Now showing items 21-40 of 6942

    • Volcanic gas quantification under suboptimal conditions

      Kushner, D. Skye; Lopez, Taryn; Kern, Christoph; Larsen, Jessica; Simpson, William (2023-12)
      Volcanic gas emissions are challenging to quantify. Achieving high confidence in gas composition, column concentrations, and emission rates acquired using remote sensing techniques is thought to require optimal atmospheric conditions. These conditions are often not met, creating a reluctance to preform measurements under non-ideal atmospheric conditions with inherent uncertainty about how useful those measurements may be. In the case of volcanic eruptions, the hazardous nature of the volcanic plume creates an environment where it is often not safe to collect measurements. This dissertation presents three projects which aim to constrain the quantity of two specific volcanic gases, mercury (Hg) and sulfur dioxide (SO₂), released under non-ideal measurement conditions. Specifically, chapter 2 aims to constrain Hg emission during volcanic eruptions, chapter 3 aims to characterize the uncertainty in SO₂ emission rates acquired under specific non-ideal atmospheric conditions, and chapter 4 aims to improve constraints on plume altitude for scanning remote sensing measurements of SO₂ emission rates acquired from a single instrument. Ash is a potential sink of volcanically-sourced atmospheric mercury, and the concentration of particle-bound Hg may provide constraints on Hg emissions during eruptions. In Chapter 2, the Hg concentrations in 227 bulk ash samples from the Mt. Spurr (1992), Redoubt (2009), and Augustine (2006) volcanic eruptions are examined to investigate large-scale spatial, temporal, and volcanic-source trends. No significant difference in Hg concentrations is found in bulk ash by distance from the eruption source or for discrete eruptive events at each volcano, suggesting that in-plume reactions converting gaseous Hg⁰ to adsorbed Hg²⁺ are happening on timescales shorter or longer than considered in this study (minutes to hours) and any additional in-plume controls may be masked by intra-volcanic sample variability. A significant difference is found in Hg concentration in ash among volcanic sources, which indicates that specific volcanoes may emit comparatively high or low quantities of Hg. These findings allow for the calculation of minimum, first-order estimates of volcanic Hg emissions during eruption in combination with total mass estimates of ashfall deposits. Mt. Spurr is found to be a high Hg emitting volcano such that its 1992 particulate Hg emissions likely contributed substantially to the global eruptive volcanic Hg budget for that year. Based on this study, previous approaches that used long-term Hg/SO₂ mass ratios to estimate eruptive total Hg under-account for Hg emitted in explosive events, and global volcanogenic Total Hg estimates need revisiting. A large source of error in SO₂ emission rates derived from mobile differential optical absorption spectroscopy (DOAS) is the uncertainty in atmospheric light paths between the scattered sunlight and the instrument, particularly under non-ideal atmospheric conditions such as the presence of clouds beneath the volcanic plume. In Chapter 3, numerical simulations using the McArtim model are used to examine the radiative transfer associated with zenith-facing mobile DOAS traverses for scenarios where there is a cloud layer between the instrument and the volcanic plume. In total, 217 permutations of atmospheric optical conditions are considered, allowing for the determination of errors associated with atmospheric scattering. Objective criteria are also developed for selecting SO₂ baselines and plume limits for each simulated traverse. This study then applies models to a real-world dataset from the 2021 Cumbre Vieja eruption to explore the effects of ground-level haze on a measured SO₂ column densities for the volcanic plume. All modeling results find large modifications in the shape of the analyzed plume SO₂ column density versus distance curve, even under scenarios with translucent clouds. Despite modification of the plume shape, the presence of a low cloud or haze layer is typically not a large source of error in determination of the total SO₂ quantity measured over the entirety of the traverse, which suggests that fairly accurate SO₂ emission rate measurements can be obtained even under non-ideal atmospheric measurement conditions. The real-world dataset from Cumbre Vieja is found to be best explained by a layer of ground-level laze containing SO₂ and a volcanic plume located between 2 - 4 km altitude. A large source of uncertainty in SO₂ emission rates derived from scanning DOAS instruments is the cross-sectional area of the detection, which is determined from the vertical and horizontal distance of the plume from the instrument. In Chapter 4, a novel method is employed to estimate plume altitude based on modeled wind speed data and validated against available webcam imagery at Cleveland Volcano in the Aleutian Islands, Alaska. This estimated plume altitude is used to calculate SO2 emission rates from single-station campaign scanning DOAS measurements at Cleveland Volcano, Gareloi Volcano, and Korovin Volcano (Alaska) in 2019, where the instrument was deployed for several days at each site. This method is also applied to a long-term dataset of scanning SO2 measurements acquired from a permanent scanning DOAS instrument installed at Cleveland Volcano September 2022 - June 2023. It is found that the method of estimating plume altitude in the long-term dataset produces a lower emission rate and a smaller sample variance than assuming a fixed summit plume altitude. The remaining variance in the data is then interpreted to represent variability in SO₂ emissions during times of relative quiescence at each studied volcano.
    • Biorecovery of rare earth elements from hard rock, extraction and analysis

