Introduced species can become invasive and cause catastrophic alterations to the system they invade. Both zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) have caused significant ecosystem alterations wherever they have invaded. These Dreissena species have caused changes in water quality and biodiversity and have disrupted energy pathways which can have cascading effects on other trophic levels. Recently quagga mussels invaded Lake Powell, a reservoir located in the southwestern USA, creating the possibility of a trophic cascade that could alter energy flow in the reservoir and change the trophic niche structure of the fishes in the lake. However, due to Lake Powell’s large size, dynamic nature, and complex hydrological structure, the effects of quagga mussels on fish species is uncertain. To determine impacts of quagga mussels on Lake Powell fishes, we quantified trophic niches of five species of sport fish over three years (2017-2019) using stable isotopes of nitrogen, δ15N, and carbon, δ13C. We test the following hypothesis: quagga mussels will cause a shift in trophic niche in more pelagic fishes such that pelagic fishes decrease in trophic position and shift toward use of more littoral energy. In addition, we compare the trophic niche of these species with a previous study on the trophic niche of fish in Lake Powell prior to full colonization of the lake by quagga mussels (2014-2015). In general, fish in the southern region of the lake exhibited a trend of decreasing δ15N suggesting decreasing trophic position and an enrichment of δ13C indicating a littoral energy shift in some species. Fish in the northern region of the lake exhibited a slight increase in trophic position and a shift towards pelagic energy across the same time period. These shifts support the hypothesis with pelagic fish experiencing a trophic niche shift, in the direction predicted, but only in the southern region of Lake Powell. Additionally, this shift is not exclusive to pelagic fish, but happened in all five species. Sediment laden input from the Colorado River may offset the impact of quagga mussels in the northern region of the lake resulting in observed regional differences.

The aim of this thesis is to expand the understanding of horses from ritual and everyday contexts, respectively, by investigating their diet and mobility. In this thesis, teeth of domestic horse Equus ferus caballus from the wetland Bokaren and central place Gamla Uppsala in Uppland during the late Iron Age (550-1050 A.D) are analyzed. The material consists of 44 teeth from 23 distinct horses from wetlands, wells, postholes, and settlement that were compared against each other, to discover diet and mobility similarities, differences, variations, and life history changes between different ritual and everyday contexts. It was conducted through a multi-isotope (δ13C, δ15N, δ34S and 87Sr/86Sr) analysis of equine cheek teeth in EA-IRMS and LA-MC-ICP-MS. The results indicate that the horses from ritual and everyday context were adapted to different livestock practices, according to their mobility, function, and priority. Horses used for transport were prioritized with nutritious and protein-rich feeding. In contrast to work- and multifunctional horses from Gamla Uppsala that show signs of prolonged nutritional stress caused by the fact that they did not meet their protein intake. A majority of the horses were non-local, they consumed food from the same region, and they may have come from more northern regions in Sweden and/or Finland. / Tidens Vatten

The Hurricane Fault is a 250-km long, west dipping, Basin and Range-bounding normal fault in SW Utah and NW Arizona that initiated in the mid-Miocene to Pliocene. It has been primarily active in the Quaternary, with slip rates of 0.2 – 0.6 mm/yr. There are multiple hot springs along its 250-km length and multiple late Tertiary-Quaternary basaltic centers broadly parallel the fault. Possible sources of hot spring fluids include deeply-circulated meteoric water that experienced water-rock exchange at high temperatures (>100 °C) and deep-seated crustal fluids. Aside from the source of modern hot spring fluids and heat, questions about the spatio-temporal history of fluid flow along the Hurricane Fault remain unaddressed. Abundant damage zone veins, cements, and host rock alteration are present, indicative of past fluid flow. Carbonate veining and cementation is a key feature of the Hurricane Fault zone, and is the primary feature exploited to characterize the thermochemical history of fault-related paleofluids. A combination of macroscopic and microscopic carbonate observations, chemical composition, and precipitation temperature of calcite veins was used to determine past water-rock diagenetic interaction and vein evolution in the Hurricane Fault zone. Calcite iv in concretions and veins from the damage zone of the fault shows a wide range of carbon and oxygen stable isotope ratios, with δ13CPDB from -4.5 to 3.8 ‰ and δ18OPDB from -17.7 to -1.1‰. Fluid inclusion microthermometry homogenization temperatures range from 45 to 160 °C, with fluid salinities of 0 to 15 wt% NaCl calculated from melting temperatures. Combining the two datasets, two main fluids that interacted with the fault zone are inferred: (1) basin brines with a δ 18OSMOW of 9.2 ‰ and (2) altered meteoric fluids with a δ 18OSMOW of -11.9 to -8.3 ‰. Calculated dissolved CO2 δ 13CPDB (-8.5 to -1.3 ‰) indicates mixed marine carbonate and organic or magmatic sources. Fault zone diagenesis was caused by meteoric water infiltration and interaction with carbonate-rich rocks, mixed with upwelling basin brines. Fluid-rock interaction is concentrated in the damage zone, where fracture-related permeability was utilized for fluid flow. A distinct mineralization event punctuated this history, associated with basin brines that were chemically influenced by nearby basaltic magmatism. This implies a hydrologic connection between the fault and regional magmatism.

Unicellular algae (microalgae) are able to produce a number of substances such as starches, oils, proteins, carotenoids, polyphosphates, or crystalline purines directly from inorganic sources by photosynthesis. Different species of microalgae can be used for the economic production of various biomolecules. Due to their autotrophic nature, microalgae are also unique as they can synthesize complex isotopically labeled biomolecules from simple isotopically labeled inorganic substances. Analysis of the chemical composition of microalgae by means of chemical-analytical methods is relatively complex, time-consuming, and laborious. Confocal Raman microscopy represents one of the optical methods by which the chemical composition of microalgae can be determined in situ, i.e. directly within intact cells. This technique combining confocal optical microscopy with Raman spectroscopy enables fast and non- destructive analysis of the chemical composition of substances in the investigated objects, including the effect of isotopic labeling. The chemical composition of the investigated objects is reflected by their Raman spectra, in the case of Raman mapping of microscopic objects by their chemical maps. In this work, a specific case of isotopic labeling was studied, namely the effect of heavy water (D2O) on the deuteration...

