Postglacial sea-level change: novel insights from physical and statistical modelling

Developing accurate projections of future sea-level change is a key challenge for the entire science community under the current warming climate. Due to the fact that modern instrumental sea-level observations are only available since the 19-20th century, sea-level projections based on them can only capture short-term effects, leaving physical processes that dominate over longer timescales underestimated. Therefore, an essential step towards accurate and robust long-term sea-level projections is to investigate the physical processes that impact the spatio-temporal evolution of sea-level change over centennial to millennial timescales. Due to sometimes scarce and often noisy palaeo sea-level observations, mechanisms of sea-level change over geological timescales are still not well-understood, with many outstanding questions to be resolved. This thesis develops novel physical and statistical models to better understand the mechanisms behind postglacial sea-level change. Specifically, this thesis focuses on three outstanding problems that are not only important in postglacial sea-level change but also in understanding past ice sheet dynamics and palaeoclimate change. Firstly, a statistical framework is developed to invert the sources of meltwater pulse 1A, the largest and most rapid global sea-level rise event of the last deglaciation, with sophisticated treatment of uncertainties associated with sea-level reconstructions and geophysical modelling. The results suggest there were contributions from North America, 12.0 m (5.6-15.4 m; 95% probability), Scandinavia, 4.6 m (3.2-6.4 m), and Antarctica, 1.3 m (0-5.9 m), giving a total global mean sea-level rise of 17.9 m (15.7-20.2 m) in 500 years. Secondly, the missing ice problem (distinctive imbalance between observed global mean sea-level rise and the reconstructed amount of ice-sheet melt) is revisited by including an extra physical process (sediment isostatic adjustment, SIA) which has not been considered in this problem before. In particular, this thesis investigates the impact of SIA on local RSL variation across the Great Barrier Reef (GBR), the world's largest mixed carbonate-siliciclastic sediment system. Based on a Bayesian calibration method, SIA can contribute up to 1.1 m relative sea-level rise in the outer shelf of the southern central GBR from 28 ka to present. Because the SIA-induced RSL rise is unrelated to ice mass loss, failing to correct for this signal will lead to systematic overestimation of grounded ice volume. Therefore, incorporating the SIA process will reduce the global grounded ice volume estimate for the Last Glacial Maximum (LGM), which can help to mitigate the missing ice problem. Lastly, robust global barystatic sea-level maps with minimum dependency on the detailed geometry of past ice sheet change are reconstructed. Estimating such maps requires physical simulation of relative sea-level corresponding to thousands of different ice histories, which is computationally prohibitive. To improve this situation, this thesis develops a statistical emulator which can mimic the behaviour of a physics-based model and is computationally much cheaper to evaluate. The results highlight the Seychelles as an exceptionally good place to map barystatic sea level throughout the last deglaciation because RSL at this location only slightly departs from global barystatic sea level, with minor dependency on the assumed ice history. Together, these physical and statistical models present powerful tools to yield novel insights into postglacial sea-level change mechanisms and hence they have the potential to yield more robust, accurate and trust-worthy sea-level change projections

Using FTIR-ATR to Predict Saccharification from Enzymatic Hydrolysis of Physically Pretreated Lignocellulosic Biomass

Producing biofuels from lignocellulosic biomass (i.e., non-edible plants) can reduce greenhouse gas emissions. The main challenge in converting lignocellulose to fuel, however, lies in the bioconversion process of biomass to sugars. To overcome the recalcitrance of the plant cell walls, pretreatment (e.g., ball milling) can be coupled with enzymatic hydrolysis to produce sugar monomers (e.g., glucose and xylose). The research question in this thesis study was “Can Fourier Transform Infrared Spectroscopy Attenuated Total Reflectance (FTIR-ATR) applied to untreated and physically pretreated lignocellulosic biomasses coupled with chemometric analysis predict sugar yields from enzymatic hydrolysis?” PLS models were constructed by correlating the X matrix—i.e, the FTIR-ATR spectra of raw and physically pretreated samples—to the Y vector—measured values of 72-hour glucose and xylose yields. It was determined that the PLS models constructed from the fingerprint region of FTIR-ATR spectra (800-1800 cm-1) of the five raw biomasses which underwent various physical pretreatment levels (no treatment, 1 hour of ball milling, 2 hours of ball milling, and shatterbox for five minutes) were able to predict the glucose yields (g sugar per fraction of Total Solids). The initial glucose model resulted in a coefficient of determination for cross-validation (Q2) value of 0.8262 with four latent variables. Using regression coefficients and variables important of projection (VIP) scores, regions of the spectra were truncated. These truncated regions were associated with bonds, identified as contributing regions for predicting glucose yields, suggesting that PLS regression models were created based on real chemical information and not chance correlation

