• Constraining the H₂O/CO₂ molar ratio, the volume fraction of exsolved volatiles, and the magma compressibility of the 2006 Augustine eruption, Alaska

      Wasser, Valerie; Lopez, Taryn; Izbekov, Pavel; Larsen, Jessica; Anderson, Kyle; Freymueller, Jeffrey (2019-08)
      Geodetic modeling of volcano deformation can be used to estimate the volume of magma presumed to be mobilized within a volcanic system. These geodetically modeled subsurface reservoir volume changes are commonly much smaller than simultaneous eruptive volumes, where the eruptive volume is estimated based on geological mapping of units, their thicknesses, and their densities. This discrepancy is thought to be at least partially due to magma compressibility, which describes the phenomena where the volume of a given mass of magma changes as pressure increases/decreases primarily due to the presence of highly compressible exsolved volatiles. In this study, I combine deformation, volcanic gas, and petrologic constraints acquired prior to and during the 2006 eruption of Augustine volcano, Alaska, to estimate the amount of exsolved volatiles present in the magma storage region prior to the eruption and calculate the resulting compressibility of the magma. By doing so, I am able to constrain the H₂O/CO₂ molar ratio of the syn-eruptive gas emissions to between 24 and 59, with my best estimate of 28. My results suggest that for the specific parameters of Augustine's magmatic system, including a pressure of 120-170 MPa, a temperature of 880 ± 13 °C, and 40 ± 2% phenocrysts by volume, an exsolved volatile phase of about 8.2 vol% and a magma compressibility of ~7.1 x 10⁻¹⁰ 1/Pa are required to explain the observed eruptive volume to deformation volume ratio equal to three. The exsolved volatile volume and magma compressibility values determined here agree with results of previous studies of volatile-rich volcanic systems. This study reiterates that magma compressibility is an important factor that must be considered when interpreting deformation data within volatile-saturated volcanic systems.
    • Constraints upon the history of Meridiani Planum, Mars using sub-kilometer crater counting

      Pitiss, Sharon Ellen; Sharpton, Virgil; Herrick, Robert; Dean, Ken; Christensen, Doug (2005-05)
      Analysis of a surface's crater population provides information to reconstruct the geologic history of a regional surface. Therefore, the population of sub-kilometer impact craters within Meridiani Planum, Mars has been assessed to constrain the nature and origin of unique hematite-rich deposits that occur in this region. Crater size-frequency distributions were compiled for 16,540 small craters in eleven images with varying hematite concentration. Results show that a complex crater obliteration process, probably aeolian activity, has operated continuously on the Meridiani region between 10 My and 3 Gy. More recently the surface process seems to have halted, possibly due to dune stabilization associated with a major climate shift. There is no evidence in the cratering record of an extensive, long-lived body of water that could have created the region's hematite deposits. While not required by the size-frequency distribution, some regional stripping and removal is permitted. In this case, the maximum erosional depth incurred in the last 3 Gy is limited to less than 50 meters. This is insufficient to have metamorphosed hematite as Lane et al. (2002) previously suggested. The size-frequency distributions suggest the hematite would have had to be emplaced very early in the history of Mars.
    • Contaminant Exposure And Associated Biological Responses In Southern Beaufort Sea Polar Bears

      Knott, Katrina K.; O'Hara, Todd; Miller, Debra; O'Brien, Diane; Hueffer, Karsten (2011)
      Concentrations of mercury (Hg) and polychlorinated biphenyls (PCBs) were examined in polar bear (Ursus marititnus) to assess variations among sex and age cohorts, and evaluate possible adverse impacts of combined toxicant exposures. Biomarkers of selenium (Se) status (whole blood and serum Se concentrations, glutathione peroxidase activity), and thyroid status (total and free concentrations of thyroxine and tri-iodothyronine) were examined in Southern Beaufort Sea (SBS) polar bears. Both Hg and PCBs tended to be greater in female than in male polar bears and likely related to the type and proportion of marine-based prey in their overall diet. Significant positive relationships between circulating concentrations of PCBs, specific blood lipids (e.g., triglycerides and free fatty acids) and reduced body condition scores suggest combined contaminant-environmental stressors for SBS polar bears. Polar bear milk contained detectable concentrations of both Hg and PCBs. Estimated tolerable daily intake levels for PCBs through milk consumption by cubs of the year (< 6 months of age) exceeded available toxicity thresholds and could indicate possible adverse consequences of contaminant exposure during critical stages of neonatal development. Significantly positive and negative associations between contaminants and biomarkers indicated a possible oxidative stress response and thyroid disruption in SBS polar bears. Definitive relationships between contaminants and these physiologically-based biomarkers, however, could not exclude natural variations and equally possible impacts of nutritional stress and changes in physiological status. Female and young polar bears are the cohorts of concern for chronic low-level exposure to chemical mixtures. These data provide a better understanding of the physiological interactions underlying toxicity, and the multiple environment-toxicant stressors projected for arctic species with changes in climate.
    • Contrasting diet, growth, and energy provisioning in loons breeding sympatrically in the Arctic

