- Related Topics:
- Marine ecosystem
- abyssal plain
abyssal zone
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What is the abyssal zone?
The abyssal zone is a deep ocean environment that lies between 2,000 and 6,000 meters (6,600 to 20,000 feet). It is characterized by stable environmental conditions, which are reflected in the unique life forms that inhabit it.
Abyssal waters originate in polar regions, particularly in the Antarctic, where cold temperatures lead to the formation of sea ice and cold brine. This dense brine sinks and flows toward the Equator along the ocean bottom.
The abyssal zone is very calm because it is far removed from surface storms. The sediment in this realm primarily consists of the remains of microscopic plankton from the upper waters.
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Where is the abyssal zone found in the ocean?
The abyssal zone is a portion of the ocean that lies deeper than about 2,000 meters (6,600 feet) and shallower than about 6,000 meters (20,000 feet). It is defined by its uniform environmental conditions and distinct life forms. The abyssal zone is the largest environment for life on Earth, covering 300,000,000 square kilometers, or 60 percent of the global surface.
Abyssal waters originate at the air-sea interface in polar regions, mainly the Antarctic, where the cold climate produces sea ice and residual cold brine. Because of its high density, the brine sinks and slowly flows along the bottom toward the Equator.
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How deep does the abyssal zone extend?
The abyssal zone is a portion of the ocean that extends from a depth of about 2,000 meters (6,600 feet) to about 6,000 meters (20,000 feet). It is defined by its uniform environmental conditions and distinct life forms. The abyssal zone is the largest environment for life on Earth, covering 300,000,000 square kilometers, about 60 percent of the global surface and 83 percent of the area of oceans and seas. The deepest region of the oceans, below the abyssal zone, is the hadal zone, found in deep-sea trenches at depths greater than 6,000 meters.
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What are the main features of the abyssal zone's environment?
The abyssal zone, found at depths of 2,000–6,000 m, has very uniform environmental conditions, which are reflected in the distinct life forms inhabiting it. Abyssal waters originate in polar regions, mainly the Antarctic, where the cold climate produces sea ice and residual cold brine. The brine sinks because of its high density and slowly flows along the bottom toward the Equator.
Abyssal plains are flat seafloor areas at abyssal depths, generally adjacent to a continent. They vary in depth by only 10–100 cm per kilometer of horizontal distance.
The main features of the abyssal zone include:
* Temperatures between 0° and 4° C
* Salinity between 34.6 and 35 parts per thousand
* High pressure, increasing with depth
* High concentrations of nutrient salts
* Calm waters
* Darkness
* Soft sediment bottoms2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What kinds of organisms live in the abyssal zone?
The abyssal zone, found at depths of 2,000 to 6,000 meters, is home to unique organisms adapted to its uniform environmental conditions. Though sparse, the abyssal fauna includes representatives of major marine invertebrate phyla and several fish species.
These organisms often have delicate structures and are gray or black in color. Mobile species have long legs, while those attached to the sea floor have stalks to rise above the oxygen-scarce water near the bottom. Some abyssal crustaceans and fish are blind.
Life in the abyssal zone concentrates on the sea floor, where animals feed on mud and suspended matter; carnivores and scavengers are less common with increasing depth. Hydrothermal vents in this zone support unique biological communities that rely on chemosynthesis by sulfur-fixing bacteria rather than photosynthesis. These organisms include mussels, large bivalve clams, and vestimentiferan worms, many of which have symbiotic relationships with chemoautotrophic bacteria.
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How do geological processes like plate tectonics affect the abyssal zone?
Plate tectonics significantly influences the abyssal zone, which lies at depths of 2,000 to 6,000 meters.
Seafloor spreading at mid-ocean ridges, such as the Mid-Atlantic Ridge, creates new oceanic crust. Magma upwells and cools, pushing the plates apart. This process leads to volcanic activity and shallow earthquakes.
At subduction zones, one plate descends beneath another, causing the incorporation of water and carbon dioxide-rich sediments into the mantle, which decreases the melting temperature of magma. This process often results in volcanoes.
Abyssal plains, flat areas adjacent to continents, are formed from sediments that accumulate in abyssal depressions, smoothing the topography. Abyssal hills, small submarine hills, are created through volcanism and faulting, covering much of the ocean floor.
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abyssal zone, portion of the ocean deeper than about 2,000 m (6,600 feet) and shallower than about 6,000 m (20,000 feet). The zone is defined mainly by its extremely uniform environmental conditions, as reflected in the distinct life forms inhabiting it. The upper boundary between the abyssal zone and the overlying bathyal zone is conveniently defined as the depth at which the water temperature is 4° C (39° F); this depth varies between 1,000 and 3,000 m. Waters deeper than 6,000 m are treated separately as the hadal realm by ecologists.
The abyssal realm is the largest environment for Earth life, covering 300,000,000 square km (115,000,000 square miles), about 60 percent of the global surface and 83 percent of the area of oceans and seas.
Abyssal waters originate at the air-sea interface in polar regions, principally the Antarctic. There, the cold climate produces sea ice and residual cold brine. Because of its high density, the brine sinks and slowly flows along the bottom toward the Equator. Abyssal salinities range narrowly between 34.6 and 35.0 parts per thousand, and temperatures are mostly between 0° and 4° C (32° and 39° F). Pressure increases by about one atmosphere (approximately 14.7 pounds per square inch at sea level) with each 10-metre increment in depth; thus, abyssal pressures range between 200 and 600 atmospheres. Pressure presents few problems for abyssal animals, however, because the pressures within their bodies are the same as those outside them.
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The concentrations of nutrient salts of nitrogen, phosphorus, and silica are very uniform in abyssal waters and are much higher than in overlying waters. This is because abyssal and hadal waters are the reservoir for the salts from decomposed biological materials that settle downward from upper zones, and the lack of sunlight prevents their uptake by photosynthesis.
The oxygen content of abyssal water depends entirely upon the amounts dissolved into it at its polar site of origin and the absence of photosynthesis, which precludes the introduction of new oxygen at depth. Abyssal waters retain several cubic centimetres of dissolved oxygen per litre, because the sparse animal populations do not consume oxygen faster than it is introduced into the abyssal zone. Abyssal life is concentrated at the seafloor, however, and the water nearest the floor may be essentially depleted in oxygen.
The abyssal realm is very calm, being far removed from storms that agitate the ocean at the air-sea interface. These low energies are reflected in the character of abyssal sediments. The abyssal realm is usually far enough from land that the sediment is composed predominantly of microscopic plankton remains produced in the food chain in the overlying waters, from which they settle. Abyssal sediment in waters shallower than 4,000 m in equatorial to temperate regions is composed primarily of the calcareous shells of foraminiferan zooplankton and of phytoplankton such as coccolithophores. Below 4,000 m, calcium carbonate tends to dissolve, and the principal sediment constituents are brown clays and the siliceous remains of radiolarian zooplankton and such phytoplankton as diatoms.
Abyssal fauna, though very sparse and embracing relatively few species, include representatives of all major marine invertebrate phyla and several kinds of fish, all adapted to an environment marked by no diurnal or seasonal changes, high pressures, darkness, calm water, and soft sediment bottoms. These animals tend to be gray or black, delicately structured, and unstreamlined. Mobile forms have long legs; and animals attached to the bottom have stalks, enabling them to rise above the water layer nearest the bottom, where oxygen is scarce. Abyssal crustaceans and fish may be blind. With increasing depth, carnivores and scavengers become less abundant than animals that feed on mud and suspended matter. Abyssal animals are believed to reproduce very slowly.
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