Current and Turbidity Variations in the Western Part of Suo-Nada, the Seto Inland Sea, Japan: A Hypothesis on the Oxygen-Deficient Water Mass Formation |
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| Authors: | Tomoharu Senjyu Hidekazu Yasuda Shigehiko Sugihara Masato Kamizono |
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| Institution: | (1) Department of Fishery Science and Technology, National Fisheries University, 2-7-1, Nagata-honmachi, Shimonoseki, Yamaguchi, 759-6595, Japan;(2) Department of Fisheries Information and Management, National Fisheries University, 2-7-1, Nagata-honmachi, Shimonoseki, Yamaguchi, 759-6595, Japan;(3) Fukuoka Fisheries and Marine Technology Research Center, Buzen-kai Laboratory, 76-30, Unoshima, Buzen, 828-0022, Japan |
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| Abstract: | A hydrographic survey and a 25-hour stationary observation were carried out in the western part of Suo-Nada in the summer of 1998 to elucidate the formation mechanism of the oxygen-deficient water mass. A steep thermocline and halocline separated the upper layer water from the bottom water over the observational area except for near the Kanmon Strait. The bottom water, in comparison with the upper layer water, indicated lower temperature, higher salinity, lower dissolved oxygen, higher turbidity, and higher chlorophyll a. Turbidity in the upper layer water changed with semi-diurnal period while the bottom water turbidity showed a quarter-diurnal variation, though the M2 tidal current prevailed in both waters. From the turbidity distribution and the current variation, it is revealed that the turbidity in the upper layer water is controlled by the advection due to the M2 tidal current. On the other hand, the quarter-diurnal variation in the bottom water turbidity is caused by the resuspension of bottom sediments due to the M2 tidal current. The steep thermocline and halocline were maintained throughout the observation period in spite of the rather strong tidal currents. This implies an active intrusion of the low temperature and high salinity water from the east to the bottom of Suo-Nada. Based on the observational results, a hypothesis on the oxygen-deficient water mass formation was proposed; the periodical turbidity variation in the bottom water quickly modifies the oxygen-rich water in the east to the oxygen-deficient bottom water in Suo-Nada in a course of circulation. |
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| Keywords: | Turbidity resuspension advection M2 tidal current oxygen-deficient water mass stratification halocline quarter-diurnal variation oxygen consumption suspended matter |
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