Reconstructing the development of sampled sites on fluvial island surfaces of the Tagliamento River,Italy, from historical sources          下载免费PDF全文

Ulfah Mardhiah  Matthias C Rillig  Angela Gurnell 《地球表面变化过程与地形》2015,40(5):629-641

In parallel with research on surface sediment characteristics of evolving island features (patches) along an island‐braided reach of the Tagliamento River, Italy, the present research reconstructed the development of the sampled sites using historical information coupled with field measurements. Since any field sediment sampling programme inevitably focuses on small areas (of the order of a few metres), the historical sources were assessed bearing in mind their spatial resolution and geographical accuracy in relation to the size of the sampled sites, and the information they could provide regarding the historical evolution of those sites. The analysis combined four sources of information: (i) river stage records revealed flood events that had the potential to reset bar surfaces and float in wood and seeds to initiate vegetation colonization; (ii) oblique ground photographs identified areas of the river's active corridor where riparian vegetation colonization appeared to have been initiated by specific flood events; (iii) dendrochronology was used to estimate the age of sampled sites; (iv) field‐measured geographical locations of the sampled sites were combined with historical vertical areal imagery to further establish sampling site age and changes in vegetation cover from 1944 to 2012. A chronosequence of sampled sites (0, 2, 8, 12, 40 years) was established. Vegetation colonization and island development showed a statistically significant development trajectory among sites of each age across the 40 year period following formative floods in 1965–1966, 2000, 2004 and a flow pulse in 2010. The trajectory progressed through pioneer and building island stages until vegetated areas became part of established islands. Evidence from the younger sites indicates that the pioneer island phase lasts up to eight years. Evidence from the oldest site indicates a building island phase lasting a maximum of 30 years, but probably a lot less. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

On the repeatability and consistency of three-component ambient vibration array measurements   总被引：1，自引：0，他引：1  

Brigitte Endrun  Matthias Ohrnberger  Alexandros Savvaidis 《Bulletin of Earthquake Engineering》2010,8(3):535-570

Ambient vibration measurements with small, temporary arrays that produce estimates of surface wave dispersion have become increasingly popular as a low-cost, non-invasive tool for site characterisation. An important requirement for these measurements to be meaningful, however, is the temporal consistency and repeatability of the resulting dispersion and spatial autocorrelation curve estimates. Data acquired within several European research projects (NERIES task JRA4, SESAME, and other multinational experiments) offer the chance to investigate the variability of the derived data products. The dataset analysed here consists of repeated array measurements, with several years of time elapsed between them. The measurements were conducted by different groups in different seasons, using different instrumentations and array layouts, at six sites in Greece and Italy. Ambient vibration amplitude spectra and locations of dominant sources vary between the two measurements at each location. Still, analysis indicates that this does not influence the derived dispersion information, which is stable in time and neither influenced by the instrumentation nor the analyst. The frequency range over which the dispersion curves and spatial autocorrelation curves can be reliably estimated depends on the array dimensions (minimum and maximum aperture) used in the specific deployment, though, and may accordingly vary between the repeated experiments. The relative contribution of Rayleigh and Love waves to the wavefield can likewise change between repeated measurements. The observed relative contribution of Rayleigh waves is generally at or below 50%, with especially low values for the rural sites. Besides, the visibility of higher modes depends on the noise wavefield conditions. The similarity of the dispersion and autocorrelation curves measured at each site indicates that the curves are stable, mainly determined by the sub-surface structure, and can thus be used to derive velocity information with depth. Differences between velocity models for the same site derived from independently determined dispersion and autocorrelation curves—as observed in other studies—are consequently not adequately explained by uncertainties in the measurement part.  相似文献   

Optically stimulated luminescence dating of fluvioglacial (sandur) sediments from north-eastern Germany     

Christopher Lüthgens  Matthias Krbetschek  Margot Böse  Margret C. Fuchs 《Quaternary Geochronology》2010,5(2-3):237-243

