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This PhD thesis has been carried out within an interdisciplinary cooperational project between the Deutsches Bergbau-Museum Bochum and the Goethe-Universität Frankfurt, which is dedicated to ancient Pb-Ag mining and metal production in the hinterland of the municipium Ulpiana in central Kosovo. Geochemical analysis (OM, XRD, EMP, MC-ICP-MS) of ores, metallurgical (by-) products and metal artefacts allowed to reconstruct the local chaîne opératoire and to decipher significant chronological differences between presumably Roman/late antique and medieval/early modern metallurgical processing. Pb isotope provenance studies documented the relevance of local metal production within the Roman Empire and confirmed the actual existence of a Metalla Dardanica district, which until now solely has been suspected on basis of epigraphy.
The predominant abundance of the by-products matte (Cu, Pb, Fe and Zn sulphides) and speiss (ferrous speiss: Fe-As compounds; base metal speiss: ~(Cu,Ni,Fe,Ag )x(Sb,Sn,As )y ) at smelting sites with a preliminary Roman/late antique dating points to treatment of complex polymetallic ore. Pb isotope analysis demonstrated that the mining district of Shashkoc-Janjevo (partially) supplied six of the ten investigated metallurgical sites. In this mineralisation, parageneses with elevated Cu, As and Sb abundances comprise significant proportions of particularly tennantite-tetrahedrite minerals, chalcopyrite, arsenopyrite and were generated during the early and main stages of ore formation. Later precipitated ore in contrast is marked by a significantly less versatile mineralogy and consists almost exclusively of galena, sphalerite and pyrite/marcasite. Besides increased Cu, As and Sb contents, ore from the main formation stage also exhibits generally higher Ag abundances, which are mainly hosted by fahlore and locally abundant secondary Cu sulphides (chalcocite, digenite and covellite) and oxidised phases (e.g. malachite, azurite). The higher precious metal grades of this ore type, whose geochemical signature (i.e. higher proportions of Cu, As and Sb) is mirrored by the abundance of the metallurgical by-products matte and speiss (almost exclusively found at potentially Roman/late antique smelting sites; see above), presumably were a pivotal factor leading to its preferential exploitation in earlier times. Matte and base metal-rich speiss contain notable amounts of Ag, which are mainly present in Cu-(Fe) sulphides and particularly antimonides ((Cu,Ni)2Sb, Ag3Sb), respectively. While the speiss compounds due to their close association with Pb bullion presumably were cupelled automatically, the metallurgical treatment of matte could not have been proven unambiguously, but overall certainly is highly likely.
The beneficiated ore (i.e. crushed and sorted, potentially also treated by more lavish techniques such as grinding, sieving or wet-mechanical methods) possibly was partially roasted and subsequently together with fluxes and charcoal submitted to the furnaces. The working temperatures approximately ranged between 1100 and 1400 °C. Slags from all presumably Roman/late antique dated and few of their potentially medieval/early modern analogues were produced from smelting of (partially roasted) ore with charcoal and added siliceous material, thus resulting in fayalite-dominant phase assemblages or rarely observed glassy parageneses. Even though several subtypes of fayalite slags have been established on basis of the abundance of Fe-rich oxide phases (i.e. spinel ss and wüstite), late clinopyroxene and the general solidification sequence of the slags, the process conditions (i.e. temperature, fO2, added fluxing agents) must have been widely similar; chemical variations could be explained by varying degrees of interaction of the slag melt with charcoal ash and furnace material. The other investigated metallurgical remains indicate employment of a calcareous flux, which led to formation of Ca-rich olivine-, olivine+clinopyroxene-, clinopyroxene- or melilite-type slags. These types as well as glassy slags were generated at more oxidising conditions outside the fayalite stability field (FMQ buffer equilibrium, cf. Lindsley, 1976) than their olivine-dominant analogues. Conclusions on the furnace construction could be drawn on basis of the typology of the slags, which mostly were tapped into a basin located outside the furnace, but partially (at two presumably medieval/early modern sites) also accumulated in a reservoir within the smelter.
Lead artefacts excavated in Ulpiana could be isotopically related to ores from mineralisations in its vicinity and demonstrate that the resources were at least utilised for local metal production. However, also ship wreck cargo from Israel - including several lead ingots with the inscription 'MET DARD' (Raban, 1999) - and late antique lead-glazed pottery from Serbia and Romania (Walton & Tite, 2010) could be related to a possible Kosovarian/Serbian provenance of the raw material and thus indicate flourishing trade of metal from the Metalla Dardanica district within the Roman Empire.
References:
Lindsley, D. H. (1976). Experimental studies of oxide minerals. In D. Rumble, III (Hrsg.), Oxide minerals (61-88). Reviews in Mineralogy, Volume 3. Washington, DC: Mineralogical Society of America.
Raban, A. (1999). The lead ingots from the wreck site (area K8). Journal of Roman Archaeology, Supplementary Series, 35, 179-188.
Walton, M. S., & Tite, M. S. (2010). Production technology of Roman lead-glazed pottery and its continuance into late antiquity. Archaeometry, 52(5), 733-759.
Geoelektrische Methoden sind weit verbreitet und werden häufig zur Erkundung des oberflächennahen Untergrundes eingesetzt. Angewendet werden standardmäßig meist nur linienhafte Anordnungen der Sender- und Empfängerelektroden, die nur wenige Zehner Meter lang sind. Hierdurch haben diese Methoden nur geringe Eindringtiefen. Um größere Eindringtiefen und 3-dimensionale Informationen über den Untergrund zu erhalten, sind in der vorgestellten Studie die Empfänger- und Senderdipole in mehr oder weniger regelmäßigen Abständen über das Untersuchungsgebiet verteilt worden. Mit jeder Empfängerstation sind kontinuierlich die elektrischen Spannungen in bis zu drei Richtungen aufgezeichnet worden. Für die Einspeisungen wurde ein Rechtecksignal verwendet, das sich gut von den Störfrequenzen und den natürlichen Spannungen abhebt. Die Richtungen der Einspeisedipole sind entsprechend den örtlichen Gegebenheiten, jedoch möglichst parallel zu den Messrichtungen, gewählt worden. Zur Auswertung der erhobenen Messdaten wurde ein Programmpaket entwickelt, das eine weitestgehend automatisierte Auswertung der Daten erlaubt. Die Bestimmung der scheinbaren spezifischen Widerstände und ihrer Messfehler wurde an den fouriertransformierten Datenzeitreihen durchgeführt. Hierdurch konnten Störeinflüsse minimiert werden und es wurde möglich selbst stark verrauschte Datensätze auszuwerten. Um die erhobenen Daten interpretieren zu können sind die berechneten scheinbaren spezifischen Widerstände als Grundlage für Inversionen und Modellstudien verwendet worden. Die oben beschriebene Methode wurde im Rahmen der vorliegenden Arbeit in zwei unterschiedlichen Messgebieten angewandt.
Messgebiet im Hohen Vogelsberg
Im Juli 2007 wurde damit begonnen, die Forschungsbohrung Sichenhausen-Eschwald im Hohen Vogelsberg abzuteufen. Ziel war es, Informationen über den strukturellen Aufbau des größten geschlossenen Vulkankomplexes Mitteleuropas zu gewinnen. Die Gesteinsansprache der Tiefbohrung lieferte bereits relativ früh Hinweise darauf, dass ein großer magmatischer Körper aufgeschlossen wurde.Aufgrund der begrenzten räumlichen Aussagekraft der Bohrung und fehlender Geländebefunde war es nicht möglich, den Mechanismus der Platznahme und die Größe des Körpers näher zu beschreiben. Die Kampagne hatte das Ziel diese Lücke zu schließen und ein 3-dimensionales Modell des Untergrundes zu erstellen.In dem annähernd quadratischen Untersuchungsgebiet, das eine Fläche von ca. 25 $km²$ aufweist, wurden 20 Datenlogger zur Aufzeichnung der elektrischen Spannungen aufgebaut. Die Empfängerdipole waren zwischen 20 m und 30 m lang. Insgesamt wurden 36 Stromeinspeisungen mit Stromstärken zwischen 28 A und 40 A an 16 unterschiedlichen Positionen für jeweils 2 bis 3 verschiedene Dipolrichtungen vorgenommen. Die Einspeisedipole waren zwischen 100 m und 300 m lang. Insgesamt konnten 1.439 scheinbare spezifische Widerstände berechnet werden.Die Ergebnisse der Modellierungen und der Inversion der Daten zeigen, dass mit der Forschungsbohrung ein domartiger Körper angebohrt wurde. Anhand der Ergebnisse kann die räumliche Ausdehnung des Körpers eingegrenzt und ein vorher noch nicht kartierter Gang nachgewiesen werden.
Messgebiet im Bereich der Kinzigtalsperre
Das etwa Ost-West verlaufende Kinzigtal bildet die naturräumliche und geologische Grenze zwischen dem vulkanischen Vogelsberg im Norden und dem, in diesem Bereich aus Sedimentgesteinen aufgebauten, Spessart im Süden.Die zwischen Steinau a. d. Str. und Bad Soden-Salmünster befindliche Kinzigtalsperre dient dem Hochwasserschutz und der Regulierung des Pegels der Kinzig bei Dürreperioden. Der aufgestaute See ist relativ flach und weist im Normalstau maximale Tiefen von ca. 6~m auf. Der Stausee ist jedoch über weite Teile etwa 4~m tief. In dieser Kampagne betrug der Abstand zwischen den einzelnen Empfängerstationen etwa 100 m bis 300 m. Es wurde aufgrund der beengten Platzverhältnisse eine Dipollänge von ca. 48 m für die Einspeise- und die Empfängerdipole im Messgebiet gewählt. Insgesamt wurden 14 Empfängerstationen im Messgebiet aufgebaut, von denen sich Neun auf dem Seegrund befanden. Das Messraster orientierte sich am vermuteten Verlauf der Kinzigtalstörung. An 8 Positionen sind in 21 Richtungen elektrische Ströme mit Stärken zwischen 2,2 A und 40 A in den Untergrund eingespeist worden. Es konnten 536 scheinbare spezifische Widerstände berechnet werden. Ziel war es, den Verlauf der Störung näher zu bestimmen und die Tiefe der im Untergrund vorhandenen salinären Grundwässer zu bestimmen. Die Bestimmung des Verlaufs der Kinzigtalstörung sowie die Tiefenbestimmung der salinären Grundwässer war mit den erhobenen Daten jedoch nicht möglich.
