Theses (Earth and Ocean Sciences)

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Climate variability of seasonal wind extreme events in North America
(2025) Mollasharifi Targhi, Ameneh; Monahan, Adam Hugh
This study investigates the climate variability and seasonal predictability of largescale wind extreme events across North America, with a particular focus on their relationship with Pacific sea surface temperature (SST) patterns. Wind Droughts (WD) and Wind Floods (WF) are defined as prolonged seasonal anomalies in surface wind speed, with substantial implications for climate science and renewable energy systems. Using large ensembles of historical simulations from three climate models (CanESM2, CanRCM4, and CESM2), the frequency, spatial distribution, and predictability of these extreme events are analyzed across six North American regions. Time-series analysis reveals that WF events occur most frequently in northern regions during winter, while WD events are more prevalent in southern regions during summer. Composite wind and SST anomaly maps indicate distinct and largely opposing patterns associated with WF and WD events in most regions in North America. WD events are characterized by a band of warm anomalies in the Gulf of Alaska—occasionally extending into the subtropical and tropical Pacific—coupled with a contrasting band of cold anomalies spanning from Asia to the eastern Pacific, whereas WF events display the opposite pattern. In the Southeast of North America (SENA), however, wind extremes exhibit a localized response with a reversed SST pattern, likely tied to the Pacific–North American (PNA) pattern. Furthermore, our evaluation of the predictive skill of Pacific SST anomalies shows that WF events are more predictable than WD events, with extratropical Pacific SST anomalies enhancing predictability more effectively than equatorial or full-basin SST patterns. Importantly, the relationships between SST patterns and WD/WF events are predominantly statistically significant at the 5% level, further bolstering confidence in SST-based seasonal predictability. These findings provide new insights into the large-scale drivers of wind extremes and their seasonal predictability, offering valuable implications for renewable energy resource management and climate modeling.
Neotectonics of major faults in the Canadian Cordillera
(2025) Finley, Theron; Nissen, Edwin; Cassidy, John Francis
The Canadian Cordillera is an 800 to 1000 km-wide accretionary orogen comprised of numerous terranes and crustal fragments, which are bounded and crosscut by major, mature fault zones. Despite being most active during Mesozoic to early Cenozoic mountain building, the Cordillera continues to be tectonically active in the present, with elevated seismicity and strain rates compared to the stable continental interior. The role of the major faults within the Cordillera in accommodating ongoing deformation has remained unclear, in part due to sparse seismic and geodetic instrumentation, but also due to the challenging surficial environment (i.e., recent glaciation, high precipitation, dense vegetation) that has hindered tectono-geomorphic and paleoseismic studies. In this thesis, I leverage a recent expansion of high-resolution topographic data coverage across the Canadian Cordillera to investigate the geomorphic signature of faulting in the landscape. I make use of new airborne lidar (light detection and ranging) data made available by provincial and territorial governments, and I also collect new lidar using a novel drone system – the first of its kind applied to tectonic geomorphology. In addition, I take advantage of the new ArcticDEM dataset, derived from optical satellite imagery, and covering all regions north of the 60th parallel. These datasets enable the mapping of subtle fault scarps, as well as the glacial landforms that constrain the timing of past ruptures. I focus on three major fault zones: the Tintina fault in northern Yukon, the Eastern Denali fault in southwestern Yukon, and the Southern Rocky Mountain Trench fault in southeastern British Columbia. The Tintina fault is a major, ~1000-km-long fault that has accommodated over 400 km of dextral offset in the Eocene but is generally not considered active today. I show that it has in fact ruptured numerous times throughout the Quaternary, is capable of future large earthquakes (>Mw 7.5), and may be late in a seismic cycle, representing a major seismic hazard to the region. The Southern Rocky Mountain Trench fault is thought to have been a locus of significant extensional deformation in the Eocene. Using new airborne lidar, surficial mapping, and shallow geophysical surveys, I provide evidence of multiple extensional surface ruptures in the Holocene. A potential decrease in slip rate through time is speculated to be related to glacial isostatic adjustment. The Eastern Denali fault, a major terrane-bounding fault, is already known to be a potential seismogenic source, however its kinematics and the level of tectonic activity have remained topics of debate. Using a new, comprehensive lidar dataset covering nearly the entire fault, I demonstrate that its kinematics are dominantly dextral despite being in an overall compressive setting, highlighting the role of inherited fault geometry. The results of this work have significant implications for seismic hazard assessments in Canada. Much of Canada’s National Seismic Hazard Model is based on historical and instrumental records of seismicity to define probabilities of shaking over broad areas. My work will enable the inclusion of additional discrete fault sources in the hazard model. In addition to seismic hazard, these geomorphic studies shed light on the driving mechanisms and characteristics of neotectonic deformation across the Cordillera and provide broader insight into how pre-existing, mature faults behave in regions of moderate to low strain.
A characterization of trace metal distributions in Canada’s Pacific and Arctic marine waters
(2025) Anderlini, Tia; Cullen, Jay T.
