Northern peatlands are complex wetland ecosystems that are characterized as bogs, fens, or tundra. Since these systems are flooded for much of the growing season, organic matter often decomposes anaerobically. Methanogenesis is the dominant means of anaerobic metabolism occurring in these wetlands and can occur via two separate pathways. Acetoclastic methanogenesis involves the formation and subsequent degradation of acetate to form carbon dioxide and methane. Methane can also be produced by the reduction of carbon dioxide by hydrogen gas. This research uses natural abundance isotopes to discern the proportion of methane produced by each of these mechanisms in peatlands along a north-south transect across Alaska. The focus of this research was to investigate pathway shifts in methane production across latitudinal and vegetation gradients in order to discover if acetoclastice methanogenesis becomes less important at higher latitudes. Our study concluded that factors other than latitude (vegetation type and/or pH) have greater impact on methane production mechanism than does latitude. Another objective of this research was to determine if the methanogenic pathway influences the stable deuterium (äD) isotope ratios of the methane produced. This study provided further evidence that methane production mechanism influences the äD of methane causing an antipathetic relationship between the fractionation factors of D and 13C (áD and áC). / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of >Master of Science. / Summer Semester, 2004. / September 19, 2003. / Methane Production, Natural Abundance Isotopes, Methane, Stable Isotopes, Alpha, Fractionation Factors / Includes bibliographical references. / Jeffrey P. Chanton, Professor Directing Thesis; Joel Kostka, Committee Member; William M. Landing, Committee Member.

Adding mulch to a landfill clay cover is a cost effective way to mitigate methane emissions from landfills. This was determined by setting up 3 plots (18x32m) at the Leon County landfill. Two bio-covers consisted of a 15-20 cm thick glass dispersion layer overlain by a layer of mulch either 60cm or 30cm thick over a temporary clay layer. Flux and isotope measurements were collected monthly from 8/3/2004 until 9/22/2005. In addition to the bio-covers, a control area was also measured. Overall, the deep treatment significantly decreased the flux from the landfill. The deep mulch had an average flux, geospatial mean and median flux of 19, 16 and 16 g CH4 m-2d-1. The shallow mulch had an average flux, geospatial mean and median flux of 121, 98 and 17 g CH4 m-2d-1. Finally the control had an average flux, geospatial mean and median flux 104, 98 and 98 g CH4 m-2d-1. Therefore, the deep mulch area decreased flux emissions five times compared to the no mulch area. The shallow mulch area was dominated by high emissions from a single area, a hot spot. Two biocover areas had frequent numbers of zero and negative fluxes while the control area had only one such observation. A negative flux indicates a downward flux of atmospheric CH4 into the landfill. In this case all of the CH4 coming from the landfill is oxidized before it reaches the surface, or else it is blocked by an impermeable zone below the surface. The deep mulch significantly increased the percent oxidation relative to the control. Based upon isotope-determined values, the average and median were 41 and 37%. The shallow mulch had an average and median of 21 and 22%. / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Masters of Science. / Summer Semester, 2006. / April 25, 2006. / Landfill, Methane, Biocover, Oxidation / Includes bibliographical references. / Jeffrey Chanton, Professor Directing Thesis; Tarek Abichou, Committee Member; Joel Kostka, Committee Member.

This dissertation presents an experimental study of the buoyancy fluxes produced by salt fingers in the presence of a laminar shear flow. An annular tank was used in the experiments. Sugar and salt were used as the diffusing components. Salt fingers, initially aligned in the vertical, were observed to tilt when the shear flow was imposed. The fingers were also observed to be 3-dimensional structures at all times during the experiments. A consistent decrease in the salt fluxes was measured as the the Reynolds number was increase by increasing the shear velocity magnitudes. Through a regression analysis, the salt fluxes were found to depend upon the Reynolds number as powers given by -0.025, -0.1 and -0.34, when the density ratio was equal to 1.2, 1.54 and 2.1 respectively. A polynomial expression that encompasses the dependence of the salt fluxes with Reynolds number and density ratio is also suggested. A linear stability theory for fingers tilted by a shear flow together with a flux reduction mechanism, proposed by Krishnamurti (personal communication), are suggested as possible explanations for the experimental results. / A Dissertation submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2007. / November 7, 2006. / Convection, Instability Analysis, Double-Diffusion, Navier Stokes Equations, Cylindrical Coordinates, Particle Image Velocimetry / Includes bibliographical references. / Ruby Krishnamurti, Professor Directing Dissertation; T. N. Krishnamurti, Outside Committee Member; Georges Weatherly, Committee Member; Louis St. Laurent, Committee Member; Thorsten Dittmar, Committee Member.

