Microscopic, chemical and spectroscopic investigations on emeralds of various origins

In dieser Arbeit werden die mikroskopischen, chemischen und spektroskopischen Charakteristika von 260 natürlichen Smaragden und 66 synthetischen „Smaragden“ untersucht. Die Konzentrationen der chemischen Elemente von Smaragden wurden mit Hilfe der LA-ICP-MS und EMS bestimmt. Ergänzende Raman- und IR spektroskopische Methoden ermöglichen es, die Herkunft der verschiedenen Smaragde und ihrer synthetischen Analoga zu bestimmen. Auf Grund der verschiedenen Gehalte von Si, Al und Be können synthetische „Smaragde“ von natürlichen getrennt werden. Die Smaragde von Malipo, Chivor und auch synthetische „Smaragde“ können von allen anderen natürlichen Smaragden wegen der unterschiedlichen Cr-, V-, und Fe-Gehalte von einander getrennt werden. Wegen der unterschiedlichen Mg-, Na-, K-Gehalte lassen sich eher „schiefer-gebundene“ Smaragde identifizieren. Dabei wird festgestellt, dass die Unterscheidung in „schiefer-„ und „nichtschiefer-gebundene“ Smaragd-Vorkommen im Wesentlichen nur die Endglieder einer offensichtlich kristallchemisch sehr variablen Mineralchemie der Berylle, bzw. Smaragde beschreibt, dass damit aber keinesfalls eine petrologisch vertretbare Trennung belegbar ist, sondern dass Smaragde nur das jeweils regierende chemische Regime unter geeigneten Druck-Temperatur-Bedingungen widerspiegeln. Einschlussmerkmale spielen eine große Rolle bei der Unterscheidung verschiedener Lagerstätten und Herstellungsmethoden. Zum Beispiel können die Smaragde der drei Lagerstätten Santa Terezinha, Chivor, und Kafubu mit Hilfe ihrer charakteristischen Pyriteinschlüsse identifiziert werden. Die Band-Positionen und FWHM -Werte der Raman-Bande bei 1068 cm-1 und der IR-Bande bei 1200 cm-1 ermöglichen eine Differenzierung zwischen synthetischen und natürlichen Smaragden, und können darüber hinaus auch Auskunft geben über die Lagerstätte. Zusammen mit chemischen Messwerten kann bewiesen werden, dass diese Banden von Si-O Schwingungen verursacht werden. Die Raman- und IR-Banden im Bereich der Wasserschwingungen und insbesondere das IR-Band um 1140 cm-1 führen zur Trennung von Flux-Synthesen, Hydrothermal-Synthesen und natürlichen Smaragden.

Exploring physical processes related to past climate proxies: lake sediments and stable water isotopes

