• Cloud condensation nuclei

      Ji, Qiang; Shaw, Glenn E.; Stamnes, Knut; Bowling, Sue Ann; Benner, Richard; Kienle, Juergen; Watkins, Brenton (1995)
      In this study the supersaturation spectra of Cloud Condensation Nuclei (CCN) and the size distribution spectra of aerosols were investigated. These studies were conducted because it is believed that atmospheric aerosols, especially CCN, can affect the climate of the Earth. First, the size distributions of aerosols and the number concentrations of CCN were measured at different times in different meteorological airmass systems. The results indicate that the CCN supersaturation spectrum can be calculated from the size distribution of aerosols in only a few cases, suggesting that the direct measurement of CCN is of importance. Second, based on the measurements, a new general equation is proposed to describe the CCN supersaturation spectrum for some types of aerosols. The corresponding equation for CCN size distribution is derived. It is also shown theoretically that, with certain assumptions, the aerosol size distribution in the accumulation mode can be described by a bell-shaped distribution, in agreement with our measurements. The new equations are compared with actual data. Finally, a new method is devised to facilitate the measurement of CCN. The new instrument, which we call the "CCN Remover", separates CCN from the rest of aerosols by activation and removal. Together with a particle sizer, a new CCN measurement system, the CCN Remover Spectrometer, can provide information on both the supersaturation spectrum and the size distribution of CCN. Preliminary laboratory tests show close agreement between measurement results and theoretical predictions. The Remover Spectrometer was successfully tested in the NASA SCAR-B (Smoke, Clouds, and Radiation-Brazil) biomass burning experiment.
    • Cold ions of ionospheric origin observed at the dayside magnetopause and their effects on magnetic reconnection

      Lee, Sun-Hee; 이, 선희; Zhang, Hui; Ng, Chung-Sang; Otto, Antonius; Zong, Qiu-Gang (2015-08)
      Magnetic reconnection at the dayside magnetopause is one of the most important mechanisms that efficiently transfers solar wind particles, momentum, and energy into the magnetosphere. Magnetic reconnection at the magnetopause is usually asymmetric since the plasma and magnetic field properties are quite different in the magnetosphere and the magnetosheath. Cold dense plasma, originating either directly from the ionosphere or from the plasmasphere, has often been observed at the adjacent magnetopause. These cold plasmas may affect reconnection since they modify the plasma properties on the magnetospheric side significantly. This dissertation presents case and statistical studies of the characteristics of the cold ions observed at the dayside magnetopause by using Cluster spacecraft datasets. The plasmaspheric plumes have been distinguished from the ionospheric outows using ion pitch angle distributions. The ionospheric outows feature unidirectional or bidirectional field-aligned pitch angle distributions, whereas the plasmaspheric plumes are characterized by 90° pitch angle distributions. The occurrence rates of the plasmaspheric plumes and ionospheric outows and their dependence on the solar wind/Interplanetary Magnetic Field (IMF) conditions have been investigated. It is found that the occurrence rate of plasmaspheric plume or ionospheric plasma strongly depends on the solar wind/IMF conditions. In particular, plasmaspheric plumes tend to occur during southward IMF while ionospheric outows tends to occur during northward IMF. The occurrence rate of the plasmaspheric plumes is significantly higher on the duskside than that on the dawnside, indicating that the plasmaspheric plumes may lead to a dawn-dusk asymmetry of dayside reconnection. Furthermore, this dissertation investigates the behavior of the cold dense plasma of ionospheric origin during magnetic reconnection at the dayside magnetopause. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection near the subsolar magnetopause, the colder ions are simply entrained by E x B drift at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play a very limited role in magnetic reconnection process. Finally, this dissertation examines a controlling factor that leads to the asymmetric reconnection geometry at the magnetopause. It is demonstrated that the separatrix and ow boundary angles are greater on the magnetosheath side than on the magnetospheric side of the magnetopause, probably due to the stronger density asymmetry rather than magnetic field asymmetry at this boundary.
    • Cold tolerance in Arabidopsis kamchatica and related species

