The abyssal plain is a large tract of flat floor on the bottom of the ocean. It extends seaward from the base of the continental slope, or from the seaward edge of an ocean trench, to the mid ocean ridge. This important geographical feature of the world's oceans lies at depths that range between 4,000 m (13,000 ft) and 6,000 m (20,000 ft). It is remarkable for its sediments, manganese nodules, and life forms.
The floor of abyssal plain consists of particles of brown and red clay piled up by current deposition and volcanic eruptions. The shell of microscopic marine organisms also contributed to build up a significant portion of the layers of sediments. Quiet waters of the deep ocean do not disturb the particles as they accumulate on the seafloor. Marine scientists usually study the sediments to glean data about the age of the ocean floor and changes in the ocean depths, temperature, salinity, and circulation.
Turbidites form distinctive layers of sediments on the edges of abyssal plains, next to continental slopes. Turbidites originate from river sediments, which are deposited on the outer edge of the continental shelf. Then turbidity currents stir and carry the sediments from the shelf to the plain deep below. These currents are slurries of suspended sediments and water. They slide down a continental slope similar to an avalanche and the resulting turbidites form tongue-like abyssal fans near the mouth of rivers of submarine canyons.
Turbidites are less abundant in the Pacific Ocean than in the Atlantic and Indian Ocean, because fewer large rivers supply sediment to the Pacific as its deep sea trenches trap sediments, preventing their spread to the abyssal plain. Seamounts are rarely seen on the Atlantic and Indian Ocean abyssal plains. However, their presence is a common feature on the abyssal plains of the Pacific Ocean. This is due to the paucity of turbidites there. Mysterious, potato-size rocks litter the surface of the abyssal plain. They contain thin concentric layers of metals, like iron, nickel, copper, manganese, and cobalt.
Below, a schematic picture of the seafloor, showing the abyssal plain and other geographical features.
A photograph of the abyssal plain at 4,050 m of depth taken by a remote control deep ocean probe.
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