The Abyssal Zone, or Abyssopelagic Zone, is a layer in the pelagic zone of the ocean. “Abyss” derives from the Greek word ἄβυσσος, meaning bottomless. This zone remains in perpetual darkness at depths of 4,000 to 6,000 meters (13,300 to 20,000 feet). The ocean covers 83% of the world’s surface and 60% of the ocean’s area. Throughout the majority of its mass, the abyssal zone has temperatures between 2 and 3 °C (36 and 37 °F). Because of the lack of light, there are no plants producing oxygen, which comes mostly from ice that has melted long ago in the polar regions.
The water along the bottom of this zone is actually devoid of oxygen, making it a death trap for organisms unable to return to the oxygen-rich water above. The region also has a much higher concentration of nutrient salts, such as nitrogen, phosphorus, and silica, as a result of the large amount of dead organic material that drifts down from the above ocean zones and decomposes. Up to 76 megapascals of water pressure can be achieved.
The Abyssal Zone
Definition
Imagine the deepest, darkest part of the ocean. Glow-in-the-dark fish, gigantic sea worms, and explosive hydrothermal vents. The abyssal zone is a frightening sight. The abyssal zone is the deepest layer of the ocean near the seafloor and starts at 13,000 feet and goes up to about 20,000 feet.
There is no sunlight reaching this layer of the ocean because it’s so deep. As a result of the lack of sunlight, the communities are perpetually in the dark and the temperatures are cold, hovering near freezing. Abyssal pressure is also extreme due to the amount of water covering the zone, between 200 and 600 times greater than the surface pressure. Despite these challenges, organisms have evolved to survive in this environment. We will discuss this in more detail as we progress through this article.
Layers of the Ocean
We need to know about the other layers of the ocean in order to understand the abyssal zone. Up to about 200 feet below the surface of the ocean is called the epipelagic zone. There is a wide variety of sea life in these waters where sunlight penetrates. Immediately following the epipelagic zone is the mesopelagic zone, where sunlight is very faint and you can find creatures that glow in the dark or are bioluminescent.
The midnight zone is the next bathypelagic zone after the mesopelagic zone. Despite the abundance of sea life, this water is completely dark and has extreme pressure. These layers are followed by the abyssal zone, which is the focus of this article. A layer deeper than the abyssal zone is the hadalpelagic zone, which extends from the seafloor to the deepest trenches, or vertical caverns, in the ocean. The following diagram shows the layers of the ocean:
Abyssal Zone: Depth, Ecosystem, And Location
An abyssal zone is a portion of the ocean deeper than about 2,000 m (6,600 feet) and shallower than about 6,000 m (20,000 feet). This zone is characterized by highly uniform environmental conditions, as reflected in the different types of life that inhabit it.
The upper boundary between the abyssal zone and the overlying bathyal zone is conveniently defined as the depth at which the temperature of the water reaches 4°C (39°F); this depth varies between 1,000 and 3,000 m. Waters deeper than 6,000 m are considered the hadal realm by ecologists.
Approximately 60 percent of the earth’s surface and 83 percent of the oceans and seas is covered by the abyssal realm, which covers 300,000,000 square kilometers (115,000,000 square miles).
Polar regions, especially the Antarctic, are home to abyssal waters that originate at the air-sea interface. The cold climate there produces sea ice and residual cold brine. The brine sinks due to its high density and flows slowly toward the Equator along the bottom. The abyssal salinities are between 34.6 and 35.0 parts per thousand, and temperatures are between 0° and 4° C (32° and 39° F).
Every ten meters of depth increases the pressure by about one atmosphere (about 14.7 pounds per square inch at sea level); abyssal pressures range between 200 and 600 atmospheres. Abyssal animals do not need to worry about pressure because the pressures within their bodies are the same as that outside.
The concentration of nutrient salts of nitrogen, phosphorus, and silica in abyssal waters is much higher than in overlying waters. Abyssal and hadal waters are the reservoirs for decomposed biological materials that settle downward from upper zones, and the lack of sunlight prevents the salts from being absorbed by photosynthesis.
Absent photosynthesis at depth, abyssal water’s oxygen content depends entirely on the amount dissolved into it at its polar origin and the amount dissolved into it at its polar source.
The abyssal zone retains several cubic centimeters of dissolved oxygen per liter because the sparse animal populations do not consume oxygen faster than it is introduced. At the seafloor, however, abyssal life is concentrated, and the water nearest the seafloor may be oxygen-deficient.
The abyssal realm is very calm, being removed from the storms that agitate the ocean at the air-sea interface. Low energies are reflected in the character of abyssal sediments. Usually, the abyssal realm is far enough from land that the sediment contains mostly microscopic plankton remains, produced in the food chain in the overlying waters.
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. The main sediment constituents below 4,000 m are brown clays and the siliceous remains of radiolarian zooplankton and phytoplankton such as diatoms.
