Refine
Year of publication
Document Type
- Article (122)
- Doctoral Thesis (44)
- Book (19)
- Working Paper (8)
- Contribution to a Periodical (2)
- Review (2)
- Report (1)
Language
- English (151)
- German (46)
- Multiple languages (1)
Has Fulltext
- yes (198)
Is part of the Bibliography
- no (198)
Keywords
- Frankfurt am Main (5)
- precipitation (4)
- COSMO-CLM (3)
- Carbonate (3)
- Baltic age spectra (2)
- Canary Islands (2)
- Clausius–Clapeyron scaling (2)
- Detrital zircons (2)
- Devonian (2)
- Holy Cross Mountains (2)
Institute
- Geowissenschaften / Geographie (198) (remove)
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.
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.
We performed an experiment under long-term microgravity conditions aboard the International Space Station (ISS) to obtain information on the energetics and experimental constraints required for the formation of chondrules in the solar nebula by ’nebular lightning’. As a simplified model system, we exposed porous forsterite (Mg2 SiO4) dust particles to high-energetic arc discharges. The characterization of the samples after their return by synchrotron microtomography and scanning electron microscopy revealed that aggregates had formed, consisting of several fused Mg2SiO4 particles. The partial melting and fusing of Mg2SiO4 dust particles under microgravity conditions leads to a strong reduction of their porosity. The experimental outcomes vary strongly in their appearance from small spherical melt-droplets (∅≈90 µm) to bigger and irregularly shaped aggregates (∅≈350 µm). Our results provided new constraints with respect to energetic aspects of chondrule formation and a roadmap for future and more complex experiments on Earth and in microgravity conditions.
In light of the global sea-level rise and climate change of the 21th century, it is important to look back into the recent past in order to understand what the future might hold. A multi-proxy data set was compiled to evaluate the influence of geomorphological and environmental factors, such as antecedent topography, subsidence, sea level and climate, on reef, sand apron and lagoon development in modern carbonate platforms through the Holocene. Therefore, a combination of remote sensing and morphological data from 122 modern carbonate platforms and atolls in the Atlantic, Indian and Pacific Oceans were conducted, along with a case study from the oceanic (Darwinian) barrier-reef system of Bora Bora, French Polynesia, South Pacific.
The influence of antecedent topography and platform size as factors controlling Holocene sand apron development and extension in modern atolls and carbonate platforms is hypothesized. Antecedent topography describes the elevation and relief of the underlying Pleistocene topography (karst) and determines the distance from the sea floor to the rising postglacial sea level. Maximum lagoon depth and marginal reef thickness, when available in literature, were used as proxies for antecedent topography. Sand apron proportions of 122 atolls and carbonate platforms from the Atlantic, Indian and Pacific Oceans were quantified and correlated to maximum lagoon depth, total platform area and marginal reef thickness. This study shows that sand apron proportions increase with decreasing lagoon depths. Sand apron proportions also increase with decreasing platform area. The interaction of antecedent topography and Holocene sea-level rise is responsible for variations in accommodation space and at least determines the extension of the lateral expansion of sand aprons. In general, sand apron formation started when marginal reefs approached relative sea level. Spatial and regional variations in sea-level history let sand apron formation start earlier in the Indo-Pacific region (transgressive-regressive) than in the Western Atlantic Ocean (transgressive).
The influence of sea level, antecedent topography and subsidence of a volcanic island on late Quaternary reef development was evaluated based on six rotary core transects on the barrier and fringing reefs of Bora Bora. This study was designed to revalue the Darwinian model, the subsidence theory of reef development, which genetically connects fringing reef, barrier reef and atoll development by continuous subsidence of the volcanic basement. Postglacial sea-level rise, and to a minor degree subsidence, were identified as major factors controlling Holocene reef development in that they have created accommodation space and controlled reef architecture. Antecedent topography was also an important factor because the Holocene barrier reef is located on a Pleistocene barrier reef forming a topographic high. Pleistocene soil and basalt formed the pedestal of the fringing reef. Uranium-Thorium dating shows that barrier and fringing reefs developed contemporaneously during the Holocene.
In the barrier–reef lagoon of Bora Bora, the influence of environmental factors, such as sea level and climate, tsunamis and tropical cyclones controlling Holocene sediment dynamics was evaluated based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession comprises mixed carbonate-siliciclastic sediments overlying peat and Pleistocene soil. The multi-proxy data set shows variations in grain-size, total organic carbon (proxy for primary productivity), Ca and Cl element intensities (proxies for carbonate availability and lagoonal salinity) during the mid-late Holocene. These patterns could result from event sedimentation during storms and correlate to event deposits found in nearby Tahaa, probably induced by elevated cyclone activity. Accordingly, elevated erosion and runoff from the volcanic island and lower lagoonal salinity would be a result of rainfall during repeated cyclone landfall. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery peaked out in the early Holocene and declined since the mid-Holocene. Benthic foraminifera assemblages do not indicate reef-to-lagoon transport. Alternatively, higher and sustained hydrodynamic energy is probably induced by stronger trade winds and a higher-than-present sea level during the mid-late Holocene. The increase in mid-late Holocene sediment dynamics within the back-reef lagoon is supposed to display sediment-load shedding of sand aprons due to the oversteepening of slopes at sand apron/lagoon edges during their progradation rather than an increase in tropical storm activity during that time.
The influence of sea-level and climate changes on sediment import, composition and distribution in the Bora Bora lagoon during the Holocene is validated. Lagoonal facies succession comprises siderite-rich marly wackestones, foraminifera-siderite wackestones, mollusk-foraminifera marly packstones and mollusk-rich wackestones during the early-mid Holocene, and mudstones since the mid-late Holocene. During the early Holocene, enhanced weathering and iron input from the volcanic island due to wetter climate conditions led to the formation of siderite within the lagoonal sediments. The geochemical composition of these siderites shows that precipitation was driven by microbial activity and iron reduction in the presence of dissolved bicarbonate. Chemical substitutions at grain margins illustrate changes in the oxidation state and probably reflect changes in pore water chemistry due to sea-level rise and climate change (rainfall). In the late Holocene, sediment transport into the lagoon is hampered by motus on the windward side of the lagoon, which led to early submarine lithification within the lagoon.
Droughts are anticipated to intensify in many parts of the world due to climate change. However, the issue of drought definition, namely the diversity of drought indices, makes it difficult to compare drought assessments. This issue is widely known, but its relative importance has never been quantitatively evaluated in comparison to other sources of uncertainty. Here, encompassing three drought categories (meteorological, agricultural, and hydrological droughts) with four temporal scales of interest, we evaluated changes in the drought frequency using multi-model and multi-scenario simulations to identify areas where the definition issue could result in pronounced uncertainties and to what extent. We investigated the disagreement in the signs of changes between drought definitions and decomposed the variance into four main factors: drought definitions, greenhouse gas concentration scenarios, global climate models, and global water models, as well as their interactions. The results show that models were the primary sources of variance over 82% of the global land area. On the other hand, the drought definition was the dominant source of variance in the remaining 17%, especially in parts of northern high-latitudes. Our results highlight specific regions where differences in drought definitions result in a large spread among projections, including areas showing opposite signs of significant changes. At a global scale, 7% of the variance resulted independently from the definition issue, and that value increased to 44% when 1st and 2nd order interactions were considered. The quantitative results suggest that by clarifying hydrological processes or sectors of interest, one could avoid these uncertainties in drought assessments to obtain a clearer picture of future drought change.
First-principles modeling techniques offer the ability to simulate a wide range of systems under different physical conditions, such as temperature, pressure, and composition, without relying on empirical knowledge. Density functional theory (DFT), a quantum mechanical method, has become an exceptionally successful framework for materials science modeling. Employing DFT makes it possible to gain valuable insights into the fundamental state of a system, enabling the reliable determination of equilibrium crystal structures. Over time, DFT has become an essential tool that can be incorporated into various schemes for predicting the properties of a material related to its structure, insulating/metallic behavior, magnetism, and optics. DFT is regularly applied in numerous fields, spanning from fundamental subjects in condensed matter physics to the study of large-scale phenomena in geosciences. In the latter, the effectiveness of DFT stems from its ability to simulate the properties found on the Earth, other planets, and meteorites, which may pose challenges for their direct study or laboratory investigation.
In this thesis, a comprehensive examination of a family of monosulfides and a perovskite heterostructure was conducted. These materials are relevant for their potential applications in technology, energy harvesting, and in the case of monosulfides, their speculated abundance on the planet Mercury.
Firstly, a DFT approach was used to analyze two non-magnetic monosulfides, CaS and MgS. We determined their structural properties and then focused on the modeling of their reflectivity in the infrared region. The calculation of the reflectivity considered both harmonic and anharmonic contributions. In the harmonic limit, the non-analytic correction was employed to accurately determine the LO/TO splitting, which is necessary to delimit the retstrahlend band, that is, the maximum of the reflectivity. The anharmonic effects given by up to three-phonon and isotopic scatterings, which were included using perturbation theory, primarily smeared the reflectivity spectra edges in the high-wave region.
Secondly, four polymorphs of MnS were studied using a combination of first-principles methods to simulate their antiferromagnetic (AFM) and paramagnetic (PM) states. The integration of DFT+$U$ with special quasirandom structures (SQS) supercells, and occupation matrix control techniques was crucial for achieving convergence, structural optimization accuracy, and obtaining finite energy band gaps and local magnetic moments in the PM phases. The addition of the Hubbard $U$ correction was necessary to treat the highly-correlated Mn $d$-electrons. The success of our approach was clear based on our electronic structure predictions for the PM rock-salt B1-MnS polymorph. Experimentally this phase has been observed to be an insulator, but multiple \emph{ab initio} works resulted previously in metallic behavior. Our computations, on the other hand, predicted insulating and magnetic properties that compare well with available measurements. Additionally, the pressure-field stability of the four MnS polymorphs was studied. In the case of the PM phases, B1-MnS was identified to be the most stable up to about 21 GPa, then transforming into the B31-MnS polymorph. This finding was in close agreement with high-pressure experiments reporting a similar phase transformation. The optical properties of B1-, B4-, and B31-MnS were also simulated. The SQS technique was used to obtain soft-mode-free phonon band structures within the harmonic approximation. Then, the anharmonic effects were included, and the reflectivity was calculated for B1-MnS and B4-MnS. In both cases, a good agreement for the LO/TO splitting was achieved in comparison to experimental results.
Lastly, the oxygen-deficient heterostructure of LaAlO$_{3-\delta}$ /SrTiO$_{3-\delta}$ was investigated also employing DFT+$U$, with a particular emphasis on the potential impact of vacancy clustering at the interface. Six distinct configurations of pairs of vacancies were studied and their energies were compared to find the most stable one. The orbital reconstruction of Ti orbitals was also examined based on their location with respect to the vacancies and the local magnetic moments were calculated. The final results showed that linearly arranged vacancies located opposite to Ti ions give the most energetically stable configuration.
The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.
Ob Klimawandel oder Luftverschmutzung: Die chemischen und physikalischen Prozesse in der Atmosphäre haben wichtige Auswirkungen auf die menschliche Gesundheit und Ökosysteme. Dabei ist die Atmosphäre mehr als ein Gemisch aus Stickstoff, Sauerstoff, Wasserdampf, Helium und Kohlenstoffdioxid. Es gibt zahlreiche Spurengase, deren Gesamtanteil am Volumen weniger als 1 % ausmacht. In dieser Arbeit werden Stickstoffoxide, Schwefeldioxid, Kohlenstoffmonoxid und Schwefelsäure näher betrachtet, die im Rahmen der flugzeugbasierten Messkampagne Chemistry of the Atmosphere: field experiment in Europe (CAFE-EU)/BLUESKY gemessen wurden.
Die Stickstoffoxide NO und NO2, als NOx zusammengefasst, besitzen hauptsächlich anthropogene Quellen, allen voran fossile Verbrennung und industrielle Prozesse. Zwischen NO und NO2 besteht ein photochemisches Gleichgewicht, sodass in der Atmosphäre vor allem NO2 in relevanten Konzentrationen vorkommt; dies wirkt aufgrund der Bildung von Salpetersäure, HNO3, in wässriger Lösung beim Einatmen ätzend und ist entsprechend gesundheitsschädlich. Troposphärisches Ozon, O3, wesentlicher Bestandteil von Sommersmog, wird hauptsächlich durch die Reaktion von NO mit Peroxiden (HO2 und RO2) gebildet. In der Stratosphäre entstehen NOx hauptsächlich durch die Photodissoziation von Lachgas, N2O, das aufgrund seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann und dort die wichtigste Stickstoffquelle darstellt. In der Stratosphäre tragen NOx zum katalytischen Abbaumechanismus des Ozons bei (Bliefert, 2002; Seinfeld and Pandis, 2016).
Schwefeldioxid, SO2, ist ein toxisches Gas, dessen atmosphärische Quellen hauptsächlich anthropogen sind, nämlich fossile Verbrennung und industrielle Prozesse; Senken sind trockene und feuchte Deposition, wobei letztere zu saurem Regen führen kann. Seit den 1980ern sinken die globalen SO2-Emissionen. SO2 kann in der Atmosphäre zu Sulfat und Schwefelsäure oxidiert werden, was Hauptbestandteil des Wintersmogs ist. Der wichtigste Mechanismus ist die Oxidation mit dem Hydroxylradikal, OH˙, unter Beteiligung von Wasserdampf. In der Stratosphäre ist Carbonylsulfid, OCS, die wichtigste Schwefelquelle, da es analog zum N2O dank seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann (Bliefert, 2002; Seinfeld und Pandis, 2016). Typische Konzentrationen von Schwefelsäure sind 105 cm–3 nachts und 107 cm–3 tagsüber in der Troposphäre sowie 105 cm–3 tagsüber in der Stratosphäre (Clarke et al., 1999; Weber et al., 1999; Fiedler et al., 2005; Arnold, 2008; Kürten et al., 2016; Berresheim et al., 2000).
Kohlenstoffmonoxid, CO, ist ein toxisches Gas, das zu gleichen Teilen durch direkte Emissionen (v.a. Biomasseverbrennung und fossile Verbrennung) und In-situ-Oxidation (v.a. von Methan, Isopren und industriellen Kohlenwasserstoffen) in die Atmosphäre gelangt. Die Hauptsenke ist die Reaktion mit OH˙ in der Troposphäre. Seit 2000 sinkt die globale CO-Konzentration (Bliefert, 2002).
Doch neben Gasen sind auch Aerosolpartikel fester Bestandteil des Gemisches Luft, welche luftgetragene feste oder flüssige Teilchen sind. Primäre Aerosolpartikel werden direkt als solche in die Atmosphäre emittiert, während sekundäre Aerosolpartikel in der Atmosphäre gebildet werden, indem gasförmige Vorläufersubstanzen mit geringer Flüchtigkeit auf primären Partikeln kondensieren oder durch Zusammenclustern und Anwachsen komplett neue Partikel bilden. Aerosolpartikel ermöglichen als Wolkenkondensationskeime erst die Bildung von Wolken und wirken somit – neben ihrem direkten reflektierenden Effekt – durch Änderung der Wolkenbedeckung und -eigenschaften insgesamt kühlend aufs Klima und beeinflussen die lokalen und globalen Wasserkreisläufe. Doch sie haben auch negative Auswirkungen auf die menschliche Gesundheit und sind für eine Verkürzung der durchschnittlichen Lebensdauer in Regionen mit hohen Feinstaubbelastungen verantwortlich (Seinfeld und Pandis, 2016; Bellouin et al., 2020; World Health Organization, 2016).
