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The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.
Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound
(2022)
Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
We performed an experiment under long-term microgravity conditions aboard the International Space Station (ISS) to obtain information on the energetics and experimental constraints required for the formation of chondrules in the solar nebula by ’nebular lightning’. As a simplified model system, we exposed porous forsterite (Mg2 SiO4) dust particles to high-energetic arc discharges. The characterization of the samples after their return by synchrotron microtomography and scanning electron microscopy revealed that aggregates had formed, consisting of several fused Mg2SiO4 particles. The partial melting and fusing of Mg2SiO4 dust particles under microgravity conditions leads to a strong reduction of their porosity. The experimental outcomes vary strongly in their appearance from small spherical melt-droplets (∅≈90 µm) to bigger and irregularly shaped aggregates (∅≈350 µm). Our results provided new constraints with respect to energetic aspects of chondrule formation and a roadmap for future and more complex experiments on Earth and in microgravity conditions.
Several past summer floods in Central Europe were associated with so-called Vb‑cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. This study illustrates the usefulness of the parametric transfer entropy measure TE‑linear in investigating heavy Vb‑cyclone precipitation events in the Odra catchment (Poland). With the application of the TE‑linear approach, we confirm the impact of the Mediterranean Sea on precipitation intensification. Moreover, we also detect significant information exchange to Vb‑cyclone precipitation from evaporation over the European continent along the typical Vb‑cyclone pathway. Thus, the Mediterranean Sea could enhance the Vb‑cyclone precipitation by pre-moistening continental moisture source regions that contribute to precipitation downstream in the investigated catchments. Overall, the transfer entropy approach with the measure TE‑linear proved to be computationally effective and complementary to traditional methods such as Lagrangian and Eulerian diagnostics.
The infrastructure for parking and parked cars themselves (e.g., parked cars blocking bike lanes and sidewalks or the visibility range) can lead to conflicts for pedestrians and cyclists. The perception of conflicts could discourage walking and cycling in neighborhoods and undermine municipalities’ efforts to provide more sustainable urban mobility. The aim of this study was therefore to analyze the effect of on-street car parking in urban neighborhoods on perceived parking and traffic-related conflicts. In addition, it examines in what way the intention to reduce one’s car use influences the perception of the conflicts (Stage Model of Self-Regulated Behavior Change (SSBC)). A household survey was conducted in the inner-city neighborhood of Frankfurt-Bornheim, Germany (N=1027). The residents most often observed the conflicts in which parked cars impeded walking and cycling as well as situations in which pedestrians felt threatened by cyclists biking on the sidewalk. Results from multiple linear regression models revealed that the influencing factors for the perception of conflicts were the use of different means of transportation and the intention to change one’s behavior (SSBC model) to reduce car use rather than car ownership. In addition, a resident’s age and household structure seemed to affect awareness of conflicts in which pedestrians and cyclists were involved. The results suggest a group-serving bias, meaning that the residents mostly observed those conflicts that they did not cause. A separate infrastructure for pedestrians and cyclists could help prevent most of the conflicts described in this study.
Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands
(2022)
Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.
Location: Canary Islands, Spain.
Major taxa studied: Spermatophytes.
Time period: Present day.
Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non-endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non-endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.
Results: Trait space of endemic and non-endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non-endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.
Main conclusions: We found that endemic and non-endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.
In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.
Convective rain cell properties and the resulting precipitation scaling in a warm-temperate climate
(2022)
Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low-level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge-adjusted radar dataset in a mid-latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super-CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells.
Moisture sources of heavy precipitation in Central Europe in synoptic situations with Vb-cyclones
(2022)
During the past century, several extreme summer floods in Central Europe were associated with so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. The processes intensifying the precipitation in synoptic situations with Vb-cyclones in the Danube, Elbe, and Odra catchments are only partially understood. Our study aims to investigate these processes with Lagrangian moisture-source diagnostics for 16 selected Vb-events. Moreover, we analyse the characteristics of typical moisture source regions during 1107 Vb-events from 1901 to 2010 based on ERA-20C reanalysis dynamically downscaled with COSMO-CLM+NEMO. We observe moisture contributions by various source regions highlighting the complex dynamical interplay of different air masses leading to moisture convergence in synoptic situations with Vb-cyclones. Overall, up to 80% of the precipitation originates from the European continent, indicating the importance of continental moisture recycling, especially within the respective river catchment. Other major moisture uptake regions are the North Sea, the Baltic Sea, the North Atlantic, and for a few events the Black Sea. Remarkably, anomalies in these oceanic source regions show no connection to precipitation amounts in synoptic situations with Vb-cyclones. In contrast, the Vb-cyclones with the highest precipitation are associated with anomalously high evaporation in the Mediterranean Sea, even though the Mediterranean Sea is only a minor moisture source region on average. Interestingly, the evaporation anomalies are not connected with sea-surface temperature but with wind-speed anomalies (Spearman’s rank correlation coefficient R≈0.7, significant with p<0.01) indicating mainly dynamically driven evaporation. The particular role of the Mediterranean Sea hints towards possible importance of Mediterranean moisture for the early-stage intensification of Vb-cyclones and the pre-moistening of the continental uptake regions upstream of the target catchments.
The Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third-order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U-Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U-Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time-framed depositional systems.
Atmospheric particles play an important role in the radiative balance of the Earth, as well as they affect human health and air quality. Hence, the chemical characterization constitutes a crucial task to determinate their properties, sources and fate. Particularly, the analysis of nanoparticles (d<100 nm) represents an analytical challenge, since these particles are abundant in number but have very little mass.
This accumulative thesis focuses on the chemical characterization of nanoparticles, performed in both laboratory and field studies. Here, I present four manuscripts, two of which are my main project as a lead author.
The first manuscript (Caudillo et al., 2021) focuses on the gas and the particle phase originated from biogenic precursor gases (α-pinene and isoprene). The experiments were performed in the CLOUD chamber at CERN to simulate pure biogenic new particle formation. Both gas and particle phases are measured with a nitrate CI-APi-TOF mass spectrometer, while the TD-DMA is coupled to it for particle-phase measurements, this setup allows a direct comparison as both measurements use the identical chemical ionization and detector. This study demonstrates the suitability of the TD-DMA for measuring newly formed nanoparticles and it confirms that isoprene suppresses new particle formation but contributes to the growth of newly formed particles.
The second manuscript (Caudillo et al., 2022) presents an intercomparison of four different techniques (including the TD-DMA) for measuring the chemical composition of SOA nanoparticles. The measurements were conducted in the CLOUD chamber. The intercomparison was done by contrasting the observed chemical composition, the calculated volatility, and the thermal desorption behavior (for the thermal desorption techniques). The methods generally agreed on the most important compounds that are found in the nanoparticles. However, they did see different parts of the organic spectrum. Potential explanations for these differences are suggested.
The third manuscript (Ungeheuer al., 2022) presents both laboratory and ambient measurements to investigate the ability of lubricant oil to form new particles. These new particles are an important source of ultrafine particles in the areas nearby large airports. The ambient measurements were performed downwind of Frankfurt International Airport, and it was found that the fraction of lubricant oil is largest in the smallest particles. In the laboratory, the main finding was that evaporated lubricant oil nucleates and forms new particles rapidly. The results suggest that nucleation of lubricant oil and subsequent particle growth can occur in the cooling exhaust plumes of aircraft-turbofans.
The fourth manuscript (Wang et al., 2022) is a new particle formation study in the CLOUD chamber at CERN. This study shows that nitric acid, sulfuric acid, and ammonia interact synergistically and rapidly form particles under upper free tropospheric conditions. These particles can grow by condensation (driven by the availability of ammonia) up to CCN sizes and INP particles. The ability of these particles to act as a CCN and INP was also investigated and it was found to be as efficient as for desert dust. This mechanism constitutes an important finding and it can account for previous observations of high concentrations of ammonia and ammonium nitrate over the Asia monsoon region.
Titanite is a potentially powerful U–Pb petrochronometer that may record metamorphism, metasomatism, and deformation. Titanite may also incorporate significant inherited Pb, which may lead to inaccurate and geologically ambiguous U–Pb dates if a proper correction is not or cannot be applied. Here, we present laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)-derived titanite U–Pb dates and trace element concentrations for two banded calcsilicate gneisses from south-central Maine, USA (SSP18-1A and SSP18-1B). Single spot common Pb-corrected dates range from 400 to 280 Ma with ±12–20 Ma propagated 2SE. Titanite grains in sample SSP18-1B exhibit regular core-to-rim variations in texture, composition, and date. We identify four titanite populations: (1) 397 ± 5 Ma (95% CL) low Y + HREE cores and mottled grains, (2) 370 ± 7 Ma high Y + REE mantles and cores, (3) 342 ± 6 Ma cores with high Y + REE and no Eu anomaly, and (4) 295 ± 6 Ma LREE-depleted rims. We interpret the increase in titanite Y + HREE between ca. 397 and ca. 370 Ma to constrain the timing of diopside fracturing and recrystallization and amphibole breakdown. Apparent Zr-in-titanite temperatures (803 ± 36°C at 0.5 ± 0.2 GPa) and increased XDi suggest a thermal maximum at ca. 370 Ma. Population 3 domains dated to ca. 342 Ma exhibit no Eu anomaly and are observed only in compositional bands dominated by diopside (>80 vol%), suggesting limited equilibrium between titanite and plagioclase. Finally, low LREE and high U/Th in Population 4 titanite dates the formation of hydrous phases, such as allanite, during high XH2O fluid infiltration at ca. 295 Ma. In contrast to the well-defined date–composition–texture relationships observed for titanite from SSP18-1B, titanite grains from sample SSP18-1A exhibit complex zoning patterns and little correlation between texture, composition, and date. We hypothesize that the incorporation of variable amounts of radiogenic Pb from dissolved titanite into recrystallized domains resulted in mixed dates spanning 380–330 Ma. Although titanite may reliably record multiple phases of metamorphism, these data highlight the importance of considering U–Pb data along with chemical and textural data to screen for inherited radiogenic Pb.
Reliable identification of chondrules, calcium-aluminum-rich inclusions (CAIs), carbonate grains, and Ca-phosphate grains at depth within untouched, unprepared chondritic samples by a nondestructive analytical method, such as synchrotron X-ray fluorescence (SXRF) computed tomography (CT), is an essential first step before intrusive analytical and sample preparation methods are performed. The detection of a local Ca-enrichment could indicate the presence of such a component, all of which contain Ca as major element and/or Ca-bearing minerals, allowing it to be precisely located at depth within a sample. However, the depth limitation from which Ca-K fluorescence can travel through a chondrite sample (e.g., ∼115 µm through material of 1.5 g cm−3) to XRF detectors leaves many Ca-bearing components undetected at deeper depths. In comparison, Sr-K lines travel much greater distances (∼1700 µm) through the same sample density and are, thus, detected from much greater depths. Here, we demonstrate a clear, positive, and preferential correlation between Ca and Sr and conclude that Sr-detection can be used as proxy for the presence of Ca (and, thus, Ca-bearing components) throughout mm-sized samples of carbonaceous chondritic material. This has valuable implications, especially for sample return missions from carbonaceous C-type asteroids, such as Ryugu or Bennu. Reliable localization, identification, and targeted analysis by SXRF of Ca-bearing chondrules, CAIs, and carbonates at depth within untouched, unprepared samples in the initial stages of a multianalysis investigation insures the valuable information they hold of pre- and post-accretion processes in the early solar system is neither corrupted nor destroyed in subsequent processing and analyses.
Questions: Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity.
Location: La Palma, Canary Islands.
Methods: We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient.
Results: The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation.
Conclusions: Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species.
Positive plant–plant interactions are thought to drive vegetation patterns in harsh environments, such as semi-arid areas. According to the stress-gradient hypothesis (SGH), the role of positive interactions between species (facilitation) is expected to increase with harshness, predicting associated variation in species composition along environmental gradients. However, the relation between stress and facilitation along environmental gradients is debated. Furthermore, differentiating facilitative interactions from other underlying mechanisms, such as microtopographic heterogeneity, is not trivial. We analysed the spatial co-occurrence relationships of vascular plant species that form patchy vegetation in arid lapilli fields (tephra) from recent volcanic eruptions on La Palma, Canary Islands. Assuming a harshness gradient negatively correlated with elevation because the lower elevations are more arid and water availability is considered the most limiting resource, and that an outcome of facilitation is plants co-occurring in the same patch, from the SGH we expected a greater degree of co-occurrence at lower elevation. We tested this at both the species and the individual plant level. We analysed the species composition of 1277 shrubby vegetation patches at 64 different sampling points, ranging from the coast to around 700 m a.s.l. Patch morphology and microtopographic heterogeneity variables were also measured, to account for their potential effects on the species composition of patches. We used generalized linear models and generalized mixed-effects models to analyse species richness, number of individuals in patches and percentage of patches with positive co-occurrences, and a pairwise co-occurrence analysis combined with a graphical network analysis to reveal positive links between 13 of the species. We found that the percentage of patches with positive co-occurrences increased at higher elevations, in contrast to the predictions of the SGH, but in accordance with a refined stress-gradient hypothesis for arid sites, in which characteristics of the interacting species are incorporated.
This thesis presents the experimental and numerical analysis of seismic waves that are produced by wind farms. With the aim to develop renewable energies rapidly, the number of wind turbines has been increased in recent years. Ground motions induced by their operation can be observed by seismometers several kilometers away. Hence, the seismic noise level can be significantly increased at the seismic station. Therefore, this study combines long-term experiments and numerical simulations to improve the understanding of the seismic wavefields emitted by complete wind farms and to advance the prediction of signal amplitudes.
Firstly, wind-turbine induced signals that are measured at a small wind farm close to Würzburg (Germany) are correlated with the operational data of the turbines. The frequency-dependent decay of signal amplitudes with distance from the wind farm is modeled using an analytical method including the complex effects of interferences of the wavefields produced by the multiple wind turbines. Specific interference patterns significantly affect the wave propagation and therefore the signal amplitude in the far field of a wind farm. Since measurements inside the wind turbines show that the assumption of in-phase vibrating wind turbines is inappropriate, an approach to calculate representative seismic radiation patterns from multiple wind turbines, which allows the prediction of amplitudes in the far field of a complete wind farm, is proposed.
In a second study, signals with a frequency of 1.15 Hz, produced by the Weilrod wind farm (north of Frankfurt, Germany) are observed at the seismological observatory TNS (Taunus), which is located at a distance of 11 km from the wind farm. The propagation of the wavefield emitted by the wind farm is numerically modeled in 3D, using the spectral element method. It is shown that topographic effects can cause local signal amplitude reductions, but also signal amplification along the travel path of the seismic wave. The comparison of simulations with and without topography reveals that the reduction and amplification are spatially linked to the shape of the topography, which could be an explanation for the relatively high signal amplitude observed at TNS.
Finally, the reduction of the impact of wind turbines on seismic measurements using borehole installations is studied using 2D numerical models. Possible effects of the seismic velocity, attenuation, and layering of the subsurface are demonstrated. Results show that a borehole can be very effective in reducing the observed high-frequency signals emitted by wind turbines. However, a borehole might not be beneficial if signals with frequencies of about 1 Hz (or lower) are of interest, due significant wavelength-dependent effects. The estimations of depth-dependent amplitudes with a layered subsurface are validated with existing data from wind-turbine-induced signals measured at the top and bottom of two boreholes.
The experimental analysis of measurements conducted at wind farms and the advances of modeling such signals improve the understanding of the propagation of wind-farm induced seismic wave fields. Furthermore, the methods developed in this work have a high potential of universal application to the prediction of signal amplitudes at seismometers close to wind farms with arbitrary layout and geographic location.
This thesis is focusing on the impact of Paratethys and Mediterranean water bodies over the Eurasian climate and the interplay between climate, tectonics and biosphere during the late Miocene. This target was the interval between 12.7 and 7.65 Ma for Paratethys, following the Eastern Paratethys restriction and isolation, and 7.2−6.5 Ma (the early Messinian) in Mediterranean, zooming on the effects of gateway restrictions over the eastern Mediterranean and the new born Aegean domain. In both cases restriction is overlapping with large scale climatic changes and tectonic reconfiguration, leading a sort of symbiotic relationship.
