Now showing items 272-291 of 1029

• #### Effects of climatic variability on the active layer and permafrost

This thesis represents a collection of papers on the response of the active layer and permafrost to climatic variations on different time scales. Quantitative estimates of the amplitudes of the Milankovich rhythms in several regions of the Russian permafrost zone were used in numerical simulations of permafiost dynamics. The results of modeling explained many aspects of the permafrost distribution and its vertical structure within Russia. Spatial and temporal variability of the air, ground surface and permafrost temperatures were also analyzed using daily temperature data (upper 0.9 m) from 1986-1993 and results of annual temperature measurements in boreholes (nominally 60 m) from 1983-1995 at three sites in the Prudhoe Bay region of Alaska. Three numerical models which are based on different numerical methods and are used for calculations of the ground thermal regime were compared with each other, with analytical solutions, and with temperature data. Several approximate analytical solutions for the temperature regime and thickness of the active layer were introduced. The calculations were used to estimate the interannual variability of the thermal properties of soils which appear to be a result of interannual variations of the average water content during the summer in the upper part of the active layer. Precise temperature data together with computer modeling provided essential new information on dynamics of unfrozen water content in the ground in natural undisturbed conditions during freezing and the subsequent cooling of the active layer. A layer with unusually large unfrozen water content was found to exist at the depth of freeze-up. The same set of data was used to reconstruct daily permafrost temperatures from 1986-1993 for all depths down to 55 m. Mean annual temperature profiles for each year of 1987-1992 show significant interannual variations within the upper 40 m in a good agreement with published data. A numerical model of the temperature field in permafrost near its southern limits was developed to study the influence of short-term climatic variations (with periods of 300 and 90 years) on permafrost dynamics.
• #### Effects of defoliation on sandbar willow (Salix interior) chemistry, production, and subsequent overwinter browsing by mammalian herbivores

Herbivory can cause changes in plant characteristics, allowing temporally isolated herbivores to indirectly affect one another through their effects on shared host plants. The objective of this thesis was to test how defoliation of the willow Salix interior affects current annual stem production and chemistry, and how changes in these traits may indirectly affect mammalian herbivores. I studied the effect of manual defoliation on S. interior leaf and stem chemistry, and the effect of insect folivory on S. interior stem chemistry, production, and mammal herbivore offtake. Manual defoliation of S. interior affected stem chemistry by significantly increasing stem N concentration and decreasing stem C:N ratio, but did not alter leaf chemistry. Neither stem nor leaf protein precipitation capacity (PPC), a measure of tannin activity, were affected by manual defoliation. In a second field experiment I investigated the effects of natural levels of insect folivory on S. interior stem characteristics, testing the effects of insect herbivore suppression on stem production, chemical composition, protein precipitation capacity, and overwinter mammal browsing. Insect folivory did not significantly alter stem chemistry, but significantly reduced stem production by reducing mean stem diameter the following year. These findings indicate that defoliation of S. interior can improve nutritional quality and reduce availability of stems for mammal herbivores foraging over the subsequent winter.
• #### Effects of diet quality and quantity on caribou and reindeer (Rangifer tarandus)

Caribou and reindeer (Rangifer tarandus) encounter natural and anthropogenic disturbances across the landscape. In late winter, Rangifer encounter acute food from disturbances such as icing events. Furthermore, as shrubs expand into the Arctic tundra, the proportion of low quality browse may increase in the summer diet of Rangifer. This study evaluated how Rangifer tolerate 1) fluctuations in food quantity in late winter and 2) changes in forage quality over the summer. Rangifer can compensate for food shortages by increasing intake after restriction, which would allow animals to restore body mass quickly during migration. High body fat reserves increase the tolerance of food shortages. During the summer, Rangifer can consume exclusively browse to meet daily energy requirements; however, low nitrogen supply and high toxin load would require the use of alternative forages to supplement nitrogen and reduce toxins.
• #### Effects of gravity waves on the polar oxygen and hydroxyl airglow