Neben den bisher betrachteten neutralen, also ungeladenen Gasen und Partikeln sind Ionen in der Gasphase sowie geladene Partikel ebenfalls Bestandteil der Atmosphäre. Sie spielen bei vielen atmosphärischen Prozessen eine wichtige Rolle, wie etwa bei Gewittern, Radiowellenübertragung und ionen-induzierter Nukleation von Aerosolpartikeln. Die Hauptquellen für Ionisation in der Tropo- und Stratosphäre ist die galaktische kosmische Strahlung, die entgegen ihrem Namen hauptsächlich aus Protonen und α-Partikeln (primäre Partikel genannt) besteht und in der Erdatmosphäre durch Kollision mit Luftmolekülen Teilchenschauer von sekundären Partikeln (u.a. Myonen, Pionen und Neutrinos) hervorruft. Die primären und sekundären Partikel können die Luftmoleküle ionisieren unter Entstehung von N+, N2+, O+, O2+ und Elektronen. Sauerstoff reagiert rasch mit letzteren zu O– und O2–. Diese Kationen und Anionen reagieren weiter, bis Ionenclustern der Summenformeln (HNO3)n(H2O)mNO3– und H+(H2O)n(B)m gebildet werden, wobei B Basen wie Methanol, Aceton, Ammoniak oder Pyridin sind. Weitere Ionisationsquellen sind der Zerfall des Radioisotops 222Rn in Bodennähe und ionisierende Solarstrahlung oberhalb der Stratosphäre. Atmosphärische Ionen haben zwei wichtige Senken: die Wiedervereinigung, auch Rekombination genannt, bei der sich ein Kation und ein Anion gegenseitig neutralisieren sowie das Anhaften an Aerosolpartikeln. Letztere Senke ist vor allem in der Troposphäre aufgrund der relativ hohen Konzentration an Aerosolpartikeln relevant (Arnold, 2008; Viggiano und Arnold, 1995; Bazilevskaya et al., 2008; Hirsikko et al., 2011).
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.
In Germany, a grave labor shortage in the nursing and elderly care sectors has prompted the response of recruiting skilled nursing staff from abroad in recent years. This article analyzes these recruitment practices as forms of “migration management”: German migration policy has changed according to this paradigm to attempt utilitarian control over migration processes and mediate between labor market concerns on the one hand and isolationist, politico-cultural seclusion on the other. Based on original research through interviews and document analysis, we identify four relevant levels of analysis in researching migration management in the context of the recruitment of skilled nurses: (1) Definition of problem areas: How is migration programmatically legitimized as a solution to social problems? (2) Categorization of migration: How are migration processes classified? (3) Change in statehood: How are sites and actors of migration control being privatized and diversified? (4) Technologies: By means of which procedures, legal foundations and political instruments does migration management take place in the everyday? We believe that taking these four foci as points of departure would be beneficial for further inquiries in critical migration research.
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.
Atmospheric particles play an important role in the radiative balance of the Earth, as well as they affect human health and air quality. Hence, the chemical characterization constitutes a crucial task to determinate their properties, sources and fate. Particularly, the analysis of nanoparticles (d<100 nm) represents an analytical challenge, since these particles are abundant in number but have very little mass.
This accumulative thesis focuses on the chemical characterization of nanoparticles, performed in both laboratory and field studies. Here, I present four manuscripts, two of which are my main project as a lead author.
The first manuscript (Caudillo et al., 2021) focuses on the gas and the particle phase originated from biogenic precursor gases (α-pinene and isoprene). The experiments were performed in the CLOUD chamber at CERN to simulate pure biogenic new particle formation. Both gas and particle phases are measured with a nitrate CI-APi-TOF mass spectrometer, while the TD-DMA is coupled to it for particle-phase measurements, this setup allows a direct comparison as both measurements use the identical chemical ionization and detector. This study demonstrates the suitability of the TD-DMA for measuring newly formed nanoparticles and it confirms that isoprene suppresses new particle formation but contributes to the growth of newly formed particles.
The second manuscript (Caudillo et al., 2022) presents an intercomparison of four different techniques (including the TD-DMA) for measuring the chemical composition of SOA nanoparticles. The measurements were conducted in the CLOUD chamber. The intercomparison was done by contrasting the observed chemical composition, the calculated volatility, and the thermal desorption behavior (for the thermal desorption techniques). The methods generally agreed on the most important compounds that are found in the nanoparticles. However, they did see different parts of the organic spectrum. Potential explanations for these differences are suggested.
The third manuscript (Ungeheuer al., 2022) presents both laboratory and ambient measurements to investigate the ability of lubricant oil to form new particles. These new particles are an important source of ultrafine particles in the areas nearby large airports. The ambient measurements were performed downwind of Frankfurt International Airport, and it was found that the fraction of lubricant oil is largest in the smallest particles. In the laboratory, the main finding was that evaporated lubricant oil nucleates and forms new particles rapidly. The results suggest that nucleation of lubricant oil and subsequent particle growth can occur in the cooling exhaust plumes of aircraft-turbofans.
The fourth manuscript (Wang et al., 2022) is a new particle formation study in the CLOUD chamber at CERN. This study shows that nitric acid, sulfuric acid, and ammonia interact synergistically and rapidly form particles under upper free tropospheric conditions. These particles can grow by condensation (driven by the availability of ammonia) up to CCN sizes and INP particles. The ability of these particles to act as a CCN and INP was also investigated and it was found to be as efficient as for desert dust. This mechanism constitutes an important finding and it can account for previous observations of high concentrations of ammonia and ammonium nitrate over the Asia monsoon region.
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.
In many parts of the world, the centralized grid provides energy to the population only to a limited extent. The electrification for sub-Saharan Africa countries is the lowest in the world, representing half of the world's population withoutelectricity. However, during the last years there has been an increased attention to rural areas in the Global South beyond the centralised grid, especially with respect to improved possibilities of solar power systems. The transition from one dominant form of energy provision to various alternatives includes different dimensions and depends on specific socio-spatial contexts. Energy systems are framed within systems of spatial practices, performed by a variety of involved actors, like consumers, local suppliers, international for-profit companies, international development donors as well as national and regional authorities. As such power systems arealways cause and effect of socio-technical change This study takes the example of Rwanda to analyse the marketization of decentralised energy systems. Based on empirical field work with energy entrepreneurs it combines Post-Colonial Theory with Science and Technology-Studies to theorise the role of energy to the social production of space beyond the grid.
The segregation of refugees in collective accommodation centres represents an integral component of the European border regime and its complex interplay of inclusion and exclusion. The corresponding spatial, symbolic and discursive demarcations, however, are not simply implemented politically from above, but negotiated on the ground on a daily basis. One crucial group of actors in the German context are neighbourhood-based volunteers. These groups frequently accompany accommodation centres with support structures. Based on contributions in the field of critical border studies and on the example of a municipal accommodation facility in Frankfurt, Germany, this paper demonstrates how volunteers, through their practices and engagement with refugees and others, on one hand, and dominant discourses, institutions and regulations on the other, participate in the production of locally specific spaces of asylum that are marked by simultaneous and contradictory processes of bordering and debordering.
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.
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).
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Observed weather and projected climate change suggest an increase in the transmission of vector-borne diseases (VBDs) in the Hindu Kush Himalayan (HKH) region. In this study, we systematically explore the literature for empiric associations between the climate variables and specific VBDs and their vectors in the HKH region. We conducted a systematic synthesis of the published literature on climate variables, VBDs and vectors in the HKH region until the 8th of December 2020. The majority of studies show significant positive associations of VBDs with climatic factors, such as temperature, precipitation, relative humidity, etc. This systematic review allowed us to identify the most significant variables to be considered for evidence-based trend estimates of the effects of climate change on VBDs and their vectors in the HKH region. This evidence-based trend was set into the context of climate change as well as the observed expansion of VBDs and disease vectors in the HKH region. The geographic range of VBDs expanded into previously considered non-endemic areas of highlands (mountains) in the HKH region. Based on scarce, but clear evidence of a positive relationship of most climate variables and VBDs and the observed climatic changes, we strongly recommend an expansion of vector control and surveillance programmes in areas of the HKH region that were previously considered to be non-endemic.
Air-sea feedbacks between the Mediterranean Sea and the atmosphere on various temporal and spatial scales play a major role in the Mediterranean regional climate system and beyond. The Mediterranean Sea is a source of moisture due to excess evaporation and, on a long-term average, is associated with a warming of the lower atmosphere in contact with the sea surface due to heat loss at the air-sea interface. The complex air-sea interactions and feedbacks in the Mediterranean basin strongly modulate the sea surface fluxes and favor several cyclogenetic activities under certain meteorological conditions. Examples of such cyclonic activities are medicanes (Mediterranean hurricanes) and Vb-cyclones. Medicanes are mesoscale, marine, and warm-core Mediterranean cyclones that exhibit some similarities to tropical cyclones, while Vb-cyclones are extra-tropical cyclones, that propagate from the Western Mediterranean Sea and travel across the Eastern European Alps into the Central European region. Extremely strong winds and heavy precipitation associated with these cyclones can lead to severe destruction and flooding. Changes in the intensity and frequency of these cyclones are also projected under changing future climate conditions, where the Mediterranean region has been identified as a hotspot in terms of rising temperatures.
The development of high-resolution regional climate models (RCMs) has progressed our understanding of the processes characterizing the Mediterranean climate. However, large uncertainties still exist regarding the estimates of air-sea fluxes, which, in turn, affect the simulation of the Mediterranean climate. Several factors can be attributed to such discrepancies, such as data quality, temporal and spatial resolution, and the misrepresentation of physical processes. To overcome some of these inconsistencies and deficiencies of the existing climate simulations, a new high-resolution atmosphere-ocean regional coupled model (AORCM) has been developed to simulate the air-sea feedback mechanisms. This coupled model incorporates the coupling of RCM COSMO-CLM (CCLM) and the regional ocean model NEMO-MED12 for the Mediterranean Sea (MED) as well as NEMO-NORDIC for the North- and Baltic Sea (NORDIC). Several experiments were performed using both the coupled and uncoupled models to investigate the impact of air-sea interactions and feedbacks on sea surface heat fluxes, wind speed, and on the formation of Mediterranean cyclones (i.e., medicanes and Vb-cyclones). These experiments were performed using different horizontal atmospheric grid resolutions to analyze the effect of resolution on sea surface heat fluxes, wind speed, and the development of medicanes.
The results of the present study indicate that a finer atmospheric grid resolution ([is as appreciated as]9 vs. [is as appreciated as]50 km) improved the wind speed simulations (particularly near coastal areas) and subsequently improved the simulations of the turbulent heat fluxes. Both parameters were better simulated in the coupled simulations than in the uncoupled simulations, but coupling introduced a warm SST bias in winter. Radiation fluxes were slightly better represented in coarse-grid simulations than in fine-grid simulations. However, the higher-resolution coupled model could reproduce the observed net outgoing total surface heat flux over the Mediterranean Sea. In addition to that sub diurnal SST variations have a strong effect on sub-daily heat fluxes and wind speed but minor effects at longer timescales. Regarding the impact of atmospheric grid resolution ([is as appreciated as]50, 25, and [is as appreciated as]9 km) and ocean coupling on medicanes, it was detected that the coupled model with a finer atmospheric grid ([is as appreciated as]9 km) was able to not only reproduce most medicane events, but also improved the track length, warm core, and wind speed compared to the uncoupled model. The coupled model with the coarse-grid ([is as appreciated as]50 and [is as appreciated as]25 km) did not show any improvement in simulating medicanes compared to the uncoupled model. The spectral nudging technique, applied on the wind components above 850 hPa in the interior domain to keep large-scale circulation close to the driving data (i.e., ERAInterim reanalysis), improved the accuracy of the times and locations of generated medicanes, but no improvement was found in the track length and intensity.
Concerning the role of the Mediterranean Sea coupling on Vb cyclones, the investigation showed that atmosphere-ocean coupling had an overall positive impact, although with a strong case-by-case variation, on the trajectories and intensity of Vb-cyclones as a result of the variation in moisture source for each event. In general, all model configurations could replicate Vbcyclones, their trajectories, and associated precipitation fields. The average structure of the precipitation field was best represented in the coupled simulations. Coupling of the North- and Baltic Seas also showed an improvement in some of the simulated Vb-cyclones.
The atmosphere-ocean coupling showed an overall positive impact on the simulation of sea surface heat fluxes and Mediterranean cyclones (medicanes and Vb-cyclones). Moreover, the representation of sea surface heat fluxes, wind speed, and medicane features was more realistic when using a finer atmospheric grid resolution (less than 10 km). The present study suggests that the combination of a finer atmospheric grid resolution together with atmosphere-ocean coupling is advantageous in simulating the Mediterranean climate system.
Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands
(2022)
Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.
Location: Canary Islands, Spain.
Major taxa studied: Spermatophytes.
Time period: Present day.
Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non-endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non-endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.
Results: Trait space of endemic and non-endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non-endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.
Main conclusions: We found that endemic and non-endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.
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).
Positive plant–plant interactions are thought to drive vegetation patterns in harsh environments, such as semi-arid areas. According to the stress-gradient hypothesis (SGH), the role of positive interactions between species (facilitation) is expected to increase with harshness, predicting associated variation in species composition along environmental gradients. However, the relation between stress and facilitation along environmental gradients is debated. Furthermore, differentiating facilitative interactions from other underlying mechanisms, such as microtopographic heterogeneity, is not trivial. We analysed the spatial co-occurrence relationships of vascular plant species that form patchy vegetation in arid lapilli fields (tephra) from recent volcanic eruptions on La Palma, Canary Islands. Assuming a harshness gradient negatively correlated with elevation because the lower elevations are more arid and water availability is considered the most limiting resource, and that an outcome of facilitation is plants co-occurring in the same patch, from the SGH we expected a greater degree of co-occurrence at lower elevation. We tested this at both the species and the individual plant level. We analysed the species composition of 1277 shrubby vegetation patches at 64 different sampling points, ranging from the coast to around 700 m a.s.l. Patch morphology and microtopographic heterogeneity variables were also measured, to account for their potential effects on the species composition of patches. We used generalized linear models and generalized mixed-effects models to analyse species richness, number of individuals in patches and percentage of patches with positive co-occurrences, and a pairwise co-occurrence analysis combined with a graphical network analysis to reveal positive links between 13 of the species. We found that the percentage of patches with positive co-occurrences increased at higher elevations, in contrast to the predictions of the SGH, but in accordance with a refined stress-gradient hypothesis for arid sites, in which characteristics of the interacting species are incorporated.
Africa's protected areas (PAs) are the last stronghold of the continent's unique biodiversity, but they appear increasingly threatened by climate change, substantial human population growth, and land-use change. Conservation planning is challenged by uncertainty about how strongly and where these drivers will interact over the next few decades. We investigated the combined future impacts of climate-driven vegetation changes inside African PAs and human population densities and land use in their surroundings for 2 scenarios until the end of the 21st century. We used the following 2 combinations of the shared socioeconomic pathways (SSPs) and representative greenhouse gas concentration pathways (RCPs): the “middle-of-the-road” scenario SSP2–RCP4.5 and the resource-intensive “fossil-fueled development” scenario SSP5–RCP8.5. Climate change impacts on tree cover and biome type (i.e., desert, grassland, savanna, and forest) were simulated with the adaptive dynamic global vegetation model (aDGVM). Under both scenarios, most PAs were adversely affected by at least 1 of the drivers, but the co-occurrence of drivers was largely region and scenario specific. The aDGVM projections suggest considerable climate-driven tree cover increases in PAs in today's grasslands and savannas. For PAs in West Africa, the analyses revealed climate-driven vegetation changes combined with hotspots of high future population and land-use pressure. Except for many PAs in North Africa, future decreases in population and land-use pressures were rare. At the continental scale, SSP5–RCP8.5 led to higher climate-driven changes in tree cover and higher land-use pressure, whereas SSP2–RCP4.5 was characterized by higher future population pressure. Both SSP–RCP scenarios implied increasing challenges for conserving Africa's biodiversity in PAs. Our findings underline the importance of developing and implementing region-specific conservation responses. Strong mitigation of future climate change and equitable development scenarios would reduce ecosystem impacts and sustain the effectiveness of conservation in Africa.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
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.
