title: Chlorine isotope fractionation associated with volcanic activity at the Kusatsu-Bandaiko hot spring in Japan.
abstract: Stable chlorine isotope compositions (delta(37)Cl, per-mil: per thousand, vs. a standard sample of sea water) of Kusatsu-bandaiko hot water samples, taken regularly in the years between 1974 and 1995 in the Kusatsu-Shirane volcanic region, Japan, were measured mass-spectrometrically. The results show that the delta(37)Cl values of the waters taken before 1984 were at around-0.12 per thousand, whereas those after 1984 were at around+0.18 per thousand. The delta(37)Cl values are thus distinct across 1984, which is consistent with the classification by the Cl to S molar ratio (Cl/S): the higher the Cl/S ratio, the larger the delta(37)Cl value. The delta(37)Cl value increased as much as 0.30 per thousand during 5 years between 1980 and 1984. This isotopic enrichment is likely correlated with increasing Cl/S ratios, suggesting that the heavier isotope ((37)Cl) may have preferentially increased in the original Cl source of the hot spring across 1984 when volcanic activity likely increased at Mt Kusatsu-Shirane.
authors.affiliation: Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan. musashi@esa.c.u-tokyo.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Musashi
authors.forename: Takao
authors.initials: T
authors.lastname: Oi
authors.forename: Hans G M
authors.initials: HG
authors.lastname: Eggenkamp
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Matsuo