the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Nov 2025
Lacustrine methane release on the Tibetan Plateau as an important driver of Early Miocene global warming
Abstract. The Early Miocene was a key period of significant global warming. While previous studies often attributed this warming to the India-Asia collision and associated volcanism, an alternative mechanism may involve large-scale methane release from organic-rich lake sediments. To test the hypothesis that methane emissions from Tibetan Plateau lakes contributed to Early Miocene warming, we analyzed organic carbon, stable isotopes, and elemental concentrations in samples from the organic-rich Dingqinghu Formation in the Lunpola Basin, central Tibetan Plateau. Our results identify an exceptionally strong positive carbonate carbon isotope excursion (δ13Ccarb up to +13.79 ‰) within the lacustrine deposits. The large carbon isotope difference between carbonate and organic matter (Δ13C > 32 ‰) indicates that methanogenesis, specifically via acetate fermentation, was the dominant microbial process. Extremely low sulfur contents likely suppressed sulfate-driven anaerobic oxidation of methane, facilitating direct methane release to the atmosphere. Furthermore, volcanic activity during this interval was limited, suggesting a negligible role in carbon cycle perturbations. The close temporal correspondence between Early Miocene warming, rising atmospheric CO2, and methane emissions documented on the Tibetan Plateau indicates that methane release from these plateau lakes may have played an important role in driving global warming and increasing contemporary CO2 levels.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-5342', Gerald R. Dickens, 15 Dec 2025
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AC1: 'Reply on RC1', Cheng Yang, 06 Jan 2026
Dear referee:
On behalf of all co-authors, we thank you for the careful review and constructive comments on our manuscript，We appreciate the reviewer's expertise and time invested in evaluating our work. The feedback has significantly improved the manuscript. We have carefully addressed all major concerns, including performing mass balance calculations, adjusting the interpretation to emphasize positive feedback rather than direct driving, adding comparative data from other sites, and substantially revising the writing for clarity. We will revise the manuscript and submit a marked-up version of the manuscript.We believe the revised manuscript now fully addresses the concerns raised and hope it is suitable for publication.
Sincerely, Authors of manuscript number EGUSPHERE-2025-5342.
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AC1: 'Reply on RC1', Cheng Yang, 06 Jan 2026
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RC2: 'Comment on egusphere-2025-5342', Anonymous Referee #2, 26 Jan 2026
In this manuscript, the authors use bulk geochemistry and stable isotopes (carbon, nitrogen) to evaluate methane release from an early Miocene lake on the Tibetan Plateau. The role of the terrestrial methane cycle in amplifying global temperatures during the Miocene is certainly interesting - however, the conclusions that the authors report are not supported by existing datasets. As the study is a single site, it is also unclear whether their findings would be of regional or global importance. This study may be more appropriate in a more specific journal (e.g., Organic Geochemistry)
1) Learning from other paleo-lakes
We know that during other past warm climate intervals that many anoxic lakes have an active and persistent methanotroph population that prevents CH4 escaping into the atmosphere (see seminal papers on Green River formation during early Eocene, for example). Thus, without any supporting evidence for enhanced methanogenesis or changes in methane oxidation (e.g. d13C of bacterial lipids), the overall conclusions are unsupported by the existing data. I would suggest the authors explore whether there are other more direct indicators for methane cycling that can either support or disprove their conclusions.
2) Globally important?
These results are from a single site and its very unlikely that this contributed globally to warming during Miocene. I suggest the authors incorporate data from other nearby sites and confirm that this is likely to be regionally important. Or perhaps look at other early Miocene lakes from around the globe.
3) Lack of references
There are many geochemical ratios used throughout but unsupported by references. e.g. "W(V)/W(V+Ni) ratio indicate deposition under anoxic/reducing conditions" - need to add more detail about the approach and what a high vs low value means...
4) Influence of terrestrial input
The authors argue strongly that terrigenous input is minimal (e.g. L286), but your C/N ratio increases dramatically to ~10-2- during the middle of the section, indicating substantial terrigenous input. Anything over 7 is considered to reflect a mixed source of OC (either soil and/or plant OC). Please re-evaluate these sections.