Lightning climate change projections show large uncertainties caused by limited empirical knowledge and strong assumptions inherent to coarse-grid climate modeling. This study addresses the latter issue by implementing and applying the lightning potential index parameterization (LPI) into a fine-grid convection-permitting regional climate model (CPM). This setup takes advantage of the explicit representation of deep convection in CPMs and allows for process-oriented LPI inputs such as vertical velocity within convective cells and coexistence of microphysical hydrometeor types, which are known to contribute to charge separation mechanisms. The LPI output is compared to output from a simpler flash rate parameterization, namely the CAPE × PREC parameterization, applied in a non-CPM on a coarser grid. The LPI’s implementation into the regional climate model COSMO-CLM successfully reproduces the observed lightning climatology, including its latitudinal gradient, its daily and hourly probability distributions, and its diurnal and annual cycles. Besides, the simulated temperature dependence of lightning reflects the observed dependency. The LPI outperforms the CAPE × PREC parameterization in all applied diagnostics. Based on this satisfactory evaluation, we used the LPI to a climate change projection under the RCP8.5 scenario. For the domain under investigation centered over Germany, the LPI projects a decrease of 4.8% in flash rate by the end of the century, in opposition to a projected increase of 17.4% as projected using the CAPE × PREC parameterization. The future decrease of LPI occurs mostly during the summer afternoons and is related to (i) a change in convection occurrence and (ii) changes in the microphysical mixing. The two parameterizations differ because of different convection occurrences in the CPM and non-CPM and because of changes in the microphysical mixing, which is only represented in the LPI lightning parameterization.
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.
Convective rain cell properties and the resulting precipitation scaling in a warm-temperate climate
(2022)
Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low-level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge-adjusted radar dataset in a mid-latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super-CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells.
In the last decade, the Climate Limited-area Modeling Community (CLM-Community) has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM-Community model, ERA-Interim reanalysis and eight global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44∘ (∼ 50 km), 0.22∘ (∼ 25 km), and 0.11∘ (∼ 12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia, and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version, and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modeling communities is needed to increase the reliability of the GCM–RCM modeling chain.
In the last decade, the Climate Limited-area Modeling (CLM) Community has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM community model, ERA-Interim reanalysis and eight Global Climate Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44◦(∼50 km), 0.22◦ (∼25 km) and 0.11◦ (∼12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modelling communities is needed to increase the reliability of the GCM-RCM modelling chain.
Diese Arbeit nimmt Weiße Freiwillige aus Deutschland in den Blick, die einen Freiwilligendienst im Ausland geleistet haben und in rassistischen Machtverhältnissen eine privilegierte, das heißt Weiße Position einnehmen. Dabei dienen die Critical Whiteness Studies als fruchtbare Grundlage, um die Auseinandersetzung mit Rassismus aus Weißer privilegierter Perspektive zu untersuchen. Die Arbeit geht daher der Frage nach: Inwiefern die Erfahrungen im Freiwilligendienst und die begleitenden rassismuskritischen Seminare Weiße Nord-Nord und Nord-Süd Freiwillige dazu anregen, ihre Privilegien zu reflektieren und sich kritisch im rassistischen Machtsystem zu positionieren. Die Analyse der Interviews mit Weißen Freiwilligen zeigt, dass die Interviewten zum einen unterschiedliche Konfrontationserfahrungen mit Whiteness gemacht haben und zum anderen ihre daraus resultierenden Reflexionsprozesse und Umgangsweisen sehr divers ausfallen. Unterschiede zeigen sich jedoch nicht nur zwischen den Nord-Nord und Nord-Süd Freiwilligen, sondern auch situationsabhängig anhand der jeweiligen Erfahrungen der einzelnen Weißen Freiwilligen. Aus diesen Untersuchungen lässt sich ableiten, dass es auch für rassismus- und machtkritische Begleitseminare weiterhin eine zu bewältigende Herausforderung bleibt, die Relevanz der persönlichen Auseinandersetzung mit Whiteness und somit mit eigenen Privilegien und Verstrickungen in Rassismus – unabhängig vom Zielland des Freiwilligendienstes – zu vermitteln.
As part of two drilling campaigns of the International Continental Scientific Drilling Program (ICDP), several geophysical borehole measurements were carried out by the Leibniz Institute for Applied Geophysics (LIAG) in two lakes. The acquired data was used to answer stratigraphic and paleoclimatic research questions, including the establishment of robust age-depth models and the construction of continuous lithological profiles.
Lake Towuti is located on Sulawesi (Indonesia), within the "Indo-Pacific Warm Pool" (IPWP), a globally important region for atmospheric heat and moisture budgets. The lake exists for approximately one million years, but its exact age is uncertain. We present the first agedepth model for the approximately 100 m continuous sediment sequence from the central part of the lake. The basis for this model is the magnetic susceptibility measured in the borehole and a tephra layer with an age of about 797 ka at 72 m depth. Our age-depth model is inferred from cyclostratigraphic analysis of borehole data and covers a period from 903 ± 11 to 131 ± 67 ka. We suggest that orbital eccentricity and/or changes between global cold and warm periods are responsible for hydroclimatic changes in the IPWP, that these changes affect sedimentation processes in Lake Towuti, and that we can measure and observe this effect in the sediment properties today. Additionally, we created a continuous artificial lithological profile from a series of different borehole data using cluster analysis. This provides information from parts of the borehole where no sediment is available due to core loss.
Lake Ohrid is 1.36 million years old and is located on the Balkan Peninsula on the border between Albania and North Macedonia. The primary hole 'DEEP' in the central part of the lake has been the subject of several investigations, but information about sediments of the marginal locations 'Pestani' and 'Cerava' have not been published yet. In our study, we use natural gamma radiation (GR) measured in the borehole to generate an age-depth model for DEEP. This is performed using the correlation of GR to the global LR04 reference record of Lisiecki and Raymo (2005).
The age information is then transferred via prominent seismic marker horizons to the other two sites, Pestani and Cerava, where it provides the first age-control points for the construction of age-depth models from correlation of GR to LR04. The generated age-depth models are tested using cyclostratigraphic methods, but the limits of this approach are revealed. At DEEP, sedimentation rates (SR) from the cyclostratigraphic method and the correlative approach differ by 2.8 %, at Pestani this difference is 16.7 %, and at Cerava the quality of the data does not allow a reliable evaluation of SR using the cyclostratigraphic approach. We used cluster analysis to construct artificial lithological profiles at all three sites and integrated them into the respective age-depth models. This enables us to determine which sediment types were deposited at what time, and we recognize the change between warm and cold periods in the sediment properties at all three locations. The analyses in this study were all performed on borehole and seismic data and thus do not involve sediment core data. Especially at Pestani and Cerava, new insights into the sedimentological history of Lake Ohrid could be obtained.
In the last part we discuss the occurrence of the half-precession (HP) signal in the European region during the last one million years. The focus is on Lake Ohrid, but a range of other proxies, from the eastern Mediterranean, across the European continent, up to Greenland are analyzed in regards to HP. Applying filters, we focus on the frequency range with a period of 13-8.5 ka and only HP remains in the records. We use correlative methods to determine the clarity of the HP signal in proxies distributed across the European realm. Additionally, we determined the development of HP over time. The HP signal is clearest in the southeast and decreases toward the north. It is further more pronounced in interglacial periods and in the younger part (<621 ka) of most proxies. We suggest that there are mechanisms that transmit the HP signal from its origin near the equator to higher latitudes via different processes. In this context, for instance, the African monsoon, the Nile River and the Mediterranean outflow via the Strait of Gibraltar can be important factors.
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.
Upper mantle shear zones are complex systems where deformation is commonly closely interacting with metamorphic (solid-solid) and/or melt/fluid-rock reactions. Here, feedback processes between deformation, reactions, grain size reduction and phase mixing result in strain weakening and the localization of deformation. The expression of these interlinked processes is portrayed by the microfabrics of strained peridotites and pyroxenites. The present thesis is focusing on these processes and their impact on the deformation in three upper mantle shear zones situated in the peridotite massifs of Lanzo (Italian Alps), Erro-Tobbio (Italian Alps) and Ronda (Betic Cordillera, Spain). In all three shear zones, the presence of melt led to phase mixing either by interstitial crystallization of pyroxenes from a Si-saturated and partially also highly evolved melt or by melt-rock reactions of pyroxene porphyroclasts with a Si-undersaturated melt. The effect of melt on the localization of strain is twofold and variable. Enhanced deformation by melt-wetted boundaries is assumed for all shear zones. Additionally, phase mixing by crystallization of interstitial pyroxenes or melt-rock reactions reduce or maintain the grain size by the formation of fine grained neoblasts and secondary phase boundary pinning. In this regard, pre- to early syn-kinematic, map-scale percolation of OH-bearing, evolved melts in the NW Ronda peridotite massif and the associated crystallization of interstitial pyroxenes result in the activation of grain size sensitive deformation mechanisms in the entire melt-effected area. In the rocks collected at Erro-Tobbio, syn-kinematic melt-rock reactions of pyroxene porphyroclasts and Si-undersaturated melt led to the formation of ultramylonitic neoblast tails (grain size ~10 μm). Compared to the adjacent coarser-grained olivine-dominated matrix, the activation of diffusion creep led to an increase in the strain rate by an order of magnitude within interconnected ultramylonitic layers. Strain localization and softening in ultramylonitic layers are also documented in the Lanzo samples. Neoblast tails of pyroxene porphyroclasts were likewise identified as their precursor. The phase assemblage of the tails, including ortho- and clinopyroxene, olivine, plagioclase, and spinel (± amphibole), and their geochemical trends suggest, unlike in Erro-Tobbio, a formation by continuous net-transfer reactions enhanced by the spinel lherzolite to plagioclase lherzolite transition.
The new results obtained from the three studied shear zones underscore the importance of reactions for the interlinked processes of grain size reduction, phase mixing, strain localization and strain softening in upper mantle shear zones. Concerning strain localization, the nature of the reaction (solid-solid, melt/fluid-rock) seems to play a subordinate role compared to its timing. Pre- to early syn-kinematic melt-triggered reactions result in strain localization along map-scale shear zones. Late stage syn-kinematic melt-rock or metamorphic reactions under high stress conditions are capable of localizing the deformation along discrete, sub-centimeter thick ultramylonites.
The Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third-order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U-Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U-Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time-framed depositional systems.
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.
...
Transforming the current rather centralized electricity generating system into a climate neutral system based on renewable energy is an important approach to reduce greenhouse gas emissions and thus mitigate climate change. Stakeholders have each of them their own perception of the best strategies to achieve such a transformation. All perspectives are equally legitimate and needed for developing a specific transformation strategy suited for the region in focus....
Abstract: Subaqueous carbonates from the Devils Hole caves (southwestern USA) provide a continuous Holocene to Pleistocene North American paleoclimate record. The accuracy of this record relies on two assumptions: That carbonates precipitated close to isotope equilibrium and that groundwater temperature did not change significantly in the last 570 thousand years. Here, we investigate these assumptions using dual clumped isotope thermometry. This method relies on simultaneous analyses of carbonate ∆47 and ∆48 values and provides information on the existence and extent of kinetic isotope fractionation. Our results confirm the hypothesis that calcite precipitation occurred close to oxygen and clumped isotope equilibrium during the last half million years in Devils Hole. In addition, we provide evidence that aquifer temperatures varied by less than ±1°C during this interval. Thus, the Devils Hole calcite δ18O time series exclusively represents changes in groundwater δ18O values. Plain Language Summary: The oxygen isotope composition of cave carbonates records changes in Earth's climate. However, the reliability of such records depends on how stable the carbonate precipitation environment was. Here, we use a novel method called dual clumped isotope thermometry that can provide simultaneous information on a carbonate's growth temperature and whether any additional fractionation processes affected its oxygen and clumped isotope signatures. Specifically, we investigated the Devils Hole caves, which provide a reference oxygen isotope time series for North America. We find that groundwater temperature did not change significantly in the last half-million years. Variations in the oxygen isotope composition of the deposited carbonates solely reflect variations in the oxygen isotope composition of the groundwater.
Das Studium der Diplomgeographie an der Universität Frankfurt am Main ist auf die Verknüpfung des Mensch-Umwelt-Verhältnisses in seiner räumlichen Bewertung ausgerichtet und so angelegt, daß die Studierenden im Grundstudium mit den entsprechenden Analyse-und Bewertungsverfahren vertraut gemacht werden, während sie im Hauptstudium verstärkt durch Projektstudium reale Berufsfeldsituationen einüben sollen. Unter dem Leitbild der nachhaltigen Raumentwicklung werden inhaltlich die Veranstaltungen auf vier Felder konzentriert: die naturräumliche Situation (Landschaftshaushalt, Erkundung und Analyse des oberflächlichen Untergrunds), Geographie der Alltagswelt (Individualebene des Wohnens, der Freizeit, der Identität), Wirtschaft und Logistik und Strukturen der dritten Welt.
In der kritischen Stadtforschung wird die These der postdemokratischen Stadt aktuell immer wieder aufgegriffen und dabei eng mit Prozessen der Neoliberalisierung verknüpft. Ausgehend von einer kritischen Diskussion der konzeptionellen Zugänge bei Colin Crouch und Jacques Rancière geht der Beitrag anhand der Geschichte der kommunalen Selbstverwaltung in Frankfurt am Main dem Gehalt der beiden Begriffsbestimmungen in der konkreten historischen Analyse nach. Verwiesen wird dabei auf die unterschiedliche Analysetiefe der beiden Konzepte. Entgegen der bei Crouch vorherrschenden Annahme, dass es vor der neoliberalen Stadt eine demokratische Form städtischen Regierens gegeben hat, wird unter Rückbezug auf die Argumentation Rancières zur Demokratie betont, dass der Fordismus keinesfalls als egalitärer, inklusiver oder demokratischer charakterisiert werden kann. Vielmehr vertreten wir die These, dass die fordistische Stadt zwar aus anderen Gründen, aber vom Grundsatz her nicht weniger postdemokratisch gewesen ist als die neoliberale der Gegenwart und dass die demokratischen Momente am ehesten in den Brüchen und Spalten der sozialen Konflikte der 1970er und 1980er Jahre gefunden werden können.
Plant community biomass production is co-dependent on climatic and edaphic factors that are often covarying and non-independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan-European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species-specific biomass responses to the environment in the climate-corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co-limited by climatic and soil drivers, with each species experiencing its own unique set of co-limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.
One of the most important events in human history occurred during the Early Pleistocene: the dispersal of early hominins out of Africa and into Europe and Asia. In Western Europe, the earliest evidences of the genus Homo have been found in the Baza Basin, at the sites of Orce in the SE of the Iberian Peninsula. These sites contain fossils and lithic industry dated approximately as 1.4–1.3 Ma.While hominin remains and artifacts at Orce, as well as the accompanying fauna, have been extensively studied, the properties and evolution of the Early Pleistocene vegetation in the basin remain unknown. The general effect of climate change on the expansion of early hominins from Africa into Eurasia still remains unclear. It is not known if the Early Pleistocene climate changes and the development of glacials periods led to the extirpation of European communities, or if those communities were able to endure and persist through such adverse climatic periods. This open question highlights the need for climate and environmental analyses for the time before, during and after the first presence of Homo in Europe. This PhD thesis contributes to that need by the presentation of the first long pollen record of the Baza Basin, where the oldest hominin sites in Western Europe are found.
Atmosphärische Schwerewellen spielen eine wichtige Rolle für die Zirkulation der mittleren Atmosphäre, die wiederum die Troposphäre auf saisonalen und längeren Zeitskalen beeinflusst, und stellen somit ein Schlüsselelement für das Wetter- und Klimageschehen dar. Eine adäquate Beschreibung des Lebenszyklus atmosphärischer Schwerewellen in den operationellen Modellen zur Wettervorhersage und Klimasimulation ist daher sehr wünschenswert. Um zu einer verbesserten mathematischen Darstellung der Schwerewellendynamik in den Modellen beizutragen, wurden in den vergangenen Jahren zahlreiche numerische Studien durchgeführt. Wenngleich auch viele der ablaufenden Prozesse gegenwärtig gut verstanden sind, stellt die Wechselwirkung zwischen den mesoskaligen Schwerewellen und den synoptischskaligen Prozessen aufgrund der hohen Komplexität der Strömung weiterhin eine besondere Herausforderung für die Erforschung der Schwerewellenaktivität dar und erfordert oftmals hochaufgelöste numerische Simulationen über große Modelldomänen.
