Deep-sea environment

Abstract

The deep sea, defined as the part of the ocean over 1,000 m deep, covers 60 % of the Earth’s surface, making it the planet’s largest biome (homogeneous ecological formation). The geological, geochemical and physical conditions of the seabed and water column define varied habitats, sheltering specific biological communities. The ocean floor is composed of various distinct environments, including continental margins, abyssal plains, oceanic trenches, mid-ocean ridges and seamounts. Over 90 % of the deep seabed is covered with fine sediments composed of particles of biogenic (i.e. Produced by living organisms), terrigenous, volcanic and authigenic (i.e. Originating from the rock where it is found) origin: They are found on abyssal plains, but also on continental slopes. The seabed is however rockier on mid-ocean ridges and seamounts, as well as in some isolated areas of continental slopes, into which submarine canyons with abrupt cliffs may be cut. The marine environment is globally characterised by an absence of sunlight, high pressure, low and relatively constant temperatures, low currents and an oxygen content generally sufficient for animal life to develop. In the case of the total absence of dissolved oxygen, in specific situations and in small areas, only anaerobic bacteria can develop.