This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: How deep is the deepest ocean—and how precisely can we actually measure it? A Japanese research team led by the National Institute of Polar Research (NIPR), SOKENDAI, the University of Tokyo and other Japanese institutions has mapped the Challenger Deep in the Mariana Trench using the EM124 multibeam echosounder aboard the research vessel Hakuho-maru.
Their study is published in the journal Scientific Data. The Challenger Deep has been measured repeatedly for decades, from the 10,920 m (35,827 feet) depth value based on the 1984 survey by the Japanese survey vessel Takuyo to recent full-ocean-depth surveys and dives, including the Five Deeps Expedition. Yet even modern high-precision measurements still differ by several to more than 10 m (33 feet).
Rather than seeking a new "deepest point" record, the study asks a more fundamental question: What controls a depth estimate when the seafloor lies nearly 11,000 m below the ocean surface? Acoustic depth measurement is based on a simple principle: Depth ≈ sound speed in seawater × round-trip travel time ÷ 2. At the Challenger Deep, sound takes roughly 15 seconds to travel from the ship to the seafloor and back.
But sound speed in seawater varies with temperature, salinity and pressure. The team processed the same multibeam dataset using five different seawater sound-speed models. The maximum gridded depth in the eastern basin ranged from 10,914 m to 10,932 m (35,807 to 35,866 feet), a spread of 18 m (59 feet) caused by the choice of sound-speed model.
The preferred model combined upper-ocean XCTD observations acquired by Hakuho-maru in 2023, extending to about 1,900 m, with a full-depth CTD profile acquired by the same vessel in 1992. This combination reflects upper-ocean conditions closest in time to the 2023 survey while also providing sound-speed information through the full water column. Using this model, the maximum depths of the western, central and eastern basins were 10,926 m (35,846 feet), 10,912 m (35,800 feet) and 10,927 m (35,850 feet), respectively.
The study therefore gives 10,927 m (35,850 feet) as its preferred estimate of the maximum depth of the Challenger Deep. The result does not mean that other recent depth estimates are simply wrong. Rather, it shows that meter-scale comparisons at full-ocean depth must consider the sound-speed model, vertical reference, observing conditions and processing method used to derive the value.
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