Interannual Variability of Summer Net Ecosystem CO2 Exchange in High Arctic Tundra

Arctic terrestrial ecosystems may be contributing to increasing atmospheric carbon dioxide (CO2) concentrations under amplified climate change at high-latitudes. This research investigates how summer net ecosystem CO2 exchange (NEE) and its component fluxes, gross primary production (GPP), and ecosystem respiration (R-eco) varied over five years (2008, 2009, 2010, 2012, and 2014) at the Cape Bounty Arctic Watershed Observatory (74.92 degrees N, 109.58 degrees W). The eddy covariance technique was used to measure NEE and a combined light and temperature response model was used to partition NEE into GPP and R-eco. Total summer NEE varied from -19.8 to 7.9 g C m(-2). Despite two summers with net CO2 uptake, this tundra was likely a source of CO2 on an annual basis. In most years, growing degree days with a base 0 degrees C (GDD(0)) had more predictive power than other environmental variables in random forest analyses of daily NEE. Interannual variability in total summer NEE over the five study years was also attributed to greater variability in GPP than R-eco (coefficient of variation: 62% and 27%, respectively). However, total summer GDD(0) significantly correlated with total summer R-eco but not NEE nor GPP. Instead, summer total NEE and GPP significantly correlated with satellite-derived normalized difference vegetation index (NDVI), which may have exhibited carry-over effects from one year to the next to limit the impact of current year GDD(0) on total summer NEE at this tundra site.