雅鲁藏布江流域风成沉积空间格局、沉积模式及其环境效应

青藏高原南部雅鲁藏布江(雅江)流域位于印度板块和欧亚板块碰撞产生的缝合带,是地球系统科学研究的热点地区。该区域中更新世以来的风成沉积物不仅是揭示青藏高原气候变化与大气环流演化的重要窗口,而且有助于深入认识构造、气候及地表景观之间的内在联系,然而我们对于该区域风成沉积物的空间格局、沉积模式及其环境效应至今仍然缺乏系统的认识。本文在大量野外考察和已有研究结果基础上,结合典型沉积物样品的综合分析,对雅江流域风成沉积体系进行了梳理,绘制了《雅江风成沉积空间分布图》,包括1幅序图和6幅区域分布图,其中风沙和黄土沉积呈斑块状分布,二者通常相伴而生。黄土与沙丘、河流砂等松散沉积物之间存在密切的物质联系,区域内的风成沉积以自循环过程为主,记录了区域气候的空间差异。河谷沉积物在接受有限的远源粉尘输入的同时,在高空西风的作用下向全球贡献粉尘物质。中更新世以来的粉尘活动受控于构造运动和全球气候变化的耦合,而全新世粉尘活动受河谷环境影响表现较为复杂,区域气候变化受中纬度西风和印度夏季风的协同作用影响。

2017年兰州市大气污染物输送来源及传输特征模拟分析

利用HYSPLIT后向轨迹模式,结合兰州市AQI (空气质量指数)及常规大气污染物质量浓度数据,模拟研究了2017年1月1日-12月31日以兰州市为受点的大气污染物输送特征.通过聚类分析确定了抵达兰州市气团的主要输送途径和每类路径所对应的污染物质量浓度特征,并利用受体模型PSCF (潜在源贡献因子分析法)和CWT (权重浓度轨迹分析法),分析了大气污染区域传输对兰州市空气质量的影响,探讨了影响兰州市空气质量的污染物输送来源和可能的潜在源区.结果表明,在影响兰州市的气流轨迹中,污染轨迹多来自兰州市以西和以北方向,污染轨迹约占总轨迹的39. 52%,说明外部污染物的输入对兰州市空气质量具有重要影响.其中,第3类轨迹(对应来向为西)的气团对兰州市的空气质量有较大的影响,该类轨迹虽仅占总轨迹的15. 21%,但其中污染轨迹数占56. 76%,是影响兰州市空气质量的主要传输路径;第4类轨迹(对应来向为东南)的气团最为清洁.研究显示,对兰州市空气质量影响最大的强潜在源区主要分布在青海共和盆地、兰州市本地及周边区域,中等强度潜在源区为内蒙古自治区南部、宁夏回族自治区及甘肃省河西走廊等地区.

沙尘暴对天山托木尔峰青冰滩72号冰川环境的影响

基于沙尘暴发生前后在天山托木尔峰青冰滩72号冰川末端采集的7个大气气溶胶样品和在水文断面采集的9个融水径流样品,探讨了沙尘暴事件对天山冰川区大气环境和水环境的影响。结果表明,Ca^(2+)和SO_4^(2-)是青冰滩72号冰川大气和融水径流的主要离子,当沙尘暴发生时,这两种介质中的离子浓度显著升高,而且升高存在同时性。由于影响因素不同,浓度随时间变化的趋势不同,大气环境对沙尘事件的响应能力强,水环境则对温度变化的响应能力更强。通过相关性分析和主成分分析认为,青冰滩72号冰川大气中Ca^(2+)、Mg^(2+)、Na^+、K^+、Cl^-和SO_4^(2-)主要以自然源为主; NO_3^-和NH_4^+则以人为源为主。轨迹分析发现,由源于东欧、西伯利亚经中亚南下的冷气团引发的大风降温天气以及区域沙尘暴对冰川区环境有显著影响。

