The "Furiwakeshio" ("Kinan Bifurcation Current"), which is caused by the Kuroshio hitting the southwestern coast of the Kii Peninsula, is studied using a high-resolution OGCM. A hindcast experiment using the OGCM is analyzed and compared with the observed data in this area. The results are summarized as follows. The mean sea level around the Kii Peninsula is characterized by a cyclonic depression in the coastal zone and the bifurcation of contours between the Kuroshio and the "Furiwakeshio" offshore of the southwestern Ku Peninsula. The OGCM with 1/18-degree horizontal resolution cannot reproduce this climatology, but can reproduce the sea' level pattern quite similar to the observed bifurcation only in a snapshot sense. The model and observations are also compared for the sea level difference between Kushimoto and Uragami, a famous index of the Kuroshio large meander. Because of the insufficiency of resolution to reproduce the tiny cape called Shiono-misaki, the model fails in reproducing observed values over 25 cm and only results in values less than 25 cm. The bifurcation patterns of current vectors and temperature contours as observed in this area in 1997 by the synoptic hydrographic surveys were not reproduced by the model in the sense of a successful hindcast. The frequency of bifurcation events through 1997 was estimated by calculating the model's westward transport along the western coast of the Kii Peninsula. The frequency of the Furiwakeshio is under-estimated by the model by about 10% when compared with the observed frequency of about 78%. Nevertheless, the lifetime and spatial structure of the Furiwakeshio once it appeared in the model are quite similar to those of the actual phenomenon. The model result shows a series of events in which the anticyclonic and cyclonic disturbances propagating on the Kuroshio 's offshore side generate a torque that changes the direction angle of the Kuroshio path between Muroto-misaki and Shiono-misaki. This is thought to be the main mechanism which causes the Furiwakeshio and is a notable feature found by the present model study.

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A trend of oceanic origin sea level change was deduced from tide gauge records for the last 30 years around Honshu. The relation between the trend of oceanic origin sea level and the sea surface temperature was also investigated. The Height Difference Data (results of ground leveling from 1969 to 1998 by the Geographical Survey Institute of Japan) was used to remove the effect of crustal movements from the tide gauge records. Fig. 5 shows the trend of oceanic origin sea level change around Honshu. It was assumed that the Japan Datum of Leveling is stable. The trend of sea level is different east and west of 137°E longitude (see Fig. 2). The average rate of oceanic origin sea level change for western Japan was 2.4 mm year^-1, while it was -3.1 mm year^-1 for eastern Japan. This trend of oceanic origin sea level had a good correlation with the trend of the sea surface temperature (see Fig. 9).

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Non production in Ariake Bay was severely damaged by a bloom of diatoms in FY2000. Environmental changes which occurred in this bay were analyzed using data collected at 22 stations in the coastal area of Kumamoto, Japan from FY1995 to FY2000. Decrease in dissolved inorganic nitrogen (DIN) with increase of chlorophyll a (Chl-a) was observed in the latter half of the crop producing season in FY2000. Although the seawater temperature in FY2000 was slightly lower than that in FY1995-1999, no difference was detected in salinity. This suggests that temperature and salinity may not be the major parameters affecting the physiologies of layer and phytoplankton. On the other hand, the decrease in DIN for four years after construction of the dike at the mouth of Isahaya Bay had statistically significant effect on the physiologies of lava and phytoplankton for the six years. Variation in Secchi disk depth was not appeared in the six years but the increase in Secchi disk depth was significant after construction of the dike. This implies that the change of the ecosystem in Ariake Bay could have been induced by the artificial topographical change accompanied by construction of the dike in addition to some long-term environmental changes such as tide variation.

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Understanding the mechanisms controlling the long-term mean state of the climate system is the basis for all kinds of climate research. The ocean is a dominant factor in determining the long-term mean state due to its large thermal inertia and global-scale circulation. The oceanic thermohaline circulation is especially important in this regard, as it links the world ocean from the surface to the bottom. Since the state of the climate system is a result of nonlinear interaction of various processes existing in subsystems, numerical modeling is a useful method to investigate it. Because of nonlinearity, on the other hand, simplification adopted in a single process could significantly change the whole result. Idealized modeling is sometimes an effective way of understanding the physical essence of climatic phenomena, but is useful only when the applicability of such idealization is clarified. Modeling studies of the climate system should first be based upon models of climatic subsystems which can reproduce their states as realistically as possible. Accurate modeling of the oceanic thermohaline circulation is of primary importance for investigating the long-term mean state of the climate.

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A synthetic index of environmental monitoring for conservation of the coastal sea ecosystem is proposed. The synthetic index is generated by normalized nutrient concentration in the surface layer, dissolved oxyxgen concentration in the bottom layer and proportion of natural coast. Year-to-year variation of this synthetic index in Hiroshima Bay during 1973 and 1997 coincides well with the number of species of benthic animals near the coast.

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