      Rizzolo, Daniel J.; Lindberg, Mark; Schmutz, Joel; Springer, Alan; Hundertmark, Kris (2017-05)
      Red- throated (Gavia stellata) and Pacific (G. pacifica) loons breed throughout Arctic Alaska, often on adjacent lakes. Despite having similar life histories and distributions, these species have contrasting population trends in Alaska. Red-throated Loon populations have fluctuated dramatically over the past 3 decades, while the population trend of Pacific Loons has remained stable. These species-specific, population-level differences may be related to the foraging behaviors of breeding adults: Red-throated Loons feed on marine fishes using central place foraging behavior, while Pacific Loons feed primarily on freshwater prey captured from their breeding lakes. In this dissertation, I examined how differences in diet composition during the breeding season were associated with individual fitness parameters, namely adult body condition, chick growth performance, and breeding success. I used results from this research to address the hypothesis that interspecific differences in foraging behaviors contribute to the contrasting population dynamics of Pacific and Red-throated Loons breeding in Alaska. Using stable isotopes and fatty acid biotracers of diet, I found that the diet of breeding Pacific Loons was composed of a mix of freshwater and marine prey, and that variation in diet composition was related to the size of the breeding lake. Pacific Loons nesting on small lakes consumed more marine prey, suggesting that small lakes were not profitable foraging habitat, but their use for nesting was enabled by the close proximity of marine foraging habitat. In contrast, Red-throated Loons nested on very small lakes and ate a diversity of marine fishes. Despite differences in diet, both species had similar body condition during late-incubation, indicating that their diets met adult energy requirements, and adults maintained similar lipid reserves despite differences in foraging behavior. I found that Red-throated Loon chicks grew rapidly, yet were only 66% of adult body mass when they departed their natal lakes for the sea at fledging. This pattern of chick growth reduced the length of the postnatal period, and, consequently, the amount of time adults had to fly to marine habitat to capture fish for their chicks. Red-throated Loons provisioned their chicks with sufficient energy to support high growth rates. Other loon species which do not fly to the sea to capture fish for their chicks, like the Pacific Loon, likely do not face similar selection pressure for reduced parental energy investment through rapid chick growth. In Red-throated Loons, the total energy demands of chicks over the postnatal period were reduced at the expense of increased daily energy demands during the period of rapid growth. Given this pattern of chick growth, variation in the availability of high-energy content prey exerts a strong influence on breeding success. Pacific Loons provisioned their chicks mostly freshwater invertebrates with low-lipid content. Consequently, Pacific Loon brood provisioning rates were much higher than those of Red-throated Loons, which provisioned their chicks large-bodied marine fishes. Brood-rearing Pacific Loons commonly departed their breeding lakes for marine habitat, presumably to forage for themselves; however, parents rarely fed their chicks marine fishes, suggesting that central place foraging was not an energetically profitable provisioning behavior for larger-bodied Pacific Loons. Reproductive success over 3 years was higher in Red-throated Loons than Pacific Loons due to higher chick survival rates. Estimates of maximum energy provisioning rates for broods demonstrated that the provisioning rates and diet composition of Red-throated Loons could more easily meet peak brood energy requirements than the provisioning rates and diet composition of Pacific Loons. Thus, lower survival of Pacific Loon chicks was associated with lower maximum energy provisioning rates. The use of both freshwater and marine prey may insulate Pacific Loons from changes in either foraging habitat. Further, Arctic lakes provide a reliable source of invertebrate prey for chicks, but a diet of invertebrates may limit chick production rates because of their small size and low lipid content. Although meeting maximum brood energy requirement by provisioning freshwater invertebrates was difficult for Pacific Loons, particularly for adults rearing the maximum brood size of 2 chicks, chick production rates were sufficient to maintain a stable population trend. Red-throated Loons' specialization on marine prey strongly links their energy intake to the availability of marine fishes, which can vary suddenly and dramatically with ocean climate. Foraging conditions for Red-throated Loons in this study supported high chick growth rate and high chick production rates. Low chick growth rate and low chick production documented at other sites in Alaska indicate that Red-throated Loon breeding success is highly variable. Low chick production rates may contribute to Red-throated Loon population dynamics in Alaska if the availability of important forage fish species is low over multiple breeding seasons. Pacific Loons may be better suited than Red-throated Loons to adapt to the changing Arctic environment given the flexibility of their foraging behavior and diet. Because Pacific and Red-throated loon chicks in coastal tundra habitat rely on different types of prey, chick survival can function as a sensitive indicator of changes in lentic and marine habitats in the Arctic.
    • A contribution to the taxonomy and phylogeny of Oxytropis section arctobia (Fabaceae) in North America

