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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.
The organic matter in the hadal zone is more quickly buried than in the abyssal zone, allowing it to avoid oxidative degradation and become available for subsurface microbes. This sedimentation of labile, organic matter is the reason why microbial communities distinct to the hadal zone may be observed globally.
The hadopelagic (or hadal) zone, refers to depths below 6000 meters, which occur mostly in the deep ocean trenches. The term hadal is a reference to the Greek god of the underworld Hades . In these trenches, the temperature is just above freezing, and the water pressure is enormous.
The pelagic zone contrasts with the benthic and demersal zones at the bottom of the sea. The benthic zone is the ecological region at the very bottom, including the sediment surface and some subsurface layers. Marine organisms such as clams and crabs living in this zone are called benthos. Just above the benthic zone is the demersal zone.
The region of rapid density change is known as the pycnocline, and it acts as a barrier to vertical water circulation; thus it also affects the vertical distribution of certain chemicals which play a role in the biology of the seas. The sharp gradients in temperature and density also may act as a restriction to vertical movements of animals. [6]
In contrast to organisms in the water column, benthic organisms in this region tend to have limited to no bioluminescence. [47] The bathypelagic zone contains sharks, squid, octopuses, and many species of fish, including deep-water anglerfish, gulper eel, amphipods, and dragonfish. The fish are characterized by weak muscles, soft skin, and ...
Organisms in the abyssal zone rely on the natural processes of higher ocean layers. When animals from higher ocean levels die, their carcasses occasionally drift down to the abyssal zone, where organisms in the deep can feed on them. When a whale carcass falls down to the abyssal zone, this is called a whale fall. The carcass of the whale can ...
Many organisms in the mesopelagic zone move up into the epipelagic zone at night, and retreat to the mesopelagic zone during the day, which is known as diel vertical migration. [8] These migrators can therefore avoid visual predators during the day and feed at night, while some of their predators also migrate up at night to follow the prey.