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 -: art. no. GB2001

This paper investigates seasonally averaged atmospheric CO2 source or sink signals observed at Waliguan Baseline Observatory (WLG, 36 degrees 17'N, 100 degrees 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 Delta delta(13)C/Delta CO2 due to the seasonality in CO2 and delta(13)C is (-0.050 +/-\ 0.004)% ppm(-1), the mean source/sink isotopic signatures delta(s) (i.e., delta(13)C(s) and delta(18)O(s)) are (-26.159 +/- 1.924)% and (-7.662 +/- 2.113)%, respectively, and the mean atmospheric delta(13)C discrimination delta(dis) (i.e., delta(s) minus delta(bg)) where the delta(bg) is the isotopic value of the background atmosphere was (-18.174 +/- 1.959)% 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, delta(13)C and delta(18)O seasonal cycles at WLG. In addition, atmospheric CO2 and delta(13)C 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 Delta delta(13)C/Delta CO2 discrepancies among sites will be useful to better understand carbon uptake and release especially on the Eurasian continent. The estimated delta s during certain times at each specific site could possibly provide useful information on CO2 fluxes.