Knowledge of mercury concentrations in fish is essential for human health protection. Mercury is a naturally occurring element that acts as a neurotoxin to humans and other species. The biologically available mercury form, methylmercury (MeHg), bio accumulates from small benthic invertebrates to large pelagic fish, and therefore high end consumers and terminal predators have elevated Hg concentrations. The main pathway of MeHg exposure in humans is by consumption of contaminated fish. In this study total Hg concentrations were measured in 10 Gulf of Mexico pelagic fish species using a DMA 80 analyzer. Total Hg concentrations ranged from 0.004 to 3.55 ppm (wet wt). The highest mean concentration (1.04 ppm, wet wt) recorded in king mackerel (Scomberomorus cavalla) exceeded FDA recommended criteria of 1ppm. Dolphinfish (Coryphaena hippurus) and vermilion snapper (Rhomboplites aurorubens) had lowest mean Hg concentrations (<0.3 ppm). The rest of the species were above the EPA advisory level of 0.3 ppm. Wahoo (Acanthocybium solandri), greater amberjack (Seriola dumerili) and gag grouper (Mysteroperca microlepsis) had high Hg concentrations of approximately 0.7 ppm wet wt. Blackfin tuna (Thunnus atlanticus) and yellowfin tuna (Thunnus albacores) had moderate Hg concentrations (0.39 and 0.36 ppm wet wt respectively). Little tunny (Euthynnus alletteratus) and blacktip shark (Carcharhinus limbatus) had mean concentrations of 0.69 and 0.51 ppm respectively. The relationship between fish length and Hg concentrations was significant for four species.

Hurricanes are the leading cause of economic loss in the United States, and recent studies have shown that they have increased in intensity. The growth of population and wealth to coastal regions has exacerbated catastrophic losses. The purpose of this study is to examine the role of three modes of natural climate variability as well as hurricane intensification on destructiveness along the Gulf Coast. The study utilized R programming software to create raster grids and evaluate spatial and temporal relationships between intensification, intensity, sea surface temperatures and destructiveness. Destructiveness was synthesized using the Pielke Landsea 2018 (PL18) normalized losses dataset. The principal findings revealed that the Atlantic Multidecadal Oscillation (AMO) has the greatest influence on hurricane intensification and associated damages. The study offers a contribution to research on hurricane intensification and destructiveness associated with natural climate variability and urges stakeholders to dedicate funds for mitigation measures to reduce the vulnerability to Gulf Coast counties.

The Tuscaloosa Marine Shale (TMS) in southwest Mississippi and south-central Louisiana has potential to become a prolific source of fossil fuels using hydraulic fracturing technology. The objective of this study is to better understand the sequence and regional stratigraphy, lithology, and character of the TMS. Studying the TMS’s lithologic, depositional, and diagenetic properties is essential to maximize potential production. Characterization of the eastern TMS was performed with cuttings from two wells provided by the Mississippi Oil and Gas Board through MDEQ, and two provided by the USGS. Thirty-one petrophysical logs were correlated, to make cross sections and trace sequence stratigraphic intervals within the TMS. Results of the study showed lithologic variability and compaction across the study area, and a sequence stratigraphic correlation of the highstand systems track between the Tuscaloosa and Eagle Ford Groups. This research aims to work toward the greatest potential of the TMS as an unconventional reservoir.

The Macondo 252 oil spill occurred on April 20, 2010 and persisted for 86 days. Oil spill exposed Gulf fish demonstrated reduced lymphocyte counts and increased ethoxyresorufin-O-deethylase (EROD) values. Alligator gar were exposed to 0, 0.5 and 4.0 g oil/L of tank water for 48 hours, then moved to oilree water for a 7 day recovery period. After forty-eight hours exposure, lymphocyte and hematopoietic precursor populations were significantly decreased in dose responsive by exposure to oil. Following a 7 day recovery period, lymphocyte and precursor cell numbers increased. After 48 hours exposure, tissue changes included hepatocellular vacuolization and necrosis, necrotizing pancreatitis, splenic congestion and epicarditis. This demonstrates that oil exposure negatively impacts immune cells and tissues in fish and increases their disease susceptibility. Prolonged oil exposure has the potential to dramatically impact the health status of fish populations.

