Evidence for the presence of the Vedde Ash in Central Europe     

S.P.E. Blockley  C.S. Lane  A.F. Lotter  A.M. Pollard 《Quaternary Science Reviews》2007,26(25-28):3030-3036

As part of ongoing research to find distal tephra, two lacustrine cores were analysed for the presence of volcanic ash layers, not visible to the naked eye: Soppensee, in Switzerland, and Rotmeer, in Southern Germany. The Laacher See Tephra (12,900 ka BP) is present as a visible layer in both sites. In both cores we found a discrete tephra horizon, with similar morphologies, in the middle of the biostratigraphic units equivalent to the Younger Dryas stadial. The vitreous components of these two tephra layers are geochemically identical. Comparison of the geochemical, stratigraphical, and chronological data from both sites, strongly suggest that the tephra can be attributed to the Icelandic Vedde Ash, a widely distributed horizon found throughout the North Atlantic and Northern Europe. Our results indicate that a precise and direct correlation between the Greenland ice cores and Central European sequences is now possible, based on a co-located tephra layer. This means that there is now the potential, to independently test climate synchronicity between Greenland and Europe, as far south as the Alps.  相似文献   

Scattered ground‐roll attenuation using model‐driven interferometry          下载免费PDF全文

Phil Bilsby  Lee West  Ed Kragh  John Quigley 《Geophysical Prospecting》2015,63(1):116-132

Scattered ground roll is a type of noise observed in land seismic data that can be particularly difficult to suppress. Typically, this type of noise cannot be removed using conventional velocity‐based filters. In this paper, we discuss a model‐driven form of seismic interferometry that allows suppression of scattered ground‐roll noise in land seismic data. The conventional cross‐correlate and stack interferometry approach results in scattered noise estimates between two receiver locations (i.e. as if one of the receivers had been replaced by a source). For noise suppression, this requires that each source we wish to attenuate the noise from is co‐located with a receiver. The model‐driven form differs, as the use of a simple model in place of one of the inputs for interferometry allows the scattered noise estimate to be made between a source and a receiver. This allows the method to be more flexible, as co‐location of sources and receivers is not required, and the method can be applied to data sets with a variety of different acquisition geometries. A simple plane‐wave model is used, allowing the method to remain relatively data driven, with weighting factors for the plane waves determined using a least‐squares solution. Using a number of both synthetic and real two‐dimensional (2D) and three‐dimensional (3D) land seismic data sets, we show that this model‐driven approach provides effective results, allowing suppression of scattered ground‐roll noise without having an adverse effect on the underlying signal.  相似文献   

Uncertainty estimation for operational ocean forecast products—a multi-model ensemble for the North Sea and the Baltic Sea     

Inga Golbeck  Xin Li  Frank Janssen  Thorger Brüning  Jacob W. Nielsen  Vibeke Huess  Johan Söderkvist  Bjarne Büchmann  Simo-Matti Siiriä  Olga Vähä-Piikkiö  Bruce Hackett  Nils M. Kristensen  Harald Engedahl  Ed Blockley  Alistair Sellar  Priidik Lagemaa  Jose Ozer  Sebastien Legrand  Patrik Ljungemyr  Lars Axell 《Ocean Dynamics》2015,65(12):1603-1631

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Residual drift demands in moment‐resisting steel frames subjected to narrow‐band earthquake ground motions     

