• The 1931 eruption of Aniakchak volcano, Alaska: deposit characteristics and eruption dynamics

      Nicholson, Robert Stokes (2003-12)
      The 1931 eruption of Aniakchak progressed through several eruptive phases from multiple vents that totaled 1.4 x 10⁸ m³ dense rock equivalent of magma. The sequence of phases began with a sub-plinian eruption followed by a phreatomagmatically-influenced vulcanian phase originating from the primary vent. Effusive activity from two separate vents occurred simultaneously with the vulcanian phase. The eruption from the main vent progressed to strombolian in nature and eventually subsided into an effusive eruption. The composition of the magma ranged from trachydacite at the onset of the eruption to basaltic andesite at its conclusion. Volcanoes commonly exhibit variations in eruptive style similar to those seen at Aniakchak. Previous studies at other volcanoes have attributed changes in the nature of an eruption to such factors as the compositional variation in magma, magma flux, the presence of external water, conduit and surface morphology, and volatile degassing behavior. The differences in style of the 1931 Aniakchak eruption are the result of variations in magma flux, the presence or absence of external water, and differences in magma composition. Evidence of a zoned magma chamber indicates that properties associated with the magma chamber might have indirectly influenced the eruption style at Aniakchak.
    • 60,000 year climate and vegetation history of Southeast Alaska

      Wilcox, Paul S.; Fowell, Sarah; Bigelow, Nancy; Mann, Daniel; Dorale, Jeffrey (2017-08)
      Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until ~14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between ~13,000 and ~11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 ± 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on δ¹³C and δ¹⁸O values spanning the interval from ~60,000 yr. BP to ~11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative δ¹³C values are attributed to predominance of angiosperms in the vegetation above the cave at ~22,000 yr. BP and between ~53,000 and ~46,000 yr. BP while more positive δ¹³C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data suggest limited or no ice cover above El Capitan Cave for the duration of the record, possibly indicating that this region was a nunatak during glacial periods.
    • An 8 ka record of vegetation cover, fire history and moisture availability from North-Central Mongolia

      Molhoek, Emily (2007-05)
      Analysis of pollen, charcoal, and stable carbon and nitrogen isotopes ([delta]¹³C and [delta]¹⁵N) from a sediment core of Mongolian Lake Terhiyn-Tsagaan show increases in moisture availability coincident with mid- to late Holocene expansion of the Asian monsoon. The lake is freshwater and located in an intermontane depression on the flanks of the Hangai Range of north-central Mongolia. The site lies within the forest-steppe biome ~400 m below tree line. The low C:N of the sediments indicates that organic matter is primarily composed of autochthonous material. Artemisia and Chenopodiaceae pollen are indicators of dry steppe and semi-desert vegetation, whereas Poaceae pollen is more abundant in humid meadow-steppe or forest-steppe assemblages. An aridity index, calculated by dividing Artemisia + Chenopodiaceae by Poaceae pollen, is used to identify changes in moisture availability. High aridity indices and spikes of charcoal influx record relatively humid conditions at the site between 8.0 and 5.5 k years BP. Low charcoal influx rates and peak values of the aridity index between 4.5 and 4.0 k years BP correspond to a documented interval of drought in southern Asia and northern Africa attributed to a weak Asian monsoon. A decrease in charcoal influx since 7.5 k years BP combined with progressive increase in [delta]¹⁵N indicates increasing aridification from the mid-Holocene to nearly the present. Intervals of humidification at Lake Terhiyn-Tsagaan are thus synchronous with the waxing and waning of the Asian monsoon and out of phase with humid intervals recorded at Lake Telmen, approximately 250 km to the northwest. It is possible that the Terhiyn-Tsagaan drainage lies at the northern and/or western edge of the region that received precipitation from an expanded Holocene summer monsoon.
    • A comparative study of contrasting structural styles in the range-front region of the northeastern Arctic National Wildlife Refuge, northeastern Brooks Range, Alaska

