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A comparative study on the ionospheric current systems in the Antarctic and Arctic regions 总被引:1,自引:0,他引:1
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AcomparativestudyontheionosphericcurrentsystemsintheAntarcticandArcticregionsXuWenyao(徐文耀)(InstituteofGeophysics,AcademiaSini... 相似文献
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青海苏干湖表层沉积物粒度分布模式与大气粉尘记录 总被引:11,自引:0,他引:11
位于干旱区柴达木盆地具有年纹层的苏干湖是以地下水补给为主的内陆封闭湖泊, 其表层沉积物粒度具有多组分峰态分布特征, Weibull 函数的拟合结果发现, 其粒度分布全部具 有4 个基本组分: 超细粒组分, 众数粒径在1 μm 上下; 细粒组分, 众数粒径在5~10 μm; 粗粒组分, 众数粒径在50~100 μm; 砂组分, 众数粒径在500 $m 左右。粒度主峰出现在细 粒组分或者粗粒组分。直接来自大气粉尘的冬季湖泊冰面样品及当地尘暴样品的Weibull 函数粒度拟合也显现出了相似的分布模式, 冰面样品的粒度主峰位于众数粒径在15~20 μmm 的 细粒组分, 砂组分(众数粒径452.9μm) 的出现指示出砂粒在冬半年沿冰面而进入湖泊中心。 尘暴降尘样品在尘暴季节(5 月份) 和非尘暴季节(11 月份) 的粒度分布普遍具有3 个组分, 缺少砂组分, 强沙尘暴事件样品则由4 个组分组成, 粒度主峰均位于众数粒径在100~200 μm 的粗粒组分。结果显示, 苏干湖湖泊沉积能够较好记录当地大气粉尘, 砂组分与湖泊周边干旱地表经历的近地面强沙尘活动有关, 粗粒组分记录了区域性的尘暴事件, 细粒组分主要反映 流域径流状况, 超细粒组分代表干旱区的大气背景粉尘和气溶胶。研究表明, 苏干湖内陆湖 泊沉积客观记录了区域大气粉尘和尘暴事件, 具有重建干旱区大气粉尘变化历史的潜在优势。 相似文献
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Samples of glaciomarine sediments and suspended matter from the eastern and central Weddell Sea Shelf were collected during the Norwegian Antarctic Research Expedition (NARE) in 1978/79. Ice-rafted clastic materials are in general the main sediment sources. On the eastern shelf, biogenic materials are abundant (sponges and bryozoan debris). Fine-grained materials, clastic and bioclastic, are additionally supported as fecal aggregates and by currents. The composition of the bottom sediments shows only small variations laterally and within the profiles. Dissolution of the biogenic materials appears to be slight. The suspended matter is dominated by fine silt and clay particles of clastic, biogenic (mainly diatoms) and authigenic (Fe, Mg-rich silicates) origin. Metalliferous particles (Fe, Ti, Zn, Cr, Ni-rich) of possibly anthropogenic and/or cosmic origin are observed. On the upper continental slope and the outer shelf the sedimentation rates are in the range of 2–5 cm/1000 years, which are slightly higher than for the rest of the shelf. The bioclastic glaciomarine deposits grade southward into bioclastic free sediments, showing that glaciomarine deposits outside an ice shelf may form a sequence of alternating bioclastic-rich and bioclastic-free layers. Similarly, late Precambrian carbonate tillite sequences, especially in the case of thin carbonate layers interbedded with tillite layers, may reflect variations in glaciomarine facies rather than interglacial/glacial cycles. 相似文献