Ziel der Arbeit war es, die Flugzeitmassenspektrometrie als neue Analysemethode für die instrumentelle Analytik halogenierter Spurengase in der Luft zu etablieren. Die grundle-gende Motivation dafür ist, dass anthropogene Emissionen vieler Vertreter dieser Sub-stanzklasse einen negativen Einfluss auf die Umwelt zeigen: in der Atmosphäre agieren die Substanzen bzw. ihre Abbauprodukte als Katalysatoren für den stratosphärischen Ozonab-bau und verstärken den Strahlungsantrieb der Erde durch Absorption elektromagnetischer Strahlung im sogenannten atmosphärischen Fenster. Um diese Effekte und deren Auswir-kung quantifizieren zu können, ist es notwendig, Konzentrationen und Trends der Substan-zen in der Atmosphäre zu überwachen. Nur so können Gegenmaßnahmen wie Produktions-reglementierungen geplant und bewertet werden. In Kombination mit inverser Modellie-rung können zudem Rückschlüsse über tatsächlich emittierten Mengen gezogen werden. Dies stellt den Anspruch an die Analytik, sehr geringe Mengen dieser Gase sehr präzise quantifizieren zu können, um auch schwache Trends zu erkennen. Zudem muss die Analy-semethode die Möglichkeit zu bieten, mit der wachsenden Anzahl bekannter und zu über-wachender Substanzen Schritt zu halten. Besonders für letzteren Aspekt bietet die Flug-zeitmassenspektrometrie einen entscheidenden Vorteil gegenüber der „konventionellen“ Methode, der Quadrupolmassenspektrometrie: sie zeichnet das gesamten Massenspektrum auf ohne dadurch an Empfindlichkeit einzubüßen. Um das atmosphärische Mischungsver-hältnis von Substanzen im Bereich von pmol mol−1 bis fmol mol−1 bestimmen zu können, muss das Quadrupolmassenspektrometer im Single Ion Monitoring Modus betrieben wer-den – so wird zwar eine hohe Sensitivität erreicht, es wird aber auch nur die Intensität eines bestimmten Masse zu Ladungsverhältnisses (kurz: Masse) zu einem Zeitpunkt aufgezeich-net. Ein Flugzeitmassenspektrometer hingegen extrahiert Ionen mit einer Frequenz im Ki-loherzbereich und zeichnet für jede Extraktion das vollständige Flugzeitspektrum und da-mit Massenspektrum auf.
Aufgabe dieser Arbeit war es, ein Flugzeitmassenspektrometer mit vorgeschalteter Pro-benanreicherungseinheit sowie Gaschromatograph zur Trennung des Subtanzgemisches vor der Detektion aufzubauen und Werkzeuge zur Datenauswertung zu entwickeln. Um einen zukünftigen Feldeinsatz vorzubereiten, sollte der Aufbau möglichst kompakt, mobil und vollständig automatisiert sein. Anschließend sollte Empfindlichkeit, Präzision und dynami-scher Messbereich geprüft, optimiert und die Anwendbarkeit zur Analyse halogenierter Spurengase gezeigt werden. Die Ergebnisse aus der in der vorliegenden Arbeit präsentier-ten Geräteentwicklung finden sich in drei Publikationen wieder, welche in thematischer Reihenfolge die Probenanreicherung (Obersteiner et al., 2016b), den Vergleich von Quadrupol- und Flugzeitmassenspektrometrie (Hoker et al., 2015) sowie Eigenschaften und Anwendung des neuen Aufbaus (Obersteiner et al., 2016a) behandeln. Mit den genannten Aufsätzen ist die Arbeitsgruppe Engel weltweit die erste, welche hochpräzise Analytik ha-logenierter Spurengase routinemäßig mittels Flugzeitmassenspektrometrie durchführt. Der nächste Schritt ist der Übergang von der Laboranwendung zur Feldmessung, z.B. in Form von bodenbasierter in situ Analyse troposphärischer Luftmassen am Taunus Observatorium auf dem Kleinen Feldberg. Da es bisher keine Messstation für die hier beschriebene analy-tische Fragestellung in Deutschland gibt, könnte eine deutliche Verbesserung der Überwa-chung halogenierter Treibhausgase und ozonzerstörender Substanzen in Europa erzielt wer-den. Weiterhin wäre eine Flugzeugapplikation in Zukunft denkbar, welche neben der durch das Flugzeitmassenspektrometer abgedeckten Substanzbandbreite auch von dessen hoher möglicher Spektrenrate profitieren könnte. In Kombination mit Hochgeschwindigkeitsgas-chromatographie könnte eine bisher unerreichte Zeitauflösung der Beprobung der Atmo-sphäre mittels Gaschromatographie-Massenspektrometrie erzielt werden.
Clouds and precipitation are essential climate variables. Because of their high spatial and temporal variability, their observation and modeling is difficult. In this thesis multiple observational data sources, including satellite data and station data are globally analyzed to understand the distribution and variability of clouds and precipitation, while a special focus is on the diurnal cycle of both variables. Substantial diurnal cycles of clouds and precipitation are observed in the tropics, with different properties over land and ocean. But also in Europe cloud diurnal cycles are observed in the summer season. Overall the maximum cloud cover and also the maximum precipitation is observed in the afternoon over land, and in the morning over ocean. The analyzed climate model simulations and the model-based reanalysis fail to simulate the observed diurnal cycles. Owing to their limited resolution, models can not fully resolve the processes responsible for the existence of diurnal cycles of clouds and precipitation.
Many natural minerals exist in the form of a solid solution. The systematic changes in structural and physical properties of oxide solid solutions are of geological importance and allow for wide applications. In order to understand the composition-structureproperty relations, substitutional solid solutions of CuxZn2−xTiO4, ZnxMg1−xTi2O5 and CuxMg1−xTi2O5 have been synthesised by mechanochemical activation assisted solid state synthesis. Self-propagating high-temperature synthesis has been employed to achieve the interstitial solid solutions of Ti5Si3Zx (Z refers to the element boron or oxygen).
The changes in the crystal structure and physical properties due to the formation of solid solutions are investigated by employing X-ray diffraction, neutron diffraction, Raman spectroscopy, low-temperature heat capacity, thermal expansion, scanning electron microscopy, UV-vis spectroscopy, plane-wave ultrasound spectroscopy and density functional theory calculations.
This thesis addresses the reconstruction of the topographic evolution and the climate dynamics of the Early Cenozoic North American Cordillera through integrated geochronology, sedimentology, stable isotope, and clumped isotope thermometry studies. It encompasses the scientific disciplines of geochemistry, tectonics, and Earth surface processes.
In Belize, which is well known for the Belize Barrier Reef and its offshore atolls, coastal lagoons are frequent morphological features along the coast. They represent transitional environments between siliciclastic and carbonate settings. In order to shed light into the Holocene evolution of coastal lagoon environments, five localities along the central coast of Belize were selected as coring sites. These include four coastal lagoons and one marsh area, namely Mantatee Lagoon, Mullins River Beach, Colson Point Lagoon, Commerce Bight Lagoon and Sapodilla Lagoon. A total of 26 sediment cores with core lengths ranging from 109 cm to 500 cm, were drilled using a Lanesky-vibracorer. Overall, 73 m of Holocene sediments and Pleistocene soil were recovered. Together with 58 radiocarbon dates the sediments reveal details on the sediment architecture and depositional features of the localities.
Marine inundation of the mainland and coastal lagoon formation started around 6 kyrs cal BP.
As a response to sea-level rise during the Holocene transgression, facies retrograded towards the coast, as seen in marginal marine overlying brackish mollusk faunas. Evidence for late Holocene progradation of facies due to sea-level stagnation is largely lacking. The occurrence of landward thinning sand beds, hiatuses and marine fauna in lagoonal successions are indications of event (overwash) sedimentation. Sediments recovered are largely of Holocene age (<7980 cal BP), overlying Pleistocene sections. Analyses of sediment composition and texture, radiocarbon dating and mollusk shell identification were used to describe and correlate sedimentary facies.
XRD analyses have identified quartz as the dominant mineral, with the Maya Mountains as main source of coastal lagoon sediments. The most common sedimentary facies include peat and peaty sediment, mud, sand, and poorly sorted sediments. Pleistocene soil forms the basement of Holocene sediments. Holocene mud represents lagoon background permanent sedimentation.
Peats and peat-rich sequences were deposited in mangrove swamp environments, whereas sandy facies mainly occur in the shoreface, beach, barriers, bars, barrier spits and overwash deposits. Facies successions could be identified for each locality, but it has proven difficult to correlate the stratigraphic sequences, especially among localities. These differences among the five locations studied suggest that apart from regional influence such as sea-level rise, local environmental factors such as small-scale variation in geomorphology and resulting facies heterogeneity, connectivity of the lagoon with the sea, antecedent topography and river discharge, were responsible for coastal sedimentation and lagoon development in the Holocene of Belize.
Faunal composition and distribution patterns of mollusk assemblages from 20 shell concentrations in cores collected in coastal lagoons, a mangrove-fringed tidal inlet and the marginal marine area (shallow subtidal) show considerable variation due to environmental heterogeneity and the interplay of several environmental factors in the course of the mid-late Holocene (ca. 6000 cal BP to modern). The investigated fauna ≥2 mm comprises 2246 bivalve, gastropod and 11 scaphopod specimens. Fifty-three mollusk species, belonging to 42 families, were identified. The bivalve Anomalocardia cuneimeris and cerithid gastropods are the dominant species and account for 78% of the total fauna. Diversity indices are low in concentrations from lagoons and relatively high in the marginal marine and tidal inlet areas.
Based on cluster analysis and nonmetric multidimensional scaling (NMDS), seven lagoonal assemblages and three marginal marine/tidal inlet assemblages were defined. A separation between lagoonal and marginal marine/tidal inlet assemblages seen in ordination indicates a lagoon-onshore gradient. The statistical separation among lagoonal assemblages demonstrates environmental changes during the Holocene evolution of the coastal lagoons, which is probably related to the formation of barriers and spits. The controlling factors of species distribution patterns are difficult to figure out, probably due to the heterogeneity of the barrier-lagoon systems and the interaction of paleoecological and paleoenvironmental factors. In addition to the taxonomic analysis, a taphonomic analysis of 1827 valves of A. cuneimeris from coastal lagoons was carried out. There is no relationship between depth and age of shells and their taphonomic condition. Size-frequency distributions and right-left valve ratios of A. cuneimeris suggest that valves were not transported over long distances but were deposited parautochthonously in their original habitat. Shells from tidal inlet and marginal marine environments were also predominantly deposited in their original habitats.
Since the Belize coast was repeatedly affected by hurricanes and the paleohurricane record for this region is poor, the sediment cores have been examined in order to identify storm deposits.
The paleohurricane record presented in this study spans the past 8000 years and exhibits three periods with increased evidences of hurricane strikes occurring at 6000-4900 cal yr BP, 4200-3600 cal yr BP and 2200-1500 cal yr BP. Two earlier events around 7100 and 7900 cal yr BP and more recent events around 180 cal yr BP and during modern times have been detected. Sand layers, redeposited corals and lagoon shell concentrations have been used as proxies for storm deposition. Additionally, hiatuses and reversed ages may indicate storm influence. While sand layers and corals represent overwash deposits, the lagoon shell concentrations, which mainly comprise the bivalve Anomalocardia cuneimeris and cerithid gastropods, have been deposited due to changes in lagoon salinity during and after storm landfalls. Comparison with other studies reveals similarities with one record from Belize, but hardly any matches with other published records. The potential for paleotempestology reconstructions of the barrier-lagoon complexes along the central Belize coast differs depending on geomorphology, and deposition of washovers in the lagoon basins is limited, probably due to the interplay of biological, geological and geomorphological processes.
