Carbon and oxygen isotope records and paleoclimate reconstruction (140–250 ka B.P.) from a stalagmite of Shuinan Cave, Guilin, China     

Zhang Meiliang  Cheng Hai  Yuan DaoXian  Zhu Xiaoyan  Lin Yushi  Qin Jiaming  R. L. Edwards 《Environmental Geology》2006,49(5):752-764

The time sequence of paleoclimatic changes from 245.2 to 147.9 ka B.P. has been established by high precision U-series dating by Thermal Ionization Mass Spectrometry and the analysis of the oxygen isotopes from a stalagmite of Shuinan Cave in Guilin. The oxygen isotope pattern is divided into three main intervals. The top part of the stalagmite (interval C) displays mainly relatively heavy oxygen isotopes, mostly −7 to −5‰_VPDB, but at a depth of 86.5 cm below the top, there is a sharp change to values lighter than −8 ‰. This boundary, dated at 192.6 ±3.9 ka B.P. is correlated with the boundary between marine oxygen isotope stages 6 and 7. The underlying interval B has δ¹⁸O values consistently between −7.5 and −8.5‰ until 271 cm depth when there is a sharp rise in δ¹⁸O values towards values as heavy as −5‰. The upper position of this change is dated at 242.5±6.4 ka B.P. and is correlated with the boundary between marine isotope stages 7 and 8. Carbon isotope values lie between −8.5 and −11‰ and are not uniquely high or low in the three intervals, but also show rapid changes at the boundaries between intervals in the same sense as the shifts in δ¹⁸O. The pronounced shifts in δ¹⁸O are attributed to changes in the paleo-monsoon intensity which reflect major reorganizations of the climate system, but some regional characteristics are also present. The results are also consistent with previous studies of climate proxies from loess-palaesol sequences in northern China. These characteristics show that paleo-climate evolution since the late stage of the middle Pleistocene Epoch in the Guilin area not only follows the global characteristics, but also has the strong district or regional patterns.  相似文献   

Changes of PTSD Symptoms and School Reconstruction: A Two-year Prospective Study of Children and Adolescents after the Taiwan 921 Earthquake   总被引：5，自引：0，他引：5  

S.-H. Chen  Y.-C. Wu 《Natural Hazards》2006,37(1-2):225-244

Children and adolescents living in earthquake impacted areas may present various post-traumatic responses and adjustment along the post-traumatic reconstructive phases. Their surrounding environmental damage and reconstructive conditions may influence their adjustment as well. As part of a prospective and longitudinal research project aims to investigate the range and severity of post-traumatic stress disorder (PTSD) symptoms in children and adolescents residing near the epicenter after the Taiwan 921 Earthquake, this paper reports the changes of PTSD symptoms over a 2-year period. The study also examines the effects of school damage and reconstructive condition on PTSD symptoms. Earthquake Exposure Index for Youths and Child Posttraumatic Stress Disorder Reaction Index were administered to 2,028 and 2,077 youths at the first and second year, respectively, from two heavily impacted townships. Given that location, gender, individual and dwelling trauma exposure dose effect were controlled through a balanced sampling procedure and prior statistical confirmation, post-traumatic phase and school damage condition yield significant main effects. Students from the heavily damaged schools consistently displayed significantly more PTSD symptoms, including re-experiencing/avoidance and numbness/maladaptive symptoms, than their counterparts at the first and second year. Decline of prevalence of PTSD symptoms was noted from the first year to the second. Accordingly, there may be a need to implement a broad disaster recovery project with periodic screenings as well as school-specific and school-based mental health program.  相似文献   

The Necessity of a Multiple-Point Prior Model   总被引：9，自引：0，他引：9  

Andre Journel  Tuanfeng Zhang 《Mathematical Geology》2006,38(5):591-610

Any interpolation, any hand contouring or digital drawing of a map or a numerical model necessarily calls for a prior model of the multiple-point statistics that link together the data to the unsampled nodes, then these unsampled nodes together. That prior model can be implicit, poorly defined as in hand contouring; it can be explicit through an algorithm as in digital mapping. The multiple-point statistics involved go well beyond single-point histogram and two-point covariance models; the challenge is to define algorithms that can control more of such statistics, particularly those that impact most the utilization of the resulting maps beyond their visual appearance. The newly introduced multiple-point simulation (mps) algorithms borrow the high order statistics from a visually and statistically explicit model, a training image. It is shown that mps can simulate realizations with high entropy character as well as traditional Gaussian-based algorithms, while offering the flexibility of considering alternative training images with various levels of low entropy (organized) structures. The impact on flow performance (spatial connectivity) of choosing a wrong training image among many sharing the same histogram and variogram is demonstrated.  相似文献   

珠江三角洲软土地基变形的混沌特性研究     

刘勇健 《岩土力学》2006,27(1):73-76

混沌是非线性系统较普遍存在的一种现象，本文以混沌理论为基础，对珠江三角洲软土地基的变形特性进行了研究。从软土的工程特性和微观结构出发，分析了软土地基变形混沌性的根本原因，并对软土变形混沌性进行了定性判别和基于Lyapunov指数的定量判别。研究结果表明，珠江三角洲地区的天然地基及处理后的复合地基的最大Lyapunov指数 均大于0，软土地基的变形具有明显的混沌性。混沌理论为软基变形研究提供了一种新的途径，在工程领域具有广阔的应用前景。  相似文献   

