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1.
不同时间尺度青海湖沉积物总有机碳对气候变化的敏感性 总被引：1，自引：0，他引：1
湖泊沉积物总有机碳（TOC）含量通常作为表征流域和湖泊生产力的指标，在亚洲季风区也常常被当作夏季风的代用指标，被广泛应用于气候与环境变化研究.本文梳理了过去千年、全新世以及冰期-间冰期时间尺度上青海湖沉积物TOC的变化特征，并探讨了其指示气候变化的敏感性与有效性.结果表明，过去千年青海湖沉积物TOC含量与区域暖季温度和降水表现出较为一致的周期性波动.通过对比全新世区域夏季温度、基于孢粉的降水定量重建结果，以及湖泊水位、风沙活动反映的湿度状况等，发现不能简单地将青海湖沉积物TOC含量或沉积通量作为夏季风强度或者季风降水强度的代用指标.青海湖沉积物TOC含量在冰期和间冰期表现出巨大的差异，指示了冰期-间冰期时间尺度上较大的温度与降水变幅.因此，不同地域条件及不同时间尺度下，湖泊沉积物TOC对气候变化的敏感性不同，将湖泊沉积物TOC含量作为亚洲夏季风的代用指标需要特别谨慎，特别是在高寒气候区. 相似文献
2.
云南杞麓湖沉积物记录的近现代生态环境变化及影响因子识别 总被引：1，自引：0，他引：1
随着云南社会经济的持续发展与极端气候事件的频发,高原大中型湖泊面临着水质恶化、生态与环境功能退化的长期胁迫.为识别亚热带大型湖泊面临的主要环境压力,以杞麓湖为研究对象,在对沉积物钻孔进行物理(粒度、烧失量)、生物(色素、硅藻)等指标分析的基础上,结合现代监测和湖泊调查数据,重建了近两百年来湖泊水文条件、富营养化和环境变化的历史,并对硅藻群落结构的演化进行了驱动过程识别.沉积物粒度在1958年之前变化总体较为稳定且有较高的黏土含量;随着围湖造田等流域开发的增强,沉积物粒度组成自1960s开始频繁波动且粗颗粒组分快速增加.1981—2000年期间,随着落水洞泄水工程的修建杞麓湖的水位控制与水文调控得到加强,沉积物砂质含量降低且粒度组成变化较小;2000—2013年期间,湖泊疏浚工程的开展和区域降水的持续减少都导致了沉积物粒度组成波动较大、粗颗粒组成较高.沉积物色素记录了湖泊初级生产力的缓慢上升出现于19世纪中后期,并自1960s开始总叶绿素与蓝藻色素含量总体出现了较大幅度的增加趋势并持续至今.而在2000—2005年期间,湖泊浅水区的疏浚清淤导致了内源营养盐输入量的降低与藻类生物量的明显下降;沉积物蓝藻色素含量在1998、2008和2012—2013年左右出现明显的峰值,指示杞麓湖可能出现了较大范围的蓝藻暴发事件.统计分析结果显示,湖泊硅藻群落结构出现了多次明显转变且呈现底栖硅藻百分比长期降低的特征,水体富营养化的持续是驱动硅藻群落结构演替的主要因子,而水生植物退化、水文条件与气候变化也对硅藻群落的构建产生了重要的叠加影响.本文的沉积物分析结果表明,亚热带大型湖泊的生态治理与环境保护需要重点围绕营养盐负荷控制、水文调控优化与底栖生境恢复,并需应对全球变暖与极端气候事件产生的叠加影响. 相似文献
3.
不同时间尺度下的湖泊沉积物环境记录——以沉积物粒度为例 总被引：68，自引：2，他引：68
在湖泊沉积记录与古气候研究中, 沉积物粒度的环境意义常常解释为: 粗粒沉积物指示低水位时期的干旱气候, 细粒沉积物指示高水位时期的湿润气候. 本文通过对云南洱海和程海现代沉积物粒度的研究, 揭示了沉积物粒度在不同时间尺度、不同时间分辨率的研究中具有不同的环境指示意义. 在长时间尺度、低分辨率(百年、千年)研究中, 粗粒沉积物指示湖泊收缩、湖水较浅的干旱气候期; 细粒沉积物指示湖泊扩张、湖水较深的湿润气候期. 在短时间尺度、高分辨率(年际、10 a)研究中, 粗粒沉积物指示降雨量较大的湿润年份; 细粒沉积物指示降雨量相对较小的干旱年份. 由于不同时间尺度研究中沉积分辨率、采样分辨率和定年精度的不同, 湖泊沉积物记录所反映的环境信息在不同尺度下因此可能存在差异. 在由以往的长时间尺度、低分辨率研究转向短时间尺度、高分辨率研究的过程中, 不能简单套用各种指标在长尺度研究中的环境指示意义, 必须结合研究的时间尺度和分辨率, 综合分析各种因素对环境记录的影响方式和程度, 才能得出可靠结论. 相似文献
4.