The discharge of groundwater into surface water bodies is a hidden, but significant pathway for the input of water and matter into lakes, rivers, estuaries and the coastal sea. Since groundwater is most often characterized by higher levels of nutrients or heavy metals, its discharge has often a crucial effect on the surface water body´s chemistry and the ecosystem health as well as on the related ecosystem service supply. For instance, groundwater-derived nutrient inputs are essential to fuel primary productivity, but if critical thresholds are exceeded groundwater-derived nutrient inputs can cause eutrophication, which may trigger harmful algal blooms or the creation of oxygen minimum zones – a serious threat to aquatic life. This thesis focuses on quantifying submarine and lacustrine groundwater discharge by applying environmental tracer based methods with emphasis on radionuclide (radon and radium isotopes) and stable water isotope (δ18O, δ2H) techniques. These tracers are suitable for determining groundwater discharge as they show distinct concentration and isotope ratio gradients between groundwater and the receiving surface water. Four studies are presented in this thesis: (1) The quantification of the response delay of the mobile radon detector RAD7 applied for radon-in-water mapping. The response delay of the mobile radon-in-air detector RAD7 is determined for two detection set-ups (radon extraction via RADaqua and via a membrane module) as well as for a range of water flow rates. For the membrane module the response delay is less pronounced compared to the RADaqua. For instance, at a water flow rate of 1 l min-1 the peaks of the instruments recordings lag behind the radon-in-water concentrations by ~10 min for the membrane module and by ~18 min for the RADaqua. Further, it was demonstrated that faster water flow rates decrease the response delay. An algorithm is presented that allows the inverse calculation of radon-in-water concentrations from RAD7 records for the described detection set-ups and water flow rates. Thus, it allows a more precise localization of radon-in-water anomalies and, consequently a more precise localization of groundwater discharge areas. (2) Determination of submarine groundwater discharge into a large coastal bay (False Bay, South Africa) SGD consists generally of two components: (a) fresh terrestrial SGD (FSGD) driven by the inland hydraulic gradient and (b) seawater re-circulation (RSGD) through the coastal aquifer driven by seaward effects such as tidal pumping. A bay-wide radon mapping resulted in identification of a SGD site, where subsequently detailed investigations were conducted. At this SGD site a salt and a radon mass balance were applied consecutively for determining FSGD and total SGD, respectively. RSGD was inferred from the difference between FSGD and total SGD. For the radon mass balance, new approaches for calculating the radon degassing and mixing loss were proposed. The tracer mass balance revealed median FSGD of 2,300 m³ d-1 or 0.9 m³ d-1 per m coastline and median RSGD of 6,600 m³ d-1 or 2.7 m³ d-1 per m coastline. The FSGD rate was validated using (a) a hydrological model for calculating the groundwater recharge rate and (b) a groundwater flow model for delineating the subsurficial FSGD capture zone. This validation supported the tracer based findings. The relevance of this study is foremost the presentation of new methodological approaches regarding the radon mass balance as well as the validation of FSGD under consideration of hydrological and hydrogeological information. (3) Differentiation of fresh and re-circulated submarine groundwater discharge in an estuary (Knysna Estuary, South Africa) Knysna Estuary is a more complex system than False Bay since besides seawater, FSGD and RSGD also river water mixes within the estuary. Both FSGD and RSGD were differentiated by applying a mixing analysis of the estuary water. For this purpose, an end-member mixing analysis (EMMA) was conducted that simultaneously utilizes radon and salinity time series of estuary water to determine fractions of the end-members seawater, river water, FSGD and RSGD. End-member mixing ratio uncertainty was quantified by stochastic modelling (Monte Carlo simulation) under consideration of end-member characterization uncertainty. Results revealed highest FSGD and RSGD fractions in the estuary during peak low tide. Median fractions of FSGD and RSGD were 0.2 % and 0.8 % of the estuary water near the mouth over a 24 h time-series. In combi-nation with a radon mass balance median FSGD of 46,000 m³ d-1 and median RSGD of 150,000 m³ d-1 were determined. By comparison to other sources, this implies that the SGD is a significant source of dissolved inorganic nitrogen (DIN) fluxes into the estuary. This study demonstrates the ability of EMMA to determine end-member fractions in a four end-member system under consideration of end-member uncertainty. Further, the importance of SGD for the water and DIN budget of Knysna Estuary was shown. (4) Quantification of groundwater discharge and water residence time into a groundwa-ter-fed lake (Lake Ammelshainer See, Germany). The presented approach utilizes the stable isotopes of water (δ18O, δ2H) and radon for determining long-term average and short-term trends in groundwater discharge rates. The calculations were based on measurements of isotope inventories of lake and groundwater in combination with climatic and isotopic monitoring data (in precipita-tion). The results from steady-state annual isotope mass balances for both δ18O and δ2H are consistent and reveal an overall long-term average groundwater