Challenger Deep

The Challenger Deep is the deepest-known point of the seabed of Earth, with a depth of by direct measurement from deep-diving submersibles, remotely operated underwater vehicles and benthic landers, and (sometimes) slightly more by sonar bathymetry.

The Challenger Deep is located in the western Pacific Ocean, at the southern end of the Mariana Trench, near the Mariana Islands. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the Challenger Deep is deep at .
This location is in the ocean territory of the Federated States of Micronesia.

The depression is named after the British Royal Navy survey ship , whose expedition of 1872–1876 made the first recordings of its depth. The high water pressure at this depth makes designing and operating exploratory craft difficult. The first descent by any vehicle was by Jacques Piccard and Don Walsh in the manned bathyscaphe ''Trieste'' in January 1960; unmanned visits followed in 1996, 1998 and 2009. In March 2012 a manned solo descent was made by film director James Cameron in the deep-submergence vehicle '' Deepsea Challenger''. Between 28 April and 4 May 2019, the DSV Limiting Factor completed four manned dives to the bottom of Challenger Deep. Between 6 June and 26 June 2020, the DSV ''Limiting Factor'' added six completed dives during the first Ring of Fire Expedition. The deep-sea submersible ''Fendouzhe'' (奋斗者, ''Striver'') completed a crewed dive to the bottom of the Challenger Deep on 10 November 2020 with three scientists onboard whilst livestreaming the descent. Between 1 March and 13 April 2021, the DSV ''Limiting Factor's'' second Ring of Fire Expedition added five completed dives. During the third Ring of Fire Expedition in the summer of 2022, the DSV ''Limiting Factor'' made an additional nine descents to the Challenger Deep. As of July 2022 the list of people who descended to Challenger Deep includes twenty-seven people.

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 shallower. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), southwest, and Guam, to the northeast.
Detailed sonar mapping of the western, center and eastern basins in June 2020 by the DSSV ''Pressure Drop'' combined with crewed 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.

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.

The accuracy of determining geographical location, and the beamwidth of (multibeam) echosounder systems, limits the horizontal and vertical bathymetric sensor resolution hydrographers can obtain from onsite data. This is especially important when sounding in deep water, as the resulting footprint of an acoustic pulse gets large once it reaches a distant sea floor. Further, sonar operation is affected by variations in sound speed, particularly in the vertical plane. The speed is determined by the water's bulk modulus, mass, and density. The bulk modulus is affected by temperature, pressure, and dissolved impurities (usually salinity).

1875 – HMS ''Challenger''

In 1875, during her transit from the Admiralty Islands in the Bismarck Archipelago to Yokohama in Japan, the three-masted sailing corvette HMS '' ''Challenger'' ''attempted to make landfall at Spanish Marianas (now Guam), but was set to the west by "baffling winds" preventing them from "visiting either the Carolines or the Ladrones." Their altered path took them over the undersea canyon which later became known as the Challenger Deep. Depth soundings were taken by Baillie-weighted marked rope, and geographical locations were determined by celestial navigation (to an estimated accuracy of two nautical miles). One of their samples was taken within fifteen miles of the deepest spot in all of Earth's oceans. On 23 March 1875, at sample station number #225, HMS ''Challenger'' recorded the bottom at deep, (the deepest sounding of her three-plus-year eastward circumnavigation of the Earth) at – and confirmed it with a second sounding at the same location. The serendipitous discovery of Earth’s deepest depression by history’s first major scientific expedition devoted entirely to the emerging science of oceanography, was incredibly good fortune, and especially notable when compared to the Earth’s third deepest site (the Sirena Deep only 150 nautical miles east of the Challenger Deep), which would remain undiscovered for another 122 years.

