Geochemistry of dust aerosol over the Eastern Pamirs

Abstract

The Pamirs are situated in the inner part of the Asian continent, a region which plays a critical role in Asian dust emission and transport. This study measured the elemental composition of atmospheric dust aerosol samples collected during the period between July 2004 and April 2006 at Mt. Muztagata, Eastern Pamirs, at a high-altitude (38°17′N, 75°01′E, 4430 m). The Muztagata aerosol samples show Ca/Al (∼0.7) and Fe/Al (∼0.7) ratios that are distinguishable from those from other sites. The La/Th ratios (averaging 2.30–2.36) and Th/U ratios (averaging 2.75–3.11) indicate typical eolian deposition. The dust aerosol samples have very similar rare earth element (REE) patterns, with relative enrichment of light REE, a slight depletion of heavy REE, and a strongly negative europium anomaly (δEu values averaging 0.65). The Muztagata dust shows homogeneity of composition during the sampling period, with minor variations due to seasonal effects and possible different air mass, suggesting the possibility of a well-mixed atmospheric background dust on a regional scale. The zonal Westerlies dominate and the longitude circulations are relatively very weak for dust transport dynamics in the Pamirs and Tien Shan regions. Our results demonstrate a distinct difference in elemental composition between dust over the Eastern Pamirs and that over Inilchek, Central Tien Shan, indicating that the Asian dust emission regions have great variations in their chemical properties, and provide a better constraint on the climatic impact of Asian dust.