• Lake Area Change In Alaskan National Wildlife Refuges: Magnitude, Mechanisms, And Heterogeneity

      Roach, Jennifer; Griffith, Brad; Harden, Jennifer; Verbyla, David; Jones, Jeremy (2011)
      The objective of this dissertation was to estimate the magnitude and mechanisms of lake area change in Alaskan National Wildlife Refuges. An efficient and objective approach to classifying lake area from Landsat imagery was developed, tested, and used to estimate lake area trends at multiple spatial and temporal scales for ~23,000 lakes in ten study areas. Seven study areas had long-term declines in lake area and five study areas had recent declines. The mean rate of change across study areas was -1.07% per year for the long-term records and -0.80% per year for the recent records. The presence of net declines in lake area suggests that, while there was substantial among-lake heterogeneity in trends at scales of 3-22 km a dynamic equilibrium in lake area may not be present. Net declines in lake area are consistent with increases in length of the unfrozen season, evapotranspiration, and vegetation expansion. A field comparison of paired decreasing and non-decreasing lakes identified terrestrialization (i.e., expansion of floating mats into open water with a potential trajectory towards peatland development) as the mechanism for lake area reduction in shallow lakes and thermokarst as the mechanism for non-decreasing lake area in deeper lakes. Consistent with this, study areas with non-decreasing trends tended to be associated with fine-grained soils that tend to be more susceptible to thermokarst due to their higher ice content and a larger percentage of lakes in zones with thermokarst features compared to study areas with decreasing trends. Study areas with decreasing trends tended to have a larger percentage of lakes in herbaceous wetlands and a smaller mean lake size which may be indicative of shallower lakes and enhanced susceptibility to terrestrialization. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the unfrozen season. Future research should characterize the relative habitat qualities of decreasing, increasing, and stable lakes for fish and wildlife populations and the ability of the fine-scale heterogeneity in individual lake trends to provide broad-scale system resiliency. Future work should also clarify the effects of terrestrialization on the global carbon balance and radiative forcing.
    • Land cover change on the Seward Peninsula: the use of remote sensing to evaluate the potential influences of climate change on historical vegetation dynamics

      Silapaswan, Cherie Sumitra (2000-12)
      Vegetation on the Seward Peninsula, Alaska, which is characterized by transitions from tundra to boreal forest, may be sensitive to the influences of climate change on disturbance and species composition. To determine the ability to detect decadal-scale structural changes in vegetation, Change Vector Analysis (CVA) techniques were evaluated for Landsat TM imagery of the Seward Peninsula. Scenes were geographically corrected to sub-pixel accuracy and then radiometrically rectified. The CVA results suggest that shrubbiness is increasing on the Seward Peninsula. The CVA detected vegetation change on more than 50% of the burned region on TM imagery for up to nine years following fire. The use of both CVA and unsupervised classification together provided a more powerful interpretation of change than either method alone. This study indicates that CVA may be a valuable tool for the detection of land-cover change in transitional regions between tundra and boreal forest.
    • Landfast sea ice formation and deformation near Barrow, Alaska: variability and implications for ice stability

      Jones, Joshua M.; Hajo, Eicken; Shapiro, Lewis; Hutchings, Jennifer; Weingartner, Thomas (2013-12)
      Climate change in the Arctic is having large and far-reaching effects. Sea ice is declining in annual extent and thinning with a warming of the atmosphere and the ocean. As a result, sea ice dynamic behaviour and processes are undergoing major changes, interacting with socio-economic changes underway in the Arctic. Near Barrow, Alaska, landfast sea ice is an integral part of native lñupiaq culture and impacts the natural resource extraction and maritime industries. Events known as breakouts of the landfast ice, in which stable landfast ice becomes mobile and detaches from the coast, have been occurring more frequently in recent years in northern Alaska. The current study investigates processes contributing to breakout events near Barrow, and environmental conditions related to the detachment of landfast sea ice from the coast. In this study, synoptic scale sea level pressure patterns are classified in an attempt to identify atmospheric preconditioning and drivers of breakout events. An unsupervised classification approach, so called Self-Organizing Maps, is employed to sort daily sea level pressure distributions across the study area into commonly observed patterns. The results did not point to any particular distributions which favored the occurrence of breakouts. Because of the comparatively small number of breakout events tracked at Barrow to date (nine events between 2006 and 2010), continued data collection may still yield data that support a relationship between breakout events and large scale sea level pressure distributions. Two case studies for breakout events in the 2008/09 and 2009/10 ice seasons help identify contributing and controlling factors for shorefast ice fragmentation and detachment. Observational data, primarily from components of the Barrow Sea Ice Observatory, are used to quantify stresses acting upon the landfast ice. The stability of the landfast ice cover is estimated through the calculation of the extent of grounded pressure ridges, which are stabilizing features of landfast ice. Using idealized ridge geometries and convergence derived from velocity fields obtained by coastal radar, effective grounding depths can be calculated. Processes acting to destabilize or precondition the ice cover are also observed. For a medium-severity breakout that occurred on March 24, 2010, the calculated atmospheric and oceanic stresses on the landfast ice overcame the estimated grounding strength of ridge keels, although interaction with rapidly moving pack ice cannot be ruled out as the primary breakout cause. For another medium-severity breakout that took place on February 27, 2009, the landfast ice was preconditioned by reducing the draft of grounded ridge keels, with subsequent detachment from the shore during the next period of oceanic and atmospheric conditions favoring a breakout. For both of these breakouts, in addition to their potential role in destabilizing the landfast ice by overcoming the ridge grounding strength, current and/or wind forcing on the landfast ice were found to be important factors in moving the stationary ice away from shore.
    • Landscape sensitivity to climate change in northern Alaska: lessons from the past

