Fig.9. Year to year variations of saline water higher than 35.00 along the 137゜E meridian observed in winter by the Japan Meteorological Agency. Domains in which saline water is higher than 35.00 are shown by black areas. Additional isohaline contours of 34.90 are given for the high salinity region found to the north of 8゜N (Saeki, personal communication).
The abnormally saline water in case (c) was found near 28゜N. The Japan Meteorological Agency maintains a long observation line along 137゜E and surveys it twice a year from 1967. Saline water higher than 35.00 is usually found in the region between 10゜N and 20゜N and that to the south of 5゜N (Andow,1987). Saline water higher than 35.00 appears to be very common to the south of 20゜N. The variations of area of the saline water higher than 35.00 are shown in Fig.9 from the winter cruises in the period from 1967 to 1982 (Saeki, personal communication). The area of the high salinity domain between 10゜N and 20゜N are very changeable year by year, and sometimes its northern edge exceeds 25゜N. The abnormally saline water seen near 28゜N in Fig.8c may be considered to originate from this saline water, though it is isolated in cross-section.
5. Possible Source of the Abnormally Saline Water
High salinity water would be produced at the surface by excess evaporation. Levitus et al.(1994a) produced an annual mean salinity atlas for the world ocean at various depths. The salinity distributions in the North Pacific Ocean are cited and are shown in Fig.10 for the surface, and the 30 m, 50 m, 100 m, 150 m and 250 m depths. Saline water higher than 36.25 is found in the sub-tropical central South Pacific (around 120゜W, 15゜S), but no such saline water is found in the North Pacific. The salinity of the most saline water in the North Pacific is less than 35.50. Saline water higher than 35.00 can be found in the domain roughly between 150゜E and 130゜W, and between 20゜N and 30゜N. The maximum value does not appear at the surface, but at 30 m depth. In the corresponding temperature atlas (Levitus et al.,1994b), no significant temperature difference is found between the surface and 30 m depth. Presumably, the high salinity waters generated sporadically at the surface have sunken due to their relatively high density. The area of the saline water domain is also at a maximum at the 30 or 50m depths. No such saline water is found below 250 m depth.
The abnormally saline water found in August, 1984 suggests that the water might have been carried into region by the current of the outer edge of Kuroshio. However, the salinity in the Kuroshio area near the Philippines is considerably low (Fig.10). The temporal variation of the highest salinity value found in the section crossing the Kuroshio northwest of Okinawa (PN line) is shown in Fig.11 (Saeki, personal communication) for the period from 1955 to 1982. The maximum salinity value does not exceed 35.00 during this period. The surface Kuroshio water is usually affected by the coastal water from the East China Sea and diluted somewhat before it flows out again into the North Pacific. So, it is hard to assume that the abnormally saline water carried directly by the current of the Kuroshio.
The abnormally saline water found in May,1981 appears to be influenced by the current of the Kuroshio Counter Current, however, as the water in the Counter Current would have been influenced by the less saline Oyashio water, it is hard to consider that the Counter Current brings this abnormally saline water directly, too.
Presumably, eddy activities or other sporadic events would play an important role in the process which brings the abnormally saline water into the region under consideration, and this results in the very low occurrence frequency of the abnormally saline water.
