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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.
With the Earth system being about to leave Holocene conditions and thus the known safe operating space for humanity, frameworks such as the Planetary Boundaries (PBs) and the Sustainable Development Goals (SDGs) provide quantitative metrics to guide sustainability transformations. In order to strive, not only for compliance with the PBs but also for societal well-being, some approaches attempt to combine both PBs and SDGs within a single assessment. We focus on two prominent examples, the “Doughnut” by Kate Raworth and the #SDGinPB project of the 2018 report to the Club of Rome, which are not only aimed at public outreach, but also at guiding policy-making. To meet these objectives, the approaches should possess a certain accuracy in determining the progress in achieving the SDGs and in complying with the PBs. We evaluate, by using a multi-indicator approach for comparison, whether both approaches’ limited set of indicators can still represent the SDGs’ complexity. This comparative approach estimates the progress in achieving SDGs, especially in the Global North, to be significantly lower. Based on these results and against the approaches’ purposes, we discuss their simplifications and at which point the results are no longer reliable. We conclude that global assessments can be an important factor in initiating transformative processes by stimulating public discourse, but that the actual implementation of these would require approaches with greater recognition of local particularities.
We combine structural analysis of fractures with 22 U–Pb dates measured in fracture-filling carbonate cements from bed-parallel fibrous calcite veins (beef), conjugated veins and faults within the Vaca Muerta Formation along the Andean fold and thrust belt in the Neuquén Basin. The measured ages constrain accurately the relationships between overpressures caused by hydrocarbon generation and Andean compression as mechanisms for natural fracturing and vein formation. Two generations of fibres have been identified in beef. The first one, consists of dark fibres from the inner zones, which are perpendicular to bedding and contain abundant cone-in-cone structures and hydrocarbon inclusions. U–Pb dating of these fibres yielded Early to Late Cretaceous ages from 116.7 ± 17.7 to 78.8 ± 10.2 Ma. The second generation of fibres corresponds to the outer zones and consists of white fibres oblique to bedding, indicating growth during layer-parallel shortening. Bed-perpendicular veins cutting beef yielded Late Cretaceous-late Palaeocene dates from 72.8 ± 22.4 to 60.9 ± 10.4 Ma. Eocene ages from 52.0 ± 2.9 to 42.2 ± 18.9 Ma were measured in bed-parallel slip surfaces and reverse and strike-slip faults, whereas Miocene dates from 13.9 ± 2.6 to 6.2 ± 1.1 Ma were measured in E-W calcite veins. U–Pb dating of veins, structural analysis of fractures and subsidence curves, indicate that beef inner zones formed in the oil window during burial of the Neuquén basin, and that tectonic stresses could enhance their formation. Beef outer zones and bed-perpendicular veins formed during E-W Late Cretaceous-late Palaeocene layer-parallel shortening. Contrarily, late Palaeocene-late Eocene bed-parallel slip surfaces and faults and Miocene E-W veins formed during NE-SW and E-W syn-to post-folding deformation, respectively. In both cases, syn-to post-folding compression occurred synchronously with forelandward migration of magmatic activity attributed to flat subduction of the Pacific slab beneath the Andes.
The impact of local environment characteristics on individual cycling behaviour has been discussed in transport research for several years. Many previous studies have, however, primarily focused on the presence and distribution of built environment elements, considered using georeferenced or census data. This paper argues that not only is the objectively measured environment an influencing factor, but also the individual perception of this environment. Furthermore, besides built elements, the evaluation of perceived non-built attributes, such as discourses and policies, as well as the environment’s impact on cycling attitudes, should be taken into account for a more comprehensive view. For this purpose, this study examines the responses to a household survey in the German city of Offenbach am Main (n = 701). The impact of the perceived local environment on cycling behaviour and cycling attitudes has been analysed using 21 perception items as well as socio-demographics, travel mode availability and general travel attitudes. For a more detailed view on cycling behaviour, this study applies the stage model of self-regulated behavioural change (SSBC) indicating a level of openness to use a bicycle frequently in everyday life. The results of the multivariate analysis show that the perceptions of built and non-built environment characteristics interrelate. Furthermore, certain perceptions encourage bicycle use and positive attitudes towards cycling, such as perceived cycling safety and pleasure. Primarily, these perceptions are safe and appropriate cycling infrastructures, cycling as a common practice and the absence of vandalism, dirt and high car pressure.
Motions on planetary spatial scales in the atmosphere are governed by the planetary geostrophic equations. However, little attention has been paid to the interaction between the baroclinic and barotropic flows within the planetary geostrophic scaling. This is the focus of the present study, which utilizes planetary geostrophic equations for a Boussinesq fluid supplemented by a novel evolution equation for the barotropic flow. The latter is affected by meridional momentum flux due to baroclinic flow and drag by the surface wind. The barotropic wind, on the other hand, affects the baroclinic flow through buoyancy advection. Via a relaxation towards a prescribed buoyancy profile the model produces realistic major features of the zonally symmetric wind and temperature fields. We show that there is considerable cancellation between the barotropic and the baroclinic surface zonal mean zonal winds. Linear and nonlinear model responses to steady diabatic zonally asymmetric forcing are investigated, and the arising stationary waves are interpreted in terms of analytical solutions. We also study the problem of baroclinic instability on the sphere within the present model.
Chondrules are thought to play a crucial role in planet formation, but the mechanisms leading to their formation are still a matter of unresolved discussion. So far, experiments designed to understand chondrule formation conditions have been carried out only under the influence of terrestrial gravity. In order to introduce more realistic conditions, we developed a chondrule formation experiment, which was carried out at long-term microgravity aboard the International Space Station. In this experiment, freely levitating forsterite (Mg2SiO4) dust particles were exposed to electric arc discharges, thus simulating chondrule formation via nebular lightning. The arc discharges were able to melt single dust particles completely, which then crystallized with very high cooling rates of >105 K h−1. The crystals in the spherules show a crystallographic preferred orientation of the [010] axes perpendicular to the spherule surface, similar to the preferred orientation observed in some natural chondrules. This microstructure is probably the result of crystallization under microgravity conditions. Furthermore, the spherules interacted with the surrounding gas during crystallization. We show that this type of experiment is able to form spherules, which show some similarities with the morphology of chondrules despite very short heating pulses and high cooling rates.
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.
Die angespannte Lage am Wohnungsmarkt hat in vielen Städten eine neue Welle von Verdrängungsprozessen induziert und insbesondere die Situation einkommensschwacher Haushalte häufig prekär werden lassen. Angesichts dieser Entwicklungen haben sich vielerorts mietenpolitische Bewegungen konstituiert, die sich für eine Abkehr von einer neoliberalisierten und zunehmend finanzialisierten Wohnungsversorgung einsetzen. Lisa Vollmer nimmt in ihrer Forschungsarbeit zwei solcher Bewegungen in den Blick und fragt danach, wie sich politische Kollektivität in den alltäglichen Praktiken von Mieter*innen in Berlin bzw. New York formiert.
Motivated by the question of whether and how wave–wave interactions should be implemented into atmospheric gravity-wave parametrizations, the modulation of triadic gravity-wave interactions by a slowly varying and vertically sheared mean flow is considered for a non-rotating Boussinesq fluid with constant stratification. An analysis using a multiple-scale WKBJ (Wentzel–Kramers–Brillouin–Jeffreys) expansion identifies two distinct scaling regimes, a linear off-resonance regime, and a nonlinear near-resonance regime. Simplifying the near-resonance interaction equations allows for the construction of a parametrization for the triadic energy exchange which has been implemented into a one-dimensional WKBJ ray-tracing code. Theory and numerical implementation are validated for test cases where two wave trains generate a third wave train while spectrally passing through resonance. In various settings, of interacting vertical wavenumbers, mean-flow shear, and initial wave amplitudes, the WKBJ simulations are generally in good agreement with wave-resolving simulations. Both stronger mean-flow shear and smaller wave amplitudes suppress the energy exchange among a resonantly interacting triad. Experiments with mean-flow shear as strong as in the vicinity of atmospheric jets suggest that internal gravity-wave dynamics are dominated in such regions by wave modulation. However, triadic gravity-wave interactions are likely to be relevant in weakly sheared regions of the atmosphere.