      Hanks, Catherine Leigh; Stone, David B.; Crowder, R. Keith; Keskinen, Mary J.; Watts, Keith W.; Ave Lallemant, Hans G.; Mull, C. G. (1991)
      The range front of the northeastern Brooks Range in the Arctic National Wildlife Refuge (ANWR) is defined by anticlinoria cored by a 'basement' complex of weakly metamorphosed sedimentary, volcanic and intrusive rocks. These anticlinoria are interpreted to reflect horses in a northward-propagating regional duplex between a floor thrust at depth in the 'basement' complex and a roof thrust near the base of the cover sequence. Lateral variations in the geometry of these range-front anticlinoria reflect changes in lithology and deformational style of both the 'basement' and its cover. Two distinct structural geometries are displayed along the range front of northeastern ANWR. To the east, the large range-front anticlinorium is interpreted to reflect multiple horses of Cenozoic age within the stratified, slightly metamorphosed sedimentary and volcanic rocks of the pre-Mississippian 'basement'. During Cenozoic thrusting, these mechanically heterogeneous rocks deformed primarily via thrusting and related folding with minor penetrative strain. The Mississippian and younger cover sequence shortened via both thrust duplication and detachment folding above a detachment in the Mississippian Kayak Shale. In contrast, to the west the pre-Mississippian rocks consist primarily of the mechanically homogeneous Devonian Okpilak batholith. The batholith was transported northward during Cenozoic thrusting and now forms a major topographic and structural high near the range front. The batholith probably shortened during thrusting as a homogeneous mass via penetrative strain. Because the Kayak Shale is thin to absent in the vicinity of the batholith, Mississippian and younger rocks remained attached to the batholith and shortened via penetrative strain and minor imbrication. These two range-front areas form the central portion of two regional transects through northeastern ANWR. General area-balanced models for both transects suggest that the amount of total shortening is governed by the structural topography and the geometry of the basal detachment surface. While the structural topography of northeastern ANWR is reasonably well-constrained, the geometry of the basal detachment is not. Given a range in reasonable basal detachment geometries, shortening in both transects ranges from 16% to 61%. Detailed balanced cross sections based on subsurface and surface geologic data yield 46-48% shortening for both transects.
    • A Concept To Assess The Performance Of A Permafrost Model Run Fully Coupled With A Climate Model

      Paimazumder, Debasish (2009)
      Soil-temperatures simulated by the fully coupled Community Climate System Model LCM version 3.0 (CCSM3) are evaluated using three gridded Russian soil-temperature climatologies (1951-1980, 1961-1990, and 1971-2000) to assess the performance of permafrost and/or soil simulations. CCSM3 captures the annual phase of the soil-temperature cycle well, but not the amplitude. It provides slightly too high (low) soil-temperatures in winter (summer) with a better performance in summer than winter. In winter, soil-temperature biases reach up to 6 K. Simulated near-surface air temperatures agree well with the near-surface air temperatures from reanalysis data. Discrepancies in CCSM3-simulated near-surface air temperatures significantly correlate with discrepancies in CCSM3-simulated soil-temperatures, i.e. contribute to discrepancy in soil-temperature simulation. Evaluation of cloud-fraction by means of the International Satellite Cloud Climatology project data reveals that errors in simulated cloud fraction explain some of the soil-temperature discrepancies in summer. Evaluation by means of the Global Precipitation Climatology Centre data identifies inaccurately-simulated precipitation as a contributor to underestimating summer soil-temperatures. Comparison to snow-depth observations shows that overestimating snow-depth leads to winter soil-temperature overestimation. Sensitivity studies reveal that uncertainty in mineral-soil composition notably contributes to discrepancies between CCSM3-simulated and observed soil-temperature climatology while differences between the assumed vegetation in CCSM3 and the actual vegetation in nature marginally contribute to the discrepancies in soil-temperature. Out of the 6 K bias in CCSM3 soil-temperature simulation, about 2.5 K of the bias may result from the incorrect simulation of the observed forcing and about 2 K of the bias may be explained by uncertainties due network density in winter. This means that about 1.5 K winter-bias may result from measurement errors and/or model deficiencies. Overall, the performance of a permafrost/soil model fully coupled with a climate model depends partly on the permafrost/soil model itself, the accuracy of the forcing data and design of observational network.
    • A Mechanism For Current Sheet Thinning In The Growth Phase Of Magnetospheric Substorms