      Gaglioti, Benjamin V.; Mann, Daniel H.; Wooller, Matthew J.; Arp, Christopher D.; Jones, Miriam C.; Jones, Jeremy B.; Swanson, David K. (2016-05)
      The climate is now changing rapidly at high-latitudes, and observing how the Arctic and sub-Arctic environment responded to prehistoric climate changes can hold valuable lessons as we adapt in the future. This dissertation presents four studies that use biogeochemical proxies to reconstruct environmental changes in northern Alaska over the last 40,000 years (40 ka). These records are used to infer how the environment responded to climate changes at different locations and over varying spatial and temporal scales. The first study presents a time series of stable oxygen isotopes contained in radiocarbon-dated (¹⁴C) willow wood to quantify the nature and rates of climate change on the North Slope of Alaska over the last 40 ka. The second study examines how past temperature fluctuations affected permafrost thaw and the release of ancient carbon over the last 14.5 ka by compiling ¹⁴C-age offsets in the sediment of a small lake in the Brooks Range foothills. In the third study, I document human-caused changes to boreal wildfire frequency near the city of Fairbanks to test whether the primeval forest type and permafrost in the surrounding watershed will be vulnerable to more frequent fires in the future. The fourth study examines how ice age (40-9 ka) climate changes impacted the activity of sand dunes, vegetation productivity, and the dynamics of permafrost recorded in a unique sedimentary exposure located near the Arctic Coastal Plain on Alaska’s North Slope. Overall, I present several new and interesting approaches and findings stemming from this work. Ancient willow isotopes show that between 17 and 8 ka, during the time when ice sheets were in retreat worldwide, temperatures fluctuated widely on the North Slope mostly in concert with those in Greenland. Most notably, rapid changes in temperature and moisture occurred during the initial deglacial warming (ca. 16 ka), and during the Younger Dryas cold period (12.9-11.7 ka). These climate trends were amplified on the North Slope by changes in sea-ice extent in adjacent seas, which also controlled the availability of local precipitation evaporated from these seas. However, these warming and cooling trends were occasionally dampened by the advent of more maritime climate accompanying sea-level rise during the early Holocene, and by the breakdown of the atmospheric circulation patterns created by continental ice sheets in North America during the last glacial maximum. Over the last 7 ka, a gradual, insolation-driven cooling trend ended in ca. AD 1850 when the exceptional rates of recent warming began that continue to today. I found that the vegetation, permafrost and sand dunes in Arctic Alaska were sensitive to external climate forcing, but their responses were moderated by strong, internal feedbacks, including the temperature-buffering effects that thick peat layers have on the underlying permafrost. Prior to peat buildup in the early Holocene, the timing of sedimentary transitions indicate permafrost and aeolian processes were highly responsive to the volatile climate during the last ice age, which included Greenland interstadials. This incessant ice age climate change, coupled with the complex biophysical landscape responses that are particular to the unglaciated Arctic, helped maintain the ecological mosaic of the Mammoth Steppe ecosystem. Prehistoric warming events triggered permafrost thaw and the release of ancient carbon during the Bølling-Allerød (14.5-12.9 ka) and early Holocene warm period (11.7-8.0 ka), and this release is likely to occur again given enough warming. In the boreal forest watershed near Fairbanks, Alaska, the current ecological regime has remained intact despite a three-fold increase in pre-settlement wildfires during the Fairbanks gold rush (1902-1940). Once continued warming surpasses the buffering effects of the current internal feedbacks of the North Slope and boreal forest and the threshold for change is reached, more dynamic aeolian and permafrost processes may again dominate as they did on the more unstable and diverse ice age landscape. Overall, the results of this work will be useful for understanding how climate and landscape change in northern Alaska will respond to global climate forcing in the future.
    • Late Cenozoic unroofing sequence and foreland basin development of the central Alaska Range: implications from the Nenana Gravel

