• Rabies Virus In Arctic Fox (Vulpes Lagopus): A Study Of Pantropic Distribution

      Gildehaus, Lori A.; Runstadler, Jonathan (2010)
      Rabies is endemic in Arctic foxes, in Alaska and other Arctic regions and cold temperatures may preserve the virus in Arctic climates in infected animal carcasses. These frozen carcasses may provide a source of infection throughout winters and thereby propagate the rabies virus within animal populations in the Arctic. It was hypothesized that rabies virus antigen is present in the soft tissues of naturally infected Arctic foxes, Vulpes lagopus. Using a direct rapid immunohistochemistry test (DRIT) and a fluorescent antibody test (FAT), thirteen organ tissues from twelve naturally infected and three experimentally infected Arctic foxes were tested. All tissues, except testes, tested positive for rabies virus antigen by the DRIT, the FAT, or both in at least one fox. Although the DRIT detected rabies virus antigen in non-neuronal tissues, it did not detect antigen in as many non-neuronal tissues as the FAT. Spleen and stomach tissues had the highest rate of rabies virus detection by the FAT and using a combination of non-neuronal tissues would be the best substitute for brain if brain were unavailable.
    • Radar studies of turbulence and lidar studies of the nickel layer in the Arctic mesosphere

      Li, Jintai; Collins, Richard L.; Simpson, William R.; Newman, David E. (2016-05)
      This thesis presents studies of the Arctic middle atmosphere using Incoherent Scatter Radar (ISR) and resonance lidar at Poker Flat Research Range (PFRR), Chatanika, Alaska. The Poker Flat Incoherent Scatter Radar (PFISR) provides measurements of mesospheric turbulence and the resonance lidar provides measurements of mesospheric nickel layer. We develop retrieval and analysis techniques to determine the characteristics of the turbulence and the nickel layer. We present measurements of mesospheric turbulence with PFISR on 23 April 2008 and 18 February 2013. We characterize mesospheric turbulence in terms of the energy dissipation rate as a function of altitude and time on these days. We present an extensive analysis of the radar measurements to show that the use of high quality PFISR data and an accurate characterization of the geophysical conditions are essential to achieve accurate turbulent measurements. We find that the retrieved values of the energy dissipation rate vary significantly based on how the data is selected. We present measurements of mesospheric nickel layer with resonance lidar on the night of 27-28 November 2012 and 20-21 December 2012. We characterize the mesospheric nickel layer in terms of the nickel concentration as a function of altitude on these days. We find that our nickel concentrations are significantly higher than expected from studies of meteors. We present an extensive analysis of the lidar measurements to show that these measurements of unexpectedly high values of the nickel concentrations are accurate and not biased by the lidar measurements.
    • Radial and azimuthal dynamics of the io plasma torus

      Copper, Matthew; Delamere, Peter; Ng, Chung-Sang; Otto, Antonius (2015-05)
      The moon Io orbits Jupiter emitting neutral particles from its volcanic surface. This emission is ionized and forms the Io plasma torus around Jupiter. The variation of conditions at Io and Jupiter lead to variations in the content of the plasma in the torus. Volcanoes on Io's surface erupt and change the rate of neutral input. Hot electrons (30-100 eV), whose abundances vary in azimuth, create highly ionized species. Radial variation in subcorotation velocities, velocities less than than that of the motion of the dipole magnetic field, creates shears while maintaining coherent radial structure in the torus. Poorly understood changes in plasma density circulate through the torus creating the anomalous System IV behavior that has a period slightly longer than the rotation of Jupiter's magnetic field. This thesis summarizes the research that has produced a two-dimensional physical chemistry model, tested several existing theories about subcorotation velocities, System IV variation, and hot electrons, and adopted new methods of Io plasma torus analysis. In an attempt to understand important dynamics, the thesis modeled differing scenarios such as an initialized two-peak structure, a subcorotation profile dictated by mass loading and ionospheric conductivity, and a critical combination of two populations of hot electrons that accurately mimics the observed System IV phenomenon. This model was also used to solve the inverse problem of determining the best fit for the model parameters, neutral source input rate and radial transport rate, using observations of density, temperature, and composition. In addition the thesis shows the need for multi-dimensional modeling and the results from its groundbreaking two-dimensional model.
    • Radiation transport in cloudy and aerosol loaded atmospheres

