Theses - Earth Sciences

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Open Access
Speleothem Palaeoclimatology in the Maya Lowlands of Northwestern Yucatán, Mexico
James, Daniel
The sociopolitical and demographic changes in the Maya civilisation during the Terminal Classic Period (800 – 1000 CE) are increasingly thought to coincide with climate change, specifically drought. Two challenges facing interdisciplinary analysis of the complex interactions between climate and society in the Terminal Classic Yucatán Peninsula, Mexico, are the low chronological resolution of local palaeoclimate records, and the lack of quantitative reconstructions of palaeorainfall changes. I present new proxy records of climate in the Maya Classic Period from two speleothems in northwestern Yucatán which help address these issues. First, I provide a high resolution δ¹⁸O record of seasonal climate variability in the Terminal Classic. Using lamina counting and uranium series disequilibrium dating on the stalagmite Tzab06-1, I reconstruct the precise duration, timing, and relative severity of wet season droughts in the Terminal Classic. This is the first proxy record from the northern Yucatán resolved on seasonal timescales, and can be directly compared to the history of local Maya archaeological sites, as I demonstrate at Uxmal and Chichén Itzá. Secondly, I provide a multiproxy palaeoclimate record from the stalagmite HOBO-5, spanning the last 1,500 years. I use combination of the traditional stable isotopes δ¹⁸O and δ¹³C, and calcium isotopes (δ⁴⁴Ca), a novel speleothem proxy which I use to estimate semiquantitative palaeorainfall changes. As well as corroborating previous records of Terminal Classic climate, the δ⁴⁴Ca record reconstructs additional climatic variability, including a significant wet period punctuating drought events, and persistently low groundwater availability for over a century after the Terminal Classic. The assumptions in proxy interpretation in both stalagmites are tested by the establishment of monitoring at both caves of origin, and the ability of the karst system at the site of Tzab06-1 to transmit and record seasonal climate change is confirmed. This work provides new records with which spatiotemporally high-resolution analysis of human-climate-environment interactions in the Terminal Classic can be assessed to aid understanding of the complex decline of Classic Maya society, and move beyond the narrative of catastrophic collapse.
Open Access
Dissolution of mixed uranium thorium oxides under geological disposal conditions
Perry, Emma
Uranium dioxide alone offers enough complexity to provide the subject matter for 50 years of dissolution studies, not least due to uranium’s redox sensitivity and the orders of magnitudes between the solubility of U(IV) and U(VI). The addition of plutonium dioxide as a solid solution opens up a whole new realm of intrigue. How does plutonium affect the oxidation of uranium? How does plutonium affect interactions with radiolytic species of the surface? The aim of this PhD project is to piece together answers to these questions to build a picture of the dissolution mechanism for mixed actinide oxides, specifically in the environments that materials of this type will be exposed to during the long term storage of spent nuclear fuel. Due to the restrictions on the use of plutonium, except on nuclear-licensed premises, thorium is used as a plutonium surrogate. Studying thorium simplifies the experiment since the influence of the additional actinide can be observed separately to the production of radiolytic oxidants and the dissolution of end member pellets can be studied in the same environment. This work extends to developing methods that better simulate spent fuel by continuously delivering hydrogen peroxide using a syringe pump. It has been found that homogeneously mixed oxide pellets suppress the uranium dissolution by a factor of 10, as compared to end member uranium dioxide pellets, without affecting the consumption of hydrogen peroxide. The percentage of consumed hydrogen peroxide leading to dissolution is found to be dependant on the initial hydrogen peroxide concentration. Therefore, the batch dissolution experiment with continuous additions improves the simulation of (U,Pu)O₂ samples where the initial peroxide concentration is 0 mol.L⁻¹. Less homogeneously mixed oxide pellets dissolved less homogeneously, with the height of uranium rich regions decreasing relative to the thorium rich regions as visible by stereographic reconstruction of the surface using Scanning Electron Microscopy. Blank experiments provided evidence that the dissolution rate increase coincided with the onset of background disproportionation of hydrogen peroxide in the solution away from the pellet surface.
Open Access
Mapping the Core-Mantle Boundary Using Sdiff Postcursors
Martin, Carl; Martin, Carl [0000-0002-2882-543X]
The core-mantle boundary – the interface between the rocky mantle and the fluid iron outer core – is host to a diverse collection of phenomena across all length scales. At the largest length scales, continent-sized structures characterised by low velocity anomalies lie opposite to each other on the core-mantle boundary. These structures, known as large low shear velocity provinces (LLSVPs), are predominantly situated beneath the Pacific Ocean and the African continent. Smaller, more extreme phenomena (10s km thick, up to 100s km wide, dVs -10–50%, dVp -5–25%) have been identified on top of the core-mantle boundary, called ultra-low velocity zones (ULVZs). The largest of these anomalies have been associated with whole-mantle plumes at the base of major hotspots (Hawaii, Iceland, Samoa, and Galapagos), and have been suggested to act as a plume root and geochemical reservoir. In this thesis, we use the S core-diffracted phase (Sdiff) to detect ULVZs. Sdiff wavefronts propagating across the core-mantle boundary refract through low velocity anomalies and create additional wavefronts, called ‘postcursors’, whose move-out pattern is determined by the size, velocity, and shape of the ULVZ. These structures can then be detected by searching for the move-out of postcursory energy across a large seismic array sequenced by azimuth and inferences made about the ULVZ. We perform an extensive global search for Sdiff postcursors from earthquakes between 1990–2022 with magnitudes ≥5.7 at any depth in the IRIS earthquake catalogue. This results in the identification of 100 events sampling the Hawaiian ULVZ, and 100s more sampling the Iceland, Galapagos, and several newly discovered ULVZs. By pushing the dataset to higher frequencies than previously used, we find evidence for a thinner ULVZ beneath the mid-Pacific (less than 10 km) – which we refer to as the ‘ultra-thin ULVZ’. Modelling of these structures using Sdiff postcursors has, so far, required computing 3D full waveform synthetics to the periods corresponding to the length scales of ULVZs (approximately 10 s). Doing this is computationally expensive, resulting in simplified models and limiting the exploration of the parameter space. Accurate models of ULVZ morphology and physical parameters is essential to understanding their origins, and role in mantle dynamics and core-mantle interaction. We adapt a wavefront tracking software to model waves propagating across a spherical shell in 2D to decrease the forward model computational time from 100s CPU hours to a few seconds. We implement this forward model – the 2D wavefront tracker (2DWT) – into a Bayesian inversion to better explore the parameter space of these structures and, for the first time, to estimate the associated errors. For the Hawaiian ULVZ, we selected five high quality events with good azimuthal coverage to apply the inversion. We found a 2D elliptical shape with a shear velocity reduction of 22 ± 4%. The ULVZ is aligned along the edge of the LLSVP, suggesting it might be piled up there. Using our 2D shape in full waveform modelling, we constrained the height to be 25 ± 5 km based on comparison of the frequency content to the waveforms. We also apply the inversion to the ultra-thin ULVZ. Data coverage for this structure is limited to one azimuthal direction, so we are unable to resolve a precise location or morphology. However, we are able to build a probabilistic picture of its properties: it is likely quasi-cylindrical, with a radius of 280 ± 50 km, shear velocity reduction of 20 ± 4%, and height of 8–12 km. We go on to perform Bayesian inversions with the 2DWT on other ULVZs. We characterise two known ULVZs (Iceland and Galapagos) and two newly identified ones (near Vanuatu and near Marquesas), and show evidence for several other new structures as well. Despite detections of ULVZs in the literature being prevalent across the core-mantle boundary, all of the ULVZs detected with Sdiff are unambiguously clustered around the edges of the LLSVPs. This suggests a multi-scale dynamical relation between the two phenomena. Furthermore, all of the observations and inferred properties of ULVZs are consistent with an iron-enriched (Mg,Fe)O compositional origin.
