Helium isotopes of seawater in the Japan Sea

Autor: Yuji Sano, Keika Horiguchi, Toshitaka Gamo, Naoto Takahata, Kotaro Shirai
Rok vydání: 2008
Předmět:
Zdroj: Journal of Oceanography. 64:293-301
ISSN: 1573-868X
0916-8370
DOI: 10.1007/s10872-008-0023-3
Popis: We have collected fifty-five seawater samples at seven stations at various depths in the Yamato and Japan Basins of the Japan Sea and measured their helium isotopic ratios. The 3He/4He ratios vary from 0.997 Ratm to 1.085 Ratm where Ratm is the atmospheric ratio. The maximum 3He excesses about 8%, are observed at mid-depth (1000 m), and these values are significantly lower than those observed in deep Pacific waters. This implies that mantle-derived helium in deep Pacific water cannot enter the Japan Sea since it is an almost landlocked marginal sea. The observed 8% excess 3He may be attributable to the decay product of tritium. Slightly higher 3He/4He ratios in the Bottom Water were observed in the Yamato Basin than in the Japan Basin. The ventilation ages of seawater shallower than 1000 m are calculated as about 5 to 20 years, which is consistent with the CFC ages reported in the literature. There is a positive correlation between the apparent oxygen utilization and 3H-3He ages. The estimated oxygen utilization rate from the correlation in a layer between 500 m and 1000 m is about 3 µmol/kg/yr, which is similar to that in the eastern subtropical North Atlantic.
Databáze: OpenAIRE
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