      Armstrong, Jessica J.; Wolf, Diana; Takebayashi, Naoki; Olson, Matthew (2013-05)
      Cold is a major limiting factor in the development and distribution of plants. Many plants increase cold tolerance via cold acclimation. We determined the cold tolerance strategy of Arabidopsis thaliana and A. kamchatica by comparing the extent that plants cooled below the freezing point without freezing, the supercooling capacity, to the temperatures at which 50% of freeze damage occurred (LT50). In A. kamchatica LT50 and supercooling values were similar before cold acclimation; after acclimation LT50 was much colder than supercooling, indicating non-acclimated A. kamchatica avoids freezing by supercooling but after acclimation appears to tolerate freezing. In A. thaliana, LT50 and supercooling were not different, regardless of acclimation, indicating this species avoids freezing year-round. We compared cold hardiness in populations from five Arabidopsis taxa by measuring freeze induced electrolyte leakage. There were differences among taxa; A. kamchatica, A. lyrata subspecies lyrata, and A. lyrata subspecies petraea were more cold tolerant, whereas A. thaliana and A. halleri subspecies gemmifera were less tolerant. There was no correlation between latitude of population origin and cold tolerance for any of the species we tested. Our results indicate a shared evolutionary history may be more important than latitude of origin as a predictor of cold hardiness.
    • Common ravens in Alaska's North Slope oil fields: an integrated study using local knowledge and science

      Backensto, Stacia Ann (2010-05)
      Common ravens (Corvus corax) that nest on human structures in the Kuparuk and Prudhoe Bay oil fields on Alaska's North Slope are believed to present a predation risk to tundra-nesting birds in this area. In order to gain more information about the history of the resident raven population and their use of anthropogenic resources in the oil fields, I documented oil field worker knowledge of ravens in this area. In order to understand how anthropogenic subsidies in the oil fields affect the breeding population, I examined the influence of types of structures and food subsidies on raven nest site use and productivity in the oil fields. Oil field workers provided new and supplemental information about the breeding population. This work in conjunction with a scientific study of the breeding population suggests that structures in the oil fields were important to ravens throughout the year by providing nest sites and warm locations to roost during the winter. The breeding population was very successful and appears to be limited by suitable nest sites. The landfill is an important food source to ravens during winter, and pick-up trucks provide a supplemental source of food throughout the year. Further research will be necessary to identify how food (anthropogenic and natural) availability affects productivity and the degree to which ravens impact tundra-nesting birds.
    • Community, Population, and Growth dynamics of Alnus tenuifolia: Implications for nutrient cycling on an Interior Alaskan floodplain

      Nossov, Dana Rachel; Ruess, Roger; Kielland, Knut; Hollingsworth, Teresa (2008-12)
      This study describes the community, population, and growth dynamics of Alnus tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N accumulation with time. N-fixation itself was likely limited by soil P. Soil N was positively related to alder stem density in early successional stands. Community structure varied along a temporal gradient of changing environmental characteristics, but variations in successional patterns were found. Landscape scale alder recruitment varied temporally and was apparently linked to interactions between geofluvial processes, seed production and dispersal, and herbivory. A widespread stem canker outbreak has resulted in high alder mortality and likely reductions in N-fixation inputs. Disease incidence and mortality were positively related to stem density. Alder radial growth was sensitive to drought during June and August. Alder growth was positively related to river level, suggesting that fluctuation in hyporheic flow is important to alder water balance, especially on lower terraces. The sensitivity of alder growth to meteorological drought was heightened with increasing terrace elevation. Long-term climatic trends suggest that drought will become more common and severe, resulting in reductions in alder-mediated ecosystem N inputs.
    • Comparative analysis of spring flood risk reduction measures in Alaska, United States and the Sakha Republic, Russia

