Heterogeneous CO 2 and CH 4 content of glacial meltwater from the Greenland Ice Sheet and implications for subglacial carbon processes

• Published in: The Cryosphere
• Main Authors: A. J. Pain, J. B. Martin, E. E. Martin, Å. K. Rennermalm, S. Rahman
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Arctic; Arctic Ocean; Greenland; glacier; Ice Sheet; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-15-1627-2021; https://doaj.org/article/6f7e2e5d0aaa4910b5c98f71e3759bfe

Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for 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. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH 4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH 4 concentrations by up to 50 % during periods of low discharge. CO 2 concentrations range from supersaturated at sub-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 . At the sub-Isunnguata site, the predominant source of CO 2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO 2 sources maintain atmospheric CO 2 concentrations at Russell but not at Kiattut Sermiat, where CO 2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.