Abstracts of Annual Meeting of the Geochemical Society of Japan

Oxygen and carbon isotopic composition of land-snail shells (carbonates) have been used as an indicator of terrestrial paleo-environmental variables such as plant vegetation, precipitation, temperature and climate change. Evaluated temperature of carbonates in environment may give us information about oxygen isotopic ration in precipitated water. Clumped-isotopes analysis of carbonates (₁₃C-18O bond in crystal lattice of carbonate minerals) is only sensitive to their growth temperature. Here we analyzed different types of modern land-snails collected at several sampling sites in Japan and evaluated the applicability of clumped-isotopes and d18O of land snail's shells as paleo-environmental indicators.

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MBT/CBT index based on the composition of branched Glycerol Dialkyl Glycerol Tetraethers(GDGTs) was recently proposed as a proxy of terrestrial paleo-air temperature. In this study, we reconstructed paleotemperature changes during the Holocene at the upstream of the Ono River Basin by analyzing a soil sequence exposed at the flank of Mr. Kuju and a marine sequence drilled at the mouth of the Ono River, Kyushu, Japan.

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Branched GDGTs in soils taken from the watershed of Lake Biwa and in sediment core (BIW07-6) retrieved from the lake were analyzed. The dependency of CBT and MBT on pH and mean annual air temperature (MAAT) in our sample set is different from that in global set of soil samples. This difference suggests that some local factor(s) is(are) crucial in the relationship between MBT/CBT and pH/MAAT. The branched GDGT distributions of the surface sediment of BIW07-6 were remarkably different from those of soils, which suggests that branched GDGTs of the sediment were not derived from the watershed soils, but were most likely produced in the lake. CBT-pH supports that branched GDGTs in the sediment were produced in the bottom water and/or the sediment. The variation of estimated paleotemperatures in core BIW07-06 is in harmony with pollen records in nearby cores, suggesting that MBT/CBT index is useful for paleotemperature estimate.

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A powerful tsunami generated by the earthquake occurred at eastside of Japan on March 11, 2011 caused serious damage to several reactors of the Fukushima Nuclear Power Plant #1 (37.42N, 141.04E) on their cooling system. Explosive release of radionuclides, such as iodine 131 (131I) and caesium 137 (137Cs), was occurred for several days. The Nuclear Safety Commission of Japan estimated that 150 PBq of iodine 131 was released into the atmosphere by this accident. This value is expected to be about 8% of 131I released at Chernobyl accident. We have implemented wet deposition, dry deposition, and the radioactive decay of 131I and 137Cs into a regional chemical transport model WRF/Chem (Weather Research and Forecast model / Chemistry) to estimate the budget of total deposition of radionuclides into the land and ocean. Temporal variation of the emission rate was estimated by using the estimated total budget (150 PBq and 12 PBq for 131I and 137Cs, respectively) and the radiation dose observed at the front gate of the Fukushima Nuclear Power Plant #1. As the release of radionuclides was caused by the complex of each reactor's explosion, 11 tagged-tracers were introduced to evaluate each event. The results demonstrate that most of the emitted radionuclides were transported to the Pacific, and the largest deposition on the land was occurred after the eventual release at 03Z 15 March.

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