Embargo
The Rise of Modern Avian Flight: Wing Movement and Joint Mobility Within Ornithurae
Demuth, Oliver
How and when avian powered flight arose has intrigued scientists for well over a century. Birds have a remarkable fossil record demonstrating their macroevolutionary transition from dinosaurs to birds during the Mesozoic Era. Thus, Mesozoic fossils offer us a unique opportunity to study the evolution of avian flight. The origin of many bird-like characteristics (e.g., feathers, a toothless beak, small body size) among non-avian theropod dinosaurs and Mesozoic bird-like taxa are now well understood. Yet, despite more than a century of research, the origin and evolution of avian flight itself remain poorly understood and the precise timing and mechanisms behind the emergence of active, flapping flight remain elusive. This thesis aims to quantitatively resolve the ancestral flying capabilities of crown birds and elucidate the emergence of avian flight through modelling of the flight performance of *Ichthyornis dispar*, which can provide crucial insights into the evolution of flight in birds due to its phylogenetic position just outside the avian crown. It is essential to assess the ancestral morphologies and flying capabilities of such stem birds to investigate the evolution of the different morphologies and the associated locomotor specialisations in the pectoral girdle of living birds. I developed a novel technique for the retrodeformation of taphonomically deformed fossils to reconstruct the remains of *Ichthyornis*. To decipher a link between 3D wing joint mobility and the flight ecology in living birds, I captured and analysed the 3D wing kinematics of bird cadavers representing nine species through biplanar fluoroscopy (XROMM) and quantified their *ex vivo* movement envelopes. I developed a new quantitative framework for joint mobility analyses in a phylogenetic context: the *EcoPhyloMobilitySpace*. This enabled me to investigate links between flight ecology and joint mobility in living birds and trace the evolution of their locomotor specialisations through time. I projected the simulated range of motion envelopes of *Ichthyornis* into the data of extant birds to infer its locomotory behaviour and retrace the evolution of bird flight ecology. The results highlight that a flight analogue to modern seabirds was already achieved in the Cretaceous period before other bird characteristics, such as a toothless beak, evolved.
Open Access
The rheology and dynamics of the Precambrian lithosphere – insights from the British Isles
Miocevich, Sophie
This thesis combines a range of petrological, geochemical, and geophysical techniques to investigate the properties, behaviour, and evolution of the Precambrian lithosphere. In Chapter One, I summarise some of the key open questions regarding lithospheric evolution and the development of strength contrasts, and how they will be addressed in this thesis. Chapter Two investigates the feasibility of ‘sagduction’, which is a tectonic process that has been proposed to occur during Earth’s early history. I focus on a case-study from north-west Scotland, a region where Archean sagduction has been suggested. I integrate results from fieldwork, phase equilibria modelling, and numerical modelling to show that sagduction was unlikely to be feasible. Furthermore, I develop a method that allows the feasibility of sagduction to be assessed at other sites. I conclude that sagduction is unlikely to be an important Archean tectonic process. Chapters Three and Four focus on understanding how strength contrasts develop and persist in the lithosphere. I consider a region in England and Wales, known as the ‘Midlands Microcraton’. The microcraton formed in the late Precambrian and has behaved as a relatively strong block compared to its surroundings, displaying ‘craton-like’ properties. In Chapter Three, I integrate results from fieldwork, phase equilibria modelling, and geochronology. I demonstrate that the microcraton experienced a syn- to post- subduction metamorphic event. Using geotherm modelling, I infer that this event led to partial melting in the mid-to-lower crust, resulting in the development of the microcraton as a strong region. In Chapter Four, I compare the characteristics of the mantle on and off the microcraton using mantle xenoliths. I find that England and Wales are underlain by non-cratonic lithosphere that records a complex history of melting and metasomatic processes, confirming the untypical mode of formation of the strong crust proposed in Chapter Three. I then use the Phanerozoic deformation record to show that the microcraton has persisted as an (anisotropic) strong region throughout the Phanerozoic, and has exerted a strong influence on Britain’s geological evolution throughout this period. Although focused on Britain, the results in this thesis provide insights into the general concepts that control the rheology, deformation, and evolution of the lithosphere.
Embargo
Comparative Morphology and Macroevolution of the Avian Quadrate
Kuo, Pei-Chen
In birds, the quadrate acts as a hinge between the lower jaw and the skull, playing an important role in cranial kinesis. Therefore, the evolution of avian quadrate morphology presumably has been influenced by selective pressures related to feeding. Owing to its complex and variable morphology, the avian quadrate has been relatively overlooked with respect to other aspects of the crown bird skeleton, and previous researchers have frequently used different names to describe the same anatomical characters. Meanwhile, none have attempted to quantify evolutionary changes in quadrate shape to examine its geometric variation in light of ecological information. Here, we investigated the morphological variation of the quadrate across over 249 bird species covering all major lineages of extant birds to produce a clearly labelled anatomical atlas of the avian quadrate and describe the shape variance among different clades. Following this anatomical investigation, we used three-dimensional geometric morphometrics to quantify morphological variation of the quadrate to examine its relationship with an array of key ecological categories and perform ancestral shape reconstructions in the context of an up‐to‐date galloanseran phylogeny as a case study. We found non-ecological factors, such as allometry and phylogeny, exhibit stronger relationships with quadrate shape than ecological factors do. The avian quadrate evolved as an integrated unit and exhibits strong associations with the morphologies of neighbouring bones with which it articulates. Our results also illustrate the importance of incorporating fossil taxa into ancestral shape reconstructions and helps elucidate important aspects of the morphology and function of the avian feeding apparatus early in crown Galloanserae evolutionary history. Collectively, our results suggest a complex macroevolutionary scenario in which quadrate morphology evolved jointly with other elements of the avian kinetic system. With the knowledge of quadrate morphologies in crown birds, we plan to apply this explicitly quantitative framework to avian quadrates of stem group birds in future investigations.