Abyssal Zone: Animals Adaptations
Abyssal zones are located between 3,000 and 6,000 meters (or 9,800 and 19,700 feet) below the surface of the ocean. Temperatures here are frigid, and pressures are hundreds of times greater than at the surface of the ocean. In the abyssal zone, life appears ill-adapted to survive in a strange, harsh world. However, life has found ways to thrive here.
Food
In the ocean, photosynthesis occurs in the sunlit upper layers. As organisms living in these upper layers die, their remains drift toward the ocean floor like soft snow. This detritus provides food to the animals of the abyssal plain. There are organisms that eat detritus directly, as well as organisms that eat detritus indirectly. The only exception is around rifts, where tectonic plates are spreading apart and new seafloor is being formed.
Some bacteria can harness chemical energy to make their own food, and become food for other abyssal animals like tube worms. These bacteria, for example, convert hydrogen sulfide into sulfate and store the energy from this reaction as chemical energy by synthesizing carbon-based compounds.
Species
We don’t know how many species inhabit the abyssal ecosystem because the depths of the ocean are poorly explored. Science frequently discovers new species when scientists collect abyssal specimens for study. Due to the limited availability of food, the deep sea is also sparsely populated compared to continental shelves.
As a result of the frigid temperatures of the ocean water, the animals here have very slow metabolic rates and only eat occasionally – sometimes only every few months. Hagfish, for example, can go as long as seven months without eating because their metabolism is so slow.
Characteristics
The animals of the abyssal plain are the same as those of the continental shelf; octopi, squid, fish, worms, and mollusks are found there. The animals of the abyssal plain, however, tend to have some adaptations that help them cope with their unusual environment. Animals in the abyssal plain, for example, tend to be small, but they usually have large, flexible stomachs and largemouths.
Food is hard to find, so they must swallow as much as they can when they find it — and store some of it, because their next meal may be a long time away. The viperfish, for example, has a hinged skull that can rotate upwards so it can eat large fish, as well as a large stomach to store plenty of food and a set of fangs that look ferocious to chomp down on its prey.
Special Features
Many abyssal animals are bioluminescent, which means they can produce their own light. Because the deep sea is completely black, the ability to produce light can help fish lure prey, find prey, and attract mates.
They often have special adaptations to help them reproduce since finding mates in the dark and sparsely-populated world of the abyssal plain can be difficult. Anglerfish, for example, physically attach themselves to a female, using her blood as food and fertilizing her eggs in return.
Abyssal Zone: Plants
There are no plants in the abyssal zone because it is too deep for sunlight to penetrate, and the sunlight is necessary for plants to grow. Some organisms can live in this zone by using chemosynthesis, which is energy that is produced by chemical reactions.
The abyssal zone lies between 2 1/2 and 3 1/2 miles beneath the surface of the water. Not including the hadal zone, which is the water in the ocean’s trenches, this is the lowest zone. The abyssal zone is so deep that it cannot receive sunlight, so there is no photosynthesis and no plant light. The water is pitch black, and the only light visible is bioluminescence.
While there are no plants in the abyssal zone, there are other living organisms that survive here. The abyssal zone is populated by squid, octopi, echinoids, worms, mollusks, and fish that feed on organic material that falls from higher areas. Many of these organisms have similar characteristics, such as soft bodies, long lifespans, and long gestation periods.
Anglerfish are one of the organisms found in the abyssal zone. The females have an appendage that is attached to a bioluminescent ball. Scientists believe that this lure attracts other fish for its food or mating.
FAQs
What type of animals lives in the abyssal zone?
Abyssal life includes chemosynthetic bacteria, tubeworms, and small fish that are dark in color or transparent. In addition to sharks, invertebrates such as squid, shrimp, sea spiders, sea stars, and other crustaceans are also included.
What are the conditions like in the abyssal zone?
The conditions of the Abyssal Zone are almost constant. At 4000 meters, it is always dark and cold (average temperature 2 degrees Celcius). Far above, it is calm and unaffected by sunlight or turbulent seas.
Where can the abyssal zone be found?
The abyssal zone, also known as the abyssopelagic zone, is one of the levels into which the oceans are divided and it is found between 3,000 and 6,000 meters below the surface.
What causes abyssal gigantism?
Colder temperatures, food scarcity, reduced predation pressure, and increased dissolved oxygen concentrations in the deep sea are a few explanations for this type of gigantism. The inaccessibility of abyssal habitats has hampered the study of this topic.
How much sunlight does the abyss get?
The abyssal zone has no sunlight and extreme temperatures near freezing. It also has incredible pressure, up to 600 times that of the surface.
How do deep-sea creatures get oxygen?
The surface layers of the ocean generally obtain oxygen from diffusion and brisk circulation. This water sinks to the seafloor, supplying oxygen to deep-sea life.
How do organisms survive in the abyssal zone?
Organisms have adapted to the harsh environment of the abyssopelagic zone in order to survive. A few examples of these adaptations include blindness to semi-blindness due to the lack of light, bioluminescence, and slow metabolism.