Proxy data are essential for the investigation of climate variability on time scales larger than the historical meteorological observation period. The potential value of a proxy depends on our ability to understand and quantify the physical processes that relate the corresponding climate parameter and the signal in the proxy archive. These processes can be explored under present-day conditions. In this thesis, both statistical and physical models are applied for their analysis, focusing on two specific types of proxies, lake sediment data and stable water isotopes.rnIn the first part of this work, the basis is established for statistically calibrating new proxies from lake sediments in western Germany. A comprehensive meteorological and hydrological data set is compiled and statistically analyzed. In this way, meteorological times series are identified that can be applied for the calibration of various climate proxies. A particular focus is laid on the investigation of extreme weather events, which have rarely been the objective of paleoclimate reconstructions so far. Subsequently, a concrete example of a proxy calibration is presented. Maxima in the quartz grain concentration from a lake sediment core are compared to recent windstorms. The latter are identified from the meteorological data with the help of a newly developed windstorm index, combining local measurements and reanalysis data. The statistical significance of the correlation between extreme windstorms and signals in the sediment is verified with the help of a Monte Carlo method. This correlation is fundamental for employing lake sediment data as a new proxy to reconstruct windstorm records of the geological past.rnThe second part of this thesis deals with the analysis and simulation of stable water isotopes in atmospheric vapor on daily time scales. In this way, a better understanding of the physical processes determining these isotope ratios can be obtained, which is an important prerequisite for the interpretation of isotope data from ice cores and the reconstruction of past temperature. In particular, the focus here is on the deuterium excess and its relation to the environmental conditions during evaporation of water from the ocean. As a basis for the diagnostic analysis and for evaluating the simulations, isotope measurements from Rehovot (Israel) are used, provided by the Weizmann Institute of Science. First, a Lagrangian moisture source diagnostic is employed in order to establish quantitative linkages between the measurements and the evaporation conditions of the vapor (and thus to calibrate the isotope signal). A strong negative correlation between relative humidity in the source regions and measured deuterium excess is found. On the contrary, sea surface temperature in the evaporation regions does not correlate well with deuterium excess. Although requiring confirmation by isotope data from different regions and longer time scales, this weak correlation might be of major importance for the reconstruction of moisture source temperatures from ice core data. Second, the Lagrangian source diagnostic is combined with a Craig-Gordon fractionation parameterization for the identified evaporation events in order to simulate the isotope ratios at Rehovot. In this way, the Craig-Gordon model can be directly evaluated with atmospheric isotope data, and better constraints for uncertain model parameters can be obtained. A comparison of the simulated deuterium excess with the measurements reveals that a much better agreement can be achieved using a wind speed independent formulation of the non-equilibrium fractionation factor instead of the classical parameterization introduced by Merlivat and Jouzel, which is widely applied in isotope GCMs. Finally, the first steps of the implementation of water isotope physics in the limited-area COSMO model are described, and an approach is outlined that allows to compare simulated isotope ratios to measurements in an event-based manner by using a water tagging technique. The good agreement between model results from several case studies and measurements at Rehovot demonstrates the applicability of the approach. Because the model can be run with high, potentially cloud-resolving spatial resolution, and because it contains sophisticated parameterizations of many atmospheric processes, a complete implementation of isotope physics will allow detailed, process-oriented studies of the complex variability of stable isotopes in atmospheric waters in future research.rn

Palaeo wind system reconstruction of the last glacial period over Europe, using high resolution proxy data and model-data-comparison

The atmosphere is a global influence on the movement of heat and humidity between the continents, and thus significantly affects climate variability. Information about atmospheric circulation are of major importance for the understanding of different climatic conditions. Dust deposits from maar lakes and dry maars from the Eifel Volcanic Field (Germany) are therefore used as proxy data for the reconstruction of past aeolian dynamics.rnrnIn this thesis past two sediment cores from the Eifel region are examined: the core SM3 from Lake Schalkenmehren and the core DE3 from the Dehner dry maar. Both cores contain the tephra of the Laacher See eruption, which is dated to 12,900 before present. Taken together the cores cover the last 60,000 years: SM3 the Holocene and DE3 the marine isotope stages MIS-3 and MIS-2, respectively. The frequencies of glacial dust storm events and their paleo wind direction are detected by high resolution grain size and provenance analysis of the lake sediments. Therefore two different methods are applied: geochemical measurements of the sediment using µXRF-scanning and the particle analysis method RADIUS (rapid particle analysis of digital images by ultra-high-resolution scanning of thin sections).rnIt is shown that single dust layers in the lake sediment are characterized by an increased content of aeolian transported carbonate particles. The limestone-bearing Eifel-North-South zone is the most likely source for the carbonate rich aeolian dust in the lake sediments of the Dehner dry maar. The dry maar is located on the western side of the Eifel-North-South zone. Thus, carbonate rich aeolian sediment is most likely to be transported towards the Dehner dry maar within easterly winds. A methodology is developed which limits the detection to the aeolian transported carbonate particles in the sediment, the RADIUS-carbonate module.rnrnIn summary, during the marine isotope stage MIS-3 the storm frequency and the east wind frequency are both increased in comparison to MIS-2. These results leads to the suggestion that atmospheric circulation was affected by more turbulent conditions during MIS-3 in comparison to the more stable atmospheric circulation during the full glacial conditions of MIS-2.rnThe results of the investigations of the dust records are finally evaluated in relation a study of atmospheric general circulation models for a comprehensive interpretation. Here, AGCM experiments (ECHAM3 and ECHAM4) with different prescribed SST patterns are used to develop a synoptic interpretation of long-persisting east wind conditions and of east wind storm events, which are suggested to lead to an enhanced accumulation of sediment being transported by easterly winds to the proxy site of the Dehner dry maar.rnrnThe basic observations made on the proxy record are also illustrated in the 10 m-wind vectors in the different model experiments under glacial conditions with different prescribed sea surface temperature patterns. Furthermore, the analysis of long-persisting east wind conditions in the AGCM data shows a stronger seasonality under glacial conditions: all the different experiments are characterized by an increase of the relative importance of the LEWIC during spring and summer. The different glacial experiments consistently show a shift from a long-lasting high over the Baltic Sea towards the NW, directly above the Scandinavian Ice Sheet, together with contemporary enhanced westerly circulation over the North Atlantic.rnrnThis thesis is a comprehensive analysis of atmospheric circulation patterns during the last glacial period. It has been possible to reconstruct important elements of the glacial paleo climate in Central Europe. While the proxy data from sediment cores lead to a binary signal of the wind direction changes (east versus west wind), a synoptic interpretation using atmospheric circulation models is successful. This shows a possible distribution of high and low pressure areas and thus the direction and strength of wind fields which have the capacity to transport dust. In conclusion, the combination of numerical models, to enhance understanding of processes in the climate system, with proxy data from the environmental record is the key to a comprehensive approach to paleo climatic reconstruction.rn

