• The role of Alaskan missile defense in environmental security

      Fritz, Stacey Anne (2002-12)
      In 2002, the United States abandoned the Anti-Ballistic Missile Treaty and began constructing a missile defense system in Alaska. Questions about how missile defense will contribute to U.S. security remain. Moreover, beliefs about what constitutes security are expanding to include considerations of global environmental stability. According to environmental security theories on arms control, non-proliferation, and environmental degradation, deploying missile defense may make the U.S. and the world less secure. This analysis addresses the issue by exploring the military's role in Alaska and resulting environmental damage, followed by a history of missile defense systems and a description ofthe Alaskan project's components. Arguments for and against missile defense are explained, and the history of Kodiak Island's rocket launch facility illustrates how these issues are evolving in Alaska. The conclusion discusses why pursuing the system is seen by many as a risky policy choice in both traditional and environmental security contexts.
    • Role Of Antennas And The Propagation Channel On The Performance Of An Ultra Wide Band (Uwb) Communication System

      Venkatasubramanian, Arun; Sonwalkar, Vikas (2007)
      The objectives of this dissertation are to experimentally and numerically quantify the effect of antennas and the propagation channel on the performance of an Ultra Wide Band (UWB) receiver. This work has led to the following new results: (1) the variation in the time duration of the impulse response of the oval dipole in the vertical plane is within 5% up to an angle theta = 60° off the broadside direction (theta = 90°); at larger angles a factor of six elongation in the time duration of the impulse response along the antenna axis (theta = 0°) is observed, (2) for an axial ratio of 0.5, the oval dipole has a Voltage Standing Wave Ratio (VSWR) of 2:1 (~11% reflection coefficient) in a 3.1 GHz bandwidth with a lower cut off frequency of 2.8 GHz; for an axial ratio of 2.0 this scales to 0.5 GHz bandwidth with a lower cut off frequency of 1.75 GHz, (3) a new theoretical model has been developed for UWB pulse propagation over the ground which takes into account the geometrical properties of the propagation channel (such as the heights of the transmitter (h1) and the receiver (h2) over the ground) and the nature of the radiated UWB pulse (such as pulse duration (taup) and cycle time (tauc)), (4) an improvement in bit error rate by up to a factor of 100 can be achieved for a matched filter receiver by careful orientation of the transmitting and the receiving oval dipole antennas used in the measurements presented in this dissertation.
    • Role of antioxidant supplementation and exercise regimen in handling oxidative stress from natural PM2.5 exposure due to boreal forest fire

      Witkop, Jacob J.; Dunlap, Kriya; Duffy, Lawrence; Reynolds, Arleigh (2019-05)
      Particulate matter 2.5 (PM2.5) exposure induces oxidative stress that causes many negative health outcomes such as cancer, cardiovascular disease and neurodegenerative disease. Research shows that dietary antioxidants and an up-regulated endogenous antioxidant response from exercise play key roles in the antioxidant defense against oxidative stress. This study is the first to use an animal model to investigate the cumulative effects of using lifestyle interventions of antioxidant supplementation (Arthrospira platensis) and exercise regimen on the antioxidant response before, during, and after ambient PM2.5 exposure. In a two-factorial, longitudinal design, sled dogs (n=48) were divided into four groups (exercise and supplemented, exercise, supplemented, and control) to (1) test the effects of exercise and antioxidant regimen on antioxidant response after one month of implemented exercise and supplementation protocol and (2) measure the antioxidant response of all groups during and after a natural forest fire event in 2015. Commercial assays for Total antioxidant Power (TAP) and the enzymatic antioxidant Superoxide Dismutase (SOD) were used as markers for the total antioxidant response and the endogenous response at all time points. During the forest fire, SOD was increased 5-10-fold over pre/post-exposure levels in all groups suggesting potential implication for using SOD as a marker for the acute response to environmental stress. TAP was increased in the exercise groups after one month of exercise protocol implementation, demonstrating the cytoprotective increase of antioxidants after repeated exercise.
    • Role of Arctic Sea Ice Variability in Climate Models