discharge that ranges from 2,800 to 3,350 m³ d-1. These findings were supported by the good agree-ment of the simulated annual cycles of δ18O and δ2H lake inventories utilizing the de-termined groundwater discharge rates with the observed lake isotope inventories. However, groundwater discharge rates derived from radon mass balances were signifi-cantly lower, which might indicate a distinct seasonal variability of the groundwater discharge rate. This application shows the benefits and limitations of combining δ18O/δ2H and radon isotope mass balances for the quantification of groundwater con-nectivity of lakes based on a relatively small amount of field data accompanied by good quality and comprehensive long-term meteorological and isotopic data (precipitation). This thesis presents important methodological achievements with respect to radon and stable water isotope mass balances, uncertainty quantification, geochemical differentia-tion between FSGD and RSGD and validation of FSGD. Further, first SGD estimates are reported for False Bay and Knysna Estuary in South Africa. / Der Austritt von Grundwasser in Oberflächengewässer stellt einen unsichtbaren Ein-tragspfad von Wasser und Stoffen in Seen, Flüsse, Ästuare und das küstennahe Meer dar. Die Konzentrationen vieler Stoffe wie beispielsweise von Nährstoffen und Schwermetallen ist im Grundwasser im Allgemeinen signifikant höher als in Oberflächengewässern. Daher können selbst volumetrisch verhältnismäßig kleine Grundwasseraustritte entscheidenden Einfluss auf Wasserchemie und den Gesundheitszustand des aquatischen Ökosystems haben, womit Auswirkungen auf die Bereitstellung von Ökosystemleistungen verbunden sein können. Beispielsweise sind grundwasserbürtige Nährstoffeinträge eine entscheidende Steuergröße für die Primärproduktivität. Überschreiten diese grundwasserbürtigen Nährstoffeinträge jedoch einen Schwellenwert, kann es zur Eutrophierung des Oberflächengewässers kommen. Dies wiederum kann toxische Algenblüten oder die Entstehung von Sauerstoffminimumzonen zur Folge haben und das aquatische Leben bedrohen. Diese Dissertation beschäftigt sich mit Methoden zur Quantifizierung von Grundwas-sereinträgen in den küstennahen Ozean, Ästuare und in Seen. Dabei stützt sich diese Arbeit primär auf Umwelttracer, vor allem auf Radionuklide (Radon- und Radium-Isotope) sowie die stabilen Isotope des Wassers (δ18O, δ2H). Diese Umwelttracer sind für die untersuchten Systeme in besonderer Weise geeignet, da zwischen Grundwasser und Oberflächenwasser ein ausgeprägter Gradient hinsichtlich Konzentration bzw. Isotopensignatur besteht. Vier Einzelstudien stellen den Kern dieser Arbeit dar: (1) Die Quantifizierung der Antwortverzögerung des mobilen Radon-Detektors RAD7, an-gewendet für die Radon-in-Wasser-Kartierung. Die Antwortverzögerung des mobilen Radon-in-Luft-Detektors RAD7 wurde für zwei Messanordnungen (Radonextraktion via RADaqua und via Membranmodul) sowie für einen Bereich von Wasserdurchflussraten bestimmt. Für die Radonextraktion via RADaqua ist die Antwortverzögerung stärker ausgeprägt als für das Membranmodul. Bei einer Wasserdurchflussrate von 1 l min-1 treten die Peaks der aufgezeichneten Werte ~10 min nach den Radon-in-Wasser Peaks auf, während die Verzögerung bei Radonextraktion via RADaqua ~18 min beträgt. Weiterhin wurde eine Reduktion der Antwortverzögerung mit zunehmenden Wasserdurchflussraten beobachtet. Der vorgestellte Algorithmus ermöglicht in Kombination mit den berechneten Radontransfer-Koeffizienten die inverse Modellierung der Radon-in-Wasser-Konzentrationen, basierend auf den RAD7-Messwerten. Dies ermöglicht beispielsweise eine genauere Lokalisierung von räumlichen Radon-in-Wasser Anomalien und folglich eine präzisere Bestimmung von Grundwasseraustrittsstellen. (2) Quantifizierung untermeerischer Grundwasseraustritte in eine große Meeresbucht (False Bay, Südafrika) Untermeerische Grundwasseraustritte (“Submarine Groundwater Discharge” – SGD) bestehen aus zwei Komponenten: (a) Süßwasser-SGD (“Fresh SGD” – FSGD) angetrieben durch den meerwärtsgerichteten hydraulischen Gradienten, und (b) re-zirkuliertem SGD („re-circulated SGD“ – RSGD), verursacht durch Prozesse wie gezeitengesteuerte Infiltration von Meerwasser in den Aquifer. Eine Radon-Kartierung entlang der gesamten Küstenlinie der Bucht führte zur Lokalisierung von SGD, woraufhin dort vertiefende Untersuchungen durchgeführt wurden. In diesem Bilanzgebiet wurden eine Salz- und eine Radon-Massenbilanz durchgeführt, um FSGD bzw. Gesamt-SGD zu bestimmen. RSGD wurde aus der Differenz von FSGD und SGD abgleitet. Für die Radon-Massenbilanz wurden neue Ansätze für die Berechnung der Radon-Entgasung in die Atmosphäre und des Radon-Mischungsverlustes mit küstenfernerem Wasser präsentiert. Die Tracer-Massenbilanzen ergaben einen FSGD-Median von 2.300 m³ d-1 bzw. 0,9 m³ d-1 pro Meter Küstenlinie und einen RSGD-Median von 6.600 m³ d-1 bzw. 2,7 m³ d-1 pro Meter Küstenlinie. Die FSGD-Rate wurde mit Hilfe eines hydrologischen Modells zur Abschätzung der Grundwasserneubildungsrate und eines Grundwasserströmungsmodells zur Abgrenzung des unterirdischen Einzugsgebiets des Bilanzraums bestimmt. Diese unabhängige Methode bestätigte die Tracer-basierten Ergebnisse. Die Bedeutung dieser Studie besteht zuvorderst in der Vorstellung neuer methodischer Ansätze bei der Radon-Massenbilanzierung sowie in der Validierung von FSGD unter Berücksichtigung hydrologischer und hydrogeologischer Daten. (3) Unterscheidung von FSGD und RSGD in einem Ästuar (Knysna Ästuar, Südafrika). Das Knysna-Ästuar ist hinsichtlich der Bestimmung von SGD im Vergleich zur False Bay ein komplexeres