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

• Main Authors: Pain, Andrea J., Martin, Jonathan B., Martin, Ellen E., Rahman, Shaily
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Arctic Ocean; Greenland; Ice Sheet
• Online Access: https://doi.org/10.5194/tc-2020-155; https://tc.copernicus.org/preprints/tc-2020-155/

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 (CO 2 ) and methane (CH 4 ) concentrations and δ 13 C values and use geochemical models to evaluate subglacial CH 4 and CO 2 sources and sinks in water discharging from three subglacial outlets of the GrIS in southwest (Isunnguata and Russell Glaciers) and southern Greenland (Kiattut Sermiat). CH 4 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. CO 2 concentrations range from supersaturated at Isunnguata to undersaturated at Kiattut Sermiat. CO 2 is consumed by mineral weathering throughout the melt season at all sites, however differences in the magnitude of subglacial CO 2 sources result in meltwaters that are either sources or sinks of atmospheric CO 2 . The predominant source of CO 2 at Isunnguata is organic matter (OM) remineralization, but Russell and Kiattut Sermiat sites have multiple or heterogeneous subglacial CO 2 sources that maintain atmospheric CO 2 concentrations at Russell but not at Kiattut Sermiat where CO 2 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.