1951 – SV HMS ''Challenger II''

Seventy-five years later, the 1,140-ton British survey vessel '' HMS Challenger II'', on her three-year westward circumnavigation of Earth, investigated the extreme depths southwest of Guam reported in 1875 by her predecessor, HMS ''Challenger''. On her southbound track from Japan to New Zealand (May–July 1951), ''Challenger II'' conducted a survey of the Marianas Trench between Guam and Ulithi atoll, using seismic-sized bomb-soundings and recorded a maximum depth of . The depth was beyond ''Challenger II'' echo sounder capability to verify, so they resorted to using a taut wire with "140 lbs of scrap iron", and documented a depth of .Ritchie, G. S., ''Challenger, the Life of a Survey Ship'', Abelard-Shuman (1958), p. 225
In New Zealand, the ''Challenger II'' team gained the assistance of the Royal New Zealand Dockyard, "who managed to boost the echo sounder to record at the greatest depths". They returned to the "Marianas Deep" (sic) in October 1951. Using their newly improved echo sounder, they ran survey lines at right angles to the axis of the trench and discovered "a considerable area of a depth greater than " – later identified as the Challenger Deep’s ''western'' basin. The greatest depth recorded was , at . Navigational accuracy of several hundred meters was attained by celestial navigation and LORAN-A. Note that the term "Challenger Deep" came into use after this 1951–52 ''Challenger'' circumnavigation, and commemorates both British ships of that name involved with the discovery of the deepest basin of the world’s oceans.

1957–1958 – RV ''Vityaz''

In August 1957, the 3,248-ton Vernadsky Institute of Geochemistry research vessel recorded a maximum depth of at in the western basin of the Challenger Deep during a brief transit of the area on Cruise #25. She returned in 1958, Cruise #27, to conduct a detailed single beam bathymetry survey involving over a dozen transects of the Deep, with extensive examination of the western basin and a quick peek into the eastern basin. Fisher records a total of three ''Vityaz'' sounding locations on Fig.2 "Trenches" (1963), one within yards of the 142°11.5' E location, and a third at , all with depth. The depths were considered statistical outliers, and a depth greater than 11,000 m has never been proven. Taira reports that if ''Vityaz'' depth was corrected with the same methodology used by the Japanese RV ''Hakuho Maru'' expedition of December 1992, it would be presented as , as opposed to modern depths from multibeam echosounder systems greater than with the NOAA accepted maximum of in the western basin.

1959 – RV ''Stranger''

The first definitive verification of both depth and location of the Challenger Deep (western basin) was determined by Dr. R. L. Fisher from the Scripps Institution of Oceanography, aboard the 325-ton research vessel ''Stranger''. Using explosive soundings, they recorded at/near in July 1959. ''Stranger'' used celestial and LORAN-C for navigation. LORAN-C navigation provided geographical accuracy of or better. According to another source RV ''Stranger'' using bomb-sounding surveyed a maximum depth of at . Discrepancies between the geographical location (lat/long) of ''Stranger'' deepest depths and those from earlier expeditions (''Challenger II'' 1951; ''Vityaz'' 1957 and 1958) "are probably due to uncertainties in fixing the ships' positions".Fisher, "Trenches", ''The Earth Beneath the Sea'', p. 416, 1963 ''Stranger'' north-south zig-zag survey passed well to the east of the eastern basin southbound, and well to the west of the eastern basin northbound, thus failed to discover the eastern basin of the Challenger Deep. The maximum depth measured near longitude 142°30’E was , about 10 km west of the eastern basin’s deepest point. This was an important gap in information, as the eastern basin was later reported as deeper than the other two basins.
''Stranger'' crossed the center basin twice, measuring a maximum depth of in the vicinity of 142°22’E. At the western end of the central basin (approximately 142°18’E), they recorded a depth of .
The western basin received four transects by ''Stranger'', recording depths of toward the central basin, near where ''Trieste'' dove in 1960 (vicinity , and where ''Challenger II'', in 1950, recorded . At the far western end of the ''western'' basin (about 142°11’E), the ''Stranger'' recorded , some 6 km south of the location where ''Vityaz'' recorded in 1957–1958. Fisher stated: "differences in the ''Vitiaz'' icand ''Stranger''–''Challenger II'' depths can be attributed to the oundvelocity correction function used".
After investigating the Challenger Deep, ''Stranger'' proceeded to the Philippine Trench and transected the trench over twenty times in August 1959, finding a maximum depth of , and thus established that the Challenger Deep was about deeper than the Philippine Trench. The 1959 ''Stranger'' surveys of the Challenger Deep and of the Philippine Trench informed the U.S. Navy as to the appropriate site for ''Trieste'' record dive in 1960.

