Trimlines as evidence for palaeo-tsunamis     

Anja Scheffers  Sander Scheffers  Peter Squire 《Natural Hazards》2012,63(1):165-179

As seen in many of the satellite images from the tsunami in the Indian Ocean which struck in 2004, there is a distinctive limit between an area with sand coverage, vegetation destruction, and soil erosion on the one hand, and the unaffected natural vegetation on the other. This distinction provides a good landmark to map the inundation width, delimited on the landward side by a trimline. In this study, older trimlines, dating back about 300?years, from tsunamis that occurred throughout the world were documented. We discuss the origin and chronology of trimline modification and extinction, both of which depend on local topography, rock type, and climate.  相似文献   

Fate of microbial biomass-derived amino acids in soil and their contribution to soil organic matter   总被引：2，自引：0，他引：2  

Anja Miltner  Reimo Kindler  Heike Knicker  Hans-Hermann Richnow  Matthias Kstner 《Organic Geochemistry》2009,40(9):978-985

Soil organic matter (SOM) is important for soil fertility and for the global C cycle. Previous studies have shown that during SOM formation no new compound classes are formed and that it consists basically of plant- and microorganism-derived materials. However, little data on the contribution from microbial sources are available. Therefore, we investigated previously in a model study the fate of C from ¹³C-labelled Gram-negative bacteria in soil (Kindler, R., Miltner, A. Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil – mineralization and contribution to SOM. Soil Biology and Biochemistry 38, 2860–2870) and showed that 44% of the bulk ¹³C remained in the soil. Here we present the corresponding data on the fate of amino acids hydrolysed from proteins, which are the most abundant components of microbial biomass. After 224 days incubation, the label in the total amino acids in the soil amended with ¹³C-labelled cells decreased only to >95%. The total amino acids therefore clearly showed a lower turnover than the bulk ¹³C and a surprisingly stable concentration. Proteins therefore have to be considered as being stabilised in soil in dead, non-extractable biomass or cell fragments by known general stabilisation mechanisms. The label in the amino acids in a fraction highly enriched in living microbial biomass decreased to a greater extent, i.e. to 25% of the initially added amount. The amino acids removed from this fraction were redistributed via the microbial food web to non-living SOM. All amino acids in the microbial biomass were degraded at similar rates without a change in isotopic signature. The nuclear magnetic resonance (NMR) spectra of the soils were very similar and indicate that the residues of the degraded microbial biomass were very similar to those of the SOM and are a significant source for the formation of the SOM.  相似文献   

The zircon evidence of temporally changing sediment transport—the NW Gondwana margin during Cambrian to Devonian time (Aoucert and Smara areas,Moroccan Sahara)     

Gärtner  Andreas  Youbi  Nasrrddine  Villeneuve  Michel  Sagawe  Anja  Hofmann  Mandy  Mahmoudi  Abdelkader  Boumehdi  Moulay Ahmed  Linnemann  Ulf 《International Journal of Earth Sciences》2017,106(8):2747-2769

International Journal of Earth Sciences - Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope...  相似文献   

Digital Elevation Model from the Best Results of Different Filtering of a LiDAR Point Cloud     

Tomaž Podobnikar  Anja Vrečko 《Transactions in GIS》2012,16(5):603-617

The LiDAR point clouds captured with airborne laser scanning provide considerably more information about the terrain surface than most data sources in the past. This rich information is not simply accessed and convertible to a high quality digital elevation model (DEM) surface. The aim of the study is to generate a homogeneous and high quality DEM with the relevant resolution, as a 2.5D surface. The study is focused on extraction of terrain (bare earth) points from a point cloud, using a number of different filtering techniques accessible by selected freeware. The proposed methodology consists of: (1) assessing advantages/disadvantages of different filters across the study area, (2) regionalization of the area according to the most suitable filtering results, (3) data fusion considering differently filtered point clouds and regions, and (4) interpolation with a standard algorithm. The resulting DEM is interpolated from a point cloud fused from partial point clouds which were filtered with multiscale curvature classification (MCC), hierarchical robust interpolation (HRI), and the LAStools filtering. An important advantage of the proposed methodology is that the selected landscape and datasets properties have been more holistically studied, with applied expert knowledge and automated techniques. The resulting highly applicable DEM fulfils geometrical (numerical), geomorphological (shape), and semantic quality properties.  相似文献   

Episodic mineralization of hydrothermal illite in the Soultz-sous-Forêts granite (Upper Rhine Graben, France)     

