Rb and Sr Geochemical Characterization of the Chinese Loess Stratigraphy and Its Implications for Palaeomonsoon Climate

Concentrations and distributions of Rb and Sr in loess and palaeosol samples from the Luochuan profile have been studied, in grain-size fractions and chemical forms. Results show that Rb is quite rich in the fraction of less than 2μm, and exits only in the residual phase, while Sr is distributed in sand and silt fractions, occurring in the residual and carbonate phases. Therefore, variations of the concentrations of Rb and Sr in loess and palaeosols are closely related not only to dustfall compositions depending on winter monsoon wind strength but also to summer monsoon-induced pedogenic intensity. This indicates that variations of Rb/Sr ratio in Chinese loess sequences represent cyclic alternations of East Asian summer and winter monsoon climates on the orbital time-scale. Variations in Sr concentrations along the sequence bear a high similarity to the oxygen isotope record of the deep sea sediments over the past 2.5 Ma, whereas variations in Rb concentrations are in good agreement with the record of     

黄土堆积与冰期事件

黄土高原早期环境 ,应该同其周边环境大体相似 ,也存在冰期问题 :三套“砂质黄土”是冰期遗物的唯一表象 ,这是因为冰体夹在黄土层中间 ,基本丧失了冰川形成条件 ,故虽有冰期而无冰川 ,自然也就没有山岳冰川所形成的各类遗物 ,当然也包括冰川地貌的形踪     

青藏高原地面加热场与四川主汛期降水及伏旱关系

分析了高原地面加热场强度距平指数与四川盆地伏旱及主汛期降水的联系。结果表明,高原前期加热强度同四川盆汛期降水和伏旱程度密切相关。把这些关系引入汛期降水预测模型对提高短期气候预测能力有一定积极意义。     

青藏高原平流层臭氧和气溶胶的变化趋势研究

通过分析SAGEⅡ资料,发现青藏高原平流层臭氧存在递减趋势,15—50 km臭氧的变化对臭氧总量变化贡献最大,其中25—50 km和15—25 km两层的贡献大致相当。通过青藏高原和中国东部地区平流层臭氧变化的对比,清楚地看出:两地臭氧总量变化的差异主要是由于在15—25 km臭氧变化不同所致。5—7月臭氧变化趋势的情况与年平均的变化类似,两地臭氧变化的差异主要在平流层低层,即15—25 km。青藏高原平流层气溶胶面密度的时间变化序列显示:大的火山喷发对青藏高原平流层气溶胶具有重要影响,其影响可持续6年左右。从1997年至今,青藏高原18—25 km气溶胶面密度增加,最大的增长出现在23 km,每年大约增长4%—5%。而在16—17 km气溶胶的面密度出现减少趋势。与此同时,在37 km以下,青藏高原的温度出现递减的趋势,而且其递减速度比中国东部地区快;在37—50 km,温度出现增加的趋势,青藏高原的增温也比中国东部地区快。青藏高原平流层低层气溶胶的增加和温度的降低都将增强该区域非均相反应的作用。     

Attribution of trends in meteorological drought during 1960–2016 over the Loess Plateau,China

This study uses two forms of the Palmer Drought Severity Index(PDSI), namely the PDSI_TH(potential evapotranspiration estimated-by the Thornthwaite equation) and the PDSI_PM(potential evapotranspiration estimated by the FAO Penman-Monteith equation), to characterize the meteorological drought trends during 1960–2016 in the Loess Plateau(LP) and its four subregions. By designing a series of numerical experiments, we mainly investigated various climatic factors' contributions to the drought trends at annual, summer, and autumn time scales. Overall, the drying trend in the PDSI_TH is much larger than that in the PDSI_PM. The former is more sensitive to air temperature than precipitation, while the latter is the most sensitive to precipitation among all meteorological factors. Increasing temperature results in a decreasing trend(drying) in the PDSI_TH, which is further aggravated by decreasing precipitation, jointly leading to a relatively severe drying trend. For the PDSI_PM that considers more comprehensive climatic factors, the drying trend is partly counteracted by the declining wind speed and solar radiation. Therefore, the PDSI_PM ultimately shows a much smaller drying trend in the past decades.     

青藏高原高寒区生物地理学研究进展

近年来,随着DNA测序技术的发展,青藏高原及周边地区的生物地理学研究取得重大成果,从生物演化方面着手探讨了青藏高原隆升历史及其气候效应.综合近年来地质学、古生物学与生物地理学研究进展,我们发现高原及周边地区高寒生物类群的起源和分化时间以及多样性演化过程表明早在渐新世青藏高原部分地区就已经存在高寒生态系统,晚中新世以来青...     