Container-breeding Aedes spp. (Diptera: Culicidae) mosquitoes can be surveilled at low cost using ovitraps. Hence, this method is a preferred monitoring approach of dengue vectors in low-resource settings. The ovitraps consist of a cup filled with water and an oviposition substrate for female mosquitoes. The attractiveness of the substrates for female mosquitoes can greatly differ due to differences in texture, color, and smell of the materials used. We compare four oviposition substrates, which are all low priced, easy to transport, and easy to purchase, to maximize the success of Aedes egg sampling. Sampled egg material is often reared to adulthood for further taxonomic identification and transported to (international) laboratories for specialized vector research. Here we introduce a transport technique for sampled eggs. In addition, we explored the impact of international transport by means of a bilateral hatching experiment in Nepal, the country of origin, and in Germany, in a laboratory specialized in ecophysiological research. The best low-cost oviposition substrate for the dengue vectors Aedes albopictus (Skuse) and Aedes aegypti (L.) was found to be a white cotton sheet. The introduced transport technique of sampled eggs is easy to build from laboratory and household materials and ensures good transport conditions (i.e., temperature and relative humidity). Even under good temperature (17.4–31.0 °C) and humidity conditions (58.9–94.2%), hatching success of eggs was found to be reduced after international transport to Germany when compared to the hatching success of eggs in Nepal. We postulate that air pressure during international transport may have reduced the hatching success and strongly recommend pressure-regulated transport boxes for egg transport via airplane. As the proposed operation procedure is useful in assisting the monitoring of Ae. albopictus and Ae. aegypti in low-resource settings, Aedes researchers are encouraged to follow it for the sampling and transport of Aedes eggs.
Triple oxygen isotope measurements are an emerging tool in paleoclimate reconstructions. In this contribution we develop the application of triple oxygen isotope measurements to lacustrine sediments to reconstruct past elevations. We focus on a well-constrained sample set from the Eocene North American Cordillera (Cherty Limestone Formation, Elko Basin, NV, United States, 42–43.5 Ma) on the east side of the elevated Nevadaplano. We present triple oxygen isotope measurements on freshwater lacustrine chert samples from the Cherty Limestone Formation. Across an evaporation trend spanning 6.5‰ in δ18O values we observe a negative correlation with Δ′17O ranging from −0.066 to −0.111‰ (λRL = 0.528), with an empirical slope (λchert, δ′17O vs. δ′18O) of 0.5236. Additionally, we present new carbonate clumped isotope (Δ47) temperature results on the overlying fluvial-lacustrine Elko Formation, which indicate an error-weighted mean temperature of 32.5 ± 3.8°C (1σ), and evaporatively enriched lake water spanning δ18O values of −3.7 to +3.5‰ (VSMOW). Paired chert and carbonate δ18O values demonstrate that co-equilbrium among the carbonate and chert phases is unlikely. Thus, as also previously suggested, it is most likely that Elko Basin chert formed during early diagenesis in equilbirium with pore waters that reflect evaporatively 18O-enriched lake water. Using this scenario we apply a model for back-calculating unevaporated water composition to derive a source water of δ′18O = −16.1‰ (VSMOW), similar to modern local meteoric waters but lower than previous work on paired δ18O- δD measurements from the same chert samples. Further, this back-calculated unevaporated source water is higher than those derived using δD measurements of Late Eocene hydrated volcanic glass from the Elko Basin (average δ′18O equivalent of approximately −18.4‰, VSMOW). This suggests, assuming Eocene meteoric water Δ′17O values similar to today (∼0.032‰), either that: (1) the hypsometric mean elevation recorded by the lacustrine Cherty Limestone was lower than that derived from the average of the volcanic glass δD measurements alone; or (2) there was hydrogen exchange in volcanic glass with later low δD meteoric fluids. Nonetheless, our new findings support a relatively high (∼2.5–3 km) plateau recorded in the Elko Basin during the mid-Eocene.
Climate controls the broad-scale distribution of vegetation and change in climate will alter the vegetation distribution, biome boundaries, biodiversity, phenology and supply of ecosystem services. A better understanding of the consequences of climate change is required, particularly in under-investigated regions such as tropical Asia, i.e., South and South-east Asia, which is a host to 7 of the 36 global biodiversity hotspots. Conservation strategies would also require an in-depth understanding of the response of vegetation to climate change. Therefore, the main objective of this thesis was to investigate the impact of climate change and rising CO2 vegetation in tropical Asia. Dynamic global vegetation model (DGVMs) are the well-known tools to investigate vegetation-climate interactions and climate change impacts on ecosystems. In this thesis, I used a complex trait-based DGVM called adaptive dynamic vegetation model version 2 (aDGVM2).
In Chapter 1, I presented a brief background of the phytogeography and discussed the exiting knowledge gap on vegetation-climate interactions in the region. One major disadvantage for available DGVMs studies for the tropical Asia is that most of them have used fixed plant functional types (PFTs) and do not explicitly represent the distinct varieties of vegetation type of the region such as Asian savannas. In Chapter 2, I discussed at great length to improve DGVMs for South Asia and discussed ways to include them in the model for better representation of region vegetation-climate interaction.
I upgraded the current version of aDGVM2 and added a new vegetation type i.e., C3 grasses, and modified the sub-module to simulate photosynthesis for each individual plants to aDGVM2. In chapter 3, I used this updated version of aDGVM2 to simulate the current and future vegetation distribution in South Asia under RCP4.5 and RCP8.5 (RCP: representative concentration pathway). The model predicted an increase in biomass, canopy cover, and tree height under the presence of CO2 fertilization, which triggered transitions towards tree-dominated biomes by the end of the 21st century under both RCPs. I found that vegetation along the Western Ghats and the Himalayas are more susceptible to change due to climate change and open biomes such as grassland and savanna are prone to woody encroachment.
In Chapter 4, the study domain was extended to include South-east Asia to verify if the model configuration used in Chapter 3 can also simulate vegetation patterns in tropical Asia. The aDGVM2 simulations showed a robust trend of increasing vegetation biomass and transitions from small deciduous vegetation to taller evergreen vegetation across most of tropical Asia. Shifts in plant phenology also affect ecosystem carbon cycles and ecosystem feedback to climate, yet the quantification of such impacts remains challenging. The study showed increased biomass due to CO2 fertilization, indicates that the region can remain a carbon sink given there is no other resource limitation. However, nutrient limitations on CO2 fertilization effects were not included in the study, and carbon sink potential has to be seen with caution.