      Kebe, Moustapha; Ghosh, Tathagata; Briggs, Brandon R.; Aggarwal, Srijan (2023-12)
      The advancement toward green energy, the development of precise weaponry, and the conquest of space have made the consumption of rare earth elements and critical elements supersede their production. Rare earth elements are vital and critical for modern technology. Rare earth elements consist of Scandium, Yttrium, and the fifteen elements in the Lanthanide group. These elements are mainly categorized into two types based on their atomic number: Light Rare Earth Elements (LREE) and Heavy Rare Earth Elements (HREE). The conventional methods of extracting economic rare earth elements are widely known, and these methods are found in abundance. However, considering the critical nature of rare earth elements, and the challenge to avoid environmental degradation, finding an alternate method of extracting rare earth elements that is both economically and eco-friendly is needed to overcome the disruption in demand and supply of these elements. One of the many potential methods of rare earth elements extraction is bioleaching or bio-recovery using bacteria, fungi, and archaea. This method has drawn the attention of several researchers in the quest for sustainable and feasible extraction techniques of rare earth elements and other critical elements (CEs). Bio-recovery or bioleaching as compared to physicochemical methods is considered one of the most promising techniques for recovering critical elements. A specific type of bacterial strain the Shewanella oneidensis MR-1 was incubated with rock samples from two distinct locations (North Pole Hills and the Prince of Wales Island) to recover rare earth elements. The experiment was performed under standardized conditions to ensure the reliability of the results. Three major parameters such as the process duration, particle size, and incubation period were tested to evaluate their impact on the recovery process. A total recovery of 30.85 ppb and 7.6 ppb at North Pole Hills and Prince of Wales Island, respectively. The process duration parameter was found to be irrelevant throughout the experiment and the effect of particle sizes ranging below 150 Mesh shows a positive response to the bio-recovery processes compared to particle sizes ranging between +-0.5mm. Maximum recovery was recorded with the samples from North Pole Hills compared to the samples from the Prince of Wales Island. The Bioleaching process was compared with the traditional acid leaching process, and a total of 291.73 ppb was recovered from the North Pole Hills and 107.75 ppb at the Prince of Wales Island. This experiment sets a road map to understand the microbial interaction on hard rock with varying sample sizes and process time.
    • The effect of cold exposure and activity on skeletal muscle physiology: a study of human and animal models

      Johannsen, Michelle M.; O'Brien, Kristin; Fedorov, Vadim; Oliver, Scott Ryan; O'Brien, Diane; Barnes, Brian (2023-12)
      Environmental factors and physical activity have the potential to modulate skeletal muscle physiology in beneficial ways. Cold exposure and endurance exercise, specifically, may improve aerobic capacity and atrophy resistance. I utilized three models to examine the effect of cold exposure and activity level on skeletal muscle physiology: quantitation of body composition and energy expenditure estimates in humans participating in a transmountain race, comparative proteomic analysis of skeletal muscle in hibernating and summer active American black bears (Ursus americanus), and an experimental study of the combined effects of cold exposure and endurance training on white adipose tissue, and gastrocnemius and soleus muscles in Sprague-Dawley rats. Body composition analysis of participants of the transmountain race revealed significant fat but not lean body mass loss despite significant caloric deficit. Proteomic analysis of American black bear skeletal muscle revealed an upregulation of glycolytic, inflammatory, immune response, and lipid transport proteins, and a decrease of lipid, and amino acid catabolism proteins during hibernation. Modulation of metabolism and the immune system during hibernation appears to mitigate skeletal muscle atrophy, despite prolonged inactivity and fasting. In Sprague-Dawley rats, cold or exercise alone have similar effects on body composition but exert unique effects on oxidative and glycolytic skeletal muscles that overall supports enhanced aerobic capacity. When combined, cold and exercise appear to improve oxygen diffusion via reduced cross-sectional area of some fiber types in oxidative skeletal muscle but have opposing effects in glycolytic muscles. In summary, skeletal muscle is highly plastic and perturbations such as cold, fasting, and endurance training result in cellular remodeling and changes in protein expression that improves aerobic capacity and conserves skeletal muscle mass across species.
    • Dynamics of the Earth's thermosphere across a range of spatial and temporal scales