初至波地震层析技术及其在四川复杂地区的应用   总被引：1，自引：0，他引：1  

陈爱萍  梁波  邹文  何光明  李亚林  李志荣 《世界地质》2006,25(4):440-444,449

近地表速度场的重建是获得准确静校正量的关键。根据实际地震数据的初至波时间建立初始速度模型;采用改进的最短路径射线追踪算法进行正演;利用改进的约束带阻尼联合迭代重建技术(CDSIRT)求解大型、稀疏的方程组来反演近地表的速度场。理论模型和实际资料的反演结果表明,该方法能稳定、快速、准确地重建复杂地区的近地表速度场,建立准确的近地表速度场,从而可计算准确的静校正量,保证复杂地区的构造成像。  相似文献   

西藏纳木错过去200年来的环境变化^*   总被引：6，自引：6，他引：6       下载免费PDF全文

王荣  羊向东  朱立平 《第四纪研究》2006,26(5):791-798

文章通过纳木错浅钻沉积硅藻研究,结合青藏高原湖泊现代硅藻-电导率转换函数,对过去200年来的湖水盐度(电导率)变化进行了定量重建。纳木错在小冰期冷期为淡水环境;小冰期结束后,湖水盐度开始增加;至20世纪60年代中期以来,盐度增加幅度更加明显。过去100年来湖水盐度的增加与钻孔粒度变化所揭示的入湖径流量的增多,反映了增温背景下湖泊水文的响应特点。温度的上升,一方面引起了流域冰雪融水补给量的增加,但另一方面,湖泊水量平衡明显偏负,说明小冰期结束以来,尤其是最近40年,冰融水的增加并不足以弥补湖泊水量的负平衡。由此提出蒸发量在湖泊水量平衡中起重要作用,温度是影响湖泊水文变化的关键因子。区域湖泊综合对比结果进一步表明,不同湖泊盐度和水文变化趋势一致,反映了封闭湖泊对区域气候变化的共同响应特点。  相似文献   

论湿地脆弱性与生态恢复重建--以洞庭湖区为案例     

沈彦  李婷婷 《云南地理环境研究》2006,18(1):10-13

洞庭湖区是长江中游流域最重要的以河湖系统为主的湿地分布区之一。由于人类长期垦殖活动，已成为中国重要的农业商品基地。洞庭湖区湿地生态系统受到自然因素和人为因素的影响，湖区湿地生态系统表现出脆弱性特征。在此基础上分析其主要脆弱性影响因子包括：地貌脆弱因子、气候脆弱因子、水文脆弱因子以及过度围湖造田、过度利用湖泊资源、超标污染物排放等。然后对湖区湿地生态系统的脆弱生态环境特征进行了分析，最后提出科学有效的生态恢复重建的措施。  相似文献   

Selection of prior distributions and multiscale analysis in Bayesian temperature reconstructions based on fossil assemblages     

Panu Erästö  Lasse Holmström 《Journal of Paleolimnology》2006,36(1):69-80

It is possible to reconstruct the past variation of an environmental variable from measured historical indicators when the modern values of the variable and the indicators are known. In a Bayesian statistical approach, the selection of a prior probability distribution for the past values of the environmental variable can then be crucial and the selection therefore should be made carefully. This is particularly the case when the data are noisy and the statistical model used is complex since the influence of the prior on the results can then be especially strong. It can be difficult to elicit the prior probability distribution from the available information, since usually there are no measured data on the past values of the variable one wants to reconstruct and different reconstructions are typically consistent with each other only at a coarse level. To overcome these difficulties we propose to use a non-informative smoothing prior, possibly in combination with an informative prior, that simply penalizes for roughness of the reconstruction as measured by the variability of its values. We believe that it can sometimes be easier to set an overall prior distribution on the roughness than to agree on a prior for the actual values of the reconstructed variable. Note that by using a smoothing prior one incorporates into the model itself the smoothing step usually done before or after the actual numerical reconstruction. Another idea proposed in this paper is to integrate the reconstruction model with a multiscale feature analysis technique known as SiZer. Multiscale analysis of the posterior distribution of the reconstructed variable makes it possible to infer its statistically significant features such as trends, maxima and minima at several different time scales. While only temperature is considered in this paper, the technique can be applied to other environmental variables.  相似文献   

Holocene thermal optimal and climate variability of East Asian monsoon inferred from forest reconstruction of a subalpine pollen sequence, Taiwan     

P.M. Liew  C.Y. Lee  C.M. Kuo   《Earth and Planetary Science Letters》2006,250(3-4):596-605

The East Asian monsoon Holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation. In this study we show Holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central Taiwan, based on modern analogues of various altitudinal biomes in the region. A warmer interval occurred between 8 and 4 ka BP (calibrated ¹⁴C years) when the subtropical forests were more extensive. The Holocene thermal optimum is represented by an altitudinal tropical forest at 6.1–5.9 ka BP and 6.9 ka BP and only the latter was accompanied by wet conditions, indicating decoupling of thermal and precipitation mechanism in the middle Holocene. Abrupt and relative severe cold phases, shown by biome changes, occurred at about 11.2–11.0 ka BP; 7.5 ka BP; 7.2 ka BP; 7.1 ka BP; 5.2 ka BP, 5.0 ka BP and 4.9 ka BP. A spectral analysis of pollen of a relatively cold taxon — Salix, reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of Indian and western Pacific Oceans. The cold–warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of Be-10.  相似文献   

CHANGES IN ICE-MARGIN PROCESSES AND SEDIMENT ROUTING DURING ICE-SHEET ADVANCE ACROSS A MARGINAL MORAINE     

PETER G. KNIGHT  CARRIE E. JENNINGS  RICHARD I. WALLER  ZOE P. ROBINSON 《Geografiska Annaler: Series A, Physical Geography》2007,89(3):203-215

Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice‐marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice‐proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris‐rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations.  相似文献