      Kylling, Arve; Stamnes, Knut; Shaw, Glenn E.; Weeks, Wilford W.; Rees, Manfred H.; Smith, Roger W. (1992)
      The equation for radiation transport in vertical inhomogeneous absorbing, scattering, and emitting atmospheres is derived from first principles. It is cast in a form amenable to solution, and solved using the discrete ordinate method. Based on the discrete ordinate solution a new computationally efficient and stable two-stream algorithm which accounts for spherical geometry is developed. The absorption and scattering properties of atmospheric molecules and particulate matter is discussed. The absorption cross sections of the principal absorbers in the atmosphere, H$\sb2$O, CO$\sb2$ and O$\sb3,$ vary erratically and rapidly with wavelength. To account for this variation, the correlated-k distribution method is employed to simplify the integration over wavelength necessary for calculation of warming/cooling rates. The radiation model, utilizing appropriate absorption and scattering cross sections, is compared with ultraviolet radiation measurements. The comparison suggests that further experiments are required. Ultraviolet (UV) and photosynthetically active radiation (PAR) is computed for high and low latitudes for clear and cloudy skies under different ozone concentrations. An ozone depletion increases UV-B radiation detrimental to life. Water clouds diminish UV-B, UV-A and PAR for low surface albedos and increase them for high albedos. The relative amount of harmful UV-B increases on overcast days. The daily radiation doses exhibit small monthly variations at low latitudes but vary by a factor of 3 at high latitudes. Photodissociation and warming/cooling rates are calculated for clear skies, aerosol loaded atmospheres, and atmospheres with cirrus and water clouds. After major volcanic explosions aerosols change O$\sb3$ and NO$\sb2$ photodissociation rates by 20%. Both aged aerosols and cirrus clouds have little effect on photodissociation rates. Water clouds increase $(\sim$100%) photodissociation rates that are sensitive to visible radiation above the cloud. Solar warming rates vary by 50% in the stratosphere due to changing surface albedo. Water clouds have a similar effect. The net effect of cirrus clouds is to warm the troposphere and the stratosphere. Only extreme volcanic aerosol loadings affect the terrestrial warming rate, causing warming below the aerosol layer and cooling above it. Aerosols give increased solar warming above the aerosol layer and cooling below it.
    • Radiation transport in the atmosphere - sea ice - ocean system

      Jin, Zhonghai; Stamnes, Knut; Lynch, Amanda; Rees, Manfred H.; Shaw, Glenn E.; Tsay, Si-Chee; Weeks, Wilford F. (1995)
      A comprehensive radiative transfer model for the coupled atmosphere-sea ice-ocean system has been developed. The theoretical work required for constructing such a coupled model is described first. This work extends the discrete ordinate method, which has been proven to be effective in studies of radiative transfer in the atmosphere, to solve the radiative transfer problem pertaining to a system consisting of two strata with different indices of refraction, such as the atmosphere-ocean system and the atmosphere-sea ice-ocean system. The relevant changes (as compared to the standard problem with constant index of refraction throughout the medium) in formulation and solution of the radiative transfer equation, including the proper application of interface and boundary conditions, are presented. This solution is then applied to the atmosphere-sea ice-ocean system to study the solar energy balance in this coupled system. The input parameters required by the model are observable physical properties (e.g., the profiles of temperature and gas concentrations in the atmosphere, and the profiles of temperature, density, and salinity in the ice). The atmosphere, sea ice and ocean are each divided into a sufficient number of layers in the vertical to adequately resolve changes in their optical properties. This model rigorously accounts for the multiple scattering and absorption by atmospheric molecules, clouds, snow and sea water, as well as inclusions in the sea ice, such as brine pockets and air bubbles. The effects of various factors on the solar energy distribution in the entire system have been studied quantitatively. These factors include the ice salinity and density variations, cloud microphysics as well as variations in melt ponds and snow cover on the ice surface. Finally, the coupled radiative transfer model is used to study the impacts of clouds, snow and ice algae on the light transport in sea ice and in the ocean, as well as to simulate spectral irradiance and extinction measurements in sea ice.
    • Radiative transfer modeling in the coupled atmosphere-ocean system and its application to the remote sensing of ocean color imagery

