LICHENOMETRIC AGES OF THE LITTLE ICE AGE MORAINES ON KING GEORGE ISLAND AND OF THE LAST VOLCANIC ACTIVITY ON PENGUIN ISLAND (WEST ANTARCTICA)     

PIOTR JAN ANGIEL  MACIEJ DĄBSKI 《Geografiska Annaler: Series A, Physical Geography》2012,94(3):395-412

The recently observed recession of glaciers on King George Island is associated with decades of climate warming in the Antarctic Peninsula region. However, with only 60 years of glaciological observations in the study area ages of the oldest moraines are still uncertain. The goal of the study was to estimate ages of lichen colonization on the oldest moraines of the Ecology and White Eagle Glaciers on King George Island and on the Principal Cone of Penguin Island volcano. The first lichenometric studies on these islands from the late 1970s used rates that had about four to five times slower Rhizocarpon growth rates. We re‐examined the sites and measured 996 thalli diameters to establish the surface ages. To estimate the age we used (1) long‐term Rhizocarpon lichen group growth rates established by authors using data from a previous lichenometric study on King George Island, and (2) previous data of lichen growth rates from other sub‐Antarctic islands. Our results suggest growth rates between 0.5 and 0.8 mm yr^–1. According to these rates the ages of the oldest moraine ridges are of the Little Ice Age and were colonized at the beginning of the twentieth century. The mid‐twentieth century age of lichen colonization on the historically active Penguin Island volcano might support the date of the last eruption reported by whalers in the end of the nineteenth and the beginning of the twentieth century.  相似文献   

浙江南部近海主要鱼类的时空生态位及种间联结性     

叶深  杨蕊  丁朋朋  彭欣  刘伟成 《海洋学报》2022,44(1):48-62

基于2016年8月(夏季)、11月(秋季)、2017年3月(冬季)、5月(春季)浙江南部近海的鱼类调查数据,利用生态位宽度、生态位重叠、聚类分析、方差比率法、卡方检验、联结系数以及种对共同出现百分率对主要鱼类种间关系进行研究.结果表明:(1)调查共采集鱼类169种,主要鱼类共有26种;(2)在空间维度上,日本鲭(Sco...  相似文献   

2050年前气候变暖冰川萎缩对水资源影响情景预估   总被引：42，自引：34，他引：42  

施雅风 《冰川冻土》2001,23(4):333-341

根据有不确定性的综合预测 ,到 2 0 5 0年左右青藏高原温度可比 2 0世纪末升高 2 .5℃左右 ,其导致冰川强烈消融的夏季升温为 1.4℃ ,将使平衡线上升 10 0m以上 .冰舌区消融冰量超过积累区冰运动来的冰量 ,冰川出现变薄后退 ,初期以变薄为主融水量增加 ,后期冰川面积大幅度减少 ,融水量衰退 ,至冰川消亡而停止 .考虑冰川大小 ,冰川类型响应气候变暖的敏感性有重大差别 ,应用新编中国冰川目录的统计数据 ,选择若干区域 ,预估 2 0 5 0年前冰川萎缩对水资源影响情景 .祁连山北麓河西地区 ,天山北麓准噶尔盆地南缘 ,天山南麓吐鲁番 哈密盆地的多数出山河流的冰川 ,以面积小于 2km2 者占绝对优势 ,对气候变暖最为敏感 ,衰退迅速 ,本世纪初期出现融水量高峰 ,中期融水量减少 ,对每条河流的影响以 10 6～ 10 7m3 ·a-1计 .少数流域如疏勒河、玛纳斯河等 ,冰川融水量占河川径流 1/ 3以上 ,有若干 5～ 30km2 左右中等规模冰川存在 ,预期至本世纪中期才出现融水高峰 ,融水增加值以 10 8m3 ·a-1计 .塔里木盆地周围高山冰川总面积达 2 2 0 0 9km2 ,有面积超过 10 0km2 、冰舌为厚表覆盖的大冰川 2 2条 ,退缩缓慢 ,冰川融水量在叶尔羌河、玉龙喀什河与阿克苏河等占 5 0 %～ 80 % .现在塔里木河干流主要靠天山西南部  相似文献   

