In a groundbreaking study published recently in Nature Communications, researchers have unveiled compelling evidence of a millennial-scale thermogenic carbon dioxide (CO₂) release event that preceded the Paleocene-Eocene Thermal Maximum (PETM). This discovery sheds new light on the complex carbon cycle feedbacks and climate dynamics associated with one of Earth’s most dramatic global warming intervals, offering critical insights that resonate strongly with today’s climate change concerns. The research spearheaded by Jiang, Cui, Wang, and their colleagues represents a seismic advancement in our understanding of how ancient geologic processes contributed to rapid greenhouse gas emissions and extreme climatic conditions sustained over thousands of years.
The Paleocene-Eocene Thermal Maximum, which occurred approximately 56 million years ago, marks an iconic example of rapid global warming, during which average surface temperatures rose by 5 to 8 degrees Celsius within a few thousand years. This event caused profound changes in ecosystems and ocean chemistry, making it a natural analog for modern anthropogenic climate change. While prior studies have largely focused on the carbon isotope excursions and ocean acidification that characterize the PETM, the precise sources of the immense volumes of CO₂ that fueled this hyperthermal event have remained contentious. The new findings provide robust geochemical and stratigraphic evidence revealing an extended phase of thermogenic CO₂ release from organic-rich sedimentary rocks well before the onset of the PETM’s peak warming.
The term “thermogenic CO₂” refers to carbon dioxide generated through the thermal decomposition of organic matter in sedimentary basins, often linked to deep burial heating or magmatic intrusions. Unlike biogenic CO₂ produced by microbial respiration or volcanic CO₂ from mantle degassing, thermogenic CO₂ reflects a geologically mediated carbon source intimately connected to sediment lithology and thermal dynamics. Jiang et al. combined cutting-edge isotope geochemistry with sedimentological analyses to trace the origin and timing of CO₂ emissions relative to the warming onset. Their data suggest that escalating heat-driven organic matter breakdown released significant quantities of isotopically distinctive thermogenic CO₂ over several millennia preceding the PETM’s climatic apex.
One of the key methodological breakthroughs enabling this research was the high-resolution sampling of sediment cores spanning the Paleocene-Eocene boundary, coupled with advanced compound-specific isotope ratio mass spectrometry. By analyzing the isotopic signatures of molecular fossils known as biomarkers, the team was able to differentiate thermogenic carbon from marine and terrestrial organic carbon, painting a nuanced picture of carbon cycling dynamics. These biomarker-derived isotope data revealed a marked increase in thermogenic CO₂ input beginning roughly 6,000 years before the PETM peak, gradually intensifying and correlating with subtle shifts in marine sediments indicative of early ocean warming and stratification.
Moreover, the authors contextualize these thermogenic emissions within regional geological frameworks, highlighting the role of tectonic uplift, basin subsidence, and magmatic intrusions in triggering deep heating of organic-rich shales. In particular, the East Greenland sedimentary basin emerges as a critical locus where intrusive igneous bodies intersected with carbon-rich strata, facilitating pyrobitumen formation and consequential CO₂ liberation. The interplay of geodynamics and sedimentary organic content thus emerges as a primary control valve modulating ancient greenhouse gas release, revealing processes that mirror modern anthropogenic destabilization of fossil carbon reservoirs.
In ecological terms, this advance elucidates how preparatory carbon inputs influenced biotic mortality and migrations during the early stages of the PETM. Elevated CO₂ concentrations would have progressively stressed marine and terrestrial life, altering nutrient cycling, ocean oxygen levels, and habitat distributions long before temperatures reached their zenith. This gradual carbon release scenario challenges prior assumptions that PETM warming was driven solely by rapid methane hydrate dissociation or volcanic outgassing, instead underscoring a multi-source, temporally extended carbon input pattern with important ramifications for paleoclimate modeling.
Climate modelers and Earth system scientists have eagerly anticipated such integrative studies to refine carbon cycle feedback parameters under warming conditions. The explicit quantification of thermogenic carbon contributions enables the recalibration of global carbon budget reconstructions during critical hyperthermal intervals. It also provides an analog for evaluating long-term carbon reservoir stability and the lag effects of geothermally mediated CO₂ release, factors that bear directly on forecasts of fossil fuel exploitation and permafrost melting under contemporary warming.
