Cosmogenic^(10)Be dating of the oldest moraine in the Hengduan Mountains

The Hengduan Mountains is in the transitional zone between the Qinghai-Tibet Plateau(QTP)and the YunnanGuizhou Plateau in China,and a key area for elucidating the Quaternary environmental changes in Asia.The paleo-Daocheng ice cap was located on the Shaluli Hilly Plateau in the northeastern Hengduan Mountains,the oldest moraines in the Hengduan Mountains region were found in the ice cap area.Such glacial landforms provide key evidence to study the timing when this area entered the cryosphere with the uplift of the QTP.However,it is difficult to collect suitable glacial boulders from these moraines for traditional terrestrial in-situ cosmogenic nuclide(TCN)exposure dating because of long-term severe moraine degradation.Here,we collected clast samples from the moraine surface and depth profile to constrain the age of the oldest moraine in Kuzhaori(moraine E)using TCN^(10)Be dating technique.The minimum^(10)Be ages of five clast samples from the moraine surface range from 187.4±1.5 to 576.8±4.3 ka,implying that the moraine has been seriously degraded since deposition.Based on the TCN^(10)Be concentrations of the samples from a depth profile and simulations,the exposure-erosion-inheritance history of the profile was obtained.By fitting to the profile^(10)Be concentrations using the chi-square test,the simulations yielded a reliable age of 626.0±52.5 ka for the moraine.Therefore,the oldest moraine(moraine E)in Kuzhaori was most likely formed at about 0.63Ma ago,corresponding to the marine isotope stage(MIS)16.This glaciation represents the maximum Quaternary glaciation after the QTP was elevated into the cryosphere by the Kunlun-Yellow River Tectonic Movement.

Ice-volume and insolation influences on hydroclimate changes in central eastern China during the antepenultimate glacial period

The rainfall changes in East Asian summer monsoon(EASM)regions on the orbital timescale remain controversial due to the lack of reliable rainfall records.Here,we present new multiproxy records(δ^(18)O,δ^(13)C,Sr/Ca and Mg/Ca)of a230Thdated stalagmite from Hulu Cave in central eastern China.Multiproxy records reconstruct a regional hydroclimate history from 340 to 261 kyr BP(thousand years before present),approximately covering the antepenultimate glacial period.Theδ^(18)O record is dominated by the precessional cycles,suggesting that EASM responds to changes in Northern Hemisphere summer insolation(NHSI)on the orbital timescale.Significant correlations amongst theδ^(13)C,Sr/Ca and Mg/Ca suggest that a common factor,i.e.,the local hydrological cycle,controlled their variability,and their leading principal component can be used as a proxy linked to regional rainfall.This composite record bears a good similarity to those from the Chinese Loess Plateau,showing a gradually decreasing rainfall during the antepenultimate glacial period,consistent with changes in global ice volume.Superimposed on the long-term trend,three relative wetter intervals were responding to the higher NHSI periods,suggesting that EASM rainfall variability was induced by integrated effects of global ice volume and NHSI.The increased ice sheets and lower NHSI resulted in an increased meridional temperature gradient and southward shift of the westerlies,which shortened the duration of Meiyu and midsummer rainfall.The differences between the rainfall record and the stalagmiteδ^(18)O record indicate that the latter represents the overall EASM intensity linked to monsoon circulation,but does not directly reflect the rainfall changes at the cave sites.

MC-ICP-MS铀同位素的高精度法拉第杯静态分析

铀同位素是地球和环境等科学领域的重要研究工具,然而铀同位素极大的丰度差异一直是高精度测试分析的难题.近年来质谱分析仪器公司推出的10^(13)Ω高阻信号放大器显著提高了信噪比,适用于测试低丰度的^(234)U.组合使用10^(11)、10^(12)和10^(13)Ω的高阻信号放大器可实现多接收器电感耦合等离子体质谱(Multiple Collector Inductively Coupled Plasma Mass Spectrometry,MC-ICP-MS)的铀同位素静态分析,即用10^(13)Ω高阻放大器的法拉第杯接收^(234)U,10^(12)Ω的法拉第杯接收^(233)U和^(236)U,以及10^(11)Ω的法拉第杯接收^(235)U和^(238)U.MC-ICP-MS静态测试^(234)U/^(238)U和^(238)U/^(235)U比值的主要校正因子包括法拉第杯的基线、放大器相对增益、仪器本底、^(238)U拖尾、铀氢化物干扰以及质量歧视等.组合使用这3种放大器多次重复测试了国际标准物质HU-1和SRM950a,以及国内标准物质GBW04412和GBW04428的铀同位素组成.新方法的测试结果与国内外已发表的测试数据高度一致,验证了新方法的可靠性.实验表明,新的MC-ICP-MS铀同位素法拉第杯静态分析方法高效便捷,可以对20~30 ng铀同步分析^(234)U/^(238)U和^(238)U/^(235)U,精度可分别达到0.3‰~1‰和0.3ε~0.7ε(±2σ),用时约为20 min.此外,在样品测试时可以根据样品的铀含量以及对分析精度的要求灵活调整MC-ICP-MS检测系统的高阻信号放大器的排列方式,因此新方法可以广泛用于地质样品的铀同位素分析.

