• Salmonid Phenology, Microevolution, And Genetic Diversity In A Warming Alaskan Stream

      Kovach, Ryan P.; Tallmon, David; Lindberg, Mark; Milo, Adkison,; Gharrett, Anthony (2012)
      Climate change is a formidable challenge for fish and wildlife conservation because it will directly influence the ecology and evolution of wild populations. Though climate-induced temporal trends in phenological events are common in many populations, there remains considerable uncertainty in the patterns, mechanisms, and consequences of phenological shifts. To address this, and clarify how climate change has impacted salmonid migration timing and microevolution in a warming (0.34�C per decade) Alaskan stream, long-term demographic and genetic data were used to answer these questions: how has migration timing changed in multiple salmonid species; what sources of variation influence migration timing; are changes in migration timing a result of microevolution; and does migration timing and change in migration timing influence intra-population genetic variation? For most salmonid species, life stages, and life histories, freshwater temperature influenced migration timing, migration events occurred earlier in time (mean = 1.7 days earlier per decade), and there was decreasing phenotypic variation in migration timing (mean 10% decrease). Nonetheless, there were disparate shifts in migration timing for alternative life history strategies indicative of biocomplexity. Population abundances have been stable during these phenotypic changes (lambda ≈ 1.0), but adult salmon availability as a nutrient resource in freshwater has decreased by up to 30 days since 1971. Experimental genetic data spanning 16 generations in the odd-year pink salmon population demonstrate that earlier migration timing is partly due to genetic changes resulting from selection against late-migrating fish and a three-fold decrease in this phenotype. However, circadian rhythm genes hypothesized to influence migration timing in Pacific salmon showed no evidence of inter-generational selective change. Migration timing itself influences the distribution of genetic variation within pink salmon, as there were genetic differences between early- and late-migrating fish. Despite shifts in migration timing, genetic structure and the genetic effective population size were both stable across years, indicating that in the absence of demographic change patterns of genetic diversity are resilient to climate change. These findings indicate that climate change has significantly influenced the ecology and evolution of salmon populations, which will have important consequences for the numerous species, including humans, who depend on this resource.
    • Satellite remote sensing of active wildfires in Alaska's boreal forest

      Waigl, Christine F.; Stuefer, Martin; Prakash, Anupma; Verbyla, David; Ichoku, Charles (2017-12)
      This research addresses improvements to the detection and characterization of active wildfires in Alaska with satellite-based sensors. The VIIRS I-band Fire Detection Algorithm for High Latitudes (VIFDAHL) was developed and evaluated against existing active fire products from the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS). This new algorithm is based on VIIRS 375 m spatial resolution imagery and was tuned using fires in Alaska's boreal forest. It provides improved fire detection of low-intensity fires, especially during daytime and at sensor zenith angles smaller than approximately 50° off nadir. Low-intensity active fires, which represent residual combustion present after the passage of a high-intensity fire front, are not very well detected by existing active fire products. A second topic was fire remote sensing with ~30 m resolution imaging spectrometer (or hyperspectral instrument), the Hyperion sensor on NASA's EO-1 spacecraft, which was in use from 2000 to 2016. Hyperion had a much higher spectral resolution than VIIRS or MODIS, but no repeat imagery of the same active fire was available in Alaska. The investigation relied on absorption and emission features in the radiance spectra acquired at every pixel location. Three fire detection methods were evaluated using archived Hyperion data from three fires in interior Alaska from 2004 and 2009: A version of the Hyperspectral Fire Detection Algorithm (HFDI) produced excellent active fire maps; an approach that relies on a shortwave infrared carbon dioxide absorption feature and associated Continuum Interpolated Band Ratio (CO₂ CIBR) proved to be useful, but was affected by sensor noise and clouds; finally, a potassium emission feature from biomass burning was not detectable in the Hyperion data. Fire temperatures were determined using the Hyperion shortwave infrared spectra between 1400 nm and 2400 nm. The temperatures of active fire, the corresponding partial pixel areas, and the pixel areas occupied by unburned and already-burned vegetation, respectively, were modeled within each fire pixel. A model with two reflected background components and two temperature endmembers, applied to the same three study scenes, yielded an excellent fit to Hyperion spectral radiance data. Fire temperatures ranged from approximately 500-600 K to approximately 800-900 K. The retrieved lower fire temperatures are within the range of smoldering combustion; high-temperature values are limited by Hyperion's saturation behavior. High-temperature fire occupying 0.2% of a pixel (2 m²) was detectable. Sub-pixel fire area and temperature were also retrieved using VIIRS 750 m (M-band) data, with comparable results. Uncertainties were evaluated using a Monte Carlo simulation. This work offers insight into the sensitivity of fire detection products to time of day (largely due to overpass timing), spatial distribution over the study area (largely due to orbital properties) and sensor zenith angle. The results are relevant for sensor and algorithm design regarding the use of new multi- and hyperspectral sensors for fire science in the northern high latitudes. Data products resulting from this research were designed to be suitable for supporting fire management with an emphasis on real-time applications and also address less time-sensitive questions such as retrievals of fire temperature and time series of fire evolution.
    • Satellite thermal remote sensing of the volcanoes of Alaska and Kamchatka during 1994-1996, and the 1994 eruption of Kliuchevskoi volcano

