UVicSpace | Institutional Repository
UVicSpace is the University of Victoria’s open access scholarship and learning repository. It preserves and provides access to the digital scholarly works of UVic faculty, students, staff, and partners. Items in UVicSpace are organized into collections, each belonging to a community.
For more information about depositing items, see the Submission Guidelines.
Recent Submissions
Numerical and stratigraphic expression of anomalous carbon cycling in the terminal Neoproterozoic, and Phanerozoic
(2025) van Wieren, Connor Stephan; Dyer, Blake; Husson, Jon
Carbon on Earth’s surface plays a central role in regulating climate. Most surface carbon in the ocean-atmosphere exists as CO2, sourced from the mantle and released through volcanism. Over geologic timescales, this carbon is removed from the ocean-atmosphere system by burial as organic matter or as carbonate sediments (CaCO3). The isotopic composition of marine carbonates (δ13Ccarb) records the balance between these two sinks and, because organic carbon is predominantly produced through oxygenic photosynthesis, also records information about net oxygen release to the atmosphere. The global carbon cycle thus links the deep Earth, surface climate, and the redox state of the ocean-atmosphere system. Tracking variations in δ13Ccarb through time provides insight into the co-evolution of life and environment, planetary habitability, and the development of Earth’s biosphere. This dissertation investigates intervals of Earth history when carbonate δ13C values were highly variable, potentially marking major changes to biogeochemical cycles. My thesis has two foci: (1) the Neoproterozoic Era (∼1000-539 Ma), particularly the Ediacaran Period (∼635-539 Ma), and (2) modern shallow-water carbonate platforms, where local processes shape the stratigraphic record of δ13C change over time. The results of my thesis research are presented in three data chapters. In chapter 2, I present data from Ediacaran sediments of the Old Fort Point Formation in the southern Canadian Cordillera that record a highly negative excursion in δ13Ccarb values (below –12‰). I argue that this excursion is linked to the globally observed Shuram excursion, and that the geochemistry of these carbonates was acquired at or near the time of deposition, ruling out late-stage alteration. This chapter highlights the global nature of the Shuram and underscores the potential for local changes to seawater chemistry, rather than late diagenesis, as drivers for excursions such as the Shuram. In chapter 3, I examine how sediment transport and redistribution influence geochemical records such as values of δ13Ccarb in shallow-water carbonate platforms, using numerical modelling. Model simulations show that sediment transport and offshore gradients in δ13CDIC can lead to correlative isotope excursions. These results demonstrate that δ13C excursions, such as the Hirnantian carbon isotope excursion (HICE) of the terminal Ordovician (∼487-443 Ma), can arise without requiring changes to global biogeochemical cycles. In chapter 4, I expand upon the numerical model I developed in chapter 3 to investigate the potential for growth of early diagenetic carbonate cements and organic matter respiration as a driver for highly negative δ13Ccarb values over Earth history. Here I show that simple interactions between high TOC margins and local sea-level cycles naturally generate large negative δ13Ccarb excursions, with magnitudes reaching ∼12‰ when respired carbon is incorporated into authigenic cements. This framework provides an alternative mechanism for the generation of highly negative carbon isotope excursions, including the Shuram, throughout Earth history. Together, my findings demonstrate how local depositional and diagenetic processes, operating at basin scales, can generate isotopic signals that mimic global perturbations. Recognizing these systematic spatial patterns in basin δ13Ccarb is critical for distinguishing local diagenetic overprints from true global perturbations, and for more reliably linking carbon isotope excursions to changes in the global carbon cycle.
Light as a probe: Harnessing optical resonances for sensing chemical diffusion and mechanical strain
(2025) Daxini, Swapnil; Loock, Hans-Peter
Sensors are fundamental to modern technology, supporting applications from environmental monitoring and industrial safety to structural health assessment and healthcare. However, conventional electrical and mechanical sensors often face limitations in sensitivity, robustness, and scalability. Rapid advances in optics and photonics are overcoming these challenges by harnessing light-matter interactions to detect physical, chemical, and mechanical changes with exceptional precision. These optical approaches enable remote, real time, and multiplexed measurements while offering enhanced sensitivity and immunity to electromagnetic interference. This thesis uses optical resonance-based sensors to study VOC diffusion in polymers and to perform long-range strain sensing.