Structure-aware image denoising, super-resolution, and enhancement methods

Denoising, super-resolution and structure enhancement are classical image processing applications. The motive behind their existence is to aid our visual analysis of raw digital images. Despite tremendous progress in these fields, certain difficult problems are still open to research. For example, denoising and super-resolution techniques which possess all the following properties, are very scarce: They must preserve critical structures like corners, should be robust to the type of noise distribution, avoid undesirable artefacts, and also be fast. The area of structure enhancement also has an unresolved issue: Very little efforts have been put into designing models that can tackle anisotropic deformations in the image acquisition process. In this thesis, we design novel methods in the form of partial differential equations, patch-based approaches and variational models to overcome the aforementioned obstacles. In most cases, our methods outperform the existing approaches in both quality and speed, despite being applicable to a broader range of practical situations.Entrauschen, Superresolution und Strukturverbesserung sind klassische Anwendungen der Bildverarbeitung. Ihre Existenz bedingt sich in dem Bestreben, die visuelle Begutachtung digitaler Bildrohdaten zu unterstützen. Trotz erheblicher Fortschritte in diesen Feldern bedürfen bestimmte schwierige Probleme noch weiterer Forschung. So sind beispielsweise Entrauschungsund Superresolutionsverfahren, welche alle der folgenden Eingenschaften besitzen, sehr selten: die Erhaltung wichtiger Strukturen wie Ecken, Robustheit bezüglich der Rauschverteilung, Vermeidung unerwünschter Artefakte und niedrige Laufzeit. Auch im Gebiet der Strukturverbesserung liegt ein ungelöstes Problem vor: Bisher wurde nur sehr wenig Forschungsaufwand in die Entwicklung von Modellen investieret, welche anisotrope Deformationen in bildgebenden Verfahren bewältigen können. In dieser Arbeit entwerfen wir neue Methoden in Form von partiellen Differentialgleichungen, patch-basierten Ansätzen und Variationsmodellen um die oben erwähnten Hindernisse zu überwinden. In den meisten Fällen übertreffen unsere Methoden nicht nur qualitativ die bisher verwendeten Ansätze, sondern lösen die gestellten Aufgaben auch schneller. Zudem decken wir mit unseren Modellen einen breiteren Bereich praktischer Fragestellungen ab

Interatomic potentials: Achievements and challenges

Interactions between atoms can be formally expanded into two-body, three-body, and higher-order contributions. Unfortunately, this expansion is slowly converging for most systems of practical interest making it inexpedient for molecular simulations. This is why effective descriptions are needed for the accurate simulation of many-atom systems. This article reviews potentials designed towards this end with a focus on empirical interatomic potentials not necessitating a-priori knowledge of what pairs of atoms are bonded to each other, i.e., on potentials meant to describe defects and chemical reactions from bond breaking and formation to redox reactions. The classes of discussed potentials include popular two-body potentials, embedded-atom models for metals, bond-order potentials for covalently bonded systems, polarizable potentials including charge-transfer approaches for ionic systems and quantum-Drude oscillator models mimicking higher-order and many-body dispersion. Particular emphasis is laid on the question what constraints on materials properties ensue from the functional form of a potential, e.g., in what way Cauchy relations for elastic tensor elements can be violated and what this entails for the ratio of defect and cohesive energies. The review is meant to be pedagogical rather than encyclopedic. This is why we highlight potentials with functional forms that are sufficiently simple to remain amenable to analytical treatments, whereby qualitative questions can be answered, such as, why the ratio of boiling to melting temperature tends to be large for potentials describing metals but small for pair potentials. However, we abstain for the most part from discussing specific parametrizations. Our main aim is to provide a stimulus for how existing approaches can be advanced or meaningfully combined to extent the scope of simulations based on empirical potentials

