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Acesta excavata (Fabricius, 1779) is a slow growing bivalve from the Limidae family and is often found associated with cold-water coral reefs along the European continental margin. Here we present the compositional variability of frequently used proxy elemental ratios (Mg/ Ca, Sr/Ca, Na/Ca) measured by laser-ablation mass spectrometry (LA-ICP-MS) and com- pare it to in-situ recorded instrumental seawater parameters such as temperature and salin- ity. Shell Mg/Ca measured in the fibrous calcitic shell section was overall not correlated with seawater temperature or salinity; however, some samples show significant correlations with temperature with a sensitivity that was found to be unusually high in comparison to other marine organisms. Mg/Ca and Sr/Ca measured in the fibrous calcitic shell section display significant negative correlations with the linear extension rate of the shell, which indicates strong vital effects in these bivalves. Multiple linear regression analysis indicates that up to 79% of elemental variability is explicable with temperature and salinity as independent pre- dictor values. Yet, the overall results clearly show that the application of Element/Ca (E/Ca) ratios in these bivalves to reconstruct past changes in temperature and salinity is likely to be complicated due to strong vital effects and the effects of organic material embedded in the shell. Therefore, we suggest to apply additional techniques, such as clumped isotopes, in order to exactly determine and quantify the underlying vital effects and possibly account for these. We found differences in the chemical composition between the two calcitic shell lay- ers that are possibly explainable through differences of the crystal morphology. Sr/Ca ratios also appear to be partly controlled by the amount of magnesium, because the small magne- sium ions bend the crystal lattice which increases the space for strontium incorporation. Oxi- dative cleaning with H2O2 did not significantly change the Mg/Ca and Sr/Ca composition of the shell. Na/Ca ratios decreased after the oxidative cleaning, which is most likely a leaching effect and not caused by the removal of organic matter.
Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Hyrrokkin sarcophaga is a parasitic foraminifer that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Lophelia pertusa. Here, we present measurements of the elemental and isotopic composition of this parasitic foraminifer for the first time, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe micro analysis (EPMA) and mass spectrometry (MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest L. pertusa, which could be an indication that dissolved host carbonate material is utilised in shell calcification, given that the aragonite of L. pertusa has a naturally higher Sr concentration compared to the calcite of A. excavata.Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on20 L. pertusa, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn/Ca ratios in foraminifers that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifer, these data also indicate that the geochemistry of this parasitic foraminifer is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Geochemical investigations on biogenic carbonates are commonly conducted to reconstruct the environmental conditions of the past. However, different carbonate producers incorporate elements to varying degrees, due to biological vital effects. Detecting and quantifying these effects is crucial to produce reliable reconstructions. These paleoreconstructions are of great importance to evaluate the consequences of our recent climate change and identify control mechanisms on the distribution of endangered species such as Desmophyllum pertusum. In chapter three we tested Mg/Ca, Sr/Ca and Na/Ca ratios on this species, among other coldwater scleractinians, to test if they provide reliable proxy information. The results reveal no apparent control of Mg/Ca or Sr/Ca ratios through seawater temperature, salinity or pH. Na/Ca ratios appear to be partly controlled by the seawater temperature, which is also true for other aragonitic organisms such as warm-water corals and the bivalve Mytilus edulis. However, a large variability complicates possible reconstructions by means of Na/Ca. In addition, we explore different models to explain the apparent temperature effect on Na/Ca ratios based on temperature sensitive Na and Ca pumping enzymes.
The bivalve Acesta excavata is commonly found in cold-water coral reefs among the North Atlantic, together with D. pertusum. Multiple linear regression analysis, presented in chapter four, indicates that up to 79% of the elemental variability in Mg/Ca, Sr/Ca and Na/Ca is explainable with temperature and salinity as independent predictor variables. Vital effects, for instance growth rate effects, are evident and make paleoreconstructions not feasible. Furthermore, organic material embedded in the shell, as well as possible stress effects can drastically change the elemental composition. Removal of these organic matrices from bulk samples for LA-ICP-MS (laser ablation inductively coupled mass spectrometer) measurements by means of oxidative cleaning is not possible, but Na/Ca ratios decrease after this cleaning. This is presumably an effect of leaching and not caused by the removal of organic matrices.
Interesting biogeochemical relations were found in the parasitic foraminifera H. sarcophaga. We report Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca ratios measured in H. sarcophaga from two different host species (A. excavata and D. pertusum) in chapter five. Sr/Ca ratios are significantly higher in foraminifera that lived on D. pertusum. This could indicate that dissolved host material is utilized in shell calcification of H. sarcophaga, given the naturally higher strontium concentration in the aragonite of D. pertusum. Mn/Ca ratios are highest in foraminifera that lived on A. excavata but did not fully penetrate the host’s shell. Most likely, this represents a juvenile stadium of the foraminifera during which it feeds on the organic
periostracum of the bivalve, which is enriched in Mn and Fe. The isotopic compositions are similarly affected, both δ18O and δ13C values are significantly lower in foraminifera that lived 23on D. pertusum compared to specimen that lived on A. excavata. Again, this might represent the uptake of dissolved host material or different pH regimes in the calcifying fluid of the hosts (bivalve < 8, coral > 8) that control the extent of hydration/hydroxylation reactions. Temperature reconstructions are possible using stable oxygen isotopes on this foraminifera species; however, the results are only reliable if the foraminifera lived on A. excavata. Samples of H. sarcophaga from D. pertusum would lead to overestimations of the seawater temperature due to the lower δ18O values.
Apart from biological vital effects, storage and preservation methods can significantly change the geochemical composition of different marine biogenic carbonates. In chapter six this is presented on the example of ethanol preservation, a common technique to allow extended storage of biogenic samples. The investigation reveals a significant decrease of Mg/Ca and Na/Ca ratios even after only 45 days storage in ultrapure ethanol. Sr/Ca ratios on the other hand are not influenced.
Besides temperature, salinity and pH further environmental parameters are important such as nutrient availability, especially for the distribution of cold-water corals. In chapter seven we extend the investigations on A. excavata by including the elemental ratios Ba/Ca, Mn/Ca and P/Ca. We expected P/Ca to be helpful in the otherwise difficult process of dentifying growth increments. Based on our observations we had to refute this theory. P/Ca ratios are not systematically enriched in the vicinity of growth lines. Instead, we found a regular sequence of peaks of Ba/Ca, P/Ca and Mn/Ca. This sequence as well as the peaks in general are potentially caused by equential blooms of different algae, diatoms and other planktonic organisms ...
Im Anschluss an die globale Finanzkrise von 2008 lässt sich in vielen deutschen Städten eine neue Welle der Gentrifizierung beobachten. Am Beispiel des traditionellen Arbeiterviertels Gallus in Frankfurt am Main zielt der Beitrag darauf ab, die gegenwärtigen Verdrängungsprozesse aus dem spezifischen Zusammenspiel von stadtpolitischen Aufwertungsbestrebungen und immobilienwirtschaftlichen Verwertungsstrategien zu erklären. Vertreten wird dabei die These, dass die Frankfurter Stadtpolitik, entsprechend ihrer neoliberalen Ausrichtung, im Gallus jahrelang Gentrifizierungsprozesse und die Entstehung einer Ertragslücke zwischen gegenwärtiger und potenzieller Verwertung aktiv gefördert hat – letztere aber erst jetzt im Zuge der Krise an Relevanz gewinnt. Nahezu idealtypisch kann man daher anhand des Gallus zeigen, dass Gentrifizierung wesentlich von lokalen politischen Kräfteverhältnissen abhängt, wobei der Rhythmus jedoch von immobilienwirtschaftlichen Verwertungszyklen diktiert wird.
Die angespannte Lage am Wohnungsmarkt hat in vielen Städten eine neue Welle von Verdrängungsprozessen induziert und insbesondere die Situation einkommensschwacher Haushalte häufig prekär werden lassen. Angesichts dieser Entwicklungen haben sich vielerorts mietenpolitische Bewegungen konstituiert, die sich für eine Abkehr von einer neoliberalisierten und zunehmend finanzialisierten Wohnungsversorgung einsetzen. Lisa Vollmer nimmt in ihrer Forschungsarbeit zwei solcher Bewegungen in den Blick und fragt danach, wie sich politische Kollektivität in den alltäglichen Praktiken von Mieter*innen in Berlin bzw. New York formiert.
Die lakustrinen Sedimente im Vorotan-Becken (Armenien) wurden palynologisch untersucht. Aus den Ergebnissen konnte die Vegetationsgeschichte im Südlichen Kaukasus während des Frühpleistozäns teilweise rekonstruiert werden.
Bei den Sedimenten handelt es sich um diatomeenreiche Tone, Silte und Feinsande, in denen Pollen gut und pflanzliche Makroreste ausgezeichnet erhalten sind. Die Datierung ist durch die Kombination von Paläomagnetik und 39Ar/40Ar-Methode eindeutig: Die Sedimente decken den Beginn der „mid Pleistocene transition“ (1?110?–?960 ka) ab.
An zehn Aufschlüssen wurden insgesamt 506 Sedimentproben genommen und die darin enthaltenen Pollen untersucht. So konnten insgesamt 64 Taxa nachgewiesen werden. Sie wurden in Pollenprofilen zusammengefasst und ökologisch bewertet. Die erhobenen Daten wurden zudem einer Faktorenanalyse und einer Clusteranalyse unterzogen, deren Ergebnisse ebenfalls in die Pollenprofile eingingen.
Die Pollenprofile lassen deutlich regionale Vegetationszyklen während des Frühpleistozäns erkennen. Diese Zyklen werden ausführlich beschrieben und mit Ergebnissen anderer Autoren aus dem Mittelmeerraum verglichen. Auch ein Bezug zur rezenten Vegetation im Südlichen Kaukasus und den angrenzenden Gebieten wird hergestellt.
Die Paläovegetation im Südlichen Kaukasus ist demnach während des Frühpleistozäns geprägt von einem Vegetationsmosaik aus Grassteppe und offenen Wäldern. Je nach Klima lassen sich Einflüsse von angrenzenden Vegetationszonen erkennen: borealer Nadelwald der Höhenlagen des Kaukasus, thermophiler Laubwald der euxinischen und hyrkanischen Wälder sowie xerotherme Steppe des Nordiran.
Während der Interglaziale herrscht eine Waldsteppe aus thermophilem Laubwald (z.?B. Quercus, Carpinus, Ulmus, Zelkova, Tilia) vor, in der bei starken Erwärmungsphasen die Grassteppe deutlich dominiert und die Wälder wohl an Nordhänge und in Uferbereiche zurückgedrängt werden. In den Glazialphasen finden sich zunehmend Koniferen in der Vegetation (z.?B. Tsuga, Abies, Picea, Pinus) – bis hin zu einem nahezu geschlossenen Kiefernwald am Ende des ersten lang andauernden Glazials MIS 30.
Es zeigt sich, dass sich die einzelnen Klimazyklen in der Ausprägung der Vegetation signifikant unterscheiden. Hierbei spielt sowohl die Amplitude der Erwärmung als auch die Dauer der jeweiligen Phase eine Rolle.
Der Vergleich mit anderen Untersuchungen zeigt, dass die Vegetationszyklen im Südlichen Kaukasus teilweise deutlich anders verlaufen als im westlichen, zentralen und östlichen Mittelmeerraum. Entlang einer Ost-West-Achse ist hier ein „Vegetationsgradient“ zu erkennen.
Das hat Auswirkungen auf die Interpretation der Ausbreitung früher Menschen aus Afrika nach Eurasien. Es ist davon auszugehen, dass sich nicht jeder Vegetationszyklus des Frühpleistozäns gleichermaßen gut für ein Vordringen nach Eurasien eignete. Geeignete Bedingungen (offene Landschaft, Vegetationsmosaik, warmes Klima) herrschten im Südlichen Kaukasus vor allem während stark ausgeprägter Interglaziale. Dagegen brachten lang anhaltende Glazialphasen wohl eher lebensfeindlichere Bedingungen für Homo erectus.
Weil in den südlichen Regionen Europas teilweise eine stark abweichende Vegetation während der unterschiedlichen Klimaphasen vorherrschte, ist es naheliegend, dass der Südliche Kaukasus für die frühen Menschen eine Rolle als Refugium spielte.
Deutlich zeichnen sich in den Ergebnissen Veränderungen in der Vegetation beim Übergang von den obliquitätsdominierten 41-ka-Klimazyklen zu den exzentrizitätsbestimmten 100-ka-Zyklen ab („mid Pleistocene transition“). Diese Veränderungen haben sich sicherlich auch auf die Population der Menschen ausgewirkt und größere Wanderbewegungen und/oder Anpassungen hervorgerufen. Möglicherweise haben in dieser drastischen Veränderung sogar kulturelle Entwicklungen ihren Anfang – zum Beispiel die Nutzbarmachung des Feuers.
Droughts are anticipated to intensify in many parts of the world due to climate change. However, the issue of drought definition, namely the diversity of drought indices, makes it difficult to compare drought assessments. This issue is widely known, but its relative importance has never been quantitatively evaluated in comparison to other sources of uncertainty. Here, encompassing three drought categories (meteorological, agricultural, and hydrological droughts) with four temporal scales of interest, we evaluated changes in the drought frequency using multi-model and multi-scenario simulations to identify areas where the definition issue could result in pronounced uncertainties and to what extent. We investigated the disagreement in the signs of changes between drought definitions and decomposed the variance into four main factors: drought definitions, greenhouse gas concentration scenarios, global climate models, and global water models, as well as their interactions. The results show that models were the primary sources of variance over 82% of the global land area. On the other hand, the drought definition was the dominant source of variance in the remaining 17%, especially in parts of northern high-latitudes. Our results highlight specific regions where differences in drought definitions result in a large spread among projections, including areas showing opposite signs of significant changes. At a global scale, 7% of the variance resulted independently from the definition issue, and that value increased to 44% when 1st and 2nd order interactions were considered. The quantitative results suggest that by clarifying hydrological processes or sectors of interest, one could avoid these uncertainties in drought assessments to obtain a clearer picture of future drought change.
Tectonics and geothermal gradients from subduction to collision in the NW Variscan Iberian Massif
(2022)
The earliest tectonometamorphic record of tectonic slices incorporated to the base of an orogen holds the key to understand how an orogen is built. The tectonic pile of the NW Iberian section of the Variscan Orogen includes tectonic slices separated by crustal-scale thrusts. The earliest tectonometamorphic record in the uppermost parautochthon is calculated at 11–14 kbar and 450–500°C (P-T gradient about 13°C/km), suggesting a subduction-related metamorphic recrystallization at lower pressure than the overlying Lower Allochthon. Early conditions calculated in the autochthon (9–10 kbar and 425–450°C; 16°C/km) point to a relatively ‘cold’ collisional setting. Higher thermal gradients obtained from some sections of the autochthon (11–12 kbar and 700–725°C; 21°C/km) and the Lower Parautochthon (7.5 kbar and 550–700°C; 24–31°C/km), correspond to more advanced and ‘hot’ stages of collision. New U–Pb monazite geochronology indicates a 318–311 Ma age for the final formation of HT domes in the region. We propose the rapid decrease in P-T gradient (from <10 to 16°C/km) documents a fail to sustain further burial along a regular subduction zone. We consider the subsequent increase in the geothermal gradient (from 16 to 31°C/km) as the culmination of previous crustal accretion and the onset of crustal underthrusting and later processes in a collisional stage. We propose these switches in the early tectonometamorphic record of individual tectonic slices as potential markers to track the transition from subduction to collision in collisional orogens.
Finanzielle Armut prägt Mobilitätspraktiken und kann dabei zum Prozess von mobilitätsbezogener sozialer Exklusion beitragen. Zu den Personen, deren Armutsrisiko besonders hoch ist, zählen in Deutschland Haushalte mit Kindern, insbesondere Alleinerziehende. Ältere Menschen haben nicht die höchste Armutsgefährdung, jedoch besteht bei ihnen das Risiko von Verharrung in Armut, da die Möglichkeiten, die finanzielle Situation aus eigener Kraft zu ändern mit zunehmendem Alter sinken.
Um ein tieferes Verständnis davon zu erhalten, wie finanzielle Armut die Mobilitätspraktiken und soziale Teilhabe von Haushalten mit Kindern sowie älteren Menschen prägt, wurden mit diesen beiden Personengruppen problemzentrierte Interviews in Ronnenberg (Region Hannover) geführt und analysiert. Die Ergebnisse belegen, dass, wenngleich alle Befragten mit ähnlich geringen finanziellen Ressourcen haushalten und Verzicht sowie Abwägungsprozesse notwendig sind, sich ihre Mobilitätspraktiken und Alltagsbewältigungsstrategien unterscheiden, was sich in zwei Typologien widerspiegelt. Erstens, eine Typologie der Mobilitätspraktiken von Haushalten mit Kindern: (i) autozentriert, (ii) autoreduziert, (iii) ÖPNV-orientiert und (iv) nichtmotorisiert. Zweitens, eine Typologie älterer Menschen anhand ihrer Mobilitätspraktiken: (i) aktive ältere Menschen mit vielseitigen sozialen Interaktionen, (ii) nachbarschaftsorientierte ältere Menschen mit lokalen Kontakten und (iii) ältere Menschen, die überwiegend zu Hause sind und wenig soziale Kontakte haben.
