Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item No change in ENSO hydroclimate variability after the industrial revolution as recorded in ?18O of Tectona grandis L.F. from Southeast Sulawesi, Indonesia(2023) Herho, Sandy Hardian Susanto; Evans, Michael MNE; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)El Niño-Southern Oscillation (ENSO) is a quasi-periodic interannual oscillation of the ocean-atmosphere system in the tropical Pacific which greatly influences global climate variability. However, the long-term response to greenhouse gas forcing is still controversial. In this study, we measured the oxygen isotopic composition of ?-cellulose samples at intraannual resolution from independently crossdated teak cores (Tectona grandis L. f.) collected at Muna, Indonesia (5.3ºS, 123ºE, elev. 10m). The site and observation has been previously shown to provide an indirect measure of ENSO activity via local precipitation amount variations associated with ENSO. We created an ensembled composite of the interannual variability for the period 1680-2005 (316 years) using empirical high pass filtering and random sampling of intra-annual resolution measurements. In processing this time series composite, we used Singular Spectrum Analysis (SSA) to high pass filter the data for the interannual variability associated with ENSO. The annually-resolved composite time series of ?18O that we constructed has a higher resolution than other studies that have been conducted to reconstruct ENSO-hydroclimate activities in the western tropical Pacific region over this period. Using this ?18O composite, we compared the distribution of events in the period before and after the industrial revolution using the two-sample Kolmogorov-Smirnov(KS) test. We found no statistically significant change in the distribution of ?18O anomalies. The same statistical test was applied to the Niño 3.4 reconstruction from the Last Millennium Reanalysis (LMR). The results of this study suggest that if there is indeed a forced response of ENSO, it is as yet indetectable. This may be because the forcing is not yet large enough or the forced response is small relative to the unforced variability. Additional factors that might explain this result in the ?18O composite include its observational and interpretational uncertainty, and in the LMR reconstruction, the scarcity of tropical observational constraints and systematic error in the representation of ENSO in climate simulations.Item Biogeographic, Geochemical, and Paleoceanographic Investigations of Ostracodes in the Bering, Chukchi, and Beaufort Seas(2022) Gemery, Laura; Cooper, Lee W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this study, I investigated the continental shelf environments of the Bering, Chukchi, and Beaufort Seas using species of Ostracoda and their shell chemistry as indicators of oceanographic conditions and change. Ostracodes are bivalved Crustacea that secrete a calcareous shell commonly preserved in sediments in the Arctic. Because ostracode species have survival limits controlled by temperature, salinity, oxygen, sea ice, food, and other habitat-related factors, they are useful ecological indicators. A primary objective of my dissertation research was to establish how their ecology, biogeography and shell geochemistry is related to ocean variability in water mass properties and productivity at high latitudes. First, I examined community assemblages of ostracodes over several decades (1970-2018) in the northern Bering, Chukchi, and Beaufort Seas, and the main environmental factors that affect their biogeography. Results showed that large-scale south-to-north and small-scale nearshore-offshore gradients in ostracode community structure were tied to changes in water mass properties in combination with food sources and sediment substrate. Although the dominant species did not significantly change over the investigated period, the frequency of two cold-temperate species that are primarily and previously restricted to shallow North Pacific sediments off Asia has increased during the last decade. This suggests that these species are responding to recent increases in coastal and mid-shelf bottom water temperatures and/or carbon flux to the benthos. A second goal was to assess the feasibility of using stable oxygen isotopes (δ18O) of carbonate from ostracode shells as paleoceanographic proxies for water mass identification on Arctic and subarctic continental shelves. Through the use of regression analyses, I established that the δ18O values of carbonates from two species (of five investigated) can be reliable recorders of summer water mass changes in temperature and seawater δ18O content. The third part of the study was to use results from these prior two goals in combination with data on biogenic silica, foraminifera assemblages and stable isotope composition of biogenic carbonates, to reconstruct 2,000 years of paleoceanography from a radiocarbon-dated sediment core on the Mackenzie Shelf of the Beaufort Sea. This high-resolution (sub-centennial) record identified shifts in multiple proxies that are related to climate oscillations such as the Medieval Climate Anomaly, the Little Ice Age, and the modern period of anthropogenic change. The overall findings of my dissertation research support the premise that on complex and dynamic continental shelves, paleoceanographic uncertainties can be addressed by documenting microfossil faunal