      Meyers, Zachary J.; Ickert-Bond, Stefanie; Takebavashi, Naoki; Huttmann, Falk (2012-08)
      North American species of Oxytropis section Arctobia are reviewed through herbarium vouchers, scanning electron microscopy of seed coats, and phylogenetic analysis of sequence data to test the validity of the circumscription of section Arctobia as previously proposed. Morphologically, section Arctobia is characterized by few flowered inflorescences, few leaflets per leaf, and a mainly cushion-like habit. The micro-morphological data found considerable infraspecific variation in seed coat patterns. Sequence data from the nuclear TRPT, CNGC5, GA3ox1 genes and the plastid matK gene were used to infer phylogenetic relationships among members of section Arctobia. Analyses using maximum parsimony, maximum likelihood and Bayesian inference of these sequences resulted in a phylogeny that unambiguously supports the monophyly of Oxytropis. None of the infrageneric subdivisions of Oxytropis were supported by our genetic analyses. Section Arctobia was found nested within species of section Orobia, Glaeocephala, and Baicalia. However, TRPT and matK sequence data support Oxytropis arctobia as a distinct species, which has previously been included under Oxytropis nigrescens under the North American treatment. Here eight species are recognized in section Arctobia for North America and a lectotype of Oxytropis arctobia is selected based on herbarium specimens.
    • Control And Inverse Problems For One Dimensional Systems

      Mikhaylov, Victor S. (2009)
      The thesis is devoted to control and inverse problems (dynamical and spectral) for systems on graphs and on the half line. In the first part we study the boundary control problems for the wave, heat, and Schrodinger equations on a finite graph. We suppose that the graph is a tree (i.e., it does not contain cycles), and on each edge an equation is defined. The control is acting through the Dirichlet condition applied to all or all but one boundary vertices. The exact controllability in L2-classes of controls is proved and sharp estimates of the time of controllability are obtained for the wave equation. The null controllability for the heat equation and exact controllability for the Schrodinger equation in arbitrary time interval are obtained. In the second part we consider the in-plane motion of elastic strings on a tree-like network, observed from the 'leaves.' We investigate the inverse problem of recovering not only the physical properties, i.e. the 'optical lengths' of each string, but also the topology of the tree which is represented by the edge degrees and the angles between branching edges. It is shown that under generic assumptions the inverse problem can be solved by applying measurements at all leaves, the root of the tree being fixed. In the third part of the thesis we consider Inverse dynamical and spectral problems for the Schrodinger operator on the half line. Using the connection between dynamical (Boundary Control method) and spectral approaches (due to Krein, Gelfand-Levitan, Simon and Remling), we improved the result on the representation of so-called A---amplitude and derive the "local" version of the classical Gelfand-Levitan equations.
    • Control Theoretic Approach To Sampling And Approximation Problems

      Bulanova, Anna S. (2009)
      We present applications of some methods of control theory to problems of signal processing and optimal quadrature problems. The following problems are considered: construction of sampling and interpolating sequences for multi-band signals; spectral estimation of signals modeled by a finite sum of exponentials modulated by polynomials; construction of optimal quadrature formulae for integrands determined by solutions of initial boundary value problems. A multi-band signal is a function whose Fourier transform is supported on a finite union of intervals. The approach used in Chapter I is based on connections between the sampling and interpolation problem and the problem of the controllability of a dynamical system. We prove that there exist infinitely many sampling and interpolating sequences for signals whose spectra are supported on a union of two disjoint intervals, and provide an algorithm for construction of such sequences. There exist numerous methods for solving the spectral estimation problem. In Chapter II we introduce a new approach to this problem based on the Boundary Control method, which uses the connection between inverse problems of mathematical physics and control theory for partial differential equations. Using samples of the signal at integer moments of time we construct a convolution operator regarded as an input-output map of a linear discrete dynamical system. This system can be identified, and the exponents and amplitudes of the signal can be found from the parameters of the system. We show that the coefficients of the signal can be recovered by solving a generalized eigenvalue problem as in the Matrix Pencil method. Our method allows to consider signals with polynomial amplitudes, and we obtain an exact formula for these amplitudes. In the third chapter we consider an optimal quadrature problem for solutions of initial boundary value problems. The problem of optimization of an error functional over the set of solutions and quadrature weights is a problem of optimal control of partial differential equations. We obtain estimates for the error in quadrature formulae and an optimality condition for quadrature weights.
    • Controls On Antimony And Arsenic Speciation Via Sorption And Redox Chemistry At The Clay Mineral - Water Interface In Natural And Laboratory Settings