Um herauszufinden, inwiefern mobilitätsbezogene Barrieren der sozialen Teilhabe reduziert werden können, wurden fünf Maßnahmen bezüglich ihrer Wirkung auf die Mobilitätspraktiken einkommensarmer Haushalte mit Kindern untersucht: einerseits die Wirkung des 9-Euro-Tickets anhand von problemzentrierten Interviews mit einkommensarmen Haushalten mit Kindern, andererseits anhand von Expert:inneninterviews die Wirkung von Radlernkursen für Frauen mit Migrationshintergrund, eines Mietertickets, eines Quartierstickets und der Verbesserung der Nahraum- und Aufenthaltsqualität am Beispiel von Tempo 30. Die Ergebnisse zum 9-Euro-Ticket belegen, dass ein erschwingliches ÖPNV-Ticket erheblich zur Reduzierung mobilitätsbezogener Barrieren der sozialen Teilhabe im Armutskontext beiträgt. Die Expert:inneninterviews zeigen auf, dass eine Förderung des Umweltverbunds zielführend ist, um zu einer sozial-ökologischen Verkehrswende beizutragen und insbesondere Maßnahmenbündel Wirkung auf die Reduzierung von mobilitätsbezogenen Barrieren der sozialen Teilhabe entfalten.
Die Erkenntnisse dieser Dissertation ergänzen den wissenschaftlichen Forschungstand um ein tiefergehendes Verständnis der Wirkung von finanzieller Armut auf die Mobilitätspraktiken und soziale Teilhabe von Haushalten mit Kindern und älteren Menschen und helfen dabei, Maßnahmen zur Reduzierung mobilitätsbezogener Barrieren der sozialen Teilhabe zu konzipieren und umzusetzen.
Seasonal forecasting systems still have difficulties predicting temperature over continental regions, while their performance is better over some maritime regions. On the other hand, the land surface is a substantial source of (sub-)seasonal predictability. A crucial land surface component in focus here is the snow cover, which stores water and modulates the surface radiation balance. This paper’s goal is to attribute snow cover seasonal forecasting biases and lack of skill to either initialization or parameterization errors. For this purpose, we compare the snow representation in five seasonal forecasting systems (from DWD, ECMWF, Météo-France, CMCC, and ECCC) and their performances in predicting snow and 2-m temperature over a Siberian region against ERA5 reanalysis and station data. Although all systems use similar atmospheric and land initialization approaches and data, their snow and temperature biases differ in sign and amplitude. Too-large initial snow biases persist over the forecast period, delaying and prolonging the melting phase. The simplest snow scheme (used in DWD’s system) shows too-early and fast melting in spring. However, systems including multi-layer snow schemes (Météo-France and CMCC) do not necessarily perform better. Both initialization and parameterization are causes of snow biases, but, depending on the system, one can be more dominant.
Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound
(2022)
Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather Research and Forecasting model in large eddy simulation mode (WRF-LES). The short-term, high-resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 h and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.
We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather Research and Forecasting model in large eddy simulation mode (WRF-LES). The short-term, high-resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 h and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.
Convective rain cell properties and the resulting precipitation scaling in a warm-temperate climate
(2022)
Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low-level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge-adjusted radar dataset in a mid-latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super-CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells.
Extreme convective precipitation is expected to increase with global warming. However, the rate of increase and the understanding of contributing processes remain highly uncertain. We investigated characteristics of convective rain cells like area, intensity, and lifetime as simulated by a convection-permitting climate model in the area of Germany under historical (1976–2005) and future (end-of-century, RCP8.5 scenario) conditions. To this end, a tracking algorithm was applied to 5-min precipitation output. While the number of convective cells is virtually similar under historical and future conditions, there are more intense and larger cells in the future. This yields an increase in hourly precipitation extremes, although mean precipitation decreases. The relative change in the frequency distributions of area, intensity, and precipitation sum per cell is highest for the most extreme percentiles, suggesting that extreme events intensify the most. Furthermore, we investigated the temperature and moisture scaling of cell characteristics. The temperature scaling drops off at high temperatures, with a shift in drop-off towards higher temperatures in the future, allowing for higher peak values. In contrast, dew point temperature scaling shows consistent rates across the whole dew point range. Cell characteristics scale at varying rates, either below (mean intensity), at about (maximum intensity and area), or above (precipitation sum) the Clausius–Clapeyron rate. Thus, the widely investigated extreme precipitation scaling at fixed locations is a complex product of the scaling of different cell characteristics. The dew point scaling rates and absolute values of the scaling curves in historical and future conditions are closest for the highest percentiles. Therefore, near-surface humidity provides a good predictor for the upper limit of for example, maximum intensity and total precipitation of individual convective cells. However, the frequency distribution of the number of cells depending on dew point temperature changes in the future, preventing statistical inference of extreme precipitation from near-surface humidity.
Extreme convective precipitation events are among the most severe hazards in central Europe and are expected to intensify under global warming. However, the degree of intensification and the underlying processes are still uncertain. In this thesis, recent advances in continuous, radar-based precipitation monitoring and convection-permitting climate modeling are used to investigate Lagrangian properties of convective rain cells such as precipitation intensity, cell area, and precipitation sum and their relationship to large-scale, environmental conditions.
Firstly, convective precipitation objects are tracked in a gauge-adjusted radar-data set and the properties of these cells are related to large-scale environmental variables to investigate the observed super-Clausius-Clapeyron (CC) scaling of convective extreme precipitation. The Lagrangian precipitation sum of convective cells increases with dew point temperature at rates well above the CC-rate with increasing rates for higher dew point temperatures. These varying, high rates are caused by a covarying increase of CAPE with dew point temperature as well as the effect of high vertical wind shear causing an increase in cell area and thus precipitation sum. At the same time, cells move faster at high vertical wind shear so that Eulerian scaling rates are lower than Lagrangian but still above the CC-rate. The results show that wind shear and static instability need to be taken into account when transferring precipitation scaling under current climate conditions to future conditions. Secondly, the representation of convective cell properties in the convection-permitting climate model COSMO-CLM is evaluated. The model can simulate the observed frequency distributions of cell properties such as lifetime, area, mean and maximum intensity, and precipitation sum. The increase of area and intensity with lifetime is also well captured despite an underestimation of the intensity of the most severe cells. Furthermore, the model can represent the temperature scaling of intensity, area, and precipitation sum but fails to simulate the observed increase of lifetime. Thus, the model is suitable to study climatologies of convective storms in Germany. Thirdly, two COSMO-CLM projections at the end of the century under emission scenario RCP8.5 were investigated. While the number of convective cells and their lifetime remain approximately constant compared to present conditions, intensity and area increase strongly. The relative increase of intensity and area is largest for the highest percentiles meaning that extreme events intensify the most. The characteristic afternoon maximum of convective precipitation is damped, and shifted to later times of day which leads to an increase of nighttime precipitation in the future. Scaling rates of cell properties with dew point temperature are nearly identical in present and future in the simulation driven by the EC-Earth model which means that the upper limit of cell properties like intensity, area, and precipitation sum could be predicted from near-surface dew point temperature. However, this result could not be reproduced by the simulation driven by MIROC5 and needs further investigation.
The climate system is one of the classical examples of a complex dynamical system consisting of interacting sub-systems through mass, momentum, and energy exchange across various spatial and temporal scales. This thesis aims to detect and quantify sub-component interactions from an information exchange (IE) perspective. For this purpose, IE estimators derived from information theory are explored and applied to the available climate data obtained from observations, reanalysis, global and regional climate models. Specifically, this thesis investigates the usefulness of information theory methods for process-oriented climate model evaluation.
Firstly, methods derived from the concepts of information theory such as transfer entropy and information flow along with their linear and non-linear estimation techniques are initially tested and applied to idealized two-dimensional dynamical systems. The results revealed an expected direction and magnitude of IE providing insights into underlying dynamics. However, as expected the linear estimators are robust for linear systems but fail for non-linear systems. Though the non-linear estimators (kernel and kraskov) showed expected results for all the idealized systems, their free tuning parameters are to be tested for consistent results. Moreover, these methods are sensitive to the available time series length.
A real world example case study involving the dynamics between the Indian and Pacific oceans revealed a physically consistent bi-directional IE. However, unexpected IE was detected in the example of North Atlantic and European air temperatures indicating hidden drivers. Though IE provides insights into system dynamics, the availability of time series length and the system at hand must be carefully taken into account before inferring any possible interpretations of the results.
Quantifying the IE from El-Ni\~{n}o southern oscillation (ENSO) and Indian Ocean Dipole (IOD) to the Indian Summer Monsoon Rainfall (ISMR) with the observational and reanalysis data sets revealed that both ENSO and IOD are synergistic predictors for the inter-annual variability of the ISMR over central India i.e., the monsoon core region. Though the investigated three Global Climate Models (GCM) could not reveal the underlying IE dynamics of ENSO, IOD, and ISMR, a Regional Climate Model (RCM) simulation downscaling one of the GCMs with realistic large scale signals across the lateral boundaries showed good agreement with the observations.
Evaluating a coupled regional climate modeling system driven by two different global data sets with IE estimators revealed significant differences between the process chains linking the north-west Mediterranean sea surface temperatures, evaporation, wind speed, and the Vb-cyclone induced precipitation over Danube, Odra, and Elbe catchments in the historical period (1951-2005). Detailed investigation revealed that the north-west Mediterranean Sea in the coupled regional simulation driven by ERA-20C reanalysis corresponded to the Vb-cyclone precipitation over the three catchments while no such correspondence is noted in the EC-EARTH driven simulation. This discrepancy is attributed to the inheritance of the simulation biases from GCM into the RCM. In the future period (1965-2099), no significant changes in the processes are noted from the simulation.
Overall, this thesis used IE estimators in investigating the underlying dynamics of climate system and climate models. The estimators proved useful in providing insights into climate system dynamics assisting in a process based climate model evaluation.
Drought is understood as both a lack of water (i.e., a deficit compared to demand) and a temporal anomaly in one or more components of the hydrological cycle. Most drought indices, however, only consider the anomaly aspect, i.e., how unusual the condition is. In this paper, we present two drought hazard indices that reflect both the deficit and anomaly aspects. The soil moisture deficit anomaly index, SMDAI, is based on the drought severity index, DSI (Cammalleri et al., 2016), but is computed in a more straightforward way that does not require the definition of a mapping function. We propose a new indicator of drought hazard for water supply from rivers, the streamflow deficit anomaly index, QDAI, which takes into account the surface water demand of humans and freshwater biota. Both indices are computed and analyzed at the global scale, with a spatial resolution of roughly 50 km, for the period 1981–2010, using monthly time series of variables computed by the global water resources and the model WaterGAP 2.2d. We found that the SMDAI and QDAI values are broadly similar to values of purely anomaly-based indices. However, the deficit anomaly indices provide more differentiated spatial and temporal patterns that help to distinguish the degree and nature of the actual drought hazard to vegetation health or the water supply. QDAI can be made relevant for stakeholders with different perceptions about the importance of ecosystem protection, by adapting the approach for computing the amount of water that is required to remain in the river for the well-being of the river ecosystem. Both deficit anomaly indices are well suited for inclusion in local or global drought risk studies.
There seems to be a wide agreement in critical geographic thought that Hegel is dead, as to end up with Hegel’s idealism serves to be the starting point for the materialist project of critical geographies. This paper aims to call this starting point into question by confronting Henri Lefebvre with Slavoj Žižek. While Lefebvre, one of the pioneers of materialist geographic thought, intensively worked on a metaphilosophical critique to open Hegel’s testament, Žižek’s Hegel supposed to pave the way for a new philosophical materialism. This paper seeks to claim that such a materialist Hegel not only survives the critical encounter of Lefebvre’s metaphilosophy, but also encourages us to inquire about the possibilities and consequences of a geographical turn to Hegel. What if there is a Hegel out there that geography has not even detected?
There is a broad consensus that psychoanalytic theory cannot offer an account to further engage with the ontological turn toward the object that human sciences face today. In particular, the structuralist side of psychoanalysis, most prominently promoted by Jacques Lacan, is supposed to be unable to grasp an object independently from the subject. Against this background, it is no surprise that ‘object-oriented’ geographers ignore psychoanalytic theory. My aim is to investigate the interstices between the object-oriented turn and Lacanian psychoanalysis. I argue that the critiques miss a crucial aspect of Lacan’s ontology: he does not question that there are objects located ‘out there’, but rather adds that psychoanalysis engages with another object whose location remains uncertain. I follow Lacan’s most important invention, the object a, to argue that this object is crucial to understanding the ontology of Lacan as an ‘object-disoriented’ ontology. While object-oriented approaches in cultural geography give ontological priority to the material conditions of existence, Lacanian ontology allows us to understand how material objects become spectralized through an immaterial surplus. To substantiate this claim, I explore the role of anxiety with regard to the Sathorn Unique Tower, an abandoned skyscraper sitting in the middle of Bangkok. Widely known as the ‘Ghost Tower’, this ruin is internationally considered to be haunted. By focusing on a movie and an interview about the Ghost Tower as well as my own ethnographic observation of it, I not only explore the topological dimension of the ghost but also demonstrate that it is precisely the impossibility of localization that enables an object to disorientate the subject.
This paper investigates the global stratospheric Brewer–Dobson circulation (BDC) in the ERA5 meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of stratospheric mean age of air, including the full age spectrum, with the Lagrangian transport model CLaMS (Chemical Lagrangian Model of the Stratosphere), driven by reanalysis winds and total diabatic heating rates. ERA5-based results are compared to results based on the preceding ERA-Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA-Interim, manifesting in weaker diabatic heating rates and higher age of air. In the tropical lower stratosphere, heating rates are 30 %–40 % weaker in ERA5, likely correcting a bias in ERA-Interim. At 20 km and in the Northern Hemisphere (NH) stratosphere, ERA5 age values are around the upper margin of the uncertainty range from historical tracer observations, indicating a somewhat slow–biased BDC. The age trend in ERA5 over the 1989–2018 period is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear but steplike, potentially caused by multi-annual variability or changes in the observations included in the assimilation. During the 2002–2012 period, the ERA5 age shows a similar hemispheric dipole trend pattern as ERA-Interim, with age increasing in the NH and decreasing in the Southern Hemisphere (SH). Shifts in the age spectrum peak and residual circulation transit times indicate that reanalysis differences in age are likely caused by differences in the residual circulation. In particular, the shallow BDC branch accelerates in both reanalyses, whereas the deep branch accelerates in ERA5 and decelerates in ERA-Interim.
State-of-the-art climate models contain, to a significant degree, empirical components. In particular, subgrid-scale (SGS) parameterizations are usually highly tuned against observations or high-resolution model data. While this enables the models to minimize the error during hindcasts, it is not guaranteed that it yields a benefit for climate projections because of climate change. In this thesis the Fluctuation-Dissipation theorem (FDT) is used to update the statistics of the system in the presence of an external forcing. If the empirical parameters are tuned objectively to the data (i.e., they depend on the statistics of the data), then they might be updated with the FDT. This ansatz is tested within a framework of a semi-empirical model (SEM) based on the leading variance patterns of a quasigeostrophic three-layer model (QG3LM) and supplemented by a purely data-driven parameterization. We show that the FDT is able to successfully update the tuning parameters of the data-driven SGS closure, resulting in a systematic improvement in model performance in comparison to an untreated SEM. Ideally, SGS parameterizations should contain little to no tuning parameters. Thus, complementary to the FDT approach we investigate a stochastic SGS closure constrained by first principles that is calculated using the stochastic mode reduction (SMR). The SMR allows for an analytic derivation of the SGS closure from the model equations while requiring only minimal tuning. We successfully apply the SMR to the QG3LM and construct the reduced stochastic model (RSM). Furthermore, we show that the RSM is more robust against an external forcing than the SEM. Additionally, we find that, under appropriate conditions, the FDT is able to update the empirical parts of the RSM. Yet, only for the response in mean streamfunction the RSM provides useful results, while the response in covariance of the streamfunction is incorrect for most cases. Nevertheless, we obtain a remarkably accurate response in both moments for the RSM in an idealized setting. In combination with the results of the FDT study this indicates that the considered RSM is too low dimensional and encourages us to investigate the response of larger RSMs in the future.
Carbon is an element that controls planetary habitability, and is fundamental for life on Earth. Its behaviour has important consequences for the global climate system, the origin and evolution of life on Earth. While the biosphere and atmosphere’s carbon cycle only accounts for less than 1% of the global carbon budget, hidden reservoirs of deep carbon in the Earth’s interior comprise the predominant storage of carbon on the planet. At the Earth’s surface, 60-70 % of carbon is hosted by carbonate minerals, which are then transported to the Earth’s interior, mainly in the form of sediments, by subduction of the oceanic lithosphere. Subducting plates are subjected to decarbonation, dehydration, and melting with CO2 release via supra-subduction volcanism. Nevertheless, part of the subducted carbonates’ may survive and be further transported to the deep mantle. Direct evidence of the existence of carbonates in the Earth’s interior, possibly reaching down to the lower mantle, comes from the finding of syngenetic inclusions of carbonates in diamonds and mantle xenoliths. The presence of carbonates in the deep Earth has a critical effect on the physical properties of the mantle. Melting and chemical speciation of the mantle are strongly affected by the form of C and carbonate stability. Therefore, the study of the stability and physical properties of carbonates at high pressures and temperatures is fundamental, because understanding the processes involved in the deep carbon cycle helps to improve our picture of the whole mantle.