      Dammann, Dyre O.; Bhatt, Uma; Polyakov, Igor; Zhang, Xiang (2011-08)
      Arctic sea ice plays an important role in climate by influencing surface heat fluxes and albedo, so must be accurately represented in climate models. This study finds that the fully coupled ice-ocean-atmosphere-land Community Climate System Model (CCSM3.0) underestimates day-to-day ice variability compared to observations and employs the Community Atmosphere Model (CAM3.0) to investigate the atmospheric sensitivity to sea ice variability. Three 100-ensemble experiments are forced with climatological, daily-varying, and smoothly-varying sea ice conditions from an anomalously low ice period (September 2006-February 2007). Daily ice variability has a large local impact on the atmosphere when ice undergoes rapid changes, leading to local cooling and subsequent circulation changes. The most notable example of a large-scale atmospheric response occurs over Northern Europe during fall where daily ice variability forces reductions in the number and strength of cyclones, leading to positive sea level pressure anomalies, surface warming, and reduced cloud cover.
    • Role Of Conductivity Spatial Structure In Determining The Locations Of Sprite Initiation

      Tavares, Fernanda De Sao Sabbas; Jeffries, Martin O. (2003)
      Sprites are transient optical signatures of mesospheric electrical breakdown in response to lightning discharges. Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. This dissertation investigates the role of neutral density perturbations in determining the locations of sprite initiation. The work was performed in three interrelated studies. (1) A detailed statistical study of the temporal-spatial relationships between sprites and the associated CG was performed for July 22, 1996. The distribution of sprite offsets relative to the underlying lightning had a mean of ~40 km. The distribution of sprite onset delays following the parent lightning had a mean of ~20--30 ms, consistent with theoretical estimates for the electron avalanche-to-streamer transition in the mesosphere. (2) A follow-up study for the same observations was performed to investigate the relationship of the sprites to convective activity in the underlying thunderstorm, using GOES-8 infrared imagery of cloud-top temperatures. The sprite generating thunderstorm was a Mesoscale Convective System (MCS). The maximum sprite and -CG production of the system were simultaneously reached at the time of maximum contiguous cloud cover of the coldest region, corresponding to the period of greatest convective activity of the system. Thunderstorm convective activity is a potential source of gravity waves and mesospheric turbulence. (3) Computer simulations of the temporal-spatial evolution of lightning-induced electric fields in a turbulent upper atmosphere were performed. The modeled turbulence in the simulations spanned the amplitude range 10% to 40% of the ambient background neutral density, with characteristic scale sizes of 2 km and 5 km, respectively. The results indicate that neutral density spatial structure, similar to observed turbulence in the mesosphere, facilitates electrical breakdown in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets.
    • The role of corticosterone and corticosteroid-binding globulin in reproduction of red-legged kittiwakes (Rissa brevirostris)

      Dempsey, Thomas D. (2006-12)
      The goal of this study was to determine to what extent, and by what physiological and behavioral mechanisms, avian reproductive performance is related to environmental variability. Specifically, I explored relationships between components of the physiological stress response, reproductive behavior, and reproductive performance in the red-legged kittiwake (Rissa brevirostris), a long-lived seabird. I found that individuals respond to food-related stress by altering levels of both corticosteroid-binding globulin (CBG) and the primary avian glucocorticoid, corticosterone (Cort). I also found a negative association between breeding adults' Cort concentrations and population-level reproductive success; although no such association existed between CBG and reproductive success. The relationship between Cort and reproductive performance does not appear to result from Cort concentrations affecting an adult's decision to initiate or forego reproduction in a given year. In conclusion, this study suggests that environmentally-induced physiological stress affects reproductive success of red-legged kittiwakes, although the behavioral mechanism remains unknown.
    • Role of dietary fat and supplementation in modulating neurodegenerative pathology in two animal model systems

