 During the study, the most widespread surface melt on record for the past 120 years was observed in Greenland; on 12 July 2012, unfrozen water was present on almost the entire ice sheet surface (98.6%).The findings indicate that methanotrophs could serve as a biological methane sink in the subglacial ecosystem, and the region was, at least during the sample time, a source of atmospheric methane.Scaled dissolved methane flux during the 4 months of the summer melt season was estimated at 990 Mg CH4.