1962 – RV ''Spenser F. Baird''

The ''Proa Expedition, Leg 2'', returned Fisher to the Challenger Deep on 12–13 April 1962 aboard the Scripps research vessel ''Spencer F. Baird'' (formerly the steel-hulled US Army large tug ''LT-581'') and employed a Precision Depth Recorder (PDR) to verify the extreme depths previously reported. They recorded a maximum depth of (location not available). Additionally, at location "H-4" in the Challenger Deep, the expedition cast three taut-wire soundings: on 12 April, the first cast was to 5,078 fathoms (corrected for wire angle) at in the central basin (Up until 1965, US research vessels recorded soundings in fathoms). The second cast, also on 12 April, was to 5,000⁺ fathoms at in the central basin. On 13 April, the final cast recorded 5,297 fathoms (corrected for wire angle) at (the western basin). They were chased off by a hurricane after only two days on-site. Once again, Fisher entirely missed the eastern basin of the Challenger Deep, which later proved to contain the deepest depths.

1975–1980 – RV ''Thomas Washington''

The Scripps Institution of Oceanography deployed the 1,490-ton Navy-owned, civilian-crewed research vessel '' Thomas Washington'' (AGOR-10) to the Mariana Trench on several expeditions from 1975 to 1986. The first of these was the ''Eurydice Expedition, Leg 8'' which brought Fisher back to the Challenger Deep’s western basin from 28–31 March 1975. ''Thomas Washington'' established geodetic positioning by ( SATNAV) with Autolog Gyro and EM Log. Bathymetrics were by a 12 kHz Precision Depth Recorder (PDR) with a single 60° beam. They mapped one, "possibly two", axial basins with a depth of . Five dredges were hauled 27–31 March, all into or slightly north of the deepest depths of the western basin. Fisher noted that this survey of the Challenger Deep (western basin) had "provided nothing to support and much to refute recent claims of depths there greater than ." While Fisher missed the eastern basin of the Challenger Deep (for the third time), he did report a deep depression about 150 nautical miles east of the western basin. The 25 March dredge haul at encountered , which pre-shadowed by 22 years the discovery of HMRG Deep/Sirena Deep in 1997. The deepest waters of the HMRG Deep/Serina Deep at are centered at/near , approximately 2.65 km from Fisher's 25 March 1975 dredge haul.

On Scripps Institution of Oceanography's ''INDOPAC Expedition Leg 3'', the chief scientist, Dr. Joseph L. Reid, and oceanographer Arnold W. Mantyla made a hydrocast of a free vehicle (a special-purpose benthic lander (or "baited camera") for measurements of water temperature and salinity) on 27 May 1976 into the western basin of the Challenger Deep, "Station 21", at at about depth. On ''INDOPAC Expedition Leg 9'', under chief scientist A. Aristides Yayanos, ''Thomas Washington'' spent nine days from 13–21 January 1977 conducting an extensive and detailed investigation of the Challenger Deep, mainly with biological objectives. "Echo soundings were carried out primarily with a 3.5 kHz single-beam system, with a 12 kHz echosounder operated in addition some of the time" (the 12 kHz system was activated for testing on 16 January). A benthic lander was put into the western basin () on 13 January, bottoming at and recovered 50 hours later in damaged condition. Quickly repaired, it was again put down on the 15th to depth at . It was recovered on the 17th with excellent photography of amphipods (shrimp) from the Challenger Deep’s western basin. The benthic lander was put down for the third and last time on the 17th, at , in the central basin at a depth of . The benthic lander was not recovered and may remain on the bottom in the vicinity of . Free traps and pressure-retaining traps were put down at eight location from 13 to 19 January into the western basin, at depths ranging from . Both the free traps and the pressure-retaining traps brought up good sample amphipods for study. While the ship briefly visited the area of the eastern basin, the expedition did not recognize it as potentially the deepest of the three Challenger Deep basins.

''Thomas Washington'' returned briefly to the Challenger Deep on 17–19 October 1978 during ''Mariana Expedition Leg 5'' under chief scientist James W. Hawkins. The ship tracked to the south and west of the eastern basin, and recorded depths between . Another miss. On ''Mariana Expedition Leg 8'', under chief scientist Yayanos, ''Thomas Washington'' was again involved, from 12–21 December 1978, with an intensive biological study of the western and central basins of the Challenger Deep. Fourteen traps and pressure-retaining traps were put down to depths ranging from ; the greatest depth was at . All of the 10,900-plus m recordings were in the western basin. The depth was furthest east at 142°26.4' E (in the central basin), about 17 km west of the eastern basin. Again, focused efforts on the known areas of extreme depths (the western and central basins) was so tight that the eastern basin again was missed by this expedition.