In Chapter 5, I focused on Asian savannas, which have been mismanaged since the colonial era due to misinterpretation as a degraded forest. I proposed a biome classification scheme to distinguish between degraded forest or woodland and savanna based on the abundance of grass biomass and canopy cover. I found that considering vegetation systems as woodland or degraded forest could easily be mistaken as a potential for forest restoration within a tree-centric perspective. This would put approximately 35% to 40% of a unique savanna biome at risk. Although projected woody encroachments may imply a transition toward the forest that benefits climate mitigation. This raises potential conflicts of interest between biodiversity conservation in open ecosystems, i.e., savanna and active afforestation, to enhance carbon sequestration. Proper management strategies should be taken into account to maintain a balance for both objective
In conclusion, the model predicted that vegetation in South and South-East Asia would significantly shift towards tree-dominated biomes due to CO2-induced fertilization of C3-photosynthesis. The simulation under fixed CO2 and rising CO2 scenarios clearly showed that rising level of atmospheric CO2 is responsible for most of the predicted change in biome properties. This study is an important step towards understanding ecosystems of South and Southeast Asia, specifically savannas. The aDGVM2 can serve as tools to inform decision making for climate adaptation and mitigation for savanna. The thesis, thus contributes to our ability to improve conservation strategies to mitigate the consequences of climate change.
The weather of the atmospheric boundary layer significantly affects our life on Earth. Thus, a realistic modelling of the atmospheric boundary layer is crucial. Hereby, the processes of the atmospheric boundary layer depend on an accurate representation of the land-atmosphere coupling in the model. In this context the land surface temperature (LST) plays an important role. In this thesis, it is examined if the assimilation of LST can lead to improved estimates of the boundary layer and its processes.
To properly assimilate the LST retrievals, a suitable model equivalent in the weather prediction model is necessary. In the weather forecast model of the German Weather Service used here, the LST is modelled without a vegetation temperature. To compensate for this deficit, two different vegetation parameterizations were investigated and the better one, a conductivity scheme, was implemented. In order to make optimal use of the influence of the assimilation of the LST observation on the model system, it is useful to pass on the information of the observation to land and atmosphere already in the assimilation step. For that reason, a fully coupled land-atmosphere prediction model was used. Therefore, the existing control vector of the assimilation system, a local ensemble transform Kalman filter, was extended by the soil temperature and moisture. In two-day case studies in March and August 2017, different configurations of the augmented assimilation system were evaluated based on observing system simulation experiments (OSSE).
LST was assimilated hourly over two days in the weakly and strongly coupled assimilation system. In addition, every six hours a free 24-hour forecast was simulated. The experiments were validated with the simulated truth (a high-resolution model run) and compared against an experiment without assimilation. It was shown that the prediction of the boundary layer temperature, especially during the day, and the prediction of the soil temperature, during the whole day and night, could be improved.
The best impact of LST assimilation was achieved with the fully coupled system. The humidity variables of the model benefited only partially from the LST assimilation. For this reason, covariances in the model ensemble were investigated in more detail. To check their compatibility with the high-resolution model run the ensemble consistency score was introduced. It was found that the covariances between the LST and the temperatures of the high-resolution model run were better represented in the ensemble than those between the LST and the humidity variables.
Drought is understood as both a lack of water (i.e., a deficit compared to demand) and a temporal anomaly in one or more components of the hydrological cycle. Most drought indices, however, only consider the anomaly aspect, i.e., how unusual the condition is. In this paper, we present two drought hazard indices that reflect both the deficit and anomaly aspects. The soil moisture deficit anomaly index, SMDAI, is based on the drought severity index, DSI (Cammalleri et al., 2016), but is computed in a more straightforward way that does not require the definition of a mapping function. We propose a new indicator of drought hazard for water supply from rivers, the streamflow deficit anomaly index, QDAI, which takes into account the surface water demand of humans and freshwater biota. Both indices are computed and analyzed at the global scale, with a spatial resolution of roughly 50 km, for the period 1981–2010, using monthly time series of variables computed by the global water resources and the model WaterGAP 2.2d. We found that the SMDAI and QDAI values are broadly similar to values of purely anomaly-based indices. However, the deficit anomaly indices provide more differentiated spatial and temporal patterns that help to distinguish the degree and nature of the actual drought hazard to vegetation health or the water supply. QDAI can be made relevant for stakeholders with different perceptions about the importance of ecosystem protection, by adapting the approach for computing the amount of water that is required to remain in the river for the well-being of the river ecosystem. Both deficit anomaly indices are well suited for inclusion in local or global drought risk studies.
Analysing the composition of ambient ultrafine particles (UFPs) is a challenging task due to the low mass and chemical complexity of small particles, yet it is a prerequisite for the identification of particle sources and the assessment of potential health risks. Here, we show the molecular characterization of UFPs, based on cascade impactor (Nano-MOUDI) samples that were collected at an air quality monitoring station near one of Europe's largest airports, in Frankfurt, Germany. At this station, particle-size-distribution measurements show an enhanced number concentration of particles smaller than 50 nm during airport operating hours. We sampled the lower UFP fraction (0.010–0.018, 0.018–0.032, 0.032–0.056 µm) when the air masses arrived from the airport. We developed an optimized filter extraction procedure using ultra-high-performance liquid chromatography (UHPLC) for compound separation and a heated electrospray ionization (HESI) source with an Orbitrap high-resolution mass spectrometer (HRMS) as a detector for organic compounds. A non-target screening detected ∼200 organic compounds in the UFP fraction with sample-to-blank ratios larger than 5. We identified the largest signals as homologous series of pentaerythritol esters (PEEs) and trimethylolpropane esters (TMPEs), which are base stocks of aircraft lubrication oils. We unambiguously attribute the majority of detected compounds to jet engine lubrication oils by matching retention times, high-resolution and accurate mass measurements, and comparing tandem mass spectrometry (MS2) fragmentation patterns between both ambient samples and commercially available jet oils. For each UFP stage, we created molecular fingerprints to visualize the complex chemical composition of the organic fraction and their average carbon oxidation state. These graphs underline the presence of the homologous series of PEEs and TMPEs and the appearance of jet oil additives (e.g. tricresyl phosphate, TCP). Targeted screening of TCP confirmed the absence of the harmful tri-ortho isomer, while we identified a thermal transformation product of TMPE-based lubrication oil (trimethylolpropane phosphate, TMP-P). Even though a quantitative determination of the identified compounds is limited, the presented method enables the qualitative detection of molecular markers for jet engine lubricants in UFPs and thus strongly improves the source apportionment of UFPs near airports.
Shrubs are a characteristic component of savannas, where they coexist with trees and grasses. They are often part of woody encroachment phenomena, which have been observed globally, and the determinant of shrub encroachment cases, which are particularly of concern in African savannas. In response to climate change and land use change, African savannas are vulnerable to biome shifts and shrub encroachment is a process driving and explaining this risk.
We contribute to furthering the understanding of shrubs biogeography and ecology by considering the number of stems of woody plants to characterise shrubs phenotype and strategy. We postulate that shrubs are multi-stemmed, compared to single-stemmed trees and integrate this assumption in aDGVM2 (adaptive Dynamic Global Vegetation Model 2). Modelling a trait representing the number of stems of a woody plant implies a trade-off between single-stemmed plants having higher height growth potential and multi-stemmed plants having higher hydraulic capacity but limited height growth. Multi-stemmed individuals, being shorter, are more likely to suffer severe damage from fires than tall single-stemmed trees managing to grow their crown out of the flame zone.
We simulate potential vegetation over sub-Saharan Africa at 1° spatial resolution, with aDGVM2 and compare it to simulations without our shrub model turned on. We also test the impact of fire by including or excluding it from our simulations. To assess the accuracy and relevance of our approach, we benchmark our overall model’s performance against multiple satellite derived products of above ground biomass (AGBM), and against specific field measurements of AGBM. We further benchmark our results against vegetation cover type derived from satellite data.