Despite mounting evidence of the anthropogenic influence on the Earth's climate, underlying mechanisms of climate change often remain elusive. The investigation of periods of rapid climate change from geological archives may provide crucial information about magnitude, duration, teleconnections of and regional responses to global and hemispheric scale climate perturbations. Thus, paleoclimate reconstructions may help in mitigating and adapting to the challenges of the coming decades. The '8.2 kyr B.P. climatic event' has previously been proposed as a possible analogue for the future climatic scenario of a reduced Atlantic Meridional Overturning Circulation (AMOC). The catastrophic drainage of the Laurentide meltwater lakes through the Hudson Bay and into the Labrador Sea, that occurred ca. 8.47 kyr B.P., caused the slowdown of the AMOC around 8.2 kyr B.P.. Subsequently, reduced heat transfer towards Europe triggered a substantial decline in (winter) temperature and pronounced changes in atmospheric circulation patterns in many regions of the northern hemisphere, especially the North Atlantic realm and Europe. Among the regions affected by the 8.2 kyr B.P. climatic event, the Eastern Mediterranean region is of particular interest for both past and future climate developments. Traditionally characterized as a region highly sensitive to variations in the climate systems of the high and low latitudes, abrupt climate changes have the potential to strongly alter atmospheric circulation patterns and thus precipitation distribution in the region that may have severe socioeconomical consequences. The analysis of stable hydrogen (δD) and oxygen isotopes (δ18O) in precipitation is an excellent tool to trace changes in atmospheric circulation. Here, we present a comparative study of δD and δ18O in precipitation from the Eastern Mediterranean region both in a present day scenario and during the 8.2 kyr B.P. climatic event. We analyze the influences of topography, air mass trajectory, climate and seasonality among others the stable isotopic compositions of meteoric waters from the Central Anatolian Plateau (CAP), Turkey, in order to create a first-order template which may serve as a reference against which paleoenvironmental proxy data may be more accurately interpreted and tested. Further, we employ a multiproxy approach on the early Holocene peat deposits of the classical site of Tenaghi Philippon (TP), NE Greece, to investigate paleoenvironmental responses to northern hemisphere cooling during the 8.2 kyr B.P. climatic event and aim to determine changes atmospheric circulation from δD of leaf wax n-alkanes (δDwax).
Based on δD and δ18O data from more than 480 surface water samples from the CAP, we characterize moisture sources affecting the net isotopic budget of precipitation, manifesting in a systematic north-south difference in near-sea level moisture compositions. Rainout, induced by the major orographic barriers of the plateau, the Pontic Mountains to the north and the Taurus Mountains to the south, strongly shape the modern patterns of δD and δ18O. Stable isotope data from the semi-arid plateau interior provide clear evidence for an evaporitic regime that drastically affects surface water compositions. Strong evaporative enrichment contrasts rainfall patterns along the plateau margins, in part obfuscating the effects of topography and air mass trajectory.
Consequently, in order to address possible influences of evaporation on δD and δ18O in paleoprecipitation from TP, we analyze n-alkane abundances and distributions along with stable carbon isotope compositions of total organic carbon (δ13CTOC) and palynological data to estimate surface moisture conditions during the early Holocene (ca. 8.7 - 7.5 kyr B.P.) and especially during the 8.2 kyr B.P. climatic event. A period of relatively dry surface conditions from ca. 8.7 to 8.2 kyr B.P., indicated by low values of the 'aquatic index' (Paq ) and by elevated Average Chain Length (ACL) values, in concert with elevated δ13CTOC values, precedes the 8.2 kyr B.P. climatic event. The event itself is characterized by slightly wetter, more humid conditions, as suggested by an increase in Paq values as well as reduced ACL and δ13CTOC values between ca. 8.2 and 7.9 kyr B.P.. In the upper section of the core, a distinct change in paleohydrology becomes. A steep increase in Paq and a decrease in ACL values as well as variations in δ13CTOC from 7.9 kyr B.P. onwards imply considerably elevated surface moisture levels, likely caused by the increased activity of the karstic system of the surrounding mountains. Collectively, the biomarker proxies presented here, reveal a concise picture of changing moisture conditions at TP that is consistent with palynological data and provide detailed paleoenvironmental information for the analysis of δDwax as a paleoprecipitation proxy. The long-term decline in δDwax values characterizes the lower section of the core until ca. 8.2 kyr B.P.. The 8.2 kyr B.P. climatic event itself is connected to two distinct positive hydrogen isotope excursions: a minor shift in δDwax around 8.2 kyr B.P. and a major shift in δDwax between ca. 8.1 and 8.0 kyr B.P.. The upper part of the section shows a progressive trend towards higher δDwax values. With no indication of increased evaporitic conditions at TP during the 8.2 kyr B.P. climatic event, as evident in biomarker proxies and pollen data, we link shifts in δDwax to changes in Mediterranean air mass trajectories supplying precipitation to northeastern Greece, with variations in the relative contributions of northerly derived, D-depleted moisture and southerly-derived, D-enriched moisture. Possible control mechanisms include changes in the influence of the Siberian High and differences in the influence of the African and Asian monsoon circulations on anticyclonic conditions in the Mediterranean region as well as regional inflow of moist air from the Aegean Sea.
Im Fokus der vorliegenden Arbeit standen die Landschaftsrekonstruktion und die Abschätzung der Mensch-Umwelt Wechselwirkungen im Umfeld der kupferzeitlichen (ca. 5. Jts. v. Chr.) Siedlung Magura Gorgana im heutigen Süd-Rumänien. Im Zuge der sedimentologischen Untersuchungen wurde deutlich, dass zur Zeit der kupferzeitlichen Besiedlung in der Donauaue ein Paläosee existierte, welcher sich nahezu über den gesamten Auenbereich im Untersuchungsgebiet erstreckte. Mit der Entdeckung des Paläosees ‚Lacul Gorgana‘ ergaben sich, durch die exzellenten Eigenschaften von Seesedimenten als Geoarchiv, neue Möglichkeiten zur Paläomilieurekonstruktion und zur Abschätzung von Mensch-Umwelt-Interaktionen. Bis etwa in das 8. Jt. v. Chr. war die Donau in diesem Gebiet durch ein fluviales System charakterisiert, welches vermutlich aus einer Vielzahl von Gerinnen bestand und einem ‚braided river‘ ähnelte. Während des 8. Jt. v. Chr. begann die Bildung des Paläosees ‚Lacul Gorgana‘. Die Gründe hierfür sind unbekannt, wenngleich ein Zusammenhang zum Anstieg des Schwarzmeerspiegels in diesem Zeitraum naheliegt. Spätestens ab dem 13. Jh. n. Chr. kommt es zur Aggradation- bzw. Verlandung des Paläosees ‚Lacul Gorgana‘. Infolge progradierender Zuflüsse wurde die einstige Seefläche in kleinere Seen fragmentiert. Dies dauerte bis zu den Trockenlegungsmaßnahmen in den 1960er Jahren an. Somit ist die Verlandung zum gegenwärtigen Zeitpunkt, zumindest theoretisch, noch nicht abgeschlossen. Die Ausprägung des rezenten Flussbettes der Donau begann spätestens mit der Verlandung des Paläosees, genaue chronologische Angaben sind jedoch anhand der aktuellen Datenlage nicht möglich. Auf der Grundlage geochemischer Untersuchungen geben die Sedimente des Paläosees ‚Lacul Gorgana‘ Hinweise auf alternierende Bedingungen bezüglich aerober und anaerober Akkumulationsmilieus. Dabei sind die aeroben Abschnitte durch einen höheren Anteil klastischen Materials, einem niedrigeren Anteil organischen Materials und allgemein helleren Sedimenten gegenüber den anaeroben, allgemein dunkleren Abschnitten gekennzeichnet. Die Gesamtheit der sedimentologischen Befunde, und der Vergleich mit Untersuchungen anderer Autoren in benachbarten Einzugsgebieten legen nahe, dass das alternierende Seemilieu in erster Linie durch Variationen der klimatischen Bedingungen im Einzugsgebiet der Donau verursacht wurde. Diese Variationen führten zur Veränderung der Stärke von Erosion und dem Charakter des erodierten Materials. Der hohe, zeitlich begrenzte Eintrag organisch gebundenen Phosphates in Bereichen der unteren Dunklen Lage, welcher weitestgehend zeitgleich zur neolithischen und kupferzeitlichen Besiedlung akkumuliert wurde und mit hoher Wahrscheinlichkeit zu einer Eutrophierung des ‚Lacul Gorganas‘ führte, lässt sich vermutlich durch die menschliche Besiedlung der Uferzone des Sees in diesem Zeitraum erklären. Im Verlauf der Untersuchungen im Einzugsgebiet erwies sich der ‚Regionalisierungsansatz‘ als effektives und unabdingbares Werkzeug bei der Differenzierung der Seegenese. Diese Methode dient der Relativierung bzw. Abschätzung der raumzeitlichen Heterogenität des Akkumulationsmilieus anhand des Vergleiches von Sedimentstratigraphien bzw. Sedimentbohrkernen von unterschiedlichen Standorten innerhalb des Paläosees. So konnten die alternierenden Milieubedingungen innerhalb der Seesedimente deutlich als allgemeine und nicht nur als lokale Eigenschaft einzelner Bereiche des Paläosees Lacul Gorgana identifiziert werden. Daneben zeigte die Regionalisierung, dass die aeroben Bereiche nicht nur durch einen erhöhten klastischen Eintrag gekennzeichnet sind, sondern dass dieser auch in Richtung des nördlichen Litorals zunimmt. Dies spricht für eine Herkunft des Materials aus dieser Richtung und erlaubt eine räumlich differenzierte Betrachtung der Seegenese. Darüber hinaus ermöglicht der ‚Regionalisierungsansatz‘, die räumliche Variabilität bestimmter Parameter, beispielsweise des TOC/TN Anstiegs in Richtung Litoral, zu relativieren. Diese Relativierung trägt zum besseren Verständnis spezifischer Prozessabläufe bei. Während der Untersuchung wurde ebenfalls deutlich, dass das Geoarchiv Seesediment eine Vielzahl verschiedenster Signale unterschiedlichster Genese aus dem Einzugsgebiet und dem Gewässermilieu selbst als Proxy-Information speichert. Die Überlagerung dieser Signale innerhalb der Sedimentstratigraphie erschwert mitunter die Identifikation einzelner Prozesse oder Prozesskaskaden. In diesem Zusammenhang erweist sich der ‚Regionalisierungsansatz‘ erneut als sinnvolles Hilfsmittel, da über diesen eine Signaldifferenzierung erfolgen kann, unter der Annahme, dass es eher unwahrscheinlich ist, dass alle Signale in allen Bereichen des Milieus in gleicher Intensität vorliegen. Gerade für die Untersuchung sowohl allochthoner als auch autochthoner Ereignissedimentation ist jedoch die Differenzierung zur ‚Hintergrundsedimentation‘ unabdingbar für ein umfassendes Prozessverständnis.
The Earth’s surface condition we find today is a result of long exposure to metabolism of life forms. Particularly, molecular oxygen in the atmosphere is a feature which developed over time. The first substantial and lasting rise of atmospheric oxygen level happened ≈ 2.5 Ga ago, but localities are reported where transiently elevated oxygen levels appeared before this time-point. To trace the timing and circumstances of the earliest availability of free oxygen in the atmosphere is important to understand the habitats of early microbial life forms on Earth.
This thesis focuses to obtain information of oxygen levels and the related atmospheric cycling of metals in sediments of the 3.5 to 3.2 Ga Barberton Greenstone Belt. First, as iron was a ubiquitous constituent of Archean seawater, I investigated its isotopic composition in minerals of chemical sediments. Hereby, I tried to resolve the changes within the water basin on small scale sedimentary sequence cycles. Second, I focused on the minor constituents of Archean seawater. The Re-Os geochronologic system and the abundance patterns of the platinum-group elements were chosen to integrate information of oxygen promoted weathering of a large source area. To integrate information of a large time interval, the isotopes of uranium were investigated over a large stratigraphic section.