The systematic characterization of the elastic properties of carbonates as a function of their structure and chemical composition is of great importance because it may allow to identify their presence and distribution by seismology. Inverting seismic observations to successfully constrain the chemical composition and mineralogy of the Earth’s interior requires knowledge of the physical properties of all possible Earth’s materials at pressures and temperatures applicable to the Earth’s interior. Up to now, a multitude of studies has focused on the construction of phase diagrams and structural transitions by means of X-ray diffraction and vibrational spectroscopy experiments.
Few studies are available on the complete elastic tensor of carbonates, however most of the datasets are not accompanied by an accurate characterization of the samples, which are often solid solutions and the exact chemical composition, density or the details about the experimental methods used are not presented. The aim of this thesis is to study the effect of chemical composition on the elastic properties of carbonates, providing a reliable dataset on the elasticity of the main carbonates. In particular, the elastic properties of crystalline aragonite, CaCO3, and Fe-dolomite, (Ca, Mg, Fe)(CO3)2, with different compositions were studied by Brillouin spectroscopy at ambient conditions. Brillouin spectroscopy was also used to investigate the elastic behaviour of amorphous calcium carbonate samples with different water contents (up to 18 wt%) at high pressures, up to 20 GPa.
Furthermore, the importance of cationic substitution on the structure and high pressure behaviour of carbonates was investigated by studying a synthetic CaCO3-SrCO3 solid solution at ambient conditions and at high pressures, up to 10 GPa, by single crystal X-ray diffraction. Finally, the study of the effect of composition on the elastic properties of families of isostructural solids was also extended to a different class of materials, the metal guanidinium formates. The elasticity of a family of perovskite metal organic frameworks, metal guanidinium formates C(NH2)3MII(HCOO)3, with MII =Mn, Zn, Cu, Co, Cd and Ca was investigated by combining Brillouin spectroscopy, resonant ultrasound spectroscopy, density functional theory and thermal diffuse scattering analysis.
Mistral and Tramontane are wind systems in southern France and the western Mediterranean Sea. Both are caused by similar synoptic situations and channeled in valleys. Their relevance for the climate of the western Mediterranean region motivated this work. The representation of Mistral and Tramontane in regional climate simulations was surveyed with the models ALADIN, WRF, PROMES, COSMO-CLM, RegCM, and LMDZ. ERA-Interim and global CMIP5 simulations (MPI-ESM, CMCC-CM, HadGEM2-ES, and CNRM-CM5) provided the lateral boundary data for the regional simulations regarding the 20th century and two representative concentration pathways for the 21st century (RCP4.5 and RCP8.5).
A Mistral and Tramontane time series, a principal component analysis of pressure fields, and a Bayesian network were combined to develop a classification algorithm to identify pressure patterns in favor of Mistral and Tramontane. The regional climate models were able to reproduce the observed climatology of Mistral and Tramontane. Compared to observational data (SAFRAN and QuikSCAT), the simulations underestimate the wind speed over the Mediterranean Sea, mainly at the borders of the main flow. Simulations with smaller grid spacing showed better agreement with the observations.
A sensitivity study tested the influence of the Charnock parameter on the Mistral wind field. Its value impacted both wind speed and wind direction. Decreasing the orographic resolution in idealized simulations using COSMO-CLM caused a reduction in wind speed and a broader flow area. Including a parameterization for subgrid scale orography improved the simulation. However, an accurate simulation of Mistral and Tramontane still requires a high-resolution orography.
The classification algorithm also was applied to pressure fields from regional climate simulations driven by global simulation data. At the end of the 21st century, only small, non-significant changes in the number of Mistral days per year occur in the projection simulations. The number of Tramontane days per year decreased significantly.
State of the simulation of mesoscale winds in the Mediterranean and opportunities for improvements
(2022)
The Mediterranean region is a densely populated and economically relevant area with complex orography including mountain ranges, islands, and straits. In combination with pressure gradients, this creates many mesoscale wind systems that cause, e.g., wind gusts and wildfire risk in the Mediterranean. This article reviews the recent state of the science of several mesoscale winds in the Mediterranean and associated processes. Previous work, including case studies on several time ranges and resolutions, as well as studies on these winds under future climate conditions, is discussed. Simulations with grid spacings of 25 to 50 km can reproduce winds driven by large-scale pressure patterns such as Mistral, Tramontane, and Etesians. However, these simulations struggle with the correct representation of winds channeled in straits and mountain gaps and around islands. Grid spacings of 1–3 km are certainly necessary to resolve these small-scale features. The smaller grid spacings are widely used in case studies, but not yet in simulations over large areas and long periods, which also could help to understand the interaction between small-scale phenomena in separate locations. Furthermore, by far not all Mediterranean straits, islands, and mountain gaps were studied in-depth and many interesting Mediterranean small-scale winds still need to be studied.
Bilder stellen auf vielfältige Weise Bezüge zu Räumen und raumbezogenen Praktiken her. Als humangeographische Forschungsmethode fragt die Bildanalyse nach der Wirklichkeit und der Wirkungsweise von Bildern im Verhältnis von Gesellschaft und Raum. Der Beitrag führt fachlich und methodisch in die humangeographische Bildanalyse ein und diskutiert ihren Beitrag zur geographischen Bildungsforschung im Hinblick auf die Vermittlung von Bild(lese)kompetenz und den mündigen Umgang mit medialer Bildlichkeit. Als Unterrichtsbeispiel wird eine Analyse visuellen Materials für eine differenzierte Auseinandersetzung mit dem Problem Müll vorgestellt.
While high-quality climate reconstructions of some past warm periods in the Cenozoic era now exist, the geological processes responsible for driving the observed longterm changes in atmospheric CO2 are not sufficiently well understood. The long-term change in atmospheric CO2 across the Cenozoic has been proposed to be driven by processes such as terrestrial weathering, organic carbon production and burial, reverse weathering, and volcanic degassing. One way of constraining the relative importance of the various driving forces proposed so far is to better understand the degree to which ocean chemistry has changed because the chemistry of seawater responds to geologic processes that drive atmospheric CO2. In addition, knowledge of the concentration of the major elements in seawater is crucial for accurately applying proxies such as those based on the boron isotopic composition and Mg/Ca of marine carbonates (a proxy for palaeo pH/CO2 and palaeotemperature, respectively). Previously reported records of seawater composition are primarily derived from fluid inclusions in marine evaporites; however, the results are sparse due to the limited availability of such deposits. In this thesis, changes in the Eocene seawater chemistry were reconstructed using trace element (elements/Ca) and isotopic (δ26Mg) proxies in a Larger Benthic Foraminifera (LBFs), i.e., Nummulites sp., to constrain the driving processes of long-term changes in seawater chemistry.
To achieve the objective of this thesis, first, a measurement protocol was established using LA-ICPMS to measure the K/Ca ratio simultaneously with other element/calcium ratios, which is challenging due to the interference of ArH+ on K+. Utilising this newly established measurement protocol, laboratory-cultured Operculina ammonoides grown at different seawater calcium concentrations ([Ca2+]), repeated at different temperatures, as well as modern O. ammonoides collected from different regions exhibiting a range of seawater parameters, were investigated. A significant correlation was observed between K/Casw and K/CaLBF, allowing K/CaLBF to potentially be used as a proxy for seawater major ion reconstructions. In addition, modern O. ammonoides demonstrated no significant influence of most seawater parameters (temperature, salinity, pH, or [CO32-]) on K/CaLBF. Modern O.
ammonoides were also assessed for their Mg isotopic composition (δ26Mg), revealing no significant effect of temperature or salinity on δ26MgLBF. Furthermore, the Mg isotopic fractionation in O. ammonoides was found to be close to that of inorganic calcite, indicating minimal vital effects in these large benthic foraminifera.
Operculina ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling the reconstruction of seawater chemistry using the calibration based on O. ammonoides. The trace elemental/calcium proxies, including Na/Ca, K/Ca, and Mg/Ca, as well as the δ26Mg proxy, were investigated in Eocene Nummulites. The result showed that during the Eocene, [Ca2+]sw was 1.6-2 times higher, while [K+]sw was ~2 times lower than the modern seawater composition. Furthermore, [Mg2+]sw decreased from the early Eocene (54.3− +9 7..69 mmol kg-1 at ~55 Ma) to Late Eocene (37.8− +4 4..3 4 mmol kg-1 at ~31 Ma), followed by
an increase toward modern seawater [Mg]. In contrast, the variability in δ26Mgsw values remained within a narrow range of ~0.3 ‰ throughout the Cenozoic. The reconstructed [Ca2+]sw agrees with the suggestion that Cenozoic seawater chemistry changes can be explained via a change in the seafloor spreading rate. When combined with existing records, the observed minimal change in δ26Mgsw with an increase in [Mg2+]sw suggests an additional possible role of a decrease in the formation of authigenic clay minerals coincident with the Cenozoic decline in deep ocean temperature, which is also supported by the increase in the [K+]sw reconstructed here for the first time. This finding highlights that the reduction in seafloor-spreading rate and decline in reverse weathering during the Cenozoic era has played a significant role in the evolution of seawater chemistry, emphasizing the importance of these processes in driving long-term changes in the carbon cycle.
Emissions of the potent greenhouse gas perfluorocyclobutane (c-C4F8, PFC-318, octafluorocyclobutane) into the global atmosphere inferred from atmospheric measurements have been increasing sharply since the early 2000s. We find that these inferred emissions are highly correlated with the production of hydrochlorofluorocarbon-22 (HCFC-22, CHClF2) for feedstock (FS) uses, because almost all HCFC-22 FS is pyrolyzed to produce (poly)tetrafluoroethylene ((P)TFE) and hexafluoropropylene (HFP), a process in which c-C4F8 is a known by-product, causing a significant fraction of global c-C4F8 emissions. We find a global emission factor of ∼0.003 kg c-C4F8 per kilogram of HCFC-22 FS pyrolyzed. Mitigation of these c-C4F8 emissions, e.g., through process optimization, abatement, or different manufacturing processes, such as refined methods of electrochemical fluorination and waste recycling, could reduce the climate impact of this industry. While it has been shown that c-C4F8 emissions from developing countries dominate global emissions, more atmospheric measurements and/or detailed process statistics are needed to quantify c-C4F8 emissions at country to facility levels.
In the digital condition, social networks are part of the everyday practices that produce constructions of space. To include this phenomenon in the Geography classroom, the corresponding knowledge that teachers require and how to measure it need to be determined. For this purpose, a specific instrument is necessary. We analyse constructions of space as a teacher knowledge domain through the lens of the TPACK model and deduce pedagogical and technological knowledge. We then combine these results with available TPACK survey instruments. The product is a self-assessment survey for Geography teachers on constructions of space and social networks. Scale consistency measures and item discrimination yielded good results. Initial results indicate technological and pedagogical knowledge to be greater than content knowledge. The instrument we present is valid for determining future Geography teachers’ TPACK more broadly, and can reveal implications for interventions in Geography teacher education.
Digital spatial processes have been widely explored and investigated in subject-specific geographic research. So far, however, this research has not been sufficiently reflected in classrooms or teacher education, and remains unconnected to notions of geographical digital literacy. Viral constructions of space – realities shaped in everyday life that are experienced and (re-)produced by students and teachers alike through social media – present an opportunity for Geography education to adapt to the digital society. This paper attempts to connect viral constructions of space, the digital society and the knowledge teachers need to include viral constructions of space in the classroom using Mishra and Koehler’s (2006) TPACK model, a well-established means for summarizing teachers’ technological, pedagogical and content knowledge for a specific topic. The paper focuses on content knowledge, identifies five sub-types of viral constructions of space, and extracts nine descriptors of teachers’ content knowledge. By focusing on content knowledge, the paper presents a starting point for future investigations of pedagogical and technological teacher knowledge as well as their intersections. It also raises awareness of viral constructions of space as both a new essential topic in the Geography classroom and a phenomenon already shaping learning environments for spatial acquisition.
Raumkonstruktionen, die über Handlung und Bedeutungszuschreibungen im Kontext sozialer Medien entstehen, sind ein Fallbeispiel dafür, wie vor dem Hintergrund von Digitalität Fachinhalte re-innoviert werden müssen. Mit dem Ziel eines Beitrags zur Konzeption professionellen Lehrkräftewissens im Kontext von Digitalität werden, ausgehend von der Fragestellung, welche professionellen Fähigkeiten Lehrkräfte benötigen, um Raumkonstruktionen im Unterricht zu thematisieren, in dieser kumulativen Dissertation Raumkonstruktionen aus normativer und empirischer Perspektive als exemplarischer geographischer Fachinhalt adressiert.
Als theoretischer Rahmen dient dabei das TPACK Modell von Mishra & Koehler (2006), das professionelles Lehrkräftewissen in die Bereiche fachliches, pädagogisches und technologisches Wissen sowie deren Überschneidungsbereiche einteilt. Zunächst erfolgt eine Anwendung des Modells als Reflexionsperspektive auf Fachinhalte zur Erzeugung normativer Fähigkeitsbeschreibungen. Diese Fähigkeitsbeschreibungen fließen in die Entwicklung eines TPACK-Selbsteinschätzungsfragebogens für Lehramtsstudierende der Geographie ein. Im Rahmen der damit durchgeführten Studie (n= 364) zeigen sich auf deskriptiver Ebene vergleichsweise niedrige Selbsteinschätzungen der Bereiche inhaltlichen und fachdidaktischen Wissens. Durch die Anwendung einer konfirmatorischen Faktorenanalyse kann das TPACK Modell als zufriedenstellend für die Beschreibung der Daten identifiziert werden. Auffällig ist allerdings die niedrige Korrelation des Konstrukts technologischen Wissens mit den angrenzenden Wissensbereichen. In Bezug auf die Selbsteinschätzungen im phasen- und kontextübergreifenden Vergleich lässt sich, ausgehend von linearen Regressionsanalysen, eine tendenzielle Zunahme der selbsteingeschätzten Fähigkeiten entlang der Fachsemesterzahl ermitteln. Mittels Zweistichproben-t-Tests können außerdem höhere Selbsteinschätzungen der pädagogischen Wissensbereiche durch Studierende, die als Vertretungslehrkräfte tätig sind, festgestellt werden.
In Bezug auf die zur Thematisierung von Raumkonstruktionen im Unterricht benötigten Fähigkeiten ist zunächst die Relevanz der Förderung der Integration fachlichen, pädagogischen und fachdidaktischen Wissens hervorzuheben. Die Studie gibt darüber hinaus Hinweise auf eine niedrigere Bedeutung technologischen Wissens im Hinblick auf soziale Medien als Beispiele alltäglicher Technologien. Vor dem Hintergrund des positiven Effekts von Selbstwirksamkeitsprozessen bieten die Ergebnisse Implikationen für eine Diskussion von praktischen Erfahrungen als Aspekt professionellen Lehrkräftewissens im Sinne der Förderung einer kritisch-reflexiven Auseinandersetzung mit der Tätigkeit als Vertretungslehrkraft aus fachdidaktischer Perspektive. Insgesamt leistet die kumulative Dissertation einen Beitrag zum Diskurs um fachliche geographische Bildung im Kontext von Digitalität und zur Konzeption des professionellen Lehrkräftewissens vor diesem Hintergrund.
Mongolia covers a huge area in Asia and provides excellent Palaeozoic successions although large regions still lack detailed information on fauna and flora in Palaeozoic rocks. Of special interest is the Central Asian Orogenic Belt (CAOB), one of the largest collisional complexes on Earth. The CAOB is composed of a large number of terranes, continental margins, island arcs, backarc/forearc basins and accretionary wedges (Badarch et al. 2002; Safonova et al. 2017). Many terranes and regions underwent strong metamorphism, such as areas north of the Main Mongolian Lineament. To the south, Palaeozoic rocks exhibit low-grade metamorphism, thrusting and folding. Two promising long successions of Palaeozoic rocks were studied, namely the Hushoot Shiveetiin gol section and the Bayankhoshuu Ruins section. The intention of the PhD was to study marine facies settings in Palaeozoic rocks of southern and southwestern Mongolia, in an area little is known in terms of biostratigraphy and events. In order to get a better understanding on events and what might have been the driving forces I studied sections in Mongolia which have not been in the focus of research in the last decades. In order to complement studies on Late Devonian events elsewhere, I decided to study sections in open ocean environments (CAOB), far away from mainly studied epicontinental areas.As stated in many publications, events are the driving force for evolution. They exhibit dramatical changes in the palaeontological record of organisms and they are often associated with dramatic extinctions (Walliser 1996) and anoxic sediments (but not always). Mass extinctions are episodes in which a large number of plant and animal species became extinct within a few thousand to a hundred thousand years. Most events (first and second order events) are traceable worldwide. For instance, in the Late Devonian, mass extinction events recognized at the Frasnian–Famennian (F/F) stage boundary and at the Devonian–Carboniferous (D/C) boundary (McLaren and Goodfellow 1990; Sepkoski 1996; Walliser 1996). Overall, 19% of all families, 50% of all genera and at least 70% of all species became extinct (Raup and Sepkoski 1982; Sepkoski 1996; McGhee et al. 2013), but extinctions also concerned palaeoecosystems and due to Late Devonian events whole coral/stromatoporoid reef ecosystems became extinct. What might be the reason(s) for these dramatical changes? Why did the carbonate factory brake down? There are several reasons which have been discussed. For instance, extraterrestrial bolide impacts (McLaren 1970), anoxia within the water column due to climate changes (House 1985; Becker and House 1994; Caplan and Bustin 1999; Bond and Wignall 2005), transgressions and regressions (Newell 1967; Hallam and Wignall 1999; Purdy 2008; Ruban 2010, 2013; Smith and Benson 2013), eutrophication and increased sediment transport (Joachimski et al. 1993; Schobben et al. 2016), explosive volcanism (Paschall et al. 2019) and/ or large igneous provinces (LIP’s, Ernst et al. 2019; Racki et al. 2020, among others) and much more has been considered. The main problem is that previous studies preferably have been done along former epicontinental margins between Laurassia and Gondwana. Less information is available in deep open oceanic successions and shallow-water areas around island arcs. Generally, events are characterized by bituminous rocks, such as black limestones and shales within marine realms, but they do not necessarily occur everywhere (see Carmichael et al. 2016). So, the question was: “Can we recognize Palaeozoic event layers or equivalents in the CAOB?” If so, is this comparable to already published data? What might be the main trigger, as there are many reasons still in discussion? And finally, what has happened in the aftermath of those events as it seems that the CAOB may have acted as a refugium for at least some groups, such as for crinoids (Waters and Webster 2009; Tolokonnikova and Ernst 2010). In this thesis, I will provide data from isolated ecosystems from a rather unstudied region, which will complement studies from other parts of the World.