We demonstrate that shrubs can be modelled as multi-stemmed woody plants in African savannas based on whole-plant trait trade-off without being predefined as static functional types. Indeed, the addition of our shrub model to aDGVM2 allows for shrubs to emerge dynamically through community assembly processes without a priori categorisation. Our shrub model also improves the simulated vegetation patterns simulated by aDGVM2 in sub-Saharan Africa, particularly in savannas. The simulated pattern of stem number per woody individual broadly follows our assumptions about biogeographic patterns as it is lowest in equatorial African forests and increases in savannas and grasslands as precipitation decreases. Shrubs are more abundant in more water-stressed regions where they have a competitive advantage over trees due to their increased relative water transport potential. However, in arid and hyper-arid regions, further investigations are required. Simulated shrub prevalence is higher in more open and fire prone landscapes, where woody cover and biomass are reduced.
Adding shrubs to aDGVM2, while increasing complexity allows for greater simulated diversity. As resilience and resistance of ecosystems have been shown to be influenced by diversity, such model development is necessary to improve our ability to forecast ecosystems responses to changes. However, there are challenges to fully tap this benefit. Assessing the accuracy and relevance of our approach is challenging. Data and simulations are conceptually different which limit the possibility to conclude based on comparison. Benchmarking challenge is exacerbated by the variability existing among satellite derived products and site studies observations. In areas of extremely low biomass and vegetation cover, such as deserts and semi-deserts, the accuracy of our model is more concerning as small differences in absolute values are relatively more important.
Categorisation of life-forms shapes our understanding of their ecology and biogeography, thus, consensus about their definition is direly needed. To contribute to this debate, we investigate how vegetation distribution patterns arising from our shrub model inform our understanding of shrub biogeography. First, shrub distribution in trait space (considering stem number), relatively to environmental drivers, concurs with our assumptions. Second, shrub spatial distribution is consistent with our characterisation assumptions. Third, the role of simulated shrubs in an ecosystem supports realistic ecological dynamics. Our model allows for, shrubs to exhibit a specific phenotype, but also a specific life-strategy, which we characterise in terms of persistence strategy (shrubs are mainly resprouters, in contrast to trees, which can be either resprouters or reseeders) and in terms of resource acquisition (rooting strategy) and allocation (carbon investment). Adding stem count as a trait to aDGVM2 increase the range of simulated functional diversity.
Our shrub model allows for aDGVM2 to simulate realistic ratio of grass to woody vegetation across sub-saharan Africa. Similarly, it simulates ratio of shrubs to trees consistent with our hypotheses.
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The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense SWATH-D seismic network as a complementary experiment to the AlpArray seismic network provides unprecedented lateral resolution to address this ongoing discussion. We analyze the shear-wave splitting of this data set including stations of the AlpArray backbone in the region to obtain new insights into the deformation at depth from seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by the azimuthal pattern of the measured fast axis direction across all analyzed stations. However, the temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic properties of the mantle. We, therefore, perform a cluster analysis based on a correlation of energy tensors between all stations. The energy tensors are assembled from the remaining transverse energy after the trial correction of the splitting effect from two consecutive anisotropic layers. This leads to two main groups of different two-layer properties, separated approximately at 13°E. We identify a layer with a constant fast axis direction (measured clockwise with respect to north) of about 60° over the whole area, with a possible dip from west to east. The lower layer in the west shows N–S fast direction and the upper layer in the east shows a fast axis of about 115°. We propose two likely scenarios, both accompanied by a slab break-off in the eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with a lithospheric origin or as an asthenospheric flow evading the retreat of the European slab that would precede the break-off event. In both scenarios, the upper layer in the east is a result of a flow through the gap formed in the slab break-off. The N–S direction can be interpreted as an asthenospheric flow driven by the retreating European slab but might also result from a deep-reaching fault-related anisotropy.
Abstract:
The mid Miocene represents an important target for paleoclimatic study because the atmospheric CO2 concentration ranged from near modern values to ∼800 ppm, while a large, dynamic Antarctic ice sheet was likely to have been present throughout much of this interval. In this special issue, Modestou et al. (2020) (doi.org/10.1029/2020PA003927) reconstruct deep ocean warmth based on the clumped isotopic composition of benthic foraminifera, a technique that allows the ice volume and thermal components of the benthic oxygen isotope stack to be separated. These data reveal a very warm deep ocean while simultaneously suggesting that continental ice volume may, at times, have been greater than today. Here, I review these results in the context of recent developments in geochemical proxies and ice sheet modeling, and explore how the presence of a large Miocene ice sheet could be reconciled with CO2 at least as high as present. More broadly, I argue that many of the 'paradoxes' that pepper the paleoclimate literature result as much from our imperfect understanding of the proxies, as from our understanding of the climate system. Robust proxies with a well-understood mechanistic basis, as employed by Modestou et al. (2020), as well as advances in model-data comparability usher in a new era of palaeoclimate research; an exciting future of untangling Earth's myriad past climate states awaits.
Plain Language Summary:
Reconstructing climate variation in Earth's geologic past informs us of the broad features of warm climates, which is relevant to preparing for climate change over the coming centuries. Moreover, these data can be compared to state-of-the-art climate models, which provides a test of the degree to which our models can reproduce warm climate states. A paper recently published in this journal applies a new method in order to reconstruct the temperature of the deep ocean in the middle Miocene (between 17 and 12 million years ago), when the atmospheric CO2 concentration was naturally similar to or higher than it is today. Coupled with decades of previous study, these exciting results depict an unfamiliar world characterized by a warm deep ocean, and yet a large ice sheet was present on Antarctica. Both models and data agree that the Antarctic ice sheet in the Miocene was highly responsive to changes in the atmospheric CO2 concentration, a clear cause of concern in the context of ongoing anthropogenic climate change.
Extreme convective precipitation is expected to increase with global warming. However, the rate of increase and the understanding of contributing processes remain highly uncertain. We investigated characteristics of convective rain cells like area, intensity, and lifetime as simulated by a convection-permitting climate model in the area of Germany under historical (1976–2005) and future (end-of-century, RCP8.5 scenario) conditions. To this end, a tracking algorithm was applied to 5-min precipitation output. While the number of convective cells is virtually similar under historical and future conditions, there are more intense and larger cells in the future. This yields an increase in hourly precipitation extremes, although mean precipitation decreases. The relative change in the frequency distributions of area, intensity, and precipitation sum per cell is highest for the most extreme percentiles, suggesting that extreme events intensify the most. Furthermore, we investigated the temperature and moisture scaling of cell characteristics. The temperature scaling drops off at high temperatures, with a shift in drop-off towards higher temperatures in the future, allowing for higher peak values. In contrast, dew point temperature scaling shows consistent rates across the whole dew point range. Cell characteristics scale at varying rates, either below (mean intensity), at about (maximum intensity and area), or above (precipitation sum) the Clausius–Clapeyron rate. Thus, the widely investigated extreme precipitation scaling at fixed locations is a complex product of the scaling of different cell characteristics. The dew point scaling rates and absolute values of the scaling curves in historical and future conditions are closest for the highest percentiles. Therefore, near-surface humidity provides a good predictor for the upper limit of for example, maximum intensity and total precipitation of individual convective cells. However, the frequency distribution of the number of cells depending on dew point temperature changes in the future, preventing statistical inference of extreme precipitation from near-surface humidity.
