Ocean trenches are steep depressions in the deepest parts of the ocean [where old ocean crust from one tectonic plate is pushed beneath another plate, raising mountains, causing earthquakes, and forming volcanoes on the seafloor and on land. The deepest parts of a trench, however, represent only about 1 percent or less of its total area. The vast submarine slopes and steep walls of trenches make up much of the hadal zone, where unique habitats extending across a range of depths are home to diverse number of species, many of which are new or still unknown to science.
Trenches are formed by subduction, a geophysical process in which two or more of Earth's tectonic plates converge and the older, denser plate is pushed beneath the lighter plate and deep into the mantle, causing the seafloor and outermost crust the lithosphere to bend and form a steep, V-shaped depression.
Subduction also generates an upwelling of molten crust that forms mountain ridges and volcanic islands parallel to the trench. Examples of these volcanic "arcs" can be seen in the Japanese Archipelago, the Aleutian Islands, and many other locations around this area called the Pacific "Ring of Fire.
Trenches are long, narrow and very deep and, while most are in the Pacific Ocean, can be found around the world. The deepest trench in the world, the Mariana Trench located near the Mariana Islands, is 1, miles long and averages just 43 miles wide. It is home to the Challenger Deep, which, at 10, meters 35, feet , is the deepest part of the ocean.
The Tonga, Kuril-Kamatcha, Philippine, and Kermadec Trenches all contain depths greater than 10, meters 33, feet. The great depth of ocean trenches creates an environment with water pressures more than 1, times greater than the surface, constant temperatures just above freezing, and no light to sustain photosynthesis. While this may not seem like conditions suitable to life, the combination of extremely high pressure, the gradual accumulation of food along trench axes, and the geographical isolation of hadal systems are believed to have created habitats with an extraordinarily high abundance of a few highly specialized organisms.
Many of the organisms living in trenches have evolved surprising ways to survive in these unique environments. Recent discoveries in the hadal zone have revealed organisms with proteins and biomolecules suited to resisting the crushing hydrostatic pressure and others able to harness energy from the chemicals that leak out of hydrocarbon seeps and mud volcanoes on the seafloor. Other hadal species thrive on the organic material that that drifts down from the sea surface and is funneled to the axis of the V-shaped trenches.
Because of their extreme depth, trenches present unique logistical and engineering challenges for the researchers who want to study them. Trench exploration to date has been extremely limited only three humans have ever visited the seafloor below 6, meters and much of what is known about trenches and the things that live there has been derived from two sampling campaigns in the s the Danish G alathea and the Soviet Vitjaz Expeditions and from a handful of photographic expeditions and seafloor samples taken remotely from the deep with little knowledge of their precise location.
Despite their scarcity, these initial attempts at studying trenches have hinted at the existence of previously unknown processes, species, and ecosystems. Knowledge of ocean trenches is limited because of their depth and their remoteness, but scientists do know they play a significant role in our lives on land. Seafloor earthquakes generated in subduction zones were responsible for the Indian Ocean tsunami and for the Tohoku Earthquake and tsunami in Japan.
By studying ocean trenches, scientists can better understand the physical process of subduction and the causes of these devastating natural disasters. The study of trenches also gives researchers insight into the novel and diverse adaptations of deep-sea organisms to their surroundings that may hold the key to biological and biomedical advances.
Studying the way that hadal organisms have adapted to life in their harsh surroundings could help advance understanding in many different areas of research, from diabetes treatments to improved laundry detergents. Researchers have already discovered microbes inhabiting deep-sea hydrothermal vents that hold potential as new sources of antibiotics and anti-cancer drugs.
The discovery presents opportunities for further research on the role of trenches both as a source through volcanism and other processes and a sink in the planetary carbon cycle that could influence the way scientists eventually come to understand and predict the impacts of human-generated greenhouse gases and global climate change. The development of new deep-sea technology, from submersibles to cameras to sensors and samplers, will provide greater opportunity for scientists to systematically investigate trench ecosystems over extended periods of time.
This will eventually give us a better understanding of earthquakes and geophysical processes, revise how scientists understand the global carbon cycle, provide avenues for biomedical research, and potentially contribute new insights into the evolution of life on earth.
