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51.
52.
Constraining the time span between the Early Holocene Hässeldalen and Askja‐S Tephras through varve counting in the Lake Czechowskie sediment record,Poland 下载免费PDF全文
53.
通过对昌都树轮d13C、达索普冰芯d18O和先前重建的整个高原温度序列的分析,以及与其他气候代用记录的比较,揭示了青藏高原近1000 a来的温度变化特征。依据昌都树轮d13C年表,指出青藏高原的中世纪暖期发生于1200-1400 AD,该时期的夏季温度比长期平均值或现代(20世纪,下同)约高1.2℃,小冰期(1400-1700 AD)的夏季温度比长期平均值或现代约低0.5℃。近1000 a最暖的时期是13世纪,而最冷的时期是1000-1200 AD,温度比现代约低0.9℃。20世纪的气候变暖主要表现在冬季温度的升高,同期的夏季温度呈微弱的下降趋势。 相似文献
54.
Stefan Lauterbach Achim Brauer Nils Andersen Dan L. Danielopol Peter Dulski Matthias Hüls Krystyna Milecka Tadeusz Namiotko Milena Obremska Ulrich Von Grafenstein Declakes Participants 《第四纪科学杂志》2011,26(3):253-267
Investigation of the sedimentary record of pre‐Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long‐term evolution of the lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub‐annual resolution for µ‐XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large‐scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ18O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500–750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ18O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150–300 a. Three short‐term Lateglacial cold intervals, corresponding to Greenland isotope substages GI‐1d, GI‐1c2 and GI‐1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
55.
Clara Mangili Achim Brauer Birgit Plessen Peter Dulski Andrea Moscariello Rudolf Naumann 《第四纪科学杂志》2010,25(2):135-145
Contamination with detrital matter is a well‐known bias in δ18O records from lake carbonates but quantitative information of this effect is yet lacking. Therefore, we developed a new methodological approach combining isotope analyses with microfacies, X‐ray diffraction and micro‐X‐ray fluorescence data and applied this in a case study for the Piànico interglacial lake record in order to provide a quantitative estimate of the effect of detrital carbonate on stable δ18O and δ13C data. The Piànico record contains a long series of distinct and well‐preserved calcite varves and is correlated to Marine Isotope Stage 11. Intercalated in the varve sequence are detrital layers triggered by surface erosion events. These detrital layers are mainly composed of dolomite, thus reflecting the mineralogical signature of the catchment. Microfacies analyses of a 9350 varve year interval allows the identification of detrital layers down to sub‐millimetre scale and a precise selection of three different types of samples for isotope analyses: (1) pure endogenic calcite varves (five varves per sample) without detrital contamination; (2) individual detrital layers; and (3) ‘mixed’ samples including five calcite varves and up to four thin detrital layers. Detrital samples show the isotopic signature of the catchment dolomite and are up to 5.7‰ enriched in δ18O values with respect to endogenic calcite samples. In mixed samples, the degree of isotopic enrichment is directly related to the amount of detrital contamination; δ18O of bulk carbonates is significantly biased when the detrital component amounts to more than 5% of the sample. It is also shown that samples containing detrital material have an influence on the calculation of the covariance between δ13C and δ18O. Covariance is high (r = 0.76) when the correlation coefficient is calculated on the base of all samples, but absent (r = ?0.43) when samples containing detrital dolomite are excluded. It has been demonstrated that microfacies analysis is a quick tool to avoid or reduce detrital contamination in bulk carbonate samples during sample selection. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
56.
Juan Pablo Corella Achim Brauer Clara Mangili Valentí Rull Teresa Vegas‐Vilarrúbia Mario Morellón Blas L. Valero‐Garcés 《Quaternary Research》2012,78(2):323-332
The karstic Lake Montcortès sedimentary sequence spanning the last 1548 yr constitutes the first continuous, high-resolution, multi-proxy varved record in northern Spain. Sediments consist of biogenic varves composed of calcite, organic matter and detrital laminae and turbidite layers. Calcite layer thickness and internal sub-layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability. Higher temperatures occurred in Lake Montcortès in AD 555–738, 825–875, 1010–1322 and 1874–present. Lower temperatures and prolonged winter conditions were recorded in AD 1446–1598, 1663–1711 and 1759–1819. Extreme and multiple precipitation events dominated in AD 571–593, 848–922, 987–1086, 1168–1196, 1217–1249, 1444–1457, 1728–1741 and 1840–1875, indicating complex hydrological variability in NE Spain since AD 463. The sedimentary record of Lake Montcortès reveals a short-term relation between rainfall variability and the detrital influx, pronounced during extended periods of reduced anthropogenic influences. In pre-industrial times, during warm climate episodes, population and land use increased in the area. After the onset of the industrialization, the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio‐economic factors. 相似文献
57.
Ocean Dynamics - The input of mechanical power to the ocean due to the surface wind stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from... 相似文献
58.
Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China) 总被引:4,自引:0,他引:4
Jianliang Jia Zhaojun Liu Achim Bechtel Susanne A. I. Strobl Pingchang Sun 《International Journal of Earth Sciences》2013,102(6):1717-1734
Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST. 相似文献
59.
Grace Xingxin Gao Liang Heng Achim Hornbostel Holmer Denks Michael Meurer Todd Walter Per Enge 《GPS Solutions》2013,17(4):561-573
The Galileo E5a/E5b signals and the Global Positioning System (GPS) L5 signal lie within the aeronautical radionavigation services (ARNS) band. They suffer interference from the services in this frequency band, in particular, pulsed signals from distance measuring equipment (DME) and tactical air navigation (TACAN) systems. To maintain system accuracy and integrity, interference mitigation is beneficial and necessary. We first present the real DME/TACAN environment at Stanford, CA as an example to illustrate the need for mitigating DME/TACAN interference. We then propose a time and frequency joint mitigation algorithm—Hybrid Blanking and its simplified version, frequency domain adaptive filtering (FDAF) for hardware implementation. Finally, a flight measurements campaign was performed over a European DME/TACAN hotspot near Frankfurt, Germany, to record a worst-case DME interference environment. Recorded data from the flight tests mixed with injected GNSS signals verify the effectiveness of the proposed mitigation algorithm. 相似文献
60.
The recent sediment record of Lake Belau (Schleswig–Holstein, Germany), deposited in the period 1945–2002, was compared with instrumental meteorological and limnological data. The sediments deposited during this period are annually laminated. A varve chronology was established and supported by 137Cs measurements. Micro-facies and diatom assemblage composition analyses were confirmed in thin sections and compared statistically with limnological and meteorological data. Comparison of phytoplankton data with diatom assemblage data from the sediment for the time interval from 1988 to 1999 proved that the sediments reflect limnological processes in the lake and record seasonal changes in the primary producer communities. Among the climatological data, the number of contiguous ice days (days with maximal temperatures ≤0 °C) and the state of the winter NAO are strong predictors for micro-facies development and diatom assemblage composition. Furthermore, solar and local (nutrient input) influences are visible in the diatom assemblage compositions. Our study illustrates the high potential for using analyses of micro-facies and diatom assemblages to reconstruct past weather conditions in varved sediments of Lake Belau. 相似文献