Geochemical Investigation or Waters on YONAGUNI-JIMA

From March 22 to March 29,1972. the University of the Ryukyus has conducted a scientific survey of Yonaguni Island in the field of geology, geography. geochemistry, animals, plants and oceanbiology. This paper is a report on the gcochemical aspect of waters collected from Yonaguni Island as a part of studies of nature of the same island. Yonaguni Island is a small island located in the mid-ocean at the most southern shores of Japan in which is independent of continental affect in many respects. The rolling expanse of plains on the island and rocks such as sandstones. argillites and limestones are full of variety resulted from geological transitions and alterations. The water resources are also abundant throughout the island. Headsprings with large quantity of water and which have been used for ordinary life are originated and reservored in limestone area showing calcium bicarbonate types of water. In contrarily, the waters with low rate of flow, low hardness and NaCl as main species dissolved in are collected from sandstone area. . The interrelations of ions in the water will also be discussed in this paper illustrating the graphical representations. The reasons so-called ' the water on Yonaguni Island is bitter' will also be discussed from the point of the fact that the positive correlations on the values for Na/C1, Mg/Cl and Mg/SO_4 in waters are fairly agree with that of in sea water showing high coincidency for Na/C1 ratios and high Mg content compared with waters from other islands of carbonate area in the Ryukyus. In general, the water on Yonaguni Island is largely affected by sea water as a characteristic feature of such a island isolated from the continent. Consequently, the cations in the water decrease in the order of Na> Ca>Mg>K and anions of C1>HCO_3>SO_2, respectively