This study utilizes a multidisciplinary approach to the investigation of the extent, timing, and potential effects of repeated Pleistocene glaciation in Bering Strait region. A major focus of this study was directed toward testing the hypothesis that a continental-scale ice sheet existed in Beringia during the Late Wisconsin glacial period. Satellite synthetic aperture radar (SAR) imagery was used to compile a map of glacial moraines in Chukotka, Russia, and to attempt preliminary correlations with the glacial record in Alaska. Geophysical modelling of the solid-earth response to postulated glacial loading, and the reconstruction of regional snowline were combined with the results of the SAR investigation to test the ice sheet hypothesis. Finally, a detailed study of the Quaternary stratigraphy and surficial geology of St. Lawrence Island was used to correlate the glacial and sea level histories of western Alaska and Chukotka, Russia. The sequences of moraines in Chukotka, mapped from SAR imagery, are similar in morphology and position to moraine sequences described in Alaska, recording a succession of glacial events that most likely began in the middle Pleistocene and ended with the Late Wisconsin. The record of repeated mountain glaciation, characterized by radial flow out of high topographic areas provides strong evidence against the existence of a southward-flowing, continental-scale ice sheet in Beringia at any time in the latter part of the Pleistocene. Geophysical modelling of the solid-earth response to glacial loading predicted relative sea level changes on the scale of meters to tens of meters (rising or falling depending on forebulge effect) around the shores of present-day Bering Strait if a large ice sheet had, indeed, occupied the Beringia during Late Wisconsin time. There is no evidence of these predicted sea level changes anywhere in the region. The reconstruction of Late Wisconsin snowlines in Russian and Alaska show that the paleoclimatic conditions needed to 'grow' the hypothesized ice sheet did not exist. Field mapping and stratigraphic work on St. Lawrence Island revealed that ice advanced onto the island twice in the late Pleistocene, once in the Middle Pleistocene and once after the Last Interglacial, probably during the Early Wisconsin. The record of glaciers advancing from Chukotka onto the island provides an important 'Rosetta Stone' for correlating the glacial histories of northeast Siberia and Alaska.

The patterns of occurrence and the underlying processes of two important seismological phenomena at volcanoes, earthquake swarms and volcanic tremor, were investigated. A global database of volcanic earthquake swarm parameters was compiled and was used to evaluate the March 10-14, 1996 seismo-volcanic crisis at Akutan Volcano, Alaska. Earthquake swarm durations and magnitudes were compared with eruptive activity using this database. Trends identified using the database suggest that the Akutan swarm was not precursory and, no eruption occurred. We postulate that a deep instrusion with a large opening component occurred under the flanks of Akutan. The global swarm database has provided an important baseline and has proved to be useful in preparing eruption scenarios for public information releases. The duration-amplitude distribution or frequency-size scaling of volcanic tremor was also examined. The hypothesis tested was that the duration-amplitude distribution may be approximated by an exponential function. The exponential model, implying a scale-bound source process, is found to be a better fit to data then a power-law (scale invariant) model. The exponential model gives a satisfactory description of tremor associated with a wide range of volcanic activity. We propose that exponential scaling of tremor amplitude is due to fixed source geometry driven by a variable excess pressures. This implies that the characteristic amplitude of the duration-amplitude distribution is proportional to a geometric dimension of the source. Broadband seismic data recorded at Arenal volcano, Costa Rica, provide new constrains on tremor source processes. Arenal's tremor contains as many as seven harmonics, whose frequencies vary temporally. This source is inferred to be a shallow, 200-660 m-long resonator, radiating seismic energy from displacement antinodes. We infer that the resonator is gas-charged magma with variable bubble concentration within the conduit and also changes as a function of time, thereby changing the acoustic velocity and the boundary conditions. Polarization analyses for the fundamental mode show particle motion azimuths abruptly rotating, which may be explained by a decrease in incidence angle near the recording site. We suggest that energy for this mode is radiated predominantly from a displacement antinode that is changing position with time.

