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The Ultimate Guide to Deep Exploration 6.5: Features, Benefits, and Legal Options

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 6 to 10 km (3.7 to 6.2 mi) long, 2 km (1.2 mi) wide, and over 10,850 m (35,597 ft) in depth, oriented in echelon from west to east, separated by mounds between the basins 200 to 300 m (656 to 984 ft) higher. The three basins feature extends about 48 km (30 mi) west to east if measured at the 10,650 m (34,941 ft) isobath.[10] Both the western and eastern basins have recorded depths (by sonar bathymetry) in excess of 10,920 m (35,827 ft), while the center basin is slightly shallower.[11] The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast.[12]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.[13]

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The accuracy of determining geographical location, and the beamwidth of (multibeam) echosounder systems, limits the horizontal and vertical bathymetric sensor resolution that 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).

On Leg 3 of the Hawaii Institute of Geophysics' (HIG) expedition 76010303, the 156-foot (48 m) research vessel Kana Keoki departed Guam primarily for a seismic investigation of the Challenger Deep area, under chief scientist Donald M. Hussong.[57] 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 7,800 m (25,591 ft).[58] Seismic information developed from this survey was instrumental in gaining an understanding of the subduction of the Pacific Plate under the Philippine Sea Plate.[59] In 1977, Kana Keoki returned to the Challenger Deep area for wider coverage of the forearc and backarc.

The regional bathymetric map made from the data obtained in 1998 shows that the greatest depths in the eastern, central, and western depressions are 10,922 74 m (35,833 243 ft), 10,898 62 m (35,755 203 ft), and 10,908 36 m (35,787 118 ft), respectively, making the eastern depression the deepest of the three.[14]

In November 2019, as cruise SR1916, a NIOZ team led by chief scientist Hans van Haren, with Scripps technicians, deployed to the Challenger Deep aboard the 2,641-ton research vessel Sally Ride, to recover a mooring line from the western basin of the Challenger Deep. The 7 km (4.3 mi) long mooring line in the Challenger Deep consisted of top-floatation positioned around 4 km (2.5 mi) depth, two sections of Dyneema neutrally buoyant 6 mm (0.2 in) line, two Benthos acoustic releases and two sections of self-contained instrumentation to measure and store current, salinity and temperature. Around the 6 km (3.7 mi) depth position two current meters were mounted below a 200 m (656 ft) long array of 100 high-resolution temperature sensors. In the lower position starting 600 m (1,969 ft) above the sea floor 295 specially designed high-resolution temperature sensors were mounted, the lowest of which was 8 m (26 ft) above the trench floor. The mooring line was deployed and left by the NIOZ team during the November 2016 RV Sonne expedition with the intention to be recovered in late 2018 by Sonne. The acoustic commanded release mechanism near the bottom of the Challenger Deep failed at the 2018 attempt. RV Sally Ride was made available exclusively for a final attempt to retrieve the mooring line before the release mechanism batteries expired.[117] Sally Ride arrived at the Challenger Deep on 2 November. This time a 'deep release unit' lowered by one of Sally Ride's winch-cables to around 1,000 m depth pinged release commands and managed to contact the near-bottom releases. After being nearly three years submerged, mechanical problems had occurred in 15 of the 395 temperature sensors. The first results indicate the occurrence of internal waves in the Challenger Deep.[118][119]

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 10,984 m (36,037 ft) after analysis of their multibeam data on a 100 m (328 ft) grid. Dr. Hans van Haren, chief scientist on the RV Sally Ride cruise SR1916, indicated that Gardner's calculations were 69 m (226 ft) too deep due to the "sound velocity profiling by Gardner et al. (2014)."[117]

Another 2021 paper by Scott Loranger, David Barclay and Michael Buckingham, besides a December 2014 implosion shock wave based depth estimate of 10,983 m (36,033 ft), which is among the deepest estimated depths, also treatises the differences between various maximum depth estimates and their geodetic positions.[123][124]

