Variation Of Monsoon Precipitation Since The Last Interglacial Period Revealed By Boron Isotope Proxy Of The Acid-Leachable Phase In Loess-palesol From Southern Loess Plateau

The widely mantled loess deposit has a large thickness in north China and is continuous sediment in Quaternary.It is one of the most ideal geological records of the Asian monsoon variation in the past.Moreover,the loess sediments in Weinan of the southern Chinese Loess Plateau are typical and are well dated.In this study,we accurately determinated the boron concentration and boron isotopic composition of the acid-soluble in loess and palesol from southern Loess Plateau by using the inductively coupled plasma atomic emission spectroscopy(ICP-AES)and the multiple collector-inductively coupled plasma mass spectrometry(MC-ICP-MS)respectively.The boron concentration of the acid-soluble phases of loess-palesol samples in three individual profiles(Yangguo,Dali and Yangguo Reservoir)vary from 0.39 to 3.94 ?g/g and the ?11B values vary in the range from-23.8‰ to +9.5‰.In general,both the mean[B]and ?11B values in paleosol layers are higer than those in loess layers.The dominant sources of the boron in the acid-soluble phases of loess and paleosol sequences are attributed to atmospheric input and weathered silicate rocks.The variation in ?11B values correspond to the magnetic susceptibility,Sr concentration and CaCO3 content in three profiles.In the typical YGSK profile,the higher ?11B correspond to higher magnetic susceptibility,relatively positive organic carbon isotopic composition values,higher acient precipitation and lower Sr concentration,providing the consistent information on the climate and environment.Three most positive ?11B values reflect the warm and humid climate condition associated with the strongest summer monsoon during the last interglaciation and the interglacial stages.of the last glaciation.Therefore,the ?11B can be used as a potential proxy to indicate the intensity of summer monsoon in the southern Loess Plateau,and can be well compared with the known traditional proxies.Fortunately,the forcing mechanism of ?11B value variation related to reconstruction of monsoon precipitation is clearer than thoses proxies.