Microbial communities play critical roles in biogeochemical cycles of aquatic and terrestrial ecosystems, but studies of soil microbial communities have been limited by the diversity and complexity found in most ecosystems. Here we report on work investigating the functional diversity of microbial mat and underlying soil communities in the McMurdo Dry Valleys of Antarctica across a gradient of phosphorus availability on glacial tills of distinct age and mineral composition in Taylor Valley, Antarctica. Microbial mat and soil DNA were extracted and sequenced on an Illumina NextSeq500 in a 150 bp paired end format. Raw sequences were uploaded to the MG-RAST server for processing and annotation. Community taxonomic and functional annotation were determined using the RefSeq and SEED Subsystem databases, respectively. The results revealed significant variation in microbial mat community taxonomic composition between the two tills, strongly associated with visual assessment of mat morphology, e.g., "black" and "orange" mats, and soil N:P ratios. The underlying soil microbial communities did not exhibit significant differences in diversity between the two tills, but community composition varied significantly across gradients of soil chemistry, particularly extractable-phosphate content even within tills. The relative abundance of biogeochemistry-relevant pathways determined from the SEED database varied amongst soil microbial communities between the two tills. For example, microbial mat communities exhibited significant variation in the relative abundance of key nitrogen and phosphorus metabolism associated genes strongly associated with the underlying soil N:P. These results suggest that spatial variation in geochemistry influences the distribution and activity of microbial mats, but that the microbial mats themselves also exert a significant homogenizing effect on the underlying soil communities and some of the key biogeochemical processes they facilitate. / Master of Science / Microbial communities play critical roles in the processes of aquatic and terrestrial ecosystems. Still, studies of soil microbial communities have been limited by the complex nature of the ecosystems we study. This study examined the diversity of microbial communities in the McMurdo Dry Valleys of Antarctica, specifically looking at how different levels of phosphorus availability in the soil affected microbial function. We used DNA sequencing and databases to determine the taxonomic and functional makeup of these communities. We found that while the microbial mat communities varied significantly based on soil chemistry and appearance, the underlying soil microbial communities did not. We also found evidence suggesting that the microbial mats played a role in regulating some of the key ecosystem processes in the soil. Overall, this study sheds light on how microbial communities are impacted by their environment and how they, in turn, impact their surroundings.

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This dissertation investigates the emergence and evolution of United States' national interests in the Arctic region, as well as examines the factors that influence how the U.S. engages in cooperative endeavors in the region with other Arctic states. Though geographically located on the periphery of broader global politics, the region nevertheless is geopolitically situated at the convergence of three continents—North America, Asia, and Europe—in an area historically significant to, but often underappreciated by, the U.S. Government. Two research questions frame this study. The primary research question asks: How have U.S. national interests in the Arctic region evolved over time, and what factors help explain the evolution of U.S. engagement in the region? U.S. perceptions of the region's geopolitical significance gives rise to a subsidiary question: To what degree has the U.S viewed the Arctic region as a zone of competition or a zone of cooperation? Drawing on a range of archival sources, academic literature, historical and contemporary U.S. Government documents—including several declassified documents, as well as personal interviews of key Arctic experts, this study analyzes the development of U.S. interests in the Arctic over four distinct time periods, collectively spanning over a hundred years. These time periods are pre-World War I to the end of World War II (1906-1945); the first half of the four-decade-long Cold War (1945-1967); the second half of the Cold War (1968-1989); and the post-Cold War period (1990-2017). The study produces three major findings. First, U.S. overall interest in the Arctic region increased and decreased in conjunction with how the U.S. perceived the region's overall geopolitical significance. This waxing and waning of U.S. involvement in the polar north generally aligned with the U.S. viewing the Arctic as either a zone of insignificance, competition, or cooperation at different phases over the study's time period. The study's second major finding is that U.S. security interests in the Arctic singularly dominated and shaped America's overall set of national interests that emerged in the region, particularly since World War II. While constituting a number of issues, the most important U.S. security interest in the Arctic has been ensuring freedom of navigation in and through the Arctic. The region's overwhelming maritime composition, along with freedom of navigation's centrality to America's broader global power and interests, ensures the security-driven focus of America's overall Arctic national interests. The final key finding reveals that U.S. Arctic cooperative engagement is conditional. Geopolitical perceptions of the Arctic as either a zone of competition or a zone of cooperation conditions America's willingness to engage with other Arctic states in the region. Since the end of the Cold War and the ensuing period of circumpolar cooperation, U.S. participation in Arctic cooperative arrangements has been conditioned on how much it perceives such arrangements intrude on U.S. autonomy and freedom to act in and through the region. / Doctor of Philosophy / The Arctic is a vast and sparsely populated region that historically has been viewed geographically and geopolitically peripheral to the rest of the world. The United States has not always considered the region important, even though it has territory there. This study asks two questions. First: How have U.S. national interests in the Arctic region evolved over time, and what factors help explain the evolution of U.S. engagement in the region? Second: To what degree has the U.S viewed the Arctic region as a zone of competition or a zone of cooperation? Three major findings emerge from this study, which covers the early 20th century to the second decade of the 21st century—more than a hundred years. First, the evolution of U.S. interests in the Arctic region have waxed and waned in concert with how important the U.S. perceives the region. Second, America's security interests in the Arctic region dominate and drive its overall approach to the region. Finally, U.S.'s willingness to cooperatively engage with other Arctic states in the region depends on how the U.S. believes such engagements effect its ability to act in and through the Arctic region. The Arctic region is becoming more geopolitically important than at any time since at least the Cold War. Rapid global warming could potentially make the region's historically inaccessible shipping routes and vast natural resources accessible by 2050. With Russia already the largest Arctic presence, and China's increased focus on the Arctic, the region could become a space for strategic competition that could threaten U.S. national interests. This study provides the policy community the background and context to navigate the geopolitical challenges and opportunities being unleashed in the Arctic region.

