深海 · ABYSS · Ocean zones
Hadal
Hadopelagic · 6,000 – 10,935 m
Named for Hades. It exists only inside trenches and accounts for 0.25% of the ocean. The trenches are not connected to one another — each is an island, and each has its own animals.
Descend this zone at true scaleDepth 6,000 → 10,935 m
Diamonds mined from the seabed
Off the coast of Namibia, specialised ships vacuum seabed sediment to mine diamonds.
A trench is where a plate is swallowed
The Mariana Trench is where the Pacific plate bends and slides beneath the Philippine Sea plate. The trench is not deep because the ocean is deep — it is deep because the plate is being pulled down. Magnitude 9 earthquakes come from places like this.
Convergence of a few centimetres a year · the trench is the shape that leaves behind
Slow enough to outlive us
In the cold deep, metabolism slows to a crawl. Some deep-sea fish are estimated to live well over a century.
A race ahead of the rules
Before international rules are finalised, nations are already racing to secure mining rights to seabed fields covered in manganese nodules.
Hadal sea spider
Its shallow-water relatives are the size of a fingernail, but down here sea spiders grow to the size of a hand. Why the deep makes them bigger still isn't fully explained.
Depth measured with rope and weight
The HMS Challenger expedition of 1872-76 first sounded the deep ocean with rope and a weight. A single reading could take hours.
Dumbo octopus
It swims by flapping two fins that sit on its head like elephant ears. It lives deeper than any other octopus and swallows its prey whole, without chewing.
Genus Grimpoteuthis · observed as deep as 6,957 m
How a cell holds together
Fish at this depth accumulate a compound called TMAO that stops pressure from crushing their proteins. The concentration rises with depth until, at roughly 8,200 metres, the cell reaches osmotic equilibrium with seawater.
In theory no fish can exist below that line
Where there is no day or night
There is no day and no night at this depth. Many hadal animals have no internal clock at all.
The deepest-living fish ever found
The Mariana snailfish holds the record for deepest fish ever confirmed. It has no scales, translucent skin you can see through, and bones that never fully harden — built to yield to the pressure instead of resisting it.
Observed 6,900-8,178 m · deepest fish on record
Alive, inside the sediment
Living microbes have been found kilometres beneath the seafloor, some apparently surviving in near-stasis for millions of years.
Eating a forest at the bottom of the sea
An enzyme that digests wood was found in the gut of a hadal amphipod. It lives on plant debris washed into the trench. Even where sunlight never reaches, these animals still depend on forests.
Hirondellea gigas · present on the floor of Challenger Deep
Alicella gigantea
Most amphipods are smaller than a fingernail; this one grows up to 34 centimetres. It turns up in trenches worldwide, though its numbers appear to be declining.
Carbon from the bomb tests reached this far
Atmospheric nuclear testing in the 1950s and 60s doubled the amount of carbon-14 in the air. In 2019 that same carbon was found in the bodies of amphipods on the floor of the Mariana and Kermadec trenches. It had travelled from the surface to the bottom in a few decades.
Wang et al., Geophysical Research Letters (2019)
Ghost snailfish
Between 2022 and 2023, several new snailfish were filmed in different trenches — still without a scientific name. The sighting records are piling up faster than the naming.
And a fish was swimming at the line
A juvenile snailfish was filmed at 8,336 metres in the Izu-Ogasawara Trench — almost exactly where theory placed the physiological limit. Its body is gelatinous, with no scales and no swim bladder.
Genus Pseudoliparis · deepest fish ever observed
Elpidiid sea cucumbers
Translucent sea cucumbers that seem to walk across the hadal floor. In some trenches, this single group makes up more than half of all the large animals there.
Turn Everest upside down here
The whole mountain disappears, and its summit is still 2,087 metres below the surface. People have climbed it more than twelve thousand times. People have descended the remaining 2,087 metres twenty-seven times.
8,848.86 m · 2020 China–Nepal joint survey
It wears a suit of aluminum
At this depth, calcium carbonate shells simply dissolve. Hirondellea gigas pulls aluminum from the mud and coats itself in an aluminum-hydroxide gel instead — and gnaws through sunken wood, even shipwreck timber, to survive.
Lives 6,800-10,935 m · dominant scavenger of the Challenger Deep
The trench floor is the crowded part
The V-shaped walls funnel organic matter down and concentrate it at the bottom. A hadal trench therefore holds more food, and more animals, than flat abyssal plain at the same depth. The deepest place is not the barest one.
Every earthquake collapses the walls and dumps sediment all at once
Still unnamed
A large share of what gets collected at this depth still has no scientific name. Discovery is simply outpacing the work of naming it.
A plastic bag
Filmed on the floor of the Mariana Trench in 2018. Humans have been down there three times. The rubbish got there first.
Deepsea Challenger
James Cameron, alone, in 2012. What he found was not a monster but a grey plain he described as emptier than the Moon.
Trieste
Jacques Piccard and Don Walsh, 1960. A viewport cracked on the way down and they kept going. Nobody returned for the next 52 years.
Other markers
What fits in this depth
| Depth | |
|---|---|
| 6,961 m | Aconcagua |
| 8,611 m | K2 |
| 10,668 m | Airliner cruising altitude |
Figures come from public observational data; sources are cited in the main descent. Do not use for navigation, diving, or any safety decision.