river canyon, extending from the Congo river, is 800 km (500 miles) long, and 1,200m (4000 ft) deep.

Amazon canyon, extending from the Amazon river.

Hudson canyon, extending from the Hudson river.

Ganges canyon, extending from the Ganges river.

Indus canyon, extending from the Indus river.

Monterey Canyon, off the coast of central California.

La Jolla and Scripps canyon, off the coast of La Jolla, southern California.

Whittard Canyon, Atlantic Ocean off southwest Ireland.

Bering Canyon, in the Bering sea Zhemchug Canyon the largest submarine canyon in the world, also in the Bering sea.

Formation of submarine canyons

Many mechanisms have been proposed for the formation of submarine canyons, and during the 1940s and 1950s the primary causes of submarine canyons were subject to active debate.
An early and obvious theory was that the canyons present today were carved during glacial times, when sea level was about 200 meters below present sea level, and rivers flowed to the edge of the continental shelf. However, while many (but not all) canyons are found offshore from major rivers, subaerial river erosion cannot have been active to the water depths as great as 3000 meters where canyons have been mapped, as it is well established (by many lines of evidence) that sea levels did not fall to those depths.
The major mechanism of canyon erosion is now thought to be turbidity currents and underwater landslides. Turbidity currents are dense, sediment-laden currents which flow downslope when an unstable mass of sediment that has been rapidly deposited on the upper slope fails, perhaps triggered by earthquakes. There is a spectrum of turbidity- or density-current types ranging from "muddy water" to massive mudflow, and evidence of both these end members can be observed in deposits associated with the deeper parts of submarine canyons and channels, such as lobate deposits (mudflow) and levees along channels.
Mass wasting, slumping, and submarine landslides are forms of slope failures (the effect of gravity on a hillslope) observed in submarine canyons. Mass wasting is the term used for the slower and smaller action of material moving downhill; and would commonly include the effects of bioerosion: the burrowing, ingestion and defecation of sediment performed by organisms. Slumping is generally used for rotational movement of masses on a hillside. Landslides, or slides, generally comprise the detachment and displacement of sediment masses. All are observed; all are contributory processes.
It is now understood that many mechanisms of submarine canyon creation have had effect to greater or lesser degree in different places, even within the same canyon, or at different times during a canyon's development. However, if a primary mechanism must be selected, the downslope lineal morphology of canyons and channels and the transportation of excavated or loose materials of the continental slope over extensive distances require that various kinds of turbidity or density currents act as major participants.

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Deep sea fish

Deep sea fish is a term for fish that live below the photic zone of the ocean. Examples include the lanternfish, flashlight fish, cookiecutter shark, bristlemouths, and anglerfish.
EnvironmentBecause the photic level zone lies only a few hundred meters below the water, about 90% of the ocean volume is invisible to humans. The deep sea is also an extremely hostile environment, with pressures between 20 and 1,000 atmospheres (between 2 and 100 megapascals), temperatures between 3 and 10 degrees Celsius, and a lack of oxygen. The fish that have evolved to this harsh environment are not capable of surviving in laboratory conditions, and any attempts to keep them in captivity have led to their deaths. For this reason little is known about them, as there are limitations to the amount of fruitful research that can be carried out on a dead specimen and deep sea exploratory equipment is very expensive. As such, many species are known only to scientists and have therefore retained their scientific names.

Characteristics

The fish of the deep sea are among the most elusive and unusual looking creatures on Earth. In this deep unknown lie many unusual creatures we still have yet to study. Since many of these fish live in regions where there is no natural illumination, they cannot rely solely on their eyesight for locating prey and mates and avoiding predators; deep sea fish have evolved appropriately to the extreme sub-photic region in which they live. Many deep sea fish are bioluminescent, with extremely large eyes adapted to the dark. Some have long feelers to help them locate prey or attract mates in the pitch dark of the deep ocean. The deep sea angler fish in particular has a long fishing-rod-like adaptation protruding from its face, on the end of which is a bioluminescent piece of skin that wriggles like a worm to lure its prey. The lifecycle of deep sea fish can be exclusively deep water although some species are born in shallower water and sink on becoming adults.
Due to the poor level of photosynthetic light reaching deep sea environments, most fish need to rely on organic matter sinking from higher levels, or, in rare cases, hydrothermal vents for nutrients. This makes the deep sea much poorer in productivity than shallower regions. Consequently many species of deep sea fish are noticeably smaller and have larger mouths and guts than those living at shallower depths. It has also been found that the deeper a fish lives, the more jelly-like its flesh and the more minimal its bone structure. This makes them slower and less agile than surface fish.

Endangered Species

A recent study by Canadian scientists, has found five species of deep sea fish – roundnose grenadier, onion-eye grenadier, blue hake, spiny eel and spinytail skate – to be on the verge of extinction due to the shift of commercial fishing from continental shelves to the slopes of the continental shelves, down to depths of 1600 meters. The slow reproduction of these fish – they reach sexual maturity at about the same age as human beings – is one of the main reasons that they cannot recover from the excessive fishing.