Trace metals in the ocean, including iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb) and vanadium (V), may act as micronutrients or toxins to marine phytoplankton and thereby directly impact primary productivity. The efficiency of the biological carbon pump can be modulated by trace metal bioavailability in the upper ocean, controlling the biological transfer of carbon dioxide from the atmosphere to the oceans. Further, the health of marine life at higher trophic levels may be negatively impacted by the ocean’s trace metal content through bioaccumulation, with significant consequences for people dependent on marine foods (e.g. coastal Inuit communities). The main objectives of this work are to address the distributions of trace metals in coastal regions of Canada’s marine waters and to assess the transport of these elements through and out of near-shore, shelf-dominated areas. We consider several trace metal sources and sinks, including biological uptake, remineralization, scavenging by particles, shelf sediment resuspension, fluvial runoff, sea-ice and glacial melt, and anthropogenic contamination. Measurements of trace metal concentrations off the coast of British Columbia indicate some of the greatest surface water concentrations are found in the southern Vancouver Island region due to a combination of upwelling, eddies, and freshwater runoff. In the more northern regions of the BC Coast, atmospheric dust and meltwater runoff become more important for explaining trace metal distributions. The BC coast is the eastern border to the Northeast Subarctic Pacific Ocean – a High-Nutrient, Low-Chlorophyll (HNLC) region in which Fe limits primary productivity. Thus, the transport of Fe and other trace metals from the coast to the ocean interior is an area of key interest. We estimate the offshore flux of trace metals from the BC shelf to the open ocean by considering the transport by the Juan de Fuca Eddy, a separation of the Shelf Break Current, and the bottom-water Ekman transport via the California Undercurrent and Davidson Current. These fluxes are compared to previous estimates of transport by atmospheric dust, tidal currents, and mesoscale eddies, to evaluate the major sources of Fe to the region. In the western Canadian Arctic, the chemical composition of Pacific- and Atlantic-derived waters are modified during transport over the Mackenzie shelf and through the Northwest Passage. Remineralization in sediments on the Chukchi shelf enriches the concentrations of dissolved Cd and Zn – a signature that can be detected in open waters of the Beaufort Sea as well as the Amundsen Gulf. Over the Mackenzie shelf, sediment resuspension acts as a source of Fe and Pb, and the Mackenzie River plume additionally provides high concentrations of most trace metals; however, this does not translate to effective trace metal transport to the Beaufort Sea’s interior. Through the Canadian Arctic Archipelago (CAA), other sources including small rivers, sea ice, and snow are found to supply trace metals to surface waters, further modifying trace metal concentrations as water is transported eastward. Waters entering the eastern Canadian Arctic via Nares Strait and Parry Channel are found to retain the Chukchi shelf signature of Zn, Cd, and Ni, while these enhanced concentrations dissipate over shallow passages prior to entering Baffin Bay. Other trace metal sources in this eastern corridor include glacial meltwater, particularly in Nares Strait and the North Water Polynya immediately south of this passage, while sea ice melt and meteoric water runoff are found to have less significance relative to the western CAA. Estimates of trace metal flux indicate greatest transport of trace metals into Baffin Bay from Nares Strait, followed by the West Greenland Current in eastern Davis Strait, and finally Lancaster Sound. Flux estimates through Davis Strait indicate the Canadian Arctic is a source of Mn, Co, Ni, Cu, Zn, Cd, Pb, Ba and V to the Atlantic, while Fe export via the Baffin Current is equivalent to Fe import via the West Greenland Current.
Multi-scale remote sensing to characterize crustal faulting in the northern Pacific Cordillera
(2025) Salomon, Guy William; Nissen, Edwin
Crustal earthquakes pose significant hazard to people all around the world, and because these events occur infrequently, relative to interplate earthquakes, they remain poorly understood. This dissertation is composed of three projects which share common themes of characterizing the geometries, kinematics, and activity of crustal faults within the northern Pacific Cordillera by making use of remote sensing techniques, albeit at several spatial scales. This region is vast with limited access which makes traditional, boots-on-the-ground fieldwork challenging and expensive. Remote sensing allows us to gather significant insights into the region from afar and focus, or motivate, future research. I begin by using InSAR and seismological analyses to study a recent earthquake within the Koryak Highlands of eastern Siberia. This is one of the most northerly earthquakes to be studied using InSAR, with additional challenges of steep terrain and snow cover; these issues were overcome by the short revisit times offered by the Sentinel-1 satellites. Understanding this event has implications for seismic hazard assessment in other parts of the cordillera, such as Alaska and western Canada which have similar crustal structures. This study highlights that previously unknown, immature faults within known suture zones can produce moderate to large earthquakes. In the second project, I describe a novel uncrewed aerial vehicle (UAV) laser scanning (ULS) platform which can be used to collect inexpensive, high-resolution topography even beneath dense vegetation. I showcase four datasets collected by this platform, across several different landscapes and vegetation types in western Canada, comparing these with conventional airborne laser scanning (ALS) and Structure-from-Motion (SfM) datasets. The ULS offers improved point density and vegetation penetration compared to ALS and SfM, creating high-resolution topographic models and allowing fine-scaled features to be identified. It also offers opportunities for rapidly collecting perishable data such as along surface ruptures of recent earthquakes and potentially could be used to capture afterslip. The last project uses ALS and ULS, as well as near-surface geophysics and field observations, to investigate whether the San Juan fault on southern Vancouver Island has been active during the Quaternary. I find a 6 km long, 30 m high scarp cutting across glacial sediments. The up-thrown southern side being composed of rheologically weaker schists and volcanics, leads me to infer that the fault has been recently active in order to have generated this feature, and that this scarp likely represents many earthquake cycles. I also find an uphill-facing scarp offsetting colluvium, which may represent the most recent rupture (late Quaternary) along the San Juan fault. Several potential targets for future paleoseismic studies are identified. In all, these works demonstrate the importance of a multi-disciplinary approach when studying active tectonics, and highlight the usefulness of remote sensing techniques for initial observations of continental deformation.
