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A human-occupied vehicle (HOV) exploring the deep Pacific Ocean has revealed an extensive hydrothermal complex of craters, carbonate walls and dozens of vents that together form a previously unknown undersea 'metropolis'. Researchers from the Laoshan Laboratory and the Chinese Academy of Sciences (CAS) have named this system the Kunlun hydrothermal field. Spanning approximately 11.1 square kilometers (4.3 square miles), Kunlun is more than a hundred times larger than the Atlantic's famed Lost City vent field and hosts roughly twenty observable vent openings amid sculpted dolomite and carbonate structures.
The discovery places Kunlun among the largest known concentrations of so-called alkaline hydrothermal vents — environments that emit hydrogen-rich, moderately warm fluids rather than the hotter, mineral-laden plumes typical of black smokers. Through particle-laden water often called "marine snow," carbonate walls and jagged outcrops shimmer where warm fluids meet cold deep ocean waters, producing a ghostly, heat-distorted landscape that appears almost mirage-like in in situ imagery.
Geological setting and formation processes
Kunlun differs markedly from most hydrogen-rich vents previously documented, which are commonly located near divergent plate boundaries or mid-ocean ridges. Instead, Kunlun lies about 80 kilometers west of a trench within the Carolina Plate, northeast of Papua New Guinea. Geological and geochemical analysis suggests the field formed when seawater penetrated deeply into mantle rocks, initiating serpentinization reactions — a process in which olivine-rich peridotite transforms to serpentine minerals while producing molecular hydrogen and heat.
The researchers propose a multi-stage formation model. Initially, seawater infiltration and rapid fluid–rock reactions would have triggered high-pressure release and an explosive phase that formed large craters. Subsequent fracturing allowed continued fluid circulation and hydrogen production. Over geological time, carbonate precipitation sealed channels intermittently, causing hydrogen to accumulate and release in episodic, smaller events. These repeated cycles produced the characteristic pipes and deep pits at Kunlun. Some depressions exceed 100 meters in depth and span hundreds of meters across; even shallower basins commonly reach depths greater than 30 meters.
Serpentinization and abiotic hydrogen
Serpentinization is central to Kunlun's significance. The interaction between seawater and mantle-derived rocks generates hydrogen abiotically (without biological activity). The team estimates that Kunlun alone may contribute up to 8% of the world's submarine abiotic hydrogen flux — a striking share for a single field. This high flux, combined with the system's spatial scale and longevity, challenges assumptions that serpentinization-driven hydrogen generation is confined to mid-ocean spreading centers.
Chemistry, temperature and comparison to other vent types
Unlike black smokers — the high-temperature (often >350°C), sulfide-rich chimneys that emit dark mineral plumes — Kunlun's fluids are hydrogen-rich and relatively cool, generally below 40°C. These lower temperatures and alkaline conditions favor carbonate and dolomite precipitation rather than the sulfide mineralization typical of black smokers. Example of deep-sea black smokers. (NOAA)
Because Kunlun resembles the alkaline, hydrogen-rich settings hypothesized for early Earth, the site is particularly relevant to origin-of-life research. The combination of sustained hydrogen flux, mineral surfaces provided by carbonates and structured microenvironments may create conditions conducive to prebiotic chemistry and to chemosynthetic microbial ecosystems that convert inorganic energy into biological biomass.
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Biology and ecological implications
Direct observations and sample collections at Kunlun show a diverse assemblage of deep-sea fauna. Shrimp, squat lobsters, anemones and siboglinid tubeworms were observed clustered near vents and in surrounding carbonate terrain. These animals are likely supported by microbial communities that harness chemical energy from hydrogen and other reduced compounds in a process called chemosynthesis, analogous to photosynthesis but using chemical energy instead of sunlight.
Weidong Sun, a marine geochemist with CAS, emphasized the site's biological promise, noting that the community composition and habitat complexity imply a stable, long-lived chemosynthetic ecosystem. The extensive carbonate pits and pipes provide spatially varied habitats and persistent chemical gradients that could sustain primary producers and higher trophic levels over long time scales — factors relevant both for modern deep-sea ecology and for hypotheses about how life could emerge in similar ancient settings.