      Wyatt, W. Christopher (2001-05)
      The Advanced Very High Resolution Radiometers on the NOAA polar orbiting satellites were used to routinely observe the volcanoes of Alaska and Kamchatka from May 1994 to July 1996, as part of the monitoring effort of the Alaska Volcano Observatory. The largest eruption observed during this period occurred at Kliuchevskoi Volcano between September 8 and October 2, 1994. Radiative temperature measurements made during this eruption were used to develop quantitative methods for analyzing volcanic thermal anomalies. Several parameters, including maximum temperature, anomalous pixels, and total volcanic signal (TVS), were compared to viewing angle and date. A new quantity, TVS7, may most effectively monitor the temporal evolution of the eruption using thermal data. By combining several observations of the thermal state of the volcano, the general nature of the volcanic activity can be described. These observations may indicate an elevation in temperature twelve to 24 hours before an ash-producing event.
    • Satellite to model comparisons of volcanic ash emissions in the North Pacific

      Steensen, Torge S.; Webley, Peter; Beget, James; Dehn, Jonathan; Stuefer, Martin (2013-12)
      To detect, analyze and predict the movement of volcanic ash in real time, dispersion models and satellite remote sensing data are important. A combination of both approaches is discussed here to enhance the techniques currently used to quantify volcanic ash emissions, based on case studies of the eruptions of the Kasatochi (Alaska, USA, 2008), Mount Redoubt (Alaska, USA, 2009) and Sarychev Peak (Russia, 2009) volcanoes. Results suggest a quantitative approach determining masses from satellite images can be problematic due to uncertainties in knowledge of input values, most importantly the ground surface temperature required in the mass retrieval. Furthermore, a volcanic ash transport and dispersion model simulation requires its own set of accurate input parameters to forecast an ash cloud's future location. Such input parameters are often difficult to assess, especially in real time volcano monitoring, and default values are often used for simplification. The objective of this dissertation is to find a quantitative comparison technique to apply to satellite and volcanic ash transport and dispersion models that reduces the inherent uncertainty in the results. The binary 'Ash -- No Ash' approach focusing on spatial extent rather than absolute masses is suggested, where the ash extent in satellite data is quantitatively compared to that in the dispersion model's domain. In this technique, neither satellite data nor dispersion model results are regarded as the truth. The Critical Success Index (CSI) as well as Model and Satellite Excess values (ME and SE, respectively) are introduced as comparison tools. This approach reduces uncertainties in the analysis of airborne volcanic ash and, due to the reduced list of input parameters and assumptions in satellite and model data, the results will be improved. This decreased complexity of the analysis, combined with a reduced error as the defined edge of ash cloud is compared in each method rather than defined threshold or mass loading, will have important implications for real time monitoring of volcanic ash emissions. It allows for simpler, more easily implemented operational monitoring of volcanic ash movements.
    • Science, perception and scale: an interdisciplinary analysis of environmental change and community adaptive capaciy

      Grunblatt, Jesse E.; Wipfli, Mark; Adams, Barbara; Carothers, Courtney; Monahan, John (2020-05)
      The discrepancy between science-based assessments of climate change and public acknowledgement of climate change has been extensively documented at a national level. The relationship of science-based assessments and public awareness of environmental change at the local community level is less studied. An understanding of how science-based information informs local perception is important to ensure that science communication effectively supports community decision making. This dissertation explores the gap between science-based assessments and local perception of environmental change within a framework of adaptive capacity. The research is divided into three interrelated studies that provide: 1) an assessment of community perception of local environmental change, 2) a local study that illustrates science-based assessment and reporting, and 3) an evaluation of the role news media plays in communicating science to the public. The first study implemented a survey of residents on Alaska's Kenai Peninsula to evaluate individual perception of environmental change as well as attitudes regarding climate change and natural resource management. Differences in perception of local environmental change were identified among respondents as well as shared perceptions. The use of property regulation to protect the Kenai River was identified as a divisive issue; however, there was a shared concern regarding the condition of local salmon populations. A second science-based ecological study was developed that examined those issues and linked conservation of riparian vegetation to juvenile salmon rearing habitat. This study examined the diet of stream-rearing juvenile Coho Salmon (Oncorhynchus kisutch) and determined that the proportion of invertebrates which enter the stream from riparian habitats varied based on vegetation type for three streams in the Kenai watershed. The third study investigated how news media play a role in the interpretation of technical, science-based reporting for the public. It demonstrated that local news media provide a unique opportunity to promote communication of science-based information to their audiences by providing content that is familiar and relevant, offering a variety of topical framings, developing authoritative or trusted voices, and providing frequent exposure to content.
    • Sea-ice habitat preference of the Pacific walrus (Odobenus rosmarus divergens) in the Bering Sea: a multiscaled approach

