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831.
The 8.2 ka event: Evidence for seasonal differences and the rate of climate change in western Europe
Sushma Prasad Annette Witt Ulrike Kienel Peter Dulski Eva Bauer Gergana Yancheva 《Global and Planetary Change》2009,67(3-4):218-226
Recent studies have drawn attention to differences in the seasonal impact of the 8.2 ka event, with longer cooler summers and shorter cooler/drier winters. However, there are no data available on the simultaneity or the rate of onset of the seasonal changes in Europe. Based on the microfacies and geochemical analyses of seasonally laminated varved sediments from Holzmaar, we present evidence of differences in duration and onset time of changes in summer temperature and winter rainfall during the 8.2 ka event. Since both summer and winter climate signals are co-registered within a single varve, there can be no ambiguity about the phasing and duration of the signals. Our data show that the onset and withdrawal of the 8.2 ka summer cooling occurred within a year, and that summer rains were reduced or absent during the investigated period. The onset of cooler summers preceded the onset of winter dryness by ca. 28 years. In view of the differences in nature and duration of the impact of the 8.2 ka event we suggest that a clearer definition of the 8.2 ka event (summer cooling or winter cooling/dryness) needs to be developed. Based on regional comparison and available modelling studies we also discuss the roles of solar variability, changes in North Atlantic Thermohaline circulation, and North Atlantic Circulation (NAO) during the period under consideration. Wavelet analyses of seasonal laminae indicates that the longer NAO cycles, linked to changes in the N. Atlantic temperatures, were more frequent during the drier periods. 相似文献
832.
Simulations of the impact of orbital forcing and ocean on the Asian summer monsoon during the Holocene 总被引:2,自引:1,他引:2
The importance of orbital forcing and ocean impact on the Asian summer monsoon in the Holocene is investigated by comparing simulations with a fully coupled ocean–atmosphere general circulation model (FOAM) and with the atmospheric component of this model (FSSTAM) forced with prescribed modern sea-surface temperatures (SSTs). The results show: (1) the ocean amplifies the orbitally-induced increase in African monsoon precipitation, makes somewhat increase in southern India and damps the increase over the southeastern China. (2) The ocean could change the spatial distribution and local intensity of the orbitally-induced latitudinal atmospheric oscillation over the southeastern China and the subtropical western Pacific Ocean. (3) The orbital forcing mostly enhances the Asian summer precipitation in the FOAM and FSSTAM simulations. However, the ocean reduces the orbitally-induced summer precipitation and postpones the time of summer monsoon onset over the Asian monsoon region. (4) The orbital forcing considerably enhances the intensity of upper divergence, which is amplified by ocean further, over the eastern hemisphere. But the divergence is weaker in the FOAM simulations than in the FSSTAM simulations when the orbital forcing is fixed. (5) The orbital forcing can enhance the amplitude of precipitation variability over the subtropical Africa, the southeastern China and northwestern China, inversely, reduce it over central India and North China in the FOAM and FSSTAM simulations. The ocean obviously reduces the amplitude of precipitation variability over most of the Asian monsoon regions in the fixed orbital forcing simulations. (6) The areas characterized by increased summer precipitation in the long-term mean are mostly characterized by increased amplitude of short-term variability, whereas regions characterized by decreased precipitation are primarily characterized by decreased amplitude of short-term variability. However, the influences of orbital forcing or dynamical ocean on regional climate depend on the model. 相似文献
833.
David L. Edwards William Cooke Danielle E. Moser Wesley Swift 《Earth, Moon, and Planets》2008,102(1-4):549-553
The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical
to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is
the lunar impact ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition
of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA’s Meteoroid
Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta
environment.
This paper reports the results of experiments on projectile impact into powered pumice targets, simulating unconsolidated
lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles
were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to
characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in
future tests. 相似文献
834.
835.
