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Where does hydrogen in the deep sea come from? An international team led by the University of Bremen addressed this question and discovered an unexpected process occurring beneath the sparsely studied hydrothermal fields at extremely slow-spreading mid-ocean ridges that could play an important role. Particularly at sites where liquids circulate through sediments. Samples from the Jøtul Hydrothermal Field off Norway were analyzed for the study. The findings have been published in the professional journal Communications Earth & Environment.
The mid-ocean ridge runs through the oceans like a suture. Where the Earth’s plates move apart, new oceanic crust is continuously formed. This is often accompanied by magmatism and hydrothermal activity. Sea water seeps into the subsurface, is heated to temperatures above 400 degrees Celsius, and rises again to the ocean floor. The scientific community until now has assumed that the high hydrogen content measured in these liquids was a clear sign of serpentinization, a process that occurs when hot, mineral-rich liquids in the Earth’s crust react with the rocks there, and hydrogen and methane, among other materials, are formed through chemical reactions. These substances form the basis for life at the hydrothermal seeps. Dr. Alexander Diehl, first author of the study and a scientist at MARUM – Center for Marine Environmental Sciences, and at the Faculty of Geosciences of the University of Bremen, and his team have now shown that there is another way in which elevated hydrogen concentrations can arise at the spreading ridges.
Recently discovered hydrothermal field off Norway
The area of study is the Jøtul Hydrothermal Field on the Knipovich Ridge. This lies off the coast of Spitsbergen in the European Norwegian Sea, and represents the junction of the North American and Eurasian tectonic plates. It was first discovered in 2022 during a MARUM expedition of the research vessel MARIA S. MERIAN. It is significant because it lies on the flank of a rift valley in an ultraslow spreading mid-ocean ridge that is overlain by sediments from the continental slope. The entire region is characterized by a multitude of different seeps and vents. During the original expedition, initial samples of hydrothermal fluids were taken by the remotely operated vehicle MARUM-QUEST 4000. "However, on the way to the surface the gases escaped and could no longer be precisely measured in the laboratory. Similar to opening a pressurized soda bottle,” explains Alexander Diehl, “the gas fizzes out.” In order to investigate the components of the hydrothermal fluids more accurately, the research team returned to the Knipovich Ridge in 2024 with gas-tight sample containers.
More than just Serpentinization
But there is another specialty associated with the Jøtul Hydrothermal Field: It lies much deeper than other sediment-accumulating hydrothermal vents. “At a depth of 3,000 meters, high pressures dominate, which, on the one hand, makes sampling a challenge – and on the other hand, also influences the geological and chemical processes taking place there,” explains Prof. Dr. Gerhard Bohrmann, who was the Chief Scientist of both MARUM expeditions to the Jøtul Hydrothermal Field. The researchers analyzed the major components and dissolved gases as well as isotopic compositions, then applied thermodynamic modelling to study how the fluids react with the surrounding rocks. “Our models showed that, because of the high pressures and temperatures in the subsurface at the hydrothermal vents, the organic materials in the sediments decompose under supercritical conditions, causing the release of hydrogen molecules,” explains Diehl. “We were able to show that serpentinization is not the only explanation for how elevated hydrogen concentrations can occur in the deep sea. These findings expand our understanding of sediment-dominated hydrothermal vents, and suggest that the interaction between fluids and sediments is a more important source for dissolved hydrogen in the ocean than was previously believed.”
New Cluster of Excellence carries on with research
The research was carried out under the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”, and further ship expeditions will return to the Knipovich Ridge in the second funding phase of the Cluster of Excellence, which starts at the beginning of 2026. “The focus of these expeditions will be to improve our understanding of the composition of the vents and the escaping fluids, and to compare them with other hydrothermal vents," adds Prof. Dr. Wolfgang Bach, scientist at MARUM – Center for Marine Environmental Sciences, and at the Faculty of Geosciences at the University of Bremen.
MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.
Dr. Alexander Diehl
Geophysics – Geodynamics Working Group
MARUM – Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen
Email: diehl@uni-bremen.de
Alexander Diehl, Eirini Anagnostou, Patrick Monien, Thomas Pape, Eva-Maria Meckel, Miriam Römer, Leila Mezri, Wolfgang Bach, Donata Monien, Christian Hansen, Aaron Röhler, Katharina Streuff, Sabina Strmic Palinkas, Yann Marcon, Ines Barrenechea Angeles, Charlotte Kleint, Stig‑Morten Knutsen, Gerhard Bohrmann: High H2 production in sediment-hosted hydrothermal fluids at an ultraslow spreading mid-ocean ridge. Commun Earth Environ 7, 12 (2026). https://doi.org/10.1038/s43247-025-02962-2
https://www.marum.de/en/The-Ocean-Floor.html - More about the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”
https://www.marum.de/MSM131.html - more about Expedition MSM 131
https://www.marum.de/en/New-hydrothermal-field-discovered-by-MARUM-expedition.ht... - Press release on the discovery of the hydrothermal field in 2022
t shimmers and sparkles in the deep sea: Under the protruding flange of the hydrothermal vent on the ...
Source: MARUM-QUEST
Copyright: MARUM – Center for Marine Environmental Sciences, University of Bremen.
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t shimmers and sparkles in the deep sea: Under the protruding flange of the hydrothermal vent on the ...
Source: MARUM-QUEST
Copyright: MARUM – Center for Marine Environmental Sciences, University of Bremen.
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