These same technological advances will also create new capabilities for scientists to study the entire ocean, from remote coastlines to the ice-covered Arctic Ocean. Trenches are long, narrow depressions on the seafloor that form at the boundary of tectonic plates where one plate is pushed, or subducts, beneath another. The deepest parts of the ocean are found in trenches—at more than 35, feet nearly 11, meters , Challenger Deep is a part of the Mariana Trench, where the Pacific Plate is subducting beneath the Philippine Plate.
It is an area where seven tectonic plates meet in various places. The plates are:. As you can imagine, this area is very unstable due to its vulnerability in shifting tectonic plates. There are several ocean trenches associated with the Ring of Fire. The deepest ocean trenches in the world are situated in the Ring of Fire that lies on the edges of the Pacific Ocean. From there, it passes along Asia through Japan. Indonesia, the Philippines, and New Zealand. The deepest oceanic trench is the Mariana Trench at 36 feet.
The trench is miles long and The reason that the Mariana Trench is so deep is that the crust at the edge of the Pacific plate is one of the oldest portions of oceanic crust in the world.
This makes it very dense. When the Pacific plate subducted, its density pulled it deeply under the Philippine plate. The Mariana Trench has been declared a protected zone by the United States. Any expeditions or scientific studies in the area must first apply for permits. This was done in in a navy submersible called the Trieste.
It took them five hours to reach the bottom, and they could only stay for twenty minutes at the bottom of the trench. Their descent stirred up so much silt that they could not take photographs. The deepest area of the Mariana Trench is known as the Challenger Deep.
It is named after the first expedition, the Challenger expedition, which attempted to determine its depth in Since then, sonar systems and seismometers have been used to measure and map the trench. Many scientists and even philosophers like Socrates felt that life could not exist at these depths. He asserted from his findings that life could not exist at depths of more than feet m.
This notion was challenged in by naturalists Michael and George Ossian Sars. They found a sea lily which is an animal in a Norwegian fjord at a depth of 10 feet m. The British decided to explore deep-sea life. Between and , the British HMS Challenger sailed over seventy-nine thousand miles on this endeavor. They found a fantastic variety of life and categorized four thousand seven hundred new marine species.
Piccard claimed to see a large flatfish that was about twelve inches long. Scientists have been doubtful about this claim and postulate that what Piccard saw was actually a sea cucumber. A new species of snailfish was detected at feet m was found in December This was a record-breaking find as no other living fish has been found deeper than this. Recently there have been many discoveries, and the conclusion is the deep-sea trenches are teaming with life.
Gigantism seems to affect life in the hadal zone. All species seem much larger than their counterparts that exist at shallower ocean depths. Oceanic trenches have no light, and it is utterly dark in these depths. Some animals have responded to the challenge by developing huge eyes to capture the faintest trace of light. An example of this is the Stout Blacksmelt fish.
The vision of other animals has completely vanished, and they rely on vibrations and touch to move around and catch prey. The tripod fish is an excellent example of this. Other animals have learned to make their own light, known as bioluminescence, as seen in the lanternfish.
The lack of light does not allow for plant growth, and so food is limited. Animals in deep-sea trenches have adapted to eat scraps of dead organisms and detritus that filter down through the water. These scraps of organisms are known as marine snow. Sometimes dead whales are heavy enough to sink into the ocean trenches, which provides a feast for the animals that occupy the trench depths. Normal body fat would solidify in these conditions. The animals have adapted by storing unsaturated fats, which remain liquid even in extreme temperatures.
The cells in deep-sea animals have been adapted to include a tiny organic molecule known as piezolytes. Piezolytes bind to the water and give the proteins space to expand and change shape as they function in the body. Proteins in normal cells would not be able to operate at such extreme temperatures and pressures. Fish seem to live at a maximum-depths of 26 to 27 feet. Beyond that, there are other life forms, such as crustaceans known as amphipods.
The amphipods grow to giant sizes in the deep cold water. Most normal amphipods are approximately an inch to two inches long, but they grow to more than a foot long in the trenches. As they look like giant shrimp, it gives an impression of an alien world down in the depths. Single-cell organisms, similar to amoeba, known as foraminifera, have been found in giant sizes in ocean trenches. Huge sea cucumbers were also discovered inhabiting deep areas.
Most of the animals found at great ocean depths do not have standard bone structure or air-filled spaces — the enormous pressure would shatter them if they did. Jellyfish and soft-bodied animals cope much better with the increased pressure. Dumbo octopuses have been found at 32 feet m in the Mariana Trench.