      Sacco, Alexander Edward; Mahoney, Andrew R.; Ray, G. Carleton; Johnson, Mark A.; Eicken, Hajo (2015-12)
      The goal of this thesis is to define specific parameters of mesoscale sea-ice seascapes for which walruses show preference during important periods of their natural history. This research thesis incorporates sea-ice geophysics, marine-mammal ecology, remote sensing, computer vision techniques, and traditional ecological knowledge of indigenous subsistence hunters in order to quantitatively study walrus preference of sea ice during the spring migration in the Bering Sea. Using an approach that applies seascape ecology, or landscape ecology to the marine environment, our goal is to define specific parameters of ice-patch descriptors and mesoscale seascapes in order to evaluate and describe potential walrus preference for such ice and the ecological services it provides during an important period of their life-cycle. The importance of specific sea-ice properties to walrus occupation motivates an investigation into how walruses use sea ice at multiple spatial scales when previous research suggests that walruses do not show preference for particular floes. Analysis of aerial imagery, using image processing techniques and digital geomorphometric measurements (floe size, shape, and arrangement), demonstrated that while a particular floe may not be preferred, at larger scales a collection of floes, specifically an ice-patch (< 4 km²), was preferred. This shows that walruses occupy ice patches with distinct ice features such as floe convexity, spatial density, and young ice and open water concentration. Ice patches that are occupied by adult and juvenile walruses show a small number of characteristics that vary from those ice patches that were visually unoccupied. Using synthetic aperture radar imagery, we analyzed co-located walrus observations and statistical texture analysis of radar imagery to quantify seascape preferences of walruses during the spring migration. At a coarse resolution of 100-9,000 km², seascape analysis shows that, for the years 2006-2008, walruses were preferentially occupying fragmented pack ice seascapes range 50-89% of the time, when, all throughout the Bering Sea, only range 41-46% of seascapes consisted of fragmented pack ice. Traditional knowledge of a walrus' use of sea ice is investigated through semi-directed interviews conducted with subsistence hunters and elders from Savoonga and Gambell, two Alaskan Native communities on St. Lawrence Island, Alaska. Informants were provided with a large nautical map of the land and ocean surrounding St. Lawrence Island and 45 printed largeformat aerial photographs of walruses on sea ice to stimulate discussion as questions were asked to direct the topics of conversation. Informants discussed change in sea ice conditions over time, walrus behaviors during the fall and spring subsistence hunts, and sea-ice characteristics that walruses typically occupy. These observations are compared with ice-patch preferences analyzed from aerial imagery. Floe size was found to agree with remotely-sensed ice-patch analysis results, while floe shape was not distinguishable to informants during the hunt. Ice-patch arrangement descriptors concentration and density generally agreed with ice-patch analysis results. Results include possible preference of ice-patch descriptors at the ice-patch scale and fragmented pack ice preference at the seascape scale. Traditional knowledge suggests large ice ridges are preferential sea-ice features at the ice-patch scale, which are rapidly becoming less common during the fall and spring migration of sea ice through the Bering Sea. Future work includes increased sophistication of the synthetic aperture radar classification algorithm, experimentation with various spatial scales to determine the optimal scale for walrus' life-cycle events, and incorporation of further traditional knowledge to investigate and interface crosscultural sea-ice observations, knowledge and science to determine sea ice importance to marine mammals in a changing Arctic.
    • Seasonal changes in the rumen microbial ecology of muskoxen

