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排序方式： 共有186条查询结果，搜索用时 15 毫秒
41.
Luisa Patiño Maria Isabel Velez Marion Weber César A. Velásquez-r Santiago David Manuela Rueda Ivonne Castañeda Diana Arboleda 《第四纪科学杂志》2020,35(8):1046-1056
This study presents the first multi-proxy palaeoenvironmental and palaeoclimatic history for northern South America based on the palaeolimnological reconstruction of a pond located in a dry paramo at 3570 masl. During the Last Glacial Maximum (LGM), the study area was under glacial conditions, then during global events Heinrich Stadial 1 (HS1), Bølling–Allerød (BA), and the Younger Dryas (YD), the pond expanded, accumulation rates and proxies for erosion reached the highest values, indicative of humid conditions, with maxima in humidity during the BA and YD. Dry conditions and pond desiccation occurred in the Greenlandian–Northgrippian and by 6010 cal a bp the area was transformed into the mire of today. Comparisons with records from other sites in South America indicate that changes in humidity are most likely controlled by the Intertropical Convergence Zone, mainly during the glacial and postglacial, and by changes in the Pacific Ocean, more pronounced after the YD. 相似文献
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Anabela Carvalho Mike D. Flannigan Kim A. Logan Lynn M. Gowman Ana Isabel Miranda Carlos Borrego 《Climatic change》2010,98(1-2):177-197
In this study, we investigated the impact of future climate change on fire activity in 12 districts across Portugal. Using historical relationships and the HIRHAM (High Resolution Hamburg Model) 12 and 25 km climate simulations, we assessed the fire weather and subsequent fire activity under a 2 × CO2 scenario. We found that the fire activity prediction was not affected by the spatial resolution of the climate model used (12 vs. 25 km). Future area burned is predicted to increase 478% for Portugal as a whole, which equates to an increase from 1.4% to 7.8% of the available burnable area burning annually. Fire occurrence will also see a dramatic increase (279%) for all of Portugal. There is significant spatial variation within these results; the north and central districts of the country generally will see larger increases in fire activity. 相似文献
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The inelastic response of elasto‐plastic SDOF oscillators subjected to 24 simple waveforms was studied. The waveforms contain linear, quadratic, sinusoidal, and triangular acceleration components that repeat for not more than several cycles. Similarities and differences in oscillator response characteristics are presented, organized by a characteristic period. The strengths and corresponding strength reduction factors required for constant ductility responses are discussed. Response data are compared with expectations based on the concepts of equal energy, equal displacement, and preservation of force. Limitations on the applicability of the equal energy concept are identified. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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The inner bay of Lourenço Marques receives the untreated sewage of the city, the run-off from five rivers and metal and hydrocarbon pollution from the activities of the port. Iron ore handling results in an increase in iron and copper concentrations in the water, particularly since loading by slurry was introduced. Large quantities of metal pollutants are probably accumulating in muds and are likely to contaminate shellfish which are an important food source in the area. Untreated sewage discharges are at such a level that eutrophication of the bay is threatened, besides constituting a public health risk on bathing beaches. 相似文献
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Christian Betzler Juan Carlos Braga José M. Martín Isabel M. Sánchez-Almazo Sebastian Lindhorst 《International Journal of Earth Sciences》2006,95(5):903-910
During the late Tortonian (upper Miocene), the Guadix Basin in S Spain formed one of the Betic corridors that connected the Mediterranean Sea with the Atlantic Ocean. The closure of this connection occurred in a series of steps, documented by three sedimentary units. A lower unit, consisting of basinal marls, shallow-water calcarenites and sands records the formation of a wide seaway. During deposition of the following unit this narrowed to a strait no more than 2 km in wide, triggering an intensification of currents that caused migration of submarine dunes preserved as giant cross-beds in bioclastic sands and conglomerates. Current flowed from the Mediterranean to the Atlantic. The third unit constitutes the youngest marine episode of the filling of the Guadix Basin. At this stage, the connection between the Mediterranean Sea and the Atlantic Ocean was broken, and a system of coastal coral reefs was established in the northern part of the Basin. 相似文献