There are deep spheres on our planet that seem almost alien. Translucent fish dart back and forth while strange flower-like crinoids sway in the water. But of all the undersea canyons and trenches out there, what are the deepest, darkest places in each of the five oceans of the world?
The deepest place in the Pacific Ocean (and counting Earth) it’s the Mariana Trench. The trench’s deepest point is Challenger Deep near the U.S. territory of Guam — a dip that’s nearly 36,000 feet (10,973 meters) below the water’s surface, according to a 2019 study published in the journal Earth-Science Reviews (opens in new tab).
The deepest area in the Atlantic Ocean is the Milwaukee Deep at the 27,585-foot (8,408 m) depth axis of the Puerto Rico Trench. At a depth of 23,917 feet (7,290 m) lies an unnamed area on the floor of the Indian Ocean. The Southern Ocean (also known as the Antarctic Ocean) descends to 24,229 feet (7,385 m) at the South Sandwich Trench and the Arctic Ocean descends to 16,000 feet (4,877 m) at Molloy Deep in the Fram Strait. .
Such areas are far from his reach sun and they may appear to be nothing but gaping mouths of impenetrable darkness. But what do scientists know about these final frontiers?
Related: Why are there so many giants in the deep sea?
The Mariana Trench
The Mariana Trench is a 1,580-mile (2,542-kilometer) oceanic abyss where many of the deepest points on the planet can be found.
Only 27 people have ever been to Challenger Deep, the deepest point in the Mariana Trench: The first to go there were explorer Jacques Piccard and Navy Lt. Don Walsh, who ventured there in 1960.
Mackenzie Gerringer, who went on a 2014 expedition to the 34,448-foot (10,500 m) Sirena Deep (one of the other deepest parts of the trench) with colleagues from the University of Hawaii at Mānoa, noted the difficult conditions present. in the dark.
“There is no sunlight,” he told Live Science in an email. “Temperatures are cold, usually around 1-2°C [33.8 to 35.6 degrees Fahrenheit]. The pressures are high, up to 15,000 pounds per square inch [1,034 bars] to the deepest depths of the ocean.” Geringer is now an assistant professor biology at the College of the State University of New York (SUNY) at Geneseo.
Despite the extreme conditions, life exists in the deepest parts of our planet’s seas. Jeff Drazen, a professor of oceanography at the University of Hawaii at Manoa, observed that the types of creatures that thrive at extreme depths tend to be similar, even though different species may be unique to different areas. He explained that certain creatures appear at certain depths.
“We found that life changed dramatically with depth,” he said. “The lower part of a species’ depth range is controlled by adaptations to pressure, and the upper part of its range may be controlled by predation or competition.”
During Gerringer’s mission, she, Drazen and colleagues sent probes to the bottom of the Sirena Deep and discovered a new species of Mariana snailfish. The newly discovered creature was a handal snail (opens in new tab)named after the Hadal zone, the part of the ocean that is between about 19,700 feet and 36,000 feet (6,000 to 10,970 m) deep and occurs only in marine trenches.
Creatures like this are specially adapted to survive in the deep. According to Gerringer, extreme stress stresses the body and damages enzymes and proteins. Mariana snails and other hadal species are equipped to handle it with enzymes that work more efficiently under extremely high pressure. They also produce a molecule known as TMAO (trimethylamine N-oxide) to keep stress from messing with proteins in their bodies.
What Gerringer and Drazen observed in the Mariana Trench mirrors what is generally seen in abyssal and abyssal zones around Earth. In the Mariana Trench, 16,000 feet (488 m) down, eels (opens in new tab) and rattail fish (opens in new tab) swam among ten-legged shrimps. As the probe cameras went deeper, these species gave way to snails and giant amphipods, and even deeper, different species of mostly smaller amphipods and shrimp appeared. The deepest at which fish were seen was 26,250 feet (8,000 meters).
