Trends in CO₂ exchange in a high Arctic tundra heath, 2000–2010

Abstract

We have measured the land‐atmosphere CO 2 exchange using the eddy covariance technique in a high Arctic tundra heath in northeast Greenland (Zackenberg). On the basis of 11 years of measurements (2000–2010), it was found that snow cover dynamics was important for the CO 2 exchange. The start of CO 2 uptake period correlated significantly with timing of snowmelt. Furthermore, for years with deep and long‐lasting snowpacks, the following springs showed increased CO 2 emission rates. In the first part of the study period, there was an increase of approximately 8 g C m −2 yr −1 in both accumulated gross primary production (GPP) and CO 2 sink strength during summer. However, in the last few years, there were no significant changes in GPP, whereas ecosystem respiration (R eco ) increased (8.5 g C m −2 yr −1 ) and ecosystem CO 2 sink strength weakened (−4.1 g C m −2 yr −1 ). It was found that temperature and temperature‐related variables (maximum thaw depth and growing degree days) controlled the interannual variation in CO 2 exchange. However, while R eco showed a steady increase with temperature (5.8 g C m −2 °C −1 ), the initial increase in GPP with temperature leveled off at the high end of observed temperature range. This suggests that future increases in temperature will weaken the ecosystem CO 2 sink strength or even turn it into a CO 2 source, depending on possible changes in vegetation structure and functioning as a response to a changing climate. If this trend is applicable also to other Arctic ecosystems, it will have implications for our current understanding of Arctic ecosystems dynamics.