This study presents first results of a project which aims to develop an absolute chronology of the Weichselian ice marginal positions in north-eastern Germany using Optically Stimulated Luminescence (OSL) dating. Owing to the special geomorphological and stratigraphical setting, many of the sampling sites were situated close to the former ice margin. At some sections the sediments showed an incomplete resetting of the OSL signal. For this study the representative sandur sediment section from the Beelitz outwash cone was chosen to elaborate a strategy to reliably detect insufficient bleaching and to choose an appropriate age model for the calculation of the true burial dose of each sample. The age determined for the formation of the Beelitz outwash cone is 34.1 ± 3.0 ka. Although this age might still be a maximum age, this study shows that by applying the proposed methodological strategy, plausible ages can be derived from insufficiently bleached, ice proximal sandur sediments.  相似文献   

The effect of fluid salinity on infiltration-driven contact metamorphism of carbonate rocks     

John M. Ferry  Matthias Gottschalk 《Contributions to Mineralogy and Petrology》2009,158(5):619-636

Calculated phase equilibria involving minerals and H₂O–CO₂–NaCl fluid lead to predictions of how infiltration of rock by H₂O–NaCl fluids with X _NaCl in the range 0–0.3 (0–58 wt% NaCl) drives the reactions calcite + quartz = wollastonite + CO₂ and dolomite = periclase + calcite + CO₂. Calculations focus on metamorphism in four aureoles that together are representative of the normal P–T conditions and processes of infiltration-driven contact metamorphic reactions. The effect of salinity on the spatial extent of oxygen isotope alteration was also computed. The time-integrated input fluid flux (q°) that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing X _NaCl. For input fluids with salinity up to approximately five times that of seawater (X _NaCl ≤ 0.05), values of q° required to explain the spatial extent of decarbonation reaction are no more than 1.1–1.5 times that computed assuming the input fluid was pure H₂O. For more saline fluids, values of q° may be up to 1.4–7.9 times that for pure H₂O. Except for reaction in the presence of halite and vapor (V), infiltration of H₂O–NaCl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction. The expansion is significant only for saline fluids with X _NaCl ≥ ~0.1. Immiscible fluid phase separation and differential loss of the liquid (L) or V phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of L or V. Decarbonation reactions driven by infiltration of fluids with even modest seawater-like salinity can explain the occurrence of salt-saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks.  相似文献   

Functional measures and food webs of high elevation springs in the Swiss alps     

Christopher Thomas Robinson  Dominik Schmid  Matthias Svoboda  Stefano M. Bernasconi 《Aquatic Sciences - Research Across Boundaries》2008,70(4):432-445

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Late Holocene tsunami traces on the western and southern coastlines of the Peloponnesus (Greece)   总被引：1，自引：0，他引：1  

Anja Scheffers  Dieter Kelletat  Andreas Vtt  Simon Matthias May  Sander Scheffers 《Earth and Planetary Science Letters》2008,269(1-2):271-279

Greece, in particular the western and southern parts close to the subduction zone of the Hellenic Trench, experiences strong earthquakes and subsequent tsunamis. Nevertheless, field evidence of tsunamis from the late Holocene is extremely rare. Our research along the coastlines of the western and southern Peloponnesus resulted in new findings of tsunami impacts in the form of clusters and ridges of large boulders and thick tsunamigenic sand layers encountered in vibracores. Many boulders contained attached marine organisms, which prove that they were transported from the foreshore environment against gravity by extreme wave events. The attached organisms, which have been dated by ¹⁴C-AMS, suggest that historical tsunami events of great energy occurred around 1300 cal AD. A wood fragment found at the base of tsunami deposits in a vibracore from Cape Punta was dated to ~ 250 cal AD.  相似文献   

Reconstruction of an approximately complete Quaternary Tibetan inland glaciation between the Mt. Everest- and Cho Oyu Massifs and the Aksai Chin. A new glaciogeomorphological SE–NW diagonal profile through Tibet and its consequences for the glacial isostasy and Ice Age cycle     

