WHAT ARE OCEAN TRENCHES? - ENVIRONMENT - 2025

The ocean trenches are depths on the seabed which are formed as a result of the activity of the tectonic plates of the Earth, which is pushed the converging one below the other.

These long, narrow V-shaped depressions are the deepest parts of the ocean and are found throughout the world reaching depths of around 10 kilometers below sea level.

The deepest trenches are found in the Pacific Ocean and are part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones.

The deepest oceanic trench is the Mariana Trench located near the Sea Islands with a length of more than 1,580 miles or 2,542 kilometers, 5 times longer than the Grand Canyon in Colorado, United States and on average it is only 43 miles (69 kilometers) wide.

There the Challenger Abyss is located, which at 10,911 meters is the deepest part of the ocean. Likewise, the Tonga, Kuril, Kermadec and Philippine graves are more than 10,000 meters deep.

By comparison, Mount Everest is 8,848 meters above sea level, which means that the Mariana Trench at its deepest point is more than 2,000 meters deep.

Ocean trenches occupy the deepest layer of the ocean. The intense pressure, lack of sunlight and the frigid temperatures of this place make it one of the most unique habitats on Earth.

How are ocean trenches formed?

Pits are formed by subduction, a geophysical process in which two or more tectonic plates of the Earth converge and the oldest and densest plate is pushed underneath the lighter plate causing the ocean floor and the outer crust (the lithosphere) to curves and forms a slope, a V-shaped depression.

Subduction Zones

In other words, when the edge of a dense tectonic plate meets the edge of a less dense tectonic plate, the denser plate curves downward. This type of boundary between layers of the lithosphere is called convergent. The place where the densest plate subducts is called the subduction zone.

The subduction process makes the trenches dynamic geological elements, being responsible for a significant part of the Earth's seismic activity and they are frequently the epicenter of large earthquakes, including some of the largest earthquakes on record.

Some ocean trenches are formed by subduction between a plate that carries continental crust and a plate that carries oceanic crust. The continental crust always floats more than the oceanic crust and the latter will always subduct.

The best known ocean trenches are the result of this boundary between converging plates. The Peru-Chile Trench off the west coast of South America is formed by the oceanic crust of the Nazca plate that subducts under the continental crust of the South American plate.

The Ryukyu Trench, which extends from southern Japan, is formed in such a way that the oceanic crust of the Philippine plate subducts under the continental crust of the Eurasian plate.

Ocean trenches can rarely form when two plates bearing continental crust meet. The Mariana Trench, in the South Pacific Ocean, forms when the mighty Pacific plate subducts under the smaller and less dense plate of the Philippines.

In a subduction zone, part of the molten material, which was previously the ocean floor, is usually lifted up through volcanoes located near the pit. Volcanoes frequently create volcanic arches, a mountain chain island that lies parallel to the trench.

The Aleutian Trench is formed where the Pacific plate subducts under the North American plate in the Arctic region between the state of Alaska in the United States and the Russian region of Siberia. The Aleutian Islands form a volcanic arc that runs off the Alaska Peninsula and just north of the Aleutian Trench.

Not all ocean trenches are in the Pacific. The Puerto Rico Trench is a complex tectonic depression that is partly formed by the subduction zone of the Lesser Antilles. Here, the oceanic crust of the huge North American plate is subducted under the oceanic crust of the smaller Caribbean plate.

Why are ocean trenches important?

Knowledge of ocean trenches is limited due to their depth and remoteness, but scientists know that they play a significant role in our life on land.

Much of the world's seismic activity takes place in subduction zones, which can have a devastating effect on coastal communities and even more so on the global economy.

Seafloor earthquakes generated in subduction zones were responsible for the Indian Ocean tsunami in 2004 and the Tohoku earthquake and tsunami in Japan in 2011.

By studying ocean trenches, scientists can understand the physical process of subduction and the causes of these devastating natural disasters.

The study of the trenches also gives researchers an understanding of the novel and diverse forms of adaptation of organisms from the deep sea to their environment, which may hold the key to biological and biomedical advances.

Studying how deep-sea organisms have adapted to life in their harsh environments can help advance understanding in many diverse areas of research, from diabetes treatments to improved detergents.

Researchers have already discovered microbes that inhabit hydrothermal vents in the deep sea that have potential as new forms of antibiotics and cancer drugs.

Such adaptations may also hold the key to understanding the origin of life in the ocean, as scientists examine the genetics of these organisms to piece together the puzzle of the story of how life expands between isolated ecosystems and eventually through the world's oceans.

Recent research has also revealed large and unexpected amounts of carbon matter accumulating in the pits, which could suggest that these regions play a significant role in Earth's climate.

This carbon is confiscated in the Earth's mantle through subduction or consumed by bacteria from the pit.

