Late Holocene change in South Asian monsoons and their influences on human activities in the southern Tibetan Plateau

Abstract

Prominent and well studied is the South Asian summer monsoon (SASM), but much less is known about changes in South Asian winter monsoon (SAWM). In this study, we analyzed a 3.0-m aeolian sedimentary sequence from the Yarlung Tsangpo Valley in the southern Tibetan Plateau. To establish the sequence chronology, fourteen sediment samples are dated using quartz optically stimulated luminescence dating technique, and five charcoal samples are dated using accelerator mass spectrometry 14C. The frequency-dependent susceptibility in the percentage and redness are used to reflect the SASM, and the recently proposed sorting coefficient of grain size data was used to reflect the SAWM for the past ∼4.5 kyr. Our results suggest an obvious anti-phase relationship between the SASM and SAWM during the late Holocene, and the SASM (SAWM) strengthened (weakened) significantly at ∼2 ka and was the strongest (weakest) at ∼1.3 ka. Such inverse monsoonal behavior may be attributed to the migration of Intertropical Convergence Zone. Moreover, a strong SASM and a weak SAWM could have facilitated human activities in the southern Tibetan Plateau after ∼1.3 ka, resulting in the significantly enhanced dust activity in Yarlung Tsangpo Valley.