A 47-year high resolution chemistry record of atmospheric environment change from the Laohugou Glacier No. 12, north slope of Qilian Mountains, China

Abstract

Based on a 20.12 m shallow ice core drilled at the Laohugou Glacier No. 12 (39°25.7′N, 96°33.4′E, 5040 m a.s.l.), north slope of Qilian Mountains in the northeastern Qinghai–Tibetan Plateau in June 2006, the changes of atmospheric environment over the Qilian Mountains and northwestern China recorded by ice chemistry and its possible connection with atmospheric circulation and the winter North Atlantic Oscillation (NAO) are investigated. A total of 606 samples were analyzed for major ions (Ca2+, Na+, K+, Mg2+, NH4+, Cl−, SO42− and NO3−) and stable oxygen isotope ratios (δ18O). The ion chemistry of the ice core, covering the past 47 years, is mainly characterized by mineral dust species (Ca2+, Na+, Mg2+, SO42−, Cl− and K+), and anthropogenic species (SO42−, NH4+ and NO3−). Ca2+ is the dominant cation in the ice core with a medium value of 2815.5 μeq L−1, accounting for 65.8% of the total cations, and SO42− is the predominant anion with a medium value of 1500.4 μeq L−1, accounting for 45.8% of the total anions. Compared with ice core records from Altai and Himalayas, at the northern and southern margin of western China, respectively, dust-related species concentrations in the Laohugou ice core are much higher due to pronounced regional crustal dust aerosol inputs from surrounding arid and semiarid deserts. The results show that dust species concentrations decreased during 1960–2006 A.D., while non-dust species (SO42−, NH4+ and NO3−, anthropogenic species) concentrations increased, which indicating that the ice core record of dust storm activity over Qilian Mountains exhibits a significant decreasing trend during the past 47 years. This change of dust species may be caused by decrease in wind speed and increase in precipitation over the Laohugou surrounding areas in Qilian Mountains and northwestern China, and wind speed decrease is probably caused by spatial differences of inter-decadal air temperature change of the 600 hPa in central Asia. The normalized time series of the winter NAO index shows a significant inverse correlation with the annual flux of Ca2+ in dust, implying a possible connection between the winter NAO and the dust storm activity over the Qilian Mountains.