Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references. / This study is a geochemical investigation of the evolution of the Kerguelen plume, on the basis of upper mantle and lower crustal xenoliths. Ultramafic xenoliths include harzburgites predominant, a lherzolite, dunites and pyroxenites, whereas lower crustal xenoliths are cumulate gabbros recrystallized under granulite facies conditions. On the basis of the whole rock major element characteristics and trace element abundance patterns in clinopyroxenes, the harzburgites were found to be residues of extensive melting at high pressures within the Kerguelen plume. These were then recrystallized at low pressures and metasomatized by plume generated melts. Details of the metasomatic process were determined from trace element variations in clinopyroxene in connection to texture. This demonstrated that meltrock reaction and the precipitation of new clinopyroxenes occurred by metasomatic carbonatitic melts. It was also found that some of the harzburgites had distinctly unradiogenic Os isotopic compositions and were identified as originating from the sub-Gondwanaland lithosphere. On the basis of major and trace element compositions, the granulite xenoliths were found to be originally gabbroic cumulates formed from plume-derived basaltic melts emplaced at the base of the crust by underplating and subsequently recrystallized isobarically under granulite conditions. The Sr, Nd and Os isotopic compositions of the peridotite and granulite xenoliths demonstrate that the Kerguelen plume is isotopically heterogeneous and displays a temporal progression toward more enriched Sr and Nd isotopic compositions from the Ninetyeast Ridge to granulite xenoliths to Kerguelen basalts and Heard Island basalts. / by Deborah Renee Hassler. / Ph.D.

Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references. / The goal of this thesis was to use high resolution analytical techniques coupled with molecular level analyses to chemically characterize high molecular weight (> 1 k Da (HMW)) dissolved organic matter (DOM) isolated from seawater in an attempt to provide new insights in to the cycling of DOM in the ocean. While a variety of sites spanning different environments (fluvial, coastal and oceanic) and ocean basins were examined, the chemical structure of the isolated HMW DOM varied little at both the polymer and monomer levels. All samples show similar ratios of carbohydrate:acetate:lipid carbon (80±4:10±2:9±4) indicating that these biochemicals are present within a family of related polymers. The carbohydrate fraction shows a characteristic distribution of seven major neutral monosaccharides: rhamnose, fucose, arabinose, xylose, mannose, glucose and galactose; and additionally contains Nacetylated amino sugars as seen by Nuclear Magnetic Resonance Spectroscopy (NMR). This family of compounds, consisting of a specifically linked polysaccharide backbone that is acylated at several positions, has been termed acylated polysaccharides (APS) by our laboratory. APS accounts for 50% of the carbon in HMW DOM isolated from the surface ocean and 20% of the carbon in HMW DOM isolated from the deep ocean. In order to identify a possible source for APS three species of phytoplankton, Thalassiossira weissflogii, Emiliania huxleyi and Phaeocystis, were cultured in seawater and their HMW DOM exudates examined by variety of analytical techniques. Both the T. weissflogii and E. huxleyi exudates contain compounds that resemble APS indicating that phytoplankton are indeed a source of APS to the marine environment. Furthermore, the degradation of the T. weissflogii exudate by a natural assemblage of microorganisms indicates that the component resembling APS is more resistant to microbial degradation compared to other polysaccharides present in the culture. Molecular level analyses show the distribution of monosaccharides to be conservative in surface and deep waters suggesting that APS is present throughout the water column. In order to determine the mechanism by which APS is delivered to the deep ocean the [delta]14C value of APS in the deep ocean was compared to the A14C value of the dissolved inorganic carbon (DIC) at the same depth. If the formation of deep water is the dominant mode of transport then both the DIC and APS will have similar [delta]14C values. However, if APS is injected into the deep ocean from particles or marine snow then the [delta]14C value of APS will be higher than the DIC at the same depth. Our results indicate that APS in the deep Pacific Ocean carries a modem [delta]14C value and is substantially enriched in 14C relative to the total HMW DOM and the DIC at that depth. Thus, particle dissolution appears to be the most important pathway for the delivery of APS to the deep ocean. / by Lihini I. Aluwihare. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1998. / Includes bibliographical references (v. 2, leaves 423-433). / The goal of this thesis is to develop a methodology to interpret sound scattered from the seafloor in terms of seafloor structure and subseafloor geological properties. Specifically, this work has been directed towards the interpretation of matched-filtered, beam-formed monostatic acoustic reverberation data acquired on the west flank of the Mid-Atlantic Ridge when the seafloor is insonified by a band-limited, lowgrazing- angle acoustic pulse. This research is based on the hypothesis that observed backscatter signals are produced by a combination.of seafloor (interface) scattering and subseafloor (volume) scattering from structure having variations at scale lengths similar to the wavelength of the insonifying acoustic field. Analysis of monostatic reverberation data acquired during the Site A experiment (Run 1) of the Acoustic Reverberation Special Research Program 1993 Acoustics Cruise suggests that the scattered signals cannot be accounted for quantitatively in terms of large-scale slope, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. In order to investigate and quantify the actual sources of seafloor scattering, a numerical modeling study of seafloor models is undertaken using a finitedifference solution to the elastic wave equation. Geological data available at Site A and published reports describing geological properties of similar deep ocean crustal regions are used to develop a realistic seafloor model for the study area with realistic constraints on elastic parameters. Wavelength-scale heterogeneity in each model, in the form of seafloor roughness and subseafloor volume heterogeneity is defined using stochastic distributions with Gaussian autocorrelations. These distributions are quantified by their correlation lengths and standard deviation in amplitude. In order to incorporate all seafloor structure in a single parameterization of seafloor scattering, large-scale slope and wavelength-scale seafloor spatial parameters (rms height and correlation length), are included, along with the acoustic beam grazing-angle relative to a horizontal seafloor, in the definition of an 'effective grazing angle'. The Rayleigh roughness parameter, which depends on grazing angle of the insonification, is then redefined using the effective grazing angle and calculated for a variety of seafloor models. Scattering strengths are shown to vary systematically but nonlinearly with the 'effective Rayleigh roughness parameters' of horizontal rough seafloor models. This leads to an approximate interpretation scheme for backscatter intensity. In general, variation in backscattering is found to be dominated by the scattering from rough seafloor. If the seafloor is smooth or very low velocity (e.g., sediment), then scattering from volume heterogeneity becomes an important factor in the backscattered field. Both wavelength-scale seafloor roughness and volume heterogeneity are shown to be capable of producing the levels of variation in intensity observed in monostatic reverberation experiments. Variations in large-scale seafloor slope and subseafloor average velocity are shown to influence the backscatter response of seafloor models. / by Robert John Greaves. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1984. / Includes bibliographical references. / by Joe Pei-Wen Hsy. / Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1984.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979. / Vita. / Includes bibliographical references. / by Stuart Forster Cogan. / Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1980. / Vita. / Includes bibliographical references. / by Alan Charles Janos. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1980.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985. / Bibliography: leaf 13. / by Joseph J. Kilian. / Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.

Thesis: M.S., Massachusetts Institute of Technology, Sloan School of Management, 1975 / Bibliography: leaves 95-97. / M.S. / M.S. Massachusetts Institute of Technology, Sloan School of Management

Thesis: M.S., Massachusetts Institute of Technology, Sloan School of Management, 1976 / Bibliography: leaf 115. / M.S. / M.S. Massachusetts Institute of Technology, Sloan School of Management

Thesis: M.S., Massachusetts Institute of Technology, Sloan School of Management, 1977 / Bibliography : leaves 123-125. / M.S. / M.S. Massachusetts Institute of Technology, Sloan School of Management