      Crater, Annie R. (2006-08)
      Ruminal fermentation must respond to seasonal changes in the behavior and digestive function of muskoxen (Ovibos moschatus) as intakes of food and water rise in autumn (August - October) and decline from winter to spring (November - May). Rumen temperatures were not static but instead were punctuated by decreases of as much as 13°C below the average of 39°C. Declines in rumen temperature were associated with water ingestion while gains in rumen temperature were associated with feeding. Food intake and water turnover rates were positively correlated. Direct microscopic counts of bacteria in rumen fluid decreased from 1.8 to 0.9 X 10¹⁰·mL⁻¹ as water turnover declined from 11.1 to 7.7 kg⁻¹·d⁻¹ between October and March. The energetic cost of warming ingesta was estimated as 5 to 14% of the predicted intake of digestible energy. Concerted ingestion of food and water may allow muskoxen to substitute heat increment of feeding for the cost of warming ingesta. Gains in food intake between May and August decreased rumen osmolality (271.9 ± 16.4 vs. 245.9 ± 11.4 mOsmol.kg⁻¹) and pH (6.81 ± 0.31 vs. 6.39 ± 0.15), indicating a shift in the allostatic set point for the rumen. Rumen fluid pH was more variable in May than in August both before and after a single meal of fermentable substrate even though concentrations of fermentation acids were lower in May than in August. Allostatic set points probably alter the homeostatic range of conditions and the microbial diversity of fermentation in muskoxen. We devised an improved method to isolate rumen bacteria and to extract their DNA for measures of rumen microbial diversity.
    • Seasonal fluctuations in the advance of a tidewater glacier and potential causes: Hubbard Glacier, Alaska, USA

      Ritchie, John Brent (2007-08)
      Satellite imagery has been used to acquire seasonal terminus positions of tidewater Hubbard Glacier, Alaska, from 1992 to 2006. During this 15 year time period the width-averaged advance of the entire terminus has been ~620 m at a mean rate of 35 m a⁻¹. Seasonal fluctuation of the terminus ranges 150 - 200 m and varies spatially. The section of the terminus near Gilbert Point exhibited little to no mean advance during this time period but displayed seasonal fluctuations of 300 - 500 m. Seasonal variability in surface ice speeds and surface seawater temperatures were also observed; both are potential forcing mechanisms for terminus fluctuations. Seasonal changes in seawater temperature of 10 to 12 °C, as well as seasonal changes in subglacial freshwater discharge are inferred to influence calving and submarine melting at the terminus, driving seasonal variations. Displacements of the medial moraine separating Hubbard Glacier and Valerie Glacier at the terminus suggest surge-like pulses of the latter with a periodicity of several years. The timing of these pulses suggests they may influence the Hubbard terminus near Gilbert Point and have implications for future closures of Russell Fjord.
    • Seasonal movements of broad whitefish (Coregonus nasus) in the freshwater systems of the Prudhoe Bay oil field

      Morris, William A. (2000-05)
      Adult broad whitefish were tagged with radio transmitters in the Little Putuligayuk and Putuligayuk rivers along the Beaufort Sea coast of the Prudhoe Bay area, Alaska. Thirty-two fish were tagged in Lake Judith, a shallow tundra lake in the Little Putuligayuk River system. An additional 5 fish were tagged in the Putuligayuk River near a suspected spawning and overwintering site. Many fish left the tundra system to overwinter in the west channel of the Sagavanirktok River, however, unexpected movements also occurred. Six (20%) of the fish found in overwintering areas moved to the east channel of the Sagavanirktok River, an area long disregarded as having much potential for overwintering fish. Additionally, 2 fish traveled west over 100 km along the coast to the Colville River. Broad whitefish in this study wintered in marginal habitat and exhibited the ability to travel between distant coastal river systems along the arctic coast of Alaska.
    • Seasonal variation in the health of high-latitude wintering mallards (Anas platyrhynchos)

      Spivey, Timothy J.; Lindberg, Mark S.; O'Brien, Diane M.; Ramey, Andrew M. (2017-05)
      Mallards (Anas platyrhynchos), the most abundant species of dabbling duck in North America, are increasingly wintering in urban centers at latitudes north of their traditional wintering grounds. We captured mallards throughout the non-breeding period in Fairbanks, Alaska in 2012/13 and 2013/14, as well as in Anchorage, Alaska, in 2014/15, to assess seasonal patterns in forage selection and body condition, as well as the influenza A virus (IAV) dynamics within these urban wintering mallard populations. Using stable isotope data (δ13C and δ15N values) from serum and whole blood, we identified seasonal shifts in diet from invertebrates and aquatic vegetation in autumn to anthropogenic food subsidies (i.e. corn and bread) during winter by mallards in both populations. Additionally, mallards wintering in Fairbanks maintained higher body mass levels throughout the winter period than mallards wintering in Anchorage, which declined in mass from autumn to late winter. To study the associated health conditions mallards wintering at these high-latitude locations experience, we examined infection dynamics of influenza A viruses (IAVs), as mallards are considered a natural reservoir host of IAV viruses. We screened mallards for both active infections and prior exposure to IAVs. Molecular screening indicated both IAV prevalence and seroprevalence varied by each season at each site/year. Age differences were pronounced for both infection and immune responses, with juvenile mallards having higher IAV prevalence and adults having higher IAV seroprevalence. Evidence for active infections and antibodies to IAVs were detected throughout each sampling year at both locations. Variability in mallard immune responses, suggests individual heterogeneity in the timing of infections and duration of immune responses to IAVs across the non-breeding period. Thus, the combination of these findings provide valuable information about when mallards may be relying most on anthropogenic food subsidies and the potential for these populations to serve as biotic reservoirs for IAVs throughout the non-breeding period. Wildlife management agencies may consider these data when developing management objectives or regulations concerning these urban wintering mallard populations.
    • Secondary reproductive strategies in Pacific black brant (Branta bernicla nigricans)

