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Modeling Ocean Alkalinity Enhancement in Subduction Regions and the Global Ocean
No full textAnthropogenic CO2 emissions have driven global warming since the Industrial Revolution, necessitating a phasing out of fossil fuels to limit warming to well below 2degC, preferably 1.5degC, as outlined in the Paris Agreement. However, emission reductions alone are unlikely to be sufficient to meet these targets, highlighting the need for large-scale carbon dioxide removal (CDR). While current CDR efforts primarily focus on land-based methods, challenges, such as land competition and biodiversity loss have led to growing interest in ocean-based approaches as a complementary solution. Ocean Alkalinity Enhancement (OAE) is one such ocean-based CDR method with high theoretical carbon sequestration potential that enhances CO2 uptake by shifting carbonate equilibria in the surface ocean.
The ocean has absorbed ~25% of anthropogenic CO2 since the Industrial Revolution and thus plays a crucial role in the global carbon cycle. Subduction regions in the Southern Ocean and North Atlantic are particularly important for anthropogenic carbon uptake as they transport carbon into the deep ocean, sequestering it for centuries to millennia. Building on this natural process, I hypothesize that deploying OAE in subduction regions will enhance deep ocean sequestration and OAE efficiency. To test this, OAE is simulated in subduction regions and globally using a low-resolution ocean circulation and biogeochemistry model (Publication I), a fully coupled emission-driven Earth System Model (ESM; Publication II), and a high-resolution ocean circulation and biogeochemistry model (Publication III).
This thesis identifies three key factors influencing simulated OAE efficiency: the amount of added alkalinity, climate feedbacks, and model resolution. Among these, alkalinity addition is the primary driver, which exhibits a strong linear relationship with oceanic CO2 uptake and atmospheric CO2 reduction after 60-70 years of OAE deployment, a relationship that is consistent across emission scenarios and aligns with previous literature. However, in contrast to this scaling observed after decades of alkalinity addition, the largest differences and highest uncertainties in OAE efficiency occur in the initial decade of deployment (2030s). During this period, OAE efficiency in subduction regions (0.60 in Publication I, 0.70 in Publication III) surpasses global OAE in ocean-only models (0.56 in Publication I, 0.57 in Publication III). In contrast, the ESM-based regional OAE simulation (Publication II) yields a lower efficiency of 0.38, with a ±55% uncertainty attributed to climate-feedback driven variability. As alkalinity perturbations disperse over time, regional differences diminish, reducing uncertainty and leading to a convergence of efficiency estimates between global and regional applications by the 2090s, with values of 0.85 (global and regional, Publication I), 0.72 (global and regional, Publication II), and 0.85-0.90 (global-regional; Publication III). The persistently lower efficiency in Publication II underscores the role of climate feedbacks as the second most influential factor in OAE efficiency. Model resolution has only a third-order impact. Notably, Publication III reports the highest regional OAE efficiency in the 2030s, potentially due to a combination of different dynamics in the high-resolution model and differences in the background state of carbonate chemistry across model setups, which further contributes to early-phase uncertainty.
Further, both high- and low-resolution ocean-only models demonstrate efficient deep-ocean carbon sequestration, with high-resolution global and regional simulations storing a relatively higher amount of carbon below 1 km throughout the simulation period than their low-resolution counterparts. Moreover, these models indicate that subduction regions transport nearly twice as much carbon to depths below 1 km as global OAE in their respective setups, although their smaller surface area leads to a lower total dissolved inorganic carbon (DIC) increase. In contrast, the regional OAE using the ESM model (Publication II) does not replicate such efficient deep transport, largely due to internal climate variability and feedbacks. The ocean-only simulations also reveal that subduction regions can be viable for OAE, but exhibit strong seasonal variability in excess carbon uptake, surface alkalinity, and DIC accumulation, driven by the seasonality of the mixed layer depth (MLD). A shallower summer MLD retains excess surface alkalinity, allowing CO2-deficient waters to equilibrate with the atmosphere and enhance CO2 uptake and DIC accumulation, while a deeper winter MLD increases mixing, leading to alkalinity loss and reduced CO2 uptake. Therefore, to optimize OAE efficiency in regional deployments, future strategies must account for these seasonal dynamics.
