Annually laminated (varved) lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme ...runoff events. In this study, the mid- to late Holocene varved sediments of Lake Mondsee (Upper Austria) were analysed by combining sedimentological, geophysical and geochemical methods. This approach allows to distinguish two types of detrital layers related to different types of extreme runoff events (floods and debris flows) and to detect changes in flood activity during the last 7100 years. In total, 271 flood and 47 debris flow layers, deposited during spring and summer, were identified, which cluster in 18 main flood episodes (FE 1–18) with durations of 30–50 years each. These main flood periods occurred during the Neolithic (7100–7050 vyr BP and 6470–4450 vyr BP), the late Bronze Age and the early Iron Age (3300–3250 and 2800–2750 vyr BP), the late Iron Age (2050–2000 vyr BP), throughout the Dark Ages Cold Period (1500–1200 vyr BP), and at the end of the Medieval Warm Period and the Little Ice Age (810–430 vyr BP).
Summer flood episodes in Lake Mondsee are generally more abundant during the last 1500 years, often coinciding with major advances of Alpine glaciers. Prior to 1500 vyr BP, spring/summer floods and debris flows are generally less frequent, indicating a lower number of intense rainfall events that triggered erosion. In comparison with the increase of late Holocene flood activity in western and northwestern (NW) Europe, commencing already as early as 2800 yr BP, the hydro-meteorological shift in the Lake Mondsee region occurred much later. These time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives. The Lake Mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern (NE) Alps, a key region at the climatic boundary of Atlantic, Mediterranean and East European air masses, aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions.
•Varved sediments of Lake Mondsee provide a 7100 yr record of spring/summer floods.•Event layers are detected by combination of thin section and micro-element scanning.•Flood frequencies indicate a variability on millennial to decadal time scales.•Main shift towards more flood events occurred after 1500 varve years BP.•More floods in the northern pre-Alps during periods of alpine glacier advances.
Dislocations in oxides can be described as charged line defects and means for one‐dimensional doping, which can tune electrical and thermal properties. Furthermore, theoretically it was shown that ...dislocations can pin ferroelectric domain walls. Broader application of this concept hinges on the development of a methodology to avail this approach to polycrystalline ceramics. To this end, we use different creep mechanisms as a method to introduce multidimensional defects and quantify structural changes. A deformation map for fine‐grained barium titanate is provided and the influences of the defects and creep regimes are correlated in this first study to modifications of electrical conductivity, dielectric, ferroelectric, and piezoelectric properties. A plastic deformation of 1.29% resulted in an increase in the Curie temperature by 5°C and a decrease in electromechanical strain by 30%, pointing toward electromechanical hardening by dislocations.
Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp2 hybridized carbon, tetrahedrally coordinated SiO4, and tetrahedrally ...coordinated silicon with carbon substitution for oxygen, called “mixed bonds.” Here we synthesize two preceramic polymers possessing both phenyl substituents as unique organic groups. In one precursor, the phenyl group is directly bonded to silicon, resulting in a SiOC polymer-derived ceramic (PDC) with mixed bonding. In the other precursor, the phenyl group is bonded to the silicon through Si-O-C bridges, which results in a SiOC PDC without mixed bonding. Radial breathing-like mode bands in the Raman spectra reveal that SiOC PDCs contain carbon nanoscrolls with spiral-like rolled-up geometry and open edges at the ends of their structure. Calorimetric measurements of the heat of dissolution in a molten salt solvent show that the SiOC PDCs with mixed bonding have negative enthalpies of formation with respect to crystalline components (silicon carbide, cristobalite, and graphite) and are more thermodynamically stable than those without. The heats of formation from crystalline SiO2, SiC, and C of SiOC PDCs without mixed bonding are close to zero and depend on the pyrolysis temperature. Solid state MAS NMR confirms the presence or absence of mixed bonding and further shows that, without mixed bonding, terminal hydroxyls are bound to some of the Si-O tetrahedra. This study indicates that mixed bonding, along with additional factors, such as the presence of terminal hydroxyl groups, contributes to the thermodynamic stability of SiOC PDCs.