Ice particle activation and evolution have important atmospheric implications for cloud formation, initiation of precipitation and radiative interactions. The initial formation of atmospheric ice by heterogeneous ice nucleation requires the presence of a nucleating seed, an ice-nucleating particle (INP), to facilitate its first emergence. Unfortunately, only a few long-term measurements of INPs exist, and as a result, knowledge about geographic and seasonal variations of INP concentrations is sparse. Here we present data from nearly 2 years of INP measurements from four stations in different regions of the world: the Amazon (Brazil), the Caribbean (Martinique), central Europe (Germany) and the Arctic (Svalbard). The sites feature diverse geographical climates and ecosystems that are associated with dissimilar transport patterns, aerosol characteristics and levels of anthropogenic impact (ranging from near pristine to mostly rural). Interestingly, observed INP concentrations, which represent measurements in the deposition and condensation freezing modes, do not differ greatly from site to site but usually fall well within the same order of magnitude. Moreover, short-term variability overwhelms all long-term trends and/or seasonality in the INP concentration at all locations. An analysis of the frequency distributions of INP concentrations suggests that INPs tend to be well mixed and reflective of large-scale air mass movements. No universal physical or chemical parameter could be identified to be a causal link driving INP climatology, highlighting the complex nature of the ice nucleation process. Amazonian INP concentrations were mostly unaffected by the biomass burning season, even though aerosol concentrations increase by a factor of 10 from the wet to dry season. Caribbean INPs were positively correlated to parameters related to transported mineral dust, which is known to increase during the Northern Hemisphere summer. A wind sector analysis revealed the absence of an anthropogenic impact on average INP concentrations at the site in central Europe. Likewise, no Arctic haze influence was observed on INPs at the Arctic site, where low concentrations were generally measured. We consider the collected data to be a unique resource for the community that illustrates some of the challenges and knowledge gaps of the field in general, while specifically highlighting the need for more long-term observations of INPs worldwide.
Determining how the elevation of the Northern Andes has evolved over time is of paramount importance for understanding the response of the Northern Andes to deformational and geodynamic processes and its role as an orographic barrier for atmospheric vapor transport over geologic time. However, a fundamental requirement when using stable isotope data for paleoaltimetry reconstructions is knowledge about the present-day changes of δ18O and δD with elevation (isotopic lapse rate). This study defines the present-day river isotopic lapse rate near the Equator (∼3°S) based on analysis of δ18O and δD of surface waters collected from streams across the Western Cordillera and the Inter-Andean depression in Southern Ecuador. The results for the two domains show a decrease of δ18O with elevation which fits a linear regression with a slope of −0.18‰/100 m (R2 = 0.73, n = 83). However, we establish a present-day lapse rate of −0.15‰/100 m for δ18O (R2 = 0.88, n = 19) and -1.4‰/100 m for δD (R2 = 0.93, n = 19) from water samples collected along the west facing slopes of the Western Ecuadorian Cordillera which is mainly subject to moisture transport from the Pacific. We argue that this empirical relationship, consistent with those obtained in different tropical areas of the world, can inform stable isotope paleoaltimetry reconstructions in tropical latitudes.
This Ph.D. thesis demonstrates i) the highly precise performance of refined and new analytical setups for clumped isotope analysis (Δ47 and Δ48) and ii) the applicability of clumped isotope analyses to biogenic and abiogenic carbonated apatite (Δ47) and abiogenic carbonates (Δ47 and Δ48) for research related to paleothermophysiology and paleoclimatology, whereas the overall analytical precision has been increased.
A comprehensive Δ47 dataset with 122 replicate analyses is provided from which the temperature dependence of Δ47 for (bio)apatite (Δ47-1/T2) is calculated between 1 °C and 80 °C. The temperature dependence of oxygen isotope equilibrium fractionation between carbonated synthetic apatite and water (1,000ln(αCHAP-H2O)) is experimentally determined. When applied to tooth enameloid from a modern Greenland shark (Somniosus microcephalus), a Late Miocene megatooth shark (Carcharodon megalodon), and an Upper Cretaceous Tyrannosaurus rex, reconstructed Δ47-based temperatures and δ18OH2O are in line with previously published data.
An analytical setup for highly precise clumped isotope analysis is described that allows for the simultaneous measurement of ∆47 and ∆48 in CO2 with external reproducibilities close to the respective shot-noise limits. The analyte gases originate from pure carbonates that were digested in hypersaturated orthophosphoric acid and purified using a fully automated device. Δ47 data sets with 117 replicate analyses in total on 22 pedogenic carbonate nodules from two Spanish Middle Miocene sections reveal the continental Southern European thermal structure during the end of the Middle Miocene Climatic Optimum (MCO) and the complete Middle Miocene Climatic Transition (MMCT; from 15.33 to 12.98 Ma).
Aim: Biological invasions are likely determined by species dispersal strategies as well as environmental characteristics of a recipient region, especially climate and human impact. However, the contribution of climatic factors, human impact, and dispersal strategies in driving invasion processes is still controversial and not well embedded in the existing theoretical considerations. Here, we study how climate, species dispersal strategies, and human impact determine plant invasion processes on islands distributed in all major oceans in the context of directional ecological filtering.
Location: Six mountainous, tropical, and subtropical islands in three major oceans: Island of Hawai'i and Maui (Pacific), Tenerife and La Palma (Atlantic), and La Réunion and Socotra (Indian Ocean).
Taxon: Vascular Plants.
Methods: We recorded 360 non-native species in 218 plots along roadside elevational transects covering the major temperature, precipitation and human impact (i.e., road density) gradients of the islands. We collected dispersal strategies for a majority of the recorded species and calculated the environmental niche per species using a hypervolume approach.
Results: Non-native species’ generalism (i.e., mean community niche width) increased with precipitation, elevation and human impact but showed no relationship with temperature. Increasing precipitation led to environmental filtering of non-native species resulting in more generalist species under high precipitation conditions. We found no directional filtering for temperature but an optimum range of most species between 10 and 20°C. Niche widths of non-native species increased with the prevalence of certain dispersal strategies, particularly anemochory and anthropochory.
Main conclusions: Plant invasion on tropical and subtropical islands seems to be mainly driven by precipitation and human impact, while temperature seems to be of little importance. Furthermore, anemochory and anthropochory are dispersal strategies associated with large niche widths of non-native species. Our study allows a more detailed look at the mechanisms behind directional ecological filtering of non-native plant species in non-temperature-limited ecosystems.
The current state of research about ancient settlements within the Nile Delta allows the hypothesizing of fluvial connections to ancient settlements all over the Nile Delta. Previous studies suggest a larger Nile branch close to Kom el-Gir, an ancient settlement hill in the northwestern Nile Delta. To contribute new knowledge to this little-known site and prove this hypothesis, this study aims at using small-scale paleogeographic investigations to reconstruct an ancient channel system in the surroundings of Kom el-Gir. The study pursues the following: (1) the identification of sedimentary environments via stratigraphic and portable X-ray fluorescence (pXRF) analyses of the sediments, (2) the detection of fluvial elements via electrical resistivity tomography (ERT), and (3) the synthesis of all results to provide a comprehensive reconstruction of a former fluvial network in the surroundings of Kom el-Gir. Therefore, auger core drillings, pXRF analyses, and ERT were conducted to examine the sediments within the study area. Based on the evaluation of the results, the study presents clear evidence of a former channel system in the surroundings of Kom el-Gir. Thereby, it is the combination of both methods, 1-D corings and 2-D ERT profiles, that derives a more detailed illustration of previous environmental conditions which other studies can adopt. Especially within the Nile Delta which comprises a large number of smaller and larger ancient settlement hills, this study's approach can contribute to paleogeographic investigations to improve the general understanding of the former fluvial landscape.