Paratethys was a giant epicontinental sea that covered a large part of Eurasia since Paleogene. Due to the Eurasia-Afro-Arabia collision and formation of the Alpine-Himalayan belt (Rögl, 1999; Popov et al., 2006), the Paratethys was divided during the late Miocene in smaller basins that in time were isolated of each other. The protracted isolation and intense continentalisation of paratethyan realm led to changes in humidity distribution, basin connectivity, sediment sources and salinity. These changes had in turn major consequences over water circulation, water availability, vegetation cover and biota. These changes are more intense after 11.6 Ma, when the Eastern Paratethys lost any sustained marine connection, evolving into an enclosed system with endemic fauna (Harzhauser and Piller, 2007).
Mediterranean Sea is a Mezozoic oceanic relic squeezed between Africa, Europe, Anatolia and Arabia, as Africa continued to subduct beneath the European plate. As opposed to Paratethys, it maintained the open connection with the ocean until Messinian, when the two Atlantic gateways (Betic and Rifian corridors) closed for a short time, isolating the basin. The cut off resulted in a dramatic drop down and onset of evaporitic precipitation in marginal basins, the event receiving the name of Messinian Salinity Crisis (5.97−5.55). The restriction affected all marine ecosystems, due to changes in salinity and stratification of water column.
The main objectives of this thesis were:
(1) build valid paleo-temperatures records for both basins based on biomarkers;
(2) reconstruct the hydrology for the late Miocene time interval;
(3) identify vegetation composition and changes;
(4) identify paleo-fires in the late Miocene sediment records;
(5) identify the biotic response to the overall climate and tectonic changes.
All the above objectives were attained with results published in specific journals (Chapters 5−7).
Based on Panagia section (Taman Peninsula, Russia) the longest Paratethys temperature record was completed (~5 Myr), covering the interval between 12.7 and 7.65 Ma. A comprehensive SST and MAT records was obtained, as well as soil pH and carbon (δ13C) and hydrogen (δ2H) stable isotopic compositions on n-alkanes and alkenones. The main findings are concentrated around three prolonged periods with severe droughts affecting the late Miocene circum-Paratethys region peaking at 9.65, 9.4 and 7.9 Ma, associated with a transition towards open land vegetation, intensification of fire activity and enhanced evaporation and aridity.
The time intervals with dryer conditions recorded in Panagia coincide with periods of mammal turnover and dispersal in Eurasia indicating that major environmental changes occurred in the circum-Paratethys region and Paratethys fragmentation had a great impact on the terrestrial ecosystems, when periods of prolonged droughts generated biotic crises and animal displacements across the Eurasian continent. The δ13CC29n-alkane values and charcoal morphologies from Panagia indicate an increased contribution of C4 plants adapted to drier conditions at 9.66 Ma. Similarly high δ13CC29n-alkane values continue until 9.4 Ma, when in Western Europe increased seasonality accelerated the demise of the evergreen subtropical woodlands and expansion of grasslands from Anatolia and Middle East to Europe.
As a result of basin fragmentation and climatic stress, the Eastern Paratethys sub-basins progressively lost their marine properties and turned into brackish-fresh water bodies fed primarily by riverine input. The shallower areas became in time emerged, obstructing connections and isolating the biota, inducing rapid adjusting or extinctions. Thus, the Paratethys harbored a highly endemic fauna (Rögl, 1999), such as dwarf whales, dolphins, seals (among mammals), as well as fish and other taxa (mollusks, ostracods, diatoms, foraminifera, algae, etc.).
Collectively the data structured and analyzed in chapter five support a model in which the Eastern Paratethys evolved as a largely (en)closed system, registering paleoenvironmental signals that are governed by interbasinal connectivity (or lack of it) and regional climate changes in the basin catchment. Acting as an important source of humidity for Western and Central Asia, the size and areal extent of the Paratethys water body is likely to have had a major impact on hydroclimate patterns in the Eurasian interior, with the cumulative fluctuations in both hydrology and surface temperature enhancing the aridity and seasonality, with different partition of moisture over the year. Our combined data suggests a decoupling of Paratethys from the global system as isolation advanced, dominated by regional tectonics and ultimately the Paratethys volume and areal extent reduction.
Ob Klimawandel oder Luftverschmutzung: Die chemischen und physikalischen Prozesse in der Atmosphäre haben wichtige Auswirkungen auf die menschliche Gesundheit und Ökosysteme. Dabei ist die Atmosphäre mehr als ein Gemisch aus Stickstoff, Sauerstoff, Wasserdampf, Helium und Kohlenstoffdioxid. Es gibt zahlreiche Spurengase, deren Gesamtanteil am Volumen weniger als 1 % ausmacht. In dieser Arbeit werden Stickstoffoxide, Schwefeldioxid, Kohlenstoffmonoxid und Schwefelsäure näher betrachtet, die im Rahmen der flugzeugbasierten Messkampagne Chemistry of the Atmosphere: field experiment in Europe (CAFE-EU)/BLUESKY gemessen wurden.
Die Stickstoffoxide NO und NO2, als NOx zusammengefasst, besitzen hauptsächlich anthropogene Quellen, allen voran fossile Verbrennung und industrielle Prozesse. Zwischen NO und NO2 besteht ein photochemisches Gleichgewicht, sodass in der Atmosphäre vor allem NO2 in relevanten Konzentrationen vorkommt; dies wirkt aufgrund der Bildung von Salpetersäure, HNO3, in wässriger Lösung beim Einatmen ätzend und ist entsprechend gesundheitsschädlich. Troposphärisches Ozon, O3, wesentlicher Bestandteil von Sommersmog, wird hauptsächlich durch die Reaktion von NO mit Peroxiden (HO2 und RO2) gebildet. In der Stratosphäre entstehen NOx hauptsächlich durch die Photodissoziation von Lachgas, N2O, das aufgrund seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann und dort die wichtigste Stickstoffquelle darstellt. In der Stratosphäre tragen NOx zum katalytischen Abbaumechanismus des Ozons bei (Bliefert, 2002; Seinfeld and Pandis, 2016).
Schwefeldioxid, SO2, ist ein toxisches Gas, dessen atmosphärische Quellen hauptsächlich anthropogen sind, nämlich fossile Verbrennung und industrielle Prozesse; Senken sind trockene und feuchte Deposition, wobei letztere zu saurem Regen führen kann. Seit den 1980ern sinken die globalen SO2-Emissionen. SO2 kann in der Atmosphäre zu Sulfat und Schwefelsäure oxidiert werden, was Hauptbestandteil des Wintersmogs ist. Der wichtigste Mechanismus ist die Oxidation mit dem Hydroxylradikal, OH˙, unter Beteiligung von Wasserdampf. In der Stratosphäre ist Carbonylsulfid, OCS, die wichtigste Schwefelquelle, da es analog zum N2O dank seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann (Bliefert, 2002; Seinfeld und Pandis, 2016). Typische Konzentrationen von Schwefelsäure sind 105 cm–3 nachts und 107 cm–3 tagsüber in der Troposphäre sowie 105 cm–3 tagsüber in der Stratosphäre (Clarke et al., 1999; Weber et al., 1999; Fiedler et al., 2005; Arnold, 2008; Kürten et al., 2016; Berresheim et al., 2000).
Kohlenstoffmonoxid, CO, ist ein toxisches Gas, das zu gleichen Teilen durch direkte Emissionen (v.a. Biomasseverbrennung und fossile Verbrennung) und In-situ-Oxidation (v.a. von Methan, Isopren und industriellen Kohlenwasserstoffen) in die Atmosphäre gelangt. Die Hauptsenke ist die Reaktion mit OH˙ in der Troposphäre. Seit 2000 sinkt die globale CO-Konzentration (Bliefert, 2002).
Doch neben Gasen sind auch Aerosolpartikel fester Bestandteil des Gemisches Luft, welche luftgetragene feste oder flüssige Teilchen sind. Primäre Aerosolpartikel werden direkt als solche in die Atmosphäre emittiert, während sekundäre Aerosolpartikel in der Atmosphäre gebildet werden, indem gasförmige Vorläufersubstanzen mit geringer Flüchtigkeit auf primären Partikeln kondensieren oder durch Zusammenclustern und Anwachsen komplett neue Partikel bilden. Aerosolpartikel ermöglichen als Wolkenkondensationskeime erst die Bildung von Wolken und wirken somit – neben ihrem direkten reflektierenden Effekt – durch Änderung der Wolkenbedeckung und -eigenschaften insgesamt kühlend aufs Klima und beeinflussen die lokalen und globalen Wasserkreisläufe. Doch sie haben auch negative Auswirkungen auf die menschliche Gesundheit und sind für eine Verkürzung der durchschnittlichen Lebensdauer in Regionen mit hohen Feinstaubbelastungen verantwortlich (Seinfeld und Pandis, 2016; Bellouin et al., 2020; World Health Organization, 2016).
Neben den bisher betrachteten neutralen, also ungeladenen Gasen und Partikeln sind Ionen in der Gasphase sowie geladene Partikel ebenfalls Bestandteil der Atmosphäre. Sie spielen bei vielen atmosphärischen Prozessen eine wichtige Rolle, wie etwa bei Gewittern, Radiowellenübertragung und ionen-induzierter Nukleation von Aerosolpartikeln. Die Hauptquellen für Ionisation in der Tropo- und Stratosphäre ist die galaktische kosmische Strahlung, die entgegen ihrem Namen hauptsächlich aus Protonen und α-Partikeln (primäre Partikel genannt) besteht und in der Erdatmosphäre durch Kollision mit Luftmolekülen Teilchenschauer von sekundären Partikeln (u.a. Myonen, Pionen und Neutrinos) hervorruft. Die primären und sekundären Partikel können die Luftmoleküle ionisieren unter Entstehung von N+, N2+, O+, O2+ und Elektronen. Sauerstoff reagiert rasch mit letzteren zu O– und O2–. Diese Kationen und Anionen reagieren weiter, bis Ionenclustern der Summenformeln (HNO3)n(H2O)mNO3– und H+(H2O)n(B)m gebildet werden, wobei B Basen wie Methanol, Aceton, Ammoniak oder Pyridin sind. Weitere Ionisationsquellen sind der Zerfall des Radioisotops 222Rn in Bodennähe und ionisierende Solarstrahlung oberhalb der Stratosphäre. Atmosphärische Ionen haben zwei wichtige Senken: die Wiedervereinigung, auch Rekombination genannt, bei der sich ein Kation und ein Anion gegenseitig neutralisieren sowie das Anhaften an Aerosolpartikeln. Letztere Senke ist vor allem in der Troposphäre aufgrund der relativ hohen Konzentration an Aerosolpartikeln relevant (Arnold, 2008; Viggiano und Arnold, 1995; Bazilevskaya et al., 2008; Hirsikko et al., 2011).
Melting inside earth is a common phenomenon and can be observed in many different regions where melt travels through the mantle and crust to eventually reach the surface where it crystallizes to build large volcanic provinces, whole stratigraphic layers of flood basalts, or even the oceanic crust. Often, melt reaching the surface is a good source of information. It can be used to achieve a better understanding about processes taking place in deeper regions inside the mantle and it is therefore essential to fundamentally understand melting and melt percolation processes. In order to achieve a deeper understanding, the aim of this thesis is to investigate processes that are connected to melting by using numerical models.
The physical model used is a so called two-phase flow model which describes the ability of melt to percolate through a viscously deforming, partially molten matrix. A famous feature of two-phase flow are solitary porosity waves, which are waves of locally higher porosity ascending through a partially molten background, keeping its shape constant, driven by decompaction and compaction of the solid matrix in front and behind the wave.
The viscosity law for shear- and volume viscosity was strongly simplified in most previous studies that modeled solitary waves. Often the porosity dependency is underestimated or its influence on the volume viscosity is even neglected, leading to too high viscosities. In this work more realistic laws are used that strongly decrease for small melt fractions. Those laws are incorporated into a 2D Finite Difference mantle convection code with two-phase flow to study the ascent of solitary porosity waves.
The model results show that an initial Gaussian-shaped wave rapidly evolves into a solitary wave with a certain amplitude, traveling upwards with constant velocity. Even though strongly weaker viscosities are used, the effect on dispersion curves and wave shape are only minor as long as the background porosity is rather small. The results are still in agreement to semi-analytical solutions which neglect shear stresses in the melt segregation equation. Higher background porosities and wave amplitudes lead to significant decrease in phase velocity and wave width, as the viscosity is strongly effected. However, the models show that solitary waves are still a possible mechanism for more realistic matrix viscosities.
While the ascending of porosity waves are mostly described by the movement of fluid melt, partially molten regions inside Earth trigger upwelling of both, solid and fluid phases, which can be called diapirism. While diapirs can have a wide variety of wavelengths, porosity waves are restricted to a few times the compaction length. The size of a melt perturbation in terms of compaction length therefore describes whether material is transported by diapirism or porosity waves. In this thesis we study the transition from diapiric rise to solitary porosity waves by systematically changing the size of a porosity perturbation from 1.8 to 120 times the compaction length. In case of a perturbation of the size of a few times the compaction length a single porosity wave will emerge, either with a positive or negative vertical matrix flux and if melt is not allowed to move relative to the matrix a diapir will emerge. In between these physical end members a regime can be observed where the partially molten perturbation will split up into numerous solitary waves, whose phase velocity is low compared to the Stokes velocity and the swarm of solitary waves will ascend jointly as a diapir, slowly elongating due to a higher amplitude main solitary wave.
Solitary waves will always emerge from a melt perturbation as long as two-phase flow is enabled, but the time for a solitary wave to emerge increases non-linearly with the perturbation radius in terms of compaction length. In nature, in many cases this time might be too long for solitary waves to emerge.
Another important feature when it comes to two-phase flow is the transport of trace elements in melt. Incompatible elements prefer to go into the melt, which eventually enriches the area where it crystallizes again. In order to model this redistribution, the code FDCON was extended to allow for fully consistent transport of elements in melt, including melting, freezing and re-equilibration with time. A 2D model, a simple representation of a volcanic back arc, is set up to investigate the behavior of trace elements. The influence of retention number and re-equilibration time is examined. Lava-lamp like convection can be observed in the lower part of the model, producing melt, that eventually leads to enrichment in trace elements in the upper high-viscous layer. The total enrichment in this layer approaches an asymptotic value and a 0D model is introduced to recreate this behavior.
Cratonic eclogite is the product of oceanic crust subduction into the subcontinental lithospheric mantle, and it also is a fertile diamond source rock. In contrast to matrix minerals in magma-borne xenoliths, inclusions in diamond are shielded from external fluids, retaining more pristine information on the state of the eclogite source at the time of encapsulation. Vanadium is a multi-valent element and a widely used elemental redox proxy. Here, we show that that xenolithic garnet has lower average V abundances than garnet inclusions. This partly reflects crystal-chemical controls, whereby higher average temperatures recorded by inclusions, accompanied by enhanced Na2O and TiO2 partitioning into garnet, facilitate V incorporation at the expense of clinopyroxene. Unexpectedly, although diamond formation is strongly linked to metasomatism and xenoliths remained open systems, V concentrations are similar for bulk eclogites reconstructed from inclusions and from xenoliths. This suggests an oxygen-conserving mechanism for eclogitic diamond formation, and implies that eclogite is an efficient system to buffer fO2 over aeons of lithospheric mantle modification by subduction-derived and other fluids.
Global water models (GWMs) simulate the terrestrial water cycle, on the global scale, and are used to assess the impacts of climate change on freshwater systems. GWMs are developed within different modeling frameworks and consider different underlying hydrological processes, leading to varied model structures. Furthermore, the equations used to describe various processes take different forms and are generally accessible only from within the individual model codes. These factors have hindered a holistic and detailed understanding of how different models operate, yet such an understanding is crucial for explaining the results of model evaluation studies, understanding inter-model differences in their simulations, and identifying areas for future model development. This study provides a comprehensive overview of how state-of-the-art GWMs are designed. We analyze water storage compartments, water flows, and human water use sectors included in 16 GWMs that provide simulations for the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). We develop a standard writing style for the model equations to further enhance model improvement, intercomparison, and communication. In this study, WaterGAP2 used the highest number of water storage compartments, 11, and CWatM used 10 compartments. Seven models used six compartments, while three models (JULES-W1, Mac-PDM.20, and VIC) used the lowest number, three compartments. WaterGAP2 simulates five human water use sectors, while four models (CLM4.5, CLM5.0, LPJmL, and MPIHM) simulate only water used by humans for the irrigation sector. We conclude that even though hydrologic processes are often based on similar equations, in the end, these equations have been adjusted or have used different values for specific parameters or specific variables. Our results highlight that the predictive uncertainty of GWMs can be reduced through improvements of the existing hydrologic processes, implementation of new processes in the models, and high-quality input data.