Folglich ist es wichtig, dass die angewendeten numerischen Verfahren effizient sind und möglichst idealisierte, aber dennoch atmosphärenähnliche Szenarien simulieren. In dieser Arbeit wird ein effizientes numerisches Verfahren zur Modellierung der Dynamik interner Schwerewellen sowie deren Einfluss auf die Zirkulation der mittleren Atmosphäre entwickelt.
Dabei wird die Diskretisierung des pseudo-inkompressiblen Finite-Volumen-Modells auf einem versetzten Gitter von Rieper et al. (2013), welches der Einfachheit halber Schallwellen aus der Dynamik herausfiltert und zur Untersuchung adiabatischer Atmosphärenprozesse auf der f-Ebene entwickelt wurde, im wesentlichen durch zwei Komponenten erweitert: 1) die Anwendung eines semi-impliziten Zeitschrittverfahrens auf die Bewegungsgleichungen zur Integration der Auftriebs- und Corioliseffekte und 2) die Berücksichtigung einer Heizung durch einen thermischen Relaxationsansatz, welcher in der Troposphäre ein baroklin instabiles Strömungsprofil erzeugt und eine zeitabhängige Dynamik des Hintergrundzustands zulässt. Zur Überprüfung der korrekten Implementierung der Erweiterungen werden eine Reihe von atmosphärischen Standardteststudien durchgeführt, welche die Konvergenzeigenschaften sowie die Effizienz des Verfahrens validieren. Darüber hinaus zeigen die Testfälle, dass die Ergebnisse des Modells mit anderen veröffentlichten Arbeiten sehr gut übereinstimmen.
Schließlich wird als Anwendungstestfall eine mesoskalige Simulation barokliner Instabilität in der Troposphäre durchgeführt, welche ferner die darin enthaltene kleinskalige Wellenaktivität sowie deren Einfluss auf die mittlere Atmosphäre modelliert. Die abschließende Betrachung der zonal und zeitlich gemittelten Felder zeigt die erwartete Zonalwindumkehr in der Höhe.
Das Wissen über die Wolkenmikrophysik und die Wechselwirkung zwischen Niederschlag und Aerosol ist ein wichtiger Baustein zur Optimierung von Klima- und Wettermodellen. Ein Großteil des Niederschlags in den mittleren Breiten fällt aus Mischphasenwolken, die aus unterkühlten Tröpfchen und Eispartikeln bestehen. Die Eispartikel bilden sich an speziellen Aerosolpartikeln, die als Eiskeime (INP) wirken können. Die Wahrscheinlichkeit eines Aerosols als Eiskeim zu wirken, nimmt mit abnehmender Temperatur und steigender Wassersättigung zu. Mineralstaubpartikel sind die häufigsten Eiskeime, die ab Temperaturen ≤−15°C aktiv sind, biologische Partikel wirken schon bei wärmeren Bedingungen. Große Wissenslücken bestehen noch bei der globalen Konzentration von Eiskeimen, inklusive deren geographischer und jahreszeitlicher Variabilität.
Im Zentrum der Experimente, die für diese Arbeit durchgeführt wurden, steht der Eiskeimzähler FRIDGE (Frankfurt Ice Deposition Freezing Experiment). Je nach Aufbau und Anwendung des Instruments werden zwei verschiedene Ansätze zur Aktivierung von Eiskeimen verfolgt. Die ursprüngliche und namensgebende Methode in Form einer Vakuum-Diffusionskammer wurde zur Untersuchung von Eisnukleation via Depositionsgefrieren (an INP_D) entwickelt (Klein et al., 2010). Danielczok (2015) nutzte einige Bestandteile des Analysegeräts, um auch Immersionsgefrieren (an INP_I) in Form von Tröpfchengefrieren à la Vali (1971) zu studieren. In der vorliegenden Arbeit wurde diese Anwendungsmöglichkeit von FRIDGE weiterentwickelt. Ein zentraler Schritt war dabei die präzise Charakterisierung des Gefrierverhaltens von Tröpfchen aus Reinstwasser ohne zusätzliches Aerosol. Die Einbeziehung dieses sogenannten Hintergrundgefrierens, das für jedes Instrument und Messverfahren spezifisch ist, ermöglichte es, die Minimaltemperatur, für die zuverlässige Ergebnisse produziert werden können, von −22°C auf −29°C herabzusetzen. Der dadurch hinzugewonnene Temperaturbereich ist für Eisnukleation in Mischphasenwolken äußerst relevant.
Beide Anwendungsmethoden wurden im Rahmen des Fifth International Workshop on Ice Nucleation – Phase 2 (FIN-02) sowie bei einer weiteren Kampagne zur Messung von Eisnukleation an Cellulosepartikeln mit über zwanzig anderen Eiskeimzählern verglichen. Mit FRIDGE als Diffusionskammer wurde für die Mehrheit der untersuchten Aerosoltypen eine zufriedenstellende Übereinstimmung mit den anderen Instrumenten beobachtet. Die Experimente mit gefrierenden Tröpfchen in FRIDGE erzielten ausnahmslos Ergebnisse, die inmitten der Werte der anderen Instrumente lagen. Die erfolgreiche Validierung – besonders der neuen Anwendungsmethode – war das erste Ziel dieser Arbeit und die notwendige Voraussetzung für die anschließenden Feldmessungen.
Atmosphärische Eiskeimkonzentrationen wurden in mehrwöchigen Feldmesskampagnen an drei sehr unterschiedlichen Orten und atmosphärischen Bedingungen untersucht: an der Hochalpinen Forschungsstation Jungfraujoch (JFJ), am Storm Peak Laboratory (SPL) in den Rocky Mountains und am Cyprus Atmospheric Observatory (CAO) in Zypern. Am JFJ wurde eine INP-Konzentration beobachtet, die um den Faktor 20 niedriger als an den anderen beiden Stationen war. Der Grund dafür war, dass sich das Jungfraujoch die meiste Zeit der Messungen in der freien Troposphäre befand. Dementsprechend waren die Bedingungen an der Station von aerosolpartikelarmer Luft mit wenigen Eiskeimen geprägt. An zwei Standorten wurde Mineralstaub als ein Parameter, der die lokale INP-Konzentration positiv beeinflusst, identifiziert. Sowohl am JFJ als auch am CAO erhöhte ferntransportierter Saharastaub die INP-Konzentration.
Die Kombination der zwei Analysemethoden, die Aerosolproben aus derselben Luft entweder in trockenem Ausgangszustand oder in Tröpfchen suspendiert untersuchen, offenbarte eine interessante Eigenschaft der INP. Es herrschte eine offensichtliche Parallelität von INP_D- und INP_I- Konzentrationen. Bei fast allen Messungen waren INP_I etwa 10-mal häufiger als INP_D. Die Aussage trifft gleichermaßen auf sehr niedrige Konzentrationen am JFJ wie auch auf hohe Konzentrationen am SPL und CAO zu. Die einzige Ausnahme bilden Cellulosepartikel. Daraus lässt sich schließen, dass INP_D und INP_I dieselben Partikel sind, die je nach Aktivierungskonditionen Eisnukleation unterschiedlich effektiv hervorrufen.
Eiskeime (INP) sind Aerosolpartikel, die das Entstehen von Eiskristallen in der Atmosphäre zwischen 0 und -37°C ermöglichen, indem sie die zur Ausbildung der Eisphase nötige Energie gegenüber einem reinen Wassersystem stark herabsetzen. Dabei sind aktive Stellen auf der Oberfläche dieser Partikel für die erste Nukleation von Eis verantwortlich. In der Folge können die Eiskristalle zulasten von verdunstenden Wasserdampfmolekülen und Wassertröpfchen weiter anwachsen. Über Eismultiplikationsprozesse zersplittern und vervielfältigen sich die Eiskristalle und wachsen über Bereifung schließlich zu einer kritischen Größe heran, wodurch sie als Niederschlag zu Boden fallen können. Auch wenn der Anteil der zur heterogenen Eisnukleation fähigen Aerosole vergleichsweise gering ist, spielen INP eine entscheidende Rolle für die Entwicklung von Niederschlag und nehmen Einfluss auf Strahlungsprozesse, indem sie auf die Phase der Wolken und damit auf deren Strahlungseigenschaften einwirken. Viele Fragen im Forschungsgebiet der heterogenen Eisnukleation sind jedoch weiterhin nicht hinreichend genau geklärt. Ohne eine verbesserte Kenntnis von Konzentrationen, geographischer und vertikaler Verteilung, sowie zeitlicher Variation, Quellen und Natur von INP, sind noch vorhandene Wissenslücken im Strahlungsantrieb durch Wechselwirkungen von Aerosolen und Wolken nur zu einem gewissem Grad zu reduzieren. Dies ist nötig, um aktuelle Beobachtungsdaten der sich erwärmenden Atmosphäre besser verstehen und die zukünftigen Änderungen des Klimas sicherer vorhersagen zu können. In dieser Arbeit wird die Vakuumdiffusionskammer FRIDGE verwendet, um atmosphärische INP-Konzentrationen zu bestimmen. Aerosolpartikel werden dabei in einem ersten Schritt auf einem Silicium-Probenträger elektrostatisch niedergeschlagen. Die Effizienz des Sammelprozesses, also der Anteil der Partikel die tatsächlich auf dem Si-Substrat abgeschieden werden, wurde mittels zweier unabhängiger Methoden auf etwa 60% bestimmt. In einem zweiten Mess-Schritt werden die Proben in FRIDGE typischen Bedingungen von Mischphasenwolken ausgesetzt, wodurch Eiskristalle an den INP aktiviert werden und im Verlauf einer Messung anwachsen. Eine Kamera beobachtet die durch das Eiswachstum entstehenden Helligkeitsänderungen auf dem dunklen Probensubstrat. Die Kriterien, wann ein Objekt als Eiskristall identifiziert und gezählt wird, mussten im Rahmen dieser Arbeit neu entwickelt werden. In der zu Beginn der Arbeit vorgefundenen Einstellung hatte bereits eine sehr geringe Helligkeitsänderung, wie sie durch das hygroskopische Wachstum von Aerosolpartikeln hervorgerufen wird, zu Signalen geführt, die fälschlicherweise als Eiskristalle gezählt wurden. Das reevaluierte Messverfahren von FRIDGE wurde im Zuge der FIN-02 Kampagne in einem groß angelegten Laborexperiment an der AIDA Wolkenkammer mit zahlreichen anderen INP-Zählern aus der ganzen Welt verglichen. Für den Großteil der Messungen der untersuchten Modell-Aerosoltypen konnte eine zufriedenstellende Übereinstimmung mit den anderen Instrumenten erzielt werden. In einer einmonatigen Feldmesskampagne im östlichen Mittelmeerraum konnten die ersten INP-Messungen an Bord eines unbemannten Flugzeugs durchgeführt werden. Während der Kampagne auf Zypern wurden mehrere Fälle von transportiertem Saharastaub beprobt, in denen die INP-Konzentration maßgeblich erhöht war. Lidar-Beobachtungen und ein Staubtransportmodell zeigten, dass sich das Maximum der Staubschichten zumeist in etwa 2-4 Kilometern Höhe befand. In der Höhe wurden INP-Konzentrationen gefunden, die im Mittel um einen Faktor 10 größer waren als auf Bodenniveau. Es wird gefolgert, dass INP-Messungen am Boden möglicherweise nur begrenzte Aussagekraft über die Situation nahe der Wolkenbildung besitzen. Im Rahmen BACCHUS-Projekts wurden zwischen August 2014 und Januar 2017 (mit Unterbrechungen) alle 1-2 Tage Proben an drei Reinluftstationen gesammelt (insgesamt über 900). Das INP-Messnetz mit einer geographischen Ausdehnung von der Arktis zum Äquator bestand aus Stationen in Spitzbergen, Martinique und im Amazonas. Die Station im brasilianischen Regenwald ist durch wechselnde Bedingungen von sauberer Regen- und verunreinigter Trockenzeit charakterisiert. In der Trockenzeit steigen die Partikelkonzentrationen durch starke Belastung aus Biomassenverbrennung um eine Größenordnung an; eine gleichzeitige Zunahme der INP-Konzentrationen konnte nicht beobachtet werden. Daraus kann vermutet werden, dass Partikel aus Feueremissionen keine ausgezeichneten Fähigkeiten zur Eisnukleation aufweisen. Die INP-Konzentrationen in der Karibik konnten mit dem Jahresgang von transportieren Saharastaub in Verbindung gebracht werden. In der Arktis wurden die niedrigsten INP-Konzentrationen der drei Stationen beobachtet. Zum Zeitpunkt des Erstellens dieser Arbeit können die determinierenden Einflussfaktoren, sowie der anthropogene Einfluss zur Zeit des arktischen Dunstes noch nicht abschließend geklärt werden.
Carbon is an element that controls planetary habitability, and is fundamental for life on Earth. Its behaviour has important consequences for the global climate system, the origin and evolution of life on Earth. While the biosphere and atmosphere’s carbon cycle only accounts for less than 1% of the global carbon budget, hidden reservoirs of deep carbon in the Earth’s interior comprise the predominant storage of carbon on the planet. At the Earth’s surface, 60-70 % of carbon is hosted by carbonate minerals, which are then transported to the Earth’s interior, mainly in the form of sediments, by subduction of the oceanic lithosphere. Subducting plates are subjected to decarbonation, dehydration, and melting with CO2 release via supra-subduction volcanism. Nevertheless, part of the subducted carbonates’ may survive and be further transported to the deep mantle. Direct evidence of the existence of carbonates in the Earth’s interior, possibly reaching down to the lower mantle, comes from the finding of syngenetic inclusions of carbonates in diamonds and mantle xenoliths. The presence of carbonates in the deep Earth has a critical effect on the physical properties of the mantle. Melting and chemical speciation of the mantle are strongly affected by the form of C and carbonate stability. Therefore, the study of the stability and physical properties of carbonates at high pressures and temperatures is fundamental, because understanding the processes involved in the deep carbon cycle helps to improve our picture of the whole mantle.
The systematic characterization of the elastic properties of carbonates as a function of their structure and chemical composition is of great importance because it may allow to identify their presence and distribution by seismology. Inverting seismic observations to successfully constrain the chemical composition and mineralogy of the Earth’s interior requires knowledge of the physical properties of all possible Earth’s materials at pressures and temperatures applicable to the Earth’s interior. Up to now, a multitude of studies has focused on the construction of phase diagrams and structural transitions by means of X-ray diffraction and vibrational spectroscopy experiments.
Few studies are available on the complete elastic tensor of carbonates, however most of the datasets are not accompanied by an accurate characterization of the samples, which are often solid solutions and the exact chemical composition, density or the details about the experimental methods used are not presented. The aim of this thesis is to study the effect of chemical composition on the elastic properties of carbonates, providing a reliable dataset on the elasticity of the main carbonates. In particular, the elastic properties of crystalline aragonite, CaCO3, and Fe-dolomite, (Ca, Mg, Fe)(CO3)2, with different compositions were studied by Brillouin spectroscopy at ambient conditions. Brillouin spectroscopy was also used to investigate the elastic behaviour of amorphous calcium carbonate samples with different water contents (up to 18 wt%) at high pressures, up to 20 GPa.
