999 resultados para 127-795


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We present an improved database of planktonic foraminiferal census counts from the Southern Hemisphere Oceans (SHO) from 15°S to 64°S. The SHO database combines 3 existing databases. Using this SHO database, we investigated dissolution biases that might affect faunal census counts. We suggest a depth/[DCO3]2- threshold of ~3800 m/[DCO3]2- = ~-10 to -5 µmol/kg for the Pacific and Indian Oceans, and ~4000 m/[DCO3]2- = ~0 to 10 µmol/kg for the Atlantic Ocean, under which core-top assemblages can be affected by dissolution and are less reliable for paleo-sea surface temperature (SST) reconstructions. We removed all core-tops beyond these thresholds from the SHO database. This database has 598 core-tops and is able to reconstruct past SST variations from 2° to 25.5°C, with a root mean square error of 1.00°C, for annual temperatures. To inspect dissolution affects SST reconstruction quality, we tested the data base with two "leave-one-out" tests, with and without the deep core-tops. We used this database to reconstruct Summer SST (SSST) over the last 20 ka, using the Modern Analog Technique method, on the Southeast Pacific core MD07-3100. This was compared to the SSST reconstructed using the 3 databases used to compile the SHO database. Thus showing that the reconstruction using the SHO database is more reliable, as its dissimilarity values are the lowest. The most important aspect here is the importance of a bias-free, geographic-rich, database. We leave this dataset open-ended to future additions; the new core-tops must be carefully selected, with their chronological frameworks, and evidence of dissolution assessed.

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To detect and track the impact of large-scale environmental changes in a the transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the Alfred- Wegener-Institute for Polar and Marine Research (AWI) established the deep-sea long-term observatory HAUSGARTEN, which constitutes the first, and until now only open-ocean long-term station in a polar region. Virtually undisturbed sediment samples have been taken using a video-guided multiple corer (MUC) at 13 HAUSGARTEN stations along a bathymetric (1,000 - 4,000 m water depth) and a latitudinal transect in 2,500 m water depth as well as two stations at 230 and 1,200 m water depth within the framework of the KONGHAU project. Various biogenic sediment compounds were analyzed to estimate the input of organic matter from phytodetritus sedimentation, benthic activities (e.g. bacterial exoenzymatic activity), and the total biomass of the smallest sediment-inhabiting organisms (size range: bacteria to meiofauna).

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The primary objective of this experiment is to measure the cross-section of $\nu_{e}$ charged-current neutrino interactions on $^{127}$I. To measure this interaction, an array of twenty-four, 7.7 kg sodium iodide (NaI[Tl]) scintillating detectors will be deployed to the Spallation Neutron Source at Oak Ridge National Laboratory. The design of the detector array is presented here along with preliminary characterization and background measurements conducted at Duke University.

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Volcanic rocks recovered from the Japan Sea during ODP Legs 127 and 128 were analyzed by 40Ar-39Ar whole-rock stepwise-heating experiments. All three experiments on samples from Site 795 in the Japan Basin revealed disturbed age spectra, but they are consistent with crystallization ages of 15 to 25 Ma for the samples. At Site 797 in the Yamato Basin, three of the five samples showed plateau ages of 18-19 Ma. At Site 794 in the northern Yamato Basin, three of the five samples revealed concordant age spectra of 20-21 Ma. The radiometric age results are consistent with the estimated ages for the oldest sediments at Site 797 based on the biostratigraphy, but are significantly older than those of the oldest sediments at Site 794. However, the radiometric ages are concordant with previously inferred ages for the formation of the Japan Sea floor based on radiometric age data from dredged igneous rocks from the Japan Sea. The present results indicate that formation of the Japan Sea floor started at least 19-20 Ma ago and give more precise age constraints.