This paper investigates the global stratospheric Brewer–Dobson circulation (BDC) in the ERA5 meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of stratospheric mean age of air, including the full age spectrum, with the Lagrangian transport model CLaMS (Chemical Lagrangian Model of the Stratosphere), driven by reanalysis winds and total diabatic heating rates. ERA5-based results are compared to results based on the preceding ERA-Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA-Interim, manifesting in weaker diabatic heating rates and higher age of air. In the tropical lower stratosphere, heating rates are 30 %–40 % weaker in ERA5, likely correcting a bias in ERA-Interim. At 20 km and in the Northern Hemisphere (NH) stratosphere, ERA5 age values are around the upper margin of the uncertainty range from historical tracer observations, indicating a somewhat slow–biased BDC. The age trend in ERA5 over the 1989–2018 period is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear but steplike, potentially caused by multi-annual variability or changes in the observations included in the assimilation. During the 2002–2012 period, the ERA5 age shows a similar hemispheric dipole trend pattern as ERA-Interim, with age increasing in the NH and decreasing in the Southern Hemisphere (SH). Shifts in the age spectrum peak and residual circulation transit times indicate that reanalysis differences in age are likely caused by differences in the residual circulation. In particular, the shallow BDC branch accelerates in both reanalyses, whereas the deep branch accelerates in ERA5 and decelerates in ERA-Interim.
Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burnt horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forest and forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition, and peatland hydrology at two sites located in predominantly light taiga (Pinus sylvestris Betula) with interspersed dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) in western Siberia in the Tomsk Oblast, Russia. We found marked shifts in past water levels over the Holocene. The probability of fire occurrence and the intensification of fire frequency and severity increased at times of low water table (drier conditions), enhanced fuel dryness, and an intermediate dark-to-light taiga ratio. High water level, and thus wet peat surface conditions, prevented fires from spreading on peatland and surrounding forests. Deciduous trees (i.e. Betula) and Sphagnum were more abundant under wetter peatland conditions, and conifers and denser forests were more prevalent under drier peatland conditions. On a Holocene scale, severe fires were recorded between 7.5 and 4.5 ka with an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybnaya and Abies sibirica at Ulukh–Chayakh) in a predominantly light taiga and fire-resister community characterised by Pinus sylvestris and lower local water level. Severe fires also occurred over the last 1.5 kyr and were associated with a declining abundance of dark taiga and fire avoiders, an expansion of fire invaders (Betula), and fluctuating water tables. These findings suggest that frequent, high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial- to millennial-scale Holocene climate variability on wildfire activity. Humans may have affected vegetation and fire from the Neolithic; however, increasing human presence in the region, particularly at the Ulukh–Chayakh Mire over the last 4 centuries, drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted by climate change scenarios for Siberia in the future will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions will probably exacerbate the frequency and severity of wildfire, disrupt conifers' successional pathway, and accelerate shifts towards deciduous broadleaf tree cover. Furthermore, climate–disturbance–fire feedbacks will accelerate changes in the carbon balance of boreal peatlands and affect their overall future resilience to climate change.
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burning horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition and peatland hydrology at two sites in Western Siberia near Tomsk Oblast, Russia. The palaeoecological records originate from forested peatland areas in predominantly light taiga (Pinus-Betula) with increase in dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) towards the east. We found that the past water level fluctuated between 8 and 30 cm below the peat surface. Wet peatland conditions promoted broadleaf trees (Betula), whereas dry peatland conditions favoured conifers and a greater forest density (dark-to-light-taiga ratio). The frequency and severity of fire increased with a declining water table that enhanced fuel dryness and flammability and at an intermediate forest density. We found that the probability of intensification in fire severity increased when the water
level declined below 20 cm suggesting a tipping point in peatland hydrology at which wildfire regime intensifies. On a Holocene scale, we found two scenarios of moisture-vegetation-fire interactions. In the first, severe fires were recorded 45 between 7.5 and 4.5 ka BP with lower water level and an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybanya and Abies sibirica at Ulukh Chayakh) mixed into the dominantly light taiga and fire-resister community of Pinus
sylvestris. The second occurred over the last 1.5 ka and was associated with fluctuating water tables, a declining abundance of fire avoiders, and an expansion of fire invaders (Betula). These findings suggest that frequent high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial to millennial-scale Holocene climate
variability on wildfire activity. Increasing human presence in the region of the Ulukh-Chayakh Mire near Teguldet over the last four centuries drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted for the future in Siberia by climate change scenarios will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions, particularly a water table decline below the threshold of 20 cm, will probably exacerbate the frequency and severity of wildfire, disrupt conifers’ successional pathway and accelerate shifts towards more fire-adapted broadleaf tree cover. Furthermore, climate-disturbance-fire feedbacks will accelerate changes in the carbon balance of forested boreal peatlands and affect their overall future resilience to climate change.
State of the simulation of mesoscale winds in the Mediterranean and opportunities for improvements
(2022)
The Mediterranean region is a densely populated and economically relevant area with complex orography including mountain ranges, islands, and straits. In combination with pressure gradients, this creates many mesoscale wind systems that cause, e.g., wind gusts and wildfire risk in the Mediterranean. This article reviews the recent state of the science of several mesoscale winds in the Mediterranean and associated processes. Previous work, including case studies on several time ranges and resolutions, as well as studies on these winds under future climate conditions, is discussed. Simulations with grid spacings of 25 to 50 km can reproduce winds driven by large-scale pressure patterns such as Mistral, Tramontane, and Etesians. However, these simulations struggle with the correct representation of winds channeled in straits and mountain gaps and around islands. Grid spacings of 1–3 km are certainly necessary to resolve these small-scale features. The smaller grid spacings are widely used in case studies, but not yet in simulations over large areas and long periods, which also could help to understand the interaction between small-scale phenomena in separate locations. Furthermore, by far not all Mediterranean straits, islands, and mountain gaps were studied in-depth and many interesting Mediterranean small-scale winds still need to be studied.
Africa's protected areas (PAs) are the last stronghold of the continent's unique biodiversity, but they appear increasingly threatened by climate change, substantial human population growth, and land-use change. Conservation planning is challenged by uncertainty about how strongly and where these drivers will interact over the next few decades. We investigated the combined future impacts of climate-driven vegetation changes inside African PAs and human population densities and land use in their surroundings for 2 scenarios until the end of the 21st century. We used the following 2 combinations of the shared socioeconomic pathways (SSPs) and representative greenhouse gas concentration pathways (RCPs): the “middle-of-the-road” scenario SSP2–RCP4.5 and the resource-intensive “fossil-fueled development” scenario SSP5–RCP8.5. Climate change impacts on tree cover and biome type (i.e., desert, grassland, savanna, and forest) were simulated with the adaptive dynamic global vegetation model (aDGVM). Under both scenarios, most PAs were adversely affected by at least 1 of the drivers, but the co-occurrence of drivers was largely region and scenario specific. The aDGVM projections suggest considerable climate-driven tree cover increases in PAs in today's grasslands and savannas. For PAs in West Africa, the analyses revealed climate-driven vegetation changes combined with hotspots of high future population and land-use pressure. Except for many PAs in North Africa, future decreases in population and land-use pressures were rare. At the continental scale, SSP5–RCP8.5 led to higher climate-driven changes in tree cover and higher land-use pressure, whereas SSP2–RCP4.5 was characterized by higher future population pressure. Both SSP–RCP scenarios implied increasing challenges for conserving Africa's biodiversity in PAs. Our findings underline the importance of developing and implementing region-specific conservation responses. Strong mitigation of future climate change and equitable development scenarios would reduce ecosystem impacts and sustain the effectiveness of conservation in Africa.
New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1,2,3,4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3–H2SO4–NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.
The Altenberg–Teplice Volcanic Complex (ATVC) is a large ~ NNW–SSE trending volcano-plutonic system in the southern part of the Eastern Erzgebirge (northern Bohemian Massif, south-eastern Germany and northern Czech Republic). This study presents high precision U–Pb CA-ID-TIMS zircon ages for the pre-caldera volcano-sedimentary Schönfeld–Altenberg Complex and various rocks of the caldera stage: the Teplice rhyolite, the microgranite ring dyke, and the Sayda-Berggießhübel dyke swarm. These data revealed a prolonged time gap of ca. 7–8 Myr between the pre-caldera stage (Schönfeld–Altenberg Complex) and the climactic caldera stage. The volcanic rocks of the Schönfeld–Altenberg Complex represent the earliest volcanic activity in the Erzgebirge and central Europe at ca. 322 Ma. The subsequent Teplice rhyolite was formed during a relatively short time interval of only 1–2 Myr (314–313 Ma). During the same time interval (314–313 Ma), the microgranite ring dyke intruded at the rim of the caldera structure. In addition, one dyke of the Sayda-Berggiesshübel dyke swarm was dated at ca. 314 Ma, while another yielded a younger age (ca. 311 Ma). These data confirm the close genetic and temporal relationship of the Teplice rhyolite, the microgranite ring dyke, and (at least part of) the Sayda-Berggießhübel dyke swarm. Remarkably, the caldera formation in the south of the Eastern Erzgebirge (caldera stage of ATVC: 314–313 Ma) and that in the north (Tharandt Forest caldera: 314–312 Ma) occurred during the same time. These data document a large ~ 60 km NNW–SSE trending magmatic system in the whole Eastern Erzgebirge. For the first time, Hf-O-isotope zircon data was acquired on the ring dyke from the ATVC rocks to better characterize its possible sources. The homogeneous Hf-O-isotope zircon data from the microgranite ring dyke require preceding homogenization of basement rocks. Some small-scale melts that were produced during Variscan amphibolite-facies metamorphism show similar Hf-O-isotope characteristics and can therefore be considered as the most probable source for the microgranite ring dyke melt. In addition, a second source with low oxygen isotope ratios (e.g. basic rocks) probably contributed to the melt and possibly triggered the climactic eruption of the Teplice rhyolite as well as the crystal-rich intrusion of the ring dyke.
Frankfurt ist Knotenpunkt globaler Güter-, Finanz-, Wissens- und Migrationsbewegungen. Die Arbeitsmärkte und -verhältnisse in der Stadt sind Ausdruck einer globalen Verwobenheit, die diskursiv oft mit dem Label der ›Global City‹ markiert wird. In einer Zeit, in der Arbeit als Feld der Produktion und Reproduktion weitreichenden Transformationsprozessen ausgesetzt ist, in der das sogenannte Normalarbeitsverhältnis zunehmend erodiert, in der Arbeitsverhältnisse oft räumlich, sozial und zeitlich entgrenzt und flexibilisiert sind und in der gut bezahlte Jobs und schlecht- bezahlte, teils prekarisierte Formen der Beschäftigung koexistieren – zum Teil im gleichen Betrieb –, muss es Aufgabe wirtschaftsgeographischer Forschung sein, die Lebenswelten von Arbeitenden in einer räumlichen Perspektive zu beleuchten. Genau dies will der vorliegende Band tun. Er versammelt engagierte, theoretisch gesättigte und empirisch geerdete Beiträge von Studierenden des Instituts für Humangeographie, die einen kritischen Blick auf die Formen, Praktiken, Beziehungen und gesellschaftliche Einbettung von Arbeit in unterschiedlichen Branchen in der ›Global City‹ Frankfurt werfen.
Wohnungs‐ und Büroimmobilienmärkte unter Stress: Deregulierung, Privatisierung und Ökonomisierung
(2009)
The modern precipitation balance in southeastern (SE) Brazil is regulated by the South American summer Monsoon and threatened by global climate change. On glacial-interglacial timescales, monsoon intensity was strongly controlled by precession-forced changes in insolation. To date, relatively little is known about the spatiotemporal distribution of tropical precipitation in SE Brazil and the resulting variability of fluvial discharge on glacial-interglacial timescales. Here, we present X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) from the Doce River basin. This area was sensitive to changes in monsoonal precipitation intensity due to its proximity to the South Atlantic Convergence Zone. The data, obtained from a marine sediment core (M125-55–7) close to the Doce river mouth (20°S), show pronounced changes in the Doce River suspension load’s mineralogical composition on glacial-interglacial and precessional timescales. While the ratio of silicates to carbonates displays precession-paced changes, the mineralogical composition of the carbonate-free fraction discriminates between two assemblages which strongly vary between glacial and interglacial time scales, with precession-forced variability only visible in MIS 5. The first assemblage, dominated by high contents of kaolinite and gibbsite, indicates intensified lowland erosion of mature tropical soils. The second one, characterized by higher contents of the well-ordered illite, quartz and albite, points to intensified erosion of immature soils in the upper Doce Basin. High kaolinite contents in the silicate fraction prevailed in late MIS 6 and indicate pronounced lowland soil erosion along a steepened topographic gradient. The illite-rich mineral assemblage was more abundant in MIS 5, particularly during times of high austral summer insolation, indicating strong monsoonal rainfall and intense physical erosion in the upper catchment. When the summer monsoon weakened in times of lower insolation, the mineral assemblage was dominated by kaolinite again, indicative of lower precipitation and runoff in the upper catchment and dominant lowland erosion.
Seasonal forecasting systems still have difficulties predicting temperature over continental regions, while their performance is better over some maritime regions. On the other hand, the land surface is a substantial source of (sub-)seasonal predictability. A crucial land surface component in focus here is the snow cover, which stores water and modulates the surface radiation balance. This paper’s goal is to attribute snow cover seasonal forecasting biases and lack of skill to either initialization or parameterization errors. For this purpose, we compare the snow representation in five seasonal forecasting systems (from DWD, ECMWF, Météo-France, CMCC, and ECCC) and their performances in predicting snow and 2-m temperature over a Siberian region against ERA5 reanalysis and station data. Although all systems use similar atmospheric and land initialization approaches and data, their snow and temperature biases differ in sign and amplitude. Too-large initial snow biases persist over the forecast period, delaying and prolonging the melting phase. The simplest snow scheme (used in DWD’s system) shows too-early and fast melting in spring. However, systems including multi-layer snow schemes (Météo-France and CMCC) do not necessarily perform better. Both initialization and parameterization are causes of snow biases, but, depending on the system, one can be more dominant.
We present the results of a multi-disciplinary investigation on a deciduous human tooth (Pradis 1), recently recovered from the Epigravettian layers of the Grotte di Pradis archaeological site (Northeastern Italian Prealps). Pradis 1 is an exfoliated deciduous molar (Rdm2), lost during life by an 11–12-year-old child. A direct radiocarbon date provided an age of 13,088–12,897 cal BP (95% probability, IntCal20). Amelogenin peptides extracted from tooth enamel and analysed through LC–MS/MS indicate that Pradis 1 likely belonged to a male. Time-resolved 87Sr/86Sr analyses by laser ablation mass spectrometry (LA-MC-ICPMS), combined with dental histology, were able to resolve his movements during the first year of life (i.e. the enamel mineralization interval). Specifically, the Sr isotope ratio of the tooth enamel differs from the local baseline value, suggesting that the child likely spent his first year of life far from Grotte di Pradis. Sr isotopes are also suggestive of a cyclical/seasonal mobility pattern exploited by the Epigravettian human group. The exploitation of Grotte di Pradis on a seasonal, i.e. summer, basis is also indicated by the faunal spectra. Indeed, the nearly 100% occurrence of marmot remains in the entire archaeozoological collection indicates the use of Pradis as a specialized marmot hunting or butchering site. This work represents the first direct assessment of sub-annual movements observed in an Epigravettian hunter-gatherer group from Northern Italy.
In recent years, many European cities have developed strategies to improve the quality of urban life by reducing car traffic and increasing the attractiveness of alternative modes and the built environment for residents. Frequently, at least in German cities, improvements to the cycling infrastructures play a key role in this transformation of urban spaces. One of those transformative interventions took place in 2020 in Frankfurt am Main (Germany). The city redesigned an arterial road close to the city centre, the Friedberger Landstrasse, by converting two car lanes to bicycle lanes. It is the aim of this study to analyse the effects of this change on the quality of urban life of its residents using a quantitative before-and-after study. The results demonstrate the expected improvements in the perceived quality of urban life for residents after the intervention. A more detailed analysis, however, shows that the residents’ perceptions vary according to their own mode use on the Friedberger Landstrasse and other sociodemographic characteristics. Thus, better cycling infrastructure does not only improve conditions for cyclists, but also contributes to a higher quality of urban life for residents and, therefore, improves the liveability of a city in two ways. We conclude that local transport policies are not only relevant for a modal shift, but also for the quality of urban life and, thus, related urban development strategies.