Saturation of internal tide generation and wake vortex energy partitioning in shallow fjord-like topography
(2025) Chang, Jia-Xuan; Klymak, Jody Michael
Internal tides and wake vortices are key processes driving energy dissipation and mixing in coastal environments. While internal tide generation over supercritical slopes has been extensively studied in deep ocean settings, much less is known about its behavior in shallow coastal systems, where barotropic tidal forcing is strong, and non-linear effects dominate. This dissertation investigates the tidal energy pathways and dissipation associated with internal tides and wake vortices in such environments, using numerical simulations to explore isolated and complex three-dimensional to- pographies. A novel phenomenon of energy saturation in internal tide generation is identi- fied, where the energy converted from barotropic tides ceases to scale quadratically with tidal velocity under highly non-linear conditions. This study characterizes the qualitative flow features associated with saturation, revealing that the flow resem- bles approach-controlled flow. Saturation is found to occur when the mean speed at the crest equals the mode-1 phase speed (Frc = Uc/c1 = 1). Moreover, the results challenge the conventional understanding that internal tides are not generated when F rc > 1; instead, they are generated but reach a saturation state. In complex topographies featuring headlands, the energy partitioning between internal tides and wake vortices is analyzed. We identify additional energy losses fed to vortices, providing a systematic framework to estimate these losses using the bluff body law. Our results highlight that ridge-constricted flow and the cross-sectional area between the ridge crest and the top of headland yield reliable estimates. While wake vortices consume most of the energy that was fed into locally, their presence does not influence the dissipation or outward propagation of internal tide energy. The dissipation and propagation pathways of both processes are quantified, offering insights into their independent roles in coastal energy budgets. These findings challenge theoretical scaling law and highlight the distinct dynam- ics of tidal energy in shallow coastal systems. By improving our understanding of tidal energy distribution and dissipation, this research contributes to refining param- eterizations in ocean models and advancing knowledge of coastal mixing processes.
δ13C of mid-Pacific carbonate sediments around the time of Ocean Anoxic Event 2
(2025) Morsink, Kalila; Dyer, Blake; Coogan, Laurence
The δ13C of marine carbonates is commonly used as a proxy for the global burial fraction of carbonate vs. organic carbon. At the same time, carbonate δ13C is understood to vary locally from the global ocean average due to coeval spatial variation in seawater geochemistry, especially in shallow marine settings, and/or post-depositional alteration of sediments. In Cretaceous-age shallow marine sections, Ocean Anoxic Event 2 (OAE2) is identified by a positive δ13C excursion near the Cenomanian-Turonian boundary (∼93.9 Ma). However, there are currently no OAE2 δ13C records from the Pacific basin, which at the time was ∼65% of ocean area and included most of the world’s deep ocean. Here I present new (n = 255) and previously published (n = 13) bulk carbonate δ13C and δ18O data from 10 mid-Pacific sites, measured in sediments recovered by the Deep Sea Drilling Program, which I use to test the hypothesis that there was a global change in the δ13CDIC of seawater at the time of OAE2. I use existing biostratigraphic data to target sediments of Cenomanian and Turonian age. Between sites, I compare δ13Ccarbonate and δ18Ocarbonate values associated with the same planktonic foraminifera species. My Pacific δ13Ccarbonate values range from 0.88‰ to 4.20‰ VPDB (excluding 3 samples within a 7-cm interval with -2.7‰ to -2.5‰ VPDB). They are generally lower than shallow marine bulk carbonate δ13C values where the OAE2 positive δ13C excursion has been identified, e.g., the well-known Eastbourne, UK section where Cenomanian and Turonian δ13C values range from 2.6 to 5.4‰ VPDB. To explain δ13Ccarbonate values within the Pacific, I invoke both factors local to the sites, such as proximity to a shallow semi-restricted carbonate platform in the case of the site with the shallowest paleodepth, and changes in global ocean δ13CDIC over time. An OAE2 positive δ13Ccarbonate excursion is not observed at most Pacific sites in this thesis, which has two possible explanations. One possible explanation is that a global ocean OAE2 δ13C excursion did occur, but that some process largely prevented its deposition, preservation, or recovery in the mid-Pacific. Another possible explanation is that the OAE2 δ13C excursion occurred only in the shallow epicontinental basins and continental slope environments where it is observed (including the Atlantic, Western Tethys, Neotethys, and Western Interior Seaway of North America) because organic carbon burial within these relatively restricted water masses changed their δ13CDICs but did not affect δ13CDIC in the mid-Pacific.
Wave run-up on a highly dissipative beach
(2025) Holmes-Smith, Carmen; Gemmrich, Johannes; Klymak, Jody Michael
Long-term observations of wave run-up were collected using video imagery. The study site is a highly dissipative sand beach on the West Coast of Vancouver Island with seasonally energetic wave behaviour. Spectral analysis of the long-term timeseries was done to characterize the run-up spectrum. These run-up spectra consistently show a peak frequency in the infragravity range, with a frequency dependence of f^1.5. This demonstrates a clear spectral shift of the characteristic developed wind-wave spectrum in deep water, which has a dominant period of approximately 10 seconds and a frequency dependence of f^4. The spectral transformation is consistent with findings from previous run-up studies, although the peak period and frequency dependence of the spectra presented here show an extreme example of this expected spectral evolution. Additional instruments utilized in the analysis include an offshore wave buoy, a Spotter buoy deployed immediately outside the surf-zone, and for a shorter three week period, an RBR pressure sensor that was deployed on the same mooring as the Spotter buoy. Correlations were evaluated between run-up behaviour and sea-state variables to understand wave transformation across the surf-zone, as well as to find useful and practical indicators of heightened wave run-up hazard that can be used by risk managers. Significant wave height (Hs), dominant period (T0), and the parameter sqrt(HL) are all positively correlated to run-up extent, with sqrt(HL) being the strongest predictor. A positive correlation was also found between large run-up events and the amount of relative infragravity energy present in the incoming wave field. The process of bore-bore capture (BBC) was shown to be a likely mechanism behind the drastic spectral shift to lower peak frequencies. BBC was also shown to drive extreme run-up events, especially when captures occur within the swash zone. Infragravity waves propagating within the surf-zone facilitate additional capture events and therefore indirectly contribute to these large run-up instances. The magnitude of the bound infragravity wave associated with wave groups can be approximated using the crest-trough correlation, which captures the groupiness of the incoming wave field. The crest-trough correlation parameter was used as a proxy for infragravity energy and found to better predict run-up behaviour when included in an empirical parametrization with sqrt(HL).