System, da sich neben Meerwasser, FSGD und RSGD auch Flusswasser in signifikanten Mengen im Ästuar mischt. FSGD- und RSGD-Anteile wurden anhand der chemischen Zusammensetzung des Ästuarwassers unterschieden. Für diesen Zweck wurde eine End-Member-Mischungsanalyse (EMMA) auf Grundlage von Radon- und Salinitätszeitreihen des Ästuarwassers durchgeführt. Durch ein Optimierungsverfahren wurde die Mischung der End-member Meerwasser, Flusswasser, FSGD und RSGD für jeden Zeitschritt mit dem Ziel der bestmöglichen Übereinstimmung mit den gemessenen Radon- und Salinitätszeitreihen bestimmt. Die Unsicherheit in der Bestimmung der End-member-Anteile wurde durch stochastische Modellierung (Monte-Carlo-Simulation) quantifiziert. Die höchsten Anteile von FSGD und RSGD traten bei Niedrigwasser auf. Die mittleren Anteile von FSGD und RSGD betrugen in der Nähe der Ästuarmündung 0,2 % und 0,8 % während einer 24-stündigen Zeitreihenmessung. Diese Informationen führten in Kombination mit einer Radon-Massenbilanz zur Bestimmung eines mittleren FSGD von 46.000 m³ d-1 sowie eines mittleren RSGD von 150.000 m³ d-1. Diese Ergebnisse implizieren unter Einbeziehung weiterer Daten, dass SGD ein bedeutender Pfad für den Eintrag von gelöstem anorganischem Stickstoff (DIN) in das Knysna-Ästuar darstellt. Diese Studie zeigt das Potenzial einer EMMA für die Bestimmung der Anteile von vier End-membern unter Nutzung von zwei gemessenen Variablen und unter Berücksichtigung der End-member-Unsicherheit. Außerdem wurde die Bedeutung von SGD für das Wasser- und DIN-Budget des Knysna-Ästuars aufgezeigt. (4) Quantifizierung von Grundwasseraustrittsrate und Wasserverweilzeit eines grundwas-sergespeisten Sees (Ammelshainer See, Deutschland). Der vorgestellte Ansatz nutzt die stabilen Isotope des Wassers (δ18O, δ2H) und von Ra-don für die Bestimmung des mittleren langfristigen sowie der aktuellen Grundwas-seraustrittsrate. Die Berechnungen beruhen auf Abschätzungen des Isotopeninventars anhand von Feldmessungen, der Isotopensignatur des Grundwassers sowie ergänzen-den Klima- und Isotopen-Daten (Niederschlag). Die Ergebnisse einer stationären Isoto-pen-Massenbilanz für δ18O und δ2H sind übereinstimmend und ergaben einen langfristigen mittleren Grundwasseraustritt von 2.800 bis 3.350 m³ d-1. Dieses Ergebnis wurde für die Modellierung des jährlichen Zyklus des Isotopeninventars im See benutzt, welches mit den gemessenen Isotopenwerten konsistent ist. Die auf Grundlage einer Radon-Massenbilanz abgeleiteten aktuellen Grundwasserzutrittsraten lagen im Gegensatz dazu deutlich niedriger, was jedoch nicht notwendigerweise einen Widerspruch darstellen muss, sondern vielmehr ein Hinweis auf eine möglicherweise ausgeprägte saisonale Variabilität des Grundwasseraustritts darstellen kann. Diese Studie zeigt Möglichkeiten und Grenzen der Anwendung von einer Kombination aus δ18O/δ2H- und Radon-Massenbilanzen für die Bestimmung der Grundwasseranbindung von Seen mit einem vergleichsweise geringen Messaufwand unter Nutzung qualitativ hochwertiger und umfangreicher Klima-und Isotopen-Daten (Niederschlag). Diese Dissertation präsentiert wichtige methodische Fortschritte hinsichtlich der An-wendung von Radon- und stabilen Isotopen-Massenbilanzen, der Quantifizierung von Unsicherheit, der Unterscheidung von FSGD und RSGD anhand geochemischer Daten und der Validierung von FSGD. Außerdem wurden erstmals SGD-Raten für Standorte in Südafrika (False Bay und Knysna-Ästuar) vorgestellt.

No description available.

A geochemical study of major springs and wells in Spring Valley, Nevada, and Snake Valley, Utah-Nevada was initiated in response to the Clark, Lincoln and White Pine Counties Groundwater Development Project proposed by the South Nevada Water Authority (SNWA). Water budget estimates suggest that interbasin flow accounts for a significant portion (~25%) of the water budgets in Spring and Snake Valleys. Although interbasin flow is possible in some areas, alternative plausible explanations place significant uncertainty on water budget allocations. To examine the plausibility of local and interbasin flow paths the groundwater flow in Spring and Snake Valleys was evaluated using solute and isotopic data. Evidence for local flow paths includes: 1) stable isotope values in local areas which are similar to isotope values in adjacent recharge zones; 2) measurable 3H content and 14C activities ≥ 50 pmc in most samples which suggests short residence times; and 3) plausible geochemical models of local flow paths. Previously defined interbasin flow paths in southern Spring Valley are marked by samples that have low 14C activities (mean = 20.14 pmc), which are consistent with long residence times and can be explained by either interbasin flow from adjacent basins or deep circulation in the basin-fill sediments of Spring Valley. Interbasin flow from southern Spring Valley to southern Snake Valley cannot be confirmed or rejected based on the current data and modeling constraints, which result in plausible models involving both local flow paths and interbasin flow paths. Interbasin flow from northern Spring Valley to northern Snake Valley is unlikely and can be explained by the deep circulation of groundwater that is mixed with modern recharge. The plausibility of alternative explanations to describe previously defined interbasin flow paths suggests that water budget allocations in Spring and Snake Valleys should be redistributed or reevaluated. The use of existing water budgets that allocate large components of water to interbasin flow to determine the distribution of water resources may result in incorrect estimations of available resources.

