Timing of the late-glacial climate reversal in the Southern Hemisphere using high-resolution radiocarbon chronology for Kaipo bog, New Zealand     

Irka Hajdas  David J. Lowe  Georges Bonani 《Quaternary Research》2006,65(2):340-345

The pattern of climate change in the Southern Hemisphere during the Younger Dryas (YD) chronozone provides essential constraint on mechanisms of abrupt climate change only if accurate, high-precision chronologies are obtained. A climate reversal reported previously at Kaipo bog, New Zealand, had been dated between 13,600 and 12,600 cal yr B.P. and appeared to asynchronously overlap the YD chron, but the chronology, based on conventionally radiocarbon-dated bulk sediment samples, left the precise timing questionable. We report a new high-resolution AMS ¹⁴C chronology for the Kaipo record that confirms the original chronology and provides further evidence for a mid-latitude Southern Ocean cooling event dated between 13,800 and 12,400 cal yr B.P. (2σ range), roughly equivalent to the Antarctic Cold Reversal.  相似文献   

Asymmetric vegetation responses to mid-Holocene aridity at the prairie-forest ecotone in south-central Minnesota     

Charles E. Umbanhowar Jr.  Philip Camill  Rebecca Teed 《Quaternary Research》2006,66(1):53-66

The mid-Holocene (ca. 8000-4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000-7000 yr ago) and out of (ca. 5000-2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼ 5-36 yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7-4.0 vs. 0.6-1.7 mm² cm^− 2 yr^− 1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming.  相似文献   

Holocene climate and cultural evolution in late prehistoric-early historic West Asia   总被引：2，自引：0，他引：2  

Michael Staubwasser  Harvey Weiss 《Quaternary Research》2006,66(3):372-387

The precipitation climatology and the underlying climate mechanisms of the eastern Mediterranean, West Asia, and the Indian subcontinent are reviewed, with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation. Holocene climate change of the region is summarized from proxy records. The Indian monsoon weakened during the Holocene over its northernmost region, the Ganges and Indus catchments and the western Arabian Sea. Southern regions, the Indian Peninsula, do not show a reduction, but an increase of summer monsoon rain across the Holocene. The long-term trend towards drier conditions in the eastern Mediterranean can be linked to a regionally complex monsoon evolution. Abrupt climate change events, such as the widespread droughts around 8200, 5200 and 4200 cal yr BP, are suggested to be the result of altered subtropical upper-level flow over the eastern Mediterranean and Asia.The abrupt climate change events of the Holocene radically altered precipitation, fundamental for cereal agriculture, across the expanse of late prehistoric-early historic cultures known from the archaeological record in these regions. Social adaptations to reduced agro-production, in both dry-farming and irrigation agriculture regions, are visible in the archaeological record during each abrupt climate change event in West Asia. Chronological refinement, in both the paleoclimate and archaeological records, and transfer functions for both precipitation and agro-production are needed to understand precisely the evident causal linkages.  相似文献   

湿地功能快速评价中的若干理论问题   总被引：9，自引：5，他引：9  

殷书柏  吕宪国 《湿地科学》2006,4(1):1-6

针对目前湿地功能快速评价中存在的不足之处,分析了产生这些不足的原因及湿地功能快速评价过程中存在的一些基本理论问题。分析表明:湿地功能快速评价方法是为了达到“湿地功能无净损失”目的,是在需要评价的湿地如此之多而从事湿地功能评价的专业人员又极其缺乏的情况下发展起来的。它对于湿地恢复与重建以及湿地受人类活动干扰程度的评价是非常有效的;在湿地功能快速评价过程中,把相对未受人类干扰的参照湿地的功能指数规定为1,这就使得快速评价方法不能对参照湿地的功能进行评价,而目前最需要评价其功能的湿地往往就是这些相对未受人类活动干扰的湿地;在相同水文地貌的湿地类型内评价湿地功能之间的差异,这使得快速评价方法不能评价湿地的水文地貌功能;由于快速评价的结果都是相对的功能指数,并不能说明湿地所提供的功能量是否满足人们的需求,因而在决策中不能单独使用;快速评价都是“一次调查就获得结果”,同时由于快速评价过程中指标选择的主观性、指标赋值的主观性、采样点空间设置的主观性以及采样时间的主观性,对于具有时空变化特征的湿地功能的评价结果的可重复性和科学性是很低的。为了使湿地功能评价的结果对管理和决策具有指导意义,基于湿地功能量计算的、定量的评价湿地功能的方法必须开发出来。针对不同的评价目的,湿地功能评价可采用双重参照标准:一是以自然为参照来评价湿地功能受人类活动影响的程度以及湿地恢复与重建成功与否;二是以人类需要为标准来评价湿地提供的功能量是否满足了我们的期望,以便采取措施改进湿地功能来满足人类的需求。  相似文献   