      Ilgen, Anastasia Gennadyevna; Trainor, Thomas P. (2010)
      Adsorption and redox transformations of contaminants in soil and aqueous environments are often controlled by the available mineral substrates. Aluminosilicates and aluminum oxides are ubiquitous and can influence the speciation and, therefore, the transport and bio-availability of toxic elements such as arsenic (As) and antimony (Sb). It is important to understand the partitioning and redox reactions promoted by these substrates in order to understand and model the transport of As and Sb in soils and surface waters. This study provides a detailed investigation of the sorption and redox behavior of As and Sb in clay-rich natural and laboratory systems. Since Fe 3+ is often found substituting for Al3+ in clay mineral structures, we also investigated the role of structural Fe in redox transformations of As and Sb adsorbed at the clay surface in controlled laboratory experiments. In a natural system affected by the release of spent geothermal fluids (Mutnovsky geothermal fields, Kamchatka, Russia), As concentrations are elevated above background levels in the Falshivaia River water and sediments (< 65 microm size fraction). Arsenic from the geothermal source fluids is in the reduced As3+ form, and is oxidized to As5+ after mixing with river water. Both As3+ and As5+ are found in aqueous and adsorbed forms. Analysis of the extended x-ray absorption fine structure (EXAFS) spectra shows that sediment-phase arsenic is associated with both Al- and Fe-rich phases with a bi-dentate corner-sharing local geometry. A series of laboratory experiments were performed in order to investigate Sb adsorption by Al-rich mineral substrates at a macroscopic and molecular level. The EXAFS analysis of the experimental samples concluded that both Sb3+ and Sb5+ form inner-sphere sorption complexes on the surfaces of hydrous aluminum oxide (HAO), and the clay minerals kaolinite (KGa-1b) and nontronite (NAu-1). Primarily, bi-dentate corner-sharing with a minor amount of mono-dentate corner-sharing complexes were formed. The oxidation state of the clay structural Fe affects the adsorption capacity of nontronite; if the clay is partially reduced, the Sb5+ uptake is increased significantly. The long term dynamics of the As aqueous speciation in clay suspensions where reduced arsenic (As3+) was added initially is complex. A fast disappearance of As3+ due to oxidation to As 5+ was followed by a slow increase of aqueous As3+. This behavior is explained by two simultaneous reactions: fast oxidation of As3+ by structural Fe3+ (anaerobic) or Fe 3+ and dissolved O2 (aerobic) and the slow reduction of As5+ by dissolved Fe2+. The ability of the structural Fe in nontronite clay to promote oxidation of As3+/Sb 3+ was greatly affected by its oxidation state: if all structural Fe was in an oxidized Fe3+ form, no oxidation was observed; however, when ~ 20 % of structural Fe was reduced to Fe2+, the clay promoted the most extensive oxidation under both aerobic and anaerobic conditions. The structural Fe2+ is not able to reduce As 5+/Sb5+, but reduction was seen when aqueous Fe 2+ was present in the systems. These research findings indicate that As and Sb can be effectively immobilized by Al-rich phases, while the substrate nature and oxidation state of structural Fe, along with the presence of dissolved Fe2+, can greatly affect the fate and transport of As and Sb. The increase in Sb5+ uptake in response to reducing structural Fe, possible increase or decrease in uptake of As due to As5+ reduction by aqueous Fe 2+, or oxidation of As3+ by clay structural Fe 3+, is likely to take place in a natural clay-rich soil or aquifer environment in moderate to slightly reducing conditions.
    • Controls on ecosystem respiration of carbon dioxide across a boreal wetland gradient in Interior Alaska

      McConnell, Nicole A.; McGuire, A. David; Turetsky, Merritt R.; Harden, Jennifer W. (2012-08)
      Permafrost and organic soil layers are common to most wetlands in interior Alaska, where wetlands have functioned as important long-term soil carbon sinks. Boreal wetlands are diverse in both vegetation and nutrient cycling, ranging from nutrient-poor bogs to nutrient- and vascular-rich fens. The goals of my study were to quantify growing season ecosystem respiration (ER) along a gradient of vegetation and permafrost in a boreal wetland complex, and to evaluate the main abiotic and biotic variables that regulate CO₂ release from boreal soils. Highest ER and root respiration were observed at a sedge/forb community and lowest ER and root respiration were observed at a neighboring rich fen community, even though the two fens had similar estimates of root biomass and vascular green area. Root respiration also contributed approximately 40% to ER at both fens. These results support the conclusion that high soil moisture and low redox potential may be limiting both heterotrophic and autotrophic respiration at the rich fen. This study suggests that interactions among soil environmental variables are important drivers of ER. Also, vegetation and its response to soil environment determines contributions from aboveground (leaves and shoots) and belowground (roots and moss) components, which vary among wetland gradient communities.
    • Controls on microbial processing of dissolved organic matter in boreal forest streams

      Schmidt, Marie; Jones, Jay; Harms, Tamara; Guerard, Jennifer (2020-05)
      In the boreal forest, permafrost thaw is resulting in changes in vegetation and deepening of watershed flowpaths. Caribou-Poker Creeks Research Watershed contains sub-catchments underlain with varying permafrost extents (4-53% cover), providing the opportunity to study how permafrost extent affects water chemistry and nutrient cycling. I measured nitrogen (N), phosphorous (P), and carbon (C) processing ectoenzyme activity in the water column and sediment of headwater streams, and related ectoenzyme activity to nutrient and dissolved organic carbon (DOC) concentration. Additionally, I used nutrient diffusing substrata (NDS) to grow biofilms with enhanced inorganic N and P and labile C alone and in combination and measured ectoenzyme activity and respiration of biofilms in response to resource amendments. High P-processing enzyme activity across streams of the CPCRW indicated microbial P limitation. Respiration and organic matter processing enzymes of biofilms grown on NDS increased with labile C or labile C in combination with nutrient additions, implying that labile C limited or co-limited rates of DOM processing. Our results suggest that as climate warming and subsequent permafrost thaw alters terrestrial inputs of dissolved organic matter (DOM) and inorganic nutrients into streams, changes in inorganic P and labile C availability will control microbial processing of DOM.
    • Coseismic deformation from the 2002 Denali Fault earthquake: contributions from synthetic aperture radar speckle tracking