      Hall, Fred, Iv; Otto, Antonius (2006)
      The thinning of the near-Earth current sheet during the growth phase of magnetospheric substorms is a fundamental problem of space physics. It is a characteristic of the slow, steady evolution of the magnetosphere during the growth phase, during which the bulk kinetic energy of the solar wind is transformed into and stored as magnetic field energy in the magnetotail lobes. The thin near-Earth current sheet at the end of the growth phase provides the conditions for the onset of the expansion phase, and is fundamentally important to understand the physical mechanism for the onset of the rapid evolution during which the stored energy is released. I propose that current sheet thinning occurs because of the evacuation of a 'magnetic flux reservoir' in the near-Earth magnetotail by convection to replace magnetic flux that is eroded on the dayside by magnetic reconnection. My hypothesis is able to predict basic properties of current sheet thinning, such as the location, temporal evolution, and dynamics of this process. I examined this new mechanism both conceptually and quantitatively. My conceptual considerations enabled the prediction of the location and duration of current sheet thinning. This location is largely independent of the detailed state of the magnetosphere. I examined this mechanism quantitatively through the use of a three-dimensional ideal MHD simulation. I was able to predict the duration of the growth phase by considering the time needed to deplete our proposed 'magnetic flux reservoir.' The simulation demonstrates the global increase of the current density in this reservoir, despite the removal of magnetic flux---which one would otherwise expect to lead to a decrease of current---as well as even greater local amplifications of the current density. The simulation results are even more significant because the model does not include other effects of the real magnetosphere that contribute to a further increase of the tail current. The increase in current density and thinning are found to be consistent with the amount of flux removed from the system. In addition, I have found a new explanation for the very thin bifurcated current sheets that have been reported in recent publications.
    • A self-consistent time varying auroral model

      Min, Qilong; Rees, M. H.; Kan, J. R.; Lummerzheim, D.; Piacenza, R.; Stamnes, K. (1993)
      A time dependent model of auroral processes has been developed by self-consistently solving the electron transport equation, the ion continuity equations and the electron and ion energy equations. It is used to study the response of ionospheric and atmospheric properties in regions subjected to electron bombardment. The time history of precipitation events is computed for a variety of electron spectral energy distributions and flux magnitudes. Examples of daytime and night-time aurorae are presented. Precipitating energetic auroral electrons heat the ambient electrons and ions as well as enhancing the ionization rate which increases the ion concentration. The consequences of electric field acceleration and an inhomogeneous magnetic field in auroral electron transport in the topside ionosphere are investigated. Substantial perturbations of the low energy portion of the electron flux are produced: An upward directed electric field accelerates the downward directed flux of low energy secondary electrons and decelerates the upward directed component. Above about 400 km the inhomogeneous magnetic field produces anisotropies in the angular distribution of the electron flux. The effects of the perturbed energy distributions on auroral spectral emission features and on the electron temperature are noted. The response of the Hall and Pederson conductivities to auroral electron precipitation is discussed as a function of the characteristic energy of the spectral distribution.
    • A simulation study of magnetic reconnection processes at the dayside magnetopause

      Shi, Yong; Lee, L. C.; Swift, D. W.; Gosink, J.; Gatterdam, R.; Akasofu, S-I. (1989)
      In this thesis, the dayside reconnection processes are studied by using computer simulations. First, the global magnetic reconnection patterns at the dayside magnetopause are studied based on a two-dimensional incompressible magnetohydrodynamic (MHD) code. It is found that multiple X line reconnection may prevail at the dayside magnetopause when the magnetic Reynolds number is large ($>$200). The formation and subsequent poleward convection of magnetic islands are observed in the simulation. The Alfven Mach number of the solar wind, $M\sb{Asw}$, can also change the reconnection patterns. For a large $M\sb{Asw}$, reconnection tends to occur at the higher latitude region. Secondly, the structure of the dayside reconnection layer is studied by a two-dimensional compressible MHD simulation. In a highly asymmetric configuration typical of the dayside magnetopause, the pair of slow shocks bounding the reconnection layer in Petschek's symmetric model is found to be replaced by an intermediate shock on the magnetosheath side and a weak slow shock on the magnetospheric side. In addition, a mechanism for the enhancement of $B\sb y$, which is observed in the magnetopause current layer and magnetic flux tubes, is proposed.
    • A simulation study of three-dimensional magnetic reconnection