Laminated sediments of the maar lake Lago Grande di Monticchio in southern Italy exhibit a unique sequence of numerous primary tephra events that provide both insights into the Late Quaternary ...eruptive history of Italian volcanoes and an archive of essential marker horizons for dating and linking palaeoclimate records throughout the Central and Eastern Mediterranean. The acquisition of new sediment cores from this lake now extends the existing 100 ka-tephra record back to 133 ka BP, the end of the penultimate Glacial. The additional ca 30 m of sediments host a total number of 52 single tephra layers forming 21 tephra clusters that have been characterised on the basis of detailed geochemical and petrographical examinations. Tephras can be assigned to hitherto poorly known Plinian to sub-Plinian eruptive events of the nearby Campanian (Ischia Island, Phlegrean Fields), Roman (Sabatini volcanic district) and Aeolian-Sicilian volcanoes (Etna, Stromboli, Salina) and are dated according to the varve and sedimentation rate chronology of Monticchio sediments. The most prominent tephra layers within the interval of investigation – TM-25 and TM-27 – can be firmly correlated with Ionian Sea tephras X-5 (ca 105 ka BP) and X-6 (ca 108–110 ka BP). In addition, a further 26 tephra layers are correlated with radiometrically and radioisotopically dated volcanic events providing the basis for a robust revised tephrochronology of the entire Monticchio sediment sequence for the last 133 ka.
► A high-resolution tephrostratigraphical record in Italy extending back to 133 ka BP. ► 52 new tephra layers were described in the 100–133 ka time period. ► The ages of tephras are revised by improved varve chronology. ► Widespread tephra markers X-5 and X-6 are identified.
In this study we present the high-temperature creep behavior of a dense SiOC glass ceramic free of segregated carbon. Solid-state NMR spectroscopy, XRD and TEM investigations indicate that the sample ...consists of β-SiC nanoparticles homogeneously dispersed in an amorphous silica matrix. Compression creep experiments were performed at 1100–1300°C and stresses of 50–100MPa. The calculated creep viscosity of SiOC is two orders of magnitude higher than that of pure silica. Whereas the activation energy for creep (696kJ/mol) is close to that determined in pure silica glass. However, a stress exponent of 1.7 was calculated, suggesting that other mechanisms might contribute to the creep in addition to the Newtonian viscous flow. The strong difference in the creep rates and creep mechanism of the SiOC glass ceramic and amorphous silica is discussed in terms of possible contributions of the interface between the silica matrix and the β-SiC nanoparticles.
Reconstructions of early human occupation of high-altitude sites in Central Asia and possible migration routes during the Holocene are limited due to restricted archeological sample material. ...Consequently, there is a growing interest in alternative approaches to investigate past anthropogenic activity in this area. In this study, fecal biomarkers preserved in lake sediments from Lake Chatyr Kol (Tian Shan, Kyrgyzstan) were analyzed to reconstruct the local presence of humans and pastoral animals in this low-human-impact area in the past. Spanning the last ∼11,700 years, this high-altitude site (∼3,500 m above sea level) provides a continuous record of human occupancy in Western Central Asia. An early increase of human presence in the area during the mid-Holocene is marked by a sharp peak of the human fecal sterol coprostanol and its epimer epicoprostanol in the sediments. An associated increase in 5β-stigmastanol, a fecal biomarker deriving from herbivores indicates a human occupancy that most probably largely depended upon livestock. However, sterol profiles show that grazing animals had already occupied the catchment area of Lake Chatyr Kol before and also after a significant presence of humans. The biomarker evidence in this study demonstrates an early presence of humans in a high-altitude site in Central Asia at ∼5,900–4,000 a BP. Dry environmental conditions during this period likely made high altitude regions more accessible. Moreover, our results help to understand human migration in Western Central Asia during the early and mid-Holocene as part of a prehistoric Silk Road territory.