Understanding the effect of food abundance on feeding behavior can benefit conservation efforts in many ways, such as to determine whether impacted environments need food supplementation, whether different locations of threatened species contain different food abundances, or whether reintroduction sites are missing key components of a species’ diet. I studied the relationship between feeding behavior and food abundance in the Lower Keys marsh rabbit (Sylvilagus palustris hefneri), an endangered subspecies endemic to the lower Florida Keys. Specifically, my study set out to measure the relative abundance of the primary plants within the natural habitat of the Lower Keys marsh rabbit and estimate the proportion of each of these plants within the rabbit’s diet. With this information, I tested the following hypotheses: first, the Lower Keys marsh rabbit selectively feeds on specific plants; second, that diet does not differ among sites; and third, that diet is not affected by food abundance. Using stable isotope analysis, I determined that two plants were prominent in the rabbit’s diet: a shrub, Borrichia frutescens, and a grass, Spartina spartinae. These two species were prominent in the rabbit’s diet in most patches, even where they were relatively rare, suggesting the rabbits are indeed selectively feeding on these species. In addition, although diet did differ among patches, selective feeding was apparent in all cases. Overall, this study determined that certain food types are important food sources for the federally endangered Lower Keys marsh rabbit and that these rabbits do not feed on plants based on plant abundance. This knowledge can be directly applied to reintroduction and restoration efforts for the Lower Keys marsh rabbit. More generally, the methods used in this study can be applied to other species of concern in order to address questions associated with diet requirements and foraging behavior.

Während der Klimawandel und die globale Erwärmung das östliche Afrika schon heutzutage beeinflussen, ist das Wissen über die klimatischen Veränderungen der Vergangenheit begrenzt. Vor allem in den letzten 15.000 Jahren hat das östliche Afrika räumlich komplexe klimatische Veränderungen erlebt. Obwohl in Ostafrika mehrere paläoklimatische Studien durchgeführt wurden, welche die Temperaturänderungen und die hydrologische Vergangenheit von Seearchiven rekonstruierten, sind die treibenden Mechanismen und Telekonnektionen noch nicht vollständig verstanden. Ein tieferes Verständnis wird verhindert durch (i) das Fehlen von zeitlich weit zurückreichenden, qualitativ hochwertigen wissenschaftlichen Daten bezüglich Umweltveränderungen, insbesondere in der Region des Horns von Afrika, (ii) das Fehlen solcher Daten aus großen Höhen und (iii) unzureichend untersuchte Regionen wie der östliche Teil Äthiopiens und Somalia. Eines der am wenigsten untersuchten Hochgebirgsgebiete der Region sind die Bale Mountains, obwohl sie das größte Gebiet des Kontinents oberhalb von 4000 m ü. NN umfassen. Diese Dissertation zielt darauf ab, den derzeitigen Mangel an paläoklimatischen Rekonstruktionen in Hochgebirgen in der untersuchten Region am Horn von Afrika weiter zu verringern. Hochgelegene perennierende Seen, insbesondere Karseen, sind wertvolle Archive für paläoklimatische und ökologische Rekonstruktionen, da sie kontinuierliche Sedimente liefern, die durch menschliche Aktivitäten nicht gestört wurden. Der einzige ganzjährige See in den Bale Mountains, der Garba Guracha, liegt in der afro-alpinen Zone auf 3950 m ü. NN. Frühere paläolimnologische Untersuchungen ergaben, dass die kontinuierlichen Sedimente des Garba Guracha paläoklimatische und ökologische Informationen seit der letzten Vergletscherung beinhalten. Um das paläoklimatische Wissen über die Bale Mountains und damit über das östliche Afrika zu erweitern, wurden neue innovative Proxies, z. B. brGDGTs, δ18Ofucose, δ18Odiatom und δ2Hn-alkane, auf neu geborgene Sedimentkerne des Garba Guracha angewendet. Die Interpretation der Ergebnisse dieser Analysen ermöglichen ein tieferes Verständnis des Sedimentkerns, vor allem in Bezug auf die Sedimentologie, die Chronologie und die Quellen abgelagerten organischen Materials. Die hochauflösende Chronologie des Garba Guracha, die unter Verwendung verschiedener Datierungsmethoden und -komponenten (210Pb-Datierung, Radiokohlenstoffdatierung an der Gesamtsedimentfraktion, an Holzkohle und komponentenklassenspezifisch an n-Alkanen) erstellt wurde, ergibt ein basales Alter von ∼ 16 cal ka BP. Die geochemische Korrelation der Tephra-Schichten in den Garba-Guracha-Sedimenten mit datierten Tephra-Schichten aus anderen Seen der Region liefert eine externe Alterskontrolle, die die Robustheit der neuen Garba-Guracha-Chronologie und die Abwesenheit von systematischen Altersverschiebungen weiter untermauert. Ähnliche Altersangaben für n-Alkane und der Gesamtsedimentfraktion deuten darauf hin, dass die Biomarker in dem sehr kleinen afro-alpinen Einzugsgebiet kein Pre-aging vorweisen, was auf eine kurze Verweildauer oder/und eine hohe aquatische Produktivität schließen lässt. Die vorherrschende autochthone Produktion von organischem Material in dem im Vergleich zur Größe des Einzugsgebiets relativ großen See wurde durch relativ niedrige TOC/N Verhältnisse, relativ positive δ13C Werte und niedrige Werte der Zucker-Biomarker-Verhältnisse nachgewiesen. Der aquatische Ursprung von Fucose wird außerdem durch einen methodischen Vergleich von δ18Ofucose mit dem rein aquatischen δ18Odiatom Rekord unterstützt. Die gute Korrelation und ähnliche Amplitude von δ18Odiatom und δ18Ofucose (7,9 ‰ bzw. 7,1 ‰) unterstreichen nicht nur das Potenzial von δ18O-Zucker-Analysen in paläoklimatischen Studien, sondern lassen auch den