Annual barotropic and baroclinic responses of sea level anomalies (ΔD_BT and ΔD_BC) in the western North Pacific to seasonally varying wind stress curl are extracted by combining the sea surface height anomaly (SSHA) observed by satellite altimeter with the dynamic height anomaly (ΔD_jdbar; j is the reference depth) calculated by the density fields observed by Argo floats, i.e., ΔD_BT＝SSHA -ΔD₂₀₀₀ and ΔD_BC＝ΔD₂₀₀₀ -D_ML (ML is the surface Mixed Layer depth). The most conspicuous feature in the seasonal change in ΔD_BT is the tongue of negative values at the region of subarctic gyre in late winter (February to March) extending southward to the Izu-Ogasawara Ridge (IOR) in subtropical gyre. For annual ΔD_BC variation, one of the much larger positive amplitude is also found in areas surrounding IOR in spring (April to May), suggesting the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion on the steep bottom slope, i.e., the impinging response. The next prominent ΔD_BC variability seems to be the adjustment of the ocean in terms of the baroclinic first-mode annual Rossby Waves, which can theoretically exist south of about 40°N.

We studied the temporal variation and changes in red tide occurrences and the dominant species composing red tides in the Seto Inland Sea based on the red tide basic dataset for the 26 years from 1979 to 2004. This included the “Red Tide Index” (RI), which is capable of as sessing the spatiotemporal scale and impacts of a red tide. We analyzed the temporal changes in the RI in the Seto Inland Sea and Osaka Bay separately. The long-term trend in the RI in the Seto Inland Sea showed both increasing and decreasing trends with a minimum value around 1990. The trend in Osaka Bay has declined markedly for about 30 years. We found that the long-term trends in the RI in both the Seto Inland Sea and Osaka Bay corresponded with the long-term trends in solar radiation and nutrient concentration. The dominant species of red tide were derived using the RI in both the Seto Inland Sea and Osaka Bay. We found that non-diatom species were dominant mainly in the Seto Inland Sea, while in Osaka Bay the dominant species has changed from non-diatom species to diatom species during the past 30 years.