Explaining spatial adjustments in the global atmospheric water cycle under multiple climate forcings
(2024) Heyblom, Kyle B.; Monahan, Adam Hugh
This dissertation examines the response of the global atmospheric water cycle to various climate forcings, with a focus on understanding how and why spatial patterns of the water cycle adjust. Through a combination of model experiments and theoretical analysis, this research identifies key mechanisms driving the spatial redistribution of atmospheric water cycle attributes in a changing climate. The findings are presented in three core chapters. The first chapter investigates the impact of variability in aerosol emissions, particularly from biomass burning, on the global hydrologic cycle. Using Earth System Model simulations, the study shows that increased variability in biomass burning emissions amplifies evaporation, atmospheric moisture, and precipitation. Regional factors, such as ocean heat storage and meridional energy transport, modulate the extent of these amplifications. This chapter underscores the significant influence of emission variability on regional hydrological projections and calls for more consistent modeling approaches in future multimodel projection efforts. The second chapter further explores aerosol variability, specifically how interannual fluctuations in biomass burning emissions reduce the time-averaged magnitude of aerosol forcing. This work presents a mechanism that explains the intensification of the hydrologic cycle under increased aerosol variability described in the first chapter. It highlights that many emissions inventories overlook this variability, leading to possible overestimation of the cooling effect of aerosols and misrepresent the associated hydrological changes. The findings emphasize the need for improved representation of aerosol variability in climate models to better capture the spatial adjustments of the water cycle. The third chapter introduces a new framework for understanding regional precipitation changes. This framework identifies three dominant contributors to regional precipitation shifts: global changes in evaporation, adjustments to the moisture cycling rate, and changes in atmospheric circulation. A key conclusion is that the global moisture cycling rate plays a critical role in explaining the spatial patterns of zonal-mean precipitation changes under warming. Furthermore, this control of the global moisture cycling rate on zonal-mean precipitation is robust under all forcing drivers investigated. This framework provides a mechanistic understanding of regional precipitation shifts and enhances our ability to predict these changes under various warming scenarios.
Characterizing soil and structural dynamic behaviour using ambient vibration techniques for earthquake hazard assessment
(2024) Leishman, Tess; Dosso, Stanley Edward; Cassidy, John Francis
This thesis considers two problems in earthquake hazard involving the dynamic (shaking) behaviour of a tall hybrid-wood building, and a preliminary assessment of site (soil) effects in shaking amplification in southwest Yukon. Ambient vibration (AV) methods, which utilize microtremor noise measurements, are employed to identify vibrational modes for both applications by quantifying the behaviour of the building and soils. This research is useful for estimating building response and ground-shaking amplification, and may be applied to mitigate earthquake-induced hazards. One of the key objectives of this research is to study the dynamic characteristics of tall hybrid-wood buildings, a growing class of structures, by identifying their vibrational mode shapes and frequencies. Specifically, the AV methodology is used to estimate the dynamic characteristics of the tallest hybrid-wood building in Canada, the 18-storey Brock Commons building at the University of British Columbia in Vancouver, BC, Canada. Horizontal translational, torsional, and rocking modes are identified, ranging in frequency from 0.94-9.08 Hz. Results reveal the fundamental period (1.06 s) is lower than the period predicted by numerical models (2.0 s), suggesting the building is stiffer than is estimated numerically. The identification of rocking modes similar to the vibrational modes of the soil suggest that soil-structure interaction contributes to these modes. As one of the first in situ modal analyses of a tall hybrid-wood building, these results contribute to improving understanding of dynamic behaviour of tall hybrid-wood buildings generally. These results may also aid in more accurately modelling and predicting the behaviour of tall hybrid-wood buildings under seismic loading. Regarding soil studies, first estimations of local site effects derived from AV methods in the Haines Junction region (Yukon) are also presented in this thesis. Fundamental frequencies (f0) are mapped for 23 sites where local amplification hazards are largely unknown to observe the distribution of soil depth and/or stiffness. AV measurements record microtremor seismic noise that is used to calculate the horizontal-to-vertical spectral ratio (HVSR) and identify fundamental and higher-order frequencies at sites, which represent subsurface impedance contrasts. The results presented in this report indicate that f0 is generally low at many sites, indicating a thick layer of soft sediment overlies bedrock. Results suggest a spatial trend of fundamental frequency varying laterally, with higher f0 values identified north of Haines Junction and lower f0 values in south-central Haines Junction. These observations are attributed to the basin of the Dezadeash river. Higher-order frequency peaks (> 20 Hz) are identified at many sites, which may represent a discontinuous near-surface permafrost layer, the presence of which is confirmed at one site.
Seismic localization and observation of tectonic tremor in the northern Cascadia subduction zone
(2024) Bombardier, Madison; Dosso, Stanley Edward; Cassidy, John Francis
Convergent tectonic boundaries release accumulated stress on a spectrum of slip modes including large megathrust earthquakes with high societal impact, and slow slip events (SSEs), which are not felt by humans. In N. Cascadia, SSEs are regularly accompanied by seismic signals of tectonic tremor, such that the combined phenomena are referred to as episodic tremor and slip (ETS). This dissertation presents three related studies that characterize and localize tremor to better understand its generative processes and geophysical sources. I use a continuous 17-year record of tremor events to define episodes containing different numbers of events. This catalogue of episodes is used to demonstrate that major episodes (considered to represent ETS) and minor episodes exhibit distinct spatial distributions. Specifically, I provide the first observational evidence that the location of the forearc mantle corner controls whether major and minor episodes are segmented or colocated along dip. Minor episodes, which have been previously understudied, are ubiquitous along the margin but exhibit location-specific tendencies for episode sizes and recurrence intervals. To improve tremor localization, I developed the differential traveltime Bayesian inversion (DTBI) method, which prioritizes well-constrained localizations over comprehensive detection. DTBI localizes sources as 3D posterior probability distributions from which rigorous quantitative uncertainties (95% credibility intervals) are estimated. A test performed on small earthquakes supports the effectiveness of the method by relocating events within 4 km horizontally (100% of events) and 10 km vertically (90% of events) of their original locations. In addition, tremor localization exhibits less scatter than previous catalogues, indicating improved accuracy. I use the DTBI method to localize tremor sources during 20 episodes in N. Cascadia. This catalogue contains average horizontal and depth uncertainties of 4 km and 8 km, respectively. These uncertainties, which are computed for every tremor source, represent a significant improvement over previously-existing regional tremor catalogues. The enhanced constraints in the DTBI catalogue support detailed depth information that facilitates exploration of the tremor source region, which is often assumed to be the megathrust fault. I find that tremor is vertically-distributed within the deep accretionary complex up to 10 km shallower than the top of the oceanic crust (usually inferred to represent the megathrust fault). The compositional heterogeneity and structural complexity of the deep accretionary complex, as inferred from paleo-geologic studies, suggest that tremor may be generated by multiple mechanisms driven by high fluid pressures and elevated strain from subduction at deeper depths.