From 20 to 30 November 1980, ''Thomas Washington'' was on site at the western basin of the Challenger Deep, as part of ''Rama Expedition Leg 7'', again with chief-scientist Dr. A. A. Yayanos. Yayanos directed ''Thomas Washington'' in arguably the most extensive and wide-ranging of all single-beam bathymetric examinations of the Challenger Deep ever undertaken, with dozens of transits of the western basin, and ranging far into the backarc of the Challenger Deep (northward), with significant excursions into the Pacific Plate (southward) and along the trench axis to the east. They hauled eight dredges in the western basin to depths ranging from , and between hauls, cast thirteen free vertical traps. The dredging and traps were for biological investigation of the bottom. In the first successful retrieval of a live animal from the Challenger Deep, on 21 November 1980 in the western basin at , Yayanos recovered a live amphipod from about 10,900 meters depth with a pressurized trap. Once again, other than a brief look into the eastern basin, all bathymetric and biological investigations were into the western basin.

1976–1977 – RV ''Kana Keoki''

On Leg 3 of the Hawaii Institute of Geophysics' (HIG) expedition 76010303, the 156-foot research vessel ''Kana Keoki'' departed Guam primarily for a seismic investigation of the Challenger Deep area, under chief scientist Donald M. Hussong. The ship was equipped with air guns (for seismic reflection soundings deep into the Earth's mantle), magnetometer, gravimeter, 3.5 kHz and 12 kHz sonar transducers, and precision depth recorders. They ran the Deep from east to west, collecting single beam bathymetry, magnetic and gravity measurements, and employed the air guns along the trench axis, and well into the backarc and forearc, from 13 to 15 March 1976. Thence they proceeded south to the Ontong Java Plateau. All three deep basins of the Challenger Deep were covered, but ''Kana Keoki'' recorded a maximum depth of . Seismic information developed from this survey was instrumental in gaining an understanding of the subduction of the Pacific Plate under the Philippine Sea Plate. In 1977, ''Kana Keoki'' returned to the Challenger Deep area for wider coverage of the forearc and backarc.

1984 – SV ''Takuyo''

The Hydrographic Department, Maritime Safety Agency, Japan (JHOD) deployed the newly commissioned 2,600-ton survey vessel ''Takuyo'' (HL 02) to the Challenger Deep 17–19 February 1984. ''Takuyo'' was the first Japanese ship to be equipped with the new narrowbeam SeaBeam multi-beam sonar echosounder, and was the first survey ship with multi-beam capability to survey the Challenger Deep. The system was so new that JHOD had to develop their own software for drawing bathymetric charts based on the SeaBeam digital data. In just three days, they tracked 500 miles of sounding lines, and covered about 140 km of the Challenger Deep with multibeam ensonification. Under chief scientist Hideo Nishida, they used CTD temperature and salinity data from the top of the water column to correct depth measurements, and later conferred with Scripps Institution of Oceanography (including Fisher), and other GEBCO experts to confirm their depth correction methodology. They employed a combination of NAVSAT, LORAN-C and OMEGA systems for geodetic positioning with accuracy better than . The deepest location recorded was at ; for the first time documenting the eastern basin as the deepest of the three en echelon pools. In 1993, GEBCO recognized the report as the deepest depth of the world’s oceans. Technological advances such as improved multi-beam sonar would be the driving force in uncovering the mysteries of the Challenger Deep into the future.

1986 – RV ''Thomas Washington''

The Scripps research vessel ''Thomas Washington'' returned to the Challenger Deep in 1986 during the ''Papatua Expedition, Leg 8'', mounting one of the first commercial multi-beam echosounders capable of reaching into the deepest trenches, i.e. the 16-beam Seabeam "Classic". This allowed chief scientist Yayanos an opportunity to transit the Challenger Deep with the most modern depth-sounding equipment available. During the pre-midnight hours of 21 April 1986, the multibeam echosounder produced a map of the Challenger Deep bottom with a swath of about 5–7 miles wide. The maximum depth recorded was (location of depth is not available). Yayanos noted: "The lasting impression from this cruise comes from the thoughts of the revolutionary things that Seabeam data can do for deep biology."