Quantification of the risk associated with high levels of mercury pollution at Temirtau, Kazakhstan     

Huiwen HSIAO Susanne M. Ullrich Trevor W. Tanton 《中国地球化学学报》2006,25(B08):233-233

This research aims to establish the risks of hurnan exposure to modeling approach. The study site was located on the River Nura 1990s, an acetaldehyde production plant located in the industrial high environmental mercury levels, based on a quantitative risk in central Kazakhstan. From the 1950s until its closure in the mid city of Temirtau released mercury-containing wastewater into the river. River sediments are highly contaminated with mercury up to a distance of 25 km and beyond. In addition, a local power station released an estimated 6 million tonnes of fly-ash into the water and the mercury has become quite tightly associated with the ash deposits. River water, fish and agricultural land in the floodplain are also contaminated with mercury, yet the risks posed to the local population have not been evaluated to date. In June and July 2005, we took samples of soil, interior and exterior dust, drinking water, and food from individual households, communal areas and markets. Additionally, water and sediment samples and fish were taken from the river. Interviews were conducted with householders to establish their age and body weight, general living conditions and sources of irrigation and drinking water. A food frequency questionnaire （FFQ） was designed to investigate the frequencies of consumption of several common regional food items, including fish from the fiver and/or local market. Human hair samples were also collected to estimate the mercury bioburden and to enable the validity of the modeling approach to be established. The paper expands on the main pathways of contamination and looks at linkages between exposure pathways and mercury concentrations found in human hair. Uncertainties inherent in risk analysis as well as their influence on the relative importance of different exposure routes are also discussed.  相似文献   

A multi-method approach to study the stability of natural slopes and landslide susceptibility mapping   总被引：8，自引：0，他引：8  

M. Fall  R. Azzam  C. Noubactep 《Engineering Geology》2006,82(4):241-263

In this paper, a multi-method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the Dakar coastal region is presented. This approach is based on the effective combination of geotechnical field and laboratory works, of GIS, and of mechanical (deterministic and numerical) stability analysis. By using this approach, valuable results were gained regarding instability factors, landslide kinematics, simulation of slope failure and coastal erosion. This led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the SW coast of Dakar. Analysis of the results shows that the slides were influenced by the geotechnical properties of the soil, the weathering, the hydrogeological situation, and the erosion by waves. The landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city.  相似文献   

Stratigraphic evolution of a fluvial–eolian succession: The example of the Upper Jurassic—Lower Cretaceous Guará and Botucatu formations, Paraná Basin, Southernmost Brazil     

Claiton M.S. Scherer  Ernesto L.C. Lavina 《Gondwana Research》2006,9(4):475-484

The Guará and Botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the Rio Grande do Sul State (Southernmost Brazil). The Guará Formation (Upper Jurassic) displays a well-defined facies shift along its outcrop belt. On its northern portion it is characterised by coarse-grained to conglomeratic sandstones with trough and planar cross-bedding, as well as low-angle lamination, which are interpreted to represent braided river deposits. Southwards these fluvial facies thin out and interfinger with fine- to medium-grained sandstones with large-scale cross-stratification and horizontal lamination, interpreted as eolian dune and eolian sand sheets deposits, respectively. The Botucatu Formation is characterised by large-scale cross-strata formed by successive climbing of eolian dunes, without interdune and/or fluvial accumulation (dry eolian system). The contact between the Guará and the Botucatu formations is delineated by a basin-wide deflation surface (supersurface). The abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change, from semi-arid (Upper Jurassic) to hyper-arid (Lower Cretaceous) conditions. A rearrangement of the Paraná Basin depocenters is contemporaneous to this climate change, which seems to have changed from a more restrict accumulation area in the Guará Formation to a wider sedimentary context in the Botucatu Formation.  相似文献   