Schluss zu, dass δ18Ofucose im Garba Guracha δ18OSeewasser widerspiegelt. Ohne den Einfluss des 'Amount effects' und des 'Source effects' völlig auszuschließen, interpretieren wir den δ18O-Datensatz des Garba Guracha daher als das Verhältnis von Niederschlag zu Verdunstung. Die hydrologische Vergangenheit des Garba Guracha wird von regionalen und nordhemisphärischen klimatischen Veränderungen beeinflusst. Zu Beginn des Holozäns nahmen die Niederschläge zu, was zu einem überlaufenden See zwischen ∼ 10 und ∼ 7 cal ka BP führte (erkennbar an den negativsten δ18O-Werten im gesamten Kern). Diese Phase entspricht der African Humid Period, einer räumlich unterschiedlich ausgeprägten feuchten Phase im äquatorialen und nördlichen Afrika, die durch eine verstärkte Aktivität des Westafrikanischen Monsuns und, im Fall der östlich gelegenen Bale Mountains, des Ostafrikanischen Monsuns bedingt wurde. Während die hydrologischen Veränderungen der AHP in Ostafrika durch meridionale Klimaprozesse angetrieben zu werden scheinen, zeigt das hochgelegene Garba Guracha Archiv zusätzliche Ähnlichkeiten mit rekonstruierten Monsunveränderungen in Oman. Eine kontinuierliche Verschiebung hin zu positiveren δ18O-Werten beginnt um 7 cal ka BP und deutet auf einen allmählichen Übergang von feuchtem zu trockenem Klima hin. Die Temperaturen am Garba Guracha wurden mit Hilfe einer modifizierten MBT'5ME Kalibrierung durch Hinzunahme von 6-Methyl-brGDGT IIIa' rekonstruiert (MBT'5ME Bale-Mountain-Index - r2 = 0,93, p < 0,05). Eine Anpassung der Kalibration war nötig, da die 6-Methyl-brGDGTs in den modernen Seesedimenten der Bale Mountains in bislang unbekannten Mengen auftreten und die Temperatur-Kalibrierung beeinflussen. Die rekonstruierten Temperaturänderungen sind stark von überregionalen klimatischen Einflüssen, wie Insolationsveränderungen und der AHP beeinflusst. Zusätzliche lokale Einflüsse, wie noch nicht abgeschmolzene Eismassen im Einzugsgebiet oder die Veränderungen der Hydrologie sind nicht auszuschließen. Im hochgelegenen Garba Guracha herrschten kalte Temperaturen, bis es kurz nach Beginn des Holozäns zu einer deutlichen Erwärmung (3,0 °C in weniger als 600 Jahren) kam. Zwischen 9 und 6 cal ka BP herrschte ein thermisches Maximum, das mit feuchten Bedingungen zusammenfiel und gefolgt war von einem Temperaturrückgang der bis 1.4 cal ka BP andauerte. Die Ergebnisse dieser Dissertation zeigen regionale und globale Antriebsmechanismen für klimatische Veränderungen in den Bale Mountains auf und erweitern damit das paläoklimatische Wissen über das Horn von Afrika. Der innovative methodische Ansatz dieser Arbeit hebt das Potenzial von δ18O-Zuckeranalysen und n-Alkan-Datierungen hervor. Darüber hinaus unterstreichen die Ergebnisse die Notwendigkeit einer verstärkten Grundlagenforschung, wie z. B. lokaler brGDGT-Kalibrierungsstudien, um die bestehenden wissenschaftlichen Konzepte voranzutreiben und zu präzisieren.:1.1 Table of Content List of Abbreviations v List of Tables vi List of Figures vii List of papers ix Abstract x Zusammenfassung xii Acknowledgements xiv 1 Introduction 1 1.1 Motivation 2 1.2 Objectives of the thesis 5 1.3 Background – The Bale Mountains and biomarker 6 1.3.1 Study area and archive 6 1.3.2 A short introduction to selected biomarkers applied in environmental geochemistry 8 1.4 Methods used in the thesis 10 1.4.1 Monosaccharide sugar biomarkers 11 1.4.2 Total lipid extraction for n-alkane and brGDGTs analyses 11 1.4.3 Branched Glycerol Dialkyl Glycerol Tetraether analyses 12 1.4.4 Biogeochemical analyses 13 1.4.5 Radiocarbon dating 13 1.4.6 Age depth model 13 1.5 Structure of the thesis 15 1.6 References 16 2 Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications 27 Abstract 28 2.1 Introduction 29 2.1.1 Study site 29 2.2 Material and Methods 31 2.2.1 Chronology and dating 31 2.2.2 XRF scanning 34 2.2.3 Biogeochemical analyses 34 2.2.4 n-Alkane and sugar quantification 35 2.3 Results 35 2.3.1 The sedimentary sequence – Master core and lithofacies 35 2.3.2 Chronology 37 2.3.3 Geochemistry 39 2.4 Discussion 41 2.4.1 Chronology 41 2.4.2 Origin of organic matter 43 2.4.3 Environmental implications 45 2.4.4 Comparison with lake level and other records 49 2.5 Conclusions 50 2.6 Acknowledgements 50 2.7 References 51 3 The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ18O records of sugar biomarker and diatoms 61 Abstract 62 3.1 Introduction 62 3.1.1 Regional setting 64 3.2 Material and methods 66 3.2.1 Material and sampling 66 3.2.2 Compound-specific δ18O analyses of sugar biomarkers 66 3.2.3 δ18O analyses of diatoms 67 3.3 Results 68 3.3.1 δ18Ofuc record of Garba Guracha 68 3.3.2 δ18Odiatom record of Garba Guracha 69 3.4 Discussion 69 3.4.1 The Garba Guracha δ18Osugar record - lake or leaf water? 69 3.4.2 The Garba Guracha δ18Odiatom record 70 3.4.3 Comparison of reconstructed δ18Olake water from δ18Ofuc versus δ18Odiatom 71 3.4.4 Paleoclimatic significance and proxy interpretation 72 3.4.5 Comparison with other records 75 3.5 Conclusions 77 3.6 Acknowledgements 78 3.7 References 78 4 A Holocene temperature (brGDGT) record from Garba Guracha, a high-altitude lake in Ethiopia 89 Abstract 90 4.1 Introduction 90 4.1.1 Regional setting 93 4.2 Material and Methods 94 4.2.1 Material and Sampling 94 4.2.2 Sample preparation and analysis 95 4.2.3 BrGDGTs – structure, statistical methods and proxy calculation 96 4.2.4 Quantitative data analyses 97 4.3 Result 97 4.3.1 BrGDGT patterns of surface sediments from lakes in the Bale Mountains 97 4.3.2 BrGDGT patterns of the Garba Guracha sediment core 100 4.4 Discussion 103 4.4.1 Possible MAT calibration functions inferred from the expanded eastern African surface sediment dataset 103 4.4.2 Paleotemperature reconstructions for the Garba Guracha sedimentary record - comparison of the different calibrations 104 4.4.3 Paleotemperature reconstructions for the Garba Guracha sedimentary record – regional comparison 106 4.5 Conclusions 111 4.6 Acknowledgements 111 4.7 References 112 5 Synthesis 121 5.1 Sedimentation and chronology - What is the time frame and age depth function of the Garba Guracha core? 122 5.2 Source identification What is the origin of the organic material in the Garba Guracha sediment core? 125 5.3 Hydrology δ18O as a proxy for Garba Guracha evaporation history 126 5.4 Hydrology δ2H – as a proxy for the Garba Guracha precipitation history 128 5.5 Temperature - brGDGTs - as a proxy for Garba Guracha MAT history 129 5.6 Garba Guracha environmental and climate reconstruction – Why and how has the climate changed? 