全新世呼伦湖区植被和气候变化的孢粉记录   总被引：2，自引：1，他引：1  

温锐林  肖举乐  常志刚  翟大有  周朗  许清海  李月从  S. Itoh 《第四纪研究》2010,30(6)

文章详细分析了内蒙古呼伦湖HL06岩芯沉积的孢粉组合,基于AMS 14C年代标尺,恢复了全新世湖区植被演变过程;并根据我国北方和蒙古表土孢粉数据和气象资料,建立了孢粉-气候参数转换函数,定量重建了呼伦湖区降水和气温的变化历史.结果表明,11000～8000aB.P.,湖区植被以蒿、藜占优,为干草原景观,气候暖干;8000～6400aB.P.,湖区禾本植物扩张,山地桦林发育,降水显著增加,气温逐渐降低;6400～4400aB.P.,湖区早生草本植物增加,降水减少,气温继续下降;4400～3350aB.P.,耐旱藜科植物大量生长,湖区荒漠化,气候极端干旱;3350～2050aB.P.,湖区草原植被有所恢复,降水略有增加,气温有所回升;2050～1000aB.P.,湖区蒿属植物减少,山地松林发育,气温降至全新世最低;最近1000年,藜科、禾本科等伴人植物大量出现,反映出人类活动对湖区自然环境的影响.全新世呼伦湖区气温变化在轨道尺度上受控于北半球太阳辐射量的变化,而在亚轨道尺度上可能与东亚夏季风强度有关.距今8000年前湖区降水较弱可能因为早全新世北半球高纬残存冰盖抑制了东亚季风雨带的北上,季风降水的千年-百年尺度波动与热带西太平洋海气相互作用密切相关.  相似文献   

Testing an approach to OSL dating of Late Devensian glaciofluvial sediments of the British Isles     

I. M. Thrasher  B. Mauz  R. C. Chiverrell  A. Lang  G. S. P. Thomas 《第四纪科学杂志》2009,24(7):785-801

In the British and Irish Isles, the understanding of expansion and retreat of the last ice sheet in Marine Isotope Stage (MIS) 2 has been hindered by a lack of chronological control for the timing of its maximum extent and subsequent retreat stages. In this research, a suite of lithofacies from a former distal ice marginal sandur at Orrisdale, Isle of Man, were identified and selected for optically stimulated luminescence dating. Different‐size fractions of quartz grains were extracted from selected lithofacies types with the aim of identifying which depositional environments and grain size fractions are best suited for optical dating. Tests have been undertaken to identify the luminescence properties of this quartz, including preheat dose recovery and constant‐wave optically stimulated luminescence (OSL) decay curve fitting. Equivalent dose distributions for all samples were wide and positively skewed, indicative of heterogeneous bleaching. A comprehensive statistically based decision‐making protocol has been defined in order to find the appropriate statistical model for burial dose estimation. Ages in the range of 17–14 ka have been obtained which agree with the expected geologically constrained chronology. The Orrisdale Formation is contemporaneous with Heinrich Event 1 and the Killard Point Stadial identified in eastern Ireland ca. 16.4 ka. The suggested approach for OSL dating of glaciofluvial sediments has the potential for much wider application to high latitude or temperate areas where there is an abundance of such sediments and where improved chronological control is much needed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Assessing global Sentinel-2 coverage dynamics and data availability for operational Earth observation (EO) applications using the EO-Compass     

Martin Sudmanns  Dirk Tiede  Hannah Augustin  Stefan Lang 《International Journal of Digital Earth》2020,13(7):768-784