      Maulik, Malabika; Bult-Ito, Abel; Taylor, Barbara E.; Duffy, Lawrence; Kuhn, Thomas; Dunlap, Kriya (2018-12)
      Neurodegenerative disorders are progressive conditions that worsen over time and results in death of neurons. Parkinson's disease (PD) is a prevalent example of one such age-related disease, which is characterized by movement disorder (ataxia) and/or cognitive disability (dementia). Pathologically, PD is characterized by a toxic accumulation of α-synuclein protein in the midbrain leading to degeneration of the dopaminergic neurons. The etiology of PD is intricate, and the cause is attributed to genetic mutations and environmental factors like insecticides or heavy metals. Moreover, treatment options are limited and often aimed at treating the symptoms rather than the actual disease progression. Using the nematode model of Caenorhabditis elegans, I examined the effect of Alaskan bog blueberry (Vaccinium uliginosum) on α-synuclein overexpression and how such indigenous natural treatment can modulate key molecular targets like sirtuins, which are proteins involved in regulating cellular processes including aging, death and their resistance to stress. The impact of extrinsic factors like dietary fat on PD pathology has been sparsely explored and the molecular basis of such changes is not known. Through my thesis research, I also further investigated the influence of fat metabolism on key hallmarks of PD: α-synuclein overexpression and dopaminergic degeneration in the nematode model. Finally, I studied the interaction of dietary fat (normal, low and high fat) and Alaskan blueberry supplementation on metal induced neurotoxicity model of Mus musculus. Our results highlight the beneficial properties of Alaskan blueberries in combating proteotoxic stress and inflammation in both animal models. They also reiterate the benefit of low fat diet, on its own or in combination with supplementation in improving several PD-like molecular features and how consuming high fat can mask such health promoting outcomes. The current thesis work therefore, provides a foundation for further exploration of neurobiological changes associated with consumption of natural products and different diets and how such alterations can be extrapolated to humans.
    • The role of environmental factors in regional and local scale variability in permafrost thermal regime

      Cable, William Lambert; Romanovsky, Vladimir E.; Christiansen, Hanne H.; Elberling, Bo; Yoshikawa, Kenji (2016-08)
      Global climate change is a topic of great concern and research interest because there are still many components of the Earth System which we do not fully understand and cannot predict how they will respond to this change. One of these components is the permafrost that underlies approximately 24% of the Northern Hemisphere land surface. Permafrost is a thermal condition, found primarily at higher latitudes and elevations, in which subsurface material remains below 0 °C for at least two, but often up to thousands of years. As such, permafrost can accumulate large amounts of carbon in the form of organic material that remains frozen, unavailable for decomposition. However, as the climate warms, permafrost warms and thaws, slowly making this stored carbon available for decomposition into greenhouse gases, which have the potential to create a large positive feedback to climatic warming. A major challenge in permafrost research is that it is not possible to directly obtain spatial information about permafrost through remote sensing alone. This means that we must infer the presence or absence of permafrost and its thermal state based on other remotely sensible parameters such as vegetation, land surface temperature, and topography using a combination of modelling and remote sensing. To do this, we must understand the effects of different environmental factors, such as vegetation, hydrology, topography, and snow on the ground thermal regime and permafrost. In this thesis, the effects of these environmental factors are examined in relation to permafrost presence or absence and the ground thermal regime on a regional and local scale. The regional scale study focuses on the use of vegetation communities, ecotypes, as integrators of variation in environmental factors to influence the ground thermal regime. At the local scale, the microtopography created by ice-wedge polygons is examined as a cause of variations in environmental factors and the impact this has on the permafrost thermal regime of these features. We find that at both scales, remotely sensible parameters such as ecotypes and microtopography show great promise in the efforts to scale-up both field measurements and modelling results.
    • The role of fire in the carbon dynamics of the boreal forest

