Climate change and human impact in a sensitive ecosystem: the Holocene environment of the Northwest Icelandic highland margin

Complex interactions of climate and volcanic activity have shaped the environment of Iceland during the Holocene. Palaeoecological records from Iceland offer a unique look at a Holocene environment that was uninhabited by humans and free of mammal herbivores until about AD 870. We present a new reconstruction of Holocene vegetation and landscape dynamics from a small lake, Barðalækjartjörn, located near the highland margin in Northwest Iceland. A multi‐proxy approach was used to reconstruct vegetation based on pollen and plant macrofossil analysis and landscape stability based on lithological proxies. The record covers the period c. 10 300–200 cal. a BP. For the first two millennia aeolian processes probably played a part in vegetation development. This period is characterized by high input of minerogenic material into the lake and a vegetation assemblage in which plants tolerant of aeolian deposition are prominent. Betula pubescens woodland reached a maximum between c. 7400 and 6500 cal. a BP. Betula nana‐dominated dwarf shrub heath replaced woodland after c. 4000 cal. a BP, following the onset of Neoglaciation. Land use following human settlement caused an environmental shift at the highland margin. Betula pubescens probably disappeared from the vicinity of the lake soon thereafter. Large‐scale soil erosion began at c. 1000 cal. a BP in the wake of human activities, such as introduction of grazing livestock and woodcutting. This study offers an important long‐term perspective of the development of the highland ecosystem under both wholly natural and human‐influenced conditions.     

福建两个块状硫化物矿床中磁黄铁矿结构的研究

福建大田前锋梅仙块状硫化物矿床中六方磁黄铁矿中的单斜磁黄铁矿有两种交生态：受结晶方位控制的叶片状交生和受颗粒边界、裂隙控制的不规则状交生。着重由六方磁黄铁矿在冷却过程中出溶形成,而后者则是单斜磁黄铁矿交代六方磁黄铁矿的结果。叶片状交生体经历后期变形、变质后产生粗化和均一化,形成了楔形边、箱形、得杂叶片等结构。单斜磁黄铁矿在变形较弱的矿区保存较好,而在强烈部位消失殆尽,说明应力对磁黄铁矿的均一化效应     

岩石膨胀性试验注意事项探讨

从室内试验的角度来探讨几类工程勘察中岩石常用膨胀性试验(自由膨胀率、膨胀力、侧向约束膨胀率、耐崩解)的注意事项,从野外取样、标准样品制取、试验操作、方法选择等方面进行了论述,力求减小试验误差,提高膨胀岩的试验水平,保证试验结果的准确性,并使膨胀岩膨胀性指标的测定方法更臻完善。     

牛角塘伴生型镉矿床特殊的成矿环境

牛角塘伴生型镉矿床镉的富集程度高,比克拉克值高4~5个数量级,比工业品位高十几倍至上百倍。早寒武世清虚洞期牛角塘地区处于台缘滩丘环境,在清虚洞组中上部形成了藻丘建造,发育了含藻类、藻球粒、藻鲕粒、核形石和生物碎屑的白云岩,是该矿床最主要的容矿岩性单元。矿体普遍呈似层状、透镜状和脉状产出,矿体产状与容矿围岩的产状基本一致,矿体的分布受清虚洞组藻丘建造以及有利岩性组合的联合控制,具明显的层控、相控、岩控的特点。藻丘建造还可能提供了部分矿源。镉的超常富集、成矿与麻江古油藏的成藏演化具有一定的关系:一是牛角塘矿床成矿年龄为433~510 Ma,即加里东运动的中晚期,而加里东运动中晚期是麻江古油藏的油气活动时期,麻江古油藏的早期演化阶段与牛角塘镉矿的成矿期大体是重合的,成藏应略早于成矿,成矿是在古油藏液态烃仍然存在的情况下进行的,且成矿期有可能一直延伸至油藏被破坏以后;二是油藏流体为成矿提供具还原性质的成矿流体和部分硫源。特殊的岩相古地理环境和古油藏为牛角塘矿床镉的富集和成矿提供了有利条件。     

