A Comparative Analysis of Primary and Extreme Characteristics of Dry or Wet Status between Asia and North America   总被引：1，自引：0，他引：1  

HUA Lijuan  MA Zhuguo  ZHONG Linhao 《大气科学进展》2011,28(2):352-362

In this study, the Palmer Drought Severity Index (PDSI) was used to analyze the average and extreme dry/wet states of Asia and North America from 1953 to 2003. The results indicate that the two continents underwent drying trends during this period. Compared with North America, Asia showed more severe drought trends. However, more significant and regular seasonal variation for drought was found in North America. The driest regions in Asia were located in the northern region of China, Mongolia, and eastern mid-Siberian plateau. Most regions in central North America were relatively wetter than other regions. The northern and southwestern regions of North America, as well as the Atlantic and Pacific coastal areas, experienced the most drought during this period. A sharp increase of the drought area and the number of extreme drought events took place from 1997 to 2003 in both Asia and North America. Severe drought events were more likely to occur during the summer on both continents. Asia had the most extreme drought events during July, but North America reached its highest drought frequency from June to September. In Asia, a persistent increasing trend of extreme drought emerged throughout the studied period. However, a more complex evolution of drought emerged in North America: a decreasing trend appeared before the mid-1960s and an increasing trend appeared after the late 1970s. A relatively steady dry/wet status was observed between the mid-1960s and the late 1970s. The role of exceptional, extreme drought events with respect to the La Nin?a event was considered during 1997–2003.  相似文献   

Amenity migration to the global south: Implications for community development     

《Geoforum》2013

Despite a growing trend of migration to countries in the global South fueled by their natural amenities (i.e., natural amenity migration), research on this topic has predominantly been conducted in the global North. This is problematic given the notable socioeconomic, attitudinal, and behavioral differences between amenity migrants (often urbanites from developed countries) and local people (often rural residents of developing countries). Grounded in community field theory, this study begins to fill this gap in the literature by increasing our understanding of the ways in which local residents and amenity migrants interact in the amenity-rich community of Nuevo Arenal, Costa Rica. We found that linguistic, cultural, and spatial barriers (real and perceived) created a social climate in which the interaction between local residents and amenity migrants was primarily based on mundane interactions and did not lead to social integration. This proved to be a hindrance to the creation of the community field, which led to a lack of joint planning and participation in activities and projects that sought to improve the overall living conditions in the community. Explanations of these findings and the implications of such a divide are offered.  相似文献   

Strain rate of the South American lithospheric plate by SIRGAS-CON geodetic observations     

《Journal of South American Earth Sciences》2013

A multiyear solution of the SIRGAS-CON network was used to estimate the strain rates of the earth surface from the changing directions of the velocity vectors of 140 geodetic points located in the South American plate. The strain rate was determined by the finite element method using Delaunay triangulation points that formed sub-networks; each sub-network was considered a solid and homogeneous body. The results showed that strain rates vary along the South American plate and are more significant on the western portion of the plate, as expected, since this region is close to the subduction zone of the Nazca plate beneath the South American plate. After using Euler vectors to infer Nazca plate movement and to orient the velocity vectors of the South American plate, it was possible to estimate the convergence and accommodation rates of the Nazca and South American plates, respectively. Strain rate estimates permitted determination of predominant contraction and/or extension regions and to establish that contraction regions coincide with locations with most of the high magnitude seismic events. Some areas with extension and contraction strains were found to the east within the stable South American plate, which may result from different stresses associated with different geological characteristics. These results suggest that major movements detected on the surface near the Nazca plate occur in regions with more heterogeneous geological structures and multiple rupture events. Most seismic events in the South American plate are concentrated in areas with predominant contraction strain rates oriented northeast-southwest; significant amounts of elastic strain can be accumulated on geological structures away from the plate boundary faults; and, behavior of contractions and extensions is similar to what has been found in seismological studies.  相似文献   

Kinetic and Equilibrium Isotope Effects and their Implications for the Formation of Sandstone-Type Uranium Deposits     

Mostafa FAYEK  Angela MEEK  WANG Guo  WEN Zhanjiu 《《地质学报》英文版》2013,87(Z1):756-757

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Intra-arc extension in Central America: Links between plate motions, tectonics, volcanism, and geochemistry     

J. Phipps Morgan  C.R. Ranero  P. Vannucchi 《Earth and Planetary Science Letters》2008,272(1-2):365-371

This study revisits the kinematics and tectonics of Central America subduction, synthesizing observations of marine bathymetry, high-resolution land topography, current plate motions, and the recent seismotectonic and magmatic history in this region. The inferred tectonic history implies that the Guatemala–El Salvador and Nicaraguan segments of this volcanic arc have been a region of significant arc tectonic extension; extension arising from the interplay between subduction roll-back of the Cocos Plate and the ~ 10–15mm/yr slower westward drift of the Caribbean plate relative to the North American Plate. The ages of belts of magmatic rocks paralleling both sides of the current Nicaraguan arc are consistent with long-term arc-normal extension in Nicaragua at the rate of ~ 5–10mm/yr, in agreement with rates predicted by plate kinematics. Significant arc-normal extension can ‘hide’ a very large intrusive arc-magma flux; we suggest that Nicaragua is, in fact, the most magmatically robust section of the Central American arc, and that the volume of intrusive volcanism here has been previously greatly underestimated. Yet, this flux is hidden by the persistent extension and sediment infill of the rifting basin in which the current arc sits. Observed geochemical differences between the Nicaraguan arc and its neighbors which suggest that Nicaragua has a higher rate of arc-magmatism are consistent with this interpretation. Smaller-amplitude, but similar systematic geochemical correlations between arc-chemistry and arc-extension in Guatemala show the same pattern as the even larger variations between the Nicaragua arc and its neighbors.  相似文献   

