Air-lake exchange of methane during the open water season in Syowa Oasis, East Antarctica

Dissolved methane (DM) concentrations were measured in 17 lakes as part of the operations of the 45th Japanese Antarctic Research Expedition in ice-free rocky areas along the eastern coast of Lützow-Holm Bay (Syowa Oasis) in East Antarctica in the summer of 2003-2004. DM at the surfaces of 14 lakes ranged from the atmospheric equilibrium concentration (about 4 nmol L ^-1 for freshwater) to 385 nmol L^-1. Relatively low DM of less than 50 nmol L^-1 were observed in about 60% of the lakes. Many of the lakes (area fraction of 85%) were supersaturated and are thus sources of methane to the atmosphere. The exchange coefficient was calculated using wind speed data at Syowa Station. Area fraction frequency distributions with four surface DM ranges were applied to all lakes at Syowa Oasis (110 lakes, total lake area of 9 km²). Extrapolation to the whole Syowa Oasis gives an estimate of total emission of about 1 t CH₄ yr^-1. This is the first estimation of methane flux from the surfaces of thawed lakes to the atmosphere in Antarctica. Since a methane efflux of about 2 t CH₄ yr^-1 was estimated in our previous study from frozen bubbles in lake ice, a total amount of 3 t CH₄ yr^-1 would be released to the atmosphere from the lakes during the ice melting season (December-January) at Syowa Oasis.