This article aims to show that a perspective that understands urban protests as a conflict between two or more interest-driven actors falls short. For a more comprehensive analysis, the complex fabric of multiple power-laden discourses, processes, networks and spatial conditions in which such conflicts are embedded must be taken into account. To this end, this article adopts an assemblage perspective. Taking the protests around the inner-city marina Port Vell in Barcelona as an example, this perspective is used to elaborate the various spatial conditions that shape this conflict.
We present the first oxidation state measurements for the subcontinental lithospheric mantle (SCLM) beneath the Rae craton, northern Canada, one of the largest components of the Canadian shield. In combination with major and trace element compositions for garnet and clinopyroxene, we assess the relationship between oxidation state and metasomatic overprinting. The sample suite comprises peridotite xenoliths from the central part (Pelly Bay) and the craton margin (Somerset Island) providing insights into lateral and vertical variations in lithospheric character. Our suite contains spinel, garnet-spinel and garnet peridotites, with most samples originating from 100 to 140 km depth. Within this narrow depth range we observe strong chemical gradients, including variations in oxygen fugacity (ƒO2) of over 4 log units. Both Pelly Bay and Somerset Island peridotites reveal a change in metasomatic type with depth. Observed geochemical systematics and textural evidence support the notion that Rae SCLM developed through amalgamation of different local domains, establishing chemical gradients from the start. These gradients were subsequently modified by migrating melts that drove further development of different types of metasomatic overprinting and variable oxidation at a range of length scales. This oxidation already apparent at ~ 100 km depth could have locally destabilised any pre-existing diamond or graphite.
Eisbildende Prozesse sind für die Wolkenbildung von großer Bedeutung und haben erhebliche Auswirkungen auf das Wetter und Klima der Erde, indem sie den Strahlungsantrieb und die Niederschlagsbildung beeinflussen. In den mittleren Breiten entsteht der meiste Niederschlag in sogenannten Mischphasenwolken (MPC), welche sowohl aus unterkühlten Wolkentröpfchen als auch aus Eiskristallen bestehen. Bei Temperaturen zwischen 0°C und -38°C erfolgt die Bildung von Eiskristallen in MPC in Gegenwart von Aerosolpartikeln, die als sogenannte Eiskeime (INP) die Fähigkeit besitzen, auf ihrer Oberfläche Eis zu nukleieren. Trotz der großen wissenschaftlichen Fortschritte in den letzten Jahrzehnten, weist der heterogene Eisbildungsprozess, als einer der wichtigsten in der Atmosphäre auftretenden Aerosol-Wolken-Wechselwirkungsprozesse, immer noch große Unsicherheiten auf. Um zukünftige Klimavorhersagen und -projektionen in Modellen besser abbilden zu können, ist es somit notwendig den Wissensgrad der räumlichen und zeitlichen Heterogenität von INP in Bezug auf Herkunft, Anzahl und Zusammensetzung zu erhöhen. Im Zentrum dieser Arbeit steht der Eiskeimzähler FINCH (Fast Ice Nucleus Chamber), der für Labor- und Feldexperimente von der Johann Wolfgang Goethe-Universität in Frankfurt am Main entwickelt wurde. Durch das Mischen des Probenstroms mit einem warm-feuchten und einem kalten-trockenen Luftstrom wird eine Übersättigung in der in-situ Eiskammer erreicht, die benötigt wird, eisbildende Partikel zu aktivieren. Die aktivierten Partikel können beim Durchströmen der Kammer zu Wassertropfen oder Eiskristallen anwachsen. Am Ausgang der Kammer wird die Anzahl und Größe der Partikel durch die FINCH-Optik erfasst. Als grundlegender Schritt und aufbauend auf den Charakterisierungsmessungen von Frank (2017) wurden in der vorliegenden Arbeit die Leistung, die Zuverlässigkeit sowie die Reproduzierbarkeit von FINCH in Validierungsexperimenten im Labor überprüft. Im Zuge dessen wurden heterogene Gefrierexperimente mit definierten Referenzaerosolproben (bspw. K-Feldspat) bei wasserübersättigten Bedingungen und verschiedenen Gefriertemperaturen durchgeführt. Für den Großteil der erzielten Resultate konnte eine zufriedenstellende Übereinstimmung mit Literaturwerten von anderen INP-Messinstrumenten aus der ganzen Welt erzielt werden. Es zeigte sich, dass die Leistungsfähigkeit von FINCH messtechnische Limitationen für Messexperimente bei Temperaturen >-10°C und <-30°C aufweist, was eine Einschränkung des Messbereichs bedeutet. Hinsichtlich der Quantifizierung des Unsicherheitsbereiches des Messgerätes in Bezug auf Temperatur und relativer Feuchte bedarf es im Nachgang an dieser Arbeit weiterer Charakterisierungsmessungen. Im Rahmen der Ice Nuclei Research Unit (INUIT) Forschergruppe wurde FINCH mit einem gepumpten Gegenstrom-Impaktor PCVI und dem online Einzelpartikel-Massenspektrometer ALABAMA gekoppelt. Diese spezielle Messmethodik dient zur chemischen und mikrophysikalischen Charakterisierung der INP und der Eispartikelresiduen (IPR). Der Fokus lag zunächst darauf die Funktionalität des gekoppelten Messsystems im Labor zu überprüfen. Ausführliche Charakterisierungsmessungen zeigten unter eisübersättigten und unterkühlten Bedingungen, dass das Prinzip der Trennung der INP von nicht-aktivierten Aerosolen und unterkühlten Tropfen hinter FINCH durch den PCVI funktioniert. Ebenso konnten erste quantitative Aussagen zur chemischen Zusammensetzung der IPR getroffen werden. Es zeigte sich, dass bei den Aktivierungsexperimenten ein geringer Anteil an Partikeltypen metallischer Art von ALABAMA detektiert wurden, der nicht dem untersuchten Aerosoltyp zugeordnet werden konnte. Der Ursprung dieser Kontamination konnte im Rahmen dieser Arbeit nicht abschließend geklärt werden und bedarf weiterer Validierungsmessungen im Labor. Atmosphärische Eiskeimkonzentrationen wurden im Rahmen von Feldmesskampagnen an der Hochalpinen Forschungsstation Jungfraujoch (JFJ) in den Schweizer Alpen und am Campus Riedberg der Johann Wolfgang Goethe-Universität in Frankfurt am Main untersucht. Hier konnten erste Erfahrungen mit Außenluftmessungen bezüglich der Leistungsfähigkeit und der Nachweisgrenze (LOD) des Messgerätes gesammelt werden. Durch den Einfluss der freien Troposphäre am JFJ waren die Messungen hauptsächlich von aerosolpartikelarmer Luft mit einer geringen Anzahl von Eiskeimen geprägt, so dass sich die gemessenen INP-Konzentrationen oftmals unter die Nachweisgrenze von FINCH fielen. Unter Einsatz eines Aerosolkonzentrators konnte die Detektionseffizienz verbessert und das LOD herabgesetzt werden. Am JFJ wurden die INP im Mittel bei einer Temperatur von -23°C und einem Wassersättigungsverhältnis von 107% beprobt. Die mediane (mittlere) INP-Konzentration inklusive LOD lag bei 2,1 (3,3) sL-1 und oberhalb des LOD bei 3,1 (4,5) sL-1. Ein Vergleich mit den Messungen am Campus Riedberg unter annähernd gleichen Bedingungen resultiert in ähnlichen Konzentrationen.
Following votes in the Coniacian Working Group, the Cretaceous Subcommission and the International Commission on Stratigraphy, on May 1st, 2021, the International Union of Geological Sciences voted unanimously to ratify the Global Stratotype Section and Point (GSSP) proposal for the base of the Coniacian Stage of the Upper Cretaceous Series and Cretaceous System. The lower boundary of the Coniacian Stage is placed at the base of Bed 46 of the Salzgitter-Salder section in northern Germany. The boundary is defined by the first appearance of the inoceramid bivalve species Cremnoceramus deformis erectus (Meek) and complemented by the Navigation carbon isotope event. Additional data include the bivalve genus Didymotis, foraminifera, ammonite, nannofossil and organic-walled dinoflagellate cyst events. Three auxiliary sections (Słupia Nadbrzeżna, central Poland; Střeleč, Czech Republic; El Rosario, NE Mexico) supplement the details of the boundary record in various facies, and in differing geographic and biogeographic contexts.
The climate system is one of the classical examples of a complex dynamical system consisting of interacting sub-systems through mass, momentum, and energy exchange across various spatial and temporal scales. This thesis aims to detect and quantify sub-component interactions from an information exchange (IE) perspective. For this purpose, IE estimators derived from information theory are explored and applied to the available climate data obtained from observations, reanalysis, global and regional climate models. Specifically, this thesis investigates the usefulness of information theory methods for process-oriented climate model evaluation.
Firstly, methods derived from the concepts of information theory such as transfer entropy and information flow along with their linear and non-linear estimation techniques are initially tested and applied to idealized two-dimensional dynamical systems. The results revealed an expected direction and magnitude of IE providing insights into underlying dynamics. However, as expected the linear estimators are robust for linear systems but fail for non-linear systems. Though the non-linear estimators (kernel and kraskov) showed expected results for all the idealized systems, their free tuning parameters are to be tested for consistent results. Moreover, these methods are sensitive to the available time series length.
A real world example case study involving the dynamics between the Indian and Pacific oceans revealed a physically consistent bi-directional IE. However, unexpected IE was detected in the example of North Atlantic and European air temperatures indicating hidden drivers. Though IE provides insights into system dynamics, the availability of time series length and the system at hand must be carefully taken into account before inferring any possible interpretations of the results.
Quantifying the IE from El-Ni\~{n}o southern oscillation (ENSO) and Indian Ocean Dipole (IOD) to the Indian Summer Monsoon Rainfall (ISMR) with the observational and reanalysis data sets revealed that both ENSO and IOD are synergistic predictors for the inter-annual variability of the ISMR over central India i.e., the monsoon core region. Though the investigated three Global Climate Models (GCM) could not reveal the underlying IE dynamics of ENSO, IOD, and ISMR, a Regional Climate Model (RCM) simulation downscaling one of the GCMs with realistic large scale signals across the lateral boundaries showed good agreement with the observations.
Evaluating a coupled regional climate modeling system driven by two different global data sets with IE estimators revealed significant differences between the process chains linking the north-west Mediterranean sea surface temperatures, evaporation, wind speed, and the Vb-cyclone induced precipitation over Danube, Odra, and Elbe catchments in the historical period (1951-2005). Detailed investigation revealed that the north-west Mediterranean Sea in the coupled regional simulation driven by ERA-20C reanalysis corresponded to the Vb-cyclone precipitation over the three catchments while no such correspondence is noted in the EC-EARTH driven simulation. This discrepancy is attributed to the inheritance of the simulation biases from GCM into the RCM. In the future period (1965-2099), no significant changes in the processes are noted from the simulation.
Overall, this thesis used IE estimators in investigating the underlying dynamics of climate system and climate models. The estimators proved useful in providing insights into climate system dynamics assisting in a process based climate model evaluation.
Carbon is an element that controls planetary habitability, and is fundamental for life on Earth. Its behaviour has important consequences for the global climate system, the origin and evolution of life on Earth. While the biosphere and atmosphere’s carbon cycle only accounts for less than 1% of the global carbon budget, hidden reservoirs of deep carbon in the Earth’s interior comprise the predominant storage of carbon on the planet. At the Earth’s surface, 60-70 % of carbon is hosted by carbonate minerals, which are then transported to the Earth’s interior, mainly in the form of sediments, by subduction of the oceanic lithosphere. Subducting plates are subjected to decarbonation, dehydration, and melting with CO2 release via supra-subduction volcanism. Nevertheless, part of the subducted carbonates’ may survive and be further transported to the deep mantle. Direct evidence of the existence of carbonates in the Earth’s interior, possibly reaching down to the lower mantle, comes from the finding of syngenetic inclusions of carbonates in diamonds and mantle xenoliths. The presence of carbonates in the deep Earth has a critical effect on the physical properties of the mantle. Melting and chemical speciation of the mantle are strongly affected by the form of C and carbonate stability. Therefore, the study of the stability and physical properties of carbonates at high pressures and temperatures is fundamental, because understanding the processes involved in the deep carbon cycle helps to improve our picture of the whole mantle.
The systematic characterization of the elastic properties of carbonates as a function of their structure and chemical composition is of great importance because it may allow to identify their presence and distribution by seismology. Inverting seismic observations to successfully constrain the chemical composition and mineralogy of the Earth’s interior requires knowledge of the physical properties of all possible Earth’s materials at pressures and temperatures applicable to the Earth’s interior. Up to now, a multitude of studies has focused on the construction of phase diagrams and structural transitions by means of X-ray diffraction and vibrational spectroscopy experiments.
Few studies are available on the complete elastic tensor of carbonates, however most of the datasets are not accompanied by an accurate characterization of the samples, which are often solid solutions and the exact chemical composition, density or the details about the experimental methods used are not presented. The aim of this thesis is to study the effect of chemical composition on the elastic properties of carbonates, providing a reliable dataset on the elasticity of the main carbonates. In particular, the elastic properties of crystalline aragonite, CaCO3, and Fe-dolomite, (Ca, Mg, Fe)(CO3)2, with different compositions were studied by Brillouin spectroscopy at ambient conditions. Brillouin spectroscopy was also used to investigate the elastic behaviour of amorphous calcium carbonate samples with different water contents (up to 18 wt%) at high pressures, up to 20 GPa.
Furthermore, the importance of cationic substitution on the structure and high pressure behaviour of carbonates was investigated by studying a synthetic CaCO3-SrCO3 solid solution at ambient conditions and at high pressures, up to 10 GPa, by single crystal X-ray diffraction. Finally, the study of the effect of composition on the elastic properties of families of isostructural solids was also extended to a different class of materials, the metal guanidinium formates. The elasticity of a family of perovskite metal organic frameworks, metal guanidinium formates C(NH2)3MII(HCOO)3, with MII =Mn, Zn, Cu, Co, Cd and Ca was investigated by combining Brillouin spectroscopy, resonant ultrasound spectroscopy, density functional theory and thermal diffuse scattering analysis.
Extreme convective precipitation events are among the most severe hazards in central Europe and are expected to intensify under global warming. However, the degree of intensification and the underlying processes are still uncertain. In this thesis, recent advances in continuous, radar-based precipitation monitoring and convection-permitting climate modeling are used to investigate Lagrangian properties of convective rain cells such as precipitation intensity, cell area, and precipitation sum and their relationship to large-scale, environmental conditions.
Firstly, convective precipitation objects are tracked in a gauge-adjusted radar-data set and the properties of these cells are related to large-scale environmental variables to investigate the observed super-Clausius-Clapeyron (CC) scaling of convective extreme precipitation. The Lagrangian precipitation sum of convective cells increases with dew point temperature at rates well above the CC-rate with increasing rates for higher dew point temperatures. These varying, high rates are caused by a covarying increase of CAPE with dew point temperature as well as the effect of high vertical wind shear causing an increase in cell area and thus precipitation sum. At the same time, cells move faster at high vertical wind shear so that Eulerian scaling rates are lower than Lagrangian but still above the CC-rate. The results show that wind shear and static instability need to be taken into account when transferring precipitation scaling under current climate conditions to future conditions. Secondly, the representation of convective cell properties in the convection-permitting climate model COSMO-CLM is evaluated. The model can simulate the observed frequency distributions of cell properties such as lifetime, area, mean and maximum intensity, and precipitation sum. The increase of area and intensity with lifetime is also well captured despite an underestimation of the intensity of the most severe cells. Furthermore, the model can represent the temperature scaling of intensity, area, and precipitation sum but fails to simulate the observed increase of lifetime. Thus, the model is suitable to study climatologies of convective storms in Germany. Thirdly, two COSMO-CLM projections at the end of the century under emission scenario RCP8.5 were investigated. While the number of convective cells and their lifetime remain approximately constant compared to present conditions, intensity and area increase strongly. The relative increase of intensity and area is largest for the highest percentiles meaning that extreme events intensify the most. The characteristic afternoon maximum of convective precipitation is damped, and shifted to later times of day which leads to an increase of nighttime precipitation in the future. Scaling rates of cell properties with dew point temperature are nearly identical in present and future in the simulation driven by the EC-Earth model which means that the upper limit of cell properties like intensity, area, and precipitation sum could be predicted from near-surface dew point temperature. However, this result could not be reproduced by the simulation driven by MIROC5 and needs further investigation.
