High Salinity Waters Found off the Kii Peninsula
YOSHITAKE MRIKAWA1 , JUNICHI TAKEUCHI2, TAKAFUMI UEMA1,
TAIJI ImoTo3 and YUTAKA NAGATA 4
1Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514, Japan
2Wakayama Prefectural Fisheries Experimental Station, 1515 Kushimoto, Nishimuro, Wakayama 645-35, Japan
3Hydrographic Department, Maritime Safety Agency, 5-3-1 Tukiji, Chuo, Tokyo 104, Japan
4Marine Information Research Center, Mishima Bldg. 5F, Ginza, Chuo, Tokyo 104, Japan
(Received 15 May 1997; in revised from 6 August 1997; accepted 7 August 1997)
Water having salinity higher than 35.00 is rarely found in the vicinity of Japan, but Takeuchi (1985) found such abnormally high salinity water to the south of the Kii Peninsula on August 2, 1984. By using the data compiled by JODC for the period from 1975 to 1996, we analyzed the occurrence frequency and structure of such high salinity water in the region south of the Kii Peninsula. The occurrence frequency distribution of the salinity values indicates that saline water higher than 34.95 is very unusual in this area. However, the occurrence frequency of saline water higher than 34.95 is about 2.5%, and that higher than 35.00 is about 0.6%. These values appear to be significant enough statistically. It should be noted that the R/V Soyo-maru observed saline water higher than 35.00 on almost the same day as the R/V Wakayama in August 1984. The oceanic structures when the high salinity water found are analyzed.
Keywords：
・High salinity water,
・Kii Peninsula,
・historical data,
・JODC.
1. Introduction
The water salinity of the north Pacific Ocean is much lower than that of the Atlantic ocean, and saline water higher than 35.00 is rarely observed in the vicinity of Japan. However, Takeuchi (1985) reported that the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station found such abnormally saline water to the south of the Kii Peninsula on August 2, 1984, though such saline water had never been found during routine observations of surveyed transects by the R/V Wakayama, at least since 1984 when the Neil-Brown CTD system was installed.
In order to examine the occurrence frequency and the structure of such abnormally saline water in the area south of the Kii Peninsula, we analyzed historical data compiled by the Japan Oceanographic Data Center (JODC) for the Period from 1975 to 1996.
2. Data Used
JODC supplied the compiled historical data in the form of a CD-ROM. We analyzed the data in the area from 28゜N to the Japanese coast and between 134゜E and 138゜E (Fig. 1) and for the period from 1975 to 1996. The toal number of the observation points is 2,167. In the preliminary stage of analysis, we surveyed the data also in the Japan Sea, and found about 13 observation points where saline water higher than 35.00 are reported. It is unbelievable that such saline waters are found in the Japan Sea where the salinity values are usually considerably lower than those in the Western North Pacific. We found that these observation points were taken by vessels belonging to one non-research organization. By way of precaution, we excluded the data observed by this organizaion from our analysis.
In the data compiled by JODC, temperature and salinity values are given both for the observed depths and the standard depths (interpolated values) in the case of serial observations, and only at the standard depths in the case of CTD observations (the same data are duplicated also for the observed depths column). We used basically the values for the observed depths column.
Much of the data observed by Japanese local agencies have not been compiled in the JODC data set, and no data taken by the Wakayama prefectural Fisheries Experimental Station is included at least since 1975.
We found 120 observation points where saline water higher than 35.00 was found in vertical sections. The names of agencies, research vessels, dates of observations and number of observation points are shown in Table 1. The case observed by the R/V Wakayama is also shown in Table 1. The occurrence frequency of saline water higher than 35.00 is quite small, so we shall call such high salinity water as "abnormally saline water”. However, 13 such observation points are significant enough for us to suggest that such abnormally saline water intrudes sporadically into the region under consideration.