ABSTRACT

Sentinel-2 scenes are increasingly being used in operational Earth observation (EO) applications at regional, continental and global scales, in near-real time applications, and with multi-temporal approaches. On a broader scale, they are therefore one of the most important facilitators of the Digital Earth. However, the data quality and availability are not spatially and temporally homogeneous due to effects related to cloudiness, the position on the Earth or the acquisition plan. The spatio-temporal inhomogeneity of the underlying data may therefore affect any big remote sensing analysis and is important to consider. This study presents an assessment of the metadata for all accessible Sentinel-2 Level-1C scenes acquired in 2017, enabling the spatio-temporal coverage and availability to be quantified, including scene availability and cloudiness. Spatial exploratory analysis of the global, multi-temporal metadata also reveals that higher acquisition frequencies do not necessarily yield more cloud-free scenes and exposes metadata quality issues, e.g. systematically incorrect cloud cover estimation in high, non-vegetated altitudes. The continuously updated datasets and analysis results are accessible as a Web application called EO-Compass. It contributes to a better understanding and selection of Sentinel-2 scenes, and improves the planning and interpretation of remote sensing analyses.  相似文献   

Sikhote Alin' meteoroid: A contribution to the story of its fragmentation and fragment scattering     

Bruno Lang  Maciej Kowalski 《Earth and Planetary Science Letters》1973,21(1):85-90

The correlation of the size and spatial distribution of fragments from the Sikhote Alin' meteoroid, 1947, was examined.With Frost's logarithmic rule of spatial sorting of meteorite fragments, supported by an ad hoc developed averaging procedure, a new approach to the size distribution was made possible.It was found that the meteoroid has been originally broken into several - presumably 5–6 - large fragments unequal in size, which further fragmented with various efficiency and speed.The conclusions are compatible with the reports of the witnesses of the fall of the meteorite.  相似文献   

乌拉山金矿113含金石英脉围岩蚀变地球化学特征初步研究     

郎殿有  张庆瑞  冯慧媛 《内蒙古地质》1994,(Z1)

本文研究了乌拉山金矿带１１３含金石英脉的围岩蚀变类型，蚀变分带及各带的常量元素（Ｋ、Ｎａ、Ｆｅ、Ｓｉ），成矿元素（Ａｕ、Ｃｕ、Ｐｂ、Ｚｎ）的分布特征，用聚类分析，Ｒ型因子分析讨论了元素组合特征和蚀变与矿化的关系。研究结果在乌拉山地区具有重要找矿意义。  相似文献   

Effects of heat and water vapor transport on eddy covariance measurement of CO2 fluxes   总被引：2，自引：0，他引：2  

R. Leuning  O. T. Denmead  A. R. G. Lang  E. Ohtaki 《Boundary-Layer Meteorology》1982,23(2):209-222

Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO₂ concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO₂, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO₂. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= _cw for CO₂, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux _c w. Thus, when the net flux of CO₂ is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., _c w = – _c w. Corrections for the mean convective flux are particularly significant for CO₂ because _cw and _c w are often of similar magnitude. The correct measurement of the net CO₂ flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.  相似文献   

Devolution vs. regionalization of power in Britain and the USA: The consequences for citizen participation     

Michael H. Lang  N. J. Camden 《GeoJournal》1977,1(6):81-86

The failure of experiments with both neighborhood government and regional government has led to attempts to weld these two administrative formats. The result is the federated local authority. The urban planning function in London, England, is utilized as an example to show the failure of the federated authority concept due to its dependence on a metropolitan spirit among its citizens and on a strict division in decision-making between area and local concerns. Neither is attainable so the experiment fails at least in regard to citizen expectations concerning involvement. The proposed solution involves a weaker role for the borough or neighborhood units in the federation and an effort to support and encourage citizen involvement in decision-making via the political process. Disparities in political resources are rectified by recourse to watchdog groups to balance the growing power of technocratic planners.  相似文献   

变形交通线路图自动制作方法     

蔡先华  王浪  付晓 《测绘通报》2020,(5):130-133

城市交通网络规模的不断扩大使得交通线路图成为一种常用地图。为了提高信息的传输效率，更好地保证图形的清晰易读性，出现了变形交通线路地图^[1]。本文分析了变形交通线路图特性并对其自动制作过程进行了总结。为解决制作过程中地图符号冲突问题，提出了作用力驱动站点位移的交通线路图变形压缩方法。建立交通线路图中站点受力移动模型并设计了以坐标轴为轴心的移位算法。试验表明，该算法能够有效解决地图符号冲突问题，为完全自动制作变形交通线路图建立了基础。  相似文献   

