Challenger Deep
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 in excess of, while the center basin is slightly less deep. The closest land to the Challenger Deep is Fais Island, 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 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.
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 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.
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, but was set to the west by "baffling winds" preventing her crew 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. 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, 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, 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, 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. The Senior Scientist aboard Challenger II, Thomas Gaskell, recalled:t took from ten past five in the evening until twenty to seven, that is an hour and a half, for the iron weight to fall to the sea-bottom. It was almost dark by the time the weight struck, but great excitement greeted the reading...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" 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. As Gaskell explained, the measurement
was not more than 50 miles from the spot where the nineteenth-century Challenger found her deepest depth and it may be thought fitting that a ship with the name Challenger should put the seal on the work of that great pioneering expedition of oceanography.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 Soviet 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 an extensive examination of the western basin and a quick peek into the eastern basin. Fisher records a total of three Vityaz sounding locations on Figure 2 "Trenches", 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 the depth and location of the Challenger Deep 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 of Stranger deepest depths and those from earlier expeditions "are probably due to uncertainties in fixing the ships' positions". 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, they recorded a depth of.
The western basin received four transects by Stranger, recording depths of toward the central basin, near where Trieste dived in 1960, the Stranger recorded, some 6 km south of the location where Vityaz recorded in 1957–1958. Fisher stated: "differences in the Vitiaz and Stranger–''Challenger II depths can be attributed to the velocity 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.