[Geography Notes] on Abyssal Zone Pdf for Exam

The abyssal zone is defined as the portion of the ocean which is deeper than about 2,000 m (that is 6,600 feet). This zone is shallower than about 6,000 m (which is 20,000 feet). The zone is defined mainly by the extremely uniform environmental conditions, which are being reflected as distinct life forms which belong to it. The upper boundary that lies between the abyssal zone and the overlying bathyal zone is the depth where the water temperature drops to 4° C (39° F). While this depth varies between 1,000 to 3,000 m. The waters that are deeper than 6,000 m are being treated separately by ecologists.

Abyssal Zone

The abyssal zone which is also called the abyssopelagic zone is the layer of the pelagic zone of the ocean. “Abyss” is a term derived from a Greek word, which means bottomless. At depths of 3,000 to 6,000 meters (which is approximately 9,800 to 19,700 ft), this zone remains in acute darkness. This zone covers around 83% of the total area of the ocean and covers 6l0% of the Earth’s surface. 

The abyssal realm is the largest environment in the Earth’s life, covering 300,000,000 square km (that is 115,000,000 square miles). Almost 60 percent of the global surface is covered by the zone and about 83 percent of the area of the oceans and seas.

At the air-sea interface, the waters of the Abyssal zone originate. The air-sea interface is in the polar regions, specifically in the Antarctic zone. For the cold climate of the Antarctic, sea-ice and residual cold brine get produced. Further for the high density in this region, the brine sinks and it slowly flows along the bottom towards the Equatorial region. Abyssal salinities range between 34.6 and 35.0 parts per thousand, while the temperature ranges mostly between 0° and 4° C (that is approximately 32° and 39° F). The Pressure system increases by about one atmosphere (which is approximately 14.7 pounds per square inch at sea level) with each 10-meter increment in the level of depth. Thereby, the abyssal pressures range between 200 and 600 atmospheres. The pressure in this zone presents fewer problems for the abyssal animals, however, because the pressures within their bodies are the same as those which are outside them.

Abyssal Zone Temperature

Majorly, the abyssal zone has a temperature ranging from 2 to 3 °C (which is 36 to 37 °F). As in the abyssal zone, there is no light, there are no plants growing in this zone, thus no oxygen is being produced. Oxygen minutely only comes from the ice that had melted long ago from the polar regions. The water on the seafloor of this zone is actually devoid of any oxygen content. This lack of oxygen results in a death trap for the organisms who are unable to quickly return to the oxygen-enriched water above. While, this region contains a much higher concentration of nutrient salts, like nitrogen, silica, and phosphorus, this happens for the large amount of dead organic material which seeps down from the above ocean zones and then decomposes in this zone. The water pressure present can reach up to 76 megapascals.

Abyssal Zone Location

This Abyssal Zone is one of the many benthic zones which is being highlighted in order to describe the deep oceans. This zone is found at the depth of around 2,000 to 6,000 meters (which is 6,560 to 19,680 feet) and it stays in perpetual darkness.

How Far Down is the Abyssal Zone?

The Abyssopelagic Zone or the abyssal zone extends from 13,100 feet (which is 4,000 meters) to 19,700 feet (that is 6,000 meters). The zone is characterized as the pitch-black bottom layer of the ocean. The name ‘abyss’ particularly comes from a Greek word that means “no bottom” or “bottomless” as previously it was wondered that the sea was bottomless.

Fun Facts about Abyssal Zone

• The concentrations of nutrient salts present in this zone are very much higher than in other zones. The nutrient salts – nitrogen, phosphorus, and silica present in this zone acts as a reservoir for the salts from the decomposed biological materials which settle downward from upper zones. Also, the lack of sunlight in this zone prevents photosynthesis thereby these nutrients are not being used as such. 

• The abyssal realm has a very calm zone which is being far removed from the storms which agitate in the ocean at the air-sea interface. The low energies are being reflected in the character of the abyssal sediments. 

• Abyssal sediment in the waters is shallower than 4,000 m in equatorial to temperate regions includes primarily the calcareous shells of zooplankton and of phytoplankton like coccolithophores. Below the 4,000 m, calcium carbonate tends to dissolve the principal sediment which are constituents which are brown clays and the siliceous remains of the radiolarian zooplankton like the phytoplankton as the diatoms.

• Abyssal fauna, is very sparse and there are relatively few species, among which includes representatives of all major marine invertebrate phyla and several other kinds of fish, all these are adapted to an environment that is being marked by no diurnal or by no seasonal changes, for high pressures, darkness, and calmer water, and softer sediment featured bottoms. These animals tend to be grey or black in colour, delicately they are being structured, and they have un-streamlined body structure. Some of these forms have long legs. Animals attached to the bottom have stalks which enables them to rise above the water layer which is nearest the bottom, where the oxygen is scarce. The abyssal crustaceans and the fish may be blind. With the increasing depth, the carnivores and the scavengers become less abundant than the animals who are fed on mud and by suspended matter. The abyssal animals are believed to reproduce at a slower rate.