The hadal zone (named after the realm of Hades, the underworld in Greek mythology), also known as the hadopelagic zone and trench zone, is the delineation for the deepest trenches in the ocean. This zone is found from a depth of around 6,000 metres (20,000 ft) to the bottom of the ocean. The hadal zone has low population and low diversity of marine life.
It is believed that most life at this depth is sustained by marine snow or the chemical reactions around thermal vents. The low nutrient level, extreme pressure and lack of sunlight create hostile living conditions in which few species are able to exist. As no sunlight reaches this layer of the ocean, deep sea creatures have reduced eyesight, with very large eyes for receiving only bioluminescent flashes.
The most common organisms include jellyfish, viperfish, tube worms and sea cucumbers. The hadal zone can reach far below 6,000 meters (20,000 feet) deep; the deepest known extends to 10,911 meters (35,814 ft). At such depths (for example, at 36,000 feet below sea level) the pressure in the hadal zone exceeds 1,100 standard atmospheres (110 MPa; 16,000 psi).
In 1960, Jacques Piccard and Don Walsh reached the bottom of the Mariana Trench, the deepest known trench on Earth, and observed life. James Cameron also reached the bottom in 2012 using the Deepsea Challenger.
- Meeresboden - down under. February 1, 2007. (German)
- "NOAA Ocean Explorer: History: Quotations: Soundings, Sea-Bottom, and Geophysics". NOAA, Office of Ocean Exploration and Research. Retrieved 2010-03-23.
- ThinkQuest. February 1, 2007.
- Than, Ker (March 25, 2012). "James Cameron Completes Record-Breaking Mariana Trench Dive". National Geographic Society.
- Alan Jamieson: The hadal zone - life in the deepest oceans. Cambridge Univ. Press, Cambridge 2015, ISBN 978-1-10-701674-3.
- Forscher filmen lebende Fische in Rekordtiefe (In German) from Spiegel 10/09/2008 about an expedition filming fish at a depth of more than 7,000 m