Abstracts of Annual Meeting of the Geochemical Society of Japan

Two silicate-rich dust layers, lie respectively at Marine Isotope Stages 12 and 13, were found in Dome Fuji ice cores in East Antarctica. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic/cometary events not identified previously in the Southern Hemisphere. These findings will be help to understand the nature of accreted materials to Earth, the flux of extraterrestrial materials at the Earth's surface, and regional climate changes which triggered by large impact explosions on polar ice sheets or by fallout of huge amounts of extraterrestrial dust particles on polar ice.

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In order to investigate relationships between cosmogenic nuclides and solar activities, we have been continuously observing the daily Be-7 concentrations in surface air using a high-volume air sampler. We have obtained the daily data set by the observation from 2000 to 2008, during which time the solar activities changing from the maximum of the 23rd solar cycle to the minimum of the next cycle. We report the result of the Be-7 variation in the 9 years compared with a simulation of production by cosmic rays.

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We revealed nitrogen isotopic hetero- and homogeneity for D-α-alanine and L-α-alanine in terms of microbial processes in domain Bacteria and chemical processes in organic symmetric synthesis. D-alanine is a physiologically essential enantiomer for microbial growth and metabolic maintenance. The nitrogen isotopic difference of amino acids in peptidoglycan in bacteria, representative gram-positive phylum Firmicutes and Actinobacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus staphylolyticus, Lactobacillus acidophilus, Bacillus subtilis, Micrococcus luteus and Streptomyces sp.), tended to be 15N-depleted in D-alanine, suggesting that isotopically heterogeneous components are mainly controlled by enzymatic pathways prior to formation of the bacterial cell wall. In contrast, the δ15N of racemic alanine in the chemical pathway during the typical nucleophilic substitution reaction (SN1 type) between 2-bromopropionic acid and ammonia showed infinitely homogeneous components for each enantiomer. The novel method of enantiomer-specific isotopic analysis (ESIA) is useful for distinguishing the origin of biogenic and abiogenic processes and is applicable to enantiomer studies.

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We report results of NT03-09 cruise, which was conducted in 2003, using ROV Hyper Dolphine (JAMSTEC). We re-discovered high temperature fluid venting activity in the center part of Jade site, where the high temperature activity was discovered. In the distal part of the active field, we found sulfur reef and emanation of liquid CO2, which would be caused by phase separation of the venting fluid.

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