柴达木盆地东部尕海短钻岩芯记录的过去近400a区域环境变化 总被引：2，自引：2，他引：0
干旱区湖泊沉积可以有效记录区域湿度变化及粉尘活动历史,位于柴达木盆地德令哈南部的咸水封闭湖泊尕海具有恢复区域环境变化的潜力.该地区的长序列环境演变研究已开展了较多的工作,但缺乏短尺度、高分辨率的近代以来的环境变化湖泊记录.通过对尕海深水区短钻岩芯放射性核素210Pb和137Cs的年代测定和沉积物各指标分析,认为尕海沉积物碳酸盐含量可以反映区域湿度变化;而粗颗粒组分(66.9μm)主要由风力搬运入湖,其含量可以指示区域粉尘活动历史.区域近400 a的环境变化可划分为3个阶段:1633 1750 AD:各指标出现大幅度波动,表现出该时期气候环境的不稳定和干湿交替,其中1650 1720 AD的变化波动尤为显著,这与太阳活动进入Maunder极小期存在一定的联系.1750 1950 AD:区域气候环境无明显波动,碳酸盐含量逐渐降低,湿度增加.1950 2010 AD:各指标变动剧烈,区域虽降水增多,但由于蒸发加强,湿度降低;1974 AD以后粗颗粒组分含量急剧上升,表现出高强度尘暴事件. 相似文献
5.
青藏高原东南部巴松措现代沉积过程及其对气候变化的响应 总被引：1，自引：1，他引：0
湖泊沉积物是记录气候演化信息的重要载体之一，在探讨过去气候变化过程研究中发挥重要作用.然而，沉积物中的许多代用指标对气候的指示意义存在多解性，不同指标所反映的环境信息相互之间有时会存在矛盾.为了能够更准确地解读湖泊沉积物中指标所记录的环境变化信息，开展现代湖泊沉积物指标与环境之间的关系研究，深入探讨各指标对环境变化的响应机制尤为关键.本文选取青藏高原东南部巴松措湖泊表层沉积物作为研究对象，利用210Pb与137Cs比活度检测结果建立年代序列，对沉积物中粒度、磁化率、有机质含量等指标进行分析，揭示巴松措现代沉积过程.结合沉积物粒度端元组分分析结果，并将不同指标变化与林芝气象站所记录的数据资料进行对比，得出以下主要结论：该地区沉积物来源主要包括径流搬运的冰川碎屑物质和来自青藏高原南部、西南部上空悬浮于大气中的风成物质两部分；其中，通过风力搬运的物质输入主要集中在冬半年，受季节性风向及风速变化影响明显；径流受到冰雪融水与夏季降水的补给，因此通过径流搬运的物质输入量受到温度与降水综合影响；湖泊中磁性矿物碎屑的产生和输入主要受区域降水量影响的流域侵蚀速率变化控制，该湖泊沉积物磁化率波动可以有效的指示该地区降水量变化；沉积物中总有机碳含量和总氮含量变化主要反映湖泊自身初级生产力的变化，对区域温度变化的响应显著. 相似文献
6.
