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Challenger Deep

Wikipedia Reference Information

The Challenger Deep is the deepest known point in the oceans. It lies in the Mariana Islands group at the southern end of the Mariana Trench. The closest land is Fais Island, one of the outer islands of Yap, 289 km southwest and Guam 306 km to the northeast. The point is named after the British Royal Navy survey ship HMS Challenger, which first surveyed the trench in 1951.

Depth

The maximum surveyed depth of the Challenger Deep is 10,923 meters (35,838 feet).

The HMS Challenger Expedition (December, 1872 - May 1876) first sounded the depths now known as the Challenger Deep. This first sounding was made on March 23, 1875 at station 225. The reported depth was 4475 fathoms (8,184 m, 26,850 ft), based on 2 separate soundings.

The 1912 book. The Depths of the Ocean, by Sir John Murray records the depth at the "Challenger Deep" at 31,614 ft. Mr. Murray was one of the Expedition scientists, a young man at the time. Page 131 of Murray's book refers to the "Challenger Deep". All of the reports of the original Challenger expedition can be viewed on the web at the Challenger Library.

About 75 years after its original discovery, the entire Mariana Trench which includes the Challenger Deep, was surveyed, in 1951, by the Royal Navy vessel HMS Challenger, named after the original expedition ship. During this survey, the deepest part of the trench was recorded, using echo sounding, a much more precise and vastly easier way to measure depth as compared with the sounding equipment and drag lines used in the original expedition. The namesake Challenger measured a depth of 5,960 fathoms (10,900 m, 35,760 ft) at 1119'N, 14215'E. This sounding was repeatedly made using earphones to hear the return of the signal as the stylus passed across the graduated depth scale, whilst the timing of the speed of the echo-sounding machine, a necessary part of the process, was made with a handheld stopwatch. For these reasons it was considered prudent by the surveyors to subtract one scale division (of 20 fathoms) when officially reporting a new greatest depth of 5,940 fathoms (10,863 m).

On 23 January 1960, the Swiss-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. They measured the depth as 10,916 metres (35,813 feet). At the ocean floor they observed small sole and flounder and noted that the floor consisted of diatomaceous ooze.

In 1984, a Japanese survey vessel using a narrow, multi-beam echo sounder took a measurement of 10,923 meters (35,838 feet).

Location of Challenger Deep within the Mariana TrenchOn 24 March, 1995 the Japanese robotic deep-sea probe Kaiko 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 rare unmanned deep-sea probes in operation that could dive deeper than 6,000 metres (19,680 feet). Its recorded depth of 10,911 m (35,797 ft) for the Challenger Deep is believed to be the most accurate measurement taken yet. Unfortunately, Kaiko was lost at sea on 29 March, 2003 after just over eight years of service when one of the secondary cables snapped during an approaching typhoon. Currently no other operational vehicle exists that is capable of reaching the same depths and no other manned vehicle has come to the same depth as Trieste.

Lifeforms

Recently, an analysis of the sediment samples collected by Kaiko before it sank, published in Science, (2005) Vol 307, Issue 5710, pq. 689[1], announced the discovery of simple organisms at 10,900 metres water depth. 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 independent taxa from those shallower ecosystems.

Out of the 432 organisms collected, the overwhelming majority of the sample consisted of simple, soft-shelled foraminifera, with four of the others representing species of the complex, multi-chambered genera Leptohalysis and Reophax. Overall, 85% of the specimens consisted of organic soft-shelled allogromids. This 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% of the total. As small organisms with hard calcated shells have trouble growing at extreme (10,000 m) depths because the water at that depth is severely lacking in calcium carbonate, scientists theorize that the preponderance of soft-shelled organisms at 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 remaining species may have been the ancestors of the Challenger Deep's current denizens.

The complete, up-to-date and editable article about Challenger Deep can be found at Wikipedia: Challenger Deep
http://en.wikipedia.org/wiki/Challenger_Deep




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