Greenhouse gas fluxes at Arctic tundra Ecosystem in winter and thawing period

Tundra ecosystem is thought to be a strong source of greenhouse gases. CO2 and CH4 efflux in the thawing period has been thought to be large amount, however there have been a few studies. In order to reveal the annual budgets of greenhouse gases of tundra ecosystems, continuous flux measurements were carried out from spring over Arctic coastal tundra at Barrow, Alaska. Micrometeorology and CO2 exchange were revealed over snow-covered tundra before and after thawing period. Measurement site point (71°19'14.2"N, 156°37'11.1"W, elevation 3m) was at Central Marsh, where the wet sedge tundra extended to several kilometers. The fetch of the site was more than 0.5 km to most directions except the nearest bank-edge where was 140 m far to northeast. CO2, sensible and latent heat fluxes were determined by eddy correlation method using 3D-sonic anemometer (Kaijo, DA-600) and CO2/H2O fluctuation meter (Advanet, E009a). The sampling rate was 10Hz and continued 27.4 min at 30-min intervals. CH4 flux was determined by flux-gradient approach using a differential type NDIR-CH4 analyzer (Horiba, GA360). The vertical CH4 concentration gradient was measured between two heights of 0.65 & 2.35 m. Positive CO2 flux (0.1-0.2 gCO2 m-2 h-1) of upward efflux from the ecosystem was observed during snow-covered period that was increased extremely with strong wind by blizzard. CO2 efflux during blizzard was in proportion to the square of friction velocity that was sucked out from snow pack layer with drive of snow. CO2 efflux level under low wind speed (friction velocity was less than 0.25 m/s) was lower than 0.09 g m-2 h-1. In clear daytime we could detect the sink CO2 flux at the snow-covered tundra ecosystem even the snow depth was more than 30 cm. The daytime sink CO2 flux (less than -0.1 g m-2 h-1) was synchronized with solar radiation, but became zero level in snow melting period when the tundra surface was flooded without active plant. We could not find huge CO2 release just after snowmelt that was observed at many tundra ecosystems, caused by emission from soil layer as accumulated CO2 in winter season. The flooded water at the site could prevent CO2 diffusion to the air.