Kuhle  Matthias 《GeoJournal》1999,47(1-2):3-276

Studies were done on new geomorphological and quaternary-geological profiles through representative reliefs of Tibet from the Central Himalaya as far as the Kuenlun. Thus, further detailed investigations on the prehistoric glaciation could be carried out. Youngest historical to neoglacial ice margin positions could be recorded. Their mapping took place in a downward direction from the modern glacier margins. They confirm snow line (ELA) depressions from decametres up to ca. 100–250 m. At distances of several kilometres to many decakilometres (depending on the relief) from the modern glaciers, névé shields and perennial snow fields, end moraines and later just remnants of lateral moraines and kame complexes of the Late Glacial (ca. Stadia IV-II) have been localized in an increasing disrupted succession and samples have been taken. The recorded, inter- and extrapolated lowest ice margin positions allowed the reconstruction of accompanying depressions of the snow line which, due to the altitude of the Tibetan plateau plains, attained a maximum of 400–700 m. Accordingly, the early Late Glacial (Stadia I to II) and High Glacial glacier traces (Riss or pre-LGM and Würm or LGM = Stadia −I and/or 0) occurred over a horizontal distance of 1620 km across the plateau with an average height of 4700 m asl without showing the key forms of ice margin positions. From the profiles introduced here, running from Mt. Everest/Cho Oyu (Central Himalaya) in the SE via Gertse (Kaitse; Central Tibet) as far as the Lingzi Thang and Aksai Chin and from there into the Kuenlun, as well as from a parallel section of the Gurla Mandhata (central S Tibet) to the currently very arid Nako Tso, located centrally in the W, sediment samples have been analysed which provide evidence for a ground moraine genesis. Thus, the macroscopic field observations are confirmed. Only the relatively small basin of Shiquanha (Ali) – like the Indus valley chamber of Leh – may have been free of ice during the High Glacial (LGM). Forms of glacial horns, as well as roches moutonnées and large, several metres-high round-polished mountain ridges with slight debris covers, flank polishings, abraded mountain spurs at intermediate valley ridges and high-lying erratics document the widespread ice cover. Important ice thicknesses of at least 1300–1400 m have been recognized by means of transfluences. Especially by and in the Nako Tso (lake) the limnic undercutting of roches moutonnées provides evidence only of a postglacial filling into a primary glacial relief. The glacial ice cover (with the LGM at the end) testified here for a further area of Tibet, is the foundation of the relief-specific hypothesis on the development of the Ice Ages, based on the global radiation geometry: accordingly, the last great geological event, the early Pleistocene plate-tectonically induced uplift of Tibet above the snow line, has brought about a glaciation which, owing to its high albedo, reflected the subtropical radiation energy into space, so that it could not be exploited for the heating of the atmosphere. This may have triggered the Ice Ages. The repeated interglacial warming-up is to be reduced to the positive radiation anomalies by the variations of the parameters of the earth's orbit – which take place rhythmically – and the overlying glacio-isostatic lowering of Tibet and the other inland ice areas. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Dynamics of the boxy elliptical galaxy NGC 1600     

Michael Matthias  Ortwin Gerhard 《Monthly notices of the Royal Astronomical Society》1999,310(3):879-891