      Ma, Zhi-Wei; Lee, L. C.; Kan, J. R.; Shaw, G. E.; Smith, R. W.; Hawkins, J. G. (1994)
      The magnetic reconnection process plays an important role in the interaction between the solar wind and the magnetosphere. It leads to the transfer of energy from the solar wind into the magnetosphere. In this thesis, we study three-dimensional (3D) aspects of magnetic reconnection based on magnetohydrodynamic (MHD) simulations. First, we examine the magnetic field topology of magnetic flux ropes formed in multiple X line reconnection (MXR). It is found that the magnetic field topology depends on the relative extent and location of the two neighboring X lines. Magnetic flux ropes with either smooth or frayed ends are obtained in our simulations. For magnetic flux ropes with smooth ends, a major amount of magnetic flux is connected at each end to only one side of magnetopause. Second, the evolution of the core magnetic field in the magnetic flux tube is studied for various magnetic reconnection processes. We find that the 3D cases always lead to a larger enhancement of core field than the corresponding 2D cases since plasma can be squeezed out of the flux tube in the third direction. The MXR process gives rise to a larger increase of the core field than the single X line reconnection process. The core magnetic field can be enhanced to three times the ambient magnetic field strength in the 3D MXR process. Finally, we examine the generation and propagation of Alfven waves and field-aligned currents in the 3D reconnection process. For cases with a zero guide field, it is found that a large portion of the field-aligned currents ($\sim$40%) is located in the closed field line region. Both the pressure gradient term and inertia term contribute to the generation of field-aligned currents. For cases with nonzero guide field, one sense of field-aligned currents is dominant due to the presence of the initial field-aligned current. In these cases, the inertia term makes a major contribution to the redistribution of field-aligned currents. The influence of the initial guide field on the longitudinal shift of the current reversal site is found to be consistent with observations.
    • A study of the link between cloud microphysics and climate change

      Hu, Yong-Xiang; Stamnes, Knut; Musgrave, David; Rees, Manfred; Shaw, Glenn E.; Tsay, Shee-Chee; Watkins, Brenton (1994)
      The climate related cloud radiative properties (fluxes and heating rates) are found to be determined by the second and the third moments of the cloud droplet size distribution. The detailed distribution of the cloud droplet size is unnecessary to obtain for climate purposes. An accurate parameterization of cloud optical properties suitable for climate models is developed. A new radiative-convective model has been developed and used for studying cloud-climate interactions. The energy balance at the Earth-atmosphere interface is treated in a self-consistent manner which avoids artificial tuning. The cloud radiative properties are accurately incorporated and are suitable for sensitivity studies of cloud-radiation-climate interactions. A sensitivity study of role of the cloud microphysical properties in the climate system is performed by studying the impact of cloud radiative forcing on the equilibrium state temperature. The cloud equivalent radius is found to be a very important variable in the climate system. A climate sensitivity study is performed to highlight the important role of the cloud absorption. An adjoint radiative transfer method is developed for use in the cloudy and aerosol-loaded atmospheres. The physical meaning of the adjoint radiative properties are discussed. The method is expected to be useful in climate modeling and remote sensing studies. A preliminary study of the atmospheric irreversibility is performed to elucidate the connection between cloud microphysical properties and the macrophysical direction of global climate. A variational principle which describes the macrophysical character of the climate system is established.
    • A study of the magnetosphere-ionosphere coupling processes

      Zhu, Lie; Kan, J. R. (1990)
      Magnetosphere-ionosphere (M-I) coupling processes are studied by using numerical modeling. An M-I coupling model of substorms on the ionospheric recombination time scale (tens of seconds) is developed. The model is two-dimensional (2-D) and time-dependent from which several signatures of substorms can be obtained and understood. The model is then extended to northward interplanetary magnetic field (IMF) conditions to study the effects of the M-I coupling on the high-latitude convection. Based on the model results, a mechanism for the origin of distorted two-cell ionospheric convection is proposed. The ionospheric and ground signatures of multiple field-aligned current sheets originating from dayside flux transfer events have been modeled. The interaction between Alfven waves and field aligned potential drops is studied by using a local model.
    • A temperature only formulation for ice sheets

      Gillispie, Lyman; Bueler, Edward; Allman, Elizabeth; Maxwell, David (2014-05)
      Temperature plays an important role in the dynamics of large flowing ice masses like glaciers and ice sheets. Because of this role many models for ice sheets model temperature in some form. One type of model for polythermal glaciers (glaciers which contain both ice below, and at the pressure-melting temperature) explicitly separates the ice into distinct cold and temperate regimes, and tracks the interface between them as a surface. Other models track the enthalpy (internal energy) across both domains, with temperature being a function of enthalpy. We present an alternative mathematical formulation for polythermal glaciers and ice-sheets, in the form of a variational inequality for the temperature field only. Using the calculus of variations, we establish some sufficient conditions under which our formulation is well-posed. We then present some numerical approximations of solutions obtained via the Finite Element Method.
    • A theoretical study of magnetosphere-ionosphere coupling processes

