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Variations in dust event frequency over the past century reflected by ice-core and lacustrine records in north China 总被引:1,自引:0,他引:1
WANG NingLian YAO TanDong YANG XiangDong SHEN Ji & WANG Yong Key Laboratory of Cryosphere Environment Cold Arid Regions Environmental Engineering Research Institute Chi- nese Academy of Sciences Lanzhou China Institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing China Nanjing Institute of Geography Limnology Chinese Academy of Sciences Nanjing China 《中国科学D辑(英文版)》2007,50(5):736-744
In this paper, we analyzed the variations of dust proxies in the Dunde, Malan and Chongce ice cores from the northern Tibetan Plateau and the Hongjiannao lacustrine sediment core from north Shaanxi Province, and found that they all showed a general decrease trend over the past century. Owing to the fact that all these ice cores and lacustrine core were retrieved from the margins and/or the leeward sides of the major areas of dust events in north China, their records could suggest that the dust event frequency in north China declined over the study period. This decrease trend might be attributed to increasing precipitation and weakening westerly. However, human activities have made the areal extent of desertification expand acceleratingly in north China. This status could make it possible that dust events would occur on a large spatial scale under the future climate change, which would be a big environmental issue we shall face. 相似文献
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豫北地区地震活动性及其与区域地壳运动的关系 总被引:3,自引:1,他引:2
本根据地震地质和地震分布条带,把豫北地区从西至东分为弱,中,强三个区段。由于区域地壳深部主断裂和大震活动的牵动作用,是造成本地震活动的重要原因,因而从区域地壳块体活动背景上探讨了本区及邻近地区地震活动趋势,中还指出,豫北西部太行山区的林县-薄壁地震带,虽不具有强震构造背景,但小震年月频率多寡和震群活动,却能反映了大区域地壳应力场强弱,亦可作为判断区域性地震活动的指标。 相似文献
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INTRODUCTIONANDBRIEFGEOLOGICALDESCRIP┐TIONSTheUpperOrdovicianmarinevolcanicrocksonthenorthmarginofQaidamhavebeenrepeatedlydis... 相似文献
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Chloritoid–glaucophane‐bearing rocks are widespread in the high‐pressure belt of the north Qilian orogen, NW China. They are interbedded and cofacial with felsic schists originated from greywackes, mafic garnet blueschists and low‐T eclogites. Two representative chloritoid–glaucophane‐bearing assemblages are chloritoid + glaucophane + garnet + talc + quartz (sample Q5‐49) and chloritoid + glaucophane + garnet + phengite + epidote + quartz (sample Q5‐12). Garnet in sample Q5‐49 is coarse‐, medium‐ and fine‐grained and shows two types of zonation patterns. In pattern I, Xgrs is constant as Xpy rises, and in pattern II Xgrs decreases as Xpy rises. Phase equilibrium modelling in the NC(K)MnFMASH system with Thermocalc 3.25 indicates that pattern I can be formed during progressive metamorphism in lawsonite‐stable assemblages, while pattern II zonation can be formed with further heating after lawsonite has been consumed. Garnet growth in Q5‐49 is consistent with a continuous progressive metamorphic process from ~14.5 kbar at 470 °C to ~22.5 kbar at 560 °C. Garnet in sample Q5‐12 develops with pattern I zonation, which is consistent with a progressive metamorphic process from ~21 kbar at 540 °C to ~23.5 kbar at 580 °C with lawsonite present in the whole garnet growth. The latter sample shows the highest P–T conditions of the reported chloritoid–glaucophane‐bearing assemblages. Phase equilibrium calculation in the NCKFMASH system with a recent mixing model of amphibole indicates that chloritoid + glaucophane paragenesis does not have a low‐pressure limit of 18–19 kbar as previously suggested, but has a much larger pressure range from 7–8 to 27–30 kbar, with the low‐pressure part being within the stability field of albite. 相似文献
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利用1998-2014年20场北疆典型寒潮天气过程的高空、地面和数值预报产品资料,对北疆寒潮天气进行了环流分型和区域分型,总结了环流型与冷空气路径、区域类型的对应关系,重点统计了不同季节北疆寒潮爆发前一天内500hPa脊前北风急流、锋区强度、中低空冷空气强度、地面冷高压等特征量的平均值和最大、最小值,并检验欧洲ECMWF数值预报产品在北疆寒潮天气预报中的预报能力,为北疆寒潮精细化预报提供了技术参考。 相似文献
80.
I. N. Estcourt 《新西兰海洋与淡水研究杂志》2013,47(2):283-290
Grab samples were taken from a population of Pectinaria australis Ehlers in Tasman Bay, New Zealand, at intervals over a 2‐year period, March 1971 to March 1973. Settlement occurred in summer with the new recruits showing rapid growth and heavy mortality, giving an apparent life cycle time of 1 y. The population density varied greatly over short distances at one time, presumably due to random settlement of aggregations of larvae from the plankton. 相似文献