      Balshi, Michael S. (2007-12)
      The boreal forest contains large reserves of carbon, and across this region wildfire is a common occurrence. To improve the understanding of how wildfire influences the carbon dynamics of this region, methods were developed to incorporate the spatial and temporal effects of fire into the Terrestrial Ecosystem Model (TEM). The historical role of fire on carbon dynamics of the boreal region was evaluated within the context of ecosystem responses to changing atmospheric CO₂ and climate. These results show that the role of historical fire on boreal carbon dynamics resulted in a net carbon sink; however, fire plays a major role in the interannual and decadal scale variation of source/sink relationships. To estimate the effects of future fire on boreal carbon dynamics, spatially and temporally explicit empirical relationships between climate and fire were quantified. Fuel moisture, monthly severity rating, and air temperature explained a significant proportion of observed variability in annual area burned. These relationships were used to estimate annual area burned for future scenarios of climate change and were coupled to TEM to evaluate the role of future fire on the carbon dynamics of the North American boreal region for the 21st Century. Simulations with TEM indicate that boreal North America is a carbon sink in response to CO₂ fertilization, climate variability, and fire, but an increase in fire leads to a decrease in the sink strength. While this study highlights the importance of fire on carbon dynamics in the boreal region, there are uncertainties in the effects of fire in TEM simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. Future studies should incorporate the role of dynamic vegetation to more accurately represent post-fire successional processes, incorporate fire severity parameters that change in time and space, and integrate the role of other disturbances and their interactions with future fire regimes.
    • Role of fire severity in controlling patterns of stand dominance following wildfire in boreal forests

      Shenoy, Aditi; Kielland, Knut; Johnstone, Jill F.; Kasischke, Eric S.; Ruess, Roger W. (2016-05)
      Global trends of climate warming have been particularly pronounced in northern latitudes, and have been linked to an intensification of the fire regime in Arctic and boreal ecosystems. Increases in fire frequency, extent, and severity that have been observed over the past several decades are expected to continue under a warming climate. Severe fires can drastically reduce or remove the deep organic layers that accumulate in mature black spruce forests. Extensive studies in the boreal forests of interior Alaska and Canada have shown that parts of the landscape that undergo severe burning provide favorable seedbeds for the recruitment of deciduous tree seedlings, and thereby reduce the relative abundance of coniferous seedling recruitment in these areas shortly after fire. The persistence of deciduous species such as aspen beyond the seedling recruitment and establishment stage is as yet relatively unknown. To address this knowledge gap, I asked the question: is increased deciduous recruitment observed in severely burned areas transient, or does it result in persistent changes in stand composition later in succession? I examined changes in relative dominance patterns of aspen and black spruce that had occurred between 8 and 14 years post-fire along an organic layer depth gradient within a single burn. I found that patterns of relative species dominance established shortly after fire persisted into the second decade of succession, resulting in productive aspendominated stands in severely burned areas with shallow organic layers, and black spruce dominated stands in lightly burned areas with deep organic layers. These patterns of stand dominance in relation to post-fire organic layer depth were also observed in several other burns in the region. Therefore, deep burning fires are likely to result in a persistent shift from black spruce to aspen dominance in severely burned parts of the boreal forest. In order to understand how variation in organic layer depth is driving these alternate successional pathways, I measured nutrient uptake rates of aspen and spruce in severely and lightly burned sites within a single burn. I also examined relationships between post-fire organic layer depth and a suite of soil variables, and evaluated the relative importance of these soil variables in explaining variation in stand level aspen biomass, spruce biomass, and the relative dominance of aspen vs. spruce. I found that variations in post-fire organic layer depth result in contrasting soil environments, with soils in shallow organic layer sites being warmer, drier, and more alkaline than soils in deep organic layer sites. Variations in aspen biomass and aspen: spruce biomass were largely being driven by substrate conditions, whereas stand level spruce biomass was less sensitive to these same variations in soil conditions. Nutrient uptake rates of both aspen and spruce were higher in severely burned areas with shallow organic layers, but the differences between species were magnified by stand biomass patterns in relation to post-fire organic layer depth. My results suggest that the positive effects of soil conditions associated with mineral soil substrates extend well beyond the initial seedling recruitment phase, and may continue to influence aspen growth rates into the second decade of succession resulting in the differential patterns of biomass accumulation and stand dominance in relation to post-fire organic layer depth. With the predicted increase in fire severity and shortening of the fire cycle, the proportion of aspen dominated stands on the landscape is likely to increase, which will incur substantial changes in ecosystem function (e.g., land-atmosphere energy exchange, C and N storage, nutrient cycling, net primary productivity, and wildlife habitat quality) compared to the current forests dominated by conifers.
    • The role of glycerol-3-phosphate acyltransferase 1 in mitochondrial phospholipid biosynthesis of cold-bodied fishes

