1000 resultados para 343.025 A662g
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Includes index.
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"March 1965."
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"June 1988."
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Includes index.
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"16 June 1977."
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"May 1977."
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Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°x1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.
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The sensitivity of the tropics to climate change, particularly the amplitude of glacial-to-interglacial changes in sea surface temperature (SST), is one of the great controversies in paleoclimatology. Here we reassess faunal estimates of ice age SSTs, focusing on the problem of no-analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods. A new calibration strategy developed here, which uses past variability of species to define robust faunal assemblages, solves the no-analog problem and reveals ice age cooling of 5° to 6°C in the equatorial current systems of the Atlantic and eastern Pacific Oceans. Classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core-top assemblages misrepresented the ice age faunal assemblages. Our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981] and thus may help to resolve a long-standing controversy. Our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems, however, and supports CLIMAP's inference of stability of the subtropical gyre centers.
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Low planktic and benthic d18O and d13C values in sediments from the Nordic seas of cold stadials of the last glaciation have been attributed to brines, formed similar to modern ones in the Arctic Ocean. To expand on the carbon isotopes of this hypothesis I investigated benthic d13C from the modern Arctic Ocean. I show that mean d13C values of live epibenthic foraminifera from the deep Arctic basins are higher than mean d13C values of upper slope epibenthic foraminifera. This agrees with mean high d13C values of dissolved inorganic carbon (DIC) in Arctic Bottom Water (ABW), which are higher than mean d13CDIC values from shallower water masses of mainly Atlantic origin. However, adjustments for oceanic 13C-Suess depletion raise subsurface and intermediate water d13CDIC values over ABW d13CDIC ones. Accordingly, during preindustrial Holocene times, the d13CDIC of ABW was as high or higher than today, but lower than the d13CDIC of younger subsurface and intermediate water. If brine-enriched water significantly ventilated ABW, brines should have had high d13CDIC values. Analogously, high-d13CDIC brines may have been formed in the Nordic seas during warm interstadials. During cold stadials, when most of the Arctic Ocean was perennially sea-ice covered, a cessation of high-d13CDIC brine rejection may have lowered d13CDIC values of ABW, and ultimately the d13CDIC in Nordic seas intermediate and deep water. So, in contrast to the idea of enhanced brine formation during cold stadials, the results of this investigation imply that a cessation of brine rejection would be more likely.
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Analysis of contribution of micronodules of sand and silt size to chemical composition of various types of pelagic sediments, as well as use of published data indicate that in some types of bottom sediments micronodules are the principal carriers of manganese and nickel. These elements appear to constitute smaller fractions of colloidal iron and manganese hydroxides, as well as terrigenous material.
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Servicios registrales
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Servicios registrales
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Doctrina
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"Al igual que en los tres años anteriores, la Universidad del Rosario, por conducto del Observatorio Legislativo y el Grupo de Investigación en Derechos Humanos de la Facultad de Jurisprudencia, se ha asociado con la Fundación Hanns Seidel para organizar el Concurso Nacional de Semilleros de Investigación, el cual tiene por objeto promover e incentivar entre los estudiantes de diferentes áreas del conocimiento, la investigación enfocada hacia temáticas de especial relevancia para el país, lo cual representa un aporte que, desde la etapa de formación, los futuros profesionales de nuestra nación hacen para el análisis y la reflexión de esos temas. Entendiendo la importancia de que las nuevas generaciones de profesionales se comprometan y construyan una visión propia y estructurada de esos temas, la cuarta versión del concurso buscó hacer una reflexión, desde diversas perspectivas, alrededor del desplazamiento forzado en Colombia y las medidas que se han adoptado desde la declaratoria del estado de cosas inconstitucional de la Sentencia T-025 de 2004, proferida por la Corte Constitucional."--presentación.