Based on the findings of this thesis, model selection for OAE research should align with the specific goals: low-resolution models capture large-scale ocean processes, high-resolution models can be useful to resolve small-scale dynamics that are potentially important for deep ocean carbon sequestration, and ESMs incorporate Earth system feedbacks vital for assessing how CDR deployment can affect the climate trajectory with respect to climate targets. Most importantly, as all model setups in this study exhibit the highest uncertainty during the initial phase of OAE deployment, future modeling efforts should focus on understanding uncertainties in estimates of OAE efficiency in the early phases of regional applications, which are crucial for developing a robust Monitoring, Reporting, and Verification (MRV) framework
Perception for imagination-enabled robots
No full textRecent advancements in robotics and computer vision have enhanced object recognition and control strategies. However, these developments do not fully tackle the challenges of autonomous manipulation in dynamic, unstructured environments like households. Current systems often rely on specialized algorithms for perception, which lack generalizability and fail to verify the plausibility of their results.
This thesis proposes a comprehensive framework that enhances robotic perception and manipulation in dynamic, unstructured environments by integrating a photorealistic, physics-enabled game engine. The core contributions of this research are threefold. First, it presents a unified perception architecture that combines imagistic reasoning, process-level control, and perception task adaptation within a single system. This architecture enables robots to construct internal hypotheses, simulate expected sensor data, and verify perceptual results against rendered scenes, facilitating grounded and introspective perception in real-world tasks.
Second, the thesis presents a game-engine-based belief representation, utilizing real-time simulation as an internal model of belief states to enable high-fidelity visual hypothesis generation. The simulated environment represents a dynamic world model, including the robot state, allowing the system to assess the plausibility of perceptual results and predict the visual consequences of actions.
Lastly, Perception Pipeline Trees (PPTs) are introduced as a modular process model for adaptive perception execution.
PPTs combine hierarchical execution with flexible control flow, supporting reactive switching, concurrent processing, and introspective verification. This model accommodates conventional vision tasks and imagistic reasoning processes within a unified representation.
The framework demonstrates effectiveness in real-world applications, including household assistance scenarios where robots perform tasks such as recognizing and manipulating objects, as well as tracking and interacting with humans. By enabling robots to not only observe but also reason about their environment through simulation, this work advances task adaptability, perception accuracy, and reasoning capability, laying the foundation for the next generation of intelligent, imagination-enabled robots
“German Version better”: Mimetic Normativity in TikTok Daʿwa
No full textThis article explores how TikTok’s short video format facilitates a distinctive mode of religious instruction that simplifies Islamic norms into binary categories of “right” (ḥalāl) and “wrong” (ḥarām). Focusing on two case studies, I highlight how Muslim content creators convey ethical guidance by referencing the Qurʾan and Hadith while omitting the nuanced discursive traditions of Islamic jurisprudence and contextual knowledge. The brevity of the videos limits critical engagement with complex theological discussions, presenting norms as supra-historical and detached from human experience. This leaves audiences to debate the norms presented in comment threads, without explicit acknowledgment of scholarly expertise. Additionally, I employ a performance-centred approach to analyse how TikTok’s functional logics and affordances, including collaboration, humour, spatial settings, and app features like hashtags and captions, shape the presentation and reception of religious content. These elements, combined with audience interactions and the app’s user interface, constitute a “technosocial setting” that frames the couple’s performative enactments of Islamic teachings. This setting not only influences audience interpretation but also facilitates memetic engagement, reinforcing TikTok’s role as a platform for disseminating simplified religious norms in an engaging, collaborative manner.4
Impacts of Arctic permafrost erosion on nearshore planktonic food webs
No full textArctic planktonic communities form the foundation of Arctic marine food webs and play a crucial role in the biological carbon pump. Global warming is increasing the thawing and erosion of permafrost coasts in the Arctic. This leads to the discharge of substantial amounts of sediment, carbon, and nutrients into the Arctic Ocean’s nearshore zone, changing the ecosystem conditions. Questions have arisen about how planktonic communities in the nearshore zone are affected by such changes in the environmental conditions.
