Wintertime CO₂ Emission from Soils of Northeastern Siberia

The emission of CO₂‚ from northeastern Siberian soil was estimated for the period December 1989 to February 1990. Concentrations of air CO₂ near the ground and 1 m above the snow cover were measured by an infrared gas analyzer. Fluxes of CO₂ across the snow cover were calculated from the differences of these two values and the predetermined CO₂ transfer coefficients at various flux rates through a layer of snow. Temperature and moisture content of the soil profiles were also observed simultaneously. The average transfer coefficient of CO₂ for packed snow measured in the winter of 1989/90 was about 0.28 cm⁻⁻·S⁻ⁱ. This value was used to estimate the average CO₂ flux from soil: 0.26 g cm⁻⁻·day⁻ⁱ in December 1989, 0.13 C·m⁻⁻·day⁻ⁱ day 1 in January 1990 and 0.07 C·m⁻⁻·day⁻ⁱ in February 1990. Thus a minimal total of about 13.8 g C·m⁻⁻ had been released from the tundra soil during the 90 days from December 1989 to February 1990. Using the study by Kelley et al. (1968) and assuming that the minimal CO₂ transfer coefficient is also applicable for the entire tundra and Northern Taiga zones between September and June, the total emission from this region would amount to 0.23 x 10ⁱ⁵ g of carbon. The main source of this CO₂ probably originated from microbial oxidation of soil organic matter. This assertion is supported by the existence of a relatively warm layer in the frozen soil at 40-120 cm depth. This warm layer was about 10-40°C higher than the ambient air, or about 5-10°C higher than the soil surface, and its moisture content was also higher than the surrounding layers. /// On a évalué l'émission de CO₂ provenant du sol dans le nord-est sibérien, durant la période allant de décembre 1989 à février 1990. On a mesuré les concentrations du CO₂ ambiant près du sol et à 1 m de la couverture de neige, à l'aide d'un analyseur de gaz infrarouge. On a calculé les flux du CO₂ à travers le couvert nival à partir des différences de ces deux valeurs et des coefficients de transfert du CO₂ prédéterminés pour divers taux de flux à travers une couche de neige. On a aussi observé simultanément la température et la teneur en humidité des profils pédologiques. Le coefficient de transfert moyen du CO₂ pour la neige tassée mesuré durant l'hiver de 1989-90 était d'environ 0,28 C·m⁻·S⁻ⁱ. Cette valeur a servi à estimer le flux moyen du CO₂ provenant du sol : 0,26 g C·m⁻⁻·jour⁻ⁱ en décembre 1989, 0.13 C·m⁻⁻·jour⁻ⁱ en janvier 1990 et 0,07 C·m⁻⁻·jour⁻ⁱ en février 1990. Par conséquent, un to