Anja M. Schleicher  Laurence N. Warr  Bernd Kober  Emmanuel Laverret  Norbert Clauer 《Contributions to Mineralogy and Petrology》2006,152(3):349-364

Episodic and localized illite mineralization is documented in the hydrothermally altered Soultz-sous-Forêts granite (Upper Rhine Graben, France). Separated grain-size fractions of altered granite and argillite vein samples contain mixtures of 2M₁ and 1M trans-vacant illite varieties. The platy pseudohexagonal 2M₁ illite phases dominate the vein fillings, whereas the 1M illite occurs largely as a fibrous pore-filling variety, which is particularly abundant in the granite matrix. Multiple phases of fluid injections into the granite body have resulted in different illite assemblages, each sample containing a mixture of polytype generations formed during different crystal growth events. On the basis of mineralogical and K–Ar isotopic constraints, the ages of these vein-mineralizing events are determined by plotting the K–Ar values of the various grain-size fractions against polytype abundance and the fitted volume-weighted crystallite thickness distributions. The results suggest a Permian age for the formation of the studied argillite veins, characterized by successive injections of hydrothermal fluids. Secondary episodes of illite crystallization occurred during Jurassic and Cretaceous (or even younger times) in both the veins and the granite matrix. There are indications that the polytype structure and composition of illite were strongly influenced by variations in fluid chemistry and the degree of fluid–rock interaction as the granite was progressively sealed during post-Variscan, episodic hydrothermal activity.  相似文献   

Darss Sill as a biological border in the fossil record of the Baltic Sea: evidence from diatoms   总被引：1，自引：0，他引：1  

Andrzej Witkowski  Anja Broszinski  Ole Bennike  Beata Janczak-Kostecka  Jrn Bo Jensen  Wolfram Lemke  Rudi Endler  Antoon Kuijpers 《Quaternary International》2005,130(1):97

Biostratigraphical and palaeoecological analyses of cores along a transect from Femer Belt to the Arkona Basin reveal that North Sea waters began to enter the western Baltic Sea between 8600 and 8400 calibrated years BP. Studies of diatoms indicate that Mecklenburg Bay was characterised by slightly brackish-water conditions between 8400 and 8000 cal. years BP. At around 8000 cal. years BP increasing salinity is indicated by a strong dominance of the diatoms Paralia sulcata and Dimeregramma minor. Some centuries later another diatom assemblage appeared and became dominant in Mecklenburg Bay. This assemblage includes Hyalinella lateripunctata and Pravifusus hyalinus species typical of shallow water areas along the Atlantic coast today. At this time the first marine molluscs made their appearance. The oldest shell of a marine mollusc found in our material is dated to 7600 cal. years BP. The associated assemblage that includes adult specimens of the gastropod Aporrhais pespelicani indicates higher salinities than today.During the Littorina Sea stage a marine diatom flora with P. sulcata, Catenula adhaerens and D. minor crossed the Darss Sill and became widely distributed in the Arkona Basin, Pomeranian Bay and the Baltic Sea proper. In contrast, taxa indicative of the Hyalinella lateripunctata/P. hyalinus assemblage are only found west of the Darss Sill in Femer Belt and Mecklenburg Bay. Apparently, the Darss Sill threshold has been acting as an important salinity border from around 7800 cal. years BP until today.  相似文献   

Similar Adsorption Parameters for Trace Metals with Different Aquatic Particles   总被引：1，自引：0，他引：1  

Beat Müller  Anja Duffek 《Aquatic Geochemistry》2001,7(2):107-126

Conditional surface binding constants and complexation capacities for Zn, Pb, Cd, and Cu were determined from surface titration experiments of heterogeneous natural aquatic particulate matter of different origin and composition. Metals and particles were evaluated in naturally occurring concentration ranges in river water.The adsorption of trace metals can be adequately described with a single conditional binding constant over a wide range of metal : particle ratios. Binding constants for aquatic particles at pH 8.0 are remarkably independent from particle composition and are specific for each metal: log K^ads _Zn = 8.39, log K^ads _Pb = 9.67, log K^ads _Cd = 8.61, log ^ads _Cu = 9.84. From competition experiments with Ca and Pb we extracted a sorption coefficient for Ca of log K^ads _Ca = 2.5 (pH 8.0). Maximum surface binding capacities for all metal ions were found for particles containing high fractions of Mn-oxides which are associated with large specific surface areas. Generally, we found sorption capacities to decrease in the sequence Cu Pb, Zn > Cd.The experiments suggest that the conditional surface binding constants and complexation capacities are applicable to model trace metal adsorption in the concentration ranges of natural waters under conditions similar to the experiments. Results also imply that the chemical nature of particle surface sites is rather uniform in the intermediate concentration range or that the array of binding sites averages out differences in sorption strength over the prevailing concentration range of metal ions, respectively.  相似文献   