      Svete, Pamela A. (1999-12)
      Waterfowl are known to use secondary reproductive strategies, both extra-pair copulations and intraspecific brood parasitism, to increase fitness. We used five polymorphic microsatellite loci to determine extra-pair paternity and nest parasitism in 30 nests of Pacific Black Brant geese (Branta bernicla nigricans) containing 108 offspring. Fourteen of the 30 nests contained offspring that were not genetically related to one or both of the attending adults: 6.5% (7/108) of the offspring resulted from extra-pair copulations (EPC); 13.9% (15/108) of the offspring resulted from intraspecific brood parasitism (IBP). All offspring resulting from EPCs were produced during the peak period of nest initiation. Adult females hosting parasitic eggs were significantly older than non-hosts. After accounting for eggs resulting from IBPs in the calculated clutch size, clutches containing IBPs were significantly smaller than unparasitized clutches. Our data indicate that secondary strategies represent an important component of reproductive effort in Black Brant.
    • Sedimentology and stratigraphy of the Nanushuk formation and related foreland basin deposits, central Brooks Range foothills, Alaska

      Shimer, Grant; McCarthy, Paul; Hanks, Catherine; Whalen, Michael; Layer, Paul; Wartes, Marwan (2013-08)
      I interpret sedimentary facies and depositional environments from the Albian-Cenomanian Nanushuk Formation of Alaska's North Slope from sedimentary structures observed in core samples and in outcrop in the National Petroleum Reserve - Alaska (NPRA) and surrounding areas, and support these interpretations with supplemental analyses of geophysical well logs and ������Ar/�_��_Ar dating of volcanogenic deposits. The results have implications for the reservoir characterization of a shallow, frozen oil field at Umiat, Alaska, and for interpretations of the Colville foreland basin. In the central Brooks Range foothills the Nanushuk Formation comprises shallow marine and non-marine fades associations that can be grouped into marine-distributive and river-distributive systems. In wells at Umiat, Alaska, shoreface and wave-influenced deltaic sandstones (marine-distributive systems) occur at the base of the Nanushuk Formation, followed by a marine transgression and subsequent progradation of a delta complex (river-distributive system). The shift from marine-distributive to river-distributive systems is related to shelf building processes during the Albian-Cenomanian. Marine-distributive systems occurred at or near the shelf edge in a high-energy coastal environment, whereas river-distributive systems rapidly prograded over the shallow Nanushuk shelf following transgression. Marine-distributive conditions resumed when rapidly progradational river-distributive systems reached the shelf edge. This pattern occurs in the Umiat, Wolf Creek, and Grandstand No. 1 subsurface wells. The reservoir quality of the Nanushuk Formation varies strongly with facies. Well-sorted sandstones at the top of upward-coarsening successions in both marine- and river-distributive units have the highest permeabilities within the Nanushuk Formation. Marine-distributive units have low permeability anisotropy in contrast to river-distributive units due to better sorting in wave-influenced environments and the higher frequency of impermeable lamination surfaces in deltaic sandstones. Despite coarser grain size and similar depositional environments as lower Nanushuk Formation sandstones, transgressive units at the top of the Nanushuk Formation have low permeability, probably due to the presence of calcite cement. These results suggest hat the highest quality Nanushuk Formation reservoirs most likely occur in time transgressive, regionally extensive marine-distributive sandstones of the lower Nanushuk Formation.
    • Sedimentology of thermokarst lakes forming within yedoma on the Northern Seward Peninsula