The effect of gravity waves on the OH (87 km) and O$\sb2$ (95 km) airglow emissions was examined using spectroscopic airglow data. The data was obtained from Longyearbyen, Svalbard (78$\sp\circ$N) and Fairbanks, Alaska (64$\sp\circ$N) using Ebert-Fastie spectrometers and a system of Meridian Scanning Photometers. The spectrometers scanned in wavelength from 8200A to 8750A which included the airglow emissions from the OH(6-2) Meinel band and the O$\sb2$(0-1) atmospheric band. The analysis was done by fitting a synthetic spectrum to the data and thereby the rotational temperature was calculated as well as the band intensity of each of the emissions. The rotational temperatures were assumed to represent the temperature of the emission region. Gravity waves were assumed to modify the density and temperature of the atmosphere in the region of the airglow emissions. These modifications were measured as fluctuations in the band intensity and rotational temperatures of the two emissions. In order to compare the data with theoretical models, it was necessary to calculate two parameters. The parameter $\eta$ is defined as the ratio of the amplitudes of the fluctuations in intensity and temperature. The other parameter is the phase angle between the fluctuations in intensity and temperature. These parameters were found to vary with wave period. The variations in $\eta$ and phase agreed fairly well, for long period waves, with the most recent models. None of the models agree with the observed values of $\eta$ and phase for short period waves. The second part of this thesis examines the vertical and horizontal wavelengths, the phase speeds, and the propagation directions of several specific gravity wave examples. During a 60 hour period of data taken from Svalbard, three well defined gravity waves were observed. The propagation directions implied a moving source south of the observing station.

• #### Effects of increased snow on growth and allocation patterns of Arctic plants

While summer warming in the Arctic has led to an increase in shrub cover on the tundra, winter processes may enhance shrub growth. In particular, greater snow accumulation around shrub patches may alter plant growth by insulating soil and facilitating overwinter nitrogen mineralization by microbes, thereby increasing nutrients available to plants at spring thaw and influencing growth patterns. We used three snow fences located across a gradient of shrub height and density at Toolik Field Station to compare plant growth and nutrient uptake on either side of the fences. Species behaved individualistically, with some showing increased growth and nutrient uptake with snow addition, others showing decreased growth and nutrient uptake, and some showing no effect of snow. The biggest increases in growth were seen in the deciduous shrub Salix pulchra due to increased carbon allocation (compared to nitrogen allocation) to stems, coinciding with increases in secondary growth, which allowed plants to support more branches and thus more leaves. Overall, secondary growth was the most responsive growth trait to snow addition, and facilitated growth of other aboveground plant parts. This provides a preliminary mechanistic explanation for the widespread increase in shrub cover across the northern latitudes. Some species, notably the evergreen shrub Ledum palustre, showed decreased growth under snow addition, but increased nitrogen uptake in stems suggesting storage of nutrients over growth. In addition, species growing in inherently more productive areas responded most strongly to added snow, indicating that larger plants are better able to modify their biomass and nutrient allocation in response to environmental alteration. We conclude that faster-growing species with the ability to respond rapidly to changes in nutrient availability will likely dominate under continued climate change, and may alter important ecosystem processes such as carbon and nitrogen storage and potentially feed back into climate warming.
• #### Effects of methylmercury and theaflavin digallate on adipokines in mature 3t3-l1 adipocytes

Diabetes is a contributor to morbidity across the globe and is often associated with obesity, metabolic syndrome and other inflammatory diseases associated with aging. In addition to genetic and lifestyle factors, environmental factors such as metals and persistent organic pollutants may increase the severity or lower the threshold of these conditions. In cell culture, methylmercury is toxic to adipocytes and may impact the adipokine secretions. In this study, I determined the effects of different concentrations of theaflavin digallate on methylmercury exposed 3T3-L1 adipocytes in cell culture. Secretions of resistin, adiponectin and lipid peroxidation product, 4-HNE were monitored using ELISA assays from Day 18 to 28. Cell morphology was assessed over the period of ten days and on day 28 was observed using Lipid (Oil Red O) staining. Results showed that exposure to methylmercury increased the levels of resistin and adiponectin as well as 4-HNE when compared to the control cells. Methylmercury treated cells resulted in smaller and highly clumped lipid droplets. These results suggest that methylmercury induces reactive oxygen species leading to development of an inflammatory response. Theaflavin digallate reduced the impact of methylmercury by restoring the morphology and secretion patterns of adiponectin, resistin and 4-HNE. With this enhanced signaling model other anti-inflammatory agents could be tested at this biochemical level eventually leading to studies in animal models.
• #### Effects of methylmercury exposure on 3T3-L1 adipocytes