      Keenan, Kelly Anne; O'Brien, Kristin; Schulte, Marvin; López, Andrés; Harris, Michael (2015-08)
      Mitochondrial biogenesis is induced by low temperature in many fish species. For example, cold acclimation of Gasterosteus aculeatus (threespine stickleback) increases mitochondrial densities in oxidative skeletal muscle. Oxidative muscles of Antarctic icefishes (suborder Notothenioidei) also have high mitochondrial densities characterized by higher densities of phospholipids compared to red-blooded notothenioids. Mitochondrial biogenesis has been well studied in mammals yet it is unknown how mitochondrial phospholipid synthesis is regulated. I hypothesized that both activity and mRNA levels of glycerol-3-phosphate acyltransferase (GPAT), the rate-limiting enzyme in glycerolipid biosynthesis, would increase in oxidative muscle of stickleback, where mitochondrial biogenesis occurs, but not in liver, in response to cold acclimation, and that GPAT1 and /or GPAT2 mRNA levels would be higher in hearts of icefishes compared to red-blooded species. To test these hypotheses, maximal activity of GPAT and mRNA levels of GPAT1 and GPAT2 were measured in liver and oxidative muscle of coldand warm- acclimated stickleback. GPAT1 and GPAT2 mRNA levels were also quantified in hearts and livers of red- and white-blooded Antarctic notothenioids. Additionally, cDNA of GPAT1 was sequenced in Antarctic and sub-Antarctic notothenioids to gain insight to the evolution of a mitochondrial membrane protein and identify candidate amino acid residues responsible for maintaining function at cold temperature. GPAT activity increased in oxidative muscle but not in liver, and transcript levels of GPAT1 increased in liver but not in oxidative muscle, in response to cold acclimation in stickleback. GPAT2 transcripts were undetectable in both tissues. GPAT1 mRNA levels were highest in liver of red-blooded Antarctic notothenioids and did not differ in hearts between red- and white-blooded fishes, and GPAT2 transcripts were undetectable. GPAT protein levels may not change concurrently with GPAT1 and GPAT 2 mRNA levels because GPAT3 or 1-acylglycerol-3-phosphate acyltransferase (AGPAT), the enzyme subsequent to GPAT, may be involved in regulating phospholipid synthesis during mitochondrial biogenesis. The amino acid sequence of GPAT1 is highly conserved (97.94-98.06%) among Antarctic and sub-Antarctic notothenioids, with three potential sites in the cytosolic region that may be important for maintaining function at cold temperature: Ser415Ala, Asp603Glu and Thr648Ala.
    • Role of ionospheric conductance in magnetosphere-ionosphere coupling

      Bhattacharya, Tapas; Otto, Antonius; Bristow, William; Conde, Mark; Lummerzheim, Dirk; Ng, Chung-Sang (2014-08)
      Magnetosphere-ionosphere (MI) coupling has been studied for a long time. However, not much work has been done on a systematic understanding of the relation between ionospheric Pedersen conductance, its effect on the evolution and modification of field-aligned currents (FACs), and the influence of conductance and FACs on the formation of parallel electric fields which cause particle precipitation. Though the roles of ionospheric conductance gradients for FACs and parallel electric field evolution are directly related, they are poorly understood. This dissertation advances the understanding of these areas and all results of this study are based on numerical simulations that employ a three-dimensional - two-fluid (ions and neutrals) simulation code. The first part of this dissertation presents a systematic study of the magnetospheric and ionospheric influences on the evolution and modification of FACs with focus on the role of ionospheric Pedersen conductance and its gradients. FACs are typically generated in the magnetosphere and are carried into the ionosphere by Alfvén waves. During their reflection from the ionosphere these FACs are modified depending on the magnitude and distribution of ionospheric conductance. For conductance gradients along the polarization of the wave, strong Pedersen currents can be generated which in turn enhance the FAC as well. The second part of this dissertation addresses the properties and evolution of parallel electric fields in an attempt to better understand the formation of discrete auroral arcs in response to the evolution of FACs for predetermined ionospheric conductance patterns. Frequently, auroral acceleration is believed to occur through U or V shaped potentials. Therefore, this part examines the properties of localized parallel electric fields in a uniform magnetic field. It is demonstrated that localized parallel electric fields generate magnetic flux in the absence of source of free energy. It is also shown that parallel electric fields generated in a FAC in the presence of a (anomalous) resistivity represent a load and can provide physical explanation for the auroral acceleration geometry. The results demonstrate that such electric fields can be significantly enhanced by Alfvén wave reflection where both magnitude and gradients of the ionospheric conductance are important. The strongly enhanced parallel electric field is associated with magnetic reconnection and modifies the FAC system such that thin current layers (with curls and folds) are observed to be embedded in the large scale current system.
    • The role of mammalian herbivores in primary succession on the Tanana River floodplain, interior Alaska

