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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Short summary
The greenhouse gases (GHG) methane and carbon dioxide can be produced or consumed by geochemical processes under the Greenland Ice Sheet (GrIS). Chemical signatures and concentrations of GHG in GrIS discharge show that organic matter remineralization produces GHGs in some locations, but mineral weathering dominates and consumes CO2 in other locations. Local processes will therefore determine whether melting of the GrIS is a positive or negative feedback on climate change driven by GHG forcing.
Preprints
https://doi.org/10.5194/tc-2020-155
https://doi.org/10.5194/tc-2020-155

  03 Jul 2020

03 Jul 2020

Review status: a revised version of this preprint is currently under review for the journal TC.

Heterogenous CO2 and CH4 content of glacial meltwater of the Greenland Ice Sheet and implications for subglacial carbon processes

Andrea J. Pain1,a, Jonathan B. Martin1, Ellen E. Martin1, and Shaily Rahman1,b Andrea J. Pain et al.
  • 1University of Florida, Department of Geological Sciences, Gainesville, FL 32611
  • anow at: University of Maryland Center for Environmental Science, Horn Point Lab, Cambridge, MD 21613
  • bnow at: University of Southern Mississippi, Department of Marine Science, Stennis Space Center, MS 39529

Abstract. Accelerated melting of the Greenland Ice Sheet (GrIS) has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of GrIS meltwater on Arctic greenhouse gas (GHG) budgets. We measured carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks in water discharging from three subglacial outlets of the GrIS in southwest (Isunnguata and Russell Glaciers) and southern Greenland (Kiattut Sermiat). CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat, but are supersaturated at southwest sites, even though oxidation reduces concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites, however differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. The predominant source of CO2 at Isunnguata is organic matter (OM) remineralization, but Russell and Kiattut Sermiat sites have multiple or heterogeneous subglacial CO2 sources that maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat where CO2 is undersaturated. These results highlight the variability in GHG dynamics under the GrIS. Constraining this variability will improve our understanding of the impact of GrIS melt on Arctic GHG budgets, as well as the role of continental ice sheets in GHG variations over glacial-interglacial timescales.

Andrea J. Pain et al.

 
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Andrea J. Pain et al.

Data sets

Hydrogeochemistry of Greenlandic proglacial and nonglacial streams, 2017-2018 A. Pain, J. Martin, E. Martin, and S. Rahman https://doi.org/10.18739/A2F76672G

Andrea J. Pain et al.

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Short summary
The greenhouse gases (GHG) methane and carbon dioxide can be produced or consumed by geochemical processes under the Greenland Ice Sheet (GrIS). Chemical signatures and concentrations of GHG in GrIS discharge show that organic matter remineralization produces GHGs in some locations, but mineral weathering dominates and consumes CO2 in other locations. Local processes will therefore determine whether melting of the GrIS is a positive or negative feedback on climate change driven by GHG forcing.
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