CH4 emission from runoff water of Alaskan mountain glaciers

Abstract Methane (CH 4 ) emissions from runoff water (RW) were observed at the terminus of glaciers in Alaska. The observed CH 4 concentration was three times higher than ambient air and a high level of dissolved CH 4 in RW was also measured. Although CH 4 is relatively well observed as the second most important greenhouse gas, observations in the glacier areas are still rare because the conditions are not considered favorable for CH 4 production. However, recent studies have observed CH 4 -saturated RW and resulting high concentrations of CH 4 in the ambient air at the glacier terminuses of the Greenland Ice Sheet and the ice cap in Iceland. This study shows that similar CH 4 production also occurs in smaller mountain glaciers. We have selected typical mountain glaciers as the study sites: the Castner, Canwell, and Gulkana Glaciers in the Alaska Range, and the Matanuska Glacier in southern Alaska. Ambient CH 4 concentrations at the meltwater outlet, surface CH 4 fluxes, and dissolved CH 4 content in the RW were measured. The results show that some glaciers have high CH 4 concentrations in the RW and in the ambient atmosphere. This is the first case where obvious CH 4 emissions have been detected at the terminus of mountain glaciers. This suggests that CH 4 release at the terminus of glaciers may be a common occurrence and has the potential to affect the global CH 4 budget and climate projections.