Diamant hat besondere physikalische und optische Eigenschaften sowie eine starke Resistenz gegenüber Strahlenschädigung. Diese Eigenschaften ermöglichen eine vielfältige Anwendung von Diamant in Wissenschaft und Technik, wie zum Beispiel als Sensormaterial in Strahlungsdetektoren.
Kubisches Zirconiumdioxid (ZrO2) wird aufgrund seiner mechanisch und optisch ähnlichen Eigenschaften unter anderem an Stelle von Diamant eingesetzt. Es ist ebenfalls ein geeignetes Material für viele technische Anwendungen und wird durch seine Strahlenresistenz in Strahlungsumgebungen verwendet. Da beide Materialien in diesem Anwendungsbereich hoher energetischer Strahlung ausgesetzt sind, sind Reaktionen auf die Bestrahlung wie etwa strukturelle Veränderungen oder die Änderungen von Materialeigenschaften von großem Interesse.
In der vorliegenden Arbeit wurde die Morphologie, Struktur und physikalischen Eigenschaften von Diamant und Yttriumoxid-stabilisiertem kubischem ZrO2 nach der Bestrahlung mit 14 MeV Au-Ionen und 1.6 GeV Au-Ionen untersucht. Die durch die Bestrahlung verursachten Veränderungen der Oberflächen und der bestrahlten Volumina wurden mit diversen komplementären analytischen Methoden charakterisiert, bewertet und für die verschiedenen Materialien und Ionenenergien verglichen.
Mittels Röntgenfluoreszenzmessungen wurde die Verteilung und Menge an implantiertem Au semi-quantitativ ermittelt. Die Oberflächen der Proben wurden mit optischer Mikroskopie, Rasterkraftmikroskopie, Rasterelektronenmikroskopie, Röntgenreflektometrie und Elektronenrückstreubeugung untersucht. Strukturelle Veränderungen wurden mit Raman-Spektroskopie analysiert. Der elektrische Widerstand, die Dichte, die Härte sowie das Ätzverhalten der bestrahlten Proben wurden ermittelt und geben Auskunft über die Änderung physikalischer Eigenschaften der Materialien.
Diamant und kubisches ZrO2 reagieren sehr unterschiedlich auf die Bestrahlung mit Au-Ionen gleicher Energien und Fluenzen. Die Diamantproben zeigen nach der Bestrahlung mit 14 MeV Au-Ionen deutliche Veränderungen und Schädigungen der Oberfläche sowie des bestrahlten Volumens. Es wird eine Änderung der Struktur, der Dichte, der Härte, des elektrischen Widerstands sowie des Ätzverhaltens der Proben beobachtet, was auf die Amorphisierung von Diamant zurückgeführt wird. Kubisches ZrO2 ist deutlich strahlungsresistenter gegenüber der Bestrahlung mit 14 MeV Au-Ionen. Es werden keine signifikanten strukturellen Änderungen im getesteten Fluenzbereich beobachtet.
Die mit 1.6 GeV Au-Ionen bestrahlten Diamanten zeigen nur geringe Schädigungen und keine deutliche Änderung der Struktur oder der physikalischen Eigenschaften. Die kubischen ZrO2 Proben sind als Folge der Bestrahlung mit 1.6 GeV Au-Ionen zerbrochen, was auf hohe interne Spannung durch Defektbildung zurückgeführt wird.
Im Sinne einer nachhaltigen Stadt- und Verkehrsentwicklung verspricht das Konzept autoreduzierter Quartiere, die Autonutzung und den Autobesitz der Bewohnenden zu verringern sowie deren autounabhängige Mobilität zu fördern. Der Forschungsstand zeigt indes, dass nicht automatisch davon auszugehen ist, dass die gelebte Praktik der Planungsvision entspricht, da die Mobilität nicht nur von oben herab geplant, sondern auch von unten, also den Bewohnenden selbst sowie den Mobilitätskontexten, geprägt ist.
Anhand zweier autoreduziert entwickelter Quartiere in Darmstadt verfolgt die Arbeit deshalb das Ziel, mittels eines planungskritischen Ansatzes zunächst die Narrative autoreduzierter Quartiere zu identifizieren, um die Planungsvision zu ergründen. Des Weiteren werden mithilfe eines biographisch inspirierten, praxistheoretischen Ansatzes die mobilitätsbezogenen Praktiken autoreduzierter Quartiere sowie etwaige Veränderungen dieser nach dem Wohnortwechsel analysiert, um das Verständnis der Alltagsmobilität und deren Wandel zu verbessern sowie Potenziale und Grenzen der Umsetzung solcher Quartierskonzepte zu ermitteln. Abschließend soll der Vergleich beider Perspektiven dazu beitragen, besser zu verstehen, was eine nachhaltige Stadt- und Verkehrsgestaltung sowie eine autounabhängige Mobilität und ein autofreies Leben unterstützt bzw. behindert.
Zur Identifikation der Narrative wurden Expert*inneninterviews mit verschiedenen Personen durchgeführt, die am Planungs- und Umsetzungsprozess beider Quartiere beteiligt waren. Die Ergebnisse legen nahe, dass die Entwicklung autoreduzierter Quartiere (i) bewusst in die Nachhaltigkeitsdebatte eingebettet und (ii) von Machtverhältnissen geprägt ist sowie (iii) normativen Indikatoren folgt und (iv) deren Planungsideale im Kontrast zur gelebten Realität stehen können.
Zur Analyse der mobilitätsbezogenen Praktiken sowie der Veränderungen derselben wurden Bewohnende qualitativ interviewt. Dabei zeigt sich, dass der materielle Kontext eines autoreduzierten Quartiers sowie die persönlich-zeitlichen und soziokulturellen Kontexte der Mobilitätspraktiken die Autounabhängigkeit der Bewohnenden stabilisieren und fördern. Behindert wird sie dagegen vom materiellen Kontext außerhalb der Quartiere, der Verwobenheit des Autofahrens mit anderen Alltagspraktiken sowie der affektiven Zufriedenheit mit der Autonutzung und dem Autobesitz.
Aus dem Vergleich beider Erhebungen und damit der Gegenüberstellung der Planungsvision mit der gelebten Praktik lässt sich schlussfolgern, dass trotz feststellbarer Unterschiede die Realität im autoreduzierten Quartier größtenteils dem Ideal einer autounabhängigen Mobilität entspricht. Dagegen erweisen sich ein autofreies Leben und die Parkrestriktionen weiterhin als kontroversere Themen. Schließlich offenbart die Arbeit sowohl Veränderungen in der Mobilitätsgestaltung von oben als auch in der Mobilitätspraktik von unten, gleichzeitig aber auch persistente automobile Abhängigkeiten, weshalb sie im Sinne der Verkehrs- und Mobilitätswende einen kontinuierlichen materiellen und immateriellen Wandel fordert.
The future of work has become a pressing matter of concern: Researchers, business consultancies, and industrial companies are intensively studying how new work models could be best implemented to increase workplace flexibility and creativity. In particular, the agile model has become one of the “must-have” elements for re-organizing work practices, especially for technology development work. However, the implementation of agile work often comes together with strong presumptions: it is regarded as an inevitable tool that can be universally integrated into different workplaces while having the same outcome of flexibility, transparency, and flattened hierarchies everywhere. This paper challenges such essentializing assumptions by turning agile work into a “matter of care.” We argue that care work occurs in contexts other than feminized reproductive work, namely, technology development. Drawing on concepts from feminist Science and Technology Studies and ethnographic research at agile technology development workplaces in Germany and Kenya, we examine what work it takes to actually keep up with the imperative of agile work. The analysis brings the often invisibilized care practices of human and nonhuman actors to the fore that are necessary to enact and stabilize the agile promises of flexibilization, co-working, and rapid prototyping. Revealing the caring sociotechnical relationships that are vital for working agile, we discuss the emergence of power asymmetries characterized by hierarchies of skills that are differently acknowledged in the daily work of technology development. The paper ends by speculating on the emancipatory potential of a care perspective, by which we seek to inspire careful Emancipatory Technology Studies.
Geochemical investigations on biogenic carbonates are commonly conducted to reconstruct the environmental conditions of the past. However, different carbonate producers incorporate elements to varying degrees, due to biological vital effects. Detecting and quantifying these effects is crucial to produce reliable reconstructions. These paleoreconstructions are of great importance to evaluate the consequences of our recent climate change and identify control mechanisms on the distribution of endangered species such as Desmophyllum pertusum. In chapter three we tested Mg/Ca, Sr/Ca and Na/Ca ratios on this species, among other coldwater scleractinians, to test if they provide reliable proxy information. The results reveal no apparent control of Mg/Ca or Sr/Ca ratios through seawater temperature, salinity or pH. Na/Ca ratios appear to be partly controlled by the seawater temperature, which is also true for other aragonitic organisms such as warm-water corals and the bivalve Mytilus edulis. However, a large variability complicates possible reconstructions by means of Na/Ca. In addition, we explore different models to explain the apparent temperature effect on Na/Ca ratios based on temperature sensitive Na and Ca pumping enzymes.
The bivalve Acesta excavata is commonly found in cold-water coral reefs among the North Atlantic, together with D. pertusum. Multiple linear regression analysis, presented in chapter four, indicates that up to 79% of the elemental variability in Mg/Ca, Sr/Ca and Na/Ca is explainable with temperature and salinity as independent predictor variables. Vital effects, for instance growth rate effects, are evident and make paleoreconstructions not feasible. Furthermore, organic material embedded in the shell, as well as possible stress effects can drastically change the elemental composition. Removal of these organic matrices from bulk samples for LA-ICP-MS (laser ablation inductively coupled mass spectrometer) measurements by means of oxidative cleaning is not possible, but Na/Ca ratios decrease after this cleaning. This is presumably an effect of leaching and not caused by the removal of organic matrices.
Interesting biogeochemical relations were found in the parasitic foraminifera H. sarcophaga. We report Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca ratios measured in H. sarcophaga from two different host species (A. excavata and D. pertusum) in chapter five. Sr/Ca ratios are significantly higher in foraminifera that lived on D. pertusum. This could indicate that dissolved host material is utilized in shell calcification of H. sarcophaga, given the naturally higher strontium concentration in the aragonite of D. pertusum. Mn/Ca ratios are highest in foraminifera that lived on A. excavata but did not fully penetrate the host’s shell. Most likely, this represents a juvenile stadium of the foraminifera during which it feeds on the organic
periostracum of the bivalve, which is enriched in Mn and Fe. The isotopic compositions are similarly affected, both δ18O and δ13C values are significantly lower in foraminifera that lived 23on D. pertusum compared to specimen that lived on A. excavata. Again, this might represent the uptake of dissolved host material or different pH regimes in the calcifying fluid of the hosts (bivalve < 8, coral > 8) that control the extent of hydration/hydroxylation reactions. Temperature reconstructions are possible using stable oxygen isotopes on this foraminifera species; however, the results are only reliable if the foraminifera lived on A. excavata. Samples of H. sarcophaga from D. pertusum would lead to overestimations of the seawater temperature due to the lower δ18O values.
Apart from biological vital effects, storage and preservation methods can significantly change the geochemical composition of different marine biogenic carbonates. In chapter six this is presented on the example of ethanol preservation, a common technique to allow extended storage of biogenic samples. The investigation reveals a significant decrease of Mg/Ca and Na/Ca ratios even after only 45 days storage in ultrapure ethanol. Sr/Ca ratios on the other hand are not influenced.
Besides temperature, salinity and pH further environmental parameters are important such as nutrient availability, especially for the distribution of cold-water corals. In chapter seven we extend the investigations on A. excavata by including the elemental ratios Ba/Ca, Mn/Ca and P/Ca. We expected P/Ca to be helpful in the otherwise difficult process of dentifying growth increments. Based on our observations we had to refute this theory. P/Ca ratios are not systematically enriched in the vicinity of growth lines. Instead, we found a regular sequence of peaks of Ba/Ca, P/Ca and Mn/Ca. This sequence as well as the peaks in general are potentially caused by equential blooms of different algae, diatoms and other planktonic organisms ...
As part of two drilling campaigns of the International Continental Scientific Drilling Program (ICDP), several geophysical borehole measurements were carried out by the Leibniz Institute for Applied Geophysics (LIAG) in two lakes. The acquired data was used to answer stratigraphic and paleoclimatic research questions, including the establishment of robust age-depth models and the construction of continuous lithological profiles.
Lake Towuti is located on Sulawesi (Indonesia), within the "Indo-Pacific Warm Pool" (IPWP), a globally important region for atmospheric heat and moisture budgets. The lake exists for approximately one million years, but its exact age is uncertain. We present the first agedepth model for the approximately 100 m continuous sediment sequence from the central part of the lake. The basis for this model is the magnetic susceptibility measured in the borehole and a tephra layer with an age of about 797 ka at 72 m depth. Our age-depth model is inferred from cyclostratigraphic analysis of borehole data and covers a period from 903 ± 11 to 131 ± 67 ka. We suggest that orbital eccentricity and/or changes between global cold and warm periods are responsible for hydroclimatic changes in the IPWP, that these changes affect sedimentation processes in Lake Towuti, and that we can measure and observe this effect in the sediment properties today. Additionally, we created a continuous artificial lithological profile from a series of different borehole data using cluster analysis. This provides information from parts of the borehole where no sediment is available due to core loss.
Lake Ohrid is 1.36 million years old and is located on the Balkan Peninsula on the border between Albania and North Macedonia. The primary hole 'DEEP' in the central part of the lake has been the subject of several investigations, but information about sediments of the marginal locations 'Pestani' and 'Cerava' have not been published yet. In our study, we use natural gamma radiation (GR) measured in the borehole to generate an age-depth model for DEEP. This is performed using the correlation of GR to the global LR04 reference record of Lisiecki and Raymo (2005).
The age information is then transferred via prominent seismic marker horizons to the other two sites, Pestani and Cerava, where it provides the first age-control points for the construction of age-depth models from correlation of GR to LR04. The generated age-depth models are tested using cyclostratigraphic methods, but the limits of this approach are revealed. At DEEP, sedimentation rates (SR) from the cyclostratigraphic method and the correlative approach differ by 2.8 %, at Pestani this difference is 16.7 %, and at Cerava the quality of the data does not allow a reliable evaluation of SR using the cyclostratigraphic approach. We used cluster analysis to construct artificial lithological profiles at all three sites and integrated them into the respective age-depth models. This enables us to determine which sediment types were deposited at what time, and we recognize the change between warm and cold periods in the sediment properties at all three locations. The analyses in this study were all performed on borehole and seismic data and thus do not involve sediment core data. Especially at Pestani and Cerava, new insights into the sedimentological history of Lake Ohrid could be obtained.
In the last part we discuss the occurrence of the half-precession (HP) signal in the European region during the last one million years. The focus is on Lake Ohrid, but a range of other proxies, from the eastern Mediterranean, across the European continent, up to Greenland are analyzed in regards to HP. Applying filters, we focus on the frequency range with a period of 13-8.5 ka and only HP remains in the records. We use correlative methods to determine the clarity of the HP signal in proxies distributed across the European realm. Additionally, we determined the development of HP over time. The HP signal is clearest in the southeast and decreases toward the north. It is further more pronounced in interglacial periods and in the younger part (<621 ka) of most proxies. We suggest that there are mechanisms that transmit the HP signal from its origin near the equator to higher latitudes via different processes. In this context, for instance, the African monsoon, the Nile River and the Mediterranean outflow via the Strait of Gibraltar can be important factors.
The endemic argan tree (Argania spinosa) populations in South Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth, but show lower soil quality than their neighbouring tree areas. Hypothetically, spatial differences of soil quality of the intertree area should result from translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) as well as the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) and analysed for soil moisture, pH, electrical conductivity, percolation stability, total nitrogen content, content of soil organic carbon and C/N ratio. 74 tension-disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with e.g., Corg- & N-content decreasing significantly from tree trunk to tree drip line. However, intertree areas near the tree drip line differed significantly from intertree areas between two trees, yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil moisture was highest in the north due to shade from the midday sun, the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil moistures, N- or Corg-content to ensure seedling survival.