      Elliott, Julie (2005-08)
      The technique of speckle tracking can provide coseismic surface offsets for an earthquake in regions where other geodetic data are not available. These offsets can be used to map the surface deformation and create slip distribution models. This thesis uses speckle tracking to study the 2002 Mw7.9 Denali Fault earthquake, with emphasis on the central section of the rupture. The Denali Fault earthquake began with a thrust event on the Susitna Glacier fault before rupturing unilaterally west to east on the Denali and Totschunda faults with overwhelmingly right-lateral strike-slip motion. A slip distribution estimated from a combination of speckle tracking data from the central section of the rupture, GPS data, and geologic data displays highly variable slip, with four major patches of high slip along the Denali fault. Compared to the primarily GPS-derived model of Hreinsdóttir [2005], the combined model is better constrained along the central rupture and predicts slip values much closer to the geologic offset measurements. A significant releasing bend in the fault just west of the pipeline can be correlated to a patch of high slip and the second-largest pulse of moment release along the rupture, suggesting that fault geometry plays an important role in earthquake mechanics.
    • Coseismic Deformation Of The 2001 El Salvador And 2002 Denali Fault Earthquakes From Gps Geodetic Measurements

      Hreinsdottir, Sigrun; Freymueller, Jeffrey T. (2005)
      GPS geodetic measurements are used to study two major earthquakes, the 2001 MW 7.7 El Salvador and 2002 MW 7.9 Denali Fault earthquakes. The 2001 MW 7.7 earthquake was a normal fault event in the subducting Cocos plate offshore El Salvador. Coseismic displacements of up to 15 mm were measured at permanent GPS stations in Central America. The GPS data were used to constrain the location of and slip on the normal fault. One month later a MW 6.6 strike-slip earthquake occurred in the overriding Caribbean plate. Coulomb stress changes estimated from the M W 7.7 earthquake suggest that it triggered the MW 6.6 earthquake. Coseismic displacement from the MW 6.6 earthquake, about 40 mm at a GPS station in El Salvador, indicates that the earthquake triggered additional slip on a fault close to the GPS station. The MW 6.6 earthquake further changed the stress field in the overriding Caribbean plate, with triggered seismic activity occurring west and possibly also to the east of the rupture in the days to months following the earthquake. The MW 7.9 Denali Fault earthquake ruptured three faults in the interior of Alaska. It initiated with a thrust motion on the Susitna Glacier fault but then ruptured the Denali and Totschunda faults with predominantly right-lateral strike-slip motion unilaterally from west to east. GPS data measured in the two weeks following the earthquake suggest a complex coseismic rupture along the faults with two main regions of moment release along the Denali fault. A large amount of additional data were collected in the year following the earthquake which greatly improved the resolution on the fault, revealing more details of the slip distribution. We estimate a total moment release of 6.81 x 1020 Nm in the earthquake with a M W 7.2 thrust subevent on Susitna Glacier fault. The slip on the Denali fault is highly variable, with 4 main pulses of moment release. The largest moment pulse corresponds to a MW 7.5 subevent, about 40 km west of the Denali-Totschunda fault junction. We estimate relatively low and shallow slip on the Totschunda fault.
    • Coupling the effects of dissolved organic matter and nutrient Stoichiometry with nutrient uptake in boreal forest headwater streams

      Fjare, Dana; Jones, Jeremy; Harms, Tamara; Kielland, Knut (2015-08)
      Discontinuous permafrost affects the hydrology and distribution of vegetation in boreal forest watersheds, which in turn influence stream water chemistry. I investigated how loss of discontinuous permafrost with projected climate change might affect nutrient cycling in boreal forest headwater streams. I hypothesized that 1) the carbon, nitrogen, and phosphorus (C:N:P) ratio in dissolved organic matter (DOM) affects nutrient uptake due to stoichiometric constraints on autotrophic and heterotrophic nutrient assimilation, and 2) labile DOM affects nutrient uptake by increasing heterotrophic production. I tested my hypotheses using a series of instantaneous nutrient additions in nine headwater streams, with a factorial design manipulating both nutrient stoichiometry and DOM source. DOM was added as either acetate or leachate from birch leaves. Ambient nutrient uptake velocity (Vf-amb) was within the upper range of previously published literature values, ranging from 4.1-67.2 mm/min for N, 4.0-25.0 mm/min for P, and 4.2-34.5 mm/min for acetate. Uptake efficiency was similar for N and P added alone, in co-additions, and with DOM. Acetate and birch-DOM had similar effects on nutrient uptake, because both were sources of highly labile carbon. In 30-day laboratory bioavailability assays, birch and acetate-DOM exhibited ≥ 70% carbon loss. Vf-amb was in part explained by ambient stream chemistry, with Vf-amb for N weakly positively correlated with ambient P concentration, while Vf-amb for P and acetate was weakly negatively correlated with ambient N and ambient dissolved organic carbon, respectively. Consequently, inorganic nutrient availability may affect uptake of solutes as well as DOM lability. High demand for nutrients in boreal forest headwater streams suggests that uptake could increase concurrently with greater inorganic nutrient flux following a loss in permafrost extent.
    • Critical Parameters In Magmatic Degassing

