The distribution of benthic polychaetes in the Mississippi Canyon was examined to evaluate impacts of environmental variables on species assemblages. Environmental variables considered included depth, bathymetric slope, hydrographic features, sediment grain size, food availability and sediment contamination. Samples were collected using GOMEX boxcorer. Density decreased with increasing depth exponentially. Diversity exhibited a unimodal pattern with depth with a maximum value in the intermediate depth range (about 1269 m). Deposit feeders were the most abundant feeding guild. Both the feeding guilds and faunal composition could be divided into three groups along the depth gradient: shallow (300 – 800 m), intermediate (800 – 1500 m) and deep (> 1500 m). Results of statistical analyses revealed that depth was the most important determinant in organizing polychaete assemblages in the study area. The Mississippi Canyon and the Central Transect (a non-canyon area) were found not contaminated by trace metals or Polynuclear Aromatic Hydrocarbons (PAHs) in sediments, although the highest PAHs concentration occurred at the head of the Canyon, MT1. The mean density was higher in the Mississippi Canyon (1668 N/m2) than in the Central Transect (979 N/m2), while the mean diversity in the Canyon (ES(100) = 26.9 ) was lower than the Central Transect (ES(100) = 33.1). Large amounts of terrigenous input from the Mississippi River to the Canyon could enhance polychaete density and accelerate competitive exclusion, and thus lead to lower diversity. The faunal composition was significantly different between the two transects, with higher species richness in the Mississippi Canyon (301 species). This could be attributed to structure complexity in the Mississippi Canyon. The distribution of feeding guilds was similar between two transects. The differences observed in polychaete assemblages between two transects may be largely due to high terrigenous sediment and organic matter input to the Mississippi Canyon by the Mississippi River.

Harmful algal blooms (HABs) in the Gulf of Mexico are primarily caused by dense aggregations of the dinoflagellate species, Karenia brevis. Karenia brevis produces a highly toxic neurotoxin, brevetoxin which has been shown to cause Neurotoxic Shellfish Poisoning (NSP) and respiratory distress in humans in addition to a wide range of negative impacts upon natural ecosystems. Karenia mikimotoi is a co-existing species present during K. brevis blooms. K. mikimotoi has caused major HAB events in other parts of the ocean, but has not been recognized as a major contributor to toxicity of blooms in the Gulf of Mexico. K. brevis and K. mikimotoi have both been associated with the presence of unidentified hemolytic toxins. Production of hemolysins has not previously been investigated for either species to date in the Gulf of Mexico. Presence of hemolysins may affect toxicity and the overall impact of HABs. Therefore, detection of hemolysins is imperative for accurate identification of potential harmful impacts of such blooms. The primary goal of this research is to define whether either species is capable of producing hemolytic activity independent of brevetoxin activity; and to identify if there is significant differentiation between a variety of clonal isolates regarding toxicity and growth rate when subjected to variable experimental conditions.

Over the past five years, gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analyses of phospholipid fatty acids (PLFAs) has been increasingly used to link organic matter (OM) sources with sedimentary bacteria. This technique has been applied across diverse estuarine and coastal sediments, including lower Laguna Madre, TX, an oligotrophic, coastal lagoon dominated by a single OM source, seagrasses; shelf stations, a eutrophic coastal region receiving multiple sources of OM, hypoxic regions that occur seasonally and deep slope and abyssal plain sediments of the Gulf of Mexico (GOM). Previous reports using the Laguna Madre data as examples, have been used to make comparisons of PLFA 16:0 and PLFA 15:0 isotope ratios and PLFA 16:0 and total organic carbon isotope ratios. Deviations from the 1:1 line in the former indicate living or recently senescent sources of organic matter are not predominantly bacterial. Deviations from the 1:1 line in the latter indicate living or recently senescent sources of organic matter differ isotopically from detrital or older OM in sediments. Prior to the work of Goni et al. (1998), carbon isotope ratios of OM in GOM sediments were interpreted as marine in origin. Based on a series of geochemical measurements, Goni et al. suggested that GOM sediments are largely composed of terrestrial organic carbon (OCterr). Furthermore, They went on to show that shelf and slope sediments were primarily C3 and C4 respectively. I report on the preferential utilization of autochthonous OM by sedimentary bacteria at the sediment surface and the shift to recalcitrant, terrestrially derived OM with depth.