Metal artifacts from the Paleometal Epoch (ca. 1100 BC–400 AD) of the Primorye (Russian Far East) have shed new light on the introduction of the earliest bronzes into the Pacific coastal areas of prehistoric Eurasia. However, little is known about raw material circulation and the role of metal in the context of inter-regional exchange. This paper investigates 12 copper artifacts from major Paleometal settlements using alloy composition, trace elements, and lead isotopes to explore the metal sources and distribution networks. The results suggest that most objects are made of a copper-tin alloy, but some have arsenic as a significant minor element . Geologically, copper is unlikely to have come from local ore sources, but rather from the Liaoxi corridor and Liaodong Peninsula in Northeast China. This may indicate an inland route of metal trade across Northeast China or alternately, a coastal route via the northern Korean Peninsula. Archaeologically, the combined study of artifact typology and chemistry indicates two possible origins for the metal: the Upper Xiajiadian culture in Northeast China and Slab Grave culture in Mongolia/Transbaikal. Remarkably, the connection with Upper Xiajiadian communities parallels the transport route along which millet agriculture spread from Northeast China to the Primorye during the Neolithic.
Community trait assembly in highly diverse tropical rainforests is still poorly understood. Based on more than a decade of field measurements in a biodiversity hotspot of southern Ecuador, we implemented plant trait variation and improved soil organic matter dynamics in a widely used dynamic vegetation model (the Lund-Potsdam-Jena General Ecosystem Simulator, LPJ-GUESS) to explore the main drivers of community assembly along an elevational gradient. In the model used here (LPJ-GUESS-NTD, where NTD stands for nutrient-trait dynamics), each plant individual can possess different trait combinations, and the community trait composition emerges via ecological sorting. Further model developments include plant growth limitation by phosphorous (P) and mycorrhizal nutrient uptake. The new model version reproduced the main observed community trait shift and related vegetation processes along the elevational gradient, but only if nutrient limitations to plant growth were activated. In turn, when traits were fixed, low productivity communities emerged due to reduced nutrient-use efficiency. Mycorrhizal nutrient uptake, when deactivated, reduced net primary production (NPP) by 61–72% along the gradient. Our results strongly suggest that the elevational temperature gradient drives community assembly and ecosystem functioning indirectly through its effect on soil nutrient dynamics and vegetation traits. This illustrates the importance of considering these processes to yield realistic model predictions.
Plant community biomass production is co-dependent on climatic and edaphic factors that are often covarying and non-independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan-European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species-specific biomass responses to the environment in the climate-corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co-limited by climatic and soil drivers, with each species experiencing its own unique set of co-limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.
Hydro-climatic causes of widespread floods in central Europe : on rain-on-snow and Vb-cyclone events
(2021)
The presented work investigates the hydro-meteorological and hydro-climatological drivers of widespread floods in Central Europe during the past century. Due to the strong seasonality of the detected flood drivers, the thesis is divided into two parts: the first part focuses on widespread winter floods and the second one on extreme summer floods. For analysing past flood events, we profited from the dynamically downscaled centennial ERA-20C reanalysis (continuously from 1901—2010). The downscaling was performed over Europe with a coupled regional atmosphere-ocean model (COSMO-CLM+NEMO) to represent the water cycle more realistic. These high resolution atmospheric data allowed us to study the four-dimensional atmospheric state during selected floods during the early decades of the 20th century for the first time with such a high temporal and spatial resolution.
During the winter half-year, the observed floods were particularly widespread. High peak discharges were recorded simultaneously in the Rhine, Elbe, and Danube catchments. Most of these trans-basin floods were compound events caused by rainfall during extensive snowmelt (i.e., rain-on-snow events). Interestingly, the winter flood time series exhibited a remarkable high flood frequency during the 1940s and 1980s, while other decades were flood-poor. We detected a synchronization of the inter-annual flood frequency with the superposition of the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCA). The negative NAO phase is often associated with large snowfall and cyclone tracks over southern Europe, while the negative SCA pattern correlates with total precipitation in the affected river catchments.
During the summer half-year, most extreme floods in Central Europe were caused by so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. So far in the literature, only a few Vb-events, which occurred during the past two decades, have been analysed. We extended the previous case studies by several past Vb-cyclone floods since 1900. We investigated the processes that intensify Vb-cyclone precipitation with Lagrangian moisture-source diagnostics and the parametric transfer entropy measure TE-linear. Overall, an enhanced and dynamically driven moisture uptake over the Mediterranean Sea was found to be characteristic for Vb-events with heavy precipitation. This is supported by high information exchange from evaporation over the western basin of the Mediterranean Sea towards heavy precipitation in the Odra catchment. The dominating moisture uptake regions during the investigated events were, however, the European continent and the North Sea. A possible cause could be the pre-moistening of non-saturated continental moisture sources upstream of the affected river catchments as indicated by significant information exchange from land surface evaporation and soil moisture content along the Vb-cyclone pathway. Besides, evaporation over the Mediterranean Sea might contribute to Vb-cyclone intensification in the early stages of their development through latent heat release. On the catchment scale, orographic rainfall and convective precipitation further enhance the flood triggering rainfall. As expected, the Vb-cyclones mainly trigger precipitation along west-east orientated mountain ranges such as the Alps or Ore mountains due to their meridional pathway. Remarkably, during summer, we detected a convective fraction of up to 90% during the afternoons of individual days and up to 23% on average (based on convective cell tracking and convection-permitting simulations of selected flood events since 1900).
The presented analyses deepened the knowledge on atmospheric and hydroclimatic drivers of widespread floods in Central Europe. This will serve as a basis for future studies on the predictability of floods induced by rain-on-snow and Vb-cyclone precipitation events in the context of a changing climate.
Atmosphärische Schwerewellen spielen eine wichtige Rolle für die Zirkulation der mittleren Atmosphäre, die wiederum die Troposphäre auf saisonalen und längeren Zeitskalen beeinflusst, und stellen somit ein Schlüsselelement für das Wetter- und Klimageschehen dar. Eine adäquate Beschreibung des Lebenszyklus atmosphärischer Schwerewellen in den operationellen Modellen zur Wettervorhersage und Klimasimulation ist daher sehr wünschenswert. Um zu einer verbesserten mathematischen Darstellung der Schwerewellendynamik in den Modellen beizutragen, wurden in den vergangenen Jahren zahlreiche numerische Studien durchgeführt. Wenngleich auch viele der ablaufenden Prozesse gegenwärtig gut verstanden sind, stellt die Wechselwirkung zwischen den mesoskaligen Schwerewellen und den synoptischskaligen Prozessen aufgrund der hohen Komplexität der Strömung weiterhin eine besondere Herausforderung für die Erforschung der Schwerewellenaktivität dar und erfordert oftmals hochaufgelöste numerische Simulationen über große Modelldomänen.
Folglich ist es wichtig, dass die angewendeten numerischen Verfahren effizient sind und möglichst idealisierte, aber dennoch atmosphärenähnliche Szenarien simulieren. In dieser Arbeit wird ein effizientes numerisches Verfahren zur Modellierung der Dynamik interner Schwerewellen sowie deren Einfluss auf die Zirkulation der mittleren Atmosphäre entwickelt.
Dabei wird die Diskretisierung des pseudo-inkompressiblen Finite-Volumen-Modells auf einem versetzten Gitter von Rieper et al. (2013), welches der Einfachheit halber Schallwellen aus der Dynamik herausfiltert und zur Untersuchung adiabatischer Atmosphärenprozesse auf der f-Ebene entwickelt wurde, im wesentlichen durch zwei Komponenten erweitert: 1) die Anwendung eines semi-impliziten Zeitschrittverfahrens auf die Bewegungsgleichungen zur Integration der Auftriebs- und Corioliseffekte und 2) die Berücksichtigung einer Heizung durch einen thermischen Relaxationsansatz, welcher in der Troposphäre ein baroklin instabiles Strömungsprofil erzeugt und eine zeitabhängige Dynamik des Hintergrundzustands zulässt. Zur Überprüfung der korrekten Implementierung der Erweiterungen werden eine Reihe von atmosphärischen Standardteststudien durchgeführt, welche die Konvergenzeigenschaften sowie die Effizienz des Verfahrens validieren. Darüber hinaus zeigen die Testfälle, dass die Ergebnisse des Modells mit anderen veröffentlichten Arbeiten sehr gut übereinstimmen.
Schließlich wird als Anwendungstestfall eine mesoskalige Simulation barokliner Instabilität in der Troposphäre durchgeführt, welche ferner die darin enthaltene kleinskalige Wellenaktivität sowie deren Einfluss auf die mittlere Atmosphäre modelliert. Die abschließende Betrachung der zonal und zeitlich gemittelten Felder zeigt die erwartete Zonalwindumkehr in der Höhe.
U–Pb age spectra of detrital zircons related to the East European Platform could be traced in paragneiss through the whole Mid-German-Crystalline Zone (Variscides, Central Europe) from the Odenwald via the Spessart to the Ruhla crystalline forming an exotic unit between Armorica and Laurussia. The depositional ages of the paragneiss are defined by the youngest age of the detrital zircons and the oldest intrusion ages as Ordovician to Silurian. The Ediacaran dominated age spectrum of detrital zircons from the paragneiss of the East Odenwald suggests the latter to be derived from the shelf of the East European Platform (Baltica), which was influenced by the 1.5 Ga old detritus delivered from a giant intrusion (Mazury granitoid, Poland). The detrital zircon age spectrum of the lower Palaeozoic paragneiss of the East Odenwald and sandstone of the northern Holy Cross Mountains are identical. The pure Sveconorwegian spectrum of the lower Palaeozoic quartzite from the Spessart, (Kirchner and Albert Int J Earth Sci 2020) and the Ruhla (Zeh and Gerdes Gondwana Res 17:254–263, 2010) could be sourced from Bornholm and southern Sweden. A U–Pb age spectrum with 88% Palaeozoic detrital zircons from a volcano-sedimentary rock of the East Odenwald is interpreted to be derived from a Silurian magmatic arc (46%), which was probably generated during the drift of the Mid-German-Crystalline Zone micro-continent to the south. A tentative plate tectonic model of Mid-German-Crystalline Zone is presented taking into account (a) the East European Platform related age spectra of the detrital zircons (b) the Ordovician to Silurian depositional age of the metasediments (c) the Silurian and Early Devonian intrusion age of the plutonic and volcanic rocks and (d) the U–Pb ages of the Middle Devonian high-grade metamorphism. The East European Platform-related part of the Mid-German-Crystalline Zone is interpreted as a micro-continent, which drifted through the Rheic Ocean to the south and collided with the Saxothuringian (Armorican Terrane Assemblage) during the Early Devonian. Such large-scale tectonic transport from the northern continent to the southern continent is also known from the SW Iberia, where Laurussia-related metasediments of the Rheic suture zone are explained by a large scale tectonic escape (Braid et al. J Geol Soc Lond 168:383–392, 2011).
A massive occurrence of microbial carbonates, including abundant sponge remains, within the Devonian Elbingerode Reef Complex was likely deposited in a former cavity of the fore-reef slope during the early Frasnian. It is suggested that the formation of microbial carbonate was to a large part favored by the activity of heterotrophic, i.e., sulfate-reducing bacteria, in analogy to Quaternary coral reef microbialites. The Elbingerode Reef Complex is an example of an oceanic or Darwinian barrier reef system. In modern barrier reef settings, microbialite formation is commonly further facilitated by weathering products from the central volcanic islands. The Devonian microbialites of the Elbingerode Reef Complex occur in the form of reticulate and laminated frameworks. Reticulate framework is rich in hexactinellid glass sponges, the tissue decay of which led to the formation of abundant micrite as well as peloidal and stromatactis textures. Supposed calcimicrobes such as Angusticellularia (formerly Angulocellularia) and Frutexites, also known from cryptic habitats, were part of the microbial association. The microbial degradation of sponge tissue likely also contributed to the laminated framework accretion as evidenced by the occurrence of remains of so-called “keratose” demosponges. Further typical textures in the microbialite of the Elbingerode Reef Complex include zebra limestone, i.e., the more or less regular intercalation of microbial carbonate and cement. Elevated concentrations of magnesium in the microbialite as compared to the surrounding metazoan (stromatoporoid-coral) reef limestone suggests that the microbialite of the Elbingerode Reef Complex was initially rich in high-magnesium calcite, which would be yet another parallel to modern, cryptic coral reef microbial carbonates. Deposition and accretion of the microbialite largely occurred in oxygenated seawater with suboxic episodes as indicated by the trace element (REE + Y) data.
In partially molten regions inside the earth melt buoyancy may trigger upwelling of both solid and fluid phases, i.e. diapirism. If the melt is allowed to move separately with respect to the matrix, melt perturbations may evolve into solitary porosity waves. While diapirs may form on a wide range of scales, porosity waves are restricted to sizes of a few times the compaction length. Thus, the size of a partially molten perturbation controls whether a diapir or a porosity wave will emerge. We study the transition from diapiric rise to solitary porosity waves by solving the two-phase flow equations of conservation of mass and momentum in 2D with porosity dependent matrix viscosity. We systematically vary the initial size of a porosity perturbation from 1 to 100 times the compaction length. If the perturbation is much larger than a regular solitary wave, its Stokes velocity is large and therefore faster than the segregating melt. Consequently, the fluid is not able to form a porosity wave and a diapir emerges. For small perturbations solitary waves emerge, either with a positive or negative vertical matrix velocity inside. In between the diapir and solitary wave regimes we observe a third regime of solitary wave induced focusing of melt. In these cases, diapirism is dominant but the fluid is still fast enough to locally build up small solitary waves which rise slightly faster than the diapir and form finger like structures at the front of the diapir. In our numerical simulations the width of these fingers is controlled by the compaction length or the grid size, whichever is larger. In cases where the compaction length becomes similar to or smaller than the grid size the finger-like leading solitary porosity waves are no more properly resolved, and too big and too fast waves may be the result. Therefore, one should be careful in large scale two-phase flow modelling with melt focusing especially when compaction length and grid size are of similar order.
The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes, and to make the method more relevant to studies of both plant evolution and fire management, more information must be extracted from charcoal particles. Here, I burned in the laboratory seven fuel types comprising 17 species from boreal Siberia, and build on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. As most of the species used in this study are common to Northern Hemisphere forests and peatlands, these results can be directly applicable over a broad geographical scale. Results show that the effect of temperature on charcoal production is fuel dependent. Graminoids and Sphagnum, and wood (trunk) lose the most mass at low burn temperatures, whereas heathland shrub leaves, brown moss, and ferns retain the most mass at high burn temperatures. In contrast to the wood of trunk, the wood of twigs retained their mass at intermediate temperature. This suggests that species with low mass retention at hotter burning temperatures might be underrepresented in the fossil charcoal record. Charred particle aspect ratio (L/W) appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoals are more elongate than those of all other fuel types, leaf charcoals are the shortest and bulkiest, and twig and wood charcoals are intermediate. Finer diagnostic features were the most useful in distinguishing between wood, graminoid, and leaf particles, but further distinctions within these fuel types are difficult. High-aspect-ratio particles dominated by graminoid and Sphagnum morphologies are robust indicators of cooler surface fires. Contrastingly, abundant wood and leaf morphologies and low-aspect-ratio particles likely indicate higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires combusting living shrubs and dead wood and leaves or high-intensity crown fires combusting living trees. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in more robustly interpreting changes in fuel source and fire type, thereby substantially refining histories of past wildfires. Further fields of investigation to improve the interpretation of the fossil charcoal records will require: i) More in-depth knowledge of plant anatomy for a better determination of fuel sources; ii) Relate the proportion of particular charcoal morphotypes to the quantity of biomass; iii) Link the chemical composition of fuels, combustion temperature, and charcoal production. The advanced use of image-recognition software to collect data on other charcoal features could also aid in extracting fire temperatures as well as a change in particles morphology and morphometry during particles transportation.
