Dating ancient wood by high-sensitivity liquid scintillation counting and accelerator mass spectrometry—Pushing the boundaries     

Alan G. Hogg  L. Keith Fifield  Chris S.M. Turney  Jonathan G. Palmer  Rex Galbraith  Mike G.K. Baillie 《Quaternary Geochronology》2006,1(4):241-248

It is critical that a comprehensive terrestrial radiocarbon (¹⁴C) calibration curve is developed beyond 26 ka for high-precision calibration and correlation of climatic, environmental and archaeological records. Abundant sub-fossil New Zealand kauri (Agathis australis) wood, preserved in Oxygen Isotope Stage-2 and 3 peat swamps, provides an important resource for ¹⁴C calibration; nowhere else in the world does such an extensive collection of ancient wood exist. Although finite ¹⁴C ages beyond 50 ka are becoming routinely reported, few attempts have been made to demonstrate their accuracy or precision. Finite ages beyond 50 ka require optimization of all elements involved in sample preparation and ¹⁴C analysis. Here we discuss the methodology employed for optimizing the ¹⁴C dating of near-background wood samples by both benzene synthesis for liquid scintillation counting (LSC) or graphite synthesis for accelerator mass spectrometry (AMS). We report the mean background blank activities for both methods and present a statistical model for assigning blank standard errors when blank activity variation is over and above counting statistics. We also present duplicate analyses (using LSC and AMS) of nine successive samples of wood obtained from a sub-fossil kauri log near-background in age to investigate the significance of the measured blank levels and variability.  相似文献   

Biodiversity of the wetlands of the Kakadu Region, northern Australia     

C. Max Finlayson  John Lowry  Maria Grazia Bellio  Suthidha Nou  Robert Pidgeon  Dave Walden  Chris Humphrey  Gary Fox 《Aquatic Sciences - Research Across Boundaries》2006,68(3):374-399

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Gaussian plume modeling of contaminant transport     

Chris Kennedy  Hans Ericsson  P. L. R. Wong 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(1-2):119-125

A technique for modeling contaminant transport based on Markov process theory is developed. Transport is quantified by summing the first two moments of independent random displacements and applying the central limit theorem (CLT) to obtain solute distributions of a Gaussian nature. For non-uniform flow fields the CLT is applied in a streamfunction/equi-travel time space and transforms are used to give concentrations in Cartesian coordinates. Simulations in uniform, radially converging and circular flow fields show the method to be two to three orders of magnitude faster than modeling with the advection-dispersion equation, using a control volume technique.  相似文献   

Episodic shear zone associated fluid flow in the Curnamona Province, South Australia     

Chris Clark  Andreas Schmidt Mumm  Martin Hand  Kevin Faure 《Journal of Geochemical Exploration》2006,89(1-3):69

Two distinct generations of fluid flow associated with shear zone activity have been identified in Willyama Supergroup rocks of the southern Curnamona Province in northeastern South Australia. Fluids in the first event are inferred to have been sourced from the devolatilisation of Willyama Supergroup metasedimentary rocks during prograde metamorphism associated with the (1.61–1.58 Ga) Mesoproterozoic Olarian Orogeny. The second episode of fluid flow occurred during the (c. 500 Ma) Cambrian Delamerian Orogeny and resulted in localised rehydration of the Willyama Supergroup. Fluids were isotopically light and most likely sourced from prograde Delamerian metamorphism and dehydration of fault rocks and entrained meteoric waters that originally were involved in (c. 700 Ma) Neoproterozoic Adelaidean rifting. A key outcome of this study is the identification of this previously unrecognised fluid flow system that was active during the Delamerian Orogeny.  相似文献   

Inference of past climate from borehole temperature data using Bayesian Reversible Jump Markov chain Monte Carlo     

Peter O. Hopcroft  Kerry Gallagher  Chris C. Pain 《Geophysical Journal International》2007,171(3):1430-1439

Estimates of past climate derived from borehole temperatures are assuming a greater importance in context of the millennial temperature variation debate. However, recovery of these signals is usually performed with regularization which can potentially lead to underestimation of past variation when noise is present. In this work Bayesian inference is applied to this problem with no explicit regularization. To achieve this Reversible Jump Markov chain Monte Carlo is employed, and this allows models of varying complexity (i.e. variable dimensions) to be sampled so that it is possible to infer the level of ground surface temperature (GST) history resolution appropriate to the data. Using synthetic examples, we show that the inference of the GST signal back to more than 500 yr is robust given boreholes of 500 m depth and moderate noise levels and discuss the associated uncertainties. We compare the prior information we have used with the inferred posterior distribution to show which parts of the GST reconstructions are independent of this prior information. We demonstrate the application of the method to real data using five boreholes from southern England. These are modelled both individually and jointly, and appear to indicate a spatial trend of warming over 500 yr across the south of the country.  相似文献   

Realizing the Literate Traveller     

William E Cartwright  Bob Williams  Chris Pettit 《Transactions in GIS》2007,11(1):9-27

A current research project is addressing the problem of finding appropriate geographical information by developing a (geo)information realization resource based upon the concepts of the Literate Traveller. It has as its main goal to provide tools for geographical knowledge building and exploration, by providing conventional spatial information plus geographical interpretation and appreciation artifacts. These artifacts are delivered in an interactive multimedia environment. This research examines the formulation of an initial prototype component to assist in providing geographical knowledge. The prototype is based on a study site in Townsville, Australia, and is being used as a vehicle to explore enhanced spatial information provision through the use of rich media. The research examines new ways to prospect for, discover and disseminate spatial knowledge within an intelligence‐briefing context. The paper reports on the concepts behind the design of the application developed for the test site, and presents initial findings from the early evaluation of the prototype.  相似文献   