对太湖西北部主要入湖河流、河口及近岸湖区64个表层沉积物样品进行粒度分析,结合粒度参数计算和聚类分析,探讨了表层沉积物的粒度分布特征及其沉积类型.研究结果表明:研究区沉积物平均粒径介于4.0~58.7μm之间,粒级组分为黏土、粉砂和砂,其含量的均值分别为7.19%、81.81%和11.00%.太湖西北部表层沉积物以粉砂和砂质粉砂为主;研究区粒度总体呈南粗北细的分布特征,太湖西部沿岸区距离物源区较近且水动力条件复杂,沉积物粒度较粗.太湖北部入湖河流沉积物的频率曲线峰形较宽,峰值位于细粒级;西岸入湖河道多呈单峰态,粒径偏粗;河口区沉积物粒径较河道偏粗,粗颗粒含量高.Q型聚类分析结果表明,研究区可分为4类沉积区,其中3类沉积区有典型特征:第1类沉积区主要分布在太湖西部沿岸,其沉积物粒度相对较粗;第2类沉积区主要位于入湖河流河口,沉积物粒度最粗;第3类沉积区位于蓝藻频发的梁溪河,其沉积物黏土含量极高,表明沉积物粒度特征可能与污染状况有一定的联系. 相似文献
7.
石梁河水库是江苏省最大的人工湖泊.开展水库沉积速率研究,对认识水库环境变化具有重要意义.本文对石梁河水库沉积物岩芯粒度组成特征进行了分析,表明沉积物以黏土质粉砂和粉砂质黏土为主,从底部向上呈明显的变细趋势,并记录了1970年的强降雨事件.采用137Cs同位素测年分析,得到1963年和1986年两个时标.通过石梁河水库的沉积年代序列,推算出平均沉积速率:1963 1970年为10.85 cm/a,1970 1986年为3.81 cm/a,1986 2005年为1.32 cm/a.对比粒度沉积特征和流域降水记录,粗颗粒物质和降雨量的变化趋势基本相同,沉积物粒度组成特点直接反映了沉积时的降水、水动力搬运强度等信息.在河川来水来沙、坝前水位变化和地形等条件下,石梁河水库表现为三角洲淤积,且沉积速率逐渐变缓,符合水库淤积的一般规律.此外,石梁河水库上游建设的众多大型水库,拦截了大量泥沙,也使得沉积速率呈现减小趋势. 相似文献
8.
筑坝拦截对黑河河道沉积物粒度空间分布的影响 总被引：2，自引：1，他引：1
河流沉积物对流域环境变化具有敏感响应，其粒度参数能反映沉积环境中物质来源和水动力环境.本文以黑河流域上中游为研究区域，探究河流沉积物粒度对流域环境变化的响应.从黑河上中游干流22个主要控制断面采集河床沉积物样品，采用筛分法和吸管法对沉积物样品粒度参数进行测定，并分析其空间分布规律对筑坝拦截为主的环境改变响应.研究结果表明：受梯级水库建设影响，黑河上中游泥沙粒径大小差异显著.干流库区泥沙粒径较自然河段明显减小，分选很好，呈正偏或极正偏尖锐分布，而且在库区不同沉积高度上表现出分层沉积特征；坝下游河段因遭受强烈冲刷，较自然河段泥沙粒径粗化显著，分选变差，偏态趋向极正偏，峰态尖锐化；水库回水区受水库壅水及下泄清水的双重制约，泥沙粒度参数介于自然河段和坝下游河段之间，整体分选中等，呈极正偏尖锐分布；沉积环境分析表明，上游支流河段沉积物粒度特征受泥沙供给和物源特征的影响较水动力条件显著，干流河段沉积物粒度特征主要受水动力条件控制.研究结果既符合河流上中游沉积物粒度分布规律，也反映了河流环境变化对沉积物粒度组成的影响. 相似文献
9.
全新世镜泊湖粒度特征记录的该地区古降水变化历史 总被引：3，自引：5，他引：3
在湖泊沉积与环境演变研究中,粒度参数通常用来反映湖泊水动力条件的变化,进而反映湖面波动状况以及湖区环境有效湿度的变化．镜泊湖JPH-1钻孔沉积物粒度分析表明:全新世以来镜泊湖沉积物粒度的变化呈现明显的粗细交替变化的规律性．结合14C测年,镜泊湖沉积物粒度特征有效地指示了历史时期镜泊湖水动力变化的情况．进而揭示了该地区古降水的变化历史．9300-8540cal aBP,是一个降水较少的偏干旱时期;8540-6350 cal aBP,降水颇丰的湿润时期; 6350-3120cal aBF,气候波动频繁,前期(6350-4800 cal aBP)由湿润向干旱过渡,后期(4800-3120cal aBP左右)又由于早转向湿润,31 20-1 580 cal aBP,降水较多,气候湿润;1 580 cal aBP至今,降水变化波动剧烈,这阶段粒度特征的变化除了与降水的自然变化有关外,还与人类活动的剧烈影响有关系．湖区周围人类活动破坏了原始植被,大量地表裸露,降水冲刷地表作用明显增大,陆源物质被携带人湖,粗颗粒含量显著增多． 相似文献
10.
