日本海海水中のヘリウム同位体比 [in Japanese] Helium isotope ratios in Japan Sea water [in Japanese]
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We have measured <sup>3</sup>He/<sup>4</sup>He and <sup>4</sup>He/<sup>20</sup>Ne ratios, and <sup>4</sup>He concentrations in water samples collected at several depths in the eastern Japan Sea. Observed <sup>3</sup>He/<sup>4</sup>He and <sup>4</sup>He/<sup>20</sup>Ne ratios vary from 1.006R<sub>atm</sub> (where R<sub>atm</sub> is atmospheric ratio of 1.343×10<sup>-6</sup>) to 1.045 R<sub>atm</sub> and from 0.24 to 0.31, respectively. There is a difference in <sup>4</sup>He concentration between in the samples shallower than 1,500m and those deeper than 2,000m. The discrepancy may be related to the existence of two water masses in the Japan Sea suggested by Gamo and Horibe (1983). Excess <sup>3</sup>He in the shallower samples is attributable to tritium decay in the sea water while that in the deeper samples is not. Emanation of mantle helium is suggested in the Japan Sea bottom. Since the number of present data is small, extensive <sup>3</sup>He/<sup>4</sup>He research should be carried out in future to verify the existence of mantle helium in the Jpan Sea.
Chikyukagaku 23(2), 61-67, 1989
The Geochemical Society of Japan