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1860年以来博斯腾湖碳沉积过程演变 总被引：1，自引：1，他引：0
选取博斯腾湖3个不同点位岩芯,在210Pb和137Cs年代序列基础上,利用沉积物中的各理化指标,分析了该湖碳沉积的时空变化特征,结合各指标的相关性、沉积速率、C/N、同位素特征等,探讨了该湖1860年以来碳沉积环境的变化过程,为干旱区湖泊碳埋藏研究提供了依据.结果表明：1860-1910年,沉积速率相对较小,受人类活动影响较小,磁化率、中值粒径、总无机碳（TIC）较为稳定,总有机碳（TOC）含量相对较低,此时该湖有较多陆源有机质的输入;1910-1950年,湖泊西部浅水域沉积速率明显高于东部深水区,西北湖区水域有大量外源物质的输入,而湖泊初级生产力较低,内源贡献相对较小;1950-1980年,全湖TOC、TIC含量均呈现升高的趋势,尤其是西北近黄水沟水域升高最快,湖泊内源贡献在增加,陆源组分的输入相对前一阶段要少;1980-2002年,沉积速率快速升高,尤其湖泊东部水域最为明显,TOC含量均呈现升高的趋势,湖泊西部水域初级生产力要高于东部深水区,湖面蒸发较强,气候比较温暖;2002年以来,全湖沉积速率相对较高,外源有机质贡献较小.过去150年博斯腾湖沉积物碳累积速率整体上呈现出升高的趋势,尤其是近50年来快速升高,东部湖区碳累积速率比西部湖区高. 相似文献
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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
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人类活动影响下的固城湖环境变迁 总被引：2，自引：1，他引：1
2005年在江苏固城湖湖心采集了连续岩芯,进行了多环境代用指标(有机碳、氮、磷以及金属元素)的分析.210Pb CRS模式计算表明,1980s后沉积速率平均约0.067 cm/a,与137Cs 1986年时标得到的沉积速率吻合.而1920s至1980s,固城湖沉积速率变化较大,在0.056-0.167cm/a之间,其中1960s沉积速率最高,对应于该阶段固城湖强烈的人类围垦活动.元素Cu、Pb、Zn、Cr的含量在表层增长迅速,对比参考元素的变化,表明固城湖受到了一定程度的人为造成的重金属污染.岩芯0.5m到1.78m深度的AMS 14C的树轮校正年龄在8000-6500BC之间,光释光数据表明同等深度其绝对年龄在7-8ka之间,多环境代用指标在岩芯30cm深度左右出现了大的转折,表明近代存在沉积物缺失的可能。这也许与该区春秋末期以来的反复围垦活动有关,人类活动改变了湖泊沉积的模式.有资料表明,固城湖彻底与太湖隔绝是在公元1556年胥溪河河段下坝建成之后.若依此时间对应于岩芯30cm深度,得到的平均沉积速率为0.067cm/a,与1980s以来的沉积速率一致,有可能指示固城湖至下坝建成以来才出现沉积物的持续沉积. 相似文献
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210PBex沉积通量突发增大对湖泊生产力的指示--以程海为例 总被引：4，自引：0，他引：4
210Pb沉积计年的基本假设是大气沉降并经由湖水转入沉积物的210Pbex通量稳定.当沉积速率相对稳定时,沉积物中210Pbex的比活度将随沉积年代呈指数衰减.湖泊水体中的210Pbex主要随有机微粒的沉降而进入沉积物.如果湖泊水体中有机质沉积通量出现突发增大时,则可能显著地增大210Pbex被清洗而转入沉积物的通量.这种突发性清洗效应,一方面显然不符合210Pb沉积计年的基本前提; 另一方面可能指示湖泊水体初级生产力的明显变化.根据云南程海近代沉积物210Pbex垂直剖面的特殊变化,对这一问题进行讨论.沉积物柱芯于1997年6月采自程海深水湖区.137Cs比活度垂直剖面呈现出3峰特征,给出了可靠的计年结果并显示出近几十年间沉积物堆积的稳定性.而210Pbex比活度垂直剖面呈现出特异的峰值分布,并与Corg垂直剖面相似.这一现象可能与制约210Pbex转入沉积物的机制有关.程海沉积物中Horg/Corg和Corg/Norg原子比平均值分别为5.51和7.04,表明其有机质主要源于内生藻类残骸.根据沉积物有机质"沉降-降解-堆积"的3阶段特征,模拟计算出1970年以来有机碳Corg的沉积通量(F(Corg)).不同年代210Pbex的沉积通量(F(210Pbex))与F(Corg)显示出很好的同步关系.特别是1972～1974年和1986～1989年的两个时段,二者同步增大.F(Corg)的变化导致F(210Pbex)的变化; F (210Pbex)的变化在一定程度上反映出湖泊生产力的历史变化. 相似文献
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湖泊沉积有机碳同位素与环境变化的研究进展 总被引：22，自引：2，他引：20
湖泊沉积有机质稳定碳同位素（δ^13Corg)在区域气候与环境变化方面的应用近年来发展迅速,成果令人瞩目,保存在各类湖泊岩芯中的δ^13Corg记录揭示了晚更新世以来大气CO2浓度的变化、湖泊水位波动、湖区生态与植被的变迁以及气温变化等重要环境信息,由于造成δ^13Corg值变化的影响因素较多,确定个湖与环境变化有关的主导因素时常有赖于其它证据的帮助,诸如地球化学、古湖沼学、孢粉学、分子同位素地层学等等,前人通过研究来自不同类型湖泊、具不同曲线形态特征的δ^13Corg记录,提出了多种环境解释模型,本文对此作了归纳和评述。鉴别和澄清湖泊沉积有机质的源物质以及有机物源随环境变化而发生过的变化,是研究δ^13Corg记录环境意义至关重要的基础性工作,由于有机质含量、碳氮比值、氢指数、生物残留物鉴别等常能提供有关有关湖泊有机质来源、产率、成岩作用等方面的有用信息,这方面的研究结果应该尽可能一并提供,以利于恰当地应用现有的环境解释模型,或者建立个湖新模型,单体生物标志化合物鉴别通常也能为区分湖积有机质中陆生、水生、细菌生等不同碳的来源提供有用信息,特定化合物同位素分析技术近年来成功地应用于建立单体生物标志化合物碳同位素地层学,为湖积有机碳同位素在生态环境演变研究方面的应用提供了思路,我国许多湖泊的湖底沉积岩芯尚未钻取,那些对过去全球变化研究有价值的δ^13Corg记录有待我们去获取和研究。 相似文献
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对江汉平原江陵剖面沉积物中的总有机碳（TOC）、总氮（TN）、有机碳同位素δ13C值和粒度参数的分布特征与环境气候的关系进行了研究.结果表明：沉积物中有机碳、总氮较高,有机质的δ13C值偏负,沉积物的平均粒径较粗时,气候温暖湿润;反之,沉积物中有机碳、总氮较低,有机质的δ13C值偏正,沉积物的平均粒径较细时,气候温凉偏干.结合14C测年,判别江汉平原江陵地区的古气候演化过程：8900-6070 aBP,为温湿时期;6000-4600 aBP为相对冷干时期;4600-2500 aBP为温暖湿润时期;2500 aBP以来为温凉偏干时期. 相似文献
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13kaBP以来滇池地区古环境演化 总被引：6，自引：1，他引：5
根据DC93一1孔孢粉组合、总有机碳（TOC）、总氮（TN）、碳氮比（C／N）、有机碳同位素δ13Corg、磁化率（χ）、频率磁化率（χfd）等资料,结合14C、210Pb和137Cs测年,滇池地区13ka以来的古环境演化历史经历了以下几个阶段：13—10．2kaBP．气候偏凉湿,湖水深度不大;10．2－7．5kaBP,气候向暖湿过渡．湖水渐深;7．5－4．0kaBP,气候暖湿,出热条件达到最佳配制,湖水也最深．6．5kaBP前后,气温最高,这一时段古气候状况存在次级波动;4．0－2．7kaBP,气候突转干旱．湖水最浅;2．7－1．7kaBP,气候温湿,湖面扩大,湖水变深;1．7kaBP,人类活动影响的加剧,使湖泊环境的变化更为复杂． 相似文献
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D. M. Pechersky A. A. Lyubushin Z. V. Sharonova 《Izvestiya Physics of the Solid Earth》2010,46(7):613-623
