Fakultät für Geowissenschaften - Digitale Hochschulschriften der LMU

The Earth mantle convects on a global scale, coupling the stress field at every point to every other location at an instant. This way, any change in the buoyancy field has an immediate impact on the convection patterns worldwide. At the same time, mantle convection couples to processes at scales of a few kilometers or even a few hundred meters. Dynamic topography and the geoid are examples of such small-scale expressions of mantle convection. Also, the depth of phase transitions varies locally, with strong influences on the buoyancy, and thus the global stress field. In order to understand these processes dynamically it is essential to resolve the whole mantle at very high numerical resolutions.

At the same time, geodynamicists are trying to answer new questions with their models, for example about the rheology of the mantle, which is most likely highly nonlinear. Also, due to the extremely long timescales we cannot observe past mantle states, which calls for simulations backwards in time. All these issues lead to an extreme demand in computing power. To cater to those needs, the physical models of the mantle have to be matched with efficient solvers and fast algorithms, such that we can efficiently exploit the enormous computing power of current and future high performance systems.

Here, we first give an extensive overview over the physical models and introduce some numerical concepts to solve the equations. We present a new two-dimensional software as a testbed and elaborate on the implications of realistic mineralogic models for efficient mantle convection simulations. We find that phase transitions present a major challenge and suggest some procedures to incorporate them into mantle convection modeling. Then we give an introduction to the high-performance mantle convection prototype HHG, a multigrid-based software framework that scales to some of the fastest computers currently available. We adapt this framework to a spherical geometry and present first application examples to answer geodynamic questions. In particular, we show that a very thin and very weak asthenosphere is dynamically plausible and consistent with direct and indirect geological observations.

The mitochondria of non-bilaterian metazoans display a staggering diversity of genome organizations and also a slow rate of mtDNA evolution, unlike bilaterians, which may hold a key to understand the early evolution of the animal mitochondrion. Octocorals are unique members of Phylum Cnidaria, harboring several atypical mitochondrial genomic features, including a paucity of tRNA genes, various genome arrangements and the presence of novel putative mismatch repair gene (mtMutS) with various potential biological roles. Thus octocorals represents an interesting model for the study of mitochondrial biology and evolution. However, besides its utility in molecular phylogenetics, the mtDNA of octocorals is not studied from the perspective of DNA repair, oxidative stress response or gene expression; and there is a general lack of knowledge on the DNA repair capabilities and role of the mtMutS gene, response to climate-change, and mtDNA transcription in absence of interspersed tRNA genes of octocoral mitochondrial genome. In order to put the observed novelties in the octocoral mitochondria in an evolutionary and an environmental context, and to understand their potential functions and the consequences of their presence in conferring fitness during climate change induced stress, this study was undertaken. This dissertation aims to explore the uniqueness and diversity of octocoral mtDNA from an environmental as well as an evolutionary perspective.

The thesis comprises five chapters exploring various facets of octocoral biology. The introductory section provides basic information and elaborates on the importance of studying non-bilaterian mitochondria. The first chapter sets the base for subsequent gene expression studies. Octocorals are extensively studied from a taxonomic and phylogenetic point of view. However, gene expression studies on these organisms have only recently started to appear. To successfully employ the most commonly used gene expression profiling technique i.e., the quantitation real-time PCR (qPCR), it is necessary to have an experimentally validated, treatment-specific set of stably expressed reference genes that will support for the accurate quantification of changes in expression of genes of interest. Hence, seven housekeeping genes, known to exhibit constitutive expression, were investigated for expression stability during simulated climate-changed (i.e. thermal and low-pH) induced stress. These genes were validated and subsequently used in gene expression studies on Sinularia cf. cruciata, our model octocoral.

The occurrence of a mismatch repair gene, and the slow rates of mtDNA evolution in octocoral mitogenome calls for further investigations on the potential robustness of octocoral mitochondria to the increased oxidative stress. The second chapter presents a mitochondrion-centric view of climate-change stress response by investigating mtDNA damage, repair, and copy number dynamics during stress. The changes in gene expression of a set of stress-related nuclear, and mitochondrial genes in octocorals were also monitored. A robust response of octocoral mitochondria to oxidative mtDNA damage was observed, exhibiting a rapid recovery of the damaged mtDNA. The stress-specific regulation of the mtMutS gene was detected, indicating its potential involvement in stress response. The results highlight the resilience potential of octocoral mitochondria, and its adaptive benefits in changing oceans.