      Yan, Banghua; Stamnes, Knut; Nielsen, Hans; Watkins, Brenton; Olson, John (2001-08)
      Ocean color is the radiance emanating from the ocean due to scattering by chlorophyll pigments and particles of organic and inorganic origin. Thus, it contains information about chlorophyll concentrations which can be used to estimate primary productivity. Observations of ocean color from space can be used to monitor the variability in marine primary productivity, thereby permitting a quantum leap in our understanding of oceanographic processes from regional to global scales. Satellite remote sensing of ocean color requires accurate removal of the contribution by atmospheric molecules and aerosols to the radiance measured at the top of the atmosphere (TOA). This removal process is called 'atmospheric correction.' Since about 90% of the radiance received by the satellitee sensor comes from the atmosphere, accurate removal of this portion is very important. A prerequisite for accurate atmospheric correction is accurate and reliable simulation of the transport of radiation in the atmosphere-ocean system. This thesis focuses on this radiative transfer process, and investigates the impact of particles in the atmosphere (aerosols) and ocean (oceanic chlorophylls and air bubbles) on our ability to remove the atmospheric contribution from the received signal. To explore these issues, a comprehensive radiative transfer model for the coupled atmosphere-ocean system is used to simulate the radiative transfer process and provide a physically sound link between surface-based measurements of oceanic and atmospheric parameters and radiances observed by satellite-deployed ocean color sensors. This model has been upgraded to provide accurate radiances in arbitrary directions as required to analyze satellite data. The model is then applied to quantify the uncertainties associated with several commonly made assumptions invoked in atmospheric correction algorithms. Since Atmospheric aerosols consist of a mixture of absorbing and non-absorbing components that may or may not be soluble, it becomes a challenging task to model the radiative effects of these particles. It is shown that the contribution of these particles to the TOA radiance depends on the assumptions made concerning how these particles mix and grow in a humid environment. This makes atmospheric correction a very difficult undertaking. Air bubbles in the ocean created by breaking waves give rise to scattered light. Unless this contribution to the radiance leaving the ocean is correctly accounted for, it would be mistakenly attributed to chlorophyll pigments. Thus, the findings in this thesis make an important contribution to the development of an adequate radiative transfer model for the coupled atmosphere-ocean system required for development and assessment of algorithms for atmospheric correction of ocean color imagery.
    • Radiowave Scattering Structure In The Disturbed Auroral Ionosphere: Some Measured Properties

      Fremouw, Edward Joseph; Philip, K.; Parthasarathy, R.; Tryon, J.; Owren, L. (1966)
    • A rain of dust

      Gaskin, Jefferson Arthur (2005-05)
      A Rain of Dust is a metaphor of confrontation, a facing of the enormous mystery of what it means to be born, to live, to die. Rather than attempt to find meaning, this collection celebrates the centrality of created meaning; Love and Hate, Good and Evil, Connection and Alienation, Life and Death are all presented as subjective spokes on a wheel with Art at its hub. As such, these poems are no more and no less than an expression of what it is to be Jefferson Arthur Gaskin, 32, struggling poet, lover of spooky women, kung-fu films, and robots, making his way from the swamps of Houston, Texas, to the frozen fields of Fairbanks, Alaska, and grasping at memories, fantasies, visions and dreams all along the way.
    • Rainsong in sawdust