There is an increasing clinical need to develop novel biomaterials that combine regenerative and biocidal properties. In this work, we present the preparation of silver/silica-based glassy bioactive ...(ABG) compositions via a facile, fast (20 h), and low temperature (80 °C) approach and their characterization. The fabrication process included the synthesis of the bioactive glass (BG) particles followed by the surface modification of the bioactive glass with silver nanoparticles. The microstructural features of ABG samples before and after exposure to simulated body fluid (SBF), as well as their ion release behavior during SBF test were evaluated using infrared spectrometry (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), electron microscopies (TEM and SEM) and optical emission spectroscopy (OES). The antibacterial properties of the experimental compositions were tested against Escherichia coli (E. coli). The results indicated that the prepared ABG materials possess antibacterial activity against E. coli, which is directly correlated with the glass surface modification.
Multi-proxy investigations on geological archives provide valuable information about environmental variations in the past. As opposed to single-proxy studies, the combination of several proxies can ...reveal more detailed information and strengthen subsequent paleoenvironmental reconstructions. However, there is still no consensus about how to deal with resulting highly dimensional datasets in a statistical manner. In many cases, the interpretations of multi-proxy datasets rely on visually matching several proxy records, which can lead to incorrect or insufficient interpretations. Here we report an innovative approach that combines the novel dimension reduction technique Uniform Manifold Approximation and Projection (UMAP) and the time series analysis R package asdetect to identify and characterize Holocene environmental phases and phase boundaries in a sediment core from Lake Chatyr Kol, southern Kyrgyzstan. Despite the fact that the Holocene climate evolution of Central Asia has been intensively studied during the last decades, knowledge about regional climate development during the Holocene and the underlying mechanisms is still relatively scarce. We particularly focus on phase transitions and differentiate between event-based shifts as opposed to gradual phase transitions. For this study, long-chain alkenones were used as a paleotemperature proxy and variations in long-chain alkyl diol distributions were ascribed to relative changes of algal input. The compound-specific stable hydrogen isotope compositions (δD) of individual n-alkanes were utilized as paleohydrological proxies, with the δD of mid-chain n-alkanes reflecting changes in the δD of the lake water and the δD of long-chain n-alkanes recording the δD of the meteoric water. We show the potential of modern analysis tools for data-driven paleoenvironmental reconstructions and advocate for their more frequent implementation in multi-proxy studies.
This study presents a record of Holocene surface runoff events and several large earthquakes, preserved in the sediments of pre-Alpine Lake Iseo, northern Italy. A combination of high-resolution ...seismic surveying, detailed sediment microfacies analysis, non-destructive core-scanning techniques and AMS 14C dating of terrestrial macrofossils was used to detect and date these events. Based on this approach, our data shed light on past seismic activity in the vicinity of Lake Iseo and the influence of climate variability and human impact on allochthonous detrital matter flux into the lake. The 19 m long investigated sediment sequence of faintly layered lake marl contains frequent centimetre- to decimetre-scale sandy-silty detrital layers. During the early to mid Holocene, these small-scale detrital layers, reflecting sediment supply by extreme surface runoff events, reveal a distinct centennial-scale recurrence pattern. This is in accordance with regional lake-level highstands and minima in solar activity and thus apparently mainly climate-controlled. After c. 4200 cal. yr BP, intervals of high detrital flux occasionally also correlate with periods of enhanced human settlement activity. In consequence, deposition of small-scale detrital layers during the late Holocene apparently reflects a rather complex interplay between climatic and anthropogenic influences on catchment erosion processes. Besides the small-scale detrital layers, five up to 2.40 m thick large-scale detrital event layers, composed of basal mass-wasting deposits overlain by large-scale turbidites, were identified, which are supposed to be triggered by strong earthquakes. The uppermost large-scale event layer can be correlated to a documented Mw=6.0 earthquake in ad 1222 in Brescia. The four other large-scale event layers are supposed to correspond to previously undocumented local earthquakes. These occurred around 350 bc, 570 bc, 2540 bc and 6210 bc and most probably also reached magnitudes in the order of Mw = 5.0–6.5.
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