At depths greater than 4000 meters shells dissolve, leaving behind a seafloor of brown clay and silica from dead zooplankton and phytoplankton. Above 4000 meters the seafloor usually consists of calcareous shells of foraminifera, zooplankton, and phytoplankton. The composition of the abyssal plain depends on the depth of the sea floor. The biomass of the abyssal zone actually increases near the seafloor as most of the decomposing material and decomposers rest on the seabed. The relative sparsity of primary producers means that the majority of organisms living in the abyssal zone depend on the marine snow that falls from oceanic layers above. However, as of Maone vehicle, the Deepsea Challenger was able to penetrate to a depth of 10,898.4 meters (35,756 ft). Previously, only the bathyscaphe Trieste, the remote control submarine Kaikō and the Nereus have been able to descend to these depths. The deep trenches or fissures that plunge down thousands of meters below the ocean floor (for example, the mid-oceanic trenches such as the Mariana Trench in the Pacific) are almost unexplored. Main article: Hadal zone Layers of the pelagic zone The area below the abyssal zone is the sparsely inhabited hadal zone. This region also contains a much higher concentration of nutrient salts, like nitrogen, phosphorus, and silica, due to the large amount of dead organic material that drifts down from the above ocean zones and decomposes. The water along the seafloor of this zone is actually devoid of oxygen, resulting in a death trap for organisms unable to quickly return to the oxygen-enriched water above or survive in the low-oxygen environment. The water pressure can reach up to 76 MPa (750 atm 11,000 psi).ĭue to there being no light, there are no plants producing oxygen, which instead primarily comes from ice that had melted long ago from the polar regions. The abyssal zone has temperatures around 2–3 ☌ (36–37 ☏) through the large majority of its mass. It covers 83% of the total area of the ocean and 60% of Earth's surface. The word abyss comes from the Greek word ἄβυσσος ( ábussos), meaning 'bottomless'.

The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean.

How to survive abyssal depths