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湖泊粉尘记录是研究区域大气粉尘演化历史的重要载体,而现代过程研究是定量提取湖泊沉积物中粉尘信号的重要基础。对山西公海湖泊沉积岩芯样品及周边不同类型的表土样品开展了粒度分析,并对岩芯样品进行粒度组分的定量分离。结果表明:全新世湖泊岩芯样品以黏粒(<2 μm)、细粉砂(2~19 μm)和粗粉砂(19~78 μm)为主,粗粉砂组分的粒度特征与湖泊沉积物中的石英颗粒、黄土样品中的粗粒组分及现代大气降尘的粒度特征相似,石英颗粒的表面微形态也具有典型风成特征。因此,公海湖泊沉积物中粒径19~78 μm的粗粉砂组分可用来代表大气粉尘的变化,这与湖泊沉积物中粗粉砂组分是大气尘暴降尘主要组分的认识一致。另外,公海湖泊冰面粉尘样品的平均粒径还具有从西北向东南递减的趋势,表现出与冬季风方向一致的特征,进一步表明公海湖泊沉积物中粗粉砂组分可以代表东亚冬季风强度的变化。因此,公海湖泊岩芯中的粗粉砂组分可用来重建全新世大气粉尘变化以及可能的东亚冬季风强度演化历史。 相似文献
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中纬度荒漠区河西走廊沙丘地貌的演化特征及其环境指示 总被引:2,自引:0,他引:2
北半球中纬度地区的沙丘地貌变化和粉尘活动历史是探索全球环境变化与景观响应问题的良好档案。本文从风沙地貌学、粒度沉积学、地球化学和气候学等方面综合分析了中纬度典型荒漠区河西走廊的典型沙丘动态变化、物质来源、粉尘活动历史及其影响因素等。结果表明,20世纪60年代以来研究区典型新月形沙丘和新月形沙丘链等发生了较大的移动或摆动,平均移动速度介于0.8~6.2 m/a之间。沙丘的动态变化主要受年降水量、年平均风速和年大风日数的影响,表明气候是沙丘地貌变化的首要影响因素。沙丘沙(三段式)与戈壁沉积物的两段式粒度曲线模式明显不同,揭示了后者在沉积学上的“不成熟性”而前者经历了高效的风成分异作用且非局地起源。古地理、沉积学和地球化学综合证据揭示沙丘沙的母源物质主要是冲洪积物和古河流沉积物等,包括南北山麓剥蚀带的碎屑沉积等。地表细颗粒物质的比例、表层盐结皮的覆盖率和可蚀性砂质物质含量等指标指示了西部戈壁区不是中东部风尘的主要来源区。沙丘移动方向与区域性主导风向在空间分布上具有相似性,表明河西走廊东、西部间之间在沙丘地貌动态演化上的差异应受控于区域尺度的环流风系,即受控于动力机制而不是物质来源上的差异。区域气候的暖湿化是对全球增温和亚洲夏季风增强的同步响应,也是研究区沙尘暴减少的主要原因,同期河西走廊潜在的逆沙漠化过程亦受控于气候变化;但绿洲区沙漠化过程还是起因于人类活动影响的地下水波动。 相似文献
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Monitoring data on radioactive contamination of the atmosphere have been used in analyzing the seasonal variability in concentrations
and fallout flux of technogenic cesium-137 radionuclide contained in atmospheric suspended particles. It is found that an
increase in dust and radionuclide concentration is taking place during dust storms in deserts of Asia. It is shown that the
increase in the concentrations of dust and cesium-137 is accompanied by an increase in its specific activity in atmospheric
suspended particles. This bears witness to the continental origin of the radionuclide in the atmosphere over the southern
part of the Far East. 相似文献
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Georg Schettler Qiang Liu Jens Mingram Jörg F. W. Negendank 《Journal of Paleolimnology》2006,35(2):239-270
The varved sediments of the dimictic Lake Sihailongwan (Long Gang mountain area, Jilin Province, Northeast China) represent
a palaeoclimatic archive which documents the local precipitation frequency during the summer monsoon, and variations in the
aeolian flux of dust with their remote sources in the arid and semi-arid regions of inner Asia. Based on a detailed discussion
of sediment genesis in Lake SHL, dust flux rates and palaeohydrological conditions were reconstructed on a decadal scale over
the past 220 years. The aeolian influx by dry and wet deposition was quantified and characterised in its chemical composition.