美国国家公园地质旅游特色及借鉴意义   总被引：12，自引：0，他引：12  

谢洪忠  刘洪江 《中国岩溶》2003,22(1):73-76

自1872 年美国建立第一个国家公园以来, 全世界国家公园数已达2600个, 对于资源环境、生态系统、地质景观的保护起着十分重要的作用, 特别是美国,在保护地质景观的同时, 开展地质旅游, 效果明显。与之比较, 我国的地质公园建设还存在着许多不足。本文主要说明了美国国家公园的主要地质旅游特色, 比较了两国在地质旅游认识、管理方面存在的差异, 并总结了一些值得我们借鉴学习的经验。   相似文献   

An overview of physical and ecological processes in the Rio de la Plata Estuary     

E. Marcelo Acha  Hermes Mianzan  Raúl Guerrero  José Carreto  Diego Giberto  Norma Montoya  Mario Carignan 《Continental Shelf Research》2008

The Rio de la Plata is a large-scale estuary located at 35°S on the Atlantic coast of South America. This system is one of the most important estuarine environments in the continent, being a highly productive area that sustains valuable artisanal and coastal fisheries in Uruguay and Argentina. The main goals of this paper are to summarize recent knowledge on this estuary, integrating physical, chemical and biological studies, and to explore the sources and ecological meaning of estuarine variability associated to the stratification/mixing alternateness in the estuary. We summarized unpublished data and information from several bibliographic sources. From study cases representing different stratification conditions, we draw a holistic view of physical patterns and ecological processes of the stratification/mixing alternateness. This estuary is characterized by strong vertical salinity stratification most of the time (the salt-wedge condition). The head of the estuary is characterized by a well-developed turbidity front. High turbidity constrains their photosynthesis. Immediately offshore the turbidity front, water becomes less turbid and phytoplankton peaks. As a consequence, trophic web in the estuary could be based on two sources of organic matter: phytoplankton and plant detritus. Dense plankton aggregations occur below the halocline and at the tip of the salt wedge. The mysid Neomysis americana, a key prey for juvenile fishes, occurs all along the turbidity front. A similar spatial pattern is shown by one of the most abundant benthic species, the clam Mactra isabelleana. These species could be taken advantage of the particulate organic matter and/or phytoplankton concentrated near the front. Nekton is represented by a rich fish community, with several fishes breeding inside the estuary. The most important species in terms of biomass is Micropogonias furnieri, the main target for the coastal fisheries of Argentina and Uruguay. Two processes have been identified as producing partially stratified conditions: persistent moderate winds (synoptic scale), or low freshwater runoff (interannual scale). Less frequently, total mixing of the salt wedge occurs after several hours of strong winds. The co-dominance of diatoms (which proliferate in highly turbulent environments) and red tides dinoflagellates and other bloom taxa (better adapted to stratified conditions), would indicate great variability in the turbulence strength, probably manifested as pulses. Microplankton and ichthyoplankton assemblages defined for the stratified condition are still recognized during the partially mixed condition, but in this case they occupy the entire water column: vertical structure of the plankton featuring the stratified condition become lost. Bottom fish assemblages, on the contrary, shows persistence under the different stratification conditions, though the dominant species of the groups show some variations. Summarizing, the Río de la Plata Estuary is a highly variable environment, strongly stratified most of the time but that can be mixed in some few hours by strong wind events that occur in an unpredictable manner, generating stratification/partially mixed (less frequently totally mixed) pulses all along the year. At larger temporal scales, the system is under the effects of river discharge variations associated to the ENSO cycle, but their ecological consequences are not fully studied.  相似文献   

Algal pigment patterns and phytoplankton assemblages in different water masses of the Río de la Plata maritime front     

José I. Carreto  Nora MontoyaRut Akselman  Mario O. CarignanRicardo I. Silva  Daniel A. Cucchi Colleoni 《Continental Shelf Research》2008

The composition of phytoplankton assemblages were studied in three sections across the continental shelf between the Río de la Plata and the oceanic waters of the Subtropical Convergence, during late spring. Algal communities were examined using microscopy and HPLC-derived pigment concentrations. The CHEMTAX program was used to estimate the chlorophyll a (chl a) biomass of different algal classes. Trends in pigment ratios due to phytoplankton photo-adaptation and photo-acclimation were also examined. In order to accommodate the natural diversity of phytoplankton assemblages the original data have been split to represent five ecosystems. In addition, the pigment data for the Brazil Current ecosystem has been split by sample depth.  相似文献   

A maroon legacy? Sketching African contributions to live fencing practices in early Spanish America     

Chris S. Duvall 《Singapore journal of tropical geography》2009,30(2):232-247

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Community forest management in Mexico: carbon mitigation and biodiversity conservation through rural development   总被引：1，自引：0，他引：1  

Daniel Klooster  Omar Masera   《Global Environmental Change》2000,10(4):2184

Forest management is an important carbon mitigation strategy for developing countries. As demonstrated by the case of Mexico, community forest management is especially effective because it offers tangible local benefits while conserving forests and sequestering carbon. Community forestry receives minimal government support now, but the clean development mechanism (CDM) of the Kyoto Protocol could leverage additional resources to promote the approach in Mexico and elsewhere. We argue that adequately designed and implemented, community forestry management projects can avoid deforestation and restore forest cover and forest density. They comprise promising options for providing both carbon mitigation and sustainable rural development. These kinds of projects should be included in the CDM.  相似文献