The abyssal zone is a very flat surface found from 4,000-6,000 meters (13,123- 19,685) in the deep basins of the ocean floor. The abyssal zone is unable to receive the Sun’s rays; therefore it remains in complete darkness. The abyssal zone has temperatures ranging from 2-3 °C (35-37 °F). Its inhabitants have had to develop especial adaptations to withstand the extremely high pressures and cold temperatures. The icy and saline waters in the deep ocean floor originate at the poles, moving sluggishly along the abyssal plain. The abyssal zone covers an area of approximately 300 million square km (115, million miles), creating small valleys, hills and pockets of varied sedimentation.
Abyssal zone’s environmental conditions
The environmental conditions in the abyssal zone are characterized by total darkness and cold temperatures. The oxygen and salt levels present in the abyssal zone originate from the cold water currents at the Polar Regions. The abyssal zone is saturated with nutrients, such as nitrogen, phosphorous and silica, of decayed organic matter from the waters above. The abyssal sea floor at 4,000 meters of depth and shallower regions is composed of calcareous shells of zooplankton and phytoplankton. At deeper regions the calcareous shells will dissolve and the sediment is principally composed of siliceous remains of radiolarian zooplankton, brown clays and diatomic phytoplankton.
Pressure increases with increasing depth. At the surface of the ocean, there is an atmospheric pressure of one atmosphere. In the ocean the pressure increases at a rate of one atmosphere for every 33 ft. with increasing depth. The deep ocean is characterized by extreme cold temperatures. The point in the ocean where the abyssal plain starts, which is about 4,000 meters deep, is where the water temperature plummets to 4 °C, and the deeper you go from there, the colder it gets. Sunlight is unable to penetrate below the mesopelagic zone (1,000 meters or 3,300 ft.). Animals at these and deeper regions have developed large eyes and some others have developed bioluminescence, which help them attract food or a mate.
The ocean holds most of the biomass at the surface where most of the sea creatures thrive. Descending along the water column, the biomass decreases gradually to an insignificant amount. This amount remains constant down the water column until reaching the sea floor, where the quantity of living organisms increases again. This occurs due to the great amount of decaying animal and plant matter that descends from above. The decayed matter deposited on the ocean floor becomes the nourishment for bacteria and sea floor creatures. Many fish on the ocean floor have developed elongated mouths with jaws that help them dig into the sand and mud for food.
Even though there is no oxygen in the ocean floor, there are a number of creatures thriving in this zone. The abyssal zone is the habitat of marine animals including the angler fish, the umbrella mouth gulper, the fang tooth, the vampire squid (vampyroteuthis infernalis), the long-nosed chimaera, black shallower, tripod fish, etc. Some creatures can tolerate extreme pressures by lacking empty spaces within their bodies. Some others have flaccid bones and muscle tissue to tolerate the extreme pressure. A large stomach helps them store food which is scarce at the sea floor. Large eyes help them gather more light and hunt. Bioluminescence allows them to attract their prey and mating. The ostracod shrimp s one of the most abundant animals in the abyssal zone; it usually uses mirrors to focus light.
Although the ocean floor does not contain as much life as the upper zones, the abyssal biome is amazingly interesting, yet zones of the abyssal plain have been less explored than the surface of the moon. All abyssal organisms must compete for a place to live and food, along with environmental factors, including salinity, light, temperature and the permanent nature of the sea floor. Mining companies are doing research on how to extract minerals form the ocean bottom, but mining could distress the ocean floor biological diversity. According to noaa.gov, the deepest a fish has ever been seen was in the Puerto Rico Trench, 8,372 meters (27,460 ft.) below sea level.