You may have already heard that the Mariana Trench is the deepest part of the ocean, but what exactly is it?
While coral reefs, kelp beds, and other coastal areas might be reasonably familiar, the deep ocean is an incredible and largely unknown world of canyons, seamounts, abyssal plains, and other astonishing geological features.
Undoubtedly, the most impressive of all the terrain beneath the waves has to be the Mariana Trench.
This article will answer all your questions, starting right at the beginning.
What Is the Mariana Trench?
Deep below the surface, at an area in the Western Pacific Ocean between The Philippines, Papua New Guinea, and Japan, the crescent-shaped Mariana Trench dramatically opens up the seabed and is the deepest oceanic trench on Earth.
To make it easier to imagine, we can think of oceanic trenches like canyons on land, but they’re considerably longer and wider.
Why Is It Called the Mariana Trench?
The deepest part of the world’s ocean was named after the nearby Mariana Islands, which lie about 200 kilometers (124 miles) westwards from the trench, a little north of Guam.
These islands were named after the Spanish Queen Mariana of Austria when European settlers colonized them in the 17th century.
However, it’s worth noting that the first humans arrived from the Philippines significantly earlier, between 1500 to 1400 BC.
It is unclear who specifically came up with the name “Mariana Trench.” However, the earliest known reference was in a report by the British survey ship HMS Challenger (known as Challenger II.)
The Royal Navy team explored the trench “using explosives and a hand-held stopwatch, a wire-line sounding machine with a 40-lb weight, and an echo sounder” in 1951.
Before that, the trench was discovered during an expedition of the original HMS Challenger in March 1875. This ship used the traditional method of ocean exploration, a weighted rope.
The crew measured a depth of 4,475 fathoms, equivalent to 8,184 meters (26,850 feet), and named the spot “Challenger Deep” rather than using the more sober description from their survey logs “sample station 225.”
How Deep Is the Mariana Trench?
The Mariana Trench measures approximately 10,984 meters deep at its lowest point, equivalent to 36,036 feet or 6.83 miles below the surface.
The deepest area at the southern end of the trench remains named Challenger Deep after the first expedition, and the lowest spot is located at coordinates 11.329903°N 142.199305°E.
Challenger Deep is a slot-shaped depression in the base of the much larger main trench, and it consists of three basins separated by mounds named the Western, Central, and Eastern Pools.
The Central is slightly shallower than the other two but is still at least 10,915 meters (35,810 feet) below sea level.
The generally referenced maximum measurement was made in 2010 during the University of New Hampshire’s survey of the deepest sections of the Mariana Trench.
The study used a multibeam echosounder fitted to the research vessel USNS Sumner to produce the most accurate trench measurements to date. The reading is considered accurate to ± 25 m.
Measuring extreme ocean depths is not a completely precise science. In 2021 a study using pressure sensors suggested that the maximum depth may be slightly shallower at 10,935 meters (35,876 feet) with an accuracy of ±6 m.
However, at such extremes, a few meters here or there doesn’t seem worth fighting over.
Is There Anything Deeper Than the Mariana Trench?
Less than 10% of the world’s ocean has been mapped with pinpoint accuracy. However, the whole planet has been surveyed using satellites that bounce radar beams off the ocean’s surface to create generally accurate maps of the ocean’s depths.
No deeper places than the Mariana Trench have ever been discovered.
What Is at the Bottom of the Mariana Trench?
The bottom of the Mariana Trench is covered in sediment that has a muddy consistency and is composed of dead organisms, rocks, and other materials that have fallen to the seafloor over millions of years.
James Cameron described it as “very lunar-like” after his dive into the Challenger Deep.
In terms of life, the area surrounding the Mariana Trench as a whole is home to some of the ocean’s scariest and weirdest-looking creatures.
However, the extreme depth and associated pressure at the very bottom mean that only very few extraordinary lifeforms can survive there.
There is a complete absence of any light, which means that no regular plants can grow. Diatoms, a type of algae, are found, but these do not require light to live.
What Is the Water Pressure at the Bottom of the Mariana Trench?
The massive column of water above the seabed in the Mariana Trench exerts a tremendous pressure of 1,086 bar or 15,750 psi.
This number is pretty hard to imagine, so to make it easier, it’s often described as the equivalent of around 100 adult elephants standing on your head.
Put it like that, and you can probably imagine why not much life can survive there.
How Cold Is It at the Bottom of the Trench?
The water temperature in Challenger Deep has been measured at 1.4 °C (34.5 °F).
In general, deep ocean waters have relatively consistent temperatures. Anything below about 200 meters (656 feet) is always below 4 °C (39 °F.) The deeper you go, the cooler it gets.
Cold water is denser than warm water, so it will sink downwards.
The extreme depth of Challenger Deep means that temperatures are cold and remain so year-round.
What Lives at the Bottom of the Mariana Trench?
The first life from the bottom of the Mariana Trench was collected by the HMS Challenger in 1875 when tiny radiolaria protozoa ( single-celled animals that feed on organic matter) were found in samples of bottom sediment collected from 8,184 meters.
Across the course of numerous expeditions, scientists have identified over 200 different species of microorganisms in collected sediment samples, many of which feed on chemicals, including hydrogen and methane, released underwater.
Sediment-feeding saucer-sized single-celled xenophyophores have been discovered along with shrimp-like amphipods, scale worms, and small sea cucumbers called holothurians.