Scientific importance and implications for origin-of-life studies
Alkaline hydrothermal vents have been proposed as plausible cradles for life on early Earth because they can generate proton gradients, supply reduced gases like hydrogen and provide mineral surfaces that catalyze organic reactions. Kunlun's scale and hydrogen output make it a rare natural laboratory for testing these ideas at a system level rather than at a single chimney or small vent cluster.
Researchers argue that Kunlun's deep, long-lived pipes and pits could offer a more sustained and stable chemical environment than the thin carbonate towers seen at the Lost City. Stability and duration are key factors in origin-of-life experiments: prolonged exposure to energy and catalytic surfaces increases the chance of building complexity from simpler molecules. As such, Kunlun may help constrain models of prebiotic chemistry and the environmental constraints necessary for life to arise from inorganic material.
Exploration, resource considerations, and future research
Kunlun's exceptionally high abiotic hydrogen flux raises questions about deep-sea hydrogen as a possible resource. The research team suggested the field could be a model target for evaluating deep-sea hydrogen extraction technologies. However, potential resource use raises substantial technical, ecological and ethical challenges: operating at abyssal depths requires robust submersibles and remotely operated systems; extracting hydrogen without disrupting fragile chemosynthetic ecosystems is a major conservation concern; and international governance issues remain unresolved for seabed resource exploitation.
Future research priorities include expanded mapping, time-series monitoring of fluid chemistry and flow rates, microbiological and geobiological studies to characterize microbial metabolisms, and modeling the long-term evolution and lifespan of the vents. Continued multidisciplinary expeditions — combining HOV dives, remotely operated vehicles (ROVs), seafloor observatories and laboratory analyses — will be necessary to quantify Kunlun's role in global geochemical budgets and biological productivity.
Expert Insight
Dr. Maria Álvarez, a marine geochemist at the University of Lisbon (expert commentary), says: "Kunlun is a rare window into serpentinization operating at scale. From a scientific perspective, it offers an unprecedented opportunity to study how sustained hydrogen fluxes shape both chemistry and biology. But the discovery also underlines the need to balance curiosity-driven exploration with conservation — these ecosystems are delicate and likely host species and processes we barely understand."
"Technically, extracting hydrogen from such systems is conceivable in principle, but the engineering would be non-trivial, and the ecological trade-offs must be weighed carefully," she added.
Research mission and methods
The Kunlun field was characterized using a combination of direct HOV dives, high-resolution bathymetry, visual surveys and in situ fluid sampling. Geochemical analyses quantified concentrations of hydrogen and other dissolved gases and characterized temperature profiles and pH. Petrological studies of carbonate and dolomite deposits, together with structural mapping of craters and pipes, informed the proposed formation sequence. The study detailing these results has been published in Science Advances (2025) and lists lead investigators including Lianfu Li and Hongyun Zhang from Laoshan Laboratory.
Potential for additional discoveries
Kunlun suggests that large, hydrogen-rich hydrothermal systems may be more widespread than previously thought, particularly in intraplate or off-axis settings. If serpentinization-driven hydrogen generation can operate far from mid-ocean ridges, as Kunlun demonstrates, more such "undersea metropolises" may await discovery in the ocean abyss. Systematic deep-sea exploration, leveraging autonomous and human-occupied platforms, will be critical to identifying similar sites and understanding their contribution to ocean chemistry and biodiversity.
Conclusion
The Kunlun hydrothermal field is a striking new example of an extensive, hydrogen-rich deep-sea ecosystem that dwarfs the Lost City in area and hydrogen output. Its geological setting, sustained abiotic hydrogen flux and abundant chemosynthetic life make Kunlun a pivotal site for studies ranging from the origins of life to deep-sea ecology and potential resource assessments. Continued multidisciplinary exploration will be essential to unlock the field's scientific value while ensuring protection of its unique biological communities.
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