It has been suggested in older and recent literature that a broad deep eastern boundary flow is linking the equatorial Pacific Ocean to the Southern Ocean. The depth range of this flow corresponds to the Pacific Deep Water (2500m) where it is suggested by the distribution of primordial 3He originating from the East Pacific Rise. In this study, we propose to use a large set of data along with inverse techniques to estimate the stationary advection and diffusion of water properties and tracer concentrations (potential vorticity, potential temperature, salinity, dissolved oxygen and silica concentration) in the area of interest. The various data are combined into an new inverse model first developed by McKeague et al. (2005), Herbei et al. (2006). The model uses a forward advection-diffusion model and Markov Chain Monte-Carlo techniques to give estimates of velocities along and across surfaces of neutral density as well as isopycnal diffusivities. It is composed of 9 layers between the 27.4 and 28 neutral densities. The circulation in the upper layers of the model compares well with direct independent estimates of velocities from subsurface float trajectories (WOCE and Argo). We investigate the water exchange in the deeper layers in regards to the 3He distribution along the Eastern boundary and its mixing with the Antarctic Circumpolar Current. The model is able to estimate vertically dependent rates of oxygen utilization as well as lateral eddy diffusivities of tracers. / A Dissertation submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester, 2009. / April 25, 2008. / Deep Currents, Eastern South Pacific Ocean, Ocean Tracers, Helium, Inverse Problem, Advection-Diffusion / Includes bibliographical references. / Kevin Speer, Professor Directing Dissertation; Carol Anne Clayson, Outside Committee Member; Doron Nof, Committee Member; Georges Weatherly, Committee Member; William Landing, Committee Member; Philip Froelich, Committee Member.

Direct observation of velocities with drifting floats near 1500m depth in the North Atlantic Ocean north of about 45 N are combined to derive a new basin-wide mean circulation within the layer of Labrador Sea Water. Inverse methods are used to determine a basin-scale circulation constrained by non-divergence and conservation of climatological large-scale potential vorticity, with the aim of investigating large-scale potential vorticity dynamics, improving circulation estimates near the basin boundaries, and determining the relative amount of recirculation in sub-basin gyres with (aliased) direct velocity data. Eulerian averages are created from combined datasets and a stream function of the non-divergent flow is computed from the velocity curl and the imposed boundary conditions. Unlike deep flow regimes at low latitudes, where the mid-depth interior circulation is dominated by zonal currents, the mid-depth subpolar flow is dominated by gyres. As suggested by previous estimates of mid-depth circulation, the Labrador Sea Water layer is rapidly circulating around the periphery of the subpolar basin in northern and western boundary currents. Recirculation within basins and exchange between the Labrador Basin and Irminger Basin is modified by the large-scale PV constraints. Eastward flow across the Mid-Atlantic Ridge is concentrated in the Charlie Gibbs Fracture Zone with return flow above the Reykjanes Ridge. A weaker subtropical return flow around the Azores Plateau appears, but data are insufficient to map adequately this region. / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2005. / October 1, 2004. / Circulation, Subsurface Floats, Labrador Sea Wate, r North Atlantic / Includes bibliographical references. / Kevin Speer, Professor Directing Thesis; Georges Weatherly, Committee Member; Doron Nof, Committee Member.

