Hydrogen, the most abundant element in the solar system, continues to captivate the scientific community due to its immense potential as a clean and sustainable energy source. On Earth, where clean energy alternatives are urgently sought to mitigate climate change, hydrogen holds a unique promise. Despite its abundance in the cosmos, the terrestrial formation and storage of hydrogen in geological settings remain poorly understood. Until recently, characterized hydrogen vents have been relatively small, leaving many questions about the magnitude and mechanics of geological hydrogen formation unanswered. A groundbreaking study led by the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) sheds new light on this enigmatic phenomenon by revealing a vast geological feature that could redefine our understanding of hydrogen reservoirs deep beneath the ocean floor.
This pioneering research focuses on a colossal pipe swarm, a clustered formation of cylindrical geological structures identified on the east Caroline Plate, west of the ancient and now inactive Mussau Trench. The Mussau Trench, a relic trench which ceased tectonic activity about 25 million years ago, serves as the backdrop for this discovery. The pipe swarm has been christened “Kunlun,” and its pipes measure between 450 and 1,800 meters in diameter, dimensions that dwarf previously documented hydrogen vent sites. The geological significance of this discovery lies in its size and the intricate processes inferred to have caused its formation, indicating extensive hydrogen-related hydrothermal activity that challenges existing paradigms tying such phenomena only to active plate margins or tectonic fault lines.
Hydrothermal fluids, steam-like mixtures of superheated water and dissolved minerals, typically escape from the ocean floor through microscopic channels or cracks. In the Kunlun pipe swarm, these fluids traverse through minuscule tubes—often just centimeters or even sub-centimeters wide—adjacent to pockmarks, which are crater-like depressions etched into the large pipe walls. These fluids also seep through fractured piles of breccia, deposits composed of angular rock shards. Interestingly, many breccia fragments exhibit partial yellowish staining, likely the result of dense microbial mats proliferating in these hydrothermal environments. Such biological mats play critical roles in biogeochemical cycles and are indicative of active, life-supporting ecosystems surrounding hydrogen-rich vents.
The marine ecosystem thriving within the Kunlun pipe swarm mirrors other hydrothermal fields, harboring diverse biotas adapted to the harsh and chemically unique conditions. Foremost among these is the scorpionfish, an apex predator within this ecosystem that preys upon smaller organisms sustained by microbial mats. The relatively high population of such top-level predators implies a substantial biomass of prey species, which in turn suggests extensive microbial colonization on breccia deposits deep within the pipes. This intricate food web underscores the fundamental role hydrothermal hydrogen systems may play not just geologically but biologically, providing energy and sustenance for complex communities far from sunlight penetration.
Seismic monitoring over a one-month period along a 150-kilometer transect crossing the Mussau Trench revealed more than 800 minor earthquakes, highlighting ongoing active gas leakage in the region. Such seismicity may be directly linked to degassing processes, where hydrogen and other volatiles escape through fractures and faults, maintaining dynamic fluid fluxes within the pipe swarm structures. Isotopic studies focusing on clumped nitrogen isotopes within hydrothermal fluid samples indicate that much of the gas component originates from atmospheric sources, intermingling with deep-seated geological gases. This complex interplay enriches our understanding of gas genesis and migration along ancient tectonic scars like the Mussau Trench.
Contrasting with prior discoveries of hydrogen hydrothermal activity primarily near active spreading ridges or transform faults—regions where mantle rocks like peridotite are exposed—the Kunlun pipe swarm is situated approximately 80 kilometers away from any active plate boundary. This suggests that significant hydrogen production, migration, and preservation can occur in more tectonically subdued and mature geological settings. Such findings expand the potential range of environments where economically viable hydrogen accumulations may be found, breaking from the traditional notion that hydrogen vents are exclusive to volcanically or tectonically active margins.
The internal morphology of the Kunlun pipes reveals steep walls filled with abundant breccia clasts and multiple generations of smaller, shallow bowl-shaped pockmarks on their floors. These features bear resemblance to kimberlite pipes, which are volcanic structures formed by explosive eruptions transporting mantle materials rapidly to the surface. The multiple depositional layers and repetitive crater formation imply episodic explosive events, each driven by vast subterranean energy releases. Using empirical blast energy models, scientists estimate that the formation of these massive pipes required the equivalent blasting force of millions of tons of TNT, an extraordinary magnitude demanding a powerful and sustained energy source from within the Earth.
Hydrogen emerges as the most plausible agent capable of generating such intense explosive energy from below the seafloor. When compressed hydrogen expands rapidly, it releases large amounts of energy. For example, the adiabatic expansion of one ton of hydrogen from a pressure of 1500 bar (typical of lithospheric depths) to 400 bar (corresponding to the hydrostatic pressure at Kunlun’s depth) releases roughly the same energy as 0.21 tons of TNT. Even more striking is the potential of hydrogen gas to react explosively with oxygen; the exothermic reaction emits about 143 gigajoules of heat per ton of hydrogen combusted, approximately 150 times the energy released from physical expansion alone. Such reactions could readily drive the violent venting and cavity formation observed in the pipe formations.
These findings, therefore, support a model in which vast quantities of hydrogen accumulate deep beneath the oceanic lithosphere. Its sudden and violent release, either purely by physical expansion or through combustion with oxygen infiltrated from seawater or other sources, would explain the multiple explosive episodes shaping the Kunlun pipe swarm. This insight fundamentally alters our understanding of deep Earth volatile dynamics and suggests that hydrogen may be generated, stored, and mobilized in unprecedented quantities within the oceanic mantle, far from conventional tectonic hotspots.
Prof. XIAO Yuanyuan, who spearheaded the study, expressed optimism that these extensive hydrogen reservoirs could eventually transform the hydrogen economy. “The evidence points to enormous amounts of hydrogen having been generated deep within the oceanic lithosphere, potentially equating to a vast, untapped resource,” noted Prof. XIAO. She further emphasized the possibility that such reservoirs might someday be mined sustainably, powering the global transition away from fossil fuels towards clean energy based on Earth’s own primordial chemistry.
This discovery invites a paradigm shift in our geological and environmental perspectives, positioning deep ocean hydrogen systems not only as subjects of fundamental Earth science but also as promising frontiers for sustainable energy exploration. The Kunlun pipe swarm stands as a testament to the intricate and dynamic interactions governing Earth’s lithosphere and hydrosphere, revealing hidden dimensions of the planet’s internal energy budget and inspiring future research into deep-sea resource potential. As scientists continue to probe such enigmatic structures, geological hydrogen could emerge as a cornerstone in humanity’s quest for clean, abundant, and renewable energy.
Subject of Research: Geological hydrogen formation and hydrothermal activity in oceanic lithosphere
Article Title: (Not explicitly provided in the source content)
News Publication Date: September 5 (year inferred as 2023)
Web References: http://dx.doi.org/10.1126/sciadv.adx2600
References: Published in Science Advances
Image Credits: Image by Prof. XIAO Yuanyuan et al.
Keywords: Hydrogen, Geologic history, Earth sciences
