首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 0 毫秒
1.
Dry Lake (2763 m), located in the San Bernardino Mountains of southern California, USA, provides a high-resolution climate record from the coastal southwest depicting early Holocene terrestrial climate. 27 AMS 14C dates and multi-proxy analyses, including magnetic susceptibility, total organic mater, microfossil counts, and grain size, suggest the early Holocene was significantly wetter then present, due to an enhanced North American Monsoon (NAM). Elevated insolation at 9000 cal year B.P., raised summer sea surface temperatures in the Gulf of California and the eastern tropical Pacific, as well as land surface temperatures, extending the NAM into southern California. The data also provide evidence of the 8.2 ka event, which registers as a 300-year cool period characterized by reduced monsoonal precipitation, depressed basin productivity, and increased erosion. We suggest this event is the most likely period for the early to middle Holocene (9000–5000 cal year B.P.) glacial advance in the San Bernardino Mountains proposed by Owen et al. (2003, Geology 31: 729–732).  相似文献   

2.
《Urban geography》2013,34(3):217-240
An international comparative urban analysis requires an effort to reconcile not only the variables, but also the units of observation from each country. In a multivariate analysis, failure with regard to the former jeopardizes the validity of the results while failure with regard to the latter risks a priori bias in the interpretation of the results. This comparative, multivariate analysis of urban quality-of-life variables from Canada and the United States calls into question the distinctiveness of the Canadian City in the North American City debate because of such potential bias. As a point of departure from past research, not only is an attempt made to harmonize the set of urban quality-of-life variables with regard to definition, year, and geography, but also to control for the definitional, geographic, and hierarchical differences between the Canadian and U.S. urban systems. Such efforts reveal the Canadian City is indeed distinct from the U.S. City, but also distinct from the North American City, which is a regional entity encompassing Canada and the United States.  相似文献   

3.
4.
5.
The Tyrrhenian coastal sector of North Calabria, stretching between Torre S. Nicola and the Lao river, belongs to the inner extensional sector of the Neogene Apennines thrust belt. It is characterised by a stair of Quaternary marine and fluvial terraces representing the geomorphic response to the interaction between the Quaternary sea level fluctuations and the regional trend of tectonic uplift experienced by the margins of the Tyrrhenian back-arc basin. Since the last century, several authors studied the North Calabria coasts, where the flight of terraces preserves significant marine and continental successions, and proposed several paleo-geomorphological and tectonic reconstructions. In this paper we present a new stratigraphic and morphostructural setting of the North Calabria coasts based on both chronostratigraphical constraints obtained from marine deposits and detailed geomorphological analysis. A ten order stair of marine terraces, stepping between 240 and 0 m a.s.l., was recognized and time-constrained by the age of the Fornaci S. Nicola marine succession which was ascribed by integrated paleoecological, biostratigraphical and paleomagentic analyses to the early Middle Pleistocene (MIS 19–15). In particular, the 240, 200 and 160 m a.s.l. high strandlines were ascribed to the Early Pleistocene and the ones between 100 and 15 m a.s.l. to the Middle Pleistocene. The total amount of the vertical motion experienced by the studied area was estimated, and evaluation of the average rates of uplift for the Middle and Late Pleistocene times were also given. Considering the elevation a.s.l. of the oldest terraces, a tectonic uplift of at least 240 m was calculated for the North Calabria coasts since the Early Pleistocene times, 100 m of which gained from the beginning of the Middle Pleistocene. On the other hand, the 8-m high Late Pleistocene strandlines display a negligible vertical displacement affecting the area during the last 130 ka. The entire staircase of terraces preserves a record of slowing down in the rate of uplift, which attained an average value of 0.15 mm/year during the Middle Pleistocene.  相似文献   