基于DEM小流域复杂网络的黄土高原地貌自动识别研究

地貌识别,对于人类建设,地质构造研究,环境治理等相关领域都有着重要意义。传统的基于像素单元或面向对象的地貌识别方法存在局限性。由于流域小单元具有表面形态的完整性,在地貌演化中具有明确的地理意义,基于流域小单元的地貌识别成为了该领域的一个新热点。然而,基于传统地形因子的地貌识别方法使用的因子往往较为单一或者在地学描述上存在重复性,目前尚无针对流域小单元进行空间结构描述和拓扑关系特征量化的地貌识别研究。基于此,本文基于DEM进行水文分析并通过坡谱方法解决了小流域稳定面积难以确定的问题,在黄土高原样区提取了181个稳定小流域。根据复杂网络理论和地貌学原理提出了流域加权复杂网络的概念和相应的8个定量指标用于流域空间结构的模拟和量化描述。最后采用了基于决策树的XGBoost机器学习算法进行地貌识别,实验对于黄土高原主要地貌类型的识别显现出较好的效果,Kappa系数为86.00%,总体精度达到了88.33%。对于地貌形态特征明显的地貌,复杂网络方法其顾及空间结构和拓扑特征的特性导致了其较高的识别性能,精度和召回率都在90%～100%之间。通过与前人的研究进行对比,其识别结果亦呈现出较高的精度,这些...     

The Impact of Climatic and Environmental Factors on n-Alkanes Indices in Southwestern Tibetan Plateau

n-Alkanes are widely used in paleoenvironmental reconstructions.However,our understanding of changes in the distribution of n-alkanes with climatic and environmental factors remains unclear in arid/semi-arid regions.We sampled 26 surface sediments from three climatic zones across the southwestern Tibetan Plateau to evaluate the sensitivity of chain length distributions of n-alkanes to climatic and environmental parameters.Our observations demonstrate that average chain length (ACL), proportion of aquatic macrophyte (Paq),carbon preference index (CPI) and ratio of the contents of nC27 and nC31 (nC27/nC31) are all sensitive to hydroclimatic conditions.In contrast to commonly-adopted assumptions,the correlations between these indices and hydrological parameters are not always good,which indicates that the interpretation of n-alkane indices is special on the southwestern Tibetan Plateau.These might be related to the vegetation characteristics and seasonality of biological activity,and need to be considered in paleoclimatic reconstruction.The impact of seasonal precipitation on n-alkanes indices was also evaluated.     

青藏高原气候变化若干前沿科学问题

在全球变化的背景下,青藏高原冰冻圈和大气圈正在发生快速变化,对"亚洲水塔"和"第三极"的生态环境带来深刻影响.研究并梳理了近年来青藏高原气候变化的若干前沿科学问题的研究进展,如高原极端气候事件变化及其与大气环流的关系;高原变暖放大效应及海拔依赖型变暖的物理机制;再分析资料在高原气候变化应用的适用性;气候模式在高原资料稀...     

Estimation of regional evapotranspiration in alpine area and its response to land use change: A case study in Three-River Headwaters region of Qinghai-Tibet Plateau, China

Three-River Headwaters(TRH) region involved in this paper refers to the source region of the Changjiang(Yangtze) River,the Huanghe(Yellow) River and the Lancang River in China.Taking the TRH region of the Qinghai-Tibet Plateau as a case,the annual evapotranspiration(ET) model developed by Zhang et al.(2001) was applied to evaluate mean annual ET in the alpine area,and the response of annual ET to land use change was analyzed.The plant-available water coefficient(w) of Zhang’s model was revised by using vegetation-temperature condition index(VTCI) before annual ET was calculated in alpine area.The future land use scenario,an input of ET model,was spatially simulated by using the conversion of land use and its effects at small regional extent(CLUE-S) to study the response of ET to land use change.Results show that the relative errors between the simulated ET and that calculated by using water balance equation were 3.81% and the index of agreement was 0.69.This indicates that Zhang’s ET model based on revised plant-available water coefficient is a scientific and practical tool to estimate the annual ET in the alpine area.The annual ET in 2000 in the study area was 221.2 mm,11.6 mm more than that in 1980.Average annual ET decreased from southeast to northwest,but the change of annual ET between 1980 and 2000 increased from southeast to northwest.As a vast and sparsely populated area,the population in the TRH region was extremely unbalanced and land use change was concentrated in very small regions.Thus,land use change had little effect on total annual ET in the study area but a great impact on its spatial distribution,and the effect of land use change on ET decreased with increasing precipitation.ET was most sensitive to the interconversion between forest and unused land,and was least sensitive to the interconversion between cropland and low-covered grassland.