In der kritischen Stadtforschung wird die These der postdemokratischen Stadt aktuell immer wieder aufgegriffen und dabei eng mit Prozessen der Neoliberalisierung verknüpft. Ausgehend von einer kritischen Diskussion der konzeptionellen Zugänge bei Colin Crouch und Jacques Rancière geht der Beitrag anhand der Geschichte der kommunalen Selbstverwaltung in Frankfurt am Main dem Gehalt der beiden Begriffsbestimmungen in der konkreten historischen Analyse nach. Verwiesen wird dabei auf die unterschiedliche Analysetiefe der beiden Konzepte. Entgegen der bei Crouch vorherrschenden Annahme, dass es vor der neoliberalen Stadt eine demokratische Form städtischen Regierens gegeben hat, wird unter Rückbezug auf die Argumentation Rancières zur Demokratie betont, dass der Fordismus keinesfalls als egalitärer, inklusiver oder demokratischer charakterisiert werden kann. Vielmehr vertreten wir die These, dass die fordistische Stadt zwar aus anderen Gründen, aber vom Grundsatz her nicht weniger postdemokratisch gewesen ist als die neoliberale der Gegenwart und dass die demokratischen Momente am ehesten in den Brüchen und Spalten der sozialen Konflikte der 1970er und 1980er Jahre gefunden werden können.
The Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third-order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U-Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U-Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time-framed depositional systems.
A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a “data-forward” approach, that clearly decouples the presentation of proxy data from plausible environmental inferences.
Due to massive energetic investments in woody support structures, trees are subject to unique physiological, mechanical, and ecological pressures not experienced by herbaceous plants. Despite a wealth of studies exploring trait relationships across the entire plant kingdom, the dominant traits underpinning these unique aspects of tree form and function remain unclear. Here, by considering 18 functional traits, encompassing leaf, seed, bark, wood, crown, and root characteristics, we quantify the multidimensional relationships in tree trait expression. We find that nearly half of trait variation is captured by two axes: one reflecting leaf economics, the other reflecting tree size and competition for light. Yet these orthogonal axes reveal strong environmental convergence, exhibiting correlated responses to temperature, moisture, and elevation. By subsequently exploring multidimensional trait relationships, we show that the full dimensionality of trait space is captured by eight distinct clusters, each reflecting a unique aspect of tree form and function. Collectively, this work identifies a core set of traits needed to quantify global patterns in functional biodiversity, and it contributes to our fundamental understanding of the functioning of forests worldwide.
Monitoring woody cover by remote sensing is considered a key methodology towards sustainable management of trees in dryland forests. However, while modern very high resolution satellite (VHRS) sensors allow woodland mapping at the individual tree level, the historical perspective is often hindered by lack of appropriate image data. In this first study employing the newly accessible historical HEXAGON KH-9 stereo-panoramic camera images for environmental research, we propose their use for mapping trees in open-canopy conditions. The 2–4 feet resolution panchromatic HEXAGON satellite photographs were taken 1971–1986 within the American reconnaissance programs that are better known to the scientific community for their lower-resolution CORONA images. Our aim is to evaluate the potential of combining historical CORONA and HEXAGON with recent WorldView VHRS imagery for retrospective woodland change mapping on the tree level. We mapped all trees on 30 1-ha test sites in open-canopy argan woodlands in Morocco in the field and from the VHRS imagery for estimating changes of tree density and size between 1967/1972 and 2018. Prior to image interpretation, we used simulations based on unmanned aerial system (UAS) imagery for exemplarily examining the role of illumination, viewing geometry and image resolution on the appearance of trees and their shadows in the historical panchromatic images. We show that understanding these parameters is imperative for correct detection and size-estimation of tree crowns. Our results confirm that tree maps derived solely from VHRS image analysis generally underestimate the number of small trees and trees in clumped-canopy groups. Nevertheless, HEXAGON images compare remarkably well with WorldView images and have much higher tree-mapping potential than CORONA. By classifying the trees in three sizes, we were able to measure tree-cover changes on an ordinal scale. Although we found no clear trend of forest degradation or recovery, our argan forest sites show varying patterns of change, which are further analysed in Part B of our study. We conclude that the HEXAGON stereo-panoramic camera images, of which 670,000 worldwide will soon be available, open exciting opportunities for retrospective monitoring of trees in open-canopy conditions and other woody vegetation patterns back into the 1980s and 1970s.
Africa's protected areas (PAs) are the last stronghold of the continent's unique biodiversity, but they appear increasingly threatened by climate change, substantial human population growth, and land-use change. Conservation planning is challenged by uncertainty about how strongly and where these drivers will interact over the next few decades. We investigated the combined future impacts of climate-driven vegetation changes inside African PAs and human population densities and land use in their surroundings for 2 scenarios until the end of the 21st century. We used the following 2 combinations of the shared socioeconomic pathways (SSPs) and representative greenhouse gas concentration pathways (RCPs): the “middle-of-the-road” scenario SSP2–RCP4.5 and the resource-intensive “fossil-fueled development” scenario SSP5–RCP8.5. Climate change impacts on tree cover and biome type (i.e., desert, grassland, savanna, and forest) were simulated with the adaptive dynamic global vegetation model (aDGVM). Under both scenarios, most PAs were adversely affected by at least 1 of the drivers, but the co-occurrence of drivers was largely region and scenario specific. The aDGVM projections suggest considerable climate-driven tree cover increases in PAs in today's grasslands and savannas. For PAs in West Africa, the analyses revealed climate-driven vegetation changes combined with hotspots of high future population and land-use pressure. Except for many PAs in North Africa, future decreases in population and land-use pressures were rare. At the continental scale, SSP5–RCP8.5 led to higher climate-driven changes in tree cover and higher land-use pressure, whereas SSP2–RCP4.5 was characterized by higher future population pressure. Both SSP–RCP scenarios implied increasing challenges for conserving Africa's biodiversity in PAs. Our findings underline the importance of developing and implementing region-specific conservation responses. Strong mitigation of future climate change and equitable development scenarios would reduce ecosystem impacts and sustain the effectiveness of conservation in Africa.
National Greenhouse Gas Inventories (GHGI) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGI. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emissions Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high Global Warming Potentials (GWPs) and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions in the since 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35%, indicating progress toward the target of a 79% decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83)% of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI inventory. There are also significant discrepancies between the two estimates for the individual HFCs.
National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35 %, indicating progress toward the target of a 79 % decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83) % of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.
This Ph.D. thesis demonstrates i) the highly precise performance of refined and new analytical setups for clumped isotope analysis (Δ47 and Δ48) and ii) the applicability of clumped isotope analyses to biogenic and abiogenic carbonated apatite (Δ47) and abiogenic carbonates (Δ47 and Δ48) for research related to paleothermophysiology and paleoclimatology, whereas the overall analytical precision has been increased.
A comprehensive Δ47 dataset with 122 replicate analyses is provided from which the temperature dependence of Δ47 for (bio)apatite (Δ47-1/T2) is calculated between 1 °C and 80 °C. The temperature dependence of oxygen isotope equilibrium fractionation between carbonated synthetic apatite and water (1,000ln(αCHAP-H2O)) is experimentally determined. When applied to tooth enameloid from a modern Greenland shark (Somniosus microcephalus), a Late Miocene megatooth shark (Carcharodon megalodon), and an Upper Cretaceous Tyrannosaurus rex, reconstructed Δ47-based temperatures and δ18OH2O are in line with previously published data.
An analytical setup for highly precise clumped isotope analysis is described that allows for the simultaneous measurement of ∆47 and ∆48 in CO2 with external reproducibilities close to the respective shot-noise limits. The analyte gases originate from pure carbonates that were digested in hypersaturated orthophosphoric acid and purified using a fully automated device. Δ47 data sets with 117 replicate analyses in total on 22 pedogenic carbonate nodules from two Spanish Middle Miocene sections reveal the continental Southern European thermal structure during the end of the Middle Miocene Climatic Optimum (MCO) and the complete Middle Miocene Climatic Transition (MMCT; from 15.33 to 12.98 Ma).
We present the results of a multi-disciplinary investigation on a deciduous human tooth (Pradis 1), recently recovered from the Epigravettian layers of the Grotte di Pradis archaeological site (Northeastern Italian Prealps). Pradis 1 is an exfoliated deciduous molar (Rdm2), lost during life by an 11–12-year-old child. A direct radiocarbon date provided an age of 13,088–12,897 cal BP (95% probability, IntCal20). Amelogenin peptides extracted from tooth enamel and analysed through LC–MS/MS indicate that Pradis 1 likely belonged to a male. Time-resolved 87Sr/86Sr analyses by laser ablation mass spectrometry (LA-MC-ICPMS), combined with dental histology, were able to resolve his movements during the first year of life (i.e. the enamel mineralization interval). Specifically, the Sr isotope ratio of the tooth enamel differs from the local baseline value, suggesting that the child likely spent his first year of life far from Grotte di Pradis. Sr isotopes are also suggestive of a cyclical/seasonal mobility pattern exploited by the Epigravettian human group. The exploitation of Grotte di Pradis on a seasonal, i.e. summer, basis is also indicated by the faunal spectra. Indeed, the nearly 100% occurrence of marmot remains in the entire archaeozoological collection indicates the use of Pradis as a specialized marmot hunting or butchering site. This work represents the first direct assessment of sub-annual movements observed in an Epigravettian hunter-gatherer group from Northern Italy.
The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense SWATH-D seismic network as a complementary experiment to the AlpArray seismic network provides unprecedented lateral resolution to address this ongoing discussion. We analyze the shear-wave splitting of this data set including stations of the AlpArray backbone in the region to obtain new insights into the deformation at depth from seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by the azimuthal pattern of the measured fast axis direction across all analyzed stations. However, the temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic properties of the mantle. We, therefore, perform a cluster analysis based on a correlation of energy tensors between all stations. The energy tensors are assembled from the remaining transverse energy after the trial correction of the splitting effect from two consecutive anisotropic layers. This leads to two main groups of different two-layer properties, separated approximately at 13°E. We identify a layer with a constant fast axis direction (measured clockwise with respect to north) of about 60° over the whole area, with a possible dip from west to east. The lower layer in the west shows N–S fast direction and the upper layer in the east shows a fast axis of about 115°. We propose two likely scenarios, both accompanied by a slab break-off in the eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with a lithospheric origin or as an asthenospheric flow evading the retreat of the European slab that would precede the break-off event. In both scenarios, the upper layer in the east is a result of a flow through the gap formed in the slab break-off. The N–S direction can be interpreted as an asthenospheric flow driven by the retreating European slab but might also result from a deep-reaching fault-related anisotropy.
Since the publication of Nikolas Rose’s ‘The Politics of Life Itself’ (2001) there has been vivid discussion about how biopolitical governance has changed over the last decades. This article uses what Rose terms ‘molecular politics’, a new socio-technical grip on the human body, as a contrasting background to ask anew his question ‘What, then, of biopolitics today?’ – albeit focusing not on advances in genetics, microbiology, and pharmaceutics, as he does, but on the rapid proliferation of wearables and other sensor-software gadgets. In both cases, new technologies providing information about the individual body are the common ground for governance and optimization, yet for the latter, the target is habits of moving, eating and drinking, sleeping, working and relaxing. The resulting profound differences are carved out along four lines: ‘somatic identities’ and a modified understanding of the body; the role of ‘expert knowledge’ compared to that of networks of peers and self-experimentation; the ‘types of intervention’ by which new technologies become effective in our everyday life; and the ‘post-discipline character’ of molecular biopolitics. It is argued that, taken together, these differences indicate a remarkable shift which could be termed aretaic: its focus is not ‘life itself’ but ‘life as it is lived’, and its modality are new everyday socio-technical entanglements and their more-than-human rationalities of (self-)governance.
Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen/Germany. Average power spectral densities (PSD) are calculated from 10 min time segments extracted from (up to) 6-months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify 7 distinct PSD peaks in the frequency range between 1 Hz and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b-values exhibit a linear frequency dependence and range from b = 0.39 at 1.14 Hz to b = 3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach which approximates the surface-wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source-signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase-shift-elimination-method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the 7 prominent frequencies shows very good agreement and allows to constrain shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen, Germany. Average power spectral densities (PSDs) are calculated from 10 min time segments extracted from (up to) 6 months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify seven distinct PSD peaks in the frequency range between 1 and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b values exhibit a linear frequency dependence and range from b=0.39 at 1.14 Hz to b=3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach that approximates the surface wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase shift elimination method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the seven prominent frequencies shows very good agreement and allows the constraint of shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
This thesis presents the experimental and numerical analysis of seismic waves that are produced by wind farms. With the aim to develop renewable energies rapidly, the number of wind turbines has been increased in recent years. Ground motions induced by their operation can be observed by seismometers several kilometers away. Hence, the seismic noise level can be significantly increased at the seismic station. Therefore, this study combines long-term experiments and numerical simulations to improve the understanding of the seismic wavefields emitted by complete wind farms and to advance the prediction of signal amplitudes.
Firstly, wind-turbine induced signals that are measured at a small wind farm close to Würzburg (Germany) are correlated with the operational data of the turbines. The frequency-dependent decay of signal amplitudes with distance from the wind farm is modeled using an analytical method including the complex effects of interferences of the wavefields produced by the multiple wind turbines. Specific interference patterns significantly affect the wave propagation and therefore the signal amplitude in the far field of a wind farm. Since measurements inside the wind turbines show that the assumption of in-phase vibrating wind turbines is inappropriate, an approach to calculate representative seismic radiation patterns from multiple wind turbines, which allows the prediction of amplitudes in the far field of a complete wind farm, is proposed.
In a second study, signals with a frequency of 1.15 Hz, produced by the Weilrod wind farm (north of Frankfurt, Germany) are observed at the seismological observatory TNS (Taunus), which is located at a distance of 11 km from the wind farm. The propagation of the wavefield emitted by the wind farm is numerically modeled in 3D, using the spectral element method. It is shown that topographic effects can cause local signal amplitude reductions, but also signal amplification along the travel path of the seismic wave. The comparison of simulations with and without topography reveals that the reduction and amplification are spatially linked to the shape of the topography, which could be an explanation for the relatively high signal amplitude observed at TNS.
Finally, the reduction of the impact of wind turbines on seismic measurements using borehole installations is studied using 2D numerical models. Possible effects of the seismic velocity, attenuation, and layering of the subsurface are demonstrated. Results show that a borehole can be very effective in reducing the observed high-frequency signals emitted by wind turbines. However, a borehole might not be beneficial if signals with frequencies of about 1 Hz (or lower) are of interest, due significant wavelength-dependent effects. The estimations of depth-dependent amplitudes with a layered subsurface are validated with existing data from wind-turbine-induced signals measured at the top and bottom of two boreholes.
The experimental analysis of measurements conducted at wind farms and the advances of modeling such signals improve the understanding of the propagation of wind-farm induced seismic wave fields. Furthermore, the methods developed in this work have a high potential of universal application to the prediction of signal amplitudes at seismometers close to wind farms with arbitrary layout and geographic location.
The goal of limited area models (LAMs) is to downscale coarse-gridded general circulation model output to represent small-scale features of weather and climate. The LAM needs information from the driving coarse-gridded model passing through its lateral boundaries. The treatment of this information transfer causes inconsistencies between driving and nested models and, subsequently, issues in regional weather and climate simulations. This work examines errors arising from choices taken by the modeler (temporal update frequency of boundary data, spatial resolution jump, and numerical lateral boundary formulation) systematically in an idealized simulation environment. So-called Big-Brother Experiments were performed with the LAM COSMO-CLM (0.11° grid spacing). A baroclinic wave in a zonal channel was simulated over flat terrain with and without a Gaussian hill. The results reveal that the quality of the driving data, here represented by simulations only differing from the LAM simulations by reduced spatial resolution, dominates the performance of the nested model. Consequently, at the simulated mesoscale, the performance of the nested small-scale model simulations is weakly sensitive to the numerical lateral boundary formulation (Davies relaxation or the newly implemented, computationally less demanding Mesinger Eta-model formulation). The performance sensitivity to boundary update frequency and resolution jump is small when at least 6-hourly updates and a resolution jump factor of maximally six is used. Gaussian hill LAM simulations illustrated the strength of downscaling; they can represent small-scale features missing in the coarse-scale driving simulations. In the idealized simulation experiments, spectral nudging is not advisable as it imprints the driving models deficits on the nested simulation.
