Fakultät für Geowissenschaften - Digitale Hochschulschriften der LMU

Volcanic glass is often considered an ideal recording material for paleointensities. Experiments to determine the ancient field intensity are time consuming and mostly have low success rates. Studies have shown that the usage of glassy samples can increase success rates very much as the remanence carriers are in or close to the single domain range. Further, effects like magnetic anisotropy and cooling rate correction can be corrected for. The aim of this thesis is to clarify whether an ideal behavior can be expected when working on volcanic glass. Studies were done on samples of different compositions (phonolite, pantellerite and rhyolite) and varying degrees of devitrification/hydration. Rock magnetic measurements were done to determine the remanence carriers of remelted glass samples of phonolitic composition. Single domain (SD) titanomagnetites were identied to carry the stable remanence and in the course of paleointensity experiments the validity of a cooling rate correction method that makes use of the natural cooling rate of the samples as determined

from relaxation geospeedometry was shown. After correction the samples reproduce the intensity of the previously applied field. For the unhydrated samples from Montana

Blanca, Tenerife (phonolitic composition, 2 ka old) and from Mayor Island, New Zealand (pantelleritic composition, 8 ka old) remanence carriers in or close to the SD range were found and high quality well defined paleointensities were obtained. Success rates of the paleointensity experiments were 70%. The results compare very well with other paleointensities from close-by studies at the respective times. These data support the ideal

recording behavior of volcanic glass. Yet, rock magnetic and paleointensity experiments on devitrified and hydrated samples give contrary results: It was found that hydration and devitrification result in a loss of magnetic stability and remanence carriers, an increase in grain size of magnetic particles and a decrease of the "apparent" paleointensity. A possible explanation for these obsevations is a partial or full overprint of the original thermoremanent magnetization by a chemical remanence. It is therefore obvious that suchlike altered glasses are far from being ideal recorders. Great care has thus to be taken when sampling volcanic glass. If pristine glass is sampled, an ideal behavior during paleointensity experiments is probable and - as the here presented data suggest - a good estimate of the ancient field intensity is likely to be gained. If, however, the glass is unknowingly altered

the determined paleointensities are prone to underestimate the true field value.

Satellitengestützte geodätische Messmethoden, insbesondere GPS (Global Positioning System), sind von zunehmender Bedeutung in den Geowissenschaften und erlauben neue Einblicke in verschiedenste geophysikalische Prozesse. Zeitreihen hochpräziser Positionsmessungen von Punkten auf der Erdoberfläche ermöglichen unter anderem die Bestimmung von Relativgeschwindigkeiten tektonischer Einheiten, die Messung von Verformungsraten der Kruste an aktiven Störungen und Vulkanen und erlauben es Rückschlüsse auf die rheologischen Parameter der Lithosphäre und der Asthenosphäre zu ziehen. Mit zunehmender Länge und Genauigkeit der Zeitreihen ist es möglich, auch zeitabhängige dynamische tektonische Prozesse in GPS Zeitreihen zu identifizieren.

Die Schwierigkeiten in der Interpretation der Messungen bestehen unter anderem darin, von Punktmessungen auf kontinuierliche Deformationsmuster zu schließen, zeitlich korreliertes Rauschen zu quantifizieren, um realistische Fehlergrenzen anzugeben, und schließlich zeitabhängige tektonische Signale von zeitabhängigem Rauschen zu trennen. In dieser Arbeit werden Lösungsansätze zu diesen Punkten erarbeitet. Zunächst wird ein Algorithmus entwickelt, durch den aus einem diskreten Geschwindigkeitsfeld, ohne Vorgabe weiterer Randbedingungen (Geometrie der Störungen etc.), der kontinuierliche zweidimensionale Tensor der Verformungsraten abgeleitet werden kann. Aus der Tensoranalysis erhält man Informationen zur maximalen Scher- und Rotationsverformungsrate, sowie zur Dilatationsrate. Die Anwendung dieses Algorithmus auf verschiedene Datensätze in Südkalifornien und Island zeigt, dass hiermit sowohl aktive Störungen identifiziert, als auch Informationen uber Bruchflächen von Erdbeben aus ko- bzw. postseismischen GPS Messungen abgeleitet werden können. Außerdem wurden zeitabhängige Signale in den GPS Geschwindigkeitsfeldern ersichtlich.

