Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands     

Johanna A. A. Bos  Sjoerd J. P. Bohncke  C. Roel Janssen 《Journal of Paleolimnology》2006,35(2):211-238

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.  相似文献   

Effects of mode coupling and location of rotational axis on glacial induced rotational deformation in a laterally heterogeneous viscoelastic earth     

Patrick Wu  Hansheng Wang 《Geophysical Journal International》2006,167(2):853-859

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检波器尾锥与地表耦合阻尼研究   总被引：1，自引：0，他引：1  

ZHANG Feng-jiao HAN Li-guo DONG Shi-xue College of GeoExploration Scinece  Technology  Jilin University  Changchun  China 《吉林大学学报(地球科学版)》2006,(Z2)

结合检波器与松散地表耦合的实际,设计了双自由度耦合模型,从理论上分析了检波器与地表耦合系统的特性,并结合野外实验定性地分析了在不同表土情况下,检波器尾锥与地表耦合系统中尾锥与地表之间的阻尼变化时对耦合系统特性及地震资料的影响,揭示了合理的选择检波器尾锥与地表之间的阻尼在地震信号采集中的意义。  相似文献   

笼状水合物拉曼光谱特征与结构水合数的耦合关系   总被引：3，自引：0，他引：3  

雷怀彦  官宝聪  刘建辉  李震 《现代地质》2005,19(1):83-88

为了探讨不同气体组分和环境介质对形成笼状结构类型水合物和水合数的影响, 开展了一元体系 (CH4、CO2、C3H8 )和二元体系(CH4 +CO2、CH4 +C3H8、CH4 +N2 )的水合物生成结晶充填过程、结晶构型和动力学特性分析, 并对生成的水合物进行了拉曼光谱分析。结果表明单组分甲烷充填小孔穴 512和大孔穴 512 62 形成Ⅰ型笼状结构水合物(SⅠ), 二氧化碳和丙烷只占据大孔穴 512 64 形成Ⅱ型笼状结构水合物 (SⅡ ); 而二元混合组分中小孔穴中只充填有甲烷, 而没有CO2、N2 和C3H8。应用反褶积的ν1 对称谱带测定了CH4 分子在Ⅰ型结构大孔穴和小孔穴中的相对占有率,并根据谱带的面积比(对应于小孔穴与大孔穴)计算了平衡条件下甲烷水合物孔穴占有率及其耦合的水合数, 认为气体分子的大小不仅影响它所充填的孔穴形态和类型, 而且影响水合物生成的结构类型和水合数。  相似文献   

IAP/LASG全球海-陆-气耦合系统模式的纬向平均大气气候态分析(英文)     

Zhang Tao  Guo Yufu  Wu Guoxiong 《大气科学进展》2002,19(6):1091-1102

分海洋和陆地两种情况来讨论IAP/LASG全球海-陆-气耦合系统模式（GOAL）四个版本的结果,并与观测资料进行对比分析。一些重要的大气变量包括表面空气温度,海平面气压和降水率用来评估GOALS模式模拟当代气候和气候变率的能力。总的来说,GOALS模式的四个版本都能够合理地再现观测到的平均气候态和季节变化的主要特征。同时评估也揭示了模式的一些缺陷。可以清楚地看到模拟的全球平均海平面气压的主要误差是在陆地上。陆地上表面空气温度模拟偏高主要是由于陆面过程的影响。值得注意的是降水率模拟偏低主要是在海洋上,而中高纬的陆地降水在北半球冬天却比观测偏高。 通过模式不同版本之间的相互比较研究,可以发现模式中太阳辐射日变化物理过程的引入明显地改善了表面空气温度的模拟,尤其是在中低纬度的陆地上。太阳辐射日变化的引入对热带陆地的降水和中高纬度的冬季降水也有较大改进。而且,由于使用了逐日通量距平交换方案（DFA）,GOALS模式新版本模拟的海洋上的温度变率在中低纬度有了改善。 比较观测和模拟的年平均表面空气温度的标准差,可以发现GOALS模式四个版本都低估了海洋和陆地上的温度变率,文中还对影响观测和模拟温度变率差异的可能原因进行了探讨。  相似文献   

沙漠化:从圈层耦合到全球变化   总被引：3，自引：0，他引：3  

段怡春  陈建平  厉青  丁火平  黄定华 《地学前缘》2002,9(2):277-285

从沙漠化概念提出伊始 ,沙漠化成因机理的研究就一直成为学术界关注的焦点。沙漠化过程究竟有多少是由自然因素所致 ,多少是由人类活动所为 ,诸因素与沙漠化之间有何内在关系 ,沙尘天气发生发展过程及其诱因等 ,当属地球系统科学应解决的难题。文章从全球变化的角度 ,将沙漠系统视作一种类生命的非线性动力系统 ,指出沙漠化源于地球表层系统各圈层之间复杂的相关与耦合作用 :气候变化是控制沙漠进退的首要因素 ;陆表水持续亏损则是导致干旱、半干旱地区沙漠化发展的直接原因 ;岩石圈构造运动塑造了不同的地形地貌单元 ,奠定了沙漠分布的地理格局 ;人类的不当活动和气候变化引起的生物生产力的衰退及土地覆盖的破坏 ,造成了现代沙漠化的快速扩张。  相似文献   

The Migif–Hafafit gneissic complex of the Egyptian Eastern Desert: fold interference patterns involving multiply deformed sheath folds     

Abdel-Rahman Fowler  Baher El Kalioubi 《Tectonophysics》2002,346(3-4)