基于太阳光度计的兰州市秋季气溶胶光学特性

利用2015年9-11月兰州市CE318太阳光度计地基观测数据,反演了这期间气溶胶光学厚度(Aerosol Optical Depth,AOD)、Angstrom波长指数(α)、大气浑浊度系数(β)等气溶胶光学特性参数,研究了兰州市秋季气溶胶光学特性的时间变化特征,并根据Angstrom阈值范围和图解分析法对兰州市气溶胶主要类型及其分布特征进行分析。结果表明:兰州市秋季AOD500 nm均值为0.47±0.22。10月α440~870 nm最小,为0.95±0.26;9月α440~870 nm最大,为1.21±0.14。9月大气浑浊度系数最低,为0.15±0.05;11月最高,为0.28±0.12。AOD秋季日变化较小,AOD500 nm变化范围在0.27~0.52之间。2015年9-10月AOD500 nm集中在0.2~0.6之间,11月AOD500 nm集中在0.4~0.8之间,说明兰州市2015年秋季AOD500 nm分布较为集中,大气气溶胶含量逐月增加。9月波长指数集中在1.0~1.4之间,峰值中心在1.2~1.4区间;10月波长指数主要集中在0.6~0.8和1.0~1.2两个区间;11月波长指数集中在1.0~1.4区间。总体来看,兰州市秋季气溶胶以细粒子为主。AOD500 nm与β显著相关,大气光学厚度与大气浑浊度系数均能表征大气污染程度。兰州市秋季气溶胶主要类型为细颗粒模态下的人为源和混合型气溶胶,分布特征表现为高AOD时受细颗粒气溶胶的吸湿增长影响,其中细颗粒吸湿增长是兰州市秋季气溶胶光学厚度偏高的主要原因。

3500年来祁连山中段天鹅湖岩芯记录的沉积环境变化

湖泊沉积,特别是内陆高山封闭湖泊沉积是古气候研究的重要载体,可以高分辨率、敏感地记录连续的古气候环境变化。选取祁连山中段天鹅湖沉积岩芯TEB孔的10个陆生植物残体进行AMS^(14)C测年并建立年代框架,结合对总有机碳(TOC)含量、矿物成分及元素相对含量等指标的分析结果,重建了天鹅湖3 500年来的沉积环境变化特征。初步研究结果表明:碳酸盐含量变化主要受控于地下水补给量的变化,进而反映区域降水量,1 534 BC^1 300 AD期间,天鹅湖区降水呈减少的趋势,尤其是中世纪暖期(720~1 300 AD),是3 500年来最干旱的时期;小冰期开始于1 300 AD,共出现三次降水较多的时期,1 600~1 730AD为小冰期最盛期。受西风环流影响,天鹅湖沉积记录了该区域中世纪暖期相对暖干,而小冰期较为冷湿的变化特征。同时,该湖记录的小冰期气候相比于中世纪暖期更不稳定。

风电场运行对地表温度的影响——以河北张家口北部风电场为例

正确认识风力发电对气候的可能影响,尤其是对地表温度的影响,对于科学利用风能资源,确保我国能源可持续发展具有重要的意义。本文基于2003-2019年MODIS卫星地表温度数据,结合风向、植被指数、地表反照率及土地利用数据探讨了河北省西北部坝上地区尚义、张北县大型风电场对地表温度的影响。结果表明,风机运行会对风电场内及其下风方地表温度产生影响。在春季、秋季和冬季,夜间风电场建成前后下风向增温幅度高于上风向,白天则是下风向增温幅度低于上风向,即风电场下风向夜间存在增温,白天存在降温。与周边非风电场影响区域相比,春季和夏季风电场内地表温度显著增高,特别是春季夜间,风电场影响区增温幅度达0.379℃·(10a)^(-1),其次为夏季和秋季夜间,风电场影响区增温幅度分别达0.206℃·(10a)^(-1)和0.211℃·(10a)^(-1),冬季存在增温但不显著,与其他研究相比增温较弱,且远小于坝上地区地表温度年际增温趋势。风电场内部地表温度变化不仅受风电场运行的影响,气候变化、植被变化以及土地利用类型变化均对地表温度有影响。

Near-surface wind environment in the Yarlung Zangbo River basin,southern Tibetan Plateau

Aeolian processes have been studied extensively at low elevations,but have been relatively little studied at high elevations.Aeolian sediments are widely distributed in the Yarlung Zangbo River basin,southern Tibetan Plateau,which is characterized by low pressure and low temperature.Here,we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area,and examined the interaction between the near-surface wind and aeolian environment.The wind environment exhibited significant spatial and temporal variation,and mean wind speed has generally decreased on both annual and seasonal bases since 1980,at an average of 0.181 m/(s•10a).This decrease resulted from the reduced contribution of maximum wind speed,and depended strongly on variations of the frequency of sand-driving winds.The drift potential and related parameters also showed obvious spatial and temporal variation,with similar driving forces for the wind environment.The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern,but with variation caused by local topography and sediment sources.The drift potential and resultant drift direction were two key parameters,as they quantify the dynamic conditions and depositional orientation of the aeolian sediments.Wind affected the spatial variation in sediment grain size,but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands.These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.

Fluvial sediments in the Alagxa Plateau as a dust source: iron mineralogical and geochemical evidence

The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits(loess) in the adjacent Chinese Loess Plateau(CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt(goethite) and similarity of the Gt/(Hm(hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics(χ(magnetic susceptibility), χARM(anhysteretic susceptibility), SIRM(saturation isothermal remanent magnetization) and SIRM_(AF100 mT)(SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.

