Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions   总被引：19，自引：0，他引：19  

Larry D. Hinzman  Neil D. Bettez  W. Robert Bolton  F. Stuart Chapin  Mark B. Dyurgerov  Chris L. Fastie  Brad Griffith  Robert D. Hollister  Allen Hope  Henry P. Huntington  Anne M. Jensen  Gensuo J. Jia  Torre Jorgenson  Douglas L. Kane  David R. Klein  Gary Kofinas  Amanda H. Lynch  Andrea H. Lloyd  A. David McGuire  Frederick E. Nelson  Walter C. Oechel  Thomas E. Osterkamp  Charles H. Racine  Vladimir E. Romanovsky  Robert S. Stone  Douglas A. Stow  Matthew Sturm  Craig E. Tweedie  George L. Vourlitis  Marilyn D. Walker  Donald A. Walker  Patrick J. Webber  Jeffrey M. Welker  Kevin S. Winker  Kenji Yoshikawa 《Climatic change》2005,72(3):251-298

The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.  相似文献   

Core-mantle interactions     

K. D. Aldridge  J. Bloxham  V. Dehant  D. Gubbins  R. Hide  J. Hinderer  K. A. Hutcheson  D. Jault  C. A. Jones  H. Legros  J. -L. Le Mouël  D. Lloyd  J. M. Wahr  K. A. Whaler  K. Zhang 《Surveys in Geophysics》1990,11(4):329-353

Several aspects of core-mantle interactions were considered during a Royal Astronomical Society Discussion Meeting on 12th May 1989, including modelling the geomagnetic field at the core surface, the morphology of the field between 1600 and 1820 AD, dynamo theory, Taylor's constraint, fluid motions at the top of the core that reproduce the observed secular variation, pressure coupling between the core and mantle and its geophysical consequences, topographic core-mantle coupling, angular momentum transfer at the core-mantle interface, the detection and implications of core oscillations, particularly those with associated fluctuations in the Earth's rotation rate, and the seismological determination of the core-mantle boundary topography from lateral inhomogeneities in the mantle.  相似文献   

Yield and overflow from a finite stochastic reservoir     

E. H. Lloyd  D. Warren 《Stochastic Hydrology and Hydraulics》1990,4(3):227-240

The paper discusses the overflow (spillage) and yield rates and the total overflow and total yield over a specified time from a finite discrete stochastic reservoir, in which the yieldY _t during the working interval (t,t+1) is a function of the storageZ _t at timet, the inflow sequence {X _t } being IID.The distribution vector of the spillage rate at timet is a telescoped version of the distribution of a certain Markovian variable whose transition matrix is derived. Formulae are given for the distribution of the total spillageW _h given suitable initial conditions, forh=1,2,3; and a simple expression derived forE(W _h ).  相似文献   

The role of fluorine in the evolution of ultrapotassic magmas     

A. D. Edgar  F. E. Lloyd  D. Vukadinovic 《Mineralogy and Petrology》1994,51(2-4):173-193

Summary The distribution of F and, to a lesser extent, Cl between phlogopite, amphibole, apatite, and glass in kamafugites from the West Eifel, Germany, and South-West Uganda, and from lamprophyres (minettes) from Hopi-Navajo, Arizona has been determined. In addition, these elements have been analyzed in the same phases from mantle-derived xenoliths from the kamafugitic rocks. All halogen determinations were made using a JEOL 8600 electron microprobe. The F contents and trends in the minerals and glass in the kamafugites and lamprophyres are very similar to those reported for lamproites (Edgar and Charbonneau, 1991). The results indicate that F in the minerals of ultrapotassic magmas is much greater then that found in the xenoliths that are believed to represent likely source regions for such magmas. Chlorine is present in much lower amounts and in the same phases. The discrepancy between F in the xenoliths and in the lavas, and the preference for F to be incorporated in solid phases suggest that F is insufficient to account for the F found in ultrapotassic magmas or to provide for the reduced fluid conditions proposed by Foley (1988) for the genesis of such magmas. Based on these results, the genesis of ultrapotassic magmas may occur if they are partial melts of a mantle source that has been further enriched in F by repeated partial melting of mantle-derived xenoliths such as those of southwest Uganda. Alternatively the slightly higher Cl in the minerals of the xenoliths relative to the magmas suggests that Cl has been lost during degassing of the ascending magma. This may enrich the magmas in F by a dilution effect that may take place prior to the formation of phenocrystal F-rich phlogopites that are often present in ultrapotassic magmas.