In recent years, many European cities have developed strategies to improve the quality of urban life by reducing car traffic and increasing the attractiveness of alternative modes and the built environment for residents. Frequently, at least in German cities, improvements to the cycling infrastructures play a key role in this transformation of urban spaces. One of those transformative interventions took place in 2020 in Frankfurt am Main (Germany). The city redesigned an arterial road close to the city centre, the Friedberger Landstrasse, by converting two car lanes to bicycle lanes. It is the aim of this study to analyse the effects of this change on the quality of urban life of its residents using a quantitative before-and-after study. The results demonstrate the expected improvements in the perceived quality of urban life for residents after the intervention. A more detailed analysis, however, shows that the residents’ perceptions vary according to their own mode use on the Friedberger Landstrasse and other sociodemographic characteristics. Thus, better cycling infrastructure does not only improve conditions for cyclists, but also contributes to a higher quality of urban life for residents and, therefore, improves the liveability of a city in two ways. We conclude that local transport policies are not only relevant for a modal shift, but also for the quality of urban life and, thus, related urban development strategies.
The overarching goal of the thesis was to create a holistic predictive framework, a vegetation model, by improving the representations of and interactions between the biosphere, hydrosphere, atmosphere and pedosphere. Vegetation models rep- resent a crucial component of Earth system model since the properties of the land surface, via interactions with the atmosphere, can have extremely large climatic effect. Yet, there remains great uncertainty associated with the dynamics of the vegetated land surface. Various vegetation models have been critiqued for numerous reasons including overly simplistic representations of vegetation, prescribed vegetation, poor representations of diversity, inaccurate representations of competition, non-transparent model calibration, and poor responses to drought. The purpose of the creation of this "next generation" model was to address deficiencies common to current vegetation modelling paradigms.
The representation of the biosphere within this framework was improved via two separate development axes. First, ecological realism was improved by integrating concepts from community assembly theory, co-existence theory, and evolutionary theory. Explicitly, rather than defining teleonomic rules to define plant behaviour the process of natural selection is modelled. By modelling the pro- cess of natural selection and its affect on relative fitness, myriad "rules" which continually adapt to biotic and abiotic conditions "come out" as a consequence of the modelled dynamics rather than being "put in". In aDGVM2 (adaptive Dynamic Global Vegetation model 2) communities of plants and their trait values evolve through time, this evolution is constrained by trade-offs between traits. Poorly performing individuals are more likely to die and produce fewer copies of themselves, this results in a filtering of trait values. Further, the community and species’ trait values can evolve through successive generations via reproduction, mutation and crossover which we approximate by using a genetic optimisation algorithm. Thus, a plant community consisting of individuals and species with potentially novel and diverse trait values is assembled iteratively through time.
We tested the assertion that improved integration of concepts from community assembly, evolutionary, and co-existence theory could address limitations of DGVMs in Chapter 2. We demonstrated that such an approach does indeed allow diverse communities of plants to emerge from the modelling framework. We showed that the position of the emergent communities in trait space differed along abiotic gradients and that, in simulations where reproductive isolation was simulated, communities emerged which were composed of multiple co-existing clusters in trait-space. Simulated trait values of co-existing strategies emerging from aDGVM2 were often multimodal, indicative of the emergence of multiple life- history strategies.
Second, to successfully model how natural selection forms a community requires accurate representation of how resource availability affects fitness. In the majority of dynamic global vegetation models (DGVMs) there is no real representation of plant hydraulics with plant water availability being calculated as a simple function of relative soil moisture content and root fractions across a number of soil layers. Worryingly, a number vegetation models appear to under represent the magnitude of these observed responses to drought. This was deficiency was ad- dressed in Chapter 3 by designing a simplified version of the cohesion tension theory of sapwood ascent where elements determining plant conductances are considered in series and implementing a set of trait trade-offs which influence a plant’s hydraulic strategy whereby hydraulic safety trades-off against xylem and leaf conductivity.
Interactions between the biosphere, pedosphere, and hydrosphere can also potentially mediate water resource availability and thus fitness. In the majority of DGVMs the volume of soil explored and explorable by plant roots in fixed glob- ally and usually constrained to a depth not greater than 3m. However, we know that soils can have a strong effect on vegetation distributions, that soil depth is not constant globally, and that plants root to variable depths.
In Chapter 4 I explored interactions between soil depth, plant rooting and the emergent properties of communities and highlighted the importance of considering interactions between the biosphere, hydrosphere, pedosphere, and fire. Here I demonstrated that, in addition to fire and precipitation, edaphic constraints on the volume of soil explorable by plant roots (e.g. by shallow soils, lateritic layers, anoxic conditions due to water logging, toxicity resulting from heavy metal concentrations) can affect the process of plant community assembly, alter the mean values of multiple traits in communities, and the trait diversity of communities.
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Auf Basis ethnographischer Feldforschung untersucht der Beitrag den Zusammenhang zwischen prekären Wohnverhältnissen und der Entstehung politischer Kollektivität unter Mieter*innen. Theoretisch-konzeptionell knüpft er dabei an Debatten der kritischen Stadtforschung zu Verdrängungsprozessen, Forschungsarbeiten zu Prekarisierung sowie poststrukturalistisch inspirierte Perspektiven der sozialen Bewegungsforschung an. Empirisch ist der Blick gerichtet auf die Lebensrealitäten von Bewohner*innen einer Frankfurter Vonovia-Wohnsiedlung. Gefragt wird danach, wie Mieter*innen ihre Wohnsituation in Anbetracht drohender Mieterhöhungen infolge von Modernisierungsarbeiten wahrnehmen, welche Bedeutung sie der Wohnungsfrage zuschreiben und welche sozialräumlichen Bedingungen, Handlungspraktiken und diskursiven Deutungsmuster die Entwicklung einer kollektiven politischen Handlungsfähigkeit erschweren.
Late Paleozoic (Variscan) magmatism is widespread in Central Europe. The Lusatian Block is located in the NE Bohemian Massif and it is part of the Saxothuringian Zone of the Variscan orogen. It is bordered by two major NW-trending shear zones, the Intra-Sudetic Fault Zone towards NE and the Elbe Fault Zone towards SW. The scarce Variscan igneous rocks of the Lusatian Block are situated close to these faults. We investigated 19 samples from Variscan plutonic and volcanic rocks of the Lusatian Block, considering all petrological varieties (biotite-bearing granites from the Koenigshain and Stolpen plutons, amphibole-bearing granites from three boreholes, several volcanic dykes, and two volcanites from the intramontane Weissig basin). We applied whole-rock geochemistry (18 samples) and zircon evaporation dating (19 samples). From the evaporation data, we selected six representative samples for additional zircon SHRIMP and CA–ID–TIMS dating. For the Koenigshain pluton, possible protoliths were identified using whole-rock Nd-isotopes, and zircon Hf- and O-isotopes. The new age data allow a subdivision of Variscan igneous rocks in the Lusatian Block into two distinct magmatic episodes. The spatial relation of the two age groups to either the Elbe Fault Zone (298–299 Ma) or the Intra-Sudetic Fault Zone (312–313 Ma) together with reports on the fault-bound character of the dated intrusions suggests an interpretation as two major post-collisional faulting episodes. This assumption of two distinct magmatic periods is confirmed by a compilation of recently published zircon U–Pb CA–ID–TIMS data on further Variscan igneous rocks from the Saxothuringian Zone. New geochemical data allow us to exclude a dominant sedimentary protolith for the Koenigshain pluton as supposed by previous investigations. This conclusion is mainly based on new O- and Hf-isotope data on zircon and the scarcity of inherited zircons. Instead, acid or intermediate igneous rocks are supposed as the main source for these I-type granitoids from the Koenigshain pluton.
Climate controls the broad-scale distribution of vegetation and change in climate will alter the vegetation distribution, biome boundaries, biodiversity, phenology and supply of ecosystem services. A better understanding of the consequences of climate change is required, particularly in under-investigated regions such as tropical Asia, i.e., South and South-east Asia, which is a host to 7 of the 36 global biodiversity hotspots. Conservation strategies would also require an in-depth understanding of the response of vegetation to climate change. Therefore, the main objective of this thesis was to investigate the impact of climate change and rising CO2 vegetation in tropical Asia. Dynamic global vegetation model (DGVMs) are the well-known tools to investigate vegetation-climate interactions and climate change impacts on ecosystems. In this thesis, I used a complex trait-based DGVM called adaptive dynamic vegetation model version 2 (aDGVM2).
In Chapter 1, I presented a brief background of the phytogeography and discussed the exiting knowledge gap on vegetation-climate interactions in the region. One major disadvantage for available DGVMs studies for the tropical Asia is that most of them have used fixed plant functional types (PFTs) and do not explicitly represent the distinct varieties of vegetation type of the region such as Asian savannas. In Chapter 2, I discussed at great length to improve DGVMs for South Asia and discussed ways to include them in the model for better representation of region vegetation-climate interaction.
I upgraded the current version of aDGVM2 and added a new vegetation type i.e., C3 grasses, and modified the sub-module to simulate photosynthesis for each individual plants to aDGVM2. In chapter 3, I used this updated version of aDGVM2 to simulate the current and future vegetation distribution in South Asia under RCP4.5 and RCP8.5 (RCP: representative concentration pathway). The model predicted an increase in biomass, canopy cover, and tree height under the presence of CO2 fertilization, which triggered transitions towards tree-dominated biomes by the end of the 21st century under both RCPs. I found that vegetation along the Western Ghats and the Himalayas are more susceptible to change due to climate change and open biomes such as grassland and savanna are prone to woody encroachment.
In Chapter 4, the study domain was extended to include South-east Asia to verify if the model configuration used in Chapter 3 can also simulate vegetation patterns in tropical Asia. The aDGVM2 simulations showed a robust trend of increasing vegetation biomass and transitions from small deciduous vegetation to taller evergreen vegetation across most of tropical Asia. Shifts in plant phenology also affect ecosystem carbon cycles and ecosystem feedback to climate, yet the quantification of such impacts remains challenging. The study showed increased biomass due to CO2 fertilization, indicates that the region can remain a carbon sink given there is no other resource limitation. However, nutrient limitations on CO2 fertilization effects were not included in the study, and carbon sink potential has to be seen with caution.
In Chapter 5, I focused on Asian savannas, which have been mismanaged since the colonial era due to misinterpretation as a degraded forest. I proposed a biome classification scheme to distinguish between degraded forest or woodland and savanna based on the abundance of grass biomass and canopy cover. I found that considering vegetation systems as woodland or degraded forest could easily be mistaken as a potential for forest restoration within a tree-centric perspective. This would put approximately 35% to 40% of a unique savanna biome at risk. Although projected woody encroachments may imply a transition toward the forest that benefits climate mitigation. This raises potential conflicts of interest between biodiversity conservation in open ecosystems, i.e., savanna and active afforestation, to enhance carbon sequestration. Proper management strategies should be taken into account to maintain a balance for both objective
In conclusion, the model predicted that vegetation in South and South-East Asia would significantly shift towards tree-dominated biomes due to CO2-induced fertilization of C3-photosynthesis. The simulation under fixed CO2 and rising CO2 scenarios clearly showed that rising level of atmospheric CO2 is responsible for most of the predicted change in biome properties. This study is an important step towards understanding ecosystems of South and Southeast Asia, specifically savannas. The aDGVM2 can serve as tools to inform decision making for climate adaptation and mitigation for savanna. The thesis, thus contributes to our ability to improve conservation strategies to mitigate the consequences of climate change.
Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth’s surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry 15 measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope δ-δ paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different 20 alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5°C) yield a near sea level precipitation δ18Ow value of -5.8 ± 0.2‰ and in conjunction with the high-Alpine phyllosilicate δD record suggest that the region surrounding the SFZ attained surface elevations of >4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between -4.2 and -7.6‰ for the Northern Alpine Foreland Basin.
Reconstructing Oligocene–Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps remain scarce. Here we present stable and clumped isotope measurements to provide a new paleoelevation estimate for the mid-Miocene (∼14.5 Ma) European Central Alps. We apply stable isotope δ–δ paleoaltimetry to near-sea-level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30±5 ∘C) yield a near-sea-level precipitation δ18Ow value of ‰ and, in conjunction with the high-Alpine phyllosilicate δD value of ‰, suggest that the region surrounding the Simplon Fault Zone attained surface elevations of >4000 m no later than the mid-Miocene. Our near-sea-level δ18Ow estimate is supported by paleoclimate (iGCM ECHAM5-wiso) modeled δ18O values, which vary between −4.2 ‰ and −7.6 ‰ for the Northern Alpine Foreland Basin.
In many parts of the world, the centralized grid provides energy to the population only to a limited extent. The electrification for sub-Saharan Africa countries is the lowest in the world, representing half of the world's population withoutelectricity. However, during the last years there has been an increased attention to rural areas in the Global South beyond the centralised grid, especially with respect to improved possibilities of solar power systems. The transition from one dominant form of energy provision to various alternatives includes different dimensions and depends on specific socio-spatial contexts. Energy systems are framed within systems of spatial practices, performed by a variety of involved actors, like consumers, local suppliers, international for-profit companies, international development donors as well as national and regional authorities. As such power systems arealways cause and effect of socio-technical change This study takes the example of Rwanda to analyse the marketization of decentralised energy systems. Based on empirical field work with energy entrepreneurs it combines Post-Colonial Theory with Science and Technology-Studies to theorise the role of energy to the social production of space beyond the grid.
Container-breeding Aedes spp. (Diptera: Culicidae) mosquitoes can be surveilled at low cost using ovitraps. Hence, this method is a preferred monitoring approach of dengue vectors in low-resource settings. The ovitraps consist of a cup filled with water and an oviposition substrate for female mosquitoes. The attractiveness of the substrates for female mosquitoes can greatly differ due to differences in texture, color, and smell of the materials used. We compare four oviposition substrates, which are all low priced, easy to transport, and easy to purchase, to maximize the success of Aedes egg sampling. Sampled egg material is often reared to adulthood for further taxonomic identification and transported to (international) laboratories for specialized vector research. Here we introduce a transport technique for sampled eggs. In addition, we explored the impact of international transport by means of a bilateral hatching experiment in Nepal, the country of origin, and in Germany, in a laboratory specialized in ecophysiological research. The best low-cost oviposition substrate for the dengue vectors Aedes albopictus (Skuse) and Aedes aegypti (L.) was found to be a white cotton sheet. The introduced transport technique of sampled eggs is easy to build from laboratory and household materials and ensures good transport conditions (i.e., temperature and relative humidity). Even under good temperature (17.4–31.0 °C) and humidity conditions (58.9–94.2%), hatching success of eggs was found to be reduced after international transport to Germany when compared to the hatching success of eggs in Nepal. We postulate that air pressure during international transport may have reduced the hatching success and strongly recommend pressure-regulated transport boxes for egg transport via airplane. As the proposed operation procedure is useful in assisting the monitoring of Ae. albopictus and Ae. aegypti in low-resource settings, Aedes researchers are encouraged to follow it for the sampling and transport of Aedes eggs.
In Germany, a grave labor shortage in the nursing and elderly care sectors has prompted the response of recruiting skilled nursing staff from abroad in recent years. This article analyzes these recruitment practices as forms of “migration management”: German migration policy has changed according to this paradigm to attempt utilitarian control over migration processes and mediate between labor market concerns on the one hand and isolationist, politico-cultural seclusion on the other. Based on original research through interviews and document analysis, we identify four relevant levels of analysis in researching migration management in the context of the recruitment of skilled nurses: (1) Definition of problem areas: How is migration programmatically legitimized as a solution to social problems? (2) Categorization of migration: How are migration processes classified? (3) Change in statehood: How are sites and actors of migration control being privatized and diversified? (4) Technologies: By means of which procedures, legal foundations and political instruments does migration management take place in the everyday? We believe that taking these four foci as points of departure would be beneficial for further inquiries in critical migration research.