      Thoms, E. E. (2000-05)
      Facies architecture analysis, lithostratigraphy, and ⁴⁰AR/³⁹AR analyses of syn-orogenic sediments from the Nenana Gravel consistently demonstrate that deformation and erosion of the Late Cenozoic Alaska Range progressed in a foreland propagating sequence. Alluvial braidplain sediments, the oldest sourced from south of the present range divide, were shed into depozones exhibiting characteristics that indicate the growth of an underlying orogenic wedge primarily controlled deposition. Those characteristics include very immature and locally derived sediments, erosional unconformities, evidence for the competing influences of uplift and subsidence, lithology transitions that are correlated with facies transitions, and evidence for drainages that were defeated by surface uplift. Deposition of the Nenana Gravel took place between roughly 7 and 3 Ma. The Nenana Gravel depositional system changed when deformation within the proximal reaches of the basin brought resistant basement rocks to the surface forcing antecedent drainages to incise and abandon the alluvial braidplain they once fed.
    • Late quaternary and future biome simulations for Alaska and eastern Russia

      Hendricks, Amy S.; Walsh, John; Saito, Kazuyuki; Bigelow, Nancy; Bhatt, Uma (2016-05)
      Arctic biomes across a region including Alaska and Eastern Russia were investigated using the BIOME4 biogeochemical and biogeography vegetation model. This study investigated past (the last 21,000 years), present, and future vegetation distributions in the study area, using climate forcing from five CMIP5 models (CCSM4, GISS-E2-R, MIROC-ESM, MPI-ESM, and MRI-CGCM3). The present-day BIOME4 simulations were generally consistent with current vegetation observations in the study region characterized by evergreen and deciduous taiga and shrub tundras. Paleoclimatological simulations were compared with pollen data samples collected in the study region. Pre-industrial biome simulations are generally similar to the modern reconstruction but differ by having more shrub tundra in both Russia and Alaska to the north, as well as less deciduous taiga in Alaska. Pre-industrial simulations were in good agreement with the pollen data. Mid-Holocene simulations place shrub tundras along the Arctic coast, and in some cases along the eastern coast of Russia. Simulations for the Mid-Holocene are in good agreement with pollen-based distributions of biomes. Simulations for the Last Glacial Maximum (LGM) show that the Bering Land Bridge was covered almost entirely by cushion forb, lichen and moss tundra, shrub tundra, and graminoid tundra. Three out of the five models’ climate data produce evergreen and deciduous taiga in what is now southwestern Alaska, however the pollen data does not support this. The distributions of cushion forb, lichen, and moss tundra and graminoid tundra differ noticeably between models, while shrub tundra distributions are generally similar. Future simulations of BIOME4 based on the RCP8.5 climate scenario indicate a northward shift of the treeline and a significant areal decrease of shrub tundra and graminoid tundra regions in the 21st century. Intrusions of cool mixed, deciduous, and conifer forests above 60°N, especially in southwest Alaska, were notable. Across eastern Russia, deciduous taiga begins to overtake evergreen taiga, except along the coastal regions where evergreen taiga remains the favored biome.
    • Lateral magma transport during the 1912 eruption of Novarupta: insights from magnetic imaging

      Hill, Graham J.; Eichelberger, John; Freymueller, Jeff; Faust-Larsen, Jessica (2003-08)
      The Valley of Ten Thousand Smokes (VTTS), on the Alaska Peninsula, was formed by the cataclysmic eruption of Novarupta (Katmai) in 1912. During the eruption, three magma types were tapped (7-8 km³ of rhyolite, 4.5 km³ of dacite, and 1 km³ of andesite). Contemporaneous collapse of Mount Katmai while Katmai-like andesite and dacite magma joined the eruption at Novarupta provides incontrovertible evidence for magma transport from beneath Mount Katmai caldera to the vent 10 km west at Novarupta (Hildreth and Fierstein, 2000). Shallow storage of the andesite and dacite magmas beneath Mt. Katmai prior to the eruption of 1912 is consistent with the volume of collapse at Katmai, equivalent to the combined volume of andesite and dacite erupted. A ground-based magnetic survey of the area was conducted to characterize the intriguing connection between Mt. Katmai and Novarupta. The magnetic field strength and gradient survey results suggest a linear anomaly that is best modelled by the presence of a shallowly (200-300 m) emplaced dike on the order of 5-10 m wide, which resembles the known physical properties of the 7 m-wide rhyolitic dike discovered during the drilling of Inyo Domes.
    • Latitudinal gradients in leaf litter decomposition in streams: Effects of leaf chemistry and temperature