Edén Bojórquez  Jorge Ruiz‐García 《地震工程与结构动力学》2013,42(11):1583-1598

This paper presents the main results of the evaluation of residual inter‐story drift demands in typical moment‐resisting steel buildings designed accordingly to the Mexican design practice when subjected to narrow‐band earthquake ground motions. Analytical 2D‐framed models representative of the study‐case buildings were subjected to a set of 30 narrow‐band earthquake ground motions recorded on stations placed in soft‐soil sites of Mexico City, where most significant structural damage was found in buildings as a consequence of the 1985 Michoacan earthquake, and scaled to reach several levels of intensity to perform incremental dynamic analyses. Thus, results were statistically processed to obtain hazard curves of peak (maximum) and residual drift demands for each frame model. It is shown that the study‐case frames might exhibit maximum residual inter‐story drift demands in excess of 0.5%, which is perceptible for building's occupants and could cause human discomfort, for a mean annual rate of exceedance associated to peak inter‐story drift demands of about 3%, which is the limiting drift to avoid collapse prescribed in the 2004 Mexico City Seismic Design Provisions. The influence of a member's post‐yield stiffness ratio and material overstrength in the evaluation of maximum residual inter‐story drift demands is also discussed. Finally, this study introduces response transformation factors, T_p, that allow establishing residual drift limits compatible with the same mean annual rate of exceedance of peak inter‐story drift limits for future seismic design/evaluation criteria that take into account both drift demands for assessing a building's seismic performance. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The potential to narrow uncertainty in projections of regional precipitation change   总被引：6，自引：1，他引：5  

Ed Hawkins  Rowan Sutton 《Climate Dynamics》2011,37(1-2):407-418

We separate and quantify the sources of uncertainty in projections of regional (～2,500 km) precipitation changes for the twenty-first century using the CMIP3 multi-model ensemble, allowing a direct comparison with a similar analysis for regional temperature changes. For decadal means of seasonal mean precipitation, internal variability is the dominant uncertainty for predictions of the first decade everywhere, and for many regions until the third decade ahead. Model uncertainty is generally the dominant source of uncertainty for longer lead times. Scenario uncertainty is found to be small or negligible for all regions and lead times, apart from close to the poles at the end of the century. For the global mean, model uncertainty dominates at all lead times. The signal-to-noise ratio (S/N) of the precipitation projections is highest at the poles but less than 1 almost everywhere else, and is far lower than for temperature projections. In particular, the tropics have the highest S/N for temperature, but the lowest for precipitation. We also estimate a ‘potential S/N’ by assuming that model uncertainty could be reduced to zero, and show that, for regional precipitation, the gains in S/N are fairly modest, especially for predictions of the next few decades. This finding suggests that adaptation decisions will need to be made in the context of high uncertainty concerning regional changes in precipitation. The potential to narrow uncertainty in regional temperature projections is far greater. These conclusions on S/N are for the current generation of models; the real signal may be larger or smaller than the CMIP3 multi-model mean. Also note that the S/N for extreme precipitation, which is more relevant for many climate impacts, may be larger than for the seasonal mean precipitation considered here.  相似文献   

Granite ages within the Archaean Pilbara Block,Western Australia     

J. R. de Laeter  J. G. Blockley 《Australian Journal of Earth Sciences》2013,60(3):363-370

Within the Pilbara Block of Western Australia, a complex of migmatite, gneissic and foliated granite near Marble Bar is intruded by a stock of younger massive granite (the Moolyella Granite) with which swarms of tin‐bearing pegmatites are associated. The age of the older granite has been determined by the Rb‐Sr method as 3,125 ± 366 m.y., and that of the Moolyella Granite as 2,670 ± 95 m.y. Initial Sr⁸⁷/Sr⁸⁶ ratios suggest that the older granite is close to primary crustal material, but that the Moolyella Granite consists of reworked material. It probably formed by partial remelting of the older granite.  相似文献   

Separating contributions from natural and anthropogenic sources in atmospheric methane from the Black Sea region,Romania     

Stela Cuna  Elise Pendall  John B. Miller  Pieter P. Tans  Ed Dlugokencky  James W.C. White 《Applied Geochemistry》2008

The Danube Delta-Black Sea region of Romania is an important wetland, and this preliminary study evaluates the significance of this region as a source of atmospheric CH₄. Measurements of the mixing ratio and δ¹³C in CH₄ are reported from air and water samples collected at eight sites in the Danube Delta. High mixing ratios of CH₄ were found in air (2500–14,000 ppb) and dissolved in water samples (∼1–10 μmol L⁻¹), demonstrating that the Danube Delta is an important natural source of CH₄. The intercepts on Keeling plots of about −62‰ show that the main source of CH₄ in this region is microbial, probably resulting primarily from acetate fermentation. Atmospheric CH₄ and CO data from the NOAA/ESRL (National Oceanic and Atmospheric Administration/Earth System Research Laboratory) were used to make a preliminary estimate of biogenic CH₄ at the Black Sea sampling site at Constanta (BSC). These data were used to calculate ratios of CH₄/CO in air samples, and using an assumed CH₄/CO anthropogenic emissions ratio of 0.6, fossil fuel emissions at BSC were estimated. Biogenic CH₄ emissions were then estimated by a simple mass balance approach. Keeling plots of well-mixed air from the BSC site suggested a stronger wetland source in summer and a stronger fossil fuel source in winter.  相似文献   

