CO2 and CH4 exchanges between moist moss tundra and atmosphere on Kapp Linné, Svalbard

We measured CO2 and CH4 fluxes using chambers and eddy covariance (only CO2) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (9 June–31 August) was negative (sink), with −0.139 ± 0.032 µmol m−2 s−1 corresponding to −11.8 g C m−2 for the whole summer. The cumulated NEE over the whole growing season (day no. 160 to 284) was −2.5 g C m−2. The CH4 flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511 ± 0.000315 µmol m−2 s−1, which corresponds to a growing season estimate of 0.04 to 0.16 g CH4 m−2. Thus, we find that this moss tundra ecosystem is closely in balance with the atmosphere during the growing season when regarding exchanges of CO2 and CH4. The sink of CO2 and the source of CH4 are small in comparison with other tundra ecosystems in the high Arctic. Air temperature, soil moisture and the greenness index contributed significantly to explaining the variation in ecosystem respiration (Reco), while active layer depth, soil moisture and the greenness index were the variables that best explained CH4 emissions. An estimate of temperature sensitivity of Reco and gross primary productivity (GPP) showed that the sensitivity is slightly higher for GPP than for Reco in the interval 0–4.5 ◦C; thereafter, the difference is small up to about 6 ◦C and then begins to rise rapidly for Reco. The consequence of this, for a small increase in air temperature of 1◦ (all other variables assumed unchanged), was that the respiration increased more than photosynthesis turning the small sink into a small source (4.5 g C m−2) during the growing season. Thus, we cannot rule out that the reason why the moss tundra is close to balance today is an effect of the warming that has already taken place in Svalbard