Challenger Deep

Location of Challenger Deep within the Western Pacific Ocean

The Challenger Deep is the deepest surveyed point in the oceans, with a depth of approximately 11,000 meters (36,000 feet). It is located at the southern end of the Mariana Trench near the Mariana Islands group. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped trench, which itself is an unusually deep feature in the ocean floor.

The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 289 km (180 mi) southwest, and Guam, 306 km (190 mi) to the northeast. The depression is named after the British Royal Navy survey ship HMS Challenger, whose expedition of 1872–76 made the first recordings of its depth.

The most recent (1 June 2009) sonar mapping of the Challenger Deep by the Simrad EM120 sonar multibeam bathymetry system for 300 – 11,000 m deep water mapping aboard the RV Kilo Moana, has indicated a spot with a depth of 10,971 m (35,994 ft) (6.82 miles). The sonar system uses phase and amplitude bottom detection, with an accuracy of better than 0.2% of water depth (this is an error of about 22 meters at this depth).

Only three descents have ever been achieved. The first was a manned descent by Trieste in 1960. This was followed by the unmanned ROVs Kaikō in 1995 and Nereus in 2009. These expeditions have measured very similar depths of 10,902 to 10,916 meters.

In January 2010, marking the fiftieth anniversary of the Trieste descent, the X Prize Foundation announced a $10 million prize for the first privately funded craft to make two repeat manned descents.

History of depth mapping from the surface

• The HMS Challenger expedition (December 1872 – May 1876) first sounded the depths now known as the Challenger Deep. This first sounding was made on 23 March 1875 at station 225. The reported depth was 4,475 fathoms (26,850 ft,8,184m), based on two separate soundings.

• A 1912 book, The Depths of the Ocean by Sir John Murray, records the depth of the Challenger Deep as 31,614 ft (9,636 m), reporting the sounding taken by the converted navy collier, USS Nero, in 1899. Murray was one of the expedition scientists, a young man at the time.

• In 1951, about 75 years after its original discovery, the entire Mariana Trench was surveyed by a second Royal Navy vessel, captained by George Stephen Ritchie (later Rear Admiral Ritchie); this vessel was also named HMS Challenger, after the original expedition ship. This survey recorded the deepest part of the trench using echo sounding, a much more precise and vastly easier way to measure depth than the sounding equipment and drag lines used in the original expedition. A depth of 5,960 fathoms (10,900 m, 35,761 ft) was measured at 11°19′N 142°15′E.

• In 1984, a Japanese survey vessel used a narrow, multi-beam echo sounder to take a measurement of 10,924 m (35,840 ft).

• The maximum surveyed depth of the Challenger Deep was reported in 2005 by National Geographic at 11,034 metres (36,201 ft) below sea level. This is 6.74 miles. The pressure at this depth is approximately 1,099 times that at the surface, or 111 MPa, roughly 16,155 PSI.

• On 1 June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 sonar multibeam bathymetry system for deep water (300 - 11,000 meters) mapping aboard the RV Kilo Moana (mothership of the Nereus vehicle), has indicated a spot with a depth of 10,971 m (35,994 ft). The sonar system uses phase and amplitude bottom detection, with an accuracy of better than 0.2% of water depth across the entire swath.

The latter maximal depths were not confirmed by the series of dives Nereus made to the bottom during the Challenger Deep Nereus May/June 2009 Expedition. The direct descent measurements by the three expeditions which have reported from the bottom, have fixed depths in a narrow range from 10,916 m (Trieste) to 10,911 m (Kaikō), to 10,902 m (Nereus). However, although an attempt was made to correlate locations, it could not be absolutely certain that Nereus (or the other two descents) reached exactly the same points found to be maximally deep by the sonar/echo sounders of previous mapping expeditions, even though the last of these echo soundings was made by the Nereus mothership.

Descents

Trieste

Main article: Bathyscaphe Trieste

On 23 January 1960, the Swiss-designed, Italian-built Bathyscaphe Trieste, acquired by the U.S. Navy, descended to the ocean floor in the trench manned by Jacques Piccard (who co-designed the submersible along with his father, Auguste Piccard) and USN Lieutenant Don Walsh. The descent took almost five hours and the two men spent barely twenty minutes on the ocean floor before undertaking the three-hour-and-fifteen-minute ascent. Their early departure from the ocean floor was due to their concern over a crack in the window caused by the intense pressure of their descent, and also because their landing on the sea bed had stirred up a cloud of silt which reduced visibility to zero and showed no sign of settling. They measured the depth as 10,916 m (35,814 ft).

Kaikō

Main article: Kaikō

On 24 March 1995, the Japanese robotic deep-sea probe Kaikō broke the depth record for unmanned probes when it reached close to the surveyed bottom of the Challenger Deep. Created by the Japan Marine Science and Technology Center (JAMSTEC), it was one of the few unmanned deep-sea probes in operation that could dive deeper than 6,000 metres (20,000 ft). Its recorded depth of 35,797 ft (10,911 m) for the Challenger Deep is believed to be the most accurate measurement taken yet. Kaikō also collected sediment cores containing marine organisms from the bottom of the deep. Kaikō made many unmanned descents to the Mariana Trench during three expeditions between 1995 and 1998.

Nereus

Main article: Nereus (underwater vehicle)

On 31 May 2009 the United States sent the Nereus hybrid remotely operated vehicle (HROV) to the Challenger Deep. Nereus thus became the first vehicle to reach the Mariana Trench since 1998 and the deepest-diving vehicle currently in operation. Project manager and developer Andy Bowen heralded the achievement as "the start of a new era in ocean exploration". Nereus, unlike Kaikō, did not need to be powered or controlled by a cable connected to a ship on the ocean surface.

Nereus spent over 10 hours at the bottom of the Challenger Deep and measured a depth of 10,902 m (35,768 ft), while sending live video and data back to its mothership RV Kilo Moana at the surface and collecting geological and biological samples from the Challenger Deep bottom with its manipulator arm for further scientific analysis.

The Nereus is operated by the Woods Hole Oceanographic Institution.

Lifeforms

The Summary Report of the HMS Challenger expedition lists radiolaria from the two dredged samples taken when the Challenger Deep was first discovered. These (Nassellaria and Spumellaria) were reported in the Report on Radiolaria (1887) 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, resembling a sole, about 1 foot long and 6 inches across" lying on the seabed. The report has since been questioned, with suggestions that it may have been a sea cucumber. The video camera on board the Kaiko probe spotted a sea cucumber, a scale worm and a shrimp at the bottom. At the bottom of the Challenger deep, the Nereus probe spotted one polychaete worm (a multi-legged predator) about an inch long.

An analysis of the sediment samples collected by Kaiko found large numbers of simple organisms at 10,900 m (35,800 ft). 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.

The overwhelming majority 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 Leptohalysis and Reophax. Eighty-five percent 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 preponderance 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. The species that survived the change in depth were the ancestors of the Challenger Deep's current denizens.

Possible nuclear waste disposal site

Like other oceanic trenches, the Challenger Deep has been proposed as being a site for nuclear waste disposal. Being a fast-moving subduction plate, the place has been considered numerous times, as the nuclear waste would theoretically be pushed into the Earth's mantle.

See also

• HMRG Deep
• Philippine Trench

External links

• Official press release regarding Challenger Deep operation.
• Mariana Trench