Holocene Dust Variability Recorded By Alpine Peat Deposits In Altai Mountains, Northern Xinjiang

The Altai Mountains are located in the central of the Eurasian continent, which is climatically affected by the Siberian High and the westerlies. The mountains are surrounded by desert lands with large areas. Thus, the mountains are an ideal area to study variability of aeolian dust over the geological times.Arid central Asia is one of the most important dust sources in the Northern Hemisphere. The variability of environmental changes in dust source areas and in atmospheric circulation patterns are crucial to understand the relationship between atmospheric dust variability and evironments of dust source area.We selected the peat deposits in the Altai Mountains,30 km north to the Altay city. We used the AMS-I4C dating to establish the chronology of the peat deposits. Rare earth elements (REE), trace elements, heavy metal elements, measured by ICP-MS device, were used to investigate the potential source and input processes of eolian dust and the Holocene dust variability. Meanwhile, the development of early Bronze civilization and the influence of human activity on dust variability were discussed.The main conclutions were drawn:(1) The REE contents in the alpine peat is less than the typical eolian deposits (e.g., loess from the Chinese Loess Plateau), but the REE distributional patterns normorlized by the chondrite are similar to those of loess deposits from different sites. The δEu values of the Altay peat deposits are close to those of loess deposits. The elemental characteristics suggest that the mineral debris is mainly inputed by winds.(2) Variations in Mn and Pb from the Altai peat deposits could be used as indicators for changes in atmospheric dust.11.2-6.5 ka BP, atmospheric dust is characterized by a high level, relecting that the capacity for dust transport by winds was strong, and that the source areas may be dry, to a certain extent.6.5～1.4 ka BP, the level of mineral dust of peat deposits declined, indicating that a weaker wind regime and/or a wetter climate may have prevailed in the study area and the dust source areas. There were three peaks of some trace elements during the early to mid Holocene, which might be correlated with the cold events on a large scale. The atmospheric dust increased gradually since 1.4 ka BP. However, the enhanced dust input at 1.4 ka BP may be strongly affected by human activity in the dust source areas.(3)During the late Holocene, the prominent high contents of heavy metal elements (e.g., Cr, Cu, and Ni) occurred from 4.2 to 3.6 ka BP, which could be ascribed to copper mining and metallurgy around the Altay Mountains, suggesting the onset of Bronze civilizations in northern Xinjiang. Increases in heavy metal elements at 1.4 ka BP may be related to the intenstified human activity since Tang Dynasty.