Furthermore, the importance of cationic substitution on the structure and high pressure behaviour of carbonates was investigated by studying a synthetic CaCO3-SrCO3 solid solution at ambient conditions and at high pressures, up to 10 GPa, by single crystal X-ray diffraction. Finally, the study of the effect of composition on the elastic properties of families of isostructural solids was also extended to a different class of materials, the metal guanidinium formates. The elasticity of a family of perovskite metal organic frameworks, metal guanidinium formates C(NH2)3MII(HCOO)3, with MII =Mn, Zn, Cu, Co, Cd and Ca was investigated by combining Brillouin spectroscopy, resonant ultrasound spectroscopy, density functional theory and thermal diffuse scattering analysis.
Cratonic eclogite is the product of oceanic crust subduction into the subcontinental lithospheric mantle, and it also is a fertile diamond source rock. In contrast to matrix minerals in magma-borne xenoliths, inclusions in diamond are shielded from external fluids, retaining more pristine information on the state of the eclogite source at the time of encapsulation. Vanadium is a multi-valent element and a widely used elemental redox proxy. Here, we show that that xenolithic garnet has lower average V abundances than garnet inclusions. This partly reflects crystal-chemical controls, whereby higher average temperatures recorded by inclusions, accompanied by enhanced Na2O and TiO2 partitioning into garnet, facilitate V incorporation at the expense of clinopyroxene. Unexpectedly, although diamond formation is strongly linked to metasomatism and xenoliths remained open systems, V concentrations are similar for bulk eclogites reconstructed from inclusions and from xenoliths. This suggests an oxygen-conserving mechanism for eclogitic diamond formation, and implies that eclogite is an efficient system to buffer fO2 over aeons of lithospheric mantle modification by subduction-derived and other fluids.
National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35 %, indicating progress toward the target of a 79 % decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83) % of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.
National Greenhouse Gas Inventories (GHGI) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGI. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emissions Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high Global Warming Potentials (GWPs) and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions in the since 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35%, indicating progress toward the target of a 79% decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83)% of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI inventory. There are also significant discrepancies between the two estimates for the individual HFCs.
During the last decades mammalian intracranial structures like the ethmoidal region have rarely been a focus of morphological studies, as they required invasive techniques. Contrary, the ontogeny of the fetal nasal capsule could easily be investigated based on histological material. Since the early 21st century modern imaging techniques like high-resolution computed tomography (μCT) reveal non-destructive insights into the mammalian skull. Furthermore, visualization software enables the virtual reconstruction of the tissues and additionally their morphometric analyses. However, the use of morphometric approaches on the nasal cavity is still scarce. Moreover, the turbinal skeleton is generally regarded as a unit, or the rostral respiratory part is compared to the caudal olfactory part; but the distinct olfactory turbinals have been considered only in a few studies.
The present study focuses on the highly diverse facial shape of the dog (Canis lupus familiaris) that evolved during domestication. Due to human-controlled breeding and care the natural selective pressure in prehistoric dogs has been replaced continually by artificial selection. As a consequence, harmful mutations on gene loci which e.g., control facial length growth got fixed within an extremely short time. According to veterinarian studies the turbinals of short snouted breeds continue their growth after the elongation of the facial bones has stopped prematurely. However, such investigations are based on low-resolution CT or MRT data and the morphological descriptions are vague. Referring to the elongation of the face in dolichocephalic breeds no former study has dealt with the detailed morphology of their turbinal skeleton so far.
The current study is based on comparative anatomical, morphometric, morphofunctional, and ontogenetic patterns of the dog’s turbinal skeleton. The 32 macerated skulls and four histological serial sections represent eleven breeds which cover different snout lengths (brachycephalic, mesaticephalic, dolichocephalic; according to two length indices), functional groups (scent hound, sighthound, companion/toy), and breeding histories (ancient pure-breeding associated with an unchanged appearance, modern time fashion breeding). The nasal cavity of the selected skulls was μCT-scanned and virtual 3D models of the turbinal skeleton were reconstructed. The breeds have been compared with each other in their number of olfactory turbinals, in the morphology of all turbinals and the lamina semicircularis as well as in their morphometrics and ontogeny. Based on morphological and ontogenetic patterns a new terminology of the interturbinals was established. The morphometric data covers the measurement of the relative turbinal surface area (IAT) and the calculation of the surface density (SDEN) and the turbinal complexity (TC). For the latter parameter a new morphometric approach was developed. For the ontogenetic comparison histological serial sections of perinatal dog stages have been consulted. As the dog’s ancestor macerated skulls of three adult Eurasian wolves (Canis lupus lupus) function for outgroup comparison and represent the grundplan with which the breeds are compared.
The results support former studies concerning a species-specific number of the fronto- and ethmoturbinals: in the Eurasian wolf and all postnatal dogs under study three ethmoturbinals and three frontoturbinals are observed. Additionally, two types of interturbinals are distinguished, namely four prominent interturbinals which are present in nearly all individuals and show a homologous pattern, and a variable number of additional interturbinals which differ in their shape among the dogs. Generally, longer snouted breeds have more additional interturbinals, so the total number of olfactory turbinals is increased to a maximum of 16 in the borzoi, whereas several short snouted breeds have only nine olfactory turbinals due to the loss of additional interturbinals and one prominent interturbinal. Regarding ontogeny the growth of the respiratory and the olfactory turbinals and the lamina semicircularis is highly associated with the growth of the facial bones after birth. As the viscerocranium of brachycephalic breeds is subjected to a postnatal growth inhibition the ethmoidal region stops growing prematurely, too. The turbinals of both functional parts develop less accessory lamellae that results in the reduction of the three morphometric parameters IAT, SDEN, and TC. The increase of all these three parameters with increasing snout length proves a correlation between both variables in the maxilloturbinal, all olfactory turbinals, and the lamina semicircularis in the dog. With the help of the perinatal dog stages plesiomorphic patterns which are present in all adult specimens (e.g., separation of ethmoturbinal I into two laminae, the presence of the uncinate process) were distinguished from less established morphological traits which get preferably reduced in association with brachycephaly (e.g., the anterior process of the posterior lamina of ethmoturbinal I, the caudal processes of frontoturbinal 1 and 2 within the frontal sinus due to the latter’s reduction). Obviously, the driving mechanism behind these and further variations are mutations on gene loci which control ontogenetic processes: the in other studies already described postnatal growth inhibition in the dermal bones of the midface of brachycephalic breeds seems to have a similar effect on the ethmoidal region. The results of the present study serve as basis for the evaluation how far the bony turbinals’ morphology, morphometrics, and ontogeny might be associated with physiological, genetic, neurological, and phylogenetic patterns. Additionally, the growth patterns of the hard tissues need to be compared to those of the soft tissues (i.e. the nasal epithelium).
This thesis presents the experimental and numerical analysis of seismic waves that are produced by wind farms. With the aim to develop renewable energies rapidly, the number of wind turbines has been increased in recent years. Ground motions induced by their operation can be observed by seismometers several kilometers away. Hence, the seismic noise level can be significantly increased at the seismic station. Therefore, this study combines long-term experiments and numerical simulations to improve the understanding of the seismic wavefields emitted by complete wind farms and to advance the prediction of signal amplitudes.
Firstly, wind-turbine induced signals that are measured at a small wind farm close to Würzburg (Germany) are correlated with the operational data of the turbines. The frequency-dependent decay of signal amplitudes with distance from the wind farm is modeled using an analytical method including the complex effects of interferences of the wavefields produced by the multiple wind turbines. Specific interference patterns significantly affect the wave propagation and therefore the signal amplitude in the far field of a wind farm. Since measurements inside the wind turbines show that the assumption of in-phase vibrating wind turbines is inappropriate, an approach to calculate representative seismic radiation patterns from multiple wind turbines, which allows the prediction of amplitudes in the far field of a complete wind farm, is proposed.
In a second study, signals with a frequency of 1.15 Hz, produced by the Weilrod wind farm (north of Frankfurt, Germany) are observed at the seismological observatory TNS (Taunus), which is located at a distance of 11 km from the wind farm. The propagation of the wavefield emitted by the wind farm is numerically modeled in 3D, using the spectral element method. It is shown that topographic effects can cause local signal amplitude reductions, but also signal amplification along the travel path of the seismic wave. The comparison of simulations with and without topography reveals that the reduction and amplification are spatially linked to the shape of the topography, which could be an explanation for the relatively high signal amplitude observed at TNS.
Finally, the reduction of the impact of wind turbines on seismic measurements using borehole installations is studied using 2D numerical models. Possible effects of the seismic velocity, attenuation, and layering of the subsurface are demonstrated. Results show that a borehole can be very effective in reducing the observed high-frequency signals emitted by wind turbines. However, a borehole might not be beneficial if signals with frequencies of about 1 Hz (or lower) are of interest, due significant wavelength-dependent effects. The estimations of depth-dependent amplitudes with a layered subsurface are validated with existing data from wind-turbine-induced signals measured at the top and bottom of two boreholes.
The experimental analysis of measurements conducted at wind farms and the advances of modeling such signals improve the understanding of the propagation of wind-farm induced seismic wave fields. Furthermore, the methods developed in this work have a high potential of universal application to the prediction of signal amplitudes at seismometers close to wind farms with arbitrary layout and geographic location.
The analysis of charcoal fragments in peat and lake sediments is the most widely used approach to reconstruct past biomass burning. With a few exceptions, this method typically relies on the quantification of the total charcoal content of the sediment. To enhance charcoal analyses for the reconstruction of past fire regimes, and to make the method more relevant to studies of both plant evolution and fire management, more information must be extracted from charcoal particles. Here, I burned in the laboratory seven fuel types comprising 17 species from boreal Siberia, and build on published schemes to develop morphometric and finer diagnostic classifications of the experimentally charred particles. As most of the species used in this study are common to Northern Hemisphere forests and peatlands, these results can be directly applicable over a broad geographical scale. Results show that the effect of temperature on charcoal production is fuel dependent. Graminoids and Sphagnum, and wood (trunk) lose the most mass at low burn temperatures, whereas heathland shrub leaves, brown moss, and ferns retain the most mass at high burn temperatures. In contrast to the wood of trunk, the wood of twigs retained their mass at intermediate temperature. This suggests that species with low mass retention at hotter burning temperatures might be underrepresented in the fossil charcoal record. Charred particle aspect ratio (L/W) appeared to be the strongest indicator of the fuel type burnt. Graminoid charcoals are more elongate than those of all other fuel types, leaf charcoals are the shortest and bulkiest, and twig and wood charcoals are intermediate. Finer diagnostic features were the most useful in distinguishing between wood, graminoid, and leaf particles, but further distinctions within these fuel types are difficult. High-aspect-ratio particles dominated by graminoid and Sphagnum morphologies are robust indicators of cooler surface fires. Contrastingly, abundant wood and leaf morphologies and low-aspect-ratio particles likely indicate higher-temperature fires. However, the overlapping morphologies of leaves and wood from trees and shrubs make it hard to distinguish between high-intensity surface fires combusting living shrubs and dead wood and leaves or high-intensity crown fires combusting living trees. Despite these limitations, the combined use of charred-particle aspect ratios and fuel morphotypes can aid in more robustly interpreting changes in fuel source and fire type, thereby substantially refining histories of past wildfires. Further fields of investigation to improve the interpretation of the fossil charcoal records will require: i) More in-depth knowledge of plant anatomy for a better determination of fuel sources; ii) Relate the proportion of particular charcoal morphotypes to the quantity of biomass; iii) Link the chemical composition of fuels, combustion temperature, and charcoal production. The advanced use of image-recognition software to collect data on other charcoal features could also aid in extracting fire temperatures as well as a change in particles morphology and morphometry during particles transportation.
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.
The climate system is one of the classical examples of a complex dynamical system consisting of interacting sub-systems through mass, momentum, and energy exchange across various spatial and temporal scales. This thesis aims to detect and quantify sub-component interactions from an information exchange (IE) perspective. For this purpose, IE estimators derived from information theory are explored and applied to the available climate data obtained from observations, reanalysis, global and regional climate models. Specifically, this thesis investigates the usefulness of information theory methods for process-oriented climate model evaluation.
Firstly, methods derived from the concepts of information theory such as transfer entropy and information flow along with their linear and non-linear estimation techniques are initially tested and applied to idealized two-dimensional dynamical systems. The results revealed an expected direction and magnitude of IE providing insights into underlying dynamics. However, as expected the linear estimators are robust for linear systems but fail for non-linear systems. Though the non-linear estimators (kernel and kraskov) showed expected results for all the idealized systems, their free tuning parameters are to be tested for consistent results. Moreover, these methods are sensitive to the available time series length.
A real world example case study involving the dynamics between the Indian and Pacific oceans revealed a physically consistent bi-directional IE. However, unexpected IE was detected in the example of North Atlantic and European air temperatures indicating hidden drivers. Though IE provides insights into system dynamics, the availability of time series length and the system at hand must be carefully taken into account before inferring any possible interpretations of the results.
Quantifying the IE from El-Ni\~{n}o southern oscillation (ENSO) and Indian Ocean Dipole (IOD) to the Indian Summer Monsoon Rainfall (ISMR) with the observational and reanalysis data sets revealed that both ENSO and IOD are synergistic predictors for the inter-annual variability of the ISMR over central India i.e., the monsoon core region. Though the investigated three Global Climate Models (GCM) could not reveal the underlying IE dynamics of ENSO, IOD, and ISMR, a Regional Climate Model (RCM) simulation downscaling one of the GCMs with realistic large scale signals across the lateral boundaries showed good agreement with the observations.
Evaluating a coupled regional climate modeling system driven by two different global data sets with IE estimators revealed significant differences between the process chains linking the north-west Mediterranean sea surface temperatures, evaporation, wind speed, and the Vb-cyclone induced precipitation over Danube, Odra, and Elbe catchments in the historical period (1951-2005). Detailed investigation revealed that the north-west Mediterranean Sea in the coupled regional simulation driven by ERA-20C reanalysis corresponded to the Vb-cyclone precipitation over the three catchments while no such correspondence is noted in the EC-EARTH driven simulation. This discrepancy is attributed to the inheritance of the simulation biases from GCM into the RCM. In the future period (1965-2099), no significant changes in the processes are noted from the simulation.
Overall, this thesis used IE estimators in investigating the underlying dynamics of climate system and climate models. The estimators proved useful in providing insights into climate system dynamics assisting in a process based climate model evaluation.
The Izu–Bonin–Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered samples within the forearc basalt stratigraphy that contained unusual macroscopic globular textures hosted in andesitic glass (Unit 6, Hole 1440B). It is unclear how these andesites, which are unique in a stratigraphic sequence dominated by forearc basalts, and the globular textures therein may have formed. Here, we present detailed textural evidence, major and trace element analysis, as well as B and Sr isotope compositions, to investigate the genesis of these globular andesites. Samples consist of K2O-rich basaltic globules set in a glassy groundmass of andesitic composition. Between these two textural domains a likely hydrated interface of devitrified glass occurs, which, based on textural evidence, seems to be genetically linked to the formation of the globules. The andesitic groundmass is Cl rich (ca. 3000 µg/g ), whereas globules and the interface are Cl poor (ca. 300 µg/g ). Concentrations of fluid-mobile trace elements also appear to be fractionated in that globules and show enrichments in B, K, Rb, Cs, and Tl, but not in Ba and W relative to the andesitic groundmass, whereas the interface shows depletions in the latter, but is enriched in the former. Interestingly, globules and andesitic groundmass have identical Sr isotopic composition within analytical uncertainty ( 87Sr∕86Sr of 0.70580 ± 10 ), indicating that they likely formed from the same source. However, globules show high δ11 B (ca. + 7 ‰ ), whereas their host andesites are isotopically lighter (ca. – 1 ‰ ), potentially indicating that whatever process led to their formation either introduced heavier B isotopes to the globules, or induced stable isotope fractionation of B between globules and their groundmass. Based on the bulk of the textural information and geochemical data obtained from these samples, we conclude that these andesites likely formed as a result of the assimilation of shallowly altered oceanic crust (AOC) during forearc basaltic magmatism. Assimilation likely introduced radiogenic Sr, as well as heavier B isotopes to comparatively unradiogenic and low δ11B forearc basalt parental magmas (average 87Sr∕86Sr of 0.703284). Moreover, the globular textures are consistent with their formation being the result of fluid-melt immiscibility that was potentially induced by the rapid release of water from assimilated AOC whose escape likely formed the interface. If the globular textures present in these samples are indeed the result of fluid-melt immiscibility, then this process led to significant trace element and stable isotope fractionation. The textures and chemical compositions of the globules highlight the need for future experimental studies aimed at investigating the exsolution process with respect to potential trace element and isotopic fractionation in arc magmas that have perhaps not been previously considered.