Embargo
The Role of the Ocean in MIS 4 Climatic Changes and Atmospheric CO₂ Variability: a Geochemical Fingerprinting Approach
Radionovskaya, Svetlana
Since the industrial revolution, humans have caused profound climate changes, primarily by releasing geological carbon into the atmosphere and increasing atmospheric CO₂, with current levels reaching >400ppm, a concentration unprecedented in the last 800ka. This has led to far-reaching socioeconomic consequences for human society and risks for all levels of ecosystem. A better understanding of rapid climatic changes is desperately needed in order to inform mitigation and adaptation strategies for future climate change. The last glacial cycle experienced orbital and millennial scale climatic variability, as indicated by high latitude ice core records and many other high-resolution marine and terrestrial records. These climatic changes included, but were not limited to, changes in atmospheric CO₂, temperature, the hydroclimate, sea surface temperature (SST), ocean circulation and ocean biogeochemistry. The ocean is thought to have played a key role in controlling and modulating these changes through its impacts on both heat transport and the carbon cycle. High resolution marine sediment cores can be used to reconstruct these changes and may help to elucidate the mechanisms behind them. To date, most studies have focused on the deglaciation, and only sparse, low-resolution records exist for Marine Isotope Stage (MIS) 4, a key paleoclimatic interval for the last glacial inception. MIS 4 is characterised by a rapid CO₂ drop of ~40ppm, which is comparable in duration and magnitude to the first rapid increase seen during the last deglaciation. It also involved a large drop in temperature, as indicated by Greenland and Antarctic ice cores, a decrease in sea level, and a possible slowdown of Atlantic Meridional Overturning Circulation (AMOC) as reconstructed from various proxy records. Several millennial events occurred during MIS 4, including Heinrich Stadial 6 and Dansgaard-Oeschger (DO) events 16-19. MIS 4 is thus an ideal interval to study and disentangle, glacial-interglacial and millennial variability. It also provides a window into the mechanisms of rapid CO₂ change and their contribution to longer-term (orbital) climate change. Furthermore, the termination of MIS 4 allows for a comparison with the last deglaciation. In this thesis, I collect paleoceanographic data to improve coverage of this important interval from a suite of sediment cores retrieved from the Iberian Margin in the Northeast Atlantic, and a single core from the deep Sub-Antarctic Atlantic core site. This thesis ultimately aims to enhance the current understanding of the ocean’s role in and response to abrupt and orbital-scale climate changes during MIS 4 and to draw lessons on its wider implications for climate variability. Ultimately, this may contribute to our understanding of natural carbon cycle-climate feedbacks that will play a role in anthropogenic climate changes in the future. High resolution planktonic foraminifera Mg/Ca-based SST reconstructions from the Iberian Margin during MIS 4 show that certain aspects of the surface ocean response may not always track Greenland temperature and that Greenland ice core records do not serve as a universal template for climatic variability across the whole of the North Atlantic, likely due to the seasonal habitat biases associated with SST reconstructions. A strong hydroclimate signal is shown in planktic foraminifera δ¹⁸O from the Iberian Margin, whereby glacial (MIS 4) hydroclimate variability is coupled to a combination of the high-latitude North Atlantic changes and low-latitude tropical hydroclimate. Furthermore, for the first time, a high-resolution Mg/Ca-based SST record from the Iberian Margin, covering the last 85ka, demonstrates clear similarities between MIS 4 and MIS 2. This includes a similar decoupling of sub-tropical summer SST from Greenland temperatures recorded in ice core records during pre-HS 6 MIS 4 and the Last Glacial Maximum (LGM). The record also emphasises that the most severe (coldest and driest) conditions occurred in the midlatitude North Atlantic during Heinrich Stadials, rather than the ‘peak’ glacial conditions of MIS 4 or the LGM. The deep ocean likely played a key role in modulating CO₂ on millennial and astronomical timescales, for example through changes in its respired carbon inventory. Conservative parameters that are indicative of deep-water hydrography, and by extension circulation, are deep water temperature (T_dw) and associated δ¹⁸O_dw. Reconstructed T_dw changes from the Iberian Margin show a larger influence of southern sourced waters during MIS 4 and particularly during HS 6. Atlantic sector Southern Ocean (SO) T_dw closely follows Antarctic temperature, atmospheric CO₂ and the mean ocean temperature, implying that the deep SO contributed significantly to the global ocean energy budget on multi-millennial time scales across MIS 4, likely mediated by buoyancy forcing in the SO. This in turn was likely linked to sea-ice expansion at the MIS 5a/4 transition, aided by a parallel shoaling of North Atlantic Deep Water (NADW) as suggested by the North Atlantic Tdw record. Together with (arguably smaller) contributions from reduced air-sea gas exchange efficiency in the SO, these changes would have lowered atmospheric CO₂ during MIS 4, through their impact on the solubility- and soft tissue “pumps” (i.e. the ocean’s disequilibrium and respired carbon budgets). Because the amount of respired carbon in deep-water broadly scales with the dissolved oxygen concentration, bottom water O₂ reconstructions, [O₂]_bw, were investigated for a depth transect from the Iberian Margin and for the Atlantic sector of the Southern Ocean. Qualitative benthic foraminiferal assemblage records from a depth transect on the Iberian Margin show that shifts in oxygenated environments are primarily controlled by the quality and/or quantity of C_org reaching the sea floor, rather than [O₂]_bw. There are distinct shifts in assemblages associated with more periodic and/or degraded C_org flux during MIS 4 and an indication of low [O₂]_bw during HS 6 at the mid-depths, however no significant changes in the flux of C_org (i.e. ‘export production’) were found. Multi-proxy foraminiferal geochemical [O₂]_bw reconstructions from the Iberian Margin show a gradual decrease in [O₂]_bw at the mid-depth North Atlantic during MIS 4 with a minimum during HS 6, likely controlled by ventilation changes (i.e. changes in ocean circulation, including water mass sourcing combined with active but diminished transport, or altered preformed ‘end-member’ values). In the meantime, the [O₂]_bw record from the South Atlantic closely follows atmospheric CO₂, likely indicative of ocean ‘ventilation’ impacts on ocean-atmosphere carbon exchange. Indeed, the Southern Ocean appears to have represented a significant reservoir for sequestering CO₂ away from the atmosphere during MIS 4, as indicated by the respired- and equilibrium carbon inventory changes that are implied by the [O₂]_bw and T_dw reconstructions.