A Statistical Analysis of the North Atlantic Oscillation and its Impact on European Temperature     

Anja Werner  Christian-D. Sch  nwiese 《Journal of Atmospheric & Ocean Science》2002,8(4):293-306

In this study the behaviour of the North Atlantic Oscillation (NAO) and its impact on the surface air temperature in Europe 1891-1990 is analysed using statistical time series analysis techniques. For this purpose, both the NAO index (NAOI) and the surface air temperature time series from 41 European stations are split up into typical variation components. Various measures of correlation indicate that the NAOI-temperature relationships are approximately linear and most pronounced in winter. The spatial correlation patterns show a correlation decrease from North West to South East (winter) exceeding correlation coefficients of 0.6 in the Scotland-South Norwegian area. In summer, these correlations are very weak, in spring and autumn stronger but smaller than in winter. These correlations change significantly in time indicating increasing correlations in Central and North Europe and decreasing correlations in the North West. Low-frequent episodic components represented by related polynomials of different order are very outstanding in both NAO and temperatures showing up in all seasons, except summer, relative maxima roughly 1900 and in recent times, relative minima in the beginning ( ca . 1870) and roughly 1960-1970. Periodogramm analysis reveals a dominant cycle of 7.5 years (NAOI and a majority of temperature time series) whereas in case of the polynomial component one may speculate about a 80-90 year cycle.  相似文献   

Climatic and limnological changes at Lake Karakul (Tajikistan) during the last ~29 cal ka     

Liv Heinecke  Steffen Mischke  Karsten Adler  Anja Barth  Boris K. Biskaborn  Birgit Plessen  Ingmar Nitze  Gerhard Kuhn  Ilhomjon Rajabov  Ulrike Herzschuh 《Journal of Paleolimnology》2017,58(3):317-334

We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last ~29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO₂ (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOC _Br ), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, δ¹⁸O _Carb ) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes.  相似文献   

Late Quaternary barrier and fringing reef development of Bora Bora (Society Islands,south Pacific): First subsurface data from the Darwin‐type barrier‐reef system          下载免费PDF全文

Eberhard Gischler  J. Harold Hudson  Marc Humblet  Juan C. Braga  Anton Eisenhauer  Anja Isaack  Flavio S. Anselmetti  Gilbert F. Camoin 《Sedimentology》2016,63(6):1522-1549

The universally known subsidence theory of Darwin, based on Bora Bora as a model, was developed without information from the subsurface. To evaluate the influence of environmental factors on reef development, two traverses with three cores, each on the barrier and the fringing reefs of Bora Bora, were drilled and 34 uranium‐series dates obtained and subsequently analysed. Sea‐level rise and, to a lesser degree, subsidence were crucial for Holocene reef development in that they have created accommodation space and controlled reef architecture. Antecedent topography played a role as well, because the Holocene barrier reef is located on a Pleistocene barrier reef forming a topographic high. The pedestal of the fringing reef was Pleistocene soil and basalt. Barrier and fringing reefs developed contemporaneously during the Holocene. The occurrence of five coralgal assemblages indicates an upcore increase in wave energy. Age–depth plots suggest that barrier and fringing reefs have prograded during the Holocene. The Holocene fringing reef is up to 20 m thick and comprises coralgal and microbial reef sections and abundant unconsolidated sediment. Fringing reef growth started 8780 ± 50 yr bp ; accretion rates average 5·65 m kyr^?1. The barrier reef consists of >30 m thick Holocene coralgal and microbial successions. Holocene barrier‐reef growth began 10 030 ± 50 yr bp and accretion rates average 6·15 m kyr^?1. The underlying Pleistocene reef formed 116 900 ± 1100 yr bp , i.e. during marine isotope stage 5e. Based on Pleistocene age, depth and coralgal palaeobathymetry, the subsidence rate of Bora Bora was estimated to be 0·05 to 0·14 m kyr^?1. In addition to subsidence, reef development on shorter timescales like in the late Pleistocene and Holocene has been driven by glacioeustatic sea‐level changes causing alternations of periods of flooding and subaerial exposure. Comparisons with other oceanic barrier‐reef systems in Tahiti and Mayotte exhibit more differences than similarities.  相似文献