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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.
...
Historically, the expansion of soy plantations has been a major driver of land-use/cover change (LUCC) in Brazil. While a series of recent public actions and supply-chain commitments reportedly curbed the replacement of forests by soy, the expansion of the agricultural commodity still poses a considerable threat to the Amazonian and Cerrado biomes. Identification of areas under high risk of soy expansion is thus paramount to assist conservation efforts in the region. We mapped the areas suitable for undergoing transition to soy plantations in the Legal Amazon with a machine-learning approach adopted from the ecological modeling literature. Simulated soy expansion for the year 2014 exhibited favorable validation scores compared to other LUCC models. We then used our model to simulate how potential future infrastructure improvements would affect the 2014 probabilities of soy occurrence in the region. In addition to the 2.3 Mha of planted soy in the Legal Amazon in 2014, our model identified another 14.7 Mha with high probability of soy conversion in the region given the infrastructure conditions at that time. Out of those, pastures and forests represented 9.8 and 0.4 Mha, respectively. Under the new infrastructure scenarios simulated, the Legal Amazonian area under high risk of soy conversion increased by up to 2.1 Mha (14.6%). These changes led to up to 11.4 and 51.4% increases in the high-risk of conversion areas of pastures and forests, respectively. If conversion occurs in the identified high-risk areas, at least 4.8 Pg of CO2 could be released into the atmosphere, a value that represents 10 times the total CO2 emissions of Brazil in 2014. Our results highlight the importance of targeting conservation policies and enforcement actions, including the Soy Moratorium, to mitigate future forest cover loss associated with infrastructure improvements in the region.
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.
During my PhD, I was applying the clumped isotope technique to modern brachiopods and fossil belemnites, and I conducted methodological work. Carbonate clumped isotope thermometry is a tool to reconstruct carbonate precipitation temperatures. In contrast to oxygen isotope thermometry, i.e., the δ18O-thermometer, the carbonate clumped isotope thermometer does not require an estimate for the oxygen isotope composition of the seawater, as it considers the fractionation of isotopes exclusively amongst carbonate isotopologues. The ∆47 value of a carbonate expresses the abundance of the 13C–18O bond bearing carbonate isotopologue, within the carbonate, relative to its random distribution. In thermodynamic equilibrium, the ∆47 value of a given carbonate is solely a function of the carbonate precipitation temperature. However, kinetic isotope fractionations, i.e., vital effects, driven by diffusion, pH or incomplete oxygen isotope exchange between water and dissolved inorganic carbonate species can cause the carbonate to be precipitated with isotopic compositions that are offset from those predicted for thermodynamic equilibrium.
Brachiopods serve as important geochemical archives of past climate conditions. To investigate the nature and significance of kinetic controls on brachiopod shell δ18O and ∆47 values, in collaboration with the BASE-LiNE Earth ITN, I analysed the bulk and clumped isotope compositions of eighteen modern brachiopod shells, collected from different geographic locations and water depths that cover a substantial range of growth temperatures. Growth temperatures and seawater δ18O values for each brachiopod were independently determined. Most of the analysed brachiopods exhibit combined offsets from clumped and oxygen isotope equilibrium, and there is a significant negative correlation between the offset values. The observed correlation slope between offset ∆47 and offset δ18O point to the importance of kinetic effects associated with Knudsen diffusion and incomplete hydration and hydroxylation of CO2 (aq), occurring during biomineralisation. The correlations between the growth rates of the analysed brachiopods and both the offset ∆47 and the offset δ18O values provide further arguments for the presence of kinetic effects. In conclusion, the oxygen and clumped isotope composition of modern brachiopod shells are affected by growth rate-induced kinetic effects that hinder their use for palaeoceanography.
In der vorliegenden Arbeit wurde ein neuer optischer Aufbau für das Laserlabor der Abteilung Kristallographie im FB 11 an der Goethe-Universität Frankfurt beschrieben. Mit Hilfe dieses Aufbaus konnten verschiedene spektroskopische Methoden genutzt werden, um die - von Druck und Temperatur abhängige - Phasenstabilität von Calcium- und Eisencarbonaten zu untersuchen. Mit Hilfe von Raman-Spektroskopie konnte das Phasendiagramm von Calciumcarbonat (CaCO3) teilweise neu bestimmt werden. Fluoreszenzuntersuchungen an dotierten CaCO3 Proben ergaben, dass sich Europium-dotierter Calcit zunächst in eine amorphe Form umwandelt, bevor er bei ca. 15 GPa in eine amorphe 'aragonitische' Form umgewandelt wird. Die Umwandlung ist nicht reversibel. Laserheizexperimente bei 18.5 GPa an dotiertem Siderit (FeCO3) führten zur Bildung eines neuen Hochdruck-Hochtemperatur FeCO3 -Polymorphs. Die Strukturlösung erfolgte mit Hilfe von Röntgendaten, die am Deutschen Elektronen-Synchrotron (DESY) in Hamburg gewonnen wurden. Schließlich wurde eine neue Methode zur Bestimmung von Temperaturen in Laserheizexperimenten beschrieben. Sie beruht auf der Abschwächung eines Fluoreszenzsignals durch die Temperatur, welche durch die Wechselwirkung eines Heizlasers mit der Probe erzeugt wird.