Embargo
Skeletal evolution and convergence in the hyperdiverse passerine radiation
Steell, Elizabeth; Steell, Elizabeth [0000-0002-3999-3500]
Among vertebrates, passerine birds are an exceptionally diverse group (>6,000 living species) encompassing more than half of living bird diversity. In this thesis I present primary descriptive anatomical work (Chapters 2 & 4), phylogenetic inference (Chapter 2), and novel quantitative approaches (Chapters 3 & 4) to shed light on aspects of passerine evolutionary history and diversification. Chapter 2 comprises a novel, comprehensive anatomical dataset of the passerine carpometacarpus, an anatomically variable bone in the wing. Using these data, I attempt to elucidate the phylogenetic affinities of several early passerine fossils from the Oligocene of Europe using Bayesian phylogenetic analyses of discrete carpometacarpus characters with a large-scale taxon sample encompassing >70% of passerine family-level clades. My results provide evidence that crown group suboscines (one of the two primary clades of passerine birds) were present in Europe by the early Oligocene, and that crown group oscines (the other primary clade of passerines) were present by the late Oligocene. Inadvertently, this project revealed evidence of pervasive convergent evolution, or homoplasy, in the passerine carpometacarpus. In Chapter 3, I present a new method of quantifying homoplasy in discrete character datasets and re-evaluate longstanding hypotheses about expected patterns of homoplasy considering changing variables in phylogenetic datasets. Through analyses of simulated and empirical datasets, I show that my new metric, the ‘relative homoplasy index’, outperforms the two most frequently used methods in the literature—the retention index and consistency index—in terms of accurately measuring homoplasy in discrete matrices. I also show that, contrary to expectations based on previous studies, relative homoplasy within phylogenetic matrices decreases as taxa are added to phylogenetic datasets. These results indicate that passerines exhibit high levels of homoplasy compared to other bird datasets. In Chapter 4, I investigate evolutionary constraints in the passerine wing and hindlimb skeleton. With my carpometacarpus dataset from Chapter 2 and an additional novel discrete anatomical dataset for the passerine tarsometatarsus (foot), I explore patterns of homoplasy and character state exhaustion across the two major sister clades of passerines, Tyranni (suboscines) and Passeri (oscines). I show that oscines, the more diverse subclade in terms of present-day species richness, exhibits substantially more homoplasy in the appendicular skeleton than suboscines. Simulated null distributions of character state exhaustion patterns reveal that oscines evolved under significant constraints to morphological diversification, whereas suboscines did not. Within discrete character morphospace for the carpometacarpus and tarsometatarsus, oscines show highly overlapping subclades, in contrast to pronounced separation among suboscine subclades; these results indicate differences in the mode of evolution for oscines and suboscines, which have culminated in greater levels of convergence among oscines. This thesis lays the foundation for future work investigating passerine macroevolution and constitutes an important step in broadening our understanding of how passerines became so spectacularly diverse.
Open Access
The Relationship Between Intraplate Earthquakes and Temperature
Emmerson, Brian
This dissertation uses a combination of techniques to investigate the rheological properties of the lithosphere in continental areas and subducting slabs. In these settings, the relationship between temperature and the distribution of seismicity, particularly in the mantle, is examined. The dissertation is divided into three studies, which are largely self-contained and deal with different geographical and seismotectonic settings. To begin, the properties of the lithosphere in the Lake Baikal region are examined in a multidisciplinary study incorporating observations of seismicity, gravity anomalies, topography, and seismic velocity and thermal structures. Teleseismic waveform-modelling is used to constrain the focal depths of 18 earthquakes, which are used along with published teleseismic and local-event studies to examine the seismogenic thickness (T_s) in the Baikal region. All sets of earthquake data show that the mantle in this region is not a significant source of seismicity. Estimates of elastic thickness (T_e) in the areas surrounding Lake Baikal are everywhere less than the seismogenic thickness, consistent with the simple interpretation that the long term strength of the lithosphere resides in its seismogenic layer, which in this region involves the whole crust but not, to any significant extent, the mantle. The apparent weakness of the mantle in the Baikal region is explained by its high temperature. The thermal conductivity of mantle rocks is strongly dependent on temperature, and has been shown to have a significant effect on the modelled thermal structure of cooling oceanic plates. The second study in this dissertation models temperatures in subducting slabs, taking into account the temperature-dependence of the relevant physical parameters, and investigates the maximum temperatures, potential temperatures, and homologous temperatures up to which intraslab earthquakes occur. An analysis of the world’s subduction zones reveals that intraslab seismicity is consistent with being limited to material having potential temperatures less than 600 °C. Apparent exceptions to this pattern occur in regions where the Nazca Plate subducts subhorizontally beneath South America, with which the final study in this dissertation is concerned. The unusual subduction geometry in the Peruvian and Pampean segments of the South American subduction zone keeps the overriding plate and the subhorizontal subducting slab in contact for several hundreds of km. Thermal modelling including this unusual geometry shows the subducting slab to be relatively cold in these regions, as compared with typical subduction zones where more immediate contact with the mantle wedge results in a hotter slab temperature structure. In the Peruvian and Pampean regions, intraslab seismicity is found to occur at potential temperatures less than 600 °C. Furthermore, the continental mantle above the slab is shown to be cold enough to generate earthquakes. Teleseismic waveform-modelling is used to constrain 39 earthquake focal depths, and confirms that the continental mantle of Peru is indeed seismogenic.