In the first part of this work, extraordinary optical transmission (EOT) through metallic nanohole arrays (NHAs) is employed as a refractive index sensing platform to study the diffusion kinetics of volatile organic compounds (VOCs), specifically o-xylene, into thin polydimethylsiloxane (PDMS) films. Rigorous analytical models based on integrated solutions to Fick’s laws of diffusion are derived for both permeable and impermeable polymer films, extending classical approaches and enabling more accurate extraction of diffusion coefficients from experimental data. The resulting NHA-based sensor platform is simple to fabricate, operates in real time, and enables continuous, cost-effective monitoring of VOC sorption and desorption, providing new insights into diffusion dynamics in polymer analyte systems.
The second part of the thesis presents a long-range, high-resolution fiber-optic strain sensor based on a π-shifted fiber Bragg grating (π-shifted FBG) interrogated using the Pound-Drever-Hall (PDH) frequency locking technique. Enhanced field localization in the π-shifted FBG cavity, combined with sub-picometer wavelength resolution afforded by PDH interrogation, enables nanostrain-level response over fiber tethers up to 75 km, eliminating the need for in-line amplification. A coherent PDH scheme further improves the signal-to-noise ratio, extending the theoretical sensing range beyond 150 km.
Together, these studies demonstrate how optical resonance phenomena - from plasmonic nanostructures to resonant fiber gratings - can be harnessed to probe chemical and mechanical processes with high sensitivity and range, paving the way for advanced sensing platforms in environmental and structural applications.
The impact of extra mixing in low-mass stars on explaining the isotopic compositions of presolar grains
(2025) Cockshutt, Maeve; Dillmann, Iris; Herwig, Falk
Presolar oxide grains preserve isotopic signatures of stellar nucleosynthesis in oxygen-rich stellar environments, providing stringent constraints on mixing and burning processes in evolved stars. Among these, Group 2 oxygen-rich grains exhibit enhanced 17O/16O ratios and severe 18O depletion, signatures widely attributed to slow extra mixing between the convective envelope and the hydrogen-burning shell, known as cool bottom processing (CBP). The physical origin and self-limiting nature of CBP have remained poorly constrained.
This work presents a self-consistent stellar evolution model of CBP operating in low-mass asymptotic giant branch (AGB) stars, implemented directly within the stellar structure. The model reproduces the full range of oxygen isotopic ratios observed in Group 2 presolar grains and is consistent with spectroscopic measurements of AGB stars of similar mass.
By evolving CBP concurrently with the stellar structure, this approach captures the development of a stabilizing mean molecular weight gradient. CBP is inherently self-limiting: an increase in the mean molecular weight gradient as small as ∆μ ≈ μCE × 10−5 is sufficient to completely suppress further circulation, supporting the interpretation of CBP as a slow, low-energy circulation confined to the radiative zone. Modest variations in the depth and efficiency of mixing reproduce the observed spread in isotopic ratios, highlighting both the robustness and degeneracy of CBP within this stabilizing framework.
A complementary nuclear-physics sensitivity study identified the 17O(p,α)14N reaction as the dominant source of uncertainty in predicted oxygen isotopic ratios, with smaller but measurable contributions from 18O(p,α)15N and 16O(p,γ)17F. For the 17O(p,α)14N reaction, simulations that best reproduce Group 2 presolar grain compositions preferentially favor either the JINA Reaclib rate, the indirect measurement of Sergi et al. (2020), or the lower bound from Rapagnani et al. (2025), while adoption of higher rates systematically degrades agreement with the grain data.
Comparisons with 3D hydrodynamics simulations suggest that wave-driven mixing enhanced by rapid rotation may plausibly approach the efficiency required by CBP, supporting it as a viable underlying mechanism for the parameterized extra mixing.
A multi-method approach to studying a cryptic species: Mountain goats in Kitasoo Xai’xais territory
(2025) Jessen, Tyler D.; Darimont, Chris T.
