TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 61 (No. 6), pp. 1047-1058, 2005

Benthic Front and the Yamato Basin Bottom Water in the Japan Sea

Tomoharu Senjyu1*, Yutaka Isoda2, Takafumi Aramaki3,4, Shigeyoshi Otosaka3, Shinzo Fujio5, Daigo Yanagimoto5, Takashi Suzuki3, Kenshi Kuma2 and Kosuke Mori6

1Research Institute for Applied Mechanics, Kyushu University, Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
2Graduate School of Fisheries Science, Hokkaido University, Minato-cho, Hakodate 041-8611, Japan
3Marine Research Laboratory, Japan Atomic Energy Research Institute, Minato-machi, Mutsu, Aomori 035-0064, Japan
4National Institute for Environmental Studies, Onogawa, Tsukuba, Ibaraki 305-8506, Japan
5Ocean Research Institute, the University of Tokyo, Minami-dai, Nakano-ku, Tokyo 164-8639, Japan
6Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan

(Received 21 October 2004; in revised form 25 March 2005; accepted 6 April 2005)

Abstract: Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water (YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and 3.4 × 10-3 m2s-1, respectively.

*Corresponding author E-mail: senjyu@riam.kyushu-u.ac.jp

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