Mercury-containing compounds are environmental pollutants that have become increasingly consequential in the Arctic regions of North America due to processes of climate change increasing their release and availability at northern latitudes. Currently, the form of mercury known to be most detrimental to human health is methylmercury, CH₃Hg⁺, which is found in the environment primarily accumulated in the tissues of predatory fish, including those consumed by Alaska Natives through subsistence gathering. Much is known about the neurotoxicity of methylmercury after exposure to high concentrations, but little is known about toxicity to other tissues and cell types, particularly for long-term exposure and the lower concentrations that would occur through fish consumption. This study aims to investigate the potential effects of methylmercury exposure on adipocytes, the main cellular components of adipose (fat) tissue, and explore possible consequences of exposure on metabolic disorders such as obesity and diabetes. Effects of methylmercury exposure on 3T3-L1 adipocytes in culture were assessed using assays for cytotoxicity and an ELISA assay for vascular endothelial growth factor (VEGF), a signaling molecule shown to be important for maintaining metabolic status in adipose tissue. Results showed that exposure to methylmercury leads to significant toxicity in adipocytes at exposures of 100 ng/mL during later stages of differentiation, but lower methylmercury concentrations produced little to no toxicity. Results also indicate that VEGF secretion is elevated in adipocytes exposed to methylmercury after the process of differentiating into mature, fat-storing cells. These results provide a basis for further exploration into metabolic consequences of methylmercury exposure.

• #### The effects of permafrost degradation on soil carbon dynamics in Alaska's boreal region

High-latitude regions store large quantities of organic carbon (C) in permafrost soils and peatlands, accounting for nearly half of the global belowground C pool. Projected climate warming over the next century will likely drive widespread thawing of near-surface permafrost and mobilization of soil C from deep soil horizons. However, the processes controlling soil C accumulation and loss following permafrost thaw are not well understood. To improve our understanding of these processes, I examined the effects of permafrost thaw on soil C dynamics in forested upland and peatland ecosystems of Alaska's boreal region. In upland forests, soil C accumulation and loss was governed by the complex interaction of wildfire and permafrost. Fluctuations in active layer depth across stand age and fire cycles determined the proportion of soil C in frozen or unfrozen soil, and in turn, the vulnerability of soil C to decomposition. Under present-day climate conditions, the presence of near-surface permafrost aids C stabilization through the upward movement of the permafrost table with post-fire ecosystem recovery. However, sensitivity analyses suggest that projected increases in air temperature and fire severity will accelerate permafrost thaw and soil C loss from deep mineral horizons. In the lowlands, permafrost thaw and collapse-scar bog formation resulted in the dramatic redistribution of soil water, modifying soil thermal and C dynamics. Water impoundment in collapse-scar bogs enhanced soil C accumulation in shallow peat horizons, while allowing for high rates of soil C loss from deep inundated peat horizons. Accumulation rates at the surface were not sufficient to balance deep C losses, resulting in a net loss of 26 g C m⁻² y⁻¹ from the entire peat column during the 3000 years following thaw. Findings from these studies highlight the vulnerability of soil C in Alaska's boreal region to future climate warming and permafrost thaw. As a result, permafrost thaw and soil C release from boreal soils to the atmosphere should function as a positive feedback to the climate system.
• #### Effects of permafrost thaw on nitrogen availability and plant soil interaction in a boreal Alaska lowland

