Abstracts of manuscripts submitted in 1988 for publication

This volume contains the abstracts of manuscripts submitted for publication during calendar year 1988 by the staff and students of the Woods Hole Oceanographic Institution. We identify the journal for those manuscripts which are in press or have been published. The volume is intended to be informative, but not a bibliography. The abstracts are listed by title in the Table of Contents and are grouped into one of our five departments , marine policy, or the student category. An author index is presented in the back to facilitate locating specific papers

Evolutionary Feature Selection for Spiking Neural Network Pattern Classifiers

International audienceThis paper presents an application of the biologically realistic JASTAP neural network model to classification tasks. The JASTAP neural network model is presented as an alternative to the basic multi-layer perceptron model. An evolutionary procedure previously applied to the simultaneous solution of feature selection and neural network training on standard multi-layer perceptrons is extended with JASTAP model. Preliminary results on IRIS standard data set give evidence that this extension allows the use of smaller neural networks that can handle noisier data without any degradation in classification accuracy

Oceanic lithosphere magnetization : marine magnetic investigations of crustal accretion and tectonic processes in mid-ocean ridge environments

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2007The origin of symmetric alternating magnetic polarity stripes on the seafloor is investigated in two marine environments; along the ridge axis of the fast spreading East Pacific Rise (EPR) (9º 25’-9º 55’N) and at Kane Megamullion (KMM) (23º 40’N), near the intersection of the slow-spreading Mid Atlantic Ridge with Kane Transform Fault. Marine magnetic anomalies and magnetic properties of seafloor samples are combined to characterize the magnetic source layer in both locations. The EPR study suggests that along-axis variations in the observed axial magnetic anomaly result from changing source layer thickness alone, consistent with observed changes in seismic Layer 2a. The extrusive basalts of the upper crust therefore constitute the magnetic source layer along the ridge axis and long term crustal accretion patterns are reflected in the appearance of the axial anomaly. At KMM the C2r.2r/C2An.1n (~ 2.581 Ma) polarity reversal boundary cuts through lower crust (gabbro) and upper mantle (serpentinized peridotites) rocks exposed by a detachment fault on the seafloor, indicating that these lithologies can systematically record a magnetic signal. Both lithologies have stable remanent magnetization, capable of contributing to the magnetic source layer. The geometry of the polarity boundary changes from the northern to the central regions of KMM and is believed to be related to changing lithology. In the northern region, interpreted to be a gabbro pluton, the boundary dips away from the ridge axis and is consistent with a rotated conductively cooled isotherm. In the central region the gabbros have been removed and the polarity boundary, which resides in serpentinized peridotite, dips towards the ridge axis and is thought to represent an alteration front. The linear appearance of the polarity boundary across both regions indicates that the two lithologies acquired their magnetic remanence during approximately the same time interval. Seismic events caused by detachment faulting at Kane and Atlantis Transform Faults are investigated using hydroacoustic waves (T-phases) recorded by a hydrophone array. Observations and ray trace models of event propagation show bathymetric blockage along propagation paths, but suggest current models of T-phase excitation and propagation need to be improved to explain observed characteristics of T-phase data.My thesis was funded by several different sources: National Science Foundation grants OCE-9819261, OCE-0221832 and OCE-0118445, a Geological Society of America Graduate Student Research Grant and the Academic Programs Office at Woods Hole Oceanographic Institution

Division of Research and Economic Development Annual Report for FY2002

Annual report for the Division of Research and Economic Development of the University of Rhode Island for the year 2001-2002. Includes statistics of project proposals, expenditures, URI Foundation Awards, previous annual report summaries and awards received by individual academic and administrative departments