The tRNA genes in animal mitochondria play a pivotal role in mt-mRNA processing and maturation. The influence of paucity of tRNA genes on transcription of the mitogenome in octocorals has not been investigated. The third chapter steps in the direction to understand the mitogenome transcription by investigating the nature of mature mRNAs. Several novel features not present in a “typical” animal mt-mRNAs were detected. The majority of the mitochondrial transcripts were observed as polycistronic units (i.e. the mRNA carrying i

Someday in 2007, the world population reached a historical landmark: for the first time in human history, more than half of the world´s population was urban. A stagnation of this urbanization process is not in sight, so that by 2050, already 70 percent of humankind is projected to live in urban settlements. Over the last few decades, enormous migrations from rural hinterlands to steadily growing cities could be witnessed coming along with a dramatic growth of the world’s urban population. The speed and the scale of this growth, particularly in the so called less developed regions, are posing tremendous challenges to the countries concerned as well as to the world community. Within mega cities the strongest trends and the most extreme dimensions of the urbanization process can be observed. Their rapid growth results in uncontrolled processes of fragmentation which is often associated with pronounced poverty, social inequality, socio-spatial and political fragmentation, environmental degradation as well as population demands that outstrip environmental service capacity. For the majority of the mega cities a tremendous increase of informal structures and processes has to be observed. Consequentially informal settlements are growing, which represent those characteristic municipal areas being subject to particularly high population density, dynamics as well as marginalization. They have quickly become the most visible expression of urban poverty in developing world cities.

Due to the extreme dynamics, the high complexity and huge spatial dimension of mega cities, urban administrations often only have an obsolete or not even existing data basis available to be at all informed about developments, trends and dimensions of urban growth and change. The knowledge about the living conditions of the residents is correspondingly very limited, incomplete and not up to date. Traditional methods such as statistical and regional analyses or fieldwork are no longer capable to capture such urban process. New data sources and monitoring methodologies are required in order to provide an up to date information basis as well as planning strate¬gies to enable sustainable developments and to simplify planning processes in complex urban structures.

This research shall seize the described problem and aims to make a contribution to the requirements of monitoring fast developing mega cities. Against this background a methodology is developed to compensate the lack of socio-economic data and to deduce meaningful information on the living conditions of the inhabitants of mega cities. Neither social science methods alone nor the exclusive analysis of remote sensing data can solve the problem of the poor quality and outdated data base. Conventional social science methods cannot cope with the enormous developments and the tremendous growth as they are too labor-, as well as too time- and too cost-intensive. On the other hand, the physical discipline of remote sensing does not allow for direct conclusions on social parameters out of remote sensing images.

The prime objective of this research is therefore the development of an integrative approach − bridging remote sensing and social analysis – in order to derive useful information about the living conditions in this specific case of the mega city Delhi and its inhabitants. Hence, this work is established in the overlapping range of the research topics remote sensing, urban areas and social science.

Delhi, as India’s fast growing capital, meanwhile with almost 25 million residents the second largest city of the world, represents a prime example of a mega city. Since the second half of the 20th century, Delhi has been transformed from a modest town with mainly administrative and trade-related functions to a complex metropolis with a steep socio-economic gradient. The quality and amount of administrative and socio-economic data are poor and the knowledge about the circumstances of Delhi’s residents is correspo

Sponges are simple animals that mostly inhabit the marine ecosystem. The role of sponges in the marine ecosystem and the potential of their bioactive compounds for the pharmaceutical industry have already been reviewed. Because of the extensive investigations of sponges within those two disciplines, marine ecology and chemistry, sponges are among the best-studied Metazoa. Likewise, sponges have been selected as animal models for investigating the origin of the multicellularity because sponges have a simple body structure and physiology (e.g., lack of nervous and circulatory organs). Due to their diversity and abundance in the tropics, particularly in the Indo-Pacific, sponges have also attracted taxonomists, systematists and ecologists to assess their diverseness and their phylogenetic and phylogeographic relationships. Resolving those research questions is difficult, because sponges are categorised as comparatively character poor taxa. By using only conservative taxonomy or systematics, the sponge diversity might therefore be underestimated. Inevitably, sponge biologists have to employ molecular methods as additional tools.