Permafrost thaw in boreal peatlands causes an ecosystem state change as black spruce forests with permafrost transition into saturated, non-forested collapse scar bogs or fens. Previous studies have suggested that permafrost thaw can increase soil nitrogen (N) bioavailability. However, it is unclear whether these changes in N availability are directly related to changes in N pools or mineralization rates in surface soils (active layer dynamics), or whether increasing N can be attributed to N mobilization from thawing permafrost soil organic matter at depth. I examined plant species composition and aspects of N cycling along triplicate permafrost-thaw gradients in interior Alaskan peatlands. Each gradient comprised plots situated in a 1) forested plateau with intact permafrost (hereafter called permafrost forest) 2) forest experiencing active thaw (drunken forest), 3) moat representing initial stages of complete thaw (moat), and 4) collapse scar bog representing post-thaw succession following complete permafrost thaw (collapse bog). I found that both organic and inorganic N concentrations in soil solution increased with thaw. Drunken forests with active permafrost thaw had the greatest mean concentrations of total dissolved N relative to the other gradient plots. Elevated levels of dissolved N in the drunken forest plots were due primarily to high concentrations of large molecular DON. The moat and collapse scar bog plots had greater inorganic N concentrations on average than the permafrost forest or the drunken forest, suggesting that changes in plantavailable N do not occur immediately upon thaw, but are influenced by vegetation or soil succession occurring decades to centuries after thaw is initiated. However, across all of the community types, I found that deeper soil horizons corresponded to greater concentrations of DIN and DON when thaw was deepest (September), suggesting that permafrost soil horizons are playing a role in changing N availability post-thaw. Vegetation responses to permafrost thaw included changes in plant community composition, deeper rooting profiles, and changes in foliar N and δ¹⁵N values. Plant foliar and litterfall N concentrations increased with collapse bog succession and showed relationships with concentrations of DIN, suggesting that plants are utilizing additional mineralized N. Together, my results suggest that the conversion of lowland permafrost forests to collapse scar bogs increases N availability both by increasing turnover of the permafrost organic matter pool as well as through longer-term successional processes. At least some plants are able to capitalize on "new" sources of N available post-thaw, but it is unclear from my results whether plants are able to acquire N mobilized by thawing permafrost organic matter deeper in soil profiles.
• #### Effects of recreational disturbance on breeding black oystercatchers: species resilience and conservation implications

The potential conflict between increasing recreational activities and nesting birds in coastal habitats has raised concerns about the conservation of the black oystercatcher (Haematopus bachmani). To address these concerns, I studied the breeding ecology of black oystercatchers in Kenai Fjords National Park and examined the impact of recreational disturbance on breeding parameters. Most recreational disturbance of breeding territories was from kayak campers and occurred after June 13, the peak hatch of first clutches. Mean annual fledging success (24%) was low, but the results suggest that daily survival rates of nests and broods did not differ between territories with and without recreational disturbance. Nest survival varied annually and seasonally, and declined during periods of extreme high tides. Daily survival rate of broods was higher on island territories than mainland territories, presumably due to differences in predator communities. Most (95%) color-banded oystercatchers returned to their breeding territories in the subsequent year regardless of level of disturbance. On average, black oystercatchers decreased incubation constancy by 39% in response to experimental disturbance. However, I found no evidence that time off the nest was associated with probability of nest survival. Further, I found no evidence that oystercatchers habituated to recreational activity. The data suggest that black oystercatchers in Kenai Fjords National Park are resilient to the current low levels of recreational disturbance.
• #### Effects of season, sex, and dietary nitrogen on muskoxen

Growth and survival of muskoxen (Ovibos moschatus) are dependent on forage that varies in quality and quantity. One of the most limiting factors is nitrogen. In chapter 1, I predicted that growth would vary with season, sex and dietary nitrogen. While growth is highly season and results in dimorphism, it is not affected by supplemental nitrogen. In chapter 2, I predicted an inverse relationship between intake and digestibility of diets in adults. Intakes increased dramatically from spring to summer with no impact on digestibility. This resulted in increased body fat from summer to winter with little change in body protein. Cellulose digestibility decreases in winter, suggesting a seasonal regulation of digestive and absorptive systems. High solute loads did not affect plasma osmolality because renal function probably eliminates excess N and K during autumn. Differences in intake and growth patterns are probably the result of sexual and non-sexual hormonal controls.
• #### Effects of simulated climate change on the reproductive phenology of tussock cottongrass: implications for growth and reproduction of reindeer on the Seward Peninsula, Alaska

