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2.
Anders Moberg Hans Bergström Josefin Ruiz Krigsman Ola Svanered 《Climatic change》2002,53(1-3):171-212
Daily meteorological observations have been made at the old astronomical observatory in Stockholm since 1754. Complete daily mean series of air temperature and sea level pressure are reconstructed from the observational data for 1756–1998. The temperature and pressure series arereconstructed and homogenized with the aid of metadata, statistical tests and comparisons with data from other stations. Comparisons with independently reconstructed daily series for nearby Uppsala (1722–1998) show that the quality of thedaily Stockholm data is good, although the reliability is lower before the mid-19th century. The daily temperature data show that the colder winter mean temperatures of the late 18th to early 19th centuries were connected with a particularly high frequency of very cold winter days. The warmer summers of the same period are more connected with a general shift of the temperature distribution towards higher temperatures than in the late 20th century. 相似文献
3.
Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite
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Ann‐Christine Ritter Vasileios Mavromatis Martin Dietzel Ola Kwiecien Felix Wiethoff Erika Griesshaber Laura A. Casella Wolfgang W. Schmahl Jennifer Koelen Rolf D. Neuser Albrecht Leis Dieter Buhl Andrea Niedermayr Sebastian F. M. Breitenbach Stefano M. Bernasconi Adrian Immenhauser 《Sedimentology》2017,64(5):1354-1380
For the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different 18O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ47 which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ18O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ18O and Δ47 signatures reveal exchange with the aqueous fluid, whereas δ13C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments. 相似文献
4.
The authors examined the variability in wintertime cyclone activity and storm tracks and their relation to precipitation over China for the period 1951–2006 using the observational data.Two apparent modes of variability were assumed for the cyclone activity and storm tracks.The first mode describes the oscillation in the strength of the storm tracks in East Asia,which significantly increased since the mid-1980s,whereas the second mode describes a seesaw oscillation in the storm track strength between the Central-Southeast China and northern East Asia.The storm tracks over the Central-Southeast China have increased since the late 1960s.The possible causes for the variation of the cyclone activity and storm tracks are also explored.It is shown that wintertime precipitation,which has increased since the mid-1980s,concentrates in Central-Southeast China.The enhancement may be caused by the first mode of variability of storm tracks,whereas the interannual variability of precipitation may be linked to the second mode of the storm track variability. 相似文献
5.
The potentials of lime stabilization of lateritic soils 总被引:1,自引:0,他引:1
Samuel Akinlabi Ola 《Engineering Geology》1977,11(4):305-317
The paper reviews lime stabilization of lateritic soils and shows that all Nigerian lateritic soils from A-1-a soil to A-7-6 soil used in the investigation, improved their engineering characteristics substantially by the addition of lime. The plasticity indices of the soils were reduced whereas the plastic limits increased; the liquid limits increased slightly, the maximum dry density decreased and the optimum moisture content increased. From the results of Durability and CBR tests, only the A-1 soil and A-2 soil have any potential as competent base materials and consequently only these require any further field tests. 6% lime is recommended for these field tests. The other soils that do not qualify for bases may be utilized as sub-base materials. 相似文献
6.
Estimation of contaminant transport parameters for a tropical sand in a sand tank model 总被引:1,自引:1,他引:0
O. O. Ojuri Ph.D. S. A. Ola Ph.D. 《International Journal of Environmental Science and Technology》2010,7(2):385-394
This research describes the goals, design and implementation of a quasi natural gradient, laboratory scale, sand tank (aquifer) model experiment. The model was used to study the transport of an inorganic tracer (Chloride) in groundwater, within a tropical aquifer (porous medium) material. Three-dimensional sand tank (1.8 m × 0.3 m × 0.8 m) experiments were conducted to investigate contaminant transport and natural attenuation within the sand tank. In all, 360 samples were collected during 24 sampling sessions, for the three days of the tracer experiments in the Sand Tank. The Owena sand is a poorly graded sand with 88.1 % sand and 11.9 % gravel. Geotechnical properties including; coefficient of uniformity Cu = 2.53, coefficient of gradation Cz = 0.181, hydraulic conductivity K = 5.76 × 10?4 m/s, bulk density p = 1.9 Mg/m3, effective porosity ne = 0.215 and median grain diameter D50 = 0.55 mm, were determined. Other relevant hydraulic and solute transport parameters, such as dispersion coefficients and dispersivities were also established for the tropical soil. 相似文献
7.
Astrid Lyså Eiliv Larsen Jan‐Pieter Buylaert Ola Fredin Maria A. Jensen Denis Kuznetsov Andrew S. Murray Dmitry A. Subetto Aurelien van Welden 《Boreas: An International Journal of Quaternary Research》2014,43(4):759-779
The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka. 相似文献
8.