In this research, molecular tools were used in order to analyse the taxonomy, phylogeny and phylogeographic relationships of selected sponge species. Xestospongia testudinaria & Neopetrosia exigua (Family Petrosiidae, Order Haplosclerida) were selected because of their conspicuousness in the Indo-Pacific coral reef ecosystems, whereby Xestospongia testudinaria is prominently known as the Indo-Pacific giant barrel sponge. Additionally, the order Haplosclerida has been described as an example of sponge order that has been examined systematically for a number of years and displays major discrepancy between morphology and molecular phylogenies. Molecular data suggests that the order needs revision at all taxonomic levels, which is the cause for further conflicts between taxonomists and systematists. In my research I focused mostly on sponge samples that originated from South East Asia or the Indo-Australian Archipelago (IAA). This region represents one of the best-explored marine regions in the Indo-Pacific. The aim of my research is to discover to what extent molecular tools are suitable to detect a phylogenetic signal, a phylogeographical break or a genotypic difference in the two selected sponge taxa.

Several markers from the mitochondrial (mtDNA), ribosomal (rRNA) and nuclear (nucDNA) have been utilised. The 3' partition of the cytochrome oxidase subunit 1 (I3-M11 of cox1) from the mtDNA could be used to detect a genetic structure in Xestospongia testudinaria in a geographical narrow scale study of < 200 km2 in Lembeh, North Sulawesi, Indonesia (Chapter 6) and throughout the Indo-Pacific despite limitations in the sample datasets (Chapter 2). In addition, the presence of a species complex in X. testudinaria was detected with the aid of phylogenetic reconstructions from a concatenation of mtDNA sequences (I3-M11 of cox1 and the Adenosine Triphosphate Synthase F0 subunit 6 / ATP6), and a nucDNA marker, the Adenosine Triphosphate Synthase β subunit intron (ATPS-β intron) (Chapter 6). At the same time, the presence of a species complex in X. testudinaria was recognised in a broader scale study of the Indo-Australian Archipleago (IAA) (Chapter 3). As a result, selected mtDNA and nucDNA markers in this thesis are useful for the investigation of the taxonomical status and phylogeographical relationships of X. testudinaria. A phylogeographical break in the IAA region due to the Pleistocene low sea level and Holocene recolonisation events (Chapter 3) could not be recovered among X. testudinaria in a phylogeographical analysis. Similarly, overlapping I3-M11 cox1 haplotypes between X. testudinaria, X. muta and X. bergquistia were recovered. This might be due to the presence of ancient polymorphisms on the barrel sponge mtDNA markers.