      Itani, Rajan; Conde, Mark; Hampton, Donald; Bristow, William; Delamere, Peter (2023-12)
      This dissertation presents an investigation of aspects of the dynamics of Earth's thermosphere that do not harmonize with the current understanding. Three distinct thermospheric phenomena that correspond to different spatial and temporal scales were examined using Fabry-Perot interferometer measurements of wind and temperature to investigate aspects of thermospheric dynamics. Earth's thermosphere has very high kinematic viscosity and is highly convectively stable. Theory and physics-based models suggest that structures in the horizontal wind on small spatial scales (∼500 km or less) are unlikely to occur in the upper thermosphere. By contrast, a large-scale, persistent, strong wind flow that transports air parcels from the dayside of the polar cap to the nightside, known as cross-polar jet, was found to stall abruptly upon exiting the polar cap above Alaska. Stalling was observed most frequently around mid-winter during periods of low solar activity. The stalling of the crosspolar jet is considerably more abrupt than the first principle models would predict. This phenomenon was investigated as an example of dynamics occurring at intermediate spatial and temporal scales. Along with this meso-scale phenomena, oscillatory perturbations in observed winds and temperatures were examined to test whether these could be the signatures of gravity wave activity. These waves represent a local to synoptic scale behavior. Wave periods ranging from ∼30 min to ∼3 hr were observed. Our data show that gravity wave activity was a nearly ubiquitous feature of winds observed at ∼240 km altitude at auroral latitudes. The actual wave field appears to be complicated, presumably resembling ocean surface waves if they could be visualized. Oscillation amplitudes were typically found to increase with increasing geomagnetic activity and the wave response to geomagnetic activity was similar in both hemispheres. Periods and horizontal wavelengths of the observed oscillations fall within the previously reported range for thermospheric gravity waves. In addition, we examined the thermospheric neutral temperature data to see whether there is any temporal trend in measured temperatures on a time scale of decades. Studies suggest that the Earth's troposphere is warming globally because of anthropogenic emission of greenhouse gases. First principle models suggest that, unlike in the troposphere, greenhouse gases are expected to cool the thermosphere. Consistent with model expectations our data also show a thermospheric cooling trend and the rate of cooling is -27.4 ± 6.2 K/decade. The estimated rate of cooling is more than four times the corresponding uncertainty, indicating that the cooling is statistically significant. However, the observed cooling rate is up to an order of magnitude higher than suggested by simulation studies considering only the effect of CO₂. Nevertheless, the observed trend agrees well with observations of ionospheric temperature at these altitudes using incoherent scatter radar. This long-term temperature trend is an indicator of behavior at the largest spatial and temporal scales. Overall, these three studies together suggest significant shortcomings in our current paradigm for understanding the behavior of the thermosphere. Specifically, stalling of the cross-polar jet shows that spatial structures can arise on much more localized scales than currently appreciated. The ubiquitousness of gravity waves suggests that their role in thermospheric dynamics is probably much more significant than currently appreciated. The effect of anthropogenic changes in atmospheric chemistry appear to be much more substantial than expected. The lowest altitudes at which spacecraft can orbit for an operational useful length of time occur in the Earth's thermosphere. Conditions in the thermosphere impact spacecraft orbits. It is thus necessary to account for the thermospheric dynamics in order to predict the orbit with lowest possible uncertainty and for collision avoidance.
    • Model-based estimation of juvenile salmon spatial ecology in the eastern Bering Sea, Alaska

      Hart, Lilian; Cunningham, Curry; Yasumiishi, Ellen; Mueter, Franz (2023-12)
      Quantitative descriptions of juvenile salmon spatial ecology during the marine phase of their lifecycle are needed to help direct conservation efforts and uncover latent relationships between juvenile salmon and their environment. The NOAA Fisheries Essential Fish Habitat (EFH) program contributes to the conservation of species in the marine waters off of the coast of Alaska by identifying areas of particular importance to reproduction and growth. Salmon EFH definitions have not yet been updated using the species distribution modeling approach taken most recently in defining Alaska groundfish and crab EFH. Current EFH definitions for Alaskan salmon are geographically broad, do not quantitatively describe relationships between marine conditions and salmon, and lack estimates of uncertainty. This research estimated static (time-averaged) and dynamic (time-varying) juvenile salmon distributions in the eastern Bering Sea (EBS) by fitting species distribution models (SDMs) to fishery-independent survey data and environmental indices spanning the years 2002-2019. Following model selection, species distribution maps were generated using predictions based upon the best-performing static and dynamic models to inform EFH definitions for the juvenile life stage. In Chapter 1, roughly parallel nested model structures were fit within two SDM frameworks: generalized additive models (GAMs) and Vector Autoregressive Spatio-temporal (VAST) models. Results from Chapter 1 indicate that while there was evidence for spatial variation in juvenile salmon distributions through time, this variation was encompassed by the EFH boundaries predicted by static models. In terms of performance, GAM and VAST frameworks were largely comparable, although VAST models appeared to be more robust to issues associated with spatial imbalance in survey data. In Chapter 2, nested GAM model structures tested the influence of environmental covariates on variability in the abundance and/or distribution of five species of juvenile Pacific salmon in the EBS. Model selection results and mapping indicated that in-situ environmental covariates significantly influenced abundance of juvenile salmon, while annual covariates significantly influenced the distributions of juvenile salmon. Center of gravity estimates found some evidence for species distribution shifts inshore/offshore and to the north/south in response to specific hindcast environmental conditions. This work might be leveraged to update current salmon EFH definitions and inform future model-based conservation efforts.
    • Uncovering patterns and mechanisms of paralytic shellfish toxicity in Alaska's geoduck clam fishery

      Hart, Courtney E.; Eckert, Ginny; Tamone, Sherry; Greengrove, Cheryl; Tobin, Elizabeth (2023-12)
      This dissertation explores the patterns and mechanisms of paralytic shellfish toxicity in commercially harvested geoduck clams caused by the toxin-producing dinoflagellate Alexandrium catenella in Southeast Alaska. Alaska's commercial fishery for geoduck clams (Panopea generosa) is a small but lucrative fishery, with annual ex-vessel values averaging US $3.9 million (2010-2022). In recent years, the presence of paralytic shellfish toxins (PSTs) in clam tissue resulted in declines in fishery openings and harvest. PSTs can bioaccumulate in the tissues of filter feeders when A. catenella blooms in the spring and summer seasons. However, high levels of toxicity in geoduck clams occur sporadically during the fishery in the fall and winter months long after toxic blooms have subsided. Levels of PSTs in geoduck clams vary substantially from week-to-week, and elevated PSTs are increasingly causing economic loss to the fishery through sampling costs from repeated testing and by delaying or closing harvests. In the past decade (2011-2021), about 60% of geoduck clams tested for PST failed regulatory screenings, up from a 36% failure rate in the decade prior (2001-2010). Knowledge about patterns and distributions of this harmful algal species and its toxins will help improve management of geoduck dive fisheries and provide information to reduce impacts of PSTs on this fishery. In Chapter 1, Patterns in geoduck clam paralytic shellfish toxicity from two decades of shellfish testing in southeast Alaska, we show that geoduck clams are increasingly failing biotoxin screening tests in some areas and these patterns are most closely correlated with regional air temperatures. In Chapter 2, Alexandrium catenella benthic cyst distribution, sediment characteristics, and geoduck clam (Panopea generosa) toxicity in Southeast Alaska, we provide the first A. catenella cyst distribution map for this region and found that cyst counts declined over the three-year study, but patterns were not related to geoduck PST levels or sediment characteristics. Lastly in Chapter 3, Geoduck clam (Panopea generosa) toxicity dynamics across harvest areas, time, age, and cyst gut content in Alaska's commercial fishery, we confirmed the ability for geoduck clams to ingest dormant A. catenella cysts but revealed that neither this process, nor the age of a clam, is directly related to patterns of paralytic shellfish toxicity in this clam species. All together, these findings lead to a better understanding of the variability of PSTs in geoduck clams and are informative to future fishery management and the protection of human health.
    • Cross-seasonal effects in a sea ice-associated sea duck: do winter conditions affect breeding spectacled eiders?

