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Carbon Emissions From the Edge of the Greenland Ice Sheet Reveal Subglacial Processes of Methane and Carbon Dioxide Turnover

2021; Wiley; Volume: 126; Issue: 11 Linguagem: Inglês

10.1029/2021jg006308

2169-8961

Jesper Riis Christiansen, Thomas Röckmann, María Elena Popa, Célia Sapart, Christian Juncher Jørgensen,

Atmospheric and Environmental Gas Dynamics

Abstract Direct gaseous emissions of methane (CH 4 ) and carbon dioxide (CO 2 ) from the subglacial environment under Greenland Ice Sheet (GrIS) were only recently discovered and it is yet to be determined how important it is for the panarctic carbon budget. We measured in situ net gaseous emissions of subglacial CH 4 and CO 2 , dissolved concentrations and isotopic composition of gases ( 13 C and 2 H) at the onset, near maximum, and at the end of the melt season in 2018 and 2019. We found a tight relation between gaseous and dissolved CH 4 and CO 2 , respectively, indicating that degassing from the subglacial meltwater is the main source of these gases in the subglacial air. The diurnal variability of in situ mole fractions of CH 4 and CO 2 in subglacial air was related to meltwater runoff showing that the net emission magnitude is directly related to glacial hydrology. We observed that maximum in situ mole fractions of CH 4 and CO 2 appeared at the onset of the melt season and decreased over the melt season. The isotopic signature of CH 4 in the subglacial air indicated that it likely originated from microbial methanogenesis which remained constant during the season. Isotopic signatures of subglacial CO 2 indicate mixed sources from microbial oxidation of CH 4 , remineralization of sedimentary organic carbon, and possibly influenced by removal of CO 2 by weathering. Our study indicate large emissions of both CO 2 and CH 4 , but continuous studies over entire melt seasons are needed to determine the origin and emission magnitudes and their relation to the glacial dynamics.