Das Wissen über die Wolkenmikrophysik und die Wechselwirkung zwischen Niederschlag und Aerosol ist ein wichtiger Baustein zur Optimierung von Klima- und Wettermodellen. Ein Großteil des Niederschlags in den mittleren Breiten fällt aus Mischphasenwolken, die aus unterkühlten Tröpfchen und Eispartikeln bestehen. Die Eispartikel bilden sich an speziellen Aerosolpartikeln, die als Eiskeime (INP) wirken können. Die Wahrscheinlichkeit eines Aerosols als Eiskeim zu wirken, nimmt mit abnehmender Temperatur und steigender Wassersättigung zu. Mineralstaubpartikel sind die häufigsten Eiskeime, die ab Temperaturen ≤−15°C aktiv sind, biologische Partikel wirken schon bei wärmeren Bedingungen. Große Wissenslücken bestehen noch bei der globalen Konzentration von Eiskeimen, inklusive deren geographischer und jahreszeitlicher Variabilität.
Im Zentrum der Experimente, die für diese Arbeit durchgeführt wurden, steht der Eiskeimzähler FRIDGE (Frankfurt Ice Deposition Freezing Experiment). Je nach Aufbau und Anwendung des Instruments werden zwei verschiedene Ansätze zur Aktivierung von Eiskeimen verfolgt. Die ursprüngliche und namensgebende Methode in Form einer Vakuum-Diffusionskammer wurde zur Untersuchung von Eisnukleation via Depositionsgefrieren (an INP_D) entwickelt (Klein et al., 2010). Danielczok (2015) nutzte einige Bestandteile des Analysegeräts, um auch Immersionsgefrieren (an INP_I) in Form von Tröpfchengefrieren à la Vali (1971) zu studieren. In der vorliegenden Arbeit wurde diese Anwendungsmöglichkeit von FRIDGE weiterentwickelt. Ein zentraler Schritt war dabei die präzise Charakterisierung des Gefrierverhaltens von Tröpfchen aus Reinstwasser ohne zusätzliches Aerosol. Die Einbeziehung dieses sogenannten Hintergrundgefrierens, das für jedes Instrument und Messverfahren spezifisch ist, ermöglichte es, die Minimaltemperatur, für die zuverlässige Ergebnisse produziert werden können, von −22°C auf −29°C herabzusetzen. Der dadurch hinzugewonnene Temperaturbereich ist für Eisnukleation in Mischphasenwolken äußerst relevant.
Beide Anwendungsmethoden wurden im Rahmen des Fifth International Workshop on Ice Nucleation – Phase 2 (FIN-02) sowie bei einer weiteren Kampagne zur Messung von Eisnukleation an Cellulosepartikeln mit über zwanzig anderen Eiskeimzählern verglichen. Mit FRIDGE als Diffusionskammer wurde für die Mehrheit der untersuchten Aerosoltypen eine zufriedenstellende Übereinstimmung mit den anderen Instrumenten beobachtet. Die Experimente mit gefrierenden Tröpfchen in FRIDGE erzielten ausnahmslos Ergebnisse, die inmitten der Werte der anderen Instrumente lagen. Die erfolgreiche Validierung – besonders der neuen Anwendungsmethode – war das erste Ziel dieser Arbeit und die notwendige Voraussetzung für die anschließenden Feldmessungen.
Atmosphärische Eiskeimkonzentrationen wurden in mehrwöchigen Feldmesskampagnen an drei sehr unterschiedlichen Orten und atmosphärischen Bedingungen untersucht: an der Hochalpinen Forschungsstation Jungfraujoch (JFJ), am Storm Peak Laboratory (SPL) in den Rocky Mountains und am Cyprus Atmospheric Observatory (CAO) in Zypern. Am JFJ wurde eine INP-Konzentration beobachtet, die um den Faktor 20 niedriger als an den anderen beiden Stationen war. Der Grund dafür war, dass sich das Jungfraujoch die meiste Zeit der Messungen in der freien Troposphäre befand. Dementsprechend waren die Bedingungen an der Station von aerosolpartikelarmer Luft mit wenigen Eiskeimen geprägt. An zwei Standorten wurde Mineralstaub als ein Parameter, der die lokale INP-Konzentration positiv beeinflusst, identifiziert. Sowohl am JFJ als auch am CAO erhöhte ferntransportierter Saharastaub die INP-Konzentration.
Die Kombination der zwei Analysemethoden, die Aerosolproben aus derselben Luft entweder in trockenem Ausgangszustand oder in Tröpfchen suspendiert untersuchen, offenbarte eine interessante Eigenschaft der INP. Es herrschte eine offensichtliche Parallelität von INP_D- und INP_I- Konzentrationen. Bei fast allen Messungen waren INP_I etwa 10-mal häufiger als INP_D. Die Aussage trifft gleichermaßen auf sehr niedrige Konzentrationen am JFJ wie auch auf hohe Konzentrationen am SPL und CAO zu. Die einzige Ausnahme bilden Cellulosepartikel. Daraus lässt sich schließen, dass INP_D und INP_I dieselben Partikel sind, die je nach Aktivierungskonditionen Eisnukleation unterschiedlich effektiv hervorrufen.
