Deep sea

The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of 200 m (660 ft) or the point of transition from continental shelves to continental slopes.^[1][2] Conditions within the deep sea are a combination of low temperatures, darkness, and high pressure.^[3] The deep sea is considered the least explored Earth biome as the extreme conditions make the environment difficult to access and explore.^[4]

Organisms living within the deep sea have a variety of adaptations to survive in these conditions.^[5] Organisms can survive in the deep sea through a number of feeding methods including scavenging, predation and filtration, with a number of organisms surviving by feeding on marine snow.^[6] Marine snow is organic material that has fallen from upper waters into the deep sea.^[7]

In 1960, the bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam, at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean. If Mount Everest (8,848 m or 29,029 ft or 5.498 mi) were submerged there, its peak would be more than 2 km (1.2 mi) beneath the surface. After the Trieste was retired, the Japanese remote-operated vehicle (ROV) Kaikō was the only vessel capable of reaching this depth until it was lost at sea in 2003.^[8] In May and June 2009, the hybrid-ROV Nereus returned to the Challenger Deep for a series of three dives to depths exceeding 10,900 m (35,800 ft; 6.8 mi).