Prior to 1999, the harpacticoid copepod species Zausodes arenicolus had been considered to be very useful for ecological studies because its unusual shape made it easy to recognize. Bouck et al.'s (1999) taxonomic revision based on an evaluation of the morphology of specimens from the northern Gulf of Mexico near the Florida State University Coastal and Marine Laboratory split Z. arenicolus into three species, some of which co-occur. If Bouck et al. are correct, then the previous ecological results would be suspect, and Z. arenicolus would be much less useful in ecological work. It is therefore important to evaluate the validity of the species' boundaries they erected. Because convergent evolution and morphological stasis are known in harpacticoid copepods, morphologically based approaches such as those of Bouck et al. may not be sufficient. I decided to use gene-sequencing methods instead, but I saved voucher material from each specimen so I could search for new morphological characters if the initial morphological identifications and those indicated by gene sequences did not agree. A 393-base-pair region of the mitochondrial cytochrome b gene and a 478-base-pair region of the 18S rRNA gene were separately analyzed from individual Zausodes-complex specimens found at five sites within 30 km of the Florida State University Coastal and Marine Laboratory. Zausodes septimus individuals formed a single cytochrome b gene-sequence clade, whereas Z. arenicolus individuals formed five clades. The uncorrected genetic divergences among these clades were ten times greater than the divergences within them, a degree of differences that suggests that each clade is a different species. The 18S rDNA results support those from cytochrome b. Subsequent analysis of the vouchers revealed morphological differences that will allow two of the Z. arenicolus clades to be described as new species. Further analysis may reveal morphological differentiation among the other three clades. In sum, Bouck et al. (1999) perceived some but not all of the species present. / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2009. / February 26, 2009. / Species Boundary, Copepoda, Harpacticoida, Zausodes, Cytochrome b, 18 S rRNA Gene, Gene Sequencing / Includes bibliographical references. / David Thistle, Professor Directing Thesis; Amy Baco-Taylor, Committee Member; Joel Kostka, Committee Member.

Long term, near continuous, in situ monitoring of cave meteorology, cave aerochemistry, and surface meteorology allows quantitative assessment of cave ventilation and the effect on CO₂ outgassing from cave systems. Because advances in mass spectrometry methods have lowered required sample sizes and increased accuracy for U-series age and carbonate stable isotope analyses, speleothems now have the potential to produce sub-annual paleoclimate records spanning tens of thousands of years (Dorale et al., 2002; Fairchild et al., 2006; Frappier et al., 2007; Lachniet, 2009). However, the need arises for long-term in situ monitoring of the cave environment to create multiple proxies that can be applied to speleothem geochemical records for more accurate interpretations of these records. Focusing on how the local precipitation signal transfers to the cave environment through the epikarst is essential to understanding how variations in precipitation affect drip water hydrochemistry, and ultimately the speleothems precipitated from these drip waters. However, an often overlooked subject is the role cave ventilation has on speleothem formation, and this research focuses on ventilation regimes and their affects on the CO₂ cycle in the cave system. Cave meteorology, cave aerochemistry, and surface meteorology were measured from October 2007 to March 2009 at Hollow Ridge Cave, FL. Cave meteorology follows a similar, but greatly damped, pattern of temperature and barometric pressure as surface meteorology. Continuous measurements of cave air radon-222 and CO₂ indicate that ventilation primarily occurs via gravitational overturn. Strong seasonal patterns were observed in cave air radon-222 and CO₂ concentrations, with decreased ventilation in the summer allowing concentrations to rise, while increased ventilation in winter keeps concentrations near outside atmospheric values. A model developed to estimate CO₂ outgassing indicates greater CO₂ outgassing in the summer and fall than the winter, primarily due to increased CO₂ transport to the cave environment from the soil zone, where rapid degradation of organics increases soil CO₂ production. These results have been submitted and accepted in the form of a manuscript (Chapter 3) to Earth and Planetary Science Letters (Kowalczk and Froelich, 2009). Continuous records of drip rates in the cave suggest the thin overburden results in water residence times of approximately two weeks in the epikarst. However, this residence time is short enough to ensure complete mixing of infiltration waters because analyses of drip waters reveal little variation in their isotopic composition (< 0.3‰ δ18O and < 8‰ δD), while isotopic variations of up to 6‰ δ18O are observed in local precipitation over similar periods. Also, the isotopic composition (δ18O and δD) of aquifer water sampled from Hollow Ridge Cave is lighter than drip waters, indicating present rainfall is isotopically heavier than rainfall over the past 30 years, the average age of water in the North Florida Aquifer (Davis and Katz, 2007). Isotopic, trace element, computed tomography, color, and age analyses of three speleothems collected from Brooks Quarry Cave, FL indicate little variation in the δ18O of precipitation from 70 ka to the present. However, poor chronology (radiocarbon dates) prevent comparison of isotopic, trace element, and color scan records from samples BC2 and BC3 to pollen records over the past 40 ka. Nevertheless, absolute U-series dating of sample BC1 suggest the approximate 3000 year isotopic record (69 Ka) may have recorded Dansgaard-Oeschger Event 19. The ä13C records from these speleothems suggest either large shifts in the overlying vegetation composition (possibly from forest type to grassland/prairie type) or variations in cave ventilation processes that in turn affect drip water CO₂ degassing processes. U-series dating of these samples will allow accurate comparison to pollen records from pond and lake sediment cores in north Florida, and will help construct a more accurate climate history of north Florida. / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2009. / October 12, 2009. / Radon, Cave, Paleoclimate, Speleothem, Cave Ventilation, Climate Proxies, Carbon Dioxide / Includes bibliographical references. / Philip N. Froelich, Professor Directing Thesis; Yang Wang, Committee Member; Doron Nof, Committee Member; Tom Scott, Committee Member; Bill Burnett, Committee Member.

