Supported by the National Key R&D Program of China under the “14th Five-Year Plan” key project “Deep-sea and Polar Key Technologies and Equipment”, a research team from the Institute of Deep-sea Science and Engineering (IDSSE), Chinese Academy of Sciences (CAS), has discovered the deepest known chemosynthetic ecosystem and associated geological fluid activity on Earth. The discovery was made at a depth of 9,533 meters on the hadal seafloor in the Kuril–Kamchatka Trench and Aleutian Trench in the northwest Pacific Ocean. The study, entitled “Flourishing chemosynthetic life at the greatest depths of hadal trenches”, were published online in Nature on July 30, 2025 (https://doi.org/10.1038/s41586-025-09317-z). This significant research has attracted widespread attention, receiving coverage from 148 major media outlets worldwide, including CCTV, Xinhua News Agency, the BBC, CNN, and Reuters, etc.

Chemosynthesis, a novel autotrophic pathway, enables benthic biological communities to thrive under extreme conditions. Although theoretical studies have long suggested that chemosynthesis-based communities are widespread in hadal zones between 6,000 and nearly 11,000 meters deep, previously only sporadic distributions had been observed in the Japan Trench, with the deepest record at 7,434 meters. The global distribution of chemosynthetic communities in the deepest parts of the ocean and their potential impact on deep-sea ecosystems and the global carbon cycle have remained poorly understood.

Using the deep-sea manned submersible Fendouzhe (Striver), the researchers conducted the first observation of flourishing biological communities in the deepest zone of the ocean — the hadal trench. These life communities are primarily composed of deep-sea tubeworms and bivalve mollusks, which do not rely on sunlight. Instead, symbiotic chemosynthetic bacteria in their bodies harness energy through chemical reactions using methane and hydrogen sulfide present in seafloor fluids, converting inorganic compounds — such as carbon dioxide — into organic matter that supports the life activities of their hosts.

This breakthrough challenges the traditional view that hadal ecosystems are sustained mainly by the downward flux of organic particles and animal remains from surface waters. The study provides strong evidence that chemosynthetic processes may play a significant role in shaping hadal ecosystems and influencing ecosystem dynamics in the deepest marine environments.

Based on this discovery, the researchers suggest that chemosynthetic ecosystems may be far more prevalent in hadal zones than previously thought, forming a potential “Chemosynthetic Life Corridor” across global deep trenches. Furthermore, geochemical analyses indicate that methane in these environments derives from microbial decomposition of organic matter in deeper sediment layers, producing carbon dioxide that subsequently combines with hydrogen to synthesize methane. These findings suggest the presence of an extensive, previously unknown active deep biosphere beneath the hadal seafloor.

This research not only challenges traditional perceptions of the limits of life in extreme depths, but also offers a new perspective on the complex mechanisms of the deep-sea carbon cycle. It highlights China’s leading role in frontier hadal science, and has important implications for establishing a Chinese deep-sea research school, securing the commanding heights of international deep-sea science and technology, promoting major global scientific programs in hadal research, and supporting science-based diplomacy on global stage.

Figure: World's deepest chemosynthetic ecosystem discovered at the bottom of the Northwest Pacific trenches (Taken by manned submersible Fendouzhe)