      Kontar, Yekaterina Yevgenevna; Контарь, Екатерина Евгеньевна; Eichelberger, John; Bhatt, Uma; Gavrilyeva, Tuyara; Taylor, Karen; Trainor, Sarah (2017-05)
      River ice thaw and breakup are an annual springtime phenomena in the North. Depending on regional weather patterns and river morphology, breakups can result in catastrophic floods in exposed and vulnerable communities. Breakup flood risk is especially high in rural and remote northern communities, where flood relief and recovery are complicated by unique geographical and climatological features, and limited physical and communication infrastructure. Proactive spring flood management would significantly minimize the adverse impacts of spring floods. Proactive flood management entails flood risk reduction through advances in ice jam and flood prevention, forecasting and mitigation, and community preparedness. With the goal to identify best practices in spring flood risk reduction, I conducted a comparative case study between two flood-prone communities, Galena in Alaska, United States and Edeytsy in the Sakha Republic, Russia. Within a week from each other, Galena and Edeytsy sustained major floods in May 2013. Methods included focus groups with the representatives from flood managing agencies, surveys of families impacted by the 2013 floods, observations on site, and archival review. Comparative parameters of the study included natural and human causes of spring floods, effectiveness of spring flood mitigation and preparedness strategies, and the role of interagency communication and cooperation in flood risk reduction. The analysis revealed that spring flood risk in Galena and Edeytsy results from complex interactions among a series of natural processes and human actions that generate conditions of hazard, exposure, and vulnerability. Therefore, flood risk in Galena and Edeytsy can be reduced by managing conditions of ice-jam floods, and decreasing exposure and vulnerability of the at-risk populations. Implementing the Pressure and Release model to analyze the vulnerability progression of Edeytsy and Galena points to common root causes at the two research sites, including colonial heritage, unequal distribution of resources and power, top-down governance, and limited inclusion of local communities in the decision-making process. To construct an appropriate flood risk reduction framework it is important to establish a dialogue among the diverse stakeholders on potential solutions, arriving at a range of top-down and bottom-up initiatives and in conjunction selecting the appropriate strategies. Both communities have progressed in terms of greater awareness of the hazard, reduction in vulnerabilities, and a shift to more reliance on shelter-in-place. However, in neither community have needed improvements in levee protection been completed. Dialogue between outside authorities and the community begins earlier and is more intensive for Edeytsy, perhaps accounting for Edeytsy's more favorable rating of risk management and response than Galena's.
    • Comparison of blood parameters associated with exercise and the total antioxidant power in sled dogs supplemented with blueberries

      Dunlap, Kriya L.; Duffy, Lawrence K.; Reynolds, Arleigh; Drew, Kelly (2003-12)
      Oxidative damage from free radicals plays an important role in several diseases such as cancer, Alzheimer's disease, and heart disease. Research indicates that exercise may contribute to oxidative stress. Fruits, such as blueberries, are good antioxidants because they contain phenolics that preferentially react with free radicals. Maintaining antioxidant levels by supplementing the diet with blueberries may prevent exercise-induced oxidative damage. Additionally, oxidative damage from exercise can temporarily suppress the immune system. The goal of our study was to compare antioxidant levels in sled dogs supplemented with blueberries. Total antioxidant power (TAP), haptoglobin, isoprostane and other blood parameters were measured in plasma samples from racing sled dogs before exercise, post-exercise, 24 hours post-exercise, and 48 hours post-exercise. Though isoprostane levels did not change throughout the study, creatine kinase levels increased post-exercise for all exercise dogs regardless of blueberry supplementation. Conflicting data makes it unclear as to whether blueberry supplementation reduces muscle damage, adding confusion to the lack of sound antioxidant data available for dogs. Regardless, dogs fed blueberries had a significantly higher TAP than control post-exercise. This suggests that dogs fed blueberries while exercising as compared to dogs fed a control diet while exercising, may be better protected against oxidative damage.
    • A comparison of discrete inverse methods for determining parameters of an economic model