This discovery presents opportunities for further investigation of the role of trenches both as a source (through volcanoes and other processes) and as a deposit in the planet's carbon cycle that may influence how scientists eventually understand and predict. the impact of human-generated greenhouse gases and climate change.

The development of new deep-sea technology, from submersibles to cameras and sensors and samplers, will provide great opportunities for scientists to systematically investigate trench ecosystems over long periods of time.

This will eventually give us a better understanding of earthquakes and geophysical processes, review how scientists understand the global carbon cycle, provide avenues for biomedical research, and potentially contribute to new insights into the evolution of life on Earth.

These same technological advances will create new capabilities for scientists to study the ocean as a whole, from remote shorelines to the ice-covered Arctic Ocean.

Life in the ocean trenches

Ocean trenches are some of the most hostile habitats on earth. The pressure is more than 1,000 times the surface and the water temperature is slightly above freezing. Perhaps more importantly, sunlight does not penetrate the deepest ocean trenches, making photosynthesis impossible.

Organisms that live in ocean trenches have evolved with unusual adaptations to thrive in these cold, dark canyons.

Their behavior is a test of the so-called "visual interaction hypothesis" which says that the greater the visibility of an organism, the greater the energy it must expend to hunt prey or repel predators. In general, life in the dark ocean trenches is isolated and slow-moving.

Pressure

The pressure at the bottom of the Challenger Abyss, the deepest place on earth, is 703 kilograms per square meter (8 tons per square inch). Large marine animals such as sharks and whales cannot live in this crushing depth.

Many organisms that thrive in these high-pressure environments do not have organs that fill with gases, such as the lungs. These organisms, many related to starfish or jellyfish, are made mostly of water and jelly-like material that cannot be crushed as easily as lungs or bones.

Many of these creatures navigate the depths well enough to make a vertical migration of more than 1,000 meters from the bottom of the trenches each day.

Even fish in deep pits are jelly-like. Many species of bulb-headed snailfish, for example, live at the bottom of the Mariana Trench. The bodies of these fish have been compared to disposable tissues.

Dark and deep

Shallow ocean trenches have less pressure, but can still be outside the sunlight zone, where light penetrates the water.

Many fish have adapted to life in these dark ocean trenches. Some use bioluminescence, meaning that they produce their own light to live in order to attract prey, find a mate, or repel the predator.

Food nets

Without photosynthesis, marine communities depend primarily on two unusual sources of nutrients.

The first is "marine snow." Marine snow is the continuous fall of organic material from the heights in the water column. Marine snow is primarily waste, including excrement and the remains of dead organisms such as fish or seaweed. This nutrient-rich marine snow feeds animals such as sea cucumbers or vampire squid.

Another source of nutrients for the food webs of ocean trenches comes not from photosynthesis but from chemosynthesis. Chemosynthesis is the process in which organisms in the ocean trench, such as bacteria, convert chemical compounds into organic nutrients.

The chemical compounds used in chemosynthesis are methane or carbon dioxide expelled from hydrothermal vents that release their hot and toxic gases and fluids into the frigid ocean water. A common animal that relies on chemosynthetic bacteria for food is the giant tube worm.

Exploring the graves

Ocean trenches remain one of the most elusive and little-known marine habitats. Until 1950, many oceanographers thought that these trenches were unchanging environments close to being devoid of life. Even today, much of the research in ocean trenches is based on ocean floor samples and photographic expeditions.

That is slowly changing as explorers dig deep, literally. The Challenger Deep, at the bottom of the Mariana Trench, lies deep in the Pacific Ocean near the island of Guam.

Only three people have visited the Challenger Abyss, the world's deepest ocean trench: a joint Franco-American crew (Jacques Piccard and Don Walsh) in 1960 reaching a depth of 10,916 meters and National Geographic explorer-in-residence James Cameron in 2012 reaching 10,984 meters (Two other unmanned expeditions have also explored the Challenger Abyss).

Engineering submersibles to explore ocean trenches presents a large set of unique challenges.

Submersibles must be incredibly strong and rugged to combat strong ocean currents, zero visibility, and high pressure from the Mariana Trench.

Developing the engineering to transport people safely, as well as delicate equipment, is an even greater challenge. The submarine that brought Piccard and Walsh to the Challenger Deep, the extraordinary Trieste, was an unusual vessel known as the bathyscaphe (a submarine for exploring the depths of the ocean).

Cameron's submersible, Deepsea Challenger, successfully tackled engineering challenges in innovative ways. To combat deep ocean currents, the submarine was designed to turn slowly while descending.

The lights on the submarine were not made of incandescent or fluorescent bulbs, but arrangements of tiny LEDs that illuminated an area of ​​about 100 feet.

Perhaps more surprisingly, the Deepsea Challenger itself was designed to be compressed. Cameron and his team created a glass-based synthetic foam that allowed the vehicle to compress under the pressure of the ocean. The Deepsea Challenger returned to the surface 7.6 centimeters smaller than when it descended.

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