      Cao, Fei; Kan, J. R.; Akasofu, S-I.; Biswas, N.; Shaw, G.; Swift, D. (1991)
      Magnetosphere and ionosphere are coupled electrodynamically by waves, field-aligned currents and parallel electric fields. Several fundamental coupling processes are addressed in my thesis. It is shown that the Alfven wave is the dominant mode in transmitting field-aligned currents. Therefore, dynamic M-I coupling can be modeled by the Alfven wave bouncing between the ionosphere and the magnetospheric boundaries. The open magnetopause, separating the solar wind and the magnetosphere, behaves like a near perfect reflector to the Alfven wave because of the large solar wind inertia. At the plasma sheet, however, the reflection coefficient may extend over a wide range, depending on the location in the plasma sheet. As the Alfven wave propagates back and forth between the magnetosphere and ionosphere, the field-aligned current density increases dramatically at certain locations, especially near the head of the westward traveling surge, causing potential drops to develop along magnetic field lines. It is found that the existence of parallel potential drops can distort the global convection pattern and limit the upward field-aligned current. The magnetic reconnection at the dayside magnetopause is responsible for enhancing the convection in the magnetosphere, which subsequently propagates toward the ionosphere by the Alfven wave. The patchy and intermittent reconnection at the dayside magnetopause can be initiated by the 3-D tearing instability, leading to the isolated magnetic islands and X-line segments. The nonlinear evolution of tearing in terms of the magnetic island coalescence is also studied.
    • A theory of field-aligned current generation from the plasma sheet and the poleward expansion of aurora substorms

      Yamauchi, Masatoshi; Akasofu, Syun-Ichi (1990)
      This dissertation reports a study of the generation of field-aligned currents in the plasma sheet in terms of magnetosphere-ionosphere coupling. For the study, the plasma sheet and the ionosphere are treated as two-dimensional layers by height integration. In the magnetosphere between them, the Alfven wave transition time through this region is assumed to be zero. The ionospheric momentum is allowed to be transferred to the plasma sheet. Both linear analyses and numerical simulation are performed to study the field-aligned current generation. In the linear analysis, evolution from initial perturbations is studied. Zero order configurations are steady state without field-aligned currents. The field-aligned currents are treated as a perturbed quantity and linearly related with the other perturbed quantities. One result for the linear waves is that the magnetohydrodynamics (MHD) fast mode and Alfven mode are coupled through the ionospheric Hall current. The Hall current causes the dawn-dusk asymmetry: a westward-travelling wave is amplified on the region 1 current system, while an eastward-travelling wave is amplified elsewhere. The expansion phase of the magnetospheric substorm after the onset is numerically simulated on the near-earth plasma sheet. The inner edge of the plasma sheet is taken as the outflow boundary. As the initial condition, an enhanced earthward magnetospheric convection is assumed to cause a finite pressure increase at the inner edge of the plasma sheet. The numerical results are as follows. An MHD fast-mode wave is generated. It propagates tailward accompanied by the field-aligned currents. The wave propagation and the field-aligned currents account for the poleward expansion of the aurora and the region 1 field-aligned current during the expansion phase of the substorm. The region 1 field-aligned currents are linked with the dusk to dawn current on this wave, which is driven by the dynamo mechanism of the wave. The ionospheric Hall current causes asymmetry of the wave, and hence, of the field-aligned current distribution. This asymmetry accounts for the stronger field-aligned current in the premidnight sector.
    • Abundance and ecology of martens (Martes americana) in Interior Alaska

      Shults, Brad (2001-12)
      I studied marten (Martes americana) abundance and ecology in the Yukon-Charley Rivers National Preserve during 1991-1993. Using a multiple sample, mark-recapture estimator, I estimated marten densities to be 0.69, 0.41, and 0.45 martens/km² during each August for 1991-1993, respectively. Density estimates were derived with the boundary-strip method to address the edge effect inherent in live-trapping studies. During the study, marten density declined 43% between 1991 and 1992 and remained low during 1993. I hypothesize that a decline in primary prey (i.e., microtine rodents) and increased environmental stress (i.e., cold temperatures and snow cover) contributed significantly to the decline in marten abundance. Using carcassess provided by trappers, I documented that female martens had lower ovulation rates and overall fecundity during winter 1991-1992, and as a result of low recruitment during summer 1992, the number of martens harvested by trappers decreased 85% during the 1992-93 trapping season.
    • Acacia constricta gains novel benefits from ants while minimizing potential conflicts

