Early Holocene dust activity variation in the southern Tibetan Plateau and its response to solar irradiance

Abstract

The Tibetan Plateau (TP) is an important source for long-range-transported Asian dust, however, the past variation of dust activity in the TP is poorly understood. In this study, we analyzed a ∼ 4.8-m aeolian loess-sand sequence from the Yarlung Tsangpo Valley in the southern TP. A closely spaced sampling strategy was used for optically stimulated luminescence (OSL) dating. With single-aliquot regenerative-dose (SAR) OSL and post-infrared (post-IR) OSL protocols, the medium-grained (38–63 μm) quartz fraction was selected to establish a detailed chronology. The two most popular OSL readers (Lexsyg and Risø) were applied to all samples for equivalent dose measurement, and the corresponding comparison shows very good reproducibility of ages derived from the two independent reader systems. A total of 23 luminescence ages were obtained ranging from 6.7 ± 0.3 ka to 11.6 ± 0.7 ka in stratigraphical order. Aeolian sands accumulated during cold-dry Younger Dryas period, and the overlying loess deposited during Early Holocene. Frequency-dependent susceptibility is used to infer pedogenesis intensity or vegetation cover, and coarse grain size fraction is used to reflect the dust activity frequency during Early Holocene. The reconstructed variation of dust activity frequency in the southern TP shows strong cyclicity of ∼ 1 ka, ∼ 0.7 ka and ∼ 0.5 ka with confidence level of >95%, probably indicating that the regional dust activities on centennial and millennium scales are closely related to the changes of the North-Atlantic Oscillation (NAO) phase as response to solar irradiance forcing.