It has long been assumed that the world's oceans are homogeneous in δ234U, even on a sub-‰ scale, however this has not been comprehensively investigated outside of the North Pacific using modern high-precision MC-ICP-MS. In this study, the δ234U of water samples from across the Mediterranean Sea, Amazon Estuary, and North Atlantic is presented to show that the oceanic uranium system is much more variable and dynamic than previously believed and variable on a ‰-scale. Mediterranean water masses are elevated in δ234U compared to the Atlantic by ~1-2‰, allowing for the estimation of the δ234U of riverine and groundwater inputs to the basin. Analysis within the Amazon Estuary shows that there are significant geographical differences in the non-conservative behavior of U, and that the Amazon has little to no effect on the δ234U of the nearby Atlantic. The upper Atlantic is on average 1‰ lower in δ234U than the deep Atlantic, indicating that oceanic δ234U is not in steady-state but rather decreasing. Results point towards the offset seen in the upper Atlantic possibly being the result of inputs from the Indian Ocean (which has yet to be investigated at such high-precision), indicating that such oceanic δ234U variability may be a widespread phenomena.
Due to their ability to record climate change over large periods of time, stalagmites remain a primary focus of paleoclimatology. Utilizing high-precision age determination methods such as U-series dating, it is possible to measure climate-induced variations of the geochemical composition of speleothems over the time of their growth periods. This dissertation focuses on the investigation of radiocarbon (14C) concentration in several stalagmites. To this end, a new setup for the chemical preparation of carbonate samples for 14C measurements was planned and successfully put into operation. The incorporation of 14C into stalagmites is dependent on various climate-related processes in the soil and in the karst host rock above the cave. Using stable isotope ratios and trace element concentrations, this was investigated in two case studies with high-resolution 14C measurements. Reduced 14C concentration was observed in a stalagmite originating from Moomi Cave on Socotra Island which is indicative of aged soil organic matter influencing the stalagmite formation. It was demonstrated that a combination of higher soil humidity and denser vegetation towards the end of the last glacial period caused higher stalagmite 14C concentration. In a second study on a stalagmite from Sofular Cave in Turkey, the 14C signature allowed for the observation of various aspects of soil carbon dynamics from the last glacial period through into the Holocene. Moreover, the record suggests an increase of atmospheric 14C concentration coincident with the geomagnetic minimum approximately 41000 years ago. This may contribute to the ongoing effort to improve radiocarbon calibration datasets, on which the 14C dating method is based. Lastly, a summary of various stalagmite studies conducted at the Institute of Environmental Physics and a review of the relevant processes of stalagmite 14C incorporation is presented.
In this thesis the reconstruction of climatic conditions and paleotemperatures by the analysis of oxygen (δ18O) and hydrogen (δ2H) isotopes of fluid inclusions in speleothems from two different climatic zones (mid-latitudes and tropics) was performed. An extraction and processing system for fluid inclusion analysis with laser spectroscopy was developed and characterized with respect to the memory or amount effect. I could exclude disturbance effects and achieve a precision of 0.5‰ for δ18O and 1.5‰ for δ2H in replicated measurements with water volumes >0.2μl. The analysis of stable water isotopes allows the determination of paleotemperatures using the classic carbonate thermometer as well as the application of the δ2H/T - relationship with a precision down to ±0.45°C. For the western tropical Atlantic I identified a cooling during the Heinrich stadials (2 and 3) of ~3°C applying the classic carbonate oxygen isotope thermometer. Beyond direct temperature determination, the analysis of fluid inclusions provides information about karst water availability during stalagmite formation. For instance, the δ18O and δ2H values of two speleothems from Germany and Puerto Rico, show slopes of +2.3±1.1 and +3.7±0.2, respectively, that are significantly lower compared to meteoric water lines (slope of ~8). This clear evaporation signal in the related fluid inclusions probably indicates evaporation effects (cave or epikarst), which are enhanced during drier climate conditions.
Studying the air- and water-sided boundary layers is vital to understand the exchange of momentum and gases between ocean and atmosphere. While the water-sided mass boundary layer can be studied with several imaging techniques, no such technique was available for the air side. In the scope of this thesis, a laser-induced fluorescence (LIF) technique was developed, where the tracer sulfur dioxide (SO2) is illuminated with a UV laser and its fluorescence is imaged, yielding near-surface concentration profiles of SO2 with a resolution of up to 20 μm. The profiles can be used to quantify reliable boundary layer thicknesses and gas transfer velocities, which was shown in a proof-of-principle experiment in a wind-wave tank.
