A transect of cores ranging from 798 m to 1585 m water depth in the South Atlantic Ocean document the relative intermediate water mass nutrient geometry and stable isotopic variability of AAIW during the Younger Dryas cooling event. The data reveal concurrent delta^13 C and delta^18 O excursions of 0.59 ppt and 0.37 ppt within the core of Antarctic Intermediate Water (AAIW) centered at 11,381 calendar years before present based on radiometric age control. A portion of the delta^1 3C variability (0.22 ppt) can be explained by a shift in thermodynamic equilibrium concurrent with a drop in temperature of 1.8°C at the locus of AAIW formation. The remaining 0.37 ppt increase in delta^13 C most likely resulted from increased wind velocities, and a greater coupling between the ocean and the atmosphere at the locus of AAIW formation (increased efficiency of the thermodynamic process). Deepwater coral mounds are aggregates of corals, other organisms, their skeletal remains, and sediments that occur on the seafloor of the world’s oceans. In the Straits of Florida, these features have been referred to as lithoherms. We use digital, side-scan sonar data collected from the submarine NR-1 from an 10.9 km^2 area at ~650 m water depth to characterize quantitatively aspects of the morphology of 216. Their lengths, widths, heights, areas, orientations and concentration on the seafloor have been determined. Analysis indicates that the outlines of relatively small to medium sized lithoherms can be effectively described with a piriform function. This shape is less applicable to the largest lithoherms because they are aggregates of smaller lithoherms. Nearly all of the lithoherms studied have axes parallel to the northward flowing Florida Current, and the heads of 80 percent of these features face into the current. The shape and orientation of the lithoherms, and evidence of megaripples and scouring in the sonar data suggest that these features are formed by a unidirectional current. Following an extensive investigation of over 200 lithoherms via side-scan sonar imagery and direct observation, we have developed a qualitative model for the formation of the lithoherm type of deep-water coral mounds in the Straits of Florida. Lithoherm formation can be characterized by four main stages of development: nucleating, juvenile, mature singular, and fused. Fused lithoherms can form via transverse and/or longitudinal accretion, however, transverse accretion at the head of the mound is likely the most efficient mechanism. A comparison of lithoherm spatial relationship to local bathymetry agrees with previous observations of deep-water coral mound formations along the levied margins of density flow scour channels.

The study focuses mainly on two gas hydrate-related targets, located on the Northern Cascadia Margin, offshore Vancouver Island: (1) a recently identified 70-80-m high carbonate mound, Cucumber Ridge, located ~3.5-km west of Ocean Drilling Program (ODP) Site 889 and Integrated Ocean Drilling Program (IODP) Site U1327, and (2) a large cold vent, Bullseye vent, which is up to ~500 m in diameter and was drilled by IODP at Site U1328. The objective of this thesis is to analyze seismic data that provide indicators of locally focused fluid flow and characteristics of the gas hydrate occurrence associated with these two features. A grid of closely-spaced single channel seismic (SCS) data was collected at Cucumber Ridge in July/August 2001, and deep-towed multichannel seismic (MCS) lines were collected using Deep-towed Acoustics and Geophysics System (DTAGS) at the Bullseye vent area and at Cucumber Ridge in October 2002. The high-resolution SCS data, with a frequency bandpass of 40-150 Hz, recorded coherent reflectivity down to about 400 m beneath the seafloor, and provide excellent images of the subseafloor structure of Cucumber Ridge and of the gas hydrate bottom-simulating reflector (BSR) beneath it. Cucumber Ridge is interpreted to have developed as a structural topographic high in the hanging wall of a large reverse fault formed at the base of the current seaward slope. The fault zone provides pathways for fluids including gas to migrate to the seafloor where diagenetic carbonate forms and cements the near-surface sediments. Over the seismic grid, heat flow was derived from the depth of the BSR. A simple 2-D analytical correction for theoretical heat flow variations due to topography is applied to the data. Across the mound, most of the variability in heat flow is explained by topographic effects, including a local 6 mW/m2 negative anomaly over the central mound and a large 20 mW/m2 positive anomaly over the mound steep side slope. However, just south of the mound, there is a 6-7 mW/m2 positive anomaly in a 2-km-long band that has predominantly flat seafloor. Most of this anomaly is probably unrelated to topographic effects, but rather likely due to warm upward fluid flow along faults or fracture zones. Towed ~300 m above seafloor, the high frequency (220-1k Hz) DTAGS signal can provide high vertical resolution images with increased lateral resolution. The major problems of DTAGS are significant nonlinear variations of the source depths and receivers locations. New routines were developed for optimal DTAGS data processing, mainly including (1) cable geometry estimation by node depths, direct arrivals and seasurface reflections using a Genetic Algorithm inversion method, (2) acoustic image stitching based on accurate relative-source positioning by crosscorrelation of redundant data between two adjacent shots, and (3) velocity inversion of wide-angle traveltimes using a nonlinear global grid search method. The final processed DTAGS images resolve multiple seismic blanking zones and fine details of subseafloor features in the slope sediments. At Bullseye vent, where a 35-m-thick near-surface massive hydrate layer was drilled at U1328, the DTAGS data resolved the upper part of layer as a dipping diffraction zone, likely corresponding to a fracture zone. The inverted velocity structure in upper 100 m sediments successfully revealed a 17-m-thick layer of high velocity (~1650 m/s) just below seafloor, probably related to carbonate presence. A local high velocity zone, with a positive velocity anomaly of ~40-80 m/s in the upper 50 m beneath seafloor, was observed over the ~100-m wide region between U1328 and the deepest part of a seafloor depression; the high velocity zone is consistent with the dipping diffraction zone in the DTAGS image and with the massive hydrate drilled at U1328.

