Marine ice-rafted debris records constrain maximum extent of Saalian and Weichselian ice-sheets along the northern Eurasian margin     

Jochen Knies  Hans-Peter Kleiber  Jens Matthiessen  Claudia Müller  Norbert Nowaczyk 《Global and Planetary Change》2001,31(1-4)

Ice-rafted debris (IRD) (>2 mm), input in eight sediment cores along the Eurasian continental margin (Arctic Ocean), have been studied over the last two glacial/interglacial cycles. Together with the revised chronologies and new micropaleontological data of two cores from the northern Barents Sea (PS2138) and northeastern Kara Sea (PS2741) spanning Marine Isotope Stages (MIS) 6 to 1, the IRD data give new insights into the glacial history of northern Eurasian ice-sheets over the last 150 ka. The chronologies of the cores are based on stable isotope records, AMS ¹⁴C datings, paleomagnetic and biostratigraphic data.Extensive episodes of northern Barents Sea ice-sheet growth, probably to the shelf edge, occurred during the late Weichselian (MIS 2) and the Saalian (MIS 6). Major IRD discharge at the MIS 4/3-transition hints to another severe glaciation, probably onto the outer shelf, during MIS 4. IRD-based instabilities of the marine-based ice margin along the northern Barents Sea between MIS 4 and 2 are similar in timing with North Atlantic Heinrich events and Nordic Seas IRD events, suggesting similar atmospheric cooling over a broad region or linkage of ice-sheet fluctuations through small sea-level events.In the relatively low-precipitation areas of eastern Eurasia, IRD peak values during Termination II and MIS 4/3-transition suggest a Kara Sea ice-sheet advance onto the outer shelf, probably to the shelf edge, during glacial MIS 6 and 4. This suggests that during the initial cooling following the interglacials MIS 5, and possibly MIS 7, the combined effect of sustained inflow of Atlantic water into the Arctic Ocean and penetration of moisture-bearing cyclones into easterly direction supported major ice build-up during Saalian (MIS 6) and Mid-Weichselian (MIS 4) glaciation. IRD peak values in MIS 5 indicate at least two advances of the Severnaya Semlya ice-sheet to the coast line during the Early Weichselian. In contrast, a distinct Kara Sea ice advance during the Late Weichselian (MIS 2) is not documented by the IRD records along the northeastern Kara Sea margin.  相似文献   

A retrospective analysis of pan Arctic permafrost using the JULES land surface model     

Eleanor J. Burke  Rutger Dankers  Chris D. Jones  Andrew J. Wiltshire 《Climate Dynamics》2013,41(3-4):1025-1038

There is mounting evidence that permafrost degradation has occurred over the past century. However, the amount of permafrost lost is uncertain because permafrost is not readily observable over long time periods and large scales. This paper uses JULES, the land surface component of the Hadley Centre global climate model, driven by different realisations of twentieth century meteorology to estimate the pan-arctic changes in near-surface permafrost. Model simulations of permafrost are strongly dependent on the amount of snow both in the driving meteorology and the way it is treated once it reaches the ground. The multi-layer snow scheme recently adopted by JULES significantly improves its estimates of soil temperatures and permafrost extent. Therefore JULES, despite still having a small cold bias in soil temperatures, can now simulate a near-surface permafrost extent which is comparable to that observed. Changes in snow cover have been shown to contribute to changes in permafrost and JULES simulates a significant decrease in late twentieth century pan-Arctic spring snow cover extent. In addition, large-scale modelled changes in the active layer are comparable with those observed over northern Russia. Simulations over the period 1967–2000 show a significant loss of near-surface permafrost—between 0.55 and 0.81 million km² per decade with this spread caused by differences in the driving meteorology. These runs also show that, for the grid cells where the active layer has increased significantly, the mean increase is ~10 cm per decade. The permafrost degradation discussed here is mainly caused by an increase in the active layer thickness driven by changes in the large scale atmospheric forcing. However, other processes such as thermokarst development and river and coastal erosion may also occur enhancing permafrost loss.  相似文献   

A search for shocked quartz grains in the Allerød‐Younger Dryas boundary layer          下载免费PDF全文

Annelies Van Hoesel  Wim Z. Hoek  Gillian M. Pennock  Knut Kaiser  Oliver Plümper  Michal Jankowski  Maartje F. Hamers  Norbert Schlaak  Mathias Küster  Alexander V. Andronikov  Martyn R. Drury 《Meteoritics & planetary science》2015,50(3):483-498

The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød‐Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød‐Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød‐Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis.  相似文献   

Guidelines for Future UV Observatories     

Norbert Kappelmann  Jürgen Barnstedt 《Astrophysics and Space Science》2006,303(1-4):147-151

Ultra-violet image sensors and UV optics have been developed for a variety of space borne UV astronomy missions. Technology progress has to be made to improve the performance of future UV space missions. Throughput is the most important technology driver for the future. Required developments for different UV detector types – detectors are one of the most problematic and critical parts of a space born mission – and for optical components of the instruments are given in these guidelines. For near future missions we need high throughput optics with UV sensors of large formats, which show simultaneously high quantum efficiency and low noise performance.  相似文献   

Experiments on uni-directional and nonlinear wave group shoaling     

Kimmoun  Olivier  Hsu  Hung-Chu  Hoffmann  Norbert  Chabchoub  Amin 《Ocean Dynamics》2021,71(11-12):1105-1112

Ocean Dynamics - We report an experimental study addressing the characteristic hydrodynamic transformations of unstable wave groups as well as JONSWAP wave fields propagating from deep-water...  相似文献   