      Irons, John Gillam, Iii (1993)
      Autumnal leaf litter that falls into streams of forested regions forms a major source of energy for stream food webs. The processing of this litter has been studied for many years, and two generalizations have come from this research: (1) nitrogen concentration is positively correlated with breakdown rate, and (2) temperature is negatively correlated with breakdown rate. Along with investigators in Michigan and Costa Rica, I examined these generalizations by estimating breakdown rates of litter of ten tree species with widely varying nutritional quality along the latitudinal gradient of Costa Rica to Michigan to Alaska. At each site, litter processing experiments were done using leaves of the same ten tree species and the same methods in streams with similar character. We found that (1) condensed tannin, a plant defense against herbivory, was more highly correlated (negatively) with breakdown rates than was nitrogen (positively correlated with breakdown), and (2) breakdown rate showed a complex response to water temperature (i.e., latitude). I propose a model of leaf litter breakdown in which the microbial contribution to litter breakdown is negatively correlated with latitude (i.e., temperature) and the invertebrate contribution to litter breakdown is positively correlated with latitude. In addition, I suggest that secondary compounds of low solubility, especially condensed tannin, should be considered along with nitrogen when evaluating a tree species for leaf litter quality.
    • Latitudinal patterns of amino acid cycling and plant N uptake among North American forest ecosystems

      McFarland, Jack W.; Ruess, Roger; Boone, Richard; Chapin, Stuart F. III; Kielland, Knut; Hendrick, Ronald L. (2008-12)
      Interest in the role of organic nitrogen (N) to the N economy of forest ecosystems is gaining momentum as ecologists revise the traditional paradigm in N cycling to emphasize the importance of depolymerization of soil organic matter (SOM) in controlling the bioavailability of N in forest soils. Still, there has yet to be a coordinated effort aimed at developing general patterns for soil organic N cycling across ecosystems that vary in climate, SOM quality, plant taxa, or dominant mycorrhizal association: ectomycorrhizae (EM) vs. arbuscular mycorrhizae (AM). In this study, experimental additions of 13C15N-glycine and 15NH4+ were traced in situ through fine root and soil N pools for six North American forest ecosystems in an effort to define patterns of plant and microbial N utilization among divergent forest types. Recovery of 15N in extractable soil pools varied by N form, forest type, and sampling period. At all sites, immobilization by the soil microbial biomass represented the largest short-term (<24 h) biotic sink for NH4+ and amino acid-N, but differences in microbial turnover of the two N forms were linked to cross-ecosystem differences in SOM quality, particularly the availability of labile carbon (C). At the conclusion of the experiment, microbial N turnover had transferred the majority of immobilized 15N to non-extractable soil N pools. By comparison, fine root uptake of NH4+ and glycine-N was low (<10% total tracer recovery), but 15N enrichment of this pool was still increasing at the final sampling period. Since there was no significant loss of 15N tracer within the bulk soil after 14 days for any forest type except sugar maple, it suggests plants have the capacity to capitalize on multiple N turnover events and thus represent an important long-term sink for ecosystem N. Plants in all stands had some capacity to absorb glycine intact, but plant N preference again varied by forest type. Relative uptake of amino acid-N versus inorganic N was lowest in tulip poplar and highest in red pine and balsam poplar, while white oak, sugar maple, and white spruce stands were statistically near unity with respect to the two N forms. However, N uptake ratios were threefold higher in EM-dominated stands than in AM-dominated stands indicating mycorrhizal association in part mediated plant N preference. Thus, amino acids represent an important component of the N economies of a broad spectrum of forest ecosystems, but their relevance to plant nutrition likely varies as a function of microbial demand for C as well as N.
    • Lichen Availability on the Range of an Expanding Caribou (Rangifer tarandus) Population in Alaska

