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

Abstract

[1] 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)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(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 À2 yr À1 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 À2 yr À1) and ecosystem CO 2 sink strength weakened (À4.1 g C m). 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 À2 C À1 ), 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.

Monitoring the Multi-Year Carbon Balance of a Subarctic Palsa Mire with Micrometeorological Techniques

“…3; Table 1). Possibly as a consequence, a relationship between date of snow melt and accumulated growing season carbon flux could not be as clearly established as otherwise documented for other high northern ecosystems (Aurela et al 2004;Grøndahl et al 2008;Lund et al 2012). Other sites in the circumpolar North has also failed to show this clear relationship between date of snow melt and growing season uptake (Humphreys and Lafleur 2011;Parmentier et al 2011).…”

Exchange of CO<sub>2</sub> in Arctic tundra: impacts of meteorological variations and biological disturbance

“…Once the snow melts, the growing season (i.e. the part of the year when the weather conditions allow plant growth) has been reported as the most relevant period defining both spatial (Lund et al, 2010;Mbufong et al, 2014) and temporal (Aurela et al, 2004;Groendahl et al, 2007;Lund et al, 2012) CO 2 variability. The EC measurements were conducted at the EddyFen station (Fig.…”

“…Moreover, GPP and R eco estimates can be calculated in different ways. Some algorithms fit an instantaneous temperature-respiration curve to night-time data to calculate R eco and estimate GPP Reichstein et al, 2005); others calculate R eco from a light-response curve (Gilmanov et al, 2003;Lindroth et al, 2007;Lund et al, 2012;Mbufong et al, 2014;Runkle et al, 2013). Unfortunately, different interpretations of the flux gap filling and partitioning lead to different estimates of NEE, GPP and R eco as well as undefined uncertainties.…”

“…In recent decades, eddy covariance has become a fundamental method for carbon flux measurements at the landscape scale Lund et al, 2012;Reichstein et al, 2005). Eddy covariance measurements of landatmosphere fluxes or net ecosystem exchange (NEE), of CO 2 can be gap-filled and subsequently separated into the modulating components of GPP and R eco using flux partitioning algorithms (Reichstein et al, 2005).…”

Two years with extreme and little snowfall: effects on energy partitioning and surface energy exchange in a high-Arctic tundra ecosystem

“…To ensure that the eddy covariance measurements capture all scales of mixed-layer turbulence, cospectral analysis (Wyngaard and Cote, 1972) between the vertical wind velocity and turbulent energy flux was performed at both study locations. Data processing for both study locations is further summarized in Soegaard et al (2001) and Lund et al (2012Lund et al ( , 2014.…”