The Challenger Deep is the deepest known point of the seabed of Earth, located in the western Pacific Ocean at the southern end of the Mariana Trench, in the ocean territory of the Federated States of Micronesia.
The GEBCO Gazetteer of Undersea Feature Names indicates that the feature is situated at and has an approximated maximum depth of below sea level. A 2011 study placed the depth at with a 2021 study revising the value to at a 95% confidence level.
The depression is named after the British Royal Navy survey ships , whose expedition of 1872–1876 first located it, and HMS Challenger II, whose expedition of 1950–1952 established its record-setting depth. The first descent by any vehicle was conducted by the United States Navy using the bathyscaphe Trieste in January 1960. , there were 27 people who have descended to the Challenger Deep.
Topography
The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. The Challenger Deep consists of three basins, each long, wide, and over in depth, oriented in echelon from west to east, separated by mounds between the basins higher. The three basins feature extends about west to east if measured at the isobath. Both the western and eastern basins have recorded depths (by sonar bathymetry) in excess of , while the center basin is slightly less deep. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), southwest, and Guam, to the northeast.The Colbert Report, airdate 12 April 2012, interview with James Cameron Detailed sonar mapping of the western, center and eastern basins in June 2020 by the DSSV Pressure Drop combined with manned descents revealed that they undulate with slopes and piles of rocks above a bed of pelagic ooze. This conforms with the description of Challenger Deep as consisting of an elongated seabed section with distinct sub-basins or sediment-filled pools.
Tectonics
The topography above is explained by the subduction of tectonic plates and is complex.
Ecology The summary report of the expedition lists unicellular life forms from the two dredged samples taken when the Challenger Deep was first discovered. , entry on 23 March 1875. These (Nassellaria and Spumellaria) were reported in the Report on Radiolaria (1887) , Report on the Radiolaria collected by H.M.S. Challenger by Ernst Haeckel. written by Ernst Haeckel.
On their 1960 descent, the crew of the Trieste noted that the floor consisted of diatomaceous ooze and reported observing "some type of flatfish" lying on the seabed."To the bottom of the sea" , T. A. Heppenheimer, AmericanHeritage.com
Many marine biologists are now skeptical of this supposed sighting, and it is suggested that the creature may instead have been a sea cucumber."James Cameron dives deep for Avatar" , Guardian, 18 January 2011"James Cameron heads into the abyss" , Nature, 19 March 2012 The video camera on board the Kaiko probe spotted a sea cucumber, a scale worm and a shrimp at the bottom.Hadfield, Peter (2 November 1996). "Mission to Marianas" , New Scientist."The last frontier", Time, 14 August 1995 At the bottom of the Challenger Deep, the Nereus probe spotted one polychaete worm (a multi-legged predator) about an inch long.Accessed 8 October 2009 Geography of the ocean floor near Guam with some notes on exploration of the Challenger Deep.
An analysis of the sediment samples collected by Kaiko found large numbers of simple organisms at . While similar lifeforms have been known to exist in shallower ocean trenches (> 7,000 m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep possibly represent taxa distinct from those in shallower ecosystems.
Most of the organisms collected were simple, soft-shelled foraminifera (432 species according to National Geographic), with four of the others representing species of the complex, multi-chambered genera and . Eighty-five per cent of the specimens were organic, soft-shelled allogromiids, which is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20%. As small organisms with hard, calcareous shells have trouble growing at extreme depths because of the high solubility of calcium carbonate in the pressurized water, scientists theorize that the prevalence of soft-shelled organisms in the Challenger Deep may have resulted from the typical biosphere present when the Challenger Deep was shallower than it is now. Over the course of six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment died out or were unable to adapt to the increasing water pressure and changing environment.
On 17 March 2013, researchers reported data that suggested piezophilic microorganisms thrive in the Challenger Deep. Other researchers reported related studies that microbes thrive inside rocks up to below the sea floor under of ocean off the coast of the northwestern United States. Study of the depth and location of the Challenger Deep Since May 2000, with the help of non-degraded signal satellite navigation, civilian surface vessels equipped with professional dual-frequency capable satellite navigation equipment can measure and establish their geodetic position with an accuracy in the order of meters to tens of meters whilst the western, central and eastern basins are kilometers apart.