The two key findings of this thesis are:
• Quantitative oxidation of ferrous iron in surface layers of Paleoarchean seawater occurred during the onset and termination of hydrothermal FeIIaq delivery into shallow waters.
• Paleoarchean sedimentary successions of the Barberton Greenstone Belt lack any evidence of transient basin-scale oxygenation.
The Manzimnyama Iron Formation (IF, Fig Tree Group, Barberton Greenstone Belt, South Africa) has been deciphered to exist of cyclic stacks of lithostratigraphic units with varying amounts of iron oxide and carbonate minerals. In-situ femtosecond-Laser-Ablation ICP-MS iron isotope measurements showed that the majority of siderite (γ56Fe ≈ −0.5 ‰) precipitated directly from seawater of γ56Fe ≈ 0 ‰. Ferric iron from the surface layers is preserved in ≤ 1μ m hematite and in magnetite that has been grown within the consolidated sediment. During FeIIaq events, fine-grained hematite (γ56Fe ≈ 2.2 ‰) and magnetite (γ56Fe 0.5 to 0.8 ‰) indicate oxygen levels in surface waters of lower than 0.0002 μM. Upon onset and termination of iron oxide abundance, magnetite with γ56Fe ≈ 0 ‰ indicates that low concentrations of FeIIaq in surface waters were oxidized quantitatively. These observations demonstrate the existence of iron oxidation in Paleoarchean surface waters independent of FeIIaq concentration. This is the first investigation of Paleoarchean IF showing that lithostratigraphic cyclicity can be traced in iron isotopic composition of oxide minerals.
ID-ICP-MS measurement of Re, Ir, Ru, Pt and Pd, trace element (SF-ICP-MS) and ID-MCICP- MS uranium isotope determination have been applied to carbonaceous shale of the Mapepe Fm. (Fig Tree Group) after inverse Aqua Regia leaching and bulk digestion. The sediments reveal a silicified fraction which exhibits a seawater REE signature and a mixture of detrital and meteoritic PGE. Neither enrichment of the redox-sensitive elements Re or Mo nor fractionated uranium isotopes have been found on a stratigraphic interval of several hundred meters. The non-silica fraction shows no depletion of Re which indicates that the detrital material had no contact to oxidizing fluids. ID-TIMS measurements of Re and Os after the CrO3-SO4 Carius Tube method of two sample intervals showed that the Re-Os isotopic systems of the non-silica fractions are identical to two komatiite occurrences. Weltevreden Fm. and Komati Fm. rocks were uplifted, eroded and transported to the deep part of the sedimentary basin without any change to the Re-Os system. Negative fractionated uranium isotopes (γ238U = −0.41 ± 0.01 ‰) associated with detrital Ba-Cr-U occurrences suggest the existence of distal redox-processes that involve uranium species. This study demonstrates that over the time of exposure and deposition of the Mapepe Fm. sedimentation, free oxygen was not available for weathering in the catchment area.
The East African Rift System (EARS) was initiated in the Eocene epoch between 50 and 21 Ma probably due to the influence of mantle plumes that caused volcanism, flood basalts and rifting extensions in Ethiopa and the Afar region. As a result of magmatic intrusions and adiabatic decompression melting within the lithosphere caused by the impact of the Kenya plume, there was a southward propagation of the EARS of about 30 – 15 Ma from Ethiopia to Kenya, which coincide with the occurrence of volcanism. The EARS developed towards the south along the margins of the Tanzania Craton between 15 and 8 Ma. Previous findings of low-velocity anomalies within the upper mantle and the mantle transition zone indicate an upwelling of hot mantle material in the vicinity of the Afar region and the East African Rift. This study includes the analysis of P- and S-receiver functions in order to determine further impacts on the lithosphere from below. The aim was to determine the topographic undulations of further boundary layers and to identify their variability owing to the rifting processes and the formation of the EARS. The study area included the Tanzania Craton and the surrounding rift branches of the East African Rift System.
The region of the Rwenzori Mountains can be analysed in detail because of the large dataset of the RiftLink project. The use of the P-receiver function technique and the H-K stacking method enabled to determine different vP /vS ratios depending on the tectonic setting in the Rwenzori region: Rift shoulders (vP /vS =1.74), Albert Rift segment (vP /vS =1.80), Edward Rift segment (vP /vS =1.87) and Rwenzori Mountains (vP /vS =1.86). To determine the topography of the Moho, it is necessary to take into account the thickness of the sedimentary layer, the surface topography, the azimuthal variations in crustal thickness and the impact of local anomalies. After correcting these effects on the Moho depths, significant variations in Moho topography could be determined. The Moho depths range from 29 to 39 km beneath the rift shoulders of the Albertine Rift. Within the rift valley, the crustal thickness varies between 25 – 31 km in the Edward Rift segment and 22 – 30 km in the Albert Rift segment. An averaged crustal thickness of about 26 km within the rift valley indicates the lack of the crustal root beneath the Rwenzoris. Similar variations in crustal thickness were determined by using an automatic procedure for analysing S-receiver functions that was developed in this study.
The S-receiver functions are created by applying a rotation criterion in order to rotate the Z, N and E components into the L, Q and T components. It is necessary to perform trial rotations using different incident and azimuth angles to determine the correct rotation angles. The latter are identified by the use of the rotation criterion, including the amplitude ratio of the converted Moho signal to the direct S/SKS-wave signal. The L component is rotated correctly in the direction of the incident shear wave in the case of the maximum amplitude ratio. After analysing the frequency content of the receiver functions in order to sort out harmonic and long-periodic traces, the individual Moho signals are checked for consistency in order to remove atypic signals. To increase the signal-to-noise ratios on the traces, the S-receiver functions are stacked. For this purpose, the signals of the direct shear waves must originate from similar epicenters. On the basis of similar ray paths, the receiver functions show comparable waveforms and converted signals. To perform the stacking procedure, it is necessary to merge the datasets of the adjacent stations in order to obtain a sufficient number of receiver functions. This analysis is based on the assumption that the incident seismic waves arriving at the adjacent stations penetrate to some extent the same underground structures in the case of similar wave propagation paths. This approach accounts for the fact that the converted signals do not result exclusively from the piercing points at the boundary layers. Further signals originate from the conversions at the boundary layer within the Fresnel Zone. The piercing points are derived from the significant signals in the receiver functions. Depending on the order of arrival of the converted phases on the traces, the signals are attributed to the theoretical discontinuities DIS1, DIS2, DIS3 and DIS4. However, partly due to the low signal-to-noise ratios on the traces, it is difficult to identify the real conversions on the traces and to ensure that the converted signals are attributed to the correct boundary layers. For this reason, it is necessary to check the consistency of the conversion depths among each other. In the case of inconsistent conversion depths, the corresponding signals are either adjusted to another seismic boundary layer or removed from the dataset. To verify the functionality of the automatic procedure and to determine the resolvability with respect to two boundary layers, several models are tested including horizontal and dipping discontinuities. To resolve distinct discontinuities, their depths must differ by at least 60 km, otherwise, due to similar depth ranges of the different boundary layers, the converted signals cannot be separated from each other. As a consequence, the converted signals that originate from different discontinuities are attributed to a single one. Further tests including break-off edges of seismic discontinuities are performed to check the attributions of the converted signals to the discontinuities. Owing to the varying number of boundary layers, the converted signals cannot be attributed to the discontinuities according to the order of their arrivals on the traces. It is necessary to correct their attributions to the seismic discontinuities in order to resolve the boundary layers.
The crust-mantle boundary and further discontinuities within the lithospheric mantle are investigated by applying this automatic procedure. Depending on the tectonic setting, the conversion depths of the Moho range from about 30 – 45 km beneath the western rift shoulder to 20 – 35 km within the rift valley up to 30 – 40 km beneath the eastern rift shoulder. The long wavelengths of the shear waves hamper the correct identification of the converted phases in the S-receiver functions. With respect to the relative differences in conversion depth, the topographic undulations of the crust-mantle boundary are consistent with the Moho depths derived from P-receiver functions. In contrast to the Rwenzori region, it is difficult to resolve completely the trend of the Moho in the remaining area of the East African Rift due to the small dataset provided by IRIS. The results exibit an increase in crustal thickness to up to 45 km in the region of the Cenozoic volcanics such as Virunga, Kivu, Rungwe and Kenya. The greatest Moho depths of more than 50 km are located near Mount Kilimanjaro. In addition to the Moho, the analysis of the S-receiver functions revealed two further boundary layers at depths of 60 – 140 km and 110 – 260 km, which are associated with a mid-lithospheric discontinuity and the lithosphere-asthenosphere boundary, respectively. The shallowest conversion depths of the LAB are focussed to small-scale regions within the rift branches, namely the northern Albertine Rift, the Chyulu Hills and the Mozambique Belt, which are located around the Tanzania Craton. The larger thickness of the lithosphere beneath the cratonic terrain indicates that the Tanzania Craton is not significantly eroded. However, there are indications that the lithosphere beneath the craton and the rift branches is penetrated by ascending asthenospheric melts to depths of up to 140 and 60 km, respectively. The top of the ascending melts is associated with the occurrence of the mid-lithospheric discontinuity. The shallowest conversion depths of this boundary layer (60 – 90 km) are related to the rifted areas of the EARS and the Cenozoic volcanic provinces, which are located along the Albertine Rift, the Kenya Rift and the Rukwa-Malawi rift zones. The deepest conversion depths of up to 140 km are related to the Rwenzori Belt, the Ugandan Basement Complex and the interior of the Tanzania Craton.
Over the last several decades, spinel-structured minerals with the chemical formula AB2O4 (where A and B stand for divalent and trivalent cations, respectively) have attracted more and more attention, particularly with regards to their breakdown at high pressures and temperatures and the nature of the so-called "post-spinel" phases. Spinel-structured phases with different endmember compositions, like magnetite (Fe3O4), hercynite (FeAl2O4) or spinel (MgAl2O4), are known to breakdown differently at high pressure-temperature conditions (e.g., Akaogi et al. 1999; Schollenbruch et al. 2010; Woodland et al. 2012). Such phases are of particular interest when they incorporate ferric (Fe3+) and ferrous (Fe2+) cations as this makes their stability sensitive to redox conditions. Since magnetite and magnesioferrite (MgFe3+ 2O4) have been found as inclusions in diamond (e.g., Stachel et al. 1998; Harte et al. 1999; Wirth et al. 2014; Palot et al. 2016; Jacob et al. 2016), understanding their phase relations is important for setting constraints on the conditions of their formation.
This study aimed to experimentally investigate the phase relations of Fe-Mg spinel-structured phases at conditions of the deep upper mantle and transition zone. Exploring the stability of new post-spinel phases and their characterization were also major goals of this study. Approaching a pyrolitic mantle composition by adding amounts of SiO2 in the system allowed constraints on the relevance of Fe-Mg post-spinel phases coexisting with mantle silicates to be made. ...
Eisnukleierende Partikel (INP) sind ein wichtiger Bestandteil des atmosphärischen Aerosols. Trotz ihrer geringen Konzentrationen in der Atmosphäre haben sie Einfluss auf die Bildung von Eiskristallen und auf den Niederschlag. Durch Änderungen in Anzahlkonzentration oder anderer Eigenschaften der INP können sich Wolkenparameter wie Lebensdauer und Tröpfchendichte ändern, was weiter eine Ursache für Änderungen im globalen Strahlungshaushalt sein kann.