In the last decade, the Climate Limited-area Modeling (CLM) Community has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM community model, ERA-Interim reanalysis and eight Global Climate Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44◦(∼50 km), 0.22◦ (∼25 km) and 0.11◦ (∼12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modelling communities is needed to increase the reliability of the GCM-RCM modelling chain.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen/Germany. Average power spectral densities (PSD) are calculated from 10 min time segments extracted from (up to) 6-months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify 7 distinct PSD peaks in the frequency range between 1 Hz and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b-values exhibit a linear frequency dependence and range from b = 0.39 at 1.14 Hz to b = 3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach which approximates the surface-wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source-signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase-shift-elimination-method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the 7 prominent frequencies shows very good agreement and allows to constrain shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
Hyrrokkin sarcophaga is a parasitic foraminifer that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Lophelia pertusa. Here, we present measurements of the elemental and isotopic composition of this parasitic foraminifer for the first time, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe micro analysis (EPMA) and mass spectrometry (MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest L. pertusa, which could be an indication that dissolved host carbonate material is utilised in shell calcification, given that the aragonite of L. pertusa has a naturally higher Sr concentration compared to the calcite of A. excavata.Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on20 L. pertusa, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn/Ca ratios in foraminifers that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifer, these data also indicate that the geochemistry of this parasitic foraminifer is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
National Greenhouse Gas Inventories (GHGI) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGI. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emissions Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high Global Warming Potentials (GWPs) and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions in the since 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35%, indicating progress toward the target of a 79% decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83)% of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI inventory. There are also significant discrepancies between the two estimates for the individual HFCs.
The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.
Late Paleozoic (Variscan) magmatism is widespread in Central Europe. The Lusatian Block is located in the NE Bohemian Massif and it is part of the Saxothuringian Zone of the Variscan orogen. It is bordered by two major NW-trending shear zones, the Intra-Sudetic Fault Zone towards NE and the Elbe Fault Zone towards SW. The scarce Variscan igneous rocks of the Lusatian Block are situated close to these faults. We investigated 19 samples from Variscan plutonic and volcanic rocks of the Lusatian Block, considering all petrological varieties (biotite-bearing granites from the Koenigshain and Stolpen plutons, amphibole-bearing granites from three boreholes, several volcanic dykes, and two volcanites from the intramontane Weissig basin). We applied whole-rock geochemistry (18 samples) and zircon evaporation dating (19 samples). From the evaporation data, we selected six representative samples for additional zircon SHRIMP and CA–ID–TIMS dating. For the Koenigshain pluton, possible protoliths were identified using whole-rock Nd-isotopes, and zircon Hf- and O-isotopes. The new age data allow a subdivision of Variscan igneous rocks in the Lusatian Block into two distinct magmatic episodes. The spatial relation of the two age groups to either the Elbe Fault Zone (298–299 Ma) or the Intra-Sudetic Fault Zone (312–313 Ma) together with reports on the fault-bound character of the dated intrusions suggests an interpretation as two major post-collisional faulting episodes. This assumption of two distinct magmatic periods is confirmed by a compilation of recently published zircon U–Pb CA–ID–TIMS data on further Variscan igneous rocks from the Saxothuringian Zone. New geochemical data allow us to exclude a dominant sedimentary protolith for the Koenigshain pluton as supposed by previous investigations. This conclusion is mainly based on new O- and Hf-isotope data on zircon and the scarcity of inherited zircons. Instead, acid or intermediate igneous rocks are supposed as the main source for these I-type granitoids from the Koenigshain pluton.
U–Pb age spectra of detrital zircons related to the East European Platform could be traced in paragneiss through the whole Mid-German-Crystalline Zone (Variscides, Central Europe) from the Odenwald via the Spessart to the Ruhla crystalline forming an exotic unit between Armorica and Laurussia. The depositional ages of the paragneiss are defined by the youngest age of the detrital zircons and the oldest intrusion ages as Ordovician to Silurian. The Ediacaran dominated age spectrum of detrital zircons from the paragneiss of the East Odenwald suggests the latter to be derived from the shelf of the East European Platform (Baltica), which was influenced by the 1.5 Ga old detritus delivered from a giant intrusion (Mazury granitoid, Poland). The detrital zircon age spectrum of the lower Palaeozoic paragneiss of the East Odenwald and sandstone of the northern Holy Cross Mountains are identical. The pure Sveconorwegian spectrum of the lower Palaeozoic quartzite from the Spessart, (Kirchner and Albert Int J Earth Sci 2020) and the Ruhla (Zeh and Gerdes Gondwana Res 17:254–263, 2010) could be sourced from Bornholm and southern Sweden. A U–Pb age spectrum with 88% Palaeozoic detrital zircons from a volcano-sedimentary rock of the East Odenwald is interpreted to be derived from a Silurian magmatic arc (46%), which was probably generated during the drift of the Mid-German-Crystalline Zone micro-continent to the south. A tentative plate tectonic model of Mid-German-Crystalline Zone is presented taking into account (a) the East European Platform related age spectra of the detrital zircons (b) the Ordovician to Silurian depositional age of the metasediments (c) the Silurian and Early Devonian intrusion age of the plutonic and volcanic rocks and (d) the U–Pb ages of the Middle Devonian high-grade metamorphism. The East European Platform-related part of the Mid-German-Crystalline Zone is interpreted as a micro-continent, which drifted through the Rheic Ocean to the south and collided with the Saxothuringian (Armorican Terrane Assemblage) during the Early Devonian. Such large-scale tectonic transport from the northern continent to the southern continent is also known from the SW Iberia, where Laurussia-related metasediments of the Rheic suture zone are explained by a large scale tectonic escape (Braid et al. J Geol Soc Lond 168:383–392, 2011).
Questions: Habitat islands are often characterized by the presence of more or less sharp boundaries to adjacent matrix habitats. However, knowledge on boundaries of natural habitat islands is scarce, especially regarding patterns of beta diversity and its two underlying components: species turnover and nestedness. We therefore aim to quantify the effects of fine-scaled and sharp boundaries of quartz islands (quartz gravel-covered soils) on the different components of plant beta diversity and how they are linked to different soil environmental drivers. Location: Knersvlakte, Western Cape, South Africa. Methods: We sampled plant species richness in 56 fine-scale transects of 6 m × 1 m plots across eight different boundary types (four quartz island to matrix, four between habitats on quartz islands). Soil depth and chemistry (pH, electrical conductivity) were analyzed for each 1 m2 plot. Differences in the two beta diversity components (turnover and nestedness) for each boundary type were tested by t tests. We used linear models to test relationships between species and environmental dissimilarity. Results: All boundary types showed high beta diversity. Species turnover was the prevailing component for six boundary types, the nestedness component was only important for two boundary types. We found a significant linear increase of species dissimilarity with increasing dissimilarity in soil pH and distinct plant communities for the habitat types, but no significant increase for electrical conductivity or soil depth. Conclusions: The spatial distinctiveness of the quartz islands leads to sharp boundaries, which result in high beta diversity, mainly through species turnover. This reflects the high levels of diversification and adaptation of the local plant communities. Nestedness occurred at two boundaries to the matrix, indicating that the latter does not necessarily represent an impermeable boundary for all species of the respective ecosystem. Studying diversity patterns across boundaries contributes to the question of applicability of island biogeography theory to habitat islands.
The segregation of refugees in collective accommodation centres represents an integral component of the European border regime and its complex interplay of inclusion and exclusion. The corresponding spatial, symbolic and discursive demarcations, however, are not simply implemented politically from above, but negotiated on the ground on a daily basis. One crucial group of actors in the German context are neighbourhood-based volunteers. These groups frequently accompany accommodation centres with support structures. Based on contributions in the field of critical border studies and on the example of a municipal accommodation facility in Frankfurt, Germany, this paper demonstrates how volunteers, through their practices and engagement with refugees and others, on one hand, and dominant discourses, institutions and regulations on the other, participate in the production of locally specific spaces of asylum that are marked by simultaneous and contradictory processes of bordering and debordering.
Abstract: Subaqueous carbonates from the Devils Hole caves (southwestern USA) provide a continuous Holocene to Pleistocene North American paleoclimate record. The accuracy of this record relies on two assumptions: That carbonates precipitated close to isotope equilibrium and that groundwater temperature did not change significantly in the last 570 thousand years. Here, we investigate these assumptions using dual clumped isotope thermometry. This method relies on simultaneous analyses of carbonate ∆47 and ∆48 values and provides information on the existence and extent of kinetic isotope fractionation. Our results confirm the hypothesis that calcite precipitation occurred close to oxygen and clumped isotope equilibrium during the last half million years in Devils Hole. In addition, we provide evidence that aquifer temperatures varied by less than ±1°C during this interval. Thus, the Devils Hole calcite δ18O time series exclusively represents changes in groundwater δ18O values. Plain Language Summary: The oxygen isotope composition of cave carbonates records changes in Earth's climate. However, the reliability of such records depends on how stable the carbonate precipitation environment was. Here, we use a novel method called dual clumped isotope thermometry that can provide simultaneous information on a carbonate's growth temperature and whether any additional fractionation processes affected its oxygen and clumped isotope signatures. Specifically, we investigated the Devils Hole caves, which provide a reference oxygen isotope time series for North America. We find that groundwater temperature did not change significantly in the last half-million years. Variations in the oxygen isotope composition of the deposited carbonates solely reflect variations in the oxygen isotope composition of the groundwater.
Toward parametrization of precipitating shallow cumulus cloud organization via moisture variance
(2021)
The influence of the initial vertical moisture profile on precipitating shallow cumulus cloud organization in terms of the column-averaged moisture variance is investigated using large-eddy simulations. Five idealized simulations based on the Rain in Cumulus over the Ocean field experiment with different initial moisture profiles are investigated. All cases simulate precipitating shallow cumulus convection in a marine sub-tropical region under large-scale subsidence. The results show that the moisture variance is mainly generated through the interaction of the moisture flux and the moisture gradient in the gradient production term at the top of the boundary layer. The development is characterized by three regimes: initial, transition, and quasi-steady regime. During the initial regime, the moisture gradient is built up by moisture accumulation until precipitating convection starts. Within the transition regime, precipitation enables mesoscale cloud organization with enhanced convective activity and moisture fluxes. The moisture variance increases from the moist to the dry initial moisture profiles. In a following quasi-steady regime, the moisture variance is approximately preserved. Thereby, the initial moisture gradient between the average sub-cloud layer and the free atmosphere is found to be an important factor for the generation of the quasi-steady column-averaged moisture variance. The result suggests that a resolved-scale variable like the moisture gradient can be used to estimate the quasi-steady state conditions resulting from cloud organization. This finding may serve as a starting point for the parametrization of the subgrid scale cloud organization caused by precipitating shallow convection.
The goal of limited area models (LAMs) is to downscale coarse-gridded general circulation model output to represent small-scale features of weather and climate. The LAM needs information from the driving coarse-gridded model passing through its lateral boundaries. The treatment of this information transfer causes inconsistencies between driving and nested models and, subsequently, issues in regional weather and climate simulations. This work examines errors arising from choices taken by the modeler (temporal update frequency of boundary data, spatial resolution jump, and numerical lateral boundary formulation) systematically in an idealized simulation environment. So-called Big-Brother Experiments were performed with the LAM COSMO-CLM (0.11° grid spacing). A baroclinic wave in a zonal channel was simulated over flat terrain with and without a Gaussian hill. The results reveal that the quality of the driving data, here represented by simulations only differing from the LAM simulations by reduced spatial resolution, dominates the performance of the nested model. Consequently, at the simulated mesoscale, the performance of the nested small-scale model simulations is weakly sensitive to the numerical lateral boundary formulation (Davies relaxation or the newly implemented, computationally less demanding Mesinger Eta-model formulation). The performance sensitivity to boundary update frequency and resolution jump is small when at least 6-hourly updates and a resolution jump factor of maximally six is used. Gaussian hill LAM simulations illustrated the strength of downscaling; they can represent small-scale features missing in the coarse-scale driving simulations. In the idealized simulation experiments, spectral nudging is not advisable as it imprints the driving models deficits on the nested simulation.
Today in the United States, the notion that ‘the rise of the far right’ poses the greatest threat to democratic values, and by extension, to the nation itself, has slowly entered into common sense. The antecedent of this development is the object of our study. Explored through the prism of what we refer to as the domestication of the War on Terror, this publication adopts and updates the theoretical approach first forwarded in Policing the Crisis: Mugging, the State, the Law and Order (Hall et al. 1978). Drawing on this seminal work, a sequence of three disparate media events are explored as they unfold in the United States in mid-2015: the rise of the Trump campaign; the release of an op-ed in The New York Times warning of a rise in right-wing extremsim; and a mass shooting at a historic African American church in Charleston, South Carolina. By the end of 2015, as these disparate events converge into what we call the public face of the rise of the far right phenomenon, we subsequently turn our attention to its origins in policing and the law in the wake of the global War on Terror and the Great Recession. It is only from there, that we turn our attention to the poltical class struggle as expressed in the rise of 'populism' on the one hand, and the domestication of the War on Terror on the other, and in doing so, attempt to situate the role of the rise of the far right phenomenon within it.
One of the most important events in human history occurred during the Early Pleistocene: the dispersal of early hominins out of Africa and into Europe and Asia. In Western Europe, the earliest evidences of the genus Homo have been found in the Baza Basin, at the sites of Orce in the SE of the Iberian Peninsula. These sites contain fossils and lithic industry dated approximately as 1.4–1.3 Ma.While hominin remains and artifacts at Orce, as well as the accompanying fauna, have been extensively studied, the properties and evolution of the Early Pleistocene vegetation in the basin remain unknown. The general effect of climate change on the expansion of early hominins from Africa into Eurasia still remains unclear. It is not known if the Early Pleistocene climate changes and the development of glacials periods led to the extirpation of European communities, or if those communities were able to endure and persist through such adverse climatic periods. This open question highlights the need for climate and environmental analyses for the time before, during and after the first presence of Homo in Europe. This PhD thesis contributes to that need by the presentation of the first long pollen record of the Baza Basin, where the oldest hominin sites in Western Europe are found.
High-pressure single-crystal to 20 GPa and powder diffraction measurements to 50 GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10 GPa and 12 GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50 GPa. This insulator-to-semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory-based calculations show that at ambient conditions the channels in the structure host the stereochemically-active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.
This article presents the findings from systematically reviewing 26 empirical research studies published from 2005 to 2014 on the use of GIS for learning and teaching. By employing methods of narrative synthesis and qualitative content analysis, the study gives evidence about the state of knowledge of competence-based GIS education. The results explain what factors and variables effect GIS learning in terms of technology use, major subject contents, learning contexts, and didactic and pedagogical aspects. They also show what facets of knowledge, process skills, and affect the research literature has investigated. The analysis of the type and quality of the methods used indicates that current GIS education research is a heterogeneous field that needs a systematic research framework for future efforts, according to empirical education research.
A general circulation model is used to study the interaction between parameterized gravity waves (GWs) and large-scale Kelvin waves in the tropical stratosphere. The simulation shows that Kelvin waves with substantial amplitudes (∼10 m s−1) can significantly affect the distribution of GW drag by modulating the local shear. Furthermore, this effect is localized to regions above strong convective organizations that generate large-amplitude GWs, so that at a given altitude it occurs selectively in a certain phase of Kelvin waves. Accordingly, this effect also contributes to the zonal-mean GW drag, which is large in the middle stratosphere during the phase transition of the quasi-biennial oscillation (QBO). Furthermore, we detect an enhancement of Kelvin-wave momentum flux due to GW drag modulated by Kelvin waves. The result implies an importance of GW dynamics coupled to Kelvin waves in the QBO progression.
Plain Language Summary: The variability of the tropical atmosphere at altitudes of about 18–40 km is dominated by a large-amplitude long-term oscillation of wind, the quasi-biennial oscillation, which has a broad impact on the climate and seasonal forecasting. This oscillation is known to be driven by various types of atmospheric waves with multiple spatial scales. Using a numerical model, this study reports a process of interaction between those waves on different scales, which has not been illuminated before. The result implies a potential importance of this process in the progression of the quasi-biennial oscillation. Proper model representations of these multiscale waves and tropical convection are required to simulate this process.