      Mongrain, Joanna; Larsen, Jessica (2008)
      Decompression experiments conducted at pressures up to 200MPa and temperatures of 825�C-880�C on hydrated K-phonolite and rhyolite melts were used to explore the critical parameters controlling nucleation, exsolution and degassing behavior. Experiments on the low viscosity/surface tension K-Phonolite melt highlighted the role of melt properties. Although the sample porosities deviated below equilibrium values for pressures less than ~40MPa, the melt exsolved water in equilibrium over all the pressures and decompression rates studied. Melt shearing is proposed to have caused bubble deformation and alignment, lowering the porosity at which extensive permeability develops and significant degassing occurs compared to rhyolite. Experiments on a rhyolite melt decompressed slowly from 100 MPa and then held at 10 MPa for up to 900 s highlighted the critical parameters controlling the formation and stability of a highly vesicular magma: bubble number density, bubble size distribution and porosity. The porosity of the interconnected, highly vesicular network decreased during "Stage I" degassing and the bubble size distribution evolved from a unimodal population to include a population of much larger bubbles. During Stage II degassing, the network collapsed. Pre-collapse and collapse degassing rates were obtained and a coalescence-induced coalescence model proposed to explain the rapid destabilization. The ability of a melt to efficiently exsolve volatiles and the ease of bubble coalescence are both a function of the initial distribution of nucleated bubbles. The development of a new method for quantifying this distribution using spatial statistics will allow future researchers to explore the underlying controls on nucleation such as melt structure and the occurrence of a prior nucleation event. To investigate the critical parameters controlling shallow dike intrusion and therefore magmatic ascent rate, the fracture mechanics of intrusion into homogeneous and layered (weak sandstone/strong granite) particle models under lithostatic, compressive and extensional regimes were examined. Although the scale of the model intrusions were an order of magnitude greater than field observations, extensive microfracturing across the weaker layers, parallel dike jointing in the stronger layers and a length scale dependence to fracture toughness were observed suggesting that the use of a particle code is a promising approach to intrusion modeling.
    • Cross-seasonal effects on reproductive performance of Pacific black brant

      Schamber, Jason Lee (2001-12)
      We used re-sightings of Pacific Black Brant from San Quintin Bay, Ojo de Lieber Lagoon, and San Ignacio Lagoon, Baja California and Boundary Bay, British Columbia, to examine winter population structure, variation in structural size and the importance of winter location to individual reproductive performance at the Tutakoke River colony. Sexes of adults and juveniles were distributed equally among winter locations. Adult structural size and mean age were similar among winter locations. A higher proportion of juveniles over-wintered in San Quinton Bay and Ojo de Liebre Lagoon. Individuals wintering at Ojo de Liebre and San Ignacio lagoons were less likely to breed and initiated clutches later than those that wintered in Boundary Bay or San Quinton Bay. Maternal mass did not vary, although clutch size was slightly larger in individuals that wintered in southern areas. Variation in winter location and habitat quality could influence individual reproductive performance and population dynamics.
    • Crustal and upper mantle velocity structure in Alaska

      Searcy, Cheryl Kaye; Christensen, Douglas; Layer, Paul; Stringer, William; Kawasaki, Koji; Stone, David (1996)
      The crustal and upper-mantle velocity structure of Alaska testifies to a complex tectonic framework. Much of the structure and history of this framework remains to be conclusively determined. This thesis presents the results of three independent investigations of velocity structure in Alaska in an attempt to provide some insight into its tectonic development. The first study involved the analysis of receiver functions to determine velocity structure beneath College Station (COL), located in Fairbanks, Alaska. Receiver functions from several back azimuths facilitate a fairly detailed analysis of deep crustal velocity structure beneath COL, including an indication that Moho dips to the northeast. The second study also employed receiver function methods to investigate velocity structure for four temporary three-component seismic stations placed in the Brooks Range. Due to the short deployment of these stations in the Brooks Range only a rough estimate of crustal velocities were obtained. Nevertheless, crustal thickening beneath the Brooks range is clearly indicated by an increase in the depth to Moho. The final study undertaken was a three-dimensional tomographic P-wave velocity inversion for the subduction zone region of south central Alaska. Data for the tomographic inversion consisted of local and teleseismic ray paths. The resulting velocity perturbations indicate a positive velocity anomaly associated with the subducting Pacific plate. Furthermore, the tomographic images clarify physical characteristics of the subducting plate such as structure, thickness, and depth of penetration into the mantle.
    • Crustal Thickness Variation In South Central Alaska: Results From Broadband Experiment Across The Alaska Range