      Jurkowski, Caleb; Maxwell, David; Short, Margaret; Bueler, Edward (2017-08)
      We consider a time-dependent spatial economic model for capital in which the region's production function is a parameter. This forward model predicts the distribution of capital of a region based on that region's production function. We will solve the inverse problem based on this model, i.e. given data describing the capital of a region we wish to determine the production function through discretization. Inverse problems are generally ill-posed, which in this case means that if the data describing the capital are changed slightly, the solution of the inverse problem could change dramatically. The solution we seek is therefore a probability distribution of parameters. However, this probability distribution is complex, and at best we can describe some of its features. We describe the solution to this inverse problem using two different techniques, Markov chain Monte Carlo (Metropolis Algorithm ) and least squares optimization, and compare summary statistics coming from each method.
    • Comparison of geodetic and glaciological mass balance on Gulkana Glacier, Alaska

      Cox, Leif Harrington (2002-12)
      The net mass balance on Gulkana Glacier has been measured since 1966 by the glaciological method, in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier. Systematic errors accumulate through time in this method; therefore the geodetic balance, in which errors are independent of time, was calculated for comparison to and possible calibration of the glaciological method. Digital elevation models (DEMs) of the glacier in 1974, 1993, and 1999 were prepared and geodetic balances computed, giving -6.0+̲0.5 m of water equivalent (weq) from 1974 to 1993 and -11.8+̲0.5 m weq from 1974 to 1999. These were compared to the glaciological balances over the same intervals, which were -5.8+̲0.9 m weq and -11.2+̲1.0 m weq, respectively; both balances show a tripling in thinning rate in the 1990s. These cumulative balances differ by less than 6%. For this, the glaciological method on Gulkana Glacier must be largely free of systematic errors and use a changing area altitude distribution. Relatively good contrast in the accumulation area of the glacier increased accuracy in the geodetic method.
    • Comparison of lower body segment alignment of elite level hockey players to age-matched non-hockey players

      Kimbal, Jim R.; Bult-Ito, Abel; Taylor, Barbara; Duffy, Lawrence (2015-12)
      Lower body overuse and insidious onset injuries are thought to have an underlying biomechanical component which may be predisposing to injury. The purpose of this study was to compare lower body biomechanical characteristics for elite hockey players to matched controls. I hypothesize that elite hockey players have a greater degree of anterior pelvic tilt, greater varus knee angle, a higher foot arch and feet held in parallel more during gait than a matched non-skating population. Measures were taken of elite level, college aged, male hockey players and compared to cross country runners (ten subjects in each group) who served as controls for trunk angle, pelvic tilt angle, knee alignment, (varus/valgus angle), foot angle, arch index (arch height), hip, center of range of motion, hip external rotation, hip internal rotation, hip total range of motion (ROM), knee transverse plane ROM, and step width. The results obtained support the hypothesis for anterior pelvic tilt and foot angle during gait. Although knee angle was in the expected varus direction it was not significant and no differences were observed in the foot arch between the groups. All other measurements not directly related to the hypothesis were not significantly different with the exception of mean step width. The obtained results are important as recent literature describes a lower body posture of medial collapse into "dynamic valgus" as being predisposing to injury. Results show, on the spectrum from lower body varus to lower body valgus, hockey players are on the varus side of the spectrum in all attributes except arch height, which was similar in both populations. Since lower body alignment is thought to be coupled, this inconsistency appears contrary to the "medial collapse into dynamic valgus" model and may explain why foot orthotics and athletic shoes used as an injury intervention often fail.
    • Comparison of snowshoe hare populations in interior Alaska