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.
In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.
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.
Die lakustrinen Sedimente im Vorotan-Becken (Armenien) wurden palynologisch untersucht. Aus den Ergebnissen konnte die Vegetationsgeschichte im Südlichen Kaukasus während des Frühpleistozäns teilweise rekonstruiert werden.
Bei den Sedimenten handelt es sich um diatomeenreiche Tone, Silte und Feinsande, in denen Pollen gut und pflanzliche Makroreste ausgezeichnet erhalten sind. Die Datierung ist durch die Kombination von Paläomagnetik und 39Ar/40Ar-Methode eindeutig: Die Sedimente decken den Beginn der „mid Pleistocene transition“ (1?110?–?960 ka) ab.
An zehn Aufschlüssen wurden insgesamt 506 Sedimentproben genommen und die darin enthaltenen Pollen untersucht. So konnten insgesamt 64 Taxa nachgewiesen werden. Sie wurden in Pollenprofilen zusammengefasst und ökologisch bewertet. Die erhobenen Daten wurden zudem einer Faktorenanalyse und einer Clusteranalyse unterzogen, deren Ergebnisse ebenfalls in die Pollenprofile eingingen.
Die Pollenprofile lassen deutlich regionale Vegetationszyklen während des Frühpleistozäns erkennen. Diese Zyklen werden ausführlich beschrieben und mit Ergebnissen anderer Autoren aus dem Mittelmeerraum verglichen. Auch ein Bezug zur rezenten Vegetation im Südlichen Kaukasus und den angrenzenden Gebieten wird hergestellt.
Die Paläovegetation im Südlichen Kaukasus ist demnach während des Frühpleistozäns geprägt von einem Vegetationsmosaik aus Grassteppe und offenen Wäldern. Je nach Klima lassen sich Einflüsse von angrenzenden Vegetationszonen erkennen: borealer Nadelwald der Höhenlagen des Kaukasus, thermophiler Laubwald der euxinischen und hyrkanischen Wälder sowie xerotherme Steppe des Nordiran.
Während der Interglaziale herrscht eine Waldsteppe aus thermophilem Laubwald (z.?B. Quercus, Carpinus, Ulmus, Zelkova, Tilia) vor, in der bei starken Erwärmungsphasen die Grassteppe deutlich dominiert und die Wälder wohl an Nordhänge und in Uferbereiche zurückgedrängt werden. In den Glazialphasen finden sich zunehmend Koniferen in der Vegetation (z.?B. Tsuga, Abies, Picea, Pinus) – bis hin zu einem nahezu geschlossenen Kiefernwald am Ende des ersten lang andauernden Glazials MIS 30.
Es zeigt sich, dass sich die einzelnen Klimazyklen in der Ausprägung der Vegetation signifikant unterscheiden. Hierbei spielt sowohl die Amplitude der Erwärmung als auch die Dauer der jeweiligen Phase eine Rolle.
Der Vergleich mit anderen Untersuchungen zeigt, dass die Vegetationszyklen im Südlichen Kaukasus teilweise deutlich anders verlaufen als im westlichen, zentralen und östlichen Mittelmeerraum. Entlang einer Ost-West-Achse ist hier ein „Vegetationsgradient“ zu erkennen.
Das hat Auswirkungen auf die Interpretation der Ausbreitung früher Menschen aus Afrika nach Eurasien. Es ist davon auszugehen, dass sich nicht jeder Vegetationszyklus des Frühpleistozäns gleichermaßen gut für ein Vordringen nach Eurasien eignete. Geeignete Bedingungen (offene Landschaft, Vegetationsmosaik, warmes Klima) herrschten im Südlichen Kaukasus vor allem während stark ausgeprägter Interglaziale. Dagegen brachten lang anhaltende Glazialphasen wohl eher lebensfeindlichere Bedingungen für Homo erectus.
Weil in den südlichen Regionen Europas teilweise eine stark abweichende Vegetation während der unterschiedlichen Klimaphasen vorherrschte, ist es naheliegend, dass der Südliche Kaukasus für die frühen Menschen eine Rolle als Refugium spielte.
Deutlich zeichnen sich in den Ergebnissen Veränderungen in der Vegetation beim Übergang von den obliquitätsdominierten 41-ka-Klimazyklen zu den exzentrizitätsbestimmten 100-ka-Zyklen ab („mid Pleistocene transition“). Diese Veränderungen haben sich sicherlich auch auf die Population der Menschen ausgewirkt und größere Wanderbewegungen und/oder Anpassungen hervorgerufen. Möglicherweise haben in dieser drastischen Veränderung sogar kulturelle Entwicklungen ihren Anfang – zum Beispiel die Nutzbarmachung des Feuers.
Global analysis of halogenated trace gases in the UTLS: from long-lived to short-lived substances
(2023)
In this dissertation, the distribution of chlorinated and brominated substances in the upper troposphere and lower stratosphere is investigated. These substances contribute significantly to the catalytic decomposition of ozone and are involved in the recurrent formation of the polar ozone hole in the Antarctic winter and spring. The Montreal Protocol, a multilateral environmental treaty to protect the ozone layer, has successfully reduced emissions of long-lived chlorine- and bromine-containing substances. Short-lived chlorinated and brominated substances, some of which are natural and anthropogenic in origin, are not regulated by the Montreal Protocol and it can be assumed that their relative contribution to the stratospheric halogen budget will increase, while the contribution of long-lived compounds will steadily decrease. The distribution of long- and short-lived halogenated substances are part of current research. For the upper troposphere and lower stratosphere, the very short-lived substances are particularly important. The lower stratosphere needs special investigation in this respect, since its composition is influenced by different transport processes. The influences on ozone trends in the lower stratosphere are subject to great uncertainties. Especially in the Southern Hemisphere, the number of observations is very limited.
In this work, the GhOST (Gas chromatograph for Observational Studies using Tracers) instrument was used during the SouthTRAC measurement campaign on the German HALO (High Altitude and LOng range) research aircraft, providing observations of halogenated hydrocarbons in Antarctic late winter to early spring 2019, a generally poorly sampled region. The polar vortex was, compared to previous years, significantly weaker and shifted towards the eastern South Pacific and South America. From the airborne measurements of chlorinated source gases, inorganic chlorine (the sum of active chlorine and reservoir gases; Cly) could be inferred with the result that Cly within the vortex increased up to 1687 ± 19 ppt at 385 K potential temperature, accounting for about 50 % of the total chlorine within the vortex and only 15 % of the total chlorine in the southern mid-latitudes. A comparison with the Northern Hemisphere could be made using the PGS measurement campaign in the Arctic winter 2015/2016. Under comparable conditions (season and distance from the tropopause), only 40 % of the total chlorine was in the inorganic form within the Arctic polar vortex and about 20 % was found in the mid-latitudes of the Northern Hemisphere. In addition, about 540 ppt more Cly was present in the Antarctic vortex than in the Arctic vortex, exceeding the annual variations previously reported for Antarctica.
The mean age of air plays an essential role in the derivation of Cly via the organic source gases, as was done in this work. A new method for determining the mean age of air from observational data has been introduced that accounts for extra-tropical input to the stratosphere in addition to tropical input. This new method was compared with the previously used method, which considered only the tropical input. The new method shows more realistic values especially near the tropopause. On average, the air of the lower stratosphere in the Northern Hemisphere was older than in the Southern Hemisphere by about 0.5 ± 0.3 years. About 65 K above the tropopause, the pattern changed with older air in the mid-latitudes of the Northern Hemisphere, but older air in high latitudes of the Southern Hemisphere, which implies differences in the strength and isolation of the respective polar vortex as well as the wave forcing in the shallow branch of the Brewer-Dobson circulation of the respective hemisphere. This is in good agreement with the distribution of Cly. The difference in the lower stratosphere was not clearly evident with the old method and it can be assumed that investigations of the differences in Cly of Northern and Southern Hemisphere will benefit from the new method.
Finally, the global and seasonal distribution of the two most important representatives of the short-lived brominated substances, CH2Br2 and CHBr3, was investigated. For this purpose, two additional HALO measurement campaigns have been used, the 2012 TACTS measurement campaign and the 2017 WISE measurement campaign, as well as the HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography (ATom) measurement campaigns. Observations of CH2Br2 show a pronounced seasonality in the free and upper troposphere of both hemispheres with slightly larger values in the Northern Hemisphere. CHBr3, on the other hand, shows a generally higher variability and lower seasonality with larger mixing ratios at mid and high latitudes in the northern hemispheric winter and autumn. A comparison of the lower stratosphere is limited to autumn and spring of both hemispheres due to the limited data basis of the observations. The distributions in each spring are similar (less than 0.1 ppt differences for e.g., CH2Br2). In hemispheric autumn, larger differences are evident with substantially smaller mixing ratios in the southern hemispheric lower stratosphere. This suggests that the transport processes of the two hemispheres may be different and implies that the input of tropospheric air (flushing) to the Northern Hemisphere lowest stratosphere is more efficient than in the Southern Hemisphere. Vertical profiles of CH2Br2 and CHBr3 in the mid-latitudes of both hemispheres and resulting vertical gradients support this conjecture. However, the Southern Hemisphere data set is insufficient to quantify this difference and further measurements are needed.
Due to massive energetic investments in woody support structures, trees are subject to unique physiological, mechanical, and ecological pressures not experienced by herbaceous plants. Despite a wealth of studies exploring trait relationships across the entire plant kingdom, the dominant traits underpinning these unique aspects of tree form and function remain unclear. Here, by considering 18 functional traits, encompassing leaf, seed, bark, wood, crown, and root characteristics, we quantify the multidimensional relationships in tree trait expression. We find that nearly half of trait variation is captured by two axes: one reflecting leaf economics, the other reflecting tree size and competition for light. Yet these orthogonal axes reveal strong environmental convergence, exhibiting correlated responses to temperature, moisture, and elevation. By subsequently exploring multidimensional trait relationships, we show that the full dimensionality of trait space is captured by eight distinct clusters, each reflecting a unique aspect of tree form and function. Collectively, this work identifies a core set of traits needed to quantify global patterns in functional biodiversity, and it contributes to our fundamental understanding of the functioning of forests worldwide.
Several past summer floods in Central Europe were associated with so-called Vb‑cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. This study illustrates the usefulness of the parametric transfer entropy measure TE‑linear in investigating heavy Vb‑cyclone precipitation events in the Odra catchment (Poland). With the application of the TE‑linear approach, we confirm the impact of the Mediterranean Sea on precipitation intensification. Moreover, we also detect significant information exchange to Vb‑cyclone precipitation from evaporation over the European continent along the typical Vb‑cyclone pathway. Thus, the Mediterranean Sea could enhance the Vb‑cyclone precipitation by pre-moistening continental moisture source regions that contribute to precipitation downstream in the investigated catchments. Overall, the transfer entropy approach with the measure TE‑linear proved to be computationally effective and complementary to traditional methods such as Lagrangian and Eulerian diagnostics.
There seems to be a wide agreement in critical geographic thought that Hegel is dead, as to end up with Hegel’s idealism serves to be the starting point for the materialist project of critical geographies. This paper aims to call this starting point into question by confronting Henri Lefebvre with Slavoj Žižek. While Lefebvre, one of the pioneers of materialist geographic thought, intensively worked on a metaphilosophical critique to open Hegel’s testament, Žižek’s Hegel supposed to pave the way for a new philosophical materialism. This paper seeks to claim that such a materialist Hegel not only survives the critical encounter of Lefebvre’s metaphilosophy, but also encourages us to inquire about the possibilities and consequences of a geographical turn to Hegel. What if there is a Hegel out there that geography has not even detected?
Questions: Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity.
Location: La Palma, Canary Islands.
Methods: We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient.
Results: The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation.
Conclusions: Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species.
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.
The overarching goal of the thesis was to create a holistic predictive framework, a vegetation model, by improving the representations of and interactions between the biosphere, hydrosphere, atmosphere and pedosphere. Vegetation models rep- resent a crucial component of Earth system model since the properties of the land surface, via interactions with the atmosphere, can have extremely large climatic effect. Yet, there remains great uncertainty associated with the dynamics of the vegetated land surface. Various vegetation models have been critiqued for numerous reasons including overly simplistic representations of vegetation, prescribed vegetation, poor representations of diversity, inaccurate representations of competition, non-transparent model calibration, and poor responses to drought. The purpose of the creation of this "next generation" model was to address deficiencies common to current vegetation modelling paradigms.
The representation of the biosphere within this framework was improved via two separate development axes. First, ecological realism was improved by integrating concepts from community assembly theory, co-existence theory, and evolutionary theory. Explicitly, rather than defining teleonomic rules to define plant behaviour the process of natural selection is modelled. By modelling the pro- cess of natural selection and its affect on relative fitness, myriad "rules" which continually adapt to biotic and abiotic conditions "come out" as a consequence of the modelled dynamics rather than being "put in". In aDGVM2 (adaptive Dynamic Global Vegetation model 2) communities of plants and their trait values evolve through time, this evolution is constrained by trade-offs between traits. Poorly performing individuals are more likely to die and produce fewer copies of themselves, this results in a filtering of trait values. Further, the community and species’ trait values can evolve through successive generations via reproduction, mutation and crossover which we approximate by using a genetic optimisation algorithm. Thus, a plant community consisting of individuals and species with potentially novel and diverse trait values is assembled iteratively through time.
We tested the assertion that improved integration of concepts from community assembly, evolutionary, and co-existence theory could address limitations of DGVMs in Chapter 2. We demonstrated that such an approach does indeed allow diverse communities of plants to emerge from the modelling framework. We showed that the position of the emergent communities in trait space differed along abiotic gradients and that, in simulations where reproductive isolation was simulated, communities emerged which were composed of multiple co-existing clusters in trait-space. Simulated trait values of co-existing strategies emerging from aDGVM2 were often multimodal, indicative of the emergence of multiple life- history strategies.
Second, to successfully model how natural selection forms a community requires accurate representation of how resource availability affects fitness. In the majority of dynamic global vegetation models (DGVMs) there is no real representation of plant hydraulics with plant water availability being calculated as a simple function of relative soil moisture content and root fractions across a number of soil layers. Worryingly, a number vegetation models appear to under represent the magnitude of these observed responses to drought. This was deficiency was ad- dressed in Chapter 3 by designing a simplified version of the cohesion tension theory of sapwood ascent where elements determining plant conductances are considered in series and implementing a set of trait trade-offs which influence a plant’s hydraulic strategy whereby hydraulic safety trades-off against xylem and leaf conductivity.
Interactions between the biosphere, pedosphere, and hydrosphere can also potentially mediate water resource availability and thus fitness. In the majority of DGVMs the volume of soil explored and explorable by plant roots in fixed glob- ally and usually constrained to a depth not greater than 3m. However, we know that soils can have a strong effect on vegetation distributions, that soil depth is not constant globally, and that plants root to variable depths.
In Chapter 4 I explored interactions between soil depth, plant rooting and the emergent properties of communities and highlighted the importance of considering interactions between the biosphere, hydrosphere, pedosphere, and fire. Here I demonstrated that, in addition to fire and precipitation, edaphic constraints on the volume of soil explorable by plant roots (e.g. by shallow soils, lateritic layers, anoxic conditions due to water logging, toxicity resulting from heavy metal concentrations) can affect the process of plant community assembly, alter the mean values of multiple traits in communities, and the trait diversity of communities.