The low polarity of the supercritical fluid extraction (SFE) solvent, CO₂, causes problems when applying this technique to polar compounds. The objective of this research was to expand the applicability of SFE to include polar compounds. The first phase of this research investigated "inverse SFE", which is the selective extraction of the matrix while leaving behind the target analytes, as a means of isolating four polar polymyxin sulfate compounds from several challenging matrices due to the liquid-like consistency and the low concentrations (ppm) of the target analytes. Higher recoveries (>100%) were achieved with low RSD's (5.0 and 1.9% for two separate matrices), compared to the conventional method of isolation, solid phase extraction. The second portion of this research investigated the effect of high levels of polar modifier on trapping efficiency. The mode of modifier introduction was found to have a considerable effect on trapping efficiency, as in-line modifier addition rather than matrix spiking was determined to be best when introducing high levels of liquid modifier. Also, three separate mechanisms, aerosol formation, blow-by, and modifier elution, were identified which caused analyte loss at the solid phase trap, and the extraction and trapping conditions for which each mechanism was most favorable were identified. The next phase of this research developed two separate SFE methods which were used to isolate two pharmaceuticals from leaves. Each SFE method reduced the time, sample handling, costs, and liquid solvents needed as compared to the conventional liquid extraction technique. While achieving comparable recoveries, reproducibilities were much improved for the two SFE methods with RSD's of 3.8 and 5.2%, respectively, while the liquid extraction technique yielded RSD's of 14%. The last phase of this research investigated several strategies for improving selectivity in SFE. Three separate strategies for improving selectivity were studied: 1) alternative fluids (pure and modified fluoroform and tetrafluoroethane), 2) pre-extraction, and 3) selective rinsing of the solid phase trap. Advantages were realized with each technique, and it was concluded that they be used in conjunction with one another in order to maximize selectivity. / Ph. D.

The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere satellite images in the nadir at the UV wavelength of 265 nm. The camera array has an approximately 120° along track (2000 km) by 80° cross track (1000 km) field of view at a horizontal resolution of 1 by 2 km in the nadir. The satellite is in a sun synchronous orbit with an approximately noon local time equator crossing. The observed albedo is due to Rayleigh scattered sun light from an altitude of approximately 50 km and sunlight scattered from Polar Mesospheric Clouds (PMC) which occur in the summer mesosphere at 83 km. The goal of the CIPS instrument is to retrieve high horizontal resolution maps of PMC albedo and the mode radius of the particle size distribution. The first manuscript analyzes the uncertainties involved in the retrieval. The ability to infer mode radius from the PMC signal is made significantly harder by the presence of the Rayleigh signal. Much of the difference between PMC signals of different mode radii is also consistent with possible changes in the Rayleigh signal. The signal is decomposed into components which isolate the portion of the PMC signal's dependence on radius which is not consistent with changes in the Rayleigh signal. This isolated component is compared with the measurement noise to estimate and understand the uncertainties in the CIPS retrieval. The presence of the Rayleigh signal is a difficulty in the PMC retrieval, but it is also a valuable data product. The second manuscript highlights the initial findings of a new gravity wave data set developed by the author. The data set provides relative ozone variations at the stratopause with a horizontal resolution of 20 by 20 km. An abundance of gravity wave signatures can be seen in the data which appear to emanate from weather events like thunderstorms and hurricanes as well as orographic sources such as the Andes and the Antarctic Peninsula. The data set fills a gap that presently exists in our observational coverage of gravity waves, so the data set should help significantly in constraining Global Climate Models. / Ph. D.