Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa     

Andrew S. Cohen  Kiram E. Lezzar  Julia Cole  David Dettman  Geoffrey S. Ellis  Meagan Eagle Gonneea  Pierre-Denis Plisnier  Victor Langenberg  Maarten Blaauw  Derrick Zilifi 《Journal of Paleolimnology》2006,36(2):189-209

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ∼∼2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals.Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual–centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual Δ¹⁴C record for this same time period, two large Δ¹⁴C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal– centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light–dark couplets at decadal–centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake.  相似文献   

Verification of the motion fields over Southeast Asia by the Florida State University (FSU) superensemble forecast     

Mastura Mahmud  Robert S. Ross 《Singapore journal of tropical geography》2006,27(2):176-190

The Florida State University (FSU) multimodel superensemble forecast is evaluated against several other operational weather models for the Southeast Asia region. The superensemble technique has demonstrated its exceptional skills in forecasting precipitation, motion and mass fields compared to either individual global operational or ensemble mean forecasts. The motion field investigation for the season of 2001 reveals that the superensemble forecasts are closer to the observed data compared to the other global member operational models through its low systematic errors at the 850 hPa level. The FSU multimodel superensemble forecasts exhibit the lowest root mean square errors (RSMEs), the highest correlation against the best observed data and the lowest systematic errors compared to the other operational model members. These forecasts have the potential to provide better daily weather predictions over the Southeast Asia region, particularly during the early northeast monsoon that often causes heavy rainfall in the equatorial part of the Southeast Asia region.  相似文献   

Initiation and development of pull-apart basins with Riedel shear mechanism: insights from scaled clay experiments     

Nassima Atmaoui  Nina Kukowski  Bernhard Stöckhert  Diethard König 《International Journal of Earth Sciences》2006,95(2):225-238

Typical pull-apart structures were created in scaled clay experiments with a pure strike-slip geometry (Riedel type experiments). A clay slab represents the sedimentary cover above a strike-slip fault in the rigid basement. At an early stage of the development of the deformation zone, synthetic shear fractures (Riedel shears) within the clay slab display dilatational behaviour. With increasing basal displacement the Riedel shears rotate and open further, developing into long, narrow and deep troughs. The shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes. At a more evolved stage, synthetic segments (Y-shears) parallel to the basal principal fault develop and accommodate progressive strike-slip deformation. The Y-shears connect the tips of adjacent troughs developed from the earlier Riedel shears, resulting in the typical rhomb-shaped structures characteristic for pull-apart basins. The Strait of Sicily rift zone, with major strike-slip systems being active from the Miocene to the Present, comprises pull-apart basins at different length scales, for which the structural record suggests development by a mechanism similar to that observed in our experiments.  相似文献   

Decision-support systems for groundwater protection: innovative tools for resource management   总被引：1，自引：0，他引：1  

Stefan Kollarits  Gerhard Kuschnig  Miran Veselic  Ante Pavicic  Corrado Soccorso  Marina Aurighi 《Environmental Geology》2006,49(6):840-848

Governmental authorities are forced by law to make decisions within the framework of European, national and regional directives in the fields of spatial planning, groundwater and environmental protection. These tasks can be supported by a decision-support system, which integrates data from various sources and helps to make decision processes more effective and transparent. Basic work for such a decision support system has been done in a transnational and interdisciplinary project (Interreg II C: KATER), including metadata definition, metadata system, cartographic tools and GIS tools. The direct integration of these tools and information in the decision process will be implemented in the next few years (project KATER II).  相似文献   

Potential of High-Resolution Satellite Data in the Context of Vulnerability of Buildings   总被引：1，自引：2，他引：1  

Marina Mueller  Karl Segl  Uta Heiden  Hermann Kaufmann 《Natural Hazards》2006,38(1-2):247-258

High-resolution space-borne remote sensing data are investigated for their potential to extract relevant parameters for a vulnerability analysis of buildings in European countries. For an evaluation of large earthquake scenarios, the number of parameters in models for vulnerability is reduced to a minimum of relevant information such as the type of building (age, material, number of storeys) and the geological and spatial context. Building-related parameters can be derived from remote sensing data either directly (e.g. height) or indirectly based on the recognition of the urban structure type in which the buildings are located. With the potential of a fully- or semi-automatic inventory of the buildings and their parameters, high-resolution satellite data and techniques for their processing are a useful supporting tool for the assessment of vulnerability.  相似文献   

Fast computation of Hankel Transform using orthonormal exponential approximation of complex kernel function     

Pravin K. Gupta  Sri Niwas  Neeta Chaudhary 《Journal of Earth System Science》2006,115(3):267-276

