Methane concentration in the discharge water and ambient air near the outlet of Glaciers, Alaska Range, 2022-2023

Methane release is considered to be from human activities, Arctic Ocean, and the terrestrial regions such as wetland, lakes, geological seeps in the Arctic although glaciers have not been considered a source of methane emissions. A large amount of methane has been observed at the terminus of large glaciers and ice sheet, associated with methane-saturated meltwater runoff. We observed several glaciers in Alaska and found methane emissions from the runoff water of the small mountain glaciers. The observation periods, which was the beginning of the ablation season for the glacier, were June 12-14, 2022, and June 3-9, 2023. We measured methane and CO2 concentrations in ambient air over the water with a portable gas analyzer G4301 (Picarro, Inc.). Dissolved methane concentrations in runoff water were measured using the method of Morishita et al. (2015). The maximum methane concentration in the ambient air near the runoff water was higher than the background level, and the concentration decreased as the gas analyzer moved away from the tunnel. The dissolved methane concentration in runoff water was saturated. These results suggest that the high concentration methane observed in the ambient air near the glacier terminus was released from the runoff water saturated by methane underneath of the glaciers. This study was supported by ArCSII project (JPMXD1420318865).