Two sets of snow and ice thickness data of antarctic sea ice are presented in this study: drilling profiles on individual sea ice floes and spatially more extensive shipboard observations are investigated in order to reveal spatial and temporal characteristics of sea ice. The data were acquired between 1993 and 1995 in the Ross and the Amundsen/Bellinghausen Seas, two different regions of the south polar Pacific Ocean. Sea ice characteristics as well as their spatial distribution and temporal evolution are derived from the data sets. Strong regional trends are observed in ice thickness distributions of the drilling data. A spatial pattern is detected in the snow and ice thickness data as they were sorted according to distance from the ice edge. Flooding on sea ice floes is a widespread phenomenon in Antarctica and relevant for snow ice growth. Flooding is shown to correlate highly with snow loading, while it was much less distinctly correlated to ridging. Isostatic balance was tested on individual sea ice floes. Deviation from isostatic balance was shown to occur locally but was negligible on averaging scales of a few meters. With the help of ice thickness and roughness criteria an unbiased and reproducible ice classification scheme is developed. A combination of different methods from spectral and spatial statistics was used to describe the surface roughness characteristics of the three ice groups in detail. As a practical outcome from the roughness characteristics, air, water and ice surface drag coefficients were derived. With the goal to enhance sampling efficiency, the methodology of data sampling is investigated and optimized strategies are presented. Finally, a statistical ice thickness model managed to explain regional differences in the shape of the ice thickness distribution and therefore the relative significance of ice growth and development processes for a certain region.

Our view of an ecological process is influenced by the scale of our hypotheses and experiments. The forest floor can be examined as a system, where processes that affect ecosystem carbon and nutrient cycling are controlled by macroscale variables (seasonal climatic changes), which in turn affect microscale controls over microbial activity. In the forest floor of Alaskan taiga, annual layers of Equisetum (horsetail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during September 1992, and in June-September 1993. Forest floor material was separated into each of the three most recent litter cohorts, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age), but showed no change over time. Nitrogen mineralization potential increased with depth, and fluctuated over time. Microbial biomass did not vary with depth, but did increase greatly in September in conjunction with increased litter moisture. Litter C:N ratio decreased with time and varied with depth according to the year-to-year variation in litter quality. Our hypothesis that microbial activity on a particular litter cohort is a function of the litter quality, the vertical position of the litter in the forest floor, and the timing of the observation within seasonal macroclimatic cycles was supported. The distribution of some taxa of soil fauna correlated with depth. In these cases, the fauna were likely constrained mostly by differences in the microclimate of the forest floor strata. Other soil fauna varied over time, likely in response to differences in the microbial community. Yet other faunal distributions showed an interaction between depth and time, apparently responding to a combination of changes in microclimate and changes in food availability. The creatures that live in water pores may also have responded to an increase in habitat space as the top-most litter strata became wetter. "Cascading" microcosms containing material from these forest floor strata showed a temporary suppression of respiration by leachates from the newer litter on underlying forest floor material. Traditional litterbag techniques were also used to show changes in nitrogen that indicate winter microbial activity.

The Southern Alaska Peninsula Caribou (Rangifer tarandus) Herd (SAPCH) and its two sub-groups were the focus of a study addressing the hypotheses: (1) food limitation during winter caused a decline in the herd; and, (2) higher calf productivity within the Caribou River group than within the Black Hill group was related to greater forage availability on the seasonal ranges of the Caribou River group. Intense, systematic range and calving surveys in 1991 and 1992 supported the hypothesis of food limitation during winter, and indicated that greater calf production in the Caribou River group was related to earlier commencement of the season of plant growth and greater forage availability on the summer range of that group, coupled with earlier parturition among females of the Caribou River herd. In a comparative study involving the two SAPCH groups and the West Greenland Caribou Herd, daily variation in sizes of foraging groups, densities of caribou within feeding sites, distances between individuals within feeding sites, distances moved by foraging groups, and frequency of group movement was modeled using the following ecological parameters: predation risk, insect harassment (by mosquitos), range patchiness, feeding-site patchiness, feeding-site area, and range-wide density of caribou. Models revealed that intraseasonal social dynamics of foraging caribou were governed in most instances by patterns of forage availability and distribution across landscapes and within feeding sites, in some instances by insect harassment and social pressures, but in no instance by levels of predation risk inherent to the ranges on which they foraged. In a study of the interrelationships between characteristics of graminoids and intensity of grazing by caribou, vegetation on each of the Black Hill and Caribou River ranges was sampled and tested for responses to clipping. Biomass density (g/m$\sp3$) of forage, shoot density (#/m$\sp2$), and nutrient and mineral densities (g/m$\sp3$) and concentrations (g/100g tissue) correlated positively with use of sites by caribou. Productivity and responses to clipping were independent of previous use, but consistent within ranges. These results indicate that caribou are sensitive to local variation in forage quantity and quality, and preferentially use sites with higher returns of nutrients and minerals.

