We present a first analysis of data (June 1998 to December 2000) from the long-term eddy covariance site established in a Pinus sylvestris stand near Zotino in central Siberia as part of the EUROSIBERIAN CARBONFLUX project. As well as examining seasonal patterns in net ecosystem exchange (N E), daily, seasonal and annual estimates of the canopy photosynthesis (or gross primary productivity, G P) were obtained using N E and ecosystem respiration measurements. Although the forest was a small (but significant) source of CO 2 throughout the snow season (typically mid-October to early May) there was a rapid commencement of photosynthetic capacity shortly following the commencement of above-zero air temperatures in spring: in 1999 the forest went from a quiescent state to significant photosynthetic activity in only a few days. Nevertheless, canopy photosynthetic capacity was observed to continue to increase slowly throughout the summer months for both 1999 and 2000, reaching a maximum capacity in early August. During September there was a marked decline in canopy photosynthesis which was only partially attributable to less favourable environmental conditions. This suggests a reduction in canopy photosynthetic capacity in autumn, perhaps associated with the cold hardening process. For individual time periods the canopy photosynthetic rate was mostly dependent upon incoming photon irradiance. However, reductions in both canopy conductance and overall photosynthetic rate in response to high canopy-to-air vapour differences were clearly evident on hot dry days. The relationship between canopy conductance and photosynthesis was examined using Cowan's notion of optimality in which stomata serve to maximise the marginal evaporative cost of plant carbon gain. The associated Lagrangian multiplier (λ) was surprisingly constant throughout the growing season. Somewhat remarkably, however, its value was markedly different between years, being 416 mol mol −1 in 1999 but 815 mol mol −1 in 2000. Overall the forest was a substantial sink for CO 2 in both 1999 and 2000: around 13 mol C m −2 a −1. Data from this experiment, when combined with estimates of net primary productivity from biomass sampling suggest that about 20% of this sink was associated with increasing plant biomass and about 80% with an increase in the litter and soil organic carbon pools. This high implied rate of carbon accumulation in the litter soil organic matter pool seems unsustainable in the long term and is hard to explain on the basis of current knowledge.

We present a first analysis of data (June 1998 to December 2000) from the long‐term eddy covariance site established in a Pinus sylvestris stand near Zotino in central Siberia as part of the EUROSIBERIAN CARBONFLUX project. As well as examining seasonal patterns in net ecosystem exchange (NE), daily, seasonal and annual estimates of the canopy photosynthesis (or gross primary productivity, GP) were obtained using NE and ecosystem respiration measurements. Although the forest was a small (but significant) source of CO2 throughout the snow season (typically mid‐October to early May) there was a rapid commencement of photosynthetic capacity shortly following the commencement of above‐zero air temperatures in spring: in 1999 the forest went from a quiescent state to significant photosynthetic activity in only a few days. Nevertheless, canopy photosynthetic capacity was observed to continue to increase slowly throughout the summer months for both 1999 and 2000, reaching a maximum capacity in early August. During September there was a marked decline in canopy photosynthesis which was only partially attributable to less favourable environmental conditions. This suggests a reduction in canopy photosynthetic capacity in autumn, perhaps associated with the cold hardening process. For individual time periods the canopy photosynthetic rate was mostly dependent upon incoming photon irradiance. However, reductions in both canopy conductance and overall photosynthetic rate in response to high canopy‐to‐air vapour differences were clearly evident on hot dry days. The relationship between canopy conductance and photosynthesis was examined using Cowan's notion of optimality in which stomata serve to maximise the marginal evaporative cost of plant carbon gain. The associated Lagrangian multiplier (λ) was surprisingly constant throughout the growing season. Somewhat remarkably, however, its value was markedly different between years, being 416 mol mol−1 in 1999 but 815 mol mol−1 in 2000. Overall the forest was a substantial sink for CO2 in both 1999 and 2000: around 13 mol C m−2 a−1. Data from this experiment, when combined with estimates of net primary productivity from biomass sampling suggest that about 20% of this sink was associated with increasing plant biomass and about 80% with an increase in the litter and soil organic carbon pools. This high implied rate of carbon accumulation in the litter soil organic matter pool seems unsustainable in the long term and is hard to explain on the basis of current knowledge.

