Environmental Magnetic And Geochemical Characteristics Of A Late Pleistocene Loess-paleosol Sequence In The Southern Hunshandake Sandy Land

Located in the current northern margin of the East Asia summer monsoon(EASM),the Hunshandake Sandy Land(HSL)is significant for high-resolution paleoclimatic and paleoenvironmental studies,due to the joint influence of the East Asia monsoon and the westerlies and the sensitivity to environmental changes.As a typical climatic transition zone under fragile ecological conditions in northern China,it plays a crucial role in reconstructing regional climatic variability to study the high-resolution paleoclimatic records in this region.Although extensive lakes and eolian sands within and surrounding the HSL provide paleoarchives for retrieving paleoenvironmental variations in the arid and semi-arid eastern Inner Mongolia,some spatial differences in continuity of these terrestrial records exist.Specifically,these records are commonly confined to the last deglaciation,hampering a complete understanding of the exact climatic fluctuations on glacial-interglacial time scales.Recently,we found a complete late Pleistocene loess-paleosol sequence in southern extremity of the HSL(42.40°N,115.71°E).This unique record spanning the last interglacial-glacial cycle,may be the northernmost loess section which has been reported and can remove the potential discrepancies among lakes and eolian sands,providing an excellent opportunity to reconstruct regional climatic variations in the monsoonal margin on glacial-interglacial timescales.Therefore,we carried out detailed rock magnetic,geochemical and diffuse reflectance spectrometer analyses of this loess-paleosol sequence.Our combined mineral magnetic and geochemical results come to four conclusions as follows.1)We construct the depth-age model based on linear interpolation of three optically stimulated luminescence(OSL)dates and detailed correlations between the variations of our Rb/Sr ratio,a faithful proxy of EASM strength,with the LR04 benthic ?180 stack.This compelling land-ocean resemblance suggests that the sedimentation of the Beigou loess commenced since the last interglacial.2)During the last glacial,the commonly-used concentration dependent magnetic parameters(e.g.,?,SIRM and Ms),which have been successfully adopted to denote pedogenesis and EASM variations,show variations that are less correlative with loess records from the CLP,reflecting a strong control of winter vigor on magnetic signals dominated by lithological ferrimagnetic minerals.3)We found that during the last interglacial the front of the EASM can extend to middle-eastern Inner Mongolia,consistent with modern observations of climate change.The climatic conditions during the last interglacial-glacial transition are characterized by gradual retreat of EASM but stepwise propagation of EAWM,indicating an anti-phased pattern of EASM and EAWM during this climatic transition.In addition,Rb/Sr and Ba/Sr records exhibit broad comparability with summer precipitation variations and the grain size record from the western Chinese Loess Plateau(CLP),Chinese speleothem ?180 record,the ice-core 8180 record in Greenland,and the northern hemisphere summer insolation,demonstrating that eolian deposits in the southern HSL have a good potential for recording sub-orbital EASM variations as well as several millennial-scale cooling events,regardless of limited sedimentation rates.4)The geochemical characteristics of Beigou section define a lower degree of chemical weathering than CLP sections.Nevertheless,the commonly-used geochemical proxies of loess deposits from main body of CLP seem to faithfully trace weak chemical weathering processes and fine-scale monsoon oscillations especially during the last glacial.We attribute this complex magnetic record to a threshold response to the East Asian monsoon variations in eastern Inner Mongolia.