Stable Isotope Ratios of Hydrogen and Oxygen in Event-based Precipitation at Linze, the Hexi Corridor, Northwestern China

The stable isotope ratios of single precipitation events were investigated during the period June 2008 to August 2012 at Linze, which is located in the Hexi Corridor and adjacent to the northern Tibetan Plateau. The local meteoric water line (LMWL) for Linze, δ2H = 8.270δ18O + 6.215 (r2 = 0.954, n = 45), was derived using amount-weighted monthly average δ2H and δ18O values to be consistent with International Atomic Energy Agency (IAEA) established practice. The correlation equation between δ2H and δ18O values from individual samples was found to be δ2H = 8.053δ18O + 2.535 (r2 = 0.944, n = 165), which is different from the LMWL, exhibiting lower slope value and intercept value. The δ18O temperature dependences at Linze was 0.514‰/oC, smaller than the global values based on monthly average temperature. No marked amount effect was found in this study. These isotopic characteristics of precipitation may be attributed to the incorporation of inland recycled moisture into clouds and secondary evaporation during precipitations. Clear seasonal trends were identified in both oxygen isotope ratios and the deuterium-excess, and these were ascribed to the intraannual variation of moisture transport to this region. The deuterium-excess values were high in summer and autumn, when moisture was derived from westerly transport. The deuterium-excess values were low during the cold and dry periods, when moisture originated from the humid ocean surface. This finding reveals that the air mass from the westerly transport dominates the precipitation in the Hexi Corridor, while the southwest monsoon contributes little to the annual precipitation because it is blocked by Tibetan Plateau. Our data also suggest that the moisture derived from local evapotranspiration may contribute greatly to the precipitation.