Constraining Northern Cordilleran lithosphere thickness and xenolith residence times using mantle xenolith geochemistry
(2024) Gan, Yuzhe; Canil, Dante
This study re-examines 28 mantle peridotite xenoliths and their Quaternary host lavas from near Llangorse, northwest British Columbia to determine the thickness, and reconstruct the thermal history of the Cordilleran mantle lithosphere, as well as to discover the residence time of mantle xenoliths within the host magma. Based on the equilibrium textures, the Llangorse mantle xenoliths can be separated into three distinct groups: non-sieved, weakly sieved, and strongly sieved. The sieved samples are defined by partially melted pyroxenes, with weakly sieved samples exhibiting melted rims under 50 μm wide and strongly sieved samples exhibiting broader rims. Both weakly and strongly sieved samples exhibit strong Ca zoning in olivine, with Ca concentrations increasing from core to rim, indicative of substantial heating. Closure temperatures for the xenoliths were calculated using T_Al, T_BKN, and T_REE, and varied between 829 to 941 °C, 811 to 1004 °C, and 847 to 1084 °C respectively. Depth estimates for the xenoliths obtained through Ca-in-olivine barometry (P_SC) show that only non-sieved samples and a few sieved samples yield reasonable depths between 34 and 65 (± 6) km. These depths align with both adjacent seismic measurements and the depth of equilibration of the host lava derived from SiO₂ barometry. Based on the most robust xenolith samples, I construct a model geotherm consistent with a surface heat flow of 76 (± 3) mW/m² and heat production of 1.1 (± 0.2) mW/m³. This model geotherm intersects the peridotite solidus with 300 ppm H₂O, corresponding to a lithosphere-asthenosphere boundary at 1280 (± 15) °C and 74 (± 6) km depth. Diffusion chronometry is applied to Ca zoning profiles in olivine. The results show that all the sieved samples have been heated over timescales ranging from several years to hundreds of years depending on the assumed heat source temperatures and uncertainties in the diffusion coefficient for Ca in olivine. This timescale is consistent with typical magma storage time of several years to thousands of years observed from modern volcanoes in Iceland and Hawaii. The sieved xenolith samples either have been entrained by ascending magma at an early stage, with the magma subsequently stored in the upper mantle or crustal level, or underwent heating prior to being sampled by the ascending magma.
Lead and mercury inputs to lakes in Kejimkujik National Park, Nova Scotia: Sources, accumulation and remobilization
(2003) DesJardins, Michelle J'aime; Telmer, Kevin
Sediment cores were collected from two lakes in Kejimkujik National Park, Nova Scotia to investigate natural and anthropogenic inputs of Hg and Pb to the lakes and the reliability of the lake sediments to record depositional history. The total mass of Hg accumulated in the sediments of Big Dam West Lake (BOW) and Big Dam East Lake (BDE) since inception after the Wisconsinan Glaciation 13,000 years ago is estimated to be 14.7 and 3.4 kg, respectively. Hg profiles indicate that the average flux of Hg to the lakes for the last 20 years has been 25.0 and 13.0 μg/m2/yr for BDW and BOE, respectively, which is 3 times higher than pre-industrial background sediments. Hg profiles show that the timing of recent historical anthropogenic activities have been preserved in the Hg profiles of both lakes. However, the magnitudes of the Hg increases are asynchronous when plotted as a function of time, but not when plotted as a function of depth, thereby suggesting that post-depositional diagenetic remobilization may partially be responsible for the upcore emichments. Unlike the Hg flux profiles, which show BOW having a greater flux of Hg throughout the cores, the Pb flux profiles show that the two lakes had similar fluxes of Pb at pre-1850 depths. Above these depths, BOE shows significantly larger Pb flux rates than BOW. In the top 3 cm, BDE's Pb flux of 5.3 mg/m2/yr is 1.9 times greater than BDW's Pb flux of2.8 mg/m2/yr. This difference is believed to be the result of upward remobilization, with more Pb being remobilized in BDE. The total mass of Pb accumulated since inception is estimated to be 5305 and 1502 kg in BDW and BDE, respectively. Only the Pb increases in BDW coincide with historical increases in atmospheric Pb inputs associated with automobile emissions. Neither lake however records any significant decreases in the uppermost sediments as would be expected from the significant reductions in atmospheric Pb concentrations that have occurred since the phasing out of leaded gasoline in the 1970' s. Furthermore, profiles of Pb isotope ratios show fluctuations in the profiles that coincide with known historical events, but the anthropogenic component is always more radiogenic than expected, suggesting there is upward remobilization of Pb from deeper more radiogenic sediments in both lakes. This interpretation is further supported by concentration profiles from six cores which show that the Pb profiles align better when plotted as a function of depth rather than age. These results provide strong evidence that the Pb concentration profiles, at least in BDE, are more a function of depth, and thus diagenetic conditions, than of depositional history. Porewater data provide further evidence to support the interpretation of Pb and Hg remobilization in the sediments of BDW and BDE. Upward decreasing concentrations of both Hg and Pb measured in porewaters suggest that diffusion of Hg and Pb will predominantly occur in an upward direction. Dissolved oxygen, pH and Eh profiles show the disappearance of DO by 4 cm depth accompanied by significant changes in pH and redox between O and 6-7 cm. BDE in particular shows rapid changes in pH and redox between 5 and 7cm depth, indicating that the decay of organic matter is much more rapid in BDE than BDW, which supports the data from the sediment profiles that indicate more Pb is remobilized in BDE than BDW. Precipitation samples were collected over a one-year period to determine sources of anthropogenic heavy metal pollutants to the park using Pb isotope ratios. Pb isotope compositions indicate that anthropogenic pollution