浅水湖泊生态系统中的沉积物—水界面是湖泊内源氮释放的重要界面,而水动力因素是改变沉积物氮释放的重要因素.三峡大坝修建以后,长江中下游通江湖泊的水动力条件发生了明显的变化.通过采集洞庭湖湖口区域的沉积物和水样,在双向环形水槽动力模拟装置内模拟湖泊水位和流速的变化,探讨湖泊沉积物氮在沉积物和水系统中的二次释放特征.结果表明,随着扰动强度的增加,上覆水悬浮物浓度增大,上覆水中总氮浓度增加,沉积物向上覆水释放氮的强度增强,水动力条件的改变所引起的沉积物内源氮释放不容忽视.在该模拟实验条件下,沉积物存在最适扰动水位(20cm),此水位下上覆水中悬浮物浓度最低,总氮浓度最小.水动力条件的改变对上覆水和沉积物—水界面处铵态氮和硝态氮浓度的影响并不明显,孔隙水中铵态氮与硝态氮之间发生形态的转化. 相似文献
11.
A. G. Brown 《地球表面变化过程与地形》1985,10(3):281-291
The vertical and horizontal variation of sedimentary fades is the raw data for the interpretation of flood plain history from which palaeohydrological inferences are frequently drawn. Mixed and fine floodplain sediments present problems of interpretation because of a large grain size range and frequent polymodality caused by the mixing of process-associated grain size components. This paper discusses the use of traditional grain size statistics and the use of the mode and multivariate statistics. The mode, although much neglected, is indicative of up-profile grain size changes and has practical advantages over the mean for mixed and fine floodplain sediments. Constrained cluster analysis and principal components analysis are used directly on Coulter counter results. These techniques can rapidly divide a floodplain profile into grain size units and indicate the principal vectors of grain size variation which will be related to the changing processes of deposition. Principal components analysis reveals the importance of the medium to fine silt category in accounting for grain size variations, suggesting that a critical factor in determining the type of alluvial unit deposited is the degree to which it has received fine suspended material. Grain size data from the Lower Severn are used to construct a CM diagram which is compared with a texture triangle. From both the CM and multivariate analysis a generalized backswamp profile is constructed which shows the existence of a coarser top unit caused by the addition of a fine to medium sand component to the underlying sediment during the Late Holocene. 相似文献
12.
Lichenometry is a dating technique that has problems relating to questionable assumptions. The development of a size frequency approach, previously used in attempts to resolve some of the problems, is described and applied to the dating of four debris flows marginal to the San Rafael Glacier in Southern Chile. This study provides examples of the development's application, its problems and directions for further work. The size frequency approach, based on new assumptions, uses parameters derived from population size frequency distributions of the lichen species Placopsis patagonica to provide relative and absolute dating for rock surfaces. Changes in the shapes of distributions suggest the relative age of populations. Absolute dating is based on a curve (spanning a 24 year time period) derived from mean diameter size/age correlations. A stratified random sampling design permits the use of inferential statistics. Standard deviations and confidence intervals show error margins, the degree of relatedness between neighbouring populations, and populations that are anomalous. One-way analysis of variance is used to indicate where populations may safely be grouped. The size frequency approach appears to be particularly suitable for use on unstable debris flows where secondary movements are common. The approach also demonstrates that lichen growth and colonization are sensitive to aspect differences and other variations in microhabitat. 相似文献
13.