Im zweiten Teil dieser Arbeit wird ein weiterer Algorithmus eingeführt, der unter Berücksichtigung der Effekte zeitabhängigen Rauschens die Berechnung der Varianz innerhalb von GPS Geschwindigkeitsfeldern ermöglicht. Somit wird außerdem der Notwendigkeit Rechnung getragen, realistische Fehlergrenzen als Grundlage zur Konfidenzabschätzung von Modellen zu definieren. Dieser Algorithmus basiert auf der Allan Varianz, die bei der Messung der Stabilität von Oszillatoren Verwendung findet und ausschließlich im Zeitbereich berechnet wird. Er wird ausführlich mit verschiedenen synthetischen Zeitreihen und Fehlermodellen getestet und auf einen südafrikanischen Datensatz angewandt. Der Vergleich mit Methoden, die auf einer Spektralanalyse oder einem Maximum Likelihood Estimator beruhen zeigt, dass der relativ schnelle Algorithmus stabile und verlässliche Angaben liefert.

Zuletzt wird der entwickelte Algorithmus erweitert, um die Kovarianz der Geschwindigkeit zu erhalten. Die Anwendung auf verschiedene Datensätze an konvergenten Plattengrenzen, wo regelmäßig Kriechereignisse in Form von Slow Slip Events auftreten, zeigt für einige Stationen stark richtungsabhängige und räumlich korrelierte Geschwindigkeitsfehler. Des Weiteren konnte eine Zeitkorrelation beobachtet werden, die auf einen tektonischen Ursprung der Ereignisse hinweist. Die korrigierten Zeitreihen, von denen die modellierten Ereignisse subtrahiert wurden, haben dagegen richtungsunabhängig eine Zeitkorrelation, die etwa dem 1/f Rauschen entspricht, und weisen keine räumlich korrelierten stark exzentrischen Fehlerellipsen auf. Die Analyse ermöglicht somit eine qualitative Bewertung der Modelle zeitabhängiger Signale in GPS Zeitreihen.

Soil moisture is one of the key variables controlling the water and energy exchanges between

Earth’s surface and the atmosphere. Therefore, remote sensing based soil moisture

information has potential applications in many disciplines. Besides numerical weather

forecasting and climate research these include agriculture and hydrologic applications like

flood and drought forecasting.

The first satellite specifically designed to deliver operational soil moisture products, SMOS

(Soil Moisture and Ocean Salinity), was launched 2009 by the European Space Agency

(ESA). SMOS is a passive microwave radiometer working in the L-band of the microwave

domain, corresponding to a frequency of roughly 1.4 GHz and relies on a new concept. The

microwave radiation emitted by the Earth’s surface is measured as brightness temperatures in

several look angles. A radiative transfer model is used in an inversion algorithm to retrieve

soil moisture and vegetation optical depth, a measure for the vegetation attenuation of the

soil’s microwave emission.

For the application of passive microwave remote sensing products a proper validation and

uncertainty assessment is essential. As these sensors have typical spatial resolutions in the

order of 40 – 50 km, a validation that relies solely on ground measurements is costly and

labour intensive. Here, environmental modelling can make a valuable contribution.

Therefore the present thesis concentrates on the question which contribution coupled land

surface and radiative transfer models can make to the validation and analysis of passive

microwave remote sensing products. The objective is to study whether it is possible to explain

known problems in the SMOS soil moisture products and to identify potential approaches to

improve the data quality.

The land surface model PROMET (PRocesses Of Mass and Energy Transfer) and the

radiative transfer model L-MEB (L-band microwave emission of the Biosphere) are coupled

to simulate land surface states, e.g. temperatures and soil moisture, and the resulting

microwave emission. L-MEB is also used in the SMOS soil moisture processor to retrieve soil

moisture and vegetation optical depth simultaneously from the measured microwave

emission. The study area of this work is the Upper Danube Catchment, located mostly in

Southern Germany.

Since model validation is essential if model data are to be used as reference, both models are

validated on different spatial scales with measurements. The uncertainties of the models are

quantified. The root mean squared error between modelled and measured soil moisture at

several measuring stations on the point scale is 0.065 m3/m3. On the SMOS scale it is 0.039

m3/m3. The correlation coefficient on the point scale is 0.84.

As it is essential for the soil moisture retrieval from passive microwave data that the radiative

transfer modelling works under local conditions, the coupled models are used to assess the

radiative transfer modelling with L-MEB on the local and SMOS scales in the Upper Danube

Catchment. In doing so, the emission characteristics of rape are described for the first time

and the soil moisture retrieval abilities of L-MEB are assessed with a newly developed LMEB

parameterization. The results show that the radiative transfer modelling works well

under most conditions in the study area. The root mean squared error between modelled and

airborne measured brightness temperatures on the SMOS scale is less than 6 – 9 K for the

different look angles.

The coupled models are used to analyse SMOS brightness temperatures and vegetation optical

depth data in the Upper Danube Catchment in Southern Germany. Since the SMOS soil

moisture products are degraded in Southern Germany and in different other parts of the world

these analyses are used to narrow down possible reasons for this.