The 2010 maximal sonar mapping depths reported by Gardner in 2014 and Greenaway et al. study in 2021 have not been confirmed by direct descent (pressure gauge/manometer) measurements at full-ocean depth.[125]Expeditions have reported direct measured maximal depths in a narrow range.For the western basin deepest depths were reported as 10,913 m (35,804 ft) by Trieste in 1960 and 10,923 m (35,837 ft) 4 m (13 ft) by DSV Limiting Factor in June 2020.For the central basin the greatest reported depth is 10,915 m (35,810 ft) 4 m (13 ft) by DSV Limiting Factor in June 2020.For the eastern basin deepest depths were reported as 10,911 m (35,797 ft) by ROV Kaikō in 1995, 10,902 m (35,768 ft) by ROV Nereus in 2009, 10,908 m (35,787 ft) by Deepsea Challenger in 2012, 10,929 m (35,856 ft) by benthic lander "Leggo" in May 2019, and 10,925 m (35,843 ft) 4 m (13 ft) by DSV Limiting Factor in May 2019.

Caladan Oceanic's "Ring of Fire" expedition in the Pacific included six crewed descents and twenty-five lander deployments into all three basins of the Challenger Deep all piloted by Victor Vescovo and further topographical and marine life survey of the entire Challenger Deep.[150] The expedition craft used are the Deep Submersible Support Vessel DSSV Pressure Drop, Deep-Submergence Vehicle DSV Limiting Factor and the ultra-deep-sea landers Closp, Flere and Skaff.During the first crewed dive on 7 June 2020 Victor Vescovo and former US astronaut (and former NOAA Administrator) Kathryn D. Sullivan descended to the "Eastern Pool" of the Challenger Deep in the Deep-Submergence Vehicle Limiting Factor.[151][152]

On 28 February 2021 Caladan Oceanic's "Ring of Fire 2" expedition arrived over the Challenger Deep and conducted crewed descents and lander deployments into the Challenger Deep.[167] At the start the (unmanned) ultra-deep-sea lander Skaff was deployed to collect water column data by CTD for the expedition. The effects of the Pacific subducting plate crashing into the Philippine Plate was amongst the things researched onsite.On 1 March 2021 the first crewed descent to the eastern pool was made by Victor Vescovo and Richard Garriott.[168] Garriott became the 17th person to descend to the bottom.[169][170]On 2 March 2021 a descent to the eastern pool was made by Victor Vescovo and Michael Dubno.[170][171]On 5 March a descent to the eastern pool was made by Victor Vescovo and Hamish Harding.[172] They traversed the bottom of Challenger Deep.[173][174]On 11 March 2021 a descent to the western pool was made by Victor Vescovo and marine botanist Nicole Yamase.[175]On 13 April 2021 a descent was made by deep water submersible operations expert Rob McCallum and Tim Macdonald who piloted the dive.[176][177][178]A 2021 descent with a Japanese citizen is planned.[179]All crewed descents were conducted in the Deep-Submergence Vehicle DSV Limiting Factor.

In July 2022 for the fourth consecutive year, Caladan Oceanic's deep submergence system, consisting of the deep submersible DSV Limiting Factor supported by the mother ship DSSV Pressure Drop, returned to the Challenger Deep for dives into the Challenger Deep.[180]In early July, 2022 Victor Vescovo was joined by Aaron Newman as mission specialist for a dive into the Central pool.[181] On July 5, 2022 Tim Macdonald as pilot and Jim Kitchen as mission specialist for a dive into the Eastern pool.[182] On July 8, 2022 Victor Vescovo was joined by Dylan Taylor as mission specialist for a dive into the Eastern pool.[183]Victor Vescovo (for his 15th dive into the Challenger Deep) was joined by geographer and oceanographer Dawn Wright as mission specialist on the July 12, 2022 dive to 10,919 m (35,823 ft) in the Western pool.[184][185] Wright operated the world's first sidescan sonar to ever operate at full-ocean depth to capture detailed imagery along short transects of the southern wall of the Western pool.[186][187]


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