      Fleischman, Steven J.; Klein, David R.; Thompson, Steven K.; Viereck, Leslie A.; White, Robert G.; Regelin, Wayne L. (1990-05)
      Terrestrial lichen abundance, lichen availability as affected by snow, and winter fecal composition were investigated for the Delta Caribou Herd (DCH), which recently quadrupled in size and expanded its early winter range. Mean lichen abundance was relatively low (10-85 g/m2). However, even on heavily-used range, caribou ate only 7% of lichen standing crop annually. Snow affected lichen availability only slightly on peripheral tundra ranges, since lichens predominated on xeric sites with little snow. On traditional ranges, lichens were shorter and rarely found in high-density patches; disproportionate grazing and trampling of exposed lichens had caused reduced lichen availability. This was reflected in lower fecal lichen for caribou on traditional ranges, however DCH population growth or seasonal movements probably were not substantially affected. A model of caribou cratering energetics indicated that loss of potential foraging time may influence energy balance more than does cratering energy expenditure.
    • Lidar and radar studies of turbulence, instabilities, and waves in the Arctic middle atmosphere

      Li, Jintai; Collins, Richard L.; Newman, David E.; Simpson, William R.; Thorsen, Denise L.; Williams, Bifford P. (2019-08)
      This dissertation presents new studies of gravity waves and turbulence in the Arctic middle atmosphere. The studies employ lidars and radar to characterize wave activity, instability and turbulence. In the lidar-based studies, we analyze turbulence and wave activity in the MLT based on lidar measurements of atmospheric temperature, density and sodium density, temperature and wind. This combination of measurements provides simultaneous characterization of both the atmospheric stability as well as material transport that allow us to estimate the eddy diffusion coefficient associated with turbulence. We extend the scope of previous studies by developing retrievals of potential temperature and sodium mixing ratio from the Rayleigh density temperature lidar and sodium resonance density lidar measurements. We find that the estimated values of turbulent eddy diffusion coefficients, K, of 400-2800 m²/s, are larger than typically reported (1-1000 m²/s) while the values of the energy dissipation rates, ε, of 5-20 mW/kg, are more typical (0.1-1000 mW/kg). We find that upwardly propagating gravity waves accompany the instabilities. In the presence of instabilities, we find that the gravity waves are dissipating as they propagate upward. We estimate the energy available for turbulence generation from the wave activities and estimate the possible turbulent energy dissipation rate, εGW. We find that the values of εGW are comparable to the values of ε. We find that the estimate of the depth of the layer of turbulence are critical to the estimate of the values of both ε and εGW. We find that our method tends to overestimate the depth, and thus overestimate the value of ε, and underestimate the value of εGW. In the radar-based study, we conduct a retrieval of turbulent parameters in the mesosphere based on a hypothesis test. We distinguish between the presence and absence of turbulence based on fitting Voigt-based and Lorentzian-based line shapes to the radar spectra. We also allow for the presence and absence of meteoric smoke particles (MSPs) in the radar spectra. We find examples of Poker Flat Incoherent Scatter Radar (PFISR) spectra showing both the presence and absence of turbulence and the presence and absence of MSPs in the upper mesosphere. Based on the analysis, we find that relatively few of the radar measurements yield significant measurements of turbulence. The significant estimates of turbulence have a strength that is over a factor of two larger than the average of the estimates from all of the radar measurements. The probability of true positives increases with the quality factor of the spectrum. The method yields significant measurements of turbulence with probabilities of true positives of greater than 30% and false positives less than 0.01%.
    • Lidar and satellite studies of noctilucent clouds over Alaska

      Alspach, Jennifer H.; Collins, Richard; Bossert, Katrina; Thorsen, Denise; Fochesatto, Javier (2020-05)
      This thesis presents studies of noctilucent clouds (NLCs) occurring in the summer polar mesosphere over Alaska. Lidar observations of NLCs conducted at Poker Flat Research Range in Chatanika, Alaska (65° N, 147° W) from 1998-2019 are analyzed. The NLCs detected by lidar are characterized in terms of their brightness properties and duration. NLCs were detected on ~51% of the nights when lidar observations have been conducted during NLC season. The brighter NLCs are found to exist at lower altitudes, indicating a growth-sedimentation mechanism. Cloud Imaging and Particle Size (CIPS) data from the Aeronomy of Ice in the Mesosphere (AIM) satellite is used to examine NLC occurrence and brightness over the Alaska region (60-70° N, 130-170° W). In general, high frequency and brightness in the CIPS data corresponds to positive detections of NLCs by the lidar. Microwave Limb Sounder (MLS) temperature and water vapor data from the Aura satellite is used to investigate the meteorological environment of the NLCs observed by lidar at Chatanika. The occurrence of NLCs at Chatanika is found to be driven by the temperature relative to the frost point. Low temperatures relative to the frost point (> 4 K below) correspond to observations when NLCs were present. High temperatures relative to the frost point (> 8 K above) correspond to observations when NLCs were absent. The MLS data is also used to investigate the stability of an ice cloud at different latitudes (64.7°-70.3° N) relative to the equilibrium water vapor mixing ratio. The stability study suggests that the weakest NLCs detected by lidar at Chatanika were in subsaturated conditions, and it is likely that the NLCs formed over several hundred kilometers to the north of Chatanika. The Rayleigh three-channel receiver system was used to conduct NLC measurements during 2019. A technical overview of the three-channel system and the density and temperature retrieval methods is presented at the end of the thesis using observations from the winter of 2018 and the summer of 2019.
    • Life-History Patterns Of North American Elk: Effects Of Population Density On Resource Partitioning, Reproduction, And Plant Productivity