Eisbildende Prozesse sind für die Wolkenbildung von großer Bedeutung und haben erhebliche Auswirkungen auf das Wetter und Klima der Erde, indem sie den Strahlungsantrieb und die Niederschlagsbildung beeinflussen. In den mittleren Breiten entsteht der meiste Niederschlag in sogenannten Mischphasenwolken (MPC), welche sowohl aus unterkühlten Wolkentröpfchen als auch aus Eiskristallen bestehen. Bei Temperaturen zwischen 0°C und -38°C erfolgt die Bildung von Eiskristallen in MPC in Gegenwart von Aerosolpartikeln, die als sogenannte Eiskeime (INP) die Fähigkeit besitzen, auf ihrer Oberfläche Eis zu nukleieren. Trotz der großen wissenschaftlichen Fortschritte in den letzten Jahrzehnten, weist der heterogene Eisbildungsprozess, als einer der wichtigsten in der Atmosphäre auftretenden Aerosol-Wolken-Wechselwirkungsprozesse, immer noch große Unsicherheiten auf. Um zukünftige Klimavorhersagen und -projektionen in Modellen besser abbilden zu können, ist es somit notwendig den Wissensgrad der räumlichen und zeitlichen Heterogenität von INP in Bezug auf Herkunft, Anzahl und Zusammensetzung zu erhöhen. Im Zentrum dieser Arbeit steht der Eiskeimzähler FINCH (Fast Ice Nucleus Chamber), der für Labor- und Feldexperimente von der Johann Wolfgang Goethe-Universität in Frankfurt am Main entwickelt wurde. Durch das Mischen des Probenstroms mit einem warm-feuchten und einem kalten-trockenen Luftstrom wird eine Übersättigung in der in-situ Eiskammer erreicht, die benötigt wird, eisbildende Partikel zu aktivieren. Die aktivierten Partikel können beim Durchströmen der Kammer zu Wassertropfen oder Eiskristallen anwachsen. Am Ausgang der Kammer wird die Anzahl und Größe der Partikel durch die FINCH-Optik erfasst. Als grundlegender Schritt und aufbauend auf den Charakterisierungsmessungen von Frank (2017) wurden in der vorliegenden Arbeit die Leistung, die Zuverlässigkeit sowie die Reproduzierbarkeit von FINCH in Validierungsexperimenten im Labor überprüft. Im Zuge dessen wurden heterogene Gefrierexperimente mit definierten Referenzaerosolproben (bspw. K-Feldspat) bei wasserübersättigten Bedingungen und verschiedenen Gefriertemperaturen durchgeführt. Für den Großteil der erzielten Resultate konnte eine zufriedenstellende Übereinstimmung mit Literaturwerten von anderen INP-Messinstrumenten aus der ganzen Welt erzielt werden. Es zeigte sich, dass die Leistungsfähigkeit von FINCH messtechnische Limitationen für Messexperimente bei Temperaturen >-10°C und <-30°C aufweist, was eine Einschränkung des Messbereichs bedeutet. Hinsichtlich der Quantifizierung des Unsicherheitsbereiches des Messgerätes in Bezug auf Temperatur und relativer Feuchte bedarf es im Nachgang an dieser Arbeit weiterer Charakterisierungsmessungen. Im Rahmen der Ice Nuclei Research Unit (INUIT) Forschergruppe wurde FINCH mit einem gepumpten Gegenstrom-Impaktor PCVI und dem online Einzelpartikel-Massenspektrometer ALABAMA gekoppelt. Diese spezielle Messmethodik dient zur chemischen und mikrophysikalischen Charakterisierung der INP und der Eispartikelresiduen (IPR). Der Fokus lag zunächst darauf die Funktionalität des gekoppelten Messsystems im Labor zu überprüfen. Ausführliche Charakterisierungsmessungen zeigten unter eisübersättigten und unterkühlten Bedingungen, dass das Prinzip der Trennung der INP von nicht-aktivierten Aerosolen und unterkühlten Tropfen hinter FINCH durch den PCVI funktioniert. Ebenso konnten erste quantitative Aussagen zur chemischen Zusammensetzung der IPR getroffen werden. Es zeigte sich, dass bei den Aktivierungsexperimenten ein geringer Anteil an Partikeltypen metallischer Art von ALABAMA detektiert wurden, der nicht dem untersuchten Aerosoltyp zugeordnet werden konnte. Der Ursprung dieser Kontamination konnte im Rahmen dieser Arbeit nicht abschließend geklärt werden und bedarf weiterer Validierungsmessungen im Labor. Atmosphärische Eiskeimkonzentrationen wurden im Rahmen von Feldmesskampagnen an der Hochalpinen Forschungsstation Jungfraujoch (JFJ) in den Schweizer Alpen und am Campus Riedberg der Johann Wolfgang Goethe-Universität in Frankfurt am Main untersucht. Hier konnten erste Erfahrungen mit Außenluftmessungen bezüglich der Leistungsfähigkeit und der Nachweisgrenze (LOD) des Messgerätes gesammelt werden. Durch den Einfluss der freien Troposphäre am JFJ waren die Messungen hauptsächlich von aerosolpartikelarmer Luft mit einer geringen Anzahl von Eiskeimen geprägt, so dass sich die gemessenen INP-Konzentrationen oftmals unter die Nachweisgrenze von FINCH fielen. Unter Einsatz eines Aerosolkonzentrators konnte die Detektionseffizienz verbessert und das LOD herabgesetzt werden. Am JFJ wurden die INP im Mittel bei einer Temperatur von -23°C und einem Wassersättigungsverhältnis von 107% beprobt. Die mediane (mittlere) INP-Konzentration inklusive LOD lag bei 2,1 (3,3) sL-1 und oberhalb des LOD bei 3,1 (4,5) sL-1. Ein Vergleich mit den Messungen am Campus Riedberg unter annähernd gleichen Bedingungen resultiert in ähnlichen Konzentrationen.
Chondrules are thought to play a crucial role in planet formation, but the mechanisms leading to their formation are still a matter of unresolved discussion. So far, experiments designed to understand chondrule formation conditions have been carried out only under the influence of terrestrial gravity. In order to introduce more realistic conditions, we developed a chondrule formation experiment, which was carried out at long-term microgravity aboard the International Space Station. In this experiment, freely levitating forsterite (Mg2SiO4) dust particles were exposed to electric arc discharges, thus simulating chondrule formation via nebular lightning. The arc discharges were able to melt single dust particles completely, which then crystallized with very high cooling rates of >105 K h−1. The crystals in the spherules show a crystallographic preferred orientation of the [010] axes perpendicular to the spherule surface, similar to the preferred orientation observed in some natural chondrules. This microstructure is probably the result of crystallization under microgravity conditions. Furthermore, the spherules interacted with the surrounding gas during crystallization. We show that this type of experiment is able to form spherules, which show some similarities with the morphology of chondrules despite very short heating pulses and high cooling rates.
In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.
The formation of terrestrial planets was a complex process which begun in the very early stage of the Solar System in the protoplanetary disk (PPD). Chondrites are fragments of planet precursors, which have never experienced differentiation and can help to reconstruct the first processes leading to planet formation. The main components of chondrites are chondrules, calcium-aluminum-rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), metals and fine-grained material. Each of these components formed by a complex mechanism involving aggregation and/or melting. Previous research has already provided an overall view of the formation of these objects, however, there are still open questions regarding the aggregation behavior of particles, the heating mechanism(s) and the thermal history of CAIs, AOAs and chondrules. For instance, the involvement of flash-heating events and electrostatics in the aggregation and melting of these objects has been a keen topic of discussion.
The aim of this doctoral thesis was to develop and carry out an experiment to study various early Solar System processes under long-term microgravity. In the project with the acronym EXCISS (Experimental Chondrule Formation aboard the ISS), free-floating, 126(23)µm-sized Mg2SiO4 dust particles were exposed to electric fields and electric discharges.
The experimental set-up was installed inside a 10x10x15 cm3-sized container and consisted of an arc generation unit connected to the sample chamber, a camera with an optical system, a power supply unit with lithium-ion batteries and the EXCISS mainboard with a Raspberry Pi Zero and mass storage devices. The sample chamber was manufactured from quartz glass and the experiments were filmed. The complete experiment container was subsequently returned to the Goethe University and the samples were analyzed with scanning electron microscopy, electron backscatter diffraction and synchrotron micro-CT.
Video analysis has shown that particles, which were agitated by electric discharges, align in chains within the electric field with their longest axis parallel to the electric field lines. Consequently, electric fields could have influenced the inner structure and porosity of particle aggregates in the PPD.
The discharge experiments produced fused aggregates and individual melt spherules.
The fused aggregates share many morphological characteristics with natural fluffy-type CAIs and some igneous CAIs found in chondrites. Consequently, CAIs could have formed by the aggregation of particles with various degrees of melting. Further, a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to, and subsequent compaction within, developing planetesimals.
Some initial particles were completely melted by the arc discharges and formed melt spherules. The newly formed olivines crystallized with a preferred orientation of the [010] axis perpendicular to the surface of the spherule. Similar preferred orientations have been found in natural chondrules. However, the microstructure differs from the results of previous experiments on Earth, which show, for example, crystal settling on one side of the sample because of the influence of gravity. Furthermore, the melt spherules show evidence for an interaction of the melt with the surrounding hot gas. Therefore, microgravity experiments with more advanced experimental parameters bear great potential for future chondrule formation experiments.
The organisation of parking is a key challenge to more sustainable mobility in urban areas, as its pricing and availability affect the rates of private car ownership and use. However, changing parking policies is a challenging issue for local politicians and planners because residents frequently oppose changes or restrictions to conditions they have taken for granted such as on-street parking in a public space. The aim of this paper is firstly to assess how the parking policy of an urban neighbourhood can be structured to contribute to more sustainable mobility and to increase liveability in the neighbourhood. The second aim is to apply the policies reviewed to an example neighbourhood. For this purpose, we systematically reviewed academic literature and identified five types of relevant parking policies: (i) maximum parking requirements, (ii) physical detachment of residence and parking space, (iii) residential parking permits and the limitation of available parking space, (iv) performance-based pricing and (v) parking as a demand management strategy. We discovered that most research focuses on econometric models about parking and that studies rarely address the effects of parking on the quality of life in neighbourhoods. Therefore, we need further research regarding the relationship of parking and liveability. We conclude that for the implementation of such parking policies in an example neighbourhood, the municipality needs to develop a mobility vision for its city. It has to understand parking as a tool for transportation demand management to increase the acceptance of parking policy concepts and to avoid spillover problems. Finally, in the German case, as in most other countries, states and municipalities need to redesign their legal frameworks to be able to manage parking supply better and to react to changes related to digital developments and parking. The findings have implications for other European neighbourhoods regarding the transfer from research to local circumstances and applications for the whole city.
Support for innovative on-street parking policies: empirical evidence from an urban neighborhood
(2020)
Municipalities and planners often hesitate to implement restrictive parking policies because residents regularly oppose any changes to on-street parking space. Residential parking is one key factor of parking management because its location and availability influence a household's car ownership and use. Moreover, as more residents regularly use other means of transportation that need space and infrastructure in the urban realm, and as parking takes up a vast amount of land, municipalities are considering the reuse of on-street parking space for other purposes. As public acceptability is a precondition for the successful implementation of a proposed policy, our empirical analysis investigates to what extent residents support restrictive and demand-oriented on-street parking policies in the dense, highly urbanized neighborhood of Frankfurt-Bornheim, Germany (N = 1027). Surprisingly, despite some variations, the majority of the residents in our survey are in favor of the policy options suggested. Support for the demand-oriented policies (extension of bicycle infrastructure, improved sharing supply and mobility hubs, neighborhood garages, and improved public transit supply) is higher than the acceptance of the restrictive policies, and of policies that are a combination of restrictive and demand-oriented policies. However, surprisingly, a majority is still in favor of many of these (extension of parking fees and parking restrictions, and reuse of parking space for better livability). Furthermore, we classify residents who live in a household with private cars into the stage model of self-regulated behavior change to analyze their intention towards a reduction in private car use. Results from linear regression analyses indicate that residents who have intentions to change their behavior towards car use reduction assess the policy options more similarly to car-free households and regular bike users, and not like the other car-owning households. The findings suggest that while the residents support financial-related policies the least, they are more receptive towards parking policies than policy makers and planners assume if the reuse of parking lots creates space for other users or if it increases the quality of life, for instance, by adding bike lanes, wider sidewalks or greenery. Hence, a combination of restrictive and demand-oriented on-street parking policies results in high acceptance among residents, and the communication from municipalities regarding the implementation of the different policies needs to vary depending on the kind of household.
The infrastructure for parking and parked cars themselves (e.g., parked cars blocking bike lanes and sidewalks or the visibility range) can lead to conflicts for pedestrians and cyclists. The perception of conflicts could discourage walking and cycling in neighborhoods and undermine municipalities’ efforts to provide more sustainable urban mobility. The aim of this study was therefore to analyze the effect of on-street car parking in urban neighborhoods on perceived parking and traffic-related conflicts. In addition, it examines in what way the intention to reduce one’s car use influences the perception of the conflicts (Stage Model of Self-Regulated Behavior Change (SSBC)). A household survey was conducted in the inner-city neighborhood of Frankfurt-Bornheim, Germany (N=1027). The residents most often observed the conflicts in which parked cars impeded walking and cycling as well as situations in which pedestrians felt threatened by cyclists biking on the sidewalk. Results from multiple linear regression models revealed that the influencing factors for the perception of conflicts were the use of different means of transportation and the intention to change one’s behavior (SSBC model) to reduce car use rather than car ownership. In addition, a resident’s age and household structure seemed to affect awareness of conflicts in which pedestrians and cyclists were involved. The results suggest a group-serving bias, meaning that the residents mostly observed those conflicts that they did not cause. A separate infrastructure for pedestrians and cyclists could help prevent most of the conflicts described in this study.
The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.
The endemic argan tree (Argania spinosa) populations in South Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth, but show lower soil quality than their neighbouring tree areas. Hypothetically, spatial differences of soil quality of the intertree area should result from translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) as well as the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) and analysed for soil moisture, pH, electrical conductivity, percolation stability, total nitrogen content, content of soil organic carbon and C/N ratio. 74 tension-disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with e.g., Corg- & N-content decreasing significantly from tree trunk to tree drip line. However, intertree areas near the tree drip line differed significantly from intertree areas between two trees, yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil moisture was highest in the north due to shade from the midday sun, the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil moistures, N- or Corg-content to ensure seedling survival.
A general circulation model is used to study the interaction between parameterized gravity waves (GWs) and large-scale Kelvin waves in the tropical stratosphere. The simulation shows that Kelvin waves with substantial amplitudes (∼10 m s−1) can significantly affect the distribution of GW drag by modulating the local shear. Furthermore, this effect is localized to regions above strong convective organizations that generate large-amplitude GWs, so that at a given altitude it occurs selectively in a certain phase of Kelvin waves. Accordingly, this effect also contributes to the zonal-mean GW drag, which is large in the middle stratosphere during the phase transition of the quasi-biennial oscillation (QBO). Furthermore, we detect an enhancement of Kelvin-wave momentum flux due to GW drag modulated by Kelvin waves. The result implies an importance of GW dynamics coupled to Kelvin waves in the QBO progression.
Plain Language Summary: The variability of the tropical atmosphere at altitudes of about 18–40 km is dominated by a large-amplitude long-term oscillation of wind, the quasi-biennial oscillation, which has a broad impact on the climate and seasonal forecasting. This oscillation is known to be driven by various types of atmospheric waves with multiple spatial scales. Using a numerical model, this study reports a process of interaction between those waves on different scales, which has not been illuminated before. The result implies a potential importance of this process in the progression of the quasi-biennial oscillation. Proper model representations of these multiscale waves and tropical convection are required to simulate this process.
We present novel measurements of five short-lived brominated source gases (CH2Br2, CHBr3, CH2ClBr, CHCl2Br and CHClBr2) obtained using a gas chromatograph-mass spectrometer system on board the High Altitude and Long Range Research Aircraft (HALO). The instrument is extremely sensitive due to the use of chemical ionisation, allowing detection limits in the lower parts per quadrillion (10-15) range. Data from three campaigns using the HALO aircraft are presented, where the Upper Troposphere/Lower Stratosphere (UTLS) of the Northern Hemisphere mid to high latitudes were sampled during winter and during late summer to early fall. We show that an observed decrease with altitude in the stratosphere is consistent with the relative lifetimes of the different compounds. Distributions of the five source gases and total organic bromine just below the tropopause shows an increase in mixing ratio with latitude, in particular during polar winter. This increase in mixing ratio is explained by increasing lifetimes at higher latitudes during winter. As the mixing ratio at the extratropical tropopause are generally higher than those derived for the tropical tropopause, extratropical troposphere-to-stratosphere transport will result in elevated levels of organic bromine in comparison to air transported over the tropical tropopause. The observations are compared to model estimates using different emission scenarios. A scenario which has emissions most strongly concentrated to low latitudes cannot reproduce the observed latitudinal distributions and will tend to overestimate bromine input through the tropical tropopause from CH2Br2 and CHBr3. Consequently, the scenario also overestimates the amount of brominated organic gases in the stratosphere. The two scenarios with the highest overall emissions of CH2Br2 tend to overestimate mixing ratios at the tropical tropopause but are in much better agreement with extratropical tropopause values, showing that not only total emissions but also latitudinal distributions in the emissions are of importance. While an increase in tropopause values with latitude is reproduced with all emission scenarios during winter, the simulated extratropical tropopause values are on average lower than the observations during late summer to fall. We show that a good knowledge of the latitudinal distribution of tropopause mixing ratios and of the fractional contributions of tropical and extratropical air is needed to derive stratospheric inorganic bromine in the lowermost stratosphere from observations. Depending on the underlying emission scenario, differences of a factor 2 in reactive bromine derived from observations and model outputs are found for the lowermost stratosphere, based on source gas injection. We conclude that a good representation of the contributions of different source regions is required in models for a robust assessment of the role of short-lived halogen source gases on ozone depletion in the UTLS.
Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
Global analysis of halogenated trace gases in the UTLS: from long-lived to short-lived substances
(2023)
In this dissertation, the distribution of chlorinated and brominated substances in the upper troposphere and lower stratosphere is investigated. These substances contribute significantly to the catalytic decomposition of ozone and are involved in the recurrent formation of the polar ozone hole in the Antarctic winter and spring. The Montreal Protocol, a multilateral environmental treaty to protect the ozone layer, has successfully reduced emissions of long-lived chlorine- and bromine-containing substances. Short-lived chlorinated and brominated substances, some of which are natural and anthropogenic in origin, are not regulated by the Montreal Protocol and it can be assumed that their relative contribution to the stratospheric halogen budget will increase, while the contribution of long-lived compounds will steadily decrease. The distribution of long- and short-lived halogenated substances are part of current research. For the upper troposphere and lower stratosphere, the very short-lived substances are particularly important. The lower stratosphere needs special investigation in this respect, since its composition is influenced by different transport processes. The influences on ozone trends in the lower stratosphere are subject to great uncertainties. Especially in the Southern Hemisphere, the number of observations is very limited.
In this work, the GhOST (Gas chromatograph for Observational Studies using Tracers) instrument was used during the SouthTRAC measurement campaign on the German HALO (High Altitude and LOng range) research aircraft, providing observations of halogenated hydrocarbons in Antarctic late winter to early spring 2019, a generally poorly sampled region. The polar vortex was, compared to previous years, significantly weaker and shifted towards the eastern South Pacific and South America. From the airborne measurements of chlorinated source gases, inorganic chlorine (the sum of active chlorine and reservoir gases; Cly) could be inferred with the result that Cly within the vortex increased up to 1687 ± 19 ppt at 385 K potential temperature, accounting for about 50 % of the total chlorine within the vortex and only 15 % of the total chlorine in the southern mid-latitudes. A comparison with the Northern Hemisphere could be made using the PGS measurement campaign in the Arctic winter 2015/2016. Under comparable conditions (season and distance from the tropopause), only 40 % of the total chlorine was in the inorganic form within the Arctic polar vortex and about 20 % was found in the mid-latitudes of the Northern Hemisphere. In addition, about 540 ppt more Cly was present in the Antarctic vortex than in the Arctic vortex, exceeding the annual variations previously reported for Antarctica.
The mean age of air plays an essential role in the derivation of Cly via the organic source gases, as was done in this work. A new method for determining the mean age of air from observational data has been introduced that accounts for extra-tropical input to the stratosphere in addition to tropical input. This new method was compared with the previously used method, which considered only the tropical input. The new method shows more realistic values especially near the tropopause. On average, the air of the lower stratosphere in the Northern Hemisphere was older than in the Southern Hemisphere by about 0.5 ± 0.3 years. About 65 K above the tropopause, the pattern changed with older air in the mid-latitudes of the Northern Hemisphere, but older air in high latitudes of the Southern Hemisphere, which implies differences in the strength and isolation of the respective polar vortex as well as the wave forcing in the shallow branch of the Brewer-Dobson circulation of the respective hemisphere. This is in good agreement with the distribution of Cly. The difference in the lower stratosphere was not clearly evident with the old method and it can be assumed that investigations of the differences in Cly of Northern and Southern Hemisphere will benefit from the new method.
Finally, the global and seasonal distribution of the two most important representatives of the short-lived brominated substances, CH2Br2 and CHBr3, was investigated. For this purpose, two additional HALO measurement campaigns have been used, the 2012 TACTS measurement campaign and the 2017 WISE measurement campaign, as well as the HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography (ATom) measurement campaigns. Observations of CH2Br2 show a pronounced seasonality in the free and upper troposphere of both hemispheres with slightly larger values in the Northern Hemisphere. CHBr3, on the other hand, shows a generally higher variability and lower seasonality with larger mixing ratios at mid and high latitudes in the northern hemispheric winter and autumn. A comparison of the lower stratosphere is limited to autumn and spring of both hemispheres due to the limited data basis of the observations. The distributions in each spring are similar (less than 0.1 ppt differences for e.g., CH2Br2). In hemispheric autumn, larger differences are evident with substantially smaller mixing ratios in the southern hemispheric lower stratosphere. This suggests that the transport processes of the two hemispheres may be different and implies that the input of tropospheric air (flushing) to the Northern Hemisphere lowest stratosphere is more efficient than in the Southern Hemisphere. Vertical profiles of CH2Br2 and CHBr3 in the mid-latitudes of both hemispheres and resulting vertical gradients support this conjecture. However, the Southern Hemisphere data set is insufficient to quantify this difference and further measurements are needed.
In light of the global sea-level rise and climate change of the 21th century, it is important to look back into the recent past in order to understand what the future might hold. A multi-proxy data set was compiled to evaluate the influence of geomorphological and environmental factors, such as antecedent topography, subsidence, sea level and climate, on reef, sand apron and lagoon development in modern carbonate platforms through the Holocene. Therefore, a combination of remote sensing and morphological data from 122 modern carbonate platforms and atolls in the Atlantic, Indian and Pacific Oceans were conducted, along with a case study from the oceanic (Darwinian) barrier-reef system of Bora Bora, French Polynesia, South Pacific.
The influence of antecedent topography and platform size as factors controlling Holocene sand apron development and extension in modern atolls and carbonate platforms is hypothesized. Antecedent topography describes the elevation and relief of the underlying Pleistocene topography (karst) and determines the distance from the sea floor to the rising postglacial sea level. Maximum lagoon depth and marginal reef thickness, when available in literature, were used as proxies for antecedent topography. Sand apron proportions of 122 atolls and carbonate platforms from the Atlantic, Indian and Pacific Oceans were quantified and correlated to maximum lagoon depth, total platform area and marginal reef thickness. This study shows that sand apron proportions increase with decreasing lagoon depths. Sand apron proportions also increase with decreasing platform area. The interaction of antecedent topography and Holocene sea-level rise is responsible for variations in accommodation space and at least determines the extension of the lateral expansion of sand aprons. In general, sand apron formation started when marginal reefs approached relative sea level. Spatial and regional variations in sea-level history let sand apron formation start earlier in the Indo-Pacific region (transgressive-regressive) than in the Western Atlantic Ocean (transgressive).
The influence of sea level, antecedent topography and subsidence of a volcanic island on late Quaternary reef development was evaluated based on six rotary core transects on the barrier and fringing reefs of Bora Bora. This study was designed to revalue the Darwinian model, the subsidence theory of reef development, which genetically connects fringing reef, barrier reef and atoll development by continuous subsidence of the volcanic basement. Postglacial sea-level rise, and to a minor degree subsidence, were identified as major factors controlling Holocene reef development in that they have created accommodation space and controlled reef architecture. Antecedent topography was also an important factor because the Holocene barrier reef is located on a Pleistocene barrier reef forming a topographic high. Pleistocene soil and basalt formed the pedestal of the fringing reef. Uranium-Thorium dating shows that barrier and fringing reefs developed contemporaneously during the Holocene.
In the barrier–reef lagoon of Bora Bora, the influence of environmental factors, such as sea level and climate, tsunamis and tropical cyclones controlling Holocene sediment dynamics was evaluated based on sedimentological, paleontological, geochronological and geochemical data. The lagoonal succession comprises mixed carbonate-siliciclastic sediments overlying peat and Pleistocene soil. The multi-proxy data set shows variations in grain-size, total organic carbon (proxy for primary productivity), Ca and Cl element intensities (proxies for carbonate availability and lagoonal salinity) during the mid-late Holocene. These patterns could result from event sedimentation during storms and correlate to event deposits found in nearby Tahaa, probably induced by elevated cyclone activity. Accordingly, elevated erosion and runoff from the volcanic island and lower lagoonal salinity would be a result of rainfall during repeated cyclone landfall. However, Ti/Ca and Fe/Ca ratios as proxies for terrigenous sediment delivery peaked out in the early Holocene and declined since the mid-Holocene. Benthic foraminifera assemblages do not indicate reef-to-lagoon transport. Alternatively, higher and sustained hydrodynamic energy is probably induced by stronger trade winds and a higher-than-present sea level during the mid-late Holocene. The increase in mid-late Holocene sediment dynamics within the back-reef lagoon is supposed to display sediment-load shedding of sand aprons due to the oversteepening of slopes at sand apron/lagoon edges during their progradation rather than an increase in tropical storm activity during that time.
The influence of sea-level and climate changes on sediment import, composition and distribution in the Bora Bora lagoon during the Holocene is validated. Lagoonal facies succession comprises siderite-rich marly wackestones, foraminifera-siderite wackestones, mollusk-foraminifera marly packstones and mollusk-rich wackestones during the early-mid Holocene, and mudstones since the mid-late Holocene. During the early Holocene, enhanced weathering and iron input from the volcanic island due to wetter climate conditions led to the formation of siderite within the lagoonal sediments. The geochemical composition of these siderites shows that precipitation was driven by microbial activity and iron reduction in the presence of dissolved bicarbonate. Chemical substitutions at grain margins illustrate changes in the oxidation state and probably reflect changes in pore water chemistry due to sea-level rise and climate change (rainfall). In the late Holocene, sediment transport into the lagoon is hampered by motus on the windward side of the lagoon, which led to early submarine lithification within the lagoon.
Aim: Biological invasions are likely determined by species dispersal strategies as well as environmental characteristics of a recipient region, especially climate and human impact. However, the contribution of climatic factors, human impact, and dispersal strategies in driving invasion processes is still controversial and not well embedded in the existing theoretical considerations. Here, we study how climate, species dispersal strategies, and human impact determine plant invasion processes on islands distributed in all major oceans in the context of directional ecological filtering.
Location: Six mountainous, tropical, and subtropical islands in three major oceans: Island of Hawai'i and Maui (Pacific), Tenerife and La Palma (Atlantic), and La Réunion and Socotra (Indian Ocean).
Taxon: Vascular Plants.
Methods: We recorded 360 non-native species in 218 plots along roadside elevational transects covering the major temperature, precipitation and human impact (i.e., road density) gradients of the islands. We collected dispersal strategies for a majority of the recorded species and calculated the environmental niche per species using a hypervolume approach.
Results: Non-native species’ generalism (i.e., mean community niche width) increased with precipitation, elevation and human impact but showed no relationship with temperature. Increasing precipitation led to environmental filtering of non-native species resulting in more generalist species under high precipitation conditions. We found no directional filtering for temperature but an optimum range of most species between 10 and 20°C. Niche widths of non-native species increased with the prevalence of certain dispersal strategies, particularly anemochory and anthropochory.
Main conclusions: Plant invasion on tropical and subtropical islands seems to be mainly driven by precipitation and human impact, while temperature seems to be of little importance. Furthermore, anemochory and anthropochory are dispersal strategies associated with large niche widths of non-native species. Our study allows a more detailed look at the mechanisms behind directional ecological filtering of non-native plant species in non-temperature-limited ecosystems.
Triple oxygen isotope measurements are an emerging tool in paleoclimate reconstructions. In this contribution we develop the application of triple oxygen isotope measurements to lacustrine sediments to reconstruct past elevations. We focus on a well-constrained sample set from the Eocene North American Cordillera (Cherty Limestone Formation, Elko Basin, NV, United States, 42–43.5 Ma) on the east side of the elevated Nevadaplano. We present triple oxygen isotope measurements on freshwater lacustrine chert samples from the Cherty Limestone Formation. Across an evaporation trend spanning 6.5‰ in δ18O values we observe a negative correlation with Δ′17O ranging from −0.066 to −0.111‰ (λRL = 0.528), with an empirical slope (λchert, δ′17O vs. δ′18O) of 0.5236. Additionally, we present new carbonate clumped isotope (Δ47) temperature results on the overlying fluvial-lacustrine Elko Formation, which indicate an error-weighted mean temperature of 32.5 ± 3.8°C (1σ), and evaporatively enriched lake water spanning δ18O values of −3.7 to +3.5‰ (VSMOW). Paired chert and carbonate δ18O values demonstrate that co-equilbrium among the carbonate and chert phases is unlikely. Thus, as also previously suggested, it is most likely that Elko Basin chert formed during early diagenesis in equilbirium with pore waters that reflect evaporatively 18O-enriched lake water. Using this scenario we apply a model for back-calculating unevaporated water composition to derive a source water of δ′18O = −16.1‰ (VSMOW), similar to modern local meteoric waters but lower than previous work on paired δ18O- δD measurements from the same chert samples. Further, this back-calculated unevaporated source water is higher than those derived using δD measurements of Late Eocene hydrated volcanic glass from the Elko Basin (average δ′18O equivalent of approximately −18.4‰, VSMOW). This suggests, assuming Eocene meteoric water Δ′17O values similar to today (∼0.032‰), either that: (1) the hypsometric mean elevation recorded by the lacustrine Cherty Limestone was lower than that derived from the average of the volcanic glass δD measurements alone; or (2) there was hydrogen exchange in volcanic glass with later low δD meteoric fluids. Nonetheless, our new findings support a relatively high (∼2.5–3 km) plateau recorded in the Elko Basin during the mid-Eocene.
Metal artifacts from the Paleometal Epoch (ca. 1100 BC–400 AD) of the Primorye (Russian Far East) have shed new light on the introduction of the earliest bronzes into the Pacific coastal areas of prehistoric Eurasia. However, little is known about raw material circulation and the role of metal in the context of inter-regional exchange. This paper investigates 12 copper artifacts from major Paleometal settlements using alloy composition, trace elements, and lead isotopes to explore the metal sources and distribution networks. The results suggest that most objects are made of a copper-tin alloy, but some have arsenic as a significant minor element . Geologically, copper is unlikely to have come from local ore sources, but rather from the Liaoxi corridor and Liaodong Peninsula in Northeast China. This may indicate an inland route of metal trade across Northeast China or alternately, a coastal route via the northern Korean Peninsula. Archaeologically, the combined study of artifact typology and chemistry indicates two possible origins for the metal: the Upper Xiajiadian culture in Northeast China and Slab Grave culture in Mongolia/Transbaikal. Remarkably, the connection with Upper Xiajiadian communities parallels the transport route along which millet agriculture spread from Northeast China to the Primorye during the Neolithic.
Moisture sources of heavy precipitation in Central Europe in synoptic situations with Vb-cyclones
(2022)
During the past century, several extreme summer floods in Central Europe were associated with so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. The processes intensifying the precipitation in synoptic situations with Vb-cyclones in the Danube, Elbe, and Odra catchments are only partially understood. Our study aims to investigate these processes with Lagrangian moisture-source diagnostics for 16 selected Vb-events. Moreover, we analyse the characteristics of typical moisture source regions during 1107 Vb-events from 1901 to 2010 based on ERA-20C reanalysis dynamically downscaled with COSMO-CLM+NEMO. We observe moisture contributions by various source regions highlighting the complex dynamical interplay of different air masses leading to moisture convergence in synoptic situations with Vb-cyclones. Overall, up to 80% of the precipitation originates from the European continent, indicating the importance of continental moisture recycling, especially within the respective river catchment. Other major moisture uptake regions are the North Sea, the Baltic Sea, the North Atlantic, and for a few events the Black Sea. Remarkably, anomalies in these oceanic source regions show no connection to precipitation amounts in synoptic situations with Vb-cyclones. In contrast, the Vb-cyclones with the highest precipitation are associated with anomalously high evaporation in the Mediterranean Sea, even though the Mediterranean Sea is only a minor moisture source region on average. Interestingly, the evaporation anomalies are not connected with sea-surface temperature but with wind-speed anomalies (Spearman’s rank correlation coefficient R≈0.7, significant with p<0.01) indicating mainly dynamically driven evaporation. The particular role of the Mediterranean Sea hints towards possible importance of Mediterranean moisture for the early-stage intensification of Vb-cyclones and the pre-moistening of the continental uptake regions upstream of the target catchments.
Several past summer floods in Central Europe were associated with so-called Vb‑cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. This study illustrates the usefulness of the parametric transfer entropy measure TE‑linear in investigating heavy Vb‑cyclone precipitation events in the Odra catchment (Poland). With the application of the TE‑linear approach, we confirm the impact of the Mediterranean Sea on precipitation intensification. Moreover, we also detect significant information exchange to Vb‑cyclone precipitation from evaporation over the European continent along the typical Vb‑cyclone pathway. Thus, the Mediterranean Sea could enhance the Vb‑cyclone precipitation by pre-moistening continental moisture source regions that contribute to precipitation downstream in the investigated catchments. Overall, the transfer entropy approach with the measure TE‑linear proved to be computationally effective and complementary to traditional methods such as Lagrangian and Eulerian diagnostics.
Hydro-climatic causes of widespread floods in central Europe : on rain-on-snow and Vb-cyclone events
(2021)
The presented work investigates the hydro-meteorological and hydro-climatological drivers of widespread floods in Central Europe during the past century. Due to the strong seasonality of the detected flood drivers, the thesis is divided into two parts: the first part focuses on widespread winter floods and the second one on extreme summer floods. For analysing past flood events, we profited from the dynamically downscaled centennial ERA-20C reanalysis (continuously from 1901—2010). The downscaling was performed over Europe with a coupled regional atmosphere-ocean model (COSMO-CLM+NEMO) to represent the water cycle more realistic. These high resolution atmospheric data allowed us to study the four-dimensional atmospheric state during selected floods during the early decades of the 20th century for the first time with such a high temporal and spatial resolution.
During the winter half-year, the observed floods were particularly widespread. High peak discharges were recorded simultaneously in the Rhine, Elbe, and Danube catchments. Most of these trans-basin floods were compound events caused by rainfall during extensive snowmelt (i.e., rain-on-snow events). Interestingly, the winter flood time series exhibited a remarkable high flood frequency during the 1940s and 1980s, while other decades were flood-poor. We detected a synchronization of the inter-annual flood frequency with the superposition of the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCA). The negative NAO phase is often associated with large snowfall and cyclone tracks over southern Europe, while the negative SCA pattern correlates with total precipitation in the affected river catchments.
