Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last glacial-interglacial cycle

Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last glacial-interglacial cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2-4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period. © 2010 Elsevier Ltd and INQUA