Open Access
The kinematics and dynamics of active mountain ranges
Knight, Elizabeth
This thesis explores the controls on tectonic deformation in and around active continental mountain belts, and comprises three interconnected studies. The first chapter investigates lateral variations in the foreland of the New Guinea Highlands, a young mountain range which sits on the northern edge of the Australian plate. I construct new earthquake source models across central and western New Guinea, and combine these data with thermal and elastic modelling. I find that pre-existing structural contrasts in the Australian lithosphere control along-strike variations in the temperature structure, seismogenic thickness, and strength of the New Guinea foreland. The underthrusting foreland supports the elevation of the overriding mountain belt, yet the elevation of the Highlands is not closely correlated with the foreland seismogenic thickness; this is likely due to the time taken to thicken the crust following changes in the rheology and strength of the foreland over time. Using force-balance arguments, I estimate the static coefficient of friction on foreland faults to be between 0.01–0.28. The second study expands in scope to examine the forces governing deformation along mountain range fronts, by analysing slip vectors from reverse-faulting earthquakes in 15 active mountain belts. I find that, along most range margins, slip vectors are better aligned with topographic gradients than with the direction of convergent plate motion. This implies that the gravitational buoyancy force acting between a mountain and its foreland exerts a strong control on the direction of slip. This effect is observed most clearly in high-elevation ranges like the Himalayas. By considering the force balance in these deformation belts, I suggest that, in most mountain ranges, the underthrusting foreland must act as a rigid base to the overlying range front, allowing it to act like a gravity current. Local factors, such as weak sediments in the foreland basin, can allow the gravitational force to be dominant even in low elevation ranges like the Zagros. The final chapter builds on these results by modelling a viscous flow over a rigid base, to examine the underlying dynamics. I explore how varying a range of geometric and rheological parameters can influence the instantaneous velocity field within the model mountain range. I find that the gravitational buoyancy force has a strong influence on the resulting velocities along the range front, supporting the observations made in the previous chapter. The velocity field is also significantly affected by the viscosity contrast between the upper and lower crust, and by variations in viscosity (within one order of magnitude) along-strike of the mountain range.
Open Access
Dynamics of deep-submarine explosive eruptions
Newland, Eric; Newland, Eric [0000-0003-3501-8115]
This thesis explores the dynamics of explosive volcanic eruption columns in the deep-ocean. Motivated by the observations of pyroclastic deposits on the sea floor at depths of up to 4 km, we investigate the initial mixing of erupted hot fragmented magma with the ambient seawater and explore the density and spatial evolution of the subsequent flow that forms. In chapter 2, we consider the initial mixing and rise of an explosive eruption in a quiescent ambient environment via a series of numerical integral models and find that a submarine eruption column tends to evolve as a turbulent particle-laden fountain. We investigate the controls on the density evolution of the flow, such as particle separation, and consider the particle dispersal mechanisms of these complex multi-phase flows. In chapter 3 we explore the dynamics of particle-laden fountains in a stratified environment, and identify two distinct flow regimes as a function of the average size of the particles, in which the flow is controlled by the ambient stratification or by the separation of particles. We build two numerical models for the rise and fall of particle-laden fountains in a linear density stratification. We contextualise the findings of this study for submarine explosive eruptions and estimate the dispersal distances of pyroclasts in the submarine environment. Next, in chapter 4, we consider the effect of a uniform lateral crossflow on the dynamics of particle-laden fountains. We perform a series of analogue experiments and examine the impact of particle separation on the structure of the flow. We develop the theory for single-phase fountains in a crossflow to identify the location of particle separation on the flow. Using field data on the dispersal of pyroclasts from deep-submarine eruptions, we show how the present work can be used to constrain eruption parameters, such as mass eruption rate. In chapter 5, we depart from the study of submarine volcanoes and consider a complimentary problem, motivated by the sediment plumes formed during the operations of deep-sea mining. We explore the dynamics of dense sediment plumes in a uniform crossflow and consider the evolution of the gravity currents that form when these plumes interact with a solid boundary. We investigate the effect of the crossflow speed on the morphology of the gravity currents formed and compare the propagation of the flows with the classical theory of turbulent gravity currents. Finally in chapter 6, we summarise the work of this thesis and build a framework to help interpret the dynamics and deposits of submarine eruptions using the analysis presented throughout.
Embargo
Observations of Dynamic Topography from South American Atlantic Margin
Siqueira, Leonardo
Topography of the Earth is mainly controlled by its crustal and lithospheric architecture. Variations in thickness and density of the crust and of the lithospheric mantle create the most noticeable topography. However, it is also widely recognized that mantle convective processes dynamically support topography at long wavelengths (i.e. longer than ∼ 1,000km). Observations of dynamic topography, varying in space and time, are more straightforward in the oceans since less complex lithosphere facilitates necessary corrections for topography arising from density and thickness variations of the crust, sediments and flexure. The aim of this dissertation is to investigate the spatial and temporal variation of dynamic topography and its expressions along the South American Atlantic margin. First, the spatial pattern of dynamic topography is examined through the study of residual depth anomalies on oceanic crust abutting this margin. An extensive seismic reflection and refraction database is compiled, and a revised and augmented residual bathymetric map is presented. This map defines the spatial distribution of dynamic topography along South American Atlantic margin. Results are compared to a range of independent geophysical and geologic observations. Secondly, the temporal evolution of dynamic topography is studied by focusing on the southern South Atlantic Ocean. A significant oceanic depression (∼ 2000km along its axis) occurs in the region known as Argentine Basin. This anomaly has a strong negative residual depth signal observed in different dynamic topography models. This study defines the amplitude and wavelength of the Argentine Basin depression and investigates its temporal evolution by looking into the stratigraphic record of sedimentary basins fringing this oceanic depression. To further investigate the temporal evolution of dynamic topography, Cenozoic epeirogeny of Argentine Patagonia is explored. Regional uplift is identified in this region which is contemporaneous with the evolution of the nearby Argentine Basin. Patagonia uplift is studied by inverse modeling of drainage networks, which provides spatial and temporal uplift patterns. The temporal evolution of this region is also analysed by geochemistry of intraplate magmatic rocks and earthquake tomography. Relationships between long-wavelength topography, spatial distribution of intraplate magmatism and uplifted marine terraces are discussed. Finally, constraints on the sub-lithospheric structure of Southern South America are assembled and an empirical conversion for shear-wave velocities to temperature is exploited with a view to investigating possible driving mechanisms for uplift and subsidence across Patagonia and the Argentine Basin.
