Is Methane in the Arctic Ocean Once Again a Trigger for Global Warming? Where is the "Switch"? - The Dangerous Chain of the Arctic Ocean, Microorganisms, and Global Warming

Introduction: The Invisible Lever That Can Transform the Climate

When it comes to gases that accelerate global warming, carbon dioxide (CO₂) takes center stage. However, another powerful supporting actor—methane (CH₄)—could cause the climate system to suddenly shift gears depending on its behavior. A new study reported on October 18, 2025, suggests that there is a mechanism in the Arctic Ocean that can be called a **"methane switch,"** and it indicates the possibility that during the abrupt warming about 56 million years ago (PETM: Paleocene-Eocene Thermal Maximum), the Arctic Ocean may have turned into a "source" of CO₂. The central claim of the paper is this: when the main player shifts from anaerobic oxidation of methane (AOM) on the seabed to aerobic oxidation of methane (AeOM) in the water column, methane rapidly converts to CO₂, consuming oxygen, promoting ocean acidification, and prolonging warming. This "switch" might become easier to activate as the current Arctic warms and freshens, reducing oxygen levels.Nature

What Triggers the "Switch"?

1) The Identity of the Switch: AOM → AeOM

• **Anaerobic oxidation of methane (AOM)** is carried out by sulfate-reducing bacteria in seabed sediments, acting as a **"biological filter" that traps methane. As a byproduct, it produces bicarbonate ions (alkaline)**, contributing to the stabilization of ocean pH.

• Aerobic oxidation of methane (AeOM) uses oxygen in the water column to rapidly convert methane into CO₂. It depletes oxygen and promotes CO₂ emissions and acidification.
  During the PETM, it is highly likely that the ocean had low sulfate concentrations, and because AOM's processing capacity **could not keep up with the "binge eating" of methane, methane overflowed into the water column, making AeOM the main player—this is the methane switch**.Live Science

2) How Was It Determined?

The research team extracted organic molecules (biomarkers) from a drilling core (about 15m) from the central Arctic Ocean and reconstructed the diet of microorganisms at that time using carbon isotope ratios. Particularly, the isotopic fingerprint of the hopanoid "hop-17(21)-ene" indicated the activation of aerobic methane oxidation. This is one of the lines of evidence that AeOM was predominant in the water column during the PETM.Natureenglish.cas.cn

From 56 Million Years Ago to Today: The Risk of Recurrence?

Lead author Kim Beomsoo cautiously warns, "It could happen in the modern Arctic, and the likelihood is high." The Arctic Ocean is prone to oxygen depletion due to warming and freshwater inflow, creating conditions favorable for AeOM dominance. On the other hand, some researchers express skepticism about direct analogies due to differences in ocean chemistry and basin morphology between then and now, but they agree on one point: complex carbon cycle feedbacks are often underestimated in projections beyond 2100.Live Science

Additionally, there are reports that the Arctic carbon balance is shifting from a sink to a source in recent years. For example, the 2024 **NOAA "Arctic Report Card"** indicated signs that the Arctic tundra has turned into a net CO₂ emitter due to a combination of factors such as widespread fires and permafrost thaw. Together with **the "Arctic amplification" of warming,** the background for the methane switch to be easily activated is indeed building up.The Guardian

Reactions on Social Media: The Boiling Point of the Science Cluster and Skepticism About the "Methane Bomb"

• Academic and Sci-Comm Circles (X)
  The official account of Nature Geoscience introduced the paper, and the point that **"AeOM may have prolonged CO₂ supply in the latter part of the PETM" was widely shared. Science writers also spread the summary with posts emphasizing that "underestimating carbon cycle feedbacks is dangerous."**X (formerly Twitter)

• General Science Media (Live Science)
  The headline **"The Arctic Ocean was once a major source of greenhouse gases" circulated on X and news aggregators, sparking discussions on whether "the same switch could be activated again."**Live Science

• Reddit (r/climate/r/climatechange and others)
  Discussions on methane often lead to clashes between doomers and skeptics and fact-checkers. The reactions converge into a realistic summary with voices saying **"isn't it over-applying past large releases to the present?", pointing out that "the shortness of observational records leads to great uncertainty," and concluding that "still, managing methane is urgent."**Reddit

• Brakes on Exaggerated Reporting (Fact-Checking)
  Headlines like **"Methane Bomb to Explode Now" have been targets of criticism in the past, and experts repeatedly point out that overreaching conclusions from limited observations should be avoided. This time too, the stance that "uncertainties should be communicated correctly"** was reaffirmed.Climate Feedback
  
  

The "Novelty" of the Research: Key Points of Method and Significance

1. Fingerprinting the Paleocean "Crime Scene"
   By combining biomarkers (hop-17(21)-ene) and carbon isotopes, researchers traced back who (which microbial groups) ate what. They identified the AeOM dominance period from chemical traces in the strata.Nature

2. Consistency in Geochemical Models
   Boundary conditions of low sulfate, freshening, and oxygen reduction rationalize the transition from AOM→AeOM. They suggest the long-term CO₂ source formation and acidification.Nature

3. Applicability to the Modern Arctic
   The progression of oxygen decline and freshening is also observed. As a **"warning from the past,"** it serves as material to reconsider the representation of carbon cycle feedbacks in climate models.The Guardian
   
   

Implications for Today: A Checklist for Policy and Business

• Enhanced Monitoring of Ocean Oxygen (O₂): Detailed tracking of surface to mid-layer O₂ in the Arctic. Early detection of signs of transition to AeOM.

• Reevaluation of Sulfate Supply and Stratification: Precise assessment of the effects of freshwater lensing due to large river inflows and sea ice melt on sulfate concentration, stratification, and ventilation.

• "Cross Method" Methane Observation: Integration of multiple methods such as satellite, aircraft, seabed flux meters, and continuous CH₄/CO₂ observations in the water column..

• Model Updates: Incorporating the formulation of carbon cycle feedbacks (dynamic AOM/AeOM switch) with a view beyond 2100.

• Risk Communication: Transparently conveying the existence of thresholds and the need for monitoring while avoiding exaggeration of "explosive releases.".
  
  
  

Conclusion: The Switch Exists; Whether It Activates Depends on Us

This study has illustrated "the physical, biological, and chemical circuits by which the Arctic Ocean can turn into a CO₂ source" from chemical fingerprints in the strata. The switch is not simple, but it can activate if conditions align. And some of those conditions (warming, freshening, deoxygenation) are already progressing in the current Arctic. Without inciting panic, yet without becoming insensitive—accelerating both monitoring and reduction (especially of methane) is the realistic answer.Nature