The reconstruction of paleoclimate variability in Northern Germany, during marine isotope stage 5

In order to obtain a better understanding about the influence of post-depositional diagenesis on speleothem 230Th/U-ages and paleoclimate variability during Marine Isotope Stage (MIS) 5 in northern Germany, four stalagmites from the Riesenberghöhle (RBH) were investigated by thin section analysis, 230Th/U-dating as well as stable oxygen and carbon isotope and laser ablation inductively coupled mass spectrometry (LA-ICPMS) trace element analysis. The RBH is located in the Weser Hills and is one of the northernmost limestone caves in Germany.rnMulti collector (MC) ICPMS 230Th/U-ages and thin section analysis of the RBH stalagmites shows that some growth phases of the stalagmites were diagenetically altered after their deposition. The impact of post-depositional diagenesis (PDD) on the 230Th/U-ages is modeled, and potential processes leading to PDD are discussed. In this context, it is suggested that PDD may be induced by rapid climate change at the inception of the GIS.rnDespite of the dating uncertainties resulting from PDD, 230Th/U-dating shows that the RBH stalagmites grew during the Eemian and most of the Greenland Interstadials (GIS) during MIS 5. Thus, the growth phases of the RBH stalagmites might be related to a reorganization of the Atlantic Meridional Overturning Circulation (AMOC). The stable isotope (δ13C and δ18O) and the trace element variability of the stalagmites reflects rapid changes of past temperature and precipitation on millennial and sub-millennial timescales. These past climate changes can be amplified by orbitally forced variations of the July solar insolation at 65°N.

Influence of micro-site conditions and environmental gradients on tree-ring based climate reconstructions

Tree-ring chronologies are a powerful natural archive to reconstruct summer temperature variations of the late Holocene with an annual resolution. To develop these long-term proxy records tree-ring series are commonly extended back in time by combining samples from living trees with relict dead material preserved onshore or in lakes. Former studies showed that low frequency variations in such reconstructions can be biased if the relict and recent material is from different origins. A detailed analysis of the influence of various ecological (micro-) habitats representing the recent part is required to estimate potential errors in temperature estimates. The application of collective detrending methods, that comprise absolute growth rates, can produce errors in climate reconstructions and results in an underestimation of past temperatures. The appearance of these kind of micro-site effects is a wide-spread phenomenon that takes place all over Fennoscandia. Future research in this key region for dendroclimatology should take this issue into account. Especially the higher climate response at the lakeshore site is interesting to achieve smaller uncertainties when a tree-ring series is transformed to temperature anomalies. For new composite chronologies the main aim should be to minimize potential biases and this includes also micro-site effects.