The Sun powers almost all life on Earth, but chemosynthetic life is the fascinating exception. These organisms find fuel in chemical reactions, allowing them to flourish in places where the Sun doesn’t shine—like the deep sea.
Now, scientists have discovered chemosynthetic animals, such as foot-long tubeworms and mollusks, nearly six miles beneath the ocean surface, deeper than these ecosystems have ever been observed before, according to a study published on Wednesday in Nature.
Researchers witnessed the hotspots of chemosynthetic life in person during crewed dives in the Fendouzhe submersible, which descended nearly 31,000 feet to the ocean’s deepest regions, known as hadal trenches, in the North Pacific.
“Hadal trenches, some of the Earth’s least explored and understood environments, have long been proposed to harbour chemosynthesis-based communities,” said researchers co-led by Xiaotong Peng and Mengran Du of the Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, in the study. The authors did not reply to an interview request.
“Despite increasing attention, actual documentation of such communities has been exceptionally rare,” the team continued. “Here we report the discovery of the deepest and the most extensive chemosynthesis-based communities known to exist on Earth during an expedition to the Kuril–Kamchatka Trench and the western Aleutian Trench.”
The global ocean floor is etched with about 50 of these trenches, which form at the boundaries of tectonic plates and extend down to 35,876 feet at the deepest point, Challenger Deep. Chemicals like methane and hydrogen sulfide leak out of so-called “seeps” in these active zones, which can be metabolized by chemosynthetic microbes that form the basis of diverse ecosystems that live completely off the bio-solar grid.
Researchers with the Global Trench Exploration and Dive Programme, an international collaboration led by China, set out to investigate these sunless regions, which play a major role in global carbon cycling.
Over the course of several dives in the summer of 2024, the team documented thriving chemosynthetic ecosystems at otherworldly sites with names like Icy River, Cotton Field, and Wintersweet Valley. One site is simply called “the Deepest” because, at site 9,533 meters (31,276), it is the deepest known seepage location ever discovered.
Even at the Deepest, animals are living off the submerged land, including roving sea worms called polychaetes and giant tube worms called siboglinids that measure nearly a foot in length. Whereas some animals in the deep sea consume the remains of dead stuff that has sunk down from the surface, these ecosystems are entirely powered by the outflows from the seeps.
“These communities are sustained by hydrogen sulfide-rich and methane-rich fluids that are transported along faults traversing deep sediment layers in trenches,” according to the study. “Given geological similarities with other hadal trenches, such chemosynthesis-based communities might be more widespread than previously anticipated.”
The discoveries can seem remote, considering the alien environment where these ecosystems flourish. But what happens in the hadal zone doesn’t stay in the hadal zone—these trenches are a major sink in the global carbon cycle because their V-shaped topography efficiently funnels biomass to depths where it can be sequestered. As we grapple to predict the future of our warming world, it will be essential to understand dynamics that reach from the upper limits of the sky to the deepest reaches of the oceans.
“These findings underscore the complex nature of carbon cycling in the deep sea and highlight the critical need to integrate hadal processes into global carbon models to improve the accuracy of predictions about carbon dynamics and climate change responses on geological timescale,” the researchers said.
They concluded that the new “findings challenge current models of life at extreme limits and carbon cycling in the deep ocean.”