assemblages, measuring stable isotope variability in microfossil carbonates, as well as relating the distribution of species in time with an understanding of species ecology.Item EXPLORING THE TEMPERATURE AND HYDROLOGIC RESPONSE OF TROPICAL OCEANS TO VOLCANIC ERUPTIONS OVER THE LAST 400 YEARS USING CORAL GEOCHEMISTRY(2020) Perez Delgado, Zoraida Paola; Kilbourne, Kelly H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Volcanic eruptions perturb the Earth’s climate system. Open questions remain about the response of the hydrologic cycle and internal variability. Coral skeletal strontium to calcium ratios (Sr/Ca) and oxygen isotopic ratios (δ18O) record temperature and seawater oxygen isotopic signatures in the oceans, thus climatic perturbations from eruptions maybe recorded in the coral skeletal chemistry. I quantify the temperature and hydrologic response of the tropical climate system to eruptions since 1640 CE based on coral geochemical records. Data from all basins except the central and eastern Pacific show cooling and increases in seawater δ18O within the first three years of an eruption. Statistical significance of identified signals was tested by comparing against non-eruption sections from the records. Analyses with paired Sr/Ca and δ18O illustrate that the number of observations still limits detection of small signals provided by the eruptions.Item Effects of seawater Sr/Ca on coral paleothermometry in the Florida Keys and Virgin Islands revealed by multi-year continuous monitoring(2020) Hughes, Hunter Passman; Kilbourne, Kelly H; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Coral skeletal Sr/Ca is a widely applied proxy indicator for tropical sea surface temperature (SST) because the elemental ratio in coral aragonite is influenced by both SST and seawater Sr/Ca. Application of the methodology assumes that seawater Sr/Ca is a constant in coral reef environments, and the ratio can be used to solve for paleotemperatures based upon an established coral Sr/Ca – SST relationship. This study tests that assumption by documenting seawater Sr/Ca variability in the Florida Keys and in the U.S. and British Virgin Islands using continuous osmotic pumps. Samples are analyzed for Sr/Ca using a novel method via Inductively Coupled Plasma – Atomic Emission Spectrometry. While mean seawater Sr/Ca did not vary significantly between sites, all sites exhibited significant annual variability (~0.5 – 0.1 mmol/mol), with the greatest variability observed in locations most impacted by freshwater discharge. These findings correspond to large temperature offsets (>2 degrees Celsius) in standard coral Sr/Ca-based SST reconstructions.Item POTENTIAL IMPACT OF VARIATION IN THE SEAWATER STRONTIUM TO CALCIUM RATIO ON CORAL PALEOTHERMOMETRY IN THE FLORIDA KEYS, USA(2018) Khare, Agraj; Kilbourne, Kelly H; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Standard methods of reconstructing past sea surface temperatures with coral skeletal Sr/Ca ratios assume that the seawater Sr/Ca ratio is constant. However, data to support this assumption are sparse in coral reef environments, in part because analytical techniques capable of determining seawater Sr/Ca with sufficient accuracy and precision are time-consuming and not widely available. This work presents a new method to measure seawater Sr/Ca based on inductively coupled plasma atomic emission spectrometry that can be easily adopted by many coral paleothermometry laboratories. The work also presents a spatially gridded study of summer and winter seawater Sr/Ca from the middle Florida Keys Reef Tract. The results indicate that seawater Sr/Ca in nearshore waters influenced by the Florida Bay varies by ~0.1 mmol/mol. The observed variation could lead to errors of ~2°C in temperature reconstructions and suggests that corals growing in waters influenced by Florida Bay are less suited for paleoclimate studies.Item A Time-Series Geochemical Study of the ca. 2.5 Ga Batatal Formation in Brazil: Sulfur and Carbon Isotopic Insights into Environmental Conditions before the Great Oxidation Event(2013) Zhelezinskaia, Iadviga; Kaufman, Alan J; Farquhar, James; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Neoarchean metasedimentary rocks from the Batatal Formation, Brazil were studied using petrographic, elemental and stable isotopic techniques to provide a better understanding of coupling between the atmosphere-ocean system and biogeochemical cycles prior to the Great Oxidation Event. Multiple sulfur isotope data from both shale and carbonate lithofacies confirms global preservation of mass-independent fractionations, thought to be produced through photochemical reactions in an oxygen-free Neoarchean atmosphere. Isotopic differences between lithofacies within the shallow marine Batatal Formation, and beyond in deeper subtidal environments from correlative successions in Western Australia and South Africa, suggest a strong influence of environmental conditions on the preservation of distinct &Delta33S signatures. To explain the novel isotopic data, it is proposed the Batatal Formation was deposited in a shallow water evaporitic environment, which resulted in higher sulfate concentrations and greater sulfur isotope fractionation associated with the activity of sulfate-reducing bacteria. Higher temperatures associated with such environments may have also promoted carbon dioxide limitation resulting in lesser carbon isotopic fractionation by photoautotrophs.