CH4 emission from runoff water of Alaskan mountain glaciers

Abstract

Abstract Methane (CH4) emissions from runoff water (RW) were observed at the terminus of glaciers in Alaska. The observed CH4 concentration was three times higher than ambient air and a high level of dissolved CH4 in RW was also measured. Although CH4 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 CH4 production. However, recent studies have observed CH4-saturated RW and resulting high concentrations of CH4 in the ambient air at the glacier terminuses of the Greenland Ice Sheet and the ice cap in Iceland. This study shows that similar CH4 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 CH4 concentrations at the meltwater outlet, surface CH4 fluxes, and dissolved CH4 content in the RW were measured. The results show that some glaciers have high CH4 concentrations in the RW and in the ambient atmosphere. This is the first case where obvious CH4 emissions have been detected at the terminus of mountain glaciers. This suggests that CH4 release at the terminus of glaciers may be a common occurrence and has the potential to affect the global CH4 budget and climate projections.