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Die Rolle von fluor in der evolution ultrapotassischer magmen

Zusammenfassung Die Verteilung von Fluor and untergeordnet von Chlor zwischen Phlogopit, Amphibol, Apatit and Glas wurde an Kamafugiten aus der westlichen Eifel, Deutschland and aus Südwest-Uganda sowie an Lamprophyren (Minetten) aus Hopi-Navajo, Arizona bestimmt. Außerdem wurde der Gehalt an diesen Elementen in den gleichen Mineralphasen von Mantel-Xenolithen aus kamafugitischen Gesteinen analysiert. Die Halogenbestimmungen wurden an einer JEOL 8600 Mikrosonde durchgeführt. Die Gehalte und Verteilungstrends von Fluor in den Mineralphasen und im Glas der Kamafugite und Lamprophyre sind vergleichbar mit jenen aus Lamproiten (Edgar und Charbonneau, 1991). Die Resultate deuten an, daß der Fluorgehalt in Mineralen ultrapotassischer Magmen viel höher ist als in Xenolithen, die als Repräsentanten der Herkunftsregion derartiger Magmen gelten. Chlor tritt in den selben Mineralphasen in viel geringeren Mengen auf. Das unterschiedliche Auftreten von Fluor in den Xenolithen und in den Laven sowie der bevorzugte Einbau von Fluor in feste Mineralphasen lassen vermuten, daß dieser Gehalt an Fluor nicht ausreicht, um den hohen Fluorgehalt in ultrapotassischen Magmen und die reduzierenden Fluida-Bedingungen, wie sie von Foley (1988) für die Genese von solchen Magmen angenommen worden sind, zu erklären. Auf der Basis dieser Ergebnisse können ultrapotassische Magmen nur dann entstehen, wenn das Mantelmaterial als Herkunft für die partielle Schmelze zum Beispiel durch wiederholtes Teilaufschmelzen von Mantelxenolithen wie jenen aus Südwest-Uganda an Fluor angereichert worden ist. Als Alternative wird angenommen, daß die leicht höheren Chlorgehalte in den Mineralen der Xenolithe verglichen mit dem der Magmen durch Chlorverlust während Entgasung beim Aufstieg des Magmas zustande gekommen sind. Dadurch kam es zu einem Verdünnungseffekt, der zu einer Anreicherung von Fluor führt, vor der Bildung von F-reichem Phlogopit als Phenokristall, Kristalle, die häufig in ultrapotassischen Magmen auftreten.

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With 9 Figures  相似文献   

Near-surface lithogeochemical halo as an aid to discovery of deeply buried unconformity-type uranium deposits, Athabasca Basin, Canada     

Lloyd A. Clark   《Journal of Geochemical Exploration》1987,28(1-3)

Unconformity-type U deposits are being found to depths of more than 400 m where graphitic rocks underlie the Proterozoic sandstone unconformity. Exploration to date involves drilling weak electromagnetic conductors that reflect the graphitic basement. The deposits are believed to have formed through circulation of heated formation waters which discharged essentially vertically above the deposits. Geochemically detectable zones of alteration are reported for cross-sections through the Deilmann, Midwest, and McClean deposits. Information on the areal dimensions of near-surface haloes was required to justify the drilling of grids of shallow holes along conductors or favourable structures as a cost-effective exploration alternative to deep holes, and to define grid spacings.Orientation surveys were undertaken by sampling the uppermost 10 m of sandstone in a selection of holes from the Cigar Lake, Dawn Lake, and Wolf Lake areas where the deposits are, respectively, 400–430 m, 100–160 m, and 180–210 m below surface. The first two deposits have published reserves of 385 and 30–40 million pounds U₃O₈, respectively, while Wolf Lake is much smaller.Well-developed anomalies lie vertically above the richest portion of the Cigar Lake deposit in an area 150 × 600 m and a weak anomaly in many elements continues over the 1800-m length that was sampled. Total and leachable U are 13 to 8 times background with maximum values of 53 and 26 ppm, respectively. Anomalies of 14 to 8 times background are also present for V, Na₂O and Zn, and 5 to 3 times background for Sr, Y, Pb, Th, As, and P.Of the four Dawn Lake mineralized zones, only the 11B Zone was studied, with partial coverage of the 11A Zone. Anomalies 50–100 m by 250–600 m in size are often displaced up to 100 m northeast of the 11B Zone. B, MgO, Pb and both total and leachable U anomalies are 16 to 8 times background with Y, V and As 7 to 5 times background.By contrast, at the Wolf Lake deposit, only irregular variations occur for most of these elements. The unusual patterns may reflect post-alteration tectonism of the sandstone overlying the deposit as regional thrust faulting occurs nearby.Detection of near-surface lithogeochemical haloes using grids of shallow holes would facilitate discovery of deep deposits and reduce expensive, deep drilling.  相似文献   

Overwater dispersion in coastal regions     

Steven R. Hanna  Robert J. Paine  Lloyd L. Schulman 《Boundary-Layer Meteorology》1984,30(1-4):389-411