Molecular tools are also used to help identifying my second selected sponge s

Explosive volcanism is one of the most catastrophic material failure phenomena. During magma ascent, fragmentation produces particulate magma, which, if deposited above the glass transition of the interstitial melt, will sinter viscously. In-conduit tuffisites, conduit wall breccias and ash deposited from exceptionally hot pyroclastic flows are scenarios in which sintering by viscous flow is possible. Therefore, understanding the kinetics of sintering and the characteristic timescales over which magma densifies are critical to understanding the degassing timeframe in conduits and deposits. Viscous sintering is accompanied by a recovery of material strength towards that of a pore-free, dense magma. Understanding damage mechanisms and seismic behaviour prior to failure of sintered volcanic products are also crucial for the application of micromechanical models and material failure forecasting laws. Powdered standard glass and industrial glass beads have been used to explore sintering mechanisms at ambient pressure conditions and temporal evolution of connected and isolated pore-structure. I observe that sintering under low axial stress is essentially particle size, surface tension and melt viscosity controlled. I found that the timescales over which the bulk density approaches that of a pore-free melt at a given temperature is dependent on the particle-contact surface area, which can be estimated from the particle shape, the packing type and the initial total porosity. Granulometric constraint on the starting material indicates that the fraction of finer particles controls the rate of sintering as they cluster in pore spaces between larger particles and have a higher driving force for sintering due to their higher surface energy to volume ratio. Consequently, the resultant sample suite has a range of microstructures because the viscous sintering process promotes a fining of pores and a coarsening of particles. In a volcano, newly formed sintering material will then further contribute to magma-plugging of the conduit and its mechanical properties will affect magma rupture and its associated precursory signals. This consideration permitted me to explore the effect of sintering on the stress required for dynamic macroscopic failure of synthesised samples and assess the ability of precursory microseismic signals to be used as a failure forecast proxy at conditions relevant to shallow volcanic conduits. To this end, the samples were subjected to mechanical tests under a constant rate of deformation and at a temperature in the region of the material glass transition. A dual acoustic emission rig was employed to track the occurrence of brittle fracturing. The monitored acoustic dataset was then exploited to systematically assess the accuracy of the failure forecasting method as a function of heterogeneity (cast as porosity) since it acts as nucleating site for fracture propagation. The pore-emanating crack model describes well the peak stress at failure in the elastic regime for these materials. I show that the failure forecast method predicts failure within 0-15% error at porosities >0.2. However, when porosities are <0.2, the forecast error associated with predicting the failure time increases to >100%. I interpret these results as a function of the low efficiency with which strain energy can be released in the scenario where there are few or no heterogeneities from which cracks can propagate. These observations shed light on questions surrounding the variable efficacy of the failure forecast method applied to active volcanoes. In particular, they provide a systematic demonstration of the fact that a good understanding of material properties is required. Thus I wish to emphasise the need for a better coupling of empirical failure forecasting models with mechanical parameters, such as failure criteria for heterogeneous materials, and point to the implications of this for a broad range of material-based disciplines.

This dissertation explores the effects of pressure on the magnetic remanence of iron-nickel and iron-silicon alloys relevant to the solid inner cores of the terrestrial planets and Earth’s moon. The Earth’s inner core likely comprises mostly pure iron in a hexagonal close packed (hcp) structure. Experiments on pure iron powder and foil were carried out up to 21 GPa at room temperature. The most important conclusion from this work is that either hcp-iron is ferromagnetic or that a poorly understood, intermediate hcp phase of iron is ferromagnetic. It was also determined that the results must be corrected for magnetic shape anisotropy, which is related either to the original sample material (foil) or how the bulk sample volume changes shape due to increasing oblateness of the chamber during pressurization. Fe-Ni alloys in the face centered cubic (fcc) phase with compositions around Fe64Ni36, called Invar, exhibit near-null thermal expansion, making them useful for technological applications. Models explaining the Invar effect evoke magnetovolume effect that compensate for thermal expansion. Previous work suggested that the Curie temperature of Fe64Ni36 decreases 35 K per GPa, which predicts that around 5 GPa, Fe64Ni36 will turn paramagnetic. Our experiments on Fe64Ni36 found a marked decrease in magnetization between 5-7 GPa, consistent with former studies, but that it remains ferromagnetic until 16 GPa. The magnetic remanence of low Ni Invar alloys increases faster with pressure than for other body-centered-cubic compositions due to the higher magnetostriction of the low Ni Invar metals. Experimental results on body centered cubic (bcc) Fe-Ni alloys match well with those for pure iron-- again leading to the conclusion that either an intermediate hcp phase, or that the hcp phase itself, is ferromagnetic. The ubiquitous enhancement in magnetization under pressure, or during pressure release, of the Fe-Ni and Fe-Si alloys is associated with strain-induced martensitic effects. Finally, a defocused laser heating technique was developed to measure the Curie temperature in diamond or moissanite anvil cells. Preliminary results on titanomagnetite (Fe2.4Ti0.6O4) are broadly consistent with previous work.

Bereits zu Beginn des 20. Jahrhunderts entwickelte Alfred Wegener seine allgemein bekannte Rekonstruktion der Kontinente, indem er die Fragmente kontinentaler Kruste durch Schließung der großen Ozeane entlang ihrer heutigen Küstenlinien zusammenfügte, so dass alle Kontinente zu einer Landmasse vereint waren. Den resultierenden Superkontinent nannte er "Pangäa" (Wegener, 1920). In dieser Rekonstruktion liegen sich Nord- und Südamerika gegenüber und Nordwestafrika grenzt an die Südostküste Nordamerikas.