      Wharton, Matthew Eric (2004-05)
      The fabric of this novel arises from the burnt pages of Gogol's Dead Souls. It explores the metaphor of water, in all its forms, as life. Joe Hennessy is a high school dropout working construction in Lake Tahoe. Catholic shame spins his mind into Mandelbrot sets of unrealizable responsibilities toward his family. A crisis occurs when his sister forces him to start over in a new place. We hear the hush of snow, the smoothness of water and the approach of the saw blade.
    • The Ranch(er)

      Connelley, Wendy; Brashear, James; Mehner, Da-ka-xeen; Croskrey, Wendy Ernst; Jones, Zoë Marie (2020-12)
      THE RANCH(ER) is a thesis project to fulfill the requirements of an MFA degree in visual fine-arts. This project focused on exploring my connection between the land, the ranch and its tools, and generations of ancestors living and working a small family ranch. I give voice to the seldom-vocal rancher and the isolation, hardships, and tenderness of ranch life. I have chosen as subjects for this exhibition objects that are utilitarian and are items woven into the cultural fabric of ranchers and their families. They are icons of generational identity. Rather than creating purely traditional functional objects such as cups and bowls, I’ve created conceptual pieces that emphasize the intangible connection between utilitarian objects and their users, as well as the objects’ roles in its customary position. By removing the items from their original context, I point to the context of function and utility: a life of use and work. Clay is the primary material used to create this installation to tell a universal story. The ceramic and sculptural pieces were exhibited to the public as an installation in the University of Alaska Fairbanks Fine Arts Gallery in the Fine Art Complex, Room 312, from November 2-20, 2020. The artist’s public presentation was given through an open Zoom meeting on Friday, November 13, 2020. The project report summarizes the examination and investigations involved in the development of the project.
    • Range, movements, population, and food habits of the Steese-Fortymile caribou herd

      Skoog, Ronald O. (1956-05)
      The Steese-Fortymile caribou (Rangifer arcticus stonei Allen) form one of the most economically important herds in Alaska. This study of the herd took place from September, 1952, to December, 1955, under the auspices of the Alaska Cooperative Wildlife Research Unit at the University of Alaska and of the Federal Aid in Wildlife Restoration branch of the United States Fish and Wildlife Service, Project W3R. The Steese-Fortymile range occupies about 35,000 square miles of east-central Alaska and the Yukon Territory, lying mainly between the Tanana and Yukon Rivers. The terrain is mountainous, but not rugged; roads and towns are scarce, and a maximum of 60,000 people live on the fringes. Seven major plant communities comprise the range vegetation, three of them covering 60 to 70 per cent of the area and furnishing the bulk of the food for caribou. The carrying capacity is computed to be 70,000 to 90,000 caribou. The erratic and continual movements of caribou characterize this game species. Their movements vary from day to day and season to season. Most of the traveling takes place during the early morning and late afternoon; major seasonal movements take place in the spring and fall. Past and present data provide a general picture of the movement pattern of this herd throughout the year. The Steese-Fortymile herd dwindled from a peak of about 500,000 animals in the late 1920's to a low of 10,000 to 20,000 in the early 1940's. The decline is attributed to a population shift. The present population contains at least 50,000 animals and is increasing steadily. Reproduction was high during the years 1950 to 1955. The rut takes place during the first two weeks of October; most of the calves are born during the latter half of May, following a gestation period of about 33 weeks. Valuable information on caribou behavior during the calving period is presented. Counts taken in May show that at least 50 per cent of the calves survive the first year. Wolf and man are the most important mortality factors affecting this herd. The total annual mortality, excluding calves, is estimated at eight per cent. Sex and age data from composition counts and hunter-checking-station operations indicate that this herd is young and that the sex ratio approaches 100:100. The annual increment for the herd is computed to be 10 to 15 per cent. Caribou are cursory feeders and eat a wide variety of plants. The main periods for resting and feeding occur during the middle portions of the day and night. The caribou’s diet hinges upon the available food supply, and thus varies with the seasons. In winter, the diet consists mostly of lichens, grasses, and sedges, with browse plants of some importance; data from 23 stomach-samples are presented. In spring, the new shoots of willow, dwarf birch, grass, and sedge are most important; information is based only on field observations. In summer, a wide variety of plants are eaten; willow and dwarf-birch foliage are of greatest importance, followed closely by grasses and sedges; data from 27 stomach-samples are presented. In fall, the diet shifts from a predominance of woody plants and fungi in late August to one of lichens, grasses, and sedges in late September; data from 70 stomach-samples are presented. The problems of data-gathering are discussed, as related to management practices. The contributions made by this report are outlined, and the important information still needed for proper caribou management is listed.
    • Raphe Chemosensory Amplifier: A Carbon Dioxide-Sensitive Brain Network