      Farquharson, Louise M. (2012-05)
      Thermokarst lakes forming in yedoma (organic-rich permafrost containing massive syngenetic Pleistocene ice wedges) play an important role in periglacial landscape evolution. These lakes alter landscape elevation and topography, as well as redistribute upland sediment into lower basins. However, sediment deposition within yedoma thermokarst lakes is not well understood. Sedimentological, biogeochemical and macrofossil analyses enabled identification of five prominent fades in yedoma thermokarst lakes in my study region on the northern Seward Peninsula, Alaska. These include a Yedoma Taberal Silt facies situated below a sub-lacustrine unconformity, three types of basal facies and a Lacustrine Silt facies. A preliminary geomorphological model based on sediment cores from mature yedoma thermokarst lakes illustrates how fades distribution changes through the different stages of lake development. First-generation lakes (those forming in undisturbed upland) and later-generation lakes (those forming in thermokarst-affected lowland) were present on the northern Seward Peninsula. A comparison between these two lake types indicates that the depositional environments of later-generation lakes are much more variable than first-generation lakes. Understanding the depositional history and development of yedoma thermokarst lakes is critical to understanding their role in landscape evolution and the carbon cycle.
    • Sediments of the Norris Glacier outwash area, upper Taku Inlet, southeastern Alaska

      Slatt, Roger M. (1967-05)
      An 8-square mile outwash fan, composed of gravelly sediment, extends from the terminus of Norris Glacier to the waters of upper Taku Inlet, Southeastern Alaska. Thirty-seven surface sediment samples from the tidal portion of the fan form the bulk of this study. The tidal flat is largely composed of very poorly sorted muddy sediment and relatively well sorted sand which, for the most part, overlie outwash gravel. Mixing of various modal size classes has produced a complex sediment distribution pattern as well as a complicated size-sorting relationship. The sand-size fraction of the sediments consists of feldspar, quartz, rock fragments, amphiboles, pyroxenes, micas and opaques; the clay-size fraction consists of micas, chlorite, montmorillonite, feldspar and amphibole. The sediments are the product of glacial abrasion in the Juneau Ice Field area. The sand and mud are derived largely from Norris and Taku Glacier detritus; their nature indicates valley glacier detritus may be fairly rapidly sorted when subjected to hydraulic action. Absence of quartz and presence of feldspar in the clay-size fraction may indicate the physical properties of these minerals control the size to which they can be reduced by valley-glacier abrasion.
    • The seismic wavefield in Nenana basin and Cook Inlet basin of Alaska

      Smith, Kyle; Tape, Carl; West, Michael; Freymueller, Jeffrey; Koehler, Richard; Wartes, Marwan (2020-05)
      Sedimentary basins amplify ground motion from earthquakes which can have severe consequences for major cities on basins like Tokyo and Los Angeles. Ground motion on sedimentary basins is complex and it depends on the geometry and elastic properties. We study the seismic wavefield from ambient noise and earthquake sources in Nenana Basin and Cook Inlet Basin with seismic stations from the Fault Locations and Alaska Tectonics from Seismicity (FLATS) and Southern Alaska Lithosphere and Mantle Observation Network (SALMON) projects. The FLATS project consists of 13 seismic stations placed over the Nenana Basin region in Central Alaska from 2014 to 2019. In South-Central Alaska, 28 seismic stations were placed around the Cook Inlet Region from 2015-2017 for the SALMON project. In this thesis, we have established two valuable data sets of events that can be used to better understand the complex influence of sedimentary basins on the seismic wavefield. Our analyses help quantify the frequency-dependent amount of amplification that occurs within these sedimentary basins. A greater understanding of ambient noise can improve site selection as well as understanding other forces of nature. Many FLATS stations are near trees and a river, so we quantify the influence of river, wind and basin on ambient noise. We analyze ambient noise in the frequency domain with power spectral densities on annual, daily and hourly time scales. Rivers affect ground motion from shearing and turbulent forces. For FLATS stations within several meters of the Tanana River, we found consistent seasonal perturbations around 10 Hz. A comparison of the 10 Hz signal with river stage height, measured 14 km upriver, shows strong correlations exist during the summer and ambient noise increases by 40 dB. In the town of Nenana, a weather station shows wind occurs less during the winter than summer. Wind can directly interact with the ground through shearing forces or indirectly with the transfer of energy through trees. In this study, we found that wind can affect the ground motion by at least 10 dB for < 0.05 Hz. Basins amplify ground motion because it is easier to shear the materials. When we analyzed basin amplification from ambient noise we found that we had to correct for other noise sources like wind and river conditions. We also found that there were three classes of basin influence: Basin stations, marginal basin stations, and non-basin stations.
    • Seismicity analysis: New techniques and case studies