      Butler, Lemuel Gordon (2003-12)
      I compared willow (Salix) communities along the Tanana River exposed to varying levels of herbivory to examine how herbivory influences the landscape distribution of vegetation. Moose (Alces alces) and snowshoe hare (Lepus americanus) herbivory decreased plant biomass and canopy height and increased the proportion of dead stems in willow communities. Herbivory also shifted the age distribution of plants in willow communities towards younger age classes, and also decreased the number of communities dominated by willow on the landscape. A frame-based simulation model was built to incorporate the effects of herbivory and river fluvial dynamics on plant succession. My results show that herbivory, erosion and accretion are all necessary components to accurately model the landscape distribution of vegetation communities. Erosion/accretion had a major role in landscape vegetation patterns shifting the landscape toward earlier successional communities, while herbivory had a minor role, shifting the landscape towards later successional communities. The interactions among these biotic and abiotic processes account for the empirically observed landscape vegetation patterns.
    • The role of outdoor recreation in building community resilience and adaptive capacity

      Overbaugh, William L.; Alessa, Lilian; Chapin, F. Stuart III; Kliskey, Andrew; Rosay, Andrew (2014-08)
      For the first time, outdoor recreation theory is applied within the framework of resilience theory to define the conceptual relationship between recreation benefit outcomes and community resilience. A theoretical and practical disconnect between the two disciplines is evident from the lack of literature identifying conceptual and operational linkages. Emerging from the application is a Recreation System Community Resilience Framework that models agent behavior, embedded green space, networks of service providers and feedback mechanisms to demonstrate recreation connections to resilience concepts. The Recreation Benefits-Based Model is identified as the best fit to deliver sustainable high leverage and capacity-building resilience for communities. Anchorage, Alaska neighborhoods are chosen to test the operational relationship between the constructs of outdoor recreation opportunity diversity and community resilience and adaptive capacity. The findings indicate support for the hypothesis that community resilience increases as recreation diversity increases. The results demand widespread implementation of the Benefits-Based Model in order for recreation to fully participate in the community well-being, resilience, and adaptive capacity discussion. The message to resilience practitioners is to reject activity-based visitor numbers, trail miles and park acres to indicate community health and insist on meaningful recreation system outcome indicators.
    • The role of property rights in bycatch reduction: evidence from the British Columbia groundfish fishery

      Edinger, Tonya; Little, Joe; Goering, Douglas; Baek, Jungho (2014)
      The following analysis seeks to contribute to the literature by examining the effectiveness of the individual vessel bycatch quota (IVBQ) system as an incentive structure for the mitigation of halibut bycatch in the British Columbia Groundfish fishery. Through the use of an OLS regression technique, this empirical analysis intends to quantify the importance and overall effectiveness of the vessel bycatch quota incentive system in respect to mitigating bycatch. The research utilizes time series fisheries data from 1962-2012, as provided by The International Pacific Halibut Commission and Fisheries and Oceans Canada. The research indicates that the IVBQ system has proven to be highly effective, confirming the significance of private property rights as a tool for the reduction of bycatch within British Columbia. Policy makers may utilize the information provided in this paper to design more feasible and effective policy options to promote the preservation of ecological balance in the management of marine resources.
    • The role of serotonergic (5-HT) neuromodulation in respiratory chemosensitivity