In 2014, a study was conducted regarding the determination of the depth and location of the Challenger Deep based on data collected previous to and during the 2010 sonar mapping of the Mariana Trench with a Kongsberg Maritime EM 122 multibeam echosounder system aboard USNS Sumner. This study by James. V. Gardner et al. of the Center for Coastal & Ocean Mapping-Joint Hydrographic Center (CCOM/JHC), Chase Ocean Engineering Laboratory of the University of New Hampshire splits the measurement attempt history into three main groups: early single-beam echo sounders (1950s–1970s), early multibeam echo sounders (1980s – 21st century), and modern (i.e., post-GPS, high-resolution) multibeam echo sounders. Taking uncertainties in depth measurements and position estimation into account, the raw data of the 2010 bathymetry of the Challenger Deep vicinity consisting of 2,051,371 soundings from eight survey lines was analyzed. The study concludes that with the best of 2010 multibeam echosounder technologies after the analysis a depth uncertainty of ± (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ± (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is at . The depth measurement uncertainty is a composite of measured uncertainties in the spatial variations in sound-speed through the water volume, the ray-tracing and bottom-detection algorithms of the multibeam system, the accuracies and calibration of the motion sensor and navigation systems, estimates of spherical spreading, attenuation throughout the water volume, and so forth.
Both the RV Sonne expedition in 2016, and the RV Sally Ride expedition in 2019 expressed strong reservations concerning the depth corrections applied by the Gardner et al. study of 2014, and serious doubt concerning the accuracy of the deepest depth calculated by Gardner (in the western basin), of after analysis of their multibeam data on a grid. Dr. Hans van Haren, chief scientist on the RV Sally Ride cruise SR1916, indicated that Gardner's calculations were too deep due to the "sound velocity profiling by Gardner et al. (2014)."
In 2018-2019, the deepest points of each ocean were mapped using a full-ocean depth Kongsberg EM 124 multibeam echosounder aboard DSSV Pressure Drop. In 2021, a data paper was published by Cassandra Bongiovanni, Heather A. Stewart and Alan J. Jamieson regarding the gathered data donated to GEBCO. The deepest depth recorded in the 2019 Challenger Deep sonar mapping was ± at in the eastern basin. This depth closely agrees with the deepest point ( ±) determined by the Van Haren et al. sonar bathymetry. The geodetic position of the deepest depth according to the Van Haren et al. significantly differs (about to the west) with the 2021 paper. After post-processing the initial depth estimates by application of a full-ocean depth sound velocity profile Bongiovanni et al. report an (almost) as deep point at in the western basin that geodetically differs about with the deepest point position determined by Van Haren et al. ( in the western basin). After analysis of their multibeam data on a grid, the Bongiovanni et al. 2021 paper states the technological accuracy does not currently exist on low-frequency ship-mounted sonars required to determine which location was truly the deepest, nor does it currently exist on deep-sea pressure sensors.
In 2021, a study by Samuel F. Greenaway, Kathryn D. Sullivan, Samuel H. Umfress, Alice B. Beittel and Karl D. Wagner was published presenting a revised estimate of the maximum depth of the Challenger Deep based on a series of submersible dives conducted in June 2020. These depth estimates are derived from acoustic echo sounding profiles referenced to in-situ direct pressure measurements and corrected for observed oceanographic properties of the water-column, atmospheric pressure, gravity and gravity-gradient anomalies, and water-level effects. The study concludes according to their calculations the deepest observed seafloor depth was ± below mean sea level at a 95% confidence level at in the eastern basin. For this estimate, the error term is dominated by the uncertainty of the employed pressure sensor, but Greenaway et al. show that the gravity correction is also substantial. The Greenaway et al. study compares its results with other recent acoustic and pressure-based measurements for the Challenger Deep and concludes the deepest depth in the western basin is very nearly as deep as the eastern basin. The disagreement between the maximum depth estimates and their geodetic positions between post-2000 published depths however exceed the accompanying margins of uncertainty, raising questions regarding the measurements or the reported uncertainties.
Another 2021 paper by Scott Loranger, David Barclay and Michael Buckingham, besides a December 2014 implosion shock wave based depth estimate of , which is among the deepest estimated depths, also treatises the differences between various maximum depth estimates and their geodetic positions.
Direct measurements The 2010 maximal sonar mapping depths reported by Gardner et al. in 2014 and Greenaway et al. study in 2021 have not been confirmed by direct descent (pressure gauge/manometer) measurements at full-ocean depth. Expeditions have reported direct measured maximal depths in a narrow range.
For the western basin deepest depths were reported as by in 1960 and ± by DSV Limiting Factor in June 2020. For the central basin the greatest reported depth is ± by DSV Limiting Factor in June 2020. For the eastern basin deepest depths were reported as by Kaikō ROV in 1995, by ROV Nereus in 2009, by in 2012, by benthic lander "Leggo" in May 2019, and ± by DSV Limiting Factor in May 2019.
Surveys and bathymetry Over many years, the search for, and investigation of, the location of the maximum depth of the world's oceans has involved many different vessels, and continues into the twenty-first century.