Der Anteil zum globalen Strahlungshaushalt durch „Wolken-Anpassungen aufgrund von Aerosolen“, stellt weiterhin die größte Unsicherheit des Strahlungsantriebes dar. Aus diesem Grund sind Messungen und Studien über atmosphärische Aerosole und INP notwendig. Im Rahmen dieser Arbeit wurde der Eiskeimzähler FINCH („fast ice nucleus chamber“) grundlegend überholt und für Messungen von INP optimiert. FINCH ist ein in-situ Eiskeimzähler der durch Mischung unterschiedlicher Luftströme eine Übersättigung der Probeluft mit Wasserdampf erzeugt, um auf diese Weise die zu untersuchenden Aerosolpartikel zu Eiskristallen wachsen zu lassen. Am Ende einer Wachstumskammer werden die Partikel durch eine Optik, dem FINCH-OPS, anhand von Streueigenschaften klassifiziert und ausgewertet. Um FINCH im erwarteten Umfang benutzen zu können, wurden am F-OPS der Laser und die zur Detektion des Streulichts benutzen Photomultiplier ersetzt. Weiter wurde die Software zur Detektion der Partikel neu entwickelt. Durch diese Änderungen ist es möglich Partikelanzahl, Partikelgröße sowie eine Information über die Form der Partikel abzuleiten. Über einen weiteren Photomultiplier im F-OPS ist es zudem möglich eine Information über Fluoreszenz des Partikels zu gewinnen, um so auf einen biologischen Ursprung des Partikels zu schließen. Vorangegangene Probleme durch elektromagnetische Einstrahlung und dadurch entstandene Inkonsistenzen während Messungen konnten im Rahmen dieser Arbeit identifiziert und ausgeschlossen werden. Ebenfalls konnten die zur Flusskühlung benutzen Wärmetaucher als Ursache für Verunreinigungen und Kontamination ausgemacht werden. Auch dieser, für Messungen ungeeignete Zustand, wurde im Rahmen dieser Arbeit behoben.
Ausführliche Charakterisierungsmessungen konnte die Funktionsfähigkeit des F-OPS, als einzelnes Messgerät ohne FINCH-Kammer, belegen. Durch Messungen mit einer steuerbaren Lichtquelle in der Optik konnte zudem die elektrische Verarbeitung sowie die Zählqualität der Optik verifiziert werden. Weiter kann durch diese Experimente gezeigt werden, dass mit dem F-OPS größenaufgelöst gemessen werden kann.
Auch in den ersten Streulichtexperimenten mit Testaerosol kann die Funktionsfähigkeit der Optik gezeigt werden. Für Partikelgröße von Dp > 400 nm wird eine Zähleffizienz von 25% eines TSI 3025 CPCs erreicht. Die über den F-OPS abgeleitete Partikelgröße kann durch Messungen mit monodispersen Aerosolpartikeln und einer parallelen Messung mit einem TSI 3330 OPS parametrisiert werden. Weiter kann die Fluoreszenz von ausgewählten Referenzstoffen gezeigt werden.
Im Betrieb von F-OPS hinter der FINCH-Kammer, also FINCH als Komplettsystem, wurden weitere Charakterisierungsmessungen durchgeführt. Es wurde festgestellt, dass die Anzahlkonzentration der Partikel nach Schließen eines Ventils exponentiell abfällt. Die Partikel folgen demnach nicht nur einem laminaren Fluss durch die Kammer. 50% der Partikel haben nach ca. 13 s die Kammer verlassen. Auch wurde ermittelt, dass ca. 40% der Partikel in der Kammer verloren gehen.
Erste Aktivierungsexperimente zeigen, dass Eispartikel in der Kammer auf eine Größe von Dp > 6 µm anwachsen. Durch Nullfiltermessungen in Aktivierungsphasen, sowie Ändern des zur Aktivierung notwendigen feuchten Flusses, wird zudem gezeigt, dass die Aktivierung der INP durch Mischung erfolgt und außerdem keine Fremdpartikel aktiviert werden. Die neue Steuerung der Kammer lässt es zu Temperaturen in etwa einer Stunde gezielt anzusteuern. Es wird gezeigt, dass Schwankungen in der Sättigung hauptsächlich durch Temperaturphänomene beeinflusst werden.
Abschließend wurden beispielhaft Laborexperimente mit Snomax© durchgeführt, welche sehr gut mit Werten aus der Literatur verglichen werden konnten. Auch eine erste Außenluftmessung am Jungfraujoch (Schweiz) wird in dieser Arbeit präsentiert. Die gemessenen INP-Konzentrationen im gezeigten Zeitraum liegen zwischen 1,4 ± 4,1 L-1 und 53 ± 30 L-1 und entsprechen somit wiederum bekannten Literaturwerten.
The present PhD thesis comprises structural geology, petrographic and geochronological investiga-tions on crystalline rocks of the Uppermost Unit in the southern Aegean realm. Studies were carried out in three areas: (1) on the island of Anafi, (2) in the area west of Melambes in central Crete and (3) between the villages of Pefkos, Kalami and Sykologos in the municipality of Viannos in eastern Crete.
The Uppermost Unit forms together with the underlying, non-metamorphic Pindos Unit the upper nappe system of the Cretan nappe pile that, unlike the units of the lower nappe system, was not affected by Late Oligocene to Early Miocene subduction-related metamorphism. The upper nappe system must therefore have been at upper levels of the lithosphere in the Late Oligocene. This is of particular im-portance when reconstructing the tectonometamorphic evolution of the Uppermost Unit. The Upper-most Unit is very heterogeneous in composition and is subdivided into several subunits, which differ mainly in their lithological composition and the degree of metamorphic overprint. Usually, it is subdi-vided into several low-grade metamorphic subunits and one high-grade metamorphic subunit. Within the scope of this PhD thesis, three of these subunits were examined; (1) the anchimetamorphic Arvi Unit, (2) the newly described Greenschist Unit and (3) the Asterousia Crystalline Complex (ACC).
The analyses conducted during this PhD thesis include: (1) structural geology investigations in the field, (2) microstructural and petrographic analyses on thin sections, (3) radiometric dating of zircons using isotope dilution thermal ionisation mass spectrometry (ID-TIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), (4) electron microprobe (EMP) analysis, (5) quartz texture analysis using electron-backscattered diffraction (EBSD), (6) semiquantitative analysis of min-eral phases using X-ray powder diffraction (XRD), (7) analysis of the modal composition of intrusive rocks applying point counting on thin sections and (8) X-ray microtomography (micro-CT) on chias-tolite hornfels.
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The African continent is regularly portrayed as an indolent space with a well-known reputation as a chaotic continent. Viewed as lacking vision, means and capacities, Africa is perceived at best as a place that is marked by a permanent status quo, stagnation, or in worst case scenarios, as a declining continent. Various references to the continent are synonymous with famine, poverty, war, etc. Such portrayals are all the more intriguing given that the continent is known for its abundant natural resources, such as timber, oil, natural gas, minerals, etc., whose reserves are, moreover, not well known both by the African people and their leaders. As a result, there is still much progress to be made in tapping into the resources in order to improve the daily lives of African citizens.
In such a context dominated by infantile carelessness throughout the continent, the interventions of actors from outside the continent are the only hopes of bringing some vitality to this continent which is cloaked in "la grande nuit – the great darkness" (Mbembé 2013). Thus during the main sequences of recent history, representing different forms of Western penetration and activity on the African continent (slavery, imperialism, colonization), all the Western world’s contributions have obviously not sufficed to boost Africa and take it out of its never ending childhood. It has remained just as passive and apathetic today as it was yesterday.
The attraction of Asian actors to the continent is even more recent. And consistent with its abovementioned indolence, Africa is seen as an easy and defenceless prey for the Korean, Japanese, Indian, Malaysian, or Chinese conquerors. In the latter case, the insatiable appetite for natural resources whose reserves are being rapidly depleted is the cornerstone of their foreign aid policy. This led China to colonize the continent, showing a preference for Pariah Regimes which held no appeal for the West, by sending an army of workers to extract those resources (Lum et al. 2009), in defiance of all national and international regulations and based on completely opaque contracts.
Although the concept of African Agency was rapidly developed in several African countries, the aim of this study was more specific to Cameroon’s mining sector in which different entrepreneurs from abroad got involved over time. The thesis investigates whether indigenous citizens took part in any way in the development of mining projects in the country. Thus, the work assesses and analyses actions and reactions initiated and undertaken by local people in the context of China’s presence within Cameroon’s mining sector to promote and advance their interests over those of foreign investors. In addition, the author has no knowledge of any other study investigating African Agency in the mining sector as a whole in Cameroon.
In conducting this study, a multi-method research framework was developed including a series of methods used to collect data and analyse concepts of African Agency associated Political Ecology as they developed within Cameroon’s mining sector. Specifically, those methods comprised quantitative research when it came to collecting data using a positivist and empirical approach constructed by deducing evidence from statistical data collected by means of the 167 questionnaire surveys administered to local inhabitants and workers randomly selected on mining sites and in riparian communities. The questionnaires helped to capture Cameroonians' perceptions of the recent phenomenon of the gradual but significant influx of international actors and precisely Chinese players in the mining sector on the one hand, and on the other hand, observational data was collected across the GVC as developed in the Betare-Oya region. As a complement to the former technique, qualitative methods helped to study and deepen understanding of human behaviour and the social world in a holistic perspective through individual interviews, focus groups, and direct observations on the ground. In addition, the spatial analysis method based on the land use classification technique served to detect changes to land use/land cover that have been brought on by mechanised mining activities undertaken in this region. The sequencing of data collected and their processing from a ground theory perspective led to the formulation and specification of Cameroon’s Ecological Agency theory.
One of the earliest steps of this work consisted in a literature review and in placing the African Agency concept in a broader context. It then led to the state of the art, specifications about research content of the work and the main theories undergirding this thesis. Before examining developments that emerged during the last decade, a historical perspective was provided to the topic in order to show how African societies started mining operations and how they dealt with foreign partners interested in their mining resources. The aim was to show that while Western imperialism presented a challenge for the sector, it did not erase local participation, even despite the constraints associated with such involvement.
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Indian Ocean came into existence with the breakup of Gondwana in the Mesozoic era. The presence of complex aseismic ridges and plateaus in the Indian Ocean makes it the least-understood of all the oceans. Mascarene Plateau, apart from Central Indian Ridge (CIR) running north-south between 2◦N and 25◦S in the Indian Ocean, is one such complex feature in the Indian Ocean that consists of Seychelles microcontinent in the north and the volcanic islands of Mauritius, La Réunion and Rodrigues in the south.
Most of the previous seismological studies on the islands of Mauritius, Rodrigues and Seychelles are restricted as each of them has only one operational permanent station. In the current study, I present the results obtained from the investigations of the seismological data obtained from the deployment of temporary seismic network on Mauritius (November, 2012–August, 2014) and Seychelles (March, 2013–March, 2015) under Réunion Hotspot and Upper Mantle–Réunions Unterer Mantel (RHUM–RUM) project and later in Rodrigues (September, 2014–June, 2016) under a collaborative project between Goethe-Universität, Frankfurt, Germany and Mauritius Oceanography Institute (MOI), Mauritius. Additional data from the permanent stations were also used in this study. The investigations and results are presented under three themes, namely: (1) crustal structure beneath Mauritius, (2) upper mantle anisotropy below Mauritius, Rodrigues and Seychelles and (3) intraplate seismicity in the Rodrigues–CIR region.