长江源区冰川对全球气候变化的响应     

吴豪  虞孝感  许刚 《地理与地理信息科学》2001,17(4):1-5

长江源区是青藏高原内部山地冰川集中分布的地区之一 ,其冰川储量都占长江流域冰川总量的一半以上。近几十年以来由于受全球气候变化的影响 ,长江源区气候呈暖干化的倾向 ,大多数冰川呈退缩状态 ,这对长江源区的生态环境产生深刻的影响 ,进而危及整个长江流域的生态安全。用英国Hadley气候预测与研究中心的GCM模型HADCM2预测长江源区未来的气候情景 ,结果显示在不同的实验条件下 ,气候都将由现在的暖干化趋势向暖湿化方向转变。通过建立长江源区对气候变化的响应模型 ,用来预测在未来气候情景下冰川变化的趋势 ,预计在本世纪的不同时期冰川零平衡线 (雪线 )将上升 16～ 5 0m。  相似文献   

Nonparametric evaluation of environmental parameters determining the occurrence of stonefly larvae (Plecoptera) in streams     

Jan Helešic 《Aquatic Sciences - Research Across Boundaries》2001,63(4):490-501

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Multi-source spatial data-based invasion risk modeling of Striga (Striga asiatica) in Zimbabwe     

Bester Tawona Mudereri  Elfatih Mohamed Abdel-Rahman  Timothy Dube  Tobias Landmann  Zeyaur Khan  Emily Kimathi 《地理信息系统科学与遥感》2020,57(4):553-571

ABSTRACT

Monitoring of destructive invasive weeds such as those from the genus Striga requires accurate, near real-time predictions and integrated assessment techniques to enable better surveillance and consistent assessment initiatives. Thus, in this study, we predicted the potential ecological niche of Striga (Striga asiatica) weed in Zimbabwe, to identify and understand its propagation and map potentially vulnerable cropping areas. Vegetation phenology from remote sensing, bioclimatic and other environmental variables (i.e. cropping system, edaphic, land surface temperature, and terrain) were used as predictors. Six machine learning modeling techniques and the ensemble model were evaluated on their suitability to predict current and future Striga weed distributional patterns. The mentioned predictors (n = 40) were integrated into six models with “presence-only” training and evaluation data, collected in Zimbabwe over the period between the 12^th and 28^th of March 2018. The area under the curve (AUC) and true skill statistic (TSS) were used to measure the performance of the Striga modeling framework. The results showed that the ensemble model had the strongest Striga occurrence predictive power (AUC = 0.98; TSS = 0.93) when compared to the other modeling algorithms. Temperature seasonality (Bio4), the maximum temperature of the warmest month (Bio5) and precipitation seasonality (Bio15) were determined to be the most dominant bioclimatic variables influencing Striga occurrence. “Start of the season” and “season minimum value” of the “Enhanced Vegetation Index base value” were the most relevant remote sensing-based variables. Based on projected climate change scenarios, the study showed that up to 2050, the suitable area for Striga propagation will increase by ~ 0.73% in Zimbabwe. The present work demonstrated the importance of integrating multi-source data in predicting possible crop production restraints due to weed propagation. The results can enhance national preparedness and management strategies, specifically, if the current and future risk areas can be identified for early intervention and containment  相似文献   

生态位理论与方法在城市研究中的应用   总被引：33，自引：2，他引：33  

胡春雷  肖玲 《地域研究与开发》2004,23(2):13-16

引入生态学重要基础理论生态位理论,认为其在城市研究中有重要作用。表现在:生态位态势变化及生态位大小能够反映城市一般发展规律和城市特征,生态位适宜度可为城市经济发展方式的选择提供依据,生态势理论有助于城市发展动力机制的解释,生态位扩充则是城市空间结构发展和演化的生态学解释,而生态位重叠和分离理论对城市产业布局及其调整有很好的指导作用。  相似文献   

Glacier Distribution in the Alps: Statistical Modelling of Altitude and Aspect     

Ian S. Evans 《Geografiska Annaler: Series A, Physical Geography》2006,88(2):115-133

