EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Revealing unknown subglacial carbon processes using high frequency gas measurements and stable isotopes

Jesper Riis Christiansen1, Thomas Röckmann2, Elena Popa2, Celia Sapart3, and Christian Juncher Jørgensen4
Jesper Riis Christiansen et al.
  • 1Department of Geoscience and Natural Resource Management, University of Copenhagen, Frederiksberg C, Denmark (
  • 2Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, Netherlands (
  • 3Laboratoire de Glaciologie, Université Libre de Bruxelles, Bruxelles, Belgium (
  • 4Department of Bioscience, Arctic Environment, Aarhus University, Roskilde, Denmark (

Ice sheets and glaciers play an important role for the global carbon cycle through the exchange of their subglacial carbon with the proglacial aquatic environment and the atmosphere in the form of CH4 and CO2. However, the subglacial environment below ice sheets and glaciers is largely inaccessible from the surface and hence we know very little about the carbon turnover processes in these extreme habitats that lead to this carbon export.

Biological CH4 production and oxidation has been found in subglacial sediments across Canada, Antarctica, west Greenland and at the center of the Greenland Ice sheet. This points at a common glacial process for gaseous CH4 and CO2 emissions, but this knowledge is backed by very few direct field observations from two locations in Greenland and one in Iceland. The lack of field based studies is the single most-limiting factor for increasing our understanding of the magnitude and extent of subglacial carbon emission to the atmosphere and its relevance for the global carbon budget.

We present new field measurements suggesting that it is possible to quantify the carbon turnover processes in the subglacial environment using high frequency concentration measurements and stable isotope composition of CH4 and CO2 in gaseous and dissolved form sampled at a subglacial meltwater outlet.

During three field campaigns in the early, mid and late melt season in 2018 and 2019 we measured significantly elevated CH4 and CO2 concentrations in the air and water exiting a subglacial cave system. We devised a field sampling program for retrieval of discrete gas and water samples that allow identification of the original (common) source of the gaseous and dissolved CH4 and CO2 by quantifying the d13C and dH signature of the source.

Our field measurements are amongst the first to directly quantify the emission of CH4 and CO2 to the atmosphere and our isotopic investigations clearly show a biological source of CH4 and its oxidation to CO2 in the subglacial environment and point to a hydrological control on the release of both CH4 and CO2.

These types of data are instrumental to improve the understanding of subglacial carbon processes and design future field investigations to assess its climatic relevance and to narrow the uncertainty of emission estimates.

How to cite: Riis Christiansen, J., Röckmann, T., Popa, E., Sapart, C., and Juncher Jørgensen, C.: Revealing unknown subglacial carbon processes using high frequency gas measurements and stable isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8412,, 2020


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