131 5.6.1 Deglaciation 132 5.6.2 North hemisphere forcings in the Garba Guracha catchment during the Younger Dryas period 132 5.6.3 Changing climatic conditions beginning of the Holocene 133 5.6.4 The warm African Humid Period 133 5.6.5 The termination of the African Humid Period 134 5.6.6 The Late Holocene 135 5.7 Garba Guracha – Climatic implications and driving mechanisms 136 5.7.1 Comparison of high and low altitudes in eastern Africa 136 5.7.2 Atmospheric circulation 138 5.8 References 144 6 Conclusions and Outlook 157 A Supplements to Chapter 2 162 B Supplements to Chapter 3 168 C Supplements to Chapter 4 173 D Supplements to Chapter 5 182 / While climate change and global warming are affecting eastern Africa today, the understanding of past climatic changes is limited. Especially during the last 15.000 years, eastern Africa has experienced spatially complex climatic changes. Although several paleoclimatic studies have been conducted in eastern Africa, reconstructing temperature changes and the hydrological history of lake archives, the driving mechanisms and teleconnections are yet not fully understood. A deeper understanding is precluded by (i) the lack of long, high-quality records of environmental change, especially in the Horn of Africa region, (ii) the lack of high altitude records, and (iii) insufficiently studied regions like eastern Ethiopia and Somalia. One of the region's most understudied high-altitude areas are the Bale Mountains, even though they encompass the continent's largest area above 4000 m a. s. l. This dissertation aims to further reduce the current lack of paleoclimatic reconstructions in high altitudes in the understudied Horn of Africa region. High-altitude perennial lakes, especially cirque lakes, are valuable archives for paleoclimate and environmental reconstructions, yielding continuous sedimentation undisturbed by human activity. The only perennial lake in the Bale Mountains, the Garba Guracha, lies in the afro-alpine zone at 3950 m a. s. l. Previous paleolimnological research revealed that Garba Guracha comprises a continuous paleoclimatic and environmental sedimentary record since the last deglaciation. In order to enhance the paleoclimatic knowledge of the Bale Mountains and hence of eastern Africa, new innovative proxies, e.g. brGDGTs, δ18Ofucose, δ18Odiatom, and δ2Hn alkane were applied to newly retrieved sediment cores of Garba Guracha. The application of these analyses and the interpretation of the results imply a deeper understanding of the retrieved sediment cores, concerning mainly sedimentology, chronology and organic matter source identification. The high resolution chronology of Garba Guracha, established using different dating methods and compounds (210Pb dating, radiocarbon dating of bulk sedimentary OM, compound class specific n alkanes, and charcoal), yields a basal age of ∼ 16 cal ka BP. The geochemical correlation of tephra layers in the Garba Guracha sediments to dated tephra layers of the region provides an external age control, further supporting the robustness of the new Garba Guracha chronology and the non existence of systematic age offsets. Similar ages obtained for n alkanes and bulk sediments suggest no pre aging of the biomarker in the very small afro-alpine catchment indicating short residence times or/and high aquatic productivity. Predominant autochthonous production of organic matter in the relative large lake compared to the catchment size has been proven by relatively low TOC/N ratios and relatively positive δ13C values. The aquatic origin of the sugar biomarker fucose is further supported by a methodological comparison of δ18Ofucose to a pure aquatic δ18Odiatom record. The good correlation and similar ranges of δ18Odiatom and δ18Ofucose (7.9 ‰ and 7.1 ‰, respectively) not only highlight the potential of δ18Osugar analyses in paleoclimatic studies but also lead to the conclusion that the Garba Guracha δ18Ofucose record reflects δ18Olake water. Therefore, without completely excluding the influence of the ‘amount effect’ and the ‘source-effect’, we interpret the record to reflect primarily the precipitation to evaporation ratio (P/E). The hydrological history of Garba Guracha is influenced by regional and northern hemisphere climatic changes. Precipitation increased at the onset of the Holocene, resulting in an overflowing lake between ∼ 10 and ∼ 7 cal ka BP (noted by the most negative δ18O values in the record). This humid phase corresponds to the African Humid Period (AHP), a spatially complex humid phase across equatorial and northern Africa, driven by enhanced West African Monsoon (WAM) and, in the case of the easterly-situated Bale Mountains, East African Monsoon (EAM) activity. While hydrological changes during the AHP in eastern Africa seem to be driven by meridional climatic processes, the high-altitude Garba Guracha archive shows additional similarities to reconstructed monsoonal changes in Oman. A continuous