Different patterns and origins between northwestern and southeastern Tibetan ice core glaciochemical records over the past century

Abstract

Atmospheric circulation systems differ between the northern and southern Tibetan Plateau (TP) and are characterized by prevailing westerly winds and the Indian monsoon, respectively. This leads to spatial differences between glaciochemical records in the northwestern and southeastern TP. We compared the spatial differences in major soluble ion concentrations (Ca2+, SO42−, NO3−, NH4+, Cl−, Na+, K+, and Mg2+) during the last century in the Aru (northwestern TP) and East Rongbuk (ER; southeastern TP) ice cores. Ca2+ exhibited the largest difference between the ice cores (2371 ppb in the Aru ice core and 65 ppb in the ER ice core), indicating that crustal processes were more dominant in the Aru ice core. NH4+ accounted for 17% of the total ion concentration in the ER ice core but only 3% in the Aru ice core, which may be related to the Indian monsoon traveling over NH3 emission zones in southern Asia. The major soluble ion concentrations exhibited decreasing trends in the Aru ice core but increasing trends in the ER ice core (P < 0.01). Empirical orthogonal function and backward trajectory analyses indicated that the major soluble ions in the Aru ice core originated from crustal sources in central Asia; those in the ER ice core had crustal, anthropogenic, and oceanic sources from southern Asia. The results from the Aru ice core suggest that dust events and enhanced prevailing westerly winds promoted the deposition of dust aerosols from the Taklamakan Desert and arid and semi-arid regions of central Asia. Contrastingly, the results from the ER ice core suggest that the Indian monsoon transported crustal and anthropogenic sources from southern Asia and oceanic sources from the Bay of Bengal and Arabian Sea. This study contributes to the comprehensive understanding of the differences in glaciochemical records and their causes between the northwestern and southeastern TP.