Long-term record of atmospheric CO2 and stable isotopic ratios at Waliguan Observatory: Background features and possible drivers, 1991–2002

[1] This paper describes background characteristics of atmospheric CO2 and stable isotopic ratios (δ13C and δ18O) as well as their possible drivers at Waliguan Baseline Observatory (WLG) (36°17′N, 100°54′E, 3816 m above sea level) in the inland plateau of western China. The study is based on observational CO2 data (NOAA Climate Monitoring and Diagnostics Laboratory discrete and WLG continuous measurements) obtained at WLG for the period from May 1991 to December 2002. Over this period the change in monthly means is ∼+16 ppm for CO2, ∼−0.2‰ for δ13C, and ∼−0.5‰ for δ18O. The overall increase of CO2 and subsequent decline of δ13C, with a Δδ13C/ΔCO2 ratio (−0.011 ± 0.105) ‰ ppm−1 at WLG, reflect the persistent worldwide influence of fossil fuel emissions. The negative secular trend of δ18O at WLG is probably due to vigorous 18O exchange with soils in the Northern Hemisphere (NH) and conversion from C3 to C4 plants via land use change. The CO2, δ13C, and δ18O mean annual cycles with peak-to-peak annual amplitudes of ∼10.5 ppm, ∼0.499 ‰, and ∼0.819‰, respectively, at WLG show typical middle-to-high NH continental features that correspond to the seasonal cycle of the terrestrial biosphere. The significant CO2 and δ13C interannual variability at WLG is very likely caused by worldwide climate anomalies and associated regional fluctuation in biospheric CO2 uptake in the Asian inland plateau as well as long-range air mass transport. The results of this study help to provide a basic understanding of the individual sources and sinks of carbon in this area and help us to better address the role of the Asian inland terrestrial biosphere in the global carbon cycle.