      Fieldman, Deborah M. (2007-05)
      Breathing must be regulated to maintain appropriate levels of oxygen and carbon dioxide. Breathing may be influenced by serotonergic (5-HT) neurons, sensitive to CO₂, which activate the brain's respiratory network. However, this role of 5-HT neurons as CO₂-sensitive chemoreceptors in unanesthetized animals is unclear. This study used an unanesthetized in situ perfused rat brainstem preparation to test the hypothesis that 5-HT neurons contribute to CO₂ ventilatory responses. Changes in phrenic nerve discharge patterns were monitored as gas-saturated solutions supplying the preparation were switched from 5%C0₂ to 7%C0₂ (balance 0₂). The importance of 5-HT neurons was identified by comparing responses before and after application of the specific serotonin 1A receptor agonist 8-hydroxy-(dipropylamino) tetralin hydrobromide (8-OH-DPAT; at doses of 0, 1.5, 3, and 6 uM in the perfusate). The action of 8-OH-DPAT is to inhibit 5-HT neurons and reduce synaptic 5-HT release. Results indicated that changes in phrenic burst pattern similar to hypercapnic ventilatory responses observed in vivo, were greatly disrupted by 8-OH-DPAT treatment. These results illustrate that activation of 5-HT neurons is critical for CO₂ chemosensitivity in this in situ preparation and suggest that these neurons may play a key role in the regulation of breathing in otherwise intact animals.
    • The role of stratification in the spring ice edge bloom in the Bering Sea: a numerical model

      Freed, Martin (1984-09)
      Marginal ice edge zones are unique frontal systems with air-ice-sea interfaces. Phytoplankton blooms which occur along the edge of some melting ice packs in the spring, appear to be related to melt water driven density stratification. In this thesis a numerical model of a marginal ice edge zone is constructed. The wind driven circulation and spring phytoplankton bloom at the Bering Sea ice edge are simulated as functions of air-ice-sea-biology interaction. It was found that as long as the ice was allowed to melt, blooms occur regardless of wind direction. However, because of the compactness dependent melt scheme invoked, the faster the ice advects out from the pack, the faster the water column stratifies. The speed and the area of the bloom depend on the rate and extent of stratification. The model data compare favorably with field data.
    • The role of tundra vegetation in the Arctic water cycle

      Clark, Jason A.; Tape, Ken; Schnabel, William; Euskirchen, Eugénie; Ruess, Roger (2019-12)
      Vegetation plays many roles in Arctic ecosystems, and the role of vegetation in linking the terrestrial system to the atmosphere through evapotranspiration is likely important. Through the acquisition and use of water, vegetation cycles water back to the atmosphere and modifies the local environment. Evapotranspiration is the collective term used to describe the transfer of water from vascular plants (transpiration) and non-vascular plants and surfaces (evaporation) to the atmosphere. Evapotranspiration is known to return large portions of the annual precipitation back to the atmosphere, and it is thus a major component of the terrestrial Arctic hydrologic budget. However, the relative contributions of dominant Arctic vegetation types to total evapotranspiration is unknown. This dissertation addresses the role of vegetation in the tundra water cycle in three chapters: (1) woody shrub stem water content and storage, (2) woody shrub transpiration, and (3) partitioning ecosystem evapotranspiration into major vegetation components. In Chapter 1 I present a method to continuously monitor Arctic shrub water content. The water content of three species (Salix alaxensis, Salix pulchra, Betula nana) was measured over two years to quantify seasonal patterns of stem water content. I found that spring uptake of snowmelt water and stem water storage was minimal relative to the precipitation and evapotranspiration water fluxes. In Chapter 2, I focused on water fluxes by measuring shrub transpiration at two contrasting sites in the arctic tundra of northern Alaska to provide a fundamental understanding of water and energy fluxes. The two sites contrasted moist acidic shrub tundra with a riparian tall shrub community having greater shrub density and biomass. The much greater total shrub transpiration at the riparian site reflected the 12-fold difference in leaf area between the sites. I developed a statistical model using vapor pressure deficit, net radiation, and leaf area, which explained >80% of the variation in hourly shrub transpiration. Transpiration was approximately 10% of summer evapotranspiration in the tundra shrub community and a possible majority of summer evapotranspiration in the riparian shrub community. At the tundra shrub site, the other plant species in that watershed apparently accounted for a much larger proportion of evapotranspiration than the measured shrubs. In Chapter 3, I therefore measured partitioned evapotranspiration from dominant vegetation types in a small Arctic watershed. I used weighing micro-lysimeters to isolate evapotranspiration contributions from moss, sedge tussocks, and mixed vascular plant assemblages. I found that mosses and sedge tussocks are the major constituents of overall evapotranspiration, with the mixed vascular plants making up a minor component. The potential shrub transpiration contribution to overall evapotranspiration covers a huge range and depends on leaf area. Predicted increases in shrub abundance and biomass due to climate change are likely to alter components of the Arctic hydrologic budget. The thermal and hydraulic properties of the moss and organic layer regulate energy fluxes, permafrost stability, and future hydrologic function in the Arctic tundra. Shifts in the composition and cover of mosses and vascular plants will not only alter tundra evapotranspiration dynamics, but will also affect the significant role that mosses, their thick organic layers, and vascular plants play in the thermodynamics of Arctic soils and in the resilience of permafrost.
    • Role Of Waves On The Circulation Of The Arctic Middle Atmosphere: Rayleigh Lidar Measurements And Analysis