Drilling of the Long Valley Exploratory Well (LVEW) on the resurgent dome in the 760 ka Long Valley Caldera opened a window to view the geologic history of the central caldera. Stratigraphic relationships indicate piston/cylinder (Valles-type) collapse for this caldera, and a resurgent structure intimately linked to post-caldera-collapse rhyolitic intrusions. Samples recovered from this and other wells proximal to the resurgent dome were characterized through isotope microanalytical techniques, petrographic and microprobe study, and analysis of fluid inclusions within alteration minerals. This work revealed the complexity of primary magmatic and secondary hydrothermal activity involved in the formation of a resurgent dome. Measurements of the $\rm\delta\sp{18}O$ composition of silicate components forming the intracaldera lithologies display disequilibrium within samples as a result of variable exchange with hydrothermal fluids. A maximum calculated temperature of $350\sp\circ\rm C$ at 1800 m depth in LVEW indicates paleohydrothermal temperatures exceeded the known present-day hydrothermal conditions by more than $100\sp\circ\rm C.$ Contouring of $\rm\delta\sp{18}O$ values from wells on a line crossing the caldera define a pattern of convective flow with upwelling beneath the resurgent dome. Although surface volcanism at the LVEW site ended about 650 ka, laser probe $\rm\sp{40}Ar/\sp{39}Ar$ microanalysis of samples from sill-like intrusions into the intracaldera ignimbrite reveals intrusive events at ${\sim}650$ ka, ${\sim}450$ ka, and ${\sim}350$ ka. Sanidine phenocrysts from the Bishop Tuff at 1772 and 1792 m depths and whole rock samples of the Mesozoic metavolcanic basement rocks at 1957 m depth record times of disturbance by hydrothermal pulses at ${\sim}530$ ka and ${\sim}350$ ka. Repeated emplacement of intrusions into the centrally located caldera ignimbrite was a primary process of resurgence. In turn, the feeders for the intrusions and the intrusions themselves supplied heat for resurgent-dome-centered hydrothermal flow. After approximately 300 ka, all activity shut off in the central caldera only to resume at ${\sim}40$ ka in response to renewed Holocene volcanic activity in the West Moat. Geophysical evidence of recent intrusive activity beneath the resurgent dome indicates this shallow magma emplacement mechanism is not totally extinct in the central caldera. Most likely a new cycle of volcanism and hydrothermal circulation is underway as the caldera matures.

The field of neuronal transplantation has received a great deal of interest since the 1970's and is currently considered a possible treatment option for both neurodegenerative diseases and spinal cord injury. In this dissertation, fetal neostriatal transplants grafted into the lesioned striatum were studied in both the rat and rhesus monkey. Golgi-impregnation and immunohistochemical techniques were extended to the light and electron microscopic levels to determine the detailed anatomy of the developing striatal implants. Choline acetyltransferase immunoreactive and substance P-like immunoreactive neurons within the rat striatal transplants were morphologically and ultrastructurally similar to normal striatal neurons. When the striatal grafting studies were extended into the rhesus monkey, normal neuronal maturation was demonstrated three months postoperative, both at the light and electron microscopic levels, using various neuroanatomical techniques. From these studies it can be concluded that fetal striatal grafts may be a useful treatment option for Huntington's disease, although numerous difficulties including neuronal degeneration and transplant rejection need to be addressed before this approach is applied in the clinical setting. In a second group of experiments, various approaches to improve autologous bone spinal fusions were studied. Specifically, the utilization of demineralized bone matrix, Type I collagen gel, and recombinant human bone morphogenetic proteins were evaluated for their effects on autologous bone spinal fusions in canines. The study demonstrated that recombinant human bone morphogenetic protein has a strong effect on the amount of bone deposition at the fusion site and, in addition, increases the number of vertebral levels which solidly fuse. The Type I collagen gel appeared to improve the interface between the autologous bone grafts and the host bone, while the demineralized bone matrix had a strong negative effect on the autologous bone graft fusions. Spinal fusion operations in the future will be much more successful if these various methods to improve spinal arthrodesis are utilized to their full potential. It is now clear that reconstruction of the central nervous system and its bony coverings is a real possibility in the very near future, although extensive clinical studies need to be performed before they are widely used in the neurosurgery community.