from populated and industrial regions of northeastern U.S. and southeastern Canada is being transported to Kejirnkujik National Park. In general there was a dominantly Canadian source during the fall months of 2001 and a dominantly American source during the winter and spring months of 2002. The isotopic composition of the precipitation samples range from 206Pb/2°7Pb ratios of 1.165 to 1.20, indicating U.S. contributions ranging from 30-100% or Canadian contributions ranging from 0-70%. The annual average 206Pbi2° 7Pb ratio is 1.181 and indicates that on an annual basis the U.S. contribution of Pb to Kejirnkujik National Park is 62% (or 38% Canadian). The average annual Pb isotope composition of the precipitation represents the value of the anthropogenic component that should be observed in the surface sediments. However the calculated 206Pbi2°7Pb anthropogenic component in all sediments cores is more radiogenic than would be expected, indicating that there is upward remobilization of Pb from deeper more radiogenic sediments in both lakes. Knowing the true isotopic composition of anthropogenic Pb from precipitation and that of the background sediments, a calculation is presented to quantify the magnitude of remobilized background Pb in the topmost sediment layer. Only BDE provides the necessary conditions to allow such a calculation. The amount of remobilized background Pb in the topmost sediment sample from a BDE core is estimated to be approximately 25.1 μgig, which is 51 % of the total Pb in the labile fraction of that sample.
Deep learning downscaling of climate variables to convection-permitting scales
(2024) Daust, Kiri Shea; Monahan, Adam Hugh
Adapting to the changing climate requires accurate local climate information, a computationally challenging problem. Recent studies have used Generative Adversarial Networks (GANs), a type of deep learning, to learn complex distributions and downscale climate variables efficiently. Capturing variability while downscaling is crucial for estimating uncertainty and characterising extreme events—critical information for climate adaptation. Since downscaling is an undetermined problem, many fine-scale states are physically consistent with the coarse-resolution state. To address this ill-posed problem, downscaling techniques should be stochastic, able to sample realisations from a high-resolution distribution conditioned on low-resolution input. Previous stochastic downscaling attempts have found substantial underdispersion, with models failing to represent the full distribution. I propose approaches to improve the stochastic calibration of GANs in three ways: a) injecting noise inside the network, b) adjusting the training process to explicitly account for the stochasticity, and c) using a probabilistic loss metric. I tested models first on a synthetic dataset with known distributional properties, and then on a realistic downscaling scenario, predicting high-resolution wind components from low-resolution climate covariates. Injecting noise, on its own, substantially improved the quality of conditional and full distributions in tests with synthetic data, but performed less well for wind field downscaling, where models remained underdispersed. For wind downscaling, I found that adjusting the training method and including the probabilistic loss improved calibration. The best model, with all three changes, showed much improved skill at capturing the full variability of the high-resolution distribution and thus at characterising extremes. Investigating the stochastic GAN framework with other variables, I show that it successfully downscales temperature, specific humidity, and precipitation. I also find that the stochastic framework substantially improves the downscaling of extreme precipitation. Next, I find that while multivariate downscaling can improve dependence structures between downscaled variables, it leads to blurry downscaling of individual variables. I demonstrate that including high-resolution topography as an input improves spatial structure for most variables. Finally, I test the generalisability of the GAN framework to a new location with a different climate, and show that while the GAN performs well for temperature and humidity, it fails for precipitation due to mismatches between the low- and high-resolution data. These results represent important techniques and insights towards operational GAN-based downscaling.
Analyzing induced seismicity using the techniques of observational seismology: A case study of a hydraulic fracturing operation in northeast British Columbia
(2024) Goerzen, Chet; Kao, Honn; Dosso, Stanley Edward
This thesis uses techniques of observational seismology to investigate induced seismicity related to a hydraulic fracturing operation. The hydraulic fracturing operation targeted the Montney formation in the Western Canada Sedimentary Basin. This study is unique due to its unprecedented resolution in both seismic data and injection information. An initial earthquake catalog is developed, with 3377 high quality events detected from 2021-01-26 to 2021-06-06. Joint high precision double difference earthquake relocation and tomography are performed. The majority of earthquakes in the catalog were associated with the Tower Lake hydraulic fracturing operation. The study area is located near Taylor, British Columbia, and the hydraulic fracturing operation was targeting the Montney formation for the extraction of oil and gas resources. It is found that the cumulative injected fluid volume is the injection parameter with the most influence on seismicity. Injection pressure and rate have less of an effect. This is consistent with the observations that most earthquakes are likely triggered by pore pressure diffusion, rather than the poroelastic effect. Double couple focal mechanisms are also calculated for select earthquakes. The calculated focal mechanisms are generally consistent with the maximum horizontal shear stress in the area. Some small-scale faults are identified using earthquake locations and focal mechanisms. Foreshock sequences are observed along two of the identified faults, demonstrating that fault characterization may be used to help guide injection operations to avoid induced seismicity.
