Journal of Oceanography, Vol. 58 (No. 6), pp. 759-773, 2001
Rolando S. Balotro1*, Atsuhiko Isobe1, Manabu Shimizu2, Atsushi Kaneda3, Takatoshi Takeuchi3 and Hidetaka Takeoka3
1Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
2Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
3Center for Marine Environmental Studies, Ehime University, Matsuyama 790-8577, Japan
(Received 7 September 2001; in revised form 10 December 2001; accepted 17 January 2002)
Abstract: An attempt was made to reproduce the circulation pattern in Suo-Nada, Japan during spring and summer season in order to elucidate the water exchange mechanism in the basin. Two hydrographic surveys at the end of each season were conducted covering the entire Suo-Nada area. A three-dimensional hydrodynamic Princeton Ocean Model (POM) was used to compute the current resulting from the observed density and wind field. During spring, a very pronounced counter clockwise gyre is situated near the opening of the basin. This is replaced by a clockwise circulation which seemed to occupy the whole domain during summer. Within each season, however, the vertical distribution of current does not show any remarkable differences, indicating the dominance of horizontal current and a very weak estuarine flow. These observational and numerical results were used to estimate the remnant function and the corresponding average residence time of permanently dissolved matter (PDM) and transformable matter (TM). The results revealed a small difference in the average residence times of materials within each season but a large seasonal variability between spring and summer. Furthermore, calculations based on climatological density fields have indicated a similar trend of variation between the seasonal values of average residence times.