...
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burning horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition and peatland hydrology at two sites in Western Siberia near Tomsk Oblast, Russia. The palaeoecological records originate from forested peatland areas in predominantly light taiga (Pinus-Betula) with increase in dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) towards the east. We found that the past water level fluctuated between 8 and 30 cm below the peat surface. Wet peatland conditions promoted broadleaf trees (Betula), whereas dry peatland conditions favoured conifers and a greater forest density (dark-to-light-taiga ratio). The frequency and severity of fire increased with a declining water table that enhanced fuel dryness and flammability and at an intermediate forest density. We found that the probability of intensification in fire severity increased when the water
level declined below 20 cm suggesting a tipping point in peatland hydrology at which wildfire regime intensifies. On a Holocene scale, we found two scenarios of moisture-vegetation-fire interactions. In the first, severe fires were recorded 45 between 7.5 and 4.5 ka BP with lower water level and an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybanya and Abies sibirica at Ulukh Chayakh) mixed into the dominantly light taiga and fire-resister community of Pinus
sylvestris. The second occurred over the last 1.5 ka and was associated with fluctuating water tables, a declining abundance of fire avoiders, and an expansion of fire invaders (Betula). These findings suggest that frequent high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial to millennial-scale Holocene climate
variability on wildfire activity. Increasing human presence in the region of the Ulukh-Chayakh Mire near Teguldet over the last four centuries drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted for the future in Siberia by climate change scenarios will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions, particularly a water table decline below the threshold of 20 cm, will probably exacerbate the frequency and severity of wildfire, disrupt conifers’ successional pathway and accelerate shifts towards more fire-adapted broadleaf tree cover. Furthermore, climate-disturbance-fire feedbacks will accelerate changes in the carbon balance of forested boreal peatlands and affect their overall future resilience to climate change.
Wildfire is the most common disturbance type in boreal forests and can trigger significant changes in forest composition. Waterlogging in peatlands determines the degree of tree cover and the depth of the burnt horizon associated with wildfires. However, interactions between peatland moisture, vegetation composition and flammability, and fire regime in forest and forested peatland in Eurasia remain largely unexplored, despite their huge extent in boreal regions. To address this knowledge gap, we reconstructed the Holocene fire regime, vegetation composition, and peatland hydrology at two sites located in predominantly light taiga (Pinus sylvestris Betula) with interspersed dark taiga communities (Pinus sibirica, Picea obovata, Abies sibirica) in western Siberia in the Tomsk Oblast, Russia. We found marked shifts in past water levels over the Holocene. The probability of fire occurrence and the intensification of fire frequency and severity increased at times of low water table (drier conditions), enhanced fuel dryness, and an intermediate dark-to-light taiga ratio. High water level, and thus wet peat surface conditions, prevented fires from spreading on peatland and surrounding forests. Deciduous trees (i.e. Betula) and Sphagnum were more abundant under wetter peatland conditions, and conifers and denser forests were more prevalent under drier peatland conditions. On a Holocene scale, severe fires were recorded between 7.5 and 4.5 ka with an increased proportion of dark taiga and fire avoiders (Pinus sibirica at Rybnaya and Abies sibirica at Ulukh–Chayakh) in a predominantly light taiga and fire-resister community characterised by Pinus sylvestris and lower local water level. Severe fires also occurred over the last 1.5 kyr and were associated with a declining abundance of dark taiga and fire avoiders, an expansion of fire invaders (Betula), and fluctuating water tables. These findings suggest that frequent, high-severity fires can lead to compositional and structural changes in forests when trees fail to reach reproductive maturity between fire events or where extensive forest gaps limit seed dispersal. This study also shows prolonged periods of synchronous fire activity across the sites, particularly during the early to mid-Holocene, suggesting a regional imprint of centennial- to millennial-scale Holocene climate variability on wildfire activity. Humans may have affected vegetation and fire from the Neolithic; however, increasing human presence in the region, particularly at the Ulukh–Chayakh Mire over the last 4 centuries, drastically enhanced ignitions compared to natural background levels. Frequent warm and dry spells predicted by climate change scenarios for Siberia in the future will enhance peatland drying and may convey a competitive advantage to conifer taxa. However, dry conditions will probably exacerbate the frequency and severity of wildfire, disrupt conifers' successional pathway, and accelerate shifts towards deciduous broadleaf tree cover. Furthermore, climate–disturbance–fire feedbacks will accelerate changes in the carbon balance of boreal peatlands and affect their overall future resilience to climate change.
Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Hyrrokkin sarcophaga is a parasitic foraminifer that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Lophelia pertusa. Here, we present measurements of the elemental and isotopic composition of this parasitic foraminifer for the first time, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe micro analysis (EPMA) and mass spectrometry (MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest L. pertusa, which could be an indication that dissolved host carbonate material is utilised in shell calcification, given that the aragonite of L. pertusa has a naturally higher Sr concentration compared to the calcite of A. excavata.Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on20 L. pertusa, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn/Ca ratios in foraminifers that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifer, these data also indicate that the geochemistry of this parasitic foraminifer is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
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.
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.
Hydro-climatic causes of widespread floods in central Europe : on rain-on-snow and Vb-cyclone events
(2021)
The presented work investigates the hydro-meteorological and hydro-climatological drivers of widespread floods in Central Europe during the past century. Due to the strong seasonality of the detected flood drivers, the thesis is divided into two parts: the first part focuses on widespread winter floods and the second one on extreme summer floods. For analysing past flood events, we profited from the dynamically downscaled centennial ERA-20C reanalysis (continuously from 1901—2010). The downscaling was performed over Europe with a coupled regional atmosphere-ocean model (COSMO-CLM+NEMO) to represent the water cycle more realistic. These high resolution atmospheric data allowed us to study the four-dimensional atmospheric state during selected floods during the early decades of the 20th century for the first time with such a high temporal and spatial resolution.
During the winter half-year, the observed floods were particularly widespread. High peak discharges were recorded simultaneously in the Rhine, Elbe, and Danube catchments. Most of these trans-basin floods were compound events caused by rainfall during extensive snowmelt (i.e., rain-on-snow events). Interestingly, the winter flood time series exhibited a remarkable high flood frequency during the 1940s and 1980s, while other decades were flood-poor. We detected a synchronization of the inter-annual flood frequency with the superposition of the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCA). The negative NAO phase is often associated with large snowfall and cyclone tracks over southern Europe, while the negative SCA pattern correlates with total precipitation in the affected river catchments.
During the summer half-year, most extreme floods in Central Europe were caused by so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. So far in the literature, only a few Vb-events, which occurred during the past two decades, have been analysed. We extended the previous case studies by several past Vb-cyclone floods since 1900. We investigated the processes that intensify Vb-cyclone precipitation with Lagrangian moisture-source diagnostics and the parametric transfer entropy measure TE-linear. Overall, an enhanced and dynamically driven moisture uptake over the Mediterranean Sea was found to be characteristic for Vb-events with heavy precipitation. This is supported by high information exchange from evaporation over the western basin of the Mediterranean Sea towards heavy precipitation in the Odra catchment. The dominating moisture uptake regions during the investigated events were, however, the European continent and the North Sea. A possible cause could be the pre-moistening of non-saturated continental moisture sources upstream of the affected river catchments as indicated by significant information exchange from land surface evaporation and soil moisture content along the Vb-cyclone pathway. Besides, evaporation over the Mediterranean Sea might contribute to Vb-cyclone intensification in the early stages of their development through latent heat release. On the catchment scale, orographic rainfall and convective precipitation further enhance the flood triggering rainfall. As expected, the Vb-cyclones mainly trigger precipitation along west-east orientated mountain ranges such as the Alps or Ore mountains due to their meridional pathway. Remarkably, during summer, we detected a convective fraction of up to 90% during the afternoons of individual days and up to 23% on average (based on convective cell tracking and convection-permitting simulations of selected flood events since 1900).
The presented analyses deepened the knowledge on atmospheric and hydroclimatic drivers of widespread floods in Central Europe. This will serve as a basis for future studies on the predictability of floods induced by rain-on-snow and Vb-cyclone precipitation events in the context of a changing climate.
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.
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.
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.
In recent years, many European cities have developed strategies to improve the quality of urban life by reducing car traffic and increasing the attractiveness of alternative modes and the built environment for residents. Frequently, at least in German cities, improvements to the cycling infrastructures play a key role in this transformation of urban spaces. One of those transformative interventions took place in 2020 in Frankfurt am Main (Germany). The city redesigned an arterial road close to the city centre, the Friedberger Landstrasse, by converting two car lanes to bicycle lanes. It is the aim of this study to analyse the effects of this change on the quality of urban life of its residents using a quantitative before-and-after study. The results demonstrate the expected improvements in the perceived quality of urban life for residents after the intervention. A more detailed analysis, however, shows that the residents’ perceptions vary according to their own mode use on the Friedberger Landstrasse and other sociodemographic characteristics. Thus, better cycling infrastructure does not only improve conditions for cyclists, but also contributes to a higher quality of urban life for residents and, therefore, improves the liveability of a city in two ways. We conclude that local transport policies are not only relevant for a modal shift, but also for the quality of urban life and, thus, related urban development strategies.
Eisbildende Prozesse sind für die Wolkenbildung von großer Bedeutung und haben erhebliche Auswirkungen auf das Wetter und Klima der Erde, indem sie den Strahlungsantrieb und die Niederschlagsbildung beeinflussen. In den mittleren Breiten entsteht der meiste Niederschlag in sogenannten Mischphasenwolken (MPC), welche sowohl aus unterkühlten Wolkentröpfchen als auch aus Eiskristallen bestehen. Bei Temperaturen zwischen 0°C und -38°C erfolgt die Bildung von Eiskristallen in MPC in Gegenwart von Aerosolpartikeln, die als sogenannte Eiskeime (INP) die Fähigkeit besitzen, auf ihrer Oberfläche Eis zu nukleieren. Trotz der großen wissenschaftlichen Fortschritte in den letzten Jahrzehnten, weist der heterogene Eisbildungsprozess, als einer der wichtigsten in der Atmosphäre auftretenden Aerosol-Wolken-Wechselwirkungsprozesse, immer noch große Unsicherheiten auf. Um zukünftige Klimavorhersagen und -projektionen in Modellen besser abbilden zu können, ist es somit notwendig den Wissensgrad der räumlichen und zeitlichen Heterogenität von INP in Bezug auf Herkunft, Anzahl und Zusammensetzung zu erhöhen. Im Zentrum dieser Arbeit steht der Eiskeimzähler FINCH (Fast Ice Nucleus Chamber), der für Labor- und Feldexperimente von der Johann Wolfgang Goethe-Universität in Frankfurt am Main entwickelt wurde. Durch das Mischen des Probenstroms mit einem warm-feuchten und einem kalten-trockenen Luftstrom wird eine Übersättigung in der in-situ Eiskammer erreicht, die benötigt wird, eisbildende Partikel zu aktivieren. Die aktivierten Partikel können beim Durchströmen der Kammer zu Wassertropfen oder Eiskristallen anwachsen. Am Ausgang der Kammer wird die Anzahl und Größe der Partikel durch die FINCH-Optik erfasst. Als grundlegender Schritt und aufbauend auf den Charakterisierungsmessungen von Frank (2017) wurden in der vorliegenden Arbeit die Leistung, die Zuverlässigkeit sowie die Reproduzierbarkeit von FINCH in Validierungsexperimenten im Labor überprüft. Im Zuge dessen wurden heterogene Gefrierexperimente mit definierten Referenzaerosolproben (bspw. K-Feldspat) bei wasserübersättigten Bedingungen und verschiedenen Gefriertemperaturen durchgeführt. Für den Großteil der erzielten Resultate konnte eine zufriedenstellende Übereinstimmung mit Literaturwerten von anderen INP-Messinstrumenten aus der ganzen Welt erzielt werden. Es zeigte sich, dass die Leistungsfähigkeit von FINCH messtechnische Limitationen für Messexperimente bei Temperaturen >-10°C und <-30°C aufweist, was eine Einschränkung des Messbereichs bedeutet. Hinsichtlich der Quantifizierung des Unsicherheitsbereiches des Messgerätes in Bezug auf Temperatur und relativer Feuchte bedarf es im Nachgang an dieser Arbeit weiterer Charakterisierungsmessungen. Im Rahmen der Ice Nuclei Research Unit (INUIT) Forschergruppe wurde FINCH mit einem gepumpten Gegenstrom-Impaktor PCVI und dem online Einzelpartikel-Massenspektrometer ALABAMA gekoppelt. Diese spezielle Messmethodik dient zur chemischen und mikrophysikalischen Charakterisierung der INP und der Eispartikelresiduen (IPR). Der Fokus lag zunächst darauf die Funktionalität des gekoppelten Messsystems im Labor zu überprüfen. Ausführliche Charakterisierungsmessungen zeigten unter eisübersättigten und unterkühlten Bedingungen, dass das Prinzip der Trennung der INP von nicht-aktivierten Aerosolen und unterkühlten Tropfen hinter FINCH durch den PCVI funktioniert. Ebenso konnten erste quantitative Aussagen zur chemischen Zusammensetzung der IPR getroffen werden. Es zeigte sich, dass bei den Aktivierungsexperimenten ein geringer Anteil an Partikeltypen metallischer Art von ALABAMA detektiert wurden, der nicht dem untersuchten Aerosoltyp zugeordnet werden konnte. Der Ursprung dieser Kontamination konnte im Rahmen dieser Arbeit nicht abschließend geklärt werden und bedarf weiterer Validierungsmessungen im Labor. Atmosphärische Eiskeimkonzentrationen wurden im Rahmen von Feldmesskampagnen an der Hochalpinen Forschungsstation Jungfraujoch (JFJ) in den Schweizer Alpen und am Campus Riedberg der Johann Wolfgang Goethe-Universität in Frankfurt am Main untersucht. Hier konnten erste Erfahrungen mit Außenluftmessungen bezüglich der Leistungsfähigkeit und der Nachweisgrenze (LOD) des Messgerätes gesammelt werden. Durch den Einfluss der freien Troposphäre am JFJ waren die Messungen hauptsächlich von aerosolpartikelarmer Luft mit einer geringen Anzahl von Eiskeimen geprägt, so dass sich die gemessenen INP-Konzentrationen oftmals unter die Nachweisgrenze von FINCH fielen. Unter Einsatz eines Aerosolkonzentrators konnte die Detektionseffizienz verbessert und das LOD herabgesetzt werden. Am JFJ wurden die INP im Mittel bei einer Temperatur von -23°C und einem Wassersättigungsverhältnis von 107% beprobt. Die mediane (mittlere) INP-Konzentration inklusive LOD lag bei 2,1 (3,3) sL-1 und oberhalb des LOD bei 3,1 (4,5) sL-1. Ein Vergleich mit den Messungen am Campus Riedberg unter annähernd gleichen Bedingungen resultiert in ähnlichen Konzentrationen.
A general circulation model is used to study the interaction between parameterized gravity waves (GWs) and large-scale Kelvin waves in the tropical stratosphere. The simulation shows that Kelvin waves with substantial amplitudes (∼10 m s−1) can significantly affect the distribution of GW drag by modulating the local shear. Furthermore, this effect is localized to regions above strong convective organizations that generate large-amplitude GWs, so that at a given altitude it occurs selectively in a certain phase of Kelvin waves. Accordingly, this effect also contributes to the zonal-mean GW drag, which is large in the middle stratosphere during the phase transition of the quasi-biennial oscillation (QBO). Furthermore, we detect an enhancement of Kelvin-wave momentum flux due to GW drag modulated by Kelvin waves. The result implies an importance of GW dynamics coupled to Kelvin waves in the QBO progression.