Made available in DSpace on 2015-03-13T17:08:17Z (GMT). No. of bitstreams: 1 EduardoVQ.pdf: 3502040 bytes, checksum: cedac0b69deb4f4ec6d96c08f23f3160 (MD5) Previous issue date: 2008-12-15 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The study carried out in the environment of Maracaja? reef an S?o Roque channel, had as main objective to analyze the characteristics of sediments active locally expressed in the grains, through collections of sediments in the field, technical processing and data analyzes of sediments. Data processing were made on three main aspects: biotic composition, concentration of calcium carbonate and particle size of the sediment. Differences between the sediments of the reefs and channel were observed. It was emphasized the contribution of algae limestone in the production of carbonate, with some influence of foraminifera near the coast. The particle size distribution presented significant results for the understanding of locally sedimentary deposits. The results showed an environment of carbonate, with predominance of algae limestone, associated to unconsolidated sediments with gross granularity, besides the presence of rhodoliths in all samples.The fragmentation of biotic components and the prevalence of elliptical rhodoliths with little or no branch, indicate an environment of high energy hydrodynamics. This work is a further contribution to the understanding of sedimentology active locally in reef environments, in particular the of Maracaja? reef, by virtue of their complex ecosystem composed of a diversity of wild fauna and flora that still little studied in Brazil comparing to accelerated growth of teeth extractions and usufructs of natural resources causing often irreversible impacts to the environment / O estudo realizado teve como principal objetivo analisar as caracter?sticas dos sedimentos superficiais de fundo, atuantes localmente, no complexo recifal de Maracaja? e no canal de S?o R?que, sob diferentes aspectos: composi??o biog?nica, concentra??o de carbonato de c?lcio e granulometria do sedimento. Os resultados apresentaram as varia??es no sedimento superf?cial do fundo marinho quanto ? Biof?cies, An?lise Granulom?trica, Classifica??o Faciol?gica e Classifica??o de Rod?litos. Observou-se claramente diferentes padr?es sedimentol?gicos existentes nos recifes e no canal localizado entre os recifes e a costa, refletido em todos os par?metros levantados, revelando um ambiente carbon?tico, com predom?nio de algas calc?rias, associadas a um substrato inconsolidado com granula??o grossa. Enfatiza-se a contribui??o das algas calc?rias na produ??o de sedimentos carbon?ticos, com alguma influ?ncia de foramin?feros pr?ximos ? costa. A distribui??o granulom?trica apresentou resultados importantes na classifica??o dos sedimentos. Os sedimentos de tamanho m?dio se restringiram no canal numa ?rea protegida pelos recifes, enquanto que o sedimento com granula??o grossa se distribuiu no restante da ?rea, cobrindo parte da crista e toda regi?o frontal do recife, al?m de uma regi?o mais ao sul do canal. Rod?litos el?pticos se distribuiram em quase toda ?rea, excluindo apenas uma regi?o ao sul do canal e protegido pelos recifes com predom?nio de rod?litos discoidais. O predom?nio de rod?litos el?pticos com pouca ou nenhuma ramifica??o permite inferir um ambiente de alta energia hidrodin?mica, e a presen?a de rod?litos discoidais exclusivamente nos pontos ao norte do canal de S?o Roque e protegidos pelos Recifes possivelmente delimita uma ?rea de menor hidrodin?mica. O presente trabalho constitui mais uma contribui??o para o entendimento das caracter?sticas sedimentol?gicas atuantes localmente nos ambientes recifais, em especial os Parrachos de Maracaja?, em virtude de seu complexo ecossistema composto por uma diversidade de fauna e flora, ainda pouco estudadas no Brasil, contrapondo ao crescimento acelerado de extra??es e usufrutos dos recursos naturais causando impactos muitas vezes irrevers?veis ao meio ambiente