Long-term record of atmospheric CO2 and stable isotopic ratios at Waliguan Observatory: Seasonally averaged 1991-2002 source/sink signals, and a comparison of 1998-2002 record to the 11 selected sites in the Northern Hemisphere.

[1] This paper investigates seasonally averaged atmospheric CO₂ source or sink signals observed at Waliguan Baseline Observatory (WLG, 36°17′N, 100°54′E, 3816 m asl) in western China from 1991 to 2002. Both linear and geometric mean regressions as well as statistical significance test were performed between detrended CO₂ and stable isotope monthly data by means of Keeling Model and Miller-Tans Model. The estimated slope Δδ¹³C/ΔCO₂ due to the seasonality in CO₂ and δ¹³C is (-0.050 ± 0.004)‰ ppm^-1, the mean source/sink isotopic signatures δ_s (i.e., δ¹³C_s and δ¹⁸O_s) are (-26.159 ± 1.924)‰ and (-7.662 ± 2.113)‰, respectively, and the mean atmospheric δ¹³C discrimination δ_dis (i.e., δ_s minus δ_bg) where the δ_bg is the isotopic value of the background atmosphere was (-18.174 ± l.959)‰ by the Keeling Model, in agreement with results from other continental background sites in the Northern Hemisphere. We suggest that exchange with terrestrial biosphere dominates the observed CO₂, δ¹³C and δ¹⁸O seasonal cycles at WLG. In addition, atmospheric CO₂ and δ¹³C data from 11 selected NH sites in the NOAA ESRL air sampling network from 1998 to 2002 were analyzed and compared to the WLG data for the same period to better address common and specific features observed in this region. The annual cycle amplitude differences, secular and seasonal Δδ¹³C/ΔCO₂ discrepancies among sites will be useful to better understand carbon uptake and release especially on the Eurasian continent. The estimated δ_s during certain times at each specific site could possibly provide useful information on CO₂ fluxes. [ABSTRACT FROM AUTHOR]