Plain Language Summary: The variability of the tropical atmosphere at altitudes of about 18–40 km is dominated by a large-amplitude long-term oscillation of wind, the quasi-biennial oscillation, which has a broad impact on the climate and seasonal forecasting. This oscillation is known to be driven by various types of atmospheric waves with multiple spatial scales. Using a numerical model, this study reports a process of interaction between those waves on different scales, which has not been illuminated before. The result implies a potential importance of this process in the progression of the quasi-biennial oscillation. Proper model representations of these multiscale waves and tropical convection are required to simulate this process.
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.
Im Rahmen einer angewandten kritischen Geographie beschäftigen wir uns in unserer Masterarbeit mit Realen Utopien auf Quartiersebene und zeigen, dass eine alternative Neuausrichtung der Stadtplanung und -entwicklung nötig und möglich ist. Die Grundlage dafür bildet eine kritische Auseinandersetzung mit dem Begriff der Utopie und der Ebene des Quartiers. Das städtische Quartier bildet einen Möglichkeitsraum, einen space of hope (Harvey 2000), in dem Alternativen jenseits kapitalistischer Verwertungsinteressen praktiziert und gelebt werden können. Diesen Möglichkeitsraum gilt es vielfältig zu gestalten und gegenwärtigen, neoliberalen Stadtentwicklungs-paradigmen Reale Utopien(Wright 2017a) entgegenzustellen. Dabei stellt sich die Frage: Welche Gegenentwürfe zu aktuell herrschenden Paradigmen in der Stadtentwicklung zeigen uns Wege aus der Alternativlosigkeit und hin zu einer solidarischen Praxis auf Quartiersebene?Für die Beantwortung dieser Frage werden potentielle und bereits existierende Reale Utopien identifiziertund analysiert. In dieser Analyse werden Instrumente, Forderungen und Strategien herausgearbeitet, derer es Bedarf um Risse im kapitalistischem System auszuweiten, zu verteidigen und zu verstetigen. Die Ergebnisse lassen sich unter den Begriffen der Solidarität, Dekommodifi-zierung, Demokratisierung und Vergesellschaftung zusammenfassen. Sie sind die zentralen Bedin-gungen, die für die Verwirklichung Realer Utopien und damit für gesellschaftliche Transformation, entscheidend sind. Darauf basierendwird ein Kompass für ein solidarisches Quartier erarbeitet.
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.
Die Straße als Transit- und Abstellraum für Automobile ist kein Naturgesetz. Mit Michel de Certeau lässt sie sich als historisches Produkt einer Strategie verstehen, die sich in einem immerwährenden Konflikt durchsetzt. Ziel dieses Beitrags ist es, die Straße als Ort des Automobils zu denaturalisieren, um das konflikthafte Spannungsverhältnis zwischen den als rezessiv antizipierten Bewegungen des Zufußgehens und jenen dominanten automobilen Bewegungen sichtbar zu machen. Mithilfe einer interventionistischen Flächenprojektion von Fußwegen – einem selbstgemalten Zebrastreifen aus Kreide – wird anhand eines Fallbeispiels aus Frankfurt am Main aufgezeigt, wie sich die alltäglich konflikthafte Aushandlung von Straßenräumen durch Planung materialisieren und somit in die Konzeption von Straße integrieren lässt.
In this dissertation, different aspects of turbulent transport and thermally driven flows over complex terrain are investigated. Two publications concentrate on the vertical heat and moisture exchange in the convective boundary layer over mountainous terrain. To study this, Large-Eddy Simulation (LES) is used. Both turbulent and advective transport mechanisms are evaluated over the simple orography of a quasi-two-dimensional, periodic valley with prescribed surface fluxes. Here, terrain elevation varies along only one of the horizontal coordinate axes. Even a relatively shallow orography, possibly unresolved in existing numerical weather prediction models, modifies the domain-averaged moisture and temperature profiles. For the analysis, the flow is decomposed into a local turbulent part, a local mean circulation, and a large-scale part. An analysis of the turbulent kinetic energy and turbulent heat and moisture flux budgets shows that the thermal circulation significantly contributes to the vertical transport. It is found that thermal upslope winds are important for the moisture transport from the valley to the mountain tops. In total, moisture export out of the valley is mostly accomplished by the mean circulation. On the temperature distribution, which is horizontally relatively homogeneous, the thermal circulation has a weaker impact. If an upper-level wind is present, it interacts with the thermal circulation. This weakens the vertical transport of moisture and thus reduces its export out of the valley. The heat transport is less affected by the upper-level wind because of its weaker dependence on the thermal circulation. These findings were corroborated in a more realistic experiment simulating the full diurnal cycle using radiation forcing and an interactive land surface model.
Based on these results, coherent turbulent structures in the convective boundary layer over non-flat terrain are studied in further detail. A conditional sampling method based on the concentration of a decaying passive tracer is implemented in order to identify the boundary-layer plumes objectively. Conditional sampling allows to quantify the contribution of plume structures to the vertical transport of heat and moisture. In case of the idealized valley, vertical transport by coherent structures is the dominant contribution to the turbulent components of both heat and moisture flux. It is comparable in magnitude to the advective transport by the mean slope-wind circulation, although it is more important for heat than for moisture transport. A set of less idealized simulations considers the flow over three-dimensional terrain. In this case, conditional sampling is carried out by using a simple domain-decomposition approach. We demonstrate that thermal updrafts are generally more frequent on hill tops than over the surroundings, but they are less persistent on the windward sides when large-scale winds are present in the free atmosphere.
The tools for flow decomposition and budget analysis are also applied in another idealized case with a quasi-two-dimensional valley featuring the stable boundary layer. Here, the formation of a low stratus cloud is investigated. The main driver for the cloud formation is radiative cooling due to outgoing longwave radiation. Despite a purely horizontal flow, the advection terms in the prognostic equations for heat and moisture produce vertical mixing across the upper cloud edge leading to a loss of cloud water content. However, this behavior is not due to any kind of thermally-driven circulation. Instead, this spurious mixing is caused by the diffusive error of the advection scheme in regions where the sloping surfaces of the terrain-following vertical coordinate intersect the cloud top. It is shown that the intensity of the (spurious) numerical diffusion strongly depends on the horizontal resolution, the order of advection, and the choice of the scalar advection scheme. A LES with 4 m horizontal resolution serves as a reference. For horizontal resolutions of a few hundred meters, carried out with a model setup as it is used in Numerical Weather Prediction, a strong reduction of the simulated liquid-water path is observed. In order to keep the (spurious) numerical diffusion at coarser resolutions small, at least a fifth-order advection scheme should be used. In the present case, a WENO scalar advection scheme turns out to increase the numerical diffusion along a sharp cloud edge compared to an upwind scheme. Furthermore, the choice of the vertical coordinate has a strong impact on the simulated liquid-water path over orography. With a modified definition of the terrain-following sigma coordinate, it is possible to produce cloud water where the classical sigma coordinate does not allow any cloud formation.
Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound
(2022)
Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
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.
While high-quality climate reconstructions of some past warm periods in the Cenozoic era now exist, the geological processes responsible for driving the observed longterm changes in atmospheric CO2 are not sufficiently well understood. The long-term change in atmospheric CO2 across the Cenozoic has been proposed to be driven by processes such as terrestrial weathering, organic carbon production and burial, reverse weathering, and volcanic degassing. One way of constraining the relative importance of the various driving forces proposed so far is to better understand the degree to which ocean chemistry has changed because the chemistry of seawater responds to geologic processes that drive atmospheric CO2. In addition, knowledge of the concentration of the major elements in seawater is crucial for accurately applying proxies such as those based on the boron isotopic composition and Mg/Ca of marine carbonates (a proxy for palaeo pH/CO2 and palaeotemperature, respectively). Previously reported records of seawater composition are primarily derived from fluid inclusions in marine evaporites; however, the results are sparse due to the limited availability of such deposits. In this thesis, changes in the Eocene seawater chemistry were reconstructed using trace element (elements/Ca) and isotopic (δ26Mg) proxies in a Larger Benthic Foraminifera (LBFs), i.e., Nummulites sp., to constrain the driving processes of long-term changes in seawater chemistry.
To achieve the objective of this thesis, first, a measurement protocol was established using LA-ICPMS to measure the K/Ca ratio simultaneously with other element/calcium ratios, which is challenging due to the interference of ArH+ on K+. Utilising this newly established measurement protocol, laboratory-cultured Operculina ammonoides grown at different seawater calcium concentrations ([Ca2+]), repeated at different temperatures, as well as modern O. ammonoides collected from different regions exhibiting a range of seawater parameters, were investigated. A significant correlation was observed between K/Casw and K/CaLBF, allowing K/CaLBF to potentially be used as a proxy for seawater major ion reconstructions. In addition, modern O. ammonoides demonstrated no significant influence of most seawater parameters (temperature, salinity, pH, or [CO32-]) on K/CaLBF. Modern O.
ammonoides were also assessed for their Mg isotopic composition (δ26Mg), revealing no significant effect of temperature or salinity on δ26MgLBF. Furthermore, the Mg isotopic fractionation in O. ammonoides was found to be close to that of inorganic calcite, indicating minimal vital effects in these large benthic foraminifera.
Operculina ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling the reconstruction of seawater chemistry using the calibration based on O. ammonoides. The trace elemental/calcium proxies, including Na/Ca, K/Ca, and Mg/Ca, as well as the δ26Mg proxy, were investigated in Eocene Nummulites. The result showed that during the Eocene, [Ca2+]sw was 1.6-2 times higher, while [K+]sw was ~2 times lower than the modern seawater composition. Furthermore, [Mg2+]sw decreased from the early Eocene (54.3− +9 7..69 mmol kg-1 at ~55 Ma) to Late Eocene (37.8− +4 4..3 4 mmol kg-1 at ~31 Ma), followed by
an increase toward modern seawater [Mg]. In contrast, the variability in δ26Mgsw values remained within a narrow range of ~0.3 ‰ throughout the Cenozoic. The reconstructed [Ca2+]sw agrees with the suggestion that Cenozoic seawater chemistry changes can be explained via a change in the seafloor spreading rate. When combined with existing records, the observed minimal change in δ26Mgsw with an increase in [Mg2+]sw suggests an additional possible role of a decrease in the formation of authigenic clay minerals coincident with the Cenozoic decline in deep ocean temperature, which is also supported by the increase in the [K+]sw reconstructed here for the first time. This finding highlights that the reduction in seafloor-spreading rate and decline in reverse weathering during the Cenozoic era has played a significant role in the evolution of seawater chemistry, emphasizing the importance of these processes in driving long-term changes in the carbon cycle.
In partially molten regions inside the earth melt buoyancy may trigger upwelling of both solid and fluid phases, i.e. diapirism. If the melt is allowed to move separately with respect to the matrix, melt perturbations may evolve into solitary porosity waves. While diapirs may form on a wide range of scales, porosity waves are restricted to sizes of a few times the compaction length. Thus, the size of a partially molten perturbation controls whether a diapir or a porosity wave will emerge. We study the transition from diapiric rise to solitary porosity waves by solving the two-phase flow equations of conservation of mass and momentum in 2D with porosity dependent matrix viscosity. We systematically vary the initial size of a porosity perturbation from 1 to 100 times the compaction length. If the perturbation is much larger than a regular solitary wave, its Stokes velocity is large and therefore faster than the segregating melt. Consequently, the fluid is not able to form a porosity wave and a diapir emerges. For small perturbations solitary waves emerge, either with a positive or negative vertical matrix velocity inside. In between the diapir and solitary wave regimes we observe a third regime of solitary wave induced focusing of melt. In these cases, diapirism is dominant but the fluid is still fast enough to locally build up small solitary waves which rise slightly faster than the diapir and form finger like structures at the front of the diapir. In our numerical simulations the width of these fingers is controlled by the compaction length or the grid size, whichever is larger. In cases where the compaction length becomes similar to or smaller than the grid size the finger-like leading solitary porosity waves are no more properly resolved, and too big and too fast waves may be the result. Therefore, one should be careful in large scale two-phase flow modelling with melt focusing especially when compaction length and grid size are of similar order.
Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.
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.
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 Abstrahlung von internen Schwerewellen in atmosphärischen Strahlströmen und Temperaturfronten trägt vermutlich mit einem signifikanten Beitrag zum gesamten Schwerewellenspektrum bei. Das physikalische Verständnis der dabei ablaufenden Prozesse ist derzeit allerdings noch zu gering ausgeprägt, um eine adäquate mathematische Darstellung für operationelle Wetter- und Klimamodelle zu entwickeln. In dieser Arbeit wird der Mechanismus dieser Schwerewellenquelle in numerischen Simulationen des differenziell geheizten rotierenden Annulusexperiments erforscht. Dieses Experiment besitzt eine im Vergleich zur Atmosphäre deutlich verringerte Anzahl an Freiheitsgraden und eignet sich besonders gut zum Studium der Dynamik der mittleren Breiten. Analoge Untersuchungen werden in einem äquivalenten kartesischen Modellsystem vorgenommen, in dem periodische Bedingungen in den beiden horizontalen Raumrichtungen vorliegen.
Im Gegensatz zur Annuluskonfiguration, in der nachweislich auch eine Schwerwellenabstrahlung an den Zylinderwänden erfolgt, kommt in dieser Konfiguration nur die interne Dynamik als Schwerewellenquelle in Frage. Die nichtlinearen Simulationen beider Modellkonfigurationen zeigen eine großskalige barokline Wellenstruktur, die ein atmosphärenähnliches Jet-Front System beinhaltet. Darin eingelagert werden vier voneinander isolierte Schwerewellenpakete in der Annuluskonfiguration sowie zwei Schwerewellenpakete im doppeltperiodischen Modellsystem charakterisiert. Um den zugrundeliegenden Quellmechanismus zu untersuchen, erfolgt eine Aufspaltung der Zustandsvariablen in einen balancierten und einen unbalancierten Anteil, wobei erstgenannter das geostrophische und hydrostatische Gleichgewicht erfüllt und letztgenannter das Schwerewellensignal enthält. Die Strömungsaufspaltung bildet die Grundlage für die Entwicklung eines tangential-linearen Modells für den unbalancierten Strömungsanteil. Hierbei wird eine systematische Umformulierung der dynamischen Grundgleichungen hinsichtlich der Wechselwirkung beider Strömungsanteile vollzogen. Insbesondere wird der rein balancierte Antrieb der unbalancierten Strömung freigelegt, um dessen Einfluss auf die Schwerewellenaktivität zu quantifizieren. Die anschließenden tangential-linearen Simulationen zeigen, dass drei der vier Schwerewellenpakete in der Annuluskonfiguration in der internen Strömung generiert werden. Ein verbleibendes Wellenpaket entsteht an der inneren Zylinderwand, ehe es in das innere Modellvolumen propagiert. Darüber hinaus wird deutlich, dass der rein balancierte interne Antrieb der Schwerewellen einen signifikanten Beitrag zur Schwerewellengenerierung leistet. Im doppeltperiodischen Modellsystem gibt es eine nahezu perfekte Übereinstimmung zwischen den unbalancierten Strömungsmustern in den tangential-linearen und den nichtlinearen Simulationen. Auch dort nimmt der balancierte Antrieb eine zentrale Rolle bei der Schwerewellenabstrahlung ein. Die abschließende Gegenüberstellung verschiedener, voneinander unabhängiger Gleichgewichtskonzepte macht deutlich, dass die balancierte Strömung der führenden Ordnung in der Rossbyzahl bereits eine erstaunliche Übereinstimmung mit der vollen Strömung liefert. Zudem erbringt die Anwendung einer Lagrange'schen Filtermethode den Nachweis, dass die Vertikalbewegungen und die horizontalen Divergenzsignale in der Annuluskonfiguration fast ausschließlich auf die Schwerewellenaktivität zurückzuführen sind.
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.
Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth’s surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry 15 measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope δ-δ paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different 20 alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5°C) yield a near sea level precipitation δ18Ow value of -5.8 ± 0.2‰ and in conjunction with the high-Alpine phyllosilicate δD record suggest that the region surrounding the SFZ attained surface elevations of >4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between -4.2 and -7.6‰ for the Northern Alpine Foreland Basin.