the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jan 2026
Methane and carbon dioxide dynamics beneath the Greenland Ice Sheet: Insights from ice core basal materials
Abstract. Ice sheets and their subglacial environments may represent an important source of methane (CH4) and carbon dioxide (CO2), potentially contributing to the atmospheric burden of these greenhouse gases. In this study, we investigate CH4 and CO2 production, transport, and consumption at and near the sediment-ice interface beneath the Greenland Ice Sheet, utilizing basal materials from two deep-drilling projects. At the Camp Century site, on the northwestern margin of the Greenland Ice Sheet, vertical gas profiles (N2, O2, Ar, CO2, and CH4), combined with microbial DNA analyses, indicate that CH4 accumulates in subglacial environments either from the release of gases from buried soils and sediments beneath the ice sheet or via in situ methanogenesis. The CH4 then diffuses across the sediment-ice interface and undergoes partial oxidation to CO2 within debris-rich ice layers, contributing to the pronounced CO2 accumulation near the interface. CH4 and CO2 remain at higher concentrations than atmospheric levels for several tens of meters in the upper section of the basal ice sequence, suggesting mechanical mixing possibly during advection from inland. At the GRIP site, located at the summit of the Greenland Ice Sheet, biologically derived CH4 and CO2 in basal materials is transported into the ice predominantly through mechanical mixing processes such as shearing and folding, although diffusion across the sediment-ice interface could also occur in the unsampled bottom section. There is no evidence of CH4 consumption by methanotrophs at GRIP, suggesting that variations of bed conditions, ice dynamics and the nature of the organic material control the fate of CH4 produced in the subglacial environments.
Competing interests: Some authors are members of the editorial board of Climate of the Past for the special issue “The Camp Century ice and sediment core: new science from a 1966 core that touched the base of the Greenland ice sheet (CP/TC inter-journal SI)”.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 17 Mar 2026)
- RC1: 'Comment on egusphere-2025-6204', Anonymous Referee #1, 15 Feb 2026 reply
Data sets
Water isotopic measurements of the basal ice layers of the 1966 Camp Century ice core (Greenland) Lisa Ardoin et al. https://doi.org/10.1594/PANGAEA.983903
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- 1
The interface between ice sheets and bedrock represents a potential "hot spot" for geochemical reactors, and could potentially harbor life forms in one of the most extreme environment on Earth. Yet due to the difficulty in accessing subglacial samples, the (bio)chemical systematics underneath the ice sheet is poorly understood. An alternative approach is by utilizing basal ice right above the bedrock-ice interface and study the gas composition. Lisa Ardoin et al. here presents one such efforts targeting two Greenland ice cores: Camp Century and GRIP. The authors measured the depth profiles of various gases and conducted DNA sequencing to explore possible subglacial biological activities. The conclusion is that Camp Century and GRIP have distinct processes that account for their greenhouse gas profiles. While the basal ice in GRIP is subject to intense mechanical mixing, the methane content in the basal ice in Camp Century more likely results from the upward diffusion of CH4 produced underneath the bedrock-ice interface.
A comparative study like this will help us understand what subglacial bio- and geochemical processes are at play. It is therefore in principle suitable for publication TC. This work is a timely contribution to the Special Issue. However, there are some aspects of the manuscript—mostly concerning its presentation—that needs to be clarified. Although the substantive materials are in good shape already, a minor revision in my view is still needed to improve the clarity.
Most importantly, while the title seems to hint at methane and carbon dioxide, the manuscript is clearly more dedicated to methane production and consumption. Carbon dioxide will be produced by methanotrophy, but other processes could also lead to CO2 production, such as sulphide oxidation and direct organic carbon oxidation coupled with carbonate dissolution and/or silicate weathering. The point is that since there is a whole suite of inorganic geochemical reactions that could modify CO2 (but not necessarily CH4), and the current manuscript doesn't have the necessary measurements to constrain them, perhaps it is more suitable to focus the manuscript on CH4. The accumulation of those potent greenhouse gases underneath ice could become a power positive feedback during deglaciation (e.g. Wadham et al 2008, which the author cites). If true, a large methane reservoir underneath the Greenland Ice Sheet, which the author measures, bears implication for the current warming and glacier retreat. Focusing on CH4 and discussing the implications for future warming will increase the interest of the present study to a broader cryosphere/geoscience community.
Second, the hypothesis of upward diffusion of CH4 is interesting. However, this is indirectly deduced from N2 and Ar. Is it possible to model the methane diffusion directly? Of course the challenge is we don't really know how high the methane concentration is in the soil, but perhaps this is a good opportunity to do the opposite by running a series of sensitivity test. It would be interesting to know the range of CH4 concentration in the basal ice, which may inform the readers the extent of methanogenesis in the ice/soil.
Finally, there are some minor typos/grammatical errors, such as in Line 38 (subglacial and below ice sheets are repetitive) and Line 539 (their and its are repetitive). Please proofread it more thoroughly.