6.
This study was conducted to quantify agricultural land degradation in the Ruba Gered watershed, Ethiopia. The watershed was divided into 12 land mapping units (LMU) after superimposing maps of soil, slope, land use/cover, and elevation. Subsequently, cultivated land was delineated to assess degradation types and severity based on standard approaches. Sheet erosion was estimated using the revised universal soil loss equation. Composite soil samples were collected from each LMU to quantify key soil nutrients (OM, total nitrogen, available phosphorus, and available potassium) lost by sheet erosion. The annual average soil loss due to sheet erosion was estimated to be 17.4 t ha?1 yr?1, with average annual nutrient losses estimated as 246.5 kg ha?1 organic matter, 12.4 kg ha?1 total nitrogen, 0.1 kg ha?1 available phosphorus, and 1.6 kg ha?1 available potassium. The study revealed that substantial quantities of soil and nutrients are lost every year in the study area due to severe sheet erosion. This amount of nutrient loss severely degrades soil and reduces soil fertility.  相似文献   

7.
8.
The publication of the European Landscape Convention (2000) had a stimulating effect on the development of both new systems of landscape classification and new methods of their evaluation and mapping. As an example, a new classification of physiognomic landscape types was developed in Poland in 2014. The objectives of the paper are to (1) popularize, on the international scale, the classification of physiognomic landscape types in a new, improved version, (2) present the original method of physiognomic landscape types mapping with the use of the system of basic landscape units, and (3) present the results of testing of the method in the area of the Kazimierz Landscape Park, Poland. In the area of the Kazimierz Landscape Park, 491 basic landscape units were delimited, within which, on the basis of the leading traits of land relief and cover forms, the physiognomic landscape types were identified. Maps of this type can be important tools in implementing the recommendations of the European Landscape Convention. The total number of physiognomic landscape types identified within a specific area can be one of the key indicators of landscape diversity.  相似文献   

9.
信息通信技术(ICTs)在经济活动空间重组过程中的作用逐渐被认同,然而不同的空间层级不同的部门其重组过程与特征表现各异,形成的观点和争论多样。企业作为最基本的经济单元在信息化浪潮中发生的变化成为一个重要研究议题。本文以服装纺织企业为研究案例,通过企业访谈获取资料,旨在探讨传统制造业在信息技术下的演变特征,尤其是在信息技术下基于时间成本的生产链空间组织的变化特征。本文主要对服装纺织企业具体的信息技术应用进行了剖析,分析了信息技术下不同发展程度企业生产链空间组织特征及其变化。结果发现服装纺织企业在信息技术下,其设计、生产、配送的周期快速缩减,证明了时间因素在信息技术导致生产链空间组织变革中的重要意义;同时发现信息技术对传统加工制造型纺织服装企业的影响主要表现为生产链某个环节管理功能的加强;而对于产业升级后的企业来说,信息技术对整个生产链空间组织的影响明显。  相似文献   

10.
西安入境旅游者认知和感知价值与行为意图   总被引:11,自引:1,他引:11  
旅游者行为是行为地理学研究的重要内容。旅游者在旅游目的地的体验评价是旅游者对旅游目的地的一种认知评估,这种认知评估是旅游者认知在理性和情感层面的唤醒,其结果直接影响旅游者的行为意图。通过构建旅游者认知和旅游者感知价值、旅游者行为意图的结构方程(SEM),以西安入境旅游者为实例研究发现:①旅游者个体认知行为和感知价值及旅游者行为意图呈正相关关系,当个体认知评价水平增加时个体感知价值也对应增加,这种正相关关系使感知价值和行为意图也呈现正相关关系,即个体感知价值水平越高个体行为意图越强烈;②旅游者对旅游服务的感知价值、旅游设施的感知价值和旅游吸引力的感知价值是主导旅游者行为意图的主要因素;③该研究结果不仅在技术层面上证明了旅游者认知和旅游者感知价值、旅游者行为意图的关系,在理论和方法创新上也弥补了发生学中个体认知和其它行为变量之间关系研究的空缺,即个体认知评价和个体行为意图之间为正相关关系,这也支持了体验观点中"认知-感动-行为"的研究范例。研究结果说明了旅游者个体认知研究可以很好的预测旅游者行为意图,这对旅游目的地形象等研究有着重要的理论和实践意义。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号