Ocean trench

Ocean trenches were deep crevasses found below the surface of an ocean.

On Earth, ocean trenches could be found beneath the Atlantic, Pacific and Indian Oceans. The high pressure in these trenches meant that fish had to be specially adapted in order to survive. The Torchwood Hub had an aquarium containing deep-sea fish from the ocean trenches. (PROSE: Slow Decay) The Mariana Trench was the deepest point on Earth. The surface of the trench was covered in volcanic ash and marine snow. This volcanic ash was created by black smokers, which produced superheated water and hydrogen sulphide. (AUDIO: Submission)

The Doctor once saw horseshoe crabs deep in an ocean trench on Hitchemus, living in the remnants of a human city. (PROSE: The Southwell Park Mermaid)