      Flora, Bjorn (2002-12)
      Snowshoe hares, Lepus americanus, are a 'keystone' prey species in northern boreal forests and experience population fluctuations of 8-11-years. Despite intense responses of both vegetation and predators to changes in hare densities, landscape-scale comparisons of hare populations in Alaska have been limited to qualitative descriptions. We conducted capture-recapture studies of snowshoe hares at 5 locales in the Tanana valley, from Tok in the east to Clear in the west from 1999 to 2002. Snowshoe hare densities were highest in 1999 (x=6.36 ha⁻¹, SE=0.63) and declined thereafter. We were unable to detect declines in apparent survival during declining densities in our study populations. Movement distances did not vary temporally and persistence of individuals through declining densities may be associated positively with body condition at the peak. The relationship of hare pellets and hare densities was weak and limits the utility of this methodology for estimating hare densities in Interior Alaska.
    • Compiled occurrence data of migratory Hooded Cranes in Southeast Asia

      Cai, T.; Guo, Y.; Huettmann, F.; Lee, K. (Beijing Forestry University, Beijing China, 2015-01-01)
      This dataset represents the best available science-based ocurrences (presence only) of Hooded Cranes during fall and spring migration along the flyway in Asia. This dataset consists of 115 geo-referenced sightings with the source/observer in a comma delimited file format. The geo-referencing was done in decimal latitude and longitude with six decimals. Each record carries a source information and is derived from 21 sources. The biggest data sections come from field obervations of the local authors as well as GBIF, satellite telemetry, and Higuchi (1994) and Chang (1999). This data set has four columns and 115 rows with a size of 30KB.
    • Compiled Rabies and Trichinosis (presence only) outbreak data for Alaska

      Waltuch, Rebekah (2014-09-01)
      These are two data sets that were compiled during a UAF student research project, Landscape Ecology class 469/669 (eLearning). They represent a value-added data set and can easily be mapped in a Geographic Information System (GIS) etc. For rabies in Alaska, 237 confirmed cases were found of which 158 had complete information (year, coordinates and vector). The rabies cases in this database are from 1914 til 2013; vectors include Dog, Wolf, Red Fox, Coyote, Arctic Fox, Cat, Caribou, Little Brown Bat, Keen's Myotic Bat and Wolverine. The Alaskan trichinosis data cover 1976-2012 and with various details. Species covered are: Walrus Black Bear, Brown Bear, Bear (unspecified) and Polar Bear. These are student project data compiled from various accessible sources (e.g. the State of Alaska Epidiology website <http://www.epi.hss.state.ak.us> and references cited in the Methods), and they are incomplete. However, they can be used for predictive modeling and similar studies and investigations.
    • Compositional characteristics and ages of plutons in the central Ruby batholith, Alaska: implications for rare-earth-element resources

      Tuzzolino, Amy L.; Newberry, Rainer; McCarthy, Paul; Severin, Kenneth; Freeman, Lawrence (2016-12)
      The central Ruby batholith, comprising much of the Ray Mountains in central Alaska, consists of at least ten, largely monzogranitic plutons, some of which have been defined as a result of this thesis. The general age of the batholith is estimated at 111 Ma, yet recent ⁴⁰Ar/³⁹Ar muscovite and ²³⁸U/²⁰⁶Pb zircon data suggests greater variability in ages than previously known, with ages now spanning 90 to 112 Ma. Initial ⁸⁷Sr/⁸⁶Sr ratios for the area show a general increase from northeast (minimum of 0.706) to southwest (maximum of 0.727). There are two characteristic mineral assemblages distinguishing the plutons: The northern plutons typically have an oxidized, calcic mineral assemblage featuring allanite + titanite + magnetite ± hornblende ± monazite ± ilmenite. The southern plutons are characterized by the minerals monazite + xenotime + ilmenite ± muscovite ± fluorite. Total alkali-silica classification defines only the No Name Creek pluton as being truly peraluminous, a classification further supported by its unique presence of topaz. In the north, the rare-earth elements (REE) are primarily hosted in the silicates allanite-(Ce), (CaCe(Al₂Fe²⁺)(Si₂O₇)(SiO₄)O(OH)), and to a lesser extent, titanite, (CaTiSiO₅), while the phosphate minerals monazite-(Ce), (CePO₄), and xenotime, (YPO₄), are REE hosts in the southern plutons. These mineralogical differences are not necessarily due to variable REE concentrations within the melts, but rather are largely functions of peraluminosity and oxidation state, features intrinsic to the primitive source materials. Chemical analyses of stream gravels draining the batholith highlight geographic trends in trace-element concentrations: The southern gravels are enriched in REE relative to the northern gravels for several reasons. REE in the northern gravels are predominantly hosted in allanite and titanite (both of which contain relatively low REE concentrations), and the REE in the southern gravels are found in monazite and xenotime. Further, magnetite and ilmenite are more abundant in the northern gravels, effectively drowning out the REE carriers. Furthermore, the gravels in the southeast have the highest heavy-rare-earth element to light-rare-earth element ratios. In terms of economics, these ratios are generally the most significant.
    • Concentration-Discharge Patterns Across the Gulf of Alaska Reveal Geomorphological and Glacierization Controls on Stream Water Solute Generation and Export