1988 – RV ''Moana Wave''

On 22 August 1988, the U.S. Navy-owned 1,000-ton research vessel ''Moana Wave'' (AGOR-22), operated by the Hawaii Institute of Geophysics (HIG), University of Hawaii, under the direction of chief scientist Robert C. Thunell from the University of South Carolina, transited northwesterly across the central basin of the Challenger Deep, conducting a single-beam bathymetry track by their 3.5 kHz narrow (30-degs) beam echosounder with a Precision Depth Recorder. In addition to sonar bathymetry, they took 44 gravity cores and 21 box cores of bottom sediments. The deepest echosoundings recorded were , with the greatest depth at 11°22′N 142°25′E in the central basin. This was the first indication that all three basins contained depths in excess of .

1992 – RV ''Hakuhō Maru''

The 3,987-ton Japanese research vessel ''Hakuhō Maru'', an Ocean Research Institute – University of Tokyo sponsored ship, on cruise KH-92-5 cast three Sea-Bird SBE-9 ultra-deep CTD (conductivity-temperature-depth) profilers in a transverse line across the Challenger Deep on 1 December 1992. The center CTD was located at , in the eastern basin, at by the SeaBeam depth recorder and by the CTD. The other two CTDs were cast 19.9 km to the north and 16.1 km to the south. ''Hakuhō Maru'' was equipped with a narrow beam SeaBeam 500 multi-beam echosounder for depth determination, and had an Auto-Nav system with inputs from NAVSAT/NNSS, GPS, Doppler Log, EM log and track display, with a geodetic positioning accuracy approaching . When conducting CTD operations in the Challenger deep, they used the SeaBeam as a single beam depth recorder. At the corrected depth was , and at the depth was ; both in the ''eastern'' basin. This may demonstrate that the basins might not be flat sedimentary pools but rather undulate with a difference of or more. Taira revealed, "We considered that a trough deeper that ''Vitiaz'' record by was detected. There is a possibly that a depth exceeding with a horizontal scale less that the beam width of measurements exists in the Challenger Deep. Since each SeaBeam 2.7-degree beam width sonar ping expands to cover a circular area about in diameter at depth, dips in the bottom that are less than that size would be difficult to detect from a sonar-emitting platform seven miles above.

1996 – RV ''Yokosuka''

For most of 1995 and into 1996, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) employed the 4,439-ton Research Vessel ''Yokosuka'' to conduct the testing and workup of the 11,000 meter remotely-operated vehicle (ROV) '' Kaikō'', and the 6,500 meter ROV ''Shinkai.'' It was not until February 1996, during ''Yokosuka'' cruise Y96-06, that ''Kaikō'' was ready for its first full depth dives. On this cruise, JAMSTEC established an area of the Challenger Deep (11°10'N to 11°30'N, by 141°50'E to 143°00'Ewhich later was recognized as containing three separate pools/basins en echelon, each with depths in excess of ) toward which JAMSTEC expeditions would concentrate their investigations for the next two decades. The Yokosuka employed a 151-beam SeaBeam 2112 12 kHz multibeam echosounder, allowing search swaths 12–15 km in width at depth. The depth accuracy of ''Yokosuka'' Seabeam was about 0.1% of water depth (i.e. ± for depth). The ship's dual GPS systems attained geodetic positioning within double digit meter ( or better) accuracy.

1998, 1999 and 2002 – RV ''Kairei''

Cruise KR98-01 sent JAMSTEC's two-year-old the 4,517-ton Deep Sea Research Vessel RV ''Kairei'' south for a quick but thorough depth survey of the Challenger Deep, 11–13 January 1998, under chief scientist Kantaro Fujioka. Tracking largely along the trench axis of 070–250° they made five 80-km bathymetric survey tracks, spaced about 15-km apart, overlapping their SeaBeam 2112-004 (which now allowed sub-bottom profiling penetrating as much as 75 m below the bottom) while gaining gravity and magnetic data covering the entire Challenger Deep: western, central, and eastern basins.

