Paleoclimatic Changes Revealed By Luminescence Chronology And Proxy Indexes Of Loess Records In The Northeastern Tibetan Plateau Since The Last Deglaciation

The northeastern Tibetan Plateau?NETP?,located at a climatic transaction of the Westerlies and the East Asia summer monsoon?EASM?.The environmental changes in NETP is highly sensitive to global climate change.A series of Holocene palaeoclimatic records have been obtained from lacustrine cores and from other eolian archives from surrounding area of NETP.However,because of uncertainties regarding the sediment chronologies,the nature of Holocene climatic changes in the region remains unclear and even controversial.Loess deposits,widespread in NETP,is a ideal materials could be applied to paleoclimatical reconstructions.This study presents three loess-paleosol sequences?XY18,RYS17,XN17?from the NETP dated at high-resolution by quartz Optically Stimulated Luminescence?OSL?dating and K-feldspar post-Infrared Infrared Stimulated Luminescence?pIRIR?dating.The reliability of quartz OSL age and K-feldspar pIRIR dating results were monitored by internal checks of luminescence characteristics and comparison of quartz OSL ages and K-feldspar pIRIR ages.Then,the chronology of these loess sequences was reconstructed by Bacon age-depth modelling.In combining proxy records of magnetic susceptibility,grain-size,color and carbonate content,the paleoclimatical change since the last deglacial in NETP was reconstructed.Clustering endmember modeling analysis of grain-size was used to discern the dust events.The constrained atmospheric controls on loess deposition at NETP is clarified by comparing reconstructed precipitation changes at NETP with the records in the EASM,ISM and the Westerlies dominances.The main conclusion is as follows.?1?.The residual dose of pIR₅₀IR₁₇₀ signal of K-feldspar of loess at NETP is varying between 0.2-2.3 Gy,corresponding to ages vary between 0.1-16 ka,which highlight the pIR₅₀IR₁₇₀ signal is well-bleached.Comparison of quartz OSL and K-feldspar pIR₅₀IR₁₇₀ ages indicate that K-feldspar pIR₅₀IR₁₇₀ ages are generally consistent with quartz OSL ages.This indicates K-feldspar pIRIR can be used in dating young samples of NETP.?2?.The studied loess-paleosol sequences in the NETP show that loess accumulated continuously from the last deglaciation to the early Holocene under cold and dry climatic condition,while the late Holocene also cold and accumulate loess or develope weak paleosol.The paleosol is developed in moisture climate condition during the middle Holocene.Deposit hiatus has been observed for loess at Xining basin.?3?.Various loess-paleosol sedimentary sequences in NETP have highly different deposit rate,highlighting the sediment activities are not singularly controlled by climate,but influenced by comprehensive conditions such as the wind,vegetational cover and the distance from the source area.The mass accumulation rates of NETP loess records are varying between 10-100 g/cm²/ka during Holocene.The relative low values of 10-20 g/cm²/ka were observed in the middle Holocene under moisture period,while a high mass accumulation rates were observed in the early and late Holocene under relative dry period.The mass accumulation rates around Riyue Mountains even as high as 150g/cm²/ka at late Holocene.?4?.The climate change of NETP is characterized as the wettest middle Holocene and relatively dry in early and late Holocene.The results of clustering endmember modeling highlight that the coarse grain endmember represented dust storm events are widespread in the early and late Holocene.A very high proportion of fine grain endmember during middle Holocene indicating wettest climate conditions during this period.?5?.The East Asia monsoon dominated climatic changes in NETP in Holocene.A moist paleoenvironmental conditions occurred in the middle Holocene,which has shown a lag to Northern Hemisphere summer insolation.It suggests that high-latitude forcing such as ice volume,greenhouse gases might modulate EASM intensity and NETP climatic changes during Holocene.