This dissertation examines the shrimp industry in the Gulf of California from a political ecology perspective. The interaction between fishermen and their marine environment is explored, as well as the historical factors that led to vastly different types of fishermen in the communities of Guaymas and Empalme. Some have specialized in the harvesting of shrimp; others are diversified, multiple species fishermen. Some are highly industrialized offshore shrimpers; others are small-scale fishermen, more modest in their technology but more resilient when facing the current crisis in the shrimp industry. The underlaying causes of this crisis are explored by looking at state development policies, the assumptions behind fisheries management, and the configuration of markets. These have all emphasized specialization in the production of shrimp while ignoring the high interannual variability characteristic of shrimp populations. The end result: an overcapitalized, overexpanded industry and a possible overexploitation of shrimp stocks. Rather than addressing the root causes of the crisis, recent policies have instead transferred rights to the offshore fishery from cooperatives to private investors. At the same time there has been a concerted attack against small-scale producers. It is believed that by getting rid of this sector, catch per boat in the offshore sector will increase and overall "efficiency" will be improved. I compare industrialized trawlers and the small-scale sector and argue that the latter is currently producing high quality shrimp at lower monetary and ecological costs. But small-scale fishing is not equated with sustainability. Instead, differences among small-scale fishermen are analyzed. I contend that those who belong to traditional fishing families and have access to collective knowledge about the marine environment that has accumulated through generations, are better able to deal with a highly unpredictable environment and minimize risk. Those who do not have access to this knowledge have specialized in the harvesting of shrimp. I argue that a strategy of diversification is both more profitable in the short-term and sustainable in the long-run. Avoidance strategies among small-scale fishermen in response to externally imposed regulations are also examined. Fishermen are analyzed as individual profit maximizers and as community members who break the rules to serve collective interests. Just as individuals act collectively to deal with an unpredictable environment, they also act collectively to effectively challenge the institutions of rule-making.

Geophysical surveys in the Gulf of California provided the data to construct contour maps of bathymetry, free-air anomalies and total field magnetic anomalies for the area north of 27° N. Major faults such as the Ballenas- Salsipuedes, Tiburón, Guaymas, and the South Cerro Prieto are clearly observable on these maps. Spectral analysis, using 2-D Fast Fourier Transform methods, of the magnetic anomalies north of 29° N, allowed the identification of at least three distinct magnetic source horizons. The shallowest depth magnetic horizon, with an average depth to the top of 3.1 km below sea level, is interpreted as the top of the magnetic basement. The intermediate depth magnetic horizon, with an average depth to the top of 5.3 km below sea level, may represent either a lithological discontinuity in continental crust, or a transition zone characterized by the intrusion of igneous rocks, faulting, and fracturing associated with rifling processes. Some lineaments observed in the contour map on this horizon are oriented about 15° counterclockwise from the expected orientation of faults. Other lineaments are almost perpendicular to those faults. The deepest magnetic horizon is not apparent at all locations. Computed depths to the bottom of the magnetized crust average 11.5 km below sea level. The depth to the bottom of the magnetic crust is interpreted as the depth of the Curie-point isotherm. Assuming a Curie-point temperature of 580°C and a thermal conductivity of 2.2 W/m °C, the calculated heat flow averages 114 mW/m². Using a two-dimensional Maximum Entropy Method (2DMEM) to obtain the power spectrum of the magnetic anomalies increased the horizontal spatial resolution of the depth determinations by a factor of 4. This method when used to compute the depth to the top of the intermediate horizon, shows an improvement in the delineation of structures. However, the other magnetic horizons and the depth to the bottom of the magnetic crust were not clearly observable using this technique. / Graduation date: 1988