      Nicklen, E. Fleur (2006-08)
      The sum of costs and benefits in an interspecific interaction determines whether the relationship is mutualistic, neutral, or antagonistic. We investigate novel benefits Acacia constricta may gain from ant visitors and how A. constricta may minimize potential costs of ant visitation. A. constricta attracts ants onto its foliage and encourages nesting at its base with extrafloral nectaries. Plants with basal nests have significantly greater soil nutrients and produce twice as many seeds as plants lacking basal nests (Wagner 1997). Along side these benefits, however, ants can interfere with plant reproduction. This study tests whether augmented soil nutrients increase A. constricta's defenses and ant attractants. We further test mechanisms A. constricta may have to reduce the potential costs of ants to reproduction. We found that increased soil nutrients elevated defense mechanisms in A. constricta and increased extrafloral nectary number, suggesting ants that provide plants with nutrients may indirectly increase plant defense as well as participate in a feed back cycle where ants increase soil nutrients allowing plants to increase ant attractants. In addition, plants have at least two mechanisms to keeps ants separated from flowers, minimizing ant costs to reproduction.
    • Acclimation and migration potential of a boreal forest tree, balsam poplar (Populus balsamifera L.) in a changing climate

      Robertson, Amanda L.; Olson, Mattew; Takebayashi, Naoki; Wolf, Diane E.; Chapin, Stuart F. III (2012-12)
      In the North American boreal forest, 21st century climate change is projected to result in longer growing seasons, increased forest productivity, and northward expansions or shifts in species ranges. These projected impacts are largely based on observations across natural temperature gradients, e.g., latitude or altitude, or correlations between current species' distributions and modern climate envelopes. These approaches, although valuable, do not consider biological capacities important in a species' ability to cope with novel environments through physiological or phenological acclimation. Within a single species, adaptation to local environments may cause some populations to respond differently to climate change than others. Acclimation (phenotypic plasticity) is often treated as a separate phenomenon from local adaptation, but the latter may determine the range of acclimation responses or thresholds. To more accurately predict how boreal tree species will respond to a directionally changing climate, it is necessary to experimentally examine the effects of warming on the growth and physiology of individual species and how those effects differ across a species' range. This research investigated how tree growth responses to increasing temperature are influenced by differences in adaptation and acclimation across the latitudinal range of the North American boreal forest tree, Populus balsamifera L. (balsam poplar). Warming experiments, both in the greenhouse and in the field, indicated that growth of balsam poplar trees from a broad latitudinal gradient responds positively to increased growing temperatures, with increases in height growth ranging from 27-69 % in response to 3-8 °C average warming. Genotypes from southern populations grew consistently taller in both field and greenhouse experiments. The field experiment enabled investigation into the effects of warming and source latitude on balsam poplar phenology; both experimentally warmed and southern individuals grew larger and exhibited longer growing seasons (more days of active growth). Lastly, I describe a theoretical/methodological framework for exploring the role of epigenetics in acclimation (plasticity) and adaptation to changing environments. The results from these experiments are integrated with information on adaptive gradients in balsam poplar to predict both the in situ responses of balsam poplar to increased temperatures, and the potential for northward range shifts in the species.
    • The acetylcholine binding protein of Lymnaea stagnalis as a biosensor and model for ligand gated ion channel proteins

      Harms-Smyth, Abraham Edward (2008-12)
      The structural similarity of the Acetylcholine Binding Protein (AChBP) from Lymnaea stagnalis to the extracellular ligand binding domain of Ligand Gated Ion Channel (LGIC) receptors suggests that the AChBP could be used to mimic cys-loop ligand-gated ion channel (LGIC) receptors. An LGIC mimic could be used as a sensor molecule in a range of biotechnology applications including high throughput drug screening as well as in vivo and in vitro sensing of biologically active compounds. It could also be used as a lead molecule for engineering novel proteins with binding characteristics similar to non-acetylcholine receptor LGIC's. The soluble AChBP is easily expressed and purified and can be produced in reasonably large amounts. This thesis explores the potential for using the AChBP and related proteins as biosensors by evaluating their action on three key medium and high throughput systems: Scintillation Proximity Assay (SPA), Surface Plasmon Resonance (SPR), and Microcantilevers (MC). As a preliminary step to developing a 5-HT₃R-ligand binding protein, by altering the ligand specificity of the AChBP, the interaction of 5-HT₃R ligands with the AChBP is also evaluated. The work presented in this thesis contributes to improved methods of drug design and testing, and to a better understanding of LGIC structure.