We investigate various Green and Mackey functor analogs of concepts from the theory of rings and modules. In particular, we consider ideals, chain conditions, Krull dimension, decomposition theorems and completion for these functors. We characterize the Jacobson radical and the prime and maximal ideals of an arbitrary Green functor A. We prove various properties of these ideals. We also investigate the Krull dimension of a commutative Green functor. We analyze the Green and Mackey functors satisfying various chain conditions. For left-modules over Green functors A satisfying a certain noetherian-like condition we study the analog of the tertiary decomposition theorem. For the case when A is commutative we study the analog of the primary decomposition theorem. We also give induction theorems for various special types of Green and Mackey functors such as, prime and simple Green functors A, simple left-A-modules, cotertiary and coprimary left-A-modules. We end with an induction theory for the completion of a Green functor in a left ideal. This work generalizes most of the major topics from classical algebra to the category of Green and Mackey functors.

I investigated demographic components of nest-site fidelity and philopatry of Pacific black brant (Branta bernicla nigricans). My analyses included data I collected during summer 1990-1993, and also incorporated data obtained between 1986-1989. My studies of nest-site fidelity were limited to the Tutakoke River colony, Yukon-Kuskokwim River Delta, Alaska. Studies of philopatry and dispersal among colonies included observations at 7 breeding colonies of brant marked with tarsal tags (n = 20,147). I observed strong evidence that philopatry of brant was female biased. Probability of breeding philopatry, which was estimated with multi-state modeling techniques, was high (>0.9) and dispersal of adults among breeding colonies was rare. I developed an ad hoc estimator for natal philopatry that was unbiased by a confounding of homing, survival, and detection probabilities. Probability of natal philopatry for females was both age and density dependent. The density-dependent decline in natal philopatry may result from increased rate of permanent nonbreeding or increased probability of dispersal. Observed probability of natal philopatry for males was approximately equivalent to the relative size of their natal colony, suggesting that males pair at random with females from other colonies. Gene flow among populations of brant is largely male mediated, and I predict populations of brant will exhibit distinct mitochondrial DNAs if populations have been reproductively isolated for an adequate period of time. Probability of fidelity to previous nest sites for adults was high (>0.7). Probability of nest-site fidelity was affected by previous nesting success, age, and availability of nest sites. Phenology of nesting, nest-site selection, and clutch size of brant was affected by spring snowmelt. Dispersal of brant from traditional nest sites in years with late springs may represent a tradeoff between site fidelity and timing of nest initiation. Movement of young females from natal nest sites was a mechanism for colony expansion. I observed little evidence that site fidelity was advantageous, and concluded that quality of individual bird, environmental conditions, and demographic status may be more important determinants of breeding performance.

I investigated the mechanisms by which differences in body weight and body composition (fat, protein) of female caribou (Rangifer tarandus granti) from the Central Arctic and Porcupine herds might determine changes in pregnancy rate and calf growth. Allometric relations between chemical components and body weight variables were highly significant, despite tremendous seasonal changes in composition. Between October 1989 and May 1990, body fat and body protein of adult females of the Central Arctic Herd declined by maxima of 45 and 29%, respectively; an additional 32% of fat was lost by July. Extensive mobilization of fat and protein indicates winter undernutrition. Marked hypertrophy of liver and kidneys in summer suggests the presence of mobilizable protein reserves. Birth weights of calves were similar between sexes, but male calves grew relatively faster during summer and were significantly heavier than females in autumn. Both fat content and growth rate of calves declined between 4 and 6 weeks post-calving, perhaps in response to insect harassment. Weight gains of wild calves were greatly reduced or absent after 100 d of age, while captive calves continued to grow until 175 d, suggesting that first-summer growth of caribou is determined in part by nutrient availability. Birth weight and growth rate of wild calves from birth to 3-4 weeks of age accounted for nearly 79% of the variability in autumn weights, again implying summer nutrient limitation. Female caribou were unable to entirely compensate for the metabolic and ecological costs of lactation: in autumn, lactating females had 42% less fat and 9% less protein than nonlactating females. Unlike females from the Central Arctic Herd, those from the Porcupine Herd did not demonstrate compensatory weight gains over summer; instead, autumn weight was highly correlated to June weight. Probability of pregnancy was positively correlated with body weight and fat content in early winter. Females that extended lactation into November were less fertile than predicted by body size or condition. I believe that these females were exhibiting lactational infertility.