In my thesis, I applied a multiple-study approach to investigate the effects of Arctic coastal erosion and the associated changes in turbidity, carbon, and nutrient levels on planktonic community dynamics, biomass, and interactions within the nearshore zone. I decided on the shallow nearshore due to the fact that these zones represent 20% of the Arctic shelves and 7.5% of the Arctic Ocean, a proportion substantially greater than that of the nearshore zones of other oceans. In Chapter 2, the manuscript, “Future Arctic: How will increasing coastal erosion shape nearshore planktonic food webs?” sets the scene. In this chapter, I assessed how coastal erosion impacts carbon, nutrients, and light regimes in the nearshore zone, and what we can expect for the future. Additionally, I assessed the potential effects on planktonic community structure and food web dynamics. I used published literature and a formal review of our current state of knowledge. The literature data showed that sediment discharge increases turbidity and reduces light penetration into the water column. This darkening is expected to reduce phytoplankton productivity, while additional carbon will support bacterial production and shift the balance between autotrophic and heterotrophic production at the base of the food web. Given the lower energy transfer efficiency in the heterotrophic pathway, its dominance might lower zooplankton biomass with potential negative consequences for higher trophic levels.
Drawing some of the testable hypotheses from the in-depth literature synthesis, I investigated the influence of terrigenous input on planktonic community dynamics around Herschel Island-Qikiqtaruk. Located in the Western Canadian Arctic, the permafrost coast around Herschel Island-Qikiqtaruk is one of the highly eroding sites in the Arctic. The results in the manuscript, “Eroding permafrost coasts lead to lower productivity in the Arctic nearshore zone,” in Chapter 3, show that permafrost thaw and erosion impact planktonic biomass. Relative to stable sites, actively eroding sites exhibited higher turbidity, resulting in a 45% reduction in phytoplankton biomass. Moreover, the very nearshore stations zone showed higher heterotrophic dinoflagellates and microzooplankton biomass than the offshore stations, suggesting that the nearshore stations were dominated by heterotrophy, while the offshore stations were dominated by autotrophic energy mobilization. Mesozooplankton abundance decreased by 26% from the nearshore towards offshore stations, suggesting potential utilization of both marine and terrestrial OC sources.
In the third manuscript, “Impact of permafrost coastal erosion on Arctic marine food webs”, I investigated the sources, age, and utilization of marine versus terrigenous organic carbon. The results showed that although permafrost erosion discharges a substantial amount of OC into the nearshore zone, only 6% of the old permafrost OC ends up in the planktonic food web. Planktonic consumers are mainly supported by marine production, and the additional terrigenous OC carbon utilized by nearshore consumers largely comes from the active layer, representing modern terrestrial carbon. Overall, this study highlights that Arctic permafrost thaw and erosion influence planktonic community structure by reducing phytoplankton biomass and shifting the balance between autotrophs and heterotrophs in the nearshore zone. These processes might weaken the Arctic Ocean’s capacity as a CO2 sink, and potentially turn it into a net CO2 source
Studienreport zu den Interviewdaten des Projekts "Administrative Ungleichheit bei der Bearbeitung von Anträgen auf deutsche Staatsbürgerschaft - Qualitativer Teil (AdminCit-qual)"
No full textDas Projekt „Administrative Ungleichheit bei der Bearbeitung von Anträgen auf deutsche Staatsbürgerschaft (AdmInCit)“ erforschte Unterschiede bei der dezentralen Umsetzung des deutschen Staatsangehörigkeitsrechts mit quantitativen und qualitativen Methoden. Dabei wurden leitfadengestützte Expert*inneninterviews mit Personen in und um die lokale Einbürgerungsverwaltung in 16 Landkreisen und kreisfreien Städten in Bayern, Nordrhein-Westfalen und Schleswig-Holstein durchgeführt. 64 Transkripte dieser Interviews wurden über Qualiservice archiviert und interessierten Wissenschaftler*innen zur Nutzung für Forschung und Lehre bereitgestellt. Die Interviewdaten bieten einen umfassenden Einblick in die deutsche Einbürgerungspraxis zum Zeitpunkt der Untersuchung (2023), die zur Umsetzung und Vorbereitung angrenzender Forschungsvorhaben geeignet sind. Diesem Studienreport sind Kontextmaterialien beigefügt, um die Fallauswahl, Umfang und Inhalte der Interviews sowie deren Anonymisierung und Auswertung für Außenstehende nachvollziehbar zu gestalten
Staying Ahead of the Game: Extracurricular Activities and Inequalities in Educational and Occupational Attainment over the Life Course
No full textThis dissertation examines the role of extracurricular activities in the reproduction of social inequality, focusing on how participation in structured, organized activities outside formal schooling may amplify or mitigate advantages associated with family background. Through three empirical studies, this dissertation explores how participation in extracurricular activities in childhood and adolescence contributes to unequal outcomes beyond unequal participation. The first study investigates how the cognitive skill benefits of extracurricular participation vary by social background, showing that adolescents from highly educated families derive greater advantages, reinforcing existing inequalities. The second study examines the long-term effects of extracurricular participation, revealing that early engagement has lasting impacts on educational and labor market outcomes. The third study explores the role of social networks, demonstrating that friendships formed through extracurricular activities differ by educational track and can influence academic trajectories. Together, these studies highlight the complex ways in which extracurricular activities shape inequalities. By broadening the focus beyond formal education, this dissertation contributes to understanding the mechanisms that sustain or reduce social inequalities across the life course
