The deepest depths of the sea are found in the crescent shape Mariana Trench, located in the western Pacific Ocean. But what is the deepest point of the Mariana Trench?
The Mariana Trench is about 1,580 miles (2,550 kilometers) long and is located east of the Mariana Islands, which give the trench its name, according to the University of Washington (opens in a new tab). The deepest place in the Mariana Trench is a valley called Challenger Deep, located at the southern end of the Mariana Trench, according to the The National Oceanic and Atmospheric Administration (opens in a new tab) (NOAA).
According to NOAA, the Challenger Deep extends approximately 35,876 feet (10,935 meters) below the surface. This is about 7,000 feet (2,100 m) deeper than Mount Everest is tall, NOAA noted (opens in a new tab).
The NOAA estimate comes from a 2021 study in the journal Deep Sea Research Part I: Oceanographic Research Papers (opens in a new tab), based on data from a 2020 voyage. However, there are many other estimates of the depths of the Challenger Deep. The first crewed mission there, in 1960, returned an estimate of 35,797 feet (10,911 m), according to Guinness World Records (opens in a new tab). Since then, recent estimates have included 36,069 feet (opens in a new tab) (10,994 m) and 36,036 feet (10,984m (opens in a new tab)).
Why is it so difficult to estimate the depth of the Challenger Deep? “Basically it’s difficult because it’s so deep,” said Cmdr. Sam Greenaway of NOAA Corps and lead author of the 2021 study, told Live Science.
Related: What are the deepest points in the Earth’s oceans?
To measure the depth of the oceans using modern instruments, scientists basically have two options: a ship-mounted sonar on the surface of the ocean or a pressure sensor deployed on the seafloor that can help measure how much water is above it, Greenaway said.
Sonar beams from multibeam echosounders “can produce full coverage of the seafloor,” said Greenaway, marine operations manager for NOAA’s new shipbuilding team. “As good as they are, the ship’s systems are very far from the seabed, which limits both the horizontal and vertical accuracy of the measurement.”
For example, with the Challenger Deep, “it takes about 14 seconds for sound to descend to the sea floor and return”, and salinity, temperature and water pressure can affect the speed and path of sound, said Greenaway. As a result, the vertical accuracy of an echo sounder measurement is about 80 feet (25 m), he noted.
With a pressure sensor, building a pressure gauge that is accurate enough at such high pressures is quite difficult, Greenaway said. On the ground of Challenger Deep, the pressure is more than 1,000 times standard atmospheric pressure at sea level, Guinness World Records noted.
“After that, we need to correct for the density of the water above the sensor, gravity pulling that water down, the pressure of the atmosphere, and the tides,” Greenaway noted. “Deploying a pressure sensor in the right place is also a bit of a trick.”
To make their measurements, Greenaway and his colleagues laid a pressure sensor on the seafloor to serve as a reference for their echosounder readings. “Pressure sensor uncertainty has dominated our overall uncertainty, but instrument manufacturers are making great strides in improving these sensors, so I expect this component of uncertainty may improve. considerably in the future,” he said.
The surfaces of Mars and the moon are mapped with greater resolution and accuracy than the ocean floor, Greenaway said in a Reddit post (opens in a new tab). “I’ve spent most of my career working on various aspects of seabed mapping,” he told Live Science. “I think it’s surprising to a lot of people how much of this mapping work remains to be done.”
Concretely, “the difference between the Challenger Deep and its depth of 10,935 meters, as we determined, or 10,984 meters, as estimated by a recent mapping campaign, does not really matter”, said Greenaway. “However, the idea that we need to go out and measure the depth of the world’s oceans is really important.” For example, such research can help with precise positioning of underwater vehicles, as well as pressure sensors that help monitor water level fluctuations due to climate change, he said.
Depth is also important for deep-sea explorers. On March 26, 2012, the filmmaker James Cameron dived 35,787 feet (10,908 m) in the Deepsea Challenger submersible vessel in the ocean trench, setting the record for the deepest solo dive. In 2019, explorer and businessman Victor Vescovo made the deepest dive on record, at 35,853 feet (10,927 m) in the Pacific Ocean. Vescovo worked with deep-sea specialists, including Captain Don Walsh, a US Navy oceanographer known for his dives with Swiss oceanographer and engineer Jacques Piccard at the Challenger Deep on January 23, 1960. They became the first to reach the deepest part of the ocean, at around 35,814 feet (10,916 m).