Droughts are anticipated to intensify in many parts of the world due to climate change. However, the issue of drought definition, namely the diversity of drought indices, makes it difficult to compare drought assessments. This issue is widely known, but its relative importance has never been quantitatively evaluated in comparison to other sources of uncertainty. Here, encompassing three drought categories (meteorological, agricultural, and hydrological droughts) with four temporal scales of interest, we evaluated changes in the drought frequency using multi-model and multi-scenario simulations to identify areas where the definition issue could result in pronounced uncertainties and to what extent. We investigated the disagreement in the signs of changes between drought definitions and decomposed the variance into four main factors: drought definitions, greenhouse gas concentration scenarios, global climate models, and global water models, as well as their interactions. The results show that models were the primary sources of variance over 82% of the global land area. On the other hand, the drought definition was the dominant source of variance in the remaining 17%, especially in parts of northern high-latitudes. Our results highlight specific regions where differences in drought definitions result in a large spread among projections, including areas showing opposite signs of significant changes. At a global scale, 7% of the variance resulted independently from the definition issue, and that value increased to 44% when 1st and 2nd order interactions were considered. The quantitative results suggest that by clarifying hydrological processes or sectors of interest, one could avoid these uncertainties in drought assessments to obtain a clearer picture of future drought change.
A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a “data-forward” approach, that clearly decouples the presentation of proxy data from plausible environmental inferences.
In the last decade, the Climate Limited-area Modeling Community (CLM-Community) has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM-Community model, ERA-Interim reanalysis and eight global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44∘ (∼ 50 km), 0.22∘ (∼ 25 km), and 0.11∘ (∼ 12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia, and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version, and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modeling communities is needed to increase the reliability of the GCM–RCM modeling chain.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen, Germany. Average power spectral densities (PSDs) are calculated from 10 min time segments extracted from (up to) 6 months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify seven distinct PSD peaks in the frequency range between 1 and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b values exhibit a linear frequency dependence and range from b=0.39 at 1.14 Hz to b=3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach that approximates the surface wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase shift elimination method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the seven prominent frequencies shows very good agreement and allows the constraint of shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Evidence of hydrothermal activity is reported for the Mesozoic pre- and syn-rift successions of the western Adriatic palaeomargin of the Alpine Tethys, preserved in the Western Southalpine Domain (NW Italy). The products of hydrothermal processes are represented by vein and breccia cements, as well as dolomitization and silicification of the host rocks. In the eastern part of the study area, interpreted as part of the necking zone of the continental margin, Middle Triassic dolostones and Lower Jurassic sediments are crossed by veins and hydrofracturing breccias cemented by saddle dolomite. The precipitation of dolomite cements occurred within the stratigraphic succession close to the sediment–water interface. Despite the shallow burial depth, fluid inclusion microthermometry and clumped isotopes show that hydrothermal fluids were relatively hot (80–150°C). In the western part of the study area, interpreted as part of the hyperextended distal zone, a polyphase history of host-rock fracturing is recorded, with at least two generations of veins cemented by calcite, dolomite and quartz. Vein opening and cementation occurred at shallow burial depth around the time of deposition of the syn-rift clastic succession. Fluid inclusion microthermometry on both quartz and dolomite cements indicates a fluid temperature of 90–130°C, again pointing to hydrothermal fluids. Both in Fenera-Sostegno and Montalto Dora areas, O, C and Sr isotope values, coupled with fluid inclusion and clumped isotope data, indicate that hydrothermal fluids derived from seawater interacted with crustal rocks during hydrothermal circulation. Stratigraphic and petrographic evidence, and U–Pb dating of dolomitized clasts within syn-rift sediments, document that hydrothermal fluids circulated through sediments from the latest Triassic to the Toarcian, corresponding to the entire syn-rift evolution of the western portion of the Adriatic palaeomargin. The documented hydrothermal processes are temporally correlated with regional-scale thermal events that took place in the same time interval at deeper crustal levels.
National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35 %, indicating progress toward the target of a 79 % decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83) % of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.
CrB4O6N crystallizes in the non-centrosymmetric space group P63mc (no. 186) with the lattice parameters a=5.1036(1), c=8.3519(3) Å, and a volume of 188.40(1) Å3. It was synthesized in a high-pressure/high-temperature experiment at 7 GPa and 1673 K and represents the first high-pressure oxonitridoborate. It is built up of starlike-shaped entities of four BO3N tetrahedra, connected via one common nitrogen atom that resembles the fourfold-coordinated nitrogen atoms in the homeotypic nitridosilicates MYbSi4N7 (M=Sr, Ba). Building up a network with channels that contain the Cr3+ ions, CrB4O6N contains for the first time a tetrahedral building unit in contrast to trigonal planar B(O/N)3 entities in all other known oxonitridoborates. The structural relations as well as the results of spectroscopic measurements and calculations on the chromium oxonitridoborate are discussed.
We present the results of geochemical analysis of silver coinage issued by Rome and dated between the fourth and second century BCE, which are complemented by data of coinage issued by Carthage, the Brettii, and the Greek colony of Emporion. Each of these minting authorities represents one of the major parties involved in the struggle for hegemony in the fourth to second centuries BCE Western Mediterranean region. This study retraces how the metal supply shifts in response to the transforming power relations and how this change is related to Rome's rise to the virtually uncontested ruler of the region.
The impact of precipitation in shallow cumulus convection on the moisture variance and third-order moments of moisture is investigated with the help of large-eddy simulations. Three idealized simulations based on the Rain in Cumulus over the Ocean field experiment are analyzed: one nonprecipitating, on a smaller domain, and two precipitating cases, on a larger domain with different initial profiles of moisture. Results show that precipitation and the associated cloud organization lead to increased generation of higher-order moments (HOM) of moisture compared to the nonprecipitating case. To understand the physical mechanism and the role of individual processes in this increase, budgets of HOM of moisture are studied. Microphysics directly decreases the generation of HOM of moisture, but this effect is not dominant. The gradient production term is identified as the main source term in the HOM budgets. The influence of the gradient production term on moisture variance is further examined separately in cloud active and nonactive regions. The main contribution to the gradient production term comes from the smaller cloud active region because of the stronger moisture flux. Further analyses of the horizontal and vertical cross sections of moisture fluctuations show that the precipitation-induced downdrafts and updrafts are the main mechanism for the generation of moisture variance. The variance increase is linked to shallow dry downdraft regions with horizontal divergence in the subcloud layer, moist updrafts with horizontal convergence in the bulk cloud layer, and finally wider areas of horizontal divergence in the cloud inversion layer.
The formation of terrestrial planets was a complex process which begun in the very early stage of the Solar System in the protoplanetary disk (PPD). Chondrites are fragments of planet precursors, which have never experienced differentiation and can help to reconstruct the first processes leading to planet formation. The main components of chondrites are chondrules, calcium-aluminum-rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), metals and fine-grained material. Each of these components formed by a complex mechanism involving aggregation and/or melting. Previous research has already provided an overall view of the formation of these objects, however, there are still open questions regarding the aggregation behavior of particles, the heating mechanism(s) and the thermal history of CAIs, AOAs and chondrules. For instance, the involvement of flash-heating events and electrostatics in the aggregation and melting of these objects has been a keen topic of discussion.
The aim of this doctoral thesis was to develop and carry out an experiment to study various early Solar System processes under long-term microgravity. In the project with the acronym EXCISS (Experimental Chondrule Formation aboard the ISS), free-floating, 126(23)µm-sized Mg2SiO4 dust particles were exposed to electric fields and electric discharges.
The experimental set-up was installed inside a 10x10x15 cm3-sized container and consisted of an arc generation unit connected to the sample chamber, a camera with an optical system, a power supply unit with lithium-ion batteries and the EXCISS mainboard with a Raspberry Pi Zero and mass storage devices. The sample chamber was manufactured from quartz glass and the experiments were filmed. The complete experiment container was subsequently returned to the Goethe University and the samples were analyzed with scanning electron microscopy, electron backscatter diffraction and synchrotron micro-CT.
Video analysis has shown that particles, which were agitated by electric discharges, align in chains within the electric field with their longest axis parallel to the electric field lines. Consequently, electric fields could have influenced the inner structure and porosity of particle aggregates in the PPD.
The discharge experiments produced fused aggregates and individual melt spherules.
The fused aggregates share many morphological characteristics with natural fluffy-type CAIs and some igneous CAIs found in chondrites. Consequently, CAIs could have formed by the aggregation of particles with various degrees of melting. Further, a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to, and subsequent compaction within, developing planetesimals.
Some initial particles were completely melted by the arc discharges and formed melt spherules. The newly formed olivines crystallized with a preferred orientation of the [010] axis perpendicular to the surface of the spherule. Similar preferred orientations have been found in natural chondrules. However, the microstructure differs from the results of previous experiments on Earth, which show, for example, crystal settling on one side of the sample because of the influence of gravity. Furthermore, the melt spherules show evidence for an interaction of the melt with the surrounding hot gas. Therefore, microgravity experiments with more advanced experimental parameters bear great potential for future chondrule formation experiments.
Mongolia covers a huge area in Asia and provides excellent Palaeozoic successions although large regions still lack detailed information on fauna and flora in Palaeozoic rocks. Of special interest is the Central Asian Orogenic Belt (CAOB), one of the largest collisional complexes on Earth. The CAOB is composed of a large number of terranes, continental margins, island arcs, backarc/forearc basins and accretionary wedges (Badarch et al. 2002; Safonova et al. 2017). Many terranes and regions underwent strong metamorphism, such as areas north of the Main Mongolian Lineament. To the south, Palaeozoic rocks exhibit low-grade metamorphism, thrusting and folding. Two promising long successions of Palaeozoic rocks were studied, namely the Hushoot Shiveetiin gol section and the Bayankhoshuu Ruins section. The intention of the PhD was to study marine facies settings in Palaeozoic rocks of southern and southwestern Mongolia, in an area little is known in terms of biostratigraphy and events. In order to get a better understanding on events and what might have been the driving forces I studied sections in Mongolia which have not been in the focus of research in the last decades. In order to complement studies on Late Devonian events elsewhere, I decided to study sections in open ocean environments (CAOB), far away from mainly studied epicontinental areas.As stated in many publications, events are the driving force for evolution. They exhibit dramatical changes in the palaeontological record of organisms and they are often associated with dramatic extinctions (Walliser 1996) and anoxic sediments (but not always). Mass extinctions are episodes in which a large number of plant and animal species became extinct within a few thousand to a hundred thousand years. Most events (first and second order events) are traceable worldwide. For instance, in the Late Devonian, mass extinction events recognized at the Frasnian–Famennian (F/F) stage boundary and at the Devonian–Carboniferous (D/C) boundary (McLaren and Goodfellow 1990; Sepkoski 1996; Walliser 1996). Overall, 19% of all families, 50% of all genera and at least 70% of all species became extinct (Raup and Sepkoski 1982; Sepkoski 1996; McGhee et al. 2013), but extinctions also concerned palaeoecosystems and due to Late Devonian events whole coral/stromatoporoid reef ecosystems became extinct. What might be the reason(s) for these dramatical changes? Why did the carbonate factory brake down? There are several reasons which have been discussed. For instance, extraterrestrial bolide impacts (McLaren 1970), anoxia within the water column due to climate changes (House 1985; Becker and House 1994; Caplan and Bustin 1999; Bond and Wignall 2005), transgressions and regressions (Newell 1967; Hallam and Wignall 1999; Purdy 2008; Ruban 2010, 2013; Smith and Benson 2013), eutrophication and increased sediment transport (Joachimski et al. 1993; Schobben et al. 2016), explosive volcanism (Paschall et al. 2019) and/ or large igneous provinces (LIP’s, Ernst et al. 2019; Racki et al. 2020, among others) and much more has been considered. The main problem is that previous studies preferably have been done along former epicontinental margins between Laurassia and Gondwana. Less information is available in deep open oceanic successions and shallow-water areas around island arcs. Generally, events are characterized by bituminous rocks, such as black limestones and shales within marine realms, but they do not necessarily occur everywhere (see Carmichael et al. 2016). So, the question was: “Can we recognize Palaeozoic event layers or equivalents in the CAOB?” If so, is this comparable to already published data? What might be the main trigger, as there are many reasons still in discussion? And finally, what has happened in the aftermath of those events as it seems that the CAOB may have acted as a refugium for at least some groups, such as for crinoids (Waters and Webster 2009; Tolokonnikova and Ernst 2010). In this thesis, I will provide data from isolated ecosystems from a rather unstudied region, which will complement studies from other parts of the World.
Support for innovative on-street parking policies: empirical evidence from an urban neighborhood
(2020)
Municipalities and planners often hesitate to implement restrictive parking policies because residents regularly oppose any changes to on-street parking space. Residential parking is one key factor of parking management because its location and availability influence a household's car ownership and use. Moreover, as more residents regularly use other means of transportation that need space and infrastructure in the urban realm, and as parking takes up a vast amount of land, municipalities are considering the reuse of on-street parking space for other purposes. As public acceptability is a precondition for the successful implementation of a proposed policy, our empirical analysis investigates to what extent residents support restrictive and demand-oriented on-street parking policies in the dense, highly urbanized neighborhood of Frankfurt-Bornheim, Germany (N = 1027). Surprisingly, despite some variations, the majority of the residents in our survey are in favor of the policy options suggested. Support for the demand-oriented policies (extension of bicycle infrastructure, improved sharing supply and mobility hubs, neighborhood garages, and improved public transit supply) is higher than the acceptance of the restrictive policies, and of policies that are a combination of restrictive and demand-oriented policies. However, surprisingly, a majority is still in favor of many of these (extension of parking fees and parking restrictions, and reuse of parking space for better livability). Furthermore, we classify residents who live in a household with private cars into the stage model of self-regulated behavior change to analyze their intention towards a reduction in private car use. Results from linear regression analyses indicate that residents who have intentions to change their behavior towards car use reduction assess the policy options more similarly to car-free households and regular bike users, and not like the other car-owning households. The findings suggest that while the residents support financial-related policies the least, they are more receptive towards parking policies than policy makers and planners assume if the reuse of parking lots creates space for other users or if it increases the quality of life, for instance, by adding bike lanes, wider sidewalks or greenery. Hence, a combination of restrictive and demand-oriented on-street parking policies results in high acceptance among residents, and the communication from municipalities regarding the implementation of the different policies needs to vary depending on the kind of household.
The organisation of parking is a key challenge to more sustainable mobility in urban areas, as its pricing and availability affect the rates of private car ownership and use. However, changing parking policies is a challenging issue for local politicians and planners because residents frequently oppose changes or restrictions to conditions they have taken for granted such as on-street parking in a public space. The aim of this paper is firstly to assess how the parking policy of an urban neighbourhood can be structured to contribute to more sustainable mobility and to increase liveability in the neighbourhood. The second aim is to apply the policies reviewed to an example neighbourhood. For this purpose, we systematically reviewed academic literature and identified five types of relevant parking policies: (i) maximum parking requirements, (ii) physical detachment of residence and parking space, (iii) residential parking permits and the limitation of available parking space, (iv) performance-based pricing and (v) parking as a demand management strategy. We discovered that most research focuses on econometric models about parking and that studies rarely address the effects of parking on the quality of life in neighbourhoods. Therefore, we need further research regarding the relationship of parking and liveability. We conclude that for the implementation of such parking policies in an example neighbourhood, the municipality needs to develop a mobility vision for its city. It has to understand parking as a tool for transportation demand management to increase the acceptance of parking policy concepts and to avoid spillover problems. Finally, in the German case, as in most other countries, states and municipalities need to redesign their legal frameworks to be able to manage parking supply better and to react to changes related to digital developments and parking. The findings have implications for other European neighbourhoods regarding the transfer from research to local circumstances and applications for the whole city.
The Weissert Event ~133 million years ago marked a profound global cooling that punctuated the Early Cretaceous greenhouse. We present modelling, high-resolution bulk organic carbon isotopes and chronostratigraphically calibrated sea surface temperature (SSTs) based on an organic paleothermometer (the TEX86 proxy), which capture the Weissert Event in the semi-enclosed Weddell Sea basin, offshore Antarctica (paleolatitude ~54 °S; paleowater depth ~500 meters). We document a ~3–4 °C drop in SST coinciding with the Weissert cold end, and converge the Weddell Sea data, climate simulations and available worldwide multi-proxy based temperature data towards one unifying solution providing a best-fit between all lines of evidence. The outcome confirms a 3.0 °C ( ±1.7 °C) global mean surface cooling across the Weissert Event, which translates into a ~40% drop in atmospheric pCO2 over a period of ~700 thousand years. Consistent with geologic evidence, this pCO2 drop favoured the potential build-up of local polar ice.
Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones.