Methane Emitted from the Seafloor Has Minimal Direct Impact on Atmospheric Warming

Pusan National University International Study:
"Most Methane at Depths Greater Than 500 Meters
Is Absorbed by Seawater or Microorganisms"

A new study has found that subsea methane, long considered a major factor accelerating global warming, in fact has little impact on the increase of atmospheric methane.

This overturns the widely accepted hypothesis that "subsea methane emissions directly amplify global warming."

Pusan National University announced on December 16 that Professor Dongju Jeong (Department of Oceanography), through an international collaboration with researchers from the University of Rochester in the United States, experimentally confirmed that methane generated from gas hydrates and natural hydrocarbon seeps at depths greater than 500 meters mostly dissolves in seawater or is consumed by microorganisms, and does not enter the atmosphere.

Professor Dongju Jeong, Pusan National University.

Methane is a gas with a greenhouse effect about 80 times stronger than carbon dioxide, and has recently drawn attention as a key variable in climate change due to its increasing use. In particular, there have been major concerns about the "methane-climate change positive feedback loop," in which the collapse of subsea gas hydrates due to rising seawater temperatures could release large amounts of methane and accelerate global warming.

To test this hypothesis, the research team applied a method for precise analysis of radioactive carbon isotopes (¹⁴C-CH₄) contained in methane. After investigating subsea gas hydrate decomposition and natural hydrocarbon seeps in the Gulf of Mexico, the results showed that while methane released from the deep sea enters the bottom water in large quantities, it does not reach the surface and is mostly eliminated within the ocean.

These findings are consistent with Professor Jeong's 2022 deep-sea research in the Atlantic and Pacific Oceans published in Nature Geoscience. Methane released at depths greater than 500 meters enters the atmosphere only in extremely small amounts, once again demonstrating that it does not serve as a major pathway for amplifying global warming.

However, the research team also confirmed that methane generated from relatively shallow natural seep sites can actually reach the surface layer of seawater and the atmosphere. This means that the behavior of methane varies greatly depending on water depth and the subsea environment.

Professor Dongju Jeong emphasized, "Although methane is a gas that directly affects climate change, related research is insufficient worldwide, and domestic research is even more lacking. Considering the increasing use of methane and its powerful greenhouse effect, methane research will become a core field in future climate change studies."

He added, "Korea is the country in East Asia with the fastest increase in atmospheric methane concentrations. Since both natural and artificial environments in Korea are favorable for methane generation, active government support for both basic and applied research is needed."

This study also utilized a new analytical technique for ultra-precise measurement of radioactive carbon in methane. Professor Jeong's team is currently the only group in the world to have applied this technology in actual research, significantly reducing measurement errors and increasing data reliability. Professor Jeong stated, "Korea has ample potential to lead the world in this field."

He also noted, "Although direct atmospheric entry of subsea methane is minimal, if methane oxidized by microorganisms in seawater is converted to carbon dioxide, it could weaken the ocean's carbon absorption capacity. We aim to expand our research to various marine regions, including the polar regions and the East Sea, to contribute to more sophisticated climate change predictions."

This research was conducted as an international collaboration between Pusan National University, Professor John D. Kessler of the University of Rochester, and Professor Thomas Weber, and the related paper was published in the December 15 issue of the international journal Communications Earth & Environment.