      Friendly, Randall J.; Brinkman, Todd; Lindberg, Mark; Mulder, Christa; Rizzolo, Daniel (2023-12)
      Climate change in the Arctic is more rapid than anywhere on the globe and changes in the marine environment can impact the distribution and abundance of Arctic and sub-Arctic species. Understanding how a species responds to climate change can aid conservation planning and recovery. Spectacled eiders (Somateria fischeri), sea ducks listed as "threatened" under the Endangered Species Act, winter at the Bering Sea and nest along the coastal areas of Alaska and Arctic Russia. Severity of winter conditions in the Bering Sea have been associated with both reduced annual survival and reduced breeding abundance and may have sublethal effects during the breeding season. In this study, we used 24 years of nesting data from Kigigak Island, a sub-Arctic site on the Yukon-Kuskokwim Delta, and 10 years from Utqiaġvik, on the Arctic Coastal Plain, to examine the hypothesis that winter conditions in the Bering Sea influence the reproductive performance of eiders in the following breeding season. For both sites, we examined the effects of winter ice conditions and spring temperature and wind on nest initiation date, clutch size, and nest survival. Nest initiation date was not strongly associated with conditions experienced prior to the breeding season. Estimates of nest initiation date following extreme high and extreme low winter ice conditions differed by only 2 days. In contrast, the difference in mean initiation dates between sites was 20 days. We found no evidence that winter and spring conditions preceding the breeding season explained variation in clutch size (mean clutch size = 4.8, 95% CI: 4.7, 4.8), suggesting that breeding propensity may buffer against variation in clutch size. Nest survival varied among years; annual estimates ranged from 0.11 (95% CI: -0.02, 0.24) to 0.95 (95% CI: 0.92, 0.98) at Kigigak Island and 0.40 (95% CI: 0.16, 0.63) to 0.83 (95% CI: 0.66, 0.99) at Utqiaġvik. At both sites, low days of high ice during winter were associated with lower nest survival and moderate to high counts of high ice cover conditions during winter were associated with higher nest survival. After accounting for the effect of days of high ice during winter, nest survival was higher at Utqiaġvik than Kigigak Island, potentially related to later nest initiation in the Arctic. We concluded that for breeding spectacled eiders, low sea ice winters are associated with reduced nest survival through reduced body condition, and we speculate that following winters with high sea ice more individuals may possibly decide not to breed. Delayed nest initiation at Arctic breeding sites may provide additional time for spectacled eiders to recover from low ice winters and contribute to higher nest survival at Utqiaġvik compared to the sub-Arctic breeding site. Associations between changing ice conditions on multiple demographic rates may lead to future population declines for spectacled eiders at rates higher than previously predicted.
    • Icy insights: decrypting the depths with novel stochastic techniques to model and mitigate Arctic under-ice oil spills

      Frazier, Kelsey A.; Peterson, Rorik; Kasper, Jeremy; Walsh, John Jr.; Webster, Melinda (2023-12)
      The retreat and thinning of Arctic sea ice, driven by climate change, have increased the potential for maritime navigation in the region, thereby heightening concerns about the environmental impacts of potential oil spills in the Arctic. This dissertation, with a focus on the Beaufort and Chukchi Seas, seeks to develop a remote predictive method for assessing the subsurface features of Arctic sea ice, thereby facilitating rapid responses to Arctic oil spills without depending on time-consuming in situ measurements. The first paper of this dissertation addresses the need for oil spill modelers to understand oil movement along the subsurface of sea ice. Employing sonar data from the Chukchi Sea, the study investigates whether the subsurface topography of sea ice exhibits fractal scaling behavior. It was found that young sea ice exhibits multifractal scaling geometry, with parameters α, c1, and H determined as 1.2, 0.03, and 0.12, respectively. Fractal scaling behavior was not observed in other types of sea ice, highlighting the need for further research in this area. These findings are instrumental in enhancing predictive models for oil slick migration under sea ice, a crucial aspect of Arctic oil spill preparedness and mitigation. The dissertation's second paper analyzed five years of field data to determine the statistical distributions of subsurface features beneath various ice stages, using indirect assessment techniques. The analysis revealed that, with few exceptions, the subsurface features of sea ice predominantly follow lognormal distribution patterns, each characterized by distinct mean (mu) and standard deviation (sigma) values. This research represents a significant step forward in remote sea-ice characterization and is vital for formulating effective oil spill responses in the Arctic. The final paper utilized Arctic sea ice stage data, interpreted from satellite imagery, and sea ice draft data from moored sensors in the Beaufort and Chukchi Seas. This data was pivotal in accurately modeling the under-ice morphology, essential for establishing boundary conditions for realistic gravity-driven flow simulations. The study found that potential oil sequestration volumes could range from 30,000 to 1 million cubic meters per square kilometer, varying with the ice stage conditions. Additionally, the models suggest that under-ice morphology significantly influences oil slick movement, with only 20-40% of the ice surface encountering oil. This complexity highlights the intricate nature of Arctic oil spill cleanup and the potential for oil encapsulated in sea ice to cross international boundaries, emphasizing the need for comprehensive preparedness and international cooperation in Arctic oil spill response strategies.
    • Alnus viridis ssp. Fruticosa modulates local conditions to influence intra and interspecies growth

