Potential NEE Budget and Prediction of Future Emissions under Climate Change in an Arctic Wet Sedge Tundra, Barrow, Alaska .

Abstract:

Arctic ecosystems are critically affected by climate change and also play an important role in the global carbon budget. Presented here is a 14-year study of growing season CO₂ fluxes in an Alaskan wet sedge tundra ecosystem -which is about 2 km south of the Arctic Ocean and is adjacent to the NOAA Climate Monitoring & Diagnostic Laboratory (CMDL)- and the key environmental controls on these fluxes. We have measured net ecosystem exchange of CO₂ (NEE) using the eddy covariance technique from 1998 to 2014 in order to quantify the long-term seasonal and inter-annual variability in the CO₂ budget over this period. The WPL correction and the surface heating correction were applied to all CO₂ flux data from the open-path instrument (Burba et al., 2008). Despite several gaps in measurement years, we found that growing season net CO₂ uptake has significantly increased since the 2000s and that NEE is sensitive to dry conditions in tundra. Our data suggest this increase in CO₂ uptake (larger than -6 µmol m^-2 s^-1) occurred during the initial thawing period and during the June-August growing season. However, there is a decreasing trend in total summer uptake beginning in 2011, continuing until the end of 2014. The mean diurnal pattern for the summer period over the course of 14 years (Figure below), indicates inter-annual variability associated with the key environmental controls on these CO₂ fluxes. Monthly trends in Photosynthetically Active Radiation (PAR), net radiation, relative humidity as well as air temperature and soil temperature have consistently simultaneous effects on the variation in NEE. More significant effect of PAR than temperature on summer NEE had been observed for the first period of this study, however our ANOVA, multiple regression and t-test results showed a stronger effect of temperature than PAR in the recent years assuming that Arctic warming will be greater than average global warming. Also the diurnal pattern shows that the maximum daily carbon uptake occurred from early July to mid-August for most of the years.