First observation of direct methane emission to the atmosphere from the subglacial domain of the Greenland Ice Sheet.

During a 2016 field expedition to the West Greenland Ice Sheet, a striking observation of significantly elevated CH4 concentrations of up to 15 times the background atmospheric concentration were measured directly in the air expelled with meltwater at a subglacial discharge point from the Greenland Ice Sheet. The range of hourly subglacial CH4 flux rate through the discharge point was estimated to be 3.1 to 134 g CH4 hr-1. These measurements are the first observations of direct emissions of CH4 from the subglacial environment under the Greenlandic Ice Sheet to the atmosphere and indicate a novel emission pathway of CH4 that is currently a non-quantified component of the Arctic CH4 budget.