Rapid Lateglacial tree population dynamics and ecosystem changes in the eastern Baltic region     

Maija Heikkilä  Sonia L. Fontana  Heikki Seppä 《第四纪科学杂志》2009,24(7):802-815

A growing body of evidence implies that the concept of 'treeless tundra' in eastern and northern Europe fails to explain the rapidity of Lateglacial and postglacial tree population dynamics of the region, yet the knowledge of the geographic locations and shifting of tree populations is fragmentary. Pollen, stomata and plant macrofossil stratigraphies from Lake Kurjanovas in the poorly studied eastern Baltic region provide improved knowledge of ranges of north‐eastern European trees during the Lateglacial and subsequent plant population responses to the abrupt climatic changes of the Lateglacial/Holocene transition. The results prove the Lateglacial presence of tree populations (Betula, Pinus and Picea) in the eastern Baltic region. Particularly relevant is the stomatal and plant macrofossil evidence showing the local presence of reproductive Picea populations during the Younger Dryas stadial at 12 900–11 700 cal. a BP, occurring along with Dryas octopetala and arctic herbs, indicating semi‐open vegetation. The spread of Pinus–Betula forest at ca. 14 400 cal. a BP, the rise of Picea at ca. 12 800 cal. a BP and the re‐establishment of Pinus–Betula forest at ca. 11 700 cal. a BP within a span of centuries further suggest strikingly rapid, climate‐driven ecosystem changes rather than gradual plant succession on a newly deglaciated land. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

干旱荒漠区土地利用方式快速转变对土壤入渗性能的影响   总被引：3，自引：1，他引：3  

张润霞  赵学勇  李晶  吕文强  柴媛媛  岳红琴 《中国沙漠》2020,40(4):146-153

研究不同土地利用类型下土壤入渗及其影响因素，有助于城市土地利用管理及径流调节。以快速城市化的兰州新区6种土地利用类型为例，利用圆盘入渗仪，对土壤水分入渗过程进行了实地测量，并利用主成分分析对影响因素进行研究。结果表明：城市化过程中土地利用变化使土壤砂粒和容重增加，总孔隙度和饱和含水量降低；待建地和人工林地的土壤入渗参数值均低于其他土地利用类型。土壤入渗率与有机质含量、总孔隙度、饱和含水量、粉粒含量正相关，与容重和砂粒、黏粒含量负相关。城市化过程中土地利用类型向待建地的转变改变了土壤理化性质及土壤水分入渗能力。  相似文献   

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常志巧  郝金明  张成军  崔建勇 《大地测量与地球动力学》2008,28(3):83-86

???GPS?????λ??????????????????????????????????????????????M??????????????μ??????????????????????????????????????????????е????????????????????????÷??????п???????????????????????????  相似文献   

东风和西风切变环境下西北太平洋热带气旋快速增强特征的对比   总被引：8，自引：6，他引：2       下载免费PDF全文

王伟  余锦华 《大气科学学报》2013,36(3):337-345

利用1980-2009年美国联合台风警报中心(Joint Typhoon Warning Center,JTWC)整编的热带气旋(tropical cyclone,TC)最佳路径资料,定义西北太平洋TC 24 h强度变化达到总体样本96%累积概率的变化值,即35 kn作为TC快速增强的阈值。根据NCEP/NCAR资料将200~850 hPa之间 TC所处的环境纬向风切变(wind shear,WS)划分为东风切变(east wind shear,EWS)和西风切变(west wind shear,WWS)。对比了EWS和WWS环境下快速增强热带气旋(rapid intensification tropical cyclones,RITC)的统计和大尺度环境合成场特征,结果表明,近70%的TC快速增强发生在东风切变环境下。TC快速增强概率最高的月份在9月,初始强度区间为[65,75) kn。大的EWS下,850 hPa有来自南海地区的西南气流为RITC输送充沛水汽,500 hPa、200 hPa高压势力强但脊线位置偏北,RITC流出层温度低于-79 ℃,垂直结构上底层的辐合与高层的辐散也相对较强。大WWS下,850 hPa的水汽主要为来自西北太平洋的东南气流,500 hPa副热带高压断裂为几个分散的中心,200 hPa辐散相对较弱,RITC合成位置位于副热带高压西北侧的西风气流,流出层温度约-76 ℃。  相似文献   

登陆华南热带气旋强度变化与大尺度环流的关系   总被引：1，自引：0，他引：1  

于润玲  余晖  端义宏 《南京气象学院学报》2013,(5):619-625

应用UK再分析资料,采用合成分析方法,对比分析了登陆华南的登陆前迅速增强的TC（Rapid Intensifying TC,简称RITC）和迅速减弱的TC（Rapid FillingTC,简称RFTC）登陆前24h的大尺度环流背景特征。结果表明：从外流、入流强度和范围上看,RITC的低空入流和高空外流均明显强于RFTC,两类TC高空外流强度的差异比低空入流明显,RITC的次级环流径向范围大;从外流垂直伸展高度上看,RITC的平均外流主要集中在500hPa以上,而RFFC的平均外流比较分散,向下伸展到850hPa;从高空流场配置看,RITC上空除西北象限外均有较强外流,而RVrC仅在东北象限有较强外流,相应的RITC和RVrC的高空辐散在范围和强度上均有明显的差异,其中RITC的高空辐散明显强于RFTC;强烈的西南季风水汽输送是登陆华南的TC登陆前突然加强的先兆条件,RITC的对流活动明显比RFTc活跃;RITC的纬向风垂直切变比RFTC小,有利于RITC的强度增强。  相似文献   