Reply to Discussion of Liñán et al. on: 'Distinguishing eustatic and epeirogenic controls on Lower–Middle Cambrian boundary successions in West Gondwana (Morocco and Iberia)', by Ed Landing, Gerd Geyer and Wolfram Heldmaier, published in Sedimentology (2006), 53(4), 899–918     

Ed Landing  Gerd Geyer† 《Sedimentology》2008,55(4):725-727

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Assessing the sensitivity of Canada's ecosystems to climatic change   总被引：1，自引：0，他引：1  

Brian Rizzo  Ed Wiken 《Climatic change》1992,21(1):37-55

Global warming due to increased concentrations of atmospheric CO₂ is expected to be amplified in middle and higher latitudes. Consequently, ecosystems in these latitudes will experience more pronounced climatic variations. This investigation attempts to assess the sensitivity of Canada's ecosystems to climatic change. Potential ecological impacts resulting from global warming are outlined. With this background, the effects of a doubled CO₂ climate are applied to a classification model derived from the current ecological setting. Results reveal not only major shifts in ecological boundaries but also changes in the character of these broadly distributed ecosystems.  相似文献   

Oxyanion Concentrations in Eastern Sierra Nevada Rivers – 2. Arsenic and Phosphate     

Kevin H. Johannesson  W. Berry Lyons  Suey Huey  Georgia a. Doyle  Eric E. Swanson  Ed Hackett 《Aquatic Geochemistry》1997,3(1):61-97

Water samples were collected from the Truckee River-Pyramid Lake system, the Walker River-Walker Lake system, and the Carson River, all located in eastern California and western Nevada, U.S.A., at three different times (i.e., summer 1991, spring 1992, and autumn 1992) over a two year period. The concentrations of As, Na, Cl, PO4, and pH were measured in these river samples and the associated terminal lakes. Arsenic values ranged from below 13 nmol/kg near Truckee, California to 160 nmol/kg at Nixon, Nevada in the Truckee River, from 40 nmol/kg in the headwaters of both West and East Walker Rivers to 270 nmol/kg below Weber Reservoir on the main branch of the Walker River, and from <27 nmol/kg to 234 nmol/kg for the lower Carson River system. Arsenic concentrations in Steamboat Creek (0.91 mol/kg–1.80 mol/kg) in the Truckee River catchment are above the U.S. EPA drinking water maximum contaminant level of 0.67 mol/kg, as are the As concentrations in both Pyramid Lake (1.33 mol/kg–1.57 mol/kg ) and Walker Lake (13.7 mol/kg–18.7 mol/kg). Sources of As for all three rivers include weathering of As-rich rocks and/or regolith and input of high-As geothermal spring waters, both processes primarily, although not exclusively, adding As to the headwater regions of these rivers. Steamboat Hot Springs (29 mol/kg As 54.5 mol/kg), for example, is identified as a source of As to the Truckee River via Steamboat Creek. The high As concentrations in Pyramid and Walker Lakes are likely due to (1) desorption of arsenate from aquatic particulate matter in these high pH waters (9.0 pH 9.5), (2) limited biologic uptake of arsenate, and (3) evaporative concentration of the lake waters. Evaluation of molar PO4}/As ratios of river waters and geothermal spring waters (e.g., Steamboat Hot Springs), indicates that phosphate is substantially enriched in Steamboat Creek as well as the mid to lower reaches of the Walker and Carson Rivers. These regions of each river are dominated by agricultural interests and, additionally, in the case of Steamboat Creek, residential areas and golf courses. Our data strongly imply that phosphate-rich agricultural return flow has likely added P to these streams and, consequently, increased their respective P:As ratios.  相似文献