在调查、分析洋沙泡周边地质、水文地质和氟土壤特征的基础上,结合洋沙泡水库模拟实验结果对吉林西部洋沙泡水库高氟水的形成进行了深入研究。结果表明,吉林西部高氟环境的形成是地表环境长期演化的结果:大兴安岭岩浆岩和松嫩低平原松散沉积物提供了含氟丰富的物质基础,河流及地下水径流提供了氟迁移的动力条件,典型的低平原是高氟形成的地理条件,干旱半干旱的气候条件成为高氟环境的促进条件。洋沙泡的氟主要来源为二龙涛河径流携带,多年平均携带量占年内氟总来源的99%以上;周边径流占0.014%~0.28%;降水携带量占0.012%;蒸发浓缩作用对洋沙泡水库的氟质量浓度也有一定影响。此外,内源底泥的释放也是洋沙泡水库水体氟质量浓度增高的原因之一,并且在引嫩入白工程实施后,依然使洋沙泡水库水体中氟质量浓度增加。在每年引水的情况下,需要5年时间水库水体氟的质量浓度才会降至1.0mg/L以下。风动力和人为活动也对洋沙泡水库的氟质量浓度变化产生影响。 相似文献
836.
撞击地层学及其研究进展 总被引:2,自引:0,他引:2
地质历史中的地外物体撞击地球事件可在撞击点、近源区和远源区分别形成撞击坑熔融岩体、近源溅射岩席及海啸沉积和远源溅射层等一系列撞击地层层序。撞击地层有其独特的物理学和化学特征,与正常沉积作用、火山喷发和板块碰撞等成因的地层显然有别。通过对撞击地层层序的时空变化、所包含的撞击成因矿物、撞击微球粒和微玻璃陨石以及古生物和地球化学异常等的研究,可以了解撞击事件的发生频率、幅度和撞击天体的性质等,也为探索生物和地球环境的灾难性变化及其起因提供了新的思路。 相似文献
837.
气候变化对四川盆地作物生产潜力的影响评估 总被引:2,自引:0,他引:2
计算了四川盆地作物的光合生产潜力、光温生产潜力和气候生产潜力,选择代表站点分析了主要气象因子的变化特征及其对生产潜力的影响。结果表明,四川盆地日照时数和降水量在减少,气温在升高,日照时数和降水量的减少使生产潜力降低,而气温升高具有增加作用;各类生产潜力在1970 s都属于高值时期,光温生产潜力在2006年达到另一个高值;近十年各类生产潜力平均值均较1970 s有所减少,盆地平均气温升高1℃,光温生产潜力增加6%,降水量减少10%,气候生产潜力减少1.6%。 相似文献
838.
839.
840.
由火山喷发、岩浆侵入或陨石撞击作用所形成的环形构造,是地球物质活化迁移的重要场所,对区域成矿过程具有极大的制约意义。在河北省西北部坝上地区,围绕沽源县城一带,早白垩世岩浆岩、布格重力异常及水系沉积物地球化学异常均呈现明显的多级环带分布。这种现象并非尚义-崇礼-赤城深大断裂与乌龙沟-上黄旗岩浆岩带的简单复合叠置,而是以沽源为中心的火山机构的具体表现。该环形构造至少可划分为三个岩浆岩环带,分布着早白垩世(K—Ar100~123Ma)安山质火山-沉积岩和燕山旋回第四期(K—Ar100~138Ma)次粗面岩、次安山岩、二长斑岩、石英正长斑岩等浅成超浅成侵入岩体或岩株,它们的银、铅、锌、镉、铀、钍、钼、砷、锑等元素显著活化和富集。该环形构造控制着蔡家营铅锌矿、张麻井铀钼矿、彭家沟银矿、青羊沟铅锌矿、牛圈银金矿及北岔沟门铅锌银矿的时空定位。若干迹象表明,沽源环形构造可能是白垩纪时期一次陨击事件(因火星和木星之间两颗小行星的碰撞)的结果,这也许是中生代成矿大爆炸的根本诱发机制。 相似文献