Intrusion of Kuroshio-Derived bottom cold water into Osaka Bay and its possible cause |
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| Authors: | Koichi Sugimatsu Atsuhiko Isobe |
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| Institution: | 1.Interdisciplinary Graduate School of Engineering Sciences,Kyushu University,Kasuga, Fukuoka,Japan;2.Center for Marine Environmental Studies,Ehime University,Bunkyo-cho, Matsuyama,Japan |
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| Abstract: | The bottom layer in Osaka Bay was occupied in August from 1980 to 1995 by a water mass of relatively low temperature and rich
in nutrients in comparison to previous and following decades. The relationship between Osaka Bay bottom temperature and Kuroshio
axis location south of Kii Peninsula has been investigated using the dataset archived by Osaka Research Institute of Environment
of Agriculture and Fisheries and axis-location data provided by Marine Information Research Center. The correlation between
bottom temperature in the bay and Kuroshio-axis distance from Cape Shionomisaki indicates that the bottom temperature in the
bay decreases when the Kuroshio axis is a long distance from the cape, and vice versa. To investigate why the temperature
distribution depends on the axis location, composite temperature maps are depicted using summer temperature data from 1970
to 2005 archived in the Japan Oceanographic Data Center (JODC) after dividing all data into two groups with different axis
locations. These temperature maps and temperature-salinity plots using the same JODC data suggest a scenario: cold water in
the Kuroshio intermediate layer is first upwelled on the eastern side of the Kii Peninsula and thereafter moves westward as
a coastal boundary current in the Kelvin wave sense of the Northern Hemisphere when the Kuroshio axis is located around 74-km
distance from Cape Shionomisaki. This scenario is validated using internal Froude number maps depicted using the JODC-archived
hydrographic data and geostrophic current fields. In addition, the reanalysis daily data provided by Japan Coastal Ocean Predictability
Experiment are used for the validation. |
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