      Drew, Jackson W.; Bret-Harte, Marion Syndonia; Ruess, Roger W.; Drown, Devin M.; Buchwal, Agata (2023-12)
      The Arctic is warming rapidly due to anthropogenic greenhouse gas emissions. Concurrent with warming, some Arctic plant communities have transformed from short statured evergreen and graminoid shrub tundra to tall deciduous shrubs in recent decades. As warming continues, plant-plant interactions will likely change and influence future community composition. Alnus viridis ssp. fruticosa (Siberian alder) is rapidly expanding across Arctic regions and is particularly important because Siberian alder is the Arctic's only large N-fixing shrub, may alter N-cycling to further influence both C-cycling and community composition as it spreads. This dissertation addressed two main questions to better understand how Arctic deciduous shrub communities have changed, and may continue to change as Arctic warming proceeds. First, how did the climate sensitivity of Siberian alder's growth change over the past century (1920 - 2017), and how did climate sensitivity change as Siberian alder grew older? Second, how has Siberian alder affected the long-term growth of two nearby dominant deciduous shrub species: Betula nana ssp. exilis (dwarf birch) and Salix pulchra (diamondleaf willow)? I used dendrochronological techniques to assess how sensitive the growth of each of these three species was to climate over the last century. For dwarf birch and diamondleaf willow, I compared growth near and away from Siberian alder. I hypothesized that Siberian alder shrubs would become more sensitive to climate as they grew both older and larger. I expected that older alder would enhance soil N availability over time, due to the accumulated products of N-fixation. I also expected that the growth of larger, older alders would be more sensitive to climate than the growth of younger alder, because of having both a greater photosynthetic capacity (enabling more growth under good conditions), but also higher maintenance respiration (leading to less growth under poor conditions). I found that Siberian alder overall has become more sensitive to July air temperatures in the second half of the past century as climate has warmed. Also, older shrubs were more sensitive to June and July air temperatures than younger shrubs. Thus, these findings support my hypothesis. Siberian alder frequently grows in close association with dwarf birch and diamondleaf willow. However, these two deciduous neighbors differ in several functional traits. Dwarf birch is a low statured, many branched shrub that mainly grows laterally, and thus is often found on the margins of the Siberian alder canopy. In contrast, diamondleaf willow has fewer branches, grows more vertically, and often is found almost entirely within the Siberian alder canopy. Thus, I hypothesized Siberian alder would facilitate the growth of dwarf birch growth, by alleviating both resource and abiotic stressors, but would reduce diamondleaf willow growth, due to increased light competition. Siberian alder promoted dwarf birch growth and reproduction, likely by alleviating N-limitations and reducing frost damage, though growth was delayed by two weeks. In contrast, diamondleaf willows growing near alder had much smaller growth rings than diamondleaf willows growing away from alder, likely due to light competition. This negative effect on willow growth near alder occurred despite these willows likely receiving greater access to soil N and protection from herbivory damage from the neighboring alder. Overall, these results demonstrate that Siberian alder will likely grow better as they get both older and larger, and as the Arctic continues to warm. Siberian alder influence the growth of neighboring deciduous shrubs over the long term, and those effects are species-specific because they depend on the functional traits of their neighbors. Thus, the continued spread of Siberian alder will likely alter vegetation community composition, and thus influence C and N cycling.
    • The role of apex predators, habitat, and seascape complexity on nearshore fish assemblages in Southeast, Alaska

      Domke, Lia K.; Eckert, Ginny L.; Cunningham, Curry J.; Shelton, A. Ole; Pirtle, Jodi (2023-12)
      Nearshore marine ecosystems contain dynamic and complex submerged vegetated habitats that offer shelter and prey for juvenile, migratory, and residential species, including many commercial, subsistence, and recreationally important species. The efficacy of the nursery role, shelter, and source of prey of the nearshore is influenced by various abiotic and biotic forces and in this dissertation, we examine the influence of submerged vegetation type, presence of apex predators, and the seascape context on patterns of nearshore fish assemblages in southern Southeast Alaska. We found species-specific responses by juvenile salmon in the nearshore, with seasonality overwhelmingly driving juvenile salmon abundance in eelgrass meadows and Chum Salmon present in greater abundance in understory kelp beds compared to eelgrass meadows, whereas Pink Salmon exhibited no difference. As a known apex predator, the reintroduction of sea otters likewise altered the nearshore fish assemblage with increased richness in eelgrass meadows and assemblage-wide shifts in understory kelps. Finally, in addition to habitat type and apex predators, spatial patterning and presence of adjacent vegetation can affect the nursery role of nearshore habitats. We observed differences in the fish assemblage in eelgrass meadows sampled in homogeneous seascapes with continuous eelgrass meadows and heterogeneous seascapes that included adjacent habitats, including more abundant commercial and forage species in heterogeneous seascapes. This research reinforces the importance of nearshore ecosystems in supporting robust fisheries and highlights the structuring role that submerged vegetation, apex predators, and complex seascapes have in sustaining diverse fish populations. Considering the greater ecological dynamics in the nearshore is vital for decision making in habitat conservation and management and for evaluating its role for fisheries, particularly in the context of increased threats to nearshore ecosystems.
    • Effects of browser exclusion on the willow leafblotch miner (Micrurapteryx salicifoliella): host plant availability, oviposition, and survival