      Veenstra, Elizabeth (2009)
      The Broadband Experiment Across the Alaska Range (BEAAR) was a passive source seismic study in which 36 three-component broadband seismic stations were deployed over a period of 27 months to collect high quality data to study the Alaska Range and perhaps elucidate tectonic processes. The wavetrain of a teleseismic body wave may be interpreted in terms of reflection and transmission of waves converted at discontinuities. The recorded signal may be regarded as a convolution of the source-time function, the receiver function, and the instrument response. A receiver function is the contribution to the seismic waveform recorded at a single station due to the response of local crustal structure, and can be inverted for vertical velocity structure beneath the three-component broadband seismic station. Receiver function analyses reveal typical crust beneath the lowlands north of the Alaska Range is 26 km thick, while beneath the mountains typical crust is 35--45 km thick. Receiver function analysis of ~15,000 teleseismic waveforms recorded by BEAAR broadband seismometers provided over 100 crustal thickness data points. Similarity between crustal thicknesses determined from receiver function analysis and crustal thicknesses predicted from topography assuming Airy isostasy indicate the observed crustal root is sufficient to support the Alaska Range. North of the range, however, the crust is systematically thinner than predicted by simple Airy isostasy. A crustal density contrast of 4.6% across the Hines Creek Fault 2700 kgm-3 to the north and 2830 kgm-3 to the south, explains the observed difference between the crustal thicknesses predicted by simple Airy isostasy and the crustal thicknesses determined by receiver function analysis. Our results indicate that variations in both crustal thickness and density are required to explain the seismic and gravity data. Crustal thicknesses across the central Alaska Range suggest that these mountains are supported by a crustal root developed due to contractional thickening. Crustal thickness data reveal differences in terrane thickness: a thin Yukon-Tanana terrane north of the Hines Creek fault and thicker Kahiltna/Wrangellia terranes to the south. Finally, the pattern of thin crust to the north and thicker crust to the south appears to be modified by late Cenozoic structures such as the Denali fault, with contractional thickening in the Alaska Range, including areas north of the Hines Creek fault in the northern foothills fold and thrust belt. BEAAR crustal thickness data suggest that major faults extend to the base of the crust.
    • Culturability, Temporal Change, Phylogenetic Analysis, And Yield Of Bacterial Communities In A Subarctic Lake: Harding Lake

      Zhao, Xiaoming; Button, Don (2005)
      Heterotrophic bacteria, adapted to small concentrations of substrate, are a main component of the microbial flywheel. However, understandings of their activity, isolation, genetics, and nutrition are restricted to the large, easily isolated and culturable bacteria. By using the dilution culture method, apparent culturabilities could approach 10% in unamended lake water and were inversely proportional to the number of cells inoculated from mixed species in a natural environment from Harding Lake. Substrate additions could not improve bacterial culturability in the dilution cultures. Comparative sequence analyses of 16S rDNA genes showed that all bacterial species have similar lengths in the phylogenetic tree, suggesting similar evolution rates. These indicated close relationships among the six bacterial divisions: alpha-proteobacteria, beta-proteobacteria, gamma-proteobacteria, cytophaga/flexibacter/bacteriodes, acidobacteria, and cyanobacteria. Possible reasons include that metabolic enzymes of these bacteria were modified to adapt to low temperatures from tropical temperatures in arctic areas at the same time. These findings may provide insight into the recent evolution of the bacteria in near polar freshwater. Moreover, a high abundance of alpha-proteobacteria and gamma-proteobacteria was found in Harding Lake, suggesting high growth rates of these bacteria in the freshwater region. This is consistent with a rapid continuous shift in the distribution of dominant species observed in Harding Lake, according to the TRFLP, DGGE, and flow cytometry data. Our results also suggested that input of dissolved organic matter derived from terrestrial plants and soils, introduction of terrestrial bacteria, and bacteria themselves led to the bacterial species shifts associated with the seasonal change. Bacterial growth yield is used to measure this carbon conversion efficiency. However, bacterial growth yields have been seriously underestimated in previous studies. Our in situ values for bacterial growth yield from an amino acid mix were actually closer to 50% and 70% in active systems by using a modified, sensitive and accurate method and increased with the increase of temperature between 1�C and 6�C.
    • Current state of Alaska's glaciers and evolution of Black Rapids Glacier constrained by observations and modeling

