On low noble gas concentrations in Antarctic micrometeorites collected from Kuwagata Nunatak in the Yamato Meteorite Ice Field

Noble gas concentrations and isotopic compositions were determined on Antarctic Micrometeorites (AMMs) collected in Kuwagata Nunatak in the Yamato Meteorite Ice Field around the Yamato Mountains in 1998. Noble gas concentrations in Kuwagata AMMs are lower than those of previously measured Dome Fuji AMMs. The heavy noble gas composition is chondritic and shows no atmospheric contamination. In order to clarify the differences of noble gas concentrations between Kuwagata and Dome Fuji AMMs, statistic calculations were done. The differences in ^4He, ^<40>Ar, ^<84>Kr, and ^<132>Xe concentrations between the two types of AMMs are significant in both F-test and T-test. On the other hand, ^<36>Ar is not significant in the F-test, and ^<20>Ne is not significant in both tests. These results revealed a systematic decrease of noble gas concentrations in Kuwagata AMMs compared to those of the Dome Fuji AMMs. Since jarosite-a by-product mineral from aqueous alteration of sulfide minerals-was detected in Kuwagata samples, He loss may be due to aqueous alteration in Antarctic glacial ice. A contamination by atmospheric noble gases might be avoided by sample preparation using acetone to detach AMMs from stainless steal filters.