Ph.D. Dissertation Defense

Role of Thiols in Microbial Metal Reduction and Importance of Organic-Fe(III) Complexes on the Benthic Flux of Iron from Continental Margin Sediments

Iron and manganese transformation reactions greatly impact a variety of environmental and biogeochemical processes in the environment, including the transport and degradation of inorganic and organic contaminants, the cycling of organic carbon, and the transformation a variety of other biogeochemically important chemical species. In addition, as essential nutrient, iron exerts a substantial control on ocean productivity and export of organic matter to the deep ocean.

The impacts of atmospheric radiation on studies of planetary habitability

The conditions required for Earth-like life to emerge on a planetary body are thought to include the presence of liquid water, the availability of energy and the existence of organic material. There are situations when determining whether the above conditions exist on a planetary body is not possible without a detailed understanding of the radiative processes occurring in a planet's atmosphere. In this work, studies of the radiative flux and transfer within planetary atmospheres are carried out in order to elucidate whether certain planetary bodies may be habitable.

Understanding earthquake triggering and fault slip behavior based on complete earthquake catalogs

Large mainshocks can alter stress field on subsurface asperities across broad spatial and temporal windows, which would promote or inhibit fault motion. Beyond rapid rupture during earthquakes, fault can also slip at a steady rate without seismic radiation. In between these two end members, slow slip events have been documented within the conditionally stable transition zone.

Wildfires in Earth System: The Driver, Transport, and Feedback

Wildfires release large amounts of greenhouse gases, carbonaceous aerosols, and other pollutants, therefore having complex impacts on the earth climate, local weather, and air quality. To study the transport of the wildfire emissions, a plume height dataset has been developed. The resulting dataset from 2002 to 2010 captured well the observed MISR plume height distribution. By adding the plume height dataset in the climate model, the plume-rise enhanced AOD downstream of the wildfire spots by 20 to 50%.

Effects of metal impurity on the structure and reactivity of manganese oxides

Mn oxides are among the most ubiquitous and reactive mineral phases in natural environments and significantly influence the cycles of essential elements such as C and N, as well as the transport and fate of a wide range of metals. The structure and reactivity of Mn oxides were extensively studied but most of these studies used pure Mn oxide minerals, which are barely found in real geological or engineering settings.

Geochemical controls of the microbially mediated redox cycling of uranium and iron

Mining and processing of uranium ore, followed by improper disposal and aging nuclear waste infrastructure, have left behind a legacy of uranium contamination across the United States. Uranium bioreduction, an in situ bioremediation strategy which promotes microbial reduction of aqueous U(VI) to insoluble U(IV) solids, has proven successful at decreasing groundwater uranium concentrations below regulatory limits. However, iron 

Improved understanding of extent and size of tsunamigenic earthquakes through geodetic and tsunami datasets

Some of the largest earthquakes yet observed occur along the broad interface between two converging tectonic plates called the megathrust. The extent of the megathrust and its associated seismicity differs with each subduction zone, but typically crustal deformation related to the rupture extends both in submarine and terrestrial environments. On land, this coseismic deformation is common observed with stationary instruments such as Global Navigational Satellite Systems (GNSS) or through satellite imagery using Interferometric Synthetic Aperture Radar (InSAR).

Oceanographic controls of hydrocarbon degradation in the Gulf of Mexico

The risk of an oil spill accident is increasing in pristine regions of the world’s oceans due
to the development and transport of crude oil resources. The ability to predict the trajectory of
spilled oil is critical for the improvement of emergency response strategies. Although the controls of
petroleum hydrocarbon biodegradation have been studied in the ocean for years, there is as yet no
consensus on the results for predictive modeling. One of the reasons is the complexity of the

Hydrocarbon degradation by bacteria in coastal environment of northern Gulf of Mexico sediment after the Deepwater Horizon oil spill

The objective of this dissertation research was to characterize sedimentary microbial populations that are active in degrading petroleum hydrocarbons that reach the seafloor during accidental oil spills. Whereas most previous work has investigated hydrocarbon-degrading microbial communities in sediments from seep environments that are regularly exposed to high levels of oil, the focus of this study was on non-seep sediments that are not pre-exposed to high levels of petroleum.

Exploiting Subsurface Ocean Dynamics for Decadal Predictability in the Upwelling Systems of the Eastern North Pacific

Given the strong recent interest in the decadal timescale variability and the potential for its predictability, it is critical to identify dynamics that carry inherent decadal-scale predictability. This work enhances our understanding and prediction capability of the subsurface signature of the decadal variability in the eastern North Pacific upwelling systems using reanalysis products and a set of eddy-resolving ocean model simulations.

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