Upper mantle anisotropy in south-west Indian Ocean region are very limited, especially from the islands of Mauritius and Rodrigues. With the new data from the seismic stations deployed in Mauritius and Seychelles, under RHUM–RUM, and permanent stations in Rodrigues, I constrain the upper mantle flow pattern beneath these islands. From the joint-splitting analysis, I obtain fast-polarisation direction (φ) dominant in N80◦E and delay time (δt) of ≈0.85 s for Mauritius and φ tending east–west in Rodrigues with δt of ≈1.1 s. Parabolic asthenospheric flow model explains the orientation of the fast-polarisation direction beneath Mauritius, whereas deep mantle circulation patterns best explain the horizontal alignment of the fast-polarisation direction in Rodrigues. From Seychelles data, the results show φ trending NE and δt ≈0.74 s, even for the island close to Amirante Ridge, suggesting an asthenospheric deformation induced by relative motion between the plate and the deep mantle flow.
It has recently been suggested that the volcanic island of Mauritius may be underlain by a remnant of continental origin termed “Mauritia.” To constrain the crustal thickness beneathMauritius, I analysed data from 11 land stations, 10 of which were deployed recently under the RHUM–RUM project. From the recordings, I obtained 382 P-receiver functions. On the obtained receiver functions, I applied the H–κ stacking technique and derived the crustal thickness of ≈10–15 km. I observe a considerable variation in the VP/VS ratio caused by a lack of clear multiples. Using forward modelling of receiver functions, I show that the lack of clear multiples can be explained by a transitional Moho, where the velocity increases gradually. The modelling further indicates that the thickness of this gradient zone is estimated to be ≈10 km. I argue that my findings suggest oceanic crust thickened by crustal underplating due to the mantle plume currently located beneath La Réunion.
Seismicity around Rodrigues Island is generally associated with events recorded by the global networks along the CIR. Using seismological array techniques on the data collected by the temporary deployment of seismic array on Rodrigues Island for a period of 22 months (September, 2014–June 2016), 62 new events were located, which were not reported by any global network. Determination of backazimuth and apparent velocity were performed by applying array methods in the time-domain instead of the more conventional frequency-domain analysis. Event distances were calculated using a 1-D velocity model and the measured travel-time differences between S- and P-wave arrivals. Local magnitudes of the events were obtained by removing the velocity response from the seismographs and then convolving with Wood–Anderson transfer function to obtain ground motion in nanometers. Most of the newly-detected events are located off the ridge axis and can be classified as intraplate events. Three different seismic clusters were observed around the island. Most of the events were localised in the north-east of Rodrigues at a distance of ≈138 km from the reference station. A distinguishable swarm of earthquakes was observed on the west of the spreading segment from March to April 2015. The local magnitudes (ML) of the events varied between 1.6 and 3.7.
Enhanced aridification of Central Asia driven by the combined effects of orogenic surface uplift, Paratethys retreat, changes in atmospheric moisture transport and global cooling is one of the most prominent Cenozoic climate change events of the Northern Hemisphere. Deciphering regional long-term patterns of Central Asian hydrology is, therefore, a key element in understanding the role of Northern Hemisphere mid-latitude drying in the global hydrological system. Pedogenic carbonates record information of the paleoecosystem, the paleogeography, hydrology, tectonic and climatic conditions as well as the sedimentary regime during the time in which they formed. The calcrete-bearing paleosols in continental sedimentary basins yield the possibility for understanding these processes, mechanisms and controlling factors. This study characterizes long-term paleoenvironmental conditions between the late Oligocene and early Miocene in SE Kazakhstan based on stable isotopes, elemental geochemistry and laser ablation U-Pb geochronology from alluvial, fluvial and pedogenic deposits. The main topics addressed in this thesis are paleosol and calcrete formation processes in the light of geochemistry, tectonic and climatic influences on both, as well as the paleoenvironmental and hydrological conditions which led to these processes.
The sedimentological succession of the 14 km-long Kendyrlisai Valley in the Ili Basin, SE Kazakhstan in Central Asia, yields exceptional well-developed paleosols which provide an insight into the relationship between tectonics and sedimentation as well as soil formation processes. The valley accommodates more than 600 m of siliciclastic sediments deposited in a fluvial to alluvial environment in the lower part which grade into lacustrine to fluvial deposition with minor gypsum accumulation in the upper part. The yet undated sediments of Kendyrlisai Valley are compared with a biostratigraphically dated and well described succession in an adjacent location. The correlation of the two successions revealed a proximal-distal relation with the Kendyrlisai Valley succession represents the basin margin position with coarse alluvial-fluvial sediments. The calcrete nodules in Kendyrlisai Valley paleosols give the opportunity of U-Pb dating with LA-ICP-MS which uses the variation in both U and Pb to directly date the calcite. The U-Pb dating revealed a late Oligocene-early Miocene age for the investigated section. The analysis of facies and geochemistry of the paleosol profiles in Kendyrlisai Valley gives insight into calcretization stages, pedogenic processes and landscape stability. Kendyrlisai Valley paleosols show a low to moderate weathering intensity with the highest weathering intensity between 0.5 and 0.8 m depth in the paleosol profile. The comparison between acid leachable and non-acid leachable fraction indicate an incorporation of Ca and Ba in incipient calcrete calcite, whereas clay minerals adsorb Mg and Sr. During the evolution from early to more mature calcrete stages, i.e. calcrete nodules, Ba is lost by dissolution and subsequently adsorbed on clay minerals. The nodules consist almost exclusively of pure calcium carbonate with rare substitution of Ca by Mg indicating a constant supply of Ca by weathering and solution during calcrete formation. The occurrence of Mg-bearing clay minerals indicates high evaporative conditions with alkaline waters (pH >9).
Sampled calcrete nodule cross sections reveal more than one weathering and calcrete formation phase with a higher supply of Ca, Mg and Fe during early phases. The organic and inorganic carbon isotope composition of the calcrete nodules reflects C3 metabolism under occasionally moisture stress, resulting in higher δ13C values and lower respiration rates. This study also presents calculated atmospheric pCO2 values from the calcrete nodules with the equation from Cerling et al. (1999). The average calculated CO2 concentration for Kendyrlisai Valley paleosols is 313 ± 110 ppmv. The comparison with data from other studies during the late Oligocene–early Miocene reveal lower values for Kendyrlisai Valley paleosols, which may stem from an underestimation of the plant-respired CO2.
The knowledge of the variability within the paleosols and calcrete nodules enables a reliable paleoclimatic interpretation for the Kendyrlisai Valley and beyond the Ili Basin. Sedimentary facies and geochemical weathering indices suggest an increased surface and groundwater discharge fed by orographically-enhanced precipitation in the Tien Shan hinterland. In contrast, pedogenic stable isotope data and elevated rates of Mg fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification. This study posits that pronounced surface uplift of the Tien Shan Mountains during the Oligocene–Miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems.
The comparison with other studies in adjacent basins creates a precipitation pattern for Central Asia during the late Oligocene to early Miocene. The westerlies supplied Central Asia with atmospheric moisture from the West, possibly from the Eastern Paratethys. The uplifting Tien Shan Mountain ranges captured this moisture on their luv-side, resulting in a pronounced orographic rainfall in the adjacent Ili and Issyk Kul Basins. The Tarim Basin and the Valley of Lakes experienced drier conditions due to the rain shadow effect on the lee-side of the Tien Shan and Altai Mountains. In course of this findings, the thesis highlights the crucial role the Tien Shan Mountains play and had been playing in former times as an orographic barrier for the distribution of atmospheric moisture across Central Asia.
Atmospheric nanoaerosols have extensive effects on the Earth’s climate and human health. This cumulative work focuses on the development and characterization of instrumentation for measuring various parameters of atmospheric nanoaerosols, and its use to understand new particle formation from organic precursors. The principal research question is, how the chemical composition of nanoaerosol particles can be measured and how atmospheric chemistry influences aerosol processes, especially new particle formation and growth. Therefore, nanoaerosols are investigated under various aspects. More specifically, an instrument is developed to analyze nanoparticles, and field as well as chamber studies are conducted.
The main project is the instrument development of the Thermal Desorption Differential Mobility Analyzer (TD-DMA, project 1, Wagner et al. (2018)). This instrument analyzes the chemical composition of small aerosol particles. By characterization and testing in chamber experiments, it is proven to be suitable for the analysis of freshly nucleated particles.
The second project (Wagner et al. (2017)) applies a broad spectrum of aerosol measurement instruments for the characterization of aerosol particles produced by a skyscraper blasting. A comprehensive picture of the particle population emitted by the demolition is obtained.
Project 3 (K¨urten et al. (2016)) is also an ambient aerosol measurement, focusing of new particle formation in a rural area in central Germany, and the ability of a negative nitrate CI-APi-TOF to detect various substances in atmosphere. Project 4 (Heinritzi et al. (2016)) is a characterization of the negative nitrate CI-APi-TOF used in projects 1, 3, 5, 6, 7 and 8. The following projects focus on understanding new particle formation from atmospherically abundant organic precursors. Key instruments comprise the negative nitrate CI-APiTOF for gas-phase measurements of the nucleating species, and various sizing and counting instruments for quantifying the particle formation and growth. Project 5 (Kirkby et al. (2016)) shows that biogenic organic compounds formed from alpha-pinene can nucleate on their own without the influence of e.g. sulfuric acid. Project 6 (Tr¨ostl et al. (2016)) describe the subsequent growth of these particles. Project 7 (Stolzenburg et al. (2018)) covers the temperature dependence of this growth and in project 8 (Heinritzi et al. (2018)), the suppressing influence of isoprene on the new particle formation is assessed.
Cenozoic lignite deposits are widespread across Europe, Asia, America, Australia, and Indonesia. These deposits were the subject of numerous studies on changes in regional/global paleoclimates, paleobotany, paleoenvironment, and basin evolutions, which led to the formation of these lignites. In some of these Cenozoic lignite deposit basins, a succession of pale and dark lignite layers has been described in the Miocene Lower Rhine Basin in Germany, the Oligo-Miocene Gippsland Basin in southeastern Australia, and several Mio-Pliocene basins in southwestern China. Furthermore, pale and dark lithotypes in lignite seams also have been found in some Pliocene lignite deposit basins from Slovenia, Serbia, and Poland. The widespread cyclic occurrence of pale and dark layers in lignite basins might represent alternating depositional conditions related to the changes in plant communities, the regional/global climate, the tectonic setting, the Asian monsoon, and orbital periodicity during peat formation. ...
Recently, carbonates have attracted a lot of attention, due to the recognition of their importance in the global carbon cycle. This was enabled by improvement of the experimental techniques that allow for investigating the stability, structure, and physical properties of materials and high-pressures and high-temperatures, that is, they allow for investigating minerals and geochemical processes at the conditions occurring deep inside Earth. Although a lot of research has been focused on carbonates, there are still some open questions regarding their structure and physical properties at such extreme conditions. The aim of this thesis is to establish a deeper understanding of the nature of the phase transitions in carbonates by studying how do the atoms building up the crystal structure vibrate, that is lattice dynamics. The methodology adapted in this study is a combination of experimental and computational methods which allows for a very thorough examination of the problem. The computational approach allows to determine parameters that are elusive or tedious to measure, and the experimental results provide a solid benchmark for the calculations. This tandem of methods has been widely used for investigating lattice dynamics of various materials. In this study it was used to elucidate the structure and properties of carbonates in the deep Earth conditions
The main objective of this PhD work is to assess the impact of fine-scale air-sea interaction on the performance of a regional climate prediction model in marginal sea regions. Focus is on the North and Baltic Seas, the largest marginal sea area in the mid-latitudes. Motivation for this work is to better understand the interaction between the different components of the climate system, namely atmosphere, ocean and sea-ice. In addition to that, the sea regions of interest, the North and Baltic Seas, are orographically complex and cannot be resolved by a global ocean model. The ice coverage on the Baltic Sea is underestimated in the stand-alone atmospheric model COSMO-CLM due to the low water freezing temperature value assumed, which is not applicable for such brackish water body. To fulfil the thesis goal, a new regional coupled atmosphere-ocean-ice system was developed for these two seas, named COSMO-CLM/NEMO. The two-way coupling system involves active feedback from both component models: the limited-area climate model COSMO-CLM and the regional ocean model NEMO-NORDIC.