''Kairei'' returned in May 1998, cruise KR98-05, with ROV ''Kaikō'', under the direction of chief scientist Jun Hashimoto with both geophysical and biological goals. Their bathymetric survey from 14–26 May was the most intensive and thorough depth and seismic survey of the Challenger Deep performed to date. Each evening, ''Kaikō'' deployed for about four hours of bottom time for biological-related sampling, plus about seven hours of vertical transit time. When ''Kaikō'' was onboard for servicing, ''Kairei'' conducted bathymetric surveys and observations. ''Kairei'' gridded a survey area about 130 km N–S by 110 km E–W. ''Kaikō'' made six dives (#71–75) all to the same location, (11°20.8' N, 142°12.35' E), near the bottom contour line in the western basin.

The regional bathymetric map made from the data obtained in 1998 shows that the greatest depths in the eastern, central, and western depressions are , , and , respectively, making the eastern depression the deepest of the three.

In 1999, ''Kairei'' revisited the Challenger Deep during cruise KR99-06. The results of the 1998–1999 surveys include the first recognition that the Challenger Deep consists of three "right-stepping en echelon individual basins bounded by the depth contour line. The size of ach ofthe deeps are almost identical, 14–20 km long, 4 km wide". They concluded with the proposal "that these three individual elongated deeps constitute the 'Challenger Deep', and eidentify them as the East, Central and West Deep. The deepest depth we obtained during the swath mapping is in the West Deep (11°20.34' N, 142°13.20 E)." The depth was "obtained during swath mapping ... confirmed in both N–S and E-W swaths." Speed of sound corrections were from XBT to , and CTD below .

The cross track survey of the 1999 ''Kairei'' cruise shows that the greatest depths in the eastern, central, and western depressions are , , and , respectively, which supports the results of the previous survey.

In 2002 ''Kairei'' revisited the Challenger Deep 16–25 October 2002, as cruise KR02-13 (a cooperative Japan-US-South Korea research program) with chief scientist Jun Hashimoto in charge; again with Kazuyoshi Hirata managing the ROV ''Kaikō'' team. On this survey, the size of each of the three basins was refined to 6–10 km long by about 2 km wide and in excess of deep. In marked contrast to the ''Kairei'' surveys of 1998 and 1999, the detailed survey in 2002 determined that the deepest point in the Challenger Deep is located in the eastern basin around , with a depth of , located about southeast of the deepest site determined by the survey vessel ''Takuyo'' in 1984. The 2002 surveys of both the western and eastern basins were tight, with especially meticulous cross-gridding of the eastern basin with ten parallel tracks N–S and E–W less than 250 meters apart. On the morning of 17 October, ROV ''Kaikō'' dive #272 began and recovered over 33 hours later, with the ROV working at the bottom of the western basin for 26 hours (vicinity of 11°20.148' N, 142°11.774 E at ). Five ''Kaikō'' dives followed on a daily basis into the same area to service benthic landers and other scientific equipment, with dive #277 recovered on 25 October. Traps brought up large numbers of amphipods (sea fleas), and cameras recorded holothurians (sea cucumbers), White polychaetes (bristle worms), tube worms, and other biological species. During its 1998, 1999 surveys, ''Kairei'' was equipped with a GPS satellite-based radionavigation system. The United States government lifted the GPS selective availability in 2000, so during its 2002 survey, ''Kairei'' had access to non-degraded GPS positional services and achieved single digit meter accuracy in geodetic positioning.

2001 – RV ''Melville''

The 2.516-ton research vessel ''Melville'', at the time operated by the Scripps Institution of Oceanography, took the Cook Expedition, Leg 6 with chief scientist Patricia Fryer of the University of Hawaii from Guam on 10 February 2001 to the Challenger Deep for a survey titled "Subduction Factory Studies in the Southern Mariana", including HMR-1 sonar mapping, magnetics, gravity measurements, and dredging in the Mariana arc region. They covered all three basins, then tracked lines of bathymetry East-West, stepping northward from the Challenger Deep in sidesteps, covering more than north into the backarc with overlapping swaths from their SeaBeam 2000 12 kHz multi-beam echosounder and MR1 towed system. They also gathered magnetic and gravity information, but no seismic data. Their primary survey instrument was the MR1 towed sonar, a shallow-towed 11/12 kHz bathymetric sidescan sonar developed and operated by the Hawaii Mapping Research Group (HMRG), a research and operational group within University of Hawaii's School of Ocean and Earth Science and Technology (SOEST) and the Hawaii Institute of Geophysics and Planetology (HIGP). The MR1 is full-ocean-depth capable, and provides both bathymetry and sidescan data.