3维城市建模中的建筑墙面纹理快速重建研究   总被引：9，自引：0，他引：9  

吴军 《测绘学报》2005,34(4):317-323

建筑墙面纹理数据的获取是3维城市建模的重要方面和"瓶颈"问题.阐述建筑墙面纹理快速重建需要解决的问题和实现策略,并对纹理影像数据源的选择、获取方式以及重建过程中影像方位元素获取、轮廓线影像匹配关键算法的实现等各方面进行具体探讨,最后以数码相机拍摄的近景影像和直升机载视频序列影像作为纹理数据源分别进行建筑墙面纹理快速重建实验,取得较好的效率和效果.  相似文献   

Rapid vegetation change during the early Holocene in the Faroe Islands detected in terrestrial and aquatic ecosystems     

Gina E. Hannon  Richard H. W. Bradshaw  Stefan Wastegrd 《第四纪科学杂志》2003,18(7):615-619

High‐resolution pollen, plant macrofossil and sedimentary analyses from early Holocene lacustrine sediments on the Faroe Islands have detected a significant vegetation perturbation suggesting a rapid change in climate between ca. 10 380 cal. yr BP and the Saksunarvatn ash (10 240±60 cal. yr BP). This episode may be synchronous with the decline in δ¹⁸O values in the Greenland ice‐cores. It also correlates with a short, cold event detected in marine cores from the North Atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of Lake Agassiz into the northwest Atlantic, or, alternatively, a period with distinctly decreased solar forcing. The vegetation sequence begins at ca. 10 500 cal. yr BP with a succession from tundra to shrub‐tundra and increasing lake productivity. Rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal. yr BP. High pollen percentages, concentrations and influx of Betula, Juniperus and Salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation. Unstable conditions followed ca. 10 380 cal. yr BP that changed both the upland vegetation and the aquatic plant communities. A decrease in percentage values of shrub pollen is recorded, with replacement of both aquatics and herbaceous plants by pioneer plant communities. An increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery. The catchment changes are consistent with less seasonal, moister conditions. Subsequent climatic amelioration reinitiated a warmth‐driven succession and catchment stabilisation, but retained high precipitation levels influencing the composition of the post‐event communities. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Benchmarking a Light-Curve Model at Low-z     

Frederick J. Mayer  John R. Reitz 《Astrophysics and Space Science》2004,294(3-4):241-253

A set of well-measured, {low-z}, type Ia supernovae from the Calán/Tololo SNe data sets is used to determine benchmark parameters in our hydrodynamics-based, light-curve model. The light-curve data fit fairly well in B, V, and R passbands but not as well in the I passband. The fitting procedure, extracted best-fit model parameters, and their connection to type Ia SN parameters are presented. Our benchmarked light-curve model represents an alternative to empirical template methods for the analysis of light-curve data.  相似文献   

高速经济增长时期日本的农村与农业问题   总被引：2，自引：1，他引：1  

陈忠暖  甘巧林 《世界地理研究》1999,8(2):80-83

本文对战后以工业化为代表的日本高速经济增长时期,农村及农业所出现的乡村人口过疏化、兼业化、农业后继乏人、农地减少、土地经营规模零碎、农业地位不定等问题进行了分析,并探讨了产生这些问题的原因。对高速经济增长中的我国农业和农村的发展可资参照  相似文献   

南海西部浮游有孔虫记录的MIS 3期表层海洋环境变化          下载免费PDF全文

杨文瑜  黄宝琦  肖洁  周力平 《第四纪研究》2008,28(3):437-446

对南海西部越南岸外上升流区17954-2站浮游有孔虫属种组合变化、浮游有孔虫氧同位素、AMS14C测年的分析以及浮游有孔虫表层海水温度、温跃层转换函数的研究结果表明:在MIS3期,南海西部表层海水温度大体呈现暖-冷-暖的变化趋势;温跃层深度由浅到深阶段性变化;短时间尺度上温度与温跃层发生幅度较大的快速变化。暖事件（IS）对应于浮游有孔虫暖水种、混合层属种含量的增加,冷水种、温跃层属种含量的减少以及冬夏SST的升高;冷事件则与之相反。表层海水生产力亦大致呈现3个阶段（61～51ka,51～42ka和42～32ka）的变化,在千年尺度的快速气候事件中,暖事件对应浮游有孔虫生产力属种含量降低,冷事件对应升高。此外,在MIS3内部分暖事件（IS6和IS11～13）表现出表层海水温度降低,温跃层深度变浅和表层海水生产力升高的状况,表明该区此时上升流的存在,其形成原因推测是由于东亚夏季风加强的结果。  相似文献