Mass balance of glaciers in mountain areas varies not only with altitude and regional position but also with aspect, gradient, glacier size, glacier type and detailed topographic position. These factors are combined here in models of how glacier altitude varies, tested with data for the Alps edited from the World Glacier Inventory. An overall northward tendency in glacier numbers (toward 005 ± 4°) and lower altitudes (013 ± 5°) is maintained across a range of glacier sizes, types, altitudes and the major divisions of the Alps. Variation with aspect of glacier altitude (and, by implication, of glacier balance) in the Alps is essentially unimodal, and north‐facing glaciers average 220 m lower in middle altitude than south‐facing: 148 m in the Western Alps, 232 m in the West‐central, 252 m in the East‐central, and 268 m in the Eastern Alps. For smaller subdivisions, confidence intervals on estimates are broader and many differences lack statistical significance. Contrasts are greater in the higher massifs, with greater relief, and lower in cloudy, windward areas. There are small windrelated tendencies east of north along the northern and western fringes, but trends across space are weak: position is thus treated by subdivision into districts and groups. Mid‐altitude averages 2891 m overall and varies from 2552 to 3127 m for 27 glacier districts, and from 2124 to 3209 m for 103 glacier groups. Glacier mid‐altitude varies also with glacier form, nourishment, height range and area, which account for over two‐thirds of variance in combined models.  相似文献   

Flow velocities of active rock glaciers in the Austrian Alps   总被引：1，自引：0，他引：1  

Karl Krainer  Xiubin He 《Geografiska Annaler: Series A, Physical Geography》2006,88(4):267-280

High surface flow velocities of up to 3 m a^–1 were measured near the front of three active rock glaciers in the western Stubai Alps (Rei‐chenkar) and Ötztal Alps (Kaiserberg and Ölgrube) in Tyrol (Austria) using differential GPS technology. Flow velocities have increased since about 1990. The highest velocities were recorded in 2003 and 2004, but showed a slight decrease in 2005. At the Reichenkar rock glacier, flow rates are constant throughout the year, indicating that meltwater has no significant influence on the flow mechanism. At Ölgrube rock glacier, flow velocities vary seasonally with considerably higher velocities during the melt season. Meltwater is likely to influence the flow of Ölgrube rock glacier as evident by several springs near the base of the steep front. Because the high surface velocities cannot be explained by internal deformation alone on Reichenkar rock glacier, we assume that horizontal deformation must also occur along a well defined shear zone within a water‐saturated, fine‐grained layer at the base of the frozen body. The increased surface flow velocities since about 1990 are probably caused by slightly increased ice temperature and greater amounts of meltwater discharge during the summer, a product of global warming.  相似文献   

Sedimentary facies and landform genesis at a temperate outlet glacier: Soler Glacier, North Patagonian Icefield   总被引：3，自引：0，他引：3  

Neil F. Glasser  & Michael J. Hambrey 《Sedimentology》2002,49(1):43-64

This paper focuses on the structural glaciology, dynamics, debris transport paths and sedimentology of the forefield of Soler Glacier, a temperate outlet glacier of the North Patagonian Icefield in southern Chile. The glacier is fed by an icefall from the icefield and by snow and ice avalanches from surrounding mountain slopes. The dominant structures in the glacier are ogives, crevasses and crevasse traces. Thrusts and recumbent folds are developed where the glacier encounters a reverse slope, elevating basal and englacial material to the ice surface. Other debris sources for the glacier include avalanche and rockfall material, some of which is ingested in marginal crevasses. Debris incorporated in the ice and on its surface controls both the distribution of sedimentary facies on the forefield and moraine ridge morphology. Lithofacies in moraine ridges on the glacier forefield include large isolated boulders, diamictons, gravel, sand and fine-grained facies. In relative abundance terms, the dominant lithofacies and their interpretation are sandy boulder gravel (ice-marginal), sandy gravel (glaciofluvial), angular gravel (supraglacial) and diamicton (basal glacial). Proglacial water bodies are currently developing between the receding glacier and its frontal and lateral moraines. The presence of folded sand and laminites in moraine ridges in front of the glacier suggests that, during a previous advance, Soler Glacier over-rode a former proglacial lake, reworking lacustrine deposits. Post-depositional modification of the landform/sediment assemblage includes melting of the ice-core beneath the sediment cover, redistribution of finer material across the proglacial area by aeolian processes and fluvial reworking. Overall, the preservation potential of this landform/sediment assemblage is high on the centennial to millennial timescale.  相似文献