Comparative Seismic Risk Studies for German Earthquake Regions on the Basis of the European Macroseismic Scale EMS-98     

Jochen Schwarz  Mathias Raschke  Holger Maiwald 《Natural Hazards》2006,38(1-2):259-282

Within the framework of recent research projects, basic tools for GIS-based seismic risk assessment technologies were developed and applied to the building stock and regional particularities of German earthquake regions. Two study areas are investigated, being comparable by the level of seismic hazard and the hazard-consistent scenario events (related to mean return periods of 475, 2475 and 10000 years). Significant differences exist with respect to the number of inhabitants, the grade and extent of urbanisation, the quality and quantity of building inventory: the case study of Schmölln in Eastern Thuringia seems to be representative for the majority of smaller towns in Germany, the case study of Cologne (Köln) stands for larger cities. Due to the similarities of hazard and scenario intensities, the considerable differences do not only require proper decisions concerning the appropriate methods and acceptable efforts, they enable conclusions about future research strategies and needs for disaster reduction management. Not least important, results can sharpen the focus of public interest. Seismic risk maps are prepared for different scenario intensities recognising the scatter and uncertainties of site-dependent ground motion and also of the applied vulnerability functions. The paper illustrates the impact of model assumptions and the step-wise refinements of input variables like site conditions, building stock or vulnerability functions on the distribution of expected building damage within the study areas. Furthermore, and in contrast to common research strategies, results support the conclusion that in the case of stronger earthquakes the damage will be of higher concentration within smaller cities like Schmölln due to the site-amplification potential and/or the increased vulnerability of the building stock. The extent of damage will be pronounced by the large number of masonry buildings for which lower vulnerability classes have to be assigned. Due to the effect of deep sedimentary layers and the composition of building types, the urban centre of Cologne will be less affected by an earthquake of comparable intensity.  相似文献   

Relations between climatic variability and hydrologic time series from four alluvial basins across the southwestern United States   总被引：1，自引：3，他引：1  

R. T. Hanson  M. D. Dettinger  M. W. Newhouse 《Hydrogeology Journal》2006,14(7):1122-1146

Hydrologic time series of groundwater levels, streamflow, precipitation, and tree-ring indices from four alluvial basins in the southwestern United States were spectrally analyzed, and then frequency components were reconstructed to isolate variability due to climatic variations on four time scales. Reconstructed components (RCs), from each time series, were compared to climatic indices like the Pacific Decadal Oscillation (PDO), North American Monsoon (NAM), and El Niño-Southern Oscillation (ENSO), to reveal that as much as 80% of RC variation can be correlated with climate variations on corresponding time scales. In most cases, the hydrologic RCs lag behind the climate indices by 1–36 months. In all four basins, PDO-like components were the largest contributors to cyclic hydrologic variability. Generally, California time series have more variation associated with PDO and ENSO than the Arizona series, and Arizona basins have more variation associated with NAM. ENSO cycles were present in all four basins but were the largest relative contributors in southeastern Arizona. Groundwater levels show a wide range of climate responses that can be correlated from well to well in the various basins, with climate responses found in unconfined and confined aquifers from pumping centers to mountain fronts.  相似文献   

金沙江干热河谷区土壤侵蚀危险度评价——以云南元谋为例     

周红艺  熊东红杨忠 《山地学报》2006,24(B10):52-56

利用空间主成分分析方法，选取降水、坡度、植被、土地利用、土壤类型、人口、高程等作为评价指标，建立空间主成分评价模型Pi=0．78X1＋0．06X2＋0．05X3＋0．04X4，将研究区分为无险型、轻险型、危险型、强险型和极险型五种类型，较为准确地得到了危险度综合评价结果。因此，空间主成分分析模型，在土壤侵蚀危险程度评价方面的应用较为成功，是一种科学有效的研究方法。  相似文献