Analyzing the impact of streamflow drought on hydroelectricity production: a global-scale study
(2021)
Electricity production by hydropower is negatively affected by drought. To understand and quantify risks of less than normal streamflow for hydroelectricity production (HP) at the global scale, we developed an HP model that simulates time series of monthly HP worldwide and thus enables analyzing the impact of drought on HP. The HP model is based on a new global hydropower database (GHD), containing 8,716 geo-localized plant records, and on monthly streamflow values computed by the global hydrological model WaterGAP with a spatial resolution of 0.5°. The GHD includes 44 attributes and covers 91.8% of the globally installed capacity. The HP model can reproduce HP trends, seasonality, and interannual variability that was caused by both (de)commissioning of hydropower plants and hydrological variability. It can also simulate streamflow drought and its impact on HP reasonably well. Global risk maps of HP reduction were generated for both 0.5° grid cells and countries, revealing that 67 out of the 134 countries with hydropower suffer, in 1 out of 10 years, from a reduction of more than 20% of mean annual HP and 18 countries from a reduction of more than 40%. The developed HP model enables advanced assessments of drought impacts on hydroelectricity at national to international levels.
AirCore samplers have been increasingly used to capture vertical profiles of trace gases reaching from the ground up to about 30 km, in order to validate remote sens- ing instruments and to investigate transport processes in the stratosphere. When deployed to a weather balloon, accu- rately attributing the trace gas measurements to the sampling altitudes is nontrivial, especially in the stratosphere. In this paper we present the CO-spiking experiment, which can be deployed to any AirCore on any platform in order to evalu- ate different computational altitude attribution processes and to experimentally derive the vertical resolution of the profile by injecting small volumes of signal gas at predefined GPS altitudes during sampling. We performed two CO-spiking flights with an AirCore from the Goethe University Frankfurt (GUF) deployed to a weather balloon in Traînou, France, in June 2019. The altitude retrieval based on an instantaneous pressure equilibrium assumption slightly overestimates the sampling altitudes, especially at the top of the profiles. For these two flights our altitude attribution is accurate within 250 m below 20 km. Above 20 km the positive bias becomes larger and reaches up to 1.2 km at 27 km altitude. Differences in descent velocities are shown to have a major impact on the altitude attribution bias. We parameterize the time lag between the theoretically attributed altitude and the actual CO-spike release altitude for both flights together and use it to empirically correct our AirCore altitude retrieval. Regard- ing the corrected profiles, the altitude attribution is accurate within ±120 m throughout the profile. Further investigations are needed in order to test for the scope of validity of this correction parameter regarding different ambient conditions and maximum flight altitudes. We derive the vertical resolu- tion from the CO spikes of both flights and compare it to the modeled vertical resolution. The modeled vertical resolution is too optimistic compared to the experimentally derived res- olution throughout the profile, albeit agreeing within 220 m. All our findings derived from the two CO-spiking flights are strictly bound to the GUF AirCore dimensions. The newly introduced CO-spiking experiment can be used to test differ- ent combinations of AirCore configurations and platforms in future studies.
Acesta excavata (Fabricius, 1779) is a slow growing bivalve from the Limidae family and is often found associated with cold-water coral reefs along the European continental margin. Here we present the compositional variability of frequently used proxy elemental ratios (Mg/ Ca, Sr/Ca, Na/Ca) measured by laser-ablation mass spectrometry (LA-ICP-MS) and com- pare it to in-situ recorded instrumental seawater parameters such as temperature and salin- ity. Shell Mg/Ca measured in the fibrous calcitic shell section was overall not correlated with seawater temperature or salinity; however, some samples show significant correlations with temperature with a sensitivity that was found to be unusually high in comparison to other marine organisms. Mg/Ca and Sr/Ca measured in the fibrous calcitic shell section display significant negative correlations with the linear extension rate of the shell, which indicates strong vital effects in these bivalves. Multiple linear regression analysis indicates that up to 79% of elemental variability is explicable with temperature and salinity as independent pre- dictor values. Yet, the overall results clearly show that the application of Element/Ca (E/Ca) ratios in these bivalves to reconstruct past changes in temperature and salinity is likely to be complicated due to strong vital effects and the effects of organic material embedded in the shell. Therefore, we suggest to apply additional techniques, such as clumped isotopes, in order to exactly determine and quantify the underlying vital effects and possibly account for these. We found differences in the chemical composition between the two calcitic shell lay- ers that are possibly explainable through differences of the crystal morphology. Sr/Ca ratios also appear to be partly controlled by the amount of magnesium, because the small magne- sium ions bend the crystal lattice which increases the space for strontium incorporation. Oxi- dative cleaning with H2O2 did not significantly change the Mg/Ca and Sr/Ca composition of the shell. Na/Ca ratios decreased after the oxidative cleaning, which is most likely a leaching effect and not caused by the removal of organic matter.
The future physiology of marine phytoplankton will be impacted by a range of changes in global ocean conditions, including salinity regimes that vary spatially and on a range of short- to geological timescales. Coccolithophores have global ecological and biogeochemical significance as the most important calcifying marine phytoplankton group. Previous research has shown that the morphology of their exoskeletal calcified plates (coccoliths) responds to changing salinity in the most abundant coccolithophore species, Emiliania huxleyi. However, the extent to which these responses may be strain-specific is not well established. Here we investigated the growth response of six strains of E. huxleyi under low (ca. 25) and high (ca. 45) salinity batch culture conditions and found substantial variability in the magnitude and direction of response to salinity change across strains. Growth rates declined under low and high salinity conditions in four of the six strains but increased under both low and high salinity in strain RCC1232 and were higher under low salinity and lower under high salinity in strain PLYB11. When detailed changes in coccolith and coccosphere size were quantified in two of these strains that were isolated from contrasting salinity regimes (coastal Norwegian low salinity of ca. 30 and Mediterranean high salinity of ca. 37), the Norwegian strain showed an average 26% larger mean coccolith size at high salinities compared to low salinities. In contrast, coccolith size in the Mediterranean strain showed a smaller size trend (11% increase) but severely impeded coccolith formation in the low salinity treatment. Coccosphere size similarly increased with salinity in the Norwegian strain but this trend was not observed in the Mediterranean strain. Coccolith size changes with salinity compiled for other strains also show variability, strongly suggesting that the effect of salinity change on coccolithophore morphology is likely to be strain specific. We propose that physiological adaptation to local conditions, in particular strategies for plasticity under stress, has an important role in determining ecotype responses to salinity.