Open Access
Magnetism of anthropogenic airborne particulate matter
Sheikh, Hassan Aftab
The global burden of disease associated with ambient particulate matter (PM_2.5) pollution is the leading threat to life expectancy according to the Air Quality Life Index (AQLI) 2023 report. The study of airborne PM is key to understanding both its source, and its impact on human health. The focus of this thesis is the study of Fe-bearing PM which is abundant in urban microenvironments. I start by exploring ways of monitoring and constraining the source of magnetic PM signatures in Lahore, Pakistan. I employ use of First Order Reversal Curves (FORCs) to unmix signals from ’passive biomonitors’— leaves. FORC signatures of leaf samples combine aspects of both exhaust residue and brake-pad end-members, suggesting that FORC fingerprints have the potential to identify and quantify the relative contributions from exhaust and non-exhaust (brake-wear) emissions. This thesis then examines into the indoor micro-environment of the London Underground (LU). I find that the LU is dominated by ultrafine (<100 nm) maghemite particles. The oxidised nature of the magnetic PM suggests that PM exposure in the LU is dominated by resuspension of aged dust particles relative to freshly abraded, metallic particles from the wheel-track-brake system. Therefore, I suggest that periodic removal of accumulated dust from underground tunnels might provide a cost-effective strategy for reducing exposure. I then apply magnetic modelling tools to real-world LU particles for a comparison to the experimental data. The thesis then looks at determining the efficacy of roadside green infrastructure (GI) in improving local air quality through the deposition and/or dispersion of airborne PM. I use a combination of magnetic measurements, electron microscopy, and fluid flow modelling to show that air quality downwind of a carefully selected and designed GI significantly improves through the deposition of vehicle-derived PM on leaves. I then demonstrate the application of a machine learning technique on PM hyperspectral imaging data sets. The automated method improves accuracy and reliability of chemical phase identification that is often limited by subjective human interpretation. Using magnetic and microscopy methods, I conclude that ultrafine magnetic particles are abundant and ubiquitous in urban microenvironments; and that their presence may be masked by larger particles in mass-specific traditional air quality monitoring methods.
Open Access
Differential Thermal Isotope Analysis: A Method for the Study of Past Climates
Walters, Gregory
Online measurements of δ¹⁸O and δ²H can be used to reveal more information about past climates than current offline methods. In this thesis I present work carried out developing the online Differential Thermal Isotope Analysis (DTIA) method, including demonstrations of the method on gypsum samples and clay samples, and the application of DTIA to the ongoing research into climate conditions during the Paleocene-Eocene Thermal Maximum (PETM). Measurements of gypsum and clay samples demonstrate the ability of DTIA to separate out different dehydration steps for individual measurement, both for minerals with multiple water environments, and for minerals with multiple-step dehydrations. The gypsum results are also used to examine the dehydration of gypsum to anhydrite, via the intermediate bassanite. I show that this dehydration reaction is highly sensitive to sample grain size and the partial pressure of water, and crucially, that the two-step dehydration of gypsum does not result from the presence of multiple water environments that are preferentially dehydrated at different temperatures, but rather from kinetic factors upon dehydration. DTIA is also applied to a series of clays buried in the North Sea Basin across the PETM. The results from the hydroxyl isotopic composition of the clays show a trend of slowly decreasing δ²H prior to the PETM, followed by abrupt decreases in δ²H at the onset of the PETM, indicating increased precipitation intensity and weathering, and implying an enhanced hydrologic cycle response to global warming, particularly at the early stages of the PETM. These results are consistent with other research indicating higher precipitation rates during the PETM. Our results are presented alongside consistent evidence from the measurements of clay composition and plankton species concentration undertaken by previous researchers at this section, demonstrating how DTIA can be used alongside other methods. This thesis shows the potential DTIA has to aid palaeoclimate reconstruction in a number of geological settings. DTIA can be applied both to isolated hydrated minerals and to assemblages of hydrated minerals to better understand the formation environments of these minerals, and thus gain insight into the palaeoclimate conditions under which geological deposits form.
Open Access
A spatial and temporal study of the carbon cycle; the role of carbonates in buffering Earth’s climate
Knapp, William
Canonically, changes in Earth’s atmospheric CO₂ concentrations have been attributed to an imbalance between volcanic degassing rates and silicate weathering. To force environmental changes in this way, such as the CO₂ decline observed during the Cenozoic Period (66 Myr - present), requires either a decrease in volcanic degassing, or an increase in silicate weathering and a change in the total amount of carbon in the combined ocean-atmosphere (OA) system, which is hard to square against proxy observations of invariant silicate weathering and volcanic degassing rates. Recent rethinking about carbon cycling suggests that rather than increasing sources or sinks of carbon, environmental change can be forced by redistributing carbon between the ocean and atmosphere, which satisfies the condition of maintaining a similar amount of carbon in the OA system. A proposed mechanism to achieve this redistribution is via increasing rates of carbonate weathering, which provides a renewed onus on investigating the impact carbonate rocks, and dissolution thereof, may have on buffering changes in Earth’s climate. The long term process of chemical weathering is of particular interest currently, as some suggest silicate mineral dissolution reactions provide a scalable escape route from anthropogenic greenhouse-gas emissions, and subsequent disruptive environmental perturbations. This seems to be at odds with decades of work prior, showing the timescales upon which silicate weathering operates are far too sluggish to be useful in the next 50-100 years. Indeed, the energy required to catalyse silicate weathering (i.e., mining, grinding) and transport minerals to field-sites has not been convincingly shown to outweigh potential CO₂ removal, yet. Furthermore, in watersheds it is difficult to prove additionality as a consequence of enhancing silicate mineral dissolution. In large, open systems it is hard to trace additional carbon removal from the atmosphere as a consequence of enhanced silicate dissolution, data are often very noisy and the fractal nature of river networks means signals are diluted very quickly. Seemingly, appreciation of the timescales upon which chemical weathering operates have become skewed. This thesis investigates the transport of carbon between the terrestrial and ocean realm, on both short and geological timescales. Carbonate rocks weather rapidly in comparison to silicates, and carbonate terrains can be very efficient at delivering alkalinity to the oceans. However, the efficiency of the carbonate weathering alkalinity pump is hampered by the solubility of CaCO₃, which commonly precipitates at Earth’s surface and in doing so out-gasses CO₂. These inputs of alkalinity to the global oceans are measurable, and dynamic enough to be observed on short timescales and are investigated. Given this, the chemistry of contemporary carbonate terrains is investigated using stable Mg isotopes to understand how their carbon transfer capacity can be improved. A global riverine carbonate chemistry model is presented to quantify the present day maximum global carbonate weathering flux of alkalinity to the oceans. A method for quantifying carbon removal rates using radiocarbon data from sites where the chemical weathering process has been expedited is also presented. The fate of alkalinity in the global oceans requires a much longer frame of reference, given the residence time of carbon and base cations in the ocean. Therefore, a Cenozoic palaeo-record of stable Mg isotopes in seawater is presented, and potential drivers of carbon redistribution between the OA-system are assessed.