ENSO-Like Pacing of the Asian Summer Monsoon during the Early Holocene

We present a230Th-dated stalagmite oxygen isotope(δ^18O)record from Loushanguan Cave in the Yangtze River valley,China.The^δ18O record,if viewed as a proxy of the Asian summer monsoon(ASM)intensity,provides an ASM history for the early Holocene with clear centennial-scale variability.A significant approximately 200-yr cycle between 10.2 and 9.1 ka BP(before present,where"present"is defined as the year AD 1950),as revealed by spectral power analyses,is of global significance and is probably forced by the Suess or de Vries cycle of solar activity.Here,we explore a physical mechanism to explain the relationship between the solar activity and the ASM.A strong coherence between the ASM and El Ni?o–Southern Oscillation(ENSO)has been observed by performing crosswavelet analyses on this cycle.Our study suggests that a strong(weak)ASM state corresponds to a warm(cold)ENSO,which is consistent with modern meteorological observations but contrasts with previous studies on regions far from the Meiyu rainbelt.We argue that the centennial fluctuations of the ASM are a fundamental characteristic forced by the solar activity,with the ENSO variability as a mediator.The relationship between ENSO and the ASM displayed spatial heterogeneity on the centennial scale during the early Holocene,which is a more direct analogue to the observed modern interannual variability of the ASM.

Occurrence of polycyclic aromatic hydrocarbons in the estuarine sediments of the Taihu Lake and their associated toxic effects on aquatic organisms

Polycyclic aromatic hydrocarbons(PAHs)are ubiquitous toxic organic pollutants in the natural environment that are strongly associated with socioeconomic activities.Exploring the distribution,sources,and ecological toxicity of PAHs is essential to abate their pollution and biological risks.The 16 priority PAHs in different lakeside city estuarine sediments in the northern Taihu Lake in China were determined using gas chromatography-mass spectrometry.Results showed that total concentrations of PAHs(ΣPAHs)ranged from 672.07 to 5858.34 ng g^(^(-1)),with a mean value of 2121.37 ng g^(^(-1)).High-molecular-weight PAHs(4-6 rings)were dominant,accounting for 85%of theΣPAHs detected.Due to the barrier of gate/dam in the estuarine area,the concentrations of PAHs in the sediments were significantly different between the river mouth and lake side.Changes in total organic carbon(TOC)content and the spatial distribution of PAHs in the sediments were consistent.Sediment pollution assessment explored using the fuzzy evaluation model indicated 75%of slight PAH pollution.Some estuarine sediments(22%)concentrated in the east of the Wuli Lake in the Meiliang bay of the Taihu Lake were moderately or heavily polluted.The PAHs may lead to occasional detrimental biological consequences in the area.Diagnostic ratios and principal component analysis-multiple linear regression suggested vehicle emission and natural gas combustion as the primary PAH contributors(81%).

Summer Monsoon Rainfall Variability in Central China over the Past 4700 Years and Its Possible Link to Solar Activity

Based on 467 pairs ofδ^(18)O andδ^(13)C records and 8230 Th dates from a stalagmite(BF4)from Xiniu Cave,central China,we present a reconstruction of 9-yr resolution monsoon rainfall record for the past 4700 years.Ourδ^(18)O record shows good coherence with East Asian summer monsoon(EASM)rainfall proxies from adjacent regions during the overlapping intervals,suggesting thatδ^(18)O signal in BF4 can be interpreted as a monsoon rainfall proxy.Theδ^(13) C variations are related to changes in local processes at the cave site,and regional rainfall and temperature changes.Based on theδ18 O record,a series of dry periods can be identified at 4500-4200,3500-3200,2800-2500,1900-1600,1400-1200,700-500,and 400-200 yr BP,while a series of wet periods can be identified at 4200-3600,2400-2200,3200-2800,1100-900,600-400,and 200-100 yr BP.Power spectrum analysis on ourδ^(18) O record reveals significant cycles at 470 and 80 yr,coinciding with the typical solar periodic variations.This result suggests that changes in solar activity play a dominant role in driving centennial-decadal monsoon rainfall variation in central China.Due to minor changes in solar irradiance(less than 1.5 W m^(-2))over the past 4700 years,our record was further compared to the El Nino-Southern Oscillation(ENSO)and Pacific Decadal Oscillation(PDO)proxies,confirming that solar forcing on monsoon rainfall changes might be amplified by the ENSO and PDO variations.From 600 to 150 yr BP(the Little Ice Age,LIA),a positive shift of 2‰can be revealed in both theδ^(18)O andδ^(13)C records,indicating a cold/dry climatic pattern.By comparing ourδ^(18)O andδ^(13)C records with historical documents,we suggest that the climatic deteriorations between 450 and 250 yr BP may have caused serious social unrest at the end of the Ming Dynasty.