Theses and Dissertations - Department of Geological Sciences

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δ15n in mollusk shells as a potential paleoenvironmental proxy for nitrogen loading in chesapeake bay
(University of Alabama Libraries, 2014) Black, Heather Dawn; Andrus, C. Fred T.; University of Alabama Tuscaloosa
Crassostrea virginica is one of the most common oyster species in North America and is frequently found in archaeological sites and sub-fossil deposits, especially in the eastern US. Although there have been several sclerochronological studies on δ13C and δ18O in the shells of this species, little is known about δ15N stored within the shells, which could potentially be a useful paleoenvironmental proxy to determine nitrogen loading and the subsequent anthropogenic impacts within an area. In order to potentially serve as paleoenvironmental proxies for N loading, bivalve shells' organic matter needs to remain chemically unaltered. Since ancient peoples cooked most archaeological shells before depositing them in shell middens, it is necessary to determine if prehistoric cooking methods alter either %N or δ15N stored within the shells. Twenty C. virginica oysters and twenty-two Mercenaria spp. clams were treated to five different prehistoric cooking methods: direct exposure to hardwood coals, roasting above hardwood coals, roasting in a dry oven, boiling in freshwater, or boiling in seawater. Each shell was bisected through the resilifer with one half treated with one of the five prehistoric cooking methods and the remaining half serving as a control. With the exception of roasting above the hardwood coals, prehistoric cooking methods do not significantly alter either %N or δ15N within the shells. Those shells roasted above the coals were typically enriched in both %N and δ15N , which is likely an effect of smoke coming from the hardwood coals and infiltrating pore spaces within the outer layers of the shell. Ninety archaeological C. virginica shells ranging in age from ~120 to 3,400 years old and thirty-two modern C. virginica shells were collected in Chesapeake Bay at the Smithsonian Environmental Research Center in Edgewater, Maryland. One valve from each shell was sub-sampled and the calcite powder was analyzed (without acidification pretreatment) using an EA-IRMS system equipped with a CO2 trap to determine the %N and δ15N content of the shells. Comparison of %N and δ15N in C. virginica shells from the six different time periods studied show relatively constant values from ~3,400 years ago to 1820 AD. Between 1820 and 1890, there are rapid increases in both %N and δ15N in the shells, which continue to exponentially increase in value to the modern shells. The increases in %N and δ15N are correlated with increased anthropogenic impact due to human population, sewage discharge, and urbanization in Chesapeake Bay at this time. Therefore, it is likely that C. virginica shells can be used as a paleoenvironmental proxy to measure the anthropogenic impact of a specific area over time. However, the constant, relatively low %N and δ15N values from ~3,400 years ago to 1820 AD compared to the increased N concentrations and enriched δ15N shells from the modern periods could be influenced by diagenetic alteration of the shell after burial in the midden. It is possible that the shells are losing N and preferentially losing 15N over time. More research is necessary to determine if bivalve shells are geochemically stable with regard to N over time or if diagenesis is likely to have occurred in these shells.
Investigating the presence and distribution of organic components in bacterial magnetite
(University of Alabama Libraries, 2013) Spry, Jacob; Perez-Huerta, Alberto; University of Alabama Tuscaloosa
The formation of magnetites within magnetosomes is subjected to highly controlled biomineralization processes by bacteria. Similar biominerals have been observed to contain occluded ("intra-crystalline") organics, revealing significant information about such processes. The size of magnetite particles produced by bacteria (< 100 nm) and limitations in analytical instrumentation have hindered a better understanding of whether organics are located within these nanoparticles. In this study, bright field TEM images, STEM images, and EDS chemical data have been collected for magnetite particles produced by Magnetospirillum gryphiswaldense in order to investigate the potential presence and distribution of organic components. Results reveal low atomic number features in STEM images, suggesting presence of an organic matrix near the edges of nanoparticles. Additionally, STEM-EDS analysis indicates presence of phosphorous within the magnetosome nanoparticles. The mean P/Fe ratio for the outer half of the magnetsome nanoparticles was significantly higher than the mean ratio for the inner "core", suggesting that phosphorus is present with greater magnitude in the "rim" in a co-location with STEM features. Phosphorus is not accounted for in any known mineral constituent of the samples and it is a vital organic element, present in certain types of lipids, which have been associated to the formation of magnetosomes. Overall results contribute to a better knowledge of these highly controlled biomagnetite particles, with significant implications for the recognition of biomarkers and their potential applications in nanotechnology and medicine.
