Carbon dioxide fluxes in moist and dry arctic tundra during season: Responses to increases in summer temperature and winter snow accumulation

Climate-induced environmental changes are likely to have pronounced impacts on CO2 flux patterns in arctic ecosystems. We initiated a long-term experi ment in 1994 in moist tussock and dry heath tundra in arctic Alaska in whic h we increased summer air temperature (ca. 2 degrees C) and increased winte r snow accumulation (shortening the growing season approximately 4 wk). Dur ing the 1996 snow-free season, we measured ecosystem CO2 flux weekly in ord er to quantify net carbon gain or loss from these systems. Over the duratio n of the snow-free season, both dry heath and moist tussock tundra exhibite d a net loss of carbon to the atmosphere, ranging from 12 to 81 g C m(-2) d epending upon experimental treatment. Elevated summer temperatures accelera ted net CO2 loss rates over ambient temperatures in both deep and ambient s now treatments, and increased the total amount of carbon emitted during the snow-free season by 26 to 38% in ambient snow plots and by 112 to 326% in deep snow plots. Increased snow accumulation had less impact on CO2 flux th an did warming, and snow effects on total carbon loss were not consistent b etween the two temperature regimes. Ecosystem respiration exceeded assimila tion on most sampling dates throughout the season. These data, coupled with winter carbon losses recently demonstrated in the same ecosystems, indicat e that the moist and dry arctic ecosystems we examined are currently net so urces of atmospheric carbon on an annual basis, and that anticipated global warming may increase carbon losses from these systems.