Deformation of Tian Shan from coseismic to million-year timescales
(2024) Wang, Siyu; Jiao, Ruohong; Nissen, Edwin
Intracontinental deformation is often driven by tectonic forces associated with distant plate collisions. The late Cenozoic deformation of Tian Shan is accommodated by both thrust faults bounded the mountain range and strike-slip motion within the mountain. Earthquake hazards and deformation mechanics in the far-field active regions of the Tian Shan are generally poorly quantified due to slow strain accumulation, poor data coverage, and incomplete historical earthquake records. This dissertation aims to gain a better understanding of the kinematics of deformation in this far-field intracontinental mountain belt. I use multidisciplinary techniques to investigate the late Cenozoic deformation of the Tian Shan across different time scales ranging from coseismic to postseismic and interseismic to million-year scales. I start with an earthquake that occurred in the Kepingtag fold-and-thrust belt in southwestern Tian Shan, a seismically active region and a clear example of basinward migration of deformation. I use Interferometric Synthetic Aperture Radar to measure coseismic deformation, combined with teleseismic waveform modelling and calibrated relocation of the mainshock. The results reveal a fault plane situated on the d\'{e}collement at the base of the folded sedimentary cover and a prevalence of seismicity at basement depths throughout the Kepingtag belt and its foreland, indicating rheological controls on earthquake depths. Then, I apply both coseismic modelling and postseismic time series analysis to study another earthquake that happened along the northern Chinese Tian Shan front, adjacent to the Southern Junggar Fold-and-thrust Belt. The findings indicate that the coseismic rupture on a shallow dipping fault plane triggers postseismic deformation that is farther north beneath the anticline. In the third part of this dissertation, I use low-temperature thermochronology, including apatite fission track and apatite U-Th/He dating systems, to model the thermal history of samples collected from the previously overlooked region in the northern Tian Shan. Inverse modelling of over 1000 published and new thermochronological data from the Tian Shan, Pamir, and northeastern Tibetan Plateau, suggests accelerated exhumation during 15--10~Ma, which represents an acceleration of strike-slip motion. The dissertation concludes by integrating results across various timescales to discuss deformation styles throughout the region's tectonic evolution. This study also demonstrates that integrating techniques across multiple timescales effectively quantifies the evolution of active faulting and deformation in the Tian Shan.
Tetradactyl theropod ichnotaxa and their trackmakers
(2024) Dickson, Logan Teague; Arbour, Victoria; Dyer, Blake
While most theropod dinosaurs would have left behind tridactyl (three-toed) footprints, there are rare occurrences of tetradactyl (four-toed) theropod footprints in the palaeoichnological record. Previously, diagnostic criteria between the tetradactyl theropod ichnogenera Saurexallopus and Ordexallopus were poorly defined. Systematic revision of ichnotaxonomy now separates these two ichnotaxa on the basis of digit I orientation. The trackmaker for Saurexallopus has been debated since the ichnogenus was first described. Arguments were split between Oviraptorosauria and Therizinosauria. Based on morphological observation and multivariate comparison of measurements for skeletal and footprint material, an Oviraptorosaurian affinity is preferable. The discovery of a novel ichnospecies of Saurexallopus, S. neesowatchiensis, from the Aptian-Albian Gething Formation of northeastern British Columbia, Canada has implications for an earlier appearance of gigantic oviraptorosaurs in North America and an earlier appearance of Oviraptorosauria in Canada.
Exploring complex earthquake sequences through innovative automatic detection and location methods
(2024) Tan, Fengzhou; Nissen, Edwin; Kao, Honn
Earthquakes present significant risks to both human lives and infrastructure. Most large earthquakes occur in sequences, with thousands of smaller events after, and sometimes also before, the main event, known as aftershocks and foreshocks, respectively. Precise, comprehensive catalogs for these events are essential for advancing our understanding of the seismogenic processes, regional fault maps, and active tectonics, which form the foundation for effective earthquake study and hazard mitigation efforts. Existing automatic workflows for earthquake monitoring usually lack completeness and accuracy during busy earthquake sequences. Developing automatic methods capable of producing consistently high-quality catalogs in near real-time for major earthquake sequences is crucial. In this dissertation, I develop innovative earthquake sequence observation techniques and apply them to three recent large earthquakes around the world. In the first project, I improve the Seismicity-Scanning based on Navigated Automatic Phase-picking (S-SNAP) workflow to enable it to delineate the spatiotemporal distribution of dense foreshock and aftershock sequences in real time. Applied to the 2019 M 7.1 Ridgecrest, California earthquake sequence, the S-SNAP catalog usually contains 1.4–2.2 times as many events as the TriNet catalogue, a customized real-time earthquake information system for southern California. In addition, S-SNAP is more likely to solve phase association ambiguities correctly and provide a catalogue with consistent quality through time. Our new catalog details the spatiotemporal evolution of the sequence, including early foreshocks fours days before the mainshock, a subsequent acceleration in foreshock activities, a seismicity gap before the main shock around its epicentre, seismicity on discrete structures within a broad fault zone, and triggered earthquakes outside the main fault zone. In the second project, I propose a novel approach that utilizes three‐dimensional image segmentation—a computer vision technique—to detect and locate seismic sources, and develop this into a complete workflow, Source Untangler Guided by Artificial intelligence image Recognition (SUGAR). In synthetic and real data tests, SUGAR can handle complex, energetic earthquake sequences in near real time better than skillful analysts and other artificial intelligence (AI) and non‐AI based algorithms. I apply SUGAR to the 2016 M 7.8 Kaikōura, New Zealand earthquake sequence and obtain five times more events than the analyst‐based GeoNet catalog, providing the most complete catalog of the immediate aftershock sequence to date, independent from all existing catalogs. The improved aftershock distribution shows continuous clusters of seismicity under the highly segmented surface ruptures and reveals a connection between well‐studied onshore faults and a hitherto poorly characterized offshore thrust fault, suggesting the possibility of an unusual simultaneous rupture of the onshore and offshore faults. The diffuse nature of the seismicity indicates widespread secondary faulting extending well beyond the normal kilometric‐width damage zones associated with the major faults. In the third project, I apply SUGAR to the 2023 M 7.8 and M 7.6 Turkey earthquake doublet sequence with a neural network retrained using the regional station coverage. The SUGAR catalog has 2–4 times as many events as the Turkey Disaster and Emergency Management Authority (AFAD) catalog. The result resolves the detailed spatiotemporal distribution of the seismicity, showing the branch initiation of the first mainshock, the separation between the two mainshock ruptures, bifurcated aftershock clusters at the southern end, and the shallow dipping structure at the western end. More complex secondary structures, a single foreshock, and delayed aftershocks are found in and around the rupture zones, shedding lights on the dynamics of the mainshocks. These innovative methods have yielded more comprehensive and accurate catalogs for complex earthquake sequences, providing essential data for studying earthquake statistics and physics. Broader impacts can be achieved through additional case studies, applications to other seismic sources and data types, interdisciplinary research and close collaboration with hazard management departments and other stakeholders.
