Abstracts of Annual Meeting of the Geochemical Society of Japan

Morphologically diverse microfossils were reported from Archaean (3.0Ga) black chert in the Farrel Quartzite in the Pilbara Craton, Western Australia (Sugitani et al., 2007).In this study, Rare Earth elements and Yttrium concentration were analyzed to understand the origin and depositional environment of the black chert. The fossil-containing black chert occures with evaporites. Other types of black cherts in the same region(chert vein, laminated chert, chert-evaporite association with no microfossil) were also analyzed for comparison. Shale(PAAS)-normalized REE+Y pattern indicates that the fossil-containing black chert was formed in a shallow restricted basin. In addition, no high-T hydrothermal signature was shown.

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JAMSTEC will start next year time series observation at 2 sites in the western North Pacific. As a part of the observation, operation of the newly developed Ocean Primary Productivity Profiler with an underwater winch is being planned. General features of the system, as well as recent results from the operations in Sagami Bay will be shown. Possible application of operation of primary productivity profiler will also be mentioned.

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Atmospheric observation was carried out from 10S to 53.6N along 160W on board of R/V Hakuho maru in the summer of 2005. In the central Equatorial Pacific, where is little affected by land origin air, the primary productivity was relatively high. The Atmospheric concentrations of sulfate and ammonium are also factor of 2-3 higher than that in the mid latitude region. Mean particle size of sulfate is rather small in the region. Based on the observed values, ammonia flux to the atmosphere was estimated to be 17 µmol/square meter/day. Equatorial Pacific zone is the source of marine biogenic gases and place for formation of marine aerosols.

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Noble gases dissolved in porewater of marine sediments preserve primitive chemical signatures of in-situ fluids. High hydrostatic pressure increases gas solubility on sea floor also enhances the abundance of noble gases in marine sediments. Noble gases have been widely exploited as geochemical tracers. With properties of high mobility and chemical inertness, noble gases do not react with other species under almost all circumstances. The major consequence of this inertness is that noble gases pass easily into the gas phase, and is efficiently lost from the solid Earth. Scientists have adopted these great properties to elucidate the source and the evolution history of fluids for several decades. Air contamination, however, affects noble gas analysis severely, has been a key issue during core-recovering. Here we present the multi-core pore-water sampler and analysis procedures of samples from Northeastern Okinawa Trough. The sampler is capable of taking sediments from various depths, which offers information of noble gases in different depths. In addition to multi-depth sampling, this device prevents samples from air-contamination during recovering. Thus noble gas signatures could be even more primitive than those dissolved in seawater. Analysis of samples from the device requires a special extraction system. Sediments are heated within copper tubes and are blown out to a vacuum vessel in certain temperature. We further heat the vessel to advance noble gas diffusion. The sampler paired with the analysis procedure is proved to be useful and can be applied to various marine and hydrological research. The preliminary results indicate the sampling and experiment procedures are feasible. Helium isotopic ratios in pore-water samples ranged from 3.62 to 5.06 RA, and are derived from mixing of seawater and hydrothermal fluid.

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