The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The
times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized
by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and
the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between
the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic
world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by
the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle
of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes
in the organic world. 相似文献
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The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth. 相似文献
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综合APIA、HONOLULU、PAMATAI 3个地磁台三分量的11年周期变化的形态后,可定性地提出该变化源于内场。如内源为核幔边界的电涡流,则其中心点应位于3台之间。 相似文献
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The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4. 相似文献
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As is known, the secular deceleration of the Earth's diurnal rotation is explained mainly by the tidal friction in the ocean. Below we consider this mechanism in some detail, taking into account also elastic deformations of the mantle under the action of ocean loading and the interaction between the tide-generating body, ocean tidal wave, liquid outer core, and solid inner core. It is shown that elastic displacements of the core-mantle boundary under the action of ocean loading are of about the same amplitude and phase as the elastic loading displacements of the Earth's outer surface. As a result, side by side with the mechanism of secular deceleration of diurnal rotation of the mantle, there are also (1) the opposite mechanism of secular acceleration of diurnal rotation of the outer liquid core and of the solid inner core and (2) the mechanism of excitation of differential rotation in the liquid core. Taking these effects into account, we compare theoretical and modern observed data on the eastward drift of the solid inner core. It is shown that the best agreement may be obtained if the turbulent viscosity of the liquid core is about 2 × 10
3
Poise 相似文献
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On data of bottom sampling, carried out by means of grab, trawl and underwater photography in August–September of 1993 in the area of the Pechora Sea, quantitative regularities of macrobenthos distribution are described for the ecological monitoring purposes. Maps of -biodiversity and biomass indices, bottom communities and trophic zones, singled out by dominant method, are presented. Assessment of structure changes of the investigated area bottom communities during the last 60–70 years is fulfilled. It is shown that the described communities on the whole are of natural undisturbed character and that the revealed changes are within the natural fluctuations in the abundance of benthic populations or may be interpreted in terms of methodical differences in the data analysis and generalization by different authors. 相似文献
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地震激励下处于深水中的桥墩和周围水体的相互作用将对桥梁结构的动力响应产生较大影响。首先对地震作用下水-桥墩的相互作用理论做了概括,给出了动水压力对桥墩的作用效应及各自的适用范围;对主要的三种考虑流固耦合效应的分析方法做了对比,探讨了地震作用下影响水-结构相互作用的主要因素,并对今后的研究提出了建议。 相似文献
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Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan. 相似文献
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在数据完整率达到95%的基础上,为进一步确保中国大陆构造环境监测网络GNSS基准站观测数据质量,选取2010—2020年全国基准站观测数据,采用TEQC软件进行质量检验,分类整理其中多路径效应计算结果呈典型特征的台站,结合观测环境状态,对多路径效应存在的区域性特征进行分析,发现除接收机天线周围发生遮挡外,硬件更换、台站周围地势差等因素,均对多路径效应产生不同程度的影响,可为建站选址和观测环境监测工作提供参考。 相似文献