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The abyssal zone extends from 4,000 metres (13,123 ft) to 6,000 metres (19,685 ft) or 6,500 metres (21,325 ft), depending on the authority. The hadal zone refers to the greatest depths, deeper than the abyssal zone. Some twilight occurs in the mesopelagic zone, but creatures below the mesopelagic must be able to live in complete darkness. [5] [6]
The deep trenches or fissures that plunge down thousands of meters below the ocean floor (for example, the mid-oceanic trenches such as the Mariana Trench in the Pacific) are almost unexplored. [6] Previously, only the bathyscaphe Trieste , the remote control submarine KaikÅ and the Nereus have been able to descend to these depths.
It is uncommon to detect deep scattering layers below 1000m. Until recently, sonar has been the predominant method for studying the mesopelagic. [46] The Malaspina Circumnavigation Expedition was a Spanish-led scientific quest in 2011 to gain a better understanding of the state of the ocean and the diversity in the deep oceans. [49]
The hadal zone, also known as the hadopelagic zone, is the deepest region of the ocean, lying within oceanic trenches.The hadal zone ranges from around 6 to 11 km (3.7 to 6.8 mi; 20,000 to 36,000 ft) below sea level, and exists in long, narrow, topographic V-shaped depressions.
Depending on the water-body, the benthic zone may include areas that are only a few inches below the surface. The continental shelf is a gently sloping benthic region that extends away from the land mass. At the continental shelf edge, usually about 200 metres (660 ft) deep, the gradient greatly increases and is known as the continental slope.
Barophilic marine microbes have been found at more than a depth of 10,000 m (33,000 ft; 6.2 mi) in the Mariana Trench, the deepest spot in the Earth's oceans. [33] In fact, single-celled life forms have been found in the deepest part of the Mariana Trench, by the Challenger Deep, at depths of 11,034 m (36,201 ft; 6.856 mi).
The profundal zone is the deep zone of a lake, located below the range of effective light penetration.This is typically below the thermocline, the vertical zone in the water through which temperature drops rapidly.
This is a list of places on land below mean sea level. Places artificially created such as tunnels, mines, basements, and dug holes, or places under water, or existing temporarily as a result of ebbing of sea tide etc., are not included. Places where seawater and rainwater is pumped away are included.