Defining the deep sea

A simplified image showing the different oceanic layers.

What’s the difference between an ordinary sea and the deep sea? Most sea’s can be considered deep in comparison to a human’s size as such it is important to define what is meant by the deep sea.  The term deep sea or deep layer denotes the lowest layer the sea at 1800 meters or deeper under the thermocline consisting of the bathypelagic, abyssopelagic and hadopelagic layers.

Within the deep sea there are several environments that are included in the area. Hydrothermal vents and cold seeps are both ecosystems that are found only in the deep sea and of which are the area’s most abundant in life in the deep sea. Although life can be found theoretically anywhere on the sea bed, in the deep sea it is scarce consisting mainly of opportunistic scavenging vertebrates that feed on fallen bio matter, there large bulk of life on the sea floor however are invertebrates that feed on organic “fallout”  called marine snow from the photic zones above. These organism’s still rely on the energy from the sun unlike the animals that live on the hydrothermal vents and cold seeps which are the only organisms of the deep sea that can be considered entirely independent from the sun.

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