      Cummings, Martha M. T.; Wagner, Diane; Kielland, Knut; Mulder, Christa (2023-12)
      Herbivores can affect the quality and quantity of their food plants in ways that indirectly influence the food resources and habitat available to other herbivores present. This study examined indirect interactions between a mammalian browser and an insect folivore that feed on shared plant species during different seasons. On a boreal floodplain in interior Alaska, we investigated how a history of winter browsing by moose (Alces alces) affected the behavior and performance of the willow leafblotch miner moth, Micrurapteryx salicifoliella in summer. Excluding moose browsing for 8 years did not change plant density, but strongly increased canopy height, vegetative cover and overstory density. These vegetation changes led to slightly higher relative humidity and lower air and soil temperatures on moose exclosure relative to control plots. Excluding browsers did not alter the foliar quality (leaf area, water content, leaf mass per unit area, nitrogen concentration) of the three focal willow host species examined. Browsing-related effects on willow morphology and canopy structure did not influence patterns of oviposition by M. salicifoliella on host plants. However, larvae feeding within control plots exposed to vertebrate browsing were less likely to survive to pupation than those excluded from browsing, perhaps because larval predation was more frequent on the warmer and more open browsed plots. Both oviposition and subsequent larval survival were strongly affected by host species. Interestingly, the willow host species on which leaf miner larvae survived best did not correspond to that which received the highest egg abundance during oviposition. We conclude that a history of browsing reduced canopy height, cover and overstory density, which in turn affected the performance of the outbreak insect M. salicifoliella by reducing the proportion of larvae to survive to pupation.
    • Avian divergence and speciation across Beringia examined using comparative mitogenomics

      Collier, K. A.; Winker, Kevin; Wolf, Diana; Sikes, Derek (2023-12)
      Accurate knowledge of divergence and speciation processes is critical for understanding key aspects of biodiversity. As a well-known, speciose group of vertebrates, an increased understanding of how birds diverge and speciate allows us to better manage extant avian diversity and understand how it develops over time. Additionally, birds often exhibit complex and variable patterns of divergence, resulting in complexes of taxonomic uncertainty. Filling gaps in our knowledge of divergence across time and space increases our ability to correctly identify and understand not just avian diversity but clade-level patterns in speciation processes. These higher-order findings give us tools to compare and understand biodiversity more broadly across a wide range of taxa. In this thesis, I investigated both temporal and spatial elements of avian divergence, with an emphasis on the high-latitude system of Beringia, which is of particular interest for speciation due to its position at the meeting point of the Eurasian and American continental avifaunas. Chapter 1 describes my investigation of the temporal dynamics of Beringian divergence. The cyclic opening and closing of the Bering Strait due to glacial cycles intermittently isolated and reunited Asia and North America during the Pleistocene (2.6 Mya to 10 Kya). This was hypothesized to produce an uncertain number of associated 'pulses' of avian divergence events spanning that time period. I used a pairwise sampling approach among 39 taxa and a mitogenomic dataset under Bayesian modeling and found no statistical evidence for multiple vicariance events. Instead, divergence times were spread fairly evenly across a large period of time, appearing as a single vicariance event. This is biologically unusual given the system and the cyclic nature of the most likely abiotic driver (glacial cycles) and may be the result of multiple overlaid periods of divergence and gene flow in taxa with older divergence dates. In Chapter 2, I examine the relative contributions of phenotypic and genetic divergence in pairwise comparisons of diverging bird lineages in high- versus low-latitude systems in Beringia and the Philippines. Phenotypic divergence in birds is assumed to be largely due to selection (Price 2008), with genetic divergence assumed to be more driven by time in isolation. I hypothesize that the Beringian system should have less divergence overall than the Philippines, but that a greater proportion of the divergence should be phenotypic, due in part to increased population connectivity in high-latitude systems as a result of larger long- term range fluctuations as a result of Pleistocene glacial cycles. Increased connectivity should be particularly effective in removing neutral, rather than phenotypic, divergence, where selection may be in operation, in part due to a nonlinear, inverse relationship between gene flow and neutral divergence. To test this, I used standardized measures of phenetic and genetic divergence and used linear regressions to quantify the relationship between divergence metrics and the rates of divergence in each system. Beringia showed lower levels of genetic and phenotypic divergence than the Philippines, but the relationship between data types was stronger and the rate of divergence higher than in the Philippine system. I suggest that this is a result of decreased time spent in allopatry in high-latitude systems, but recognize that an increased rate of phenotypic divergence, possibly due to increased selection pressure at high latitudes, also might play a role.
    • From Siberian dawn to midnight in Siberia: the geopolitics of Anglophone travel writing about post-Soviet Siberia