      Iceman, Kimberly Erin; Harris, Michael; Edmonds, Brian; O'Brien, Kristin; Taylor, Barbara (2013)
      Central chemosensitivity is the vital ability of the brain to detect and respond to changes in tissue CO<sub>2 /pH. Changing CO<sub> 2 /pH causes brainstem central chemoreceptors to modulate ventilation, but the cellular basis of this chemosensitivity is not well understood. When studied in vitro, neurons within the rat medullary raphe are intrinsically sensitive to changes in pH. Serotonin/ substance P (5-HT) synthesizing raphe neurons are stimulated, and gamma-aminobutyric acid (GABA) synthesizing neurons are inhibited by CO<sub>2 /acidosis. The contribution of these neurons to central chemosensitivity in vivo, however, is controversial. Also unknown is whether there are other types of chemosensitive cells in the raphe. Here I tested the hypothesis that rat medullary raphe neurons are responsive to CO<sub>2 in a relatively intact preparation, that raphe 5-I-IT neurons are CO<sub> 2-stimulated, and that CO<sub>2inhibited raphe neurons are GABAergic. I used extracellular recording of individual raphe neurons in the unanesthetized juvenile rat in situ perfused decerebrate brainstem preparation to assess chemosensitivity of raphe neurons. I subsequently used juxtacellular labeling, and immunohistochemistry for markers of 5-HT and GABA synthesis to identify neurotransmitter phenotype of individually recorded cells. Results demonstrate that the medullary raphe is heterogeneous and clearly contains at least three distinct classes of CO<sub>2-sensitive neurons: modestly CO<sub>2-stimulated 5-I-IT neurons, CO<sub>2-inhibited GABAergic neurons that possess this sensitivity independent of major fast synaptic inputs, and robustly CO<sub>2-stimulated non-5-HT neurons. The CO<sub>2-stimulated non-5-HT neurons constitute a previously unrecognized class of chemosensitive raphe neuron that express receptors for substance P and are dependent on network inputs from 5-HT and GABA raphe cells for chemoresponsiveness. Based on my identification of these three distinct types of chemosensitive raphe cells, I propose a new raphe chemosensory amplifier (RCA) network model to explain raphe contributions to central chemosensitivity. In this model the three cell types interact as a CO<sub> 2-sensing network that potentially amplifies the chemosensory responses to CO<sub>2 and may limit toxic over excitation of 5-HT neurons. In this way, the RCA network could integrate inputs and respond to changes in tissue CO<sub>2 with an appropriate modulation of sympathetic and/or parasympathetic outflow, consistent with the broad role that brainstem raphe nuclei play in maintaining homeostasis.
    • A rapid assessment method to estimate the distribution of juvenile chinook salmon (Oncorhynchus tshawytscha) in an Interior Alaska river basin