Extending the Application of a Shale Volume Estimation Formula Derived from Factor Analysis of Wireline Logging Data     

Norbert P. Szabó  Mihály Dobróka 《Mathematical Geosciences》2013,45(7):837-850

A multivariate statistical procedure is developed for the estimation of shale volume in clastic sedimentary formations. The method offers an alternative for extracting the shale content from borehole geophysical measurements. Factor analysis of various well-logging data types generates a new well log that correlates with the shale content of shaly-sandy rocks. The mathematical relationship between shale volume and factor scores is represented by a nonlinear equation, which seems to be applicable for data sets originating from different sedimentary basins. A comparative study is made between three different data sets originating from Hungary and the United States of America in order to check the validity of the proposed empirical formula. Shale volumes predicted from factor analysis are confirmed by estimates from independent deterministic and inverse modeling. Petrophysical information derived by factor analysis of logs recorded in deep wells can be used for a more accurate and reliable estimation of effective porosity and absolute permeability of reservoir rocks, for decreasing the estimation error of inversion estimates and for reducing the ambiguity in the solution of the well-logging inverse problem.  相似文献   

Multi-scale Transport Processes Observed in the Boundary Layer over a Mountainous Island     

Bianca Adler  Norbert Kalthoff 《Boundary-Layer Meteorology》2014,153(3):515-537

Over complex terrain, convection and thermally-driven circulations simultaneously occur under fair weather conditions during the day. To investigate these processes on the basis of observations, simultaneous measurements on different scales are necessary. Comprehensive measurements with the mobile observation platform KITcube were performed on the mountainous island of Corsica during the HYdrological cycle in Mediterranean EXperiment (HyMeX) field campaign in late summer and autumn 2012. Using a case study, the benefit of integrated measurement systems and coordinated scan strategies was demonstrated, and experimental evidence of, and new insights into, convective and advective transport processes in a valley were obtained. Convection, thermally-driven circulations and topographic and advective venting led to the diurnal cycle of temperature, humidity and wind over complex terrain in the mountain atmospheric boundary layer (mountain ABL), which was deeper than an ABL over homogeneous terrain under equal surface forcing. Due to the combined transport processes on different scales, the mountain ABL in a valley also extended beyond the convection layer, which was characterized by surface-based, buoyancy-driven turbulent mixing. Strong subsidence, with a vertical velocity of about 1 m s \(^{-1}\) , was present within the mountain ABL for several hours around noon and suppressed the convection-layer growth. Above the layer with subsidence, elevated vertical motions, consisting of alternating updrafts and downdrafts, occurred. Once the convection layer grew to the bottom of the layer with elevated vertical motions, surface-based convective cells occasionally coupled to the elevated updrafts, as a result of which the convection layer rapidly deepened.  相似文献   

The LEGUE disk targets for LAMOST＇s pilot survey     

Li Chen  Jin-Liang Hou  Jin-Cheng Yu  Chao Liu  Li-Cai Deng  Heidi Jo Newberg  Jeffrey L. Carlin  Fan Yang  Yue-Yang Zhang  Shi-Yin Shen  Hao-Tong Zhang  Jian-Jun Chen  Yu-Qin Chen  Norbert Christlieb  Zhan-Wen Han  Hsu-Tai Lee  Xiao-Wei Liu  Kai-Ke Pan  Jian-Rong Shi  Hong-Chi Wang  Zi Zhu 《天体物理学报》2012,(7):805-812

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The LEGUE input catalog for dark night observing in the LAMOST pilot survey     

Fan Yang  Jeffrey L. Carlin  Chao Liu  Yue-Yang Zhang  Shuang Gao  Yan Xu  Li-Cai Deng  Heidi Jo Newberg  Sebastien Lepine  Jin-Liang Hou  Xiao-Wei Liu  Norbert Christlieb  Hao-Tong Zhang  Hsu-Tai Lee  Kai-Ke Pan  Zhan-Wen Han  Hong-Chi Wang 《天体物理学报》2012,(7):781-791

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A method to detect and characterize sub‐daily flow fluctuations          下载免费PDF全文

Franz Greimel  Bernhard Zeiringer  Norbert Höller  Bettina Grün  Reinhold Godina  Stefan Schmutz 《水文研究》2016,30(13):2063-2078

Hydro peaking causes an important environmental impact on running water ecosystems. Many affected rivers have a poor ecological status. In rivers affected by hydro peaking, the flow conditions are highly complex and difficult to grasp. To develop a general framework for detecting and characterizing sub‐daily flow fluctuations, we analysed more than 500 Austrian hydrographs, covering the whole range from unimpacted to heavily impacted rivers. Different fluctuation types could be identified according to the potential source: e.g. sub‐daily flow fluctuations caused by hydro peaking, rainfall or snow and glacier melt. Additionally, the term ‘hydro fibrillation’ was established, to indicate frequently occurring artificial fluctuations with comparably low intensities. An automatic procedure was used to detect frequency and intensity of each flow fluctuation. Using variables based on duration curves of flow fluctuation rates (ramping rates), amplitudes, flow ratios, durations and daily numbers of fluctuations, a predictive model (linear discriminant analysis) was fitted to classify hydrographs into predominant fluctuation regimes. This is the basis for a detailed investigation of present sub‐daily flow regimes and to analyse the differences between the regimes. Based on the results, we finally propose a general framework that enables a standardized assessment of flow fluctuations regarding event intensities and/or event timing. The proposed framework offers a standardized selection of particular flow fluctuations referring to increase and decrease events separately. The selection of specific flow fluctuations can be defined with respect to several research questions (e.g. ecologically relevant fluctuations), which offers a wide range of applications. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献