Reconciling fluid inclusion types,fluid processes,and fluid sources in skarns: an example from the Bismark Deposit,Mexico   总被引：4，自引：0，他引：4  

Timothy?BakerEmail author  James?R.?Lang 《Mineralium Deposita》2003,38(4):474-495

The Bismark deposit (8.5 Mt at 8% Zn, 0.5% Pb, 0.2% Cu, and 50 g/t Ag) located in northern Mexico is an example of a stock-contact skarn end member of a continuum of deposit types collectively called high-temperature, carbonate-replacement deposits. The deposit is hosted by massive sulfide within altered limestone adjacent to the Bismark quartz monzonite stock (~42 Ma) and the Bismark fault. Alteration concurrently developed in both the intrusion and limestone. The former contains early potassic alteration comprising K-feldspar and biotite, which was overprinted by kaolinite-rich veins and alteration and later quartz, sericite, and pyrite with minor sphalerite and chalcopyrite. Prograde exoskarn alteration in the limestone consists of green andradite and diopside, and transitional skarn comprising red-brown andradite, green hedenbergite and minor vesuvinite, calcite, fluorite, and quartz. The main ore stage post-dates calc-silicate minerals and comprises sphalerite and galena with gangue pyrite, pyrrhotite, calcite, fluorite, and quartz. The entire hydrothermal system developed synchronously with faulting. Fluid inclusion studies reveal several distinct temporal, compositional, and thermal populations in pre-, syn- and post-ore quartz, fluorite, and calcite. The earliest primary fluid inclusions are coexisting vapor-rich (type 2A) and halite-bearing (type 3A; type 3B contain sylvite) brine inclusions (32 to >60 total wt% salts) that occur in pre-ore fluorite. Trapping temperatures are estimated to have been in excess of 400 °C under lithostatic pressures of ~450 bar (~1.5 km depth). Primary fluid inclusions trapped in syn-ore quartz display critical to near critical behavior (type 1C), have moderate salinity (8.4 to 10.9 wt% NaCl equiv.) and homogenization temperatures (Th) ranging from 351 to 438 °C. Liquid-rich type 1A and 1B (calcite-bearing) inclusions occur as primary to secondary inclusions predominantly in fluorite and show a range in Th (104–336 °C) and salinity (2.7–11.8 wt% NaCl equiv.), which at the higher Th and salinity ranges overlap with type 1C inclusions. Oxygen isotope analysis was carried out on garnet, quartz, and calcite (plus carbon isotopes) in pre-, syn-, post-ore, and peripheral veins. Pre-ore skarn related garnets have a δ¹⁸O_mineral range between 3.9 and 8.4‰. Quartz from the main ore stage range between 13.6 and 16.0‰. Calcite from the main ore stage has δ¹³C values of –2.9 to –5.1‰ and δ¹⁸O values of 12.3 to 14.1‰, which are clearly distinct from post-ore veins and peripheral prospects that have much higher δ¹⁸O (16.6–27.3‰) and δ¹³C (1.3–3.1‰) values. Despite the numerous fluid inclusion types, only two fluid sources can be inferred, namely a magmatic fluid and an external fluid that equilibrated with limestone. Furthermore, isotopic data does not indicate any significant mixing between the two fluids, although fluid inclusion data may be interpreted otherwise. Thus, the various fluid types were likely to have formed from varying pressure–temperature conditions through faulting during exsolution of magmatic fluids. Late-stage hydrothermal fluid activity was dominated by the non-magmatic fluids and was post-ore.  相似文献   

Couplex Benchmark Computations Obtained with the Software Toolbox UG     

Peter Bastian  Stefan Lang 《Computational Geosciences》2004,8(2):125-147

This paper describes the numerical results for the COUPLEX benchmark obtained with the simulation software UG using vertex centered finite volume and higher order discontinuous Galerkin schemes. Multigrid solvers on unstructured grids, local mesh refinement and parallel computation are employed to yield very accurate solutions. Since the full range of results required in the benchmarks is too large to be displayed in this paper we focus on the comparison of discretization schemes, assessment of numerical errors and the presentation of parallel computations.  相似文献