The Wadi Hafafit Complex (WHC) is an arcuate belt of orthogneisses, migmatites and other high-grade metamorphic rocks, which marks the boundary between the Central Eastern and the South Eastern Deserts of Egypt. In the WHC, gneissic meta-gabbro outlines macroscopic fold interference patterns characterized by elliptical to irregular culminations cored by gneissic meta-tonalite to meta-trondhjemite. The five main culminations of the WHC have previously been labeled A (most northerly), B, C, D and E (most southerly). A detailed structural investigation of B, C, D and E reveals that these structures are a result of the interference of four macroscopic fold phases, the first three of which may represent a single deformation event. The first folding involved sheath-like fold nappes, which were transported to the N or NW, assisted by translation on gently dipping mylonite zones. The regional gneissosity and mineral extension lineations formed during this folding event. The fold nappes were deformed by mainly open upright small macroscopic and mesocopic folds with approximately NE-trending hinges. As a probable continuation of the latter folding, the sheaths were buckled into large macroscopic folds and monoclines with the same NE-trends. The fourth macroscopic folding resulted from shortening along the NE–SW direction, producing mainly NW–SE-trending upright gently plunging folds. Gravitative uplift is disputed as a component of the deformation history of the WHC. The peculiarities of the fold interference pattern result from the interesting behaviour of sheath folds during their refolding.  相似文献   

油压夯管锤蓄能器与活塞振动耦合性的数学解析          下载免费PDF全文

李国民 《探矿工程》2002,(1):52-54

蓄能器容积的变化与夯管锤的工作过程是紧密联系在一起的，由于活塞的前后运动以及在运动过程中的每一时刻所需要的油量不同的，理想状态就要通过蓄能器的容积变化来调节，就是说蓄能器的容积变化要与夯管锤的冲击振动相耦合。简要介绍了油压夯管锤结构原理，分别解释了油压夯管锤蓄能器与夯管锤的容积压力耦合。  相似文献   

A quantitative investigation into the temporal and spatial variations in the emergence of adult blackflies (Diptera: Simuliidae) from the Breitenbach, a small upland stream in Germany     

Joachim Reidelbach  Heino Christl 《Limnologica》2002,32(3)

As a contribution to the long-term emergence studies carried out as part of the “Breitenbach ecosystem project”, this paper presents the results obtained on emergence patterns and population dynamics of blackflies from 1984 to 1988. The Breitenbach is a small first order stream near Schlitz/Hesse, running into the Fulda river. Adult blackflies were caught in 4 greenhouse emergence traps, each spanning the whole width of the stream for a length of 6 m. A manual and then a partly automated method for collecting trapped insects was applied for three years and one year, respectively. Sixteen blackfly-species of different origin were found in the traps: a) autochthonous species: Prosimulium tomosvaryi, Simulium vernum s.l., S. cryophilum s.l., S. ornatum s.l. (common); S. costatum, S. trifasciatum, S. monticola, S. argyreatum (rare); b) species of doubtful origin: S. lundstromi, S. angustitarse, S. angustipes, S. aureum (very rare); c) allochthonous species: S. lineatum, S. equinum, S. erythrocephalum, S. noelleri. It was shown that the last 4 species had not emerged from the Breitenbach but had flown into the traps as adults. In addition, females of autochthonous species with blood or with mature eggs were trapped, which were also considered to have flown in. Besides revealing a limitation of the trap construction, they supported the detailed interpretation of some intricated patterns of appearance. Variations in emergence patterns and specimen numbers between years and traps were pronounced, but only in a few cases could they be attributed to changes in abiotic factors such as water temperature or discharge. P. tomosvaryi had the most simple and regular life cycle, with one well synchronised emergence peak annually from April to May (or even to June). No gradient of specimen numbers along the stream was evident. The two closely related species S. vernum and S. cryophilum had quite similar emergence patterns: There were two broad peaks per year, extending mainly from March to June and from July to October or November. In some cases the number and separation of consecutive generations was not clear. The abundance of both species clearly decreased downstream, more so for S. cryophilum than for S. vernum. In a trap closest to a tributary spring, S. cryophilum was the dominant species during three of the four years examined. The adults of S. ornatum displayed an intricate pattern of appearance, with very low specimen numbers in spring and medium to very high numbers in July/August and September/October. S. ornatum is the only blackfly species that inhabits both the Breitenbach and the adjacent section of the Fulda river. It was shown that females emerging from the Fulda river regularly invade the Breitenbach valley in greatly varying numbers and oviposit there. This leads to overlapping larval cohorts with corresponding emergence peaks. Although S. ornatum was the most abundant species in one year in the lower traps (60 to 80% of all individuals), it remains uncertain whether it is a long-term, permanent member of the autochthonous blackfly fauna of the Breitenbach. Estimates of total numbers of flown-in adults, actual emergence, dry weight biomass, the ecological separation of the species and their life cycle strategies are discussed.  相似文献   

Most likely locations of large earthquakes in the Kanto and Tokai areas, Japan, based on the local recurrence times     

Max Wyss  Shozo Matsumura 《Physics of the Earth and Planetary Interiors》2002,131(2):173-184

We examined the hypothesis that minima in local recurrence time, T_L, or equivalently maxima in local probability, P_L, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped T_L (P_L) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the T_L (P_L) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped T_L (P_L) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting T_L- and P_L-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with T_L <450 years. We interpret this to mean that areas with anomalously short T_L map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of T_L calculated are uncertain because they depend on the size of the volume used for the calculation.  相似文献