Reconstructing hydrological variability from testate amoebae analysis in Carpathian peatlands     

C. Schnitchen  D. J. Charman  E. Magyari  M. Braun  I. Grigorszky  B. Tóthmérész  M. Molnár  Zs. Szántó 《Journal of Paleolimnology》2006,36(1):1-17

Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP, 3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe.  相似文献   

A comparison of chironomid biostratigraphy from Lake Vuolep Njakajaure with vegetation, lake-level, and climate changes in Abisko National Park, Sweden     

Markus Heinrichs  Lena Barnekow  Sandra Rosenberg 《Journal of Paleolimnology》2006,36(2):119-131

Chironomid remains from the sediment of Lake Vuolep Njakajaure reflect limnological conditions resulting from changing climate and vegetation throughout the Holocene, but do not strictly follow accepted climate trends or the vegetation history based on regional pollen and macrofossil analyses. Chironomid community changes appear to be influenced by organic nutrient input from the surrounding catchment vegetation and lake hydrology, both of which are indirectly responding to some combination of climate change, hypolimnetic oxygen concentration, and changes in basin morphology. The chironomid-based quantitative mean July air-temperature reconstruction differs from other regional quantitative records; this discrepancy is likely related to limnological conditions particular to Lake Vuolep Njakajaure. Comparison of a northern Swedish temperature transfer function and one from western Canada reveals differences in the mean July air-temperature optima of several common taxa, suggesting that the existing conservative estimates of Holocene climate change in northern Sweden may be underestimated due to the limited temperature gradient captured by the Swedish training set.  相似文献   

The multilevel fast multipole method for forward modelling the multiply scattered seismic surface waves   总被引：1，自引：0，他引：1  

Özcan Çakir 《Geophysical Journal International》2006,167(2):663-678

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Crustal constraints on the uplift mechanism of the Western Ghats of India   总被引：1，自引：0，他引：1  

Pankaj Kr. Tiwari  G. Surve  G. Mohan 《Geophysical Journal International》2006,167(3):1309-1316

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Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand     

Paul Augustinus  Michael Reid  Sofia Andersson  Yanbin Deng  Mark Horrocks 《Journal of Paleolimnology》2006,35(4):789-805

Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS ¹⁴C and ²¹⁰Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO₄ addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the ²¹⁰Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes.  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   

参数在线自调整模糊控制算法研究     

谌洪茂  贾宏伟  黄国辉 《华东地质学院学报》2006,29(3):277-282

针对间歇式热处理炉温度控制对象的特性要求,提出了参数在线自调整模糊控制与智能积分相结合的一种新型模糊控制方法。该方法的基本思想是在系统误差较大时,用参数在线自调整模糊控制算法以提高系统的响应;在系统误差较小时,加入智能积分作用以消除静态误差,智能积分作用是有选择的施加积分作用,克服了一般连续积分控制的缺点。论述了带智能积分参数在线自调整模糊控制器的设计及软件实现。并且通过在MATLAB软件上的仿真分析表明该方法的合理性及可行性。  相似文献   

地学自由曲面径向基函数网络重建的详细算法   总被引：3，自引：0，他引：3  

陈明  何凯涛  王全明 《物探化探计算技术》2005,27(1):75-77

径向基函数(RadialBasisFunction,简称RBF)神经网络是一种理想的地学离散数据网格化工具,能够适应各种不同分布形式和边界条件的数据,收敛速度较快,可以逼近任何复杂曲面。这里详细介绍了RBF神经网络的算法。适当径向基函数的形式和偏差系数是使用RBF神经网络作地学曲面重建的关键。大量的实际数据验证结果表明,当选用Gauss型径向基函数时,一般可获得比较理想的网格化效果,同时具备"曲面平滑"和"拟合度高"的特点。  相似文献   

基于MAPGIS明码文件的绘图转换系统开发及应用   总被引：4，自引：1，他引：4  

段青梅  龙文华  丁天才  张玉宝  刘金宝 《物探与化探》2005,29(1):50-52,56

介绍了基于MAPGIS明码文件开发出的MAPGIS明码格式转换系统软件的结构及功能,并说明该软件在地球物理、地球化学领域中的应用。  相似文献   

地球表层系统浅论     

张猛刚  雷祥义 《西北地质》2005,38(2):99-101

地球表层系统是岩土圈、大气圈、水圈、人类圈和生物圈构成的地表自然社会综合体，笔者从系统论的观点出发，阐述了地球表层系统的边界、环境、要素、结构和功能；并分析了地球表层系统的开放性、有序性和耗散结构的特征；最后阐明了协调人地关系是地球表层系统研究的主要内容。  相似文献