DUST ACTIVITY AND WESTERLIES-MONSOON VARIATIONS DURING THE LAST GLACIAL PERIOD RECORDED IN LOESS SEDIMENTS IN LINZHI AREA,SOUTHERN TIBETAN PLATEAU
The Yarlung Zangbo River basin,located in the southern Tibetan Plateau,is an important area for loess distribution.The aeolian loess deposit serves as an excellent archive for studying the dust accumulation process and the coevolution of Westerlies and Indian monsoon systems.This study presents grain size analysis results of a 900 cm loess-paleosol section(KSM:29° 33′28.01″N,94°29′48.59″E;3150 m a.s.l.)developed during the last glacial period at Linzhi area in the middle reaches of the Yarlung Zangbo River.The luminescent dating results(pIRIR)of potassium feldspar from this loess profile indicate ages of 28.2±1.6 ka for the top 75 cm and 83.5±4.5 ka for the bottom 875 cm.This suggests that the loess primarily formed during the last glacial period,with no Holocene deposits present.The deposition rates across the entire section range from 12.1 cm/ka to 20.8 cm/ka,averaging 18.0 cm/ka.We employed a Bayesian age-depth model to establish the geochronological timescale.Using Gen.Weibull parametric end-member modeling,we isolated grain size components sensitive to climate change and dust activity.Then we reconstructed the history of dust activity and westerlies-monsoon variations during the last glacial period.The grain size end-member analysis identified four end-member components(EMs),which were interpreted as reflecting three distinct sedimentary dynamics.EM1(mode particle size of 7.76 μm)represents far-traveled dust transported by the upper-level westerlies and reflects westerly intensity;EM2(mode:21.48 μm)and EM3(mode:38.20 μm)are associated with near-surface winds,indicating short distance suspension of local dust.We contribute the combined content of(EM2+EM3)to reflect the intensity of the Indian winter monsoon(IWM).EM4(mode:78.35 μm)represents the component of strong sandstorms.Overall,dust in the Linzhi area mainly consist of local coarse particle components transported by IWM,as well as a small amount of distant fine particle components transported by the upper-level westerlies.Comparative studies indicate that KSM profile sensitively recorded the regional climate change,IWM and westerlies circulation sensitively respond to changes in mid-latitude summer insolation in the Northern Hemisphere during the last glacial period.When solar insolation decreased,the IWM strengthened,westerlies weakened,dust activity intensified,with less far-traveled dust transported by the westerlies.When solar insolation increased,the IWM weakened,the westerlies strengthened,dust activity diminished,with an increase in far-traveled dust carried by westerly increase.
万方数据
维普