The coupled system COSMO-CLM/NEMO for the North and Baltic Seas was used to study the impact of sea surface temperature and sea ice on the atmosphere on diffrent topics. The long term impact of the North and Baltic Seas was studied through 15- year long simulations driven by European Center for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis (ERA-Interim) data. Furthermore, to see whether the marginal sea modelling can advance the simulation of extreme climate events, the coupled model was used to reproduce six extreme snowband phenomena over the Baltic Sea in simulations driven by ERA-interim data. Last but not least, the role of the North and Baltic Sea model in improving long-term regional climate prediction was examined. Two sets of experiments with coupled and uncoupled models, each set has five independent decadal hindcasts forced by global climate model, were carried out.
All results were compared with observations and the stand-alone atmospheric model COSMO-CLM results. In all experiments, COSMO-CLM/NEMO showed good agreement with observations. Improvements compared with the uncoupled COSMO-CLM were also found. Coupling was found to affect the air temperature not only around the coupled sea region but also inland. The convective snowbands over the Baltic Sea were successfully reproduced by the coupled model. The high contrast of temperature in the air column, as well as considerably high amounts of surface heat fluxes exchanged between air and sea could not be simulated by COSMO-CLM without the help of reanalysis data. The coupled model also provided better forecasts in decadal scales compared with the uncoupled model and the global model. The added predictability came from the initialized regional seas and better simulated sea surface temperatures by the ocean model.
The impact of the North and Baltic Seas on the climate of the surrounding regions is in certain phases dominated by the North Atlantic Oscillation (NAO) activity. In this thesis, the relation between the NAO and the marginal sea influences was studied. It is confirmed by this study that, in strong phases, the NAO can overpower the impact of the local seas. During dominant phases of NAO, the European climate is mainly governed by large-scale circulation. On the other hand, the local seas play an important role in determining the European climate when NAO is in weak phases.
The added value of the coupled model raises promising perspectives for research in this field. It points to a potential benefit of using the coupled atmosphere-ocean-ice system for climate prediction in the region surrounding the North and Baltic Seas. Along with that, it is still a challenge to complete the model representation of the climate system by adding more climate components (such as a hydrological model). Further improvement of the coupled system can be achieved by coupling for a larger sea region, or by trying to reduce remaining low performance of the coupled model in some areas with a better configuration of the current system.
Groundwater is the largest source of accessible freshwater with its dynamics having significantly changed due to human withdrawals, and being projected to continue to as a result of climate change. The pumping of groundwater has led to lowered water tables, decreased base flow, and depletion.
Global hydrological models (GHMs) are used to simulate the global freshwater cycle, assessing impacts of changes in climate and human freshwater use. Currently, groundwater is commonly represented by a bucket-like linear storage component in these models. Bucket models, however, cannot provide information on the location of the groundwater table. Due to this limitation, they can only simulate groundwater discharge to surface water bodies but not recharge from surface water to groundwater and calculate no lateral and vertical groundwater flow whatsoever among grid cells. For instance this may lead to an underestimation of groundwater resources in semiarid areas, where groundwater is often replenished by surface water. In order to overcome these limitations it is necessary to replace the linear groundwater model in GHMs with a hydraulic head gradient-based groundwater flow model
This thesis presents the newly developed global groundwater model G3M and its coupling to the GHM WaterGAP spanning over 70,000 lines of newly developed code. Development and validation of the modeling software are discussed along with numerical challenges. Based on the newly developed software, a global natural equilibrium groundwater model is presented showing better agreements with observations than previous models. Groundwater discharge to rivers is found to be the most dominant flow component globally, compared to flows to other surface water bodies and lateral flows. Furthermore, first global maps of the distribution of gaining and losing surface water bodies are displayed.
For the purpose of determining the uncertainty in model outcomes a sensitivity study is conducted with an innovative approach through applying a global sensitivity analysis for a computationally complex model. First global maps of spatially distributed parameter sensitivities are presented. The results at hand indicate that globally simulated hydraulic heads are equally sensitive to hydraulic conductivity, groundwater recharge and surface water body elevation, even though parameter sensitivities do vary regionally.
A high resolution model of New Zealand is developed to further understand the involved uncertainties connected to the spatial resolution of the global model. This thesis finds that a new understanding is necessary how these models can be evaluated and that a simple increase in spatial resolution is not improving the model performance when compared to observations.
Alongside the assessment of the natural equilibrium, the concept of a fully coupled transient model as integrated storage component replacing the former model in the hydrological model WaterGAP is discussed. First results reveal that the model shows reasonable response to seasonal variability although it contains persistent head trends leading to global overestimates of water table depth due to an incomplete coupling. Nonetheless, WaterGAP-G3M is already able to show plausible long term storage trends for areas that are known to be affected by groundwater depletion. In comparison with two established regional models in the Central Valley the coupled model shows a highly promising simulation of storage declines.
Paläoklimarekonstruktionen, die es sich zum Ziel gesetzt haben, Klima-Mensch Interaktionen auf lange Zeitreihen betrachtet zu erforschen, nehmen begünstigt durch die aktuell intensiv geführte Klimadebatte, einen immer größer werdenden Stellenwert in der öffentlichen und wissenschaftlichen Wahrnehmung ein. Denn trotz aller wissenschaftlicher Fortschritte, die in den vergangenen Jahrzehnten im Bereich der modernen Klimaforschung gemacht wurden, bleibt die zuverlässige Vorhersage und Modellierung von zukünftigen Klimaveränderungen noch immer eine der größten Herausforderungen unser heutigen Zeit. Betrachtet man die Karibik exemplarisch in diesem Rahmen, dann prognostizieren viele Modellrechnungen, infolge steigender Ozeantemperaturen, ein deutlich häufigeres Auftreten von tropischen Stürmen und Hurrikanen sowie eine Verschiebung hin zu höheren Sturmstärken. Dieser Trend stellt für die Karibik und viele daran angrenzende Staaten eine der größten Gefahren des modernen Klimawandels dar, den es wissenschaftlich über einen langen Zeitrahmen zu erforschen gilt.
Klimaprognosen stützen sich meist vollständig auf hoch-aufgelöste instrumentelle Datensätze. Diese sind aber alle durch einen wesentlichen Aspekt limitiert. Aufgrund ihrer eingeschränkten Verfügbarkeit (~150 Jahre) fehlt ihnen die erforderliche Tiefe, um die auf langen Zeitskalen operierenden Prozesse der globalen Klimadynamik adäquat abbilden zu können. Betrachtet man das Holozän in seiner Gesamtheit, so wurde die globale Klimadynamik über die vergangenen ~11,700 Jahre von periodisch auftretenden Prozessen und Abläufen gesteuert. Diese wirken grundsätzlich über Zeiträume von mehreren Jahrzehnten, teilweise Jahrhunderten und in einigen Fällen sogar Jahrtausenden. Viele dieser natürlichen Prozesse, können in der kurzen Instrumentellen Ära nicht gänzlich identifiziert und angemessen in Klimamodellen berücksichtig werden. Die alleinige Berücksichtigung der Instrumentellen Ära bietet daher nur eine eingeschränkte Perspektive, um die Ursachen und Abläufe von vergangenen sowie mögliche Folgen von zukünftigen Klimaveränderungen zu verstehen. Um diese Einschränkung zu überwinden, ist es somit erforderlich, dass die geowissenschaftliche Forschung mit Proxymethoden ein zusammenfassendes und mechanistisches Verständnis über alle Holozänen Klimaveränderungen erlangt.
Wenn man sich diese Limitierung, die ansteigenden Ozeantemperaturen und das in der Karibik in den vergangen 20 Jahren vermehrte Auftreten von starken tropischen Zyklonen ins Gedächtnis ruft, ist es nachvollziehbar, dass im Rahmen dieser Doktorarbeit ein zwei Jahrtausende langer und jährlich aufgelöster Klimadatensatz erarbeitet werden soll, der spät Holozäne Variationen von Ozeanoberflächenwasser-temperaturen (SST) und daraus resultierende lang-zeitliche Veränderungen in der Häufigkeit tropischer Zyklone widerspiegelt. In Zentralamerika wird das Ende der Maya Hochkultur (900-1100 n.Chr.) mit drastischen Umweltveränderungen (z.B. Dürren) assoziiert, die während der Mittelalterlichen Warmzeit (MWP; 900-1400 n.Chr.) durch eine globale Klimaveränderung hervorgerufen wurde. Die aus einem „Blue Hole“ abgeleiteten Informationen über Klimavariationen der Vergangenheit können als Referenz für die gegenwärtige Klimakriese verwendet werden.
Als „Blue Hole“ wird eine Karsthöhle bezeichnet, die sich subaerisch während vergangener Meeresspiegeltiefstände im karbonatischen Gerüst eines Riffsystems gebildet hat und in Folge eines Meeresspiegelanstiegs vollständig überflutet wurde. In einigen wenigen marinen „Blue Holes“ treten anoxische Bodenwasserbedingungen auf. Die in diesen anoxischen Karsthöhlen abgelagerten Abfolgen mariner Sedimente können als einzigartiges Klimaarchiv verwendet werden, da sie aufgrund des Fehlens von Bioturbation eine jährliche Schichtung (Warvierung) aufweisen.
In dieser kumulativen Dissertation über das „Great Blue Hole“ werden die Ergebnisse eines 3-jährigen Forschungsprojekts vorgestellt, dass das Ziel verfolgte einen wissenschaftlich herausragenden spät Holozänen Klimadatensatz für die süd-westliche Karibik zu erzeugen. Beim „Great Blue Hole“ handelt es sich um ein weltweit einzigartiges marines Sedimentarchiv für diverse spät Holozäne Klima-veränderungen, das im Zuge dieser Dissertation sowohl nach paläoklimatischen als auch nach sedimentologischen Fragestellungen untersucht wurde. Die vorliegende Doktorarbeit befasst sich im Einzelnen mit (1) der Ausarbeitung eines jährlich aufgelösten Archives für tropische Zyklone, (2) der Entwicklung eines jährlich aufgelösten SST Datensatzes und (3) einer kompositionellen Quantifizierung der sedimentären Abfolgen sowie einer faziell-stratigraphischen Charakterisierung von Schönwetter-Sedimenten und Sturmlagen. Zu jedem dieser drei Aspekte, wurde jeweils ein Fachartikel bei einer anerkannten wissenschaftlichen Fachzeitschrift mit „peer-review“ Verfahren veröffentlicht.