Photosynthetic production in the lake is positively correlated with the inflow of nutrient-rich groundwater. The groundwater
discharge largely reflects the strength of the summer monsoon. Net accumulation rates for biogenic silica were determined
for annually laminated sediments from the centre of the U-shaped lake basin based on sediment data. In a Si-balance model
of the modern lake, the depositional flux of biogenic silica could be independently quantified on the base of hydrochemical
monitoring data. Comparison of the both estimates allowed to asses the focussing of the particle flux in the lake. Though
water retention in Lake SHL is rather high (ca. 30 years), changes in the hydrological conditions are sensitively recorded
in the sediments because (i) nutrient-rich groundwater discharges into the productive zone of the lake, (ii) a substantial
proportion of the total dissolved Si-inventory of the mixed lake (ca. 30%) is annually consumed by diatom growth, and (3)
sediment accumulation is substantially focussed towards the flat bottom of the lake basin. The bulk siliciclastic sediment
fraction (ca. 75 wt.%) largely originates from influx of dust of remote provenance. In sediment thin-sections, the dry-deposited
dust fraction is microscopically identifiable as seasonal silt layer. Aeolian input by wet-deposition shows a distinctly higher
variability than the influx of dust by dry-deposition. As diatom production, wet-deposition of dust is positively correlated
with the rainfall during the summer monsoon. The inferred positive correlation between rainfall and dust flux during the summer
monsoon implies that dust deposition is determined by the out-wash efficiency of mineral particles for a permanent high atmospheric
dust concentration over Northeast China in the last 220 years. 相似文献
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中亚干旱区是全球重要的粉尘源区,是全球变化与区域响应研究的关键区域之一。中亚粉尘形成搬运沉积过程一直是全球变化研究的热点科学问题。本文选取位于伊犁盆地北部、北天山南麓不同地形和气候条件下的两处黄土剖面,对其沉积速率最高的层段进行了粒度测试分析,结合聚类分析和粒度分布曲线拟合两种方法,重建了黄土粉尘的堆积过程。伊犁盆地黄土主要由远源和近源物质组成,分别由高空西风和中尺度的区域风搬运而来。高空西风所携带的远源粘粒级矿物颗粒对盆地东部降雨较高地区有一定的贡献,而在盆地西部不容易沉降下来。中尺度区域风所搬运的近源物质组成了黄土沉积物的主体,而近源区沉积物的可用性在黄土的形成过程中扮演着重要角色。另外,非风暴过程中(沙尘暴过后)出现的浮尘在沙尘暴天气频率减少的时期对黄土的发育有重要贡献,而在沙尘暴天气频发的时期,较差的植被覆盖度能够使得已经沉降下来的浮尘组分重新被扬起至大气中。由此建立了一个粉尘堆积的概念模型。认识黄土粉尘的堆积过程对现代沙尘天气的治理和人类生存环境的改善具有重要作用。 相似文献
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Ian Smalley 《Area》2008,40(1):131-134
A study of loess in Australia brings the idea of 'desert' loess back into view. Production of particles in deserts still presents problems, but deserts do make adequate storage regions for loess particles – usually produced in adjacent mountains. Straightforward for Central Asia or China (a particle source in High Asia and convenient deserts en route to eventual deposition), but the Sahara and Australian deserts traditionally present problems. If loess material is allowed to be silt-sized clay agglomerate particles as well as the usual clastic primary minerals, then loess in Australia seems reasonable. Loess acquires its remarkable loessic qualities via aeolian deposition – the nature of the particles is perhaps of lesser importance. A more generalised approach to airborne sediments might be attempted, with two major types of suspension material recognised: large dust (maybe coarse and very coarse silt, say 20–60 µm, or perhaps 4–6 phi) and small dust (fine and very fine silt, 2–8 µm, 7–9 phi). Loess is made from large dust. 相似文献
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柴达木盆地表土与大气降尘粒度Weibull组成及其环境意义 总被引:1,自引:0,他引:1
柴达木盆地北部现代地表不同沉积环境沉积物粒度分析结果显示,多数盆地地表沉积物质呈Weibull三峰分布,具有超细粒、细粒、粗粒3个组分,个别样品包含沙粒组分,绝大多数的样品匮乏细粒-超细粒组分,以高含量分选性较好的粗粒组分和低含量分选性差的细粒-超细粒组分为总体特征。现代沙尘暴天气降尘粒度分布模式较为单一,以高含量窄峰态的粗粒组分为显著特征。依据含量最高主峰所在Weibull粒度组分,本研究将全部粒度分布分为3种类型:以高含量细粒组分主导的F型、以高含量粗粒组分主导的C型和以高含量沙粒组分主导的S型。比较沙尘暴降尘、季节降尘和年降尘粒度分布模式的结果表明,研究区全年和季节大气降尘主要由沙尘暴天气降尘贡献,在细粒和超细粒组分上,同时混合有尘暴释放和正常天气条件下大气本底粉尘沉降两种来源的风尘成分。分析冬季研究区湖泊(苏干湖)冰层粉尘粒度分布模式发现,细粒组分含量显著偏高,可达70.6%,明显有别于其他沉积环境粒度组成,对比年降尘细粒-超细粒组分成因我们初步认为,细粒组分可用于指示冬季风盛行季节近地面大范围风场搬运风尘物质的状况。 相似文献