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Analytical cookies are used to understand how visitors interact with the website. What are ocean trenches? How are trenches formed?
What is it like in a trench? How does life survive there? What do we know about trenches? Why are ocean trenches important? What can ocean trenches tell us about earthquakes?
What can ocean trenches tell us about human health? What can ocean trenches tell us about Earth's climate? What's next for trench exploration and discovery? July 22, Life at Rock Bottom This digital photo essay brings you the forms, figures, and facts of life more than a mile and half deep. Ocean Robots: Challenger Deep. Nereus in the Challenger Deep. Related Topics Hydrothermal Vents. Mid-ocean Ridges. Natural Oil Seeps. We use cookies to analyze site usage and improve user experience.
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Necessary Necessary. Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information. Non-necessary Non-necessary. More rarely, ocean trenches can be formed when two plates carrying oceanic crust meet.
The Mariana Trench, in the South Pacific Ocean, is formed as the mighty Pacific plate subducts beneath the smaller, less-dense Philippine plate. In a subduction zone, some of the molten material—the former seafloor—can rise through volcanoes located near the trench. The volcanoes often build volcanic arc s—island mountain range s that lie parallel to the trench. The Aleutian Islands form a volcanic arc that swings out from the Alaskan Peninsula and just north of the Aleutian Trench.
Not all ocean trenches are in the Pacific, of course. The Puerto Rico Trench is a tectonically complex depression in part formed by the Lesser Antilles subduction zone. Here, the oceanic crust of the enormous North American plate carrying the western Atlantic Ocean is being subducted beneath the oceanic crust of the smaller Caribbean plate.
Accretionary wedge s form at the bottom of ocean trenches created at some convergent plate boundaries. Accretionary wedges form as sediment s from the dense, subducting tectonic plate are scraped off onto the less-dense plate. Sediments often found in accretionary wedges include basalt s from the deep oceanic lithosphere, sedimentary rocks from the seafloor, and even traces of continental crust drawn into the wedge. 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.
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