Laboratory incubations of Macondo oil-derived hydrocarbons in Alabama salt marsh sediments and water
(University of Alabama Libraries, 2013) Fields, Daniel; Lu, Yuehan; University of Alabama Tuscaloosa
In order to better understand the impact of the BP Deepwater Horizon and future oil spills on the Gulf of Mexico coast this study assesses the variation of alkanes and polycyclic aromatic hydrocarbons (PAH) in coastal sediments and water. 500g of Sediment and water from Bayou La Batre, Alabama was spiked with 10g Macondo oil for a time series experiment with sampling points at 0, 6, 12, 24, 48, 168, and 336 hours. Sediment and water were also spiked with 0.2g, 2g, 10g, 20g and 50g Macondo oil and were incubated for 21 days for a concentration variation experiment. The composition and concentrations of alkanes and PAHs in the sediments and the concentrations of dissolved inorganic nitrogen and phosphorous and dissolved organic carbon were characterized. Results from the time series experiment show 54.6% total alkanes in sediments were lost within the first six hours and 71.5% were lost after 14 days. Total PAHs decreased by 90.1% within the first six hours and did not show apparent decreases afterwards. The loss of hydrocarbons in the sediments may be attributed to microbial degradation. Low molecular weight (≤ C17) alkanes were preferentially degraded over high molecular weight (> C17) alkanes during the first 24 hours, whereas normal alkanes were not preferentially degraded over isoprenoid alkanes. The high degradation rates of hydrocarbons in the first 12 hours were attributed to aerobic microbial degradation rates of hydrocarbons; the decreases in the loss rates after hour 12 were perhaps due to oxygen depletion in the microcosms. The oxygen depletion was supported by the elevated iron concentration in seawater after 168 hours that indicated anaerobic microbial respiration using Fe (III) as an electron acceptor. However, the concentration of dissolved nitrate and ammonium did not show evident patterns over the course of the incubation, providing no evidence that nitrate was used by microbes as an electron acceptor during anaerobic microbial respiration. Dissolved organic carbon (DOC) concentration continuously decreased until reaching the ambient seawater concentration, indicating an active microbial degradation of oil-derived hydrocarbons that were dissolved in the seawater. In the concentration variation experiment, sterilized controls with 0.2g and 20g of oil treatment had much higher concentrations of saturated alkanes in the sediments than corresponding non-sterilized microcosms with in situ microbial community left intact. However, the microcosms with 10g and 50g of oil treatment did not show reduced concentration of hydrocarbons in the sediments relative to their non-sterilized counterparts. Similarly, variable patterns appeared from the comparison of the dissolved organic carbon concentrations between non-sterilized microcosms vs. sterile microcosms treated with the same amount of oil. Therefore, data from the concentration variation experiment provided inconclusive evidence that the in situ microbial community degraded oil-derived alkanes in sediments and seawater of the microcosms.
Seasonality across the cretaceous-paleogene boundary: a high-resolution ontogenetic study of the Antarctic bivalve, lahillia larseni
(University of Alabama Libraries, 2018) Mohr, Rachel C.; Tobin, Thomas S.; University of Alabama Tuscaloosa
High-resolution ontogenetic stable isotope (δ18O and δ13C) analysis of accretionary carbonate bivalve shells can provide subannual records of their environments. These records present an opportunity to better understand the seasonal variation of past climates and environments. Characterizing the seasonality of past environments is especially helpful in resolving subtle changes during intervals of climate change or environmental perturbations such as during extinction events. Late Cretaceous and early Paleogene bivalve shells of Lahillia larseni from Seymour Island, Antarctica, were isotopically sampled at a high ontogenetic resolution in order to characterize the seasonality of this unstable environment for a period of ~1.3 Myr across the Cretaceous-Paleogene (K-Pg) extinction interval. Ontogenetic δ18O profiles support an austral spring or summer season of growth for L. larseni, with the magnitude of seasonal temperature variation experienced during the growing season ranging from 1.6 ± 0.3°C to 9.5 ± 0.5°C (1σ). The ontogenetic δ13C profiles record isotopic variations in the bottom water dissolved inorganic carbon (DIC) reservoir resulting from the seasonal activity of primary producers. Interannual variations in the primary productivity signal are interpreted as possible evidence for a second bloom of productivity in late summer in years with an additional flux of nutrients, and for the delayed onset of primary productivity in years with winter sea ice. Abnormally low δ13C values in ontogenetic carbon isotope profiles with large seasonal variation provide evidence for the seasonal cycling of biogenic methane production and oxidation occurring during a ~180 kyr interval across the K-Pg boundary. Stratigraphic trends reveal a sudden 6.8 ± 1.3°C (1σ) warming event across the K-Pg boundary, with a duration of ~100 kyr, similar to previous estimates of warming across the K-Pg. This study, which presents the highest resolution ontogenetic sampling of L. larseni shells, provides new insights into the seasonality of an unstable paleoenvironment with no modern analogue, and highlights the potential for changes in subannual variability to destabilize an environment during an interval of extinction.
Secondary ion mass spectrometer geochemical analysis of secondary infilled areas in stylaster erubescens;
(University of Alabama Libraries, 2014) Cobb, Robin Michele; Andrus, C. Fred T.; University of Alabama Tuscaloosa
Paleoceanographers utilize geochemical proxies, such as oxygen isotopic ratios (δ;18;O), that are recorded in coral colonies to reconstruct past ocean conditions. Massive hermatypic corals precipitate skeletal aragonite with a δ;18;O composition that is in disequilibrium with seawater; therefore, compromising their use as a direct proxy for the δ;18;O of seawater (δ18;Oseawater). Previous studies on the family Stylasteridae, an ahermantypic coral, demonstrate that these corals precipitate aragonite in isotopic equilibrium with seawater. Stylasterid corals contain infilled pore spaces of secondary aragonite within the skeletal microstructure, presumably precipitated later in time. The δ;18;O values of these infilled areas have not been studied in detail to determine if they complicate paleoceanographic reconstructions. Stylaster erubescens; coral colonies were collected from the Charleston Bump (31.4°N, -78.8°W), in the Blake Plateau. Infilled and primary skeletal material was analyzed for δ;18;O values using secondary ion mass spectrometry (SIMS) on the micrometer scale. SIMS analysis determined that nine of the eleven infilled areas have δ;18;O values within analytical precision (±0.4 , 2σ) of the adjacent primary skeleton. The two infilled areas with differences in primary and secondary δ;18;O values outside 2σ analytical precision have δ;18;O values that are both higher and lower than the surrounding primary skeleton suggesting environmental changes between the time of initial precipitation and later infilling are the source of the variation. The primary skeleton is composed of 1.9% infilled area by area; therefore, when using conventional millimeter-scale sampling infilled areas would not produce a detectable offset in the geochemical record, in this coral species in this location. These results suggest S. erubescens; can be used as an environmental proxy data source in those regions and times where environmental change is minimal and coral contain few infilled pore spaces.

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