The Generosity of Social Welfare Programmes in the Soviet Union: A Comprehensive Overview
No full textThis working paper presents an overview of the gradual development of the Soviet welfare system form the October Revolution of 1917 to 1991. It examines all major social welfare programmes in the Soviet Union and their generosity – understood as the combination of their inclusiveness and the scope of benefits they offer. It provides the reader with a comprehensive and detailed picture of the development of these programmes over time covering the right to income maintenance (i.e., old-age, disability and survivor pensions, unemployment, sickness and maternity benefits, and child allowances), benefits aiming to raise living and cultural standards (i.e., healthcare and education), and so-called “hidden social welfare benefits” in the form of price subsidies for consumer goods, such as food, and services, including housing, etc..Deutsche Forschungsgemeinschaft (DFG)2
On different witness complex filtrations and their landmark choices
No full textThe main aim of this thesis is to study different Witness Complex filtrations. By the notion of Witness Complex we mean filtrations of simplicial complexes characterized by the fact that the data set they are based on is not automatically included in the complex but rather landmark points are chosen and the rest of the points is used for additional information on the higher dimensional simplices between them.
We consider two constructions that are commonly referred to in literature simply by the term Witness Complex, two constructions based on the Cech and Vietoris-Rips Complexes as well as a possible construction for a Witness Complex bifiltration.
First, we compare them to one another and to other known filtrations, look at methods of choosing the landmark points and search for approximations to the Vietoris-Rips Complex before introducing multiparameter filtrations.
One of the main parts of this work is after that to construct a different method of acquiring landmark points that is robust with respect to outliers in the data set. This method is derived from the DBSCAN algorithm and with it we can compare one of the Witness Complex constructions to the Degree-Rips filtration which is a density-sensitive bifiltration of the classical Vietoris-Rips Complex.
Another goal of this work is then to expand on some existing interleaving results for Witness Complexes to all of the different introduced constructions and especially to expand them before finally stating some additional stability results for all of the constructions which allow both the landmark points as well as the data points to shift to a certain extent
Measuring the external exposome with the internet of things: A technical perspective
No full textPublic health is increasingly influenced by environmental exposures that affect human well-being. The concept of the external exposome, the totality of environmental exposures an individual experiences throughout life, has emerged as a critical framework in this context. This paper presents a comprehensive and accessible technical overview of how the Internet of Things (IoT) can monitor the external exposome and support public health initiatives. Focusing on air, water, and land-based environmental parameters, we provide a tutorial-style introduction tailored to public health and medical researchers with limited engineering backgrounds. Our discussion covers key IoT building blocks, including sensor types, communication protocols, power management strategies, and data analytics, emphasizing their practical application in indoor and outdoor environments. We review real-world IoT deployments across domains such as air quality monitoring, radiation detection, extreme weather surveillance, and biological pollutant tracking, highlighting technical challenges and societal benefits. To support practical adoption, we introduce implementation templates that consider trade-offs among power consumption, data volume, and connectivity, offering actionable guidance for non-specialist users. This paper bridges disciplinary divides and encourages interdisciplinary collaboration in exposome research by integrating technological foundations with public health goals. We illustrate how IoT-enabled, real-time, and context-aware sensing systems can play a transformative role in advancing environmental public health
Finite element modelling of single dry-adhesive microstructures with a hyperelastic material model
No full textDry-adhesive microstructures made of silicone are an energy efficient tool for pick-and-place tasks with a diverse range of objects. Small-scale experiments with less than 50 individual adhesive elements provide the database for finite element modelling of single adhesive elements using a hyperelastic material model. Through experimental investigations and numerical parameter identification, a finite element simulation with a Neo-Hookean model was developed. The simulation could successfully describe the deformation during the compression phase. However, for the pulling phase a more complex material model, such as the Mooney-Rivlin or Ogden model in combination with a better representation of the incompressibility, is required