      Wiemer, Stefan; Wyss, Max; Christensen, Douglas; McNutt, Stephen R.; Pulpan, Hans (1996)
      Seismicity parameters can be visualized as an almost continuous function of space and time by using dense grids. This mapping technique is used to: (1) Study the seismic quiescence preceding the 1992 Landers earthquake sequence. Both the Landers and Big Bear earthquake were found to be preceded by periods of significant seismic quiescence lasting 2-4 years. (2) Image the frequency-magnitude distribution in the subducting slab underneath Alaska and New Zealand. A high b-value anomaly at 100 km depth on the top of the slab suggests that slab dehydration causes an increase in the pore pressure. (3) Investigate the plumbing system of Mt. St. Helens and Mt. Spurr. This study suggests that the detailed spatial mapping of the frequency-magnitude distribution is potentially capable of resolving the location of magma chambers and the depth of vesiculation underneath volcanoes. (4) Map out the spatial distribution of asperities along the San Andreas fault in California. Based on the observation that the Parkfield and Morgan Hill asperities show an extremely low b-value ($b <$ 0.5), a new model to calculate recurrence times for moderate size earthquakes is proposed. (5) Investigate the correlation between a currently observed period of seismic quiescence in the Tokyo region and the frequency-magnitude distribution. A modification to the seismic quiescence hypothesis is proposed, which uses the frequency-magnitude distribution as a tool to distinguish between precursory seismic quiescence and false alarms not followed by a main shock. All of these case studies show that applying these new tools in seismicity analyses can advance the understanding of a variety of complex and heterogeneous tectonic regimes in the seismogenic part of the earth's crust and upper mantle.
    • Seismicity and stresses in the Kantishna seismic cluster, central Alaska

      Burris, Lea A. (2007-12)
      The Kantishna Cluster is an enigmatic and energetic cluster of earthquakes located in central Alaska, just to the northwest of Mt. McKinley Denali and adjacent to the Denali Fault. The Kantishna Cluster has no visible fault traces, and is often speculated to have a connection to the Denali Fault. The Kantishna Cluster is located at a hub of tectonic activity including Bering Block rotation to the west, bookshelf faulting to the northeast, and rotation of southern Alaska due to Pacific plate convergence to the south. The intention of this study was to broaden the knowledge base about the Kantishna Cluster and use the Mw 7.9 Denali Fault earthquake to find a relationship between the cluster and the Denali Fault Zone. Rate calculations in conjunction with z- and b- value changes show that the Denali Fault earthquake had little influence on the seismicity of the Kantishna Cluster, with the exception being the southern most portion closest to the Denali Fault. The highly variable background rate of seismicity in the Kantishna Cluster makes seeing changes in the seismicity difficult. Stress tensor inversions suggest a change in the stresses in the Kantishna Cluster; however, triangle diagram comparisons show that the pattern of earthquake mechanism types did not change. Coulomb stress change calculations predict small changes that were not observed in the data. Double difference hypocentral relocations show that the cloud of earthquakes collapses down to several distinct features. Seismicity trends resolved from hypocentral relocations made it possible to infer fault planes or planar structures in the region. The newly uncovered structures are utilized in the formation of a model involving two wedges to describe the seismicity in the Kantishna Cluster. The two wedges are being 'squeezed' in opposite directions accommodating for compression across the cluster due to Pacific plate convergence
    • Seismicity, seawater and seasonality: new insights into iceberg calving from Yahtse Glacier, Alaska

      Bartholomaus, Timothy Chester; Larsen, Christopher; O’Neel, Shad; Pettit, Erin; Truffer, Martin; West, Michael (2013-12)
      At many of the largest glaciers and ice sheets on Earth, more than half of the annual ice loss occurs through iceberg calving into the ocean. Calving is also responsible for the most rapid ice mass changes, both directly (through the mechanical loss of ice at the terminus) and indirectly (through dynamic thinning of upstream ice initiated by terminus retreat). Yet, the mechanisms and factors that control calving are poorly understood. Recordings of glaciogenic seismic waves, known as "icequakes," produced during iceberg calving offer opportunities for insight that cannot be gleaned through other methods. In order to better understand iceberg calving and its links to calving icequakes, we conducted a 2-yr study of rapidly advancing Yahtse Glacier, site of one of the densest clusters of calving icequakes in southern Alaska. By synchronizing video of iceberg calving events with locally-recorded seismograms, we found that most icequake energy is produced after subaerial iceberg detachment from the glacier terminus, while the iceberg impacts and descends below the sea surface. Cavitation beneath the water surface generates the largest amplitude portions of icequakes-those that are detectable over several hundred km distances. Numerical simulations of these iceberg-sea surface interactions predict sources with durations that are consistent with the 1-5 Hz frequency content of calving icequakes. Oceanographic measurements in Icy Bay, where Yahtse Glacier terminates, reveal that warm water may melt most of the ice reaching the submarine terminus. During the summer, water with temperature > 10 °C flows from the Gulf of Alaska coast to within 2 km of Yahtse Glacier's terminus. We find that heat transport between 5 and 40 x 109 W can readily melt the submarine glacier terminus at a rate that matches the speed with which ice flows towards the glacier terminus (17 m d⁻¹). Subaerial iceberg calving rates may be paced by submarine melt rates. To place our calving and submarine melt observations in a broader temporal context, we construct an empirical model of iceberg size using icequake properties and tune the model with over 800 visually-observed iceberg calving events. We find that iceberg calving is at its minimum during the winter, when seawater is cool and mixing of proglacial seawater by subglacial discharge is weak. Overlaying this long period cycle, we find significant daily to inter-annual variability and sensitivity of calving to tidal stage. These observations expand our appreciation for the ocean's important role in iceberg calving: at time scales ranging from the sub-second generation of icequakes, to the annual undercutting of the glacier terminus.
    • Seismological Constraints On Tectonics Of Southern And Central Alaska: Earthquake Locations And Source Mechanisms