The thorough analysis of SMOS brightness temperatures for the year 2011 reveals that the

quality of the measurements is degraded like in the SMOS soil moisture product. T

The Earth's magnetic field underwent hundreds of reversals during its history.

But within a ~40 Myr span (84-125 Ma) during the Cretaceous no reversal happened. For comparison, the second longest chron length during the last 167 Ma is ~5 Myr. Thus, the ~40 Myr long chron is known as a superchron and is called Cretaceous Normal Superchron (CNS). Two other superchrons are now established: the Permian-Carboniferous Reversed Superchron and the Ordovician Reversed Superchron.

Why do these superchrons exist? Are they an extreme chron duration of the same statistical distribution?

Or, do superchrons reflect a distinct dynamo regime separate from an oft-reversing regime. Are the onset and end of superchrons triggered by changes in the physical conditions of outer core convection?

For example, instabilities within the convection in the outer core are suspected to trigger reversals. A `low energy' geodynamo during the superchron could stem from less turbulent convection. But also the concept of a `high energy' geodynamo during a superchron is conceivable: stronger convection would stabilize the field and increase the field intensity.

These different dynamo regimes could be be triggered by changing the temperature conditions at the core mantle boundary (CMB), for example with the eruption of deep mantle plumes or the descent of cold material such as subducted slabs.

Insights into past geodynamo regimes can be learned primarily from two paleomagnetic methods: paleosecular variation (variation in field directions) and paleointensity.

For the former, we collected 534 samples for a paleosecular variation study from a 1400 m-long, paleontologically well-described section in northern Peru. Thermal demagnetization isolates stable magnetization directions carried by greigite. Arguments are equivocal whether this remanence is syn-diagenetic, acquired during the Cretaceous normal superchron, or a secondary overprint, acquired during a chron of solely normal polarity in the upper Cenozoic, yet pre-Bruhnes (>800 kyr). We explore the ramifications on the S value, which quantifies paleosecular variation, that arises from directional analysis, sun compass correction, bedding correction, sampling frequency, outlying directions and different recording media. The sum of these affects can readily raise the S value by more than 20%. S values from northern Peru are indistinguishable from other S values for the Cretaceous normal superchron as well as those for the last 5 Ma. Summing over all the potential uncertainties, we come to the pessimistic conclusion that the S value is an unsuitable parameter to constrain geodynamo models. Alternatively, no statistical difference in paleosecular variation exists during much of the Cretaceous normal superchron and during the last 5 Ma.

Even though the S value might be unsuitable, we wanted to understand why the S value is latitude dependent. The origin of this latitude dependency is widely attributed to a combination of time-varying dipole and non-dipole components. The slope and magnitude of S are taken as a basis to understand the geomagnetic field and its evolution. Here we show that S stems from a mathematical aberration of the conversion from directions to poles, hence directional populations better quantify local estimates of paleosecular variation.

Of the various options, k is likely the best choice, and the uncertainty on k(N) was already worked out.

As we came to the pessimistic conclusion that the S value might not be the best parameter to quantify the `energy state' of the geodynamo during a superchron, we also carried out a paleointensity study on 128 samples from volcanic rocks in Northern Peru and Ecuador.

Oxidation of the remanence carriers was a problem. Only one site gave reliable results. Two methods of paleointensity determination were applied to these rocks.

The results of both methods agree quite well with each other and also with previous studies from other sites. Our results suggest that t

