Deep sea expedition reveals thriving chemical-powered life

People usually imagine the deepest ocean floor as an empty wasteland. A new expedition to the Kuril-Kamchatka and Aleutian trenches shows that life there is anything but sparse.

Using the crewed submersible Fendouzhe, researchers mapped a 1,553 mile stretch of trench floor between 19,000 and 31,267 feet and found bustling communities fueled by chemicals instead of sunlight. 

“Blood-red tentacles unfurling like delicate flowers in the trench, a stunning defiance of the harsh, crushing darkness,” said marine ecologist Mengran Du of the Chinese Academy of Sciences, describing the scene after returning to the surface.

Life exists deep in the ocean

The hadal zone starts around 19,700 feet below the surface and drops to nearly 36,000 feet. Water there hovers just above freezing, and the pressure exceeds eight tons per square inch.

Until the late 1970s, most biologists doubted anything complex could thrive so far from sunlight. They were proved wrong when hydrothermal vents turned up, and the new trench survey pushes the boundary even deeper.

Pressure at those levels would snap a human bone in an instant. Electronics must be oil-filled or specially potted, or they will implode.

Microbes fuel deep-sea animals

The team documented colonies of chemosynthesis-dependent animals at forty-one separate sites. Instead of photosynthesis, microbes embedded in the sediment convert methane and hydrogen sulfide into sugars that flow up the food chain.

“We discovered thriving chemosynthesis-based communities at an astonishing depth of 9,533 meters,” said Du, the mission’s chief scientist. Converting that figure reveals a world flourishing more than 31,200 feet down.

Laboratory tests on pore-water samples showed methane made entirely by microbes rather than heat-cracked rock, backing the idea that biology, not geology, drives the energy supply.

The same study reports methane concentrations in the mud that are 200 times higher than what seawater can hold at those depths.

Sub dives reveal trench life

Fendouzhe is built to shrug off the 16,000 pound per square foot squeeze that would crush most steel hulls. On earlier trials, the titanium sphere dipped to 35,790 feet in the Mariana Trench, so the 2024 trench transect fell well within its comfort zone.

The crew spent a combined 150 hours on the seafloor during 24 dives, collecting cores with robotic arms and steering high-definition cameras along fault scarps.

At several stops, the pilots had to ease around towering clumps of siboglinid polychaetes whose white tubes formed shag carpets across the mud.

Each dive revealed something new, from beaches of clams the size of dinner plates to fields of ghostly white microbial mats. Many of those mats sat above visible cracks, hinting at seepage routes that pipe chemicals upward from deeper sediment layers.

Every core was sealed in chilled boxes aboard the mothership within minutes to keep deep-water microbes alive. Some are already growing in pressure vessels back on shore.

Deep sea worms and clams

The most conspicuous animals were scarlet-tipped tube worms and thick-shelled bivalve molluscs. Both groups host bacteria inside their tissues that feed on trench gases and deliver nutrients to their hosts.

Adult tube worms even lack a mouth or gut, outsourcing digestion entirely to their microbial partners. That alliance lets them bloom in places where drifting organic crumbs from the surface would never be enough.

In turn, the worms create a three-dimensional forest that shelters worms, snails, and amphipods. Some clams were counted at more than 290 individuals per square yard, making these vents among the densest animal gatherings measured in the deep sea.

Why the trenches matter for carbon

Cold seeps pump methane into the ocean, but a lot of that gas gets locked into methane hydrate, an ice-like solid stable under high pressure. If hydrates are as widespread as the new cores suggest, trenches could store far more carbon than current climate models allow.

At the same time, trenches act like gutters that funnel dead plankton into narrow troughs where microbes chew it up fast and respire CO2.

A recent geochemistry survey found oxygen consumption in trench sediments double that of nearby abyssal plains, underscoring their role as carbon reactors.

Carbon that escapes as hydrate might stay buried for millennia, whereas carbon exhaled as dioxide could re-enter the atmosphere through upwelling currents centuries later. Knowing which pathway dominates is essential for predicting long-term climate feedback.

Deep sea mysteries still unsolved

Even with Fendouzhe’s reach, the team sampled just two trenches out of more than thirty. Geological maps show similar faults in the Kermadec, Tonga, and Peru-Chile trenches, all prime targets for the next cruises.

Researchers also want to know how trench animals disperse between isolated pits separated by thousands of miles. Genetic work on the worms hints at a shared ancestry across the North Pacific, suggesting larvae may ride deep water currents for years before settling.

Another puzzle is whether hydrates ever destabilize and belch methane into the water column during big earthquakes. Long-term observatories anchored near active faults could capture such rare events.

More deep sea life may exist

The discovery comes at a time when nations are racing to mine seafloor metals and drill for gas hydrates. Finding vast, fragile ecosystems beneath 30,000 feet adds weight to calls for stronger rules before industrial gear moves in.

It also broadens the search for life beyond Earth. If microbes can feed entire animal communities in pitch-black trenches, similar chemistries might support alien biospheres under the ice of Europa or Enceladus.

“Their resilience and beauty left me in awe,” said Du. Few people have seen what she saw, but the images and samples now preserve a snapshot of life at the planet’s outer limits.

The study is published in the journal Nature.

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