The Mariana Trench is an oceanic trench in the western Pacific Ocean, about 200 kilometers (124 miles) east of the Mariana Islands. It is the deepest part of the ocean on Earth. The trench is shaped like a crescent and is about 2,550 kilometers (1,580 miles) long and 69 kilometers (43 miles) wide. The deepest point, called the Challenger Deep, is located at the southern end of a narrow valley in the trench’s floor. The maximum depth there is 10,984 ± 25 meters (36,037 ± 82 feet), which is more than 2 kilometers (1.2 miles) deeper than the height of Mount Everest.
At a depth of about 11,000 meters below the ocean surface, the water above creates a pressure of 1,086 bar (15,750 psi), which is roughly 1,071.8 times greater than the air pressure at sea level or about eight tons per square inch. The temperature at the bottom of the trench is between 1 and 4 degrees Celsius (34 to 39 degrees Fahrenheit).
In 2009, the United States created the Mariana Trench Marine National Monument to protect parts of the trench within its exclusive economic zone (EEZ). This area does not include the Challenger Deep, which is located within the EEZ of the Federated States of Micronesia.
Single-celled organisms known as monothalamea have been found at a depth of 10.6 kilometers (35,000 feet) in the trench, according to researchers from the Scripps Institution of Oceanography. Studies also suggest that microorganisms live in the trench.
Etymology
The Mariana Trench is named after the nearby Mariana Islands, which are called Las Marianas in honor of Spanish Queen Mariana of Austria. The islands are part of an island arc formed on an overriding plate, called the Mariana plate (also named for the islands), located to the west of the trench.
Geology
The Mariana Trench is part of a system where two tectonic plates meet. In this system, the western edge of the Pacific plate is pushed under the smaller Mariana plate, which is located to the west. The rock from the western edge of the Pacific plate is among the oldest oceanic crust on Earth (up to 170 million years old). This makes it cooler and denser, which explains the large difference in height between this plate and the higher-riding Mariana plate. The deepest part of the trench is located at the boundary between these two plates.
The movement of the Pacific and Mariana plates also contributes to the formation of the Mariana Islands. These islands are created when the upper mantle melts due to water released from minerals in the subducted portion of the Pacific plate.
Research history
In 1875, the Challenger expedition used a weighted rope to measure the trench's depth, which was recorded as 4,475 fathoms (8,184 metres; 26,850 feet). In 1877, a map called Tiefenkarte des Grossen Ozeans ("Depth map of the Great Ocean") by Petermann showed a deep area called the Challenger Deep at the location where the first measurement was taken. In 1899, the USS Nero, a converted collier, measured a depth of 5,269 fathoms (9,636 metres; 31,614 feet).
In 1951, the Challenger II, led by Chief Scientist Thomas Gaskell, used echo sounding to survey the trench. This method was much more accurate and easier than the rope and drag lines used earlier. During this survey, the deepest point was measured at 5,960 fathoms (10,900 metres; 35,760 feet), located at 11°19′N 142°15′E, known as the Challenger Deep.
In 1957, the Soviet vessel Vityaz reported a depth of 11,034 metres (36,201 feet; 6,033 fathoms) at a location called the Mariana Hollow.
In 1984, the Japanese vessel Takuyō used a multi-beam echo sounder to collect data from the Mariana Trench. It recorded a maximum depth of 10,924 metres (35,840 feet), or 10,920 ± 10 metres (35,827 ± 33 feet; 5,971.1 ± 5.5 fathoms). In 1995, the remotely operated vehicle KAIKO reached the deepest part of the Mariana Trench, measuring a depth of 10,911 metres (35,797 feet; 5,966 fathoms).
Between 1997 and 2001, scientists from the Hawaii Institute of Geophysics and Planetology discovered a spot along the Mariana Trench with a depth similar to the Challenger Deep, possibly even deeper. This location was named the HMRG Deep after the research group that found it.
On 1 June 2009, the research vessel RV Kilo Moana mapped a spot with a depth of 10,971 metres (35,994 feet; 5,999 fathoms) using a sonar system called Simrad EM120. This system uses sound waves to measure depth with high accuracy, within ± 22 metres (72 feet; 12 fathoms) of the true depth.
In 2011, a US Navy ship used a multibeam echosounder to map the entire Mariana Trench with a resolution of 100 metres (330 feet; 55 fathoms). The mapping revealed four rocky outcrops believed to be former seamounts.
