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Methane Below 500m Depth Blocked by Dissolution and Microbial Consumption… Overturning the ‘Positive Feedback’ Hypothesis
A research team led by Professor Jeong Dong-ju of the Department of Oceanography at Pusan National University (PNU) has presented research findings showing that methane released from the deep sea has virtually no impact on the increase of atmospheric methane. This international joint study precisely analyzed deep-sea gas hydrates and natural hydrocarbon seep sites in the mid-latitude Gulf of Mexico, experimentally confirming that methane originating from the seabed deeper than 500 meters dissolves in seawater or is consumed by microbes before reaching the atmosphere.
Methane is a greenhouse gas with a warming effect approximately 80 times stronger than carbon dioxide. For a long time, the “Methane-Climate Change Positive Feedback” hypothesis—which suggests that methane released from the seafloor flows into the atmosphere and accelerates global warming—has been a major concern. However, this study fundamentally revises this perception by providing empirical data showing that deep-sea methane does not significantly contribute to such a runaway mechanism.
Tracking Methane with World-Class Radiocarbon Analysis
To identify the origin of methane from the surface to the deep layers of the ocean, the research team conducted a precise analysis of Radiocarbon isotopes within methane ($^{14}C-CH_4$). By tracking how methane derived from the deep sea behaves underwater using this method, they found that deep-sea methane dissolves and oxidizes as it rises through the water column, failing to reach the sea surface.
In particular, this study is highly significant as it verified the possibility of atmospheric influx by directly analyzing methane dissolved in seawater. The precise radiocarbon measurement technology applied by the team has drastically reduced measurement errors. Professor Jeong’s team is reportedly the only group in the world currently utilizing this specific method for actual research.
The findings also demonstrate that not all seafloor methane should be treated equally. Unlike deep-sea sources, methane released from natural seeps in relatively shallow waters was confirmed to actually flow into the sea surface and the atmosphere. This suggests that ocean methane management policies require a differentiated approach that considers depth and environmental conditions.
Impact on Ocean Carbon Cycle and Future Research
Professor Jeong pointed out that while the direct atmospheric influx of deep-sea methane is minimal, its oxidation by microbes within the seawater converts it into carbon dioxide, which can increase $CO_2$ concentrations in the ocean. This could potentially weaken the ocean’s ability to absorb atmospheric carbon dioxide, highlighting the need for comprehensive research on the Ocean Carbon Cycle.
[Photo of Professor Jeong Dong-ju / Provided by PNU]
These results are consistent with Professor Jeong’s previous research conducted in the deep Atlantic and Pacific Oceans, published in ‘Nature Geoscience’ in 2022. It indicates that seafloor methane released from depths of 500m or more has extremely limited direct access to the atmosphere, suggesting a need to recalibrate risk factors that may have been overestimated in climate change predictions.
The study was conducted as an international joint effort between Pusan National University and Professors John D. Kessler and Thomas Weber of the University of Rochester (USA). The results were published in the international academic journal ‘Communications Earth & Environment’ on December 15. The team plans to expand its research to various regions, including the polar areas and the East Sea, to more elaborately define the role of ocean methane.
#PusanNationalUniversity #MarineMethane #ClimateChangeResearch #GasHydrate #DeepSeaScience #MethaneWarming #EarthSystem
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