We use three-integral models to infer the distribution function (DF) of the boxy E3–E4 galaxy NGC 1600 from surface brightness and line-profile data on the minor and major axes. We assume axisymmetry and that the mass-to-light ratio is constant in the central ∼1 R _e. Stars in the resulting gravitational potential move mainly on regular orbits. We use an approximate third integral K from perturbation theory and write the DF as a sum of basis functions in the three integrals E , L _z and K . We then fit the projected moments of these basis functions to the kinematic observables and deprojected density, using a non-parametric algorithm. The deduced dynamical structure is radially anisotropic, with σ _θ σ _r ≈ σ _φ σ _r ≈0.7 on the major axis. Both on the minor axis and near the centre the velocity distribution is more isotropic; thus the model is flattened by equatorial radial orbits. The kinematic data are fitted without the need for a central black hole; the central mass determined previously from ground-based data therefore overestimates the actual black-hole mass. The mass-to-light ratio of the stars is M L _V =6  h ₅₀. The anisotropy structure of NGC 1600 with a radially anisotropic main body and more nearly isotropic centre is similar to that found recently in NGC 1399, 2434, 3379 and 6703, suggesting that this pattern may be common amongst massive elliptical galaxies. We discuss a possible merger origin of NGC 1600 in the light of these results.  相似文献   

Dynamic stiffness of foundation embedded in layered halfspace based on wave propagation in cones     

John P. Wolf  Matthias Preisig 《地震工程与结构动力学》2003,32(7):1075-1098

An Erratum has been published for this article in Earthquake Engineering & Structural Dynamics 33(6) 2004, 793. The dynamic stiffness of a foundation embedded in a multiple‐layered halfspace is calculated postulating one‐dimensional wave propagation in cone segments. In this strength‐of‐materials approach the sectional property of the cone segment increases in the direction of wave propagation. Reflections and refractions with waves propagating in corresponding cone segments occur at layer interfaces. Compared to rigorous procedures the novel method based on cone segments is easy to apply, provides conceptual clarity and physical insight in the wave propagation mechanisms. This method postulating one‐dimensional wave propagation in cone segments with reflections and refractions at layer interfaces is evaluated, calculating the dynamic stiffness of a foundation embedded in a multiple‐layered halfspace. For sites resting on a flexible halfspace and fixed at the base, engineering accuracy (deviation of ±20%) is achieved for all degrees of freedom with a vast parameter variation. The behaviour below the cut‐off frequency in an undamped site fixed at its base is also reliably predicted. The accuracy is, in general, better than for the method based on cone frustums, which can lead to negative damping. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Changes in trophic flow structure of Independence Bay (Peru) over an ENSO cycle     

Marc H. Taylor  Matthias Wolff  Jaime Mendo  Carmen Yamashiro 《Progress in Oceanography》2008,79(2-4):336

During the strong warm El Niño (EN) that occurred in 1997/98, Independence Bay (14°S, Peru) showed a ca. 10 °C increase in surface temperatures, higher oxygen concentrations, and clearer water due to decreased phytoplankton concentrations. Under these quasi-tropical conditions, many benthic species suffered (e.g. macroalgae, portunid crabs, and polychaetes) while others benefited (e.g. scallop, sea stars, and sea urchins). The most obvious change was the strong recruitment success and subsequent proliferation of the scallop Argopecten purpuratus, whose biomass increased fiftyfold. To understand these changes, steady-state models of the bay ecosystem trophic structure were constructed and compared for a normal upwelling year (1996) and during an EN (1998), and longer-term dynamics (1996–2003) were explored based on time series of catch and biomass using Ecopath with Ecosim (EwE) software. Model inputs were based on surveys and landings data collected by the Instituto del Mar del Perú (IMARPE). Results indicate that while ecosystem size (total throughput) is reduced by 18% during EN, mainly as a result of decreased total primary production, benthic biomass remains largely unchanged despite considerable shifts in the dominant benthic taxa (e.g. scallops replace polychaetes as secondary consumers). Under normal upwelling conditions, predation by snails and crabs utilize the production of their prey almost completely, resulting in more efficient energy flow to higher trophic levels than occurs during EN. However during EN, the proliferation of the scallop A. purpuratus combined with decreased phytoplankton increased the proportion of directly utilized primary production, while exports and flows to detritus are reduced. The simulations suggest that the main cause for the scallop outburst and for the reduction in crab and macroalgae biomass was a direct temperature effect, whereas other changes are partially explained by trophic interactions. The simulations suggest that bottom-up effects largely control the system.  相似文献