When you go really deep into the Pacific Ocean, there’s no light. The temperature is near freezing and the pressure gets over 1,000 times what we feel at sea level. Nothing should live down there, but it turns out, a lot actually does.
Using a deep-diving submersible called Fendouzhe, a team from the Ocean University of China explored two of the deepest places on Earth: the Kuril-Kamchatka Trench and the Aleutian Trench. And what they found and published in Nature, kind of breaks everything we thought we knew about life, survival, and even the carbon cycle.
These deep-sea communities run on chemosynthesis, which compared to photosynthesis means they don’t need sunlight. Down there, bacteria turn chemicals like methane and hydrogen sulfide into energy, and that energy supports an entire trophic network: colonies of tube worms from the Siboglinidae family, deep-sea mollusks from the Bivalvia class, and many strange but fascinating benthic fauna.
This is all happening in the Hadal region, a part of the ocean deeper than 6,000 meters, where we believed that the only things to ever survived in there were leaving out of crumbs from above.
A whole ecosystem where no one thought life could exist
Between July and August 2024, researchers did 23 dives using Fendouzhe. In 19 of those dives, they found thriving ecosystems between 5,800 and 9,533 meters deep.
One spot, nicknamed “The Deepest,” was located on an active fault zone. There, fluids rich in methane and hydrogen sulfide pour out of cracks in the seafloor. Microbes take these chemicals, convert them into energy, and suddenly you’ve got life.
Tube worms (Siboglinidae) build vertical colonies that look like alien forests growing from the mud. Bivalvia mollusks, some only found in extreme ecosystems, settle nearby. It’s all supported by chemosynthesis.
Thousands of tube worms, frozen methane, and life by chemistry
At a place called Wintersweet Valley, which is 9,120 meters down, scientists found a 2-kilometer stretch packed with tube worms. We’re talking thousands per square meter. These worms live in long tubes sticking out of the ocean floor, surrounded by other deep-sea critters like holothurians, amphipods, and wandering polychaetes.
And then there’s the methane hydrate, frozen methane crystals buried in the seafloor. Scientists discovered concentrations of this stuff more than 200 times above what theory says should be possible. That means there’s a lot of carbon hiding in these trenches, stored in the crust instead of moving back into the atmosphere.
The methane deep in there is being made by microbes right in the sediment. It’s bacteria breaking down old organic matter without needing oxygen or even sunlight. And that chemical energy flows up, feeding life that was never supposed to be there.
What this discovery is teaching us
“These findings don’t just stretch the limits of what’s possible, they rewrite them.”
This changes the story for Earth’s entire Geobiology playbook.
Until now, we thought deep-sea ecosystems were like leftovers surviving on whatever drifted down from above. But in these places they’re self-sustaining. Powered by chemistry and able to create and support full-blown ecosystems far below what we thought were the limits of life.
These hotspots of chemosynthesis are feeding more than just their own little communities. Nearby scavengers and predators benefit too by creating a ripple effect in the deep-sea trophic network. It’s not just isolated blobs of life. It’s an entire network.
If we are talking about the carbon cycle, then we might be missing a huge piece of the puzzle. If places like this exist in other trenches, and they probably do, then we’ve underestimated how much carbon is being stored, and how these mysterious ecosystems fit into the planet’s long-term systems.
Theres is still so much to discover, but the latest findings are already good news.