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排序方式: 共有1163条查询结果,搜索用时 15 毫秒
1.
Thomas Stephens Daniel Atkin Paul Augustinus Philip Shane Andrew Lorrey Alayne Street-Perrott Andreas Nilsson Ian Snowball 《Journal of Paleolimnology》2012,48(4):785-800
We present the first continuous paleolimnological reconstruction from the North Island of New Zealand (37°S) that spans the last 48.2?cal kyr. A tephra- and radiocarbon-based chronology was developed to infer the timing of marked paleolimnological changes in Lake Pupuke, Auckland, New Zealand, identified using sedimentology, magnetic susceptibility, grain size and geochemistry (carbon, nitrogen and sulphur concentrations and fluxes, carbon and nitrogen stable isotopes). Variable erosional influx, biomass and benthic REDOX conditions are linked to changing effective precipitation and seasonality within three inferred broad intervals of climatic change: (1) the Last Glacial Coldest Phase (LGCP) of reduced effective precipitation and cooler temperatures, from 28.8 to 18.0?cal kyr BP, (2) the Last Glacial Interglacial Transition (LGIT) of increasing effective precipitation and warmer conditions, from 18.0 to 10.2?cal?kyr?BP, and (3) a Holocene interval of high effective precipitation, beginning with a warm period of limited seasonality from 10.2?cal?kyr?BP and followed by increasing seasonality from 7.6?cal?kyr?BP. The LGCP and LGIT also contain millennial-scale climate events, including the coldest inferred glacial conditions during the LGCP from 27.8 to 26.0 and 22.0?C19.0?cal?kyr?BP, and a climate reversal in the LGIT associated with lower lake level, from 14.5 to 13.8?cal?kyr?BP, coeval with the Antarctic Cold Reversal. The onset of seasonal thermal stratification occurred at 5.7?cal?kyr?BP and was linked to natural eutrophication of Lake Pupuke, which produced enhanced organic sedimentation. 相似文献
2.
Based on a decomposition of the velocity into mean flow, turbulent and wave components, momentum and hereafter a wave-energy equation is derived. It contains a turbulent energy dissipation term which is closed by applying a wave-related mixing length model and linear wave theory solutions. This closure produces a non-linear turbulent wave-energy dissipation including the wave energy in a 5/2 power law. The theory is able to predict correctly the shape of deep-water wave spectra according to Phillips' similarity law.Responsible Editor: Hans Burchard 相似文献
3.
Sebastian?WetterichEmail author Lutz?Schirrmeister Hanno?Meyer Finn?Andreas?Viehberg Andreas?Mackensen 《Journal of Paleolimnology》2008,39(4):427-449
The aim of this study is to describe ostracods from freshwater habitats in the Siberian Arctic in order to estimate the present-day
relationships between the environmental setting and the geochemical properties of ostracod calcite. A special focus is on
the element ratios (Mg/Ca, Sr/Ca), and the stable isotope composition (δ18O, δ13C), in both ambient waters and ostracod calcite. The most common species are Fabaeformiscandona pedata and F. harmsworthi with the highest frequency in all studied waters. Average partition coefficients D(Sr) of F. pedata are 0.33 ± 0.06 (1σ) in females, and 0.32 ± 0.06 (1σ) in males. A near 1:1 relationship of δ18O was found, with a mean shift of Δmean = 2.2‰ ± 0.5 (1σ) to heavier values in ostracod calcite of F. pedata as compared to ambient waters. The shift is not dependent on δ18Owater, and is caused by metabolic (vital) and temperature effects. Temperature-dependence is reflected in the variations of this
shift. For ostracod calcite of F. pedata a vital effect as compared to inorganic calcite in equilibrium was quantified with 1.4‰. Results of this study are valuable
for the palaeoenvironmental interpretation of geochemical data of fossil ostracods from permafrost deposits. 相似文献
4.
Christian Betzler Jörn Fürstenau Thomas Lüdmann Christian Hübscher Sebastian Lindhorst Andreas Paul John J. G. Reijmer André W. Droxler 《Basin Research》2013,25(2):172-196
Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region. 相似文献
5.
A GIS-implemented, deterministic approach for the automated spatial evaluation of geometrical and kinematical properties of
rock slope terrains is presented. Based on spatially distributed directional information on planar geological fabrics and
DEM-derived topographic attribute data, the internal geometry of rock slopes can be characterized on a grid cell basis. For
such computations, different approaches for the analysis and regionalization of available structural directional information
applicable in specific tectonic settings are demonstrated and implemented in a GIS environment. Simple kinematical testing
procedures based on feasibility criteria can be conducted on a pixel basis to determine which failure mechanisms are likely
to occur at particular terrain locations. In combination with hydraulic and strength data on geological discontinuities, scenario-based
rock slope stability evaluations can be performed. For conceptual investigations on rock slope failure processes, a GIS-based
specification tool for a 2-D distinct element code (UDEC) was designed to operate with the GIS-encoded spatially distributed
rock slope data. The concepts of the proposed methodology for rock slope hazard assessments are demonstrated at three different
test sites in Germany. 相似文献
6.
Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented. 相似文献
7.
Reliability analysis is inseparably connected with the formulation of failure scenarios, and common test statistics are based on specific assumptions. This is easily overlooked when processing observation differences. Poor failure identification performance and misleading pre-analysis results, mainly meaningless minimum detectable biases and external reliability measures, are the consequence. A reasonable failure scenario for use with differenced GNSS observations is formulated which takes into account that individual outliers in the original data affect more than one processed observation. The proper test statistics and reliability indicators are given for use with correlated observations and both batch processing and Kalman filtering. It is also shown that standardized residuals and redundancy numbers fail completely when used with double differenced observations.
相似文献
Andreas WieserEmail: Phone: +43-316-8736323Fax: +43-316-8736820 |
8.
Katja Ruschel Lutz Nasdala Andreas Kronz John M. Hanchar Daniel M. T?bbens Radek ?koda Friedrich Finger Andreas M?ller 《Mineralogy and Petrology》2012,105(1-2):41-55
This study addresses whether Raman spectra can be used to estimate the degree of accumulated radiation damage in monazite-(Ce) samples whose chemical composition was previously determined. Our results indicate that the degree of disorder in monazite–(Ce), as observed from increasing Raman band broadening, generally depends on both the structural state (i.e., radiation damage) and the chemical composition (i.e., incorporation of non-formula elements). The chemical effects were studied on synthetic orthophosphates grown using the Li-Mo flux method, and non radiation-damaged analogues of the naturally radiation-damaged monazite–(Ce) samples, produced by dry annealing. We found that the “chemical” Raman-band broadening of natural monazite–(Ce) can be predicted by the empirical formula, $$ {\hbox{FWHM}} {\hbox{[c}}{{\hbox{m}}^{ - {1}}}{]} = {3}{.95} + {26}{.66} \times {\hbox{(Th}} + {\hbox{U}} + {\hbox{Ca}} + {\hbox{Pb)}} {\hbox{[apfu]}} $$ where, FWHM = full width at half maximum of the main Raman band of monazite–(Ce) (i.e., the symmetric PO4 stretching near 970?cm?1), and (Th+U+Ca+Pb) = sum of the four elements in apfu (atoms per formula unit). Provided the chemical composition of a natural monazite–(Ce) is known, this “chemical band broadening” can be used to estimate the degree of structural radiation damage from the observed FWHM of the ν1(PO4) band of that particular sample using Raman spectroscopy. Our annealing studies on a wide range of monazite–(Ce) reference materials and other monazite–(Ce) samples confirmed that this mineral virtually never becomes highly radiation damaged. Potential advantages and the practical use of the proposed method in the Earth sciences are discussed. 相似文献
9.
Andreas Maletti 《Journal of Oceanography》1990,46(5):A85-A87
JECSS news no. 7 R/V Akademik Korolyev, nautical archaeology, ts-ts meander, oki island-canyon system 相似文献
10.
Joachim Place Oshaine Blake Daniel Faulkner Andreas Rietbrock 《Pure and Applied Geophysics》2014,171(11):2887-2897
Stress variation and fluid migration occur in deformation zones, which are expected to affect seismic waves reflected off or propagating across such structures. We developed a basic experimental approach to monitor the mechanical coupling with respect to seismic coupling across a single discontinuity between a granite sample in contact with a steel platen. Piezoceramics located on the platen were used to both generate and record the P and S wave fields reflected off the discontinuity at normal incidence. This way, normal (B n ) and tangential (B t ) compliances were calculated using Schoenberg’s linear slip theory (Schoenberg, J Acoust Soc Am 68:1516–1521, 1980) when the roughness, the effective pressure (P eff, up to 200 MPa), and the nature of the filling (gas or water) vary. We observe that increasing the effective pressure decreases B n and B t , which is interpreted as the effect of the closure of the voids at the interface, permitting more seismic energy to be transmitted across the interface. Values of B n are significantly higher than those of B t at low P eff (<60–80 MPa) in dry conditions, and significantly drop under water-saturated conditions. The water filling the voids therefore helps to transmit the seismic energy of compressional waves across the interface. These results show that the assumption B n ≈ B t commonly found in some theoretical approaches does not always stand. The ratio B n /B t actually reflects the type of saturating fluids and the effective pressure, in agreement with other experimental studies. However, we illustrate that only the relative variations of this ratio seem to be relevant, not its absolute value as suggested in previous studies. Consequently, the use of B n against B t plots may allow effective pressure variation and the nature of the pore fluid to be inferred. In this respect, this experimental approach at sample scale helps to pave the way for remotely monitoring in the field the hydro-mechanical state of deformation zones, such as seismogenic faults, fractured reservoirs, or lava conduits. 相似文献