9.
2011年3月日本福岛核电站核泄漏在海洋中的传输 总被引:2,自引:0,他引:2
使用全球版本的迈阿密等密度海洋环流模式对2011年3月日本福岛核电站泄漏在海洋中的传输以及扩散进行了数值模拟。数值模式中核废料(示踪物)排放情景采取等通量连续排放,排放时间从3月25日开始,分别持续20 d以及1 a,两种情形分别积分20 a。为了减少海洋环流年际变化带来的数值模拟的的不确定性,20 a的模式积分分别用2010年、1991-2011年、1971-1991年以及1951-1971年4个不同时段的NCEP/NCAR逐日再分析资料作为大气强迫场,因此每种排放情形包含4个数值试验。模拟结果的分析表明,不同核废料排放情景及其在不同时段大气资料对海洋模式的驱动下,模拟的示踪物总体的传输扩散路径(包括表层以及次表层)、传输速率以及垂直扩展的范围没有显著的差异。集合平均数值模拟的结果显示:在两种排放情景下,日本福岛核泄漏在海洋的传输路径受北太平洋副热带涡旋洋流系统主导,其传输路径首先主要向东,到达东太平洋后,再向南向西扩散至西太平洋,可能在10~15 a左右影响到我国东部沿海海域,且海洋次表层的传输信号比表层信号早5 a左右。通过进一步分析模式积分过程中最大示踪物浓度随时间变化发现,在积分第20 a(2031年3月),海洋表层和次表层浓度的最高值分别只有模式积分第一年浓度的0.1%和1%。在积分的20 a里,排放的核废料主要滞留在北太平洋海域(超过86%±1.5%的核废料在积分结束时,滞留在北太平洋),而在积分的前10 a(2021年之前),几乎所有的核废料滞留在北太平洋;在核废料的垂直分布上,主要集中在海洋表层至600 m的深度,在积分的20 a时间里,没有核废料信号扩散至1 000 m以下的深度。数值模拟的结果也表明核废料浓度减弱的强度以及演变的时间特征主要受洋流系统的影响,与排放源的排放时间长短关系不大。值得指出的是,更加准确地评估一个真实的核泄漏事故对海洋环境所造成的可能影响,还需要考虑大气中的放射性物质的沉降以及海洋生态对核物质的响应。 相似文献
10.
使用全球版本的迈阿密等密度海洋环流模式对2011年3月日本福岛核电站泄漏在海洋中的传输以及扩散进行了数值模拟。数值模式中核废料(示踪物)排放情景采取等通量连续排放,排放时间从3月25日开始,分别持续20 d以及1 a,两种情形分别积分20 a。为了减少海洋环流年际变化带来的数值模拟的的不确定性,20 a的模式积分分别用2010年、1991-2011年、1971-1991年以及1951-1971年4个不同时段的NCEP/NCAR逐日再分析资料作为大气强迫场,因此每种排放情形包含4个数值试验。模拟结果的分析表明,不同核废料排放情景及其在不同时段大气资料对海洋模式的驱动下,模拟的示踪物总体的传输扩散路径(包括表层以及次表层)、传输速率以及垂直扩展的范围没有显著的差异。集合平均数值模拟的结果显示:在两种排放情景下,日本福岛核泄漏在海洋的传输路径受北太平洋副热带涡旋洋流系统主导,其传输路径首先主要向东,到达东太平洋后,再向南向西扩散至西太平洋,可能在10~15 a左右影响到我国东部沿海海域,且海洋次表层的传输信号比表层信号早5 a左右。通过进一步分析模式积分过程中最大示踪物浓度随时间变化发现,在积分第20 a(2031年3月),海洋表层和次表层浓度的最高值分别只有模式积分第一年浓度的0.1%和1%。在积分的20 a里,排放的核废料主要滞留在北太平洋海域(超过86%±1.5%的核废料在积分结束时,滞留在北太平洋),而在积分的前10 a(2021年之前),几乎所有的核废料滞留在北太平洋;在核废料的垂直分布上,主要集中在海洋表层至600 m的深度,在积分的20 a时间里,没有核废料信号扩散至1 000 m以下的深度。数值模拟的结果也表明核废料浓度减弱的强度以及演变的时间特征主要受洋流系统的影响,与排放源的排放时间长短关系不大。值得指出的是,更加准确地评估一个真实的核泄漏事故对海洋环境所造成的可能影响,还需要考虑大气中的放射性物质的沉降以及海洋生态对核物质的响应。 相似文献