Der insgesamt 8.55 m lange Sedimentbohrkern („BH6“), der für diese Dissertation untersucht wurde, stammt vom Boden des 125 m tiefen und 320 m breiten „Great Blue Holes“, das sich in der flachen östlichen Lagune des 80 km vor der Küste von Belize (Zentralamerika) gelegenen „Lighthouse Reef“ Atolls befindet. Durch seine besondere Geomorphologie wirkt das, innerhalb des atlantischen „Hurrikan Gürtels“ positionierte, „Great Blue Hole“ wie eine gigantische Sedimentfalle. Die unter Schönwetter-Bedingungen kontinuierlich abgelagerten Abfolgen feinkörniger karbonatischer Sedimente, werden von groben Sturmlagen unterbrochen, die auf „over-wash“ Prozesse von tropischen Zyklonen zurückzuführen sind.
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In this thesis the Quadrupole Electrical Resistivity Tomography (QERT) method is presented as a new measurement concept for profile-based geoelectric field measurements. The concept is based on a tensorial formulation of the apparent resistivity in order to make three-dimensional statements about the underground conductivity structure. For a simple application of the method a number of similarities to the classical dipole-dipole method were made, such as the presentation of the measurement data in a pseudo-section. The added value of the method compared to the classical profile-based methods is especially the differentiation of lateral structures. Anomalies, which are located laterally to the profile, can be detected with respect to their position (left-right) as well as their conductivity contrast. For the practical implementation of the concept a measuring device was developed and constructed, the CR Device. The device uses 64 channels for simultaneous signal recording of voltage and current time series with up to 1 kHz sampling rate. The current injection is freely programmable and allows any survey design. The measurement of the voltages is performed against a common reference (CR) electrode and thus allows the reconstruction of any dipole voltage by difference formation. A complementary, Matlab-based software package completes the measuring system. An evaluation module allows the raw data of the CR device to be read in, processed and displayed in a suitable form. An inversion module allows the inversion of measurement data into a three-dimensional subsurface model. With a modeling module, measurements over any subsurface situation can be simulated and subsequently analysed. A field measurement on a volcanic maar in the Eifel region, Germany, demonstrates the benefits of the method. A QERT profile was set-up tangentially to a conductive anomaly in the centre of the maar. The measurement data were successfully inverted into a geologically coherent 3D resistivity model.
This work describes the development and characterization of two instruments and their data evaluation, which contributes to a better understanding of new particle formation and growth, as well as their interactions with clouds. Both instruments were characterized at the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at the European Center for Nuclear Research (CERN).
Semi-arid African ecosystems influence trends and variability in global terrestrial carbon dynamics. However, there are uncertainties in potential effects of future climates for semi-arid ecosystems, especially for niche ecosystems. At the same time, African ecosystems provide the livelihoods and ecosystem services for around 1.4 billion people. Future population growth and associated changes in land use pose a challenge for the protection of African biodiversity. Therefore, this work focussed on future impacts of climate change on African ecosystems and carbon dynamics and also for African protected areas (PAs), where they may cooccur with other global change factors. Another focus was on uncertainties associated with future projections and with modelling the Nama Karoo, as an example of a semi-arid niche ecosystem. Dynamic vegetation models (DVMs) were the main research tool.
In Chapter 2, we analysed climate change impacts on African ecosystems and carbon pools until the end of the 21st century and associated uncertainties based on an ensemble of vegetation simulations with the DVM adaptive dynamic vegetation model (aDGVM). We investigated the impact of increased atmospheric CO2 concentrations and two climate change scenarios (medium (RCP4.5) and high emissions (RCP8.5); RCP - representative concentration pathway) on vegetation changes. Differences in the simulated vegetation were primarily driven by assumptions about the influence of CO2 on plants. Elevated CO2 concentrations led to increased total aboveground vegetation biomass and shrub encroachment into grasslands and savannas for both climate scenarios. In simulations without the direct influence of CO2 on plants, there was hardly any shrub encroachment and vegetation biomass decreased or varied between a slight decrease in some cases and a slight increase in others. Based on these results, biome changes due to climate change are likely in Africa in the future. Due to the large uncertainties in future projections, strategies to adapt to climate change must be flexible.
The simulated vegetation in Chapter 2 represented potential, natural vegetation and is particularly suitable to investigate PAs. However, PAs do not exist isolated from their environment and social developments. In Chapter 3, the vegetation projections with CO2 effect from Chapter 2 were combined with projections for population density and land use. Except for many PAs in North Africa, most PAs were adversely affected by at least one of the three drivers by the end of the 21st century in both investigated scenarios ("middle-of-the-road" and "fossil-fuelled development"). Cooccurrence of the drivers varied by region and scenario for PAs. Both scenarios implied increasing challenges for the conservation of African biodiversity in PAs. The impact of climate change on vegetation is likely to be exacerbated by socio-economic change for most African PAs. Strong mitigation of future climate change together with equitable societal development may facilitate successful ecosystem conservation.
The simulations in Chapters 2 and 3 showed large-scale patterns of vegetation change, but their low resolution makes them unsuitable for local analyses. In Chapter 4, the challenges of simulating smaller scale, semi-arid ecosystems and their carbon cycle were analysed for the Nama Karoo with the aDGVM2 and its shrub module. The aDGVM2 is based on the aDGVM, but represents plants more flexibly. In all tested aDGVM2 configurations, the carbon fluxes improved compared to initial simulations but still overestimated them. The measured morphology of the dwarf shrubs and soil water dynamics were not reproduced in aDGVM2. Semi-arid soil water dynamics and coping strategies of semi-arid dwarf shrubs under drought stress are not adequately implemented in the aDGVM2. Further field research on semi-arid water and carbon dynamics of vegetation is necessary to parameterise the aDGVM2 for dwarf shrubs. If these challenges are overcome, DVMs can be a powerful tool for much-needed research on the impacts of climate change on the Nama Karoo.
The analyses have shown that climate change under medium to high emission scenarios is likely to lead to large-scale changes in ecosystems and the carbon balance in Africa. Because lower emissions scenarios come with less uncertainty, climate change adaptation strategies likely need to be less complex or extensive if climate change is minimised. For African PAs, the challenges of climate change may be exacerbated by socio-economic factors to a regionally varying extent. This research suggests that successful ecosystem conservation depends on climate change mitigation measures and ensuring equitable, sustainable development. The shown uncertainties, e.g., in the implementation of the CO2 effect on plants or vegetation dynamics in more niche ecosystems, help to focus future research efforts and increase our understanding of the range of plausible futures we may need to adapt to.
Climatology of morphology and cloud-radiative properties of marine low-level mixed-phase clouds
(2023)
Marine stratocumuli cover about 40 - 60% of the ocean surface. They self-organize into different morphological regimes. The two organized cellular regimes are called open and closed mesoscale-cellular convective (MCC) clouds. In mid-to-high latitudes, open and closed cells are the two most frequent types of MCC clouds. In particular, many MCC clouds consist of a mixture of vapor, liquid droplets, and ice particles, referred to as mixed-phase clouds (MPCs). Even for the same cloud fraction, the albedo of open cells is, on average, lower than that of closed MCC clouds. Cloud phase and morphology individually influence the cloud radiative effect. Thus, this thesis investigates the relationships between the cloud phase, MCC organization, cell size, and differences regarding the cloud-radiative effect.
This thesis focuses on space-borne retrievals to achieve extensive temporal and spatial coverage. The liDAR-raDAR (DARDAR) version 2 product collocates two active and one passive satellite: CloudSat, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Moderate Resolution Imaging Spectroradiometer (MODIS). The cloud phase of DARDAR is vertically integrated to establish a single cloud phase at each data point. The MCC classification data set based on the liquid water path (LWP) of MODIS scenes is collocated with the DARDAR product to determine the MCC organization. Cell-size statistics of both MCC clouds are obtained using a marker-based image segmentation method on MODIS reflectance scenes. In addition, based on MODIS reflectance scenes, a convolutional neural network (CNN) is developed to classify open and closed MCC scenes to avoid missing mature MPCs with a low LWP.
The first part of this thesis explores the relationships between cloud phase, morphology, and cloud albedo in the Southern Ocean (SO). At a given cloud-top temperature (CTT), seasonal changes in the mixed-phase fraction, defined as the number of MPCs divided by the sum of MPC and supercooled liquid cloud (SLC) pixels, are stronger than the morphological changes. Therefore, external factors seem to influence these changes instead of morphology. The dependence of cloud phase on cloud-top height (CTH) is more substantial than on CTT in clouds with CTHs below 2.5 km. The previously observed acceleration of closed-to-open transition in MPCs, known as preconditioning, is not the primary driver of climatological cloud morphology statistics in the SO. The morphological differences in cloud albedo are more pronounced in SLCs than in MPCs. This change in albedo alters the cloud radiative effect in the SO by 21Wm−2 to 39Wm−2 depending onseason and cloud phase.
Open and closed MCC clouds exhibit larger equivalent cell diameters in the MPCs than in SLCs in austral summer, whereas, in austral winter, the SLCs are larger. The cell’s aspect ratio accounts for varying CTHs. Closed cells have smaller aspect ratios than open cells, so their cell diameter is smaller, independent of CTH. While the seasonal differences in closed cells are due to changes in CTH, the seasonal aspect ratio differences in open cells are mainly caused by MPCs. With increasing aspect ratios, the cloud albedo decreases in both open and closed MCC clouds, with the most substantial decrease in open MPCs clouds. This leads to cloud-radiative changes of 60 - 75Wm−2 in the SO, depending on cloud phase and aspect ratio.
The established CNN exhibits a good accuracy of 80.6%, with even higher accuracies in the Open (85.5%) and Closed (87.3%) categories. The global MCC climatology based on the CNN generally agrees well with previous MCC distributions. The most notable difference occurs in the Northern Hemisphere (NH) in boreal winter, with a higher occurrence frequency of closed and open MCC clouds. This might indicate missing MPCs in previous studies based on the LWP and some restricted to warm cloud scenes. Thus, the developed CNN seems to better represent the different morphologies in MPCs than in previous classifications.
In conclusion, this thesis shows that understanding the dependencies of cloud phase, cloud morphology, and cell size is important to enhance predictions of the cloud-radiative effect and thus, it is important to evaluate how cloud phase, cloud morphology, and cellsize change in a warming climate.
Die nachfolgende Dissertation wurde an der Goethe-Universität Frankfurt am Institut für Geowissenschaften (FB 11) in der Arbeitsgruppe Kristallographie und Mineralogie (AG Winkler) verfasst. Die Betreuung der hier durchgeführten Arbeiten erfolgte hauptsächlich durch Prof. B. Winkler in Zusammenarbeit mit Dr. L. Bayarjargal, PD Dr. E. Haussühl und PD Dr. V. Vinograd. Bei dem vorliegenden Manuskript handelt es sich um eine kumulative bzw. publikationsbasierte Dissertation, welche die Forschungsergebnisse verschiedener bereits veröffentlichter wissenschaftlicher Fachartikel zusammenfasst.
Die Arbeit beschreibt verschiedene Synthesen und Untersuchungen an Carbonaten und teilt sich im Wesentlichen in zwei Abschnitte. Zum einen wurden Experimente mit Carbonaten bei Extrembedingungen bzw. unter hohen Drücken und hohen Temperaturen durchgeführt, wie sie auch im Inneren der Erde zu finden sind. Im zweiten Teil wurden Carbonate bei Raumbedingungen synthetisiert und der Einbau von Seltenerdelementen untersucht. Grundsätzlich werden jedoch in beiden Teilen dieser Arbeit die Strukturen und Eigenschaften verschiedener Carbonate und eine mögliche Kationensubstitution bzw. die Synthese isostruktureller Verbindungen erforscht.