I investigated the experimental effects of manipulations of snowmelt on the flowering phenology and forage chemistry (digestibility and nitrogen concentration) of tussock cottongrass on the Seward Peninsula, Alaska. The early snowmelt treatment (1) accelerated reproductive phenology by 11 days, and (2) resulted in higher floral digestibility but is associated with decreased nitrogen concentration in flowers. Therefore, changes in climate that lead to changes in the timing of snowmelt can alter the timing of flowering of E. vaginatum and, consequently, its value as reindeer and caribou forage. I then used relationships between forage chemistry and body weight gain of caribou derived from White (1983) to model the possible effects of altered forage chemistry on food intake and growth in reindeer. Reindeer foraging on cottongrass flowers can potentially increase their intake of digestible dry matter and therefore energy, by selecting to forage on early-emergent inflorescences over late-emergent ones. The multiplicative effects of forage quality and food intake can result in large increases in the rate of body weight gain that have positive feedbacks on the health and reproductive status of reindeer at both the individual and population level. Comparison of effects on reindeer and caribou populations on the Seward Peninsula indicate that early emergence of cottongrass flowers may confer a greater benefit on reindeer.

• #### Effects of target properties on the formation of lunar impact craters in the simple-to-complex transition

The transition from simple to complex crater morphology in impact craters with increase in crater size has been modelled and observed in planetary bodies across the Solar System. The transition diameter depends upon the strength and gravity of the planetary body. On the Moon, this transition takes place over a diameter range of several kilometers. This range spans a diversity of crater morphologies including simple, transitional and complex craters. The diameter range of 15 20 km falls within the lunar simple-to-complex transition. All other impactor properties held constant, the 15-20 km range corresponds to a factor of three in the magnitude of impact kinetic energy. I conducted detailed geologic investigation of 244 well-preserved craters in this diameter range to elucidate the root causes of morphological variations. I used panchromatic data for observing crater and surface morphology, Digital Elevation Models (DEMs) for evaluating crater morphometry and topographic variation of pre-impact terrain, near-infrared (NIR) bands for determining the composition of crater cavity and surrounding terrain, thermal infrared bands for examining rock abundance, and Synthetic Aperture Radar (SAR) data for detecting impact melt deposits. The results of my investigation indicate that the morphological differences are primarily governed by target properties. Simple craters are confined to the highlands, and the mare are more abundant in complex craters. The mare are composed of solidified basaltic lava flows interlayered with regolith. The layering creates vertical strength heterogeneities that drive the destabilization of the transient cavity and its collapse, causing the transition to complex craters at smaller diameters in the mare. The non-layered highlands are more vertically homogeneous in strength and therefore favor simple crater formation. Eight atypically deep simple craters were identified in the highlands near the mare highlands boundaries, the most porous terrains on the lunar surface. After detailed examination of these craters in comparison to their normal-depth counterparts, I conclude that part of the energy from impact on porous target was spent in target compaction. The higher the porosity of the target, the deeper the crater and greater its volume, due to increased compaction. That only some of the craters in the high porosity terrains are deep suggests that those craters are on locally extreme-high porosity patches. However, an unusual impactor property, such as a high velocity impact, a high density impactor, or a near-vertical impact may also be a contributor. The simple craters in the highlands were observed to be located on flat or gradually sloping surfaces or degraded rims and terraces of pre-existing craters. Most craters with localized slumps superpose sharp topographic breaks such as well-developed rims and terraces of pre-existing craters. However, the topographic settings of 35% of the craters with localized slumps appeared to be similar to that of the simple craters. More detailed topographic study of the pre-impact terrains of these two morphologies revealed that the pre-impact terrains of 35% of the craters with localized slumps are gradually sloping or have subtle topographic breaks. Both sharp and subtle breaks are characterized with similar sloping directions as the adjacent craters' walls, which led to over steepening of the transient cavity walls around this part of the rim and their collapse, thereby causing the accumulation of localized slumped material. Several simple craters were also identified to have formed on pre-impact topographic breaks. However, the simple craters' walls that superpose these breaks were observed to be sloping in directions opposite to that of the breaks. So the ejecta around these walls was deposited along the break slopes, and thus syn-impact mass wasting occurred external (and not internal) to the crater cavity.
• #### Electron transport and optical emissions in the aurora