      Jenckes, Jordan; Ibarra, Daniel; Munk, Lee (2021-10-19)
      High latitude glacierized coastal catchments of the Gulf of Alaska (GoA) are undergoing rapid hydrologic changes in response to climate change and glacial recession. These catchments deliver important nutrients in the form of both inorganic and organic matter to the nearshore marine environment, yet are relatively understudied with respect to characterization of the sediment and solute generation processes and total yields. Using multiple linear regression informed by Bayesian Information Criterion analysis we empirically demonstrate how watershed characteristics affect suspended sediment and solute generation as represented by concentration-discharge relationships. We find that watershed mean slope and relief control solute generation and that solute yields are influenced most by glacier coverage. We contribute a new flux and concentration-discharge based conceptualization for understanding solute cycles across a hydroclimatic gradient of GoA watersheds that can be used to better understand future watershed responses to rapid hydrologic change.
    • A conceptual model of the Pilgrim Hot Springs geothermal system, Seward Peninsula, Alaska

      Miller, Joshua; Whalen, Michael; Prakash, Anupma; Haselwimmer, Christian; Daanen, Ronald (2013-12)
      This work has developed a conceptual geological model for the Pilgrim Hot Springs geothermal system supporting the exploration, assessment and potential development of this resource for direct use and electric power production. The development of this model involved the analysis of a variety of subsurface and geophysical data and the construction of a 3D lithostratigraphic block model. Interpretation of the data and block model aimed to establish the most likely scenario for subsurface geothermal fluid flow. As part of this work well cuttings were analyzed for permeability and correlated with geophysical logs from well to well to constrain the stratigraphic architecture of the unconsolidated sediments. Hydrothermal alteration of the sediments and bedrock core was also studied through reflectance spectroscopy and methylene blue titration in order to investigate past fluid migration pathways. The structure of the basin was interpreted through geophysical surveys including aeromagnetic resistivity, isostatic gravity, and magnetotelIuric resistivity. Based on temperature, well logs, geophysical surveys, and lithologic data, the system is subdivided into a shallow outflow aquifer and a deeper reservoir beneath a clay cap connected by a conduit with 91�C hydrothermal fluid upflow. Stratigraphic correlations indicate several clay layers throughout the section with a dominant clay cap at 200-275 m depth. Extensive pyritization and the clay mineral assemblage suggest an argillic-style alteration facies indicative of past temperatures at or slightly elevated above current conditions of hydrothermal activity at Pilgrim Hot Springs. The conceptual model Supports production from this resource in those subsurface zones where there is sufficient permeability and connectivity with the upflow zone.
    • Constraining the H₂O/CO₂ molar ratio, the volume fraction of exsolved volatiles, and the magma compressibility of the 2006 Augustine eruption, Alaska

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

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

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

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