      Kienholz, Christian; Hock, Regine; Arendt, Anthony; Bliss, Andrew; Braun, Matthias; Meyer, Franz; Truffer, Martin (2016-12)
      Glaciological studies rely on a wide range of input data, the most basic of which, accurate glacier extents, were not available on an Alaska wide scale prior to this work. We thus compiled a glacier database for Alaska and neighboring Canada using multi-sensor satellite data from 2000 to 2011. The inventory yielded a glacierized area of 86,720 km², which corresponds to ~12% of the global glacierized area outside the ice sheets. For each of the ~27,100 glaciers, we derived outlines and 51 variables, including centerline lengths, outline types, and debris cover, which provide key input for observational and modeling studies across Alaska. Expanding on this large-scale observational snapshot, we conducted two case studies on Black Rapids Glacier, Eastern Alaska Range, to assess its evolution during the late 20th and 21st centuries. Black Rapids Glacier, 250 km² in area, was chosen given its surge-type dynamics and proximity to critical infrastructure. Remotely sensed and in-situ elevation observations over the 1980--2001--2010 period indicated strong mass loss of Black Rapids Glacier (~0.5 m w.e. a⁻¹), with higher thinning rates over the 2001--2010 (~0.65 m w.e. a⁻¹) than the 1980--2001 period (~0.4 m w.e. a⁻¹). A coupled surface mass balance-glacier dynamics model, driven by reanalysis climate data, reproduced the glacier shrinkage. It identified the increasingly negative summer balances, a consequence of the warming atmosphere, as the main driver for the negative mass balance trend. Elevation observations in Black Rapids' surge reservoir suggested a surge was not imminent at the time of the analysis due to the lack of ice thickening. Re-initiation of sufficient elevation growth in the surge reservoir would require more favorable surface mass balances, as observed in the early 1980s. Compared to nearby Gulkana Glacier (a USGS benchmark glacier), the observed specific mass losses at Black Rapids Glacier were less pronounced, ~0.4 vs. 0.5 m w.e. a⁻¹ (1980--2001) and ~0.65 vs. 0.95 m w.e. a⁻¹ (2001--2010). The larger difference between the two glaciers' mass balances over the 2001--2010 period was partly caused by rockslide debris deposited on Black Rapids Glacier in 2002. This ~4.5 m thick debris layer, spread across 11.7 km² of Black Rapids lower ablation area, was modeled to suppress Black Rapids' glacier wide mass loss by ~20%. Modeling Black Rapids' evolution until 2100 suggested sustained glacier retreat, even under a repeated constant climate scenario, with ~225 km² of area remaining in 2100. Using a warming scenario (RCP 8.5), the modeled retreat was strongly accelerated with only ~50 km² of glacier area left in 2100. Given its thick, low-slope valley portion, Black Rapids Glacier is very susceptible to climate change. Its neighboring glaciers in the Eastern Alaska Range have similar properties, suggesting region wide glacier retreat in the future. To constrain this further, the Black Rapids case studies should be extended to the regional scale, a step now facilitated by the new Alaska wide glacier database.
    • Cytogenetics and sex determination in collared lemmings

      Jarrell, Gordon Hamilton; Shields, Gerald F. (1989)
      Collared lemmings (Dicrostonyx groenlandicus rubricatus) from northeastern Alaska were found to have sex chromosomes that differ from those of their Siberian congeners, because of fusion to a particular pair of autosomes. But, as in Siberian lemmings, breeding experiments showed that sex determination involves an X-linked "male-repressor," which causes carriers to develop as fertile females, despite the presence of a Y chromosome. Genotypic frequencies in offspring are consistent with Mendelian expectations of such a system, hence natal sex ratios normally favor females. X-linkage of the male-repressor in Siberia and in Alaska indicates that the gene is probably located on the "original" arms of the X chromosome rather than on the fused autosomal arms, which differ on the two continents. One consequence of the autosomal fusion to the sex chromosomes is that deleterious recessive alleles on the autosome fused to the X chromosome are more resistant to selection than at truly autosomal loci. Another consequence is that, because males are heterozygous for loci fused to the sex chromosomes, they are more resistant to inbreeding depression than XX females. One inbred line produced a natal sex ratio of 67% males. The male-bias probably resulted from loss of the male-repressor and from a lethal carried on the formerly autosomal arm of the X chromosome. As inbreeding coefficients approached 0.3, the lethal would have been homozygous in half of the homogametic (female) zygotes. This phenomenon may explain the excess of males and XY females observed in earlier work. Also, if under the natural mating system, inbreeding depression limits fitness, then fusions of autosomal chromatin to the heterochromosomes could be an adaptation to reduce inbreeding depression in heterogametic individuals. Some other genetic features of collared lemmings do suggest endogamy. Female-biased sex ratios can evolve when mating occurs between neighboring individuals who are more related than if mating occurred randomly. Two proposed sources of such "viscous" gene flow in lemmings are cyclical changes in population density and mosaic habitat. Alternatively, could climate may favor winter aggregation and inhibit the dispersal of winter-born offspring, which would mature and mate with close relatives; dispersal and outbreeding would occur in summer. Thus, inbreeding would be seasonal rather than density-dependent and it is unnecessary to suppose discontinuous habitat.