In a second experiment at two fetches of a larger wind-wave tank, the SO2 LIF technique was employed together with particle streak velocimetry, measuring local wind speeds, and surface elevation measurements. This experiment is the first simultaneous and collocated measurement of mass and momentum transfer in the air-sided mass boundary layer. The mean concentration and wind speed profiles as well as their fluctuations were analyzed and compared. Including the surface elevations, the modulation of the transport processes by waves was analyzed, resulting in wave-phase averaged transfer velocities.
Accurate models of turbulent dispersion are required for simulating the near-field concentration distribution of pollutants. However, high-resolution measurements of turbulent dispersion in the atmospheric boundary layer are sparse. This thesis describes the three artificial release experiments in the summers of 2017-2019 within the comtessa (Camera Observation and Modelling of 4D Tracer Dispersion in the Atmosphere)project and presents derived results for the turbulent dispersion of tracer puffs. Instantaneous puffs of sulfur dioxide (SO2) were released from a tower on a military site in Norway. Column-integrated SO2 concentrations were observed with SO2 cameras from up to six viewing directions while the atmospheric flow was characterised by eddy covariance measurements at different altitudes along the release tower. A novel simplified tomographic approach was applied to reconstruct the dispersion of tracer puffs separated into their centre of mass trajectories and their dispersion around the centre of mass. Using ensembles of puff releases, the meandering, relative and absolute dispersion as well as the Lagrangian velocity autocorrelations were measured. The ratio of Lagrangian and Eulerian time scales was estimated to a lower bound of TL/TE = 0.33 * 1/i where i is the turbulence intensity; agreeing with previous studies.
Halogene wie Chlor und Brom sind signifikant an stratosphärischen Ozonabbauprozessen beteiligt. Dabei ist die Bromkonzentration in der Stratosphäre zwar etwa 167-fach geringer als die Konzentration von Chlor, Brom ist pro Atom jedoch 60-65 mal effizienter im Abbau von Ozon. Obwohl seit Ende der 90-er Jahre eine Abnahme von (anorganischem) stratosphärischem Brom beobachtet wird, trägt es aktuellsten Studien zufolge zu einem globalen Ozonverlust von etwa 1/3 bei. In der unteren Stratosphäre der niedrigen Breiten kann es sogar bis zu 50% des Ozonverlusts verursachen. In dieser Arbeit wird das stratosphärische Bromsystem anhand ballongestützter Himmelsstreulichtmessungen von Brommonoxid (BrO) unter Verwendung der Differentiellen Optischen Absorptionsspektroskopie (DOAS) Methode analysiert. Dabei ermöglichen Strahlungstransportrekonstruktionen in Kombination mit Inversionsverfahren und Simulationen des dreidimensionalen chemischen Transportmodells SLIMCAT die Ableitung von BrO Konzentrationen als Funktion der Höhe. Für die im Spätsommer 2014 analysierte fünf Jahre alte Luft der mittleren Breiten lässt sich daraus das anorganische stratosphärische Brom (Bry) bzw. das gesamte Brom in der Stratosphäre zu 21.4 ± 4.8 ppt bestimmen. Weitere Untersuchungen befassen sich mit dem photochemischen Tagesgang des Bromsystems. Hierzu werden BrO DOAS Messungen mit Modellstudien eines eindimensionalen photochemischen Modells verglichen, um die Umwandlung von BrO in das nächtliche Reservoirgas Bromnitrat (BrONO2) sowie dessen Rückreaktion anhand der Reaktionsrate kBrO+NO2 respektive der Photolyserate J(BrONO2) zu quantifizieren. Die Ergebnisse weisen dabei ein 1.5 (+0.8 − 0.4) mal größeres J(BrONO2)/kBrO+NO2 Verhältnis auf, als es mit photochemischen Parametern der aktuellsten Jet Propulsion Laboratory (JPL)-Zusammenstellung erwartet wird. Diese Beobachtungen implizieren eine Verschiebung der Zusammensetzung im Bromsystem zu mehr BrO bzw. weniger BrONO2.