During the summer half-year, most extreme floods in Central Europe were caused by so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. So far in the literature, only a few Vb-events, which occurred during the past two decades, have been analysed. We extended the previous case studies by several past Vb-cyclone floods since 1900. We investigated the processes that intensify Vb-cyclone precipitation with Lagrangian moisture-source diagnostics and the parametric transfer entropy measure TE-linear. Overall, an enhanced and dynamically driven moisture uptake over the Mediterranean Sea was found to be characteristic for Vb-events with heavy precipitation. This is supported by high information exchange from evaporation over the western basin of the Mediterranean Sea towards heavy precipitation in the Odra catchment. The dominating moisture uptake regions during the investigated events were, however, the European continent and the North Sea. A possible cause could be the pre-moistening of non-saturated continental moisture sources upstream of the affected river catchments as indicated by significant information exchange from land surface evaporation and soil moisture content along the Vb-cyclone pathway. Besides, evaporation over the Mediterranean Sea might contribute to Vb-cyclone intensification in the early stages of their development through latent heat release. On the catchment scale, orographic rainfall and convective precipitation further enhance the flood triggering rainfall. As expected, the Vb-cyclones mainly trigger precipitation along west-east orientated mountain ranges such as the Alps or Ore mountains due to their meridional pathway. Remarkably, during summer, we detected a convective fraction of up to 90% during the afternoons of individual days and up to 23% on average (based on convective cell tracking and convection-permitting simulations of selected flood events since 1900).
The presented analyses deepened the knowledge on atmospheric and hydroclimatic drivers of widespread floods in Central Europe. This will serve as a basis for future studies on the predictability of floods induced by rain-on-snow and Vb-cyclone precipitation events in the context of a changing climate.
Die Abstrahlung von internen Schwerewellen in atmosphärischen Strahlströmen und Temperaturfronten trägt vermutlich mit einem signifikanten Beitrag zum gesamten Schwerewellenspektrum bei. Das physikalische Verständnis der dabei ablaufenden Prozesse ist derzeit allerdings noch zu gering ausgeprägt, um eine adäquate mathematische Darstellung für operationelle Wetter- und Klimamodelle zu entwickeln. In dieser Arbeit wird der Mechanismus dieser Schwerewellenquelle in numerischen Simulationen des differenziell geheizten rotierenden Annulusexperiments erforscht. Dieses Experiment besitzt eine im Vergleich zur Atmosphäre deutlich verringerte Anzahl an Freiheitsgraden und eignet sich besonders gut zum Studium der Dynamik der mittleren Breiten. Analoge Untersuchungen werden in einem äquivalenten kartesischen Modellsystem vorgenommen, in dem periodische Bedingungen in den beiden horizontalen Raumrichtungen vorliegen.
Im Gegensatz zur Annuluskonfiguration, in der nachweislich auch eine Schwerwellenabstrahlung an den Zylinderwänden erfolgt, kommt in dieser Konfiguration nur die interne Dynamik als Schwerewellenquelle in Frage. Die nichtlinearen Simulationen beider Modellkonfigurationen zeigen eine großskalige barokline Wellenstruktur, die ein atmosphärenähnliches Jet-Front System beinhaltet. Darin eingelagert werden vier voneinander isolierte Schwerewellenpakete in der Annuluskonfiguration sowie zwei Schwerewellenpakete im doppeltperiodischen Modellsystem charakterisiert. Um den zugrundeliegenden Quellmechanismus zu untersuchen, erfolgt eine Aufspaltung der Zustandsvariablen in einen balancierten und einen unbalancierten Anteil, wobei erstgenannter das geostrophische und hydrostatische Gleichgewicht erfüllt und letztgenannter das Schwerewellensignal enthält. Die Strömungsaufspaltung bildet die Grundlage für die Entwicklung eines tangential-linearen Modells für den unbalancierten Strömungsanteil. Hierbei wird eine systematische Umformulierung der dynamischen Grundgleichungen hinsichtlich der Wechselwirkung beider Strömungsanteile vollzogen. Insbesondere wird der rein balancierte Antrieb der unbalancierten Strömung freigelegt, um dessen Einfluss auf die Schwerewellenaktivität zu quantifizieren. Die anschließenden tangential-linearen Simulationen zeigen, dass drei der vier Schwerewellenpakete in der Annuluskonfiguration in der internen Strömung generiert werden. Ein verbleibendes Wellenpaket entsteht an der inneren Zylinderwand, ehe es in das innere Modellvolumen propagiert. Darüber hinaus wird deutlich, dass der rein balancierte interne Antrieb der Schwerewellen einen signifikanten Beitrag zur Schwerewellengenerierung leistet. Im doppeltperiodischen Modellsystem gibt es eine nahezu perfekte Übereinstimmung zwischen den unbalancierten Strömungsmustern in den tangential-linearen und den nichtlinearen Simulationen. Auch dort nimmt der balancierte Antrieb eine zentrale Rolle bei der Schwerewellenabstrahlung ein. Die abschließende Gegenüberstellung verschiedener, voneinander unabhängiger Gleichgewichtskonzepte macht deutlich, dass die balancierte Strömung der führenden Ordnung in der Rossbyzahl bereits eine erstaunliche Übereinstimmung mit der vollen Strömung liefert. Zudem erbringt die Anwendung einer Lagrange'schen Filtermethode den Nachweis, dass die Vertikalbewegungen und die horizontalen Divergenzsignale in der Annuluskonfiguration fast ausschließlich auf die Schwerewellenaktivität zurückzuführen sind.
Im Rahmen einer angewandten kritischen Geographie beschäftigen wir uns in unserer Masterarbeit mit Realen Utopien auf Quartiersebene und zeigen, dass eine alternative Neuausrichtung der Stadtplanung und -entwicklung nötig und möglich ist. Die Grundlage dafür bildet eine kritische Auseinandersetzung mit dem Begriff der Utopie und der Ebene des Quartiers. Das städtische Quartier bildet einen Möglichkeitsraum, einen space of hope (Harvey 2000), in dem Alternativen jenseits kapitalistischer Verwertungsinteressen praktiziert und gelebt werden können. Diesen Möglichkeitsraum gilt es vielfältig zu gestalten und gegenwärtigen, neoliberalen Stadtentwicklungs-paradigmen Reale Utopien(Wright 2017a) entgegenzustellen. Dabei stellt sich die Frage: Welche Gegenentwürfe zu aktuell herrschenden Paradigmen in der Stadtentwicklung zeigen uns Wege aus der Alternativlosigkeit und hin zu einer solidarischen Praxis auf Quartiersebene?Für die Beantwortung dieser Frage werden potentielle und bereits existierende Reale Utopien identifiziertund analysiert. In dieser Analyse werden Instrumente, Forderungen und Strategien herausgearbeitet, derer es Bedarf um Risse im kapitalistischem System auszuweiten, zu verteidigen und zu verstetigen. Die Ergebnisse lassen sich unter den Begriffen der Solidarität, Dekommodifi-zierung, Demokratisierung und Vergesellschaftung zusammenfassen. Sie sind die zentralen Bedin-gungen, die für die Verwirklichung Realer Utopien und damit für gesellschaftliche Transformation, entscheidend sind. Darauf basierendwird ein Kompass für ein solidarisches Quartier erarbeitet.
Vor dem Hintergrund der zunehmenden Veränderung des städtischen Lebensumfeldes durch Gentrifizierung, investorenfreundliche Stadtpolitik, Privatisierung öffentlicher Räume, Einsparung öffentlicher Investitionen und den Abbau demokratischer Beteiligungsinstrumente haben wir uns gefragt: Wie könnte eine solidarische Stadt der Zukunft aussehen? Welche Gegenentwürfe zu aktuell herrschenden Paradigmen in der Stadtentwicklung zeigen uns Wege aus der Alternativlosigkeit hin zu einer solidarischen Praxis auf Quartiersebene? Im Rahmen einer angewandten kritischen Geografie möchten wir zeigen, dass es eine Vielzahl an Projekten und Initiativen gibt, die die Kreativlosigkeit, zu der uns der Neoliberalismus erzogen hat, durchbrechen und an konkreten Ideen und deren praktischer Umsetzung arbeiten. Als theoretische Annäherung dafür setzen wir uns mit Utopien und deren Potenzialen für eine politische Praxis auseinander. Da wir selbst im Kontext stadtpolitischer Gruppen engagiert sind, nutzen wir die aktivistische Stadtforschung als methodischen Rahmen unserer Forschung. Daraus entstanden ist ein Faltblatt, der „Kompass für ein solidarisches Quartier“, welcher als aktivistisches Werkzeug und Ideengeber für die konkrete Umsetzung transformativer Stadtpolitik dienen soll.
Mit einem Stadtbegriff tue ich mich schwer. Städte zu verstehen ist gleichbedeutend damit, Wandel zu verstehen. Städte haben sich über die Jahrhunderte, über die Kontinente und Gesellschaftsformationen hinweg so häufig gehäutet, dass an einem geronnenen Zustand orientierte Definitionen zum Scheitern verurteilt sind. So hat es immer wieder Versuche gegeben, Stadt aus ihrer Bevölkerungsgröße, ihrer Siedlungsstruktur oder ihrer Wirtschafts- und Bauweise abzuleiten, also aus ihren besonderen räumlich-physischen Eigenschaften, die aber allenfalls zeithistorischen Wert haben.
The analysis of the global stratospheric meridional circulation, known as the Brewer-Dobson circulation, is an essential part of both experimental and theoretical atmospheric sciences. This large-scale circulation has a crucial influence on the global burden of greenhouse gases and ozone depleting substances throughout the complete atmosphere. This makes it an important factor for the Earth’s radiative budget, which is perceptible at the Earth’s surface despite the remote location of the stratosphere. In the course of climate change it is generally expected that also the Brewer-Dobson circulation undergoes significant changes in structure and strength, although the exact repercussions are still uncertain and thus remain an open scientific question. A general problem for the observational investigation of the dynamical processes in the stratosphere is that residual mean transport cannot be measured directly and hence requires the use of sophisticated proxies. Many studies in the past consider the so-called mean age of air, which is a measure of the average time an air parcel has spent in the stratosphere since passing a certain reference point. While changes in the strength and structure can be detected and visualized using mean age of air, a more thorough distinction between the different involved transport mechanisms of the circulation (residual circulation, mixing) cannot be made. For that, consideration of a full distribution of all relevant transit times through the stratosphere, an age spectrum, is favorable and a powerful tool to analyze the spatial structure as well as possible future changes in detail. Mean age of air and age spectra can be readily derived in atmospheric modeling studies, but an observationally based retrieval is challenging. Mean age of air is usually approximated from measurements of very long-lived trace gas species that act as a dynamical tracer for the stratosphere. The retrieval of age spectra from observations, however, remains an open task for which different methods have been proposed in the past, that often require a combination of strong assumptions and model data explicitly. This is a major issue for a precise and independent investigation of stratospheric dynamics based on measurements. The focus of this cumulative dissertation is on the development process and application of an inversion method to derive stratospheric age spectra from mixing ratios of chemically active substances that combines an applicable and precise ansatz with a minimized amount of necessary model data. Chemically active species have the important benefit that chemistry and transport in the stratosphere are strongly correlated so that the state of depletion of a trace gas can give some information on certain parts of the age spectrum. Considering a sufficient number of distinct trace gases simultaneously, a full approximation of the age spectrum should be possible. The main section of this thesis is split into three parts, which follow the main aspects and key results of the three publications involved (Hauck et al., 2019, 2020; Keber et al., 2020). The newly developed inverse method is based upon the previously established ansatz by Schoeberl et al. (2005), but constrains the shape of the age spectrum by a single parameter inverse Gaussian function. This keeps the balance between applicability and accuracy with a limited amount of measurement data. Additionally, the method introduces a seasonal scaling factor that imposes higher order maxima and minima onto the intrinsically monomodal spectrum based on the seasonal cycle of the tropical upward mass flux to incorporate phases of weaker and stronger transport. A proof of concept of the inverse method is provided using an idealized simulation of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, where the method is applied to a set of artificial radioactive trace gases with known chemical lifetime. The results imply that the method works properly and retrieves age spectra that match the EMAC reference spectra significantly well on the global and seasonal scale. Only in the lower stratosphere, the performance of the inverse method on the seasonal scale decreases as entrainment into the stratosphere is considered only across the tropical tropopause. Transport across the local extratropical tropopause, however, is a key feature for trace gases in the extratropical lowermost stratosphere so that this entrainment must be included explicitly.
In the second part, the discovered problems are approached to make the inverse method applicable to observations. The formulation of the method is extended to incorporate transport explicitly across the tropical (30° S – 30° N), northern extratropical (30° N – 90° N), and southern extratropical tropopause (30° S – 90° S) each with a single age spectrum that can be inverted independently.
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Vor rund 60 Jahren ist das Buch Mensch und Raum von Otto Friedrich Bollnow erstmals erschienen. Der folgende Beitrag geht der Frage nach, inwieweit die Überlegungen des Philosophen (unter bestimmten Aspekten) noch heute aktuell sind. Bollnows Raum-Verständnis weicht in seiner phänomenologischen Orientierung geradezu grundlegend vom heute vorherrschenden sozialwissenschaftlichen Raumdenken ab. Umso mehr regt Bollnow dazu an, die Lehren des wissenschaftlichen Mainstream kritisch gegen den Strich zu lesen. Ins Zentrum der Suche nach heute möglicherweise bedeutsamen Themen und Methoden des Denkens rückt das Wohnen. Wie denkt Bollnow das Wohnen, und was sagt uns dies in einer Zeit, in der die Menschen ganz anders wohnen als in den 1950er Jahren? Brücken zu methodologisch benachbarten Theorien und Philosophen werden ebenso geschlagen (z. B. Heidegger, Dürckheim, Müller-Freienfels) wie zu anderen thematisch relevanten Arbeiten von Bollnow.
Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b – Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345.
Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands
(2022)
Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.
Location: Canary Islands, Spain.
Major taxa studied: Spermatophytes.
Time period: Present day.
Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non-endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non-endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.
Results: Trait space of endemic and non-endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non-endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.
Main conclusions: We found that endemic and non-endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.
Questions: Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity.
Location: La Palma, Canary Islands.
Methods: We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient.
Results: The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation.
Conclusions: Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species.
Zum ersten Mal beschäftigte sich in Deutschland eine primär an Studierende gerichtete Sommerschule mit kritischer Stadtforschung. Als jemand, der daran teilgenommen hat, gehe ich in einem Erfahrungsbericht der Frage nach, ob und inwieweit eine solche Veranstaltung auch der Stärkung von kritischen Haltungen in der Wissenschaft dienen kann. Dabei verweise ich auf die Notwendigkeit, die hegemoniale Produktion von Wissen an Hochschulen zu hinterfragen und darauf, dass die Möglichkeiten zur Veränderung der Wissensproduktion auch bei den Studierenden selbst liegen.
Determining how the elevation of the Northern Andes has evolved over time is of paramount importance for understanding the response of the Northern Andes to deformational and geodynamic processes and its role as an orographic barrier for atmospheric vapor transport over geologic time. However, a fundamental requirement when using stable isotope data for paleoaltimetry reconstructions is knowledge about the present-day changes of δ18O and δD with elevation (isotopic lapse rate). This study defines the present-day river isotopic lapse rate near the Equator (∼3°S) based on analysis of δ18O and δD of surface waters collected from streams across the Western Cordillera and the Inter-Andean depression in Southern Ecuador. The results for the two domains show a decrease of δ18O with elevation which fits a linear regression with a slope of −0.18‰/100 m (R2 = 0.73, n = 83). However, we establish a present-day lapse rate of −0.15‰/100 m for δ18O (R2 = 0.88, n = 19) and -1.4‰/100 m for δD (R2 = 0.93, n = 19) from water samples collected along the west facing slopes of the Western Ecuadorian Cordillera which is mainly subject to moisture transport from the Pacific. We argue that this empirical relationship, consistent with those obtained in different tropical areas of the world, can inform stable isotope paleoaltimetry reconstructions in tropical latitudes.
Die Straße als Transit- und Abstellraum für Automobile ist kein Naturgesetz. Mit Michel de Certeau lässt sie sich als historisches Produkt einer Strategie verstehen, die sich in einem immerwährenden Konflikt durchsetzt. Ziel dieses Beitrags ist es, die Straße als Ort des Automobils zu denaturalisieren, um das konflikthafte Spannungsverhältnis zwischen den als rezessiv antizipierten Bewegungen des Zufußgehens und jenen dominanten automobilen Bewegungen sichtbar zu machen. Mithilfe einer interventionistischen Flächenprojektion von Fußwegen – einem selbstgemalten Zebrastreifen aus Kreide – wird anhand eines Fallbeispiels aus Frankfurt am Main aufgezeigt, wie sich die alltäglich konflikthafte Aushandlung von Straßenräumen durch Planung materialisieren und somit in die Konzeption von Straße integrieren lässt.
This article aims to show that a perspective that understands urban protests as a conflict between two or more interest-driven actors falls short. For a more comprehensive analysis, the complex fabric of multiple power-laden discourses, processes, networks and spatial conditions in which such conflicts are embedded must be taken into account. To this end, this article adopts an assemblage perspective. Taking the protests around the inner-city marina Port Vell in Barcelona as an example, this perspective is used to elaborate the various spatial conditions that shape this conflict.