The Puerto Rico Trench
Off the coast of Puerto Rico and south of the tip of Florida, the Puerto Rico Trench—like most deep-sea trenches—is evidence of an ancient sinking Event.
“Most of these Hadal habitats are trenches formed through subduction, where one tectonic plate slides under another, creating a deep valley,” Gerringer said.
Displacement tectonic plates they also explain the presence of a cluster of volcanic islands scattered nearby, since subduction is the same type of tectonic activity that can cause magma to emerge from beneath the Earth’s crust. These are not the only ones volcano around this trench. Deep underwater, a mud volcano erupted near 26,000 feet (8,000 meters), according to the National Oceanic and Atmospheric Administration (opens in new tab) (NOAA). The areas around this trench are prone to earthquakes and tsunamis due to subsidence. There’s even a fault in the Puerto Rico Trench that looks eerily like a submerged version of the San Andreas Fault.
The deepest part of the trench is the Milwaukee Deep, which explorer Victor Vescovo dived in a crewed submarine in 2018 (Vescovo had previously descended into the Mariana Trench and was the first person to ever dive into the Challenger Deep twice).
The Java Trench and the South Sandwich Trench
The deepest parts of the Java Trench of the Indian Ocean and the South Sandwich Trench of the Antarctic Ocean were both defined by Five Deeps Expedition (FDE) (opens in new tab) in 2021, according to British Geological Survey (opens in new tab). Before the mission, these unnamed areas were mostly unexplored – the South Sandwich Trench, the only hadal zone on Earth that has sub-zero temperatures, had not been explored at all before this mission.
Mission researchers explored the hidden depths of the ocean by sending remotely operated vehicles (ROVs). The team used a Deep Submergence Vehicle (DSV) (opens in new tab) and three additional land craft — robots carrying multiple instruments, such as sensors, that sink to the bottom and survey the sea floor. The team’s findings were published in Geoscience Data Journal (opens in new tab) of the Royal Meteorological Society.
In the Java Trench, cameras on FDE vessels spotted snails, sea cucumbers and strange life forms, such as a sea squirt which floated in the dark waters like an eerie balloon. Another FDE study published in Deep-sea research Part II: Local studies in oceanography (opens in new tab) highlighted the fauna in the South Sandwich Trench. In these frozen waters, researchers found snail amphipods, brittle stars, sea cucumbers, sponges and crinoids.
The Fram Strait
Going from Antarctica to the Arctic Ocean, the Five Deeps expedition then investigated the Molloy Deep (opens in new tab) in the Fram Strait, between East Greenland and the Svalbard Islands off the north coast of Norway. No other expedition had ever seen the bottom of Molloy Deep before.
In the Fram Strait, fluctuations in freshwater and saltwater levels affect populations of phytoplankton and other microbes. Climate change has affected the Arctic Ocean more than any of the world’s five oceans, and sea ice thickness has been steadily decreasing since 1990.
Few creatures live in Molloy Deep. It’s essentially a giant crater, and organic matter collects and falls to the sides, but there aren’t many creatures that inhabit this barren area, scientists at Maier-Kaiser Laboratory (opens in new tab) (which is part of the Woods Hole Oceanographic Institution in Massachusetts) that was found when it was searched for larvae. The only animal caught on camera there is a species of deep-sea cucumber known as sea pig (opens in new tab).
While these deep sea environments around the world may seem very remote, they are still affected by human activity. Gerringer is concerned about the effects of climate change, such as the melting of the Arctic ice and pollution they may make their way from below to the surface. There is already an amphibian found in the Mariana Trench by the name Widespread plastic (opens in new tab) due to microplastics found in his stomach. It doesn’t end there. Vescovo found a plastic bag and candies in the same ditch.
“The deep sea is closely connected to the surface oceans,” he said. “Human activities such as plastic pollution and climate change are already affecting deep-sea habitats and it is important to understand, value and protect these ecosystems.”