      Stewart, Kelley Merlet; Bowyer, R. Terry (2004)
      I examined density dependence in North American elk (Cervus elaphus ) and effects of density dependent processes on resource partitioning, physical condition, reproduction, and ecosystem processes. Specifically, I examined spatial, temporal, and dietary niche partitioning among elk, mule deer (Odocoileus hemionus) and cattle (Bos taurus ). I tested hypotheses related to density-dependent processes in elk by creating populations at high (20.1 elk/km2) and low (4.1 elk/km2) density. I hypothesized that physical condition and fecundity of females would be lower in an area of high population density than in the low-density area. Simultaneously, I tested hypotheses relating to herbivore optimization in response to varying levels of herbivory. I observed differences among elk, mule deer, and cattle in diets and use of space, particularly elevation, slope, and use of logged forest. Those 3 herbivores showed strong avoidance over a 6-h temporal window, but that effect was weaker for the previous 7 days. Changes in habitat use by elk and mule deer in response to addition and removal of cattle indicated competitive displacement. Results of the experiment to examine density dependence in elk indicated reduced physical condition and reproduction in the high-density population compared with low-density population. Pregnancy rates were most affected by body condition and mass of females. Density dependence in elk also had strong effects on plant communities; net aboveground primary productivity (NAPP) increased from no herbivory to moderate grazing intensity, and then declined as grazing intensity continued to increase. Compensatory responses by plants likely are more difficult to detect when responses to herbivory are subtle and occur at relatively low grazing intensity. I observed strong effects of density dependence on physical condition of elk and reductions in NAPP of plant communities with high levels of grazing intensity. At high-population densities resources for elk declined and NAPP was reduced. At low-population density elk were in good physical condition with high rates of reproduction, and NAPP increased, indicating compensatory responses by plants. Density-dependent feedbacks in populations of large herbivores help regulate population dynamics, and those same processes have substantial effects on ecosystem functioning.
    • The limnology of Lake Clark, Alaska

      Wilkens, Alexander Xanthus (2002-12)
      This study gathered baseline limnological data to investigate the thermal structure, water quality, phytoplankton, and zooplankton of Lake Clark, Alaska. Results indicate Lake Clark is oligotrophic and mixes biannually, but stratification is weak and thermoclines are deep. Longitudinal gradients were seen in measurements of temperature, suspended solids, turbidity, light penetration, algal biomass, and zooplankton density. Wind and tributary inputs determine the thermal regime. Glacially-influenced tributaries drive turbidity and light gradients by introducing suspended solids to the inlet end of the lake. Suspended solids likely create the algal biomass gradient by limiting the light available for photosynthesis in the inlet basin. Algal biomass and turbidity gradients may interact to create an area of high productivity and low predation risk, causing high zooplankton concentrations in the central basin. Oxygen supersaturation was discovered in the hypolimnion but remains unexplained. Because tributaries are glacially influenced, Lake Clark could be sensitive to global warming.
    • Linear partial differential equations and real analytic approximations of rough functions

      Barry, Timothy J.; Rybkin, Alexei; Avdonin, Sergei; Faudree, Jill (2017-08)
      Many common approximation methods exist such as linear or polynomial interpolation, splines, Taylor series, or generalized Fourier series. Unfortunately, many of these approximations are not analytic functions on the entire real line, and those that are diverge at infinity and therefore are only valid on a closed interval or for compactly supported functions. Our method takes advantage of the smoothing properties of certain linear partial differential equations to obtain an approximation which is real analytic, converges to the function on the entire real line, and yields particular conservation laws. This approximation method applies to any L₂ function on the real line which may have some rough behavior such as discontinuities or points of nondifferentiability. For comparison, we consider the well-known Fourier-Hermite series approximation. Finally, for some example functions the approximations are found and plotted numerically.
    • Linkages between protein ubiquitination, proteasome activity and the expression of oxygen-binding proteins in Antarctic notothenioid fishes