On 50th Anniversary of the Global Carbon Dioxide Record     

Georgii A Alexandrov  Martin Heimann  Chris D Jones  Pieter Tans 《Carbon balance and management》2007,2(1):11-2

The 50-year global CO₂ record led the way in establishing a scientific fact: modern civilization is changing important properties of the global atmosphere, oceans and biosphere. The evidence on which this scientific fact is based will be refined further, but the next challenge for scientists is broader. In addition to its traditional role in providing discovery, diagnosis, and prediction of the changes that are taking place on our planet, science has now also a role in helping society mitigate emissions by objectively quantifying them, and in helping adaptation by providing environmental forecasts on regional scales. Science is also expected to provide new options for society to tackle the transition to a new energy system, and to provide thorough environmental evaluation of all such options. This is what the meeting recognized as planetary responsibilities for scientists in the next 50 years.  相似文献   

Assessing the vulnerability of food crop systems in Africa to climate change     

Andrew Challinor  Tim Wheeler  Chris Garforth  Peter Craufurd  Amir Kassam 《Climatic change》2007,83(3):381-399

Africa is thought to be the region most vulnerable to the impacts of climate variability and change. Agriculture plays a dominant role in supporting rural livelihoods and economic growth over most of Africa. Three aspects of the vulnerability of food crop systems to climate change in Africa are discussed: the assessment of the sensitivity of crops to variability in climate, the adaptive capacity of farmers, and the role of institutions in adapting to climate change. The magnitude of projected impacts of climate change on food crops in Africa varies widely among different studies. These differences arise from the variety of climate and crop models used, and the different techniques used to match the scale of climate model output to that needed by crop models. Most studies show a negative impact of climate change on crop productivity in Africa. Farmers have proved highly adaptable in the past to short- and long-term variations in climate and in their environment. Key to the ability of farmers to adapt to climate variability and change will be access to relevant knowledge and information. It is important that governments put in place institutional and macro-economic conditions that support and facilitate adaptation and resilience to climate change at local, national and transnational level.  相似文献   

紫硫镍矿交代镍黄铁矿的水热反应机理及动力学          下载免费PDF全文

夏方  陈国荣Allan PRING Joel BRUGGER Yung NGOTHAI Brain O＇NEILL Chris COLBY Christophe TENAILLEAU王海鹏  杨云霞 《地质学报》2007,81(10):1378-1390

本工作首次在实验室条件下对浅生区紫硫镍矿(Ni,Fe)3S4交代镍黄铁矿(Ni,Fe)9S8水热反应的机理及动力学进行了研究。起始反应矿物采用高纯自然镍黄铁矿,合成纯镍黄铁矿或合成镍黄铁矿-磁黄铁矿集合体。反应pH值采用0.2M醋酸-醋酸纳缓冲溶液控制在3～5的范围内。反应进程由X-射线衍射物相定量分析及扫描电镜观察进行跟踪。结果表明,当反应温度恒定在80℃时,交代20(4)%的镍黄铁矿需792h。相同条件下加入少量H2S可将反应速率提高一倍。当反应在125℃饱和蒸汽压水热环境下进行时,完全交代纯镍黄铁矿需约168h。此过程由于磁黄铁矿的存在而被催化,交代集合体中的镍黄铁矿仅需68h,进一步反应磁黄铁矿被交代成白铁矿。磁黄铁矿的催化作用可能源于溶解产生的微裂纹加速了流体的传质过程。当反应温度升高至145℃时,速率反而下降,不遵循Arrhenius经验规律。动力学分析得80℃速率常数介于5.8×10-8～3.0×10-7/s之间,125℃及145℃速率常数分别介于2.8×10-6～2.08×10-5/s及1×10-6～5.1×10-6/s之间,远高于同温度下固相扩散反应的速率常数,表明该反应在地质时标上为一快速反应。此外,用背散射电子显微技术对矿物表面形貌进行了分析,发现交代产物紫硫镍矿具有颗粒细小及存在微裂纹等特征,与自然界浅生矿床中的紫硫镍矿非常相似;电镜实验还表明该交代作用是一个典型的耦合溶解-再沉淀反应。其耦合机制的驱动力可能与反应界面处微空隙对流体饱和度的控制有关。  相似文献   

A transboundary study of urban sprawl in the Pacific Coast region of North America: The benefits of multiple measurement methods     

Chris Davis  Tim Schaub   《International Journal of Applied Earth Observation and Geoinformation》2005,7(4):268-283

Sprawling urban development has emerged as a primary concern of policy makers, land preservationists and both urban and rural communities in developing regions across the globe. For the first time in history, more global residents lived in urban areas than not and the trend to urbanization is in full force at the start of the 21st century. An understanding of the nature and character of urban sprawl is complicated by a failure to satisfactorily define it and by the limitations of measurement techniques designed to characterize complex landscape forms. Like other landscape patterns, the quantification of urban sprawl is highly spatially and temporally scale-dependent. This paper summarizes a recent project to measure urban sprawl in the transboundary region of the Pacific Coast of North America. The metropolitan centers of Portland, OR, Seattle, WA and Vancouver, BC, span two nations, three state/provincial governments and dozens of cities. As a region, this was a global leader in population growth in the 1990s. The study relied on three separate methods – an impervious surface metric, a neighborhood density metric and a building permit metric – for quantifying urban growth. The results provide insight on the strengths and shortcomings of different methods with respect to the challenges posed by data availability and format. Taken together they demonstrate the richer understanding that combined methods may offer in characterizing phenomena as difficult to communicate and agree upon as urban sprawl.  相似文献