A chemical characterization of the Endeavour non-buoyant plume, Juan de Fuca Ridge
(2024) Zee, Meghan; Cullen, Jay T.
This study aims to provide a quantitative chemical characterization of the Endeavour non-buoyant plume and examine the processes that impact trace metal transport from vent sites to the ocean interior. The chemistry of the Endeavour non-buoyant plume was analyzed using filtered and unfiltered seawater samples collected at 5 stations, starting on-axis at the Main Endeavour Vent field and extending ~45 km southwest of the axial valley. The spatial distribution of these trace metals is likely controlled by a number of processes, including metal sulfide precipitation, oxidation, sedimentation, and plume mixing. Iron (Fe) and manganese (Mn) are limiting or co-limiting nutrients for primary productivity, nitrogen fixation and other biogeochemically important processes in the ocean. The transport of metals associated with hydrothermal plumes and the processes that impact their fate are poorly understood. High concentrations of dFe (24-68 nmol kg-1) and dMn (46-98 nmol kg-1), relative to ambient seawater concentrations at similar depths in the region, were observed proximal to the vent field, followed by a sharp decrease to 1.2-2.9 nmol kg-1 dFe and 0.76-1.4 nmol kg-1 dMn 45 km southwest of the axial valley. Roughly 66% of the Fe present in the non-buoyant plume proximal to the vent field is in the particulate phase (defined as the difference between total dissolvable and dissolved). The particulate phase decreases to ~45% at the most distal station. Particulate Mn increases with distance from the vent field with 25% proximal to the vent field and 56% 45 km off-axis. This study hypothesizes that the spatial distribution and size partitioning of Fe and Mn can be explained by a combination of sulfide precipitation near-field, oxidation and oxide formation, and plume mixing with surrounding seawater. Chalcophile elements including cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd), are trace metals often associated with hydrothermal systems. Due to precipitation processes, these trace metals are not typically found in non-buoyant plumes far from vent fields. Correlations between these chalcophile elements with particulate Fe at END1 indicate similar removal pathways and highlight the importance near-field processes (precipitation, oxidation, mixing) play in controlling their net-input to the ocean. When compared to the geochemistry of sediments at the Main Endeavour Vent field, non-buoyant plume chemistry shows similar spatial trends. Furthermore, high mass accumulations of Fe, Zn and Cu on-axis along with the presence of chalcopyrite, pyrite, and sphalerite help explain the higher proportion of the particulate phase of these elements proximal to the vent field.
Detecting ringed seal vocalizations using deep learning
(2024) Zammit, Karlee Elizabeth; Dosso, Stanley Edward; Halliday, William
Ringed seals (Pusa hispida), a species of Arctic seal, were assessed as a species of special concern in Canada due to a projected loss of habitat caused by the effects of climate change. In order to create effective conservation measures to protect this species, it is important to understand their spatial and temporal distributions. The analysis of passive acoustic monitoring (PAM) data can provide spatial, temporal, and behavioural information through the acoustic detection of a species’ vocalizations. Automated detection methods are necessary to analyze these large volumes of PAM data within realistic time-scales. Deep learning (DL) based methods have recently outperformed more traditional methods for the automated detection of marine mammal vocalizations. This thesis develops the first practical automated ringed seal vocalization detector using DL methods. Specifically, ResNet, a convolutional neural network architecture which has shown success for other marine mammal species, is used to perform binary classification of spectrograms containing ringed seal vocalizations. The ensemble model achieves an F1 score above 0.90 for manually-verified segmented spectrograms in both development environments and those unseen during development. The detector was also deployed on two continuous datasets containing data from different years and/or locations than those seen during development, and achieves greater than 0.90 recall, but reduced precision at approximately 0.50 for both datasets. These results indicate that the detector misses very few ringed seal vocalizations but has a high false positive rate. Many of the false positive detections had similar frequency-domain signatures to ringed seal vocalizations. The detector will be available as an open-source command-line-interface tool for researchers to apply to their own data.
A 2122-year tree-ring chronology of Douglas-fir and spring precipitation reconstruction at Heal Lake, southern Vancouver Island, British Columbia
(1996) Zhang, Qibin
A 2122-year tree-ring chronology was developed from living and submerged logs of Douglas-fir at Heal Lake, near Victoria, southern Vancouver Island, British Columbia. Correlations between the tree-ring indices and monthly mean temperature and monthly total precipitation indicated that the radial growth of Douglas-fir was strongly correlated with the spring and early summer (April-July) precipitation and the previous years' growth. A transfer function was established using tree-ring indices to predict the weighted 5 years' effective precipitation. The reconstructed precipitation history for the last two millennia exhibited eight distinct climatic intervals involving long periods of wetness and drought and extreme events. The result showed that the Little Ice Age was featured by wetness in the interval AD. 1567-1765 and there were occurrences of wet episodes before and after this interval. There was no evidence of Medieval Warm Period in the area. Comparison with other studies in the nearby regions showed general agreement and demonstrated a regional climatic control. The result can be applied in a broad range from the fundamental understanding of the climate system to the practical management of our natural resources.

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