967 resultados para 5-liter, Buesseler et al., 2000


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Clay mineral assemblages at ODP Site 1146 in the northern South China Sea are used to investigate sediment source and transport processes and to evaluate the evolution of the East Asian monsoon over the past 2 Myr. Clay minerals consist mainly of illite (22-43%) and smectite (12-48%), with associated chlorite (10-30%), kaolinite (2-18%), and random mixed-layer clays (5-22%). Hydrodynamic and mineralogical studies indicate that illite and chlorite sources include Taiwan and the Yangtze River, that smectite and mixed-layer clays originate predominantly from Luzon and Indonesia, and that kaolinite is primarily derived from the Pearl River. Mineral assemblages indicate strong glacial-interglacial cyclicity, with high illite, chlorite, and kaolinite content during glacials and high smectite and mixed-layer clay content during interglacials. During interglacials, summer enhanced monsoon (southwesterly) currents transport more smectite and mixed-layer clays to Site 1146 whereas during glacials, enhanced winter monsoon (northerly) currents transport more illite and chlorite from Taiwan and the Yangtze River. The ratio (smectite+mixed layers)/(illite+chlorite) was adopted as a proxy for East Asian monsoon variability. Higher ratios indicate strengthened summer-monsoon winds and weakened winter-monsoon winds during interglacials. In contrast, lower ratios indicate a strongly intensified winter monsoon and weakened summer monsoon during glacials. Spectral analysis indicates the mineral ratio was dominantly forced by monsoon variability prior to the development of large-scale glaciation at 1.2 Myr and by both monsoon variability and the effects of changing sea level in the interval 1.2 Myr to present.

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Ice cores provide a record of changes in dust flux to Antarctica, which is thought to reflect changes in atmospheric circulation and environmental conditions in dust source areas (Forster et al., 2007; Diekmann et al. 2000, doi:10.1016/S0031-0182(00)00138-3; Winckler et al., 2008, doi:10.1126/science.1150595; Reader et al., 1999, doi:10.1029/1999JD900033; Mahowald et al., 1999, doi:10.1029/1999JD900084; Petit et al., 1999, doi:10.1038/20859; 1990, doi:10.1038/343056a0 Delmonte et al., 2009, doi:10.1029/2008GL033382; Lambert et al., 2008, doi:10.1038/nature06763). Isotopic tracers suggest that South America is the dominant source of the dust (Grousset et al., 1992, doi:10.1016/0012-821X(92)90177-W; Basile et al., 1997, doi:10.1016/S0012-821X(96)00255-5; Gaiero et al., 2007, doi:10.1016/j.chemgeo.2006.11.003), but it is unclear what led to the variable deposition of dust at concentrations 20-50 times higher than present in glacial-aged ice (Petit et al., 1990, doi:10.1038/343056a0; Lambert et al., 2008, doi:10.1038/nature06763). Here we characterize the age and composition of Patagonian glacial outwash sediments, to assess the relationship between the Antarctic dust record from Dome C (refs Lambert et al., 2008, doi:10.1038/nature06763; Wolff et al., 2006, doi:10.1038/nature04614) and Patagonian glacial fluctuations (Sugden et al., 2005; McCulloch et al., 2005, doi:10.1111/j.0435-3676.2005.00260.x; Kaplan et al., 2008, doi:10.1016/j.quascirev.2007.09.013) for the past 80,000 years. We show that dust peaks in Antarctica coincide with periods in Patagonia when rivers of glacial meltwater deposited sediment directly onto easily mobilized outwash plains. No dust peaks were noted when the glaciers instead terminated directly into pro-glacial lakes. We thus propose that the variable sediment supply resulting from Patagonian glacial fluctuations may have acted as an on/off switch for Antarctic dust deposition. At the last glacial termination, Patagonian glaciers quickly retreated into lakes, which may help explain why the deglacial decline in Antarctic dust concentrations preceded the main phase of warming, sea-level rise and reduction in Southern Hemisphere sea-ice extent (Wolff et al., 2006, doi:10.1038/nature04614).

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At head of title: La cuestión "R. Samper y Cía".

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National Highway Traffic Safety Administration, Office of Research and Development, Washington, D.C.

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Brief in hearing on petition before Judge Walton for issue of $50,000 additional certificates of receiver.

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At head of title: State of Maine. Cumberland, ss. Supreme Judicial Court.

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At head of title: In the Circuit Court of the United States for the Eastern Division of the Eastern Judicial District of Missouri.