4000a B.P.以来中巴经济走廊北段塔什库尔干气候变化对东西方文化交流的影响

新疆塔什库尔干塔吉克自治县地处中巴经济走廊北段,自古以来就是东西方文化交流的核心地带。基于地质记录和考古发现,对该县4 000a B. P.以来东西方文化交流与气候环境变化的关系进行了梳理与分析。结果发现,研究区特有的地理环境和气候变化对文化发展与传播起着重要的影响,3 500~2 800a B. P.的干旱气候对应了中巴经济走廊东西方文化交流中断,随着气候好转,东西方文化交流在该区域再次畅通;2 600~2 200a B. P.气候变干与中巴经济走廊北段文化交流再次衰落对应;历史时期丝绸之路的兴衰与气候变化密切相关。

上海城市表土磁性特征对重金属污染的指示作用

选取上海市城市表土作为研究对象,结合磁学方法与传统化学方法,研究了上海市192件表土样品的磁性特征和重金属含量,并探讨了磁学参数指示重金属污染的可行性.结果表明,上海市表土磁化率平均值为187.66×10^(-8)m^3·kg^(-1),亚铁磁性矿物占主导地位,颗粒较粗.上海市表土重金属Zn、Pb、Cu、Cr、Ni、Mn、Fe含量均超过背景值,属于轻度污染.重金属和磁学参数(磁化率、饱和等温剩磁)具有相似的空间分布,高值集中在宝山区和闵行区,低值集中在崇明区.工业生产和交通活动是上海市表土重金属、磁性矿物的主要来源.磁化率χlf指示污染负荷指数的半定量结果为:χlf<38.90×10^(-8)m^3·kg^(-1)时,土壤属于清洁状态,无污染;38.90×10^(-8)m^3·kg^(-1)≤χlf<258.69×10^(-8)m^3·kg^(-1)时,土壤遭受轻度污染;258.69×10^(-8)m^3·kg^(-1)≤χlf<793.45×10^(-8)m^3·kg^(-1)时,土壤遭受中度污染;χlf≥793.45×10^(-8)m^3·kg^(-1)时,土壤遭受重度污染.因此,磁学参数对城市表土重金属污染有着一定的指示意义.

MIS 3以来雅鲁藏布江流域风成沉积及环境意义

雅江流域风成沉积广泛发育,其气候指示意义及年代的界定尚不够清晰。从雅江全流域视角出发,全面分析了不同区域风成沉积的发育机制及模式,同时对风成沉积年代数据归一化处理,并与全球气候对比研究。结果表明:①流域内风成沉积有盛行风场发育模式和局地风场发育模式,不同模式对环境的指示意义不同。②雅江流域风成沉积多堆积于末次盛冰期(LGM)以后,且主要发育于晚冰期(15 ka BP)以来的不同时段,冰川退缩地表裸露,丰富的冲洪积碎屑物源可能是风成沉积发育的主控因素;更早时段的风成沉积因LGM后气候转暖、冰川消融所致的侵蚀搬运作用而未能保存。③LGM以来风成沉积过程受区域及全球古气候环境共同控制,波动变化剧烈;其对30°N夏季太阳辐射、印度季风及西风变化信号的指示有所差异,但对YD等全球气候冷事件有较好记录,其沉积过程与高原面上其他区域既存在对全球古气候响应的同步性,又有其区域独特性。④流域内风成沉积的强烈堆积过程与全球气候变化并非简单对应关系,呈现出较复杂的响应模式。说明高山河谷环境的风成沉积除受大区域气候影响,还受许多局地环境因素控制,古气候环境的指示意义复杂。

新疆湖泊岩芯记录的未次间冰期以来气候变化初步研究

针对目前中亚西风影响区湖泊记录研究中的难点和关键科学问题，我们选择新疆的乌伦古湖、博斯腾湖、巴里坤湖钻取了湖泊岩芯，报道它们初步的研究成果。年代测定采用了AMS 14C、光释光技术，并结合古地磁的研究，初步建立了湖泊岩芯的年代框架。巴里坤湖具有末次间冰期以来连续的沉积，是研究气候环境变化的理想载体；博斯腾湖和乌伦古湖都曾经出现过沉积间断，不利于进行高分辨率的气候环境变化重建。从现有的结果来看，末次间冰期气候较为湿润，MIS 3阶段气候的湿润程度降低，LGM时期气候干旱，全新世时期湖泊普遍发育。