Thesis (M.A.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Karen Guttieri, Douglas Porch. Includes bibliographical references (p. 87-90). Also available online.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1976.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1930. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed December 15, 2009) Includes index (p. [162-163]).

Thesis--School of Advanced Airpower Studies. / Title from title screen (viewed Nov. 5, 2003). "June 1993." Includes bibliographical references.

Regional depositional systems analyses combining surface and subsurface geological and geophysical data provide the framework for a sequence stratigraphic study of the Lower Oligocene Vicksburg Formation of the Gulf Coastal Plain. The results describe the eustatic history of the Vicksburg stratigraphic unit. The two primary Texas depocenters, the Houston embayment and the Rio Grande embayment, were separated by a deep-rooted structural nose: the San Marcos arch. A barrier / strandplain intervened between the Louisiana deltaic depocenter and the Houston embayment. Within the embayments, deltaic complexes merged along strike with barrier / strandplains. Contemporaneous growth faulting controlled deltaic depositional patterns in the Rio Grande embayment and, to a lesser degree, in the Houston embayment. Smaller wave-dominated delta complexes interspersed with barrier / strandplains extended across the San Marcos arch. Updip of the paralic depocenters, fluvial systems traversed coastal plain units. Seaward of the paralic systems, sand and mud deposits prograded across and built up over the relict Jackson shelf and shelf margin. The contact between the Vicksburg Formation and the underlying Jackson Group marks the position of the Eocene - Oligocene boundary within the Gulf Coastal Plain section. On regional dip-oriented well-log cross sections there is a distinct, abrupt, seaward shift in the paralic facies at the Jackson - Vicksburg boundary; this contact corresponds to an Exxon-model Type 1 unconformity. The unconformity is related to the development of an Antarctic ice sheet in the earliest Oligocene. During middle Vicksburg time, a minor transgression (genetic stratigraphic sequence boundary) flooded the coastal plain. Overlying the progradational Vicksburg Formation, the lower Frio Formation accumulated in an aggradational mode; this switch of depositional modes corresponds to an Exxon-model Type 2 sequence boundary. Construction of genetic stratigraphic sequence diagrams and comparison to Exxon's coastal onlap curves across different areas of the Oligocene coast show that the effects of local depocenters (sediment influx) may mask eustatic effects. Only truly regional events, such as the middle Vicksburg transgression and the basal Vicksburg seaward shift in coastal position, correlate across the coastal plain and may result from a eustatic change. / text

Shallow foundations are used when designing subsea structures on the seafloor of deep water Gulf of Mexico. In order to design these subsea shallow foundations it is important to understand the behavior of the undrained shear strength of the shallow soils (i.e. upper ten to twenty feet of soil). The objective of this research is to analyze a database of soil data from deep water Gulf of Mexico originally produced by Cheon (2011) with a focus on shallow soils. The purpose of this analysis is to gain a better understanding of the soil and how it will be usable with regards to shallow foundation design. The methodology of this analysis involves studying raw data collected from different measurements taken to aid in the creation of design profiles of undrained shear strength versus depth. Within the existing database there are 18 locations with a high resolution of point data from in-situ tests (Halibut Vane) and non in-situ tests (Minivane and Torvane) that provide the clearest picture of undrained shear strength in the shallow region. The data shows that the design profiles originally created for these locations for deep foundations are generally not representative of the strength in the shallow region. They also show that in-situ test data show more variability than non in-situ data. There are also 25 Cone Penetration Tests in the existing database that show very high resolution data in the shallow region. These Cone Penetration Tests also indicate a crust that appears to be about 1 ft thick and exists along the edge of the continental shelf. Recommended future activities to build upon this work include re-evaluating the design profiles at these 43 locations at which high resolution studies have been performed in the shallow region, collecting these design profiles as well as any new design profiles and organizing them into a new database focused on shallow soils, generating a new generic profile base on the data within the new database, and creating a model that uses spatial variability analysis to calculate undrained shear strengths at new locations based on the data in the database. / text

Not available / text