Twenty sizable ocean floor craters in the western Pacific are encircled by structures known as pipe swarms, which are passageways through the rock that allow superheated fluids to rise from below, on a section of seafloor located on the Caroline Plate about 80 kilometers from the edge of the Mussau Trench. Eleven square kilometers make up the whole system. Squat lobsters, shrimp, and anemones swim about the vent ports under the lights of the Fendouzhe submersible, feeding on bacteria that use hydrogen chemistry instead of sunlight. Researchers from the Chinese Academy of Sciences described the place and published their findings in Science Advances, giving it the name Kunlun Hydrothermal Field. The hydrogen output estimate of 4.8 × 10¹ moles annually, which the researchers concluded equals at least 5% of all geological hydrogen emissions from the entire world ocean floor, caught the attention of the geochemistry community.
5% from just one field. The Kunlun finding is contextualized by that figure. Since scientists first started examining hydrothermal vent systems in the late 1970s, reports of submarine abiotic hydrogen—hydrogen created by geological processes as opposed to biological things—have been made all around the world. Over decades of measurement and modeling, the overall amount of this geological hydrogen produced worldwide has been calculated and improved. The Kunlun Field’s contribution to that worldwide total, originating from a single coherent system at a particular place on the Caroline Plate, is big enough to change current estimates of the true geographical distribution and collective significance of geological hydrogen production.
Serpentinization, a chemical reaction that occurs when ocean water seeps into fissures in iron and magnesium-rich mantle rocks known as ultramafic rocks, is the mechanism that produced Kunlun. Hydrogen gas is one of the consequences of the water’s reaction with minerals like olivine. The chemistry itself produces heat as the reaction occurs, making it exothermic and self-sustaining without the need for volcanic heat. The system may have seen periods of more energetic gas release in its geological past, as shown by the steep-walled craters at Kunlun and breccia deposits that show ancient explosive activity at the location. The contemporary manifestation of a long-running process is what the Fendouzhe saw.
A particular type of evidence on the hydrogen chemistry can be found in the biotic communities flourishing around Kunlun’s vents. Chemical energy, as opposed to photosynthesis, powers chemosynthetic habitats, such as those found at hydrothermal vents around the world. Compared to the sulfur compounds that power the more well-known black smoker populations, the organisms near a hydrogen-rich vent like Kunlun have access to a more plentiful and possibly more dependable energy supply. The shrimp, anemones, squat lobsters, and tubeworms that Fendouzhe recorded at the site are in line with what has been discovered at other alkaline, hydrogen-rich vent systems. These communities may have analogs in the early Earth’s ocean, when hydrogen was more geochemically accessible in a greater variety of seafloor environments.
In light of Pacific Ocean governance and scientific access, the discovery’s location is noteworthy. The Caroline Plate is located in an area in the western Pacific that includes waters next to Micronesian island nations that are associated with the United States. The Kunlun Field is located west of the Mussau Trench, which is in the broad geographic area where research projects from the United States, China, and other countries have been active. The Fendouzhe, a Chinese submersible that attained its 10,000-meter depth rating in the Mariana Trench in 2020 and has since been used for a variety of deep-sea scientific missions, was used by Chinese researchers to make the finding. China’s marine scientific program, which has been significantly increasing its deep-sea research capabilities over the past ten years, constructed and operated the instrument that discovered a significant geological hydrogen source in the western Pacific.
The Kunlun Field provides valuable information in a different way for scientists studying geological hydrogen as a possible energy source. The case for considering geological hydrogen as a viable energy source is based in part on scale: if the world’s overall output is significant enough to be worthwhile, and whether individual sources are sufficiently concentrated in easily accessible areas to be financially feasible. In an 11-square-kilometer area, a single field generates 5% of the world’s undersea abiotic hydrogen output, indicating that geological hydrogen is more concentrated at certain locations than diffuse background models would suggest. The question of whether that makes deep-sea geological hydrogen practically accessible is still up for debate in the fields of engineering and economics. However, the features of the Kunlun Field are precisely the kind of information that makes the question worthwhile.