All these organisms are relatively simple, and even the very largest are pretty small. For example, one expedition found a polychaete worm about an inch in length.
Fish can’t survive past about 8,500 meters (28,000 feet) depth. So, they’re not found in the deepest parts of the Mariana Trench.
The Mariana snailfish (Pseudoliparis swirei) was discovered in 2012 at a depth of about 8,000 meters (26,000 feet). This unusual species is generally regarded as being the deepest fish in the ocean.
What Is the Biggest Animal in the Mariana Trench?
There aren’t any large animals in the Mariana Trench, as the pressure is too great.
However, many fascinating and frightening-looking sea creatures are in the surrounding shallower areas.
The shallowest part of the trench lies at around 5,500 meters in depth (18,044 feet), meaning that the largest animal in the trench could be the Mariana snailfish which grows to 28.8 centimeters (11.3 inches).
Other candidates include the “supergiant” amphipods (shrimp-like creatures) that have been found below 7,000 meters (22,965 feet) and have been found to measure over 28 centimeters (11 inches) long.
It’s unlikely that any of the giant creatures in the ocean could reach into the trench. For example, the deepest dive for a whale ever recorded was made to “only” 2,992 meters (9,816 feet).
It’s often suggested that giant squid might live in the trench, but these are only thought to reach down about 1,000 meters (3,280 feet).
Could the Megalodon Still Be Alive in the Mariana Trench?
There’s no evidence that the long-extinct megalodon shark is hiding inside the Mariana Trench.
Firstly, the trench is too deep for the animal to survive in. No large fish has even been found at these extreme depths.
Secondly, the colossal megalodon needed vast amounts of food to survive, which isn’t present inside the trench.
Thirdly, large megalodon teeth are found where the shark lived prehistorically, and none have been found in the trench mud by any of the numerous expeditions.
How Long Is the Mariana Trench?
The Mariana Trench stretches for approximately 2,542 kilometers (1,580 miles) in length and is up to 43 miles (69 kilometers) wide.
The Izu-Bonin Trench borders Mariana’s crescent shape to the north, while the Yap Trench lies to the south.
How Was the Mariana Trench Formed?
The Mariana Trench was formed when two tectonic plates (the massive slabs of rock that make up the Earth’s crust and “float” on the molten mantle) slowly collided at a boundary known as a subduction zone.
The particular location is the Izu–Bonin–Mariana subduction system.
The western edge of the older and denser Pacific Plate became thrust underneath the Mariana Plate and bent to sink into the Earth’s mantle. The younger plate rode up over the top, and the trench we know today formed above the bend.
This all happened hundreds of millions of years ago, and the “wrinkle” in the seabed has remained the deepest point, partly due to its isolation.
If it were closer to land, the trench would have filled in at least partially with sediment run-off.
Are There Any Other Interesting Geological Features Found in the Mariana Trench?
In addition to the Challenger Deep, there are several other notable geological features inside the Mariana Trench.
- The Sirena Deep was discovered in 1997 and is the third deepest point in the ocean at 10,714 meters (35,151 feet), after Challenger Deep and Horizon Deep, the deepest point of the Tonga Trench
- Hydrothermal vents, which are areas where hot water and minerals are spewing out of the seafloor have been discovered in over 20 locations
- Cold seeps, which are areas where methane and other hydrocarbons are seeping out of the seafloor
- The Volcanic Unit, an undersea arc of mud volcanoes
Has Anyone Been to the Bottom of the Mariana Trench?
To date (end of 2022), there have been 22 descents carrying a total of 27 different people to the bottom of the Mariana Trench.
The first was in January 1960 when Don Walsh and Jacques Piccard descended in the bathyscaphe Trieste to 10,916 meters (35,814 feet).
The second dive (and first solo dive) was made to a recorded depth of 10,908 meters (35,787 feet) by the film director James Cameron in March 2012 as his Deepsea Challenge.
Subsequent dives were made by Victor Vescovo, who made a total of three dives in April and May of 2019 and set a new record of 10,928 meters (35,853 feet.)
Vescovo’s “Limiting Factor” two-person submarine made six further descents in June 2020, six in March and April 2021, and four in June and July 2022. The dives set several records, including the longest time at the bottom of Challenger Deep.
In between, the Chinese submersible Fendouzhe descended with a three-person crew to 10,909 meters (35,791 ft) in November 2020.
How Much of the Mariana Trench Have We Explored?
All of the crewed dives in the Mariana Trench have targeted the three pools of Challenger Deep, so there’s a vast amount that we haven’t seen for ourselves.
However, expeditions, including the one by the University of New Hampshire in 2010, have used multibeam soar to generate accurate maps of a much wider area of the deepest parts.
The Mariana Trench is probably the area of the deep ocean that has been surveyed the most. But there is still plenty of it that we haven’t mapped as accurately as is technically possible.
Conclusion
The Mariana Trench is the deepest oceanic trench on Earth and stretches down to an incredible 10,984 meters (36,036 feet) below the surface at its lowest point.
The importance of the trench was confirmed in 2009 when the United States named the area a Marine National Monument.
Unfortunately, the deepest part of the ocean has not escaped our pollution, and scientists have detected banned human-made chemicals, including PCBs, in water samples.
Sadly, even plastic debris has been seen at the bottom of the trench during exploratory dives.
The Mariana Trench was created by the unimaginable powers of shifting tectonic plates. However, much like the rest of our planet, the ability to preserve it is in our hands.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.
Very interesting and informative. I really enjoyed this article.