transition towards more positive δ18O values begins at 7 cal ka BP and indicates a gradual shift from humid to drier climate. The reconstructed temperature history is strongly linked to supraregional climatic changes associated with insolation forcing and the AHP, as well as with local anomalies associated with catchment deglaciation and hydrology. Cold temperatures prevailed in the high-altitude Garba Guracha until significant warming (3.0 °C in less than 600 years) occurred shortly after the Holocene onset. A thermal maximum prevailed between 9 and 6 cal ka BP, coinciding with humid conditions, followed by a temperature decrease until 1.4 cal ka BP. The temperatures at the Garba Guracha were reconstructed using a modified MBT'5ME calibration by adding 6 methyl brGDGT IIIa' (resulting in the MBT'5ME Bale Mountain index, r2 = 0.93, p < 0.05) due to an uncommon variation in 6 methyl brGDGTs in the modern lake surface sediment samples. The results of this dissertation reveal regional and global driving mechanisms of climatic changes in the Bale Mountains, further expanding paleoclimatic knowledge about the Horn of Africa. The innovative methodological approach of this thesis highlights the potential of δ18Osugar analyses and n alkane dating. Moreover, the results underline the need for intensified basic research like local brGDGT calibration studies to advance and specify existing scientific concepts.:1.1 Table of Content List of Abbreviations v List of Tables vi List of Figures vii List of papers ix Abstract x Zusammenfassung xii Acknowledgements xiv 1 Introduction 1 1.1 Motivation 2 1.2 Objectives of the thesis 5 1.3 Background – The Bale Mountains and biomarker 6 1.3.1 Study area and archive 6 1.3.2 A short introduction to selected biomarkers applied in environmental geochemistry 8 1.4 Methods used in the thesis 10 1.4.1 Monosaccharide sugar biomarkers 11 1.4.2 Total lipid extraction for n-alkane and brGDGTs analyses 11 1.4.3 Branched Glycerol Dialkyl Glycerol Tetraether analyses 12 1.4.4 Biogeochemical analyses 13 1.4.5 Radiocarbon dating 13 1.4.6 Age depth model 13 1.5 Structure of the thesis 15 1.6 References 16 2 Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications 27 Abstract 28 2.1 Introduction 29 2.1.1 Study site 29 2.2 Material and Methods 31 2.2.1 Chronology and dating 31 2.2.2 XRF scanning 34 2.2.3 Biogeochemical analyses 34 2.2.4 n-Alkane and sugar quantification 35 2.3 Results 35 2.3.1 The sedimentary sequence – Master core and lithofacies 35 2.3.2 Chronology 37 2.3.3 Geochemistry 39 2.4 Discussion 41 2.4.1 Chronology 41 2.4.2 Origin of organic matter 43 2.4.3 Environmental implications 45 2.4.4 Comparison with lake level and other records 49 2.5 Conclusions 50 2.6 Acknowledgements 50 2.7 References 51 3 The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ18O records of sugar biomarker and diatoms 61 Abstract 62 3.1 Introduction 62 3.1.1 Regional setting 64 3.2 Material and methods 66 3.2.1 Material and sampling 66 3.2.2 Compound-specific δ18O analyses of sugar biomarkers 66 3.2.3 δ18O analyses of diatoms 67 3.3 Results 68 3.3.1 δ18Ofuc record of Garba Guracha 68 3.3.2 δ18Odiatom record of Garba Guracha 69 3.4 Discussion 69 3.4.1 The Garba Guracha δ18Osugar record - lake or leaf water? 69 3.4.2 The Garba Guracha δ18Odiatom record 70 3.4.3 Comparison of reconstructed δ18Olake water from δ18Ofuc versus δ18Odiatom 71 3.4.4 Paleoclimatic significance and proxy interpretation 72 3.4.5 Comparison with other records 75 3.5 Conclusions 77 3.6 Acknowledgements 78 3.7 References 78 4 A Holocene temperature (brGDGT) record from Garba Guracha, a high-altitude lake in Ethiopia 89 Abstract 90 4.1 Introduction 90 4.1.1 Regional setting 93 4.2 Material and Methods 94 4.2.1 Material and Sampling 94 4.2.2 Sample preparation and analysis 95 4.2.3 BrGDGTs – structure, statistical methods and proxy calculation 96 4.2.4 Quantitative data analyses 97 4.3 Result 97 4.3.1 BrGDGT patterns of surface sediments from lakes in the Bale Mountains 97 4.3.2 BrGDGT patterns of the Garba Guracha sediment core 100 4.4 Discussion 103 4.4.1 Possible MAT calibration functions inferred from the expanded eastern African surface sediment dataset 103 4.4.2 Paleotemperature reconstructions for the Garba Guracha sedimentary record - comparison of the different calibrations 104 4.4.3 Paleotemperature reconstructions for the Garba Guracha sedimentary record – regional comparison 106 4.5 Conclusions 111 4.6 Acknowledgements 111 4.7 References 112 5 Synthesis 121 5.1 Sedimentation and chronology - What is the time frame and age depth function of the Garba Guracha core? 122 5.2 Source identification What is the origin of the organic material in the Garba Guracha sediment core? 125 5.3 Hydrology δ18O as a proxy for Garba Guracha evaporation history 126 5.4 Hydrology δ2H – as a proxy for the Garba Guracha precipitation history 128 5.5 Temperature - brGDGTs - as a proxy for Garba Guracha MAT history 129 5.6 Garba Guracha environmental and climate reconstruction – Why and how has the climate changed? 131 5.6.1 Deglaciation 132 5.6.2 North hemisphere forcings in the Garba Guracha catchment during the Younger Dryas period 132 5.6.3 Changing climatic conditions beginning of the Holocene 133 5.6.4 The warm African Humid Period 133 5.6.5 The termination of the African Humid Period 134 5.6.6 The Late Holocene 135 5.7 Garba Guracha – Climatic implications and driving mechanisms 136 5.7.1 Comparison of high and low altitudes in eastern Africa 136 5.7.2 Atmospheric circulation 138 5.8 References 144 6 Conclusions and Outlook 157 A Supplements to Chapter 2 162 B Supplements to Chapter 3 168 C Supplements to Chapter 4 173 D Supplements to Chapter 5 182

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