Essential information about the activity or even the mechanics of tectonic and erosional processes can be extracted from their surface expression. For this purpose, it is necessary to appropriately constrain the temporal as well as the spatial framework, in which to consider a specific process. While recently developed dating techniques, such as thermochronology or radiocarbon dating, allow to assess the age of landforms and therefore rates of tectonic and erosional processes, detailed spatial information is also required to assess these rates correctly. Due to a lack of appropriate topographic data in the past it was sometimes challenging to reliably approximate the spatial framework, because the size of a particular landform can often cover a wide range of spatial scales. Recently available, conventional topographic data, such as those of the Shuttle Radar Topography Mission, substantially improved the definition of an appropriate spatial framework due to their spatial coverage and resolution of down to less than 1 m. However, to constrain this framework at a detail beyond the resolution of several decimeter terrestrial laser scanning provides a highly efficient approach. This technique permits the rapid acquisition (within minutes) of tremendous amounts of topographic data with both, a high resolution of a few centimeters and a high accuracy of a few millimeters. High-resolution topographic maps of a certain area of the surface of the Earth are derived from individual laser-scanner measurements, that in turn allow to characterize the in-situ geomorphic setting at great detail. Moreover, repeated measurements of this area allow to quantify morphological changes thereby supporting the survey of surface processes on short-term scales ranging from days up to several years. The former approach is best suited for tectono- and the latter one for fluvial-geomorphic studies, and we present results from two case studies that are either based on single or repeated laser-scanner measurements. In the first case, we combined field mapping and high-resolution digital elevation model (DEM) analysis to evaluate the detailed meter- to hundred meter-scale structure and surface expression of one flank of the Rex Hills pressure ridge in the western United States. Based on terrestrial laser scanning (Riegl LMS-Z420i) we derived a DEM with cm-scale resolution and extracted high-resolution topographic cross-sections. This enabled us to identify fault scarps and determine their relative ages and geometry. In the second case, we carried out a detailed field mapping of erosion and sedimentation patterns in the Alp Valley, central Switzerland, to assess its Holocene evolution. Simultaneously, we conducted repeated high-resolution (less than 1 cm locally) laser-scanning surveys (Topcon TLS-1000) along two tributaries, the Erlenbach and Vogelbach, to determine channel-morphology changes and the nature of shortest-term sediment transport by comparing the individual DEMs derived from these measurements, as well as to evaluate the context to the longer-term evolution of the Alp Valley. Both case studies, however, highlight the potential of medium-range laser scanners with measurement distances of up to hundreds of meters. Such scanners are most appropriate to efficiently analyze closely-spaced fault scarps across a broad range of spatial scales, and to document complex morphologic changes in small mountainous torrents due to sediment transport. Moreover, terrestrial laser scanning is a key tool to monitor surface processes, but the insights gained from this method are generally evaluated best in the context of further data sets including geochronological, structural, subsurface, or climate data.

Surface processes, in particular erosion, sediment transport, and deposition in sedimentary basins are intermittent in space and time challenging both, the appropriate definition of a spatiotemporal framework addressed above and a comprehensive process understan

Sponges are abundant and species-rich in Antarctic waters, and play important roles in the benthic ecosystems of the continent. The taxonomy of Antarctic sponges is, to some extent, well established, yet the phylogenetic relationships of this fauna remain unknown. Here, the first contributions to the knowledge of the evolution of Antarctic sponges are presented. A molecular phylogeny for the common Antarctic shelf glass sponge genus Rossella is provided. Based on nuclear and mitochondrial markers, it is shown that many of the species described for the genus, which usually are morphologically poorly defined and difficult to differentiate, likely, represent a single species (Rossella racovitzae) or a species complex.

The deep Southern Ocean has yielded numerous, most likely new, species of the demosponge Familiy Cladorhizidae. Cladohizidae groups sponges largely known by their carnivorous habit, which is usually accompanied by the lack, or strong modification, of the sponge aquiferous system and by a distinct stipitate body shape. Cladorhizids are also important for the broader understanding of the phylogenetic relationships of the Order Poecilosclerida. In this study, the debated phylogenetic position of the genus Abyssocladia is clarified using recent collections of cladorhizid sponges and a (remarkable) new species of the genus Phelloderma (Phellodermidae) from the Southern Ocean, and partial sequences of the (nuclear) 28S rDNA and of the (mitochondrial) COI. The results show that Abyssocladia is a cladorhizid sponge and that Cladorhizidae is monophyletic, the consequences of these results for the prevalent interpretation of the evolution of poecilosclerid sponges are also discussed.

The diversity of Antarctic sponges occurring on the shelf has been compared to that of tropical and subtropical ecosystems. Less is known about the sponge communities inhabiting the deeper waters of the Southern Ocean. The lack of information on deep benthic habitats, mainly due to the fact that sampling remote ecosystem such as Antarctica or the deep sea is expensive and technically difficult, hampers the determination of the number of species that inhabit the vast area of the deep Southern Ocean. In this work, estimation methods are used to predict lower bounds for the number of deep sea sponge species occurring in the Weddell Sea, Western Antarctica, and to show that the deep sea can be as rich as the shelf and that the total number of sponge species in Antarctica could be more than previously considered.

Finally, a middle throughput DNA barcoding workflow for processing sponges was established and the performance of this analytical pipeline was analyzed based on a large collection (∼8300 specimens) of sponges from Australia avail- able for DNA barcoding. The barcoding workflow was also used to provide a comprehensive DNA-barcode database for the Ross Sea comprising ∼50 species of demosponges and covering ∼80% of the sponge species characteristic for this area. The generated barcode database was used to provide evidence for a long history of in situ evolution in Antarctic sponges, which is congruent with previous biogeographic hypotheses suggesting an ancient origin for Antarctic sponges.