Hadal zone or (trench zone) (Greek for "like Hades," in other words "unseen") or Hadopelagic zone is the delineation for the deepest trenches in the ocean. This zone is found from a depth of around to the bottom of the ocean.
, Jacques Piccard
and Don Walsh
reached the Mariana Trench
, the deepest trench on Earth, and observed life. It is believed that most life at this depth is sustained by marine snow
or the chemical reactions around thermal vents. The lack of light and intense pressure create hostile living conditions, and few species are adapted to these conditions. As no sunlight reaches this layer of the ocean, deep sea
creatures have adapted with reduced eyesight, having very large eyes for receiving only bioluminescent
flashes. Most of the bottom dwelling creatures lack any pigmentation since coloration is not useful in an environment with no light.
The pressure here can reach over . Creatures removed from this zone will die in the lower-pressure areas above. The most common creatures include jellyfish, viperfish, tube worms, clams, and the deep sea angler fish. The hadal zone can reach far below 6,000 meters (20,000 feet) deep; the deepest known is at 10,911 meters (35,798 ft).
Notes and references
Forscher filmen lebende Fische in Rekordtiefe (German) from Spiegel 10/09/2008 about an expedition filming fish at a depth of more than 7,000 m