Abyssal zone

The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word abyss comes from the Greek word ἄβυσσος (ábussos), meaning "bottomless".^[1] At depths of 4,000–6,000 m (13,000–20,000 ft),^[2] this zone remains in perpetual darkness.^[3][4] It covers 83% of the total area of the ocean and 60% of Earth's surface.^[5] The abyssal zone has temperatures around 2–3 °C (36–37 °F) through the large majority of its mass.^[3] The water pressure can reach up to 76 MPa (750 atm; 11,000 psi).

Due 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 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. 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.^[3]

The area below the abyssal zone is the sparsely inhabited hadal zone.^[1] The zone above is the bathyal zone.^[1]