      Christian, Benjamin D.; Heyne, Eric; Farmer, Daryl; Ehrlander, Mary (2023-12)
      The collapse of the Soviet Union in 1991 opened Siberia as a new "travelers' frontier." Travel writers seeking destinations unspoiled by the encroachment of global capitalism and the resultant "placeless" landscapes made Siberia the subject of numerous travel books. This thesis critically examines the geopolitical discourses embedded in those books. Through a close reading and discourse analysis of three representative samples spanning the post-Cold War period, it highlights the key tropes, images and discourses that Anglophone travel writers have deployed in their constructions of Russia as a geopolitical Other. Travel writers writing about Siberia during the post-Cold War period explicitly and implicitly engaged with, reproduced, argued against, adopted, and adapted popular geopolitical treatises such as Francis Fukuyama's "End of History" thesis, Samuel Huntington's "Clash of Civilizations" thesis, and Robert Kaplan's "The Coming Anarchy" thesis, ultimately producing works that frame Russia as an irredeemable and timeless rival to a normalized West. More generally, this thesis argues that scholars of critical and popular geopolitics need to engage more directly and more robustly with literary productions such as travel writing in order to elucidate the geopolitical messaging of such texts.
    • The effects of summer snowfall on Arctic sea ice radiative forcing

      Chapman-Dutton, Hannah; Webster, Melinda; Sturm, Matthew; Ballinger, Thomas; Zweiback, Simon (2023-12)
      The decline in Arctic sea ice has had major impacts on the climate system, particularly relating to the ice-albedo feedback. Since fresh snow on top of bare or melting sea ice increases the surface albedo on local scales, the impact of summer snow events can have a negative radiative forcing effect, which could inhibit sea ice surface melt. In this study, we compared snow depth and meteorological data from buoys and satellite retrievals of surface and atmospheric conditions to identify and characterize summer snow accumulation case studies across the Arctic from 2003 to 2017. Clouds and Earth's Radiant Energy System (CERES) retrievals were used to quantify the changes in surface albedo before and after the snow accumulation events. Information from these case studies was then scaled up to find similar events on a pan-Arctic scale using a Lagrangian sea ice parcel database. In this way, we characterized the frequency, magnitude, and duration of summer snow accumulation events similar to those observed by buoys. Finally, a simple radiative transfer model was used to quantify the impact of summer snowfall events on the surface and top-of-atmosphere radiative forcing over the entire Arctic region. The following work provides new information on observed snow accumulation events over Arctic sea ice in summer by combining multiple sources of in situ, satellite, and modeled data. Such results will be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice.
    • Pollution trapping by strong temperature inversions in Fairbanks, Alaska

      Cesler-Maloney, Meeta V.; Simpson, William R.; Mao, Jingqiu; Guerard, Jennifer; Stuefer, Martin (2023-12)
      In cold climates during winter, surface-based temperature inversions reduce vertical dispersion within the atmospheric boundary layer. Reduced vertical dispersion coupled with stagnant horizontal winds causes pollution emitted near the ground level to accumulate to unhealthy amounts. To study pollution trapping, we measured vertical differences in fine particulate matter and ozone across a shallow 20-meter vertical scale during surface-based inversions in Fairbanks, Alaska and showed that pollution trapping occurs on this extremely shallow scale. In winter 2022, trace gases were measured by long-path differential absorption spectroscopy to probe vertical dispersion on a taller scale, up to ~200 m above the surface. We added horizontal dispersion to a one-dimensional Eulerian chemical transport model and used the model with both vertical and horizontal dispersion, but without chemistry, to simulate the vertically resolved measurements of SO₂. The model achieved excellent results with correlation to the observations having a coefficient of R = 0.88. Steady-state transport residence times calculated from the model were on the order of hours, indicating limited time for chemical processing during winter in Fairbanks. Within the model, only ground-based emissions sources were included and there was no interaction between air above and below the boundary layer height, suggesting that ground-based sources dominate pollution measured at ground level. With the knowledge that ground level sources have a large impact on pollution, we carried out an analysis of trace gases and fine particulate matter measured near ground level that was used to better understand the response to pollution control strategies in Fairbanks. This analysis shows that the total amount of pollution in Fairbanks has been trending down over the past nine years. Following a September 2022 legal change that mandated lower sulfur content in heating oil, the amount of sulfur dioxide gas dropped significantly during winter 2022-2023 as compared to the prior three-year average.
    • Exploring the robustness of a surrogate-based ice flow model calibration

      Blum, Kyle; Aschwanden, Andy; Newman, David; Truffer, Martin; Wackerbauer, Renate (2023-12)
      When simulating ice sheets using numerical models, model parameters have a great impact on the ice flow, velocity, and response to external forces, making them key factors in accurately predicting ice sheet behavior. In order to have confidence in modeled predictions of ice sheets, we must first have confidence in the physical models we use to simulate them. In order to have confidence in these physical models, we must first have confidence in our calibrations of these ice dynamics parameters. Researchers have been training neural networks to emulate expensive ice sheet models. These surrogate ice sheet models are designed to take ice flow parameters as input, and to output ice surface speed fields that closely resemble modeled fields that physically based ice sheet models would calculate. In this way, these surrogate models act as a computationally inexpensive alternative to map model parameter values to the resulting calculated ice speeds. These surrogates have been implemented and leveraged for Bayesian statistically based approaches to ice flow parameter calibrations that would otherwise be intractable using a high fidelity ice sheet model. By examining the methods we use to train these surrogates, and the extent to which the architecture of these surrogates affect their performance, we can have more confidence in our calibrations that make use of them. Here we present an analysis of the methods with which we train surrogate models as a means of calibrating important ice flow parameters. We focus on determining desirable characteristics for data over which the neural networks are trained, as well as the architecture of the surrogates themselves.
    • Movement ecology, survival, and territorial dynamics in Canada lynx (Lynx canadensis) over a cyclic population decline

