Interpretation of palaeomonsoon dynamics on the Eastern Tibetan Plateau from a 10 kyr peat record of dust deposition and regional atmospheric model simulations

• Main Author: Ferrat, Marion
• Other Authors: Weiss, Dominik
• Published: Imperial College London 2011
• Subjects: 551.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535459

The Holocene evolution of the Asian monsoon remains poorly constrained due to the lack of information on past wind trajectories and intensities in central Asia. Mineral dust mobilized from aeolian deposits, transported by atmospheric currents and deposited in environmental archives such as peatlands, offers the potential to elucidate past changes in monsoon dynamics. This thesis examines the history of palaeomonsoon circulation in central Asia during the Holocene through the study of the fluxes and sources of dust deposited in a peatland on the eastern Tibetan Plateau, and the use of this record to constrain numerical simulations of dust transport. Different Asian dust sources capable of providing material to the peat deposit were characterized geochemically to establish a framework of provenance tracers for their identification. Rare earth element-based proxies were shown to be effective geochemical tracers to distinguish between them. These proxies were measured in a 9,500 year old peat core from Hongyuan to reconstruct the history of mineral dust deposition in this region. Results suggest that the deposits of northern and northwestern China dominated dust input to the peat throughout the Holocene and particularly during the last 5 kyr, with earlier deposition also governed by high local contributions. All geochemical proxies indicate that the northern sources dominated between 3.1-2.7 and 1.7-0.9 kyr BP, accompanied by a large increase in dust fluxes. These changes are interpreted as a strengthening of the East Asian winter monsoon, in agreement with other studies in the region. Annual fluxes and sources simulated with a regional atmosphere-chemistry/aerosol climate model show good agreement with the geochemical data. These results provide the first uninterrupted interpretation of atmospheric circulation patterns in central Asia during the Holocene and confirm the potential of peatlands as reliable repositories of dust deposition and as high-quality datasets against which regional model simulations can be evaluated.