Biodiversity conservation depends on linking ecological theory with applied monitoring and management. This challenge is particularly difficult for cryptic species that inhabit remote areas, where access and available data are limited. Yet such species can be of significant ecological, economic, and cultural value. By using multiple data sources, my dissertation confronts these challenges to provide an assessment of the population trends and habitat use of mountain goats (Oreamnos americanus) inhabiting the central coast of British Columbia (BC), Canada. This work begins with a synthesis and prospectus of the varied contributions of Indigenous Knowledge (IK) to ecology and evolution (Chapter 2). Although often discounted in the past, IK is increasingly contributing to the understandings of science, from the conceptualization of hypotheses, to the design of field methods, to the interpretation of results. Owing to the historically fraught relationship between western science and Indigenous peoples, the work also provides guidance for researchers to ensure that the processes and outcomes of collaborative research adhere to ethical standards, as defined by Indigenous peoples themselves. In Chapter 3, I apply this framework to a conservation assessment of a population of mountain goats residing in Kitasoo Xai’xais (KX) Territory, where scientific data were absent. Based on interview data from local land-users, observations of mountain goats declined precipitously from 1980 to 2019. Aerial surveys in 2019 and 2020 revealed a low-density population (mean = 0.25, SD = 0.12 goats/km2), typical of the coastal range of mountain goats. Lastly, provincial kill data (1980–2018) showed that, province-wide, goat kills per hunter/day declined among resident hunters in both coastal and interior BC. Together, these data suggest that coastal goats are likely declining in abundance and/or shifting in distribution, both of which threaten the long-standing relationship between people and mountain goats in the area. In Chapter 4, I examined intrapopulation variation in the space use of mountain goats in KX territory, specifically the differences between groups of mountain goats with kids and those without (typically solitary males). Using multi-state occupancy models derived from aerial surveys, I found that mountain goats use higher elevation areas, and that nanny groups with kids preferentially used areas of high terrain ruggedness. These results are consistent with foraging and predation-risk theory that suggest that reproductive groups trade areas with better forage for areas with greater security. More generally, our results show that considering sex- and age-specific variation in space use is important for the management of mountain goats, including for delineating spatial protections and hunting prescriptions. Collectively, my dissertation shows that coastal mountain goats are likely to be sensitive to human and natural disturbances, and that existing management strategies should consider age- and sex- composition as well as intrapopulation variation in space use. More broadly, this research demonstrates how disparate data sources and methodologies may be leveraged to elucidate trends in the distribution, abundance and behaviour of wildlife that present practical challenges to researchers and managers.
Intrinsic and extrinsic drivers of Columbian black-tailed deer population dynamics
(2025) Giguère, Isabel; Fisher, Jason Thomas
Anthropogenic landscapes fragment and reshape habitat for terrestrial mammals, favoring some species over others, triggering population shifts with cascading ecological impacts. In North America, Columbian black-tailed deer (Odocoileus hemionus columbianus; BTD) contribute to biodiversity loss, seen with both abundant urban and declining wild populations. Effective wildlife management is limited by poor understanding of how extrinsic forces influence intrinsic drivers, such as reproductive success - the key determinant of population persistence in deer. To address this gap, we studied two populations of immunocontracepted (IC) BTD on southern Vancouver Island, British Columbia, to assess how dispersal barriers and habitat quality influence the spatiotemporal dynamics of reproductive success. Using multi-year camera-trap data, we compared reproductive trends across two systems differing in permeability - one constrained by dispersal barriers and one permeable to immigration. We further examined how forage quality and cover shaped habitat selection by mothers (does with fawns) and non-mothers (does without fawns). The permeable system exhibited source-sink dynamics, where immigration drove increases in reproductive output; mothers selected energetically optimal features with nutrient-rich forage and cover, while non-mothers selected nutrient-poor, exposed and risky features. These results demonstrate how extrinsic landscape features can shape intrinsic processes like reproduction, generating temporal variation in IC effectiveness and spatial segregation among demographic groups. Integrating empirical insights from applied management with ecological theory can inform coexistence strategies for large mammals in increasingly human-dominated environments.