Abstract
Boron isotopic compositions of ten sea water samples were measured. Nine samples were surface sea waters collected close to the shores of the Boso and Izu Peninsulas, Japan. The tenth sea water (Ito Oki sea water) sample was collected off the shore of Ito, Izu, at the depth of about 120m around the hill formed by submarine volcanic eruptions in the summer of 1989. Except for the Ito Oki sea water, the waters examined had the boron isotopic ratios (11B/10B) of 4.20-4.22 (or δ11B values of +37.7-+43.4) which were in good agreement with the values previously reported for sea water. This strongly suggests that, as far as the boron isotopic composition is concerned, sea water is quite uniform worldwide, even in areas close to coasts. The Ito Oki sea water sample with a high temperature (75°C), a high boron content (7.97 mg/dm3) and a low boron isotopic ratio (4.112) indicates the existence of hydrothermal solution at the site of the eruptions in 1989 even one year after the eruptions.