Lange Zeit nahm man an, dass die Paläogeographie dieses Superkontinents sich im Laufe seiner Existenz nicht bedeutend verändert hat, sondern dass die Kontinente sich im Jura im Wesentlichen aus der gleichen Konfiguration heraus voneinander gelöst haben, zu der sie sich ursprünglich im Paläozoikum zusammengefunden hatten. In der Tat gibt es vielfältige geologische, paläontologische und geophysikalische Hinweise dafür, dass Wegeners Pangäa-Konfiguration von der späten Trias bis in den frühen Jura Bestand hatte.

In den späten Fünfzigerjahren des vergangenen Jahrhunderts entwickelte sich mit der Paläomagnetik eine Methode, die es ermöglicht, die Bewegungen der Kontinente über das Alter des ältesten bekannten Ozeanbodens hinaus zu rekonstruieren. Aufgrund des Dipolcharakters des Erdmagnetfeldes gilt das jedoch nur für die Rekonstruktion von paläogeographischen Breitenlagen, die Lage bezüglich der Längengrade kann mit Hilfe des Erdmagnetfeldes nicht eindeutig bestimmt werden. Eine nicht unerhebliche Anzahl paläomagnetischer Studien hat gezeigt, dass Wegeners Pangäarekonstruktion, auch Pangäa A genannt, mit globalen paläomagnetischen Daten in prä-triassischer Zeit nicht kompatibel ist. Zwingt man die Nord- und Südkontinente Pangäas, Laurasia und Gondwana für diese Zeit in die Pangäa A Konfiguration, so ergibt die auf paläomagnetischen Daten basierende paläogeographische Rekonstruktion ein signifikantes Überlappen kontinentaler Krustenanteile (siehe z. B. Van der Voo (1993); Muttoni et al. (1996, 2003) und darin zitierte Werke). Ein solches Überlappen lässt sich jedoch mit grundlegenden geologischen Prinzipien nicht vereinen. Im Lauf der Jahrzehnte wurden vielfältige alternative prä-triassische paläogeographische Pangäarekonstruktionen erstellt, die im Einklang mit den paläomagnetischen Daten sind. Der Hauptunterschied im Vergleich dieser Rekonstruktionen zur klassischen Pangäa A Konfiguration liegt in der Lage der Südkontinente relativ zu den Nordkontinenten. Um den kontinentalen Überlapp zu vermeiden, werden die Südkontinente unter Beibehaltung ihrer Breitenlage um ca. 30 Längengrade relativ zu den Nordkontinenten weiter im Osten platziert, so dass Nordwestafrika gegenüber Europa zu liegen kommt (Pangäa B, Irving (1977)). Da - wie erwähnt - der Dipolcharakter des Erdmagnetfeldes keine Aussagen über die Position der Kontinente bezüglich der Längengrade zulässt, ist dies mit den paläomagnetischen Daten vereinbar. Die alternativen Konfigurationen müssen jedoch alle vor dem Auseinanderbrechen Pangäas im Jura wieder in die für diesen Zeitraum allgemein akzeptierte Wegener-Konfiguration zurückgeführt werden. Dies geschieht - wiederum im Einklang mit den paläomagnetischen Daten - unter Beibehaltung der Breitenlage der Kontinente entlang einer postulierten kontinentalen dextralen Scherzone. Der Versatz von 2000 bis 3000 km fand laut Muttoni et al. (2003) in einem Zeitraum von ca. 20 Ma im frühen Perm statt. Dadurch ergibt sich eine entsprechend hohe Versatzrate von 10 bis 15 cm/a.

Diese Arbeit befasst sich im Rahmen mehrerer paläomagnetischer Studien mit der Suche nach dieser großen Scherzone, deren Existenz seit Jahrzehnten umstritten ist. Der große Versatz wurde vermutlich von mehreren Störungssegmenten aufgenommen, die eine mehrere hundert Kilometer breite diffuse und segmentierte Scherzone bildeten. Paläogeographische Rekonstruktionen legen nahe, dass die Scherzone unter Anderem den Bereich des heutigen Mittelmeerraumes umfasst hat