      Oldham, Corey A.; O'Brien, Kristin; Dunlap, Kriya; Taylor, Barbara (2015-12)
      Antarctic icefishes lack hemoglobin (Hb), and some species lack cardiac myoglobin (Mb). As iron-centered proteins, Hb and Mb can promote the formation of reactive oxygen species that may damage biological macromolecules. Consistent with this, we find higher levels of oxidized proteins in some tissues of red-blooded notothenioids than in icefishes. Oxidized proteins are marked for degradation by the conjugation of the protein ubiquitin. I hypothesized that levels of ubiquitinated proteins and 20S proteasome activity (which degrades oxidized proteins) would be higher in +Hb and +Mb notothenioids than icefishes lacking the proteins. Levels of ubiquitinated proteins and rates of proteasome activity were measured in the heart ventricle, pectoral adductor, and liver of six species of notothenioids differing in Hb and Mb expression. Previous studies in notothenioids suggest that oxidative stress declines following acclimation to 4°C. I also hypothesized that levels of ubiquitinated proteins and 20S proteasome activity would decline in response to acclimation to 4°C. Levels of ubiquitinated proteins and rates of proteasome activity were measured in the heart ventricle, pectoral adductor, and liver of the red-blooded Notothenia coriiceps held at ambient temperature and acclimated to 4°C for 3 weeks. Levels of ubiquitinated proteins were higher in tissues of the red-blooded N. coriiceps compared to icefishes, but the activity of the 20S proteasome did not follow a similar trend, suggesting that icefishes do not incur an energetic benefit resulting from reduced rates of protein degradation. Levels of ubiquitinated proteins were equivalent in heart ventricle and oxidative skeletal muscle, and proteasome activities were equivalent in all tissues between acclimated N. coriiceps and those held at ambient temperature, suggesting that protein damage and rates of protein degradation are not altered in notothenioids by long-term exposure to 4°C.
    • Linking climate history and ice crystalline fabric evolution in polar ice sheets

      Kennedy, Joseph Huston; Pettit, Erin; Truffer, Martin; Bueler, Ed; Newman, David; Szuberla, Curt (2015-08)
      An ice sheet consists of an unfathomable number of ice crystallites (grains) that typically have a preferred orientation of the crystalline lattices, termed fabric. At the surface of ice sheets, the microstructural processes that control the grain structure and fabric evolution are influenced by climate variables. Layers of firn, in different climate regimes, may have an observable variation in fabric which can persist deep into the ice sheet; fabric may have 'memory' of these past climate regimes. To model the evolution of a subtle variation in fabric below the firn-ice transition, we have developed and released an open-source Fabric Evolution with Recrystallization (FEvoR) model. FEvoR is an anisotropic stress model that distributes stresses through explicit nearest-neighbor interaction. The model includes parameterizations of grain growth, rotation recrystallization and migration recrystallization which account for the major recrystallization processes that affect the macroscopic grain structure and fabric evolution. Using this model, we explore the evolution of a subtle variation in near-surface fabric using both constant applied stress and a stress-temperature history based on data from Taylor Dome, East Antarctica. Our results show that a subtle fabric variation will be preserved for ~200ka in compressive stress regimes with temperatures typical of polar ice-sheets. The addition of shear to compressive stress regimes preserves fabric variations longer than in compression-only regimes because shear drives a positive feedback between crystal rotation and deformation. We find that temperature affects how long the fabric variation is preserved, but does not affect the strain-integrated fabric evolution profile except when crossing the thermal-activation-energy threshold (~-10°C). Even at high temperatures, migration recrystallization does not rid the fabric of its memory under most conditions. High levels of nearest-neighbor interactions between grains will rid the fabric of its memory more quickly than low levels of nearest-neighbor interactions. Because FEvoR does not compute flow, an integrated fabric-flow model is needed to investigate the flow-fabric feedbacks that arise in ice sheets. Using the open-source Parallel Ice Sheet Model (PISM) and FEvoR, we develop a combined flow-fabric model (PISM-FEvoR). We provide the first integrated flow-fabric model that explicitly computes the fabric evolution and includes all three major recrystallization processes. We show that PISM-FEvoR is able to capture the flow enhancement due to fabric by modeling a slab-on-slope glacier, initialized with a variety of fabric profiles. We also show that the entire integrated fabric-flow history affects the final simulated flow. This provides a further, independent validation of using an integrated fabric-flow model over a constant enhancement factor in ice-sheet models.
    • Linking local knowledge and fisheries science: the case with humpback whitefish (Coregonus pidschian) in Interior Alaska