Using light aircraft and at intervals of approximately 14 days, vertical profiles of temperature, humidity, CO 2 concentration and 13 C/ 12 C and 18 O/ 16 O ratio, as well as concentrations of CH 4 , CO, H 2 and N 2 O, from about 80 to 3000 m above ground level have been determined for the atmosphere above a flux measurement tower located near the village of Zotino in central Siberia (60 • 45 N, 89 • 23 E). As well as being determined from flask measurements (typically at heights of 100, 500, 1000, 1500, 2000, 2500 and 3000 m) continuous CO 2 concentration profiles at 1 Hz have also been obtained using an infrared gas analyser. This measurement program is ongoing and has been in existence since July 1998. Data to November 2000 are presented and show a seasonal cycle for CO 2 concentration of about 25 µmol mol −1 within the atmospheric boundary layer (ABL) and about 15 µmol mol −1 in the free troposphere. Marked seasonal cycles in the isotopic compositions of CO 2 are also observed, with that of oxygen-18 in CO 2 being unusual: always being depleted in the ABL with respect to the free troposphere above. This is irrespective of whether the CO 2 concentration is higher or lower in the free troposphere. We interpret this as indicating a net negative discrimination being associated with the net terrestrial carbon exchange, irrespective of whether photosynthesis or respiration dominates the net carbon flux in this region. During winter flights, large fluctuations in CO 2 concentration with height are often observed both within and above the stable ABL. Usually (but not always) these variations in CO 2 concentrations are associated with more or less stoichiometrically constant variations in CO and CH 4 concentrations. We interpret this as reflecting the frequent transport of polluted air from Europe with very little vertical mixing having occurred, despite the large horizontal distances traversed. This notion is supported by back-trajectory analyses. Vertical profiles of CO 2 concentration with supplementary flask measurements allow more information on the structure and composition of an air mass to be obtained than is the case for flask measurements or for ground-based measurements only. In particular, our data question the notion that there is usually anything like "well mixed background air" in the mid-to-high northern latitudes during the winter months.

Using light aircraft and at intervals of approximately 14 days, vertical profiles of temperature, humidity, CO2 concentration and 13C/12C and 18O/16O ratio, as well as concentrations of CH4, CO, H2 and N2O, from about 80 to 3000 m above ground level have been determined for the atmosphere above a flux measurement tower located near the village of Zotino in central Siberia (60°45′N, 89°23′E). As well as being determined from flask measurements (typically at heights of 100, 500, 1000, 1500, 2000, 2500 and 3000 m) continuous CO2 concentration profiles at 1 Hz have also been obtained using an infrared gas analyser. This measurement program is ongoing and has been in existence since July 1998. Data to November 2000 are presented and show a seasonal cycle for CO2 concentration of about 25 μmol mol−1 within the atmospheric boundary layer (ABL) and about 15 μmol mol−1 in the free troposphere. Marked seasonal cycles in the isotopic compositions of CO2 are also observed, with that of oxygen‐18 in CO2 being unusual: always being depleted in the ABL with respect to the free troposphere above. This is irrespective of whether the CO2 concentration is higher or lower in the free troposphere. We interpret this as indicating a net negative discrimination being associated with the net terrestrial carbon exchange, irrespective of whether photosynthesis or respiration dominates the net carbon flux in this region. During winter flights, large fluctuations in CO2 concentration with height are often observed both within and above the stable ABL. Usually (but not always) these variations in CO2 concentrations are associated with more or less stoichiometrically constant variations in CO and CH4 concentrations. We interpret this as reflecting the frequent transport of polluted air from Europe with very little vertical mixing having occurred, despite the large horizontal distances traversed. This notion is supported by back‐trajectory analyses. Vertical profiles of CO2 concentration with supplementary flask measurements allow more information on the structure and composition of an air mass to be obtained than is the case for flask measurements or for ground‐based measurements only. In particular, our data question the notion that there is usually anything like “well mixed background air” in the mid‐to‐high northern latitudes during the winter months.

The integrating properties of the atmospheric boundary layer allow the influence of surface exchange processes on the atmosphere to be quantified and estimates of large-scale fluxes of trace gases and plant isotopic discrimination to be made. Five flights were undertaken over two days in and above the convective boundary layer (CBL) in a vegetated region in central Siberia. Vertical profiles of CO 2 and H 2 O concentrations, temperature and pressure were obtained during each flight. Air flask samples were taken at various heights for carbon and oxygen isotopic analysis of CO 2 . Two CBL budget methods were compared to estimate regional surface fluxes of CO 2 and plant isotopic discrimination against 13 CO 2 and C 18 O 16 O. Flux estimates were compared to ground-based eddy covariance measurements. The fluxes obtained for CO 2 using the first method agreed to within 10% of fluxes measured in the forest at the study site by eddy covariance. Those obtained from the second method agreed to within 35% when a correction was applied for air loss out of the integrating column and for subsidence. The values for 13 C discrimination were within the range expected from knowledge of C 3 plant discriminations during photosynthesis, while the inferred 18 O discrimination varied considerably over the two-day period. This variation may in part be explained by the enrichment of chloroplast water during the day due to evaporation from an initial signature in the morning close to source water. Additional potential complications arising from the heterogeneous nature of the landscape are discussed.