Bibliography: leaves 122-136. / In this study, novel approaches such as artificial neural networks and generalized modelling have highlighted the variability in profile shape and enabled its improved prediction. This will lead to superior regional estimates of primary production.

Bibliography: pages 91-95. / Saldanha Bay, on the west coast of South Africa, is the only deep water port between Cape Town and Walvis Bay. It is separated into two smaller bays, Small Bay and Big Bay, by an iron-ore jetty built in 1975. With its sheltered environment it is an ideal site for the development of a mariculture industry, but a conflict of interest arises between the mussel farmers and the use of the iron-ore jetty and other sources of pollution. This thesis is a contribution to an effort to understand how the requirements of the mariculture industry in respect of food provision and clean water can be met. Seven field trips were made to Saldanha Bay with the aim of studying the circulation characteristics in the various regions of the bay. It was found that drogues were an effective method of measuring currents in Saldanha Bay, with the best method of drogue tracking being with the use of a Differential Global Positioning System (DGPS).

The main purpose of this study was to determine if a relationship exists between oceanic latent heat flux and the summer rainfall of South Africa. Such a link would be useful for a better understanding and the prediction of monthly variability in the summer rainfall for South Africa. In order to investigate possible relationships between oceanic latent heat flux and summer rainfall in South Africa, point to point and point to field statistical correlations were made between gridded monthly COADS derived bulk oceanic heat fluxes and area averaged rainfall for the period 1950 to 1988. Correlations with the oceanic latent heat flux were not significant when the summer area averaged rainfall was divided into early and late summer seasons. This is due to the fact that different oceanic latent heat flux regions correlate with a different rainfall region each month. The results of monthly latent heat flux and summer rainfall demonstrated that there exists a statistical link between oceanic latent heat flux and summer rainfall and that this link could prove useful in the prediction of summer rainfall patterns. These results of the correlation between monthly latent heat flux and summer rainfall show that summer rainfall can be grouped into an all-area index that can be used as a proxy for the entire summer rainfall region. Results of these correlations further show that there are three major mechanisms that are at work over the six month summer rainfall period. These mechanisms show a link between the oceanic latent heat flux and summer rainfall variability. This study has shown that various oceanographic areas in the surrounding oceans correlate at different lags with South African summer rainfall. These correlations can be useful as precursors in predicting wetter or dryer rainfall events. Areas identified by correlation of oceanic latent heat flux regions as important as precursors for summer rainfall prediction are similar to those areas other researchers have identified in studies using OLR, SST and upper level winds (Jury 1995). This study adds weight to the already existing knowledge of these precursors of rainfall predictability.