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Deep sea

The deep sea, or deep layer is the lowest layer in the ocean, existing below the thermocline. Little or no light penetrates this area of the ocean, and most of its organisms rely on falling organic matter produced in the photic zone for subsistence. For this reason life is much more sparse, becoming rarer still with increasing depth. The other essential ingredient for life is oxygen, which is brought to the ocean's depths via the thermohaline circulation. There is, however, another very different part of the deep sea food chain discovered in the late 1970s, which is rooted in chemosynthesis rather than photosynthesis.
The ocean depths are one of the most hostile environments for life, and represent the least explored of all the world's ecosystems. Cold, dark and almost inaccessible to humans, it is perhaps the closest environment on earth to outer space.

Physical and chemical characteristics

The deep ocean is not well mixed, consists of horizontal layers of equal density, and is often as cold as -1 to 4°C (32 to 37°F). It is characterized by a nearly constant temperature and a positive sound speed gradient caused by pressure. Pressure increases by 1 atm with every 10 meters. Water at a depth of 4 km for example exerts 400 times more pressure than that at the surface.
Light dims by 90% every 75 meters; by 200m, the waters are dimly lit and by 1000m they receive no light at all. For comparison, the human visual threshold occurs at 650m. Ninety percent of the total volume of Earth's oceans is found in the deep ocean. The deepest waters on Earth lie 10,912m below the surface in the Mariana Trench.

Biology

Regions below the epipelagic are divided into further zones, beginning with the mesopelagic which spans from 200 to 1000m below sea level, where a little light penetrates while still being insufficient for primary production. Below this zone the deep sea proper begins, consisting of the aphotic bathypelagic, abyssopelagic and hadopelagic. Food consists of falling organic matter known as 'marine snow' and carcasses derived from the productive zone above, and is scarce both in terms of spatial and temporal distribution.

Adaptations of midwater fish

The midwater fish have special adaptations to cope with these conditions - they are small, usually being under 25cm; they have slow metabolisms and unspecialized diets, preferring to sit and wait for food rather than waste energy searching for it. They have elongated bodies with weak, watery muscles and skeletal structures. They often have extendable, hinged jaws with recurved teeth. Because of the sparse distribution and lack of light, finding a partner with which to breed is difficult, and many organisms are hermaphroditic.
Because light is so scarce fish often have larger than normal, tubular eyes with only rod cells. Their upward field of vision allows them to seek out the silhouette of possible prey. Prey fish however also have adaptations to cope with predation. These adaptations are mainly concerned with reduction of silhouette, a form of camouflage. The two main methods by which this is achieved are reduction in the area of their shadow by lateral compression of the body, and counter illumination via bioluminescence. This is achieved by production of light from ventral photophores, which tend to produce such light intensity to render the underside of the fish of similar appearance to the background light.

Exploration

The deep sea is an environment totally inhospitable to humankind, and it should come as no surprise that it represents one of the least explored areas on Earth. Pressures even in the mesopelagic become too great for traditional exploration methods, demanding alternative approaches for deep sea research. Baited camera stations, small manned submersibles and ROVs (remotely operated vehicles) are three methods utilized to explore the ocean's depths. Because of the difficulty and cost of exploring this zone, current knowledge remains limited.

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Solar cell

A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified.
Fundamentally, the device needs to fulfill only two functions: photogeneration of charge carriers (electrons and holes) in a light-absorbing material, and separation of the charge carriers to a conductive contact that will transmit the electricity (simply put, carrying electrons off through a metal contact into a wire or other circuit). This conversion is called the photovoltaic effect, and the field of research related to solar cells is known as photovoltaics.
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. More recently, solar cells are starting to be used in assemblies of solar modules (photovoltaic arrays) connected to the electricity grid through an inverter, often in combination with a net metering arrangement.

First

The first generation photovoltaic, consists of a large-area, single layer p-n junction diode, which is capable of generating usable electrical energy from light sources with the wavelengths of sunlight. These cells are typically made using a silicon wafer. First generation photovoltaic cells (also known as silicon wafer-based solar cells) are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market.

Second

The second generation of photovoltaic materials is based on the use of thin-film deposits of semiconductors. These devices were initially designed to be high-efficiency, multiple junction photovoltaic cells. Later, the advantage of using a thin-film of material was noted, reducing the mass of material required for cell design. This contributed to a prediction of greatly reduced costs for thin film solar cells. There are currently (2007) a number of technologies/semiconductor materials under investigation or in mass production. Examples include Amorphous silicon, Polycrystalline silicon, micro-crystalline silicon, Cadmium telluride, copper indium selenide/sulfide. Typically, the efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells, but manufacturing costs are also lower, so that a lower cost per watt can be achieved. Another advantage of the reduced mass is that less support is needed when placing panels on rooftops and it allows fitting panels on light or flexible materials, even textiles.

Third

Third generation photovoltaics are very different from the previous semiconductor devices as they do not rely on a traditional p-n junction to separate photogenerated charge carriers. These new devices include photoelectrochemical cells, Polymer solar cells, and nanocrystal solar cells. Dye-sensitized solar cells are now in production.

Fourth

Fourth generation Composite photovoltaic technology with the use of polymers with nano particles can be mixed together to make a single multispectrum layer. Then the thin multi spectrum layers can be stacked to make multispectrum solar cells more efficient and cheaper based on polymer solar cell and multi junction technology used by NASA on Mars missions. The layer that converts different types of light is first, then another layer for the light that passes and last is an infra-red spectrum layer for the cell - thus converting some of the heat for an overall solar cell composite.

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