Open Access
Inside-out diversity of rocky planets
Guimond, Claire; Guimond, Claire [0000-0003-1521-5461]
Exoplanets orbiting distant stars have revealed to us that no one could have predicted Earth. Many stars host planets which appear to be made of rock and iron like Earth, but sit at several times its mass—we have no visible analogues nearby to show us what these massive rocky planets look like, and how differ from our own. Further, measurements of stellar photospheres show a certain variability in their rock-forming element abundances, which implies a similar spread in the rocky building blocks of planets. Consequences of a planetary mass variability and compositional variability comprise the contents of this thesis. Because the surfaces of exoplanets are not directly detectable with present technology—their nature cannot be told by astronomy alone—questions about rocky planet diversity require a theoretical approach. Drawing on the wealth of geoscientific knowledge originally developed to understand Earth, I construct physical models of other possible worlds to see how ours fits in. The first consequence of variability I model is topography. Topography sets the size of the largest ocean that planets could contain below their highest point—the capacity of the continental bathtub. I calculate the bare-minimum, dynamic topography due directly to mantle convection, by finding scaling laws of dynamic topography with convective parameters. For increasingly massive planets, topography almost disappears. Smaller ocean basins might suggest flooded worlds, all else equal. Yet large portions of a planet's water can be buried in their mantles, predictable insofar as known mantle minerals have characteristic maximum water contents. Thus for a second consequence of variability, I leverage stellar abundances to constrain the mineral phase equilibria of exoplanet mantles. I assess whether various exoplanets would plausibly sequester water in their mantles, providing a key initial condition for planetary evolution. In another chapter, I then link these surface and interior reservoirs explicitly, employing a coupled 2D mantle convection and melting model to estimate rates of volcanic outgassing on the early Earth, before modern plate tectonics—early Earth provides an elucidative case study to ground our understanding of planet diversity. These estimates focus on the possible range of mantle oxygen fugacities, a measure of how oxidising the mantle is. I show how most scenarios produce significantly lower outgassing rates in the Archean, compared to what classical thermal history models would suggest. The last consequence of variability then turns to oxygen fugacity itself. I invoke a subtle but powerful phenomenon from the petrological modelling toolbox, and predict the minimum amount by which mantle oxygen fugacity should vary across rocky exoplanets, constrained again by host star element abundances and inferred mantle mineralogy. By the end of the thesis it should become clear that there is no good prototype for a ``terrestrial planet''. Nevertheless, through the late union of exoplanet astronomers and Earth scientists, we start to appreciate how understanding planets holistically is an obligate and confrontable challenge.
Open Access
Seismic Evidence for Layering at the Core-Mantle Boundary
Russell, Stuart; Russell, Stuart [0000-0002-9477-014X]
The core-mantle boundary (CMB) is the most extreme discontinuity in Earth's interior and plays an important role in regulating planetary scale processes, including convection in both the mantle and core. The CMB is usually treated as a sharp discontinuity with direct contact between the silicate mantle and iron core, a scenario that is rarely questioned. However this is likely an over-simplification. This thesis investigates, using seismology, the possibility that the CMB is a layered transition, with an intermediate kilometre-scale layer sandwiched between the core and mantle. This thesis uses seismic data from opposite ends of the frequency spectrum - high-frequency body waves and long-period normal modes. Before applying body waves to the CMB, this thesis first addresses the problem of ellipticity corrections for seismic phases such that they can be applied correctly to any seismic phase in any planetary model. Following this advancement, the effect of a thin layer at the CMB on P waves is examined, finding that a previously underutilised diffracted phase, PKKP_diff, is very sensitive to the inclusion of even very thin layers. A global dataset of over 12,500 PKKP_diff observations and 353 normal mode centre frequencies are then applied in turn to attempt to resolve whether a thin layer exists at the CMB. Despite being vastly different data types with differing frequency contents and sensitivities, the two studies come to the same conclusion - not only is a slow kilometre-scale layer at the CMB possible within the bounds of seismic data, but both data types are better-fitted if such a structure on the order of a kilometre thick exists at the CMB. The favoured seismic parameters are a density increase of tens of percent coupled with similar magnitude reductions in both P- and S- velocity, with S-velocity more reduced than P. Both studies have their own limitations that inhibit robust conclusions that the CMB is truly layered. Nevertheless the results of this thesis suggest that this is a plausible scenario that is permissible within the bounds of current seismic data, and should therefore be considered appropriately. This conclusion has wide reaching implications which are also briefly explored.
Open Access
Box models of thermohaline circulation
Li, Scott
This thesis investigates a number of buoyancy-driven flows in stratified environments that are motivated by the thermohaline circulation of the ocean. Simple models are presented which reduce the dynamics to a few leading order processes and we present an intuitive investigation with simple experiments or numerical calculations. We study the fluid dynamics of locally intensified mixing, referred to as `boundary mixing' within the ocean literature, and also the effect of mixing between the up and downwelling flows on the steady and transient circulation within an idealised filling-box flow. In chapters 2 and 3 we present an experimental and theoretical study of boundary mixing. We investigate the transport of buoyancy and tracer through a closed basin with buoyancy fluxes supplied at the top and bottom boundaries and, in both chapters, we compare the two cases in which the mixing either occurs uniformly across the tank or is locally confined to one portion. In chapter 2 we establish the simplest case in which the buoyancy fluxes supplied at the boundaries lead to no net flow in the system. By tracking the movement of dye we are able to visualise the flow patterns. An analytical model is developed that is consistent with the vertical and lateral flows in the experiment as well as with the evolution of the salinity stratification. We investigate the interaction of this effect with a vertical buoyancy flux and a net vertical flow with boundary mixing in chapter 3. We examine the stratification and the flow that develops in the steady state case. Next we investigate the transient adjustment of the buoyancy stratification due to changes in the supplied buoyancy fluxes. In chapters 4 and 5 we shift the focus to filling-box flows and investigate the interior stratification that develops from a local finite-mass source of destabilising buoyancy and a distributed stabilising buoyancy flux, both supplied to the surface of the domain with the addition of interior diffusive mixing. In chapter 4 we present a model showing that the system is controlled by two key non-dimensional parameters relating the source volume flux to the volume flux of entrained fluid and to the diffusive flux, resulting in four distinct regimes. If this system is perturbed, it exhibits inertia in adjusting to the new equilibrium when the perturbation timescale is short compared to the adjustment timescale and is no longer representative of the quasi-steady state. However, these profiles are still consistent with the simplified `Abyssal Recipes' profiles which are controlled only by mass conservation with constant upwelling and diffusivity. In chapter 5 we present a similar box model in which the entrainment increases linearly with depth and investigate the inverted values for the diffusivity and the upwelling rate. This leads to the recognition that it is difficult to distinguish more complicated models from the simplified models just from the data. This thesis finishes with a summary and discussion of the results in chapter 6.