A one-dimensional, steady state auroral model is developed based on a linear electron transport calculation. A set of cross sections for electron neutral collisions describing elastic scattering, energy loss, and photon emission is compiled and used in conjunction with a discrete ordinate transport code. Calculated electron intensities are compared with in situ rocket measurements. Auroral optical emissions that result from direct electron impact on neutrals are calculated for synthetic and observed electron spectra. A systematic dependence of the brightness of auroral features on energy flux, characteristic energy, and atmospheric composition is found and parameterized. A method for interpreting the brightness and the ratio of brightnesses of certain auroral emissions in terms of the energy flux, characteristic energy, and relative oxygen density is described. Application of this method to auroral images acquired by nadir viewing instruments aboard a satellite is discussed and the distribution of energy flux, characteristic energy, and ionospheric conductances over the auroral oval is determined. Emissions that are suitable for analysing auroral spectra in terms of the atomic oxygen abundance in the auroral zone are identified.
• #### Electrostatic ion cyclotron waves in barium injection experiments in space

Electrostatic ion cyclotron waves are investigated in a charge-generated barium-shaped plasma directed parallel to the earth’s magnetic field. The barium plasma is generated as a result of a barium shape charge release in the upper F₂ region of the ionosphere undergoing photoionization, Using a differential velocity distribution given by Stenbaek-Nielsen et al., [1984], this situation has been modeled based on the condition of collisionless plasma. The instabilities were studied for cases with and without an ambient oxygen ion background. It was concluded that fast ionization in excess of photoionization due to the excitation of electrons by electrostatic ion cyclotron waves was not feasible for the ejection directed along the earth’s magnetic field nor would there be any contribution to Alfven’s critical velocity mechanism if the injection was directed perpendicular to the magnetic field.
• #### Emergent impacts of rapidly changing climate extremes in Alaska

The frequency and intensity of certain extreme weather events in Alaska are increasing, largely due to climate warming from greenhouse gas emissions. Future projections indicate that these trends will continue, potentially leading to billions of dollars in climate-related damages this century. Expected damages arise from increases in extreme precipitation, severe wildfire, altered ocean chemistry, land subsidence from permafrost thaw, and coastal erosion. This dissertation applies new downscaled reanalysis and climate model simulations from the fifth phase of the Coupled Model Intercomparison Project to enhance current understanding of climate extremes in Alaska. Model output is analyzed for a historical period (1981-2010) and three projected periods (2011-2040, 2041-2070, 2071-2100) using representative concentration pathway 8.5. Unprecedented heat and precipitation are expected to occur when compared to the historical period. Maximum 1-day and consecutive 5-day precipitation amounts are expected to increase by 53% and 50%, respectively, and the number of summer days per year (Tmax > 25°C) increases from a statewide average of 1.5 from 1981-2010 to 29.7 for 2071-2100. Major alterations to the landscape of Alaska are anticipated due to a decreasing frequency of freezing temperatures. Growing season length extends by 48-87 days by 2071-2100 with the largest changes in northern Alaska. In contrast, projections indicate a reduced snow season length statewide and many locations in southwest Alaska no longer have continuous winter snow cover. Changes to these metrics indicate that a climate-warming signal emerges from the historical inter-annual variability, meaning that future distributions are entirely outside of those previously observed. The largest changes to extremes may be avoided by following a lower emissions trajectory, which would reduce the impacts and associated costs to maintain infrastructure and human health.
• #### Energetics of hibernation in the Arctic ground squirrel (Spermophilus parryii kenicotti)

Arctic ground squirrels (Spermophilus parryii kenicotti) hibernate underground; experiencing burrows temperatures of -5 to -25C̊. Hibernation consists of 7-9 months of torpor interrupted every 2-3 weeks by 10-20 h arousal episodes with high body temperatures and metabolic rates. Metabolic rates and body temperatures were measured during arousal episodes under temperate and arctic conditions. No difference in cost of arousal episodes was detected. Yet, when the cost of thermogenesis during torpor was included, proportional cost of arousal episodes decreased from 86 to 27% comparing temperate to arctic conditions. The relationship between metabolic rate and body temperature was examined during the recooling phase of hibernation. As animals entered torpor, body temperature was allowed to either decrease naturally or was experimentally altered at different points along the recooling curve. The changes in metabolic rate can be explained by changes in body temperature and no sign of temperature-independent metabolic suppression was detected.