They do not look like the octopuses found closer to the surface. The most common type of continental crust found in accretionary wedges is volcanic material from islands on the overriding plate. Accretionary wedges are roughly shaped like a triangle with one angle pointing downward toward the trench.
Because sediments are mostly scraped off from the subducting plate as it falls into the mantle , the youngest sediments are at the bottom of this triangle and the oldest are at the more flattened area above. This is the opposite of most rock formations, where geologist s must dig deep to find older rocks. Active accretionary wedges, such as those located near the mouth s of river s or glacier s, can actually fill the ocean trench on which they form.
Rivers and glaciers transport and deposit tons of sediment into the ocean. The Caribbean island of Barbados, for example, sits atop the ocean trench created as the South American plate subducts beneath the Caribbean plate. Ocean trenches are some of the most hostile habitats on Earth. Pressure is more than 1, times that on the surface, and the water temperature is just above freezing.
Perhaps most importantly, no sunlight penetrate s the deepest ocean trenches, making photosynthesis impossible. Organisms that live in ocean trenches have evolve d with unusual adaptation s to thrive in these cold, dark canyon s. In general, life in dark ocean trenches is isolated and slow-moving. Pressure at the bottom of the Challenger Deep, the deepest spot on Earth, is about 12, tons per square meter 8 tons per square inch.
Large ocean animals, such as sharks and whales, cannot live at this crushing depth. Many organisms that thrive in these high-pressure environments lack gas -filled organ s, such as lung s.
These organisms, many related to sea stars or jellies, are made mostly of water and gelatinous material that cannot be crushed as easily as lungs or bones. Many of these creatures navigate the depths well enough to even make a vertical migration of more than 1, meters 3, feet from the bottom of the trench—every day.
Even the fish in deep trenches are gelatinous. Several species of bulb-headed snailfish, for example, dwell at the bottom of the Mariana Trench. The bodies of these fishes have been compared to tissue paper. Shallower ocean trenches have less pressure, but may still fall outside the photic or sunlight zone , where light penetrates the water.
Many fish species have adapted to life in these dark ocean trenches. Anglerfish, for instance, use a bioluminescent growth on the top of their heads called an esca to lure prey. The anglerfish then snaps up the little fish with its huge, toothy jaws.
Without photosynthesis, marine communities rely primarily on two unusual sources for nutrient s. Marine snow is mostly detritus , including excrement and the remains of dead organisms such as seaweed or fish. This nutrient-rich marine snow feeds such animals as sea cucumbers and vampire squid.
Another source of nutrients for ocean-trench food webs comes not from photosynthesis, but from chemosynthesis. Chemosynthesis is the process in which producer s in the ocean trench, such as bacteria , convert chemical compound s into organic nutrients. The chemical compounds used in chemosynthesis are methane or carbon dioxide eject ed from hydrothermal vent s and cold seep s, which spew these toxic , hot gases and fluids into the frigid ocean water.
One common animal that relies on chemosynthetic bacteria for food is the giant tube worm. Ocean trenches remain one of the most elusive and little-known marine habitats. Until the s, many oceanographer s thought that these trenches were unchanging environments nearly devoid of life. Even today, most research on ocean trenches has relied on seafloor samples and photographic expedition s.
That is slowly changing as explorers delve into the deep—literally. Two other unmanned expeditions have also explored the Challenger Deep. Engineering submersible s to explore ocean trenches is presents a huge set of unique challenges. Submersibles must be incredibly strong and resilient to contend with strong ocean current s, no visibility, and intense pressure of the Mariana Trench.
Engineering a submersible to safely transport people, as well as delicate equipment , is even more challenging. The sub that took Piccard and Walsh to the Challenger Deep, the remarkable Trieste , was an unusual vessel called a bathyscaphe. To combat deep-sea currents, the sub was designed to spin slowly as it descended. Lights on the sub were not incandescent or fluorescent bulbs, but arrays of tiny LED s that illuminate d an area of about 30 meters feet.
To adapt to the pressure of the deep, the sub was shaped like a sphere —the walls of a square or cylinder -shaped vessel would need to be at least three times thicker to avoid being crushed. Perhaps most startlingly, the Deepsea Challenger itself was designed to compress.
Ocean Deep. Ocean trenches were not studied and explored until the 20th century.
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