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hadal zone
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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters.
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hadal zone

oceanography
Also known as: hadal realm
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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters.
Zonation of the ocean. The open ocean, the pelagic zone, includes all marine waters throughout the globe beyond the continental shelf, as well as the benthic, or bottom, environment on the ocean floor. Nutrient concentrations are low in most areas of the open ocean, and as a result this great expanse of water contains only a small percentage of all marine organisms. Far below the surface in the midocean ridges of the abyssal zone, deep-sea hydrothermal vents supporting an unusual assemblage of organisms—including chemoautotrophic bacteria—occur.

The hadal zone refers to the deepest part of the ocean, found within deep-sea trenches and extending below 6,000 meters (approximately 20,000 feet). This zone is characterized by extreme conditions, including immense pressure, complete darkness, and near-freezing temperatures. Despite these harsh conditions, life exists in the hadal zone, adapted to its unique environment. Organisms here often rely on organic matter that sinks from shallower waters. The hadal zone is distinct from the abyssal zone, which lies above it and ranges from 4,000 to 6,000 meters deep.12

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3 Britannica Sources
  1. bathypelagic zone
  2. marine ecosystem - Geography, oceanography, and topography
  3. abyssal zone

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