Air-sea feedbacks between the Mediterranean Sea and the atmosphere on various temporal and spatial scales play a major role in the Mediterranean regional climate system and beyond. The Mediterranean Sea is a source of moisture due to excess evaporation and, on a long-term average, is associated with a warming of the lower atmosphere in contact with the sea surface due to heat loss at the air-sea interface. The complex air-sea interactions and feedbacks in the Mediterranean basin strongly modulate the sea surface fluxes and favor several cyclogenetic activities under certain meteorological conditions. Examples of such cyclonic activities are medicanes (Mediterranean hurricanes) and Vb-cyclones. Medicanes are mesoscale, marine, and warm-core Mediterranean cyclones that exhibit some similarities to tropical cyclones, while Vb-cyclones are extra-tropical cyclones, that propagate from the Western Mediterranean Sea and travel across the Eastern European Alps into the Central European region. Extremely strong winds and heavy precipitation associated with these cyclones can lead to severe destruction and flooding. Changes in the intensity and frequency of these cyclones are also projected under changing future climate conditions, where the Mediterranean region has been identified as a hotspot in terms of rising temperatures.
The development of high-resolution regional climate models (RCMs) has progressed our understanding of the processes characterizing the Mediterranean climate. However, large uncertainties still exist regarding the estimates of air-sea fluxes, which, in turn, affect the simulation of the Mediterranean climate. Several factors can be attributed to such discrepancies, such as data quality, temporal and spatial resolution, and the misrepresentation of physical processes. To overcome some of these inconsistencies and deficiencies of the existing climate simulations, a new high-resolution atmosphere-ocean regional coupled model (AORCM) has been developed to simulate the air-sea feedback mechanisms. This coupled model incorporates the coupling of RCM COSMO-CLM (CCLM) and the regional ocean model NEMO-MED12 for the Mediterranean Sea (MED) as well as NEMO-NORDIC for the North- and Baltic Sea (NORDIC). Several experiments were performed using both the coupled and uncoupled models to investigate the impact of air-sea interactions and feedbacks on sea surface heat fluxes, wind speed, and on the formation of Mediterranean cyclones (i.e., medicanes and Vb-cyclones). These experiments were performed using different horizontal atmospheric grid resolutions to analyze the effect of resolution on sea surface heat fluxes, wind speed, and the development of medicanes.
The results of the present study indicate that a finer atmospheric grid resolution ([is as appreciated as]9 vs. [is as appreciated as]50 km) improved the wind speed simulations (particularly near coastal areas) and subsequently improved the simulations of the turbulent heat fluxes. Both parameters were better simulated in the coupled simulations than in the uncoupled simulations, but coupling introduced a warm SST bias in winter. Radiation fluxes were slightly better represented in coarse-grid simulations than in fine-grid simulations. However, the higher-resolution coupled model could reproduce the observed net outgoing total surface heat flux over the Mediterranean Sea. In addition to that sub diurnal SST variations have a strong effect on sub-daily heat fluxes and wind speed but minor effects at longer timescales. Regarding the impact of atmospheric grid resolution ([is as appreciated as]50, 25, and [is as appreciated as]9 km) and ocean coupling on medicanes, it was detected that the coupled model with a finer atmospheric grid ([is as appreciated as]9 km) was able to not only reproduce most medicane events, but also improved the track length, warm core, and wind speed compared to the uncoupled model. The coupled model with the coarse-grid ([is as appreciated as]50 and [is as appreciated as]25 km) did not show any improvement in simulating medicanes compared to the uncoupled model. The spectral nudging technique, applied on the wind components above 850 hPa in the interior domain to keep large-scale circulation close to the driving data (i.e., ERAInterim reanalysis), improved the accuracy of the times and locations of generated medicanes, but no improvement was found in the track length and intensity.
Concerning the role of the Mediterranean Sea coupling on Vb cyclones, the investigation showed that atmosphere-ocean coupling had an overall positive impact, although with a strong case-by-case variation, on the trajectories and intensity of Vb-cyclones as a result of the variation in moisture source for each event. In general, all model configurations could replicate Vbcyclones, their trajectories, and associated precipitation fields. The average structure of the precipitation field was best represented in the coupled simulations. Coupling of the North- and Baltic Seas also showed an improvement in some of the simulated Vb-cyclones.
The atmosphere-ocean coupling showed an overall positive impact on the simulation of sea surface heat fluxes and Mediterranean cyclones (medicanes and Vb-cyclones). Moreover, the representation of sea surface heat fluxes, wind speed, and medicane features was more realistic when using a finer atmospheric grid resolution (less than 10 km). The present study suggests that the combination of a finer atmospheric grid resolution together with atmosphere-ocean coupling is advantageous in simulating the Mediterranean climate system.