Numerical studies of flow over a sill: sensitivity of the non-hydrostatic effects to the grid size 总被引：1，自引：1，他引：0
A non-hydrostatic terrain-following model in cross sectional form is applied to study the processes in the lee of a sill in
an idealized stratified fjord during super-critical tidal inflow. A sequence of numerical studies with horizontal grid sizes
in the range from 100 to 1.5625 m are performed. All experiments are repeated using both hydrostatic and non-hydrostatic versions
of the model, allowing a systematic study of possible non-hydrostatic pressure effects and also of the sensitivity of these
effects to the horizontal grid size. The length scales and periods of the internal waves in the lee of the sill are gradually
reduced and the amplitudes of these waves are increased as the grid size is reduced from 100 down to 12.5 m. With a further
reduction in grid size, more short time and space scale motions become superimposed on the internal waves. Associated with
the internal wave activity, there is a deeper separation point that is fairly robust to all parameters investigated. Another
separation point nearer to the top of the sill appears in the numerical results from the high-resolution studies with the
non-hydrostatic model. Associated with this shallower separation point, an overturning vortex appears in the same set of numerical
solutions. This vortex grows in strength with reduced grid size in the non-hydrostatic experiments. The effects of the non-hydrostatic
pressure on the velocity and temperature fields grow with reduced grid size. In the experiments with horizontal grid sizes
equal to 100 or 50 m, the non-hydrostatic pressure effects are small. For smaller grid sizes, the time mean velocity and temperature
fields are also clearly affected by the non-hydrostatic pressure adjustments. 相似文献
14.
Dirk Goossens 《地球表面变化过程与地形》2006,31(6):762-776
Wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits. Experiments were performed on three isolated hills having various size and aspect ratios. The longitudinal profile of the median grain diameter was investigated for each hill. The longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 µm, as were wind and dust concentration profiles in the atmosphere upwind of, over and downwind of a hill. The wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography. Most apparent is the occurrence of a zone of reduced grain size on the leeside of hills, which extends from just upwind of the summit to a distance of several times the height of the hill. Slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size, but the increase in grain size in these zones remains very small. Although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size, systematic trends are observed. The most important tendencies are: (1) a progressive extension, in the downwind direction, of a zone of decreased dust deposition on the leeside of a hill (the coarser the grains, the further downwind the zone of reduced deposition extends); (2) a progressive increase in dust deposition immediately upwind of a hill (the finer the grains, the higher the deposition value upwind of a hill becomes). Both tendencies are explained by the difference in inertia of the grains, which is controlled by grain size. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
15.
《国际泥沙研究》2016,(4):291-298
As a result of the interaction between hydrodynamics and the effects of gravity, riverbank collapse is a common occurrence in the desert reach of the upper Yellow River (also called as Ningxia-Mongolia Inner reach), of which the riverbank may be divided into three types such as sandy riverbank in the wide-valley desert reach, silt-deposition riverbank on the fluvial plain and silt–sandy riverbank. The char-acteristics of both typical riverbank collapse and the particle size distributions (PSDs) for collapsed riverbanks of sandy, silt-deposition, and silt–sandy types were determined from analysis of data obtained from the field observations. It was found that particles from the silt-deposition riverbank had the smallest median size and those from the sandy riverbank the largest, with those from the silt–sandy riverbank being intermediate in size. The PSDs of the sandy and silt-deposition riverbanks exhibited double-peaked and single-peaked structures, respectively, while those of the silt–sandy riverbank exhibited multiple peaks. Furthermore, the corresponding to three kinds of riverbank collapse mechanisms were revealed. These results are significant with regard both to the understanding of river dynamics and to the planning of river harnessing projects. 相似文献
16.
On the growth of maars and diatremes and its relevance to the formation of tuff rings 总被引：8，自引：2，他引：8
V. Lorenz 《Bulletin of Volcanology》1986,48(5):265-274
Small and large maars exist associated with small and large diatremes, respectively, their subsurface feeder structures. The problem of size and growth of maar-diatreme volcanoes is discussed from a phreatomagmatic point of view from field data, some geophysical data, and short-lived historic maar eruptions. A hydrostatic pressure barrier of usually about 20–30 bars is assumed to control the maximum depth level of explosive magma/groundwater interactions. Similar to the situation in submarine and subglacial volcanism, initial maar-forming water vapour explosions are therefore assumed to occur at shallow depth and to produce a small maar with a shallow diatreme. Because of limited availability of groundwater and ejection of groundwater in the form of steam, the confining pressure barrier is displaced downward. Consequently, water vapour explosions can take place at consecutively deeper levels with the result that the diatreme penetrates downward and grows in size. Since maars are collapse craters resulting from ejection of wallrocks fragmented by water vapour explosions at the level of the diatreme root zone, downward penetration of a diatreme not only results in increase in size of a diatreme but also in increase in size of the overlying maar. As availability of groundwater in limited amounts controls formation of diatremes and their downward penetration, lack of groundwater enables magma to rise within a diatreme and to form a scoria cone or lava lake within the maar, as is frequently found in volcanic fields such as the Eifel area in Germany. In contrast, availability of large amounts of water in near surface environments such as shallow marine, lake, water-rich coastal plains, or water-rich fluviatile gravel beds prevents formation of maars and deep diatremes but causes formation of tuff rings. 相似文献
17.