Modes of variability as simulated by a global climate model

We discussed in this thesis an orchestra of climate modes with characteristic time scales of about 5, 16 and 35 years (see Fig.6.3). Interannual variability in the Pacific is ENSO-like. This quasi-oscillatory mode can be understood as a coupled air-sea mode. We discussed the origin of ENSO variance modu- lations, which occur on time scales of. 22 and 35 years. In particular the 35 year ENSO modulation arises from an interaction between ENSO and a 35 year Northern Hemi- spheric climate mode. Interdecadal wind stress curl anomalies in the subtropical Pacific initiate Rossby lryaves, which are associated also with subsurface temperature anomalies. These waves enter the equatorial region 8-12 years later. The subsequent changes in the mean equatorial temperature structure are considered to be important for the simulated interdecadal changes of ENSO variability. However, it was shown that the simulated ENSO cycle in the ECHAM3/LSG model is rather insensitive to global warming, whereas it is revealed from the scenario A integration performed with the more realistic CGCM ECHAM4/OPYC3 that global warming will increase the ENSO variability (Timmermann et al. 1998). This discrepancy in the sensitivities of these two climate models can be ex- plained in terms of the mean thermocline structure, which in the ECHAM3/LSG model is highly diffusive, whereas in the ECHAM4/OPYC3 simulation it is relatively sharp. In the North Atlantic, two climate modes are identified with time scales of 14-18 and 30-40 years, which can be understood in terms of the coupled air-sea mode framework. The wind-driven North Atlantic gyre system provides the memory of the decadal North Atlantic mode. The North Atlantic Oscillation is the atmospheric agent in this coupled air-sea mode, serving on the one hand as a stabilizer of oceanic temperature anomalies and on the other hand as an initiator of the temperature tendency which causes the phase reversal after some delay. The dynamics can be condensed within a feedback loop, which is shown in Fig.4.11. The 30-40 year North Atlantic mode (Timmermann et al. 1998a) involves interactions between the NAO and the North Atlantic thermohaline circulation. The generation of salinity anomalies plays a crucial role for the phase reversal. A feedback loop of the interdecadal oscillation in the North Atlantic is depicted in Fig.5.15. Thus, all climate modes discussed here fit into the coupled air sea mode concept. We aimed to explore those physical processes which are relevant for the generation of climate modes on interannual to interdecadal time scales. Understanding the major pro- cesses and the space-time characteristics of long-term climate variability by means ofCGCM experiments is not only of academic but also of direct interest for societies in the context of climate predictions (Grötzner et al. 1998). Due to the fact that the thermoha- line circulation transports carbon dioxid into the deep ocean, changes of the thermohaline circulation as discussed in Chapter 5 can be linked also to the global carbon cycle. Further- more the results presented in this thesis could give oceanographers some more indications on where to monitor the variability of the deep ocean. However, translating our results which were obtained from a coupled model to reality is a highly nontrivial task. uTluth i,s much too compli,cated to allow anything but approri,nl,at'ions", (John von Neuman)

Reduced sediment supply in a fast eroding landscape? A multi-proxy sediment budget of the upper Rhone basin, Central Alps

Alpine water and sediment supply influence the sediment budget of many important European fluvial systems such as the Rhine, Rhône and Po rivers. In the light of human induced climate change and landscape modification, it becomes increasingly important to understand the mechanisms of sediment production and supply in Alpine sediment systems. This study aims to investigate the modern sediment budget of the upper Rhône basin, one of the largest Alpine intramontane watersheds, located in the Central Alps of southwestern Switzerland. Major areas of sediment generation are fingerprinted by framework petrography, heavy mineral concentrations and bulk geochemistry. The relative contributions of the three major sources to the sediment of the trunk Rhône river are identified by compositional mixing modelling. Concentrations of the terrestrial cosmogenic nuclide 10Be measured in quartz separated from fluvial sediments provide spatially averaged denudation rates for selected tributary basins. Results from sediment fingerprinting and mixing modelling suggest that tributaries located in the North and the East of the catchment are generating most of the sediment transported by the Rhône river to its primary sedimentary sink in Lake Geneva. Despite having some of the highest denudation rates within the basin, tributaries located in the southern area of the Rhône basin are relatively underrepresented in the sediment budget of the Rhône river. These tributaries are severely affected by human activities, for example through sediment mining as well as water and sediment abstraction in large hydropower reservoirs. Together, these processes reduce the basin-wide sediment discharge by about 50%, thereby explaining most of the observed compositional pattern. In addition, there is evidence suggesting that large amounts of glaciogenic sediments are currently supplied by retreating glaciers. Glaciogenic material with its low 10Be concentrations can lead to a significant overestimation of denudation rates and thus limit the applicability of cosmogenic nuclide analysis in such glaciated settings