The computation of electromagnetic (EM) fields, for 1-D layered earth model, requires evaluation of Hankel Transform (HT) of the EM kernel function. The digital filtering is the most widely used technique to evaluate HT integrals. However, it has some obvious shortcomings. We present an alternative scheme, based on an orthonormal exponential approximation of the kernel function, for evaluating HT integrals. This approximation of the kernel function was chosen because the analytical solution of HT of an exponential function is readily available in literature. This expansion reduces the integral to a simple algebraic sum. The implementation of such a scheme requires that the weights and the exponents of the exponential function be estimated. The exponents were estimated through a guided search algorithm while the weights were obtained using Marquardt matrix inversion method. The algorithm was tested on analytical HT pairs available in literature. The results are compared with those obtained using the digital filtering technique with Anderson filters. The field curves for four types (A-, K-, H-and Q-type) of 3-layer earth models are generated using the present scheme and compared with the corresponding curves obtained using the Anderson sc heme. It is concluded that the present scheme is more accurate than the Anderson scheme  相似文献   

On global forces of nature driving the Earth’s climate. Are humans involved?     

L. F. Khilyuk  G. V. Chilingar 《Environmental Geology》2006,50(6):899-910

The authors identify and describe the following global forces of nature driving the Earth’s climate: (1) solar radiation as a dominant external energy supplier to the Earth, (2) outgassing as a major supplier of gases to the World Ocean and the atmosphere, and, possibly, (3) microbial activities generating and consuming atmospheric gases at the interface of lithosphere and atmosphere. The writers provide quantitative estimates of the scope and extent of their corresponding effects on the Earth’s climate. Quantitative comparison of the scope and extent of the forces of nature and anthropogenic influences on the Earth’s climate is especially important at the time of broad-scale public debates on current global warming. The writers show that the human-induced climatic changes are negligible.  相似文献   

Construction Problems on the Karstified Limestone Tuffs of Condeixa, Central Portugal: A Case Study     

M. Quinta Ferreira  J. L. Velho 《Geotechnical and Geological Engineering》2006,24(1):101-116

During the excavations for the foundations of a three storey building on the limestone tuffs of Condeixa, Central Portugal, a large dissolution fissure and smaller dissolution voids were found. Since the area has never been the subject of engineering geology investigation, it was decided to evaluate the risk associated with the construction of the building. These limestone tuffs were formed in a continental environment by the precipitation of calcite carried by the water coming from the large limestone body in the east. The precipitated calcite mixed with the terrigenous materials and around trunks and leaves of plants, originating a very heterogeneous and porous ground, which is characteristic of limestone tuffs. The study started with a detailed geological survey followed by a large number of destructive drillings, located essentially under the pad foundations. The results revealed several karstic cavities with serious problems for the building foundations and the structure, and many smaller dissolution cavities, often filled with clayey soils. The ground treatment solutions used included, dental cleaning, filling with concrete or granular material the dissolution structures accessible at the level of the foundation, reinforcement of the footing and the structure of the building and adding a continuous foundation beam to hold the foundations together. The cost of the engineering geology study, site investigation, ground treatment, and the reinforcement of the foundation and building, increased the total construction cost from 2%, at the design stage, to 4.8%.  相似文献   

The geography of suicide terrorism in Israel     

Nurit Kliot  Igal Charney 《GeoJournal》2006,66(4):353-373

Palestinian suicide terrorism has been a key feature in the latest phase of the Israeli–Palestinian conflict. During the past decade, and particularly since September 2000, there has been a substantial increase in the use of this type of warfare. Recent studies suggest that, contrary to common belief, suicide terrorism is highly rational and driven by strategic considerations. This article explores the rationality of Palestinian suicide terrorism from a geographical perspective. It is argued that suicide terrorism works along two parallel paths: rationality and randomness. It complies with geographical fundamentals, and target selection is highly rational, subject to spatial considerations such as distance, agglomeration, and accessibility. As the permeability to Israel became more difficult, suicide bombers and their organizers had to adopt more flexible practices which emphasized other spatial considerations. Timing is of importance both for strategic and tactical reasoning. Obstructing negotiations and peace talks has been a salient objective, but the exact timing of suicide bombings has been influenced by tactical considerations, which aim at maximizing casualties.  相似文献   

大吨位基桩抗压载荷试验中的锚桩预应力保护技术     

陈雅琴  张宏光  冯忠居  谢永利 《工程地质学报》2006,14(4):531-536

竖轴向承载力是桩基础设计的重要参数,现场静载试验是目前确定桩基承载力的主要手段之一。本文依托黄陵延安段高速公路洛河特大桥试桩工程,通过对原有工程桩施加预应力,形成了以工程桩为锚桩的锚拔体系。加载过程中试桩应力、锚桩应力及桩顶位移测试,结果表明,结合预应力技术,以工程桩作为锚桩构成桩基础静载试验的锚拔体系是可行的,同时提出了施加预应力大小的原则、方法以及确保后期曾作为锚桩的工程桩有足够承载能力应采取的必要措施。  相似文献