Leg 7 of the Cook Expedition continued the MR-1 survey of the Mariana Trench backarc from 4 March to 12 April 2001 under chief scientist Sherman Bloomer of Oregon State University.

2009 – RV ''Kilo Moana''

In May/June 2009 the US Navy-owned 3,064-ton twin-hulled research vessel ''Kilo Moana'' (T-AGOR 26) was sent to the Challenger Deep area to conduct research. ''Kilo Moana'' is civilian-manned and operated by SOEST. It is equipped with two multibeam echosounders with sub-bottom profiler add-ons (the 191-beam 12 kHz Kongsberg Simrad EM120 with SBP-1200, capable of accuracies of 0.2–0.5% of water depth across the entire swath), gravimeter, and magnetometer. The EM-120 uses 1 by 1 degree sonar-emissions at the sea surface. Each 1 degree beam width sonar ping expands to cover a circular area about in diameter at depth. Whilst mapping the Challenger Deep the sonar equipment indicated a maximum depth of at an undisclosed position. Navigation equipment includes the Applanix POS MV320 V4, rated at accuracies of 0.5–2 m. RV ''Kilo Moana'' was also used as the support ship of the hybrid remotely operated underwater vehicle (HROV) ''Nereus'' that dove three times to the Challenger Deep bottom during the May/June 2009 cruise and did not confirm the sonar established maximum depth by its support ship.

2009 – RV ''Yokosuka''

Cruise YK09-08 brought the JAMSTEC 4,429-ton research vessel ''Yokosuka'' back to the Mariana Trough and to the Challenger Deep June–July 2009. Their mission was a two-part program: surveying three hydrothermal vent sites in the southern Mariana Trough backarc basin near 12°57'N, 143°37'E about 130 nmi northeast of the central basin of the Challenger Deep, using the autonomous underwater vehicle ''Urashima''. AUV ''Urashima'' dives #90–94, were to a maximum depth of 3500 meters, and were successful in surveying all three sites with a Reson SEABAT7125AUV multibeam echosounder for bathymetry, and multiple water testers to detect and map trace elements spewed into the water from hydrothermal vents, white smokers, and hot spots. Kyoko OKINO from the Ocean Research Institute, University of Tokyo, was principal investigator for this aspect of the cruise.
The second goal of the cruise was to deploy a new "10K free fall camera system" called ''Ashura'', to sample sediments and biologics at the bottom of the Challenger Deep. The principal investigator at the Challenger Deep was Taishi Tsubouchi of JAMSTEC. The lander ''Ashura'' made two descents: on the first, 6 July 2009, ''Ashura'' bottomed at at . The second descent (on 10 July 2009) was to at . The 270 kg ''Ashura'' was equipped with multiple baited traps, a HTDV video camera, and devices to recover sediment, water, and biological samples (mostly amphipods at the bait, and bacteria and fungus from the sediment and water samples).

2010 – USNS ''Sumner''

On 7 October 2010, further sonar mapping of the Challenger Deep area was conducted by the US Center for Coastal & Ocean Mapping/Joint Hydrographic Center (CCOM/JHC) aboard the 4.762-ton ''Sumner''. The results were reported in December 2011 at the annual American Geophysical Union fall meeting. Using a Kongsberg Maritime EM 122 multi-beam echosounder system coupled to positioning equipment that can determine latitude and longitude up to accuracy, from thousands of individual soundings around the deepest part the CCOM/JHC team preliminary determined that the Challenger Deep has a maximum depth of at , with an estimated vertical uncertainty of ± at two standard deviations (i.e. ≈ 95.4%) confidence level. A secondary deep with a depth of was located at approximately to the east at in the eastern basin of the Challenger Deep.