NUMERICAL STUDY ON THE EFFECTS OF SEA SURFACE TEMPERATURE ON TROPICAL CYCLONE INTENSITY-PART I:NUMERICAL EXPERIMENT OF THE TROPICAL CYCLONE INTENSITY RELATED TO SST Duan Yihong;Qin Zenghao;Gu dianfeng;Li Yongping, Shanghai Typhoon Institute.Shangh

In the context of a model of tropical cyclone intensity based on an improved meso-scaleatmospheric model, numerical simulation is performed of the track and intensity variation oftropical cyclones (TC) arising from sea surface temperature (SST) variation over a specified searegion. Evidence suggests that the model is capable of modeling quite welt the track and intensityof TC: SST variation leads to an abrupt change in the cyclone intensity: the response of thecyclone to the abrupt SST change lasts 8—12 h.     

珠江三角洲城市群污染综合指数预报的模式方法

应用全二阶矩表示的商斯烟团模式,重点引入烟团的合并与分解及各种清除过程,并利用广州热带模式（GZTM）所提供的华南地区细网格的三维数字化流场,来计算污染物浓度的长期变化。具体先模拟计算SO2、NOx、TSP的地面浓度日变化,通过求平均得到每种污染物的日均浓度,并和对应的污染物的日均浓度二级标准比较,得到每种污染物的污染指数Pi,最后求和得出污染综合指数P,从而对珠江三角洲地区的污染综合指数作出预报。     

Aerosol polarized phase function and single-scattering albedo retrieved from ground-based measurements

Aerosol optical parameters, polarized phase function and single-scattering albdeo, have been retrieved from ground-based sun photometer measurements in Beijing 2003. The measured aerosol optical thickness varies from 0.12 to 0.77 with an average value of 0.39. The measured Ångström coefficient ranges from 0.75 to 1.47 with an average value of 1.21. The retrieved single-scattering albedo at 870 nm is within the 0.76–0.94 range and the average value is 0.85, suggests there are considerable aerosol absorptions in Beijing. The maximum value of retrieved polarized phase function at 870 nm ranges from 0.068 to 0.225 with an average value of 0.16, and it illustrates good correlations with the Ångström coefficient, i.e. the relative size of aerosol particles. Analyses of measurements and theoretical calculations show the polarized phase function is sensitive to aerosol size distribution and complex refractive index, especially the imaginary part of the refractive index which denotes aerosol light absorbing effects. These results suggest that the polarized phase function is an effective and unique aerosol optical parameter and is able to improve the retrieval of aerosol physical properties.     

RETRIEVAL OF HORIZONTAL WIND PERTURBATION FIELDS FROM SIMULATED SINGLE DOPPLER RADAR OBSERVATIONS*

The application of the single Doppler radar dataset analysis is usually confined to the assumption that the actual wind is linearly distributed or uniform locally.Following some dynamic features of convective weather,a conceptual model of moderate complexity is constructed,wherewith a horizontal wind perturbation field is retrieved directly from the single Doppler radar measurements.The numerical experiments are based on a 3-D cloud model-generated convective cell,whose radial velocity component is taken as the radar observations that are put into the closed equations based on the conceptual model to retrieve the horizontal wind perturbation field.After the initial field is properly treated,the retrieval equation is solved in terms of the 2-D FFT technique and the sensitivity to noise is examined.Finally,contrast analysis is done of the retrieved and the cloud model output wind fields,indicating the usefulness of the approach proposed in this paper.     

Grouping response method for equivalent static wind loads based on a modified LRC method

Wind loading is one of the most important loads for controlling the design of large-span roof structures.Equivalent static wind loads,which can generally aim at determining a specific response,are wid...     

大暴雨雨滴平均谱的研究

根据不同地区的许多观测表明,雨滴平均谱的极限状态趋于指数形式。1984年8月10日至10日受8407号台风减弱为低压的影响,长春降了大暴雨,降水量为112.3mm,从10日06时30分开始,用滤纸色斑法,每隔5分钟观测一次雨滴谱,到11日04时,共取雨滴谱259份。本文根据这次层状云大暴雨雨滴谱资料,研究了指数形式雨滴谱N_D=N_0e~(-λD)的参数N_0和λ的确定,并对不同方法拟合的经验