Natural vents in the Gulf of Mexico are actively expelling water and hydrocarbons. They are ubiquitous along continental margins, and I characterize a single vent in the Ursa Basin at leaseblocks MC852/853. Seismic data reveal that the vent is elevated ~75 meters above the seafloor and is roughly circular with a ~1.2 km diameter. A transparent zone centered underneath the vent extends to ~1500 meters below seafloor; this zone is commonly interpreted to record the presence of gas. There is a strong negative polarity seismic reflection that rises rapidly at the vent’s boundaries and is horizontal within a few meters of the seafloor beneath the vent edifice. I interpret that this reflection records a negative impedance contrast, marking the boundary between hydrate and water above and free gas and water below: it is the bottom-simulating reflector. Salinities beneath the vent increase from seawater concentrations to >4x seawater salinity one meter below seafloor. Temperature gradients within the vent are ~15x the background geothermal gradient. I model the coexistence of high salinity fluids, elevated temperature gradients, and an uplifted bottom-simulating reflector with two approaches. First, I assume that high salinity fluids are generated by dissolution of salt bodies at depth and that these hot, saline fluids are expelled vertically. Second, I model the solidification of gas hydrate during upward flow of gas and water. In this model, free gas combines with water to form hydrate: salt is excluded and heat is released, resulting in the generation of a warm, saline brine. The two models result in predictable differences of salinity and temperature. A better understanding of the hydrogeological processes at vent zones is important for quantifying the fluxes of heat and mass from submarine vents and is important for understanding the conditions under which deep-sea biological vent communities exist. / text

Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior. / text

Seagrasses are submerged marine plants that provide essential ecosystem functions, but are declining in abundance worldwide. As angiosperms, seagrasses are capable of sexual reproduction, but also propagate asexually through clonal rhizome growth. Clonal growth was traditionally considered the primary means for seagrass propagation. Recent developments in genetic techniques and an increasing number of studies examining seagrass population genetics, however, indicate that sexual reproduction is important for bed establishment and maintenance. Few studies have investigated the reproductive biology and ecology of sub-tropical seagrass species, although this information is necessary for effective management and restoration. This work investigates the influence of pore-water nutrients on flowering, water flow on seed dispersal, consumption on seed survival, and describes the reproductive phenology in Texas for the two dominant seagrass species in the Gulf of Mexico: turtle grass (Thalassia testudinum) and shoal grass (Halodule wrightii). These species exhibit distinctive reproductive seasons that span summertime months, but reproductive output varies spatially and temporally. Results of an in situ nutrient enrichment experiment indicate that turtle grass produces fewer flowers (but more somatic tissue) when exposed to high pore-water ammonium than when exposed to low pore-water ammonium, suggesting that nutrient loading has the potential to reduce seagrass reproductive output. Seed consumption may also limit reproduction and recruitment in some areas, as laboratory feeding experiments show that several local crustaceans consume shoal grass and turtle grass seeds and seedlings, which do not survive consumption. Dispersal experiments indicate that seed movement along the substrate depends on local water flow conditions, is greater for turtle grass than shoal grass, and is related to seed morphology. Under normal water flow conditions in Texas, turtle grass secondary seedling dispersal is relatively minimal (< 2.1 m d⁻¹) compared to primary dispersal, which can be on the order of kilometers, and shoal grass secondary seed dispersal can be up to 1.1 m d⁻¹, but seeds are likely retained in the parent meadow. Results from this work can be used when developing seagrass management, conservation and restoration actions and provide necessary information concerning a life history stage whose importance was historically under-recognized. / text

The Gulf of Mexico (GOM) represents a challenge for exploration and production. Most of the sediments coming from North America has bypassed the shelf margin into Deep Water. In an Attempt to attack this challenge this thesis pretends to break the GOM's false bottom, mainly comprised by diverse salt structures and growth fault families. In this attempt, geological and geophysical data are integrated to find clues to potential hydrocarbons indicator (PHI) that could be of Reservoir Quality (RQ). 3D Pre stack depth migrated data comprised of Mississippi Canyon blocks, were interpreted: Top and base of salt, leading to the identification of a PHI represented by a consistent Amplitude Anomaly (AA) below and towards a salt structure. This AA may be of RQ and feasibility evaluation for further decisions may be taken. Following the structural sequences that Govern central GOM during Oligocene through out Miocene was important to support the results.