Air pollution sources such as oil platforms and ships are sometimes located near coastlines where the plumes can impact population centers. Models of overwater dispersion must account for the stability of the overwater boundary layer. An overwater dispersion model based on the standard Gaussian formula is described which uses measurements of the air-sea temperature difference, the wind speed, and the mixing depth to predict concentration patterns at the coastline. Internal boundary layers and complex terrain at the coastline are accounted for. This new model is evaluated using the results of three tracer experiments in United States coastal zones.  相似文献   

Mn(II) partitioning between calcium and magnesium sites in studies of dolomite origin     

David N. Lumsden  Roger V. Lloyd 《Geochimica et cosmochimica acta》1984,48(9):1861-1865

In an Electron Spin Resonance (ESR) study of over 30 dolomites, representing a variety of probable sedimentary origins, we observed a Mg-site to Ca-site ratio in the Mn distribution that suggests two groups of dolomite. In one group the dolomites have a Mn distribution ratio near 5.0 and an excess of Ca; in the other group the dolomites are near-stoichiometric but have a Mn distribution ratio that varies from near 5 to near 70. We suggest that these two groups reflect different origins for the dolomites. The wide variation in the manganese distribution ratio for the near-stoichiometric dolomites supplies a parameter against which other variables can be plotted in studies of dolomite origin.  相似文献   

An Integrated Hydrochemical Approach to Deduce the Response of an Aquifer System During Its History of Abstraction   总被引：1，自引：0，他引：1  

D. Jackson  J. W. Lloyd 《Ground water》1984,22(6):735-745

The investigation of the regional flow characteristics of aquifers is important with respect to aquifer management. To determine regional flows, use can be made of hydraulic and hydrochemical data. In a study of a Chalk Aquifer System in the south of Lincolnshire, England, a combined hydrochemical approach using major, minor and isotope chemistry is described. The chemical data have been used because hydraulic information is difficult to interpret both locally and regionally as a consequence of multi-layered hydraulic zones, nonhomogeneous fissure zones, and variable erosional features. By characterizing ground-water types on the basis of major ion chemistry, and subsequently interrelating with minor ion distributions (notably iodide supported by strontium), a reasonable assessment of operative flow paths and mechanisms has been made. Substantiation of the conclusions reached using major and minor ion chemistry is provided by the environmental isotope data of carbon and tritium.  相似文献   

Challenges posed by and approaches to the study of seasonal-to-decadal climate variability     

Cornelia Schwierz  Christof Appenzeller  Huw C. Davies  Mark A. Liniger  Wolfgang Müller  Thomas F. Stocker  Masakazu Yoshimori 《Climatic change》2006,79(1-2):31-63

The tasks of providing multi-decadal climate projections and seasonal plus sub-seasonal climate predictions are of significant societal interest and pose major scientific challenges. An outline is presented of the challenges posed by, and the approaches adopted to, tracing the possible evolution of the climate system on these various time-scales. First an overview is provided of the nature of the climate system’s natural internal variations and the uncertainty arising from the complexity and non-linearity of the system. Thereafter consideration is given sequentially to the range of extant approaches adopted to study and derive multi-decadal climate projections, seasonal predictions, and significant sub-seasonal weather phenomena. For each of these three time-scales novel results are presented that indicate the nature (and limitations) of the models used to forecast the evolution, and illustrate the techniques adopted to reduce or cope with the forecast uncertainty. In particular, the contributions (i) appear to exemplify that in simple climate models uncertainties in radiative forcing outweigh uncertainties associated with ocean models, (ii) examine forecast skills for a state-of-the-art seasonal prediction system, and (iii) suggest that long-lived weather phenomena can help shape intra-seasonal climate variability. Finally, it is argued, that co-consideration of all these scales can enhance our understanding of the challenges associated with uncertainties in climate prediction.  相似文献   

Determination of groundwater flow-through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns   总被引：2，自引：0，他引：2  

Jeffrey V. Turner  Lloyd R. Townley 《Journal of Hydrology》2006,320(3-4):451-483

A numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes, wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake. Many different possible flow regimes are identified, however, in this paper attention is focused on flow-through water bodies, as these are the flow regimes observed in field validation. Two shallow lakes on the Swan Coastal Plain of south-west Western Australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow-through groundwater flow regime predicted by the modelling confirming the validity of the approach. The flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices Cl_L/Cl₊ and (1000+δ_L)/(1000+δ₊). These ratios are introduced as an additional two of nine non-dimensional ratios that are necessary to analyse the problem. The ratios represent the chloride and isotopic composition (Cl_L and δ_L), respectively, in the groundwater release zones of the lakes, relative to these parameters in the groundwater capture zone (Cl₊ and δ₊) for the lake. Field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions. It is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake–aquifer interaction. The tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case-specific examples of groundwater–surface water interaction and will improve the scientific basis of decision-making concerning lake and wetland management and groundwater interaction by water resource and environmental managers.  相似文献