Other comments:
L68: its much more likely that volcanic CO2 was from other regions anyway – e.g., North Atlantic during early Eocene, or Columbia River Basalts during mid-Miocene.
L95: very uncertain if results from one single formation are globally relevant – or even regionally relevant.
L136: more detail on age model required. How much age is captured in the ~40m section? What is sedimentation rate?
L144: methods in 3.1 read like a lab protocol (e.g. “first grind the 10mg rock samples…”) – write in the past tense
Figure 2: why did you choose to smooth dataset? This approach can be misleading. If you truly want smoothing, use a moving average or something more sophisticated (e.g. smoothing spline/loess regression).
L243: “Influence of modifying factors” - I don’t understand what this means?
L259-260: reference needed to support this statement
L275-276 reference needed to support this statement
L286-287: this is highly unlikely as your C/N ratio increases dramatically during the middle of the section, indicating substantial terrigenous input
L289: The “pronounced “CIE in bulk carbonate is not apparent – there are multiple swings and its unclear why you have defined this as a CIE.
L323: why does the W(V)/W(V+Ni) ratio indicate deposition under anoxic/reducing conditions?
L331: again, this is not true – the C/N ratios vary markedly in the middle of the section up to about 20. Anything above 7 is indicative of at least some soil and/or plant input
L354: why as 2.5g/cm assumed?
L361-363: references needed
L374: reference for why Sr/Cu can be used to assess precipitation
L410-412: there is no evidence to support acetoclastic methanogenesis here. Additional proxy evidence for methane oxidation or methanogenesis is required (e.g. lipid d13C, GDGTs etc).
L463-365: the sulfur content is not included in Table S2, therefore this statement not supported by current evidence
545: “All raw data can be provided by the corresponding authors upon request.” – all data used in study should be provided in supplements.
Citation: https://doi.org/10.5194/egusphere-2025-5342-RC2
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Dear Editor and Authors,
I have read through the manuscript by Yang and colleagues twice.
The work presents some chemistry data generated at a single "section" in western China, and with this information suggests that methane release from ancient lakes on the Tibetan Plateau influenced early Miocene global warmth. The idea is intriguing, although I suspect incorrect given mass balance calculations, which are absent. In any case, there are major flaws in the manuscript that preclude publication. I outline these below.
I have made numerous comments on the first few pages of the submission, but I did not go all the way through in detail, because cursory readings highlight fundamental problems. This present submission should be rejected.
Sincerely,
Gerald Dickens
Professor, Trinity College Dublin
***
Major Issues:
<1> The interesting idea of this manuscript -- methane emissions from large lakes drive climate change -- demands thought but demands serious and accompanying mass balance calculations.
--> This needs to be shown up front. Indeed, it should come in a different paper. From the start, it is not obvious (at least to me) that methane emissions from lakes can DRIVE global climate change. Perhaps, the authors start afresh with a manuscript that explains how this idea is feasible but consider and focus on the intriguing notion of methane emissions from lakes as positive feedback. (Of course, for over 30 years,
methane emissions from the seafloor, peat, permafrost or some combination thereof have been suggested to enhance warming in the past ... and there remain major issues with these much larger carbon reservoirs).
<2> The chemical records shown do not convincingly suggest enhanced methane release, at least relative to other lacustrian sediment sections in the geological record. Moreover, there is no data support for an idea of "large lakes" (plural), because only one set of records from a single poorly documented location is given, and this comes with ambiguous interpretations.
--> The limited data presented so far needs comparison to other records for enhanced methane production (and release).
--> Complimentary records need to be generated, both at the studied location and at multiple sites to support the basics for the given interpretation.
<3> The writing needs major revision, even if the above was addressed.
Some basic and important information is not clearly presented, such as the section of interest, and numerous paragraphs are not constructed very well.
--> I have given some constructive commentary over the first few pages.