Wintertime CO2 efflux from arctic soils: Implications for annual carbon budgets

Estimates of annual carbon loss from arctic tundra ecosystems are based nea rly entirely on measurements taken during the growing season in part becaus e of methodological limitations but also reflecting the assumption that res piration during winter is near zero. Measurements of CO2 flux during winter , however, indicate significant amounts of carbon loss from tundra ecosyste ms throughout the 240-day nongrowing season. In our study during the 1996 a nd 1997 nongrowing seasons, winter carbon losses ranged from 2.0 g CO2 m(-2 ) season(-1) in moist dwarf shrub communities to 97 g CO2 m(-2) season(-1) in natural season season snowdrift communities, with an average wintertime CO2 efflux of 45 g CO2 m(-2) for all low Arctic tundra communities (0.14 Pg CO2 yr(-1) worldwide). These measurements indicate that current estimates of annual carbon loss from tundra ecosystems are low. Inclusion of winterti me losses of CO2 into annual carbon budgets increases the annual carbon eff lux of arctic tundra ecosystems by 17% and changes some ecosystems from net annual sinks to net sources of CO2 to the atmosphere.