What does hadal mean?
Hadal is an adjective describing the deepest region of the ocean, usually the ocean trenches and the waters within them. The hadal zone generally begins at a depth of about 6,000 metres, below the abyssal zone, and includes places such as the Mariana, Tonga, and Puerto Rico trenches. Because these environments are permanently dark and subject to extremely high pressure, hadal life has adaptations suited to cold, darkness, and scarcity of food. In scientific writing, “hadal” is especially associated with phrases such as “hadal zone,” “hadal trench,” and “hadal depths.” Its meaning is more specific than the general adjective “deep-sea” and should not be used for the whole deep ocean. The word is memorable because it identifies one of Earth’s least familiar environments: the narrow trenches that form the deepest parts of the global ocean.
adjectiveRelating to the hadal zone, the deepest region of the ocean, especially oceanic trenches and the waters within them, typically below 6,000 metres.
- Relating to the deepest zone of the ocean, especially trenches and their inhabitants.
"The submersible descended into the hadal depths of the Mariana Trench."
"Marine biologists found unusual organisms in the hadal zone of the Tonga Trench."
"Pressure-sensitive equipment is required for research in hadal environments."
Hadal names the ocean’s extreme depths—the trenches where sunlight is not merely faint but completely absent.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hadal come from?
Hadal was formed in English from the Greek hados, meaning “bottom” or “depth,” together with the suffix -al. It was adopted as a scientific descriptor for the deepest divisions of the ocean, paralleling terms such as bathyal and abyssal. The related compound hadopelagic uses the same had- element to refer to deep open-ocean regions beyond the continental shelf.
How hadal is actually used
Hadal is a technical term used in oceanography, marine biology, geology, and related disciplines. It is more precise than simply saying “deep” and should not ordinarily be used for shallow or even merely abyssal waters.
Easily confused with hadal
Hadal refers specifically to ocean depths below roughly 6,000 metres, whereas abyssal generally describes the deep-ocean zone extending from about 4,000 to 6,000 metres.