The paleoenvironmental significance of spatial distributions of grain size in groundwater‐recharged lakes: A case study in the hinterland of the Badain Jaran Desert,northwest China 
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下载免费PDF全文 For lakes in desert hinterlands that are not recharged by river runoff, sediment input solely comes from wind transport. While the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge, the spatial distribution of sediment grain size in these groundwater‐recharged lakes remains largely unknown. Moreover, whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear. In this study, five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the Badain Jaran Desert of north‐western China, and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size. Moreover, an end‐member‐modeling algorithm was used to calculate end members from all grain size measurements. Our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore, deep‐water zone. However, the lowest median and mean grain sizes were not found in the center of the lakes, in contrast to lakes recharged by surface runoff. The median grain size of sediment in the lake center was negatively correlated with lake level, and thus could help reveal lake evolution at low resolutions. Moreover, EM1 and EM2 were interpreted as wind transported sediment, and sediment perturbed by lake waves after wind transport, respectively. The modal grain size of EM1 varied slightly between lakes, while changes in the modal grain size of EM2 were related to lake area. Given the positive relationship found between EM2 content and lake level, changes in the EM2 content (%) can serve as a rough indicator of lake level fluctuations at low temporal resolutions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
18.
S. Santiago R. L. Thomas L. McCarthy J. L. Loizeau G. Larbaigt C. Corvi D. Rossel J. Tarradellas J. P. Vernet 《水文研究》1992,6(2):227-240
Ten large volume water samples were taken from the Rhône River (Switzerland-France) in November, 1989 for recovery of total suspended sediment by continuous flow centrifugation. the samples were freeze-dried and analysed for particle size, organic carbon, total nitrogen, and carbonate. for comparative purposes, four bed sediments collected in July, 1989 are also described. the Rhône can be subdivided into three sections on the basis of the origins of the water. the first section is the Upper Rhône River draining into Lake Geneva. Waters are derived from glaciers, with low temperature and conductivity and high turbidity. Suspended sediment is coarse, has a bimodal distribution, and is low in both organic matter and carbonate. the second reach is from Lake Geneva to the confluence with the Saône at Lyon and has warmer water with higher conductivity and very low turbidity. Suspended sediment is higher in organic matter, with high carbonate originating from the lake. the final section is from Lyon to Arles, with warmer water and higher conductivity and turbidity due to modification by the Saône. Sediment is rich in organic matter, which May, account for an observed decline in oxygen in the river waters downstream from Lyon. Carbonate in these sediments also decreases due to increased turbidity from the Saône. Suspended sediments other than from the Upper Rhône show a remarkable consistency in grain size, predominantly in the fine silts (mode 9-11 μm). This consistency indicates a high degree of suitability for geochemical analysis. Bed sediments were bimodal throughout, with a dominant coarse population in two out of the four samples. Grain size statistical parameters could be easily explained by application of the theory of mixing of two major populations in the sand size (bed traction load) and the fine silt/clay size (suspended sediment load). 相似文献
19.
The chemical composition of sediment sampled from a network of ice boreholes contacting the bed of the ablation zone of the Greenland Ice Sheet is compared to the composition of intact bedrock clasts. This sediment is enriched in silica and depleted in reactive cations compared to the underlying bedrock. In order to test whether these differences result from grain size biases either in sample collection or due to natural sorting, sediment samples were analyzed by grain size aliquots. Enrichment of silicon and depletion of cations is consistent across grain size classes and the compositions of bedrock and subglacial sediment are statistically separate. The difference in composition between subglacial sediment and rock aligns closely with the composition of dissolved solutes in waters sampled from the same field sites and is dissimilar to the composition of the sites' suspended sediment. This implies that chemical weathering rather than disproportionate physical removal of friable minerals is responsible for the compositional differences between rock and sediment. Mass balance analysis implies 3–10% of the sediment's mass is lost to solute dissolution, with approximately double that amount precipitated as clay minerals (a large portion of which may have been physically expelled). This result implies that temperate ice sheet subglacial environments may be more chemically active than previously realized. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献