      Robinson, Melissa Anne (2005-05)
      Humpback whitefish (Coregonus pidschian) are the main subsistence fish for the residents of the Athabascan village of Northway. Local residents' concerns over whitefish and gaps in knowledge in the scientific community about whitefish basic ecology provided a basis for collaboration between fisheries scientists, social scientists, and Northway Village. Through semi-directed interviews and participant observation, I documented and linked local and scientific knowledge about whitefish. Trust, formed in part by my engagement with the community, was essential to meaningful collaboration between local and scientific experts. Through collaboration, insights emerged about the long-distance migrations of whitefish (up to 230 km), their small-scale use of creek channels, annual site fidelity, and repeated long-term use of seasonal habitats. Partially due to gendered fishing roles, women and men differed in their knowledge about whitefish. Women observed seasonal and annual variation in the prevalence of parasite-infected whitefish, while both men and women observed increased sedimentation in area lakes. Questions surfaced about the behavioral response of whitefish to increasing water temperatures and the effects of siltation on their health. I argue that the fusion of local and scientific knowledge, gained through collaboration, enhanced the information required to make management decisions regarding whitefish in the Upper Tanana drainage and the resilience of this social-ecological system.
    • Linking proteomics to microbial kinetics

      Cherian, Suraj (2008-08)
      Oligobacterial physiology is mostly unstudied due to cultivation difficulty. New isolation techniques such as extinction culture have produced cultivable representatives of the aquatic environment namely Sphingopyxis alaskensis. Attempts were made to grow the bacterium in batch cultures using glucose and tyrosine as ideal substrates as determined from growth studies. Differential protein expression from cytoplasmic and membrane fractions of the putative culture were compared so as to identify key proteins involved in substrate uptake and metabolism followed by incorporation of protein quantities into mathematical models of oligotroph growth. However artifactual results from two dimensional gel electrophoresis led to the question of culture purity, which was eventually confirmed by light microscopy, flow cytometry and 16S rRNA gene sequencing. This research gives better insight into the possible problems that can crop up while working with hard to culture marine oligobacteria. I demonstrate the rationale used to identify the contaminant, which was difficult to detect because its slow growth was similar to the target organism. A major achievement was successful cell fractionation as it has never been attempted in oligobacteria due to culturing difficulties and the procedure is different from the routine methods adopted in bacteria and fungi. Also the research demonstrates a complete protocol for eliminating uncertainties in culture purity.
    • Lithium Storage and Release from Lacustrine Sediments: Implications for Lithium Enrichment and Sustainability in Continental Brines

      Coffey, Daniel; Munk, Lee Ann; Ibarra, Daniel; Butler, Kristina; Boutt, David; Jenckes, Jordan (2021)
      Despite current and projected future reliance on lithium as a resource, deficiencies remain in genesis models of closed-basin Li brines. Subsurface geochemical interactions between water and bulk solid phases from lacustrine sediments, are shown here to be the most important process for brine genesis and sustainability of the Clayton Valley, NV brine deposit. A new subsurface basin model was developed and used to select Li-bearing solids to test the release mechanisms for Li. Ash (20-350 ppm Li) and bulk sediments (1000-1700 ppm Li) samples across depths in the basin represent the majority of the subsurface Li-bearing materials. Temperature dependent (25-95 oC) batch reaction experiments using low-salinity groundwater from the basin indicate a positive relationship between the amount of Li released and temperature. Four-step sequential extractions on a subset of bulk sediments indicate most Li is released from water and weak acid-soluble portions with approximately 30% of the total Li contained in the sediments released overall. We conceptualize that lithium is released from these samples via three mechanisms: 1) release of adsorbed Li; 2) cation exchange of Li and Mg and; 3) possible minor release from silicate structure at elevated temperatures. Based on these results and the abundance of Li-bearing sediments in the subsurface we estimate the mean Li mass in the basin materials to be between 24.4 to 58.0 Mt. This Li provides a continuous supply from water-rock interactions. This is now the largest known accumulation of Li in a basin-fill continental setting on a global scale.