      Matter, Allison N.; Falke, Jeffrey; Sutton, Trent; Savereide, James; Lopez, J. Andres (2016-08)
      Identification and protection of water bodies used by anadromous species in Alaska are critical in light of increasing threats to fish populations, yet challenging given budgetary and logistical limitations. Non-invasive, rapid assessment sampling techniques may reduce costs and effort while increasing species detection efficiencies. I used an intrinsic potential (IP) habitat model to identify high quality Chinook Salmon Oncorhynchus tshawytscha rearing habitats and select sites to sample throughout the Chena River basin for juvenile occupancy using environmental DNA (eDNA) and distribution within tributaries using snorkel surveys. Water samples were collected from 75 tributary sites in 2014 and 2015. The presence of Chinook Salmon DNA in water samples was assessed using a quantitative polymerase chain reaction (qPCR) assay targeting that species. Snorkel surveys were conducted and physical habitat was measured for a subset of tributaries examined with the eDNA approach. Juvenile salmon were counted within 50 m reaches starting at the tributary confluence and continuing upstream until no juvenile salmon were observed. The IP model predicted over 900 stream km in the basin to support high quality (IP ≥ 0.75) rearing habitat. Occupancy estimation based on eDNA samples indicated that 80.2% (± 4.3 SE) of previously unsampled sites classified as high IP and 56.4% of previously unsampled sites classified as low IP were occupied. The probability of detection of Chinook Salmon DNA from three replicate water samples was high (0.76 ± 1.9 SE) but varied with drainage area. A power analysis indicated power to detect proportional changes in occupancy based on parameter values estimated from eDNA occupancy models. Results of snorkel surveys showed that the upper extent of juvenile Chinook Salmon within tributaries was from 200 to 1,350 m upstream of tributary confluences. Occurrence estimates based on eDNA and snorkel surveys generally agreed, but care should be taken to ensure that little temporal gap exists between samples as juvenile salmon use of tributary habitats is likely often intermittent. Overall, the combination of IP habitat modeling, occupancy estimation based on eDNA, and snorkel surveys provided a useful, rapid-assessment method to predict and subsequently quantify the distribution of juvenile salmon in previously unsampled tributary habitats. These methods will provide tools for managers to rapidly and efficiently map critical rearing habitats and prioritize sampling efforts to expand the known distribution of juvenile salmon in interior Alaska streams.
    • Rapid evaluation of the gel strength of GTL products during a prolonged trans-Alaska pipeline shutdown

      Timmcke, Michael Donovon (2002-12)
      A prolonged winter shutdown of the Trans-Alaska Pipeline (TAPS) could cause the fluid in the pipeline to form a gel with sufficient strength to prevent restart. With the economic viability of a North Slope Gas-To-Liquid (GTL) plant improving, understanding the effect the addition of GTL products to TAPS will have on the gel strength of pipeline fluids is essential to quantify the risk of such a project. This study presents the development of a fast cold ramp technique to predict the gel strength of TAPS fluids. The gel strength of various blend ratios of GTL and crude oil are determined using this fast cold ramp technique and are compared to slow cold ramp gel strength tests performed at Westport Technology Center, Houston. The study found that the gel strength of TAPS fluids may be reduced and controlled by altering the final boiling point of GTL products introduced into the pipeline system.
    • Rapid thinning and collapse of lake calving Yakutat Glacier, Southeast Alaska