Open Access
Biogeochemical investigations of methane-rich groundwaters in high Arctic glacial catchments
Kleber, Gabrielle
Permafrost and glaciers in the high Arctic form a near-impermeable ‘cryospheric cap’ that traps a potentially large reservoir of sub-surface methane and prevents it from reaching the atmosphere. The vulnerability of the cryosphere to climate warming is making releases of this methane possible, but uncertainty in the magnitude and timing of such releases makes predictions of Arctic greenhouse gas emissions difficult. In Svalbard, where air temperatures are rising more than twice as fast as the average for the Arctic, glaciers are retreating and leaving behind exposed forefields that enable rapid methane escape. Through an extensive spatial study of proglacial groundwater springs on Svalbard, groundwater systems within glaciated catchments are found to be bringing to the surface deep-seated methane gas that was previously trapped beneath glaciers and permafrost in the Arctic. In this thesis, I estimate the amount of methane being released by such springs and discuss its origin. Through a temporal study conducted at a single glacial catchment, Vallåkrabreen, I use biogeochemical data collected from groundwaters during two melt seasons to investigate the sources of groundwaters and the origin of the methane they transport to the surface. Waters collected from 123 groundwater springs in the forefields of 78 land-terminating glaciers are supersaturated with methane up to 600,000-times greater than atmospheric equilibration. The spatial sampling revealed a geologic control on the extent of methane supersaturation, with strong evidence of a thermogenic source. I estimate annual methane emissions from proglacial groundwaters could be up to 2.31 kt across the Svalbard archipelago. Further investigations into marine-terminating glaciers indicate emergent methane emissions as these glaciers transition into fully land-based glaciers. My findings within the Vallåkrabreen catchment demonstrate an interconnected hydrological system where shallow and deep groundwaters mix to moderate methane emissions. During summer, deep methane-rich groundwaters sourced from upper catchment snowmelt are diluted by shallow oxygenated groundwaters, leading to some methane oxidation prior to its emergence at the surface. Microbial activity is an important methane sink along this flow-path, removing up to 62% of methane before it is brought to the surface. During winter, deep groundwaters remain active while many shallow systems shut off, reducing subsurface methane oxidation and permitting greater emissions. Ratios of the differing groundwater sources will change markedly in years to come as aquifer capacities and recharge volumes change in a warming climate. My findings reveal that climate-driven glacial retreat facilitates widespread release of methane, a positive feedback loop that has the potential to contribute to enhanced greenhouse gas emissions in the Arctic. The findings are highly relevant for other regions of the Arctic that, due to their geology, are likely to experience similar methane emissions, either currently or with further glacial retreat.
Open Access
Application of Hydrogen and Oxygen Isotope Ratios of Water to the Study of Evaporation, Palaeoclimate, and Ancient Marine Conditions
Brady, Matthew; Brady, Matthew [0000-0003-2674-6946]
Triple-oxygen and hydrogen isotopes of water are critical to aid our understanding of the hydrological cycle on the modern and ancient Earth. As such, this thesis presents advancements in techniques and in the understanding of the isotopic behaviour of water that undergoes evaporation in different conditions. An application of these findings is made to palaeoclimate data, and an expansion of the use of water isotopes from hydrated minerals is applied to a novel mineral system. Of fundamental importance to the hydrological cycle is the process of evaporation. Yet, under- standing how water isotopes behave as they experience evaporation remains poorly quantified. One limitation is the ability to confirm theoretical models or palaoeclimatic data sets with accurate, precise, and controllable experiments. To overcome this, I developed a widely applicable experimental method that permits the measurement of the triple-oxygen and hydrogen isotope evolution of an evaporating fluid and its coincident vapour that is both highly accurate and with a precision and sampling rate previously unobtainable. Additionally, the methodology permits a wide range of variables to be controlled or manipulated, allowing future scholars to thoroughly explore the effect of differing climatic conditions on the full suite of water isotopes as they undergo evaporation. One such variable explored is the morphology of an evaporating basin. Whilst currently neglected in studies that examine lacustrine palaeoclimate records, I present experimental data for both idealised and real basin morphologies (generated by 3D printing) that highlights a significant effect on the rate of isotopic change as a function of basin morphology, despite constant environmental conditions. Experimental data suggest that unless the surface area to volume (SA:V) ratio of a lake is considered, palaeoclimatic data from two lakes with distinct morphologies but undergoing evaporation under identical climates could be misinterpreted. Similarly, the results from the real basin morphology experiments suggest that rapid changes in SA:V ratio could result in inflections in the isotopic record that are solely a response to morphology as opposed to changes in climate. Understanding from the evaporation experiments is then applied to gypsum hydration water (GHW) data obtained from Lake Petén Itzá, Guatemala. The lake is in the northern neo-tropics and provides a complete record of climate variability over the last 43 ka. Using the GHW isotopic data in combination with a Monte Carlo and combined hydrological-climate re-analysis models, I determine relative differences between the cooler, drier stadial periods that are recorded in the sediments. In addition, multiple proxies indicate that intra-stadial variability is recorded at Lake Petén Itzá and this mirrors variation observed in polar oxygen isotope records. This suggests a close climate teleconnection between the poles and the tropics during these periods. Finally, I explore the use of oxygen and hydrogen isotopes in sedimentary talc. This is achieved by experimentally determining the fractionation factors between amorphous Mg-silicate and the water from which it precipitates. This is followed by calculating the fractionation factors as these precipitates undergo synthetic metamorphism to true talc. Isotopic measurements from Neoproterozoic samples are measured and the isotopic composition of the ancient precipitating fluid is estimated using the uncertainty of these parameters and Monte Carlo modelling. This thesis provides a strong experimental backbone for future examination of evaporating water under a variety of palaeoclimatic conditions and contexts. It demonstrates how insights from evaporation experiments can be applied to interpreting palaeoclimate data and how hydrated minerals of various types, and from a range of geological settings and times, can be used to provide robust information about the climate and fluids from which they formed.