Carbonatos autigénicos e estruturas de escape de fluidos no Golfo de Cádis

Doutoramento em GeociênciasEste trabalho foca-se no estudo das ocorrências de carbonatos autigénicos do Golfo de Cádis. A mineralogia, textura e valores de δ13Ccarbonatos indica que as diferentes litologias são formadas a partir de oxidação de metano que induz a cimentação dos sedimentos por precipitação de dolomite, calcite magnesiana, calcite e aragonite autigénicas. Os diferentes carbonatos autigénicos derivados de metano (CADM) ocorrem associados a vulcões e cones de lama, cristas diapiricas ou ao longo de falhas. Dois grupos distintos de CADM foram descritos. Um grupo cuja mineralogia é dominada por dolomite e que ocorrem como crostas, chaminés ou nódulos, e um outro grupo com a mineralogia dominada por aragonite e que ocorrem sub a forma de crostas, pavimentos ou montículos, no fundo do mar. Os diferentes grupos de CADM reflectem diferentes ambientes geoquímicos de formação. Os CADM aragoniticos formam-se próximo da interface sedimento/água, enquanto que os CADM dolomíticos formam-se por cimentação ao longo de condutas por onde o fluido circulou dentro da coluna sedimentar em ambientes confinados relativamente à água do mar. A ocorrência destes CADM é interpretada como indicadora de extenso escape de metano na área do Golfo de Cádis. Biomarcadores indicadores de Archaea capaz de realizar oxidação anaeróbica de metano (OAM) e biomarcadores indicadores de bactérias sulfato-redutoras foram identificados nas amostras de CADM. Estes resultados, apoiados também pelas observações de microscópio electrónico e micro-texturas características dos CADM, confirmam um activo envolvimento microbiano na formação destes CADM. A composição isotópica destes CADM indica que na sua formação estiveram envolvidos fluidos intersticiais com um claro contributo de água resultante da dissociação de hidratos de metano. As idades de amostras representativas de CADM, calculadas pela análise de U/Th indica que estes carbonatos se formaram no decorrer dos últimos 250 ka, em períodos correlacionados com rápidas variações paleoceanográficas, como as terminações dos períodos glaciares.This work focus on the occurrences of authigenic carbonates in the Gulf of Cadiz. Mineralogy, texture and δ13Ccarbonate values clearly indicate that the different carbonate lithologies are methane-derived (MDAC), formed by the lithification of sediments as result of the precipitation of authigenic dolomite, calcite, Mg-calcite and aragonite. The MDAC are found associated with mud volcanoes and mud cones, diapiric ridges or along faults. Two distinct groups of MDAC were described in the Gulf of Cadiz. A group dominated by dolomite mineralogy (dolomite crusts, nodules and chimneys) and a group of aragonite dominated carbonates (aragonite pavements, slabs, crusts and buildups). The different MDAC morphologic types reflect different geochemical formation environments. The aragonite pavements represent precipitation of authigenic carbonates at the sediment-seawater interface or close to it. The dolomite nodules, crusts and chimneys result from the cementation along fluid conduits inside the sediment column, in more confined geochemical environments. The widespread abundance of MDAC is interpreted as an evidence of several episodes of extensive methane seepage in the Gulf of Cadiz. Specific 13C-depleted lipid biomarkers indicating archaea involvement in the anaerobic oxidation of methane and bacterial lipid biomarkers also 13Cdepleted and related to sulphate reducing bacteria were both identified on the MDAC. These results, substantiated by SEM observations and by microbial related microfabrics, confirm that microbial activity has played an important role in carbonate authigenesis. Considering the minimum and maximum temperature limits admitted to be possible to occur in the Gulf of Cadiz, some of the MDAC samples indicate a formation from 18O-enriched pore fluids, interpreted as resulting from a contribution of dissociated gas hydrates to the pore waters from which the authigenic carbonates were formed. The estimated U/Th ages of selected dolomite chimneys indicate episodes of intense precipitation of the authigenic carbonates, at least during the last 250 ka, that correlate with periods of rapid paleoceanographic changes as the onsets of glacial/interglacial terminations

Abstracts of manuscripts submitted in 1989 for publication

This volume contains the abstracts of manuscripts submitted for publication during calendar year 1989 by the staff and students of the Woods Hole Oceanographic Institution. We identify the journal of those manuscripts which are in press or have been published. The volume is intended to be informative, but not a bibliography. The abstracts are listed by title in the Table of Contents and are grouped into one of our five deparments, marine policy, or the student category. An author index is presented in the back to facilitate locating specific papers

Marine magnetic investigations of crustal accretion and tectonic processes in mid-ocean ridge environments

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007.Includes bibliographical references.The origin of symmetric alternating magnetic polarity stripes on the seafloor is investigated in two marine environments; along the ridge axis of the fast spreading East Pacific Rise (EPR) (90 25'-90 55'N) and at Kane Megamullion (KMM) (230 40'N), near the intersection of the slow-spreading Mid Atlantic Ridge with Kane Transform Fault. Marine magnetic anomalies and magnetic properties of seafloor samples are combined to characterize the magnetic source layer in both locations. The EPR study suggests that along-axis variations in the observed axial magnetic anomaly result from changing source layer thickness alone, consistent with observed changes in seismic Layer 2a. The extrusive basalts of the upper crust therefore constitute the magnetic source layer along the ridge axis and long term crustal accretion patterns are reflected in the appearance of the axial anomaly. At KMM the C2r.2r/C2An. In (- 2.581 Ma) polarity reversal boundary cuts through lower crust (gabbro) and upper mantle (serpentinized peridotites) rocks exposed by a detachment fault on the seafloor, indicating that these lithologies can systematically record a magnetic signal. Both lithologies have stable remanent magnetization, capable of contributing to the magnetic source layer. The geometry of the polarity boundary changes from the northern to the central regions of KMM and is believed to be related to changing lithology. In the northern region, interpreted to be a gabbro pluton, the boundary dips away from the ridge axis and is consistent with a rotated conductively cooled isotherm. In the central region the gabbros have been removed and the polarity boundary, which resides in serpentinized peridotite, dips towards the ridge axis and is thought to represent an alteration front. The linear appearance of the polarity boundary across both regions indicates that the two lithologies acquired their magnetic remanence during approximately the same time interval. Seismic events caused by detachment faulting at Kane and Atlantis Transform Faults are investigated using hydroacoustic waves (T-phases) recorded by a hydrophone array. Observations and ray trace models of event propagation show bathymetric blockage along propagation paths, but suggest current models of T-phase excitation and propagation need to be improved to explain observed characteristics of T-phase data.by Clare Margaret Williams.Ph.D