      Motyka, Roman; Hock, Regine; Larsen, Christopher; Trüssel, Barbara Lea; Truffer, Martin (2013-12)
      Glaciers around the globe are experiencing a notable retreat and thinning, triggered by atmospheric warming. Tidewater glaciers in particular have received much attention, because they have been recognized to contribute substantially to global sea level rise. How-ever, lake calving glaciers in Alaska show increasingly high thinning and retreat rates and are therefore contributors to sea level rise. The number of such lake calving systems is increasing worldwide as land-terminating glaciers retreat into overdeepened basins and form proglacial lakes. Yakutat Glacier in Southeast Alaska is a low elevation lake calving glacier with an accumulation to total area ratio of 0.03. It experienced rapid thinning of 4.43 ± 0.06 m w.e. yr⁻¹ between 2000-2010 and terminus retreat of over 15 km since the beginning of the 20th century. Simultaneously, adjacent Yakutat Icefield land-terminating glaciers thinned at lower but still substantial rates (3.54 ± 0.06 m w.e. yr⁻¹ for the same time period), indicating lake calving dynamics help drive increased mass loss. Yakutat Glacier sustained a ~3 km long floating tongue for over a decade, which started to disintegrate into large tabular icebergs in 2010. Such floating tongues are rarely seen on temperate tidewater glaciers. The floating ice was weakened by surface ablation, which then allowed rifts to form and intersect. Ice velocity from GPS measurements showed that the ice on the floating tongue was moving substantially faster than grounded ice, which was attributed to rift opening between the floating and grounded ice. Temporal variations of rift opening were determined from time-lapse imagery, and correlated well with variations in ice speeds. Larger rift opening rates occurred during and after precipitation or increased melt episodes. Both of these events increased subglacial discharge and could potentially increase the subaqueous currents towards the open lake and thus increase drag on the ice underside. Simultaneously, increased water input may cause lake level in rifts to rise resulting in faster rift propagation and spreading. Similar formation and disintegration of floating tongues are expected to occur in the glacier's future, as the ice divide lies below the current lake level. In addition to calving retreat, Yakutat Glacier is rapidly thinning, which lowers its surface and therefore exposes the ice to warmer air temperatures causing increased thinning. Even under a constant climate, this positive feedback mechanism would force Yakutat Glacier to quickly retreat and mostly disappear. Simulations of future mass loss were run for two scenarios, keeping the current climate and forcing it with a projected warming climate. Results showed that over 95% of the glacier ice will have disappeared by 2120 or 2070 under a constant vs projected climate, respectively. For the first few decades, the glacier will be able to maintain its current thinning rate by retreating and thus losing areas of lowest elevation. However, once higher elevations have thinned substantially, the glacier cannot compensate any more to maintain a constant thinning rate and transfers into an unstable run-away situation. To stop this collapse and transform Yakutat Glacier into equilibrium in its current geometry, air temperatures would have to drop by 1.5 K or precipitation would have to increase by more than 50%. An increase in precipitation alone is unlikely to lead to a stable configuration, due to the very small current accumulation area.
    • Rapid Uplift Of Southern Alaska Caused By Recent Ice Loss

      Larsen, Christopher Fairlamb; Freymueller, Jeffrey T. (2003)
      Changing surface loads, such as melting glaciers, can induce deformation of the Earth's crust. The speed of the Earth's response to load changes and the pattern of deformation they cause can be used to infer material properties of the lithosphere and mantle. Rapid uplift of southern Alaska has been measured with tide gauges, Global Positioning System (GPS) measurements and studies of raised shorelines. With multiple sites uplifting at rates in excess of 25 mm/yr, these measurements reveal the world's fastest regional uplift. Southern Alaska has over 75000 km2 of glaciers, the rapid melting of which is contributing more to global sea level rise than Greenland. Southern Alaska also has intense tectonic activity, and uplift driven by tectonics has been suggested to be comparable with that driven by glacial unloading. The majority of the uplift measurements examined here are located along the strike-slip portion of the Pacific - North America plate boundary. GPS measurements show little compressional strain associated with tectonic forcing. Tide gauges indicate long term linear uplift rates within the strike-slip regime, contrasting with tectonically influenced non-linear uplift to the northwest, where the Pacific Plate subducts beneath North America. Dating of raised shorelines within southeast Alaska show that the rapid uplift there began simultaneously with glacial unloading ~1790 AD. These observations indicate that the tectonic contribution to the uplift in southeast Alaska is small. Multiple independent studies are used here to constrain the load changes in southern Alaska over the past ~1000--2000 yrs. A detailed model of the advance, standstill and retreat phases of the Little Ice Age glaciation is used as input to a simple viscoelastic Earth model. This model can match the pattern and magnitude of the region's uplift observations with a low degree of misfit, verifying that the region's uplift can be entirely attributed to glacial isostatic rebound. Furthermore, the uplift observations require at the 95% confidence level a three-layer Earth model consisting of a <math> <f> 50<sup>+30</sup><inf>-25</inf></f> </math> km thick elastic lithosphere, an asthenosphere with viscosity eta A = (1.4 +/- 0.3) x 1019 Pa s and thickness <math> <f> 110<sup>+20</sup><inf>-15</inf></f> </math> km, overlaying a viscous upper mantle half-space (etaum = 4 x 1020 Pa s).