Abstracts of Annual Meeting of the Geochemical Society of Japan

There was a new finding submarine volcano near the Tokara Islands by a multibeam echo sounder survey, but still less geochemistry data. Therefore, the aim of this study is to get information of gas geochemical characteristics at hydrothermal vent sites in the adjacent region of Tokara Islands, South of Kyushu, Japan by using helium isotopes and methane concentration and its stable carbon isotope ratio to estimate the 3He flux and understand the mechanism of carbon cycling.

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Extraterrestrial organic compounds are promising raw materials for the first life on the earth. We irradiated simulated interstellar media (a mixture of CO, NH?SUB?3?/SUB?, H?SUB?2?/SUB?O, etc.) with high-energy particles. Complex amino acid precursors with high molecular weights and nucleic acid bases were detected among irradiation products. The amino acid precursors and the nucleic acid bases were found more stable than free amino acids against radiation, UV light and heat. Thus it can be said that amino acid precursors and nucleic acid bases are robust molecules for life's origin. It is important to evaluate organic compounds from the point of view of robustness.

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Extraterrestrial materials such as meteorites, comets, and interplanetary dust particles contain varieties of organic matters, including amino acids, which is important for the origins of life. Thus, it has been proposed that the extraterrestrial materials delivered organic matters that are essential for the origins of life to the early Earth. However, to verify the extraterrestrial delivery of amino acids to the early Earth, it is necessary to examine the effect of shock wave on amino acids during the extraterrestrial impacts to the Earth. In the study, we conducted a series of shock experiments to amino acids at different temperatures to examine the dependence of the shock reactions of amino acids on pressure and temperature.

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A primary goal of the international GEOTRACES program is to elucidate the fluxes and processes controlling the distributions of trace elements and their isotopes in the global ocean by mapping their distributions at the global scale. Iron (Fe), designated as a key parameter for the GEOTRACES program, is an essential micronutrient for phytoplankton, and regulates primary production in various regions of the oceans. Defining the inputs, sinks and processes controlling the distribution of Fe in the oceans is a high priority of the GEOTRACES program. An important aspect of the GEOTRACES program is that by providing full depth water column samples on which other trace elements and their isotopes with varying oceanographic behavior can be determined, it will be possible to gain insights into processes that are not revealed by the measurement of a single parameter. Additionally, the contemporary CLIVAR sampling program in the upper 1000m provides data for these elements at much higher spatial resolution. High-resolution dissolved Fe, Mn, and Al distributions were obtained using a trace metal clean rosette during the GEOTRACES GA03 zonal transect across the North Atlantic Ocean. In this talk, we present a general overview of the dFe, as well as dMn and dAl distributions that reveal several Fe inputs at varying depths across the study region. Elevated dFe concentrations correlate with elevated dissolved Al concentrations in the surface waters of the subtropical gyre, indicating a significant atmospheric source of Fe, in contrast there is no apparent significant dust source for Mn. In the subsurface oxygen minimum waters, dFe maxima are a result of the remineralization process. Within this minimum, the ratio of dFe to apparent oxygen utilization is lower than would be expected from the measured Fe content of surface water phytoplankton, suggesting that a significant amount of the remineralized dFe (~63-90%) is subsequently scavenged from the water column. Sedimentary inputs are apparent from elevated dMn signals in the eastern basin, particularly near the African coast. The largest dFe anomaly (~68 nM), which also corresponds to a dMn anomaly (up to ~33 nM) and dAl anomaly (up to 40 nM) is seen in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge, and that signal is visible for ~500 km to the west of the ridge.

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