雅鲁藏布江流域风成沉积研究进展

雅鲁藏布江位于青藏高原南部,流域内广泛发育着地质历史时期以来的黄土沉积和现代风沙沉积,蕴含着风成过程和环境演化的丰富信息。从风成沉积分布特征、堆积年代、沉积物特征、物源及其可能的形成机制以及风沙活动历史等方面综述了近些年雅鲁藏布江流域风成沉积的主要研究进展。结果表明:黄土主要发育于河流阶地及部分山体顶部,多形成于末次冰盛期以后且主要发育于深海氧同位素1阶段(约14 ka BP)以来,而风沙沉积集中发育于河流宽谷段,堆积时间相对较短。沉积物颗粒以机械搬运和物理风化为主,化学风化微弱。尽管沉积物理化性质呈现出一定的空间变化,但仍存在明显的局地特征,与附近地表堆积物联系密切。在风成背景下,黄土的近源成因得到了普遍认可,河谷底部地表松散物质是风成沉积发育的主要物源。风沙活动演变较为复杂,除大区域气候变化外,局地环境也是影响风沙活动及其区域差异的重要因素。未来应加强研究区风成沉积物理化性质、全新世以来的气候变化以及粉尘释放对人类生存环境影响等方面的系统研究。

Humid Medieval Warm Period recorded by magnetic characteristics of sediments from Gonghai Lake, Shanxi, North China

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the and S 300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.

Magnetic records of heavy metal pollution in urban topsoil in Lanzhou,China

This study is a systematic analysis of the magnetic characteristics and heavy metal elements in soil samples collected from Lanzhou City,China.The 117 surface soil samples were measured to study the feasibility and effectiveness of environmental magnetism for evaluating heavy metal pollution in urban soils.Results of the study indicate that low-coercivity magnetite dominates the magnetic properties in the samples.The high values of the soil magnetic mineral concentration parameters and low values of magnetic particle size parameters are distributed throughout the northern area of Xigu District,the industrial zones of the eastern section of Chengguan District and the districts of the narrow sections connecting Chengguan District and the other three districts;these parameters are fundamentally consistent with the distribution of the high values of the Pollution Load Index and Nemerow Pollution Index.Semi-quantitative studies which use the environmental magnetic method to monitor pollution of heavy metals(such as As,Cr,Cu,Ni,Pb,Zn,and Fe) have shown that when xlf≤35×10-8 m 3 kg-1,it is unpolluted;when 35≤xlf <150×10-8 m3 kg-1,it is moderately polluted to unpolluted;when 150≤xlf <365×10-8 m 3 kg-1,it is moderately polluted;when 365≤xlf <750×10-8 m3 kg-1,fd %<2.7 and ARM /SIRM<0.2×10-3m A-1,it is moderately to highly polluted;when xlf ≥750×10-8 m3 kg-1,xfd %<2.7 and xARM/SIRM<0.2×10-3m A-1,it is highly polluted.The region of moderately to highly polluted distribution is caused by industry and vehicles,showing that the change of pollution in Lanzhou City bears the trend of "vehicle emission + industrial".

Responses of desertification to variations in wind activity over the past five decades in arid and semiarid areas in China

There have been significant variations in wind activity over the past five decades in arid and semiarid areas in China.High wind activity occurred from the 1960s to the 1970s,but wind activity has de-creased continuously from the 1980s to the present;as a result,the potential sand transport during the latter period was only 20%-50% of the values during the 1960s and 1970s.Phases of high wind activ-ity were highly consistent with the trends in desertification over the past five decades in arid and semiarid areas in China,but spring precipitation was also a significant factor:rapid desertification during the 1960s and 1970s was due to high wind activity,generally combining with low spring pre-cipitation;subsequent rehabilitation since the 1980s has resulted from the combined effects of low wind activity and higher spring precipitation.Therefore,although modern desertification and rehabili-tation processes are being more or less affected by human activities,both processes appear to be more strongly controlled by climate change.

Spatial and temporal variation in magnetic properties of street dust in Lanzhou City,China

Urban environmental problems are of increasing concern. Lanzhou is a large industrial city in North-west China. Street dust samples representing different temporal and spatial scales were collected for magnetic properties study. Magnetic measurements indicate a high concentration of magnetic minerals in Lanzhou street dust, dominated by pseudo-single domain (PSD) magnetite. The concentration of magnetic materials is distinctly high in winter and spring, low in autumn. Similarly, higher concentra-tions associated with heavy industry, concentrated residential development, and vehicular traffic sug-gest mixed contributions of magnetic material from both anthropogenic and natural sources. χ_lf and SOFT% are effective magnetic parameters that denote seasonal differences among magnetic proper-ties in street dust, convenient and economical methods for monitoring street dust pollution.