      Thurairajah, Brentha (2009)
      Rayleigh lidar measurements of the upper stratosphere and mesosphere are made on a routine basis over Poker Flat Research Range (PFRR), Chatanika, Alaska, (65�N, 147�W). Rayleigh lidar measurements have yielded high resolution temperature and density profiles in the 40-80 km altitude. These measurements are used to calculate gravity wave activity in the 40-50 km altitude. The thermal structure of the stratosphere and mesosphere is documented using an eight year data set, and the role of small scale gravity waves on the large scale meridional circulation is analyzed in terms of the synoptic structure of the Arctic stratospheric vortex, Aleutian anticyclone, and planetary wave activity. The monthly mean temperature indicates colder January temperatures that appear to be due to the increase in frequency of occurrence of stratospheric warming events from 1997-2004. The gravity wave potential energy density is analyzed during stratospheric warming events in two experimental time periods. From the first study consisting of three winters, 2002-2003, 2003-2004, and 2004-2005, the first direct measurement of suppression of gravity wave activity during the formation of an elevated stratopause following the 2003-2004 stratospheric warming event is presented. The gravity wave potential energy density at Chatanika is positively correlated with horizontal wind speeds in the stratosphere, and indicates that the wave activity in the 4050 km altitude is partially modulated by the background flow. In the second study with more recent winters of 2007-2008 and 2008-2009, no systematic difference in the magnitude of potential energy density between the vortex displacement warming event during the 2007-2008 winter and vortex split warming event during the 2008-2009 winter is found. However, the low correlation between gravity wave potential energy and horizontal wind speed after the first warming in January 2008, and a higher correlation after the January 2009 warming suggests that while the gravity wave activity after the 2009 warming is modulated by the background flow, other wave sources modulate the gravity wave activity after the 2008 warming.
    • Role of wetlands and endogenous factors on incubation behavior of nesting spectacled eiders on the Yukon-Kuskokwim Delta, Alaska

      O'Connell, William Todd (2001-12)
      Patterns of nest attendance in ducks vary with endogenous and environmental factors. We examined variation in nest attendance of spectacled eiders on the Yukon-Kuskokwim Delta, Alaska, during 1997-1998. We also examined spatial and temporal variation in wetland characteristics and potential foods available to nesting spectacled eiders. Time spent foraging was greater when spectacled eiders traveled farther to feed, and nest attendance was lower when food was more abundant, suggesting that females made tradeoffs between foraging and energetic requirements of nesting in response to food abundance and wetland conditions. Wetlands were dynamic, and food abundance varied with pond depth and total dissolved solids. Spectacled eiders responded in complex ways to a suite of physiological and environmental variables, and employed an overall behavioral strategy that optimized foraging behavior in response to food abundance, while minimizing risk of depleting nutrient reserves sufficiently to force nest abandonment or increase the risk of female mortality.