The analysis of the global stratospheric meridional circulation, known as the Brewer-Dobson circulation, is an essential part of both experimental and theoretical atmospheric sciences. This large-scale circulation has a crucial influence on the global burden of greenhouse gases and ozone depleting substances throughout the complete atmosphere. This makes it an important factor for the Earth’s radiative budget, which is perceptible at the Earth’s surface despite the remote location of the stratosphere. In the course of climate change it is generally expected that also the Brewer-Dobson circulation undergoes significant changes in structure and strength, although the exact repercussions are still uncertain and thus remain an open scientific question. A general problem for the observational investigation of the dynamical processes in the stratosphere is that residual mean transport cannot be measured directly and hence requires the use of sophisticated proxies. Many studies in the past consider the so-called mean age of air, which is a measure of the average time an air parcel has spent in the stratosphere since passing a certain reference point. While changes in the strength and structure can be detected and visualized using mean age of air, a more thorough distinction between the different involved transport mechanisms of the circulation (residual circulation, mixing) cannot be made. For that, consideration of a full distribution of all relevant transit times through the stratosphere, an age spectrum, is favorable and a powerful tool to analyze the spatial structure as well as possible future changes in detail. Mean age of air and age spectra can be readily derived in atmospheric modeling studies, but an observationally based retrieval is challenging. Mean age of air is usually approximated from measurements of very long-lived trace gas species that act as a dynamical tracer for the stratosphere. The retrieval of age spectra from observations, however, remains an open task for which different methods have been proposed in the past, that often require a combination of strong assumptions and model data explicitly. This is a major issue for a precise and independent investigation of stratospheric dynamics based on measurements. The focus of this cumulative dissertation is on the development process and application of an inversion method to derive stratospheric age spectra from mixing ratios of chemically active substances that combines an applicable and precise ansatz with a minimized amount of necessary model data. Chemically active species have the important benefit that chemistry and transport in the stratosphere are strongly correlated so that the state of depletion of a trace gas can give some information on certain parts of the age spectrum. Considering a sufficient number of distinct trace gases simultaneously, a full approximation of the age spectrum should be possible. The main section of this thesis is split into three parts, which follow the main aspects and key results of the three publications involved (Hauck et al., 2019, 2020; Keber et al., 2020). The newly developed inverse method is based upon the previously established ansatz by Schoeberl et al. (2005), but constrains the shape of the age spectrum by a single parameter inverse Gaussian function. This keeps the balance between applicability and accuracy with a limited amount of measurement data. Additionally, the method introduces a seasonal scaling factor that imposes higher order maxima and minima onto the intrinsically monomodal spectrum based on the seasonal cycle of the tropical upward mass flux to incorporate phases of weaker and stronger transport. A proof of concept of the inverse method is provided using an idealized simulation of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, where the method is applied to a set of artificial radioactive trace gases with known chemical lifetime. The results imply that the method works properly and retrieves age spectra that match the EMAC reference spectra significantly well on the global and seasonal scale. Only in the lower stratosphere, the performance of the inverse method on the seasonal scale decreases as entrainment into the stratosphere is considered only across the tropical tropopause. Transport across the local extratropical tropopause, however, is a key feature for trace gases in the extratropical lowermost stratosphere so that this entrainment must be included explicitly.
In the second part, the discovered problems are approached to make the inverse method applicable to observations. The formulation of the method is extended to incorporate transport explicitly across the tropical (30° S – 30° N), northern extratropical (30° N – 90° N), and southern extratropical tropopause (30° S – 90° S) each with a single age spectrum that can be inverted independently.
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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.
As a cognitively-mediated response, autonomous adaptation at farm-gate levels constitutes reactionary actions by farmers against climate impacts. These actions are shaped by interacting factors such as household characteristics, livelihood scope and resources. It is driven by the goal of adapting cultivated farmlands to climate and for sustaining crop yields. Thus, interest in balancing adaptation goals with protection of vegetation conditions is less of a priority. Lack of research interest in understanding the gap between objectives of reactionary adaptation and protection of surface conditions (vegetation canopies) is a gap in research. In many studies, farm-gate level adaptation is described as a set of zero-feedback actions in response to climate impacts. This perception conceals the stress and impact-engendering attribute of reactionary adaptation. Inspired towards addressing this conceptual gap; this study investigates impact of farmers’ reactionary adaptation on vegetation cover in Keffi, Nasarawa, Nigeria. A twenty-year time-series NDVI and rainfall datasets are linearly regressed to examine the extent of NDVI-rainfall sensitivity. A weak linear relationship between NDVI and rainfall in Keffi for the period, 1999-2018 is observed. At a regression slope of 0.001, R squared, R2=0.129 (implying that only about 13% of the variability in NDVI in Keffi are explained by rainfall amount) and a bivariate regression coefficient, r=0.359; statistical evidence shows that rainfall amount are not significant predictors of NDVI in Keffi. In investigating the possible interference of non-rainfall factors on vegetation productivity (NDVI) in Keffi; a residual trend (RESTREND) analysis was carried out. Regression of residuals from NDVI-Rainfall linear regression produced a R=0.192 with a negative and downwards slope. The downward character of the RESTREND slope is suggestive of non-rainfall factors contained in the residuals. In validating the RESTREND analysis, a comparative analysis between observed and predicted NDVI derived from a reference NDVI value of 0.46 was carried out. The NDVI value of 0.46, is empirically assumed to be average NDVI value expected at a minimum rainfall amount of 850mm/year reported in tropical Savanna ecosystems. Using this empirical relationship, NDVI values were predicted for Keffi. Even at higher rainfall amounts≈1340mm/year, amounts were unable to produce corresponding higher NDVI values; rather a more plausible correlation between reference-derived predicted NDVI values and rainfall was obtained. A further analysis with predicted NDVI values, based on 1999 NDVI value in Keffi returned higher NDVI units than observed NDVI values. This strengthens the attribution of the possible interference of rainfall-NDVI sensitivity by non-rainfall factors like human activities on vegetation productivity. Surface soil analysis to exclude potential impacts of soil nutrients and moisture deficiency on vegetation productivity, showed that soil had insignificant effect on vegetation dynamics. Further inferential analysis, using the inter-annual NDVI and the reclassified bi-decadal NDVI maps showed that spatial vegetation distribution in Keffi were driven by farmers inter-annual rotational cultivation footprints than rainfall variability. With a three-class categorization, “gain, loss and significant loss”, the spatial distribution of vegetation in Keffi between (1999-2008) and (2009-2018) was assessed. Temporal condition (stressed and healthy) across the three classes supports the attribution of farmers’ reactionary adaptation and cultivation practices on the dynamic spatial vegetation distribution. Between 1999 -2018, an increase in areas with significant vegetation loss (42%), so with a decrease of -25% in areas with healthy vegetation was observed. The character of vegetation cover across the two decadal time slices, reflects landuse intensity and unsustainable farming practices. Preferences for modification of cultivation practices and changes in seed by farmers exerts positive feedbacks on vegetation cover. Higher statistical measures, 38.4% (yearly cropping) and 44% (shifting cultivation with less fallow periods) were observed in the chi-square analysis. These measures were higher than 2.0% relating to shifting cultivation with more fallow periods. While 11.6% farmers noted cultural practices as reasons for preferred cultivation methods, 48.4% farmers attributed climate as reason behind cultivation modification. This was higher than 24.4% who linked issues of tenure rights to cultivation practices. With preferences for yield- breaching strategies, the non-receding cultivation and shorter fallow practices in Keffi triggers feedback on vegetation dynamics. Evidence from this study shows that the NDVI-rainfall functional sensitivity in Keffi is plausibly dampened by effects of reactionary farm-gate level adaptation practices.
Tropical cyclones (TC) represent a substantial threat to life and property for Caribbean and adjacent populations. The prospective increase of TC magnitudes, expressed in the 15th chapter of the IPCC AR5 report, entails a rising probability of ecological and social disasters, which were tragically exemplified by several severe Caribbean TC strikes during the past 20 years. Modern IPCC-grade climate models, however, still lack the required spatial and temporal resolution to accurately consider the underlying boundary conditions that modulate long-time TC patterns beyond the Instrumental Era. It is thus necessary to provide a synoptic mechanistic understanding regarding the origin of such long-time patterns, in order to predict reliable changes of TC magnitude and frequency under future climate scenarios. Caribbean TC records are still rare and often lack the necessary continuity and resolution to overcome these limitations. Here, we report on an annually-resolved sedimentary archive from the bottom of the Great Blue Hole (Lighthouse Reef, Belize). The TC record encompasses 1885 years and extends all existing site-specific TC archives both in terms of resolution and duration. We identified a likely connection between long-term TC patterns and climate phenomena responses to Common Era climate variations and offer a conceptual and comparative view considering several involved tropospheric and oceanographic control mechanisms such as the El-Niño-Southern-Oscillation, the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. These basin-scaled climate modes exercise internal control on TC activity by modulating the thermodynamic environment (sea-surface temperature and vertical wind shear stress dynamics) for enhanced/suppressed TC formation both on millennial (primary) and multi-decadal (secondary) time scales. We interpret the beginning of the Medieval Warm Period (MWP) as an important time interval of the Common Era record and suspect that the southward migration of the intertropical convergence zone (ITCZ) caused, in combination with extensive hydro-climate changes, a shift in the tropical Atlantic TC regime. The TC activity in the south-western Caribbean changed in general from a stable and less active stage (100–900 CE) to a more active and variable state (1,100 CE-modern).