      Arnold, Derek; Kielland, Knut; Breed, Greg; Crimmins, Shawn; Laufenberg, Jared (2023-12)
      As the quintessential predator-prey cycle, research into Canada lynx (Lynx canadensis) and snowshoe hares (Lepus americanus) have led to many discoveries in population biology; however, much remains unknown about the nuances of their populations. In this dissertation, I examined the ways in which population cycles influence survival, reproduction, territoriality, and connectivity. First, I examined ways in which climate change induced shifts in fire regimes have affected lynx persistence in their current refugia. Lynx mainly sought out areas of higher hare density and lower cover, such as intermediately aged coniferous and deciduous forests. This type of forest was predicted to persist in the near future, so long as fire intervals remained higher than current levels. Secondly, I investigated how landscape connectivity varied as a function of dispersal status and survival. We found that although the landscape was physically well connected based on resident lynx, it was even more so given dispersing lynx tolerance of poor habitat. This was dampened by survival declines in dispersing lynx over the course of a population crash to a near complete loss of connectivity. Thirdly, I assessed the degree to which dispersal, reproduction, and survival patterns were consistent with those displayed by populations exhibiting a traveling wave. My results supported the hypothesized westward moving population wave, but one mediated by differential survival and spatially varying reproduction rather than directionally-biased dispersal. Additionally, these characteristics were consistent with lynx as driving a similar population wave in snowshoe hare. Finally, I applied a novel mathematical approach to parameterizing advection-diffusion equations to examine how territorial formation occurs at population highs. I found evidence for hierarchical formation of territories in available space, with boundaries defined by preferred habitat. This methodology was a considerable improvement over previous descriptive methods typically used to define territories, as evidenced by the model's ability to predict territorial annexation following sudden vacancy following harvest. These results underscore the importance of maintaining population refugia and existing physical connectivity for the duration of a population downturn, likely on wildlife refuges and national parks across the state, even as the impacts of climate change remain small in the near future.
    • Impact analysis of the marine sport fisheries of middle and lower Cook Inlet

      Hamel, Charles David; Hermann, Mark (2001-05)
      Impact analysis models such as Input-Output (I-O) can provide a view of the regional economic significance of a resource-based industry. Analysts often utilize impact analyses to predict the distributive outcomes of demand shocks to local industries; however, even if such forecasts are modeled appropriately within the impact assessment framework, the results are not particularly relevant if the motives and magnitudes of demand change are arbitrarily posed. In order for an impact analysis to be meaningful, it should not stand alone, but instead be part and parcel of a more encompassing modeling approach comprising a demand function. This paper describes a linkage between a regionally ground-truthed 1-0 model and a predictive model of participation rates for the Cook Inlet, Alaska, sport fisheries. The demand effects of environmental or regulatory induced change to the sport fishery are simulated and the resulting economic impacts are reported.
    • Effects of commercial otter trawling on essential fish habitat of the southeastern Bering Sea shelf

      Brown, Eloise (2003-05)
      Sediment properties and benthic community composition in areas subject to commercial bottom trawling were compared to control areas in a shallow sandy habitat of the southeastern Bering Sea. The top 3 cm sediments in the fished area were slightly better sorted, less variable, and contained fewer finer grains than those of the closed area. Infaunal species assemblages were distinct. The fished area was characterized by reduced infauna richness and biomass, but abundance and diversity were similar to the closed area. No shift in means of any sediment parameter were detected after experimental trawling, but significant increases in variability were observed for several grain size and organic matter parameters. Reduced richness, elimination of rare taxa, and patchy changes in infauna assemblage biomass were found, but there were no differences in abundance, diversity or total biomass relative to controls. A turbulent wake generated by the trawl was on the same order of magnitude as a winter storm wave, but of different seasonal timing and duration. Turbulence combined with friction from contact with fishing gear has the potential to erode sediments from deeper within the seabed than naturally occurring bottom currents. Trawling apparently removed finer grains from the upper sediment layers and altered infauna communities.
    • The relationship between fracturing, asymmetric folding, and normal faulting in Lisburne Group carbonates: West Porcupine Lake Valley, Northeastern Brooks Range, Alaska

      Shackleton, John Ryan (2003-05)
      The distribution of fold related fractures and other mesoscopic structures in asymmetrically folded Mississippian to Pennsylvanian Lisbume Group carbonates gives clues concerning the mechanism of folding. Since fracture sets pre-date and post-date folding, it is important, but sometimes difficult, to determine which fracture sets are related to folding. Higher density of fold related fractures and dissolution cleavage in the hinges than limbs of two folds in the study area is evidence for fixed hinge detachment folding. However, geometric modeling of box shaped folds in the study area suggests that some folds may have formed by either detachment folding or trishear fault propagation folding. Formulaic modeling of fracture density in a stratigraphic section using stratigraphic attributes such as lithology, bed thickness, and chert content predicts general trends in fracture density, but other factors such as slip along bed contacts may obscure the relationship between fracture density, lithology and bed thickness.