WINTER AND EARLY SPRING CO2 EFFLUX FROM TUNDRA COMMUNITIES OF NORTHERN ALASKA

Carbon dioxide concentrations through snow were measured in different arctic tundra communities on the North Slope of Alaska during winter a nd early spring of 1996. Subnivean CO2 concentrations were always high er than atmospheric CO2. A steady state diffusion model was used to ge nerate conservative estimates of CO2 flow to the atmosphere. The magni tude of CO2 efflux differed with tundra community type, and rates of c arbon release increased from March to May. Winter CO2 efflux was highe st in riparian and snow bed communities and lowest in dry heath, uplan d tussock, and wet sedge communities. Snow generally accrues earlier i n winter and is deeper in riparian and snow bed communities compared w ith other tundra communities, which are typically windswept and do not accumulate much snow during the winter. These results support the hyp othesis that early and deep snow accumulation may insulate microbial p opulations from very cold temperatures, allowing sites with earlier sn ow cover to sustain higher levels of activity throughout winter compar ed to communities that have later developing snow cover. Extrapolating our estimates of CO2 efflux to the entire snow-covered season indicat es that total carbon flux during winter in the Arctic is 13-109 kg CO2 -C ha(-1), depending on the vegetation community type. Wintertime CO2 flux is a potentially important, yet largely overlooked, part of the a nnual carbon cycle of tundra, and carbon release during winter should be accounted for in estimates of annual carbon balance in arctic ecosy stems.