We present novel measurements of five short-lived brominated source gases (CH2Br2, CHBr3, CH2ClBr, CHCl2Br and CHClBr2) obtained using a gas chromatograph-mass spectrometer system on board the High Altitude and Long Range Research Aircraft (HALO). The instrument is extremely sensitive due to the use of chemical ionisation, allowing detection limits in the lower parts per quadrillion (10-15) range. Data from three campaigns using the HALO aircraft are presented, where the Upper Troposphere/Lower Stratosphere (UTLS) of the Northern Hemisphere mid to high latitudes were sampled during winter and during late summer to early fall. We show that an observed decrease with altitude in the stratosphere is consistent with the relative lifetimes of the different compounds. Distributions of the five source gases and total organic bromine just below the tropopause shows an increase in mixing ratio with latitude, in particular during polar winter. This increase in mixing ratio is explained by increasing lifetimes at higher latitudes during winter. As the mixing ratio at the extratropical tropopause are generally higher than those derived for the tropical tropopause, extratropical troposphere-to-stratosphere transport will result in elevated levels of organic bromine in comparison to air transported over the tropical tropopause. The observations are compared to model estimates using different emission scenarios. A scenario which has emissions most strongly concentrated to low latitudes cannot reproduce the observed latitudinal distributions and will tend to overestimate bromine input through the tropical tropopause from CH2Br2 and CHBr3. Consequently, the scenario also overestimates the amount of brominated organic gases in the stratosphere. The two scenarios with the highest overall emissions of CH2Br2 tend to overestimate mixing ratios at the tropical tropopause but are in much better agreement with extratropical tropopause values, showing that not only total emissions but also latitudinal distributions in the emissions are of importance. While an increase in tropopause values with latitude is reproduced with all emission scenarios during winter, the simulated extratropical tropopause values are on average lower than the observations during late summer to fall. We show that a good knowledge of the latitudinal distribution of tropopause mixing ratios and of the fractional contributions of tropical and extratropical air is needed to derive stratospheric inorganic bromine in the lowermost stratosphere from observations. Depending on the underlying emission scenario, differences of a factor 2 in reactive bromine derived from observations and model outputs are found for the lowermost stratosphere, based on source gas injection. We conclude that a good representation of the contributions of different source regions is required in models for a robust assessment of the role of short-lived halogen source gases on ozone depletion in the UTLS.
Historic amphibian settlements in the northwestern Nile delta - a geoarchaeological perspective
(2020)
No concise picture of the archaeological and palaeoecological evolution can be drawn for the northwestern Nile delta, and archaeological records show significant population dynamics that still need explanation and spur the need for further palaeoenvironmental research. This study delivers a set of new methods especially in the fields of remote sensing and data analytics that can be regarded as important milestones and foundations for further palaeoenvironmental research in the area. Additionally, it shows new insights for individual time slices.
This geoarchaeological project is a cooperation with the archaeological excavations of the German Archaeological Institute (DAI) in Buto and Kom el’Gir. It expands the work of Wunderlich (1989) which laid important foundations in understanding the origin of the initial landscape that was later colonized in different cultural stages showing different dynamics, settlement intensities and even long phases of abandonment or breaks in between. This forms the starting point for relating the population dynamics of the different cultural phases reaching from Predynastic (prior to 3150 before Christ) up to the Greco-Roman era (~anno Domini 650) to the environmental history and events that occurred in the area. It is very likely that environmental changes such as the shifting of major water routes, inundation or paludification of larger areas or other environmental events affected settlements and human life in the area.
In the fields of remote sensing new methods are presented to complete information on the location of ancient settlements, and complex workflows are developed that allow the tracing of subsurface structures via indirect analysis of vegetation growth in larger time series data. It was verified that a relationship exists between vegetation performance, the appearance of archaeologic material in the topsoil, and the location of former Nile river branches.
Together with a new high resolution digital elevation model (DEM) based on TanDEM-X data, new interpretations with a high spatial significance are possible. For individual time slices, namely the Late Dynastic and Greco-Roman era, this work delivers a detailed landscape description suggesting a finely ramified subdelta, with all settlements placed on alluvial levees. This explains the massive increase in settlements in the Ptolemaic, Roman and in particular late Roman periods (4th century before Christ – anno Domini 7th century).
We sampled the Nile delta clays together with the channels and the material of the archaeologic excavations in vibracores and profile walls. This geologic inspection of the subsurface together with geochemical results from a handheld portable X-ray fluorescence device (pXRF) allowed new interpretations of the landscape and environmental history. For example, we used geochemical data to distinguish between artificial and natural channels as a measure for the anthropogenic influence, a proxy for past environmental characteristics and lastly as a basis for a new dating method. Many of the channels, for instance, were dated by our own 14C datings, comparisons with the previous work ofWunderlich (1989) and application of new dating approach based on machine learning with artificial neural networks. Additionally, we run a full methodological approach, and examine the applicability of pXRF methods in general, and test the quality of the data to detect distinct geochemical differences between the main settlement phases with advanced methods in data analytics. The dating is based, for example, on the training of artificial neural networks with pXRF data from archaeological material of well-dated context to date test data of cultural layers within the vibracores. With this method the homogeneous Nile alluvium, cultural layers and channels can be dated roughly and, as a result, fundamental changes in the landscape can be linked with the settlement history of Buto and neighboring tells.
Zum ersten Mal beschäftigte sich in Deutschland eine primär an Studierende gerichtete Sommerschule mit kritischer Stadtforschung. Als jemand, der daran teilgenommen hat, gehe ich in einem Erfahrungsbericht der Frage nach, ob und inwieweit eine solche Veranstaltung auch der Stärkung von kritischen Haltungen in der Wissenschaft dienen kann. Dabei verweise ich auf die Notwendigkeit, die hegemoniale Produktion von Wissen an Hochschulen zu hinterfragen und darauf, dass die Möglichkeiten zur Veränderung der Wissensproduktion auch bei den Studierenden selbst liegen.
Im Anschluss an die globale Finanzkrise von 2008 lässt sich in vielen deutschen Städten eine neue Welle der Gentrifizierung beobachten. Am Beispiel des traditionellen Arbeiterviertels Gallus in Frankfurt am Main zielt der Beitrag darauf ab, die gegenwärtigen Verdrängungsprozesse aus dem spezifischen Zusammenspiel von stadtpolitischen Aufwertungsbestrebungen und immobilienwirtschaftlichen Verwertungsstrategien zu erklären. Vertreten wird dabei die These, dass die Frankfurter Stadtpolitik, entsprechend ihrer neoliberalen Ausrichtung, im Gallus jahrelang Gentrifizierungsprozesse und die Entstehung einer Ertragslücke zwischen gegenwärtiger und potenzieller Verwertung aktiv gefördert hat – letztere aber erst jetzt im Zuge der Krise an Relevanz gewinnt. Nahezu idealtypisch kann man daher anhand des Gallus zeigen, dass Gentrifizierung wesentlich von lokalen politischen Kräfteverhältnissen abhängt, wobei der Rhythmus jedoch von immobilienwirtschaftlichen Verwertungszyklen diktiert wird.