      Ratchkovski, Natalia Anatolievna; Hansen, Roger; Wyss, Max; McNutt, Steven; Christensen, Douglas (2001)
      The major emphasis of this thesis is on investigations of earthquake locations and source mechanisms and what we can learn about Earth structure from them. I used a Joint Hypocenter Determination (JHD) method to improve the earthquake locations obtained after routine data processing. Over 15,000 subduction zone earthquakes in southern Alaska and over 3,600 crustal earthquakes in central Alaska with magnitudes ML ? 2 that occurred from 1988 to 2000 were relocated. I found that the relative earthquake locations can be improved with the use of the JHD relocation technique (30--60% reduction in RMS residuals). Thus, many details of the subduction zone geometry and crustal structure can be mapped. To constrain source characteristics, I use a moment tensor inversion method that simultaneously inverts for the source parameters and velocity structure. First, I apply this technique to the sequence of strong earthquakes in the Kodiak Island region, including December 6, 1999 and January 10, 2001 MW 7 events. Next, I expand this approach to moderate-sized ( ML ? 4) crustal earthquakes in central Alaska and calculate 38 moment tensors. I demonstrate that the moment tensor inversion of regional waveforms provides reliable results even when recordings from a single broadband station are used. A catalog of the moment tensors together with the focal mechanisms obtained using conventional P-wave first motion analysis is used to calculate principal stress directions in central Alaska. I find that the stress state in the crust is inhomogeneous and that the orientation of the maximum compressive stress changes from a SE-NW to SSW-NNE orientation from west to east across interior Alaska. One more topic of this thesis is the application of the array analysis to understanding characteristics of anomalous seismic phases observed in the records of the intermediate-depth Alaskan subduction zone earthquakes. I identified two secondary phases arriving with 1--3 s and 7--12 s delays after the first P-wave arrival. They are interpreted as S-to-P and P-to-S converted phases at the upper/lower surface of the subducted slab.
    • Sentinels Of Arctic Ecosystem Health: Polar Bear And Arctic Fox

      Kirk, Cassandra M.; O'Hara, Todd (2010)
      Climate change is impacting human, wildlife, and ecosystem health in the Arctic. Currently, we lack sufficient information to fully appreciate the ramifications of these changes and are thus ill equipped for predicting, mitigating or adapting to the outcome of such impacts. Warming in the Arctic has generated a need for baseline information on biodiversity and ecosystem health such that change over time may be assessed. Sentinel species can be used to monitor and therefore, intervene to prevent adverse health outcomes before they manifest at the population level. This dissertation examines the use of polar bears (Ursus maritimus) and arctic foxes ( Alopex lagopus) as sentinels for climate change in the Arctic. To this end we: develop hematological biomarkers in polar bears which can be used to model change over time in health; demonstrate relationships between this biomarker and infectious agent exposure (e.g serology); and establish prevalence and risk factors for infectious agents that can serve as indicators of change in disease occurrence at the Arctic marine-terrestrial interface. We found that den emergent female polar bears with dependent young were the most immunologically vulnerable cohort and suggest therefore, that they be targeted in future monitoring efforts. We also detected evidence suggesting serologic exposure of polar bears to morbillivirus and Toxoplasma gondii may be associated with immunological status and age (morbillivirus only). Furthermore, we used molecular epidemiologic techniques to identify the strain of the highly lethal morbillivirus in arctic fox as "arctic" canine distemper virus and the species of Echinococcus in arctic fox on the Alaska North Slope as Echinococcus multilocularis. The results of this study illustrate the utility of the "One Health" approach in addressing the impacts of climate change. Understanding Arctic ecosystem health will require the collaborative efforts of experts in diverse fields as well as input from local, traditional ecological knowledge over the proper spatial and temporal scales.