In 2012, researchers from Washington University and the Woods Hole Oceanographic Institution conducted a seismic survey at the Mariana Trench to study the subsurface water cycle. They used ocean-bottom seismometers and hydrophones to map structures as deep as 97 kilometres (318,000 feet; 53,000 fathoms; 60 miles) beneath the surface.
As of 2022, 22 crewed dives and seven uncrewed dives have been made to the Mariana Trench. The first crewed dive was in 1960, when the bathyscaphe Trieste reached the bottom at 10,916 metres (35,814 feet; 5,969 fathoms) with Don Walsh and Jacques Piccard on board. The depth was calculated from pressure readings and water density measurements.
Uncrewed dives included Kaikō in 1996 and Nereus in 2009. These dives measured depths between 10,902 and 10,916 metres (35,768 to 35,814 feet; 5,961 to 5,969 fathoms). In 2012, filmmaker James Cameron reached the trench in the submersible Deepsea Challenger, measuring a depth of 10,908 metres (35,787 feet; 5,965 fathoms).
In 2015, a hydrophone was placed in the Challenger Deep by researchers from NOAA, Oregon State University, and the Coast Guard. The device, made of titanium, recorded natural sounds like earthquakes, typhoons, and whale calls, as well as human-made sounds.
In 2019, Victor Vescovo reached a depth of 10,928 metres (35,853 feet; 5,976 fathoms) using the DSV Limiting Factor. He completed four dives to the Challenger Deep, making him the first person to return there more than once.
In 2020, the Russian autonomous underwater vehicle Vityaz-D reached a depth of 10,028 metres (32,900 feet; 5,483 fathoms) in the Mariana Trench. This was the first autonomous vehicle to operate at such extreme depths. The mission lasted over three hours, excluding diving and surfacing.
In 2020, the Chinese submersible Fendouzhe reached the bottom of the Mariana Trench at a depth of 10,909 metres (35,791 feet; 5,965 fathoms).
Life
In 1960, an expedition reported seeing large creatures at the bottom of the ocean. This surprised scientists because of the high pressure there. They saw a flatfish about 30 cm (12 in) long and shrimp. Piccard described the ocean floor as appearing light and clear, covered in firm diatomaceous ooze. Many marine biologists now question whether the flatfish was actually a sea cucumber. During a later expedition, the uncrewed vehicle Kaikō collected mud samples from the seabed. Scientists found tiny organisms living in those samples.
In July 2011, researchers used untethered landers called drop cams, which had digital cameras and lights, to explore the deep-sea region. They observed many living organisms, including very large single-celled foraminiferans over 10 cm (4 in) in size. These foraminiferans belong to the class Monothalamea, which are noted for their size, their large numbers on the seafloor, and their role in hosting other organisms.
In December 2014, scientists discovered a new species of snailfish at a depth of 8,145 m (26,722 ft; 4,454 fathoms). This broke the previous record for the deepest living fish seen on video.
During the 2014 expedition, researchers filmed several new species, including large amphipods called supergiants. Deep-sea gigantism refers to the phenomenon where species grow larger than their shallow-water relatives.
In May 2017, the Mariana snailfish, first discovered in 2014, was filmed at a depth of 8,178 meters (26,800 ft).
In 2016, scientists studied the chemical makeup of crustacean scavengers collected from depths of 7,841–10,250 m (25,725–33,629 ft; 4,288–5,605 fathoms) in the trench. They found very high levels of PCBs, a banned chemical toxin, in the sediment at all depths within the trench. Later research showed that amphipods also ingest microplastics, with 100% of studied amphipods having at least one piece of synthetic material in their stomachs.
In 2019, Victor Vescovo reported finding a plastic bag and candy wrappers at the bottom of the trench. That same year, Scientific American reported that carbon-14 from nuclear bomb testing was found in the bodies of aquatic animals in the trench.
Possible nuclear waste disposal site
The Mariana Trench, like other oceanic trenches, has been suggested as a place to store nuclear waste. This idea is based on the belief that tectonic plate movement, where one plate moves under another, might push the waste deep into Earth's mantle, which is the second layer of Earth. In 1979, Japan planned to place low-level nuclear waste near Maug in the Northern Marianas. However, international laws now stop ocean dumping of nuclear waste. Additionally, areas where tectonic plates meet are linked to large earthquakes. These earthquakes can be unpredictable, making it unsafe to store nuclear waste in the deep ocean environment for a long time.