Wintertime CO2 Emission from Soils of Northeastern Siberia

The emission of C02 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 sq. cm/s. This value was used to estimate the average CO2 flux from soil: 0.26 g C/sq. m/day in December 1989, 0.13 g C/sq. m/day in January 1990 and 0.07 g C/sq. m/day in February 1990. Thus a minimal total of about 13.8 g C/sq. 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 10**15 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.Key words: CO2 flux, Siberian tundra, soil temperature, moisture contentOn 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 cm²/s. Cette valeur a servi à estimer le flux moyen du CO2 provenant du sol: 0,26 g C/m²/jour en décembre 1989, 0,13 g C/m²/jour en janvier 1990 et 0,07 g C/m²/jour en février 1990. Par conséquent, un total minimal d'environ 13,8 g C/m² a été libéré du sol de la toundra au cours des 90 jours allant de décembre à février 1990. En nous servant de l'étude menée précédemment par Kelley et al. (1968) et en supposant que le coefficient minimal de transfert du CO2 s'applique aussi à l'ensemble des zones de toundra et de taïga septentrionale entre septembre et juin, l'émission totale provenant de cette région se monterait à 0,23 x 10**15 g de carbone. La source principale de ce CO2 venait probablement de l'oxydation microbienne de la matière organique contenue dans le sol. Cette assertion est soutenue par l'existence d'une couche de température relativement élevée dans le sol gelé, qui se trouve de 40 à 120 cm de profondeur. La température de cette couche était de 10 à 40 °C plus élevée que l'air ambiant, ou environ de 5 à 10 °C plus élevée que la surface du sol, et sa teneur en eau était aussi plus élevée que les couches adjacentes.Mots clés : flux de CO2, toundra sibérienne, temperature du sol, teneur en ea

Summer CO2 evasion from streams and rivers in the Kolyma River basin, north-east Siberia

Inland water systems are generally supersaturated in carbon dioxide (CO2) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide (pCO2) and gas exchange velocities (k) were measured at a diverse set of streams and rivers to calculate CO2 evasion fluxes. We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO2 emissions. Our results show that small streams are substantial sources of atmospheric CO2 owing to high pCO2 and k, despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO2. Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO2 evasion, accounting for 86% of the total summer CO2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget

Thermokarst Lakes as a Source of Atmospheric CH4 During the Last Deglaciation

Polar ice-core records suggest that an arctic or boreal source was responsible for more than 30% of the large increase in global atmospheric methane (CH4) concentration during deglacial climate warming; however, specific sources of that CH4 are still debated. Here we present an estimate of past CH4 flux during deglaciation from bubbling from thermokarst (thaw) lakes. Based on high rates of CH4 bubbling from contemporary arctic thermokarst lakes, high CH4 production potentials of organic matter from Pleistocene-aged frozen sediments, and estimates of the changing extent of these deposits as thermokarst lakes developed during deglaciation, we find that CH4 bubbling from newly forming thermokarst lakes comprised 33 to 87% of the high-latitude increase in atmospheric methane concentration and, in turn, contributed to the climate warming at the Pleistocene-Holocene transition