2010 – RV ''Yokosuka''

JAMSTEC returned ''Yokosuka'' to the Challenger Deep with cruise YK10-16, 21–28 November 2010. The chief scientist of this joint Japanese-Danish expedition was Hiroshi Kitazato of the Institute of Biogeosciences, JAMSTEC. The cruise was titled "Biogeosciences at the Challenger Deep: relict organisms and their relations to biogeochemical cycles". The Japanese teams made five deployments of their 11,000-meter camera system (three to 6,000 meters – two into the central basin of the Challenger Deep) which returned with 15 sediment cores, video records and 140 scavenging amphipod specimens. The Danish Ultra Deep Lander System was employed by Ronnie Glud et al on four casts, two into the central basin of the Challenger Deep and two to 6,000 m some 34 nmi west of the central basin. The deepest depth recorded was on 28 November 2010 – camera cast CS5 – }, at a corrected depth of (the central basin).

2013 – RV ''Yokosuka''

With JAMSTEC Cruises YK13-09 and YK13-12, ''Yokosuka'' hosted chief scientist Hidetaka Nomaki for a trip to New Zealand waters (YK13-09), with the return cruise identified as YK13-12. The project name was QUELLE2013; and the cruise title was: "In situ experimental & sampling study to understand abyssal biodiversity and biogeochemical cycles". They spent one day on the return trip at the Challenger Deep to obtain DNA/RNA on the large amphipods inhabiting the Deep (''Hirondellea gigas''). Hideki Kobayashi (Biogeos, JAMSTEC) and team deployed a benthic lander on 23 November 2013 with eleven baited traps (three bald, five covered by insulating materials, and three automatically sealed after nine hours) into the central basin of the Challenger Deep at , depth . After an eight-hour, 46-minute stay at the bottom, they recovered some 90 individual ''Hirondellea gigas''.

2014 – RV ''Kairei''

JAMSTEC deployed ''Kairei'' to the Challenger Deep again 11–17 January 2014, under the leadership of chief scientist Takuro Nunora. The cruise identifier was KR14-01, titled: "Trench biosphere expedition for the Challenger Deep, Mariana Trench". The expedition sampled at six stations transecting the central basin, with only two deployments of the "11-K camera system" lander for sediment cores and water samples to "Station C" at the deepest depth, i.e. , at . The other stations were investigated with the "Multi-core" lander, both to the backarc northward, and to the Pacific Plate southward. The 11,000-meter capable crawler-driven ROV ''ABIMSO'' was sent to 7,646 m depth about 20 nmi due north of the central basin (ABISMO dive #21) specifically to identify possible hydrothermal activity on the north slope of the Challenger Deep, as suggested by findings from ''Kairei'' cruise KR08-05 in 2008. ''AMISMO'' dives #20 and #22 were to 7,900 meters about 15 nmi north of the deepest waters of the central basin. Italian researchers under the leadership of Laura Carugati from the Polytechnic University of Marche, Italy (UNIVPM) were investigating the dynamics in virus/prokaryotes interactions in the Mariana Trench.

2014 – RV ''Falkor''

From 16–19 December 2014, the Schmidt Ocean Institute's 2,024-ton research vessel '' Falkor'', under chief scientist Douglas Bartlett from the Scripps Institution of Oceanography, deployed four different untethered instruments into the Challenger Deep for seven total releases. Four landers were deployed on 16 December into the central basin: the baited video-equipped lander ''Leggo'' for biologics; the lander ''ARI'' to for water chemistry; and the probes ''Deep Sound 3'' and ''Deep Sound 2''. Both Deep Sound probes recorded acoustics floating at depth, until ''Deep Sound 3'' imploded at the depth of (about above the bottom) at . The ''Deep Sound 2'' recorded the implosion of ''Deep Sound 3'', providing a unique recording of an implosion within the Challenger Deep depression. In addition to the loss of the ''Deep Sound 3'' by implosion, the lander ''ARI'' failed to respond upon receiving its instruction to drop weights, and was never recovered. On 16/17 December, ''Leggo'' was returned to the central basin baited for amphipods. On the 17th, RV ''Falkor'' relocated 17 nms eastward to the eastern basin, where they again deployed both the ''Leggo'' (baited and with its full camera load), and the ''Deep Sound 2''. ''Deep Sound 2'' was programmed to drop to and remain at that depth during its recording of sounds within the trench. On 19 December ''Leggo'' landed at at a uncorrected depth of according to its pressure sensor readings. This reading was corrected to depth. ''Leggo'' returned with good photography of amphipods feeding on the lander’s mackerel bait and with sample amphipods. ''Falknor'' departed the Challenger Deep on 19 December en route the Marianas Trench Marine National Monument

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