The temporal resolution achieved in this study reveals that the buildup to the PETM was not a sudden carbon pulse but rather the culmination of a prolonged phase of enhanced thermogenic emissions. This revelation invites a reassessment of cause-and-effect relationships between carbon release and temperature increase, potentially revising timelines of climate feedback mechanisms and their thresholds. Notably, the sustained millennial-scale CO₂ release predates the intensification of global temperatures and ocean acidification, implying that carbon emissions may have acted as a precursor or “priming” agent for subsequent environmental transformations.
Intriguingly, the study also provides insights into the isotopic heterogeneity of carbon released during this interval. The thermogenic CO₂ exhibited distinct carbon isotope ratios compared to contemporaneous methane or biogenic sources, allowing the dissection of overlapping carbon inputs in sedimentary records. This analytical capability sharpens the resolution of paleorestorations and supports more nuanced atmospheric reconstruction models. Such isotopic fingerprinting is indispensable for distinguishing natural geological sources from anthropogenic carbon emissions in the modern carbon budget context.
The implications extend beyond academic paleoclimatology by offering valuable lessons for modern climate mitigation strategies. Understanding the mechanisms and timelines controlling thermogenic carbon release highlights the potential vulnerability of deep organic carbon reservoirs to warming and tectonic activity. Contemporary energy extraction practices, including hydraulic fracturing and deep drilling, could exacerbate destabilization of such reservoirs, inadvertently mobilizing previously sequestered carbon. The PETM case thus serves as both a cautionary tale and a predictive analog for assessing anthropogenic impacts on the Earth system.
Additionally, the spatial dimension of thermogenic CO₂ release during the PETM uncovered by Jiang et al. emphasizes the regional variability of carbon source dynamics. Geological heterogeneity in reservoir properties and thermal histories generates complex spatial emission patterns that influence local climate feedbacks and ecosystem responses. This spatial complexity must be incorporated into climate models to improve predictive accuracy for regional warming phenomena and carbon sequestration potential. The study’s multidisciplinary approach combining sedimentology, geochemistry, and tectonics exemplifies the integrative research necessary to tackle these challenges.
The comprehensive dataset curated by the authors also enriches the scientific community’s repository of paleoclimate proxies, enabling cross-comparisons with other hyperthermal events such as the Eocene Thermal Maximum 2 and Oceanic Anoxic Events. Such comparative studies can isolate universal versus event-specific drivers of rapid climate change, further elucidating Earth’s climate sensitivity under different boundary conditions. The PETM’s status as a key geological benchmark will be strengthened through these refined characterizations of carbon flux dynamics.
Furthermore, Jiang and colleagues underline the relevance of sediment-hosted carbon pools as both sources and sinks in the global carbon cycle. Their recognition of feedback loops involving sediment heating, organic carbon maturation, and fluid migration enhances conceptual frameworks describing carbon reservoir stability. These processes occur on timescales that bridge human civilization lifetimes and geological epochs, serving as reminders of the inertia and complexity inherent in Earth system responses to perturbations.
In sum, this seminal research illuminates crucial facets of the Paleocene-Eocene Thermal Maximum’s carbon cycle intricacies, particularly highlighting a previously underappreciated millennial-scale thermogenic CO₂ release phase that set the stage for subsequent global warming. This work not only advances paleoclimate science through novel methodological and conceptual insights but also resonates profoundly with contemporary climate action imperatives. By unlocking these ancient geological secrets, Jiang, Cui, Wang, and their team have provided a vital piece of the climate puzzle, enhancing our ability to predict, mitigate, and adapt to ongoing environmental transformations.
As climate change accelerates in the modern era, lessons from deep time become ever more urgent and instructive. The PETM stands as a natural laboratory revealing the risks of rapid carbon release from sedimentary sources under warming conditions. This study’s revelations emphasize the importance of integrating geological perspectives into climate policy and underscore that Earth’s history holds essential warnings and guidance for humanity’s future. The thermogenic CO₂ release preceding the PETM is a testament to the intricate, multi-mechanistic pathways through which carbon shapes climate, ecosystems, and ultimately the fate of life on Earth.
Subject of Research: Carbon cycle dynamics and thermogenic CO₂ release mechanisms preceding the Paleocene-Eocene Thermal Maximum
Article Title: Millennial-timescale thermogenic CO₂ release preceding the Paleocene-Eocene Thermal Maximum
Article References:
Jiang, S., Cui, Y., Wang, Y. et al. Millennial-timescale thermogenic CO2 release preceding the Paleocene-Eocene Thermal Maximum.
Nat Commun 16, 5375 (2025). https://doi.org/10.1038/s41467-025-60939-3
Image Credits: AI Generated
